CLAAS biogas expertise.

CLAAS biogas team excellence. More energy.

AXION: Sowing

DISCO: Mowing

CARGOS: Transport

JAGUAR: Harvesting

XERION: Silo

SCORPION: Loading

Introduction. Food production has been a staple of the agricultural industry for millennia. In times of increasing scarcity of fossil fuels and with the development of efficient technologies progressing rapidly, a new business segment is coming increasingly to the fore: bioenergy generation. Today, bioenergy covers approximately 12 percent of global energy demand, with biogas now an important business segment in the agricultural industry in the field of renewable energies. Around the world, huge efforts are being made to advance modern procedures to facilitate efficient and above all sustainable energy production. Renewable materials have been of interest to CLAAS for over 20 years. We are a key technology partner for farmers, contractors and plant operators, with reliability, performance and efficiency always our main concern. In this brochure, we have worked closely alongside a number of well-known authors to bring you an up-to-date account of the challenges ahead for biomass and biogas production.

AGROCOM software: Management

XERION: application

Contents Requirements Methods Key process variables Substrates The challenge Requirements for silage quality Harvesting technology Alternative and catch crop substrates Possible supplements Production of energy crops Maize silage as coferment Compaction: the key to success Avoiding losses Harvesting logistics and framework conditions Harvesting and transport costs Software solutions Important terminology

6 8 11 13 14 18 21 22 25 26 29 30 33 34 37 41 43

Status of recommendations regarding silage production techniques for optimal gas yields. (Dr. Johannes Thaysen, Schleswig-Holstein Chamber of Agriculture) To keep biogas plants well stocked with high-quality coferments year-round, it is necessary to ensile the forage volume grown in the growth period in a facility for even application. Ensiling involves the conversion of plant sugars to preserving acid with the aid of lactic acid bacteria. The process inevitably incurs dry mass and energy losses, and the principle applies that no gas can be formed from lost dry matter or energy. Accordingly, the more that losses can be reduced through optimal silage technology, the higher the gas yield.

Biological processes of biogas production. Biogas is produced from the breakdown of organic matter in a hermetically sealed environment. The process of breakdown (decomposition) is therefore anaerobic and occurs naturally in material cycles. In the context of biogas production, the process is termed fermentation. In the process, organic materials (fats, carbohydrates and proteins) are broken down into low-molecular components by microorganisms. Anaerobic conversion is accomplished by various bacterial strains that grow consecutively during the process. Schematically, the process can be viewed as a multi-stage, multi-phase process (Fig. 1).

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The initial stage of breakdown is termed hydrolysis. During this phase, long-chain carbohydrates, proteins and fats are broken down into shorter fragments such as monosaccharides, glycerin, fatty acids and amino acids. This occurs with the help of enzymes produced and released by hydrolytic bacteria. In a second phase (acidification), the intermediate products such as monosaccharides, fatty acids and amino acids are absorbed by the fermentative microorganisms and included in their metabolism. In the main, short-chain fatty acids such as acetic acid, propionic acid and butyric acid are produced as end products. Smaller quantities of lactic acid, alcohol, hydrogen and carbon dioxide are also produced. Not all of the metabolic products of fermentation can be used by methane producers. The acetic acid formation phase (acetogenesis) combines acidification with methane formation. Feed substrates are end products of the acidification phase, i.e. short-chain fatty acids, such as butyric acid and propionic acid. Together with lactic acid, alcohols and glycerin, these substances are converted to acetic acid, hydrogen and CO2 by acetogenic microorganisms. Since acetogenic microorganisms are viable only at a low hydrogen content, even though they themselves produce hydrogen, they are reliant on a symbiosis with methanogenic bacteria. These use hydrogen as a substrate, and in so doing supply the necessary low partial hydrogen pressure. Methane formation (methanogenesis) takes place in the final stage of the process. The bacteria involved in the process are exclusively anaerobic, and react sensitively to both light and temperature fluctuations. As substrate specialists capable of breaking down only a small number of substances, around 70 percent of methanogenic bacteria utilise acetic acid, while the remaining 30 percent of known strains utilise hydrogen and carbon dioxide.

Silage as coferment.

End products of fermentation. A gas mixture is produced at the end of the stage-by-stage fermentation process, which as the product of a technical plant is termed biogas. The composition of the gas is not invariable, but fluctuates within specific limits, with varying degrees of quality discernable depending on the respective methane content. The gross calorific value of the biogas product produced increases with its methane content (CH4). The higher the proportion of easily degradable substances such as starch and fat in the substrate, the higher the gas yield. During the fermentation process, the organic substance is reduced. In the case of slurry, the extent of the reduction depends greatly on the animal species. Cattle slurry, for instance, has a high raw fibre content with a high proportion of woody plant cells present. This leads to a reduced rate of decomposition of the organic substance, which in this case is around 30 percent. In contrast, in the case of pig slurry, the decrease is 50 percent and organic acids, and hence odour-active substances are broken down at a rate of approximately 80 percent.

Figure 1: Schematic depiction of anaerobic decomposition Feed material (carbohydrates, proteins)

Hydrolysis

Basic organic compounds (amino acids, fatty acids, sugars)

Acid formation

Low fatty acids (propionic acid, butyric acid)

Other products (lactic acid, alcohols etc.)

Acetic acid formation

H2 + CO2

Acetic acid

Methane formation

Biogas CH4 + CO2 Source: Thaysen, 2010

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Requirements.

Factors affecting anaerobic fermentation.

Risk factors of the fermentation process.

As with all microbiological metabolic processes, physiologically favourable environmental conditions are a prerequisite. Temperature, pH and the concentration of nutrients and inhibitors in particular affect the rate of breakdown of the fermentation process. The requirements in relation to environmental conditions (temperature, pH) differ between individual phases.

In a relatively large proportion of plants, problems can occur in relation to the process biology, at least sporadically. Such problems can often be attributed to a deficient silage quality, the proportion of rapidly fermenting substances such as cereals being too great, or an oversupply of the plant.

Depending on the substrate and conditions for life, the generation time of acid-forming bacteria is between one and four days, and that of methane bacteria between five and fifteen days. Sudden changes in the substrate composition or in the concentration of the inhibitors ammonia and hydrogen sulphide lead to ineffectiveness in the process, and can also cause the plant itself to “fail”.

Source: Schmack Biogas GmbH

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If high levels of lignocellulose-containing substances are fermented, such as grasses or solid manure, the conversion process progresses only slowly and requires high levels of agitation. As a result, the rating capacity of the combined heat and power (CHP) plant may not be attained, and the efficiency of the process is therefore no longer guaranteed with such substrate compositions.

Source: Biogas Nord AG

A number of approaches have been developed for solving problems of this nature, some of which have been trialled in practice, although their efficacy must be rated as variable: • Heterofermentative lactic acid bacteria silage additives increase the proportion of acetic acids in the acid spectrum. They are especially useful where reheating is a concern. A temporarily higher methane content in the gas is also demonstrable in fermentation tests, although an appreciable increase in methane yield is not produced in comparison to treated silage as a consequence. • During process-controlled enzymatic hydrolysis (PEH), the biomass is exposed to enzymes in processmonitored fermenters under controlled, optimised conditions. Hemicellulose and pectins can be converted to organic acids, alcohols and hydrolysis gas in three days at a pH of 4–6. In a further PEH stage, cellulose from woody biomass is converted to the abovementioned intermediate products within six days. In this process, temperatures of between 30 and 70°C are preset. This leads to a rapidly accelerated decomposition of lignocellulose-containing substrates (grass, solid manure, maize in late stages of maturity, landscape husbandry material). • The administration of trace elements and micronutrients has helped further stabilise the process in many biogas plants.

Consequences for the plant operation in practice. The fermentation and release of biogas do not occur uniformly. The formation of gas is in fact dependent on the biological activity of the microorganisms involved in the process and the digestibility of the feed substrates. In order to deliver an optimal fermentation process for highest possible gas yields, the following points must be noted: • As far as possible, the respective temperature level must be held constant and monitored on a daily basis. • Darkness and the absence of atmospheric oxygen are crucial, as are nearly neutral pH values. • As far as possible, nutrients must be added continuously. • Regular agitation facilitates homogenisation and the release of formed gas bubbles in addition to a thorough mixing. • Harmful or poisonous substances can disrupt the sensitive conversion process. • The quantity and quality of the biogas and fermentation substrate reflect that of the material added.

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Methods.

Intermittent and flow-through methods in the delivery of fermentation substrate. Biogas plants can be distinguished from one another in terms of their feed system: continuous and intermittent material flows. The plant’s feed method is considered intermittent (storage plant) if the container is loaded with substrate and subsequently sealed in order for anaerobic fermentation to commence. After the release of gas, the container is discharged in full. The “batch” method is applied as an intermittent process in dry fermentation. The loading and discharging of the fermenter are each performed as one process. A period of between two and four weeks is allocated between the two for the decomposition process, in which the substrate is broken down. During this period, no further material is added or removed, with the result that the gas composition and the gas volumes produced are subject to relatively major fluctuations. Accordingly, at least three decomposition containers at various waste emptying stages (i.e. at different times) must be operated in parallel in order to maintain a balanced performance level in gas production. In addition to those containers used as fermenters, additional containers are required for storage and stockpiling. This means a comprehensive range of equipment is required, which in turn raises the costs incurred.

In the storage procedure, fermenters and fermentation repositories are integrated. The loading process, with fresh substrate, is generally performed several times daily. At the stage of digested sludge spreading, the containers are discharged until only a residue remains, required for seeding. Since the fermentation container is operated at a range of fill levels, the volume of gas formed can vary substantially. In order to achieve a consistent level of performance throughout the period of operation, most biogas plants are operated on the basis of the flow-through method. Flowthrough plants are filled in a single operation and subsequently supplied with further fresh substrate several times a day. With each subsequent material delivery, an equivalent volume of decomposed substrate is discharged. This volume flows via an overflow device into either a postfermentation container (flow-through storage procedure) or into a terminal storage device (flow-through procedure). As a result, the fermenter always remains at the same fill level, which provides for efficient decomposition capacity utilisation. The result is a compact and cost-effective construction with minimal heat losses. To avoid the release of methane and ammonia, repositories loaded with waste substrate from the fermenter should be be fitted with a gastight cover. This allows for the collection of leaked biogas, with the covered terminal repository also serving as a post-fermentation container. Gas production in biogas plants configured on the basis of the flow-through storage principle is a relatively smooth process. The plant loading and discharging processes can be easily automated. The decomposed material container needs to be fully emptied only to remove sinking layers or if repairs need to be made. The adding of fermentation substrates that differ greatly in their composition can lead to variable, often prolonged gas release timeframes. Subsequent gas produced is collectable in the postfermentation container. This is another reason why flowthrough storage plants are becoming ever more popular.

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One- and two-stage methods. A further distinction can be drawn in terms of technical process methodology between one-stage and two-stage plants. In the former, all four phases of the anaerobic fermentation process (see Phases of anaerobic decomposition, p. 5) are carried out in a single container. In this case, it is essential that the different environmental requirements of the various types of microorganism are compatible with one another. The temperature and pH value must be preset to suit methane bacteria as the most sensitive and slowest to reproduce. If spatial separation of hydrolysis and acidification (stages 1 and 2) and acetate and methane formation (stages 3 and 4) is configured, this produces more favourable living conditions for the microorganisms. This is known as the two-stage method. The addition of slurry usually serves to boost the stability of the fermentation process. To date, very little experience has been gained in agricultural plants of the application of the recirculation method, in which fermented substrate is reused for the liquefaction and mixture of cosubstrates, and for the fermentation of substrates without added slurry.

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Wet and dry fermentation. Biogas plants can be classified as employing dry or wet fermentation processes. The wet fermentation procedure is employed almost exclusively in the agricultural sector today. Dry fermentation or solid matter fermentation is an established procedure in the decomposition of refuse. Owing to the high cost of these plants, operation can be considered profitable only if an annual processing volume of 20,000 tonnes is exceeded. Businesses without access to slurry are showing increasing interest in this method of biogas production. The technique of dry fermentation enables stackable and free-flowing biomass to be used with no fluid in the form of slurry or water added to the fermentation process. The dry matter proportion of the substrates used in these plants can exceed 30 percent, and in some cases can be as high as 60 percent. The seeding with bacteria of the fermentation substrate in the dry fermentation process (intermittent procedure) is much more difficult than in the wet fermentation method. This is because the conventional agitation units used to routinely disperse the microorganisms in wet fermentation are not part of the system configuration. The substrate must therefore be mixed either with fermentation residues from an earlier process or with a bacteria-containing fluid.

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Many years of experience underpin the most commonly applied method of fermentation: wet fermentation. In this method, fluid is added to the fermentation process continuously or at specified intervals. The addition of fluid helps to achieve a more efficient and thorough mixing of the fermenter, which in turn boosts the rate of gas formation with no toxic effects on the microorganisms. The process of wet fermentation has become established on many farms and in many agricultural businesses, owing to the on-hand availability of slurry and the appropriate technical equipment to perform application. Slurry is most frequently added in wet fermentation to liquefy the mixture. The application of slurry also adds micronutrients and microorganisms to the fermentation process, which is further stabilised as a result. The decomposed substrate from the wet fermentation process can be stored with and applied in the field using tried-and-tested CLAAS agricultural slurry application equipment.

Key process variables.

Process variables. The most important process variables that affect process stability and biogas production are fermentation temperature, hydraulic retention time and volumetric load. Fermentation temperature. The fermentation temperature influences the speed of anaerobic decomposition. There are three distinct temperature ranges in which the corresponding bacterial strains flourish: • At 25°C (psychrophilic strains) • 32°C to 42°C (mesophilic strains) • 50°C to 57°C (thermophilic strains) The majority of agricultural biogas plants are operated in the mesophilic strain temperature range. Depending on the substrate, higher temperatures generally accelerate the speed of decomposition while shortening the retention time.

Gas formation. Gas output, gas production and gas yield are terms most frequently applied to gas formation. Gas output is calculated from the volume of gas produced daily, related to the fermentation container volume or livestock units (LUs). The terms gas production and gas yield are often used interchangeably and denote the volume of gas formed in relation to the substrate. Readings in I/g ODM, m3/kg ODM, m3/t FM (fresh matter) and m3/LU are frequently applied. Unfortunately, the retention times in relation to the respective gas yield calculations are recorded only rarely. The volume of gas that can be formed is dependent on a number of factors, most especially the substrate composition, i.e. the proportion of proteins, fats and carbohydrates, the digestibility of the substrate, and the fermentation temperature and retention time. In the fermentation of slurry without additives, a gas output of 1.0 to 1.2 m3 of biogas per LU and day is to be expected. The yield may be even higher with the addition of forage residues, litter or other waste material.

Retention time. The hydraulic retention time denotes the average number of days the substrate remains in the fermentation container. The value is calculated from the utilisable fermentation container volume and the daily substrate quantity added. Decomposition capacity load (volumetric load). The decomposition capacity load (volumetric load) is the most important variable in assessing the biological load of the process. The value denotes the maximum quantity of organic dry matter (ODM) that can be added without “overfeeding” the bacteria and upsetting the process (acidification of the process). The decomposition capacity load can be calculated from the volume of organic dry matter added daily and the utilisable fermentation container volume.

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Economic efficiency depends in large part on effective substrate management. When debating the economic efficiency of biogas plants, often it is only the technology and the costs of the plants alone that are considered. Economic efficiency in a true sense, however, also depends largely on substrate production costs, substrate quality and the outlay associated with fermentation residue exploitation. Up to 50 percent of costs incurred are in fact attributable to these procedural components upstream and downstream of the actual biogas production process (Fig. 2). Fig. 3 provides a detailed breakdown of the costs associated with substrate procurement, using silage maize as an example. Given that conditions may vary between plants and from region to region, the figures given here serve as a rough guide only. CLAAS products have demonstrated their suitability for use in over 50 percent of the procedures involved in biogas production from renewable resources. Viewed as a complete integral process, this equates to an overall proportion of the entire value chain of approximately 25 percent. With this in mind, the onus is very much on CLAAS to deliver the high levels of performance in its technology at the most affordable of prices, and not simply in respect of its existing product range; in fact, we are working tirelessly to develop new machines, new procedures and combined processes to facilitate further efficiencies in substrate procurement and logistics.

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General situation in Germany. (Ibeling van Lessen, IBS GmbH Analytik und Beratung für Biogasanlagen) The introduction of the German Renewable Energies Act (EEG) in 2004 sparked a huge increase in the number of plants in the biogas production industry. The demand for agricultural land area required to support this trend, namely for the cultivation of renewable raw materials, in turn grew substantially. In 2007, for example, the land area in Germany designated for the cultivation of energy crops for biogas plants was approximately 400,000 ha; by 2010, this had risen sharply to 650,000 ha according to the estimations of the German Specialist Agency for Renewable Resources (Fachagentur Nachwachsende Rohstoffe e. V.). Rapidly rising raw materials prices in 2007, however, led to a sharp decline in investment in biogas plants. It was not only individual biogas plant operators, however, that fell upon difficult financial times; a number of plant manufacturers, too, recorded major slumps in sales figures. The new regulations imposed by the Renewable Energies Act, which came into effect at the beginning of 2009, took account of this trend. The base compensation payable for power generated from biogas was increased along with the bonuses paid for the use of renewable resources in biogas plants. In addition, the prices of renewable resources were already seen to be falling. Various bonuses, e.g. for the use of waste heat based on the combined heat and power principle for particularly clean combustion in engines (pollution prevention bonus) or for the use of slurry in biogas plants, contribute to greater economic efficiency. Since the Renewable Energies Act was introduced in 2009, with new planning safety regulations imposed, the number of plants in Germany again began to rise swiftly. According to the German Biogas Professional Association, the number of biogas plants in the country grew from over 1,000 to around 5,000 in 2009 alone, with an electricity delivery rate of approx. 1,900 MW. This trend continued unabated in 2010, and forecasts for this year predict similar growth rates.

Substrates.

Larger biogas plants with electric output in excess of 500 kW will not benefit directly from the new regulations of the Renewable Energies Act. For these plants, the base compensation and renewable resources bonuses payable were retained from the former provisions without amendment. Here too, a noticeable, though much less dramatic increase in plant numbers has been recorded, since the preparation and supply of biogas to the natural gas network is currently profitable only for larger biogas plants. New, enhanced technologies for biogas production are expected to become available over the next few years, with prices expected to fall. At present, however, the focus is on plants producing less than 500 kW and which integrate refining companies in the processing of large volumes of slurry to qualify for payable slurry bonuses.

Figure 2: Breakdown of costs in biogas production

Fermentation residues • Transport and application

Biogas plant approx. 50%

Delivery of renewable resources substrates

• Sowing, fertilising, plant protection • Harvesting and transport • Silage costs • Substrate delivery

• Gas production • Power generation • End storage

Figure 3: Breakdown of substrate procurement costs; silage maize (example) Procedural stage

Proportion of cost

1 a) Cultivation: production resources / interest

43%

calculation 1 b) Cultivation: fixed and variable machine costs

17% 12%

2)

Interplant harvesting

3)

Interplant transport to silo (2 km distance)

5%

4)

General and administrative costs

3%

5)

Fixed and variable silage costs

6)

Silage discharge and substrate delivery to

fermenter Substrate costs (fermenter)

13% 7% 100%

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The challenge.

Arguments for and against silage maize. Yield per hectare is the foremost concern when it comes to raw material cultivation for biogas plants. The cultivation of renewable materials for biogas plants is worthwhile economically only if as much dry mass as possible can be harvested from the agricultural land designated. Maize, processed as silage, emerged very early on in the development of the biogas industry as the ideal crop for biogas production. This crop delivers a high yield per hectare and its processing is comparatively straightforward, thanks to the many years of industrial experience already gained in processing the crop as animal feed. The development of maize-specific cultivation and harvesting technology is therefore equally as advanced. The ample variety of crop types also ensures a suitable crop is available on the market to cope with a wide range of soil and weather conditions. This is why maize remains the primary crop used in biogas production and today (as at October 2010) accounts for around 80 percent of all renewable raw materials used in biogas plants.

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When looking to the immediate future, however, concentrating solely on silage maize in regards to renewable raw materials for biogas plants would be ill advised. The increasing occurrence of maize pests in recent years, such as western corn rootworm, has already induced a major rethink among growers. What’s more, the increasing regional concentration of biogas plants and the hugely increased average size of newly planned plants in the years prior to the revision of the Renewable Energies Act, which range up to entire biogas parks, show that there is not always sufficient agricultural land available in close proximity to plants for the cultivation of maize silage.

As a consequence, crop haulage distances continue to rise, which in turn is diminishing the relative appeal of maize silage, despite its high energy content. As the harvesting of maize silage must take place at relatively low dry matter, i.e. high water content, the haulage costs involved are disproportionately high. Where haulage distances increase from 2 to 20 kilometres, for instance, this increases the cost for the procurement of maize silage by 250 to 350 euros/ha. This equates to an additional expense of up to 25 percent, which can greatly impact on economic viability. Maize growers are therefore continuing to work tirelessly in pursuit of new crop types to further increase energy yield per hectare. New combined harvesting and transport procedures are also being trialed using truck haulage in attempts to further reduce procurement costs.

Alternatives. While in the past the true implications of higher haulage costs were not given their due consideration in the planning of many plant installations – in fact, a transport distance of 2 to 4 kilometres was generally assumed across the board – today, a major rethink is under way across a wide range of locations: to plan and actually construct a biogas plant before identifying the location and conditions of substrate procurement is no longer in keeping with the times. Today, these issues must first be resolved before plans for the plant itself get under way. CCM or cereals, to name but a few, are today viable alternatives to silage maize. Since only the grain is harvested, and not the entire plant, production costs are indeed higher, but they can be harvested at dry matter contents of approx. 60 or 90 percent. As a result, transport costs are significantly less. As haulage distances between harvesting zones and biogas plants increase, the difference in energy yield and costs incurred between maize silage and alternative substrates becomes increasingly insignificant, eventually reversing entirely. It must be noted, however, that a biogas plant cannot be powered with these materials alone. Owing to their high energy density, cereals are very suitable as a supplement to silage maize. Grains, however, must always be milled, crushed or squashed since, during the biogas process, the organisms are not capable of breaking down the grain's husk within a reasonable timeframe. In practice, CCM is more often held to be the more economically viable alternative where haulage distances range from 10 to 20 kilometres; from 20 to 25 kilometres, cereals are the more economical. However, both are subject to region-specific circumstances.

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Suggested supplementation: rye WCS. Rye WCS has also become well established as a viable supplement for silage maize. The crop can be ensiled as green foliage during catch crop cultivation or brought to maturity as a main crop. Rye WCS with 30-percent dry matter is roughly equivalent per tonne of fresh matter to the gas production potential of maize silage. Generally, maize is planted to replace material harvested as green rye within a crop rotation, and to replace rye WCS harvested in the semi-ripe stage: Sudan grass, millet or sunflowers can also be grown as catch crops. These catch crops reach maturity at more or less the same time as maize and are ensiled at a dry matter content of 20–27 percent. In contrast to the process of maize mono-fermentation, the intermixture of catch crops such as rye WCS is always advisable. Numerous trials have shown that this greatly improves the efficacy of the biological decomposition process. However, per-hectare yields of rye do not match those of maize. Sophisticated crop sequences, such as the planting of maize only in the first year, followed by WCS cereals, then Sudan grass, millet or sunflowers the following year, are recommended for several reasons. Three such harvests in a two-year period minimises substrate risk, makes slurry management easier, optimises environmental conditions in fermenters and avoids maize monocropping.

The use of millet is also becoming more common, particularly in drier regions. Trials are currently under way with sugar millet (Sorghum bicolor) and Sudan grass (Sorghum × drummondii). Millet appears to be much more tolerant than maize to dry periods, given the crop’s ability to temporarily suspend growth to reduce the risk of premature ripening. Special biogas crop types are currently being developed specifically for high per-hectare yields; however, in favourable growth conditions, the dry matter yields of maize cannot currently be achieved. The dry matter harvest content of ripe millet is below that of maize. The haulage costs per tonne of dry mass are therefore higher, which is why these crops are best suited to locations close to the plant or on light soils that are unsuitable for maize.

Ensilage of sunflowers difficult. Trials involving sunflowers have also been under way for some time. These trials have demonstrated that with proper preparation, i.e. short chop length to reduce grains to small pieces, sunflowers are certainly suitable for use in biogas production. The preservation process, however, is fraught with difficulty. Ensiling sunflowers on their own is virtually impossible, since the material becomes greasy when processed, inhibiting compaction. Attempts to ensile sunflowers together with maize have in fact been successful, although the differences in harvesting timeframes have frequently led to problems. The slurry bonus introduced in 2009 through the Renewable Energies Act, and the widening of scope to grassland processing regions associated with it, has enabled grass silage to outstrip its niche status. In biogas plants, however, grass requires highly stable crop gathering techniques to prevent the blockages that are commonplace with this material. Grass, like rye WCS, however, is not without its problems and can contribute to the thickening of the slurry in fermenters and to the formation of floating layers when larger volumes are processed. The grass must be chopped properly during the harvesting process, since the crushing process within the loader wagon is not sufficient as a means of processing the crop for use in biogas plants.

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Alternatives.

As a supplement to maize silage, however, grass also serves to improve the efficiency of biological decomposition.

matter content and resulting high incidence of sap seepage. Trials in which the beet is chopped up and stored in lagoons or high-silos as pulp have proven highly promising.

Sugar beet: a future contender. Interest in the use of sugar beet in biogas plants has risen massively in recent times. In beet-producing regions in particular, surplus beet (not within stipulated quotas for processing in sugar refineries) is used in biogas plants. Beet has also met with considerable interest among many operators seeking alternatives to maize monocropping. Owing to the vegetable’s high sugar content and low proportion of difficult-to-break-down stabilising substances such as cellulose and lignin, beet is highly disposable in the biogas production process – reason enough for growers to develop a high-energy beet with emphasis shifted away from sugar yield to achieving the greatest possible dry matter per-hectare yield. In contrast to the processing methods employed in sugar refineries, both the head and leaves of the vegetable can also be used in addition to the tuber in biogas plants, which in turn boosts per hectare yields by up to 10 percent. Soil clinging to the vegetable, however, remains a problem, as does storage of the harvested crop. Before the beet is delivered to biogas plants for processing, removal of soil and sand residues is essential, since these lead to sediment buildup in the fermenters. Plant designers and vegetable growers are currently working on solutions to this problem. While beet can be used fresh during the harvesting process and for several weeks thereafter, appropriate preservation is necessary where use is continuous. The suitability of ensiling is limited, owing to the proportionately low dry

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Requirements for silage quality.

Aerobic stability and hygienic quality are essential. (Dr. Johannes Thaysen, Schleswig-Holstein Chamber of Agriculture) The utilisation value of silage in biogas production is derived from a sum of characteristics for which a range of variables are considered (Fig. 4). The most important criteria are the dry matter content and the organic proportion of dry matter (ODM content). Since sap can form below a dry matter threshold of 30 percent, which owing to its easily soluble carbohydrate proportion constitutes a major source of loss, its formation must be kept under control by sufficient ripeness (or cob proportion) in maize and WCS and by an appropriate level of wilting in grass. Any sap leakage that does occur must be either absorbed or collected and fed back to the plant.

extent of methane yield. Since lignin compounds are largely indigestible, high gas yields are achievable only from material that is highly digestible and chopped to schedule. In silage containing a high proportion of starch, the grain and cob proportion is key in this respect. In terms of acidification resulting from the ensiling process, lactic acid predominance is sought (with resulting low pH value depending on dry matter content). In contrast to cattle feed, acetic acid plays a special role in methane yield: its proportion can certainly be higher than that necessary for animal feed. The basis is the central role played by acetic acid in the decomposition process. If, for instance, this can be achieved through the use of appropriate silage additives, the aerobic stability and hygienic quality (absence of mould, reheating) fundamental to the discharge quality of silage will also be optimised.

All inorganic materials, in particular sand/soil remnants, must be kept to an absolute minimum, since gas cannot be formed from these with the exception of essential minerals and trace elements. As in animal feed, the digestibility (degradability) of organic material (OM) determines the

Figure 4: Silage variables for biogas yield

Figure 5: Course of biogas formation

Unit

Target value

Organic dry mass

 % ODM

> 90

800

Sand content

 % DM

75

formation HFT), ELOS pH

< 4.2 at 30%  % NH3-N

< 10%

 % DM

> 2.0

Butyric acid

 % TS

< 0.3

Aerobic stability

Days

>3

Ammonia Acetic acid

Biogas yield in l/kg ODM

Variable

600 500 400 300 200 100

0

5

10

15 Time in days

20

25

Source: Faculty for Agricultural and Environmental Sciences, University of Rostock, 2010, unpublished

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30

Profile of harvesting requirements. (Georg Döring, CLAAS Vertriebsgesellschaft mbH) Against a backdrop of many other field crops used as substrates in biogas production, maize remains at the forefront owing to its unsurpassed rate of gas yield per hectare (Fig. 5). Even as cultivation efforts continue to focus on the yield and energy potentials of specific crop varieties, and as their growth potentials increase, the requirements on harvesting technology nonetheless closely resemble those of businesses engaged in the production of feed. Today’s harvesting technology must therefore be highly flexible and universally deployable on the basis of a comprehensive profile of requirements to facilitate optimal capacity utilisation and economic success.

Energy production requires energy.

In terms of gas yield, however, chop length is not the sole decisive factor. Microorganisms require as large a contact area as possible for methane gas production. Investigatory findings that surface area takes precedence over chop length supports the conclusion that the Cracker system with saw profile teeth and a calibrated speed differential of 30 percent is ideal for achieving maximum gas yields. Measurements taken in collaboration with the University of Rostock indicated positive results in respect of higher rates of crop decomposition. Gas yields tend to increase with unchanged or slightly decreased retention time when the degree of conditioning is increased. In heavily ripened maize crops or when full grain crops or ground ear maize are harvested, friction devices around the knife drum can be highly effective, although they are known to increase fuel consumption by up to 25 percent. The objective must therefore be to produce a homogeneous chopped material with a chop length as short as necessary or as long as possible.

The harvested co-substrate outcome, in turn, is the basis for optimal methane yield, with the energy expenditure during harvesting a key criterion. Chop quality requirements, e.g. structure, chop length, grain and crop decomposition, are time and again the central issue. The interplay of precise knife and shear bar configurations at < 0.1 mm clearance is decisive in ensuring a consistent chop quality. Demands for extremely short chop lengths of 3.5 mm can certainly be met by modern chopping technology; the rationale for extremely short chop lengths, however, is questionable. The increasing energy requirements in this respect, however, are certainly reflected in the costs; in the lower chop length range in particular, a huge increase can be observed. It is also worth noting that fuel consumption rises progressively. This has been substantiated by measurements taken in a project carried out in collaboration with the WeihenstephanTriesdorf University of Applied Sciences. Energy consumption has been measured to rise by approx. 5 to 8 percent when the chop length is reduced from 10 to 7 mm. If the chop length is reduced further from 5 to 4 mm, energy consumption increases by around 10 percent, and at under 4 mm by more than 15 percent. This indicates that the “last” millimetre taps the most energy.

19

Efficient harvesting technology. Engine output and working widths must grow to keep pace with heightened requirements governing high work rate technology. Harvesting outputs of up to 400 tonnes per hour at around 850 hp are today no longer an issue. Viable alternatives to maize in whole crop and grass silage are sought in light of cultivation and economic concerns. The versatility of attachments is therefore essential for capacity utilisation and economic efficiency. For this reason, many farms turn time and again to the flexible and versatile direct cutterbar from CLAAS to tackle a wide range of field crops. Whether picked up as a swath or chopped directly, operational quality remains the foremost concern. Through the use of high-performance and powerful harvesting technology, fuel consumption can be drastically slashed in the majority of cases. Nonetheless, in order to achieve higher work rates, the entire harvesting chain should always be properly synchronised. The weakest link in the chain determines the output achieved – and it‘s not usually the forage harvester. There are, however, factors such as the CLAAS knife drum concept (V-MAX), a clearance setting control on the accelerator and an integrated tyre pressure regulation system that contribute to further increasing efficiency. Results from forage harvester product development indicate that, through systems such as these, fuel savings of up to 7 percent can be achieved with the same engine performance. It is therefore the overall design of the machine and its own tare weight that determine economic efficiency.

20

Collection and administration of harvesting data. The uninterrupted recording of dry mass and harvest volume data and high-precision WCS yield mapping are becoming increasingly important. This data creates transparency for biogas system operators regarding the volumes of dry mass harvested. Continuous dry mass measurement at a rate of 100 measurements per second is much more accurate and precise than individual random samples remeasured in a dry box. Individual values in dry box conditions can vary greatly where random samples are taken by hand. Additionally, moisture-specific data relating to the harvested crop in the chopper is set against yield values, which further increases accuracy with regard to the harvested volume. Assuming the yield measurement of the forage harvester is calibrated consistently, yield values can be achieved with an accuracy to within 2–3 percent or less. The precision of the dry mass sensor, which measures the conveyance qualities of the chopped material, is dependent on harvesting and throughput conditions. Finally, dew and precipitation also have an impact on the dry matter content of the chopped material that should not be underestimated.

Harvesting technology.

The recording and further processing of this comprehensive range of harvesting data noticeably improves operational processes in practice. Telemetry systems in harvesting machines also play an important role. Today’s technology already allows for the monitoring online of the operating statuses of machines and for the optimisation of their settings. This can be done easily, at any time and from any location, online in consultation with the machine operator. Harvest-specific data relating to each job is also transferable to the user online in 15-minute cycles, enabling the user to track each job completed or process further data received. Greater transparency in the harvesting process allows for rapid intervention in emergencies and time saved on the job with data exporting and transfer facilities, e.g. to field catalogues, in addition to providing a secure data flow. Developments in the field of electronics are also progressing rapidly, with new possibilities opening up to biogas operators all the time. The primary objective is to deliver the harvested crop to the biogas plant as efficiently as possible and in due consideration of all ecological and economic considerations – now possible with modern chopping technology.

Figure 6: Consumption/throughput per chop length

10,1 % 4 mm

4,0 % 5 mm

Consumption l/t

5,5 % 7 mm

10 mm

Throughput (t/h)

Source: Degree dissertation, Weihenstephan-Triesdorf University of Applied Sciences, unpublished

Figure 7: Speed differential direct comparison – 20% vs. 30% Standard prior to 2010

Standard from 2010

100 70,97 %

78,83 %

19,86 %

15,92 %

9,04 % 0,13 %

5,25 % 0 CLAAS 4 mm, CC 1 m, 125Z, 20%

Very coarse

Coarse

CLAAS 4 mm, CC 1 m, 125Z, 30% Average

Fine

Source: Faculty for Agricultural and Environmental Sciences, University of Rostock, 2010, unpublished

21

Alternative and catch crop substrates. Use of cultivation alternatives on the rise.

However, the cultivation of field grasses and grassland crops is also finding increasing scope in biogas production.

(Dr. Matthias Benke, Carsten Rieckmann, Lower Saxony Chamber of Agriculture)

Distinctions can be drawn between these crop types both in terms of their methods of cultivation, and gas yield (Fig. 8), and clearly demonstrate that maize, in terms of organic dry matter, offers distinct advantages over millet, sunflower and cereal WCS. Beet, in contrast, is characterised by higher gas and methane yields per standard litre of organic dry mass and its retention time in the fermenter is just 15 to 30 days, while for maize this is usually 60 to 90 days. The use of sugar beet can therefore boost a plant’s efficiency. Grass mixtures produce medium-range results in terms of gas yield. There are, however, very clear differences in this respect between seed mixtures (grass, legume proportion) and harvesting timeframes.

Exclusive focus on maize cultivation in the supply of substrate is today meeting with increasing dissatisfaction among the population at large given the anticipated visual landscape impact, and in light of cross-compliance land management requirements is also ill-advised. The search for cultivation alternatives is therefore essential. Since 2004, there has been an increasing drive towards investigating potential alternatives in Germany. Potential crops have included various species of millet (Sorghum bicolor) and Sudan grass (Sorghum sudanense / Sorghum bicolor x Sorghum sudanense), sunflower, cereal wholecrop silage (WCS) and increasingly also sugar beet.

Figure 8: Standard values for gas yield Methane

Methane yield

Remarks/properties

Dry

mass % %

lN/kg ODM

content %

lN/kg ODM

Maize silage

-

33

95

650

52

338

CCM

-

65

Sorghum silage Cereal WCS

– 28 Average grain proportion 33

98 90

730 610

52 52

380 317

95

620

53

329

Green rye silage

–

251)

90

600

53

318

Sunflower silage

–

25

90

520

57

296

Sugar beet silage

ODM, acidity-corrected

23

90

700

52

364

Fodder beet silage

ODM, acidity-corrected

16

90

700

52

364

Cereal grain

Milled/crushed

87

97

730

52

380

Grain maize

Milled/crushed

87

98

730

52

380

Straw

Short-chopped

86

90

400

52

208

Grass silage

–

35

90

600

52

312

Landscape husbandry

–

50

85

200–400

50

100–200

grass Clover grass silage

–

30

90

580

55

319

Clover/alfalfa silage

–

30

90

530

55

292

Substrate

of which ODM Biogas yield

Renewable resources

1)

Source: After KTBL, Faustzahlen Biogas, 2nd Edition 2009

22

Field forage and grassland mixtures. Through the cultivation of field grasses in pure seed, agricultural grass mixtures and legume grass mixtures, a large volume of biomass can be produced for biogas production through a multi-stage approach. Chopped grasses that are not used as fodder can be utilised through fermentation. In regions in which maize cannot be grown, such as in high-altitude areas or swamp wetlands, grasses can serve as an excellent biogas substrate. Yield levels range between 60 and 150 dt DM/ha, sometimes higher, depending on the site conditions, grass mixture and chop frequency. All arable land is suitable for the cultivation of field grasses; swamp and wet soils as well as dry sites, however, deliver lower yields, and thus lend themselves to grassland mixtures.

retention time), since the fermentation process for celluloserich materials is more challenging. In selecting suitable seed mixtures, experience has shown that regionally established mixtures generally deliver the best yield and economic results. In the arid climatic conditions of Germany’s eastern federal states, perennial alfalfa grass and alfalfa/crimson clover grass mixtures have been shown to perform best. With sufficient water supply, the use of crimson clover grass or rye grass mixtures is to be preferred in eastern regions. In the humid climate conditions of northwest Germany, however, the use of rye-grass-heavy mixtures made up predominantly of southern European rye grasses and hybrid rye grasses is advantageous. Yield results and economic results both substantiate that a usage regime with reduced chop frequency (three to four instead of four to five cuts per year) brings distinct advantages with yields up almost 10 percent in almost all regions and in all mixture varieties.

Rye grasses are intercompatible, and as such continuous sowing or immediate re-sowing is possible in pure grass stands. Crimson clover is not intercompatible, nor is it compatible with most other legumes, and cultivation intervals of between five and six years in pure stands and between three and five years in mixture cultivations should be adhered to. In alfalfa, too, cultivation intervals of between five and six years are advisable. The favourable previous crop effects of clover grass and alfalfa grass mixtures through nitrogen fixation for subsequent crops should be noted. Very early and frequent chopping (5x) ensures a highdigestibility biomass grade, though not necessarily the highest overall yields. The grass mixture is considered ready for chopping upon ear emergence. If chopping is postponed until the conclusion of ear/panicle emergence, greater yields are achievable per chop, although raw fibre content is also increased. In clover-dominated crop stands, the harvesting process can take place during the budding to flowering stage. The plant and delivery technology of the biogas production system must be designed to cope with cellulose-rich grasses (larger agitators and fermenter volumes, longer

23

Sugar sorghum and Sudan grass.

Sunflowers.

Like maize, millets are annual C4 crops, although they are more sensitive with regard to temperature. A soil temperature of at least 12°C, or preferably 14°C, should be maintained throughout the emergence phase. Sowing, therefore, should ideally not take place before mid-May. The disadvantage of this, in contrast to maize, can be rectified by using the growth period in spring for the cultivation of green rye before sowing.

With the onset of biogas production from renewable resources, hopes soon turned to sunflowers as a potential biomass source, since excellent gas yields were attributed to the crop thanks to its high oil content. Studies have revealed a high methane content attributable to sunflowers of approx. 57 percent (Fig. 8), although gas and methane yields per kg ODM, and specifically per kg of dry matter, are significantly below those of maize.

Future cultivation objectives are primarily focused on increasing yields and improving cold tolerance and stability. In favourable conditions, however, the crop types already available on the market are able to produce good yields, although yield fluctuations are more pronounced than in maize. Millet, however, demonstrates greater tolerance to dryness, and in especially dry conditions can deliver better results than maize.

Even though cultivated sunflowers make a most impressive sight, yield measurements verify that they cannot keep pace, in terms of potential yield, with maize and, in most cases, millet crops. The practice of mixed cultivation with maize promoted heavily in the years 2004 and 2005 proved unfeasible, in practice given the difficulties in harmonising the highly specific weed control methods of each crop type. In sunflowers, for instance, this can be carried out only prior to emergence. The different maturity characteristics of the two crop types is a further problem. Specifically, the very tight harvesting window of sunflowers is a major problem. By today’s methods, sunflowers are predominantly cultivated as a monoculture. In many cases, these are planted around the edges of maize plantations to visually break up the field structure. Efforts in recent years to develop the crop further for use in biomass production have now been cut back once more.

Trials involving a wide range of crop stand densities have revealed that sugar sorghum should be sown at approx. 20 to 25 plants/m2 and Sudan grass at approx. 50 to 70 plants/m2 at row widths of between 25 and 75 cm. The advantages of narrower row widths are most apparent in Sudan grass, with a much-improved apportionment of crop stand space guaranteed. The crop variety trials, which were carried out at various locations across Germany, revealed the degree of variability in maturity characteristics to be substantial. In general, harvesting should get under way as soon as the dry matter content throughout the entire crop reaches 28 percent. Millet is a good and easy crop to ensile, and should be harvested using standard, row-independent precision choppers.

24

The harvesting of sunflowers is also performed with the use of precision choppers at relatively low dry matter contents of approx. 25 to 27 percent; desirable dry matter contents above 28 percent are usually not achievable, since the crop stands must be harvested prematurely in order to prevent the spread of disease (e.g. sclerotinia or botrytis). Passing over silage clamps is possible only with great difficulty, since the silage contained in them is usually wet, and the oil content also complicates the process of compaction of the harvested crop.

Possible supplements.

Green rye and cereal WCS. With respect to the application of green rye in biogas production, which as a crop is harvested in the ear emergence stage from late April / early May, special greencut rye varieties are recommended. These are characterised by rapid development in autumn and spring compared with grain-yield-heavy population and hybrid varieties. Early sowing from mid-September offers distinct advantages in achieving yields above 50 dt DM/ha, and in guaranteeing early sowing in the subsequent primary crop cultivation stage (usually maize). Green rye, however, achieves only low dry matter contents, in some cases rates below 20 percent. To improve ensilability, wilting of the harvested crop is recommended. When a conditioner is used to mow green rye and this is left in swaths, the harvested crop can be secured and subsequently ensiled by the chopper after an on-field retention period of one day at approx. 25 to 30 percent with no additional turning or swathing necessary.

triticale in particular, high mass-producing varieties with good grain yield values should be selected. If subsequent catch crop cultivation is planned, the rye crop should be harvested first. Alternatively, a less yield-heavy winter barley should be cultivated as whole-crop silage. WCS cultivation, as a supplement to maize, offers many cultivation-specific and economic advantages, since work peaks are equalised.

Cereal as whole-crop silage (WCS) is harvested in the milk ripeness / early wax-ripe stage from about mid-June to the beginning of July at dry matter contents of approx. 32–38 percent. In addition to rye, triticale and wheat are also highly suitable in this respect. Although favourable yields can be produced from rye in virtually all regions, wheat and triticale should be reserved primarily for better sites. As regards

25

Production of energy crops.

Sugar beet.

Further cultivation alternatives.

A new hope, sugar beet is now increasingly used in biogas production chiefly in traditional beet-producing regions. The advantages described earlier – high gas and methane yields coupled with shorter retention times in the fermenter – ultimately lead to an overall increase in the efficiency of the biogas plant. High yields in the field are a further benefit, which in respect of dry mass and methane yield can often exceed those of maize.

Silphium perfoliatum, a herbaceous perennial, is a crop currently attracting a great deal of discussion. Silphium perfoliatum has to date been cultivated on a trial basis only, with the aim of testing the requirements of the crop and its gas yield properties.

In major processing regions too, however, and with sufficient precipitation, sugar beet can also be used to replace and reduce the high proportion of maize in the crop sequence. Efforts by growers are currently under way to develop even higher yield varieties, since the quality parameters relevant to the sugar refining industry are of only minor significance in biogas production. There is little difference between conventional sugar beet cultivation and cultivation for biogas production. With regard to the cultivation of beet for biogas plants, soil residues and stones in silage clamps and the various issues associated with preservation are major stumbling blocks. Practical solutions must be developed to address these issues. The objective must be to bring the beet to processreadiness without having to subject them to a costly washing process. With regard to the storage of beet, a number of solutions are readily available, ranging from the storage of whole roots in clamps to the storage of chopped beet in plastic wrapping and of beet pulp in a soil basin. Mixed silage with maize or CCM or ground ear maize are also possibilities; in the former, however, the yield increases of the beet are not fully exploited, owing to premature harvesting. The aim is to ensure the year-round availability of beet stocks for biogas plants.

26

During these trials, yields of 130–200 dt DM/ha were recorded from the second year of cultivation. The methane yield in the biogas plant proved comparable to maize yields in initial trials; multi-year trial results, however, are not yet available. The planting of pre-cultivated young plants is currently the most practicable option in achieving closed crop stands. It is believed that the use of this technique over several years (more than 10 years) will be sufficient in compensating for the high processing plant costs associated with the precultivation and planting of young plants. In the year of planting, Silphium perfoliatum forms only a basal leaf rosette, with harvesting possible from the second year of cultivation in September at dry matter contents of approx. 28 percent.

Figure 9: Overview of production guidelines for energy crop cultivation (Germany) Base fertilisation / content class Fertilisation, C

Optimal sowing density / plants/ Optimal sowing/

Sowing

MgO

m2

planting time

N-target P₂O depth, cm value kg/ha1) kg/ha

K₂O

Crop type

kg/ha

kg/ha

Silage maize

7–11

Mid-April / early May

3–6

180

110–80

230–160

40

Green rye

250–300

Mid-September / early

2–3

150

50

90

30

250–330

October Mid-September / early

2–3

180

80–50

150–90

40

Winter rye

180–280

October Mid-September / early

2–3

150

80–50

150–90

40

Triticale

220–320

October Late  September / mid- 2–3

190

80–50

150–90

40

250–450

October Late September / early 2–3

200

80–50

150–90

40

Sugar millet

20–25

December Mid-May / late June

3–4

160–140

90–70

150–120

30–15

Sudan grass

50–75

Mid-May / late June

2–3

160–140

90–70

150–120

30–15

Sunflowers

7–8

Late March / early April 3–5

120–80

80–60

200–140

60–40

Sugar beet

8.5–9.5

Late March / mid-April

2–3

160

100–70

380–290

80

Field crops

25–45 kg/ha

August/September

1–3

Up to 320 2) 110–802)

380–2902)

60

4

Mid-May / mid-June

Bale depth 160–150

240–180

120–80

Winter barley

Winter wheat

Permanent crops Silphium perfoliatum 1) 2)

70–55

The N-fertilisation values and N-target values must be modified depending on the Nmin soil value, site conditions, previous crop and the capacity of the soil for subsequent nutrient supply. For certain crops, target values must be additionally validated through additional trials. The extent of N, P and K fertilisation is dependent on the use intensity and mixture composition of the crop stand. Legume/grass mixtures require significantly less N fertilisation.

27

Factors affecting the ensiling of maize. (Dr. Johannes Thaysen, Schleswig-Holstein Chamber of Agricultural) The objective when ensiling maize for fodder production and substrate supply should always be to furnish and supply optimal gross yields from the field with as high an energy density as possible with minimal fermentation and reheating losses. Since silage units can cope in terms of stack height, particularly in plant facilities without side walls, and since silage maize is often cut to a shorter length when destined for biogas fermentation as opposed to fodder applications, sap formation is increasingly noticeable even at higher whole crop maturity > 33 percent dry matter. Suitable preventative strategies (cultivation and silagerelated) should be explored to eliminate these avoidable sources of loss. Key factors with regard to this process include site-adapted crop variety selection, sowing schedule, N fertilisation, harvesting schedule and chop length (dependent on storage location within silage plant and dry matter content).

Harvesting schedule, dry matter content. In terms of crop maturity, which is fundamental in determining the optimal harvesting schedule, there should be no significant variation between varieties destined for biogas production and those destined for fodder production applications. Silage maize for biogas production should reach the wax-ripe stage of maize also in less favourable years. Late-maturing varieties often deliver higher fresh matter yields (i.e. higher water contents = higher transport costs), but do not always bring improved results in terms of gas yield. The fresh matter yield is not the decisive factor, but rather the fermentable mass yield. In terms of determining the harvesting schedule, this means that there is only a relatively narrow timeframe in which silage maize maturity is considered optimal (30–35 percent dry matter content). It may therefore be considered prudent on a farm-by-farm basis either to cultivate varieties with

28

varying maturity patterns or to configure the harvesting process to be staggered chronologically according to the varying maturity characteristics of the different soil types. Regional administrative authorities in Germany and the DMK are currently compiling comprehensive projections regarding crop maturity to identify the harvesting windows of each usable crop variety.

Chop length and quality, grain conditioning, excess length. Various trials (JOHANNSEN, 2005), (FNR, 2005), (KTBL, 2004) have shown that the intensive crushing of silage under otherwise identical fermentation conditions can deliver greater gas yields. A compromise must therefore be reached when determining chop length between this requirement, the compactability of the material subject to silo form, the type of plant and the level of diesel consumption. Fig. 11 lists recommendations on chop and cutting length, grain conditioning, hygienic silage quality and plant type. The chop length range should therefore be set between 4–7 mm (theoretical) where intensive grain crushing is performed by a downstream cracker roller system. The intensity of grain conditioning must be increased the more mature the grain becomes. The same also applies to chop length: the higher the overall dry matter

Figure 10: Optimal dry matter contents and chop lengths in silage maize and GPS for biogas at various stack heights Stack height

Unit

Silage maize GPS

Up to 3 m

 % DM

From 28–30

From 35–40

mm

9–6

6

3–6 m Over 6–10 m

 % DM

30–35

40–45

mm

7–5

5

 % DM

35–38

45

mm

5–4

4

Maize silage as coferment.

content of the maize silage crop stand during harvesting, the more important it is that the above recommendations are observed, since fibre content also increases with increasing maturity. Accordingly, this is an additional factor fundamental in reducing compactibility (roller rebound) and gas yield. Excess lengths can occur, e.g. from long husks, with increased maturity and if the chopper is working to capacity. Depending on the pump and agitation technology employed, problems can occur if the excess length proportion in the silage exceeds 5 percent. There is also a risk of scum layer formation.

Figure 11: Requirements for maize silage as coferment in biogas plants of different sizes Biogas plant types1) Variables

1 fermenter with up to 5 m3/ Small fermenter and postkW electrical output

Large fermenter and post-

fermenter, or large fermenter fermenter with > 10 m3/kW with 5–10 m3/kW electrical electrical output output

Retention time

Short (< 40 days)

Medium (40–60 days)

Long (> 60 days)

Volumetric load

High

Medium

Low

Lower value 80–90

Standard value 100

High > 110

Methane yield m /t FM (relative) 3

Requirements for maize silage as coferment Chop length

< 5 mm

5–7 mm

5–7 mm

Dry matter content

> 33%

30–35 %

30–35 %

Corn conditioning

Required

Dependent on maturity and Dependent on maturity and

Excess length and husk proportions

Dependent on plant system Dependent on plant system Dependent on plant system

retention time

retention time

and agitation technology

and agitation technology

and agitation technology

Silage hygiene2) Yeasts, kbE/g FM

< 104

< 104

< 104

Fungi, kbE/g FM

< 102

< 102

< 102

1) 2)

The larger the plant, the smaller the slurry proportion can become (up to 0). If the proportion of slurry is very small, pH regulation (e.g. through addition of lime) may be necessary to stabilise pH values (optimal pH value: 7.2–8.0) Silage hygiene quality must be optimal as slurry volume decreases

29

Compaction: the key to success.

Controlling factors within the silage maize harvesting process chain. (Heinz-Günter Gerighausen, North Rhine-Westphalia Chamber of Agriculture) The silage maize harvesting process chain has many controlling factors underpinning quality assurance, beginning at the cultivation stage with selection of crop variety, and then on to the scheduled harvesting time, chopping, transportation and storage. This is all carried out solely under the principle of minimal losses, maximum forage quality, from stem to (rumen) microbe.   Silage maize cultivation is, on the one hand, a relatively straightforward and calculable process. This is because the necessary process stages from cultivation to harvesting are easily manageable. At the time of harvesting, however, a process chain is triggered that must be updated annually. This is because the process variables are subject to natural changes. This applies both to dairy cattle owners with large herds and to energy farmers with large biogas plants, regardless of whether the harvesting process is carried out by themselves or by contractors.

30

Silage losses cost money. The selection of crop type also plays a role in determining when the harvesting process can take place, since nutrient densities and potential silage losses are determined from the dry matter content. The necessary chop height and length is determined based on the application. The chief concern here is to prevent avoidable losses and thus, in the case of silage maize, a great deal of money. Throughout the preservation process chain, from stem to discharge, economic and biological fermentation-specific parameters must be respected. Field losses and sap seepage are process-dependent and hence controllable. Some losses are unavoidable in the actual fermentation with specific residual respiration, however, since substance conversions occur naturally during the ensiling process. Potential deficiencies in fermentation and reheating are between the covering to discharging stages. In all, this equates to deficiencies of 3 to over 10 percent or monetary losses of 80 to over 500 euros/ha, without taking into account diminished milk and gas yields: overall, decidedly thoughtprovoking figures.

Chop quality counts. The harvesting process usually takes place over a period of four weeks. The degrees of maturity vary irrespective of crop variety. It is at this stage that chop length becomes a principal consideration. For biogas maize, rapid decomposition for bacteria is key, and thus a chop length of 5–7 mm is considered optimal. Physiological effects on the rumen of dairy cattle are expected from the forage, and this requires a certain “structural efficiency”. Dairy cattle farmers with a ration suitable for ruminants will manage well with a chop length of 9–11 mm. A longer chop length will heighten the difficulties associated with the process. Grain decomposition requires an exact configuration of crushing rollers. For a precise harvesting technology configuration, the proportion of crops cut to longer lengths must be negligible, there must be no husks and spindle discs must be thick. In recent years, maize ears have been observed at the end of the harvesting season to have already reached a highly mature stage as the entire crop’s dry matter content increases. A shorter chop length is then prudent in view of biological fermentation considerations.

The speed of the pre-compression rollers and thus both the chop length and header speed are reduced, which is also acceptable. If the rotational speed is not adjusted, excess lengths, i.e. “straw particles”, are pre-programmed. This should be avoided, since the objective is to achieve optimal compactibility with more reliable ensilability for less reheating with higher milk and gas yields.

31

Greater compaction of harvested volumes. The challenges associated with harvest management also impact on logistics. At engine outputs of 850 hp with optimised drive trains, chopper outputs in practice of 200 to 300t/h FM are not uncommon. This equates to 3.5 t/min or 60 kg/s, or a “full wheelbarrow” of maize every second – huge masses to be processed efficiently. The days of implementing loader wagons, muck spreaders or even outdated wagon technology to assist in maize haulage in the maize harvesting process are over. Today, the haulage process is much more professional. Which technology is best suited to the task? To answer this question, considerations relating to the location of the ensiling process need to be factored in. Regardless of the force applied in rolling – e.g. unloaded – distribution and rolling, each transport unit requires a cycle time of at least 5 minutes for discharging, dispensing and rolling. Per hour, this equates to a maximum of 12 transport units. At 200 t FM/h, this equates to an average of 16–17 t FM/transport unit or, as stated, above 3.5 t/min. This necessitates huge power reserves for spreading and rolling. The need for the ensiling process to be well managed is self-evident. The true value of a good rolling system is also a major topic of discussion. Quality rolling is and remains the best guarantee of a reliable and stable fermentation process. The reasonable running surfaces also conceived of in current environmentally compliant ensiling plans are also based on principles of safeguarding quality. Time and again, the debate thus returns to the issue of whether the forage should be dumped by tipping in front of the clamp or by passing over the forage stock. The answer is simple: whichever method is the easiest, most effective, fastest and most efficient to implement is the best course of action. This is because the objective is to achieve the greatest possible density. The question of “how I get to that point” is not as important as “how I achieve it”. Sufficient practical experience and investigatory studies certainly support this. Appropriate ballasting of the vehicles used for spreading and rolling is fundamental in ensuring an optimal compaction technique. This can include tractors, wheeled loaders and caterpillars fitted with modified technology for

32

distribution and/or rolling applications. The following formula serves as a guide: load volume in tonnes per hour split between four rolling weights of equal utilisation requirement. In the case in point, 50 tonnes of concentrated distribution and rolling technology distributed across several vehicles is also feasible at these hourly outputs and parameters. In small-structured farms, chopper outputs of 500 hp (140– 160 t/h FM) are appropriate and sufficient to complete the necessary operational steps at these storage capacities. The approach taken is to distribute the harvested forage in layers as thin as possible, and to immediately compact these. Edging and distribution blades have also proven their worth in maize harvesting applications. With working widths of up to 6 metres, adjustable side wings, slope and parallel control, high distribution rates are possible. The objective: thin layers from, if possible, 10 cm thickness, compressed to the greatest extent possible in maximally three passes at approx. 4–5 km/h at more than 2 bar tyre air pressure; every part of the forage stock, especially at the weak points, i.e. the edges of the clamp. This 10-cm layer thickness with a density of 350 kg/m3 equates to an “area output” of 100 m2/min for distribution, rolling and compaction at 3.5 t/min – a major challenge. This shows that at a harvesting output of 200 tonnes, a rolling weight of 50 tonnes is not excessive. The density can never be too high, as demonstrated in a number of studies at storage heights of both 2 metres and 7 metres. Whether or not there are side wings makes no difference. Aerobic stability is attained only from high compaction; gas exchange occurs either way. It is the intensity that must be kept in check. Harvest and clamp management go hand in hand. Transportation and forage stock logistics should be viewed as one operational field.

Avoiding losses.

Silage discharge – the right way. In the silage discharge process, a feed system is employed alongside a gas-tight covering. The process attempts to manage reheating and gas release at 1.5 m/week in cool temperatures and 2.5 m/week in warm temperatures. Alongside this requirement, the clamp location and emptying method are also very important when it comes to ensuring silage quality. Atmospheric conditions should also be taken into account with regard to reheating and gas release procedures. If possible, the clamp face should not face into the direction of wind, rain or direct sunlight, since these can directly and critically impact these procedures. Gripper buckets have found increasing use in the emptying process in recent years, having proven themselves in the field. The most effective ways to use these attachments have also attracted intense debate. The reality often seems alarming. Dairy cattle farmers can supervise the day-to-day discharge management process in the feeder by reviewing “crop intake and crop residue” parameters. The biogas plant is equipped with a dosing and feeding apparatus, with additives surrendered to the microbes for further processing independent of quality and hygiene. Owing to long retention times of more than 42 days, mishaps occur less rapidly than they do in dairy cattle, which have a maximum of 1.5 days.

Figure 12: Loading technology for biogas plants – comparison overview Properties

Telescopic loaders

Wheeled loaders

Range / lift height

High

Medium

Versatility

High – ideal for maintenance work on biogas

Medium – earthworks applications owing to

plant, amongst other applications

robust construction

Dimensions/manoeuvrability

Small machines – high manoeuvrability

Heavy construction – poor manoeuvrability

Cost (machine as new)

Low compared with wheeled loader

High

Lift capacity

Much less than wheeled loader

Higher

Material handling capacity

Less

Higher

Suitability as roller vehicle

Poor

Medium to high (diesel consumption high)

Clear view

Low seat position

Usually high seat position

Service network

Agricultural experience available

Minimal experience in agricultural context

Source: Norbert Täufer

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Harvesting logistics and background conditions. Sophisticated biomass logistics required. (Martin Gehring, Board of Trustees, Bayerischer Maschinenund Betriebshilfsdienste e.V.) Renewable resources are today used as substrates in many biogas plant systems. In general, the efforts required in the transportation and provisioning of biomass and in the application of fermentation residues are considerable. The costs incurred in this respect can account for a significant proportion of the overall cost structure of substrate supply. There is therefore increasingly a need for sophisticated biomass logistics systems and technology to facilitate the coordination of harvesting processes in the field, transportation on the road, and storage procedures in the silo.

A wide range of factors must be taken into account. The early planning and scheduling of designated harvesting zones is key. The volumes of substrate and fermentation residue to be transported increase in line with the size of the biomass plant, as do the distances between plant and field, given that areas for harvesting become more extensive as requirements for land increase. In any case, the outputs of chopper units, transport vehicles and in particular roller vehicles must be coordinated to ensure the effective and efficient supply of high-quality silage with zero idle times. This results in an ever-greater impact of topography and infrastructure on processes. The single-phase harvesting procedure based on the parallel guidance system continues to play a leading role in the harvesting process, especially in the harvesting of maize. In this system, the transport vehicle is loaded directly in the field by the chopper unit and transports the harvested crop directly to the silo. The tractor/chopper trailer combination constitutes the traditional transport unit in this process; these days, however, appropriately equipped agricultural trucks are also used, with transport volumes of 45 m3 to 50 m3 now standard. Other tried-and-tested procedures include parallel guidance systems with tractor/trailed dolly/articulated trailer combinations with significantly increased transport volumes; these are currently experiencing a boom in popularity. The use of available bunker systems, however, is to date less widespread. As transport distances increase, the role of multi-phase, decoupled systems in various guises becomes more important. The chopping and transportation in the field is undertaken in the “traditional” manner, i.e. with forage harvester and tractor combination or agricultural truck. At the field periphery, the harvested crop is reloaded onto an awaiting truck. This is performed in a variety of ways, either directly through the use of transfer wagons or transfer stations, or involving interim storage in a clamp with subsequent loading from the ground by a bucket excavator, loader or now commonly used loaders for renewable resources. Through vehicle combinations such as these, a

34

diverse range of requirements can be accommodated, e.g. with respect to tyres. Soil compaction in the field, and wear and tear and fuel consumption on the road, however, are often at odds in this respect. Regardless of the number of chopper units deployed, the number of transport vehicles required or the local conditions on site, the effective coordination of vehicles is crucial. In addition to the traditional means of communication between vehicles, i.e. by mobile phone, in larger harvesting chains vehicles are interlinked by EDP and Mob-GIS systems. In future, the coordination of entire harvesting logistics systems will be much easier with field navigation. Furthermore, the development of data recording systems to aid in accounting and documentation tasks continues (see page 41).

The approval of the local population is extremely important when it comes to ensuring seamless biogas plant operation. It is therefore essential that the plant is run responsibly and considerately, and that local residents are informed adequately and in good time, and that their concerns and grievances are dealt with appropriately. Without mutual consideration, both on the part of agricultural suppliers and biogas plant operators, and also on the part of the local populace and specifically local residents, a successful operation is not possible. Accordingly, there is now an obligation on the part of biogas plant operators and farmers to provide information without being prompted.

As vehicle sizes increase, the stipulated thresholds governed by applicable statutory regulations are now being reached. Adherence to statutory background conditions must be the basis of acceptable practices with regard to the harvesting of substrates and the application of fermentation residues. In turn, this means that vehicle dimensions, total weight and speed restrictions, etc. must be adhered to. The true nature of the task at hand, i.e. agricultural haulage or commercial freight haulage, must be determined before operations commence. Applicable authorisation regulations in accordance with the German Road Haulage Law (GüKG), the associated driver’s licence categories, monitoring equipment obligations and commercial driver qualification requirements, etc. must be observed accordingly. The need to ensure sufficient load safety is becoming more and more crucial. Owing to the hazards associated with dangerous and unsafe loads, much greater emphasis is now being placed on ensuring appropriate check procedures are carried out. The vehicle driver, owner and loader are each responsible for ensuring load safety. Road soiling is a traffic hazard, and suitable arrangements must therefore be made for road cleaning.

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Professional costing is essential. (Dr. Martin Wesenberg, Dr. Christoph Bollmann, Bundesverband Lohnunternehmen (BLU) e.V.) Often, a plant’s harvesting requirements are contracted out to private companies, i.e. the maize, grass or other field crops designated for harvesting are chopped, transported and compacted by private contractors. In contrast to agricultural harvesting practices, and in particular the harvesting requirements of dairy farms, contractors have traditionally been confronted with enormous volumes of crops to process. A 500-kW plant, for instance, requires some 10,000 tonnes of maize silage for the fermentation process, in addition to slurry and other biosubstrates. This volume of maize is grown on arable land of between 200 and 250 ha, and in individual cases must be transported over comparatively long distances, and must be stored under silage film for approx. 8 to 10 days.

Figure 13: Procedural costs per operational hour, subject to capacity utilisation

700

€ per hour of operation

600 500 400 300 200 100 0

Forage harvester, 350 kW 200 h (residual value 30%)

300 h (residual value 25%)

400 h (residual value 20%)

500 h (residual value 15%)

Source: BLU, 2010

36

Forage harvester, 750 kW

The large order volumes, the complex nature of harvesting processes and, not least, competition make accurate and proper costing crucial – regardless of whether a contractor, agricultural business, biogas plant or machine alliance is involved.

Harvesting. When it comes to maize harvesting, the forage harvester is the most expensive single machine. The spectrum of highperformance harvesting machines involves engine outputs from 300 to 750 kW. In most cases, 8- to 12-row (in isolated cases 14-row) maize headers are used, which facilitate work rates of 1.5 to 4 ha/h, depending on harvesting conditions. This equates to throughput values ranging from 60 to more than 200 tonnes per hour. These capacities are furthermore in accordance with the requirements of plant operators for on-schedule harvesting. In certain circumstances, weather conditions may also necessitate rapid harvesting. This means the period for maize harvesting allocated by the commissioning biogas plant is extremely tight. In the case of a 500-kW plant, daily outputs of 25 to 30 ha are necessary in order to complete harvesting safely within 8 to 10 days.

Harvesting and transport costs.

A 350-kW chopper unit achieves an average chopping output of approx. 90 to 120 t/h. Large-scale chopper units harvest on average approx. 180 t/h. Chopping-related costs depend on machine and capacity utilisation accordingly. These are shown in the following table (Figure 14). Large-scale machines operate much more efficiently in terms of cost than forage harvesters of the mediumperformance class at the same hourly capacity utilisation, as the diagram clearly shows. If a 750-kW machine is operated for only 200 drum hours per harvest (equivalent to 36,000 tonnes or 720 hectares of maize), the 350-kW version (at 400 h) has significant cost advantages. This amounts to 0.50 euros/t or 18,000 euros per harvest. Machine costs in particular should be emphasised; these are influenced more and more by variable costs associated with the increasing cost of energy and replacement parts. Specific diesel consumption amounts on average to roughly 0.7 l/t of chopped maize.

4,0 3,5 3,0 € per tonne

Regardless of the performance class and make, it is a machine’s capacity utilisation that has the greatest impact when it comes to calculating process-related costs. A forage harvester in the medium-performance class generates process-related costs of 276 euros/h at a capacity utilisation of 300 drum hours (sum of machine costs, personnel, business-related costs and risk). Processrelated costs are subject to degression as capacity utilisation increases, and are reduced to 250 euros/h at a capacity utilisation of 400 drum hours. In order to calculate an appropriate base price, process-related costs must be increased to factor in a profit margin. The exact margin should reflect regional market conditions.

Figure 14: Process-related costs per tonne, in relation to capacity utilisation

2,5 2,0 1,5 1,0 0,5 0,0

200 h (residual value 30%)

300 h (residual value 30%)

Forage harvester, 350 kW

400 h (residual value 30%)

500 h (residual value 30%)

Forage harvester, 750 kW

Source: BLU, 2010

Figure 15: Process-related costs of a maize harvesting chain, in relation to transportation distance

12 10 € per tonne

Costs.

8 6 4 2 0

2 km

Roller technology (15 t) Forage harvester (350 kW) Source: BLU, 2010

5 km

10 km

15 km

Discharge combination (40 m3)

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Transport.

Performance.

Figure 16: Transport costs per tonne in relation to distance – full/empty runs; idle times not considered

The trend in biogas production is increasingly toward larger plants. As a consequence, transport volumes and distances are also increasing, with process-related costs in maize harvesting rising, as shown in Fig. 15. If transport distances increase from 2 to 15 kilometres, process-related costs increase by approximately 4 euros/t.

7

Euros per tonne

6 5 4 3 2 1 0

1

5

10

15

20

Furthermore, an additional four tractors and silage trailers need to be deployed for the three transport combinations used over the first 2 kilometres to ensure seamless operation. This is where the limitations of contractors become evident. Farms are increasingly being forced to take alternative, efficient and inexpensive logistics concepts into consideration.

Tractor (40 km/h) and trailer (15 t) Tractor (50 km/h) and trailer (15 t)

Truck transport.

Articulated truck (20 t) Source: BLU, 2010

The truck is the machine of choice when it comes to transporting large volumes quickly and cost-effectively. The low rates of diesel consumption (< 40 l / 100 km) and tyre wear in particular are noticeable benefits. The diesel consumption of a tractor is approximately 20 l/100 km higher and a rate of tyre wear on the road in the case of tractors and trailers of more than 5 euros per hour of operation is also not uncommon.

Figure 17: Comparison of process-related costs of various transport and transfer variants

12

Euros per tonne

11

Fig. 16 illustrates the cost benefits of an articulated truck as compared with a 40-km/h tractor or 50-km/h tractor, each with trailer. It is assumed in the calculation that the 50-m3 articulated trailer is loaded with “only” 20 tonnes, because of the low bulk density of the chopped maize and a lack of compaction options.

10 9 8 7 6 5

10

15 Yard-field distance in km

Standard Transfer wagon / truck Wheeled loader / truck Source: BLU, 2010

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20

25

Crop transfer technology.

Transfer belt / truck Maus/truck

The use of a truck, however, has one major drawback: fitted with high-pressure tyres, the vehicle may be driven across agricultural land only in exceptional cases. A separate harvesting procedure is therefore necessary, with

agricultural technology in the field and transport technology on the road. This gives rise to one fundamental question: how does the maize get loaded onto the truck? A number of process-targeted solutions have been and are being developed to tackle this issue both within industry circles and by practitioners in the field. The following suggested variants have been proposed: “tractor and transfer wagon” combination, “transfer with wheeled loader and bucket excavator”, “transfer belt” (rear intake for tipper) and “Maus transfer loaders” (solid intake based on sugar beet example). Fig. 17 illustrates clearly that all of these transfermethod variants bring cost benefits over conventional techniques and procedures (tractor and chopper trailer) over a transport distance of 10 kilometres or more, and that truck transport can compensate for the additional costs associated with the transfer process. According to initial findings, these costs should not exceed 1 euro/t. This target can be most closely met where no specialist systems are employed. Lower-cost solutions, however, frequently mean a compromise needs to be reached, specifically in terms of operational results.

Exciting times ahead. The German Federal Association of Agricultural Contractors (Bundesverband Lohnunternehmen e.V.) estimates that its association members achieve combined revenues of almost 500 million euros per year in the supply and waste management of biogas plants. Contractors are expected to continue to shape the future of maize harvesting processes and are already investing in modern machinery to keep pace with the stringent requirements of this mainstay of revenue. This is no easy feat: the modern maize harvesting chain, for instance, necessitates investment in the millions, emphasising the need for cost calculation to be thorough and practice-oriented. The maize harvesting process places stringent organisational demands on the technology employed and on the plants themselves. As such, efficient harvesting is possible only if the harvesting chain itself is coordinated optimally in terms of output and the land use and storage facilities provide a favourable basis.

In addition, contractors generally use specially constructed four-axle trucks, which with their large-volume construction and soil-protecting tyres are suitable for driving over agricultural land, on roads and over silage heaps. These solutions certainly have their appeal, although here too, keeping these machines working to an efficient rate of capacity utilisation in an economic sense is always a challenge.

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The following ballpark figures provide an overview of harvesting-specific operations in silage maize with a dry matter content of 33–34 percent. These net costs should be increased by 3 percent per percentage point of additional dry matter content: Chopping

2.20

(+ 0.7 l diesel/t)

Transport

2.00

(+ 0.7 l diesel/t)

• With tractor and chopper

euros/t*

(+ 0.12 l diesel/t)

euros/t*

wagon (up to 2 km)

0.35

• Each additional kilometre

euros/t*

Rolling

0.80

(+ 0.2 l diesel/t)

euros/t* * All prices exclusive of diesel or VAT

Given the large volumes of orders received, professional contractors are expected to become a leading force in the service market for biogas plants. Every plant operator ought to realise the huge importance of retaining reliable harvesting partners since, ultimately, the objective remains to minimise business risk. This type of assurance of course is not free, and quality of service comes at a price.

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Software solutions.

The entire process in full view. (Karl-Heinz Krudewig, CLAAS Agrosystems) What materials are supplied to the plant? What substances are yielded, and where? What is the nutritional balance? These days, land resources and capacities need to be utilised very efficiently to ensure the profitability of the plant. Modern software packages support all the processes necessary for efficient utilisation. Scheduling, documentation and controlling are additional benefits in this respect. The benefits of these technologies can be seen in substrate production and application, for instance.

Integrated raw materials management. Comprehensive raw materials and substrate management is a key component of any software solution for biogas plants. Monitoring and scheduling functions enable users to ensure continuous and effective plant operation. Practitioners have all the information and numerical data they need at a glance, including transport-related costs, greatly facilitating accurate pre-costing. Achievable methane yields and potential costs are discernable as early as the raw materials or substrate purchasing stage. Silo fill level data is also available at all times, and the user kept fully up to date regarding the handling of fermentation waste.

Efficiency made easy. What needs to be supplied in due consideration of differing energy production grades to ensure a perfect mixture for profitable biogas production? And who needs to supply these materials? Software systems can determine whether existing raw material storage capacities are sufficient to produce predetermined methane volumes and the quantities of methane than can be produced from these capacities.

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Integrated operations. Interfaces are the key to success in the field. Weighing data is a classic example: professional solutions integrate a range of scale systems in processes and also enable the transfer of substrate cultivation area data from crop field mapping. The result is an excellent user overview of the locations of high-quality substrate on arable land and the best time for harvesting. Transport routes are also shown and indicated on clear maps for ease of planning.

Perfect documentation. The compilation of field-specific verification information has for some time been necessary for compliance with statutory documentation obligations. With regard to fertilisers specifically, the statutory requirement to document ingredients must be respected. Verification data is also necessary for business management, and the documentation of material supply, utilisation and logistics data is performed automatically and conveniently. All things considered, farmers today would be well advised to manage field mapping, documentation, land management and surveying, soil sampling, rating and storage administration processes on site with an appropriate software product. For more on the topic of software for biogas plants: http://www.agrocom.com/de/pflanzenbau/ biogasproduktion/agrocom-biogas.html

Better orientation. The capacity utilisation of machines must be well managed between jobs. Operators therefore require a reliable and in particular timely supply of quality information regarding jobs and routing – if possible, directly in the machine and without having to return to the farm. Steps must be taken to ensure operators are able to locate the designated land parcel and/ or process the correct fields effectively. State-of-the-art 42

GPS-assisted systems can automatically detect the location of a field and indicate the precise location of the vehicle in it as well as when the machine entered the field, and when it left. All actions performed in the field can be appropriately documented, and any obstructions or weed areas displayed. For more on the topic of software solutions and field navigation: www.claas-agrosystems.de

Definition of terms. Anaerobic = In the absence of oxygen. Biogas formation occurs only under anaerobic conditions.

Proportion of Organic Dry Matter (ODM) = Proportion of a mixture after the removal of water content and inorganic substances.

CHP = Combined Heat and Power.

ODM = Organic Dry Matter.

Biogas = Combustible gas produced through the anaerobic fermentation of biomass. Consists partially (50–65%) of the combustible component methane, an odourless and non-toxic, but highly volatile and in particular highly climate-damaging gas in specific mixture ratios with air. The gas should therefore not be allowed to escape unused into the atmosphere, and combusts within the engine to produce carbon dioxide and water. Some 35–50% of biogas is carbon dioxide (CO2), with the remainder mostly trace quantities of oxygen, ammonia and hydrogen sulphide.

Volumetric loading = Organic proportion of crop fed into fermenter, in relation to the usable fermenter volume per unit of time. A variable for the loading of the fermenter. Unit: kg ODM/m3×d.

Biogas conditioning = Conditioning of biogas to natural gas quality for feeding into the natural gas network. All traces of CO2 and other trace gases in particular must therefore be removed.

Retention time = Time that the substrate remains in the fermenter.

Combined Heat and Power plant (CHP plant) = Small power plant that simultaneously generates power and usable heat through fuel combustion (cogeneration of heat and power). Renewable Energies Act (Erneuerbare-Energien-Gesetz, EEG) = Act governing the remuneration of power generated from renewable energy sources. In order to promote the use of these technologies, the remuneration payable by energy providers to the producer is above the market price for power. A completely revised Renewable Energies Act came into force at the beginning of 2009. Fermenter = Container in which the microbiological breakdown of the substrate and simultaneous biogas formation take place. The container is heated and stirred thoroughly at regular intervals in order to provide optimal conditions for the organisms. Digestate = Biogas substrate residue; the part of the biogas substrate that does not leave the fermenter as a gas. Excellent manuring properties, since the nutrients can be taken up by the plants much more easily than in unfermented liquid manure. Digestate tank = Container, in which the digestate is stored until applied or processed further. Should at best be sealed gastight and connected to the gas line. Gas yield = Relation between applied substrate and gas formation achieved dependent on retention time. Allows for statements to be made regarding how effectively the added substrate is converted during the process. WPS = Whole-plant silage Co-substrate = For the fermentation of specific organic materials that are not farm fertilisers. Renewable resources = Biomass from predominantly forestry and agricultural cultivation used in the production of energy or as a material. Primarily agricultural crops used in the production of silage in biogas plants, e.g. maize, rye and millet. In accordance with the Renewable Energies Act (EEG), for the use of renewable resources in biogas plants, a bonus of 7 cents is paid per kWh of energy produced from these materials.

Substrate = For the fermentation of a specific material. Dry matter content (DMC) = Proportion of a mixture after removal of water content.

Farm fertilisers = Livestock excrement such as slurry and dung.

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