Cares renewable ENERGY
bIomass HEaTING Handbook
Renewable Energy Technologies This Handbook aims to help you to:
Learn the fundamentals of renewable Biomass Heating generation. Explore and discuss the range of technologies and options available to your community. Evaluate which technologies or options may be appropriate for your community. Identify and access valuable online resources for further information and advice.
It discusses the variety of technologies that have been employed by community groups across Scotland. The principles of how the technology works is provided along with the key issues regarding installation and operation as well as environmental impacts. The Biomass Heating handbook includes the following sections: Technology description. Technologies available on the market. System requirements. Is the renewables technology suitable for your community group? Introduction to available schemes and grants. Tips for project development. Environmental aspects. Case study.
This Handbook is intended as an introductory text, covering the main aspects and issues that need to be considered for each of the technologies listed above. A separate set of Toolkits, (available Autumn 2013) will provide more detailed guidance and tools to assist community groups and rural businesses to develop a renewable energy project. Like the Handbook the Toolkits will be available on the CARES web site: localenergyscotland.org.uk
Biomass heating Technology description Biomass heating is the combustion of a biomass fuel such as wood in a boiler to supply space heating and hot water. Biomass fuel is biological in origin and, when from sustainable sources, is regarded as renewable. The most common fuel is wood, which can be supplied in three forms; logs, chips and compressed wood pellets, all are widely available in Scotland. Wood fuels derived from UK sources, whether waste or forestry can generally be regarded as sustainable. This section of the Handbook will only cover wood as it is by far the most common fuel. However, biomass energy also includes energy crops, food waste streams, some agricultural residues, industrial wastes and residues which can be used for heating in certain, specific circumstances. A range of biomass boilers are available, in sizes to suit homes, small businesses, community buildings through to large hospitals and industrial processes. Since the introduction in November 2011 of the Renewable Heat Incentive (RHI), a long-‐ term Government support measure, the use of biomass heating in the commercial and community sectors has expanded rapidly. In the 18 months since its introduction, 1,421 boilers have been installed and approved under the RHI. This represents over 90% of all of the renewable heat installations supported. The market continues to grow at a rate of 200 to 300 installations per month in the UK; of these, between 40 and 60 are in Scotland. This popularity is due to two reasons; the low cost of wood fuels, and the ease with which biomass boilers can replace oil and gas boilers in an existing heating system. Biomass is particularly attractive in rural areas where wood fuel is readily available and alternative fuels, such as oil, are expensive. Typical examples include: Rural estates where a biomass boiler supplies heat to a principal building and a range of converted out-‐buildings by means of a small district-‐heating network. Community halls and centres, church buildings. Guest houses and B&Bs.
The potential to earn predictable income over 20 years from the RHI has resulted in the growth of a substantial commercial sector focussed on the design and installation of biomass heating installations and the supply of fuel. The production of wood fuel adds value to woodland management activities with increased levels of local economic activity as a result. This improves both biodiversity and rural incomes. Local biomass heating projects bring economic benefits to their area. Employment is created in fuel production and equipment installation and maintenance. Value is retained within the local economy instead of being exported, as is the case with gas and oil purchase.
System requirements Any biomass heating system requires the following main components: Fuel storage. One or more boilers. One or more heat accumulators. A chimney stack or flue. A heat meter. Fuel storage
Key issues include: Sufficient fuel must be stored on site to maintain operations in between deliveries. The amount will depend on circumstances but is typically not less than a week of operation at full load. The store must keep the fuel dry. Wet fuel will cause the boiler to malfunction. The design of the store will depend on the fuel selected; logs can be kept in a simple shed, chips in a storage bay and pellets in an enclosed hopper. Typical solutions are silos similar to animal feed storage or partitioned sections in an enclosed barn, outhouse or commodity store. Access is needed for deliveries by lorry and some means is needed to convey the fuel to the boiler on demand. Boiler
The boiler is where the biomass fuel is burned to heat the water in the building heating system. Biomass boiler technology is fully developed, systems are available with commercial guarantees. They are available in a range of sizes from very small domestic (under 45kWth1) to very large commercial (over 5MWth8) and from a choice of several manufacturers, most of whom are represented in the UK. Combustion technology has also advanced in the last two decades, driven by large-‐scale deployment in Austria, Germany and Scandinavia. Biomass equipment is now available with similar efficiencies and levels of convenience as oil fired boilers. Although there are many variations, the design of the boiler depends mainly on the scale, the fuel and the degree of automation desired. There are two main types of boiler – continuously fuelled and batch fuelled. Continuously fuelled boilers use wood chip or pellet fuels and can be made fully automatic. Batch-‐fuelled boilers use logs and require more manual intervention. Both types are described more fully in the following section. Heat accumulator
Biomass boilers do not operate in the same way as gas and oil boilers. They have a more limited operating range and cannot respond as rapidly to changes in heat demand. Hence short operating cycles are not recommended for biomass systems. Hence use of a hot water tank or accumulator in the system to balance the output of the boiler and the demand of the heating system is highly recommended. The volume for the heat accumulator depends on the type of boiler and the characteristics of the heating 1
‘th’ denotes thermal power produced
system. Pellet boilers have a good operating range and a relatively small tank would be used. Log boilers have little range and a large tank that can absorb the energy contained within one or more charges of wood is necessary. Chimney
Biomass boilers are combustion appliances and are subject to regulation on the position and height of the chimney and the composition and quantity of pollutant emissions. This should be discussed with the environmental health officer of your local authority. Heat meter
If the installation is supported by the RHI then the heat supplied to the building will need to be metered to be eligible for support. It may also be necessary to meter the heat generated. The type and placing of meters is covered by the RHI Guidance notes. See the Ofgem e-‐serve RHI information at http://www.ofgem.gov.uk/eserve/RHI/Pages/RHI.aspx Available technologies Boilers
There are two main types of boiler – continuously fuelled and batch fuelled. Continuously fuelled boilers use wood chip or pellet fuels. The fuel is fed into the boiler in a continuous stream and burned immediately on a grate. Water is heated in a jacket around the space where the fuel is burned. Continuously fuelled boilers operate largely unattended with intervention needed only for fuel loading and occasional ash removal. Small pellet boilers are manufactured for the domestic and small commercial market with outputs of approximately 12kWth upwards. Larger models up to a few hundred kWth are commonly used. Chip fuelled boilers are not generally used below 50kWth output but are available in many sizes to suit all applications up to several MWth, suitable for industry and very large buildings. In general, boilers below 50kWth are predominantly pellet fuelled, those over 100kWth are predominantly chip fuelled. Local circumstances can dictate different solutions however and most chip fuelled boilers will burn pellet fuels. Batch-‐fuelled boilers use logs. Several kilograms of logs are stacked into a chamber and lit. The chamber is then closed and air is admitted causing the logs to burn. Water is heated in a jacket around the chamber. These boilers operate best at full output and may emit smoke if the output is turned down. To allow for this they should always have a substantial hot water storage tank between the boiler and heating system to balance heat supply and demand. Batch-‐fuelled boilers require considerable manual intervention to load the fuel and because of this are rarely used for heating demands above 100kWth. Modern boilers in both categories have automatic combustion controls that measure flue gas oxygen to control air flow and maximise efficiency. Fuels
Wood fuel is supplied in three commercial forms; logs, chipped, and pellets. Logs are mainly supplied to domestic customers for use in room heaters and smaller boilers up to 50kWth output. They can be used in some small commercial applications but the amount of manual attention needed for fuelling usually restricts the potential. Projects using logs as fuel are low cost and with good community commitment can be an ideal lower technology solution for smaller projects with access to a local or cheap wood supply.
Placing a value on the logs recovered from woodland management has made this activity much more profitable. The increased management leads to improved biodiversity and increased rural incomes. Wood chips are usually supplied for use in commercial and industrial boilers. They are prepared from logs and waste wood in a chipper with knives fixed to a rotating disc or drum. Chips are sold according to the particle size and the moisture content. Moisture comes from the tree after felling and is determined by the length of time in store and the storage conditions. Typically the chips will be 30mm or 50mm in size and have a moisture content of 30 – 35%. Chips produced from recycled clean wood have lower moisture content. The recent rapid growth in the market has led to the widespread adoption of quality standards that set out minimum requirements for size, moisture and levels of contamination. Boiler suppliers will state the fuels for which their equipment is suitable and deviation from this will void any warranties. Wood chip characteristics: Higher moisture content than pellets (30%). Lower energy density than pellets results in higher storage volume required (300kg/m3). Much cheaper per kWh than wood pellets. Wood chip boilers operate in much the same way as wood pellet boilers. Wood chips are less consistent in shape, size and energy content than pellets so a higher volume is needed to provide the same duration of fuel supply. Storage space and ease of delivery access are important elements to consider. Wood chips are however often much less expensive than pellets. It is important to find a local supplier of good quality chips to ensure fairly uniform size and moisture content before deciding to install a woodchip boiler. Pellets are a relatively new form of fuel that has been introduced over the past 20 years in Austria and Scandinavia and has now become widespread in the rest of Europe and North America. They are manufactured by extruding sawdust or other finely crushed wood through a die to produce a pellet that is typically 6mm diameter and 20mm long. The pellets closely resemble cat litter or animal feed – indeed they are produced in the same pellet milling equipment. Pellets have several advantages over logs and chips: Low moisture content gives high energy content. High density results in low volume storage requirements. They are uniform in size and properties. They are clean and free flowing and seldom give problems in material handling systems. They can be delivered in bulk though a pipe by pneumatic tanker. Pellets are as close to the convenience of oil as a biomass solution can come. They are manufactured to a closely specified standard and can be purchased from a variety of suppliers as a traded commodity.
A range of dedicated pellet firing boilers and heaters has been developed to maximise the benefit from these properties and these are widely available. Pellets are however expensive compared to chipped material so tend not to be used in larger installations that can bear the additional costs of chip handling. Comparison of fuels
Fuel
Application
Fuel cost
Storage
Logs
Domestic
low to high
Shed
Very small commercial
(very local supply required)
Domestic
high
Small commercial
(national suppliers)
Pellets
Wood chip
Small and large commercial medium
Simple hoppers and bins
Live bottom bunkers and bins
(local and regional suppliers) Storage bay Is a biomass boiler suitable for my community group or rural business? Your community group or rural business could consider installing a biomass boiler if: You have a building that needs heating/domestic hot water, preferably for long periods of each day and for all months of the year. There is space in the building that could be used to accommodate a biomass boiler and the heat accumulator. You have space close to the building that could be used for wood fuel storage. You are not in an area subject to a Local Air Quality Management plan. (check with the local authority if unsure). It will be particularly advantageous if you have access to a source of inexpensive wood such as your own woodland management or waste wood from your operations. Further information is available by contacting Local Energy Scotland on 0808 808 2288 Introduction to available schemes and grants Communities, privates or companies who decide to install a biomass heating system can take advantage of different supporting schemes. These schemes are subject to significant change, so they are covered in full detail in the accompanying toolkit. This section is intended to provide a high level over view of the two main support schemes. The Renewable Heat Incentive (RHI)
The RHI is a UK Government scheme set up to encourage uptake of renewable heat technologies among householders, communities and businesses through the provision of financial incentives.
Phase 1 of the RHI provides financial incentives to eligible, non-‐domestic renewable heat generators and producers of biomethane, for the life of the installations or up to a maximum of 20 years. For the non-‐domestic sector, broadly speaking it provides a subsidy for each kWhth2 used, payable for 20 years, to eligible, renewable heat generators and producers of biomethane based in Great Britain. Of course this is subject to the detailed scheme rules. The support available to biomass projects depends on the size of the installation, small, medium or large, and the annual generation. The scheme also places demands on the level of pollution emissions to air to avoid compromising local air quality. Tips for project development Checks for site suitability
This section provides a selection of top tips for implementing biomass heating projects. It should be noted this is not an exhaustive list and all projects present individual circumstances to consider. 1. Wood-‐fuel boilers are well suited to existing buildings as they can connect to existing wet radiator systems designed for oil or gas fired boilers. 2. The capacity of the biomass boiler should be selected on the basis of the heat demand of the building(s) not the capacity of the existing oil or gas boilers. 3. You will need to have a reliable local wood fuel supplier and preferably an alternative supply in case of problems. These are now widespread in Scotland and The Biomass Energy Centre, in partnership with the Carbon Trust, has on online searchable biofuel suppliers database. 4. If you are producing your own logs then they should be seasoned for at least one year to ensure low moisture content. 5. You must ensure that your fuel supply is kept dry. A covered storage hopper or barn will be needed with sufficient capacity to cover any supply interruptions. 6. Access for fuel deliveries will be required. Pellets can be delivered pneumatically in bulk tanker lorries or in bags loaded onto pallets. Chips are delivered in bulk either pneumatically or using tippers. Logs are delivered on trailers or tipper lorries. 7. Biomass boilers are larger and heavier than their oil or gas equivalents. They are floor mounted and should normally be on the ground floor in a dedicated area or boiler house. There should also be sufficient space for a hot water storage accumulator. 8. Containerised solutions containing fuel storage, boiler, accumulator and flue are now available and should be considered for some applications where there is insufficient space in the building. Linking the container to the heating system of the building is usually straightforward. 2
“th” denotes thermal energy produced
9. Consider the level of manual intervention that is needed to operate your installation. Pellet boilers are the closest to fully automatic operation but even these will require some inspection and occasional intervention depending on the system design. Chip fuelled systems generally require refuelling every few days with a frontend loader or similar. Log boilers require manual loading of logs, often daily or more frequently. 10. Provision must be made for removal of ash, a waste product from the wood-‐ burning process. 11. While most day-‐to-‐day maintenance and cleaning can be carried out by non-‐ specialists, the boiler will probably need annual servicing by a specialist biomass boiler engineer. Checks on incentives and regulation
1. Check the level of support available through the RHI when the scale of the project becomes clear. Most community projects will be eligible but the level will depend on the scale. If the project is larger than 200kWth capacity then consider an application for preliminary accreditation. 2. Consult the Environmental Health Officer for your local authority when the scale and location become clear. It is a requirement under the Clean Air Act that all biomass boilers larger than domestic must be notified to the local authority. If the installation is in a smoke control area then it must be an exempt appliance. Special conditions may be imposed if the installation is in an air quality management area. Details of restrictions can be found at: http://www.scottishairquality.co.uk/index.php 3. Consult the local planning department. All biomass boilers require a flue discharging to atmosphere. It is likely to be larger than an equivalent oil or gas boiler flue and may be more prominent. Building work for the fuel storage and boiler may also require planning approval. Installation 1. When a suitable location has been identified, the biomass heating system can be designed. For larger systems (over 50kWth), this is a task for a qualified heating engineer with experience of biomass heating systems. The initial aim should be a feasibility study, which will act as a basis for seeking quotations from equipment installers. 2. For systems of 50kWth and less, it is sometimes appropriate to seek quotations directly from installers. However, to claim the RHI for systems of 50kWth and under, the installer and the system need to be accredited by the MCS. 3. A comprehensive guide to biomass project implementation can be downloaded from http://www.carbontrust.com/resources/guides/renewable-‐energy-‐technologies/biomass-‐ heating-‐user-‐guide/
Environmental aspects Biomass heat relies on a combustion process and so, in common with oil and gas will have a flue with emissions to the atmosphere. The requirements for the RHI will ensure that these are reduced to an acceptable level. Reduction to lower levels may be necessary in some sensitive areas, achieved by installing filters and selecting cleaner fuels.
Provision must be made for removal of ash, a waste product from the wood-‐burning process. Typically, this will be less than 1% of the weight of the fuel burned. Provision should be made to dispose of this to landfill. Case studies Hanover (Scotland) Housing Association upgraded the heating system for one of its sheltered housing developments using a 100 kWth woodchip boiler in an effort to improve efficiency and reduce running costs.
Commissioned by the Scottish Government and Energy Saving Trust. Produced by Community Energy Scotland Limited and Ricardo-‐AEA Ltd © Queen’s Printer for Scotland 2009, 2010, 2011, 2012
This document was last updated July 2013
