Status and Future Trends of Bioenergy Technologies Dr. Joan J. Manyà Associate Professor of Chemical Engineering Aragón Institute of Engineering Research (I3A), University of Zaragoza, Technological College of Huesca, crta. Cuarte s/n, E-22071 Spain.
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Outline • Introduction • Bioenergy routes technologies
and
conversion
• Pre-treatments (torrefaction and HTC) • Combustion, gasification and pyrolysis
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Introduction What is Biomass?? Biomass consists of any organic matter of vegetable or animal origin. It is available in many forms and from many different sources e.g. forestry products (biomass from logging and silvicultural treatments, process residues such as sawdust and black liquor, etc.); agricultural products (crops, harvest residues, food processing waste, animal dung, etc.); and municipal and other waste (waste wood, sewage sludge, organic components of municipal solid waste, etc.).
Bioenergy – a sustainable and reliable energy source. A review of status and prospects. IEA, 2009
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Introduction What is Bioenergy?? Bioenergy is energy derived from biomass. In essence, bioenergy is the utilization of solar energy that has been bound up in biomass during the process of photosynthesis. It is a renewable energy source. World total final energy consumption
2013 key world energy statistics. IEA, 2013
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Introduction Biomass supply potential Biomass supply potential of up to 500 EJ. Under less favorable circumstances, if residues and surplus forestry supplies remain modest and crops only deliver feedstock from surplus existing agricultural lands without additional learning in agricultural practices, the biomass potential may remain in the order of 200 EJ. This wide range (200-500 EJ) illustrates that there is still considerable uncertainty about the potential availability of sustainable biomass.
Bioenergy – a sustainable and reliable energy source. A review of status and prospects. IEA, 2009
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Outline • Introduction • Bioenergy routes technologies
and
conversion
• Pre-treatments (torrefaction and HTC) • Combustion, gasification and pyrolysis
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Bioenergy routes and conversion technologies Three main classes of conversion routes can be identified: • Thermochemical conversion, by which biomass undergoes chemical degradation induced by high temperature. • Physicochemical conversion is used to produce liquid fuels (biodiesel or vegetable oil) from oil crop (rapeseed, soybean, etc.) by oil extraction possibly followed by a transesterification process. • Biological routes use living micro-organisms (enzymes, bacteria) to degrade the feedstock and produce liquid and gaseous fuels. Biological routes are numerous, key mechanisms being fermentation from sugar (sugar-cane, sugar-beet, etc.), starch (corn/maize, wheat, etc.) and lignocellulosic (grass, wood, etc.) feedstock, anaerobic digestion (mostly from wet biomass), and the more recent bio-photochemical routes (e.g. hydrogen production using algae), which require the action of sunlight. 7
Bioenergy routes and conversion technologies
Source: E4Tech, 2008
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Bioenergy routes and conversion technologies Development status
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Bioenergy routes and conversion technologies Thermochemical conversion routes Biomass Feedstock Wet biomass Torr. Gas
Torrefaction
HTC
Aqueous phase
Torr. biomass Hydrochar
Pyrolysis
Combustion Char
Gasification
Pyrolysis gas Bio-oil Gas
Heat and/or Power
Biochar
Liquid biofuels
Biogas
Syngas
H2 10
Outline • Introduction • Bioenergy routes technologies
and
conversion
• Pre-treatments (torrefaction and HTC) • Combustion, gasification and pyrolysis
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Pre-treatments (torrefaction and HTC) Torrefaction Raw biomass as a fuel features some drawbacks such as low calorific value due to its high moisture and oxygen contents, high grinding energy requirement due to its rigidity and mechanical strength, and low flowability and fluidization properties leading to difficulties in feeding it into boilers (Sarvaramini and Larachi. Fuel 2014, 116, 158-167). During the torrefaction process, solid biomass is heated in the absence of or drastically reduced oxygen to a temperature of approx. 250-350 °C, leading to a loss of moisture and partial loss of the volatile matter in the biomass. With the partial removal of the volatile matter (about 20%), the characteristics of the original biomass are drastically changed. Torrefaction increases the energy density of biomass and reduces the fibers length and mechanical stability resulting in improved grinding properties (Medic et al., Fuel 2014, 91, 147154).
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Pre-treatments (torrefaction and HTC) Torrefaction: thermal energy balance
Status overview of torrefaction technologies. IEA, 2012
It is assumed here that the volatile gases released during torrefaction are combusted to dry the input biomass. Raw biomass: fresh clean wood (0,5% ash content, 50% moisture content )
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Pre-treatments (torrefaction and HTC) Torrefaction: high quality fuel
By pelletizing torrefied biomass, a number of advantages can be achieved in transport, handling and storage. The compression step increases the volumetric energy density by a factor of 4-8 leading to significant cost savings in shipping and storage.
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Pre-treatments (torrefaction and HTC) Torrefaction technologies
Status overview of torrefaction technologies. IEA, 2012
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Pre-treatments (torrefaction and HTC) Torrefaction: rotating drum The torrefaction process can be controlled by varying the torrefaction temperature, rotational velocity, length and angle of the drum
From Umea University, Sweden
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Pre-treatments (torrefaction and HTC) Torrefaction: screw reactor The residence time inside the reactor is determined by the length and rotational velocity of the screw. A screw reactor is relatively inexpensive, however, the scalability is limited because the ratio of screw surface area to reactor volume decreases for larger reactors. However, there are reactors designed with highly efficient agitation for improved heat transfer which makes large screw reactors highly efficient.
From ETIA, France
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Pre-treatments (torrefaction and HTC) Torrefaction: belt conveyor By controlling the belt speed, the residence time for all particles inside the reactor can be accurately controlled. It can be considered a perfect plug flow reactor, in contrast to several other reactor concepts where there might be substantial spread in residence time, leading to either charred particles or not yet properly torrefied particles from the same reactor. A disadvantage is potential clogging of the open structure of the belt from tars or small particles. Further, the volume limited throughput makes the reactor less suitable for biomass materials with low bulk densities.
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Pre-treatments (torrefaction and HTC) Torrefaction: technical challenges Feedstock flexibility
The currently developed torrefaction technologies have relatively limited feedstock flexibility in terms of particle size and moisture content; substantial pretreatment is therefore required. Typical input particle size is 5 to 20 mm, moisture content of input material for the reactor not exceeding 15% on wet basis to avoid incomplete combustion of wet torrefaction gases and minimize the process residence time. The use of agri-residues with low bulk density such as straw needs larger reactors compared to woody biomass; which leads to increases in capital cost and more difficult to operate. This is one of the reasons why most projects currently process wood.
Scaling up the process
Depending on the reactor type, it can be a serious challenge to scale up torrefaction processes from pilot (typically 20-600 kg h-1) to commercial scale (5-10 ton h-1 or larger). In case of screw reactors, drum reactors or belt conveyors, the limited scalability will often make it necessary to establish multiple production lines in parallel.
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Pre-treatments (torrefaction and HTC) Hydrothermal Carbonization (HTC) Hydrothermal carbonization (HTC) is a chemical process which emulates the natural coalification of biomass. It’s sometimes referred as “wet torrefaction”. For hydrothermal carbonization to take place, biomass is placed in a pressure vessel together with water and a suitable catalyst. The reactor is then closed, and under airexclusion is heated under pressure. The HTC process generally takes place at temperatures between 180 °C and 220 °C over a 4 to 12 hour period .
Gas (mainly CO2)
Solid biomass + H2O Wet biomass (animal manure, sewage sludge,
Pressure vessel (10-25 bar)
Hydrochar Process water Higher energy density
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Pre-treatments (torrefaction and HTC) Hydrothermal Carbonization (HTC) HTC is an exothermic process that lowers both the oxygen and hydrogen content of the feed (described by the molar O:C and H:C ratio) by 5 main reaction mechanisms which include hydrolysis, dehydration, decarboxylation, polymerization and aromatization (Funke and Ziegler. Biofuels Bioprod. Biorefin. 2010, 4, 4160-4177). HTC can be combined with anaerobic digestion for e.g. wet agricultural residues:
Oliveira et al. Bioresour. Technol. 2013, 142, 138-146
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Pre-treatments (torrefaction and HTC) HTC technology
AVA-CO2 (Swiss company)
The CarboREN Technology (from SunCoal Industries GmbH) http://www.suncoal.de/en/technology/carboren-technology
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Outline • Introduction • Bioenergy routes technologies
and
conversion
• Pre-treatments (torrefaction and HTC) • Combustion, gasification and pyrolysis
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Combustion, gasification and pyrolysis Combustion for Heating The burning of biomass for heat is the oldest and most common way of converting solid biomass to energy. Because combustion is a straightforward and well understood process, there is a wide range of existing commercial technologies tailored to the characteristics of the biomass and the scale of the application. DOMESTIC SYSTEMS • Cooking with firewood or charcoal in developing countries, typical cook-stove efficiency is 10-20%, 30-60% with improved stoves • Domestic wood chips, almond shells, and pellet stoves and boilers efficiency)
(near 100%
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Combustion, gasification and pyrolysis Combustion for Heating DISTRICT HEATING Today, biomass-based district heating provides a significant share of the heating requirements in some countries (e.g. northern European countries) 70
Fuel sources for Swedish district heating
Heat Produced (TWh/yr)
60 50
Waste Heat Heat Pumps Electric Boilers Biofuels Coal Natural Gas Oil
40 30 20 10 0 1980
1985
1990
1995 Year
2000
2005
Source: Swedish Energy Agency (2008)
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Combustion, gasification and pyrolysis Combustion for Heating INDUSTRIAL SYSTEMS An increasing number of boilers in the 0.5-10 MWth range are found in industries that consume large amounts of heat and have large volumes of biomass residues at their disposal.
Principal types of combustion reactors
The Handbook of Biomass Combustion and Co-firing. Earthscan: London, 2008)
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Combustion, gasification and pyrolysis Combustion for Heating
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Combustion, gasification and pyrolysis Combustion for Heating
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Combustion, gasification and pyrolysis Combustion for Power
Fiorese et al. Energy Policy 2014, 65, 94-114
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Combustion, gasification and pyrolysis Biomass Gasification
Biomass Heating Dry residue Moisture
Heating Char residue Gasifying agent (O2, H2O, CO2, etc)
Ash
Volatiles (Pyrolysis gas and tar)
Product gas (H2, CO, CO2, CH4)
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Combustion, gasification and pyrolysis Biomass Gasification
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Combustion, gasification and pyrolysis Gasification reactors
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Combustion, gasification and pyrolysis Gasification reactors
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Combustion, gasification and pyrolysis Gasification
Integrated Gasification Combined Cycle (IGCC)
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Combustion, gasification and pyrolysis IGCC plant at Varnamo (Sweden)
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Combustion, gasification and pyrolysis Gas cleaning (Achilles’ heel)
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Combustion, gasification and pyrolysis Gas cleaning
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Combustion, gasification and pyrolysis Syngas Route to Biofuels – Integrated Concept
Source: VTT (2011)
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Combustion, gasification and pyrolysis Biomass Pyrolysis
Biomass pyrolysis includes thermal degradation of its polymer constituents cellulose, hemicellulose, lignin, peptides and lipids. The biomass polymer fragments (volatiles) formed are driven out of the biomass particle due to the pressure that is being built up inside the particle. They are widely distributed in molecular weight, and partly still in the liquid phase (aerosols). The intrinsic pyrolysis reactions are very fast, but in practice heating of the biomass particles and mass transfer limitation delays the pyrolysis process significantly.
Pyrolysis in a biomass particle
P. Basu. Biomass Gasification and Pyrolysis (Practical Design and Theory). Academic Press: Burlington, MA, 2010
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Combustion, gasification and pyrolysis Pyrolysis
Ronsse et al. 1st Int. Summer School on Biochar, Potsdam, Sept 9 – 16, 2012
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Combustion, gasification and pyrolysis Slow Pyrolysis for Biochar purposes Pyrolysis gas Biomass
Slow Pyrolysis
Liquid fraction (high water content)
Charcoal (30-50% yield)
Manyà. Environ. Sci. Technol. 2012, 46, 7939-7954
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Combustion, gasification and pyrolysis What is Biochar?? Biochar is a carbon-rich substance, which is produced by thermal decomposition of biomass under oxygen-limited conditions and at relatively low temperatures (
