Value Chains
Priority value chains
The production of transport biofuels, heat, and electricity encompasses a number of steps from feedstocks to energy carrier products that allows value for the users and society. There are numerous different feedstocks, conversion technologies, products, and end-use market segments.
A pathway is a very specific combination of these elements, starting from a specific feedstock, using a specific conversion technology, producing a specific product that goes into a specific end-use market sector and has a certain value. A pathway can have any value of technology readiness level (TRL).
A value chain is a cluster of conversion pathways from a range of feedstocks to a range of products. Value chains are able to provide a relevant contribution to the 2030 targets and are sufficiently developed to allow for a proper description and evaluation of the “values”. The focus is on grouping pathways by technologies, as to define research needs and TRL for this group of technologies.
- Established value chains are value chains at TRL9, i.e. they are widely used in many industrial installations, e.g. (non-exhaustively) biomass boilers, AD biogas generation, FAME biodiesel and crop-based ethanol, etc. providing heat, power, biogas or biofuels.
- Priority value chains are value chains that are developed beyond the research stage while not yet being established industrially, i.e. TRL5-8. Their technology will allow the use of new and more sustainable feedstock sources in the short to medium term, which are converted to mainly biogas and biofuels, in particular “advanced biofuels”.
- Development pathways are pathways still in research and development stage, i.e. < TRL5.
The scheme below describes how ETIP Bioenergy group conversion pathways defines priority value chains and replaces the scheme of the old value chains applying advanced conversion technologies.
PVC1: Transport fuels via gasification
Thermal gasification produces a syngas, which can be used for the production of power and heat (see PVC2 ), or further processed into transport fuels.
Feedstock
Thermal gasification is very fuel-flexible; it can in principle use any reasonably low moisture content (preferable below 15%) combustible carbon-containing material as a feedstock, presently mainly various biomasses. Conversion efficiency however will be affected when using less defined feedstocks. Possible feedstocks include forest and forest industry residues, short rotation coppice (SCR), lignocellulosic energy crops such as energy grasses and reeds, agricultural and agro-industrial residues as well as sorted municipal and industrial wastes (RDF[1], SRF[2], plastic wastes, digested sewage sludge etc.), with each of these feedstocks coming with specific challenges in terms of technical or economic feasibility. Biomass from dedicated felling of forestry wood is also possible as feedstock but is not considered sustainable.
Gasification
Gasification is a thermochemical conversion process at 800-1300°C using a sub-stoichiometric amount of oxygen (typically l = 0.2-0.5). Under these conditions the biomass is fragmented into raw gas consisting of rather simple molecules, such as: hydrogen, carbon monoxide, carbon dioxide, water, methane, H2S, NH3, HCl, etc. Solid by-products are: tar, char, and inorganic matter. After clean-up of the raw gas, the gaseous molecules are chemically re-synthesized to transport fuels..
After size reduction of the raw material, it is moved into the gasifier. Typical gasification agents are: oxygen and water/steam. The choice of the gasification agent depends on the desired raw gas composition. The combustible part of the raw gas consists of hydrogen (H2), carbon monoxide (CO), methane (CH4) and short chain hydrocarbons; the non-combustible components are inert gases. A higher process temperature or using steam as gasification agent leads to increased H2 content. High pressure, on the other hand, decreases the H2 and CO.
Entrained-flow gasifiers operate at high temperatures (1000-1300 °C) and are therefore suitable when low methane content is preferred, however feedstocks with very low particle sizes are required. Bubbling and circulating bed gasifiers in contrast are operated at lower temperatures (800-1000 °C) and have the advantage of being able to use highly heterogeneous materials.
The process heat can either come from an autothermal partial combustion of the processed material in the gasification stage or allothermally via heat exchangers or a heat transferring medium. In the latter case, the heat may be generated by the combustion of the processed material (i.e. combustion and gasification are physically separated) or from external sources.
Impurities of the raw gas depend on the gasification condition and used feedstock. They can cause corrosion, erosion, deposits and poisoning of catalysts during downstream processing. It is therefore necessary to clean the raw gas. Depending on technology, impurities such as dust, inorganic matter, bed material, tars and alkali compounds are removed through various cleaning steps. The cleaned raw gas, now a clean fuel gas, must meet the quality requirement of the synthesis unit.
Fuel Synthesis
The technology for the use of the synthesis gas intermediate is well-established for fossil-derived synthesis gas and has immense industrial importance for producing hydrogen in refineries as well as many millions of tonnes of chemicals annually. Selective catalytic chemical reactions convert the synthesis gas to, by choice, methane, methanol, DME or Fischer-Tropsch hydrocarbons, respectively, at temperatures of 200 up to 400 °C. The synthesis gas can also be converted to ethanol by micro-organisms at ambient temperature. In addition, hydrogen as a product can be extracted directly from the gas.
Fischer-Tropsch hydrocarbon product is a mixture with a wide range of molecular weights from LPG over naphtha and distillates to waxes. The waxes are typically hydrotreated and then the combined liquid products are fractionated by distillation to gasoline, diesel and jet fuel. Synthesis gas can be used to produce methanol and DME (dimethyl ether), which, if desired, can be processed further to gasoline. Synthesis gas can also be converted to methane which can be distributed through the natural gas grid and used directly as renewable CNG or liquefied and used in heavy duty vehicles (LNG trucks). The typical energy conversion efficiency (biofuel output energy/biomass feedstock energy as received) from feedstock to advanced biofuel products ranges from 40 – 50 % for drop-in hydrocarbon fuels and 60 – 70 % for gases and methanol.
Demonstration plants
Please check our production facilities database to obtain most recent information on demonstration plants for this value chain (use the filter function). The status as of early 2020 is described in the report “Current Status of Advanced Biofuels Demonstrations in Europe”, published by ETIP Bioenergy in March 2020.
Factsheet: Synthetic hydrocarbons
Acknowledgement: Large parts of the texts were taken from Lars Waldheim´s contribution to the report “The Contribution of Advanced Renewable Transport Fuels to Transport Decarbonisation in 2030 and beyond”
[1] RDF: Refuse derived fuel, the fuel fraction remaining after recyclable material and non-combustible waste have been separated in a waste treatment facility however not associated with any specific quality measures.
[2] SRF: Solid recovered fuel, an RDF where certain quality parameters and procedures have been defined, for further information see standard EN 15357 and standard in development ISO/DIS 21637.
[3] SGAB Technology status and reliability of the value chains: 2018 Update. 28 December 2018. Ed. I Landälv, L Waldheim, K Maniatis. artfuelsforum.eu/news-articles/updated-sgab-report-technology-status-and-reliability-of-the-value-chains/
PVC2: Power and heat via gasification
Thermal gasification produces a syngas, which can be used for the production of power and heat, or further processed into transport fuels, see PVC1: Transport fuels via gasification.
Feedstock
For gasification, any lignocellulosic material is suitable as feedstock. What was mentioned before for PVC1 feedstock is also valid. The term lignocellulosic covers a range of plant molecules/biomass containing cellulose, with varying amounts of lignin, chain length, and degrees of polymerization. This includes wood from forestry, short rotation coppice (SRC), and lignocellulosic energy crops, such as energy grasses and reeds. Biomass from dedicated felling of forestry wood is also lignocellulosic but is not considered sustainable.
Gasification
Gasification is a thermochemical conversion process at 800-1300°C using a sub-stoichiometric amount of oxygen (typically l = 0.2-0.5). Under these conditions the biomass is fragmented into raw gas consisting of rather simple molecules, such as: hydrogen, carbon monoxide, carbon dioxide, water, methane, H2S, NH3, HCl, etc. Solid by-products are: tar, char, and inorganic matter. After clean-up of the raw gas, the gaseous molecules are chemically re-synthesized to transport fuels..
After size reduction of the raw material, it is moved into the gasifier. Typical gasification agents are: oxygen and water/steam. The choice of the gasification agent depends on the desired raw gas composition. The combustible part of the raw gas consists of hydrogen (H2), carbon monoxide (CO), methane (CH4) and short chain hydrocarbons; the non-combustible components are inert gases. A higher process temperature or using steam as gasification agent leads to increased H2 content. High pressure, on the other hand, decreases the H2 and CO.
Entrained-flow gasifiers operate at high temperatures (1000-1300 °C) and are therefore suitable when low methane content is preferred, however feedstocks with very low particle sizes are required. Bubbling and circulating bed gasifiers in contrast are operated at lower temperatures (800-1000 °C) and have the advantage of being able to use highly heterogeneous materials.
The process heat can either come from an autothermal partial combustion of the processed material in the gasification stage or allothermally via heat exchangers or a heat transferring medium. In the latter case, the heat may be generated by the combustion of the processed material (i.e. combustion and gasification are physically separated) or from external sources.
Impurities of the raw gas depend on the gasification condition and used feedstock. They can cause corrosion, erosion, deposits and poisoning of catalysts during downstream processing. It is therefore necessary to clean the raw gas. Depending on technology, impurities such as dust, inorganic matter, bed material, tars and alkali compounds are removed through various cleaning steps.
The cleaned raw gas, now a clean fuel gas, must meet the quality requirement of the power (and heat) generating unit, which normally would be a gas engine or a gas turbine. In future it could also be low temperature (PEMFC, PAFC) or high temperature (MCFC, SOFC) fuel cells, where the latter ones – and there especially the molten carbonate fuel cell – would be preferable due to their higher impurities tolerance and their ability to directly use CO, methane and higher hydrocarbons as fuel directly in the cell.
Heat and power production
Use as engine or gas turbine fuel
The clean fuel gas can be used in spark-ignited (Otto) engines and in compression (Diesel) engines and for gas turbines for power and heat production. Engines are applied for power generation in the range of 15 kW up to the order of 10 MW. Biomass-to-electricity efficiency in practice lies between 25 and 30 %, and the overall performance between 80 and 85 %.
As heat is not always a desired output of a CHP plant, some plants use an organic Rankine cycle to further convert heat into electricity, increasing the electric output by about 10 percent points, i.e. to 30-35 %.
The clean fuel gas composition will vary slightly due to variations of the feedstock. This requires engine controls to adapt engine operations to maintain load unless a sufficiently large gas buffer tank is used.
Typically, engine emissions include CO, hydrocarbons and NOx, pre-dominantly from nitrogen compounds in the gas that originates from the fuel. Therefore, exhaust gas catalysts are typically used.
At larger scale, say 10 MWe up to 100 MWe, gas turbine combined cycles are more efficient, reaching from 35 up to over 50 % electric efficiency and a total efficiency of up to 90 %. As gas turbine combustion chambers operate under pressure, also the gasifier needs to be pressurized or the fuel gas compressed prior to its use. There have been such developments at the demonstration scale in the 1990’s and early 2000’s and also now there are some companies like Synova Power (Netherlands) and Phoenix Biopower (Sweden) developing such schemes as the high efficiency is attractive.
Stand-alone power production
In the case of waste fuels (MSW, RDF etc.) the conventional incinerator technologies have a fairly low efficiency (of the order of 25 %) compared to other thermal power plants due to that the steam superheat temperature is limited to the order of 400-450 °C due to corrosion.
One option that has been developed is to link a gasifier to a gas boiler via an intermediate gas cleaning to remove alkalis and chlorine, and then overcoming such limitations on the superheat temperature and thereby allowing a more efficient steam cycle reaching 30-35 % efficiency. One notable development is by Valmet at Lahti, where two circulating fluidised bed (CFB) gasifiers, 80 MW thermal each, feed cleaned gas into a gas boiler using 540 °C superheat to generate 50 MWe[1].
Use for co-firing
The idea of co-firing is to use existing large-scale power plants and replace part of the fossil fuels (coal, oil, natural gas) with renewable sources. The gasification of the feedstock before feeding gas to the boiler (also known as indirect co-firing) offers a number of advantages compared to direct co-firing when solids are fed into the boiler:
- Higher fuel flexibility
- Gasification gases are easier to transport and manipulate.
- Combustion is more efficient and cleaner. No significant negative impact on the performance of the boiler from biomass ash and impurities.
- Less strict requirements in the producer gas quality as compared to other applications
- Possibility of keeping the gasifier ash separated from coal ash, which is used as a certified feedstock for building material.
Industrial high temperature process heat
Gasifiers are also used to produce a fuel gas that wholly or partially substitutes fossil fuels in industrial high-temperature applications.
Over the years, in the Kraft pulp and paper industries, circulating fluidised bed (CFB) gasifiers have been used to gasify bark residues from the log feedstock for use of the gas in their lime kilns where limestone is calcined to quicklime that is used in the cooking liquor regeneration cycle and reverts to limestone in the process. The advantage of gasification is that ash constituents and impurities that would give operational problems in the liquor cycle can be separated from the gas before the burners, which is not possible if biomass is directly fired.
Another application is to provide secondary fuel to cement kilns. A 100 MW thermal CFB gasifier has been operated since 1996 at CEMEX Rüdersdorf, Germany. Several other installations in cement factories are also in operation in China.
The above installations all use air for gasification and generate a low calorific value (LCV) gas. For even higher process temperatures than the 1100 to 1200 °C in lime kiln applications, a medium calorific value (MCV) gas using either oxygen-blown gasification or indirect gasification is used. There have not been many installations of this nature so far. However, at Höganäs, Sweden, Cortus Energy is commissioning an indirect gasifier of 6 MW thermal where the gas will be used for firing a steel furnace.
Demonstration plants
Please check our production facilities database to obtain most recent information on demonstration plants for this value chain (use the filter function). The status as of early 2020 is described in the report “Current Status of Advanced Biofuels Demonstrations in Europe”, published by ETIP Bioenergy in March 2020.
Factsheet: Biomass CHP facilities
[1] A description of this “Lahti II” is available in this document: https://www.ieabioenergy.com/wp-content/uploads/2019/01/IEA-Bioenergy-Task-33-Gasification-of-waste-for-energy-carriers-20181205-1.pdf
[2] Jorma Nieminen, Matti Kivelä: Biomass CFB gasifier connected to a 350 MWth steam boiler fired with coal and natural gas—THERMIE demonstration project in Lahti in Finland. Biomass & Bioenergy 15 (1198), 251-257. doi: https://doi.org/10.1016/S0961-9534(98)00022-1
[3] Markus Bolhàr-Nordenkampf, Juhani Isaksson: Refuse derived fuel gasification technologies for high efficient energy production. In Thomé-Kozmiensky: Waste Management 4, 2014
PVC3: Transport fuels via pyrolytic and thermolytic conversion
In this section, three different routes are discussed:
- Pyrolysis to bioliquid intermediates
- Hydrothermal liquefaction (HTL) to bioliquid intermediates
- Lignin to bioliquid intermediates
In most cases, the resulting oils are upgraded into transport fuels through co-processing in refineries; however, pyrolytic and thermolytic conversion plants could also include severe or complete hydrotreatment in their installations, directly providing transport fuels.
Co-processing in refineries is covered in the last section on this page.
Pyrolysis to bioliquid intermediates
Pyrolysis process
Pyrolysis is the chemical decomposition of organic matter by heating in the absence of oxygen. The feedstock decomposes into organic vapours, steam, non-condensable gases and char. The technology can in principle use any low moisture content (preferable below 15%) organic material as a feedstock. The feedstock potential for producing advanced biofuels lies in forest and forest industry residues, as well as agricultural and agro-industrial residues. Plastic wastes can also be used as feedstock, but the resulting fuel will be termed recycled carbon fuels, not biofuels.
The pre-treatment of the feedstock typically includes drying to less than 15 % moisture and crushing/milling to particles of less than 5 mm. The highest yield of the desired liquid fraction, up to 65 wt% on a dry feed basis, is obtained by thermal fast pyrolysis. Fast pyrolysis takes place in order of seconds at around 500 °C. The heating medium is typically circulating sand, but also other forms of heating have been used. On cooling, the organic vapours and the steam condense to a dark brown viscous liquid called fast pyrolysis oil (FPBO) or Fast Pyrolysis Bio Oil (FPBO). The char and gas are used internally to provide the process heat required, and additionally also energy for export.
The word “oil” used in this context is misleading, the energy content is only half of that of fuel oil, it contains ash solids, the oxygen content is almost as high as for biomass (35 – 40 %), it is acidic (pH usually below 2) and non-miscible with either conventional oil or with water. Nevertheless, this liquid is transportable, storable and can without upgrading to some extent be used as a fuel oil substitute, in particular when using a catalyst during pyrolysis. By using a catalyst during pyrolysis or in the vapour phase, the oxygen content and acidity of the oil can be reduced, at the expense of a lower mass and energy yield. There is also a development of a pressurised pyrolysis in a hydrogen atmosphere, whereby the bioliquid generated has a yet lower oxygen content and acidity and being more similar to hydrocarbon fuels.
There are developments of the upgrading of pyrolysis oil, either in an integrated facility at the production site or by co-feeding with fossil feeds at blend ratios of a few % in existing refineries. A concept for the pyrolysis technology is where the intermediate product, the pyrolysis oil, can be produced at smaller capacity in distributed plants and the upgrading of the oil to drop-in transport fuels is done in large plants fed by FPBO from a number of such plants.
Upgrading to transport fuels
The main routes from FPBO to a drop-in hydrocarbon biofuel is by fluid catalytic cracking (FCC) or by hydrodeoxygenation (HDO). In the case of the FCC route, oxygen is expelled from the FPBO as CO and CO2 and the H/C ratio adjusted by coke formation to result in a hydrocarbon mixture where gasoline is the main fraction. The HDO route is basically a treatment with hydrogen whereby oxygen is expelled as water, this process having similarities with the HVO process, and the resulting hydrocarbon mixture predominantly gives a diesel product. In both cases, a lower yield of biofuel results from the mass loss, and also some energy loss in the case of FCC, whereas the HDO treatment has a high energy yield based on the input biomass energy, as energy from external hydrogen is consumed.
Another pathway combining these routes are an initial hydrotreatment to stabilize the FPBO followed by FCC treatment. The benefit is that both acidity and oxygen are reduced, and the blend ratio for co-processing can be increased significantly.
Demonstration plants
Please check our production facilities database to obtain most recent information on demonstration plants for this value chain (use the filter function). The status as of early 2020 is described in the report “Current Status of Advanced Biofuels Demonstrations in Europe”, published by ETIP Bioenergy in March 2020.
Factsheet: Pyrolysis oil
Hydrothermal liquefaction (HTL) to bioliquid intermediates
Feedstock
The hydrothermal liquefaction (HTL) process can treat lignocellulosic or other biomasses as well as waste fractions. Lignocellulosic and other solid feeds must be pre-treated to allow the formation of a slurry at a reasonably high solid content by mechanical or thermomechanical pre-processing such as e.g. steam explosion. On the other hand, the great advantage of HTL is that wet fuels like sludges, algae etc. can be processed without drying, which would be necessary for other thermal processing methods.
Hydrothermal liquefaction process
Hydrothermal liquefaction (HTL) is a thermochemical conversion process of biomass (lignocellulosic or other biomasses) into a liquid intermediate by processing in a hot, pressurized water environment, typically 250 °C to 370 °C and the pressure range is usually 4 MPa to 20.06 MPa (i.e. water sub-critical conditions), for sufficient time (10-60 minutes) to break down biopolymeric structure to liquid and gaseous components. The operating conditions are quite challenging, the feed must be turned into a pumpable slurry, and this slurry and the liquids produced have an impact on the lifetime of pump, valves and construction materials, etc.
The HTL process usually produces four different product fractions, a gas phase, a solid residue, a liquid aqueous phase and a liquid oily phase, i.e., bio-crude. The produced bio-crude intermediate separates from water but still has 10 – 20 % oxygen and still has a relatively high acidity.
Upgrading to transport fuels
The HTL bio-crude has several more or less direct utilization routes e.g. low-blends into bunker fuel, but it can also be upgraded as an integrated process step or by co-feeding in refinery units to produce drop-in biofuels. The upgrading technology for this type of bio-crude is in principle similar to the upgrading of pyrolysis oil, see Pyrolysis to bioliquid intermediates.
Pilot and demonstration plants
Please check our production facilities database to obtain most recent information on demonstration plants for this value chain (use the filter function). The status as of early 2020 is described in the report “Current Status of Advanced Biofuels Demonstrations in Europe”, published by ETIP Bioenergy in March 2020.
Lignin to bioliquid intermediates
Feedstock
Lignin, one of the three main components of lignocellulose and also one of few aromatic compounds produced by plants, is a polymeric substance composed of phenolic monomers that can be used as an intermediate for the production of biofuels. Lignin from pulping processes is dissolved in the pulping (black or brown) liquor and currently used as a fuel in the recovery boiler, where pulping chemicals are recovered for re-use. Such liquors can be gasified by procedures discussed in PVC1: Transport fuels via gasification and the chemicals can be recovered. The pulping lignin can be withdrawn up to an estimated 10 – 20 % of the total amount with limited impact on the pulping processes. Pulping lignin can be separated from the liquor by precipitation or by membrane filtration for further separate treatment. An added advantage is that removal of a part of the lignin can allow a higher pulp production as the capacity of the recovery boiler is often a process bottleneck.
Hydrolysis lignin from lignocellulosic ethanol production is also a by-product and is available as a solid after the pre-treatment or after fermentation, depending on the process configuration. Today, it is also mainly used as a fuel for the internal energy demands of the process, plus some export energy, but could possibly be better valorized as a biofuel.
Processing
The processing of the separated lignin is in the liquid phase such that precipitated lignin is dissolved. First, de-polymerization to phenolic mono- and oligomers is accomplished by chemical catalysis using bases or acids in combination with thermal or HTL processing and/or hydrogen treatment. The oligomeric and monomeric substances, depending of the level of depolymerisation and nature of the components, are then dissolved in a fossil or a triglyceride feed fraction or reacted via esterification with e.g. mixed fatty acids to allow mixing with a fossil fuel fraction. Finally, the lignin-derived feed is co-fed to a refinery and is hydro-treated to remove oxygen and to produce cyclical aromatic or aliphatic hydrocarbons, depending on the process severity.
Upgrading to transport fuels
The upgrading technology for this type of oil is in principle similar to the upgrading of pyrolysis oil, see Pyrolysis to bioliquid intermediates.
Pilot and demonstration plants
Please check our production facilities database to obtain most recent information on demonstration plants for this value chain (use the filter function). The status as of early 2020 is described in the report “Current Status of Advanced Biofuels Demonstrations in Europe”, published by ETIP Bioenergy in March 2020.
The value of co-processing biogenic feedstock in refineries
Definition
Co-processing refers to the simultaneous conversion of biogenic residues and intermediate petroleum distillates in existing petroleum refineries for the production of renewable hydrocarbon fuels. In contrast to the now common blending of biofuels into the finished petroleum product, co-processing makes use of biomass within the processing of petroleum.
Co-processing technologies
The requirements for the biogenic feedstocks for co-processing are high. They must have reliable material properties in order to be able to process them together with fossil fuels in a petroleum refinery. Suitable for co-processing are semi-processed biogenic feedstocks, such as pyrolysis oil or triglycerides such as vegetable oils, used cooking oils etc. Lignin and sugars can also be co-processed in existing petroleum refineries.
Co-processing involves cracking, hydrogenation, or other reformation of semi-processed biogenic oils and fats in combination with petroleum intermediates to obtain finished fuels, like diesel or gasoline.
The following refining processes may be suitable for co-processing:
- Thermal cracking – In this process, the long-chain hydrocarbons are heated under pressure to 450 – 800 °C. Due to the heating, the hydrocarbon molecules started to vibrate and the hydrocarbon chains are subsequently broken. This process produces products with a high oxygen content, which actually is not desirable in the production of fuels.
- Catalytic cracking – In this case the cracking process occurs in the presence of a catalyst. This process removes the oxygen in the feedstocks via simultaneous dehydration, decarboxylation and decarbonylation. No additional hydrogen or energy is required. This saves costs and reduce GHG emissions. The usual temperatures for this process are 350 – 500 °C. (pyrolysis oil, lignin, glycerol)
- Hydrocracking – This is also a catalytic process at high temperature and high pressure. Hydrocracking is relatively expensive, but the advantages, among others the good product quality, often prevail. (triglyceride)
- Hydrotreating – The conversion occurs through decarboxylation, decarbonylation and hydro-deoxygenation. The required temperatures for this process are 300 – 350 °C. (triglyceride, HTL bio-crude, lignin)
Motivation
As an infrastructure (transport, storage, refinery) already exists, the low-carbon and renewable fuels can be produced and sold at economically competitive prices and therefor are an option for quickly increasing the renewable content of refinery products. It is expected, that the proportion of renewable raw materials can be up to 20 %.
Challenges
Many refineries across Europe have been running co-processing tests over the past few years, and the upgrading of tall oil crude is already state of the art in Sweden. Depending on the quality of the biogenic feedstock, problems could include differences in the stability during storage and handling, and corrosion caused by water and oxygenated organic compounds in the biogenic feedstocks.
Acknowledgement: Large parts of the texts were taken from Lars Waldheim´s contribution to the report “The Contribution of Advanced Renewable Transport Fuels to Transport Decarbonisation in 2030 and beyond”
[1] SGAB Technology status and reliability of the value chains: 2018 Update. 28 December 2018. Ed. I Landälv, L Waldheim, K Maniatis. artfuelsforum.eu/news-articles/updated-sgab-report-technology-status-and-reliability-of-the-value-chains/
[2] SGAB Technology status and reliability of the value chains: 2018 Update. 28 December 2018. Ed. I Landälv, L Waldheim, K Maniatis. artfuelsforum.eu/news-articles/updated-sgab-report-technology-status-and-reliability-of-the-value-chains/
[3] SGAB Technology status and reliability of the value chains: 2018 Update. 28 December 2018. Ed. I Landälv, L Waldheim, K Maniatis. artfuelsforum.eu/news-articles/updated-sgab-report-technology-status-and-reliability-of-the-value-chains/
PVC4: Intermediate bioenergy carriers for power and heat
Torrefaction
Biomass such as wood pellets, wood chips and also straw can be directly combusted or gasified for the production of power and heat. However, in existing fossil-fired (heat and) power plants, it can be easier to use torrefied material. Torrefaction significantly improves the suitability of biomass for co-firing in coal fired power plants and has the potential to enable higher co-firing percentages at reduced cost.
Torrefaction is a partial carbonisation or slow pyrolysis process. It is a thermochemical process typically at 200 – 350 °C in the absence of oxygen, at atmopsheric pressure with low particle heating rates and a reactor time of one hour. The process causes biomass to partly decompose, creating torrefied biomass or char, also referred to as ‘biocoal’. Biocoal is stable, brittle and water resistant, and is thus easier to grind than the original biomass material and also harder to be biodegraded. If combined with pelletisation, biomass materials can be converted into an intermediate bioenergy carrier that is easier to transport, handle and store and also has superior properties in many major end-use applications.
In the 20th century, big plants of Lambiotte (France) and Lurgi (Germany) were operating, but stopped charcoal production because it was too expensive. Currently, worldwide several small-scale units are operating, typically in clusters forming bigger production units. Examples are Plantar in Brazil (some 80 units together), GreenCoal in Estonia and a number of others in Poland.
An overview of torrefaction technology and market potential is provided in the report: Status overview of torrefaction technologies[1].
Factsheet: Torrefied pellets
Pyrolysis
Pyrolysis is the chemical decomposition of organic matter by heating in the absence of oxygen. The feedstock decomposes into organic vapours, steam, non-condensable gases and char. The technology can in principle use any low moisture content (preferable below 15%) organic material as a feedstock. The feedstock potential for producing advanced biofuels lies in forest and forest industry residues, as well as agricultural and agro-industrial residues. Plastic wastes can also be used as feedstock, but the resulting fuel will be termed recycled carbon fuels and not biofuels.
The pre-treatment of the feedstock typically includes drying to less than 15 % moisture and crushing/milling to particles of less than 5 mm. The highest yield of the desired liquid fraction, up to 65 wt% on a dry feed basis, is obtained by thermal fast pyrolysis. Fast pyrolysis takes place in order of seconds at around 500 °C. The heating medium is typically circulating sand, but also other forms of heating have been used. On cooling, the organic vapours and the steam condense to a dark brown viscous liquid called fast pyrolysis oil (FPBO) or Fast Pyrolysis Bio Oil (FPBO). The char and gas are used internally to provide the process heat required, and additionally also energy for export.
The word “oil” used in this context is misleading, the energy content is only half of that of fuel oil, it contains ash solids, the oxygen content is almost as high as for biomass (35 – 40 %), it is acidic (pH usually below 2) and non-miscible with either conventional oil or with water. Nevertheless, this liquid is transportable, storable and can without upgrading to some extent be used as a fuel oil substitute, in particular when using a catalyst during pyrolysis. By using a catalyst during pyrolysis or in the vapour phase, the oxygen content and acidity of the oil can be reduced, at the expense of a lower mass and energy yield. There is also a development of a pressurised pyrolysis in a hydrogen atmosphere, whereby the bioliquid generated has a yet lower oxygen content and acidity and being more similar to hydrocarbon fuels.
Pyrolysis oil can be directly combusted or co-combusted in boilers, furnaces or used in turbines to produce heat and power.
Factsheet: Pyrolysis oil
[1] Status overview of torrefaction technologies. Marcel Cremers, DNV GL, Netherlands, Jaap Koppejan, Procede Biomass, Netherlands, Jan Middelkamp, DNV GL, Netherlands, Joop Witkamp, DNV GL, Netherlands, Shahab Sokhansanj, UBC, Canada, Staffan Melin, UBC, Canada, Sebnem Madrali, CanmetENERGY, IEA Bioenergy Task 32, 2015.
PVC5: Liquid transport fuels via fermentation
Fermentation of cellulosic sugars to ethanol
Cellulosic ethanol is chemically identical to first generation ethanol (i.e. CH3CH2OH). However, it is produced from different raw materials via a more complex process (cellulose hydrolysis).
Feedstock
In contrast to first generation bioethanol, which is derived from sugar or starch produced by food crops (e.g. wheat, corn, sugar beet, sugar cane, etc.), cellulosic ethanol may be produced from agricultural residues (e.g. straw, corn stover), other lignocellulosic raw materials (e.g. wood chips) or energy crops (miscanthus, switchgrass, etc.).
Processing
The first step in the processing of lignocellulosic feedstocks to ethanol is a pre-treatment consisting of a physico-chemical step and an enzymatic liquefaction step, and fractionates the feedstock into its three main components (cellulose, hemicellulose and lignin). The most common method is the steam explosion with or without an acid catalyst but also acid and base treatment and organosolv processes have been or are in use. The nature of the pre-treatment has large impact on the accessibility of the still (partially) crystalline, de-lignified cellulose for saccharification while hemicellulose is mostly hydrolysed to sugars and oligomers and dissolves at this stage. Depending on the pre-treatment used, different amounts of inhibitors are formed that can be detrimental both for enzymatic hydrolysis performance and for yeast fermentation. A detoxification step might be necessary, although it is nowadays generally avoided under demo and pre-commercial scale.
After hydrothermal treatment, additional water is added to the mixture of solids and liquids resulting from the pre-treatment after which hydrolysis and saccharification of the cellulose and hemicelluloses oligomers take place. This step uses specifically developed enzyme cocktails, but also acid hydrolysis has been used. The enzyme treatment results in a pumpable slurry and unhydrolysed solids. After separation of solids and liquids, the slurry is either fermented in the same vessel (Simultaneous Saccharification and Fermentation (SSF)) or in a downstream fermenter (Separate Hydrolysis and Fermentation (SHF)). Lignin is separated before or after fermentation and usually dried to be used as a fuel for the process and/or for power generation. The cellulose- and hemicellulose-derived C6 sugars are fermented by yeast strains derived from traditional yeasts used for the production of wine, beer or bread, while for the fermentation of C5 sugars genetically modified yeasts have been developed in the recent years. After the fermentation has been finalized, the ethanol is recovered by distillation and dehydration.
There is a complex trade-off between the water addition, the viscosity, the enzyme consumption, the ethanol concentration achievable and the possible inhibition of the ethanol and the energy required for the downstream processing. At present, the technology can give up to 300 liters of ethanol per tonne of agricultural waste of which a significant part is derived from the C5 sugars, i.e. an efficiency to biofuels in the order of 30 %.
Lignocellulosic ethanol is an advanced biofuel in the EU.
Demoplants
Please check our production facilities database to obtain most recent information on demonstration plants for this value chain (use the filter function). The status as of early 2020 is described in the report “Current Status of Advanced Biofuels Demonstrations in Europe”, published by ETIP Bioenergy in March 2020.
Factsheet: Ethanol
Fermentation of isolated sugars to higher alcohols
Isolated sugars, today from crop or starch sources but in the future possibly also from lignocellulosic sources, are the starting point for a number of pathways to biofuels.
Some bacteria naturally produce butanol and yeast can be engineered to produce butanol instead of ethanol. This pathway can be used for producing both n-butanol and iso-butanol, the latter also having a high value as a chemical building block.
Another development is to use an engineered microorganism to produce iso-butene that can be the basis for chemicals but also oligomerized and hydrogenated to e.g. gasoline. Since iso-butene is a gas that separates from the broth, this facilitates the product separation and upgrading, as well as limiting any product inhibition issues.
Acknowledgement: Large parts of the texts were taken from Lars Waldheim´s contribution to the report “The Contribution of Advanced Renewable Transport Fuels to Transport Decarbonisation in 2030 and beyond”
[1] SGAB Technology status and reliability of the value chains: 2018 Update. 28 December 2018. Ed. I Landälv, L Waldheim, K Maniatis. artfuelsforum.eu/news-articles/updated-sgab-report-technology-status-and-reliability-of-the-value-chains/
PVC6: Gaseous transport fuels via fermentation
The production of biogas via anaerobic digestion of biomass is already widely deployed; thousands of small, farm-based biogas plants across Europe produce heat and electricity. Recently, biogas facilities have grown larger, and separating CO2 from the biogas as to upgrade it to biomethane has come into focus. Some of the upgrading facilities directly facilitate the application of the biomethane as a transport fuel, while others provide their product to industry or inject it into the gas grid.
Further pathways for the production of gaseous transport fuels from biological processes include anaerobic digestion to biogas followed by in-situ or ex-situ biological or catalytical methanation, and the fermentation of sugars to isobutene and further processing into long-chain hydrocarbons.
