See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/259543643 Biomass gasification for synthesis gas production and applications of the syngas ARTICLE · JULY 2014 DOI: 10.1002/wene.97 CITATIONS DOWNLOADS VIEWS 3 54 87 3 AUTHORS, INCLUDING: Reinhard Rauch Hermann Hofbauer Vienna University of Technology Vienna University of Technology 45 PUBLICATIONS 619 CITATIONS 124 PUBLICATIONS 1,568 CITATIONS SEE PROFILE SEE PROFILE Available from: Reinhard Rauch Retrieved on: 10 August 2015 Advanced Review Biomass gasification for synthesis gas production and applications of the syngas Reinhard Rauch,1∗ Jitka Hrbek2 and Hermann Hofbauer2 Synthesis gas from biomass can be produced and utilized in different ways. Conversion of biomass to synthesis gas can be done either in fluidized bed or entrained flow reactors. As gasification agent oxygen, steam, or mixtures are used. The most common use of biomass gasification in the last decades has been for heat and/or power production. Nowadays, the importance of transportation fuels from renewables is increased due to environmental aspects and growing fossil fuels prices. That is why the production of Fischer–Tropsch (FT) liquids, methanol, mixed alcohols, substitute natural gas (SNG), and hydrogen from biomass is now in focus of view. The most innovative and interesting ways of synthesis gas utilization and projects, BioTfueL or GoBiGas, BioLiq, Choren, etc. are discussed here. Further the microchannel technology by Oxford Catalysts and distributed production of SNG in decentral small scale are presented. The synthesis platform in Gussing,¨ Austria is also presented. The FT liquids, hydrogen production, mixed alcohols, and BioSNG, these are the projects associated with the FICFB gasification plant in Gussing.¨ Also the principle and examples of sorption-enhanced reforming to adjust H2/CO ratio in product gas during the gasification is described. Finally, in the conclusion also an outlook for the thermochemical pathway to transportation fuelsisgiven. © 2013 John Wiley & Sons, Ltd. How to cite this article: WIREs Energy Environ 2013. doi: 10.1002/wene.97 SPIRIT AND PURPOSE OF BIOMASS related to security of energy supply, much R&D GASIFICATION FOR SYNTHESIS GAS on the production of synthesis gas from biomass PRODUCTION was carried out in the past decade. The main investigated applications of the synthesis gas was ynthesis gas is one important intermediate to to produce transportation fuels over FT synthesis, Sproduce fuels for transportation and chemicals. methanol synthesis or others, like mixed alcohol Currently, synthesis gas is produced mainly from synthesis. natural gas, coal or by-products from refineries. The usage of synthesis gas is about 50% to ammonia, 25% to hydrogen, and the rest is methanol, TECHNOLOGIES FOR PRODUCTION Fischer–Tropsch (FT) products and others.1,2 OF SYNTHESIS GAS FROM BIOMASS Owing to the global warming problem, caused In the past decades much R&D was done to develop by fossil CO2 emissions, and also due to issues special gasification systems to convert biomass to ∗ synthesis gas, or to adapt coal gasification technology Correspondence to: [email protected] for biomass. These systems can be divided into several 1 + Bioenergy 2020 ,Gussing,¨ Austria groups according to Ref 3: 2Institute of Chemical Engineering, Vienna University of Technology, Vienna, Austria Conflict of interest: The authors have declared no conflicts of • Producing and transport of the heat into the interest for this article. gasification reactor: allothermal–autothermal © 2013 John Wiley & Sons, Ltd. Advanced Review wires.wiley.com/wene Fuel Fuel in fixed bed Gasification agent Fuel and bed material in fluidized bed Product gas Circulating fuel and bed material Counter-flow Cocurrent-flow Stationary Circulating Entrained-flow gasifier gasifier fluidized bed fluidized bed gasifier Fixed bed gasifier Fluidized bed gasifier FIGURE 1| Different types of gasifiers. • Type of reactor: fixed bed-fluidized bed- of the advantages over autothermal gasification entrained flow processes. Another important advantage is the • Type of gasification agent: oxygen-steam- complete carbon conversion and that there is no mixtures of steam and oxygen problematic waste produced. All carbon containing streams from the product gas cleaning (e.g., dust, tars) can be recycled to the combustion zone and there Allothermal–Autothermal converted to heat, which is used for the gasification reactions.5 Autothermal gasifiers provide the necessary heat of reaction by means of partial oxidation within the gasification reactor. If air is used as oxidizing agent Fixed Bed–Fluidized Bed–Entrained Flow during the process, the product gas contains a high According to the design of the fuel bed, the gasifiers amount of nitrogen. So for synthesis gas production can be divided into fixed bed, fluidized bed, and either pure oxygen (in entrained flow reactors) or entrained flow. The differences in the design of the mixtures of oxygen and steam (in fluidized bed gasification reactor are shown in Figure 1. reactors) are used as gasification agent. The composition of the gas and the level of The great advantage of the autothermal undesirable components (tars, dust, ash content) gasification is the direct heating of the reactants and produced during biomass gasification process are therefore more efficient energy utilization. The process dependent on many factors such as feedstock is simpler as by allothermal gasification and it is easier composition, reactor type, and operating parameters to operate it under pressurized conditions. (temperature, pressure, oxygen fuel ratio). Allothermal (or indirect) gasification is charac- terized by the separation of the processes of heat production and heat consumption.4 The allothermal Oxygen Blown–Steam Blown gasification facility almost always consists of two reac- Typical composition of a dry gas produced during the tors, connected by an energy flow. Biomass is gasified biomass gasification process is shown in Table 1. As in the first reactor and the remaining solid residue can be seen, the concentration of the gas compounds (char) or product gas is combusted in the second during oxygen and steam gasification is completely reactor to produce the heat for the first process. The different. transport of the heat can be done either by circulating During oxygen gasification, the combustion a bed material or by heat exchangers. products (CO2,H2O) are in the product gas and take Allothermal gasifiers generally produce two gas part in the chemical reactions, mainly in water-gas streams: a medium calorific product gas (gasification shift reaction. reactor) with little or no nitrogen and a flue gas On the other hand, higher amount of hydrogen (combustion reactor). The production of an N2- in the product gas can be found during the steam free gas without the need of pure oxygen is one gasification. The hydrogen found in the product gas © 2013 John Wiley & Sons, Ltd. WIREs Energy and Environment Biomass gasification for synthesis gas production TABLE 1 Typical Composition of Dry Gas During the Oxygen and Impurities like nitrogen act as inert during the Steam Gasification of Biomass synthesis and their concentration have to be as low Oxygen Oxygen as possible. The inerts reduce the partial pressure and by this effect reduce the conversion. Especially for Gasification Gasification synthesis reactions, where the product is separated as (Entrained (Fluidized Steam a liquid and where a recycle of remaining unconverted Compound Flow) Bed) Gasification gas is done (e.g., methanol), the inerts have to be bled CO (vol %) 40–60 20–30 20–25 off as they would otherwise be accumulated. Also for production of BioSNG the inerts have to be below CO2 (vol %) 10–15 25–40 20–25 1 vol%, as otherwise the heating value of the BioSNG H2 (vol %) 15–20 20–30 30–45 will not fulfill the requirements of natural gas. CH (vol %) 0–1 5–10 6–12 4 Methane and higher hydrocarbons normally act N2 (vol %) 0–1 0–1 0–1 as inert during the synthesis reaction, so they have LHV (MJ/Nm3) 10–12 10–12 10–14 to be treated similar to inerts. These components Tar content (g/Nm3) <0.1 1–20 1–10 are mainly present in fluidized bed reactors and not in high temperature gasification (Table 1). As the heating value of the hydrocarbons is much higher than that does not originate only from the fuel as in the of H2 and CO, a small amount of hydrocarbons case of oxygen gasification but also from the steam already present in the gas can contain most of the (H2O). energy of the synthesis gas. So the overall conversion The tar content depends not only on the type of from biomass to final product (e.g., FT liquids) is gasifier but also mainly on the operation temperature. reduced by the small amounts of hydrocarbons that In entrained flow gasification, where the temperature are already produced in the gasifier. So in most cases ◦ is above 1000 C, there is no tar produced, whereas the hydrocarbons are converted to H2 and CO in a in fluidized bed gasification, where the temperature is reformer to maximize the conversion from biomass ◦ below 1000 C, tar is produced and has to be removed to the final desired product. The only exemption is from the product gas. the production of BioSNG. Here a high content of methane and nontar hydrocarbons in the synthesis gas are favored, as then the highest conversion efficiency Requirements on the Gasification Reactor to BioSNG is achieved. To use the product gas from a biomass gasifier as Catalyst poisons deactivate the synthesis catalyst synthesis gas, there are several properties, which have and have to be removed to very low levels. The most to be taken into account: well-known poison is sulfur, which can be in form of H2S, COS, mercaptans, or thiophens in the synthesis • H2:CO ratio gas. The organic sulfur components are mainly present • Amount of inerts, like nitrogen in fluidized bed gasifiers, and not in high temperature • Amount of methane and higher hydrocarbons gasification.