Preliminary status note: Thermal biomass conversion technologies ...

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2.3. Moving bed gasification 2.3.1. Short description of technology 8 Moving bed biomass gasifiers operate with a bed of biomass where the gasifier agent, in most cases air and steam, passes through the biomass bed material. The flow of biomass and gasification agents can flow both counter-‐current and co-‐current in the gasifier. Counter current gasifiers obtain high conversion efficiency from biomass to fuel, but also have high tar content in the product gas. Typical reactor temperatures are in the range of 800 to 1000°C. Moving bed gasifiers do have some fuel constraints, many fines can stop the gas flow through the bed, and high alkali fuels like straw can lead to melting problems in the ash. 2.3.2. Global status of technology development Because of the limited time to write this note a status is not provided in this case. Most moving bed gasifiers have a fuel capacity of less than 5 MWth and the gas are used to produce electricity on a gas engine. 2.3.3. Danish strong positions and facilities Several Danish companies and university groups have developed moving bed gasifier technology. Some are listed here: -‐ Vølund & Wilcox gasifier. Vølund updraft gasifier (Commercial) -‐ Weiss A/S and DTU Risø. Staged down draft gasifier (Demonstration) (the Viking gasifier) -‐ Biosynergi process APs. Open core down draft gasifier (Demonstration) All gasifiers are used to production of heat and electricity using internal combustion gas engines. Generally production of chemicals and fuels are based on larger pressurized gasifiers. However, both experimental and efficiency calculations have been conducted on production of bio-‐fuels via fixed bed gasification using tri-‐generation of methanol or DME, electricity and district heating from wood chips via the small-‐scale TwoStage gasification process (Viking Gasifier). The process gas from the TwoStage gasifier is characterized by very low tar content and relatively high contents of CO and H2. Both traits are advantageous in relation to the gas cleaning systems and the synthesis of methanol or DME in subsequent catalytic processes. In Figure 1 is shown how the gasifier can be integrated with fuel synthesis process. Efficiency calculations comparing a large scale entrained flow gasifier DME plant with a tri-‐generation TwoStage gasification plant have been done. Only a 6-‐8% higher fuel and electricity efficiency can be expected by the larger DME plant. The small scale plants may have several advantages with respect to transport of biomass, integration into district heating systems and initial capital costs.
9 Figure 1: Simplified flow sheet of a small scale tri-‐generation of liquid fuel, electricity and heat from gasification of wood chips 2.3.4. Perspectives Wood Stream drying Syngas Two-stage gasification Compression Synthesis Unconverted syngas Electricity production Liquid Separation DME/MeOH With respect to moving bed gasification technology Denmark have several advantages: -‐ Several companies have developed and demonstrated small scale gasification plants that can produce heat and power -‐ Work on an integration of moving bed gasification with production of methanol and DME have been initiated at DTU Risø.
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Preliminary status note: Thermal biomass conversion technologies ...

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