Preliminary status note: Thermal biomass conversion technologies ...

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.