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Gasification of biomass with oxygen rich air in a reverse-flow, slagging gasifier



The main objective of the project is to develop an innovative, reverse flow molten slag fixed bed gasifier concept for combined heat and power generation in a capacity range of 0.5-2.5 Mwe, and with improved thermal efficiency (5 - 10 %) compared to conventional fixed bed gasifiers. The reactor enables handling of relatively wet (up to 40 % mcdb) and ash-rich biomass fuels. The gasifier will produce a gas with a caloric value of at least 6 MJ/Nm3. Specific objectives are:

Development and testing of a low-cost device for enriching the oxygen content in air (air enrichment unit). An improvement of the energy efficiency of at least 0.1% per 1% point O2 enrichment is expected. The optimum oxygen content (30 - 60%) to be used in the gasifier depends on an economic and technical analysis of the whole process.

Development and testing of a novel and compact reverse-flow, molten slag, fixed bed gasifier with integrated heat exchange and tar removal system, for operation on oxygen-rich-air. A lab-scale unit (2 kg/hr) and a mini-plant (20 kg/hr) will be constructed and operated

Assessment of cost-effective technologies, both existing and under development, for utilisation of process heat from the reverse-flow slagging gasifier for drying biomass feedstock.


In practice, several methods exist for increasing the oxygen content in air. Within this project pressure/vacuum swing adsorption and membrane separation will be studied in detail for application in biomass gasification systems. Final selection of the technology will be based on both an economic and a technical analysis. The selected technology will be built and tested on a pilot-scale.

The design of the reverse-flow gasifier will start with a literature study of slagging gasifiers. Concerning the design and operation of reverse flow reactors a lot of experience is available, and partly based on previous and running EC-projects (AIR2-CT93-1436 & JOR3-CT95-0053) for the removal of tar from producer gas in a reverse flow reactor. A small laboratory scale slagging gasifier will be designed and constructed which provide the required information for the pilot-plant installation. A pilot-plant with a capacity up to 20 kg of biomass per hour will be built, and subsequently connected with the selected air enrichment unit.


The novel, enriched-air blown fixed bed gasifier is operated in the molten slag mode. Due to extensive heat integration -which results from the reverse flow principle- this gasifier produces a tar-free, intermediate calorific gas of a low temperature. The main advantages of the proposed system are:
The gasifier will be operated with oxygen enriched air, which will cause higher reaction temperatures and enable operation in a slagging mode. This results in complete utilisation of the carbon. (no carbon remains in the ash).
Due to the use of oxygen enriched air, the fuel gas will have a higher heating value. This will lead to an increased mixture heating value of the gas/air mixture that is to be fed to the internal combustion engine and therefore enables the use of smaller (and cheaper) engines;
The reverse flow principle will lead to improved heat integration; a larger part of the biomass energy content is converted into chemical energy yielding a higher "biomass-to-electricity" efficiency.
The gasifier will have improved thermal and volumetric efficiency.
The different partners will either directly (through the manufacture of equipment or through implementation/exploitation of integrated energy systems) or indirectly (through exploitation of knowledge and experience) commercialise the results from the project.

Funding Scheme

CSC - Cost-sharing contracts


5,Drienerlolaan 5
7522 NB Enschede

Participants (4)

Aston University
United Kingdom
Aston Triangle
B4 7ET Birmingham
Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
04200 Tabernas
Utrechtseweg 310
9035 Arnhem
Kara Engineering Almelo BV
7602 PD Almelo