G-volution II - Dual Fluidised Bed Next Generation Biomass Gasifier - II

01.11.2010 - 31.10.2014
Research funding project
Efficient utilization of biomass as a primary energy source reduces greenhouse gas emissions and reduces the need for long-distance transport of energy, thus increasing the security of energy sup-plies. The main challenge is to develop new fields of application apart from simple heat generation. In this area, the dual fluidized bed steam gasification technology developed at Vienna University of Technology and successfully demonstrated in Güssing and Oberwart at a scale of 8 resp. 10 MWth represents a key technology for both efficient combined heat and power production as well as for coupled production of synthetic biofuels (2nd generation biofuels, polygeneration approach). Various syngas upgrading and utilization technologies are currently investigated in national and international research projects. Some technologies, like production of synthetic natural gas are already in the large scale demonstration phase. An increased interest from industry in technologies to substitute natural gas by using industrial waste fuels such as sewage sludge, municipal waste, saw dust, bark, waste wood, etc., leads actually to a renaissance of research regarding the gas generation section itself. In the classical design of the Güssing gasifier, the gasification reactor is designed as bubbling fluidized bed. The heat transfer to the fuel particles and the main tar destruction reactions take place in contact with the bed material particles inside the bubbling fluidized bed. Above there is a freeboard region where the solids concentration approaches zero. Such a separation between bubbling bed and freeboard leads to problems especially when inhomogeneous fuels are used. Organic fines are immediately elutriated into the freeboard where primary tars are emitted and not sufficiently converted due to lack of catalytically active solids in the freeboard. This may result in tar depositions down-stream of the gasifier and may critically affect the plant availability. Recent research performed in the field of chemical looping combustion revealed that there is a significant improvement of gas-solids contact possible by increasing the fluidization velocity up to the turbulent or fast fluidization regime. In this case the bed material is distributed over the whole gasifier volume, partly elutriated at the top and recycled into the gasifier via a cyclone and loop seal. The change in fluidization conditions of the gasifier results in the following advantages: (1) The free-board disappears in favour of a zone with significant presence of solids. Organic fines pyrolyze in poresence of catalytically active material and thus the tar destruction mechanisms work independently of fuel particle size. (2) The necessary reaction volume of the gasifier can be reduced and a scale up of the technology to larger scale is favoured. (3) The cyclone at the exit of the gasifier leads to a defined backflow of particles and catalytically relevant fines into the gasifier. It further prevents the product gas line from facing too high solid fractions. A general improvement of plant efficiency is possible if oxygen is transported in a selective way by the solid bed material from the combustion reactor to the gasifier. This can be achieved by using particles with significant content of certain metal oxides, such as iron oxide (Ilmenite, etc.). Additionally, a high tar destruction effect is expected as a secondary effect of selective oxygen transport. The aim of G-volution is to investigate this promising approach at relevant operating conditions to provide the basis for the industrial demonstration. The very promising results of the ongoing project G-volution (Neue Energien 2020, FFG-Projectnumber: 821954) will be implemented.

People

Project leader

Project personnel

Institute

Grant funds

  • Kommunalkredit Austria AG (National) Kommunalkredit Public Consulting (KPC)

Research focus

  • Sustainable Production and Technologies: 100%

Keywords

GermanEnglish
Wirbelschichtfluidization
Biomassebiomass
Vergasunggasification

External partner

  • TECON Engineering GmbH

Publications