NNE5-2001-00704 Multi-Agricultural Fuelled Staged Gasifier with Dry Gas Cleaning - LIFT-OFF

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Crops for Solid Biofuels : EESD (Energy, Environment and Sustainable Development) : Thermochemical Conversion

Proposal No:	NNE5-2001-00704
Date Prepared:	February 2004
Source:	European Bio-Energy Projects (EUR 20808)

Introduction

Utilisation of biomass and wastes is a sustainable and environmentally friendly way of producing energy, which contributes to the reduction of the greenhouse effect, reduces local environmental problems, utilises local resources and improves local employment. Small CHP plants will certainly constitute the most promising route, as they represent the major market perspective in terms of replication.

Gasification is a way to increase the utilisation of renewable energy sources as it presents a higher efficiency as well as a good flexibility to the feedstock. In addition, development of components and integration of processes is a potential export opportunity.

Activities

The research activities include developing a model and tools, which will focus on the first design of the new LIFT-OFF demo plant for woodchips. Then in a second step, the research and modelling will continue and be applied to other biomasses and operating conditions, in order to provide a tool for the design of multifuel LIFT-OFF reactors and to optimise operating conditions. The aims are to enlarge the potential market towards the cheapest biomass resources.

The gasifier will be a 2-stage 3 zone fixed bed gasifier. This principle is based on the traditional open-core gasifier, but is different in the design of the grate.

It consists of two stages. Stage one is fed with biomass, and stage two is fed with char from stage one. Stage one is placed on top of stage two so that the char from stage one falls into stage two. Between the two stages there is a combustion chamber, where the gas produced in stage one is partially oxidised, and the temperature is thereby increased to about 1 100C. This reduces the tar by thermal cracking and by oxidisation.

Impact and exploitation

The successful outcome of the project will have an important character on small-scale CHP and energy production.

• The LIFT-OFF bed solves the fixed bed upscaling problem in order to avoid a large pressure drop over the char bed and to avoid channelling.
• By turning the cold end of the fixed bed upside down it is possible to obtain a situation where the small particles that will normally create pressure drop will be lifted out of the bed. And the mechanical means of turning the bed upside down will, at the same time, provide an efficient means of breaking all channels and bridges in the bed.
• This LIFT-OFF bed separates the zones of pyrolysis, combustion and gasification in a way so that the gasifier is fuel flexible.
• Combining the LIFT-OFF principle with the Dry Gas Cleaning technology the wet gas scrubbing systems, with all the environmental drawbacks, will be technically outdated. As a consequence, CHP plants based on gasification technology will be technically and economically competitive and thus the market will increase significantly for this type of technology. This will be commercially proven in the LIFT-OFF project.
• The pyrolysis temperature of an open-core gasifier is very high, so the char being fed to stage two has a very low tar content, and there will be almost no tar production in this stage. It has been possible to obtain a gas with tar content below 50 mg/Nm³ (verified by an independent technological service institute, according to specifications from the Tar Protocol). For comparison, the counter-current gasifier produces 100-1000 mg tar/Nm³.
• The heat from the combustion chamber is used to convert the char into gas. This increases the char conversion, and thereby increases the gasifier efficiency by 10-15%. The three-stage gasifier will obtain high-energy efficiency and provide good means for returning waste heat back into the gasification process. Thus it is possible to obtain cold gas efficiencies of 85-95 % based on the lower heating value of the biomass, and electric efficiencies in the range from 30-34 % depending on the efficiency of the engine.