ERK5-1999-00003 Biomass gasification for CHP with dry gas cleaning and regenerative heat recovery

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Summary Information



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EESD (Energy, Environment and Sustainable Development) : Electricity : Thermochemical Conversion

Proposal No:	ERK5-1999-00003
Date Prepared:	February 2004
Source:	European Bio-Energy Projects (EUR 20808)

Introduction

Utilisation of biomass and waste is generally expensive and not very efficient on small and medium scale plants. For gasification systems the main problem is the gas cleaning where severe environmental impact, costly maintenance problems and low energy utilisation are the main constraints. To overcome this situation, the project combines three minor gasification companies to one powerful European consortium with a broad range of scientific and commercial contacts to develop, integrate and prove a complete biomass gasification combined heat and power prototype plant of about 250 kWth.

Activities

The most essential part of the process is the gas cleaning. The gas cleaning includes a high temperature dust separation at the gasifier outlet followed by a special regenerating counter-current tar condensing heat-exchanger, which is operated alternately in two phases. Change of phase concerns change of flow direction as well as flow side. Two separate streams of air cool the hot gas. Regeneration has the effect of decomposing the tar deposits at high temperatures and returning the cracked tar products into the gasifier by means of preheated gasification air. The cooling air for feedstock drying is uncontaminated with cracked tar products. The produced gas is cooled to 10-20°C above the dew point, so no wastewater is generated.

Results

The following technical objectives have been achieved:

• Design and construction of a hot producer gas (700-800°C) particulate cleaning system (filter/ cyclone, adhesion to tar, engine pre-filter), which operates continuously and achieves separation efficiency acceptable for engine applications, preferably without further particulate removal.
• Design and construction of a new generation small scale tar condensing, regenerative gasgas heat exchanger, which is able to provide a clean gas free from tars creating problems in an engine. The efficiency of the condensation increases with the tar concentration. Depending on the operating conditions the tar concentrations measured varied from 37.4 to 237.6 mg/Nm³. The heat exchanger cycle has been in operation more than 500 hours on one continuous run.
• Rebuilding a carburettor and exhaust on an existing gas engine, which has achieved emissions of CO below 500 ppm, hydrocarbons below 100 ppm and NO, below 500 ppm. The biofuel (20% moisture) power efficiency obtained is higher than 22%.

In general performance was superior to that of similar existing processes.

Impact and Exploitation

Utilisation of biomass and waste is a sustainable and environmentally friendly way of energy production, which may contribute to the reduction of the greenhouse effect, utilise local resources and improve local employment. Small CHP plants will certainly constitute a 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. In addition, development of components and integration of processes are potential export opportunities.

To be economically attractive the investment costs (sales price, exclusive of installation costs) of the plant should not exceed #1,500 /kWe.