Improving the performance of fluidized bed biomass/waste gasifiers for distributed electricity: A new three-stage gasification system

• Methods to increase the conversion of char and tar in fluidized bed gasifiers (FBG) are discussed, with thefocus on small to medium-size biomass/waste gasifiers for power production (from 0.5 to 10 MWe).Optimization of such systems aims at (i) maximizing energy utilization of the fuel (maximizing charconversion), (ii) minimizing secondary treatment of the gas (by avoiding complex tar cleaning), and(iii) application in small biomass-to-electricity gasification plants. The efficiency of various measures toincrease tar and char conversion within a gasification reactor (primary methods) is discussed. The optimizationof FBG by using in-bed catalysts, by addition of steam and enriched air as gasification agent, andby secondary-air injection, although improving the process, is shown to be insufficient to attain the gaspurity required for burning the gas in an engine to produce electricity. Staged gasification is identified asthe only method capable of reaching the targets mentioned above with reasonable simplicity and cost, so itis ideal for power production. A promising new stage gasification process is presented. It is based on threestages: FB devolatilization, non-catalytic air/steam reforming of the gas coming from the devolatilizer, andchemical filtering of the gas and gasification of the char in a moving bed supplied with the char generatedin the devolatilizer. Design considerations and comparison with one-stage FBG are discussed.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

Nyckelord

Tar

Gasification

Char

Fluidized bed

Optimization

Biomass

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