ENERGY RECOVERY FROM UNCONVERTED BIOMASS CHAR

Abstract

For the market of the Republic of Serbia the most interesting are biomass cogeneration plants with the thermal input between 100 and 300 kW. In this middle-power range, gas engines are the most suitable technology for electricity production from biomass. To convert biomass into the product gas, downdraft gasifiers are commonly used due to their reliable and tar-free functioning.The drawback of these reactors is the product gas, because it is laden with particulates and has are latively small heating value. These particulates and the residues from gasifiers consist of unconverted char and ash. Depending on the design, there are typically from 3 to 15% of unconverted char. The increase in the amount of unconverted char linearly decreases the chemical efficiency of gasification process. Because of the heating value of char, the energy loss contained in unconverted char is significant and different measures are performed for its reduction: recuperation, recycling and non-energy use. In this paper, an original downdraft gasifier with a system for char recycling is presented. The advantage of the proposed solution is an enlarged reduction zone, which influences a longer residence time of solids inside the gasifier.