Alternative Modes of Low-Grade Solid Fuel Gasification for Small Scale Applications

From technical viewpoint small scale gasification (up to 1 MWe) meets perfectly the need for a technology to involve low-grade solid fuels into energy balance. Neither does it economically. Having become quite economical for heating, in electricity generation the technology still is not as reliable as direct combustion. A range of possible modes of thermochemical gasification are studied using numerical thermodynamic modelling and experimental to reveal the limits of their technical efficiency. The obtained results pertain mainly to biomass. It is shown that the composition of syngas may vary in course of gasification process due to low stability of the thermal modes within the traditional range of reaction parameters. Thermal modes are compared to substantiate the choice of reaction conditions providing high calorific value of syngas and stability of its chemical composition. The experiments show the close-to-adiabatic conditions to be the easiest way to raise the reliability of gasification process. A consideration is given to the use of steam/air, carbon dioxide, and hydrogen draught. The influence of CO2 and H2 as a draught agent is counter-directional. Super-adiabatic conditions (when external energy is supplied to achieve super-adiabatic temperatures) are suitable for fuels with variable chemical composition and moisture content.