Development оf energy saving technology of two-stage biomass gasification for cogeneration plants

Abstract

A two-stage fine biomass gasification process for the low - power generation plants based on ICE, providing the tar content in the producer gas of no more than 7.1 mg/m3n that meets the requirements of the ICE producers was developed. Based on the results of experimental studies of the two-stage fine biomass gasification process, the effective process regimes were determined. The optimal range of the specific air flow, which provides a stable process of oxidative biomass pyrolysis in a dense layer at the pyrolysis temperature not exceeding 800oC is 25.0 55.0 m3/(m2 h).Efficiency of the oxidative pyrolysis process reaches 98.0% taking into account the disposal of all heat flows. Efficiency of the coke residue gasification process without the use of sensible heat of the producer gas is on average 78.0%. Using the sensible heat of the producer gas allows to improve gasification process efficiency to an average of 96.4%.Numerical and theoretical studies of gas ICE operation have shown that the gas ICE operation on the producer gas with a calorific value of 7.6 MJ/m3 is optimum. In this case, the fall of ICE effective power is 16.0%, and the cost of electric power generation is 0.39 UAH/(kW∙h). The results of studies have also shown that increasing the natural gas proportion in a mixture of more than 40.0% is not desirable, since it leads to higher cost of electric power generation up to 1.04 UAH/ (kW∙h) that corresponds to the cost of electric power from the external power system.Exergy analysis of a cogeneration plant has shown a high value of total exergy efficiency of 45 %, while exergy efficiency of individual circuit elements, such as a pyrolyzer and gasifier reaches 96 %, and the "ICE-generator" unit - 91 %. Such values of efficiency are caused by deep disposal of all heat flows in the circuit.