Modeling and exergoeconomic analysis of biomass gasification in a downdraft gasifier

Abstract: In this work it is presented an equilibrium model, capable to predict the composition of the generated gas, its Lower Heating Value (LHV), the gasification efficiency, the ratio air/biomass and the  ratio gas/biomass in a downdraft gasifier. The model describes the influence of  the moisture content of the biomass and the gasification temperatures on the composition and properties of the produced gases, like the low heating value (LHV). It is assumed that all the chemical reactions taking place  in the gasification area are in thermodynamic equilibrium. The model doesn't considered tar formation. It is not considered formation of other hydrocarbons (CxHy) than methane. The types of biomass used for modelling are: sugarcane bagasse, paddy husk, pine sawdust, mixed paper waste and municipal solid waste. The effect of gasification temperature and moisture content of biomass over the gas composition has been also investigated. Also an exergo-economic analysis of cogeneration system forming by a downdraft gasifier associated to an internal combustion engine was carried out, using sugar cane bagasse, rice husk, and pine sawdust, as fuel in gasification processes. At 700°C the highest amount of CO and CH4 are produce. The amount of CH4 and CO decrease with the temperature when the gasification temperature is increased from 700°C to 1000°C. The amount produced H2 does change so much between the gasification at 700°C and 1000°C. But the amount produced hydrogen is somewhat higher at 800°C. The lower heating value (LHV) of the synthesis gas from gasification of sugarcane bagasse the LHV of the produced gas is 4,09MJ/Nm3; for gasification of pine the LHV of the produced gas is 5,32MJ/Nm3; for gasification of rice husk the LHV of the produced gas is 3,14MJ/Nm3, for gasification of mixed paper waste the LHV of the produced gas is 4,51%, and for gasification of municipal solid  waste the LHV of the produced gas is 3,95MJ/Nm3. The cold and hot efficiency of gasification process at 800°C for bagasse with 20% moisture content are  55,32% and 84,90% respectively.