Development of a bi-equilibrium model for biomass gasification in a downdraft bed reactor

• Different biomass gasification tests in a fixed bed are used to validate a model.
• The approach is based on equilibrium models at different temperatures.
• A repartition factor is included to simulate the bypass of pyrolysis products.
• The model is simple and up to 8 times more accurate than simple equilibrium model.
• A sensitivity analysis is included to discuss practical applications of the model.

This work proposes a simple and accurate tool for predicting the main parameters of biomass gasification (syngas composition, heating value, flow rate), suitable for process study and system analysis. A multizonal model based on non-stoichiometric equilibrium models and a repartition factor, simulating the bypass of pyrolysis products through the oxidant zone, was developed. The results of tests with different feedstocks (corn cobs, wood pellets, rice husks and vine pruning) in a demonstrative downdraft gasifier (350 kW) were used for validation. The average discrepancy between model and experimental results was up to 8 times less than the one with the simple equilibrium model. The repartition factor was successfully related to the operating conditions and characteristics of the biomass to simulate different conditions of the gasifier (variation in potentiality, densification and mixing of feedstock) and analyze the model sensitivity.