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In the context of climate change, increasing efficiency and energy security, biomass gasification is likely to play an important role in energy production. Atmospheric circulating fluidised bed (CFB) technology was selected for the current study. The primary objective of this research is to develop a computer simulation model of a CFB biomass gasifier that can accurately predict gasifier performance under various operating conditions. An original model was developed using ASPEN Plus (Advanced System for Process ENgineering Plus). The model is based on Gibbs free energy minimisation. The restricted equilibrium method was used to calibrate the model against experimental data. This was achieved by specifying the temperature approach for the gasification reactions. The model predicts syn-gas composition, process conversion efficiency and syn-gas heating values in good agreement with experimental data from a laboratory rig. Operating parameters were varied over a wide range. Parameters such as equivalence ratio (ER), temperature, air preheating, biomass moisture and steam injection were found to influence product gas (syn-gas) composition, syn-gas heating value, and process conversion efficiency. The results indicate an ER and temperature range over which hydrogen (H2) and carbon monoxide (CO) production is maximised, which in turn ensures a high heating value and cold gas efficiency (CGE). Gas heating value was found to decrease with ER. Air preheating increases H2 and CO production, which increases gas heating value and gasifier CGE. Air preheating is more effective at low ERs. A critical air temperature exists after which additional preheating has little influence. Steam has better reactivity than fuel bound moisture. Increasing moisture degrades gasifier performance therefore the input fuel should be pre-dried. Steam injection should be employed if a H2 rich syn-gas is desired.
Doherty, W., Reynolds, A., Kennedy, D.: The Effect of Air Preheating in a Biomass CFB Gasifier Using ASPEN Plus Simulation. Biomass and Bioenergy (In Press), doi:10.1016/j.biombioe.2009.05.004.