Thermodynamics steam gasification, equilibria

However, a major limitation to this procedure follows from the reductive properties of syngas, which can lead to the formation of metals, with consequential loss of sorption capacity and metal evaporation further problems can arise from the substantial presence of H2O in the cases of steam gasification, resulting in thermodynamic equilibrium constraints to the reduction of hydrogen sulphide in the gaseous phase below the threshold limits for utilities and downstream process applications. 

The thermodynamics of the gasification reactions has been considered in detail in reference 177. Gasification by oxygen and hydrogen is exothermic, but reaction with steam or carbon dioxide is endothermic. The reaction between carbon and hydrogen may be restricted by equilibrium at normal working temperatures and pressures, but the other reactions are not. 

Both the thermodynamic equilibrium and the heat of reaction are reasonably well known for the heterogeneous gasification of carbonized residue with oxygen, steam, carbon dioxide and hydrogen. 

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