To simulate oxy-co-gasification, actual operation conditions are considered. Then, the fuel mixture is modified by changing the amounts of coal and coke and including up to 10% of biomass, but keeping constant the total chemical energy of the fuel. Two experiments have been carried out. In the first one, fuel composition is varied while keeping oxygen and steam flows constant. In the second, fuel composition is also modified but oxygen and steam are varied to optimise CGE.
When part of the fuel is replaced by biomass keeping oxygen and steam constant, fuel and gas mass flows increase because biomass has lower LHV and less ash than the coal/coke mix. Due to biomass high oxygen content, CO2 and H2O concentrations increase and CO concentration decreases, which implies a reduction of gas LHV. Gasification temperature slightly decreases and CGE remain roughly constant. Finally, sulphur decreases and ash mass flow usually decreases, although they can increase, depending on if the biomass replaces coal, coke or a mixture of them. As an example, in Fig. 3, CO evolution versus biomass is shown by using three lines. These lines are plotted by considering a basis coal/coke mixture (30/70% in energy, which means about 50/50% in weight) and substituting by wheat straw only coke (30% coal), coal (70% coke) or the mixture. As it can be seen, the effect of biomass is higher when coke is replaced. In conclusion, when fuel is modified, gas composition and efficiency varies substantially, so that, operation should be modified.