Due to high temperatures, which avoid tar and oils formation, and the efficient gas cleaning section, oxy-co-gasification at a large IGCC power plant is an interesting way to use a wide range of fuels (not only biomass but also solid waste, used tyres…) with high efficiency and negligible environmental impact.
Simulations of oxy-co-gasification of coal, coke and several types of biomass show that operation strategies should be modified as fuel mixture varies, so that, operation set points for a wide range of coke/coal/biomass combinations have been obtained. When a new fuel mixture is proposed, first of all, fuel, ashes and sulphur mass flows should be below limits determined by fuel feeding, ash removing and gas cleaning systems. If biomass is used, sulphur and ashes decrease, so that coal/coke relation could vary in a wider range. Second, the model should be used to determine the correct operation set point (by building graphs for coke/coal/biomass mixtures). A small amount of biomass (up to 10%) implies that the steam amount can be decreased substantially. Additionally, although properties of most types of biomass are quite similar, moisture content variations can modify the optimal steam and oxygen ratios. Last but not least, there are other fuel composition aspects that do not affect the operation set point but should be taken into account. First, some types of biomass, such as straw, contain chlorine that could produce corrosion. Second, biomass contains elements like calcium that reduce ashes melting point, which implies that limestone ratio should be reduced.
The optimum working condition of an oxygen blown gasifier is only obtained through the control of the reactive agents taking place in the reaction chamber (concentration, pressure and temperature), in opposition to combustion, which is a reaction totally developed. Operation maps are very useful to solve this issue. Accordingly, the problem of obtaining operation maps is a universal problem that every existing or planned oxy-gasification plant will have to face to. This problem cannot be solved by using only a pure theoretical analysis but an empirical feedback helping to solve the fine-tuning of a gasifier is also needed. Therefore, the methodology applied (simulation and experimental maps) can be of use for new IGCC plants provided that the experience gained from an already existing plant is considered. Operation maps shown in this paper are currently being used in Elcogas power plant daily operation. Thanks to this work, operators have a graph in which the consequences of their actions are clearly plotted, which can avoid errors and plant failures.