Gasification of organic wastes in an entrained flow reactor: behaviour of mineral matters and choice of ceramic refractories

Synthesis gas can be obtained by biomass gasification. It is composed of CO and H₂ and can be used for the production of electricity, organic compounds and biofuels. The use of sewage sludge allows exploiting this kind of waste as biomass resources. However, sewage sludge contain a large percentage of minerals (30 to 50 % wt) composed of at least 20 different oxides including silica, lime and phosphorous oxide, P₂O₅ (15 % wt of the minerals). Mineral matters of sludge are complex and not well known. So, it is necessary to study their behaviour in function of temperature to understand their impact during gasification process and avoid gas pollution and corrosion of the ceramic refractories. Firstly, liquidus temperatures of two different mineral matters were determined. The result shows that these temperatures, between 1257 and 1358 deg. C, are in the operating range of the gasifier. Thus, a study of the binary system SiO₂-P₂O₅ had enabled to enhance thermodynamic databases. Secondly, thermodynamic and kinetic studies, confirmed the low release of P₂O₅ in function of temperature due to the formation of refractory compounds like Ca₃(PO₄)₂ and Ca₉Fe(PO₄)₇. Release of inorganics from the sludge is less than 0.5 % wt. Finally, interaction between slag and different ceramic refractories was studied. Static and dynamic trials were performed to choose the most resistant ceramic refractory. One of them composed of alumina and chrome oxide proved to be a good choice to build the gasifier wall. (author)