Experimental Study Examining the Evolution of Nitrogen Compounds during the Gasification of Dried Sewage Sludge

Gasification of dried sewage sludge, which contains a high percentage of nitrogen, was experimentally studied to determine the effects of some operational parameters, such as freeboard temperature and equivalence ratio, on the partitioning of the fuel nitrogen among nitrogenous species. Experiments were performed using a bench-scale fluidized-bed gasifier and according to a well-specified procedure implemented to recover and quantify the nitrogen compounds. A mixture of argon and oxygen in similar proportions to air was used as a gasification agent in order to correctly quantify the N-2 produced in the gasification process in an experimental way. Important findings of this research include the following: applying the analytical procedure developed in this work, a reasonably good inventory of nitrogen in the gasification products was obtained (mass balance closures near to 100%); most of the nitrogen goes to form gaseous products, N-2 being the main gaseous nitrogen-containing product obtained; concentrations of N-2, NH3, and N-tar in the producer gas strongly depend on the freeboard temperature, an increase of which causes an important decrease of both NH3 and N-tar contents and a substantial increase of the N-2 amount.