Ecological and Technical Aspects of Co-Combustion of Coal with Substantial Fraction of Sludge in the Grate-Type Boilers

At the beginning of the paper the still unsolved problem of municipal sewage sludge disposal is discussed while in the following pages the possibility of satisfactory solution of the problem of utilization of increasing amount of the sludge by thermal methods is presented. The statistical data show the increasing role of thermal methods of sludge utilization in western Europe and at the same time their negligible role in Poland. The reason of such situation is the conviction of high level emission of harmful substances from the process of sludge incineration. As a most promising method of thermal sludge utilization in Poland the co-combustion of the sludge with coal is discussed. The main part of the paper shows the results of measurements of emission of harmful gaseous substances from the co-combustion process of sludge with coal performed in the unique laboratory installation in the Chair Of Technologies and Installations for Waste Management, Silesian University of Technology, Gliwice, Poland. The installation realizes wide range of parameters of combustion similar to the parameters in the real coal fired boilers with moving grates. The combustion experiments were performed for the fuel containing 40% mass fraction of the sludge of moisture content lower than 10%. The results of measurements are compared with the similar data obtained for pure coal. Special attention was put on the emission of CO, NOx and SO2 and the ignition lag in relation to the temperature history in the combustion chamber.