Abstract
The paper assesses the impact of combustion of biofuels produced based on municipal sewage sludge in stoker-fired boilers on the amount of pollutant emissions and examines the tendency of ash deposition of biofuels formed during the combustion process. The combustion tests were performed in a laboratory system enabling simulation of a combustion process present in stoker-fired boilers. The study was conducted for three types of biofuels; i.e., fuel from sewage sludge and coal slime (PBS fuel), sewage sludge and meat and bone meal (PBM fuel) and fuel based on sewage sludge and sawdust (PBT) with particle size of 35 mm and 15 mm. This paper describes and compares the combustion process of biofuels with different granulation and composition and presents the results of changes in emission values of NOx, SO2, CO, and CO2. The emission results were compared with the corresponding results obtained during combustion of hard coal. The results showed that biofuels with lower particle sizes were ignited faster and the shortest ignition time is achieved for fuel based on sewage sludge and coal slime-PBS fuel. Also, the highest NO and SO2 emissions were obtained for PBS fuel. During the combustion of fuel based on sewage sludge and meat and bone meal (PBM), on the other hand, the highest CO2 emissions were observed for both granulations. Biofuels from sludge show a combustion process that is different compared to the one for hard coal. The problems of ash fouling, slagging, and deposition during biofuels combustion were also identified. The tendency for ash slagging and fouling is observed, especially for fuel from sewage sludge and meat and bone meal (PBM) and fuel based on sewage sludge and sawdust (PBT) ashes which consist of meat and bone meal and sawdust which is typical for biomass combustion.
Highlights
Municipal sewage sludge is a product of the water-cleaning process in wastewater treatment plants
Emissions measured while burning fuels from sewage sludge were compared to the average values for hard coal combustion [38]
Changes of CO2 emissions shown in Figure 2 best reflect the variations of combustion intensity
Summary
Municipal sewage sludge is a product of the water-cleaning process in wastewater treatment plants. The problem with the disposal of municipal sewage sludge results from the introduction of new, increasingly stringent legal regulations concerning sewage sludge management, limiting the use of the sludge for agricultural and natural purposes and prohibiting its storage [1,2]. In this situation, processes that are becoming increasingly important are thermal use processes which are among the most radical methods in terms the possibility of a significant reduction in the mass and volume of sewage sludge. They allow use of the energy contained in the sludge and to reduce CO2 emissions in accordance with the principles of sustainable development
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