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1 2014

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Wpływ rodzaju czynnika zgazowującego na parametry gazu ze zgazowania osadów ściekowych

Werle S.

Rocznik Ochrona Środowiska

2014

Tom 16, cz. 1

440--452

Today, there is a rising interest in many countries in biomass utilization (e.g. combustion, co-combustion, gasification and pyrolysis). This is a result of the limited reserves of fossil fuels (and because of security of energy supplies in a world) and environmental and climate regulations on CO2 emissions. Sewage sludge is a solid, semisolid, or liquid residue that results after the treatment process of waste water. During the last twenty years, there has been a major change in the way that sludge is disposed. As a result, there is a large and pressing need for the development of thermal methods for the disposal of sewage sludge. Gasification has several advantages over a traditional combustion process. It is the process of converting a solid fuel into a gaseous fuel using gasification agent (e.g. O2, atmospheric air, H2O (g) and others). This gaseous fuel can be used for the generation of useful form of final energy. It can be also used in such processes as the drying of sewage sludge directly on waste treatment plant. Volume of produced gas is lower in comparison of volume of flue gas from combustion process. This is due to the fact that gasification is the process characterizing by low level gasification agent environment. Gasification agent strong influence on the gasification gas composition.In order check the influence of the gasification agent on the gasification gas composition equilibrium calculation of sewage sludge gasification process have been done. It was assumed that the gasification process was carried out in a downdraft fixed bed gasifier. In that way, the amount of tar at the end of the process is very low because the most of it is combusted in the oxidation zone. For that reason tars are ignored in the model, and the only species created during the process are CO, CO2, H2O, H2, CH2, N2 and O2. Two assumptions made during the calculations are important. Firstly, it was assumed that the residence time of the reactants in the reactor is long enough to achieve an equilibrium, which has also been confirmed by the authors and secondly, it was assumed that all of the carbon in the sewage sludge is gasified, so the formation of charcoal can be neglected. The calculation of the composition of the gasification gas was done for two types of sewage sludge analyzed. Gaseq software was used to calculation.Results shows that using hydrogen and water vapor as a gasification agent gives chance to produce gas with the highest lower calorific value. Nevertheless taking into consideration that those agents are expensive and not open for general use, atmospheric air seems to be better. It was the main reason that calculation results with the atmospheric air as a gasification agent was compared with experimental results. For the purpose of experimental investigations, a laboratory system was designed and built. Calculation and experimental results shows strong agreement.