| The sewage sludge incineration technology has an advantage of waste minimization,stabilization and resourcezation.However,the sludge combustion will produce NO_x,SO_x and other pollutants,the direct emission of which can cause serious secondary pollution.The combustion and pollutant emission characteristics of sludge are different from the traditional fuels such as coal,and it is of great theoretical and application value to study the sludge combustion and pollutant emission characteristics.Besides,the sludge incineration technology in China is not mature,leading to a difficult incineration choice in the engineering application.Thus,the techno-economic analysis of the incineration process has important guiding significance for the engineering application.In this paper,the combustion and pollutant emission characteristics of sludge were studied by using different experimental setups.Besides,based on the investment and operating cost data of the dewatering,thermal drying and incineration of sewage sludge in the practical engineering,the techno-economic analysis of the designed 250 tons/day sludge dewatering-thermal drying-incineration system was conducted by theoretical analysis and calculation.The detailed contents are shown as follows:The ultimate analysis and combustion characteristics of the sludge were conducted.The ultimate and proximate analysis of sludge samples showed that the volatile and ash contents in the sludge were high,whereas the fixed carbon content and calorific value were low.Besides,the N and S element in the sludge was higher than that of coal.The combustion characteristics of sludge were studied by thermo-gravimetric analysis,and effects of the heating rate on the combustion characteristics was emphasized.Results showed that there were four main weight loss stages during the sludge incineration with the stage of volatile volatilization and combustion and the burn-out stage of residue volatile and fixed carbon being the main combustion processes.The sludge combustion experiment was conducted in a 6kWth bubbling fluidized bed to study effects of combustion temperature,excess oxygen coefficient and secondary air ratio on the emission characteristics of gaseous pollutants.With the increase of the combustion temperature,both the NO and SO2 emission concentration increased.With the increase of the excess oxygen ratio,the NO emission concentration increased whereas the SO2 emission concentration decreased.With the increase of the secondary air ratio,the NO emission concentration decreased at first and then increased with little overall emission reduction,whereas the SO2 emission concentration increased slightly.The NO emission characteristics of the sludge incineration under the flue gas recirculation atmosphere were studied in the 6kWth bubbling fluidized bed.The results showed that under the flue gas recirculation atmosphere,the variation trend of the NO emission concentration with the combustion temperature and the excess oxygen coefficient was consistent with that under the air atmosphere;With the flue gas recirculation ratio increasing from 0 to 1,the NO emission concentration decreased significantly;When the flue gas recirculation ratio reached a high value,the reduction magnitude of the NO emission concentration decreased;At the early stage of the recirculation ratio increment,the CO concentration in the flue gas increased significantly.When the recirculation ratio exceeded 0.3,the CO concentration fluctuated within a certain range and no longer increased.The orthogonal experiment of sludge incineration was conducted in a 6kWth bubbling fluidized bed to study the effects of temperature,excess O2 coefficient and flue gas recirculation ratio on the NO emission characteristics.The results of the range and variance analysis showed that effects on the NO emission concentration followed the sequence:excess O2 coefficient a,temperature T and flue gas recirculation rate ?.Besides,influence caused by the interaction of three factors and the experimental error could be neglected.The techno-economic analysis of the designed 250 tons/day sludge dewatering-thermal drying-incineration system was conducted.By using the low heating value of sludge in the dry basis,the deeply dewatering sludge moisture content and the drying sludge moisture content as input variables,the variation rules of the investment cost,operating cost and efficiency could be obtained for the optimal scheme.The results showed that the heating value of sludge has the greatest influence on the investment cost of the system.The system efficiency decreased rapidly when the amount of steam produced by the incineration system could not meet the requirement of sludge thermal drying.The optimal scheme for sludge with different heating value was proposed based on the techno-economic analysis. |
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