Research On Sewage Sludge Drying And Functionality Evolution During Co-combustion Of Dry Sewage Sludge And Coal

With the increasing of wastewater discharge amount and its treatment rate, sewage sludge volume seems to be growing rapidly in the next decades in China. Disposal of sewage sludge through incineration has been encouraged due to several distinct advantages over other disposal methods. However, the microscopic mechanism and pollutant emission characteristics during incineration were still need to be improved. Co-combustion of sewage sludge and coal was a major branch of swage sludge incineration. Generally, sewage sludge was required to be dried before its co-combustion with coal. Four aspects of co-combustion sewage sludge with coal were investigated in this dissertation, including the sewage sludge drying characteristics, the existing forms of C, O, N, S in sewage sludge/coal blends and their transformation mechanism during co-combustion, NOx and SOx emission characteristics, and the co-combustion experiment in 1025t/h plant boiler. The whole paper comprised of six parts.In part one, the background was introduced through several aspects, such as the source and fundamental characteristics of sewage sludge, disposal methods of sewage sludge and their tendency, sewage sludge disposal situation and existing problems in China. Sewage sludge drying characteristics, as well as the development of co-combustion sewage sludge with coal, was also summarized.In part two, the sewage sludge drying characteristics were studied in conventional experiment equipment. The influence of several factors to moisture content in sewage sludge was discussed, including airflow velocity, airflow temperature and sludge additive agent. The experimental data combined with typical drying mathematic models was used to obtain corrected Page model which was more precise than others in this experimental condition.In part three, the achievement using X-ray Photoelectron Spectroscopy (XPS) to study the characteristic of coal and relative substances were summarized. Meanwhile, Microsoft Visual Studio.net was utilized to build functionality database (C, O, N, S) on pulverized coal surface based on XPS method. This XPS database was of several advantages, such as friendly interface, easy to use, good expansibility, and was considered to be a fundamental method for the following investigation. The existing forms of main elements in sewage sludge/coal blends, as well as their transformation mechanism during co-combustion were studied. This was useful to improve the reorganization of precursor formation mechanism of various pollutants.25 samples were obtained from tube furnace reactor with different sewage sludge blend ratio in sewage sludge/coal blends and different burn off ratio. XPS experiment was carried out to study the characteristic and evolution of the functionalities in the blends. The existing forms and transformation mechanisms of C, O, N, S in coal and sewage sludge during their mono-combustion were discussed. Then the evolution mechanisms of C, O, N, S during co-combustion, as well as the relationship between mono and co-combustion, based on the findings from mono-combustion, were analyzed. The interaction of functionalities between mono and co-combustion was also presented.In part four, single-burner furnace was utilized to study the pollutant emission characteristics during the co-combustion of sewage sludge and coal. NO and SO2 emission behaviors of different coals were investigated, then that of co-combustion were discussed based on the findings from coal combustion. The influence of sewage sludge ratio to the emission of gaseous pollutant was studied in the end of this chapter.In part five, co-combustion test of sewage sludge/coal blends (sewage sludge ratio 5%) was carried out in 1025t/h utility boiler. The affection of co-combustion to hot test was studied, and several parameters in hot test, including carbon content of fly ash, boiler efficiency, boiler combustion stability, boiler output, pollutant emission, sprinkling amount, were discussed.In part six, general summary of this paper and further research was also presented.