| Sewage sludge is a by-product of wastewater treatment plant. It always contained pathogen and heavy metals, the longterm toxicity and non-degradable characters of sewage sldudge is threatening the disposal and further utilization of the sludge. How to properly treat and make use of sewage sludge is becoming a focus.In this case, many useful method such as XRD, FT-IR, laser-particle size analyzer, BET surface area, atomic absorption spectrophotometry, Thermogravimetry and differential scanning calorimetric analyzer were employed to study the physical, chemical and thermal characters of sewage sludge, PFA, river sludge and green pellets prepared by sewage sludge, PFA and river sludge. According to the most probable mechanism functions of thermal process, it took a quadratic polynomial nonlinear fitting method to simulate the TGA (thermogravimetry analysis) curves.In accordance with the orthogonal design method and the optimal raw materials chemical composition, it designed experiments to carry out optimal mixture ratio. It also used orthogonal design method to arrange experiments to find out the optimal of firing processing parameters, and discover the influence of processing parameters against variation regularity of the main performance of ceramisite.A pilot-scale experiment of producing sewage sludge ceramisite was carried out with the optimal mixture ratio and firing processing parameters. The flue gas generated in the firing process was analysed. The microstructure of ceramisite surveyed through SEM and EDS methods. In this study, main building characteristics were tested, and the application category of ceramisite discussed.Through the researches above, the findings as follows were obtained;1)The volatile solid of sewage sludge is at about 32.09%, the distribution of particle size submit Gaussian distribution, the particles between 39.9μm1002.37μm were about 89.1% in the samples, the average particle diameter is 235.793μm; the BET surface area was small, and the vesicular structure was not obvious. The probably contained functional group were including hydrate, CO32-, SiO42-, -CH3, R2CH2, amide C=O, benzene ring isomer, etc. The crystallinity of sewage sludge were low and sand grain could be seen in it. The main crystal phase of sewage sludge wasα-SiO2.2)According to the heating rates increasing, the maximum weightless speed rate and the corresponding conversion rate were monotone decreasing, the temperature of reaching maximum weightless speed rate point was monotone increasing. There were no regularities between the weightlessness and heating rate. The synthesis combustion characteristics of sewage sludge were monotone decreasing with the increasing heating rate. The thermal process of sewage sludge under atmosphere was following a simple thermal reaction mechanism that could describe as individual and paralleled carried out reactions. The numerical simulated TGA curves could describe the change characters of experimental TGA weightlessness well. The dry ash-free basis of sewage sludge possessed heat value was at about 23.25 MJ/kg, this indicated that the sewage sludge could self-support combust in some certain cases.3)The main constituent such as Si, Fe, Ca content of PFA used in this study was higher than the average level of PFA in China. The LOI, Al and Oxygen constituent of PFA was lower than the average level. The packing density of PFA was 835.24 kg/m3, the particle size distribution of PFA was following Gaussian distribution and the average particle size was 106.504μm. The BET surface area was 0.56m2/g, BJH average pore size was 7.4982nm, pore volume was 0.001027cm3/g and the vesicular structure was not obvious. There was one main weightlessness course of PFA under atmosphere and different heating rate.The oxide of river sludge was familiar with clay and the main chemical group was including carbonas and silicate. The BET surface area of river sludge was 13.0893m2/g, BJH average pore size was 12.39552nm, pore volume was 0.041187 cm3/g and the vesicular structure was not obvious. The average particle size was 38.25μm. The total weightlessness of river sludge is relative small. There were no regularities between total weightlessness and heating rate.4)Here came out the optimal mixture ratio of green pellets in dried basis (wt%) was sewage sludge/PFA/river sludge equal to 25%/15%/60% through experiments, and the optimal firing processing parameters were the pre-heat temperature 350℃, final temperature 1190℃, heating rate 36K?min-1, holding time 1 mins and the rotary speed 18π?min-1. In accordance with the optimal mixture ratio and firing processing parameters, a pilot-scale experiment carried out. The results showed that the ceramisites appearance was light brown and the shape was uniform. The maximum temperature of flue gas during the firing process was about 306.75℃, and the gas composition analyzed results could describe as following (maximum content): SO2 was 30.07mg/m3, NO was 17.93mg/m3, NO2 was 2.06mg/m3 and CO was 88.39mg/m3. The results showed that the flue gas generated in firing process could fit the Chinese Integrated emission standard of air pollutants.5)The extraction toxicity and building material characters of ceramisite were tested, and the results showed that the ceramisite could be used as building materials, the ceramisite and its manufactures could fit environmental safety requirements. Try producing light concrete with ceramisite at the intensity level of LC30, by standard curing after 28 days to test the compression strength and coefficient of heat conductivity of the light concrete. The testing results showed that light concrete compression strength could fit the quality requirement of LC30 light concrete and coefficient of heat conductivity of the light concrete is significantly lower than normal concrete.6)The total weightlessness of pellets prepared by sewage sludge, PFA and river sludge was monotone decreasing with the increasing of heating rate. The DSC curves main peaks temperature was monotone rising with the increasing of heating rate, the synthesis combustion characteristics of pellets was monotone decreasing with the increasing of heating rate. The pellets thermal reactions under atmosphere with different heating rate could described as a simple thermal reaction mechanism that indicated the main thermal process submit individual and paralleled thermal mechanisms. The simulated TGA curves could discover the experimental TGA curves variation trend exactly. The main phase composition of ceramisite was including quartz (SiO2), cristobalite (SiO2), kyanite (Al2SiO5), albite (NaAlSi3O8), mullite (Al6Si3O13) and so on. The heavy metal compounds such as oxide of Pb and Mn were less, and quartz is the main phase composition in ceramisite.
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