| The hazardous waste output in China was 14.3 Mt in 2009. Incineration in rotary kiln is reasonable for hazardous waste treatment because of the complicated composition of hazardous wastes, while the farther investigation on combustion and slagging characteristics is necessary for application of the hazardous waste incineration. There are many problems in application of rotary kiln combustion such as incomplete combustion, ringing in kiln, corrosion to the refractory materials, and discharge of pollutants emission. Funded by National High Technology Research and Development Key Program of China (2007AA061302), Important Project on Science and Technology of Zhejiang Province of China (2007C13084), the basic characteristic of pyrolysis and combustion of typical hazardous waste were investigated and experimental studies were conducted in this paper, which is useful to hazardous waste thermal disposal and the operation optimization for incineration system.The gaseous products of hazardous waste in pyrolysis and combustion at different condition were investigated by using thermodynamic equilibrium calculation and experimental study. The products were further decomposed with temperature increasing, and the main gaseous products in pyrolysis were H2O, C2H4, C2H2, H2 and CO. The main gaseous products in gasification at low air coefficient were CO, H2O, H2 and CH4. The generation of CH4, H2, CO were promoted by present of little O2. Most chlorine element in hazardous waste was emitted as HC1 in the temperature range of 300-600℃. SO2 is the most important sulfur containing gases product, while little SO2 were emitted during hazardous waste thermal disposal when air coefficient is lower than 0.6.The similarity of thermal decomposition characteristics for the pyrolysis and low temperature stage during combustion was confirmed by TG-FTIR, and the decomposition was accelerated and advanced by present of O2. Most of the gaseous products in pyrolysis emitted during 200-500℃, and combustion of the hazardous waste almost finished before 700℃because of the low concentration of fixed carbon. The high-concentration gaseous products were emitted in a narrow temperature range during high volatile hazardous waste pyrolysis. Large amount of HNCO was emitted during high nitrogen hazardous waste pyrolysis, while SO2 is the most important gaseous product for high sulfur hazardous waste thermal disposal. The fixed carbon of organic chemical industry sludge burnt in a wide temperature range, and most of the weight lost in this stage. Heating rate has little influence on the gaseous products during hazardous waste pyrolysis.The heavy metal sludge form tannery industry has good combustion characteristics compared with paper mill sludge and lake sludge. There was some organic acid gaseous product emitted at low temperature stage in tannery sludge combustion, and the combustion almost finished before 800℃. The combustion residue of tannery sludge was sintered above 900℃. For tannery sludge,800℃is a reasonable incineration temperature to control heavy metal volatilization.The operation at different conditions of the hazardous waste two-stage incineration system consist of rotary kiln and secondary combustion chamber was simulated with Computational Fluid Dynamics code (FLUENT). The lamination of the velocity was obvious at the kiln end. Lamination of the velocity and the high-temperature zone in rotary kiln was advanced when the supplied air from the front-end increased. The proportion of the waste combustion in rotary kiln was enhanced when the air from the front-end increased. Stabilization of the combustion in kiln was strengthened by burner at the front-end.Based on the on-site investigation on the application of hazardous waste incineration system consists of rotary kiln and secondary combustion chamber, it is confirmed that the two-stage incineration system is appropriate for complete combustion and gaseous pollutants control. The dioxins content in flow gas emission is 0.016-0.035 TEQ ng/m3 during the steady operation of the incineration system, while there was a tendency of combustion residue sintering in rotary kiln operation. The fly ash, which is agglomerated particle, exhibited the loose and cracked structure, while there is no large pore structure in bottom residue. Bottom residue from the hazardous waste incineration is rigidity, and the residue was melted in high temperature zone before it is flush off from the kiln. The particle agglomeration of the fly ash was confirmed by using the microstructure analysis on the ashes sampled from different position in the incineration and flue gas purification system. The research is useful for application of hazardous waste incineration and emission control.
|
PDF Full Text Request