The Experimental Study Of Integral Medical Waste Pyrolysis Incinerator

With the development of economy, the medical and health services developed rapidly in China. The huge amounts of medical waste result in a series of environmental, social and ecological problems. The incineration technology has many advantages such as volume reduction, quantity reduction and harmless treatment. It has become an effective method of medical waste treatment. The comprehensive research on pyrolysis incineration technology is very important. In order to obtain an important reference in the design and operation of medical waste pyrolysis incinerator, this thesis focuses on the basic research and applied research of integral incinerator technology.Perfusion tube, medical gloves and bamboo rods were selected to stand for three major components in medical waste: plastic, rubber and biomass. The thermal decomposition characteristics were analyzed by the thermogravimetric analyzer. The kinetic parameters of pyrolysis were calculated by using chemical kinetic model. The results showed: the particle size and the amount of medical waste sample influenced the result of TGA experiment. However when the particle size was between 63μm and 500μm, the sample amount was between 10 mg and 25mg, the effect was not obvious. It was found in the different heating rates experiment, when the heating rate was high; the sample volatilized quickly, the pyrolysis reaction was concentrated, the amount of each decomposed stages decreased. Mixture pyrolysis experimental results showed: in the low temperature, the reaction of different components was unnoticable. In the high temperature, the reaction of different components was strong.In order to obtain the properties of medical waste pyrolysis product, the experiment of pyrolsis gas generated from typical components of medical waste was carried out in the tube furnace. The pyrolysis gas products were measured continuously by the infrared gas analyzer. The composition of pyrolysis gas was complex, including methane, carbon monoxide, acids and aldehydes etc. Methane and carbon monoxide were chosen for analysis. The results showed: When the pyrolysis temperature was high, the peak value of gas products increased. The major pyrolysis gaseous products of medical rubber glove were methane. The major pyrolysis gaseous products of perfusion tube were methane and hydrogen chloride. The major pyrolysis gaseous products of bamboo rods were methane and carbon monoxide. On this basis, the experiments of the pyrolysis gaseous products characteristics of mixed medical waste were carried out. The results showed: In the different mixture sample, the translation rate of chlorine into hydrogen chloride decreased in different degrees. Mixing inhibited the direct product of hydrogen chloride. The inhibited effect became obvious with the quantity of mixture increased. This suggested that chlorine might combine with other small molecule to form chlorinated organic material before hydrogen chloride was formatted. The solid pyrolysis residents of typical medical wastes were studied in detail by scanning electron microscopy and pore size analyzer. The results showed the higher the pyrolysis temperature was, the more porous the solid products got. As more contact surface area for gas and solid were provided, the burning condition of the resident was improved. So, the pollutants of incineration could be controlled easily.To ensure harmless treatment of the medical waste, a new pyrolysis incinerator with two coaxial combustion chambers was proposed to use the heat value of medical waste effectively. The thermal analysis of the integral incinerator was carried out. The result showed: when the total excess air ratio was kept constant and the primary air ratio was reduced, the temperature of the primary combustion chamber decreased, but the temperature of the secondary combustion chamber increased. On this basis, the batch and continuous feeding experiment of combustion were conducted on the pyrolysis incinerator. The results of batch feeding experiment showed: the temperature of primary combustion chamber was influenced seriously by the preheating temperature and the feeding quantity. The results of continuous feeding experiment showed: The stable flame and combustion in the pyrolysis incinerator was achieved, which were similar to the direct combustion. The temperature of the primary combustion chamber was more stable in the pyrolysis incineration than in the direct combustion condition. The carbon monoxide in the outlet of the integral incinerator was controlled effectively. The total flue gas was also reducing effectively by reducing the total excess air ratio. This suggested that total excess air ratio and primary combustion chamber were 1.3 and 0.5 respectively in the continuous running of the integral pyrolysis incinerator.The performance tests were carried out on the medical waste thermal treatment system based on the integral pyrolysis incinerator. Particulate matter, sulfur dioxide, carbon monoxide and nitrogen oxides in the flue gas were measured continuously in two hours at the entrance to the stack. The results showed: the integral medical waste runs stably. The gas emissions were below the China national standard emission limits. The aim of clean emissions in the new incineration was achieved. Using the gas chromatography, scanning electron microscopy, X-ray diffraction analysis techniques, the fly ash and boiler slag of the medical waste incinerator were studied in detail. The results showed: The heavy metals content in bottom slag and fly ash were high. They were still hazardous waste and need be solidified before landfilling. Under the comprehensive summary and analysis of dioxin formation mechanism in the waste incinerators including the high-temperature gas generated, precursor formation and"de novo"formation, PCDD/Fs formation in the medical waste pyrolysis incinerator was analyzed. Compared with the different structures incinerator but with the same flue gas purifying device, the dioxin test results showed: The coaxial design incinerator reduced the heat loss effectively, used the combustion heat of pyrolysis products furnace to maintain temperature stability, and inhibited the formation of dioxins.