|其他摘要||Pyrolysis/gasification technology of combustible solid waste (CSW) is conducted in the condition of non-oxygen or lean-oxygen, which will reduce the production of dioxins. Therefore, it is regarded as one of the most promising alternatives to incineration. Pyrolysis/gasification characteristics and kinetics of CSW have great instructive significances to the design and the optimization of operating parameters for industrial reactors. In this paper, CSW was divided into five categories: wood, food residue, paper, plastics-rubber and textile. Twenty components including cellulose, hemicellulose, lignin, pectin, poplar, starch, protein, potato, cabbage, rice, orange peel, printing paper, newspaper, household paper, cotton, polyester, wool flock, PE, PVC and rubber were selected as experimental samples. The thermogravimetric analyzer (TGA) and thermogravimetric-mass spectrometry (TG-MS) were applied to comprehensively and systematically study the pyrolytic characteristics, steam gasification characteristics and thermal kinetics of all components. A pseudocomponent characterization system was established, by which the thermochemical reaction behaviors of the complex CSW can be described just using a limited number of pseudocomponents. The main research contents are as follows:
(1) The pyrolytic characteristics of all components were studied in detail under N2 atmosphere at the heating rate of 5 K min-1. Results showed that materials in paper or food residue categories have similar pyrolytic behaviors: in the paper category, printing paper, newspaper and household paper all had narrow weight loss temperatures range (540~650 K); in the food residue category, the main weight loss temperature of starch was 500~733 K, and both potato and rice had similar weight loss behaviors. However, materials in wood, plastic-rubber, and textile categories all showed different pyrolytic behaviors: in wood category, there existed large differences among the three components of cellulose, hemicellulose and lignin; hemicellulose was observed to be the first to loss weight, cellulose took the second place, and lignin was the last; in the textiles category, the main weight loss temperature range for wool flock was 540~740 K, but it was 500~640 K for cotton, indicating that it was harder for wool flock to lose weight than cotton; in plastic-rubber category, PE had only one weight loss stages, PVC had two weight loss stages, and rubber had three weight loss stages.
(2) The thermogravimetric curves of all CSW components under steam atmosphere were obtained. Firstly, thermogravimetric curves under steam and N2 atmosphere were comparatively studied. It was found that the weight loss process of lignin, hemicellulose, poplar, cabbage, printing paper, pectin, zein, cotton and dacron were divided into pyrolysis and gasification stages. When the temperature was lower than 850 K, the existence of steam had almost no effect on thermogravimetric curves for all CSW components; however, when the temperature was higher than 850 K, the existence of steam promoted the gasification of char and fixed carbon, and one more weight loss stage was emerged. Secondly, TG-MS was applied to investigate the generated light molecular weight gases of CH4，CO2，CO，H2 during the weight loss process under steam atmosphere for all CSW components. Resutls showed that the trends of envolved curves for all gases were consistent with their DTG curves in the pyrolysis stage, indicating the four gases were produced from the pyrolysis process. The trends of envolved curves for CO2 and H2 were also consistent with their DTG curves in the gasification stage, which verified the ractions between char or fixed carbon and steam.
(3) A novel multiple Gaussian DAEM reaction model was established based on multiple-peaks method, which can be used to describe the pyrolysis and gasification behaviors of CSW. Results showed that the calculated curves using the multiple Gaussian DAEM reaction model provided a good fit with experimental curves. The kinetic parameters of all CSW components were obtained using the pattern search method. The activation energy (E) of the pyrolysis stage was in the range of 150~270 kJ mol-1, which was lower than that in the gasification stage (280~330 kJ mol-1). The kinetic mechanism functions of all components in pyrolysis and gasification stages were obtained using the master plot method.
(4) The pseudocomponent characterization system was established based on weight loss curves. Cellulose, hemicellulose, lignin, starch, pectin, protein, dacron, rubber, PE and PVC were all confirmed as pseudocomponents in this paper. On the basis of linear pseudocomponent characterization, the interactions between two pseudocomponents were detailed studied. And a method of reproducing reaction characteristics of multiple pseudocomponents using interactions between two pseudocomponents was established. The reliability of above-mentioned pseudocomponent characterization system had been validated using nine actual typical combustible solid wastes. The thermal reaction kinetic parameters were obtained using the pseudocomponent characterization method, whose values were consistent with those optimized from the multiple Gaussian DAEM reaction model.|