Study On Hydrothermal Treatment Of Degradable Organic Wastes And Drying Of The Treated-Products

With the development of society and economy, the producing amount of the MSW (municipal solid waste), agriculture and forest wastes gradually increases. The amount of the degradable organic components among the wastes accounts for over half of the whole amount of wastes, whose disposal affects the disposal of the whole wastes. Furthermore, the treatment of the organic parts of the wastes catches the social and governmental attention. The hydrothermal degradation provides an interesting alternative for the disposal of degradable organic wastes in wastes owing to the whole process being environment-friendly. It utilizes saturated steam of a given pressure to treat degradable organic wastes in wastes as soil conditioners, amendments of high quality. This produces void of toxic products with greatly reduced mass. Therefore, this thesis studied on it extensively and deeply.1. Under the condition of hydrothermal degradation treatment, according to the main chemical components of the degradable organic matters, the fundamentals of the hydrothermal degradation processing was made clear combined with the related theory of the hydrothermal degradation of biomass. And the path of the humic formation was interpreted during hydrothermal degradation treatment. A severity parameter, which combines time and temperature, was introduced. Under different severities, the changes of matter and the formation of humus during hydrothermal processing of organic wastes further checked the fundamentals of the hydrothermal processing.2. In order to study the effect of inorganic acid on the hydrothermal reaction, this thesis carried out the research that added sulfuric acid of the ultra-low concentration during hydrothermal degradation. The effects of sulfuric acid on solid and liquid products were deeply analyzed. The kinetic models based on pseudo-fist order kinetics as a function of severity parameter were successfully employed, whichsupplied strong theoretical basis for hydrothermal processing.3. To supply reasonable theoretical basis for safety agriculture application of treated-products, the experimental facility was designed. The stability of the products was studied under the natural soil as reference:(1) The mixture of hydrothermal-treated products and compost separately mixed with soil in the same ratio was put into the culture flask. The changes of substances and the germination during incubating were measured.(2) Three different ratios of hydrothermal-treatment products and soil, compost and soil (1:3, 1:5, 1:10, wet weight) were incubated for 63 days in soil to determine hydrothermal-treatment products substance changes and maturity.(3) The different hydrothermal-treatment products were mixed with soil in the ratio of 1:3 (wet weight). Their substance changes during incubating were measured.4. The drying of hydrothermal-treatment products is necessary to be convenient for using, storage and conveying. But the drying is a costly energy intensive processing, the superheated steam (SHS) drying instead of air-drying is potentially more energy efficient. Combined the advantage of the SHS drying with the thermal energy and steam requirement of hydrothermal processing, this thesis presented a novel combination system which combined hydrothermal processing and SHS drying processing. The energy and exergy balances of the system were analyzed. Compared with air-drying, the system reduces the drying energy consumption.5. The hydrothermal degradation technology provides an interesting alternative for the disposal of degradable organic wastes in organic wastes owing to the whole process being environment-friendly. To meet the demand of large scale industrialization, the experimental equipment of the continuous operation of hydrothermal treatments was designed, and the problem of the feed sealing was solved, which supply a platform for the following research of hydrothermal treatment.