Researches On Pyrolysis Mechnics And Gasification Of Livestock Manure

Global energy shortages and environmental negative impacts by using fossil rules have caused the fast development of renewable energy. Biomass energy has been given more and more attention for its advantages of large storage capacity, recovery and neutrality of greenhouse gas emission, and it has become the forth energy resources followed by petroleum, coal and natural gas. Development and utilization of biomass energy have the social ,economic, and ecological meaning in China. The utilization technologies of biomass include direct combustion, densification briquetting, biochemical and thermochemical conversion. Animal manure is a special shape of biomass and also a kind of pollutants during agricultural development ,so there have ecocomic and environmental benefits to make them into available resources.On the base of current research progress in biomass thermochemical conversion technologies at home and abroad, the author carried out the study on physicochemical characteristics, pyrolytic characteristics and mechanics of animal maure. On the ground of above study, the author designed and developped a lab-scale fluidized bed gasifier and employed this system to carry out air gasification experiments on swine manure. The main conclusions are as follows.(1) Proximate and chemical analysis,as well as ultimate and heating value analysis, were carried out to investigate the feasibility of thermochemical conversion of four kinds of manure such as swine, cattle, goat and chicken manure.The results showed that animal manure have some obvious differences to some kinds of farm crop residues on chemical consititution, ash and alkali salt metal content. The detailed includes the lower content of cellulosic material, higher content of neutral dissolving solids(NDS), ash, alkali metal and nitrogen. The heat value showed them having thermochemical conversion potential. These varible parameters require special handlings as we go on experimental research on them.Theoritical analysis on thermochemical and biochemical conversion efficiency was conducted on every kind of maure. By establishing the chemical equation, every kind of fule gases and total energy output were obtained and energy conversion efficiences were derived according to corresponding conversion processes. From the data we got the conclusion that thermochemical technology converts the raw material more thoroughly and efficiently than that of biochemical technology.(2) The pyrolysis characteristics of animal manure were investigated by the thermogravimetric analyzer coupled with the Fourier infrared spectroscopy(TG-FTIR).The experimental results showed that animal maure pyrolysis process can be devided into three stages which are dehydration stage, pyrolysis stage and carbonization stage. There were some different features on end residuum, weight loss rate and peak features indicated by TG and DTG curves.The produced gas detected by FTIR consists of H₂O, CO₂, CO, H₂, CH₄, aldehyde, carboxylic acid, and so on. By analyzing the infrared spectrum, the evolving characteristics of each different gas could be found. Water evolving curve has two peaks corresponding to losing free moisture and combined crystal water. Carbon monoxide and carbon dioxide evolving curve have the similar two peaks corresponding to pyrolysis and carbonization stage, but the second peak of carbon dioxide is weaker than that of carbon monoxide. Methane evolving cure appears single peak corresponding to pyrolysis terminal stage and carbonization early stage. Other hydrocarbons evolving curve display single peak corresponding to pyrolysis stage.The effluence of heating rate on pyrolysis and gas evolving characteristics of swine manure were also conducted, and its effects mainly appeared on weight loss rate and making each gas evolving peak move to high temperature zone.(3) Thermoanalysis dynamics method was employed to get the mathematic model of weight loss rate (a) to temperature (T) so that mathematical foundation could be offered for subsequent thermochemical conversion process simulation and control. By establishing and solving pyrolysis model, the kinetic triplet of mechanics function[f(α)] apparent activation energy(E) and frequency factor(A) were achieved using thermogravimetric experimental data.The calculation results showed that the average apparent activation energy of swine, cattle, goat, and chicken manure is 72.89kJ/mol, 75.38kJ/mol, 50.83 kJ/mol, 74.76 kJ/mol separately, and they are lower than those of farm crop residues which indicats these manure are easy to thermal cracking. The research also found single constituent global integration model is adaptive to swine manure and single constituent phased integration model is suitable to other three kinds of manure. (4) A fluidized bed gasifier system with the load from 1 to 5kg/h was designed and manufactured which consists of main reacting tube, screw feeder, cyclone separator, condenser, filter, heating and controling elements, and so on.The main reactor tube is applicable to different types of thermochemical conversion technological requirements. The screw feeder has a air delivery position to ensure discharge the fine materials easily. Double pipe condenser make fule gas and condensing agent non-contacting. Three 4kw heating elements can be controled by thermostat independently so that the system power can be adjusted according to practical situation. The equipment attached to steam generator and steam heater can be applicable to air-steam or steam gasification technologies. All components assembly are connected by flange which make them to be demounted and the system to be modified easily.(5) Cold condition and hot condition start-up experiments were carried out on set of equipments.The output of screw feeder could be linearity control by frequency modulator and their linear dependent coeffient was above 0.9 which could meet the test requirements. Pressure drop to fludized flow velocity test was conducted to get theΔp-v curve from which the critical fluidized flow velocity could be found. The experimental results showed that the Vf of silica sand between 0.2-0.5mm particle size was 0.035m/s so that we could determine the operational velocity. The fluidizing curve obtained from the trial showed that amplitude of pressure drop variation was quite small which could satisfy the fluidization demand. The hot empty bed condition experiments were done to test the performance of the heating and controling elements and showed that they can heat the gasifier to demanded temperature in a short time.(6) The air gasification experiments on swine manure were conducted to discover the influence of three main operational parameters which are raw material particle size, equivalence ratio and initial temperature on gasification process. Subjects investigated included reactor inner temperature field, products distribution, solid product character, fule gas components and heat value, carbon conversion rate and gasification efficiency. The experimental main goal is to supply suggested operational parameters for actual work conditionsThe experimental results showed that the parameter of particle size had some effects on some gasification indexes except inner reactor temperature field and the size of 0.5mm was benefit to gas production. Combined with other effects the suggested particle size was 0.5mm.ER has double-faced and complicated influence on gasification process because it can directly effect reactor inner temperature field and residence time of gas and solid. The experimental results showed ER of 0.15 was favorable to gas formation and connected to other aspects the suggested ER was 0.15.The experiment showed higher initial temperature was advantageous to gas production, but integrated with economy and other aspects, temperature of 300℃could meet the application demand of producted fule gas.From above experiments the suggested operational parameters of swine manure air gasification was : particle size of 0.5mm, ER of 0.15 and initial temperature of 300℃.As the project fundamental research, the author not only generalized the shortages of this paper but put forward some advice on further studies.