A Study On Heat Production Of Straw Aerobic Fermentation Based On The Influence Of Fermentation Conditions

In northern rural areas of China,a large amount of bulk coal is consumed for heating in winter,which not only causes high carbon emissions but also leads to serious pollution.However,a large number of energetic agricultural wastes produced in northern rural areas have not been fully utilized as resources.Aerobic fermentation of straw is a process that biomass is slowly oxidized by microorganisms to release heat energy and obtain organic fertilizer.Aerobic fermentation heat(AFH)is a low-carbon,clean and ecological heat source,which is expected to replace coal as an important heat source in northern rural areas in the future.At present,the research on AFH mainly focuses on livestock manure due to its fast degradation rate,while the research on the straw is relatively few.The traditional aerobic fermentation model is difficult to reasonably calculate the energy conversion efficiency and residual heat,which makes it difficult to quantitatively control the start-up,maintenance and heat output of straw fermentation.Therefore,it is necessary to establish a new thermal model of straw aerobic fermentation to guide the actual fermentation and predict the heat output(heating)capacity.Based on the kinetic model of thermogenic degradation of aerobic compost,the relevant process parameters of straw fermentation were obtained through laboratory scale aerobic fermentation experiments.The straw degradation rate factors were determined,the straw aerobic fermentation degradation kinetic model was established,and the straw aerobic fermentation thermogenic model was established based on this.Finally,the model used to explore the start-up and heating of straw aerobic fermentation under different fermentation conditions was established.The main research results and conclusions are as follows:The effects of fermentation temperature,initial carbon-nitrogen ratio(C/N)and moisture content on the degradation rate of straw organic matter were explored through the thermostatic aerobic reactor,and the degradation rate factor k of straw under different conditions was obtained through the first-order kinetic model.The corrected equations of fermentation temperature,initial C/N and moisture content of raw materials were obtained through empirical equations.Finally,a kinetic model of degradation for straw organic matter was established.The model showed that the daily degradation rate of straw organic matter could reach 9.49%when the fermentation temperature was 50℃,the initial C/N was 30 and the moisture content was 60%,which was quite different from that of other biomass.Finally,a kinetic model of degradation for straw,a heat production model of straw aerobic fermentation was established,and the model was preliminarily verified by laboratory and pilot scale aerobic fermentation experiments.The results showed that the model can better simulate the temperature of the fermentation process,effectively guide the design of conditions for the successful start of straw fermentation under different ambient temperatures and predict the heating performance of the fermentation reactor.Based on the heat production model of aerobic fermentation for straw,this study provided a quantitative scheme for exogenous energy supplementation for laboratory-scale straw fermentation for the first time(based on domestic and foreign literature reports).And the minimum volume of the open system for the successful initiation of straw fermentation under cold conditions was predicted,that is,when the ambient temperature was reduced from 25°C to-30°C,the minimum reactor volume was increased from 0.002 m~3 to 173 m~3 required for successful start-up of the fermentation.The heat supply capacity of straw fermentation under low temperature conditions was also predicted by model.The prediction results showed that the large-volume straw aerobic fermentation pile has a large heat supply potential.Taking a 100 m~3fermentation pile as an example,even at an extreme ambient temperature of-20°C,its dry matter heating efficiency was able to achieve more than 5 MJ/kg under suitable fermentation conditions,and the heat output accounts for more than half of the total heat production.