| China is a large agricultural country and rich in agriculture and forestry resources,the total output of many crops are in the forefront of the world.With the rapid development of economy,China’s existing rural farming,aquaculture and other production patterns will produce a lot of organic waste(such as straw,food waste,livestock and poultry manure),which are both pollution sources and potential agriculture and forestry biomass and green chemical raw materials resources.If are not properly handled,not only would cause resources waste and environmental pollution,but also affect the healthy life of mankind and economic development.According to current situation of the rural,this article used the biogas technology of mesophilic two-phase anaerobic digester combined with solar thermal under the pilot system to deal with rural waste biomass,researched the start-up process,the effect of organic load rate(OLR)on the system operating efficiency,annual operating characteristics of system,Fluent simulation of the gas tank.The main research conclusions are as follows:The start-up characteristics of two-phase anaerobic digester system were investigated.The changes of oxidation reduction potential(ORP),the pH value,total alkalinity,ammonia nitrogen and biogas yield in the two phases were used for assessing the anaerobic digestion performance and the process stability.The results showed that the acid phase and the gas production phase were kept stable after the domestication of 30 days.The pH value was in the range of 6.80～7.00 and 7.10～7.20,ORP remained between-300～-260mV and-320～-290mV,the total alkalinity remained 1210 and 1802mgCaCO3/L,respectively.At the same time,the SMA of the gas production phase in the system was stably kept at 0.33LCH4/(gVS d)after 22 days of reaction time.Effects of different organic loading rate(OLR)on hydrolytic acidification and gas production performance of two-phase anaerobic digester system was studied.In order to obtain the optimal OLR of two-phase anaerobic digester of waste biomass,the experiment was carried out with the semi-continuous stirred-tank reactors for producing biogas at 35 ± 1 ℃for 100 days,which could be maintained as a semi-continuous feed by controlling three hydrolysis acidification units.The reaction time was 25 days while the OLR was set at 1.2,2.4,4.8,7.2gVS/(L d)respectively during the whole study.The result showed that the optimal organic load rate was 2.4gVS/(L d),limit organic load rate was 4.8gVS/(L d).The average COD removal rate and methane production rate reached the maximum value of 90%and 0.32m3CH4/(kgVS)respectively when the OLR was 2.4gVS/(L·d),The average methane content of the acidogenic phase and the gas phase were stably kept at 60%～66%and 55%～60%respectively when the OLR was kept lower than 4.8gVS/(L·d),while dropped to 45%when the OLR was increased to 7.2gVS/(L d).When the OLR was 1.2～2.4gVS/(L-d),the pH value of acidogenic phase and gas phase was stably kept at 6.70～7.00 and 7.20～7.42,and the biogas yield rate reached the maximum value of 0.56 and 0～54m3/(kgVS),respectively.The ORP of the acidogenic phase and the gas phase was kept between-300～-320mV and-330～-350mV during the whole study.The concentrations of VFAs in the acid phase was 7100-24370mg/L,and the ammonia nitrogen concentrations of the acid phase and the gas phase were 375～825mg/L and 916～1746mg/L respectively when the organic load rate was 1.2～7.2gVS/(L·d).The results provided a theoretical basis for improving the efficiency of biogas production by anaerobic digester.The annual operating characteristics of the two-phase anaerobic digester system were studied.Two kinds of different heating modes of the solar collector combined with the phase change heat storage tank system and the sole solar collector were investigated,for researching the effect of seasonal solar energy on the heating of the two-phase anaerobic device,and the ambient temperature of different seasons on the acidification and gas production of the two-phase system.The results show that the daily ambient temperature had no significant correlation with the solar radiation intensity during the whole year,and the daily average of the winter experimental period is-1.4℃ and 280.87W/(m2·h),respectively.In addition,the monthly average collector temperature of solar collectors was the lowest in winter control group(46℃),the highest was summer control group(68℃).The change of the ambient temperature had little effect on the pH value of the experimental system during the whole year.The temperature in the two phases of the control group was influenced by the ambient temperature.The total gas production in the experimental and experimental groups was 96.84m3 and 67.69m3,respectively.Compared with the control group,the gas production of the experimental group increased by 43%In the winter,the production rate of the winter experimental group was much higher than that of the control group.Using the heating mode of the solar collector combined with the phase change heat storage tank,the two-phase anaerobic fermentation system colud achieve stable and efficient biogas production during the whole year.The simulation of heat transfer and flow in the production of biogas slurry tank by using Fluent software was studied,and combined with the measured temperature data,analysis of the different heating temperature and stirring on the distribution of the temperature field and the flow field of the gas tank.The simulation resulted show that the increase of the heating temperature and stirring mode could improve the rate of temperature increase in the gas tank,and enhanced the uniformity of the temperature field distribution in the gas tank and prevented the heat exchanger coil fouling caused by the long-term service.The results were in good agreement with the measured temperature.Through the simulation experiment,it could effectively improve the design parameters of the actual operation of the system,so as to provide a reliable basis for engineering applications. |
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