| Biomass fermentation to produce biogas is a commonly used anaerobic treatment technology.When maintained at 35°C or 55°C,the anaerobic fermentation tank can maintain a high gas production rate and gas production,but the ambient temperature is generally lower than the fermentation temperature,and the reaction There must be heat loss in the process,and the traditional heating method cannot take into account the feasibility and environmental protection.In view of the above problems,this paper proposes a biogas system for heat supply with waste heat from thermal oxidizer of diluted biogas source,which is suitable for Nanjing and surrounding rural areas,which is conducive to making full use of biomass resources such as straw in surrounding rural areas and forming a mutual promotion of gas production and heat supply.Stabilize the system,keep the fermentation process at a constant temperature,and achieve the effect of stable gas production.The main research work of this paper is as follows:(1)Based on the characteristics of the multi-phase flow fermentation system,a new type of biogas source thermal oxidizer waste heat heating system was designed.Combined with the local climate conditions(Nanjing City,Jiangsu Province),the thickness of the economic insulation layer was calculated,and the thickness of the economic insulation layer was calculated.By constructing the energy model of the anaerobic fermentation system,the parameters such as heat load and fermentation heat production of the fermentation system during the fermentation process were analyzed and calculated.Fermentation When the fermentation period is shorter,the feed load is larger.When in high temperature fermentation,the heat load of the feed with a fermentation period of 10 days was 70.6% higher than that of20 days;when in medium temperature fermentation,the heat load of the feed with a fermentation period of 10 days was 100.0% higher than that of 20 days;Compared with fermentation at high temperature of 55°C,fermentation at a medium temperature of 35°C has a higher average daily net output of heat energy and higher comprehensive benefits.(2)Taking the heating of the fermentation system as the goal,the mathematical model and physical model of the unit flow channel model of the thermal oxidizer were determined,so as to realize the modeling of the basalt fiber bundle thermal oxidizer,and the safety concentration and anaerobic fermentation system.The scale matching was analyzed,and the operating conditions of the thermal oxidizer suitable for the self-sustaining operation of the fermentation system were obtained as flow rate 1m/s,commutation half cycle 30 s,and 0.6% methane concentration;and the thermal oxidizer with unit flow channel was obtained.The volume flow rate of the diluted biogas of the entire RTO device,and the formula for the volume flow rate of the biogas produced by the fermentation system maintained by the heating system is derived through the formula.The total volume of the fermentation system and the total heat load of the fermentation were calculated to obtain the initial parameters of the heating simulation.(3)Based on the parameters in Chapter 3,a three-dimensional spiral tube heat exchanger model is built.According to the simulation results,RNG type K – ε The simulation research of the model is closer to the actual situation.By comparing the outlet temperature of circulating biogas slurry with different proportion of fermentation biogas used by RTO,it can be concluded that the proportion of fermentation gas produced by RTO is more than 20%,and the temperature of circulating biogas slurry is increasing;When the proportion of fermentation gas production reached 10%,the temperature of circulating biogas slurry increased first and then decreased,and the heating rate decreased slowly in the process of heating up;When the proportion of fermentation gas production in RTO is as low as 5%,the temperature of circulating biogas slurry shows a decreasing trend.Among them,when the utilization ratio is 5%,the temperature of circulating biogas slurry has a small temperature rise within 245 s,but it is difficult to maintain the fermentation temperature after 245 s.It is lower than the reasonable gas production temperature range in 474 s,so the temperature cannot be maintained constant,and the fermentation reaction cannot continue to produce gas.Then RTO cannot take part of the diluted biogas to heat the fermentation system,and the total system cannot operate independently.Therefore,10% is selected as the standard.The variable flow rate control scheme in the initial stage of fermentation is: when the temperature increases to 310 K(62 s),reduce the flow rate to 0.6 V,and when the temperature decreases to 306 K(610 s),increase the flow rate to 1.2 V,so as to stabilize the temperature in the initial stage of fermentation within a reasonable fermentation temperature range.(4)Based on the simulation results of working conditions and the construction cost of system equipment,the NPV of the system in 20 years is 106.91 million,indicating that the project investment has a good profit in the 20-year return cycle.Considering the increased subsidies for new energy under the background of carbon emission and carbon peak and the increasingly mature process,the engineering cost of the system will show a downward trend.The system can save 8924.74 kg of standard coal and 0.99 t of carbon dioxide emission reduction in one year.The development of biogas source thermal oxidizer heating and fermentation system plays a very positive role in improving air pollution and haze in the country.As a clean energy,the combination of biogas and thermal oxidizer is conducive to the effective utilization of biomass energy such as straw resources,promote the positive cycle of agricultural ecology and build a socialist ecological civilization. |
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