| Energy is the lifeblood of a country.With the increasingly prominent contradiction between traditional energy consumption and the ecological environment,it is increasingly urgent to seek cleaner,low-carbon,and safe energy.Due to the volatile and intermittent characteristics of renewable energy,as well as the mismatch between supply and demand,it is necessary to develop renewable energy storage technologies.Among the existing technologies,only pumped storage and air storage technologies can store energy on a large scale and for a long time.However,due to geographical constraints,there are problems such as high capital investment and low round-trip efficiency.The existing methane storage and distribution infrastructure is complete,and the conversion of renewable electricity into synthetic methane that is easy to store and transport through electricity to methane technology is considered an effective way to achieve high-density,efficient,and large-scale long-term energy storage,The electrolytic methane production system based on solid oxide electrolyzers has high system efficiency and durability,and stands out among the existing electrolytic methane production technologies.In this paper,a system model is established for the electric methane production system of a solid oxide electrolytic cell,and material balance data under design operating conditions are selected.Heat exchange network synthesis is performed for the entire system through pinch point analysis and mathematical planning methods.Iterative calculation and optimization are performed using the thermodynamic calculation method of a two-stream heat exchanger based on multi-objective genetic algorithm.Then,tradeoffs are made between heat transfer coefficient,pressure drop ratio,and surface area,Select the heat exchanger design point.On the basis of the above method,in order to reduce the number and volume of heat exchangers required for the system,improve the space utilization rate of the system,increase the system heat recovery,and improve the system economy and efficiency,an innovative method was developed that couples Aspen EDR software with a multi-objective genetic algorithm,with the allowable pressure drop of each flow layer as the decision variable,and the total heat transfer coefficient and total pressure drop as the objective functions,A design optimization method for multi-stream plate-fin heat exchangers with geometric constraints on the size of the heat exchanger is used to evaluate performance through the volume of the heat exchanger,the heat recovered by the system,and the efficiency of the system.In the solid oxide electrolytic cell heat absorption mode,the current density is selected as 0.5A/cm2,the operating temperature is selected as 800℃,the fuel utilization rate is selected as 90%,and the methanation reaction temperature is selected as 290℃.The impact of the four stream heat exchanger on the system compared to the two stream heat exchanger is as follows:(1)The overall volume of the heat exchanger is reduced from 90494cm3 to 37240cm3,a decrease of 59%,greatly reducing the volume of the heat exchanger,greatly improving the compactness and flexibility of the system;(2)The external electric heating of 1.93 kW has been reduced,and the system efficiency has been increased from 73.78%to 76.14%,an increase of 2.36%.This has improved the overall system efficiency and brought it closer to commercialization;(3)Under variable operating conditions,the system efficiency of a four-stream heat exchanger system is always 2%to 6%higher than that of a two-stream heat exchanger,and the system efficiency under the four-stream heat exchanger changes slightly with the current density,increasing the stability of the system under variable operating conditions. |
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