Abstract
The exothermic reactor for ammonia synthesis is a primary device determining the performance of the energy storage system. The Braun-type ammonia synthesis reactor is used as the exothermic reactor to improve the heat release rate. Due to the entirely different usage scenarios and design objectives, its parameters need to be redesigned and optimized. Based on finite-time thermodynamics, a one-dimensional model is established to analyze the effects of inlet gas molar flow rate, hydrogen–nitrogen ratio, reactor length and inlet temperature on the total entropy generation rate and the total exothermic rate of the reactor. It’s found that the total exothermic rate mainly depends on the inlet molar flow rate. Furthermore, considering the minimum total entropy generation rate and maximum total exothermic rate, the NSGA-II algorithm is applied to optimize seven reactor parameters including the inlet molar flow rate, lengths and temperatures of the three reactors. Lastly, the optimized reactor is obtained from the Pareto front using three fuzzy decision methods and deviation index. Compared with the reference reactor, the total exothermic rate of the optimized reactor is improved by 12.6% while the total entropy generation rate is reduced by 3.4%. The results in this paper can provide some guidance for the optimal design and application of exothermic reactors in practical engineering.
Highlights
As solar illumination fluctuates greatly with weather conditions, the thermal storage system is pivotal for the stable operation of solar thermal power generation systems
We analyzed the effects of eight single variables on the total exothermic rate and system entropy generation rate, and the variables includes the inlet molar flow rate, inlet gas hydrogen to nitrogen ratio, three reactor lengths and three reactor inlet temperatures
A one-dimensional model of Braun-type ammonia synthesis exothermic reactor is established based on finite-time thermodynamics, and the effects of parameters such as inlet molar flow rate, hydrogen-nitrogen ratio, reactor length, and reactor inlet temperature on system performance are analyzed
Summary
As solar illumination fluctuates greatly with weather conditions, the thermal storage system is pivotal for the stable operation of solar thermal power generation systems. The existing studies of ammonia synthesis exothermic reactors mainly focus on single-tube reactors, with the maximum exothermic rate as well as the minimum exergy destruction rate as their analysis and optimization objectives [8,9,10,11,12,13,14,15]. This paper applies finite-time thermodynamics to establish a one-dimensional model to analyze the influence of inlet gas molar flow rate, hydrogen to nitrogen ratio, length and inlet temperature of individual reactors on the entropy generation rate and the total exothermic rate. Taking inlet flow rate, lengths and temperatures of three reactor towers as optimization variables, the NSGA-II algorithm is carried out for the multi-objective optimization of the minimum entropy generation rate and the maximum total exothermic rate
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