Entropy Generation Analysis Based Multi-Objective Optimization For Chemical Reaction Process Enhancement

Chemical reaction is the core in chemical process.In addition to the chemical reaction process proceeding in the industrial reactor,the processes of fluid flow,heat transfer and mass transfer,also exist.They influence and permeate into each other,and affect the technical and economic indicators of the reaction,such as the conversion rate,yield,energy consumption and so on.All of these processes need to be regulated in order to improve these technical and economic indicators,so the optimal design of the reactor is very challenging.In this paper,a multi-objective optimization approach for chemical reaction process enhancement based on non-equilibrium thermodynamic entropy generation analysis was proposed.It is different from the"design-experiment(simulation)-improvement"method used in the traditional optimization design,but a more rational and systematic method.In this paper,based on the entropy generation extremum principle,the various entropy generations including chemical reaction and transfer processes,or their combination were set as the objective function.The optimal flow pattern,the corresponding external body force,temperature and concentration distribution were obtained by solving this multi-objective optimization problem using the calculus of variation method.These optimal results can be regarded as the thermodynamic limit for reaction process enhancement under the given conditions and used to guide the optimization design of the internal structure of the related reactors.In this paper,the validity of the method is validated by the enhancement of a first order irreversible reaction process firstly.Then the enhancement of three processes:methane combustion,hydrogen combustion and solar thermal decomposition of methane for hydrogen were studied by using the proposed method.To achieve the maximal thermodynamic second law efficiency in methane combustion process,the minimum of the total entropy generation was set as the objective function.The thermodynamic optimal solution of the combustion process was obtained by optimization calculation.The thermodynamic second law efficiency of the process was increased from 91.68%to 92.02%.Inspired by the optimized flow field,a variety of modified structures in the combustor were constructed to improve the thermodynamic efficiency of the process.For some industrial thermal applications,it is expected to obtain the maximal heat released from the walls of the combustor.Taking this as the goal,the hydrogen combustion process was optimized by using the proposed optimization method.The entropy generation due to heat transfer was set as an indirect objective function.And the heat released from the walls of the combustor(0.0115 m~2)was increased from 3210 W to 3263 W.Finally,the process of solar thermal dissociation of methane for hydrogen production was optimized.The effects of entropy generation due to heat transfer and the reaction on methane conversion rate were analyzed respectively.The sum of these two entropy generations was set as the objective function,and the conversion rate of methane was increased from 49.29%to56.50%.In this paper,the proposed optimization method is performed through the enhancement of several typical chemical reaction processes,and it is effectively verified that various parameters to ensure the process reach the thermodynamic limit for reaction process enhancement can be obtained.In the future,the application of this method in other reaction or separation processes enhancement analysis will be of great research value.