Abstract
The methanol synthesis via CO2 hydrogenation (MSCH) reaction is a useful CO2 utilization strategy, and this synthesis path has also been widely applied commercially for many years. In this work the performance of a MSCH reactor with the minimum entropy generation rate (EGR) as the objective function is optimized by using finite time thermodynamic and optimal control theory. The exterior wall temperature (EWR) is taken as the control variable, and the fixed methanol yield and conservation equations are taken as the constraints in the optimization problem. Compared with the reference reactor with a constant EWR, the total EGR of the optimal reactor decreases by 20.5%, and the EGR caused by the heat transfer decreases by 68.8%. In the optimal reactor, the total EGRs mainly distribute in the first 30% reactor length, and the EGRs caused by the chemical reaction accounts for more than 84% of the total EGRs. The selectivity of CH3OH can be enhanced by increasing the inlet molar flow rate of CO, and the CO2 conversion rate can be enhanced by removing H2O from the reaction system. The results obtained herein are in favor of optimal designs of practical tubular MSCH reactors.
Highlights
Over the past century, a huge amount of CO2 produced through burning fossil fuels has been released into the atmosphere, which has led to global warming
Compared with the results of the reference reactor in [43], the total entropy generation rate (EGR) of the optimal reactor decreases by 20.5%, the total EGR due to the heat transfer decreases by 68.8%, the total EGR due to two chemical reactions decreases by 3.3%, and the total EGR
The minimum EGR caused by heat transfer, viscous flow and chemical the exterior wall temperature (EWT) using finite time thermodynamic (FTT) theory
Summary
A huge amount of CO2 produced through burning fossil fuels has been released into the atmosphere, which has led to global warming. Much effort is being put into carbon emission reduction. There are mainly three ways to reduce carbon emissions:. (1) Utilizing clean energy sources, such as the solar, wind, nuclear, and tidal energy; (2) utilizing carbon sequestration and storage technology; (3) collecting and recycling CO2 through chemical reactions. The methanol synthesis via CO2 hydrogenation (MSCH) reaction is an effective scheme for alleviating the greenhouse effect. Methanol is a primary liquid petrochemical, and is widely used in the chemical and energy fields in applications such as hydrogen storage, dimethyl ether and hydrocarbon production, etc. The methanol synthesis via CO2 hydrogenation reaction still has some problems to be solved, e.g., high energy-consumption, low conversion rate and poor selectivity [5]. The studies for MSCH mainly include: (1) developing new catalysts and establishing the corresponding kinetic models [6,7,8]; (2) improving the MSCH reaction process by modeling and simulation [9,10,11,12];
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