Advanced Process Integration Aspects of Tubular Reactors

Abstract

The chemical industry had the third largest energy demand of Swedish industry in 2011. One way to lower the energy requirement is to increase the energy efficiency of a process through energy integration and therefore lower the demand of primary energy. Chemical reactors are often the part of a chemical process where most of the primary energy is consumed such as in form of combustion heat, or where large amount of heat is available which can for instance used for steam production for power generation, heating or even for cogeneration. The choice of the reactor design is a crucial aspect that can influence significantly the share of energy cost in the overall process costs. This master’s thesis was partially motivated by the 2011 years course project in the Preliminary Plant Design within the master program in Innovative and Sustainable Chemical Engineering at Chalmers University of Technology. The outline of the project was to design a plant for production of methyl-ethyl-ketone, MEK, where the suggested reactor design for the plant had a very high primary energy demand due to reactor specifications. This master’s thesis has investigated important aspects for energy integration of tubular reactors and how Pinch Analysis can be used to find the optimal reactor design. Two case studies have been performed to achieve this, one for an endothermic reaction and one for an exothermic reaction. The endothermic case study was based on the production of MEK and one intermediate target was to find a better reactor design than the design in the course Preliminary Plant Design. The exothermic case study was based on the methanation process in production of synthetic natural gas. The results from the case studies showed that pinch analysis is not a sufficient tool to evaluate the best choice in utility temperatures for heated or cooled reactors because of the intrinsic relation between heat transfer and kinetics cannot be taken into account rigorously when selecting different type of utility streams. This makes it impossible to define an energy target for the utility consumption of a tubular reactor system independent of the specific design. Nonetheless pinch analysis can be used to evaluate energy consequences of different reactor design thus allowing to identify the most suitable configuration based on the trade-off between investment and energy targets.