(186g) Scheduling and Optimisation of the Fixed Bed Catalytic Reactors Network

Sustainability of any industry requires efficient use of raw materials. The inefficient use of raw materials in the chemical process industries (CPIs) can be attributed mainly to inefficient chemical reactors. Catalytic chemical reactors form a significant part of the chemical reactors used in the CPIs and performance of this type of reactors are most vulnerable due to catalyst deactivation by coking [1]. This research work addresses simultaneous design of catalyst and reactor in order to achieve efficient use of raw materials in the chemical reactors. In particular, the effect of catalyst deactivation on the performance of the catalytic reactors has been investigated. In the present research work, this has been considered as an integral part of the catalyst and reactor design [2].

Catalyst deactivation is an important parameter determining design and reliability of a catalytic reactor. One of the objectives of this research work is to study deactivation and scheduling of fixed bed catalytic reactors in a single cycle operation. In order to decide the most economic reaction - regeneration cycle, different network configurations of the fixed bed catalytic reactors have been analysed. A case study of methanol to olefins as given in Castilla et al. [3] has been used in the analysis. The results obtained suggest that the performance of the catalyst particles in different reactors can be significantly improved through life time of catalysts or plant cycle of catalytic reactor networks. Also, optimum design of catalysts, catalytic reactors and reactor network can achieve efficient use of raw materials. Different reactor networks can be used at different times through the plant cycle to provide regeneration time for each reactor of the reactor network.

Also, simultaneous optimisation of operating parameters, such as inlet reactant temperature and catalyst load, has been carried out for various reactor structure configurations. The economy of the reactor network depends on the relative rates of the reactions and deactivation of catalyst. Also, optimum performance measured in terms of yield is achieved by decreasing the inlet temperature with time as the catalyst deactivation rate is more sensitive compared to the reaction rate. In contrast to this, it is widely believed in industry that increase of inlet temperature with respect to time results in constant performance of the reactors. This results in lower impact on the separation networks. Therefore, two types of objectives in terms of olefin yield have been considered, a. maintaining average yield constant through plant cycle which results in increasing inlet temperature profile through time, b. optimising for the maximum overall yield results in decreasing inlet temperature profile through time. This could mean that optimisation of the operational variables of the catalytic reactors mainly depend on the downstream processing requirements. Overall, scheduling and optimisation of the catalytic reactors can result in improvement of the performance of the catalytic fixed bed reactors.

References

1. Beeckman, J. W. and Froment, G. F., (1980), Catalyst deactivation by site coverage and pore blockage: Finite rate of growth of the carbonaceous deposit, Chemical Engineering Science, 35, 805-815

2. Hwang, S. (2004). Synthesis of continuous heterogeneous catalytic reactors, Ph.D. Thesis, The University of Manchester

3. Castilla, M., Gayubo, A., Aguayo, A., Arandes, J., and Bilbao J. (1998). Simulation and optimisation of methanol transformation into hydrocarbons in an isothermal fixed-bed reactor under reaction-regeneration cycles, Ind. Eng. Chem. Res., 37, 2383-2390