Peter Van Erdeghem

Conceptual modelling and optimization of jacketed tubular reactors for the production of LDPE

Abstract This paper deals with the model based optimization of tubular reactors for the production of LDPE. Due to the high complexity, solving an optimization problem of an industrial application is not straightforward. Often researchers seek the shortest way to reach their final goal by going directly to the development of a high-complexity model and optimize this with respect to a certain objective. Although this approach seems the fastest way to success, it can be a bumpy road with a lot of dead ends. Therefore, a divide and conquer strategy is adopted, i.e., first develop a conceptual low-complexity model, set up the optimization problem and then use the obtained knowledge during the optimization of more complex models. The aim of this paper is to give the results of the three steps which have to be accomplished in order to achieve this subgoal. First, the multizone process of LDPE production is modelled as a sequence of conceptual modules which simulate the steady-state characteristics of one reaction and cooling zone. Then, this model is fitted to industrial data such that it quantitatively describes the real process. Finally, a multiple objective design optimization problem is formulated, i.e., where along the reactor and which amount of initiator has to be injected to maximize the profit at different economic situations.

Model based optimisation of tubular reactors for LDPE production

This paper presents a study on the model based optimisation of an industrial tubular reactor for the production of low-density polyethylene (LDPE). First a detailed reactor simulator is presented. Second, a well-posed optimisation problem is formulated. To this end, an economic cost function consisting of conversion and energy terms is derived and constraints due to operational and safety reasons are added. The degrees of freedom involve parameters such as the initiator feed rates, the cooling water temperatures and the switching position between hot and cold cooling water. The optimal design of a dual water circuit operating at a low and a high temperature achieved in this work allows significant improvements in conversion with respect to the reference case of a single temperature circuit, while maintaining similar molecular characteristics.

Detailed steady-state simulation of tubular reactors for LDPE production: plug flow versus cascaded CSTR model

Abstract This paper compares two approaches for simulating the steady state of tubular reactors for the production of LDPE, i.e., the plug flow and the cascaded CSTR approach. In principle, both strategies should yield similar predictions. However, numerical discretization issues related to, e.g., the large-scale and complex system of equations with various time scales needed to model this polymerization, may lead to serious discrepancies. First, this paper gives a condensed overview of the detailed model, i.e., the reaction mechanisms, the balance equations and the physical, transport and thermodynamical properties. Then, the two simulation approaches are discussed and the intrinsic differences are unraveled. Finally, the influence of discretization during integration is studied in simulation. Although this aspect is crucial to ensure accurate steady-state simulations, it is in practice too often overlooked.