Optimal Operation of a Membrane Reactor Network

Abstract

In this work, a two-dimensional model for a conventional packed-bed membrane reactor (CPBMR) is developed for the oxidative coupling of methane, which uses a nonselective porous membrane to continuously feed oxygen to the catalytic bed. The model incorporates radial diffusion and thermal conduction and assumes convective transport for the axial direction. In addition, two 10 cm long cooling segments for the CPBMR were implemented based on the idea of a fixed cooling temperature outside the reactor shell. The resulting model is discretized using two-dimensional orthogonal collocation on finite elements with a combination of Hermite polynomials for the radial and Lagrangian polynomials for the axial coordinate. The simulation study shows that it is necessary to make all transport coefficients dependent on local temperatures and compositions. This leads to a simulation with roughly 130,000 variables, which is then used to generate initial points for the optimization of the CPBMR stand-alone operation. In addition, inequality constraints and variable bounds are introduced so as to avoid potentially hazardous mixtures of methane and oxygen in both shell and tube as well as to keep the temperatures below levels stressing reactor materials (< 1,100 °C). Moreover, membrane thickness, feed compositions, temperatures at the reactor inlet and for the cooling segments, diameters of tube and shell, and finally the amount of inert packing in the reactor are considered as decision variables. The optimization procedure uses IPOPT as a solver. Afterwards, the 2D model is integrated into a membrane reactor network (MRN) proposed by H. Godin, 2010 which is simulated. Finally, attempts are made to optimize its operation

Divide to Conquer: On the Use of Distributed Feed Strategies in Oxidative Coupling of Methane

“…In addition to these attempts to use porous membranes to boost the efficiency for the OCM process, researchers have explored the concept of a “multi-membrane network”. The primary focus here was on process engineering. − For example, Godini et al proposed a network illustrated in Figure , which comprises three units: a plug flow reactor and packed bed membrane reactors. Although the overall yield is improved using this configuration, the absence of an accurate economic evaluation does not allow a fair comparison between the standalone fixed bed reactor or membrane reactors and such networks.…”

CO2 methanation: Optimal start‐up control of a fixed‐bed reactor for power‐to‐gas applications

“…However, in packed-bed reactor modeling this level of complexity is nonetheless necessary to depict real world behavior. 18 The first physical parameter which needs to be considered more in detail is the effective radial dispersion coefficient D eff r,α . To incorporate the influence of the axial convection on the radial diffusion Tsotsas and Schlünder 19 established the following correlation:…”

Mosaic

“…In addition, both outlet streams contain a number of byproducts, namely: CO, CO2, H2, H2O, and leftover CH4 as well as N2. The modeling of the reactor has already been discussed in (Esche et al, 2012) and (Esche et al, 2011). At this point the model itself will only be sketched very roughly to facilitate the procedure outlined above.…”