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This work presents an approach for the model-based design of a load-flexible fixed-bed reactor for performing the partial water–gas shift (WGS) reaction in the gas cleanup section of a coal-to-methanol plant. Three optimization problems with various combinations of objective functions (H2/CO ratio, pressure drop, and operating costs) are formulated and solved using the nondominated sorting genetic algorithm (NSGA-II) to obtain the Pareto-optimal fronts, and the selected solutions are subjected to dynamic stability analysis. The optimum values of decision variables such as the weight of the catalyst, catalyst particle size, ratio of the reactor length and diameter, feed gas temperature, and steam to CO ratio are estimated and are found to be dependent on the choice of the objectives and tolerable deviation from their required values. The dependence of the H2/CO ratio on the inlet gas temperature varies with the choice and combination of the objectives. In contrast, higher values of the steam to CO ratio (S/C) are associated with a lower deviation from the desired H2/CO ratio for all three cases. However, optimum values of S/C are found to be below 1:1 because of its effect on the pressure drop and operating costs. The solutions obtained in the equilibrium-limited regime are found to be more stable in the presence of fluctuations in the feed flow rates but show intermediate stability with fluctuations in the inlet gas temperature. Four designs are recommended as the feasible designs, and the criteria of their application are discussed. Even though the work is related to a WGS reactor, the methodology used can be applied for the design of any other reactor system operating under variable feed conditions.

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The injection of nitrogen monoxide (NO) into an internal combustion engine has been shown in the literature to reduce the net generation of nitrogen oxides (NOx). In this work, engine simulations are performed using two different microkinetic models to carry out an analysis of reaction pathways responsible for the net decrease in NOx formation when NO is injected into a hydrogen–fuelled internal combustion engine. The net NOx formed when 5000 ppm NO is injected at the engine intake is found to be 60% lower than the case without any NOx injection. The major reactions contributing to the formation and conversion of NO are obtained for various phases of combustion, and the corresponding reaction pathway diagrams are constructed. During the early phase of combustion with an increasing in-cylinder temperature and pressure, the Zeldovich reactions primarily contribute toward NO formation (60–82% contribution). During this phase, NO is primarily a product for various reactions, and the net rate of production of NO decreases with the external injection of NO. Further, any nitrogen dioxide (NO2) present in the intake mixture gets decomposed to NO owing to the high temperature. Thus, the in-cylinder NOx concentrations at the end of the power stroke are governed by the rate of consumption and formation of NO, irrespective of the NOx speciation at the intake. During the later phase of combustion with a decreasing in-cylinder temperature and pressure, the NOx concentration decreases, and the reactions constituting the Zeldovich mechanism dominate NO consumption, with the reactions involving fuel-NOx interactions playing a secondary role (<14% contribution). A comparison of the net rate of consumption of NO, the rate of formation of N2, the major reactions involved in NO reduction, and their relative contribution shows conclusively that the mechanism of NOx reduction is not impacted by the addition of NO.

The absorption of model tar compounds (benzene, toluene, and xylene) in methyl oleate is studied in a fixed-bed absorption column. The dynamic system involving the recirculation of the tar-rich solvent is modeled as a combination of various steady-state snapshots in time, and this approach effectively predicts the performance of the absorber. The rate-based model shows a good agreement with the experimental data as compared to the equilibrium-based model. Further, a pilotscale absorber is designed for the removal of tars from syngas generated in a coalto-methanol plant. The validated rate-based model is used to predict the effect of various operating and geometry parameters on the absorption efficiency of the pilot-scale absorber. The regeneration of the solvent by steam stripping and reboiled stripping is evaluated.