No abstract

SUMMARY In this work, tri‐reforming and steam reforming processes have been coupled thermally together in a reactor for production of two types of synthesis gases. A multitubular reactor with 184 two‐concentric‐tubes has been proposed for coupling reactions of tri‐reforming and steam reforming of methane. Tri‐reforming reactions occur in outer tube side of the two‐concentric‐tube reactor and generate the needed energy for inner tube side, where steam reforming process is taking place. The cocurrent mode is investigated, and the simulation results of steam reforming side of the reactor are compared with corresponding predictions for thermally coupled steam reformer and also conventional fixed‐bed steam reformer reactor operated at the same feed conditions. This reactor produces two types of syngas with different H2/CO ratios. Results revealed that H2/CO ratio at the output of steam and tri‐reforming sides reached to 1.1 and 9.2, respectively. In this configuration, steam reforming reaction is proceeded by excess generated heat from tri‐reforming reaction instead of huge fired‐furnace in conventional steam reformer. Elimination of a low performance fired‐furnace and replacing it with a high performance reactor causes a reduction in full consumption with production of a new type of synthesis gas. The reactor performance is analyzed on the basis of methane conversion and hydrogen yield in both sides and is investigated numerically for various inlet temperature and molar flow rate of tri‐reforming side. A mathematical heterogeneous model is used to simulate both sides of the reactor. The optimum operating parameters for tri‐reforming side in thermally coupled tri‐reformer and steam reformer reactor are methane feed rate and temperature equal to 9264.4 kmol h−1 and 1100 K, respectively. By increasing the feed flow rate of tri‐reforming side from 28,120 to 140,600 kmol h−1, methane conversion and H2 yield at the output of steam reforming side enhanced about 63.4% and 55.2%, respectively. Also by increasing the inlet temperature of tri‐reforming side from 900 to 1300 K, CH4 conversion and H2 yield at the output of steam reforming side enhanced about 82.5% and 71.5%, respectively. The results showed that methane conversion at the output of steam and tri‐reforming sides reached to 26.5% and 94%, respectively with the feed temperature of 1100 K of tri‐reforming side. Copyright © 2013 John Wiley & Sons, Ltd.

In this novel paper, application of chemical looping combustion (CLC) instead of furnace in a steam reformer assisted by Pd−Ag hydrogen perm-selective membranes (CLC-SRM) for CO 2 capture and hydrogen production has been analyzed. NiO18-αAl 2 O 3 particles have been employed as oxygen carriers in CLC-SRM. These particles have shown very high reactivity and allow for working at high temperatures in a CLC process with full methane conversion due to Ni-based oxygen carriers. In the CLC-SRM configuration, the air reactor (AR) and fuel reactor (FR) operate in fast and bubbling fluidization, respectively. In this configuration, reforming tubes are located vertically inside the AR so that methane steam reforming occurs in these fixed bed catalytic tubes that have been covered by the membranes. A steady state one-dimensional heterogeneous catalytic reaction model is applied to analyze the performance of CLC-SRM. Performance of conventional steam reformer (CSR) has been compared with CLC-SRM by investigation of important parameters such as temperature, mole fractions, heat of reaction, rate of reactions, methane conversion, and hydrogen production. The simulation results of CLC-SRM show that by employing CLC-SRM, methane conversion and hydrogen production increase 7.54% and 25.48%, respectively, in comparison with CSR. In addition, results indicated that by increasing feed flow rate of FR from 90 to 180 mol s −1 methane conversion and hydrogen production can increase 16.73% and 40%, respectively. In CLC-SRM, the total amount of methane consumed in the FR and combustion efficiency increases to 1 in the FR, and a huge amount of almost pure carbon dioxide (410 ton day −1 ) can be captured by removal of water from the FR outlet stream with condensation.

From the environmental perspective, because of the increasing level of CO2 in the atmosphere, different methods are presented for the separating and capturing of CO2 from combustion. One of these new methods is chemical looping combustion (CLC). In this work, the required heat for the endothermic steam reforming process is provided by coupling the CLC as an unprecedented technique with the steam reforming process. Endothermic reactions of methane steam reforming and reduction of Fe-based oxygen carriers in a fuel reactor (FR) are coupled with exothermic reaction of oxygen-carrier oxidation in an air reactor (AR) of thermally double coupled reactors. In this novel configuration, the AR and FR operate in fast and bubbling fluidization, respectively, and steam reforming occurs in vertically fixed-bed catalytic tubes. The results show that, by application of CLC, not only the amount of produced synthesis gas is the same as the conventional method but also the process whereby CO2 is separated from flue gas inherently. This is the most obvious advantage of the CLC technique. Although the CO2 separation process is very costly, it is necessary for the conventional method. In this study, temperature, mole fraction, methane and air conversion, combustion efficiency, and hydrogen yield have been investigated. Results indicate that the methane conversion and hydrogen yield obtained in this novel method are 29% and 1.04, respectively. Also, the combustion efficiency and gas conversion (O2 and CH4) in both of the CLC reactors (air and fuel reactors) are nearly 100%.

The present paper focuses on simulation of a catalytic thermally double-coupled reactor (TDCR) in cocurrent mode. In this novel configuration, the endothermic reaction of cyclohexane dehydrogenation has coupled with two exothermic reactions: methanol production and direct DME synthesis from syngas to improve the heat transfer between the endothermic and the exothermic sides. A multitubular reactor with 2962 three concentric tubes has been considered for TDCR. A steady state heterogeneous catalytic reaction model is applied to analyze the performance of TDCR for simultaneous production of methanol, hydrogen, and dimethyl ether (DME). Simulation results of TDCR have been compared with corresponding predictions for an industrial methanol reactor (CMR) and thermally coupled reactor (coupling of methanol synthesis with cyclohexane dehydrogenation), operated at the same feed conditions. Results showed that by this novel configuration production of methanol and hydrogen increases from 345.48 to 373.21 kmol h −1 and 250.6 to 1066.3 kmol h −1 in comparison with TCR, respectively. In addition, production of DME with a rate of 277.24 kmol h −1 is another superiority of TDCR. In addition, hydrogen production in the endothermic side of TDCR in each of the three concentric tubes (0.1 mol s −1 ) is higher than hydrogen consumption in methanol synthesis (0.076 mol s −1 ).