High-temperature Shift Reaction Research Articles

A high-efficient anisotropic continuum model for the optimization of heat transfer and chemical reaction in a packed-bed water gas shift reactor

The packed bed reactor with the high-temperature shift reaction has been a competitive industrial device for the production of hydrogen fuel. While the temperature distribution in the packed bed plays an important role in improving the reaction efficiency, and numerical simulation is a powerful way to recover the heat transfer inside the reactor. Nevertheless, the current simulation methods are either high computational cost or low accuracy for the high-temperature shift. To accomplish the effective computational cost and accuracy simultaneously, we developed a two-dimensional anisotropic continuum model with modified space-dependent effectiveness factor and anisotropic thermal conduction based on the pseudo continuum model. Meanwhile, the simulation results were compared with those by the particle-resolved 3D computational fluid dynamics to validate the model accuracy. Due to the overestimation of the radial thermal conductivity by the pseudo continuum model, the axial temperature rise in the packed bed was only 10 K, but a significant temperature rise of 50 K was presented by the other two methods, suggesting the coordinate computational accuracy of the anisotropic continuum model. However, the computational time consumed by the particle-resolved 3D computational fluid dynamics was up to 1320 min, which exceeds a thousand times more than that in current advanced model. All the comparisons indicate the anisotropic continuum model can predict the heat transfer through the packed bed with sufficient computational accuracy and efficiency, making a powerful and time-saving method to conduct the effective heat management in packed bed reactors for actual industrial applications.

Elucidating the effect of Ce/Zr ratio on high temperature shift activity with sulfur poisoning

To elucidate the effect of CeO2/ZrO2 ratio on the sulfur-tolerance in high temperature shift using waste derived synthesis gas, the Ce/Zr ratio in Pt/CexZr1-xO2 catalysts was systematically changed. Pt/CexZr1-xO2 catalysts were applied to the high temperature shift reaction with 500 ppm H2S. In the presence of H2S, the catalysts were deactivated with time on stream due to the poisioning of H2S. Sulfur-tolerance in high temperature shift activity depended upon the oxygen storage capacity of the catalysts. The regeneration rate of the catalysts was also related with the oxygen storage capacity. In addition, the Pt dispersion matched the oxygen storage capacity trend. The oxygen storage capacity is a main function to determine the sulfur tolerance in high temperature shift activity compared to the dispersion of Pt.

Hydrogen production via solid waste gasification with subsequent amine-based carbon dioxide removal using Aspen Plus

This simulation study presents the municipal solid waste gasification, along with a detailed design of CO2 capturing unit using monoethanolamine (solvent). The gasifier's operational parameters, such as pressure, temperature, and equivalence ratio, are chosen to optimize the gasified H2-enriched product stream. At optimal operational parameters, such as temperature (800 °C), pressure (1 bar), and equivalence ratio (0.2), a maximum H2 content of 27.9% could be attained. Following that, 39.5% H2 is found at the high-temperature shift reactor's exit, followed by 42.1% at the low-temperature shift reactor's output. It is observed that the absorber (16.5 m) and stripper (6 m) packing heights are required to capture 95% CO2 from the product effluent obtained after shift reactors, along with column diameters of 2.70 and 3.61 m, respectively. Hence, the proposed model can give vital information for large-scale gasifier and CO2 capture unit design, operation, and optimization with respect to different flue gases.

Parametric Study on Co-Feeding of Municipal Solid Waste and Coal in an IGCC Power Plant with Pre-Combustion Carbon Capture

Municipal solid waste (MSW) is one of the top contributors in greenhouse gas (i.e. methane) emissions - particularly from landfill disposals. However, it could be a remarkable source of renewable energy. In Bangladesh, generation of municipal solid waste is at least 2.7 million tonne per year in the major cities, implying a heavy environmental burden. On the other hand, there are several coal-based power plants are in the pipeline to meet the increasing energy demand in Bangladesh with the potential of significant CO2 emission. To find a remedy to the above situation, a power plant using Integrated Gasification and Combustion Cycle (IGCC) technology with pre-combustion carbon capture is considered in this study. IGCC has the advantage of producing high quality syngas from a wide variety of feed and assists in the capture of CO2 at a lower cost while providing high electric efficiency. The power plant was simulated by commercial simulation packages (Aspen PLUS™ and Aspen HYSYS™) using MSW and bituminous coal (Indonesian) as a combined feed. With a feed rate of 1800 tonne per day, Syngas produced from an entrained flow type gasifier was then treated for CO2 removal using mono-ethanol amine (MEA) solvent after necessary shift in a high temperature shift reactor. About 91% efficiency was achieved in the shift reactor while the CO2 capture efficiency was varied for this study from 30% to 85%. Further parametric variation was studied by varying the moisture content of MSW and MSW to coal feed ratio. Through combustion of the H2 rich syngas in a gas turbine and subsequent steam cycle with reheat resulted in 125 MW of electricity at an efficiency of 28.95% while capturing 50% of the CO2 generated in the process for an MSW to Coal feed ratio of 1:1. With variation in moisture content especially during monsoon season, the plant efficiency could be affected remarkably. On the other hand, it was observed that the energy requirement varied from 6 to 8 MW for every 10% increase in CO2 capture quantity. Overall, by capturing 50% of the generated CO2, it is possible to reduce the emission of a same size ultra-supercritical coal-based power plant from about 700 kg CO2/MWh to about 360 kg of net CO2/MWh incorporating co-feeding and pre-combustion capture in an IGCC power plant.
 Chemical Engineering Research Bulletin 21(2020) 37-42

Multi-scale model based design of membrane reactor/separator processes for intensified hydrogen production through the water gas shift reaction

This work aims to first quantify the impact of various diffusion models (Maxwell-Stefan, Wilke, Dusty-Gas) on the predictions of a multi-scale membrane reactor/separator mathematical model, and to then demonstrate this model's use for the design and process intensification of membrane reactor/separator systems for hydrogen production. This multi-scale model captures velocity, temperature and species' concentration profiles along the catalyst pellet's radial direction, and along the reactor's axial direction, by solving the momentum, energy, and species transport equations, accounting for convection, conduction, reaction, and diffusion mechanisms. In the first part of work, the effect of pellet-scale design parameters (mean pore diameter, volumetric porosity, tortuosity factor, etc.) and various species' flux models on the model predictions is studied. In the second part, the study focuses on the comparison, in terms of their process intensification characteristics, of various hydrogen production processes. These include a conventional high-temperature shift reactor (HTSR)/low-temperature shift reactor (LTSR) sequence, a novel HTSR/membrane separator (MS)/LTSR/MS sequence, and a process that involves low-temperature shift membrane reactors-LTSMR in a series.

Steam-to-carbon ratio control strategy for start-up and operation of a fuel processor

The purpose of this work is to suggest a steam-to-carbon ratio (SCR) control strategy for the start-up and operation of a fuel processor and to experimentally verify this strategy. To overcome ambient temperature variability and manufacturing deviations, a controlled SCR method (CSM) is suggested. The CSM controls the water flow rate independently through heat exchangers (HEXs) to maintain a constant inlet temperature of the reactors. To consistently satisfy the target SCR value, the remaining water after control is fed to the last HEX used as a buffer. To verify the CSM, seven gasoline fuel processors (GFPs) were constructed. The GFPs consisted of an autothermal reformer (ATR), hydrodesulphurization (HDS), a high-temperature shift reactor (HTS), a medium-temperature shift reactor (MTS), a preferential oxidation reactor (PROX), a HEX, and an exhaust gas burner. Water was individually supplied to HEX #1 ∼ HEX #4 as a cool-side fluid. One of the GFPs was operated at a low (−32 °C) and a high (50 °C) temperature. The CSM maintained a constant inlet temperature of the reactors; only the inlet temperature of the PROX was affected by the ambient temperature thanks to the CSM. Temperature results for the other six GFPs showed that manufacturing deviations appeared only in the inlet temperature of the PROX by the CSM. To confirm the effect of the CSM on durability, 38 start–stop cycles were performed over 314 h of operation. The results showed that the repeated use of the CSM led to a slow degradation of efficiency, while the temperatures of the reformer and reactor remained steady during cycling testing.

Design studies for monolithic high temperature shift catalysts: Effect of operational parameters

In this study, the performance of a commercial high temperature shift (HTS) catalyst has been investigated. The catalyst was a wash-coated ceramic monolith type and used to adjust the H2/CO ratio in a simulated syngas stream. In the experiments, the effects of inlet gas composition, gas hourly space velocity, inlet steam to CO ratio and reaction temperature have been investigated. The results showed that all these parameters have considerable influence on the design of HTS reactor. Precious metal based monolith catalysts enable working under high space velocities and thus reduce the volume of HTS reactor. Specifically defined selectivity, as ratio of the total amount of CO2 and H2 to the amount of CO2 formed during the process, seems to be a good measure of possible unwanted side reactions that might occur. It was found that the selectivity ratio should be ideally about two for HTS process, minimizing the formation of side reactions. Selectivity values below 2.0 indicate the presence of unbalanced H2 which is incompatible with WGS reaction stoichiometry. Results showed that steam is an effective parameter in determining the probability of side reactions, especially the reactions leading to the catalyst deactivation through coke deposition. Another point is that coking tendency of the catalyst is more severe at lower operating temperatures. The formation of methane, an unwanted by-product, was seen to be favored by lower gas hourly space velocities, possibly via the reaction with H2. The formation of methane results in hydrogen consumption to some extent and consequently alters the product composition. The optimum operating conditions of the wash-coated monolith type HTS catalyst studied were found to be as follows: Temperature=~375–400°C, GHSV=~50,000h−1 and the inlet steam to CO ratio=~2.0.

가스화기에서 WGS 반응을 통한 합성가스의 수소 전환

A gasification process with pre-combustion <TEX>$CO_2$</TEX> capture process, which converts coal into environment-friendly synthetic gas, might be promising option for sustainable energy conversion. In the coal gasification for power generation, coal is converted into <TEX>$H_2$</TEX>, CO and <TEX>$CO_2$</TEX>. To reduce the cost of <TEX>$CO_2$</TEX> capture and to maximize hydrogen production, the removal of CO and the additional production of hydrogen might be needed. In this study, a 2l/min water gas shift system for a coal gasifier has been studied. To control the concentration of major components such as <TEX>$H_2$</TEX>, CO, and <TEX>$CO_2$</TEX>, MFCs were used in experimental apparatus. The gas concentration in these experiments was equal with syngas concentration from dry coal gasifiers (<TEX>$H_2$</TEX>: 25-35, CO: 60-65, <TEX>$CO_2$</TEX>: 5-15 vol%). The operation conditions of the WGS system were <TEX>$200-400^{\circ}C$</TEX>, 1-10bar. Steam/Carbon ratios were between 2.0 and 5.0. The commercial catalysts were used in the high temperature shift reactor and the low temperature shift reactor. As steam/carbon ratio increased, the conversion (1-<TEX>$CO_{out}/CO_{in}$</TEX>) increased from 93% to 97% at the condition of CO: 65, <TEX>$H_2$</TEX>: 30, <TEX>$CO_2$</TEX>: 5%. However the conversion decreased with increasing of gas flow and temperature. The gas concentration from LTS was <TEX>$H_2$</TEX>: 54.7-60.0, <TEX>$CO_2$</TEX>: 38.8-44.9, CO: 0.3-1%.

Syngas production from oxidative methane reforming and CO cleaning with water gas shift reaction

Fuel cell based heat and power cogeneration is considered to be well qualified for a distributed energy system for residential and small business applications. A fuel processing unit including an oxidative steam methane reformer, a high temperature shift reactor and a low temperature shift reactor is under development in South China University of Technology. Performance of the unit is experimentally investigated in a bench-scale experimental setup. Processor performance under typical operating conditions is tested. The influence of reaction temperature, methane space velocity in the oxidative steam methane reformer, and air to carbon molar ratio on unit performances is experimentally studied. It is found that under the typical operating conditions, the total energy efficiency reaches 88.3%. The efficiency can further be improved by utilizing the sensible heat of the reformate gas. The current study has been focused on the chemical performances such as methane conversion of the reformer and CO concentration in the synthesis gas downstream water gas shift reactors. Heat integration of the unit will be further implemented in future to improve energy efficiency.

Hydrogen production from high temperature shift reaction of the simulated waste-derived syngas over metal oxide incorporated Fe/Al catalysts

Hydrogen production from high temperature shift reaction of the simulated waste-derived syngas over metal oxide incorporated Fe/Al catalysts

The effect of Zn addition into NiFe2O4 catalyst for high-temperature shift reaction of natural gas reformate assuming no external steam addition

In this study, the effect of the addition of Zn to a NiFe2O4 catalyst was investigated for a high-temperature shift (HTS) of the natural gas reformate under the assumption that no external steam was added. In our previous study, NiFe2O4 proved to be a notable HTS catalyst, but it produced methane as a by-product in the presence of such a highly reductive reformate. In this study, we found that the addition of Zn to NiFe2O4 was effective in suppressing methanation as well as in promoting HTS activity. Such improvements were expected to be related to the enhanced redox property of the inverse-spinel species included in the catalyst. To elucidate the effects of Zn addition, inductively coupled plasma spectroscopy (ICP), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermo-gravimetric analysis under a CO gas atmosphere (CO-TGA), and temperature-programmed reduction of H2 (H2-TPR) were performed.

Cs-promoted Ni/Fe catalyst as a Cr-free, high temperature shift catalyst for steam methane reformate without additional supply of steam

Abstract The goal of this study was to investigate the Cs-promoted Ni/Fe catalysts for high temperature shift reaction. The performance of all the catalysts was evaluated at 400 °C and 75,000 ml/gcat h under the reactant composition: 56.7% H2, 10% CO, 26.7% H2O, and 6.7% CO2, assuming gas production from the steam methane reformer at a H2O/CH4 ratio = 3 with 100% CH4 conversion and with no extra steam added for the protection of the catalyst. The Cs/Ni/Fe (Ni:Fe = 34:66; weight ratio) catalysts of 3.9–6.0 Cs wt.% showed excellent CO removal activities and suppressed the progress of methanation effectively. This performance was related to the increment of amount in weakly basic sites through Cs promotion.

Hydrogen production from water gas shift reactions in association with separation using a palladium membrane tube

SUMMARY Hydrogen production from water gas shift reactions (WGSRs) of synthesis gas (syngas) followed by separation via a Pd membrane was studied experimentally. In the reactions, a variety of combinations of a high-temperature shift reaction (HTSR), a low-temperature shift reaction (LTSR) and a palladium (Pd) membrane tube were considered. The results indicated that the CO conversion from the LTSR was close to that of the HTSR and LTSR in series; however, the latter with the Pd membrane could provide a much low CO concentration at the permeate side. On the other hand, while the produced hydrogen diffused through the membrane, methane was also found at the both sides of the membrane due to the methanation reaction activated by the Pd membrane. In the present system, increasing the steam/CO ratio enhanced the forward reaction of the WGSRs and elongated the residence time of the reactants in the catalyst beds, resulting in the increases of CO conversion and hydrogen recovery. As a whole, the concentration of CO in the separated hydrogen was lower than 50 ppm from the combination of the HTSR and the LTSR with the membrane, whereby the produced hydrogen could be applied in proton exchange membrane fuel cells. Copyright © 2010 John Wiley & Sons, Ltd.

Modeling and simulation of hydrogen generation from high-temperature and low-temperature water gas shift reactions

Chemical kinetic models of high-temperature and low-temperature water gas shift reactions (WGSRs) are established in the present study, in accordance with experimental measurements. The reactions are simulated to aid in recognizing the detailed phenomena of the WGSRs. In the developed models, the effects of both the reaction temperature and the steam/CO ratio are taken into account. It is found that the predictions in terms of the conducted models agree with the experimental results very well. When the high-temperature shift reaction (HTSR) and the low-temperature shift reaction (LTSR) in catalyst beds are examined, the CO conversion near the wall is always higher than that along the centerline of the reactor or surrounding it. This is a result of slower velocity or longer residence time of the reactants in the vicinity of the wall. Meanwhile, by virtue of the higher CO concentration at the entrance of the catalyst bed, the intensity of the WGSR is significant nearby and it decays rapidly downstream. When a HTSR and a LTSR are connected together, the CO conversion is nearly completed if the reaction temperature of the LTSR is fixed at 200 °C and no matter what temperature of the HTSR is. It follows that a HTSR followed by a LTSR in series is a recommended method in industry for the operation of hydrogen generation. The simulations have provided a detailed and useful insight into the reaction phenomena of the catalytic WGSRs.

Characterization of HTS and LTS Reactions in Microstructured Reactors

The production of hydrogen from synthesis gas with a high CO content is investigated with microstructured reactors. The main advantages of using microstructured reactors are the excellent heat and mass transfer characteristics inside of the reactor and the possibility to include heat exchangers to reduce the system size and heat losses. High- and low-temperature water gas shift reactions are examined for the ability to decrease the CO fraction of the synthesis gas down to a level tolerable for proton exchange membrane fuel cells. These gas purification methods have the advantage of a higher hydrogen yield being achievable by converting CO into H 2 , thus leading to a higher overall efficiency of the fuel cell system. A next step in further reducing the CO content could be-if necessary-preferential oxidation. The high-temperature shift reaction takes place at a temperature of approximately 350 °C in the presence of an iron- or chromium-based catalyst. The low-temperature shift reaction is operated at approximately 250 °C with copper catalysts. The performance of microstructured reactors fitted with different catalysts is discussed within this paper as a function of the temperature, gas flow rate, and gas composition.

Catalytic properties of iron oxides impregnated with copper acetate

Textural and catalytic properties of iron oxides impregnated with copper acetate were investigated. In order to get satisfactory performance in the high temperature shift reaction, 4 impregnation hours are necessary.

Effect of addition sequence during neutralization and precipitation on iron-based catalysts for high temperature shift reaction

The preparation of the iron-based catalysts promoted by cobalt with a small amount of copper and aluminum for the high temperature shift reaction (HTS) with different sequences of adding catalyst raw materials during neutralization and precipitation was investigated. XRD, BET and particle size distribution (PSD) were used to characterize the prepared catalysts. It was found that the catalyst crystals were all γ-Fe2O3, and the intermediate of the catalyst after aging was Fe3O4. The crystallographic form of the catalyst and its intermediate was not affected by the addition sequence in the neutralization and precipitation process. The results showed that the specific surface area and the particle size of the catalysts depended on the addition sequence to the mother liquor. Cobalt with a small amount of copper and aluminum could increase the specific surface area and decrease the particle size of catalysts.

Hydrogen Production from Ethanol Using a CO2 Absorption Ceramic and Base Metal Catalysts

With the aim of developing a non-equilibrium reactor with a CO 2 recovery function for proton exchange membrane fuel cell (PEMFC) systems and other applications, steam reforming of ethanol was performed in a preliminary study in the presence of a CO 2 absorption ceramic at atmospheric pressure in a temperature range of 450-650°C using a plug flow reactor and commercially available reforming catalysts. The CO 2 absorption ceramic consisted of lithium silicate powder, which was granulated and coated with coarse alumina particles. Reaction products were analyzed by gas chromatography. The effects of the CO 2 absorption ceramic on hydrogen selectivity and species concentrations were estimated. It was concluded that steam reforming ethanol in the presence of the CO 2 absorption ceramic has high potential for application to a non-equilibrium reactor. Hydrogen production was enhanced and CO and methane production was suppressed significantly in the presence of the CO 2 absorption ceramic. For example, at a temperature of 500°C and with a commercial FCR-4-02 catalyst, hydrogen selectivity was 1.3 times higher than that in the absence of the CO 2 absorption ceramic, and the hydrogen concentration was 95 mol%-dry. This hydrogen concentration was considerably higher than that at chemical equilibrium, which was 63 mol%-dry. The methane concentration decreased from 10 to 4.2 mol%-dry, and the CO concentration decreased dramatically from 2.0 mol%-dry to less than the detection limit, which was about 100 ppm. The CO and methane concentrations were considerably lower than those at chemical equilibrium, which were 3.4 and 11 mol%-dry, respectively. These results indicate the potential for constructing a fuel processor system, which will not need either a high-temperature shift reactor (HTS) or a low-temperature shift reactor (LTS), for PEMFC applications.

Integrated Fuel Cell Processor for a 5-kW Proton-Exchange Membrane Fuel Cell

A fuel processor is a combination of a few reactors to generate hydrogen required for a fuel cell. The study deals with the production of hydrogen suitable for a 5-kW proton-exchange membrane fuel cell (PEMFC) for household applications using liquefied petroleum gas (LPG) as the fuel. The aim is to energy integrate the five reactors in a fuel processor, i.e., desulfurizer, steam reformer, high-temperature shift reactor, low-temperature shift reactor, preferential oxidation reactor, and various heat exchangers. Heat-exchanger network synthesis analysis has been carried out for the entire process to make the process efficient. The results obtained from the studies show that the steam reforming with LPG gives a higher concentration of hydrogen in the product of about 74%. The fuel cell efficiency is around 34%, and the thermal efficiency including lean gas is about 93%. The model developed can serve as the basis for the development of an integrated PEMFC decentralized power pack for household applications.

Cold start simulations of a gasoline based fuel processor for mobile fuel cell applications

The cold start behaviour of the gas processing unit is one crucial issue for the use of gasoline based fuel reformers for mobile fuel cell systems. In this contribution different cold start strategies for a mobile fuel reformer based on gasoline are presented and discussed. The simulation studies are based on 1-d, dynamic multiphase models for both an autothermal gasoline reformer (ATR) and a thermally integrated reforming unit consisting of an ATR, a heat exchanger and a high-temperature-shift-reactor (HTS). Setup and geometric parameters for both models correspond to pilot stage systems considered by DaimlerChrysler. Results on the reactive heat-up of the ATR by partial and total oxidation of gasoline show the impact of the air/fuel-ratio and the thermal load on the cold start duration. The use of the reformat during the rapid start-up of the ATR is mainly limited by the availability of steam for autothermal operation. Due to the high thermal capacities of the system, the whole reforming unit requires much longer time for the cold start. Especially the slow convective heat-up of the HTS restricts the conversion of CO and the subsequent use of the reformat in the fuel cell. Several options for the acceleration of the cold start were investigated. Both a simple λ-control strategy and the reactive heat-up of the HTS by (partial) oxidation of the reformat with injected air reduce the cold start time significantly. With these measures a hydrogen-rich reformat with acceptable CO-concentration is available within two minutes. Moreover, the cold start time can be further reduced, if the HTS is heated up electrically to their ignition temperature at the beginning of the cold start. Thereby the CO-conversion in the HTS already starts in the first minute and, depending on the availability of steam for the feed stream, a cold start of the reforming unit below one minute seems to be possible.