Sorption Enhanced Steam Methane Reforming Research Articles

Sorption-enhanced steam-methane reforming: CaO–CaCO3 capture technology

Calcium oxide (CaO) has been investigated in the context of CO2 capture. In its application for the sorption-enhanced steammethane reforming process (SE-SMR), CO2 is captured in a sorption mode through the formation of CaCO3, at which stage, the conversion of CH4 to H2 is also enhanced. Subsequently, the CO2 is released in a separate desorption mode where the CaCO3 is calcined to CaO. In a combined system modeling and experimental approach a sweet-spot in operational conditions has been determined in terms of adsorption–reaction and desorption temperature and pressure. Additionally the required performance in terms of cyclic capacity has been determined in relation to system efficiency. Long term cyclic capacity under sweet-spot conditions has been demonstrated in a lab-scale experiment in excess of 200 loading cycles, with stabilization of cyclic capacity occurred after 100 cycles, and above the required minimum of 15% of the thermodynamic capacity. Increasing the adsorption temperature above 600 ∘C reactivated the CaO–CaCO3 sorbent system.

Sorption Enhanced Steam Methane Reforming Process Performance and Bubbling Fluidized Bed Reactor Design Analysis by Use of a Two-Fluid Model

This paper discusses simulations of reactive flows in a two-dimensional cylindrical bubbling fluidized bed reactor by using an Eulerian modeling approach. The study is intended to elucidate some aspects of high relevance for the development of novel concepts in the area of hydrogen production by means of steam methane reforming (SMR). The work is initiated with a practical model validation of reactive gas−solid flows with simulations of laboratory-scale experiments of the ozone decomposition reaction. The predicted outlet concentrations for various fluidization velocities are in very good agreement with reported experimental data. Further, investigations of sorption enhanced steam methane reforming (SE-SMR) in bubbling fluidized beds are conducted with lithium zirconate as the CO2 adsorbent. As long as extensive gas mixing is avoided, wide reactors are the most favorable choice for industrial applications since variations in bed diameter have a minor influence on the outlet hydrogen concentration. Running...

Development of novel two-interconnected fluidized bed system

Two-interconnected fluidized bed systems are widely used in various processes such as Fisher-Tropsch, hot gas desulfurization, CO2 capture-regeneration with dry sorbent, chemical-looping combustion, sorption-enhanced steam methane reforming, chemical-looping hydrogen generation system, and so on. However, conventional two-interconnected fluidized bed systems are very complex, large, and difficult to operate because most of these systems require a riser and/or pneumatic transport line for solid conveying and loopseals or seal-pots for gas sealing, recirculation of solids to the riser, and maintaining of pressure balance. To solve these problems, a novel two-interconnected fluidized bed system has been developed. This system has two bubbling beds, solid injection nozzles, solid conveying lines, and downcomers. In this study, the effects of operating variables on solid circulation rate and gas leakage between two beds have been investigated in a cold mode two-interconnected fluidized bed system. The solid circulation rate increased as the hole diameter on the injection nozzle, the diameter of the injection nozzle, the solid height above the holes, and the number of holes on the injection nozzle increased. The gas leakage between the beds was negligible. Moreover, long-term operation of continuous solid circulation up to 60 hours was performed to check the feasibility of stable operation. The pressure drop profiles in the system loop were maintained steadily and solid circulation was smooth and stable.

Hydrogen production through sorption-enhanced steam methane reforming and membrane technology: A review

Abstract With the rapid development of industry, more and more waste gases are emitted into the atmosphere. In terms of total air emissions, CO 2 is emitted in the greatest amount, accounting for 99 wt% of the total air emissions, therefore contributing to global warming, the so-called “Greenhouse Effect”. The recovery and disposal of CO 2 from flue gas is currently the object of great international interest. Most of the CO 2 comes from the combustion of fossil fuels in power generation, industrial boilers, residential and commercial heating, and transportation sectors. Consequently, in the last years’ interest in hydrogen as an energy carrier has significantly increased both for vehicle fuelling and stationary energy production from fuel cells. The benefits of a hydrogen energy policy are the reduction of the greenhouse effect, principally due to the centralization of the emission sources. Moreover, an improvement to the environmental benefits can be achieved if hydrogen is produced from renewable sources, as biomass. The present paper provides an overview of the steam methane reforming (SMR) process and methodologies for performances improvement such as hydrogen removal, by selective permeation through a membrane or simultaneous reaction of the targeted molecule with a chemical acceptor, and equilibrium shift by the addition of a CO 2 acceptor to the reactor. In particular, attention was focused on the sorption - enhanced steam methane reforming (SE-SMR) process in which sorbents are added in order to enhance the reactions and realize in situ CO 2 separation. The major operating parameters of SE-SMR are described by the authors in order to project and then realize the innovative carbonation reactor developed in previous studies.

Ni catalysts for sorption enhanced steam methane reforming

Sorption enhanced steam methane reforming (SESMR) is a process for H2 production at low temperatures. The process requires an active and stable catalyst. For this purpose, a series of hydrotalcite-like catalysts (HT) with different Ni loadings have been prepared by a co-precipitation technique and compared with catalysts prepared by conventional incipient wetness impregnation. The co-precipitation route resulted in a stronger interaction between the support and nickel than the incipient wetness route. As a result, smaller Ni crystals with excellent stability and high activity for steam reforming of methane were obtained, even at high loadings. 40 wt% Ni/HT was found to be the most promising candidate for application in SESMR.

Modeling of Multiple Cycles for Sorption-Enhanced Steam Methane Reforming and Sorbent Regeneration in Fixed Bed Reactor

Mathematical models of multiple cycles for sorption-enhanced steam methane reforming and Ca-based sorbent regeneration in a fixed bed reactor are developed. Empirical correlations are used to describe steam methane reforming, the water−gas shift, and CO2 capture kinetics. The processes of multiple carbonation/calcination cycles of a Ca-based sorbent are taken into account to describe the sorption-enhanced hydrogen production process with the simultaneous removal of carbon dioxide by a Ca-based sorbent. The mathematical models are validated through comparing simulated results with experimental data. The model results qualitatively agree with experimental data. The effect of reactivity decay of dolomite, CaO/Ca12Al14O33, and limestone sorbents on sorption-enhanced hydrogen production and sorbent regeneration processes was studied through numerical simulation. The simulated results indicated that the operation time of producing high-purity hydrogen (that is defined as the time for the start of breakthrough, ...

Numerical Investigation of Sorption Enhanced Steam Methane Reforming Using Li2ZrO3 as CO2-acceptor

A fixed-bed reactor for the production of hydrogen via sorption-enhanced steam methane reforming (SE-SMR) is investigated. Pseudo-homogeneous and heterogeneous models have been formulated and used to simulate the process performance. The capture kinetics of CO2 on Li2ZrO3 have been characterized experimentally for determination of a kinetic model that is used in the simulations of SE-SMR. The simulations show that hydrogen with purities of >87 mol % can be produced at a temperature of 848 K and a total pressure of 10 bar, but with long reactors and low production capacities. To make SE-SMR an industrial alternative, materials with better capture properties are required.

High-temperature attrition of sorbents and a catalyst for sorption-enhanced steam methane reforming in a fluidized bed environment

Mechanical degradation of the solid particles used in sorption-enhanced steam methane reforming (SE-SMR) was investigated in a gas jet attrition apparatus. The performance of a dolomite, a limestone and a commercial reforming catalyst were compared based on the air jet attrition index (AJI). The dolomite showed the poorest resistance to attrition, likely due to the extra pore volume caused by calcination of MgCO 3. The degree of loss of fines from the catalyst was significant, pointing to the need to develop catalysts suited to fluidized bed operation. Co-fluidization of the harder catalyst and the dolomite did not lead to additional attrition of the dolomite.

Process design simulation of H2production by sorption enhanced steam methane reforming: evaluation of potential CO2acceptors

A concept for pure H2 production with CO2 capture by sorption enhanced steam methane reforming (SESMR) has been investigated. Conventional steam reforming with CO2 capture has been used as a base case for comparison. SESMR resulted in competitive thermal efficiencies, which were highly dependent on the CO2 acceptor material. Thus, CaO and other more novel solid acceptors such as Li2ZrO3, K-doped Li2ZrO3, Na2ZrO3 and Li4SiO4 were screened in terms of thermodynamics, kinetics and stability. It was concluded that higher H2 yields and efficiencies can be obtained for the acceptors that have good ability for removing CO2 at low partial pressures. The best efficiencies were obtained using CaO as acceptor due to its more favourable thermodynamics and high reaction rates; however, the stability of CaO has to be improved. On the other hand, Na2ZrO3 is a promising alternative due to the good kinetics for CO2 removal and the stability.

Continuous Production of Hydrogen from Sorption-Enhanced Steam Methane Reforming in Two Parallel Fixed-Bed Reactors Operated in a Cyclic Manner

Hydrogen with purity higher than 90% was produced continuously by sorption-enhanced steam methane reforming reactions in two parallel fixed-bed reactors operated in a cyclic manner. The process involved sorption-enhanced steam methane reforming reactions and a sorbent regeneration reaction. First, through addition of a CO2 sorbent into a reforming reactor, the reactions of reforming, water−gas shift, and CO2 sorption were combined, and more CH4 was expected to convert H2 in one reactor. Second, regeneration of the sorbent was carried out in the other reactor. The hydrogen production and sorbent regeneration processes were carried out simultaneously in the two fixed-bed reactors, operated in a cyclic manner by switching a methane/steam feed and an Ar-containing feed between the two reactors at a fixed feed switchover time. The critical value of the feed switchover time for achieving the production of higher concentrations of hydrogen was investigated and analyzed.

Modeling of Sorption-Enhanced Steam Reforming in a Dual Fluidized Bubbling Bed Reactor

This paper highlights the use of a dual fluidized bed reactor system for producing hydrogen by sorption-enhanced steam methane reforming. Hydrogen concentrations of >98% are predicted for temperatures of ∼600 °C and a superficial gas velocity of 0.1 m/s, using a simple two-phase bubbling bed model for the reformer. The kinetics of the steam methane reforming and water-gas shift reactions are based on literature values, whereas experimentally derived carbonation kinetics are used for the carbonation of a dolomite. It is shown that the reformer temperature should not be <540 °C or >630 °C for carbon capture efficiencies to exceed 90%. Operating at relatively high solids circulation rates to reduce the need for fresh sorbent is predicted to give higher system efficiencies than for the case where fresh solid is added. This finding is attributed to the additional energy required to decompose both CaCO3 and MgCO3 in fresh dolomite.

Hydrogen production from steam methane reforming coupled with in situ CO 2 capture: Conceptual parametric study

The work deals with fundamental analysis of the sorption-enhanced steam methane reforming (SE-SMR) process in which the simultaneous removal of carbon dioxide by hydrotalcite-based chemisorbent is coupled. A two-section reactor model is developed to describe the SE-SMR reactor, decoupling the complexity in process analysis. The model defines two subsequent sections in the reactor: an equilibrium conversion section (upstream) and an adsorption reforming section (downstream). The material balance relationship in the equilibrium conversion section is directly determined by thermodynamic equilibrium calculation, providing an equilibrated atmosphere to the next section. The adsorption reforming section is described using an isothermal multi-component dynamic model into which the SMR reactions and the high-temperature CO 2 adsorption are embedded. The multiple requirements (including H 2 purity, H 2 productivity, CH 4 conversion enhancement, and carbon oxides concentrations) are taken into account simultaneously so as to analyze and define feasible operation window for producing high-purity hydrogen with ppm-level CO impurity. The performances of the reactors with different dimensions (laboratory-scale and pilot-scale) are explored, highlighting the importance of operation parameter control to the process feasibility.

Subsection-Controlling Strategy for Improving Sorption-Enhanced Reaction Process

The subsection-controlling strategy was applied to the design of the adsorptive reactor to improve the sorption-enhanced steam–methane reforming (SMR), by using subsection-packing ratio of adsorbent and catalyst, and subsection-controlling wall temperature. In the case of the subsection-controlling wall temperature, there is a lower operating temperature zone at the outlet of the adsorptive reactor, where the remaining CO and CO2 concentrations in gas stream can be decreased further by the principle of temperature-induced equilibrium shift. The feasibility and effectiveness of the subsection-controlling strategy for improving the sorption-enhanced steam–methane reforming process is analysed by numerical simulation based on literature data. At low operating pressure, in the range 222–445.7 kPa, combined with subsection-controlling strategy [higher temperature, 450–490°C, for subsections I (inlet zone of the adsorptive reactor) and II (middle zone of the adsorptive reactor) and lower temperature, 400–450°C, for subsection III (outlet zone of the adsorptive reactor); lower packing ratio of adsorbent and catalyst for subsections I and III and higher ratio for subsection II] a product gas with hydrogen purity above 85% and traces of CO2 (less than 300 ppm) and CO (less than 30 ppm) can be continuously produced with higher hydrogen productivity by a four-step one-bed (a 6 m long adsorptive reactor) pressure swing sorption-enhanced steam–methane reforming cyclic process, and may be directly used in fuel cell applications.

Alternative generation of H 2, CO and H 2, CO 2 mixtures from steam—carbon dioxide reforming of methane and the water gas shift with permeable (membrane) reactors

Replacing coal and oil with natural gas reduces greenhouse gas emissions without weakening economic development. Sorption enhanced steam methane reforming (SESMR) is an emerging process for an affordable transition towards cleaner energy systems, as it exploits natural gas coupled with in-situ CO2 capture to produce hydrogen. SESMR is performed on a steam reforming catalyst and a sorbent (cyclically regenerated by calcination) or, alternatively and more efficiently, on bi-functional Combined Sorbent-Catalyst Materials (CSCM). A double fluidized bed (reformer and oxyfuel combustor for calcination) with circulation of particulate material is anticipated for continuous SESMR at commercial scale. In this work, a Ni-CaO-mayenite CSCM was investigated in multicycle experimental tests under mild (pure N2, 850 °C) and severe (pure CO2, 925 °C) regeneration conditions, in thermogravimetric analysis for CO2-capture/regeneration and in an automated packed bed test rig for SESMR/calcination: the evolution of Ni and CaO functionalities as functions of cycle number was highlighted, also with the aid of scanning electron microscopy. Moreover, experimental results obtained with the hybrid material, collected under mild regeneration conditions, were used to simulate both CO2 sorption in TGA and packed bed SESMR multicycle tests: a Particle Grain Model (PGM) and an Axial Dispersion Plug Flow Reactor (ADPFR) model were integrated numerically, respectively. The same parameter values needed to characterize the material behaviour allowed a good fitting of both types of multicycle tests, thus demonstrating the possibility to use CO2-capture TGA data as a predictive tool for the CSCM performance in SESMR, provided that the catalytic activity is preserved.

Formaldehyde as an intermediate in the steam reforming of methane

Sorption Enhanced Steam Methane Reforming (SESMR) provides a promising method to produce high purity hydrogen by in-situ CO2 capture. Ni-doped CaO (Ni-CaO) with catalytic and adsorption active sites can effectively improve the hydrogen production in the SESMR process. It is difficult to determine the enhancement mechanism of Ni-CaO in the SESMR simply by the research experiment. In this study, the reaction mechanisms of SESMR promoted by Ni in the presence of CaO were investigated by the density functional theory (DFT) calculations. The reaction pathway was determined by analyzing the activation barriers along the possible reaction pathways in the SESMR reaction. The SESMR reaction promoted by CaO was also studied as a comparison to clarify the catalysis of Ni. The reaction mechanism of SESMR on Ni and Ni-CaO surfaces was also compared. The results show that the SESMR reaction is more prone to follow path CH4 → CH3 → CH2 → CH → CHO → HCOO → CO2. The OH-assisted dissociation assists in the breaking of first C–H bond in CH4. Process CH3 → CH2 → CH is accomplished by direct dissociation in two steps. Next, CHO is spontaneously formed from CH and O. CHO is oxidized to generate HCOO. Finally, the CO2 is formed by the HCOO dehydrogenation path. The presence of Ni atoms causes a change in the reaction rate limiting step of the SESMR reaction from CH dissociation (on CaO surface) to CH3 dissociation (on Ni-CaO surface). Compared with the reaction energy barrier of CH dissociation (3.215 eV), the SESMR reaction of the Ni-CaO surface is easier to occur with lower reaction energy barrier of 2.030 eV. Besides, Ni reduces the adsorption energy of CH4 (-0.106 eV) and H2O (-1.32 eV) as well as increases the adsorption energy of H2 (-0.047 eV). The SMR reaction is easier to occur on the Ni surface than Ni-CaO surface. The DFT calculations determine the possible mechanism of Ni-CaO in SESMR for H2 production.