Catalytic Flow Reversal Reactor Research Articles

Adaptive temperature control of a reverse flow process by using reinforcement learning approach

This work focuses on the design of an optimal adaptive control system for temperature regulation in a catalytic flow reversal reactor (CFRR), utilizing a reinforcement learning (RL) approach. First, a policy iteration algorithm is introduced to learn the optimal solution of the associated linear-quadratic control problem online. It should be mentioned that this approach is not reliant on the internal dynamics of the CFRR system, which is a complex process and is most effectively modeled using Partial Differential Equations (PDEs). The convergence of the iteration algorithm is established, assuming the initial policy is stabilizing. Additionally, a second algorithm is presented to enhance the implementability of the reinforcement learning algorithm from a practical perspective. Numerical simulations are carried out to illustrate the efficacy of the proposed algorithm.

Error-feedback temperature regulation for a reverse flow reactor driven by a distributed parameter exosystem

This work is devoted to solve the state and error-feedback control problems for a catalytic reverse flow reactor (CFRR), which is modeled by nonlinear partial differential equations (PDEs). These two regulation problems will be solved based on the linearized infinite-dimensional representation. The objective is to track a desired output reference under the presence of disturbances. Both the reference trajectory and the disturbance profiles are generated by a distributed parameter exosystem. First, a state feedback stabilizing regulator is designed which drives the process output to a reference trajectory. The second main aim is to develop a dynamical controller that uses the tracking error as an input. Furthermore, it has been demonstrated that the closed-loop plant is exponentially stable and the tracking error asymptotically goes to zero. The developed regulators are evaluated through numerical simulations for the case study of methane combustion.

Catalyst optimization in a catalytic flow reversal reactor for lean methane combustion

This paper describes a detailed catalyst configuration study for a catalytic flow reversal reactor for lean methane combustion using computational modelling. The design is based on the use of a platinum group metals catalyst in the form of a washcoated monolith. A small-scale pilot plant reactor is used as the basis for the study. The computational model is based on the fundamental conservation equations of mass and energy that are solved using the finite element method with commercial software. Extensive model validation is performed using experimental data previously obtained on the pilot plant system. It is found that catalyst activity and length of the reaction section play key roles in the stable operation and performance of the system. For methane feed concentrations above about 0.5% by volume, the catalyst activity plays a relatively small role. For concentrations down to about 0.2% both the catalyst activity and reactor length become increasingly important. The complete transient history of the reactor also plays an important role in determining whether or not a stable stationary state can be achieved for a given set of inlet conditions. Computational modelling is shown to be an extremely valuable tool for the design of the reactor system.

The Efficiency of Pd Addition and Sr Substitution on La1−xSrxMnO3 to Remove Ventilation Air Methane in a Catalytic Flow Reversal Reactor

Ventilation air methane (VAM) is the main cause of greenhouse gas emissions in coal mining. Catalytic flow reverse reactor (CFRR) is widely used in VAM to mitigate methane emissions. In this study, palladium (Pd) and La1−xSrxMnO3 were used as catalysts in a CFRR. Different types of catalysts were prepared by loading La0.8Sr0.2MnO3, La0.9Sr0.1MnO3, and 0.1%Pd-La0.9Sr0.1MnO3 on a cordierite honeycomb reactor coated with γ-Al2O3 to compare their performances. In addition, this study compared the performance of the three catalysts in an 800 °C reactor based on different methane inlet concentrations, inlet speeds, and conversion times. The results showed: (1) 0.1% addition of Pd increased methane conversion. (2) La0.8Sr0.2MnO3 had higher efficiency at lower methane inlet concentrations, whereas La0.9Sr0.1MnO3 was more efficient at higher methane concentrations. This study demonstrates that a higher Sr loading is worth implementing only when the methane concentration of VAM is lower than 0.6%. (3) To achieve a higher methane conversion efficiency, the inlet velocity of methane should also be considered.

Optimal output-feedback temperature regulation of a catalytic reverse flow reactor PDEs model

In this work, control and estimation problems have been studied for a catalytic reversal flow reactor (CFRR). A stabilizing compensator is developed on the basis of the infinite-dimensional state-space description of the CFRR. Linear–quadratic technique is used to design both an optimal state-feedback controller and an output injection operator. The later is developed based on the duality fact between regulation and estimation. Indeed, the output injection operator is the adjoint of the feedback control operator of the dual process. The developed compensator is tested numerically for the catalytic combustion of lean methane emissions.

Dinamika Reaktor Katalitik Aliran Bolak-Balik untuk Oksidasi Emisi Gas Metana

The performance of a reverse flow reactor (RFR) is strongly influenced by the switching time used to alternate the flow direction. This research aimed to study the effect of the switching time on reactor dynamics including the heat propagation along the bed and reaction rate in the oxidation methane for low concentration using catalytic reverse flow reactor. The experimental results show that the reverse flow operating mode can influence heat propagation along the reactor and reaction conversion. Based on the three switching times was tested, the temperature dynamics formed were in the sliding regime. The effect of switching time on RFR on conversion is very significant. When compared to steady operation, RFR operation provides the highest conversion at smaller switching times. At large switching times, the effect of reversal of flow direction becomes less dominant and reactor behavior approaches steady state.

Lean VOC-Air Mixtures Catalytic Treatment: Cost-Benefit Analysis of Competing Technologies

Various processing routes are available for the treatment of lean VOC-air mixtures, and a cost-benefit analysis is the tool we propose to identify the most suitable technology. Two systems have been compared in this paper, namely a “traditional” plant, with a catalytic fixed-bed reactor with a heat exchanger for heat recovery purposes, and a “non-traditional” plant, with a catalytic reverse-flow reactor, where regenerative heat recovery may be achieved thanks to the periodical reversal of the flow direction. To be useful for decisions-making, the cost-benefit analysis must be coupled to the reliability, or availability, analysis of the plant. Integrated Dynamic Decision Analysis is used for this purpose as it allows obtaining the full set of possible sequences of events that could result in plant unavailability, and, for each of them, the probability of occurrence is calculated. Benefits are thus expressed in terms of out-of-services times, that have to be minimized, while the costs are expressed in terms of extra-cost for maintenance activities and recovery actions. These variable costs must be considered together with the capital (fixed) cost required for building the plant. Results evidenced the pros and cons of the two plants. The “traditional” plant ensures a higher continuity of services, but also higher operational costs. The reverse-flow reactor-based plant exhibits lower operational costs, but a higher number of protection levels are needed to obtain a similar level of out-of-service. The quantification of risks and benefits allows the stakeholders to deal with a complete picture of the behavior of the plants, fostering a more effective decision-making process. With reference to the case under study and the relevant operational conditions, the regenerative system was demonstrated to be more suitable to treat lean mixtures: in terms of time losses following potential failures the two technologies are comparable (Fixed bed plant: 0.35 h/year and Reverse flow plant: 0.56 h/year), while in terms of operational costs, despite its higher complexity, the regenerative system shows lower costs (1200 €/year).

Demonstration of mitigation and utilization of ventilation air methane in a pilot scale catalytic reverse flow reactor

The mitigation and utilization of ventilation air methane was demonstrated in a pilot scale catalytic reverse flow reactor. A kind of non-noble metal oxide catalyst of 1.8m3 was loaded and lean methane with a concentration of 0.2–1.0vol% and a maximum feed flow rate of 800m3/h was processed. The schemes of reactor control and heat recovery, viz., a simple logic-based controller plus hot gas withdrawal from reactor center, as proposed previously by simulation, were verified in this pilot scale reactor. The results prove that the autoregulative time to switch the gas flow direction will drop quickly to zero if a large amount of hot gas is withdrawn from the reactor by using the traditional method. The switching time has a great influence on the heat recovery efficiency, whereas the amount of hot gas removed out of the reactor impacts significantly on the reactor stability. All these experimental observations are in line with the simulation results. The long term operation proves the feasibility of hot gas withdrawal with a heat recovery efficiency of about 56% and the reliable performances of the non-noble metal catalyst in lean methane oxidation with a methane conversion over 90%. These results prove that the catalytic reverse flow reactor and control schemes used in this work are quite effective in the mitigation and utilization of lean methane.

Modelling of the energy use of ventilation air from the mines

In this paper an attempt is a comprehensive presentation of the problem of methane emissions from ventilation air from the mines to the atmosphere and possible solutions are suggested. Methane is released during excavation work in coal mines is a big problem in terms of safety and environmental protection. At the same time, it is a further potential source of energy that has been not yet used on a larger scale [1]. In order to properly identify ventilation air methane as an energy source will be presented its properties and possible complications due to the nature of this type fuel. A very important part will also determine the methane potential from ventilation air in Poland [2]. The work provides an overview of available technology for methane utilization from ventilation air as a fuel. Important from the point of view of the rest of the work is presentation of catalytic flow-reversal reactor technology created in Poland. Main objective of the topic is the development and modeling of heat recovery system cooperating with the IUMK-1000 installation [3]. The premise is the electricity production and also heat for central heating when it is technically feasible and justified in economic terms. Different concepts of heat recovery are modeled by the IPSE-Pro software. Then an analysis of the efficiency and performance of the proposed system is carried out. Based on the results, an individual concepts cycle works were analyzed and assessed and the best solutions possible for implementation on an industrial scale is selected.

Experimental Investigations of Cold Flow Mass Distribution and Pressure Drop Characteristics in a Structured Honeycomb Monolith Bed

The thermal flow reversal reactor (TFRR) and catalytic flow reversal reactor (CFRR) can utilize the ventilation air methane (VAM) from coal mines effectively. The initial cold feed flow mass distribution uniformity in the monolith oxidation bed, the critical part of both reactors, has a great influence on the stability of methane oxidation process and conversation rate. So the emphases are put on the experimental investigations of the cold flow mechanics in the monolith bed based on a simplified reactor test rig. Firstly, the flow resistance coefficients of the monolith bed were calculated, and then the flow resistance mathematical model was built. It was found that the flow mass distribution uniformity was affected by the pressure drop distribution in the monolith bed, and obviously decreased with increasing inlet velocity. The pressure drop distribution was analyzed through a modified momentum equation. The total pressure loss in the lower header was evidently higher than that in the upper header or monolith bed. Additionally, the local losses at the inlet and outlet of the monolith bed were small, so they could be ignored. Finally, the formula of total pressure losses under different flow conditions was established based on the simplified reactor test rig.

An efficient computational scheme for building operating maps for a flow reversal reactor

This paper describes the use of a two dimensional heterogeneous computational model for the catalytic reverse flow reactor for the combustion of lean methane mixtures. A uniform design method is used to generate a table of 41 operating points. The results from these points were used to generate a simple empirical model for the reactor at a single specified value of the superficial gas velocity. Stability maps that show the envelope for operation that satisfy a minimum level of conversion and a maximum operating temperature are generated using the empirical model. These maps delineate all possible combinations of methane concentration, switch time and mass extraction rate that are capable of giving stable operating conditions that meet these two criteria. The model is potentially useful in model predictive control of the reactor.

Experimental demonstration and modeling of an adsorption-enhanced reverse flow reactor for the catalytic combustion of coal mine ventilation air methane

Ventilation air methane is a major contributor to the carbon footprint of the coal mining industry. This contribution can be mitigated by combustion of methane to carbon dioxide. The use of efficient combustion devices, such as catalytic reverse flow reactors, can improve the economy of the process. However, the high water content of the ventilation air can inhibit catalysts (such as palladium) used in this process. The overcome this issue a novel reverse flow reactor with integrated separation, capable of adsorbing water from the feed before reaching the catalyst, is studied. The adsorbent is regenerated in situ thanks to the characteristic thermal pattern of reverse flow reactors. The application of this reactor design to the combustion of ventilation air methane has been demonstrated in a bench-scale device, operated at 0.15m/s (n.t.p.) superficial velocity and different methane concentrations (1800–5400ppm) and switching times (100–600s). A mathematical model for this reactor has been proposed, the water adsorption parameters have been determined experimentally, and the model has been validated by comparison to bench-scale experimental results.

Coal mine ventilation air methane combustion in a catalytic reverse flow reactor: Influence of emission humidity

The role of the humidity content on the performance of catalytic reverse flow reactors (RFRs) for the abatement of methane emissions from coal mines is studied in this manuscript. It has been demonstrated that this technique is very useful for the abatement, and even upgrading, of these emissions. However, the effect of humidity on the reactor performance has not been addressed yet, in spite of being well known that water is an inhibitor in catalytic combustion.Experimental studies in a lab-scale isothermal fixed bed reactor demonstrated that water decreases the activity of a palladium on alumina catalyst for the combustion of methane, but this inhibition is entirely reversible, results fitting well to a Langmuir–Hinshelwood kinetic model. Then, the influence of water was studied in a bench-scale RFR operating at near adiabatic conditions at different switching times (100–600s) and methane feed concentrations (2700–7200ppm). Finally, a mathematical model for the reverse flow reactor, including the kinetic model with water inhibition, has been validated using the experimental results. This model is of key importance for designing this type of reactors for the treatment of mine ventilation emissions.

Steady and Transient Characteristics of Catalytic Flow Reverse Reactor Integrated with Central Heat Exchanger

A Pd/Al2O3 monolith catalyst was prepared by wet impregnation. Its excellent performance was demonstrated in the removal of lean methane. After 1000 h of operation, a higher catalytic activity can be sustained. On this basis, a pilot-scale catalytic flow reversal reactor (CFRR) coupled with a central heat exchanger was designed for catalytic removal of ventilation air methane. Experiments showed high methane destruction ratios were achieved at elevated reactor temperatures maintained by reverse flow operations. Transient and steady characteristics of the reactor were also studied experimentally and analyzed under various operating parameters involving methane concentration, cycle period, and heat transfer flux. The coupling of central heat exchanger caused the complex quasi-periodic states and the significant divergences on the reactor behaviors compared with the results in the literature. To further verify the robustness of the heat recovery method, the experimental unit was operated in a long-time course. The lean methane can be efficiently eliminated and utilized.

Simulation of a Reverse Flow Reactor for the Catalytic Combustion of Lean Methane Emissions

This work is focused on the performance prediction of pilot scale catalytic reverse flow reactors used for combustion of lean methane–air mixtures. An unsteady one-dimensional heterogeneous model for the reactor was established to account for the influence of the reactor wall on the heat transfer. Results of the simulation indicate that feed concentration, switch time and compensatory temperature impose important influence on the performance of the reactor. The amount of the heat extracted from the mid-section of the reactor can be optimized via adjusting the parameters mentioned above. At the optimal operating conditions, i.e. switching time of 400s, feed concentration of 1% (by volume), and insulation layer temperature of 343K, the axial temperature of the reactor revealed a comparatively symmetrical “saddle” distribution, indicating a favorable operating status of the catalytic reverse flow reactor.

A logic-based controller for the mitigation of ventilation air methane in a catalytic flow reversal reactor

The control system of a catalytic flow reversal reactor (CFRR) for the mitigation of ventilation air methane was investigated. A one-dimensional heterogeneous model with a logic-based controller was applied to simulate the CFRR. The simulation results indicated that the controller developed in this work performs well under normal conditions. Air dilution and auxiliary methane injection are effective to avoid the catalyst overheating and reaction extinction caused by prolonged rich and lean feed conditions, respectively. In contrast, the reactor is prone to lose control by adjusting the switching time solely. Air dilution exhibits the effects of two contradictory aspects on the operation of CFRR, i.e., cooling the bed and accumulating heat, though the former is in general more prominent. Lowering the reference temperature for flow reversal can decrease the bed temperature and benefit stable operation under rich methane feed condition.

Study on the Coal Mine Ventilation Air Methane Utilization Technologies Based on Flow-Reversal Oxidation Principle

There is a huge amount of coal mine ventilation air methane emitted into the atmosphere directly each year in china, not only causes a lot of energy was wasted, but also do severe harm to the protection of the environment. The Utilization Technologies of coal mine ventilation air methane (VAM) are receiving more and more attention from people, Aiming at the domestic and international development status of VAM utilization, Thermal flow reversal reactor (TFRR) and catalytic flow reversal reactor (CFRR) are introduced, as two kind of flow-reversal oxidation technology which are the most popular and used widely. The economic and applicability about service life, total cost, space and performance of device are comparative analyzed, and illustrate the trends about the technology of flow-reversal oxidation of VAM from two aspects: to solve the problem of running stability well and improve its work efficiency reasonably. Finally, this paper outlines the future prospect for the development of this technology.

Reactors Used for Catalytic Combustion of Methane

This paper introduces several kinds of reactors for methane catalytic combustion. Furthermore, we briefly summarize and compare advantages, disadvantages, research progresses and experimental applications of fixed-bed reactor, catalytic fluidized-bed reactor, catalytic reverse flow reactor, micro-channel reactor and catalytic membrane reactor for methane catalytic combustion.

Homogeneous Combustion of Fuel Ultra-Lean Methane–Air Mixtures: Experimental Study and Simplified Reaction Mechanism

The use of ventilation air methane (VAM) has attracted more and more attention in recent years. The experimental investigation on homogeneous combustion of fuel ultra-lean methane–air mixtures is carried out in reactors packed with and without a monolith. The experimental results show that the methane oxidation follows a consecutive reaction scheme. In the reaction process, although a little CH4 may be directly oxidized to CO2 at low temperatures, most CH4 is oxidized to CO as the intermediate product and then further oxidized to CO2 at high temperatures. The present experimental results also show that the presence of a monolith has an obvious effect on the combustion of methane. The methane combustion can be enhanced by both expanding the specific surface area and decreasing the diameter of the monolith channel. However, an extremely small diameter may lead to the quenching of combustion. Moreover, it is found that the effect of homogeneous combustion cannot be neglected for the catalytic flow reversal reactor (CFRR) at high temperatures. On the basis of the analysis of the present experimental data, a simplified two-step consecutive mechanism is developed and the kinetic parameters are determined to describe the methane combustion in an empty reactor and a reactor packed with a monolith. The present research is helpful for understanding the reaction mechanism for VAM use.

Enhanced model predictive control of a catalytic flow reversal reactor

AbstractThe combustion of lean methane air mixtures in a catalytic flow reversal reactor (CFRR) is studied using a two dimensional heterogeneous continuum model, based on mole and energy balance equations for the solid (the inert and catalytic sections of the reactor) and the fluid phases. Following a design of experiments (DOE), many simulations were carried out to investigate the reactor performance. The results show the impact on the methane conversion and the maximum temperature in the reactor of key process parameters such as the methane inlet concentration, the superficial gas velocity, the switching time, and the mass extraction rate. A simple empirical model is deduced to predict the maximum temperature and conversion of methane in the reactor at stationary state. This model is combined with a model predictive control (MPC) strategy in the form of a terminal constraint to improve the controller performance. Results show that the control of the reactor is improved.