Coal dust gasification in the filtration combustion mode with syngas production

A new method for the gasification of fine solid fuel was proposed and worked out, by partial oxidation in a flow of gaseous oxidant with filtration of the suspended fuel through an inert porous matrix. In this case, the solid fuel gasification was carrying out similar to the filtration combustion of gases. The gasification of fine solid coal allows one to produce a combustible gas rich in H₂ and CO was studied. A possibility of pulverized coal gasification in a fixed bed reactor with production of gaseous products containing up to 13% by volume of hydrogen and carbon monoxide was shown experimentally.     

The use of inert porous media based reactors for hydrogen production

The present review paper examines the production of hydrogen in inert porous media based reformer by thermal partial oxidation. Here we consider, specifically, the rich combustion of hydrocarbon fuels and the conversion of H₂S to hydrogen. The different technologies to produce hydrogen beside the experimental and numerical work done in this field are presented. The effect of different operating conditions, such as the equivalence ratio, the mass flow rate and the reactant feed temperature are explained. Additionally, design parameters, including the reactor geometry and porous material specifications, are discussed.     

Conversion of hydrocarbons to synthesis gas in a counterflow moving bed filtration combustion reactor

The conversion of hydrocarbons to synthesis gases via partial oxidation in a non-premixed filtration combustion is considered in a continuous reactor wherein filtration medium/inert solid matrix comprises a moving bed of a granular material flowing countercurrently to the gas flow. Similar to the previously considered conversion in a reversed-flow reactor, such embodiment provides a possibility of attaining high combustion temperature due to efficient heat recuperation, while performing the process continuously without transients associated with the flow reverse. In the moving bed process, the flowrate of the granular material becomes an independent control parameter. A thermodynamic assessment of the macrokinetic conversion regimes as dependent on fuel composition and oxidant gas and fuel supply rates and granular solid flowrate is performed under the assumption that the combustion temperature is self-consistent according to thermodynamic equilibrium with the composition of syngas. Calculations for the methane/air-steam and 2-propanol/air-steam conversion are provided as examples. The calculations show that the process provides a possibility to combine in a stationary continuous process a high combustion temperature with low net heat effect and thus, a high chemical efficiency of conversion. The parametric domain for control parameters providing highly efficient conversion is determined.     

Numerical and experimental study of the conversion of methane to hydrogen in a porous media reactor

In this paper, conversion of methane to hydrogen within a porous media reactor was investigated over the fuel-rich equivalence ratio range of 1.5 to 5. Experimental data were taken to validate the computational model and good agreement was established between the two. The characteristics of interest were wave velocity, peak combustion temperature, flame structure, volumetric heat release, wave thickness, and hydrogen yield. The parameters investigated that affect these characteristics included inlet velocity, equivalence ratio, and the thermal conductivity and the specific heat of the porous media. The computational model predicted a peak percentage conversion of methane to hydrogen of approximately 59% while experimental results show a peak of approximately 73%. The model also predicted the experimental trend that conversion efficiency increases as the inlet velocity of the initial fuel-air mixture increases. Species profiles obtained from the computational model showed the signature dual-reforming regimes known as partial oxidation and steam reforming inherent with fuel-rich filtration combustion. The main contribution of this paper is an understanding of the transient nature of the combustion wave for fuel-rich conditions and how the nature of the combustion wave influences conversion efficiency. As the combustion wave progresses, the steam-reforming zone thickness increases, resulting from the constant heat addition to the solid. A thick, high-temperature zone, which promotes steam reforming and is heavily dependent upon the specific heat of the porous media, is preferred to maximize conversion efficiency.     

Enhancing efficiency of hydrocarbons to synthesis gas conversion in a counterflow moving bed filtration combustion reactor

An improvement is considered for the partial oxidation conversion of hydrocarbon gases to synthesis gas in a continuous non-premixed filtration combustion reactor with inert solid granular material flowing countercurrently to the gas flow. The reactor is supplemented with an additional heat exchanger, wherein the second reactant gas is preheated prior to supply to the middle part of the reactor. The composition of the gaseous products self-consistent with the temperature of combustion are assessed using approximation of established thermodynamic equilibrium in the products. The parametric domain for major control parameters, namely oxygen-to-fuel supply ratio, granular solid flowrate, and steam supply rate providing highly efficient conversion is determined. Calculations for the POX conversion of methane and a model biogas composition (50% methane, 40% carbon dioxide, 10% nitrogen) with air and steam are provided as examples. The calculations show that the process gives a possibility to substantially improve energy efficiency and provides a flexibility to control hydrogen yield through steam supply. The process provides a high chemical efficiency of conversion even with air used as an oxidant for conversion of low-caloric gases.     

Analysis of an idealized counter-current microchannel-based reactor to produce hydrogen-rich syngas from methanol

In an effort to investigate the suitability of the concept of portable hydrogen production, we examine numerically the combustion of a very rich methanol-air mixture in a micro-gap assembly consisting of multiple counter-current channels of finite length separated by thin solid conducting walls. Within the mathematical framework of the narrow-channel approximation, the problem can be formulated as a one-dimensional model for a single channel with an extra term representing heat transfer from the hot stream products to the fresh reactants in adjacent channels. We show that the heat recirculation enables superadiabatic temperatures inside the reactor and promotes the oxidation of methanol far beyond the conventional rich limit of flammability. The result is a feasible thermal partial oxidation that produces hydrogen without the need for a catalyst. The paper presents an analysis of the model burner performance with detailed gas-phase kinetics in stationary regimes in terms of operating variables such as the equivalence ratio and the gas inflow velocity, and in terms of physical parameters such as the length of the reformer and the conductivity of the wall material. The idealized microreactor predicts maximum hydrogen yield of the order of 60% at equivalence ratios between 3 and 6.     

Hydrogen production by reforming of liquid hydrocarbons in a membrane reactor for portable power generation—Experimental studies

One of the most promising technologies for lightweight, compact, portable power generation is proton exchange membrane (PEM) fuel cells. PEM fuel cells, however, require a source of pure hydrogen. Steam reforming of hydrocarbons in an integrated membrane reactor has potential to provide pure hydrogen in a compact system. Continuous separation of product hydrogen from the reforming gas mixture is expected to increase the yield of hydrogen significantly as predicted by model simulations. In the laboratory-scale experimental studies reported here steam reforming of liquid hydrocarbon fuels, butane, methanol and Clearlite^® was conducted to produce pure hydrogen in a single step membrane reformer using commercially available Pd–Ag foil membranes and reforming/WGS catalysts. All of the experimental results demonstrated increase in hydrocarbon conversion due to hydrogen separation when compared with the hydrocarbon conversion without any hydrogen separation. Increase in hydrogen recovery was also shown to result in corresponding increase in hydrocarbon conversion in these studies demonstrating the basic concept. The experiments also provided insight into the effect of individual variables such as pressure, temperature, gas space velocity, and steam to carbon ratio. Steam reforming of butane was found to be limited by reaction kinetics for the experimental conditions used: catalysts used, average gas space velocity, and the reactor characteristics of surface area to volume ratio. Steam reforming of methanol in the presence of only WGS catalyst on the other hand indicated that the membrane reactor performance was limited by membrane permeation, especially at lower temperatures and lower feed pressures due to slower reconstitution of CO and H₂ into methane thus maintaining high hydrogen partial pressures in the reacting gas mixture. The limited amount of data collected with steam reforming of Clearlite^® indicated very good match between theoretical predictions and experimental results indicating that the underlying assumption of the simple model of conversion of hydrocarbons to CO and H₂ followed by equilibrium reconstitution to methane appears to be reasonable one.     

Numerical modelling of a three-zone combustion for heavy fuel oil in inert porous media reactor

Numerical model for heavy fuel oil and air mixtures combustion is presented to simulate the behavior of the fuel in an inert porous medium reactor for hydrogen production. Three-zone combustion of oil and petroleum cokes separated by temperature ranges starting from ambient temperature to 560 K, from 560 K to 673 K, and above 673 K, is presented. Hydrogen production is achieved using water gas shift equilibrium reaction on the combustion products at different temperatures. Results show a high enthalpy contribution due to coke combustion formed in the low temperature oxidation reaction, being the most important reaction in relation to its zone size. Simulations increasing filtration velocity (from 0.05 to 0.9 m/s) has a favorable effect on the maximum temperature and the combustion front velocity. The effect of the simplified combustion model lowers computational time, with acceptable results for temperature as well as hydrogen production in contrast to laboratory tests and other software simulation such as COMSOL Multiphysics.     

Low-temperature catalytic partial oxidation of hydrocarbons (C1–C10) for hydrogen production

The catalytic partial oxidation of hydrocarbons to provide hydrogen for fuel cells, mobile or stationary, requires high temperatures (900°C), multireactors and incurs the highest incremental costs for the gasoline fuel processor. New experimental data between 500°C and 600°C, supported by equilibrium calculations, show that hydrogen with low carbon monoxide concentrations can be produced from liquid and gaseous hydrocarbons, thus simplifying the reactor chain. Low sulphur refinery feeds (C₄–C₆, C₄–C₁₀), simulated natural gas (C₁–C₃) and single compounds are used and safety procedures discussed. Results from laboratory reactors with 1 wt% rhodium on mixed oxide catalysts show that hydrogen rates of 43,000 lH₂/h/l reactor (power density 129 kWth/l reactor) are produced with RON=95 feeds. However, the cost and availability of rhodium limit the catalyst rhodium content to 0.1 wt% when 31,100 lH₂/h/l reactor were measured. Optimisation and reactor scale-up for heat management is in progress.     

Modeling study on the production of hydrogen/syngas via partial oxidation using a homogeneous charge compression ignition engine fueled with natural gas

The production of hydrogen and syngas from natural gas using a homogeneous charge compression ignition reforming engine is investigated numerically. The simulation tool used was CHEMKIN 3.7, using the GRI-3 natural gas combustion mechanism. This simulation was conducted on the changes in hydrogen and syngas concentration according to the variations of equivalence ratio, intake temperature, oxygen enrichment, engine speed, initial pressure, and fuel additives with partial oxidation combustion. The simulation results indicate that the hydrogen/syngas yields are strongly dependent on the equivalence ratio with maxima occurring at an optimal equivalence ratio varying with engine speed. The hydrogen/syngas yields increase with increasing intake temperature and oxygen contents in air. The hydrogen/syngas yields also increase with increasing initial pressure, especially at lower temperatures, yet high temperature can suppress the pressure effect. Furthermore, it was found that the hydrogen/syngas yields increase when using fuel additives, especially hydrogen peroxide. Through the parametric screening studies, optimum operating conditions for natural gas partial oxidation reforming are recommended at 3.0 equivalence ratio, 530 K intake temperature, 0.3 oxygen enrichment, 500 rpm engine speed, 1 atm initial pressure, and 7.5% hydrogen peroxide.     

High-temperature electrolysis for large-scale hydrogen and syngas production from nuclear energy – summary of system simulation and economic analyses

A research and development program is under way at the Idaho National Laboratory (INL) to assess the technological and scale-up issues associated with the implementation of solid-oxide electrolysis cell technology for efficient high-temperature hydrogen production from steam. This work is supported by the US Department of Energy, Office of Nuclear Energy, under the Nuclear Hydrogen Initiative. This paper will provide an overview of large-scale system modeling results and economic analyses that have been completed to date. System analysis results have been obtained using the commercial code UniSim, augmented with a custom high-temperature electrolyzer module. Economic analysis results were based on the DOE H2A analysis methodology. The process flow diagrams for the system simulations include an advanced nuclear reactor as a source of high-temperature process heat, a power cycle and a coupled steam electrolysis loop. Several reactor types and power cycles have been considered, over a range of reactor outlet temperatures. Pure steam electrolysis for hydrogen production as well as coelectrolysis for syngas production from steam/carbon dioxide mixtures have both been considered. In addition, the feasibility of coupling the high-temperature electrolysis process to biomass and coal-based synthetic fuels production has been considered. These simulations demonstrate that the addition of supplementary nuclear hydrogen to synthetic fuels production from any carbon source minimizes emissions of carbon dioxide during the production process.     

Experimental quantification and modelling of reaction zones in a cyclic watergas shift reactor

The cyclic watergas shift reactor (CWGSR) is a cyclically operated fixed bed reactor for the production of hydrogen. It is based on the alternating reduction of an iron oxide fixed bed with synthesis gas and its subsequent oxidation with steam. We show experimental data of moving reaction zones in a tubular CWGSR. Based on this data and to help further design of these reactors, we propose a dynamic, one-dimensional model of the reactor. The formulated process model was fitted to experimental data by adjusting only two parameters describing the catalytic activity and the oxygen capacity of the fixed bed. Exemplary simulation results are shown.     

Step-by-step methodology of developing a solar reactor for emission-free generation of hydrogen

This study presents a methodology to develop a solar reactor based on the thermodynamics and kinetics of methane decomposition to produce hydrogen with no emissions. The kinetic parameters were obtained in the literature for two cases; methane laden with carbon particles and methane without carbon particles. Results show that there is significant difference in experimentally obtained and theoretically predicted methane conversion. The paper also presents a parametric study on the effects of temperature, pressure and the influence of inert gas composition, which is fed along with methane, on the thermodynamics of methane decomposition. Results show that there is significant effect of the inert gas presence in the feeding gas mixture on the equilibrium of methane conversion and product gas composition. Results also show that higher conversions are obtained when the carbon particles laden with methane. The step-by-step reactor design methodology for homogenous methane decomposition and the parametric study results presented in this paper can provide a very useful tool in guiding a solar reactor design and optimization of process operating conditions.     

Mathematical modeling of hydrogen production using methanol steam reforming in the coupled membrane reactor when the output materials of the reformer section is used as feed for the combustion section

Hydrogen is one of the most abundant elements on Earth's surface. It is not in nature in its pure form, but it can produce by various methods such as methanol steam reforming, partial oxidation, electrolysis, etc. In the present study, using the mass and energy conservation law, hydrogen production in coupled membrane reactors has been modeled using the methanol steam reforming process using two different methods in the coupled membrane reactor. A separate (fresh) methanol is used as feed for the combustion section in the first method. While in the second method, the reformer reactor's output material is used as feed for the combustion section. After simplifying using the required assumptions, the governing equations solved using the ode45 (shooting method) numerical method using MATLAB software. The results of this study show that the conversion of methanol in the coupled membrane reactor when separate methanol is used as feed in the combustion reactor, while in the same reactor, the output material of the reformer section used as feed in the combustion section, is 92% and 88.5% respectively. In this study, the effect of different parameters on the methanol conversion rate is investigated. Finally, it found that with increasing temperature and pressure and decreasing membrane thickness in coupled membrane reactors, methanol conversion rate increases. The percentage of hydrogen recovery in the two coupled membrane reactors is almost equal to 92%.     

Hydrogen production by reforming of liquid hydrocarbons in a membrane reactor for portable power generation—Model simulations

One of the most promising technologies for lightweight, compact, portable power generation is proton exchange membrane (PEM) fuel cells. PEM fuel cells, however, require a source of pure hydrogen. Steam reforming of hydrocarbons in an integrated membrane reactor has potential to provide pure hydrogen in a compact system. In a membrane reactor process, the thermal energy needed for the endothermic hydrocarbon reforming may be provided by combustion of the membrane reject gas. The energy efficiency of the overall hydrogen generation is maximized by controlling the hydrogen product yield such that the heat value of the membrane reject gas is sufficient to provide all of the heat necessary for the integrated process. Optimization of the system temperature, pressure and operating parameters such as net hydrogen recovery is necessary to realize an efficient integrated membrane reformer suitable for compact portable hydrogen generation. This paper presents results of theoretical model simulations of the integrated membrane reformer concept elucidating the effect of operating parameters on the extent of fuel conversion to hydrogen and hydrogen product yield. Model simulations indicate that the net possible hydrogen product yield is strongly influenced by the efficiency of heat recovery from the combustion of membrane reject gas and from the hot exhaust gases. When butane is used as a fuel, a net hydrogen recovery of 68% of that stoichiometrically possible may be achieved with membrane reformer operation at 600 °C (873 K) temperature and 100 psig (0.791 MPa) pressure provided 90% of available combustion and exhaust gas heat is recovered. Operation at a greater pressure or temperature provides a marginal improvement in the performance whereas operation at a significantly lower temperature or pressure will not be able to achieve the optimal hydrogen yield. Slightly higher, up to 76%, net hydrogen recovery is possible when methanol is used as a fuel due to the lower heat requirement for methanol reforming reaction, with membrane reformer operation at 600 °C (873 K) temperature and 150 psig (1.136 MPa) pressure provided 90% of available combustion and exhaust gas heat is recovered.     

Efficiency of hydrogen production systems using alternative nuclear energy technologies

Nuclear energy can be used as the primary energy source in centralized hydrogen production through high-temperature thermochemical processes, water electrolysis, or high-temperature steam electrolysis. Energy efficiency is important in providing hydrogen economically and in a climate friendly manner. High operating temperatures are needed for more efficient thermochemical and electrochemical hydrogen production using nuclear energy. Therefore, high-temperature reactors, such as the gas-cooled, molten-salt-cooled and liquid-metal-cooled reactor technologies, are the candidates for use in hydrogen production. Several candidate technologies that span the range from well developed to conceptual are compared in our analysis. Among these alternatives, high-temperature steam electrolysis (HTSE) coupled to an advanced gas reactor cooled by supercritical CO₂ (S-CO₂) and equipped with a supercritical CO₂ power conversion cycle has the potential to provide higher energy efficiency at a lower temperature range than the other alternatives.     

Characteristics of a multi-pass membrane reactor to improve hydrogen recovery

Membrane reactors are a potential tool to produce high purity hydrogen on-site but sufferfrom immense losses in hydrogen recovery under reaction conditions. For high-temperature operations, these losses mostly occur due to the presence of lesser permeable gases in the reformate that develop into a concentration polarization barrier around the membrane. Based on our previous findings, a multi-pass design was manifested to alleviate hydrogen losses through the membrane tested with synthetic gas mixtures. The same design is currently employed to establish improvement in hydrogen recovery under reaction conditions. Having a catalyst and membrane integrated into a single unit termed as a membrane reactor, its performance is optimized with varying membrane assembly and catalyst bed configurations. This study shows that a packed bed multi-pass membrane reactor is an optimal design to target high hydrogen recovery. Further, multi-pass membrane reactor design also improves the hydrogen recovery in fluidized bed operations which opens immense scope for future studies.     

Enhancement effect of heat recovery on hydrogen production from catalytic partial oxidation of methane

The effect of heat recovery on hydrogen production from catalytic partial oxidation of methane (CPOM) and its reaction characteristics in a reactor are investigated using numerical simulations. The reactor is featured by a Swiss-roll structure in which a rhodium (Rh) catalyst bed is embedded at the center of the reactor. By recovering the waste heat from the product gas to preheat the reactants, it is found that the combustion, steam reforming and dry reforming of methane in the catalyst bed are enhanced to a great extent. As a result, the methane conversion and hydrogen yield are improved more than 10%. Considering the operation conditions, a high performance of hydrogen production from CPOM can be achieved if the number of turns in the reactor is increased or the gas hourly space velocity (GHSV) of the reactants in the catalyst bed is lower. However, with the condition of heat recovery, the flow direction of the reactants in the reactor almost plays no part in affecting the performance of CPOM. In summary, the predictions reveal that the reactor with a Swiss-roll structure can be applied for implementing CPOM with high yield of hydrogen.     

Upgrading of oil residues by hydrogen production: A preliminary experimental investigation

Oil residues can be upgraded by converting them by partial oxidation into gaseous products, namely hydrogen which is acceptable as a clean fuel gas. As an initial stage in this work, this paper is concerned primarily with the non-catalytic partial oxidation of pure hydrocarbons. The technical feasibility of hydrogen production using an n-hexadecane/air system is considered. The yield of hydrogen as well as the H₂:CO ratio are experimentally determined for different operating conditions.