横火焰玻璃窑炉燃烧空间流动与传热的数值模拟

对横火焰玻璃窑炉燃烧空间内的流动、燃烧及辐射传热等过程进行了数值模拟研究,建立了玻璃窑炉燃烧空间内的综合数学模型,给出了诸控制方程的统一的数值解法,得到了炉内燃烧空间的速度场、温度场、组分浓度分布及燃烧空间向玻璃液面传递的热流分布。     

Efficient operation of autothermal microchannel reactors for the production of hydrogen by steam methane reforming

Efficient conversion of methane to hydrogen has emerged as a significant challenge to realizing fuel cell-based energy systems. Autothermal microchannel reactors, coupling of exothermic and endothermic reactions in parallel channels, have become one of the most promising technologies in the field of hydrogen production. Such reactors were utilized as an intensified design for conducting the endothermic steam methane reforming reaction. The energy required by the endothermic process is supplied directly through the separating plates of the reactor structure from the exothermic process occurring on the opposing side. Optimal design problems associated with transport phenomena in such an autothermal system were analyzed. Various methods for designing and operating autothermal reactors employed in steam methane reforming were discussed. Computational fluid dynamics simulations were performed to identify the underlying principles of process intensification, and to delineate several design and operational features of the intensified reforming process. The results indicated that the autothermal reactor is preferable to be thermally conductive to ensure its structural integrity and maximum operating regime. However, the thermal properties of the reactor structure are not essential due to efficient heat transfer existing between endothermic and exothermic process streams. A reactor design which minimizes the mass transfer resistance is highly required, and the channel dimension is of critical importance. Furthermore, the challenges presented by the efficient operation of the autothermal system were identified, along with demonstrating the implementation of transport management in order to improve overall reactor performance and to mitigate extreme temperature excursions.     

Techno-economic analysis of H2 production processes using fluidized bed heat exchangers with steam reforming – Part 1: Oxygen carrier aided combustion

This work presents the techno-economic assessment for a new process where a fluidized bed heat exchanger (FBHE) is used as heat source for steam reforming in a hydrogen production plant. This suggested process configuration is compared with a reference case representing a conventional steam methane reforming (SMR) large-scale hydrogen production plant. The use of a FBHE as a heat source for the endothermic reforming is an advantage because of the high heat transfer coefficient to the reformer tubes. The suggested process configuration utilizes oxygen carrier particles as bed material and a bubbling fluidized bed reactor with immersed reformer tubes to ensure sufficient heat production for the reforming and improved heat transfer to the reformer tubes compared a conventional plant. The results include a comparison of hydrogen production efficiency and levelized production costs (LCOH) of the two plants where the production efficiency is more than 11% higher and the LCOH is more than 7% lower for the suggested process configuration.     

Analysis of chemical-reaction-coupled mass and heat transport phenomena in a methane reformer duct for PEMFCs

Mass, heat and momentum transport processes are coupled with catalytic chemical reactions in a methane steam reforming duct. It is often found that endothermic and exothermic reactions in the ducts are strongly integrated by heat transfer from adjacent catalytic combustion ducts. In this paper, a three-dimensional calculation method is developed to simulate and analyze reforming reactions of methane, and the effects on various transport processes in a steam reforming duct. The reformer conditions such as mass balances associated with the reforming reactions and gas permeation to/from the porous catalyst reforming layer are applied in the analysis. The predicted results are presented and discussed for a composite duct consisting of a porous catalyst reaction layer, the fuel gas flow duct and solid layers. Parametric studies are conducted to reveal the importance of reformer designs and operating conditions. The results show that the variables, such as porous layer configuration, temperature and catalyst loading, have significant effects on the transport processes and reformer performance.     

Chemical reactions in a solar furnace 2: Direct heating of a vertical reactor in an insulated receiver. Experiments and computer simulations

The performance of a solar chemical heat pipe was studied using CO₂ reforming of methane as the endothermic reaction. A directly heated vertical reactor, packed with a rhodium catalyst was used. The solar tests were carried out in the Schaeffer solar furnace of the Weizmann Institute of Science. The power absorbed was up to 6.3 KW, the maximal flow rates of the gases reached 11,000 1/h, and the methane conversions reached 85%. A computer model was developed to simulate the process. Agreement of the calculations with the experimental results was quite satisfactory.     

Four different configurations of a 5 kW class shell-and-tube methane steam reformer with a low-temperature heat source

The methane steam reforming reaction is an extremely high endothermic reaction that needs a high temperature heat source. Various fuel cell hybrid systems have been developed to improve the thermal efficiency of the entire system. This paper presents a low temperature steam reformer for those hybrid systems to maximize the utilization of energy from a low temperature waste heat source. In this study, the steam reformer has a shell and tube configuration that is divided into the following zones: the inlet heat exchanging zone, the reforming zone and the exit heat exchanging zone. Four different configurations for methane steam reformers are developed to examine the effect of heat transfer on the methane conversion performance of the low temperature steam reformer. The experimental results show that the overall heat transfer area is a critical parameter in achieving a high methane conversion rate. When the heat transfer area increases about 30%, the results showed elevated dry mole fractions of hydrogen about 3% with about 30 °C rise of reformer outlet temperature.     

CFD simulation with detailed chemistry of steam reforming of methane for hydrogen production in an integrated micro-reactor

micro-reactor has drawn more and more attention in recent years due to the process intensification on basic transport phenomena in micro-channels, which would often lead to the improved reactor performance. Steam reforming of methane (SRM) in micro-reactor has great potential to realize a low-cost, compact process for hydrogen production via an evident shortening of reaction time from seconds to milliseconds. This work focuses on the detailed modeling and simulation of a micro-reactor design for SRM reaction with the integration of a micro-channel for Rh-catalyzed endothermic reaction, a micro-channel for Pt-catalyzed exothermic reaction and a wall in between with Rh or Pt-catalyst coated layer. The elementary reaction kinetics for SRM process is adopted in the CFD model, while the combustion channel is described by global reaction kinetics. The model predictions were quantitatively validated by the experimental data in the literature. For the extremely fast reactions in both channels, the simulations indicated the significance of the heat conduction ability of the reactor wall as well as the interplay between the exothermic and endothermic reactions (e.g., the flow rate ratio of fuel gas to reforming gas). The characteristic width of 0.5 mm is considered to be a suitable channel size to balance the trade-off between the heat transfer behavior in micro-channels and the easy fabrication of micro-channels.     

Experimental investigation of temperature distribution of planar solid oxide fuel cell: Effects of gas flow,power generation,and direct internal reforming

The temperature distribution of an operating planar solid oxide fuel cell (SOFC) is experimentally investigated under direct internal reforming conditions. An in situ measurement is conducted using a cell holder and an infrared (IR) camera. The effects of the gas flow configuration, exothermic power generation reaction, and endothermic steam–methane reforming reaction are examined at a furnace temperature of 770 °C. The fuel flow and airflow are set to a coflow or counterflow configuration. The heat generation and absorption by the reactions are varied by tuning the average current density and the concentration of methane in the supplied fuel. The maximum value of the local temperature gradient along the cell tends to increase with increasing internal reforming ratio, regardless of the gas flow configuration. From the view point of a small temperature gradient, the counterflow configuration clearly shows better characteristics than that of the coflow, regardless of the internal reforming ratio.     

A numerical analysis of heat and mass transfer processes in a macro-patterned methane/steam reforming reactor

The presented paper focuses on a numerical analysis of a heat and mass transfer process in a novel type of methane/steam reforming reactor. The novelty of the macro-patterned reactor design lies in dividing a reformer into segments of various lengths and reactivity. Precisely, splitting the catalyst and filling the created empty volume with porous, non-reactive, thermal conducting material such as metallic foam. This approach allows for moderating a sharp temperature drop at the inlet of the reactor typical for the endothermic methane/steam reforming process. To analyze the considered system, the mathematical and numerical models of transport phenomena and the reaction kinetics were developed and implemented into an in-house solver. The kinetics of methane/steam reforming was taken from the literature. The outlet composition obtained from the kinetic model was compared with the experimental measurements and good agreement was found. The conducted numerical analysis includes cases that differ from a number and lengths of catalytic and non-catalytic segments. The obtained results indicate that the macro-patterned design is a promising strategy that allows for a significant improvement of temperature distribution in a reforming reactor. It was shown that the proposed approach could help to cut the cost of the catalyst material by allowing for the conversion of methane with a smaller amount of the catalyst close to the reference case.     

Thermodynamic analysis of hydrogen production via sorption-enhanced steam methane reforming in a new class of variable volume batch-membrane reactor

Combined reaction–separation processes are a widely explored method to produce hydrogen from endothermic steam reforming of hydrocarbon feedstock at a reduced reaction temperature and with fewer unit operation steps, both of which are key requirements for energy efficient, distributed hydrogen production. This work introduces a new class of variable volume batch reactors for production of hydrogen from catalytic steam reforming of methane that operates in a cycle similar to that of an internal combustion engine. It incorporates a CO₂ adsorbent and a selectively permeable hydrogen membrane for in situ removal of the two major products of the reversible steam methane reforming reaction. Thermodynamic analysis is employed to define an envelope of ideal reactor performance and to explore the tradeoff between thermal efficiency and hydrogen yield density with respect to critical operating parameters, including sorbent mass, steam to methane ratio and fraction of product gas recycled. Particular attention is paid to contrasting the variable volume batch-membrane reactor approach to a conventional fixed bed reaction–separation approach. The results indicates that the proposed reactor is a viable option for low temperature distributed production of hydrogen from methane, the primary component of natural gas feedstock, motivating a detailed study of reaction/adsorption kinetics and heat/mass transfer effects.     

Thermal modeling of radiation and convection sections of primary reformer of ammonia plant

The primary reformer is basically a furnace containing burners and tubes packed with supported nickel catalyst. Due to the strongly endothermic nature of the process, a large amount of heat is supplied by fuel burning (commonly natural gas) in the furnace chamber. Accordingly, selection of primary reformer operating parameters has an important influence on reduction of operating costs and increasing the reactor performance (conversion efficiency).In this paper, the radiation and convection sections of primary reformer are investigated. The effects of key parameters on reformer performance are studied and the related developed software program is presented. The stirred-reactor furnace model which was used to simulate the radiation section of primary reformer was found to make substantially correct predictions of the overall heat transfer process in the furnace.Comparison of the numerical data obtained from the simulation program with the measured data collected from primary reformer of Razi petrochemical plant showed a mean difference of 0.23% in estimating produced hydrogen mole fraction, as well as 1.7% and 7.25% in computing the outlet temperature of process fluids and induced draft fan (ID) speed, respectively.     

How to choose endothermic process for thermochemical waste-heat recuperation?

The thermochemical waste-heat recuperation (TCR) systems by steam reforming of various hydrocarbon fuels are considered. A method for determining the TCR systems efficiency is proposed. The methodology is based on the determination of the heat recuperation rate and heat transformation coefficient. TCR due to steam reforming of methanol, ethanol, glycerol, propane, and methane was analyzed. To obtain the initial data for energy analysis of TCR systems, the thermodynamic analysis was performed. With the help of Aspen HYSYS was determined the synthesis gas composition and reaction enthalpy for all investigated variants. The investigation was performed for a wide temperature range from 400 to 1200 K, for the steam-to-fuel ratio of 1, and pressures of 1 bar. It was established that TCR due to the steam reforming of ethanol, glycerol, and propane in the temperature range above 800 K, it is possible to achieve complete recuperation of the exhaust after the furnace. As a results of investigation, the practical recommendations were given for choosing endothermic reaction for the thermochemical waste-heat recuperation systems: in the temperature range up to 600 K for TCR it is necessary to choose a methanol steam reforming reaction; in the temperature range from 600 to 1000 K - the reaction of steam reforming of ethanol and glycerol; in the temperature range above 1000 K - the reaction of steam reforming propane and methane.     

Modeling and optimization of an industrial hydrogen unit in a crude oil refinery

The main goal of this research is the modeling and optimization of an industrial hydrogen unit in a domestic oil refinery at steady state condition. The considered process consists of steam methane reforming furnace, low and high temperature shift converters, CO₂ absorption column and methanation reactor. In the first step, the reactors are heterogeneously modeled based on the mass and energy balance equations considering heat and mass transfer resistances in the gas and catalyst phases. The CO₂ absorption column is simulated based on the equilibrium non-ideal approach. In the second step, a single objective optimization problem is formulated to maximize hydrogen production in the plant considering operating and economic constraints. The feed temperature, firebox temperature, and steam flow rate in the reformer, feed temperature in shift converters, lean amine flow rate in the absorption column, and feed temperature in the methanator are selected as decision variables. The calculated effectiveness factors and mass transfer coefficients prove that the methane reforming is inertia-particle mass transfer control, while shift and methanation reactions are surface reaction control. The simulation results show that applying the optimal condition on the system increases hydrogen production capacity from 85.93 to 105.5 mol s⁻¹.     

板坯加热炉内加热特性的数值分析

以某公司热轧厂常规与双蓄热烧嘴组合供热的板坯加热炉为研究对象,建立该加热炉炉内流动、传热、燃烧和板坯运动吸热过程的三维物理数学模型,运用CFD仿真技术对其进行详细的数值计算,得到炉内稳态的速度场和温度场分布规律、板坯的升温曲线以及板坯温度分布均匀性,计算结果与"黑匣子"实验测量数据吻合良好。本文给出的板坯加热特性计算方法为研究加热炉新工艺、优化板坯加热温度制度提供了科学依据。     

Coupled Heat Transfer Simulation of the Spiral Water Wall in a Double Reheat Ultra-supercritical Boiler

This paper presented a coupled heat transfer model combining the combustion in the furnace and the ultra-supercritical(USC) heat transfer in the water wall tubes. The thermal analysis of the spiral water wall in a 1000 MW double reheat USC boiler was conducted by the coupled heat transfer simulations. The simulation results show that there are two peak heat flux regions on each wall of spiral water wall, where the primary combustion zone and burnt-out zone locate respectively. In the full load condition, the maximal heat flux of the primary combustion zone is close to 500 kW/m~2, which is higher than that in the conventional single reheat USC boilers. The heat flux along the furnace width presents a parabolic shape that the values in the furnace center are much higher than that in the corner regions. The distribution of water wall temperature has a perfect accordance with the heat flux distribution of the parabolic shape curves, which can illustrate the distribution of water wall temperature is mainly determined by heat flux on the water wall. The maximal water wall temperature occurs at the middle width of furnace wall and approaches 530°C, which can be allowed by the metal material of water wall tube 12Cr1MoVG. In the primary combustion zone, the wall temperatures in half load are almost close to the values in 75% load condition, caused by the heat transfer deterioration of the subcritical pressure fluid under the high heat flux condition. The simulation results in this study are beneficial to the better design and operational optimization for the double reheat USC boilers.     

一种蓄热式换热器应用探讨

针对目前殡葬行业普遍采用的列管式换热器存在的传热效率较低,设备紧凑型较差的问题,将蓄热式换热器应用于火化机中,设计了蓄热式烟气余热回收系统,改造现有火化机的燃烧室布局和炉体结构,可将800℃以上烟温直接降至150℃以下,高效回收利用火化烟气中的热量,提高燃烧效率,最后对其中存在的问题进行了探讨。     

Comparison of conventional and metal fiber burners in a compact methane reformer using CFD modeling

Compact reformers can be used to produce hydrogen for fuel-cell automobiles. The heat of the mehane seam reforming reaction is provided by methane burning. Generally, conventional burners have been used in combustion chambers. The Computational Fluid Dynamic (CFD) approach was used for the comparison of conventional burners with metal fiber burners and their locations for the first time. The rate of steam reforming reactions and methane combustion reactions were introduced to the CFD model and the Finite Rate/Eddy Dissipation model was used for reactions on the reforming and combustion sections. After validation of the compact reformer results by available experimental data, metal fiber was modeled using the porous-jump interior boundary condition. The results show that the best burner position for the metal fiber is the Bottom (near the catalyst) and for the conventional burner is the Top (far from the catalyst). The results show that the conventional burner in both the Middle and Bottom positions leads to an increase in the reaction zone temperature above 1200 K, which is higher than the catalyst tolerance, but placing a simple burner on the Top of the reactor does not have an out-of-range temperature problem. The hydrogen mass yield for a conventional burner at the Top position is 27.75% relative to methane. Due to the thermal uniformity in the metal fiber burner, the temperature does not exceed the catalyst limitation in the three positions (Top, Middle, and Bottom). The metal fiber burner at the Bottom of the combustion chamber shows the best performance with a hydrogen mass yield of 40.82%. The results indicate that metal fiber burners can distribute the flame more uniformly than conventional burners and increase the available heat for the reformer side.     

An integrated approach for the production of hydrogen and methane by catalytic hydrothermal glycerol reforming coupled with parabolic trough solar thermal collectors

An integrated catalytic hydrothermal reforming process for the production of hydrogen and methane from wet biomass feedstock is proposed where the process heat is provided by molten salts previously heated by solar energy. The simulated reactor consists of double tubes in which the reactants and the heat transfer fluid (i.e. molten salts) are concurrently pumped through the inner and the outer tubes, respectively. The first section of the reactor essentially serves as a preheater to increase the feed temperature to 20 K below the desired reaction temperature (i.e. 773 K), while the second section is comprised of a catalyst appropriate for the reforming of glycerol and water-gas shift reaction (e.g. Ru and Ni catalysts). The required energy for heating up the reactants to the final reaction temperature in the preheating section as well as the heat of reaction needed throughout the catalyst bed is provided by a co-currently fed molten salts mixture previously heated to 823 K in parabolic trough solar collectors. After heat recovery, the product mixture is cooled down to ambient temperature and depressurized to form liquid and gas phases. The gas products are subsequently separated into hydrogen, methane, and carbon dioxide or can be alternatively used for electricity generation using solid oxide fuel cells (SOFC). Glycerol was considered as a biomass model compound throughout this study, but the same methodology with minor changes can be applied to other oxygenated biomass compounds such as carbohydrates. The simulation results indicated that the degree of heat recovery has considerable effects on the process efficiency, the required parabolic mirror area, and the corresponding molten salt flow rate. Also, the higher the extent of the heat recovery, the smaller the dependence of the overall efficiency to the feed concentration.     

CFD study of heat and mass transfer in ethanol steam reforming in a catalytic membrane reactor

This work shows the analysis of ethanol steam reforming process within a catalytic membrane reactor. A 2-D non-isothermal CFD model was developed using Comsol Multiphysics, based on previous experimentally validated isothermal model. A comprehensive heat and mass transfer study was carried out utilizing the model. Operating conditions such as liquid hourly space velocity (LHSV) (3.77–37.7 h^?1), temperature (673–823 K), reaction side pressure (4–10 bar) and permeate side sweep gas flow pattern were discussed. A temperature gradient along the reactor was observed from the model and a “cold spot” was seen at the reactor entrance area, which is unfavorable for the highly endothermic ethanol steam reforming process. By changing the sweep gas pattern to counter-current, the “cold spot” appears to be smaller with a reduced temperature drop. By studying the individual reaction rates, reverse methane steam reforming (methanation) was observed, caused by the low temperature in the “cold spot”. Optimal operating conditions were found to be under LHSV = 37.7 h^?1 and counter-current sweep gas conditions.     

Thermochemical waste‐heat recuperation by steam methane reforming with flue gas addition

The process flow schematic of fuel‐consuming equipment with thermochemical waste‐heat recuperation by steam methane reforming with an addition of flue gas to the reaction mixture is suggested. The advantages of such a thermochemical recuperation (TCR) system compared with the TCR system by steam methane reforming are shown and justified. Based on the first law energy analysis, the heat inputs and outputs of the TCR system were determined. To determine the exhaust gases heat transformed into chemical energy of a new synthetic fuel, the thermodynamic analysis by minimizing Gibbs energy via Aspen HYSYS was performed. It was found that with an increase in the mole fraction of combustion products in the reaction mixture, the enthalpy of the methane reforming reaction increases, especially noticeable at the temperature range above 1000 K. Based on the heat, balance of the TCR system was established that the addition of combustion products to the reaction mixture has the following effects: reducing the heat input for steam production in a steam generator; reduction of the steam generator size because of the need to produce a smaller amount of steam in comparison with TCR by pure steam methane reforming; and reducing the amount of heat transferred through the wall of the reformer and, as a consequence, reduction in size of the reformer.