Heat Exchanger Reactor Research Articles

Optimal conditions in converting methanol to dimethyl ether, methyl formate, and hydrogen utilizing a double membrane heat exchanger reactor

Following importance of investigating new sources of energy with highly efficient processes, a new configuration for simultaneous production of high purity dimethyl ether (DME), hydrogen and methyl formate (MF) is numerically studied in this work. In this regard, a catalytic heat-exchanger reactor assisted with two different membranes for methanol conversion and in-situ separation of products is simulated. The interesting feature of this system is utilizing only one feedstock (i.e. methanol) to produce different valuable products. Methanol is dehydrated through an exothermic reaction and supplies required energy for the methanol dehydrogenation reaction. Produced water in the exothermic side and produced hydrogen in the endothermic side are separated by permeation to particular membranes. A steady state one-dimensional plug flow model is developed to evaluate molar and thermal behavior of the system. Optimum operating conditions are determined applying genetic algorithm as a powerful optimization method. The proposed configuration working under optimum conditions promotes methanol conversion to DME to % 95.1 and methanol conversion to MF to % 99.6 providing high purity products in the output streams.

Development of thermal storage material using vermiculite and calcium hydroxide

A chemical heat storage (CHS) material that utilizes waste heat (with temperatures over 450 °C) from industrial plants, thermal generation plants, and nuclear power plants was developed. Calcium hydroxide (Ca(OH)2) was selected as the CHS material because it decomposes at temperatures over 450 °C under atmospheric pressure. A support that holds the CHS material dispersed in micrometer-sized clusters was needed to prohibit Ca(OH)2 agglomeration; this support also permitted the moldability of the Ca(OH)2 material for loading into practical heat-exchange reactors. Vermiculite was selected as the support for Ca(OH)2 because of its high porosity, chemical stability, and low cost. Using the impregnation method, composite materials were developed, which consisted of Ca(OH)2 and vermiculite. The reaction performance was then studied with thermal gravimetric analysis (TGA). It was confirmed that, in comparison with the original Ca(OH)2, the reaction rate of the composite material was enhanced because of the incorporated vermiculite.

Визначення оптимальних умов реалізації процесу термохімічної регенерації для використання теплоти відпрацьованих газів газотурбінної установки

The problem of the use of thermal secondary energy resources, being formed in gas-turbine plants working on natural gas, is important from the viewpoint of energy saving. The most efficient way of its solution is connected with the technology of thermochemical recuperation, based on fuel reforming with exhaust gases. We have developed 4 schemes of thermochemical recuperation for using the heat of exhaust gases and carried out thermodynamic calculations of their efficiency. We have established that the highest efficiency can be obtained by using scheme G4, where the process of fuel reforming as well as the heating of air spent for fuel combustion and ballast (a certain part of exhaust gases), providing the cooling of the working medium after combustion chamber to an acceptable temperature, are realized in the reactor-heat exchanger. We have revealed and explained a paradoxical, on the face of it, dependence of the efficiencies of different schemes on the initial pressure. We have found the optimal conditions of the scheme G4, under which its efficiency reaches 60 %. In addition to fuel economy, this scheme enables one to decrease the emission of harmful substances to the atmosphere.

Ammonium carbamate-based heat exchanger reactor as an endothermic heat sink for thermal management

We present our work on the investigation of a chemical reactor heat sink which used an endothermic reaction to absorb low-grade heat. Ammonium carbamate, which has an enthalpy of decomposition of ∼2MJ/kg and decomposes over a wide range of temperatures, was used as the endothermic chemical. The objective of the effort was to develop the methods and apparatus required to demonstrate endothermic cooling. Ammonium carbamate (AC) particles were suspended in propylene glycol (PG) and pumped through a heat exchanger, where it chemically reacted and decomposed as it absorbed heat from a hot fluid. Two conditions involving the reactants (AC in PG) were studied: (1) elevated decomposition temperatures occurring at near-ambient pressures and (2) near-ambient decomposition temperatures occurring at low pressures. The influences of reactant pressure, relative reactant temperature, reactant residence time, AC particle size, and AC mass flow rate on the heat absorption rate were investigated. Reaction pressure, residence time, and temperature were found to be the dominant factors.

Prototype reactor simulation for on-board use of hydrogen in a hybrid MTH (methylcyclohexane–toluene–hydrogen)–gasoline system and a simplified dynamic modeling for the startup

A novel reactor-heat exchanger system has been proposed and simulated for the use of hydrogen in an internal combustion engine based on methylcyclohexane–toluene–hydrogen (MTH) system. A 1200cc engine capable of producing 66.2kW is chosen and the performance of the prototype system is studied for a hybrid MTH–gasoline system. The effects of parameters such as flow direction (cocurrent and countercurrent), inlet exhaust gas temperature, number and size of catalyst tubes, number of fins, catalyst activity and catalyst deactivation, and an appropriate material of construction (MoC) are studied in order to find out the best combination of design and operation of the prototype. Moreover, dynamic modeling of the system is carried out to estimate the time required for the cold startup of the hybrid MTH–gasoline system.

Compact heat exchange reactor for synthesis of mixed alcohols

Stainless steel compact heat exchanger reactor with 66mL catalyst loading was built and tested for synthesis of mixed alcohols. Compared to the fixed bed reactor, the compact heat exchanger reactor have much better heat and mass transfer due to the small particle sizes and miniaturized channels. Development of NiMo2C catalyst for synthesis of mixed alcohols is also reported. The compact reactor demonstrated two to four times process intensification.

Design and modeling of large-scale cross-current multichannel Fischer–Tropsch reactor using channel decomposition and cell-coupling method

Design and modeling of a micro channel Fischer–Tropsch reactor was considered in this study. A cross-current heat-exchange reactor was modeled using a new method, in which all the process and cooling channels are decomposed into a number of unit cells. Each neighboring process and cooling channel unit cells are coupled to set up material and energy balance equations, including heat-transfer equations for the entire reactor domain, which are then solved simultaneously. The model results were compared with the experimental data for a pilot-scale reactor described in the literature, and were found to be in good agreement. Several case studies were performed to see the effect of variables such as catalyst loading ratio, coolant flow rate, and channel layout on design of a reactor with state-of-the-art Fischer–Tropsch catalyst. The developed model could handle more than 5800 process channels, 7500 cooling channels, and 130 layers, with implementation of six complex reaction kinetics.

Pressure drop and axial dispersion in industrial millistructured heat exchange reactors

Hydrodynamic characterization by means of pressure drop and residence time distribution (RTD) experiments is performed in three millistructured heat exchange reactors: two Corning reactors (further referred to as Corning HP and Corning RT) and a Chart reactor. Pressure drop is measured for different flow rates and fluids. Fanning friction factor is then calculated and its evolution versus Reynolds number is plotted for each reactor, showing the influence of the geometrical characteristics of the reactors on this parameter. From RTD experiments, axial dispersion coefficients that allow calculating Péclet numbers are identified by solving the convection-dispersion equation. The results highlight plug flow behavior of these reactors for the range of flow rates studied. Péclet number in Corning HP remains constant in the range of Reynolds number studied. Its specific pattern is designed to generate mixing structures that allow homogenization of the tracer over the cross-section. It explains the plug flow behavior of this reactor even at low Reynolds number but generates high pressure drop. Péclet number in Corning RT and Chart ShimTec® increases with Reynolds number. This evolution is encountered for straight circular pipes in turbulent regime and confirms the pressure drop analysis.

Optimal design and operation of a UASB reactor for dairy cattle manure

Optimal design and operation of a planned full-scale UASB reactor at a dairy farm are determined using optimization algorithms based on steady state simulations of a dynamic AD process model combined with models of the reactor temperature and heat exchanger temperatures based on energy balances. Available feedstock is 6m3/d dairy manure produced by the herd. Three alternative optimization problems are solved: Maximization of produced methane gas flow, minimization of reactor volume, and maximization of power surplus. Constraints of the optimization problems are an upper limit of the VFA concentration, and an upper limit of the feed rate corresponding to a normal animal waste production at the farm. The most proper optimization problem appears to be minimization of the reactor volume, assuming that the feed rate is fixed at its upper limit and that the VFA concentration is at its upper limit. The optimal result is a power surplus of 49.8MWh/y, a hydraulic retention time of 6.1d, and a reactor temperature of 35.9°C, assuming heat recovery with an heat exchanger, and perfect reactor heat transfer insulation. In general, the optimal solutions are improved if the ratio of the solids (biomass) retention time to the hydraulic retention time is increased.

Analysis of Loss-of-Flow Accidents for the NIST Research Reactor with Fuel Conversion from HEU to LEU

A program is underway to convert the current high-enriched uranium (HEU) fuel to low-enriched uranium (LEU) fuel in the 20-MW D2O-moderated research reactor (NBSR) at the National Institute of Standards and Technology. A RELAP5 model has been developed to analyze postulated accidents in the NBSR with the present HEU fuel and a proposed LEU fuel. The model includes the reactor vessel, primary pumps, shutdown pumps, various valves, heat exchangers, and average and hottest fuel elements and flow channels in the region where flow enters through an inner plenum (6 fuel elements) and a region where flow enters through an outer plenum (24 elements). The equilibrium cycle power distributions in the fuel elements were determined based on three-dimensional Monte Carlo neutron transport calculations performed with the MCNPX code. In this paper we discuss safety analyses conducted for the loss-of-flow accidents resulting from either loss of electrical power or inadvertent throttling of flow control valves at the inlets to the inner and outer plena. The analysis shows that the fuel conversion will not lead to significant changes in the safety analysis and that the calculated maximum clad temperatures, minimum critical heat flux ratios, and minimum onset of flow instability ratios assure that there is adequate margin to fuel failure.

Scientific design of a large-scale sodium thermal–hydraulic test facility for KALIMER—Part II: Validation of reactor pool design using CFD analyses

A one-fifth scale test loop for a sodium cooled fast reactor (SFR), KALIMER-600, is designed based on scaling analyses. The coolant flow and temperature distribution inside the prototype reactor pool and 1/5 scale model are numerically analyzed using a CFD package. In order to perform the numerical analyses, numerical models are created for the reactor core and heat exchangers. The analyses results are compared with each other in terms of normalized pressure, velocity magnitude, and temperature distributions. These comparisons demonstrate that the scaling analyses for the reactor pool described in Part I are appropriate and that the one-fifth scale thermal hydraulic test facility provides appropriate simulation of the KALIMER-600 prototype.

Degradation Behaviour of HR-120 Alloy Exposed to CH4–CO–H2–H2O Mixed-Gas Environments at 950 °C

The HR-120 alloy is a candidate structural material for heat-exchanger reactors of steam methane reforming. Consequently, the behaviour at high-temperature of this alloy in oxidizing/carburizing atmosphere is of considerable interest for industrial applications. In this study, the behaviour of HR-120 alloy was evaluated in Ar, CH4, CO, H2, H2O oxidant/carburizing gas mixtures at 1,223 K, with or without pre-oxidation. In the former case, the as-grown scale layer consisted of inner Cr2O3 layer and an outer MnCr2O4 spinel layer. This scale structure, which is completely transformed into carbide layer in Ar–CH4 atmosphere, exhibits an excellent stability in CH4, CO, H2, H2O gas mixture. However, the oxidation of particles rich in Nb promoted cracking and spalling of protective scale layer, resulting in exposure of substrate metal.

Over 99.6 wt%-pure, sub-millimeter-long carbon nanotubes realized by fluidized-bed with careful control of the catalyst and carbon feeds

To establish a method for sub-second conversion of acetylene to sub-millimeter-long carbon nanotubes (CNTs), we have proposed and developed an internal heat-exchange reactor for fluidized-bed chemical vapor deposition (FBCVD). This reactor enabled sufficient heating of the reaction gas and uniform heating of the bed of alumina beads at a space velocity as high as 3600h−1. The direct feeding of the catalyst vapors (aluminum isopropoxide for the alumina support layer and ferrocene for the iron particles) to the bed separately from the other gases, which were fed through the heat-exchange and preheating zone and the distributer, enabled the careful control of the catalyst particles deposited on the beads. By decreasing the acetylene feed concentration and preventing the deactivation of small Fe particles, we realized semi-continuous production of 99.6–99.8wt%-pure, sub-millimeter-long, few-wall CNTs with an average diameter of 6.5nm at a carbon yield of 42%. The FBCVD reactor with an internal heat-exchanger can be scaled-up for practical mass production with uniform and energy-saving heating.

Dehydration kinetic study of a chemical heat storage material with lithium bromide for a magnesium oxide/water chemical heat pump

The reaction performance of a novel chemical heat storage composite as thermal energy storage medium were evaluated for use in a magnesium oxide/water chemical heat pump. The composite, called EML, is composed of pure Mg(OH)2 powder and support materials, including LiBr and expanded graphite to improve reactivity and heat transfer, respectively. The heat storage and heat output capacities of the EML composites were evaluated based on laboratory experiments of dehydration and hydration processes for various molar mixing ratios α of LiBr to Mg(OH)2 using the thermogravimetric method. The heat storage and heat output capacity of the EML composites increased with increasing α. The EML composite with α = 0.100 was estimated to be able to store 1.3 times the heat stored in pure Mg(OH)2 powder after 30 min. Based on these evaluations, the EML composites exhibited sufficient heat storage, heat output capacity, and good mold-ability for practical use in a heat exchange reactor. The EML composite was accordingly confirmed as a candidate material for use in chemical heat pumps. Thus, potential use of the EML composite in a magnesium oxide/water chemical heat pump coupled with a small nuclear reactor for district heating systems was evaluated based on the experimental results.

Scale-up of Microwave Assisted Flow Synthesis by Transient Processing through Monomode Cavities in Series

A new scale-up concept for microwave assisted flow processing is presented where modular scale-up is achieved by implementing microwave cavities in series. The scale-up concept is demonstrated for case studies of a packed-bed reactor and a wall-coated tubular reactor. With known kinetics and reaction temperature, a packed-bed reactor gave a conversion of 99% with the highest production rate of 170 kgprod/kgcat·h for esterification of acetic acid and ethanol catalyzed by ion-exchange resin in 18 cavities. A similar approach for a multicomponent reaction of benzaldehyde, piperidine, and phenylacetylene catalyzed by a thin Cu film in a wall-coated tubular reactor gave 99% conversion with the highest production rate of 7740 kgprod/kgcat·h in 28 cavities. In both cases, the pseudo first order reaction rate with respect to the limiting reactant yielded a typical rise in conversion and production rate. In a packed-bed reactor-heat exchanger operated at a temperature between 343 and 348 K, the conversion in the e...

Safety enhancement by transposition of the nitration of toluene from semi-batch reactor to continuous intensified heat exchanger reactor

The behavior of a continuous intensified heat exchanger (HEX) reactor in case of process failure is analyzed and compared to the behavior of a semi-continuous reactor. The nitration of toluene is considered as test reaction to identify the main failure scenarios that can lead to thermal runaway in both processes using the HAZOP method. No flow rate of process fluid and utility fluid in the continuous process. No stirring during feeding of the reactor followed by normal stirring for the semi-continuous reactor. These scenarios are simulated for both processes and the temperature profiles are observed. This study shows that the temperature is better controlled in the continuous process because of the intrinsic characteristics of the HEX reactor. In fact, this device has a low reactive volume relative to the mass of the reactor, allowing a good dissipation of the heat produced by the reaction, even in case of failure. This characteristic of the intensified reactor is confirmed by an experimental work.

Optimal design of large‐scale chemical processes under uncertainty: A ranking‐based approach

An approach for the optimal design of chemical processes in the presence of uncertainty was presented. The key idea in this work is to approximate the process constraint functions and model outputs using Power Series Expansions (PSE)‐based functions. The PSE functions are used to efficiently identify the variability in the process constraint functions and model outputs due to multiple realizations in the uncertain parameters using Monte Carlo (MC) sampling methods. A ranking‐based approach is adopted here where the user can assign priorities or probabilities of satisfaction for the different process constraints and model outputs considered in the analysis. The methodology was tested on a reactor–heat exchanger system and the Tennessee Eastman process. The results show that the present method is computationally attractive since the optimal process design is accomplished in shorter computational times when compared to the use of the MC method applied to the full plant model. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3243–3257, 2014

Preparation of micro-channel catalytic reactor coated with macro-porous Al2O3 for fuel reformer

Macroporous ordered alumina was synthesized in a micro-channel reactor, using polystyrene colloidal spherical nano-beads as a template for the formation of the macro pores. A 0.1 M aluminum nitrate solution, used as the precursor for the synthesis of alumina, was mixed with a polystyrene colloidal solution at a volumetric ratio of 1:1. In this study, SUS-316, stainless steel material was used as a micro-channel plate and the buffer layer was homogeneously coated over the micro-channel plate. Scanning electron microscopy confirmed the synthesis of high quality ordered macro porous alumina over the micro channels through the application of a buffer layer. To use the ordered macro porous alumina as a catalytic support, the precursor of the active components, Ni, was added to a mixed solution of the aluminum precursor and polystyrene colloid. A channel type heat exchange reactor was used as a fuel reformer for SOFC in this study. The macro-porous Ni-Al2O3 based catalyst coated over the micro-channel plate was inserted into the outside channel. It could be confirmed through this study that the efficiency of heat exchange was enhanced through the use of the micro-channel plate, and the metal foam and the catalytic activity of nickel based catalyst for reforming of dodecane was improved through the use of the macro-porous alumina support.

Transient heat transfer for forced flow of helium gas along a horizontal plate with different widths

This study is aimed to clarify transient heat transfer process between the surface of solid and the neighboring helium gas in Very High Temperature Reactor (VHTR) or Intermediate Heat Exchanger (IHX). In this paper a series of plate heaters with different widths under various pressures inside a circular channel have been tested for forced convective flow. The heat generation rate of the plate heater was increased with a function of Q0exp(t/τ) (where t is time and τ is period of heat generation rate or e-fold time). The heaters were platinum plates with a thickness of 0.1mm and widths of 2mm, 4mm and 6mm. The heat flux, surface temperature, and transient heat transfer coefficients were measured for helium gas passing by horizontal plates under wide experimental conditions such as velocities, pressures, widths of plate and periods of heat generation rate. It was clarified that the heat transfer coefficient approaches the quasi-steady-state value when the period is more than around 1s and it becomes higher when the period is shorter than around 1s. It was found that the heat transfer coefficient becomes higher with the increase of gas pressure under the same velocity and period of heat generation rate. It was also found that the widths have a great influence on the heat transfer coefficient: the heat transfer coefficients of narrow heaters are much higher than those of wide ones under the same velocity and the same pressure. Based on the experimental data, empirical correlations were obtained for both quasi-steady state heat transfer and transient state one at various plate-widths.

Multi-channel heat exchanger-reactor using arborescent distributors: A characterization study of fluid distribution, heat exchange performance and exothermic reaction

A multi-functional heat exchanger-reactor comprising arborescent (tree-like) distributors and collector, 16 mini-channels in parallel and T-mixers is introduced in this paper. Flow distribution property, pressure drop and heat exchange performance of proposed heat exchanger-reactor are tested and discussed. Firstly, flow distribution uniformity is characterized by CFD simulation and then qualitatively confirmed by visualization experiment. Results show that for total flowrates ranging from 5 mL s−1 to 20 mL s−1, good distribution uniformity is obtained, with maximum flowrate deviation less than 10%. Then, experiments of heat exchange between hot and cold water are carried out. High values of overall heat transfer coefficient ranging from 2000 to 5000 W m−2 °C−1 are obtained under our working conditions. The volumetric heat exchange capability (UA/V) is found to be around 200 kW m−3 °C−1, showing a high heat exchange capability with compact design. The roles of end-effect and non-established flow are discussed and are supposed to be responsible for efficient heat transfer. Finally a typical fast exothermic reaction, neutralization between acid and basic solutions, is carried out to test the thermal control capability of the studied heat exchanger-reactor. Results indicate that isothermal condition could be realized by circulating appropriate flowrate of coolant through the heat exchanger.The design of heat exchanger-reactor with arborescent distributor and collector makes possible the application of multi-channel systems. This paper introduces systematically the successful integration of heat exchanger-reactor and its performance evaluation.