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Abstract: Sorption enhanced methane reforming (SER), employing a CaO-based solid as a high temperature CO2 sorbent, is generally considered to be a promising route for H2 production. In this paper we present a dynamic pseudo-homogeneous model to describe the operation of a packed bed reactor in which the SER reaction is carried out under adiabatic conditions. This reactor can be implemented according to several process schemes, including a novel Ca/Cu looping process for hydrogen generation with inherent CO2 capture. The proposed SER model is based on the well-established principles of gas–solid contact and heat transfer in fixed-bed reactors and on the kinetic expressions published in the literature that describe the main reactions involved in the process. The resulting model describes the transient performance of the SER reaction and confirms the theoretical viability of this critical reaction stage in a large scale H2 production facility. It is demonstrated that the SER process can yield a CH4 conversion and H2 purity of up to 85% and 95%, respectively, under operating conditions of 923K, 3.5MPa, a steam/carbon ratio of 5 and a space velocity of 3.5kg/m2 s. [Copyright &y& Elsevier]

Abstract: The metal hydride heat transformer shows great potential for the low-grade heat recovery. However, the heat output is variable, and these dynamics have to be taken into account in realistic applications. In this paper, a new index called true temperature boost is introduced together with conventional indices to assess the performance of the heat transformer system. Detailed analyses are carried out using a mathematical model that authors developed, investigating effects of key design and operating factors on the system’s performance. The amount of hydrogen transferred between coupled reactors is found to be crucial to obtain a high coefficient of performance, while specific heating power is very sensitive to the cycle time. On the true temperature boost, the driving force of reaction and the heat transfer conditions exert the most significant effects. [Copyright &y& Elsevier]

Abstract: This paper describes the design, fabrication and performance evaluation of a high efficiency, compact heater that uses the catalytic oxidation of hydrogen to provide heat to a hydrogen storage system. The heater was designed to transfer up to 30kW of heat from the catalytic reaction to the hydrogen storage system via a recirculating heat transfer fluid. The catalytic heater consists of three main parts: 1) the reactor, 2) the gas heat recuperator, and 3) oil and gas flow distribution manifolds. The reactor and recuperator are integrated, compact, finned-plate heat exchangers to maximize heat transfer efficiency and minimize mass and volume. Detailed, three-dimensional, multi-physics computational models were used to design and optimize the system. At full power the heater was able to catalytically combust a 10% hydrogen/air mixture flowing at over 80 cubic feet per minute and transfer 30kW of heat to a 30 gallon per minute flow of oil over a temperature range from 100°C to 220°C. The total efficiency of the catalytic heater, defined as the heat transferred to the oil divided by the inlet hydrogen chemical energy, was determined to exceed the design goal of 80% for oil temperatures from 60°C to 165°C. [Copyright &y& Elsevier]

Abstract: The paper presents a model-based investigation of a metal hydride reactor applied as a solid state hydrogen storage device. The elements of a metal hydride reactor are hydrogen supply duct, internal hydrogen distribution, hydride bed, reactor shell and the flow domain of the heat transfer fluid. Internal hydrogen distribution and hydride bed are porous media. Therefore, hydrogen flows through non-porous and porous regions during its reversible exothermic absorption and endothermic desorption, respectively. The interface between porous and non-porous regions is a discontinuity with respect to energy transport mechanisms. Hence, Danckwerts-type boundary conditions for the energy balance equation are introduced. Application of the first and second law of thermodynamics to the interface reveals that temperature jumps may occur at the hydrogen inlet but are not allowed at the hydrogen outlet. Exemplarily the loading behavior of a metal hydride storage tank based on sodium alanate is analyzed. It is demonstrated and experimentally validated that only Danckwerts-type boundary conditions predict the important cooling effect of the inlet hydrogen on the exothermic absorption process correctly. [Copyright &y& Elsevier]

Abstract: This paper presents a two-dimensional mathematical model to evaluate transient heat and mass transfer in a metal hydride tank (hereinafter MHT) with metal foam heat exchanger. The model is validated by comparison with experimental data. A good agreement is obtained. A study of the geometric and the operating parameters of the metal foam (such as base material, pore size and relative density) has been carried out to identify their influence on the performance of the charging process of the MHT. After that, the model was used as a tool to predict the performance of the hydrogen-charging process of two configurations of MHTs with metal foam heat exchangers. The obtained results showed that the reduction of the storage time due to the metal foam heat exchanger can be more important when the MHT is equipped with a concentric heat exchanger tube. [Copyright &y& Elsevier]

Abstract: The main focus of this paper is the modeling, simulation, and analysis of the calcium bromide hydrolysis reactor stage in the calcium–bromine thermochemical water-splitting cycle for nuclear hydrogen production. One reactor concept is to use a spray of calcium bromide into steam, in which the heat of fusion supplies the heat of reaction. Droplet models were built up in a series of steps incorporating various physical phenomena, including droplet flow, heat transfer, phase change, and reaction, separately. Given the large heat reservoir contained in a pool of molten calcium bromide that allows bubbles to rise easily, using a bubble column reactor for the hydrolysis appears to be a feasible and promising alternative to the spray reactor concept. The two limiting cases of bubble geometry, spherical and spherical-cap, are considered in the modeling. Results for both droplet and bubble modeling with COMSOL MULTIPHYSICS™ are presented, with recommendations for the path forward. [Copyright &y& Elsevier]