Measured Steam Conversion and Chemical Kinetics in a Hydrolysis Packed Bed Reactor for Hydrogen Production

AbstractActive research on the thermochemical Cu-Cl cycle is providing a promising potential for sustainable hydrogen production. The thermal efficiency of the hydrolysis reaction can drastically influence the viability and cost of the cycle. In the Cu-Cl cycle, the extent of the hydrolysis reaction has a major effect on cycle efficiency. Un-reacted superheated steam is difficult to efficiently separate from the gaseous reactor product, potentially dissipating a significant amount of thermal energy. In this paper, the upper limit of steam conversion in a copper (II) chloride reactor is investigated and new experimental results are presented. The experimental apparatus is designed to provide superheated steam, at 375°C, to excess CuCl2 and provide sufficient reaction time to approach the steam conversion limit. This is achieved by introducing a low steam flowrate to a packed bed reactor with six meters of packing solids. Variable reaction temperature, residence time, and flow rate are investigated for their effect on reaction extent and chemical kinetics. This research provides useful new data to effectively design and integrate a Cu-Cl hydrogen production cycle

Integrated fossil fuel and solar thermal systems for hydrogen production and CO2 mitigation

In most current fossil-based hydrogen production methods, the thermal energy required by the endothermic processes of hydrogen production cycles is supplied by the combustion of a portion of the same fossil fuel feedstock. This increases the fossil fuel consumption and greenhouse gas emissions. This paper analyzes the thermodynamics of several typical fossil fuel-based hydrogen production methods such as steam methane reforming, coal gasification, methane dissociation, and off-gas reforming, to quantify the potential savings of fossil fuels and CO2 emissions associated with the thermal energy requirement. Then matching the heat quality and quantity by solar thermal energy for different processes is examined. It is concluded that steam generation and superheating by solar energy for the supply of gaseous reactants to the hydrogen production cycles is particularly attractive due to the engineering maturity and simplicity. It is also concluded that steam-methane reforming may have fewer engineering challenges because of its single-phase reaction, if the endothermic reaction enthalpy of syngas production step (CO and H2) of coal gasification and steam methane reforming is provided by solar thermal energy. Various solar thermal energy based reactors are discussed for different types of production cycles as well

Calcium oxide/steam chemical heat pump for upgrading waste heat in thermochemical hydrogen production

This paper presents a numerical study of a chemical heat pump (CHP) for upgrading waste heat from a cement plant for thermochemical hydrogen production. A calcium oxide/steam CHP is investigated as a potential system to upgrade waste heat from industrial processes for thermochemical hydrogen production. The heat produced by the CHP drives the decomposition of copper oxychloride (CuO·CuCl2) in a copper–chlorine (Cu–Cl) thermochemical cycle. A transient analysis of the temperature distribution in each sub process in the combined CHP/Cu–Cl cycle is presented in this study. The numerical results of hydration temperature distribution are compared with experimental results to validate the predictive model. A maximum hydrogen production of 12.28 mol/kg Ca(OH)2 can be achieved from the combined system analyzed in this study. The effect of heating load and oxygen decomposition supply temperature is reported for the hydration, dehydration, condenser and evaporator heat transfer processes

Transient response of thermocapillary pumping of a droplet in a micro heat engine

A new analytical model is developed to predict the transient velocity and voltage generated due to thermocapillary pumping in a micro heat engine (MHE). Modeling, fabrication, and experimental studies of the MHE are presented in this paper. The fabrication technique uses lead zirconate titanate (PZT) as a substrate for the MHE. Analytical and experimental results are reported for Ti-W microheaters that transfer heat to the thermocapillary motion. The effect of surface roughness on thermocapillary motion of the droplet in the MHE is examined. The results show that a higher bulk droplet velocity reduces the effect of surface roughness on the displacement of the droplet. The analytical model of the efficiency of the system considers the electromechanical coupling factor and frictional irreversibilities to yield about 1.6% efficiency with a maximum voltage of 1.25 mV for the range of displacement considered in this study

Upgrading waste heat from a cement plant for thermochemical hydrogen production

A calcium oxide/steam chemical heat pump (CHP) is presented in the study as a means to upgrade waste heat from industrial processes for thermochemical hydrogen production. The CHP is used to upgrade waste heat for the decomposition of copper oxychloride (CuO.CuCl2) in a copper–chlorine (Cu–Cl) thermochemical cycle. A formulation is presented for high temperature steam electrolysis and thermochemical splitting of water using waste heat of a cement plant. Numerical models are presented for verifying the availability of energy for potential waste heat upgrading in cement plants. The optimal hydration and decomposition temperatures for the calcium oxide/steam reversible reaction of 485 K and 565 K respectively are obtained for the combined heat pump and thermochemical cycle. The coefficient of performance and overall efficiency of 4.6 and 47.8% respectively are presented and discussed for the CHP and hydrogen production from the cement plant

Droplet evaporation and de-pinning in rectangular microchannels

Experimental and numerical studies are presented for evaporation of micro-droplets of deionised (DI) water and toluene on lead zirconate titanate (PZT) substrates. The microchannels are fabricated with SU-8 2025 and 2075. The effects of channel width and depth on the evaporation and de-pinning rates of embedded micro-droplets are presented and compared for both fluids. The study reveals a partially hydrophobic nature of SU-8/PZT microchannel to DI water and a complete wetting when toluene is used as the droplet. The rate of evaporation of toluene is about double the rate of evaporation of DI water. Comparisons of the rates of evaporation and de-pinning show that the channel width has a larger effect on evaporation than the depth of the channel. The equivalent contact angle of the pinned film and bulk fluid compensated for the evaporation of the droplet. Surface roughness was also shown to have a significant effect on the pinned film in the rectangular microchannels

Process integration of material flows of copper chlorides in the thermochemical Cu–Cl cycle

The copper–chlorine (Cu–Cl) thermochemical hydrogen production cycle consists of three chemical reactions, i.e., electrolyisis of copper(I) chloride (CuCl) and hydrogen chloride (HCl), hydrolysis of copper(II) chloride (CuCl2), and thermolysis of copper oxychloride (Cu2OCl2). The outlet stream of the electrolysis includes aqueous CuCl2, CuCl, and HCl. The CuCl2 product of the electrolysis is the reactant of downstream hydrolysis. In this paper, three integration pathways for the copper chloride flows between electrolysis and hydrolysis reactors are investigated in terms of energy saving and reduction of auxiliary operations for the processing of the flows. The integration pathways include solid precipitation of CuCl2 using a crystallization process, water vaporization in the hydrolysis reactor by introducing the electrolyzer outlet stream directly to the reactor, and vaporization in an intermediate spray dryer

Thermodynamic and transport properties of fluids and solids in a Cu–Cl solar hydrogen cycle

Sustainable methods of clean fuel production are needed in the face of depleting oil reserves and to reduce carbon dioxide emissions. The technology of fuel cells for electricity production or the transport sector is already developed. However, a key missing element is a large-scale economical method of hydrogen production. The Cu–Cl thermochemical cycle is a promising thermochemical cycle to produce hydrogen. This paper focuses on a copper–chlorine (Cu–Cl) cycle and solar hydrogen production technology and describes the models how to calculate thermodynamic and transport properties. This paper discusses the mathematical model for computing the thermodynamic properties for pure substances and their mixtures such as CuCl in the solid phase with an aid of statistical thermodynamics and kinetic theory. The developed mathematical model takes into account vibrations of atoms in molecules and intermolecular forces. This mathematical model can be used for the calculation of thermodynamic properties of polyatomic crystals on the basis of the Einstein and Debye equations. We developed the model in the low-temperature and high-temperature region. All analytical data are compared with experimental results, and these show good agreement. For the transport properties, we have used kinetic theory. For fluid phase, we have calculated viscosity and thermal conductivity on the basis of the Chung–Lee–Starling kinetic model; for the solid phase, we have developed a model for calculations of thermal conductivity on the basis of electron and phonon contributions

Particle morphology of CuCl2 droplets in evaporative spray drying of aqueous slurries by laser diffraction and microscopy

New empirical correlations that predict the evaporative spray drying behavior of slurries are developed in this paper. The analysis examines a single droplet of CuCl2 solution in a continuum drying media. The results indicate a combination of convection and spray drying modes could improve the drying process. Validation of the experimental results involves comparisons based on non-dimensional analysis. The Ohnesorge number has a greater effect on the particle diameter than the Nusselt numbers. Analytical models of heat and mass Spalding numbers are developed for the aqueous solution, subject to various drying conditions. Also, the effect of temperature on the atomization flow rate is reported. The Log-normal distribution provides the most accurate fit for the measured data. Particle size diameters are predicted and compared with experimental results using SEM and laser diffraction. The results indicate the average particle size is about 229.5 μm