Isopropanol Acetone Hydrogen Chemical Heat Pump Research Articles

Exergy analysis and performance enhancement of isopropanol-acetone-hydrogen chemical heat pump

Exergy loss analysis was conducted to identify the irreversibility in each component of the isopropanolacetone-hydrogen chemical heat pump (IAH-CHP). The results indicate that the highest irreversibility on a system basis occurs in the distillation column. Moreover, the effect of operating parameters on thermodynamic performances of the IAH-CHP was studied and the optimal conditions were obtained. Finally, the potential methods to reduce the irreversibility of the IAH-CHP system were investigated. It is found that reactive distillation is apromising alternative. The enthalpy and exergy efficiency of the IAH-CHP with reactive distillation increases by 24.1% and 23.2%, respectively.

Technical and economic feasibility of the Isopropanol-Acetone-Hydrogen chemical heat pump based on a lab-scale prototype

Chemical heat pump are promising alternatives in waste heat recovery applications. The present paper focuses on the technical and economic feasibility analysis of the Isopropanol-Acetone-Hydrogen Chemical Heat Pump (IAH-CHP) system. A small scale prototype of the IAH-CHP was established. Coefficient of performance (COP), exergy efficiency and entransy efficiency analysis were adopted to evaluate the performance of the IAH-CHP prototype. The stable operation is given with the waste heat temperature of 90 °C and the high-level output temperature of 160 °C. The COP, exergy efficiency and entransy efficiency of the system are up to 24.3%, 42.3% and 29.1%, respectively. Moreover, based on the detailed experimental results of the lab-scale apparatus, a 100 kWth model was built to evaluate economic feasibility of the IAH-CHP. The exergy cost and the thermoeconomic cost based on the structural theory, as well as the payback period were evaluated. The results indicate that the exergy destruction and investment cost of the distillation column is the highest, and the payback period is 5.6 year for the case of the optimal performance. The unit exergy cost of the final exergetic product is 6.56 W/W. The results proved that the IAH-CHP system is efficient in recovering the low-level waste heat.

3D CFD simulations of acetone hydrogenation in randomly packed beds for an isopropanol–acetone–hydrogen chemical heat pump

Isopropanol–acetone–hydrogen chemical heat pump (IAH-CHP) is a system having the ability to improve energy-grade and to achieve energy storage simultaneously. Acetone hydrogenation is an important part of IAH-CHP and directly affects the performance of IAH-CHP. In this work, the fully three-dimensional simulations on acetone hydrogenation in randomly packed-bed reactors with small tube-to-particle diameter ratio D/dp were carried out by Computational Fluid Dynamics (CFD). The study focused on the heat and mass transfer characteristics at inter- and intra-particles of the bed. The results indicate that the resistance of mass transfer at intra-particles is maximum in the entire transport process. Particle-to-fluid heat transfer is the main resistance of heat transfer in the bed. In addition, the synergy between transport of components and reaction rate at intra-particles was analyzed for various structural parameters, such as porosity εp, pore diameter do, particle diameter dp and tube-to-particle diameter ratio D/dp, in order to improve the utilization efficiency of catalyst. This study provides a detailed understanding on transport characteristics both at intra-particles and in fluid zone in randomly packed-bed reactors with small D/dp, providing a guideline for catalyst and reactor design for this type of chemical heat pump.

Ultrasound promoted catalytic liquid-phase dehydrogenation of isopropanol for Isopropanol–Acetone–Hydrogen chemical heat pump

The apparent kinetic of the ultrasound assisted liquid-phase dehydrogenation of isopropanol over Raney nickel catalyst was determined in the temperature range of 346–353K. Comparison of the effects of ultrasound and mechanical agitation on the isopropanol dehydrogenation was investigated. The ultrasound assisted dehydrogenation rate was significantly improved when relatively high power density was used. Moreover, the Isopropanol–Acetone–Hydrogen chemical heat pump (IAH-CHP) with ultrasound irradiation, in which the endothermic reaction is exposure to ultrasound, was proposed. A mathematical model was established to evaluate its energy performance in term of the coefficient of performance (COP) and the exergy efficiency, into which the apparent kinetic obtained in this work was incorporated. The operating performances between IAH-CHP with ultrasound and mechanical agitation were compared. The results indicated that the superiority of the IAH-CHP system with ultrasound was present even if more than 50% of the power of the ultrasound equipment was lost.

Acetone hydrogenation in exothermic reactor of an isopropanol–acetone–hydrogen chemical heat pump: effect of intra-particle mass and heat transfer

Intra-particle mass and heat transfer plays an important role in performance of the exothermic fixed-bed reactor for an isopropanol–acetone–hydrogen chemical heat pump. In this work, an exothermic fixed-bed reactor model, taking into account the actual packing structure, is established in the commercial software Fluent. A 120° segment of a tube with tube-to-particle diameter ratio (n) of 4, where realistic particles are packed and set to porous media, is used to simulate the 3D external flow, concentration and temperature fields in the exothermic packed-bed reactor. The influence of catalyst particle diameter (d p) and micropore diameter (d 0) on the intra-particle temperature, species distribution, reaction rate and selectivity is discussed. The appropriate d p and d 0 are obtained. Simulation results showed that intra-particle temperature gradient is not obvious. Large d p and small d 0 lead to remarkable gradient of reaction rate inside the catalyst particle and the decrease in the catalyst efficiency and reduce the acetone conversion and the selectivity in isopropanol. The optimal results reveal that the spherical catalyst with d p of 1 mm and d pore of 10 nm is appropriate for high-temperature acetone hydrogenation.

Thermodynamic analysis of an isopropanol-acetone-hydrogen chemical heat pump

An isopropanol–acetone–hydrogen chemical heat pump is investigated in the ASPEN Plus shell, the influences of some important operation parameters on the six different evaluation criteria are presented, and the different evaluation criteria for the heat pump are also analyzed. The decrease of distillation to feed ratio improves the performance of the chemical heat pump, and the increase of endothermic reaction temperature improves the performance of heat pump based on first law of thermodynamics but weakens the performance of heat pump from the viewpoint of second law of thermodynamics. There exists an optimum reflux ratio in terms of enthalpy efficiency, entransy efficiency, and exergy efficiency, but the performance of heat pump deteriorates as the reflux ratio increases in terms of entropy generation number, revised entropy generation number, and ecological COP. The entransy efficiency tends to integrate the behaviors of enthalpy efficiency and exergy efficiency. Compared with entropy generation number, the behavior of revised entropy generation number is more consistent with the practice. Copyright © 2014 John Wiley & Sons, Ltd.

Design of an isopropanol–acetone–hydrogen chemical heat pump with exothermic reactors in series

The isopropanol–acetone–hydrogen chemical heat pump system with a series of exothermic reactors in which the reaction temperatures decrease successively is proposed. This system shows the better energy performances as compared with the traditional system with a single exothermic reactor, especially when the higher upgraded temperature is need. At the same amounts of the heat released, the work input of the compressor and the heater are both reduced notably. The results indicate that the advantages of the IAH-CHP system with exothermic reactors in series are obvious.

A structured packed-bed reactor designed for exothermic hydrogenation of acetone

Fixed-bed reactors randomly packed with catalysts have many disadvantages that may adversely affect the desired chemical reaction. The increasingly used monolithic reactor, in contrast, has many operational advantages; however, for a kinetically-controlled reaction, it does not contain sufficient catalyst to sustain the reaction. To address the problems associated with both randomly packed-bed reactor and the monolithic reactor, a structured packed-bed reactor was proposed and mathematical models were built for randomly packed-bed reactor and structured packed-bed reactor. Their respective performances were compared when applied to the exothermic reaction of the isopropanol–acetone–hydrogen chemical heat pump system. The results showed that the structured packed-bed reactor performed better in terms of pressure drop and heat transfer capacity, and had a lower radial temperature gradient, indicating that this reactor had a higher effective heat conductivity. Isopropanol on the catalyst particle surfaces was more concentrated near the tube wall because a wall effect existed in the boundary layer around the particle-wall contact points.

Equilibrium Model and Performances of an Isopropanol–Acetone–Hydrogen Chemical Heat Pump with a Reactive Distillation Column

The intrinsic kinetic of the liquid-phase dehydrogenation of isopropanol over an amorphous Raney nickel catalyst was determined to be in the temperature range of 348 to 355 K. The kinetic model based on the Langmuir–Hinshelwood mechanism was adopted for experimental data fitting. An isopropanol–acetone–hydrogen chemical heat pump (IAH–CHP) with a reactive distillation column was proposed in this paper. A mathematical model was established to evaluate the energy performance of the IAH–CHP in terms of coefficient of performance (COP) and exergy efficiency, in which the obtained intrinsic kinetic was incorporated. The optimal feed location and operating pressure of the distillation column were determined first. Moreover, the thermodynamic performance of the IAH–CHP improved with the increase of hydrogen–acetone molar ratio in the entrance of the exothermic reactor and the decrease of feed temperature of the distillation column. The operating performances between IAH–CHP with and without reactive distillation part were compared. The results indicate that the COP and exergy efficiency of an IAH–CHP system with reactive distillation part increase by 19.2% and 16.7% at most, respectively, compared with an IAH–CHP without reactive distillation part.

The application of entransy theory in optimization design of Isopropanol–Acetone–Hydrogen chemical heat pump

In the present work, a multi-parameter optimization approach of Isopropanol–Acetone–Hydrogen (IAH) chemical heat pump is developed based on the entransy theory. In the optimization process, the total low-temperature heat consumed by the heat pump system generally decreases while the high-temperature heat recovered by the heat pump increases remarkably. When the temperatures of the reboiler and endothermic reaction are fixed, the temperature of exothermic reaction in the optimal design scheme is larger than that in the initial design scheme, and the high-temperature heat released from the exothermic reactor increases significantly in the optimal design scheme. The enthalpy efficiency (COP) and exergy efficiency monotonously increase as the entransy efficiency increases in the optimization process. The entransy efficiency has a definite physical meaning and pays more attention to the quality of the high-temperature heat recovered by the heat pump than enthalpy efficiency; it does not introduce an additional parameter and has more succinct expression than exergy efficiency. The multi-parameter optimization approach taking entransy efficiency as the objective function is very effective in the optimization design of IAH chemical heat pump.

Isopropanol–acetone–hydrogen chemical heat pump: A demonstration unit

The chemical heat pump is an alternative for improving the effectiveness of energy use. Waste heat at low temperatures will be recovered via a reversible chemical reaction. It will be absorbed by an endothermic reaction and transferred to new chemicals.The new chemicals are then reacted and liberate heat at high temperatures by an exothermic reaction. This paper presents a study on the development of a demonstration unit of a isopropanol–acetone–hydrogen chemical heat pump system. All major components in the system were individually investigated, which are endothermic and exothermic reactors and a distillation column. These components were then assembled and the system run. Finally, data were collected and the performance evaluated.