Catalyst-assisted chemical heat pump with reaction couple of acetone hydrogenation/2–propanol dehydrogenation for upgrading low-level thermal energy: Proposal and evaluation

Abstract

A chemical heat pump for upgrading low‐level thermal energy has been proposed by adopting a reversible organic reaction couple, endothermic liquid‐phase dehydrogenation of 2–propanol at low temperature and exothermic gas‐phase hydrogenation of acetone at high temperature, where thermodynamical work is done by separating condensed 2–propanol from the gaseous mixture of 2–propanol, acetone and hydrogen in a fractionation column. In the system constitution of the continuous type, the overhead vapour of the fractionation column is fed through the heat exchanger into the exothermic reactor, where acetone and hydrogen in excess are changed at 200°C into the equilibrium mixture, from which condensable 2–propanol is separated in the column by cooling at 30°C. The reverse reaction of 2–propanol decomposition into acetone and hydrogen proceeds in the endothermic reactor, i.e. the reboiler of the column, absorbing heat at 80°C. On the contrary, acetone and hydrogen in the overhead vapour of the fractionation column are stored at 30°C as liquid and metal hydride, respectively, in the system constitution of the storage type; when necessary, metal hydride is decomposed by heating at 80°C, with hydrogen at high pressure evolved and fed through the heat exchanger into the exothermic reactor, giving the equilibrium mixture at high pressure and temperature. Product condensates are transferred through a valve into the fractionation column in order to separate 2–propanol and acetone, the former of which is dehydrogenated in the endothermic liquid‐phase reactor, regenerating acetone and hydrogen at 80°C and atmospheric pressure. Energy efficiencies were evaluated for the system constitutions of both the continuous and storage types; the 80°C heat supplied was convertible into the 200°C heat continuously at the enthalpy efficiency or coefficient of performance (COP) of 0·36 in the former, whereas the 270°C heat was obtainable with the aid of metal hydride from the same heat source at COP of 0·21 in the latter.

Advances in Organic Liquid‐Gas Chemical Heat Pumps

“…In addition, it is also found that the exergy efficiency remains almost unaltered when T H increases from 433 K to 493 K for any given value of T L . Obviously, it is contradictory to the conclusion by Saito et al [7].…”

“…Definitions and expressions of these parameters are described in [5]. Saito et al [7] calculated the energy efficiencies (enthalpy efficiency and exergy efficiency) for both continuous-type and storage-type organic CHP systems whose design parameters are summarized in Tab. 3.…”

“…There are two different ways for these constituents to be connected to conceptually upgrade the temperature level, i.e., the continuous type and storage type [7].…”

“…Based on the fact that the reaction system can absorb huge amounts of reaction heat at a relatively low temperature and has fewer hazards than other reaction systems [15], the isopropanol/acetone/hydrogen CHP has been extensively studied, being a promising representative CHP type [4,7,8,15,[22][23][24][25][26][27]. The endothermic dehydrogenation reaction of liquid isopropanol at about 353 K and 0.1 MPa proceeds with proper catalysts (e.g., Ru/C, Ru-Pt/C, Ru-Pd/C, Raney nickel, etc.)…”

Thermodynamic and kinetic investigation of a chemical reaction-based miniature heat pump

“…Saito et al [17] proposed a waste heat recovery design concept with the 2-propanol reaction driven by a distillation column at fixed pressure. Waste heat is supplied to the endothermic reactor and the reboiler of the distillation column.…”