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

摘要

AbstractA 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