Gas-to-gas recuperation with both high thermal effectiveness and order-of-magnitude improvement in cost effectiveness is critical to addressing global energy needs, especially via fuel synthesis from waste CO2 and renewable H2. An uncommon compound recuperator with liquid intermediary (CRLI) has been simulated for high-ε heat exchange between a first shell-side gas stream and a second shell-side gas stream of similar thermal capacity rates (W/K). The compound recuperator uses a first Gas-to-Liquid (GL) recuperator for a nearly complete transfer of available energy from a shell-side gas to an intermediary tube-side heat transfer liquid (HTL), followed by a second GL recuperator to transfer the heat from the liquid intermediary to the second gas stream. Each GL recuperator resembles an arrangement of thermally isolated, serially connected, adjacent, cross-flow, finned-tube cores, such as used in AC condensers. They are arranged so to effectively achieve counterflow exchange between the HTL and the shell-side gas stream. The HTL may be water, an organic liquid, a molten alloy, or a molten salt. Minimization of exergy destruction for the case where there is a substantial temperature difference between the hot and cold sources requires (1) a fairly large number of series connected, thermally isolated cores, (2) similar thermal capacity rates in all three streams (the two gases and the liquid intermediary), (3) a relatively large value for the number of transfer units (NTU), and (4) no phase change. The simulations show that the optimized CRLI recuperator can achieve effectiveness above 97% at very low pumping losses and has the potential for order-of-magnitude reduction in manufacturing costs compared to current technologies for clean gases at pressures above 0.3 MPa at heat transfer rates above ∼200 kW.

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