Practical Application of a Compact, High-Effectiveness, Gas-To-Gas, Compound Recuperator With Liquid Intermediary (CRLI)

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.