Electrochemical Methods for Exploiting Low‐Temperature Heat Sources: Challenges in Material Research

Abstract

stationary non-imaging optics [1] coupled with vacuum tubes and selective adsorbers. [2] ii) Household co-generation or "combined heat and power" generation, that is, the efficient simultaneous room heating and production of electrical current by using fossil fuels, can be performed at household-scale. [3] Household applications involve heat released at low temperature. iii) Low-temperature geothermal heat: Geothermal sources below 100 °C are abundant all over the world [4] and could be tapped by drilling relatively shallow wells.

Multistage Surface-Heated Vacuum Membrane Distillation Process Enables High Water Recovery and Excellent Heat Utilization: A Modeling Study

“…SHVMD can achieve greater water recovery than that achieved by VMD in this study and similar water recovery to that achieved by other larger-scale VMD and thermal desalination processes. However, SHVMD demonstrates higher GOR and energy efficiency than that of conventional VMD, and both GORs and energy efficiencies are comparable to other large-scale VMD and established thermal desalination technologies. , It is expected to have higher water recovery, GOR, and energy efficiency when the stage number is further increased (as shown in Section ) and other operating conditions are optimized. We also compared the specific surface area of membranes and HXs between SHVMD and VMD.…”

“…The capital expense (CapEx) of thermal desalination systems is relatively small compared to the operating expense (OpEx). , HXs and membranes are the two primary components of the CapEx. They are evaluated through two metrics, membrane surface area per liter of produced distilled water and HX surface area per liter of produced distilled water. , In terms of OpEx, the cost of heat dominates . Therefore, all commercially used thermal desalination units rely heavily on heat recovery and reuse in an effort to minimize the injection of new heat into the system, which is also true for MD systems .…”

“…In practice, this translates into using multistage, rather than single-stage, systems, which enable heat recovery and reuse . GOR and energy efficiency (defined as the ratio between the free energy of separation of the produced solutions and the consumed heat) are used as the parameters to evaluate the energy performance of the system. , …”

“…Membrane distillation (MD) is capable of converting high-TDS brines into distillate quality product water in a single pass, − and MD can desalinate waters of higher TDS than reverse osmosis (currently limited to ∼100,000 ppm TDS); MD also may offer a lower capital cost (particularly in applications <500 m 3 day –1 ) than the traditional thermal distillation process. ,− However, dramatic evaporative heat losses in the feed stream lead to a hard limit on the degree of water recovery in a single pass . To target higher water recoveries, the feed stream needs to be repeatedly reheated with different process schemes used to achieve this (e.g., multistage MD, single-stage feed-and-bleed MD). ,− Interestingly, the retentate from the high-recovery MD process can be leveraged for use in salinity gradient power generation devices, which have been shown to be more effective with high-TDS streams. , …”

Thermodynamics of Ionic Thermoelectrics for Low-Grade Heat Harvesting

“…170 Comprehensive reviews of these electrochemical methods for harvesting low-grade heat can be found in the published literature. 15,171 TIC devices are not included in the comparison due to their fast decay in output power. The typical power density of liquid TGCs ranges from 1 W/m 2 to 10 W/m 2 , while the efficiency is limited by both the heat conduction across the device and the achievable ΔT across the device.…”