Techno-economic analysis of conversing the low-grade heat to hydrogen by using reverse electrodialysis – Air gap diffusion distillation coupled method for iron and steel industry

This study devotes to the reverse electrodialysis (RED) – air gap diffusion distillation (AGDD) coupled system of converting the low-grade waste heat recovered from the steel production to hydrogen for steelmaking. This approach not only recovers waste heat but also reduces carbon emissions. To assess the feasibility of the coupled system, a techno-economic model has been developed. The influences on the levelized cost of hydrogen (LCOH) of the ion exchange membranes (cost and lifetime), the operating condition of RED stack (current density and feed solution velocity), the AGDD unit (feed solution flowrate), and the numbers of RED stacks in a multistage series system are investigated. The high price of ion exchange membrane is currently the main factor causing non-commercialization, which is almost 6.63–19.9 times larger than the LCOH of hydrogen production from renewable electricity. The membrane lifetime is the critical factor in increasing the maximum permitted membrane cost. Assuming the membranes cost is 1 RMB/m2, the optimal current density, feed solution velocity (in RED stack), and the solution volume flowrate (in AGDD unit) of are 50 A/m2, 0.00075 m/s, and 0.7 m3/h, respectively. The series systems take a considerable advantage in reducing the required AGDD units compared with one stage.