Thermo-economic study of waste heat recovery from condensing steam for hydrogen production by PEM electrolysis

Abstract

The hydrogen production potential and cost from waste heat recovered from condensing steam in a combined heat and power facility has been calculated. Two different concepts for using the recovered energy by an organic Rankine cycle in PEM water electrolysis have been developed and compared. Thermo-economic analysis has been employed to calculate the exergetic unit cost of the produced hydrogen as function of ORC working fluid, steam condensing pressure and hours of available waste heat per year for a mass flow rate of 10 kg/s of condensing steam between 80 kPa and 200 kPa condenser pressure in the steam cycle. Hydrogen production rates in the range from 0.647 to 1.27 g H2/kg steam were obtained. The exergetic unit cost of uncompressed, compressed (350 bar) and liquefied hydrogen were calculated. Costs as low as $3.06/kg H2 (uncompressed) could be achieved, when the use of waste heat was maximised. The lowest cost of compressed (350 bar) and liquefied hydrogen were $4.11/kg H2 and $16.53/kg H2, respectively. Depending on the chosen scenario, between 186 and 364 tonne hydrogen can be produced annually.