Process design and dynamic simulation of solar hydrogen production via intermediate temperature steam electrolysis

Abstract

Hydrogen production by high temperature electrolysis has a great potential of reducing the carbon dioxide emissions if operated by the use of renewable resources. The JU-FCH project ADEL (ADvanced Electrolyser for Hydrogen Production with Renewable Energy Sources) aims to develop a new generation of intermediate temperature steam electrolyser (ITSE), which will be operated at about 700 °C. Operation at lower temperatures is expected to increase the durability of the stack by decreasing its degradation rate. Furthermore, the operation of the electrolyser unit at lower temperature is expected to allow a more efficient coupling of the electrolyser unit to renewable energy sources. The total energy demand of the electrolyser unit consists of electricity and heat. This could be generated by solar concentrating energy systems (solar tower). High concentrated solar radiation is used in the solar receiver placed on the top of the tower to produce hot air at 680°C, which will act as heat transfer fluid to generate electricity in a Rankine cycle as well as feed steam for the intermediate temperature steam electrolyser. This technology offers the advantage of producing hot air, which is anyway necessary in the electrolyser as sweep gas for the anode in order to remove the oxygen. This present study will analyse the intermediate temperature steam electrolysis coupled to an 80 MWth air solar tower by using the commercial tool Aspen Plus. The power conversion unit will be a Rankine steam cycle with a power conversion efficiency of 18%. The electrolyzer operates at 700°C and 1.5 bar and utilizes an air sweep system to remove the excess oxygen that is evolved on the anode (oxygen) side of the electrolyzer. The overall system thermal to hydrogen production efficiency is 26% at a hydrogen production rate of 0.18 kg/s. Additionally, a dynamic simulation of the process is performed in order to analyse the behaviour of the system while energy supply fluctuating.