CFD analysis for optimizing superheater components for high temperature steam production for use in an SOEC

A solid oxide electrolyzer cell (SOEC) can reversibly generate hydrogen by electrolyzing superheated steam or produce electricity from a fuel cell by using hydrogen. Converting water into steam by using the waste heat from other processes can improve the efficiency of high-temperature electrolysis for directly converting steam. In the present study, steam at over 180°C and 3.4 bars generated from a boiler is converted into superheated steam at over 700°C and 3 bars by using a cylindrical steam superheater and the waste heat of flue gas at 900°C from a solid refuse fuel combustor. However, during the production of steam at 700°C and its transportation to the SOEC, a conventional superheater cannot produce a temperature of 700°C owing to poor heat transfer and energy loss. To determine the optimal conditions for generating steam at 700°C or above, we evaluate the effect of varying different superheater components, such as the shape of the top part of the superheater, number of steam inlet pipes, length, and coil rotation diameter of coil injection pipes, and steam inlet and outlet pipe diameters, through computational fluid dynamics analyses. Under the optimal conditions, the superheater with two steam injection pipes is the most effective, producing a maximum outlet steam temperature of ~753°C.