Analysis of purification methods for contaminated hydrogen intended for fuel cell application after salt cavern storage

Abstract

The demand for hydrogen fuel cell electric vehicles and hydrogen as a source of energy is clearly increasing. Hydrogen quality is critical for improving the dependability, stability, and durability of proton exchange membrane fuel cells. However, contaminants might appear during production, transportation and storage of hydrogen. DIN EN 17124 specifies the technical requirements for permitted contaminants concentration in hydrogen used in fuel cells applications in the mobility sector. This research examines purifying methods for hydrogen with various kinds of contaminants expected especially after storage in salt cavern and other contaminants that significantly affect the performance of fuel cells. An experimental approach was used to analyze test gas mixtures of hydrogen and different contaminants expected after storage in a salt cavern environment. The contaminants investigated were H2S, CS2, HCl, N2, SO2, NH3, CO2, and CH3SH. Three distinct purification methods were used: metal hydride, Gatekeeper® gas purification unit, and H2S filter. To determine the level of purification, a mass spectrometer was employed to test the gases before and after each of the three techniques. This instrument can analyze and identifying rapidly changing gas compositions. Hydralloy® C5, an AB2-type alloy, was used in the metal hydride purification analysis due to its selective hydrogen absorption/desorption characteristics. The metal hydride analysis revealed that the alloy purified hydrogen from contaminants such as H2S, CS2, HCl, N2, SO2, NH3 and CH3SH at moderate temperatures ranging from 20 °C to 75 °C and pressures ranging from 30 bar to 5-10 bar, which represent the absorption and desorption conditions for hydrogen, respectively. It also removed CO2, however, the investigation revealed that CO2 reacts at the Hydralloy® C5 surface, producing CH4, which is also a fuel cell contaminant. Furthermore, it was also seen that by continuously passing the contaminated test gases through Hydralloy® C5 at ambient temperature (20 °C) without waiting for absorption and desorption, the alloy cleaned hydrogen of all contaminants except N2. Both processes produced hydrogen that complies with DIN EN 17124. The Gatekeeper® gas purification unit was also used in the hydrogen purification analysis; the device works by chemisorption and physisorption of impurities by an inbuilt absorbent. The analysis removed CO2, H2S, CH3SH, CS2, HCl, SO2, and NH3 from H2. However, it did not remove N2.ii Abstract The H2S filter specifically designed to purify H2S by selective reabsorption of impurities proved that it could also purify CH3SH, and SO2 alongside H2S. The Gatekeeper® gas purifier and the H2S filter operating conditions are ambient temperature and atmospheric pressure and the purity level attained complied with DIN EN 17124. This research has potential application in hydrogen purification for fuel cells, for instance after storage in salt caverns. It could also be employed in hydrogen refuelling infrastructures.