Hydrogen Production from Water

The process under analysis comprises two major sections: (1) Electrolysis; and (2) Hydrogen purification.

Electrolysis. The circulating electrolyte (potassium hydroxide solution) is mixed with demineralized water and fed to the electrolyzer system (filter press type with bipolar electrodes separated by diaphragm). Oxygen gas is generated during the electrolysis at the anode, while Hydrogen is formed at the cathode. The gas from each cell is passed through a different liquid/gas separator. The electrolyte solution streams, recovered from each separator, are mixed and recycled back to the electrolyzers. The oxygen gas obtained is vented to the atmosphere, while Hydrogen generated is routed to the purification section.

Hydrogen purification. The Hydrogen product from the electrolysis contains residual traces of electrolyte entrained in the gas. Most of such impurities are removed by direct contact with fresh demineralized water in a gas scrubber. The water containing the traces of recovered electrolyte is sent to the electrolysis, while the Hydrogen gas is sent to a gas holder, installed to mitigate any fluctuations in the Hydrogen stream. Hydrogen is then compressed to 30 bar and subsequently passed through deoxidizing and drying steps. In the deoxidizing step, the residual oxygen is removed from hydrogen by catalytic reaction with hydrogen and, in the drying step, the moisture contained in the Hydrogen is removed by adsorption in a molecular sieve dryer. The purified Hydrogen product is finally directed to nearby consumers.