Phosphoric Acid, Phosphates & Fertilizers Experts

Hydrogen Formation in Sulfuric Acid Plants and Considerations for Risk Mitigation

The formation of hydrogen in sulfuric acid plants is a known phenomenon resulting from the corrosion of metallic materials under specific conditions. Those conditions are strongly dependent on acid strength and temperature. As a result, a mixture of hydrogen and oxygen containing process gas can occur with the potential risk of a hydrogen explosion.

Over the last few years, several incidents related to this have been reported. The majority of the reported hydrogen events took place in intermediate absorption systems, converters or heat recovery systems. In general, the incidents occurred during maintenance or after stopping the gas flow through the plant. In all cases, water ingress, resulting in low acid concentration, caused the formation of the hydrogen. In most of the cases, the water ingress wasignored or not noted and mitigation measures were not in place. As a result, plant equipment was severely damaged.

An international group from the sulfuric acid industry formed an expert committee dedicated to this topic. The members of this committee are from plant operation, consultancy as well as equipment/plant design disciplines.The aim of the group was to analyze well documented hydrogen incidents in acid plants and identify high level considerations to assist operators and plant designers in avoiding/minimizing risk and mitigating potential consequences. This document summarizes the findings.