Investigation of a Cost-Effective Method of Nitrogen Inerting of Multicomponent Hydrocarbon Gas Mixtures in Large Storage Tanks

Abstract

The heavy dependence of the world on oil and gas for daily activities has made it highly vital that we do not lose them to incidents such as fires, spills, etc. In addition to economic losses, these incidents also result in damage to life and property. One of the most common forms of tank fires are those caused due to ignition of hydrocarbons in the vapor space of these tanks. And consequently, lightning has been found to be one of the major sources of ignition. The first choice of protection against such fires is complete purging of the vapor space with an inert gas such as nitrogen. Preventing ignition of flammable gases requires that we have accurate data of their flammability characteristics. This project focuses on experimentally developing a section of the flammability diagram between the lower and upper flammability limits by spark discharge method in a vertical cylindrical vessel. The system under study is a mixture of methane, ethane and propane. The flammability data developed here helps to determine the exact amount of nitrogen gas required to partially inert the gas mixture, as an alternative to completely purging it with inert gas. The cost-effectiveness of addition of air versus addition of nitrogen over a range of mixture compositions was compared and the more feasible option was identified.