The purpose of the catalytic gas conditioning is to convert all the unsaturated hydrocarbons in the clean product gas to useable CO, H2, and methane. The converted compounds comprise the alkenes and alkynes (ethylene and acetylene), as well as remaining traces of aromatic compounds (e.g. benzene, toluene, and naphthalene). Destruction of the alkenes and alkynes, i.e. ethylene and especially acetylene, is necessary to prevent soot formation on, and deactivation of, the downstream typically nickel-based methanation catalyst. Thermal or catalytic reforming options to remove these compounds also result in significant destruction of the desired product methane.
Steam is added to the feed gas to ensure a sufficient H/C ratio to prevent (thermodynamic) soot formation. The feed gas inlet temperature is 350°C. In this catalytic section the water-gas shift also takes place, therefore, a separate shift step is not required. Furthermore, the NH3 in the gas will be converted into N2. Feed gas specifications to protect the catalyst are <100 ppbV for total sulphur and <100 ppbV chloride.