Bio-SNG - CNG Services

Contaminent mg/Nm3 gasContaminent mg/Nm3 gasBIO-SNG FEASIBILITY STUDY – ESTABLISHMENT OF A REGIONAL PROJECT5.3 GAS PROCESSINGSyngas processing requirements are determined by the gas quality limitations imposed by catalysts usedin the methanation reaction. The methanation reactions are moderately exothermic and simplyrepresented as follows:CO + 3H2 → CH4 + H 2 O - 217kJ/mole…………………… (1)C0 2 + 4H 2 → CH 4 + 2H 2 0 - 175kJ/mole……………………. (2)The reaction takes place at elevated temperature over a catalyst, for which there are a number of materialoptions including nickel, iron, chromium and copper based catalysts, however, these are invariablyintolerant of even traces of heavy metals such as mercury, lead and arsenic and intolerant of smallparticles of tar, or of sulphur and chlorine compounds. The main technical challenge posed by an SNGfacility is therefore the syngas cleaning that is required upstream of the methanation reactor.Figure 5.5shows the practical scale of syngas quality improvement that must be achieved to enablesatisfactory catalyst life to be achieved.30002500Raw Engine Synthesis1614200012101500810006450020Tars Particulate Sulphur Halides0Tars Particulate Sulphur HalidesFigure 5.5Syngas quality ex-gasifier, requirement for use in engine and for synthesisState-of–the-art gas processing technologies are capable of achieving the necessary syngas quality, thechallenge being to do this economically on a process plant of relatively modest scale and at a reasonablelevel of energy efficiency. The syngas leaving the gasifier will be at temperatures around 900 0 C and willcarry therefore a significant amount of sensible heat; this should be recovered efficiently for thegeneration of steam for use in the process and for power generation to meet plant electricity demand.39