7 OVERVIEW GAS CLEANING
Each synthesis gas production plant requires gas treatment facilities to purity product gases and also, in many cases, to condition them. Whereas the gas purification system eliminates the components that would affect downstream processing or utilization of these gases, the purpose of a conditioning system is to remove undesired main gas compounds and to adjust gas components to the appropriate ratio. Especially, the ratio of hydrogen to carbon monoxide must be matched to the requirements of downstream synthesis units or gas consumers [5].
Depending on the type and composition of feedstock and the type of gasification process used, the gas purification and conditioning must handle the following impurities and undesired compounds:
Particulates.
Sulphur compounds, e.g. hydrogen sulphide, carbonyl sulphide, organic sulphur.
Nitrogen compounds, e.g. mainly ammonia.
Halogens ,e.g. chlorides.
Volatile metals, e.g. alkali and earth alkali compounds.
Tars.
Hydrocarbons (if removal is necessary for usage), e.g. CH4, C2+ aliphatic hydrocarbons and aromatics like benzene and toluene.
Carbon dioxide (if removal is necessary for usage).