Natural Gas Impurities. Summary.

The water in the NG in the vapor state does not present any problem, as long as it remains at conditions below saturation, otherwise, it would be in the presence of free water, which causes operational problems. Hence, the importance of controlling this parameter.
One of the problems observed is the formation of carbonic acid when carbon dioxide is present, so it is necessary to use the De Waard-Millams equation or the NORSOK STD M-506.
Another problem is the formation of metal sulphides when hydrogen sulphide and carbon dioxide and/or oxygen are present, so it is necessary to use NACE MR0175.
Additionally, the presence of water promotes the formation of hydrates.
On the other hand, there are liquid hydrocarbons, which unlike the previous ones are economically usable pollutants. In natural gas these cause transport issues, in measuring equipment, etc. In addition, liquid content is a specification in gas systems.
Another impurity is sulfur compounds, among which are: hydrogen sulfide, carbonyl sulfide, and mercaptans. These must be checked if free water is present, and are a specification for sales gas.
Carbon dioxide, in addition to problems with the presence of water, decreases the calorific value of the gas.
Oxygen must be controlled in the presence of free water and at high pressures, and ensure that its molar percentage is less than 17% of the mixture.
The presence of hydrogen and carbon monoxide must be considered when natural gas is mixed with refinery gases.
The presence of solid particles causes transport problems.
Finally, mercury causes operational issues, and it is found in some natural gas reservoirs.