Definition - What does Sweet Gas mean?
Sweet gas is the natural gas that contains very little or no the hydrogen sulfide. The H2S is undesirable due to its toxicity in addition to being corrosive to all metals used in the equipment for gas processing, handling and transportation. The absence of the corrosive H2S makes the sweet gas more environmentally friendly, in addition to lower manufacturing costs of pipelines and associated equipment as well as lower installation and maintenance costs.
Corrosionpedia explains Sweet Gas
Sweet gas is sometimes available in its natural state, in which it can be used with little purifying. However, if the natural gas from the well contains a higher concentration of the H2S, a suitable gas sweetening process must be used to remove the toxic gas and convert the sour gas into sweet gas.
The concentrations hydrogen sulfide, carbon dioxide and various hydrocarbon components in natural gas usually vary depending on the well and other factors. The H2S component may vary from very low and barely detectable quantities to more than 30 mole percent. Due to the toxicity and corrosion-causing properties of the H2S, the regulations in the gas industry requires that the sulfide should not exceed a certain limit, - maximum H2S be less than 4 ppm.
The sweetening process removes any excess H2S to improve the quality and helps meet regulatory requirements. In particular, the removal of the H2S and CO2 help prevent corrosion and also increase heating value due to the removal of the CO2.
There are two types of desulfurization: the absorption, which is a dry process, and the adsorption, which is a wet process. The two methods can either be chemical or physical, and may further be classified into other categories.
The gas sweetening method depends on conditions such as the H2S concentration, the total sulfur limit in the sale gas, cost, disposal of the waste products, if the sulfur is to be recovered, and the raw gas inlet pressure.
The process may be non-regenerative, regenerative with the recovery of H2S, or a regenerative with the recovery of the elemental sulfur. The H2S gas removal is sometimes accompanied by the removal of the equally corrosive CO2 and COS if they are available.
Sweet gas is environmentally friendly, less corrosive and its combustion has less SO2 production, hence less acid rain.