- Title : Petroleum & Gas Field Processing 11 by H.K. Abdel-Aal and Mohamed Aggour - King Fahd University of Petroleum & Minerals Dhahran, Saudi Arabia, M.A Fahim Kuwait University Safat, Kuwait
- Publish : Marceld Ekkeirn, C New York Basel
- Type Document : pdf
- Release : December 2003
- Total Page : 34 page
- Size : 0.43 Mb
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Decrypted Contents
Sour Gas Treating
INTRODUCTION
Natural gas usually contains some impurities such as hydrogen sulfide (H2S), carbon dioxide (CO2), water vapor (H2O), and heavy hydrocarbons such as mercaptans. These compounds are known as ‘‘acid gases.’’ Natural gas with H2S or other sulfur compounds (such as COS, CS2 and mercaptans) is called ‘‘sour gas,’’ whereas gas with only CO2 is called ‘‘sweet gas.’’ It is usually desirable to remove both H2S and CO2 to prevent corrosion problems and to increase heating value of the gas.
Sweetening of natural gas is one of the most important steps in gas processing for the following reasons:
Natural gas usually contains some impurities such as hydrogen sulfide (H2S), carbon dioxide (CO2), water vapor (H2O), and heavy hydrocarbons such as mercaptans. These compounds are known as ‘‘acid gases.’’ Natural gas with H2S or other sulfur compounds (such as COS, CS2 and mercaptans) is called ‘‘sour gas,’’ whereas gas with only CO2 is called ‘‘sweet gas.’’ It is usually desirable to remove both H2S and CO2 to prevent corrosion problems and to increase heating value of the gas.
Sweetening of natural gas is one of the most important steps in gas processing for the following reasons:
- Health hazards. At 0.13 ppm, H2S can be sensed by smell. At 4.6 ppm, the smell is quite noticeable. As the concentration increases beyond 200 ppm, the sense of smell fatigues, and the gas can no longer be detected by odor. At 500 ppm, breathing problems are observed and death can be expected in minutes. At1000 ppm, death occurs immediately.
- Sales contracts. Three of the most important natural gas pipeline specification are related to sulfur content, as shown in Table 1.Such contracts depend on negotiations, but they are quite strictabout H2S content.
- Corrosion problems. If the partial pressure of CO2 exceeds15 psia, inhibitors usually can only be used to prevent corrosion.The partial pressure of CO2 depends on the mole fraction of CO2 in the gas and the natural gas pressure. Corrosion rates will alsodepend on temperature. Special metallurgy should be used ifCO2 partial pressure exceeds 15 psia. The presence of H2S will cause metal embrittlement due to the stresses formed around metal sulfides formed.
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