Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 23

Many gas streams, while ostensibly being hydrocarbon in nature, contain large amounts of acid gases such as hydrogen sulfide (H₂S) and carbon dioxide (CO₂) and acid gas is natural as or even process gas that contains significant amounts of hydrogen sulfide, carbon dioxide, or similar contaminants. The terms acid gas and sour gas are often (incorrectly) treated as synonyms.

A gas stream containing hydrogen sulfide or carbon dioxide is referred to as sour and a gas stream that is free from hydrogen sulfide is referred to as sweet. The corrosive nature of hydrogen sulfide and carbon dioxide in the presence of water (giving rise to an acidic aqueous solution) and because of the toxicity of hydrogen sulfide and the lack of heating value of carbon dioxide. However, because gas streams from a variety of renewable sources have a wide range of composition, including the concentration of the two acid gases, processes for the removal of acid gases vary and are subject to choice based upon the desired end-product.

In addition to hydrogen sulfide and carbon dioxide, a gas stream may contain other contaminants, such as mercaptan derivatives (such as methyl mercaptan, CH₃SH, and carbonyl sulfide, COS). The presence of these impurities may eliminate some of the sweetening processes since some processes remove large amounts of acid gas but not to a sufficiently low concentration. On the other hand, there are those processes that are not designed to remove (or are incapable of removing) large amounts of acid gases. However, these processes are also capable of removing the acid gas impurities to low levels when the acid gases are there in low to medium concentrations in the gas.

To sweeten (i.e., remove sulfur compounds from) the high acid content gas, it is first pre-scrubbed to remove entrained brine, hydrocarbons, and other constituents. The sour gas then enters an absorber, where lean amine solution chemically absorbs the acid gas components, as well as a small portion of hydrocarbons, rendering the gas ready for processing and sale. An outlet scrubber removes any residual amine, which is regenerated for recycling. Hydrocarbon contaminants entrained in the amine can be separated in a flash tank and used as fuel gas or sold. Process efficiency can be optimized by mixing different types of amine to increase absorption capacity, by increasing the amine concentration, or by varying the temperature of the lean amine absorption process.

See also: Gas Cleaning, Gas Processing, Gas Treating.