Technical and economic comparison of natural gas sweetening process.

摘要

Natural gas has a wide variety of uses and, as obtained from the reservoir, is either sweet or sour. Sweet natural gas has little, if any, hydrogen sulfide (H2S) content, but sour gas contains contaminants, such as hydrogen sulfide (H2S), carbon dioxide (CO2), and others. In order to make use of this sour gas, it must be sweetened using various gas-sweetening processes.;The main three types of available gas sweetening technologies are: chemical, physical and hybrid solvents processes for reducing H2S and CO 2 contents. The chemical solvent processes, such as alkanolamines (MEA, DEA, DGA, DIPA, and MDEA), have lower energy consumption, and lower maintenance cost than physical solvent processes. The chemical solvent processes are good for gas-sweetening applications in which, the natural gas contains heavy hydrocarbons, has a low H2S/CO2 ratio, is a low-pressure (less than 500 psig) system, and has low sulfur requirements.;The physical solvent processes such as: SelexolRTM (DEPG), Purisol (NMP), RectisolRTM (methanol), and FLUOR solvent (1,2-propylene carbonate) have higher corrosive potential, less foaming tendencies, and more complex nature than chemical solvent processes. The physical solvent processes are good for natural gases having high acid gas concentrations, and when there is a requirement to treat and dehydrate gas simultaneously, with the best-known example being the Molecular Sieve Process.;Hybrid solvent processes, such as SulfinolRTM-D, use a mixture of DIPA, water, and sulfolane (C4H8O 2S), and hybrid (or mixed) amine mixtures are mixtures of MDEA and DEA or MEA. Hybrid solvents enhance H2S and CO2 removal efficiency; increase concentration and stability while retaining the capabilities of DIPA (or MDEA), such as: low heat of reaction, and lower corrosion potential. Hybrid solvents have 5% to 10% more operating cost, but generate negligible losses compared to other processes. Their capital cost requirements are less than other processes for the same capacity, because smaller-sized equipment is required due to (20% to 25%) lower foaming, lower energy consumption (15% to 18%), and much lower circulation rates.;The selection of solvent is very important because the right solvent can lower the capital costs and the operating costs by as much as 30% to 40%, and fuel cost by as much as 50%. The prime objective of gas sweetening is to produce a specification-quality product as economically as possible. A detailed gas sweetening process using DEA as the chemical solvent has been designed (Refer to Appendix -2.1) in which, all the process conditions and parameters have been calculated and described for a sour gas plant that is processing 10 MMSCFD of sour gas that contains 9.8% H2S and 1.7% CO2.