Gas Sweetening Processes

Numerous processes have been developed for gas sweetening based on a variety of chemical and physical principles. These processes can be categorized by the principles used in the process to separate the acid gas and the natural gases as follows  

Chemical solvents Monoethanol amine (MEA) Diethanol amine (DEA) Methyldiethanol amine fMDEA) Diglycol amine (DGA) Diisopropanol amine (DIPA) 

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FIGURE 9.6 Flowsheet giving the schematic details of Girbotol and related sour gas sweetening processes. Twenty to twenty-four plates are used in the absorbers and strippers [25] for efficient contacting and desorption with monoethanolamine (MEA),... 

Elf Activated MDEA (1994) An important improvement in natural gas sweetening processes. 19th World Gas Conference, Milan. 

There are two main processes in the thioarsenate category. The first, the Thylox process, was developed in the late twenties and used in the U.S. for many years, especially for the purification of coke-oven and other manufactured gases. The second, the Giammarco-Vetro-coke (G-V) process, is a dual H2S/CO2 gas sweetening process introduced in Italy in 1955, which was extensively used in Europe and Asia, especially in applications where the H2S concentration in the feed gas was relatively low. 

Bhatia, K., and Brown, T. M., 1986, Examination of Field Data From a New Gas Sweetening Process, presented at the 61st Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, New Orleans, LA, Oct. 5-8, SPE 15456. 

Trahan, D. O., and Manning, W. P., 1992, Batch Gas Sweetening Processes presented at the GRI Liquid Sulftir Recovery Conference, Oct. 4-6. 

Naturai Gas Sweetening Processes These processes remove CO2 from high-pressure methane stemming from natural gas walls. Many natural gas streams are... 

Carbonyl sulfide occurs as a by-product ia the manufacture of carbon disulfide and is an impurity ia some natural gases, ia many manufactured fuel gases and refinery gases, and ia combustion products of sulfur-containing fuels (25). It tends to be concentrated ia the propane fraction ia gas fractionation an amine sweetening process is needed to remove it. 

The formation of sulfuric acid cannot be economically retarded in the combustion process. The best method of eliminating sulfuric acid as a combustion product is to remove sulfur from the incoming fuel gas. Two separate sweetening processes are used to remove all sulfur from the fuel gas that will be burned. 

J Consider the coke-oven gas COG sweetening process shown in Fig. 3.22. The basic objective of COG sweetening is the removal of acidic impurities, primarily hydrogen sulfide, from COG (a mixture of H2, CH4, CO, N2, NH3, CO2, and H2S). Hydrogen sulfide m undesirable impurity, because it is corrosive and contributes to SO2 emission when the G... 

LOCAT units can be used for tail-gas clean-up from chemical or physical solvent processes. They can also be used directly as a gas sweetening unit by separating the absorber/oxidizer into two vessels. The regenerated solution is pumped to a high-pres.sure absorber to contact the gas. A light slurry of rich solution comes off the bottom of the absorber and flows to an atmospheric oxidizer tank where it is regenerated. A dense slurry is pumped off the base of the oxidizer to the melter and sulfur separator. 

Sour gas sweetening may also be carried out continuously in the flowline by continuous injection of H2S scavengers, such as amine-aldehyde condensates. Contact time between the scavenger and the sour gas is the most critical factor in the design of the scavenger treatment process. Contact times shorter than 30 sec can be accommodated with faster reacting and higher volatility formulations. The amine-aldehyde conden-... 

The R D activities of GRI led to a group of two patents, for gas sweetening (and also useful for flue gas treatment), based on biocatalytic processes for the selective removal of sulfur compounds in the presence of other reactive gases. 

Alkanolamines. Gas sweetening, ie, removal of hydrogen sulfide and carbon dioxide, using alkanolamines was patented in 1930. Several amine solvents are available as of the mid-1990s. The most widely used are monoethanolamine [141-43-5], diethanolamine [111-42-2], diglycolamine [929-06-6], and methyldiethanolamine [105-59-9]. Amine processes are generally applicable when hydrogen sulfide concentration in the feed gas is relatively low (eg,... 

The chemical processing techniques considered for synfuels flowsheet for the removal and recovery of sulfur are similar to those employed in other industries - notably natural gas sweetening, petroleum hydrodesulfurization, and coke oven gas treatment -but with certain significant differences attributable to the operating conditions encountered in synfuels processing. 

Selective Absorption in the Sweetening Process. In recent years removal of the acid gas (H2S, CO2) components from a gas stream has increasingly been by absorption in a solvent system containing amines. While non-reactive solvent sweetening processes are in use, the ability of the basic amine to react chemically with the acid gas to yield water soluble salts has favored the chemical sweetening system. Thus... 

The production of COS in the front end reaction furnace presents special problems since sulfur in this form may be difficult to remove in the downstream catalytic beds under conditions that are optimal for the Claus redox reaction between H2S and SO COS (and CS2) were known to be generated from hydrocarbon impurities carried over in the acid gas feed thus the efficiency of the up-stream sweetening process became an important factor. The reaction of CO2, a common constituent of the acid gas feed, with H2S and/or sulfur under furnace temperature conditions has also been shown to be an important source of COS. 

Alkanolamines are used during the sweetening process in the oil and gas industry to remove toxic levels of gases such as hydrogen sulfide and carbon disulfide from raw gas condensates. Various alkanolamines such as A-methyldiethanolamine (23) and triethanolamine (25) may be utilized. They are therefore of concern as environmental contaminants of groundwater and wetland areas. Headley et al. (66)... 

Slurrisweet A process for removing sulfur dioxide from gas streams by absorption in an aqueous suspension of iron oxide particles. Developed by Gas Sweetener Associates from the 1980s but later abandoned. 

SulfaTreat A process for removing hydrogen sulfide and mercaptans from natural gas or carbon dioxide streams, using a proprietary solid absorbent, which is subsequently dumped. First developed by Gas Sweetener Associates, now licensed by Sulfa Treat, a business unit of MI-SWACO, MO. More than 1,000 plants were operating in 2000. 

Figure 1.2 shows the basic block diagram for the acid-gas injection process, including a block for the natural gas sweetening unit. For CCS, the sweetening block is replaced by a carbon capture block, but the rest of the process is unchanged. The four main components of the injection scheme are 1. compression, 2. pipeline, 3. injection well, and 4. reservoir. Each of these will be discussed in some detail in this book. 

Liquid water and sometimes water vapor are removed from natural gas to prevent corrosion and formation of hydrates in transmission lines and to attain a water dew point requirement of the sales of gas. Many sweetening agents employ an aqueous solution for treating the gas. Therefore dehydrating the natural gas that normally follows the sweetening process involves ... 

The mercaptans may be regenerated by acidification of the caustic solutions, or these solutions may be deliberately oxidized to yield disulfides (57). It should be pointed out that, just as in the case of the gas purifying processes, hydrogen sulfide reacts with all the other alkalis in the aforementioned processes. Because the amount of hydrogen sulfide is usually large and because of its activity toward ordinary caustic solutions, a common refinery practice is to remove a major part of the hydrogen sulfide with inexpensive caustic so as not to overload the subsequent sweetening processes. 

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