Gas treating processes

There are so many gas treating processes that one hardly knows where to begin. That makes the selection process for a given situation difficult. Economics ultimately decide, but some initial rough screening will be required to eliminate inordinate study. The author has attempted to condense the mass of information in the literature into some brief, user-friendly guidelines for the rough cut. 

Physical/chemical type Biological type Solid bed scavengers 

Sulfinol Shell-Paques Iron sponge, zinc oxide, mol sieve, activated carbon 

Ballard, D., and Manning, W., Design Techniques For Amine Plans, Presented at PETRO ENERGY, October 1988. 

and Nielson, R., Gas Purification, 5 Ed., Gulf Professional Publishing, 1997. 

The selected popular processes are grouped as follows Reaction type MEA, DEA, MDEA, DGA, Stretford (also produces sulfur) 

Physical solvent type Fluor solvents (propylene carbonate example), Selexol Physical/chemical type Sulfinol Carbonate type Potassium carbonate Solution batch type Lo-Cat, Chemsweet Bed batch type Iron Sponge, Mol Sieve 

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Other gas-treating processes involving sulfolane are (/) hydrogen selenide removal from gasification of coal, shale, or tar sands (qv) (108) (2) olefin removal from alkanes (109) (J) nitrogen, helium, and argon removal from natural gas (110) (4) atmospheric CO2 removal in nuclear submarines (5) ammonia and H2S removal from waste streams (6) H2S, HCl, N2O, and CO2 removal from various streams (111—120) and (7) H2S and SO2 removal from... 

A bleed from the scmbbing system is sent to a sour slurry stripper. The water is then clarified and can be recycled to minimize the volume of effluent to be biotreated and discharged or evaporated. The acid gas from the acid gas removal system and from the sour slurry stripper is fed to a Claus plant, where salable elemental sulfur (qv) is produced. For maximum sulfur recovery and minimal sulfur emissions, the Shell Claus off-gas treating process (SCOT) is used. 

Low acid gas partial pressures (product of system pressure and concentration of acid gases—HiS and CO2 in the feed) of roughly 50psi and below. Another way of looking at selection based upon acid gas concentration is Figure 1 in the previous section entitled Gas Treating Processes. 

Chen [133] highlights the long-term growth of the technically popular use of bubble cap trays, valve and sieve trays, followed by the increased popularity of packed columns accompanied by the development of random and structured packings. There are some applications in chemical/ petrochemical/petroleum/gas treating processes where one type of contacting device performs better and is more economical than others. Chen [133] points out ... 

S.A. Newman, Acid and Sour Gas Treating Processes , Gulf, Houston, 1985, Ch. 20. 

Tail gas cleanup is required because a well-designed Claus plant with three catalytic stages and fresh catalyst will recover only 95-97% of its feed sulfur (8), which is not generally sufficient to meet current emission standards. In addition, feed impurities and catalyst aging will reduce overall recovery in some plants to about 92% just before catalyst changeout. Therefore, tail-gas cleanup is required. Tail-gas treating processes are generally classified as follows ... 

Tail Gas Cleanup Process Efficiency - Required process efficiency depends on applicable emission regulations. Low-efficiency processes result in up to 99.0-99.5% overall sulfur recovery when combined with the Claus plant and include the Sulfreen, SNPA/Haldor-Topsoe, CBA, IFP, and Beavon Mark II processes. High-efficiency tail-gas treating processes can achieve overall sulfur recoveries of 99.8% and above under ideal conditions. These include the Beavon Mark I, SCOT, Trencor, and Wellman-Lord processes. 

Since the Claus process by itself removes only about 90% of the hydrogen sulfide in the gas stream, the Beavon process (Speight, 1993, p. 268), SCOT (Shell Claus Off-Gas Treating) process (Speight, 1993, p. 316 Hydrocarbon Processing,... 

A further question arises on the need for the exceptionally high purity tail-gas treating processes. The energy demands of these systems are excessive, compared with less efficient systems. 

Indeed, more pollutants may be emitted in the production of energy to replace the energy used for tail-gas treatment, than are recovered by the more efficient tail-gas treating processes. 

The example to be considered concerns the removal of CO2 from a natural gas stream free of H2S using an aqueous MEA-solution [98]. Amine gas treating processes follow a basic liquid-phase reaction system. All reactions are reversible however instantaneous (a proton transfer) and finite-rate reactions should be differentiated here again (cf. Section 9.5.2.1). 

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