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Table 1  Natural Gas Pipeline Specifications
            Characteristic               Specification          Test method
            Water content         4–7 lb/MMSCF maximum     ASTM (1986), D 1142
            Hydrogen sulfide content  0.25 grain/100 SCF    GPA (1968), Std. 2265
                                    maximum                GPA (1986), Std. 2377
            Gross heating value   950 Btu/SCF minimum      GPA (1986), Std. 2172

            Hydrocarbon dew point  15 F at 800 psig maximum  ASTM (1986), D 1142
            Mercaptan content     0.2 grain/100 SCF maximum  GPA (1968), Std. 2265
            Total sulfur content  1–5 grain/100 SCF maximum  ASTM (1980), D 1072
            Carbon dioxide content  1–3 mol% maximum       GPA (1990), Std. 2261
            Oxygen content        0–0.4 mol% maximum       GPA (1990), Std. 2261
            Sand, dust, gums, and
              free liquid         Commercially free


            Delivery temperature ( F)  120 F maximum
            Delivery pressure (psia)  700 psig minimum
            MMSCF   1,000,000 standard cubic feet.




            11.2  GAS-SWEETENING PROCESSES
            There are more than 30 processes for natural gas sweetening. The most
            important of these processes can be classified as follows:
                 1.  Batch solid bed absorption. For complete removal of H 2 Satlow
                    concentrations, the following materials can be used: iron sponge,
                    molecular sieve, and zinc oxide. If the reactants are discarded, then
                    this method is suitable for removing a small amount of sulfur when
                    gas flow rate is low and/or H 2 S concentration is also low.
                 2.  Reactive solvents. MEA (monoethanol amine), DEA (diethanol
                    amine), DGA (diglycol amine), DIPA (di-isopropanol amine),
                    hot potassium carbonate, and mixed solvents. These solutions
                    are used to remove large amounts of H 2 S and CO 2 and the
                    solvents are regenerated.
                 3.  Physical solvents. Selexol, Recitisol, Purisol, and Fluor solvent.
                    They are mostly used to remove CO 2 and are regenerated.
                 4.  Direct oxidation to sulfur. Stretford, Sulferox LOCAT, and
                    Claus. These processes eliminate H 2 S emissions.
                 5.  Membranes. This is used for very high CO 2 concentrations.
                    AVIR, Air Products, Cynara (Dow), DuPont, Grace, Interna-
                    tional Permeation, and Monsanto are some of these processes.







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