System and Method for Removing Hydrogen Sulfide From Sour Natural Gas

Abstract

A method for processing includes reacting hydrogen sulfide (H.sub.2S), in a sour NG stream, and a sulfur dioxide (SO.sub.2) stream, the sour NG stream having a molar concentration of at least about 0.5% H.sub.2S, the reactor output including sulfur, water, and a reacted NG stream having a lower molar concentration of H.sub.2S compared to the sour NG stream; contacting the reactor output and a liquid solvent in a solvent wash column to remove at least some H.sub.2S from the reacted NG stream to produce a treated NG stream, the treated NG stream having a lower molar concentration of H.sub.2S compared to the reacted NG stream, the solvent wash column further outputting a solvent mixture stream that includes at least the liquid solvent and the sulfur; and separating, with a centrifuge, the solvent mixture stream into solid sulfur and a recyclable liquid solvent stream.

Claims

1. A system for processing sour natural gas, comprising: a sour natural gas source outputting a sour natural gas stream, the sour natural gas stream having a molar concentration of at least about 0.5% hydrogen sulfide (H.sub.2S); a sulfur dioxide (SO.sub.2) source outputting an SO.sub.2 stream; a mixer having inputs fluidly coupled to the sour natural gas source and the SO.sub.2 source, the mixer configured to mix the sour natural gas stream and the SO.sub.2 stream to produce a mixed gas stream; a reactor having an input that receives the mixed gas stream and reacts the H.sub.2S and SO.sub.2 to form sulfur and water, the reactor outputting a reacted natural gas stream, the sulfur, and the water, the reacted natural gas stream having a lower molar concentration of the H.sub.2S compared to the sour natural gas stream; a solvent source outputting a liquid solvent stream; a solvent wash column having a first input that receives the reacted natural gas stream and a second input that receives at least the liquid solvent stream, the first input at or near a bottom of the solvent wash column, the second input at or near a top of the solvent wash column, the liquid solvent stream removing at least some of the H.sub.2S from the reacted natural gas stream to produce a treated natural gas stream at a first output of the solvent wash column, the treated natural gas stream having a lower molar concentration of the H.sub.2S compared to the reacted natural gas stream; and a centrifuge having an input fluidly coupled to a second output of the solvent wash column to receive a solvent mixture stream that includes at least liquid solvent and sulfur, the centrifuge separating the sulfur and the liquid solvent and producing the sulfur and the liquid solvent at first and second outputs, respectively.

2. The system of claim 1, further comprising a solvent recycling system fluidly coupled to the second output of the centrifuge.

3. The system of claim 1, wherein the mixer is configured to adjust a flow rate of the sour natural gas stream and a flow rate of the SO.sub.2 stream such that the mixed gas stream has a ratio of about 3 mols H.sub.2S per mol of SO.sub.2.

4. The system of claim 1, wherein the centrifuge comprises a decanter centrifuge.

5. The system of claim 1, wherein the liquid solvent comprises a glycol.

6. The system of claim 5, wherein the glycol comprises triethylene glycol.

7. The system of claim 1, wherein a sulfur cake is produced at the first output of the centrifuge.

8. A method for processing sour natural gas, comprising: reacting, in a reactor, hydrogen sulfide (H.sub.2S) in a stream of sour natural gas and a stream of sulfur dioxide (SO.sub.2) to form sulfur and water, the sour natural gas stream having a molar concentration of at least about 0.5% of the H.sub.2S, the reactor having an output that includes the sulfur, the water, and a reacted natural gas stream that has a lower molar concentration of the H.sub.2S compared to the stream of sour natural gas; contacting the output of the reactor and a liquid solvent in a solvent wash column, the liquid solvent removing at least some of the H.sub.2S from the reacted natural gas stream to produce a treated natural gas stream at a first output of the solvent wash column, the treated natural gas stream having a lower molar concentration of the H.sub.2S compared to the reacted natural gas stream, the solvent wash column including a second output that produces a solvent mixture stream that includes at least the liquid solvent and the sulfur; and separating, with a centrifuge, the solvent mixture stream into a solid sulfur and a recyclable liquid solvent stream.

9. The method of claim 8, further comprising removing one or more impurities from the recyclable liquid solvent stream using a solvent stripper to form a purified recyclable liquid solvent stream.

10. The method of claim 9, further comprising flowing the purified recyclable liquid solvent stream into the solvent wash column.

11. The method of claim 8, further comprising: adjusting a flow rate of the stream of sour natural gas and a flow rate of the SO.sub.2 to produce a mixed gas stream having a ratio of about 3 mols H.sub.2S per mol of SO.sub.2; and introducing the mixed gas stream into the reactor.

12. The system of claim 8, wherein the centrifuge comprises a decanter centrifuge.

13. The system of claim 8, wherein the liquid solvent comprises a glycol.

14. The system of claim 13, wherein the glycol comprises triethylene glycol.

15. The system of claim 8, wherein the solid sulfur comprises a sulfur cake.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a fuller understanding of the nature and advantages of the concepts disclosed herein, reference is made to the detailed description of preferred embodiments and the accompanying drawings.

[0013] FIG. 1 is a block diagram of a system for processing sour natural gas according to one or more embodiments.

[0014] FIG. 2 is a flow chart of a method for processing sour natural gas according to one or more embodiments.

DETAILED DESCRIPTION

[0015] Hydrogen sulfide (H.sub.2S), in a sour natural gas (NG) stream, and a sulfur dioxide (SO.sub.2) stream are combined and reacted, in a reactor to form sulfur and water. The sour NG stream has a molar concentration of at least about 0.5% H.sub.2S. The reactor output includes a reacted NG stream having a lower molar concentration of H.sub.2S compared to the sour NG stream. The reactor output also includes sulfur and water. The reactor output and a liquid solvent are contacted in a solvent wash column to remove at least some H.sub.2S from the reacted NG stream to produce, at a top output of the solvent wash column, a treated NG stream. The treated NG stream has a lower molar concentration of H.sub.2S compared to the reacted NG stream. A bottom output of the solvent wash column produces a solvent mixture stream that includes at least the liquid solvent and sulfur. The liquid solvent and sulfur are separated using a centrifuge into solid sulfur (e.g., sulfur cake) and a recyclable liquid solvent stream. The recyclable liquid solvent stream can be purified (e.g., using a solvent stripper) and recycled back to the solvent wash column.

[0016] FIG. 1 is a block diagram of a system 10 for processing sour natural gas (NG) according to one or more embodiments. The system 10 includes a sulfur dioxide (SO.sub.2) source 101, an optional pump 102, a sour NG source 103, an optional vessel 104, a mixer 105, an optional heat exchanger 106, an optional vessel 107, a reactor 108, an optional vessel 109, an optional divider 110, a solvent wash column 111, an optional vessel 112, an optional heat exchanger 113, a centrifuge 114, a solvent source 115, and an optional solvent recycle system 116.

[0017] The mixer 105 is fluidly coupled to the SO.sub.2 source 101 and the sour NG gas source 103 to receive and mix respective streams of SO.sub.2 and sour NG to produce a gas mixture. The sour NG includes hydrogen sulfide (H.sub.2S) at a high concentration such as about 0.5 molar percent to about 5 molar percent including about 1 molar percent, about 2 molar percent, about 3 molar percent, about 4 molar percent, and any value or range between any two of the foregoing values. As used herein, about means plus or minus 10% of the relevant value. The relative flow rates of the SO.sub.2 and sour NG streams can be adjusted such that the mixer 105 produces a mixture having a ratio of about 3 mols H.sub.2S per mol of SO.sub.2 (e.g., a 3:1 molar ratio of H.sub.2S and SO.sub.2, respectively). In one or more embodiments, the mixer 105 produces a mixture having a molar ratio of about 2:1 to about 5:1 of H.sub.2S and SO.sub.2, respectively, including any value or range therebetween.

[0018] The pump 102 can pressurize and/or regulate flow of the SO.sub.2 stream. The SO.sub.2 in the SO.sub.2 stream can be in liquid or gas form. In one or more embodiments, the SO.sub.2 source 101 can be pressurized and a valve, instead of or in addition to the pump 102, can be used to regulate flow of the SO.sub.2 stream.

[0019] The output of the mixer 105 is fluidly coupled to the input of the optional heat exchanger 106 and/or to the input of the optional vessel 107.

[0020] The reactor 108 is configured to cause a reaction between SO.sub.2 and H.sub.2S in the sour natural gas to substantially reduce the concentration of H.sub.2S in the sour natural gas. The SO.sub.2 and H.sub.2S can react according to the Claus reaction:

2H.sub.2S+SO.sub.2.fwdarw.S+2H.sub.2O

[0021] The reactor 108 can operate at about 200 psig to about 250 psig, including any value or range therebetween, and at a temperature of about 80 F. to about 120 F., including any value or range therebetween. The SO.sub.2 and H.sub.2S can come into contact over conventional packing media in the reactor 108. The output of the reactor 108 is or includes a slurry of sulfur (e.g., crystals, particles, and/or other form(s) of sulfur), purified natural gas, and any unreacted SO.sub.2. The purified natural gas has an H.sub.2S concentration that is lower than the H.sub.2S concentration of the sour natural gas. In a simulation, the purified natural gas had an H.sub.2S concentration of 7.8454 ppm (parts per million) and the sour natural gas had a molar concentration of 4% H.sub.2S and a molar flow rate of 4.3919 lbmol/hour H.sub.2S.

[0022] The Claus reaction is exothermic resulting in temperature increases in the purified gas at the output of the reactor 108 compared to the temperature of the gas mixture at the input of the reactor 108. The reactor 108 can be air cooled to remove some or all of the heat of reaction.

[0023] The output of the reactor 108 is fluidly coupled to (via placeholder A) an optional vessel 109 and/or to an input of the solvent wash column 111. The purified natural gas can be introduced at or near a bottom input of the solvent wash column 111 and can flow upwards through the solvent wash column 111. A liquid solvent flows downward through an top input of the solvent wash column 111 such that liquid solvent and the purified natural gas contact each other throughout some or all of the height of the solvent wash column 111. The solvent can reduce the concentration of H.sub.2S in the purified natural gas stream, for example by aiding in the conversion of H.sub.2S to sulfur. In addition, the solvent can absorb unreacted SO.sub.2 and can remove water (e.g., dehydrate) that may be flowing in the purified natural gas stream. In some embodiments, the absorbed SO.sub.2 can be recovered from the solvent in a recycling process.

[0024] The solvent can include or consist of a glycol (e.g., a glycol derivate) such as triethylene glycol (TEG). Additional and/or alternative solvent(s) can be used in other embodiments. The solvent can be provided from the solvent source 115 which is fluidly coupled to (e.g., a top input of) the solvent wash column 111.

[0025] A treated natural gas stream is output at a top output of the solvent wash column 111. The treated natural gas in the treated natural gas stream has an H.sub.2S concentration that is lower than the H.sub.2S concentration of the purified natural gas output from the reactor 108 and lower than the H.sub.2S concentration of the sour natural gas (e.g., from the sour natural gas source 103). In a simulation, the treated natural gas had a molar concentration of 0.00074367%, the purified natural gas had an H.sub.2S concentration of 7.8454 ppm, and the sour natural gas had a molar concentration of 4% H.sub.2S with a molar flow rate of 4.3919 lbmol/hour H.sub.2S. Thus, the molar concentration of H.sub.2S was reduced by a factor of over 5,000 in the treated natural gas compared to the sour natural gas.

[0026] A solvent mixture stream is output at the bottom output of the solvent wash column 111. The solvent mixture stream is input to an optional vessel 112 and/or to an optional heat exchanger 113. The solvent mixture stream includes at least the liquid solvent that has passed through the solvent wash column 111 and sulfur (e.g., in solid or crystalline form). The solvent mixture stream can also include water and/or any chemicals (e.g., H.sub.2S) absorbed from the treated natural gas stream.

[0027] The output of the solvent wash column 111, of the optional vessel 112, and/or of the optional heat exchanger 113 is fluidly coupled to the input of the centrifuge 114. The centrifuge 114 separates the solvent mixture stream into solid sulfur (e.g., sulfur cake) at a first output of the centrifuge 114 and recyclable solvent at a second output of the centrifuge 114. The solid sulfur is generally non-hazardous to transport. At lower volumes, the solid sulfur may be disposed of at a landfil. There may be regional interest for fertilization use of the solid sulfur as well. In some embodiments, the centrifuge 114 can be or comprise a decanter centrifuge.

[0028] The second output of the centrifuge 114 can be fluidly coupled to the input of the solvent recycle system 116. Alternatively, the recyclable solvent can be discarded (e.g., when the system 10 does not include a solvent recycle system 116).

[0029] The optional solvent recycle system 116 includes a solvent stripper 117, an optional vessel 118, an optional K-100 119, an optional pump 120, an optional heat exchanger 121, and a mixer 122.

[0030] When the system 10 includes a solvent recycle system 116, the second output of the centrifuge 114 is fluidly coupled to the input of the solvent stripper 117 to receive the recyclable solvent stream. The solvent stripper 117 is configured to remove one or more impurities from the recyclable solvent stream. A purified recyclable solvent stream is output from the K-100 119. Impurities can be output from the vessel 118, which is fluidly coupled to the top of the solvent stripper 117.

[0031] The purified recyclable solvent stream is combined with a solvent stream (e.g., a virgin solvent stream) from the solvent source 115 in the mixer 122. The purified recyclable solvent stream can optionally be pumped by the pump 120 and/or cooled/heated by the heat exchanger 121.

[0032] Example physical and chemical properties of the sour natural gas stream and the treated natural gas streams from the simulation are provided in Table 1.

TABLE-US-00001 TABLE 1 Sour Treated Natural Name Units Natural Gas Gas Pressure psig 120 119.5 Temperature F. 200 130.87 Std Vapor Volumetric MMSCFD 1 0.96305 Flow H.sub.2S (mole fraction) % 4 0.00074367 N.sub.2 (mole fraction) % 1 1.0372 CO.sub.2 (mole fraction) % 2 2.036 C1 (mole fraction) % 78.52 81.391 C2 (mole fraction) % 8 8.2919 C3 (mole fraction) % 5 5.1823 iC4 (mole fraction) % 0.32 0.33181 nC4 (mole fraction) % 0.6 0.62159 iC5 (mole fraction) % 0.1 0.10318 nC5 (mole fraction) % 0.4 0.41419 C6 (mole fraction) % 0.05 0.051713 C7 (mole fraction) % 0.01 0.010318 H.sub.2O (mole fraction) % 0 0.016241 S1 (mole fraction) % 0 0 S2 (mole fraction) % 0 0 S3 (mole fraction) % 0 0 S4 (mole fraction) % 0 0 S5 (mole fraction) % 0 0 S6 (mole fraction) % 0 1.0751e05 S7 (mole fraction) % 0 1.1681e05 S8 (mole fraction) % 0 0.0008583 SO2 (mole fraction) % 0 0.49469 Ethylene Glycol % 0 0.016021 (mole fraction)

[0033] FIG. 2 is a flow chart of a method 20 for processing sour NG according to one or more embodiments. The method 20 can be performed using system 10.

[0034] In step 201, H.sub.2S in sour NG and SO.sub.2 are reacted in a reactor 108 to form sulfur and water (e.g., according to the Claus reaction). The flow rates of the sour NG and the SO.sub.2 can be controlled such that there is molar ratio of about 2:1 to about 5:1 of H.sub.2S and SO.sub.2 where the H.sub.2S is present in the sour NG. The sour NG and the SO.sub.2 can be mixed before entering the reactor 108. The output of the reactor 108 is or includes a slurry of sulfur (e.g., crystals, particles, and/or other form(s) of sulfur), purified natural gas, and any unreacted SO.sub.2. The purified natural gas has an H.sub.2S concentration that is lower than the H.sub.2S concentration of the sour natural gas.

[0035] In step 202, the reactor output is fed into the bottom input of a solvent wash column 111 where the reactor output and a solvent contact one another. The solvent can reduce the concentration of H.sub.2S in the purified natural gas stream, for example by aiding in the conversion of H.sub.2S to sulfur. In addition, the solvent can absorb unreacted SO.sub.2 and can remove water (e.g., dehydrate) that may be flowing in the purified natural gas stream. In some embodiments, the absorbed SO.sub.2 can be recovered from the solvent in a recycling process. The solvent can include or consist of a glycol (e.g., a glycol derivate) such as TEG. The solvent can be fed into the top input of the solvent wash column 111. The solvent can be provided by a solvent source 115 and optionally by a solvent recycle system 116.

[0036] The solvent wash column 111 produces a treated natural gas stream at the top output of the solvent wash column 111 and a solvent mixture stream at the bottom output of the solvent wash column 111. The treated natural gas in the treated natural gas stream has an H.sub.2S concentration that is lower than the H.sub.2S concentration of the purified natural gas output from the reactor 108 and lower than the H.sub.2S concentration of the sour natural gas (e.g., from the sour natural gas source 103). The solvent mixture stream includes at least the liquid solvent that has passed through the solvent wash column 111 and sulfur (e.g., in solid or crystalline form). The solvent mixture stream can also include water and/or any chemicals absorbed from the treated natural gas stream.

[0037] In step 203, the solvent mixture stream is fed into a centrifuge 114 to separate the solvent mixture stream into a recyclable solvent stream and solid sulfur. The centrifuge 114 can be or can comprise a decanter centrifuge.

[0038] In optional step 204, one or more impurities is/are removed from the recyclable solvent stream. The impurity (ies) can be removed using a solvent stripper 117.

[0039] In optional step 205, a purified recyclable solvent stream is fed into the top input of the solvent wash column 111. Additional (e.g., virgin) solvent can be combined with the purified recyclable solvent stream.

[0040] The invention should not be considered limited to the particular embodiments described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the invention may be applicable, will be apparent to those skilled in the art to which the invention is directed upon review of this disclosure. The claims are intended to cover such modifications and equivalents.

[0041] Also, as described, some aspects may be embodied as one or more methods. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.