CA2995557A1 - A method for separating hydrogen sulphide from effluent gas - Google Patents
A method for separating hydrogen sulphide from effluent gas Download PDFInfo
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- CA2995557A1 CA2995557A1 CA2995557A CA2995557A CA2995557A1 CA 2995557 A1 CA2995557 A1 CA 2995557A1 CA 2995557 A CA2995557 A CA 2995557A CA 2995557 A CA2995557 A CA 2995557A CA 2995557 A1 CA2995557 A1 CA 2995557A1
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- hydrogen sulphide
- scrubber
- sea water
- effluent gas
- gas
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1456—Removing acid components
- B01D53/1468—Removing hydrogen sulfide
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1406—Multiple stage absorption
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2252/00—Absorbents, i.e. solvents and liquid materials for gas absorption
- B01D2252/10—Inorganic absorbents
- B01D2252/103—Water
- B01D2252/1035—Sea water
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2252/00—Absorbents, i.e. solvents and liquid materials for gas absorption
- B01D2252/60—Additives
- B01D2252/602—Activators, promoting agents, catalytic agents or enzymes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/30—Sulfur compounds
- B01D2257/304—Hydrogen sulfide
Abstract
The invention provides a method for separating hydrogen sulphide from effluent gas generated from a gas treating process such as a gas sweetening process, the method comprising the steps of feeding the effluent gas into at least one scrubber, the scrubber operating at a pressure less than 100 psig (or 700 kPa); and feeding sea water into the scrubber counter-currently to the direction of the gas flow, so that the effluent gas is contacted with the sea water thereby to reduce the hydrogen sulphide content in the effluent gas to less than 0.50% by weight by dissolution in the sea water.
Description
2 A METHOD FOR SEPARATING HYDROGEN SULPHIDE
FROM EFFLUENT GAS
Field Of Invention The invention relates to a method for treating effluent gas containing hydrogen sulphide that is generated from a gas treating process such as a gas sweetening process. More particularly, the invention pertains to a method for selectively separating hydrogen sulphide from the effluent gas stream using sea water.
Background Of The Invention Natural gas as well as other hydrocarbon gases from the oil and gas production usually contain significant amounts impurities, particularly hydrogen sulphide and carbon dioxide. Gases containing hydrogen sulphide are known as sour gas and they are undesirable due to their toxic and corrosive properties. Therefore, the sour gas must be treated to remove the hydrogen sulphide and carbon dioxide to meet downstream production or export requirements or venting to atmosphere.
Hydrogen sulphide and carbon dioxide are commonly removed from the sour gas by absorption in an alkaline solution. The sour gas is subjected to an amine gas treating process, where the sour gas is fed into a tower containing an amine solution which absorbs hydrogen sulphide and carbon dioxide as it passes through. The solution most widely used is an aqueous solution of alkanolamine, such as monoethanolamine, diethanolamine and methyldiethanolamine. The resultant gas stream is substantially free of the impurities, whilst the amine solution leaving the absorption tower is rich in the absorbed gases (which are hydrogen sulphide and carbon dioxide).
The absorbed gases are removed from the amine solution using a regenerator by preheating the solution and stripping hydrogen sulphide and carbon dioxide, from the solution in a reboiler. The effluent gas therefrom, which contains high concentrations of hydrogen sulphide and carbon dioxide, has to be disposed in a safe manner to avoid negative impacts on either workers or the environment. Where the concentration of the gases components in the effluent gas meets the environmental and safety regulatory limits for atmospheric disposal, it is possible to vent the effluent gases.
However, if the gases are present in high concentration, it is not safe and environmentally acceptable to vent the gases into the atmosphere. Therefore, there exists a need for a method for selectively and effectively removing or reducing hydrogen sulphide content prior to disposal of the effluent gas.
Dissolved hydrogen sulphide is known to react readily with dissolved oxygen in the seawater and decomposes into various products such as sulphates, sulphites etc. which have less negative impact to the marine environment. It is thus possible to extract the hydrogen sulphide in a single-stage or a multistage scrubbing system using sea water from the ocean and then dispose the scrubber effluent into the ocean. Further decomposition of the dissolved hydrogen sulphide into various products will then take place in the ocean which is rich in dissolved oxygen.
Summary Of Invention One of the objects of the present invention is to provide a method for treating sour effluent gas generated from a sweetening process. Specifically, the method provided is capable of selectively separating hydrogen sulphide from the effluent gas stream to substantially reduce the hydrogen sulphide content therein, thus eliminating air pollution problems.
Another object of the invention is to introduce an effective absorbing agent for removing hydrogen sulphide from the effluent gas stream generated from a gas processing unit such as a gas sweetening process. Fresh sea water that contains rich
FROM EFFLUENT GAS
Field Of Invention The invention relates to a method for treating effluent gas containing hydrogen sulphide that is generated from a gas treating process such as a gas sweetening process. More particularly, the invention pertains to a method for selectively separating hydrogen sulphide from the effluent gas stream using sea water.
Background Of The Invention Natural gas as well as other hydrocarbon gases from the oil and gas production usually contain significant amounts impurities, particularly hydrogen sulphide and carbon dioxide. Gases containing hydrogen sulphide are known as sour gas and they are undesirable due to their toxic and corrosive properties. Therefore, the sour gas must be treated to remove the hydrogen sulphide and carbon dioxide to meet downstream production or export requirements or venting to atmosphere.
Hydrogen sulphide and carbon dioxide are commonly removed from the sour gas by absorption in an alkaline solution. The sour gas is subjected to an amine gas treating process, where the sour gas is fed into a tower containing an amine solution which absorbs hydrogen sulphide and carbon dioxide as it passes through. The solution most widely used is an aqueous solution of alkanolamine, such as monoethanolamine, diethanolamine and methyldiethanolamine. The resultant gas stream is substantially free of the impurities, whilst the amine solution leaving the absorption tower is rich in the absorbed gases (which are hydrogen sulphide and carbon dioxide).
The absorbed gases are removed from the amine solution using a regenerator by preheating the solution and stripping hydrogen sulphide and carbon dioxide, from the solution in a reboiler. The effluent gas therefrom, which contains high concentrations of hydrogen sulphide and carbon dioxide, has to be disposed in a safe manner to avoid negative impacts on either workers or the environment. Where the concentration of the gases components in the effluent gas meets the environmental and safety regulatory limits for atmospheric disposal, it is possible to vent the effluent gases.
However, if the gases are present in high concentration, it is not safe and environmentally acceptable to vent the gases into the atmosphere. Therefore, there exists a need for a method for selectively and effectively removing or reducing hydrogen sulphide content prior to disposal of the effluent gas.
Dissolved hydrogen sulphide is known to react readily with dissolved oxygen in the seawater and decomposes into various products such as sulphates, sulphites etc. which have less negative impact to the marine environment. It is thus possible to extract the hydrogen sulphide in a single-stage or a multistage scrubbing system using sea water from the ocean and then dispose the scrubber effluent into the ocean. Further decomposition of the dissolved hydrogen sulphide into various products will then take place in the ocean which is rich in dissolved oxygen.
Summary Of Invention One of the objects of the present invention is to provide a method for treating sour effluent gas generated from a sweetening process. Specifically, the method provided is capable of selectively separating hydrogen sulphide from the effluent gas stream to substantially reduce the hydrogen sulphide content therein, thus eliminating air pollution problems.
Another object of the invention is to introduce an effective absorbing agent for removing hydrogen sulphide from the effluent gas stream generated from a gas processing unit such as a gas sweetening process. Fresh sea water that contains rich
3 dissolved oxygen is preferred as the absorbing agent as it is effective in dissolving and decomposing the hydrogen sulphide.
Still another object of the invention is to provide a method for further reducing hydrogen sulphide content in an effluent gas stream released from a gas sweetening process. It can be achieved by introducing dissolved alkaline agent, such as carbonates, into the sea water to increase alkalinity and thereby enhance the efficiency of hydrogen sulphide removal.
Yet another object of the invention is to provide a method for further reducing hydrogen sulphide content in an effluent gas stream by introducing catalyst, such as transition metals in form of dissolved salts, into the sea water to increase the rate of decomposition of dissolved hydrogen sulphides into products such as sulphates, sulphites etc. that have less negative impact to the marine environment At least one of the preceding objects is met, in whole or in part, by the invention, in which one of the embodiments of the invention describes a method for separating hydrogen sulphide from effluent gas released from a gas sweetening process, the method comprising the steps of feeding the effluent gas into at least one scrubber, the scrubber operating at a pressure less than 100 psig (or 700 kPa); and feeding sea water into the scrubber counter-currently to the direction of the gas flow, so that the effluent gas is contacted with the sea water thereby to reduce the hydrogen sulphide content in the effluent gas stream to less than 0.50% by weight by dissolution in the sea water.
The sea water may contain dissolved alkaline agent or transition metals which can act as catalyst. If required, an additional metal catalyst may be added into it prior to the scrubber process, in order to further reduce the hydrogen sulphide content in the effluent gas stream.
Still another object of the invention is to provide a method for further reducing hydrogen sulphide content in an effluent gas stream released from a gas sweetening process. It can be achieved by introducing dissolved alkaline agent, such as carbonates, into the sea water to increase alkalinity and thereby enhance the efficiency of hydrogen sulphide removal.
Yet another object of the invention is to provide a method for further reducing hydrogen sulphide content in an effluent gas stream by introducing catalyst, such as transition metals in form of dissolved salts, into the sea water to increase the rate of decomposition of dissolved hydrogen sulphides into products such as sulphates, sulphites etc. that have less negative impact to the marine environment At least one of the preceding objects is met, in whole or in part, by the invention, in which one of the embodiments of the invention describes a method for separating hydrogen sulphide from effluent gas released from a gas sweetening process, the method comprising the steps of feeding the effluent gas into at least one scrubber, the scrubber operating at a pressure less than 100 psig (or 700 kPa); and feeding sea water into the scrubber counter-currently to the direction of the gas flow, so that the effluent gas is contacted with the sea water thereby to reduce the hydrogen sulphide content in the effluent gas stream to less than 0.50% by weight by dissolution in the sea water.
The sea water may contain dissolved alkaline agent or transition metals which can act as catalyst. If required, an additional metal catalyst may be added into it prior to the scrubber process, in order to further reduce the hydrogen sulphide content in the effluent gas stream.
4 In another embodiment of the invention, the method further comprises the step of discharging the sea water with dissolved hydrogen sulphide from the scrubber back into the ocean.
The method may also comprise additional step of treating the contaminated sea water prior to disposal to the ocean.
The method according to the preceding embodiment further comprises the step of releasing the effluent gas stream with reduced hydrogen sulphide content into atmosphere or for use as a fuel gas or for further processing of the remaining stream as necessary.
One skilled in the art will readily appreciate that the invention is well adapted to carry out the aspects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the invention.
Brief Description Of Drawings For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawing the preferred embodiments from an inspection of which when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated.
Figure 1 is the schematic diagram of the process flow showing a method for separating hydrogen sulphide from an effluent gas stream by using a single scrubber, in accordance with a preferred embodiment.
Figure 2 is the schematic diagram of the process flow showing a method for separating hydrogen sulphide from an effluent gas stream by using more than one scrubber, according to another preferred embodiment.
The method may also comprise additional step of treating the contaminated sea water prior to disposal to the ocean.
The method according to the preceding embodiment further comprises the step of releasing the effluent gas stream with reduced hydrogen sulphide content into atmosphere or for use as a fuel gas or for further processing of the remaining stream as necessary.
One skilled in the art will readily appreciate that the invention is well adapted to carry out the aspects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the invention.
Brief Description Of Drawings For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawing the preferred embodiments from an inspection of which when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated.
Figure 1 is the schematic diagram of the process flow showing a method for separating hydrogen sulphide from an effluent gas stream by using a single scrubber, in accordance with a preferred embodiment.
Figure 2 is the schematic diagram of the process flow showing a method for separating hydrogen sulphide from an effluent gas stream by using more than one scrubber, according to another preferred embodiment.
5 Detailed Description Of The Invention Hereinafter, the invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description and drawings. However, it is to be understood that limiting the description to the preferred embodiments of the invention and to the drawings is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim.
The invention provides a method for treating effluent gas generated from a gas sweetening process. More particularly, the method utilizes fresh sea water as an absorbing agent to effectively and selectively separate hydrogen sulphide present in the effluent gas stream.
Although the method is depicted and described herein for treating effluent gas generated from a gas sweetening process, it should be noted that the effluent gas to be treated shall not be limited thereto or thereby, but it also includes the waste gas from a sour gas field and those associated with production and refining of crude petroleum oil or any such processes as to generate an effluent of sour gas composition that requires further sweetening treatment. Correspondingly, it should be appreciated to note that the term "effluent gas", "acid gas", "waste gas", "exhaust gas" or any like term can be used interchangeably herein throughout the description and shall refer to a gas stream containing 0.50 wt% (which is equivalent to 5000 ppm) or more hydrogen sulphide with the remaining made up of hydrocarbon, carbon dioxide, moisture, nitrogen and other possible impurities in gaseous form, that the hydrocarbon
The invention provides a method for treating effluent gas generated from a gas sweetening process. More particularly, the method utilizes fresh sea water as an absorbing agent to effectively and selectively separate hydrogen sulphide present in the effluent gas stream.
Although the method is depicted and described herein for treating effluent gas generated from a gas sweetening process, it should be noted that the effluent gas to be treated shall not be limited thereto or thereby, but it also includes the waste gas from a sour gas field and those associated with production and refining of crude petroleum oil or any such processes as to generate an effluent of sour gas composition that requires further sweetening treatment. Correspondingly, it should be appreciated to note that the term "effluent gas", "acid gas", "waste gas", "exhaust gas" or any like term can be used interchangeably herein throughout the description and shall refer to a gas stream containing 0.50 wt% (which is equivalent to 5000 ppm) or more hydrogen sulphide with the remaining made up of hydrocarbon, carbon dioxide, moisture, nitrogen and other possible impurities in gaseous form, that the hydrocarbon
6 is present in a minor amount therein, preferably a few percent.
Referring now to the present invention, the method for separating hydrogen sulphide from an effluent gas stream comprises the steps of feeding the effluent gas into at least one scrubber, the scrubber operating at a pressure less than 100 psig (or 700 kPa); and feeding sea water into the scrubber counter-currently to the direction of the gas flow, so that the effluent gas is contacted with the sea water thereby to reduce the hydrogen sulphide content in the effluent gas stream to less than 0.5% by weight by dissolution in the sea water.
In accordance with the preceding description, at least one scrubber which can either be a packed bed type, a structured packing type or a type configured to have flow distributors positioned to at least one of its bottom, top and intermediate locations is used to remove hydrogen sulphide from the effluent gas. Nevertheless, the number of scrubbers is dependent on flow rate or amount of the effluent gas to be treated. In the industrial plant, the effluent gas stream flow rate is usually ranging from 10 to 200 MMSCFD (or approximately 3 to 7 m3/s). At higher flow rate, the exhaust gas stream is preferably divided into several parallel streams and routed to a predetermined number of scrubbers. The scrubbers can be arranged in series, in parallel to each other or in a combination thereof to ensure efficient design of the overall system for removing hydrogen sulphide therefrom to the required emission specification.
Reference is now made specifically to Figure 1 when a single scrubber is used to separate hydrogen sulphide from the effluent gas. The scrubber is configured to receive the effluent gas stream feeding near bottom of the scrubber whilst the absorbing agent is routed to the opposite end of the scrubber to the entry point of the gas stream, such that the gas stream and the liquid stream (i.e. the absorbing agent) are fed counter-currently. The gas and the liquid streams can also be fed to the scrubber co-currently, continuously or intermittently, depending on operating
Referring now to the present invention, the method for separating hydrogen sulphide from an effluent gas stream comprises the steps of feeding the effluent gas into at least one scrubber, the scrubber operating at a pressure less than 100 psig (or 700 kPa); and feeding sea water into the scrubber counter-currently to the direction of the gas flow, so that the effluent gas is contacted with the sea water thereby to reduce the hydrogen sulphide content in the effluent gas stream to less than 0.5% by weight by dissolution in the sea water.
In accordance with the preceding description, at least one scrubber which can either be a packed bed type, a structured packing type or a type configured to have flow distributors positioned to at least one of its bottom, top and intermediate locations is used to remove hydrogen sulphide from the effluent gas. Nevertheless, the number of scrubbers is dependent on flow rate or amount of the effluent gas to be treated. In the industrial plant, the effluent gas stream flow rate is usually ranging from 10 to 200 MMSCFD (or approximately 3 to 7 m3/s). At higher flow rate, the exhaust gas stream is preferably divided into several parallel streams and routed to a predetermined number of scrubbers. The scrubbers can be arranged in series, in parallel to each other or in a combination thereof to ensure efficient design of the overall system for removing hydrogen sulphide therefrom to the required emission specification.
Reference is now made specifically to Figure 1 when a single scrubber is used to separate hydrogen sulphide from the effluent gas. The scrubber is configured to receive the effluent gas stream feeding near bottom of the scrubber whilst the absorbing agent is routed to the opposite end of the scrubber to the entry point of the gas stream, such that the gas stream and the liquid stream (i.e. the absorbing agent) are fed counter-currently. The gas and the liquid streams can also be fed to the scrubber co-currently, continuously or intermittently, depending on operating
7 preference. It should be noted that the absorbing agent referred herein is fresh sea water taken from the surrounding ocean. Fresh sea water is used due to its rich dissolved oxygen concentration, as dissolved oxygen is capable of dissociating and decomposing the dissolved hydrogen sulphide into products such as sulphates, sulphites etc. which have less negative impact to the marine environment.
Inside the scrubber, the hydrogen sulphide in the effluent gas stream is first absorbed into the sea water based on Henry's Law. Mass transfer of hydrogen sulphide from gas stream to liquid stream is further enhanced by using counter-current flow in the scrubber, where the fresh sea water is exposed to lower hydrogen sulphide gas concentration to enhance hydrogen sulphide removal. The hydrogen sulphide absorbed into the sea water then begins to interact with the dissolved oxygen and other constituents naturally present in the sea water to produce various compounds such as sulphates, sulphites etc., thereby reducing the hydrogen sulphide content in the effluent gas.
If more than one scrubber is used as illustrated in Figure 2, the scrubbers may be configured to receive the fresh sea water feeding at the top of each scrubber, whilst the effluent gas stream is fed into the first scrubber and the treated effluent gas stream from the first scrubber will then be fed into the second scrubber.
Correspondingly, it is worth noting that the treated gas stream from the N-th scrubber will be the inlet feed of the (N+1)-th scrubber. It should also be appreciably noted that the effluent gas or the treated effluent gas stream is fed to the respective scrubber near the bottom thereof, so that the gas flows upwards and counter-currently to the direction of the sea water.
According to the preferred embodiment of the invention, the effluent gas stream flows into the scrubber (or scrubbers) at a temperature close to but not exceeding by 30 C
than that of the fresh sea water. In addition, the effluent gas can be pre-processed
Inside the scrubber, the hydrogen sulphide in the effluent gas stream is first absorbed into the sea water based on Henry's Law. Mass transfer of hydrogen sulphide from gas stream to liquid stream is further enhanced by using counter-current flow in the scrubber, where the fresh sea water is exposed to lower hydrogen sulphide gas concentration to enhance hydrogen sulphide removal. The hydrogen sulphide absorbed into the sea water then begins to interact with the dissolved oxygen and other constituents naturally present in the sea water to produce various compounds such as sulphates, sulphites etc., thereby reducing the hydrogen sulphide content in the effluent gas.
If more than one scrubber is used as illustrated in Figure 2, the scrubbers may be configured to receive the fresh sea water feeding at the top of each scrubber, whilst the effluent gas stream is fed into the first scrubber and the treated effluent gas stream from the first scrubber will then be fed into the second scrubber.
Correspondingly, it is worth noting that the treated gas stream from the N-th scrubber will be the inlet feed of the (N+1)-th scrubber. It should also be appreciably noted that the effluent gas or the treated effluent gas stream is fed to the respective scrubber near the bottom thereof, so that the gas flows upwards and counter-currently to the direction of the sea water.
According to the preferred embodiment of the invention, the effluent gas stream flows into the scrubber (or scrubbers) at a temperature close to but not exceeding by 30 C
than that of the fresh sea water. In addition, the effluent gas can be pre-processed
8 before being subjected to the scrubber or scrubbers using an acid gas removal unit or an acid gas enrichment unit, where the unit can be solvent based, sorbent based or membrane based, in order to prepare the effluent gas stream in the desired operating conditions for sea water scrubbing. Further, the effluent gas stream may also require adequate conditioning by utilizing a knock-out scrubber, a heater or a combination thereof, so as to minimize any liquid drop-out within the scrubber.
Whilst the sea water is filtered and treated if necessary, it facilitates to ensure that the scrubber is not severely fouled during operation. The amount of sea water required should be such that there is adequate sea water to absorb the hydrogen sulphide in the incoming gas stream and the seawater contains enough dissolved oxygen for hydrogen sulphide oxidation to be initiated.
In another preferred embodiment of the invention, the sea water can include dissolved alkaline agent therein, such as carbonates, hydroxides, bicarbonates and other buffer solutions. Such alkaline agent can be added to the sea water stream either at the inlet or at predefined positions of the scrubber. It should be appreciably noted that presence of the alkaline agent in the sea water substantially improves the efficiency in removing hydrogen sulphide from the effluent gas by converting it to bisulphide ions (HS) and hydrosulphides and forming products such as sulphates, sulphites, etc., thus reducing the dissolved hydrogen sulphide content to a concentration, either as required by the environmental regulation set forth by the respective country or according to the system setup such as number of scrubbers. However, selection of the alkaline agent is not limited thereto or thereby. Transition metals in form of salts can also be added to and dissolved in the sea water prior to scrubbing, for example, iron (II) ions (Fe2'). These metal ions are known to enhance or catalyze the dissociation reaction of hydrogen sulphide to other compounds in the sea water. In addition, the sea water can further be aerated by bubbling air into the sea water prior to scrubbing, so as to substantially increase the dissolved oxygen content to enhance hydrogen
Whilst the sea water is filtered and treated if necessary, it facilitates to ensure that the scrubber is not severely fouled during operation. The amount of sea water required should be such that there is adequate sea water to absorb the hydrogen sulphide in the incoming gas stream and the seawater contains enough dissolved oxygen for hydrogen sulphide oxidation to be initiated.
In another preferred embodiment of the invention, the sea water can include dissolved alkaline agent therein, such as carbonates, hydroxides, bicarbonates and other buffer solutions. Such alkaline agent can be added to the sea water stream either at the inlet or at predefined positions of the scrubber. It should be appreciably noted that presence of the alkaline agent in the sea water substantially improves the efficiency in removing hydrogen sulphide from the effluent gas by converting it to bisulphide ions (HS) and hydrosulphides and forming products such as sulphates, sulphites, etc., thus reducing the dissolved hydrogen sulphide content to a concentration, either as required by the environmental regulation set forth by the respective country or according to the system setup such as number of scrubbers. However, selection of the alkaline agent is not limited thereto or thereby. Transition metals in form of salts can also be added to and dissolved in the sea water prior to scrubbing, for example, iron (II) ions (Fe2'). These metal ions are known to enhance or catalyze the dissociation reaction of hydrogen sulphide to other compounds in the sea water. In addition, the sea water can further be aerated by bubbling air into the sea water prior to scrubbing, so as to substantially increase the dissolved oxygen content to enhance hydrogen
9 sulphide dissociation by oxidizing and converting the dissolved hydrogen sulphide to products such as sulphates, sulphites, etc. which has less negative impact to environment.
It is also desirable in the present invention that the scrubber is configured to operate at low pressure preferably less than 100 psig (approximately 700 kPa or 6 bar).
One skilled in the art will appreciate the fact that high operating pressure is not required in the scrubber depicted herein, because of the absence of large amounts of hydrocarbon components in the exhaust gas. High operating pressure is required when significant amount of hydrocarbon is present in the gas stream, so as to create a partial pressure sufficiently large to separate hydrogen sulphide preferably from the exhaust gas stream.
In still another preferred embodiment of the invention, the method further comprises the step of discharging the sea water contaminated with dissolved hydrogen sulphide from the scrubber back to the ocean at a distance and depth sufficient in order to avoid the sea water contaminated with dissolved hydrogen sulphide from contaminating the fresh sea water intake for the scrubber, the processing facility, the seabed or the ocean surface. More specifically, the contaminated sea water is first routed to a collector where the sea water from the scrubber (or the scrubbers) are comingled and then routed to the subsea discharge system. The subsea discharge system preferably comprises a single discharge pipe or a network of pipes with each discharge pipe being connected to a subsea diffuser outlet. The diffuser outlet is designed such that it allows maximum entrainment of fresh sea water and dissolved oxygen to accelerate and continue dissociation of hydrogen sulphide and its reactions. Ambient ocean currents assist to dissipate the dissolved hydrogen sulphide for interaction with more fresh sea water in the ocean, thereby effectively reducing the concentration of dissolved hydrogen sulphide in the discharge stream. Typically, the seawater discarded contains a negligible increase in dissolved sulphates therein than in the fresh seawater used. The resulting subsea plume presents a localized but transitory impact to the ocean environment due to constant changes in current direction and strength in the open ocean and hence, gives no detrimental environmental effects on the ecosystems of the ocean. Further, the increase of the seawater effluent temperature 5 caused by the scrubbing operation is very slight due to the high heat capacity of sea water and thus, any potential thermal pollution can be avoided.
Meanwhile, the effluent gas with reduced hydrogen sulphide content from the scrubber can be disposed by releasing into atmosphere, depending on the
It is also desirable in the present invention that the scrubber is configured to operate at low pressure preferably less than 100 psig (approximately 700 kPa or 6 bar).
One skilled in the art will appreciate the fact that high operating pressure is not required in the scrubber depicted herein, because of the absence of large amounts of hydrocarbon components in the exhaust gas. High operating pressure is required when significant amount of hydrocarbon is present in the gas stream, so as to create a partial pressure sufficiently large to separate hydrogen sulphide preferably from the exhaust gas stream.
In still another preferred embodiment of the invention, the method further comprises the step of discharging the sea water contaminated with dissolved hydrogen sulphide from the scrubber back to the ocean at a distance and depth sufficient in order to avoid the sea water contaminated with dissolved hydrogen sulphide from contaminating the fresh sea water intake for the scrubber, the processing facility, the seabed or the ocean surface. More specifically, the contaminated sea water is first routed to a collector where the sea water from the scrubber (or the scrubbers) are comingled and then routed to the subsea discharge system. The subsea discharge system preferably comprises a single discharge pipe or a network of pipes with each discharge pipe being connected to a subsea diffuser outlet. The diffuser outlet is designed such that it allows maximum entrainment of fresh sea water and dissolved oxygen to accelerate and continue dissociation of hydrogen sulphide and its reactions. Ambient ocean currents assist to dissipate the dissolved hydrogen sulphide for interaction with more fresh sea water in the ocean, thereby effectively reducing the concentration of dissolved hydrogen sulphide in the discharge stream. Typically, the seawater discarded contains a negligible increase in dissolved sulphates therein than in the fresh seawater used. The resulting subsea plume presents a localized but transitory impact to the ocean environment due to constant changes in current direction and strength in the open ocean and hence, gives no detrimental environmental effects on the ecosystems of the ocean. Further, the increase of the seawater effluent temperature 5 caused by the scrubbing operation is very slight due to the high heat capacity of sea water and thus, any potential thermal pollution can be avoided.
Meanwhile, the effluent gas with reduced hydrogen sulphide content from the scrubber can be disposed by releasing into atmosphere, depending on the
10 environmental and safety regulatory requirement. Alternatively, the treated effluent gas from the scrubber is routed to a combustor for producing energy upon combustion with a fuel gas and to oxidize any remnants of contaminants. However, the treated effluent gas may still contain the less absorbable components such as carbon dioxide, nitrogen, hydrocarbon and other impurities. Therefore, the treated exhaust gas may also be routed to other post-treatment system for further processing prior to disposal so as to ensure that the gas to be disposed is no longer detrimental to the environment and personnel.
In a further embodiment of the invention, the scrubber or scrubbers can be equipped with appropriate monitoring and control instrumentation, such as pressure and temperature monitoring as well as level, flow control and dissolved oxygen monitoring. The scrubber can also include internal parts facilitating for effective distribution of the streams such as distributor trays and sprays. Other internal compartments such as demisters or other liquid droplet removal mechanisms may also be included to prevent sea water from being carried over into the exiting treated gas stream.
Further, since the scrubber operates in low pressure and that the scrubber is used to separate hydrogen sulphide using sea water, the scrubber is preferably constructed
In a further embodiment of the invention, the scrubber or scrubbers can be equipped with appropriate monitoring and control instrumentation, such as pressure and temperature monitoring as well as level, flow control and dissolved oxygen monitoring. The scrubber can also include internal parts facilitating for effective distribution of the streams such as distributor trays and sprays. Other internal compartments such as demisters or other liquid droplet removal mechanisms may also be included to prevent sea water from being carried over into the exiting treated gas stream.
Further, since the scrubber operates in low pressure and that the scrubber is used to separate hydrogen sulphide using sea water, the scrubber is preferably constructed
11 using a material resistant to corrosion caused by the sea water as well as the corrosive components in the effluent gas (hydrogen sulphide and carbon dioxide in particular).
The material used can be any one or a combination of stainless steel, glass, polymeric plastic, glass reinforced epoxy and fiber reinforced plastic. However, the material used should not be limited thereto or thereby, as other appropriate materials could be used for the design and operating conditions.
Though Figure 1 shows that the scrubber is positioned and operating at above sea level, it shall be noted that this does not limit the position of the scrubber thereto, but the scrubber can be positioned and operating at subsea level (or below sea level).
The disclosure includes as contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a degree of particularity, it is understood that the disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the invention.
The material used can be any one or a combination of stainless steel, glass, polymeric plastic, glass reinforced epoxy and fiber reinforced plastic. However, the material used should not be limited thereto or thereby, as other appropriate materials could be used for the design and operating conditions.
Though Figure 1 shows that the scrubber is positioned and operating at above sea level, it shall be noted that this does not limit the position of the scrubber thereto, but the scrubber can be positioned and operating at subsea level (or below sea level).
The disclosure includes as contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a degree of particularity, it is understood that the disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the invention.
Claims (8)
1. A method for separating hydrogen sulphide from effluent gas generated from a gas sweetening process, the method comprising the steps of feeding the effluent gas into at least one scrubber, the scrubber operating at a pressure less than 100 psig (or 700 kPa); and feeding sea water into the scrubber counter-currently to the direction of the gas flow, so that the effluent gas is contacted with the sea water thereby to reduce the hydrogen sulphide content in the effluent gas to less than 0.50% by weight by dissolution in the sea water.
2. A method of claim 1 further comprising the step of discharaing the sea water contaminated with dissolved hydrogen sulphide from the scrubber to ocean.
3. A method of claim 1, wherein the sea water is added with dissolved alkaline agent to further reduce the hydrogen sulphide content in the effluent gas.
4. A method of claim 3, wherein the alkaline agent is carbonate, hydroxide, bicarbonate or other buffer solution.
5. A method of claim 1, wherein the sea water is added with transition metal ions to further reduce the hydrogen sulphide content in the effluent gas.
6. A method of claim 2 further comprising the step of treating the contaminated sea water prior to disposal to the ocean.
7. A method of claim 1 further comprising the step of releasing the treated effluent gas from the scrubber with reduced hydrogen sulphide content into atmosphere or for use as a fuel gas or for further processing or for other means of disposal.
8. A method of claim 1, wherein the scrubber is positioned at subsea level or above sea level.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| MYPI2015702418 | 2015-07-24 | ||
| MYPI2015702418A MY172682A (en) | 2015-07-24 | 2015-07-24 | A method for separating hydrogen sulphide from effluent gas |
| PCT/MY2016/050006 WO2017018872A1 (en) | 2015-07-24 | 2016-01-28 | A method for separating hydrogen sulphide from effluent gas |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2995557A1 true CA2995557A1 (en) | 2017-02-02 |
Family
ID=57885072
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2995557A Abandoned CA2995557A1 (en) | 2015-07-24 | 2016-01-28 | A method for separating hydrogen sulphide from effluent gas |
Country Status (5)
| Country | Link |
|---|---|
| CN (1) | CN108430602A (en) |
| AU (1) | AU2016299641A1 (en) |
| CA (1) | CA2995557A1 (en) |
| MY (1) | MY172682A (en) |
| WO (1) | WO2017018872A1 (en) |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3934012A (en) * | 1972-06-19 | 1976-01-20 | Texaco Inc. | Method of separating hydrogen sulfide from carbon dioxide |
| GB1495690A (en) * | 1975-11-29 | 1977-12-21 | Texaco Development Corp | Method of removing hydrogen sulphide from a gas carbon dioxide |
| AU9087698A (en) * | 1997-09-15 | 1999-04-05 | Den Norske Stats Oljeselskap A.S. | Separation of acid gases from gas mixtures |
| US6881389B2 (en) * | 2002-09-24 | 2005-04-19 | Edg, Inc. | Removal of H2S and CO2 from a hydrocarbon fluid stream |
| CN102559313B (en) * | 2011-11-09 | 2016-07-06 | 中国石油大学(华东) | Offshore oil platform natural gas seawater Claus hydrogen sulfide removing process method |
| CA2909345A1 (en) * | 2013-04-15 | 2014-10-23 | Siemens Aktiengesellschaft | Absorption medium, process for producing an absorption medium, and also process and apparatus for separating hydrogen sulfide from an acidic gas |
| CN104119946B (en) * | 2014-07-08 | 2016-07-06 | 宁夏宝塔石化科技实业发展有限公司 | A kind of catalytic cracking flue gas desulfurization and Acidic Gas Treating technique |
| CN104307365A (en) * | 2014-10-17 | 2015-01-28 | 陕西华陆化工环保有限公司 | Cleaning method of hydrogen sulfide gas |
-
2015
- 2015-07-24 MY MYPI2015702418A patent/MY172682A/en unknown
-
2016
- 2016-01-28 WO PCT/MY2016/050006 patent/WO2017018872A1/en active Application Filing
- 2016-01-28 CN CN201680051579.1A patent/CN108430602A/en active Pending
- 2016-01-28 CA CA2995557A patent/CA2995557A1/en not_active Abandoned
- 2016-01-28 AU AU2016299641A patent/AU2016299641A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| AU2016299641A1 (en) | 2018-02-22 |
| CN108430602A (en) | 2018-08-21 |
| WO2017018872A1 (en) | 2017-02-02 |
| MY172682A (en) | 2019-12-10 |
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