Direct Desulfurization System and Method

This application claims the benefit of U.S. Provisional Application No. 63/528,989 filed on Jul. 26, 2023, which application is incorporated herein by reference as if reproduced in full below.

Not Applicable.

Many hydrocarbon-containing fluids, including naturally occurring gas streams such as sub-surface natural gas, contain sulfur compounds, including hydrogen sulfide (HS). Governmental regulations limit plant emissions of sulfur-bearing gases. Refineries commonly include sulfur reduction units to decrease emissions of sulfur compounds.

The use of a Claus catalytic reaction is widely known in the field and commonly used in sulfur recovery units. Many currently practiced Claus processes consists of a thermal stage and a catalytic stage. In the thermal stage, a waste gas containing hydrogen sulfide is injected into a thermal reactor where hydrogen sulfide is partially oxidized with air at high temperatures to form a quantity of sulfur dioxide. The thermal reaction further serves to oxidize ammonia. Combustion gases are cooled in a waste heat boiler in which a portion of the hydrogen sulfide reacts with sulfur dioxide to form water and elemental sulfur. The elemental sulfur is condensed and removed. One such system is described in U.S. Pat. No. 7,250,149 to Smith, which is incorporated by reference herein in its entirety to the extent non inconsistent herewith. In another sulfur removal process based on the Claus reactor, sulfur dioxide (SO) is introduced into the process stream at determined locations during a multiple stage reactor process, as disclosed in U.S. Pat. No. 8,795,625 to Smith, which is incorporated by reference herein in its entirety to the extent non inconsistent herewith.

While there exists utility in these systems, they each possess certain drawbacks and/or undesirable features. A need therefore exists for an improved sulfur removal system for natural gas streams and the like.

Embodiments of a desulfurization system of the present invention generally include a series of components designed to utilize an input of fluid comprising hydrogen sulfide as an impurity, such as a refinery fuel gas stream, and an input of a gaseous stream comprising sulfur dioxide, whereby the combined streams progress through the individual components such that within one or more such components molecular sulfur (S) created within the system, in molten form, is removable therefrom. In one aspect, embodiments of a desulfurization system of the present invention function such that the SOreacts with the HS to form the Sand thereby purify the fluid by diminishing the amount of the HS present therein.

The exemplary embodiments are best understood by referring to the drawings, like numerals being used for like and corresponding parts of the various drawings. In the following description of embodiments, orientation indicators such as “top,” “bottom,” “up,” “down,” “upper,” “lower,” “front,” “back,” etc. are used for illustration purposes only; the invention, however, is not so limited, and other possible orientations are contemplated.

Referring to, therein is depicted an embodiment of a direct desulfurization systemof the present invention. In this embodiment, a direct desulfurization systemcomprises a mixing vessel. In one embodiment, a mixing vesselmay comprise any useful size, shape, dimensions or internal mixing features for combining a gas stream with a liquid stream, as would be understood by one skilled in the art. In one embodiment, a direct desulfurization systemcomprises a (first) heating vessel (reheater), a (first) reactorand a (first) condenser. In one aspect, the section of an embodiment of a direct desulfurization systemcomprising a reheater, a reactor and a condenser constitutes a desulfurization zone. In the embodiment depicted in, direct desulfurization systemcomprises additional desulfurization zones, namely, a second reheater, a second reactorand a second condenser, as well as a third reheater, a third reactorand a third condenser, although the invention is not so limited and a direct desulfurization systemmay comprise a single desulfurization zoneor any useful number of desulfurization zones.

In one embodiment, a reheater,and/ormay comprise a vessel adapted and configured to adequately heat the process stream (not separately labeled) flowed thereinto. In one embodiment, a reactor,and/ormay comprise a vessel adapted and configured to effect the catalyzed reaction between HS and SOwhereby Sand HO are produced, in accordance with the chemical reaction stoichiometry shown below:

In one embodiment, a reactor of the present invention comprises a conventional Claus catalytic reactor, as would be understood by one skilled in the art, although the invention is not so limited and other types of catalytic reactors may be employed. In one embodiment, a condenser,and/ormay comprise a separation vessel adapted and configured to provide for the condensation of Sand separation thereof from the remainder of the process stream, as would be understood by one skilled in the art.

Referring now to, in one embodiment a direct desulfurization systemmay comprise a “back-end” systemwhich may be utilized to further process the fluid stream. In one embodiment, the back-end systemmay be fluidly connected to the final condenser in the series of components that constitutes the desulfurization system, although the invention is not so limited and the back-end systemmay be otherwise fluidly connected to the desulfurization systemand/or fluidly connected to two or more components of the desulfurization system.

In one embodiment, a back-end systemcomprises a heater (pre-heater), a hydrogenation reactor, a coolerand a contacter (i.e., mixing device providing for physical contact and interaction of fluids). In one embodiment, a pre-heatermay comprise a vessel adapted and configured to adequately heat the process streamflowing from the desulfurization system. In one embodiment, a hydrogenation reactormay comprise a vessel adapted and configured to mix an input stream comprising hydrogen gas (H) (not shown) with the heated desulfurization systemoutput stream. In one embodiment a hydrogenation reactormay comprise an existing refinery hydrogenation reactor, although the invention is not so limited and other types and/or purposed hydrogenation reactors may be employed. In one embodiment a coolermay comprise a vessel adapted and configured to cool the fluid stream exiting the hydrogenation reactor. In one embodiment (not shown), a back-end systemmay comprise a quench tank, in additional to, or in lieu of, a cooler, as would be understood by one skilled in the art. In one embodiment, a contactercomprises a vessel adapted and configured to separate the fluid gas stream into an overhead gas streamand a bottoms liquid stream. In one embodiment, a back-end systemcomprises a contacter inlet linethat directs liquid from an external source (now shown) into the contacter.

In another embodiment, depicted in, a back-end systemA comprises one or more cold bed absorbers. In the embodiment shown in, two cold bed absorbersA andB are utilized. In one embodiment, fluid output streamis first only directed to cold bed absorberA, wherein that cold bed absorber is operated below the dew point of sulfur (˜250° F. to ˜300° F.), and sulfur contained in fluid output streamis deposited as Stherein. In one embodiment, during this operational step, the fluid contained within fluid output streamthat makes it past the cold bed absorber (without being deposited as S) flows through cold bed absorberA drain pipingA and enters cold bed absorber fluid output stream. In one embodiment, the Smay be deposited in pores within a catalyst contained within the cold bed absorberA, i.e., the “bed,” as would be understood by one skilled in the art. This process continues until a desired amount of Shas been deposited. In one aspect, such determination can be made through monitoring of deactivation of the catalyst. At this time, the fluid output streamis diverted to cold bed absorberB to undergo similar processing. In one embodiment (not shown), a vessel may be provided between one or more of the cold bed absorbersand the cold bed absorber fluid output stream, i.e., along drain pipingA and/orB, to collect fluid from one cold bed absorberwhile Sis being collected from the other cold bed absorber.

In one embodiment, once the flow of fluid output streamis diverted to cold bed absorberB, a hot gas is passed through the cold bed absorberA, thereby vaporizing the Scontained there within and flowing it into cold bed absorber fluid output stream. Therein, the fluid is introduced to a cold bed absorber condenserin fluid communication with cold bed absorber fluid output stream, and liquid Sis diverted therefrom as another Soutput stream. In one embodiment, the cold bed absorbersA,B are operated alternatively in this fashion to continuously process fluid output stream, as would be understood by one skilled in the art.

Any fluid contained within cold bed absorber fluid output streamthat does not condense within cold bed absorber condenser(and therefore exit via the accompanying Soutput stream) flows into one or more crystallizers. In the embodiment shown in, crystallizersA andB are utilized. In one embodiment, a crystallizermay comprise an exchanger whereby, similar to the process that occurs with the cold bed absorbers, the crystallizeris operated alternatively in a “cold” mode (i.e., below the dew point of sulfur) and “hot” mode. In one embodiment, temperature control of a crystallizermay be maintained via introduction of a hot fluid (e.g., steam) and a cold fluid (e.g., chilled water), (neither shown in). When the crystallizeris being operated in the cold mode, any sulfur entering the crystallizeris deposited therein as S. In the hot mode, any solid Sin the crystallizer is liquidized and flows though crystallizer drain pipingA orB into crystallizer fluid output stream. Thereupon, the liquidized Sis introduced to a crystallizer condenserin fluid communication with crystallizer fluid output stream, and Sis diverted therefrom as another Soutput stream. In one embodiment, the crystallizersA,B are operated alternatively in this fashion to continuously process cold be absorber fluid output stream, as would be understood by one skilled in the art. In one embodiment (not shown), a vessel may be provided between one or more of the crystallizersand the crystallizer fluid output stream, i.e., along drain pipingA and/orB, to collect fluid from one crystallizerwhile Sis being collected from the other crystallizer.

Although the embodiment of back-end systemA includes both one or more cold bed absorbers and one or more crystallizers, the embodiment is not so limited an in other embodiments (not shown), a back-end systemA may comprise only one or more cold bed absorbers or one or more crystallizers. In addition, in an embodiment of a back-end systemA (not shown), the sequence of the cold bed absorber(s) operationally preceding the crystallizer(s) can be reversed.

Still referring to, in one embodiment back-end systemA comprises a quench tower. In one embodiment, a quench towermay be provided to remove any remaining SOin the gas stream by circulating a slightly basic stream therethrough. In one embodiment NaOH may be employed therefor. In this manner, the SOcan be removed without removing COor HS, as would be understood by one skilled in the art. In one embodiment shown in, this quench system (not separately numbered) comprises a quench tower, a circulating pump, a heat exchangerand a filter. In one embodiment, the circulation loop comprises a waste output line, an overhead output lineand a base input line, as would be understood by one skilled in the art. In one aspect, the total dissolved solids may be controlled by purging some of the circulating solution and making up with fresh water. To maintain a pH>7 of the circulating water, a base such as NaOH may be added. A filteron the circulating water stream can remove the remaining sulfur vapor that will be solidified when it is contacted with the water stream. In one embodiment, fluid flowing out of waste output linecan be treated as waste and fluid flowing out of overhead output linemay be further processed (not shown).

In operation, an embodiment of a desulfurization system, two fluid streams are combined in a mixing vessel. In one aspect, a mixing vesselmay comprise any useful mixing component(s) and/or mixing technology that can be configured and adapted to thoroughly mix the tow fluid streams, as would be understood by one skilled in the art. In one embodiment, a first streamcomprises a hydrocarbon and, as an impurity, hydrogen sulfide. In one embodiment, the first fluid streamconsists substantially of a gas, such as, but not limited to, natural gas. In one embodiment, the gas comprises a refinery fuel gas stream, although the invention is not so limited and other gas streams may be employed. In one embodiment, the first gas stream is supplied to the mixing vesselunder a pressure of about 60-100 psig, although other gas supply pressures may be employed. In one embodiment, the first gas streamis supplied to the mixing vesselat a temperature of about 75-150° F., although the invention is not so limited and other first streamtemperatures may be employed. In one embodiment, the first gas streammay comprise about five percent hydrogen sulfide, although the invention is not so limited and the first streammay comprise other concentrations of hydrogen sulfide.

In one embodiment, a second streamcomprises gaseous sulfur dioxide. In one embodiment, the sulfur dioxide streammay originate in an SOproduction unit, although any sulfur dioxide source(s) may be utilized. In one embodiment, the second gas stream is supplied to the mixing vesselunder a pressure of about 60-100 psig, although other gas supply pressures may be employed. In one embodiment, the second gas streamis supplied to the mixing vesselat a temperature of about 120-300° F., although the invention is not so limited and other second streamtemperatures may be employed.

In one embodiment, the combined streamsandare mixed within mixing vesseland then the mixed fluid stream is flowed therefrom into a first desulfurization zonewhich comprises a first reheater, a first reactorand a first condenser. In one embodiment, this entails flow of the mixed fluid stream output of mixing vesselbeing directed to the first reheater. In one embodiment, the reheaterheats the mixed fluid stream to about 550° F., although other reheating temperature profiles may be employed. In one embodiment, the fluid stream output of the first reheateris directed to the first Claus catalytic reactor (converter). In one aspect, the reheateris operated such that the temperature in the converteris maintained about 30° F. above the sulfur dew point to prevent temporary deactivation of the Claus reactor catalyst.

In one embodiment, the output fluid stream of the first converteris maintained at about 600° F. as it is flowed into the first condenser, although other converter temperature profiles may be employed. In one embodiment, the fluid stream is cooled within the condenserto about 300-310° F., although other condenser temperature profiles may be employed. In one embodiment, a liquid (molten) sulfur output streamflows from the first condenserand the Sthus obtained may be handled as desired, as would be understood by one skilled in the art.

In one embodiment, as depicted inand described below, a desulfurization systemmay comprise a series of three desulfurization zones, but the invention is not so limited and in other embodiments (not shown) a desulfurization systemmay comprise any configuration employing one or more desulfurization zones. Factors which may influence the number of desulfurization zonesemployed include, but are not limited to, the composition of the hydrocarbon input stream, purity of the SOinput streamand the desired removal efficiency of the desulfurization system, as would be understood by one skilled in the art.

In one embodiment the fluid stream exiting the first condenseris directed to a second reheaterwherein it is heated to about 460° F., although other reheating temperature profiles may be employed. In one embodiment, the fluid stream exiting the second reheateris directed to a second converter, wherefrom it exits at about 470° F., (although other converter temperature profiles may be employed) and is directed to a second condenser. In one embodiment, the fluid stream is cooled to about 300-310° F. by the second condenser, although other condenser temperature profiles may be employed. In one embodiment, a liquid (molten) sulfur output streamflows from the second condenserand the Sas described above with regard to the first condenser.

In one embodiment, the fluid stream exiting the second condenseris directed to a third reheaterwherein it is heated to about 400° F., although other reheating temperature profiles may be employed. In one embodiment, the fluid stream exiting the third reheateris directed to a third converter, wherefrom it exits at about 410° F., (although other converter temperature profiles may be employed) and is directed to a third condenser. In one embodiment, the fluid stream is cooled to about 270° F. by the third condenser, although other condenser temperature profiles may be employed. In one embodiment, a liquid (molten) sulfur output streamflows from the third condenserand the Sas described above with regard to the first condenserand second condenser. In one embodiment, a substantially desulfurized fluid streamexits from the third condenser, which, as described below regarding, may be further manipulated. In embodiment, the desulfurization systemcan remove about 98% of the HS introduced thereto.

In one embodiment, a desulfurization systemcomprising a back-end systemmay be operated such that the fluid streamexiting the third condenseris directed to a pre-heater, wherein it is heated to about 450° F., although other pre-heating temperature profiles may be employed. In one embodiment, the fluid stream exiting the pre-heateris directed to a hydrogenation reactor. In one embodiment, a hydrogen source (not shown) flows hydrogen gas (H) into the hydrogenation reactorwherein any residual SOand/or sulfur vapor is hydrogenated and thereby converted to hydrogen sulfide. In one aspect, the hydrogen source may be a refinery gas stream, although any useful hydrogen source may be employed.

In one embodiment, the hydrogenated fluid stream exits the hydrogenation reactorat about 400-500° F. although other hydrogenation temperature profiles may be employed. In one embodiment, the fluid stream exiting the hydrogenation reactoris directed to a cooler, wherein the fluid stream is cooled to about 300° F. In one aspect, the coolermay be employed to produce steam, as would be understood by one skilled in the art. In one embodiment, the fluid stream exiting the cooleris flowed directly to a contacter, although the invention is not so limited, and in other embodiments (not shown) additional equipment may be employed between the coolerand the contacterto further cool the fluid stream.

In one embodiment (not shown), when a quench tank is employed, a water source (not shown) may be utilized to introduce water into the quench tank. In one aspect, water within the quench tank serves to ensure that substantially all SOis removed from the vapor therewithin. In one embodiment, (also not shown) a small amount of caustic (NaOH) may be introduced into the quench tank to control the pH of the liquid therewithin. In one embodiment, a fluid streamcomprising an amine, such as, but not limited to, diethylamine (DEA), is introduced into the contacter. In one embodiment, the amine-containing fluid streammay originate in an industrial amine unit, although any source of amine may be employed. In one embodiment, the contacterbottoms effluentmay be further manipulated, as would be understood by one skilled in the art. In one aspect, the liquid bottoms effluentmay be directed back to the same amine unit from which the fluid streamoriginates. In one embodiment, an overhead gaseous streamexits the contacterwhich may be further manipulated, as would be understood by one skilled in the art. In one aspect, the overhead gaseous effluentmay be directed back to the same refinery fuel gas stream.

In other embodiments, a desulfurization systemcomprising a back-end systemA may be operated as described above therefor. In one embodiment, in an “absorption mode,” a cold bed absorberis operated below the sulfur dew point, at about 250° F. to about 300° F. In one aspect, this greatly increases the Claus conversion which is favored by low temperature. Since the bed is operated below the sulfur dew point, sulfur is deposited in the converter bed which temporarily deactivates the catalyst. In a subsequent “regeneration mode,” a hot gas (in one embodiment, ˜600° F.) is introduced to the cold bed absorberand the Sis vaporized. The thus vaporized Sflows as described above into cold bed absorber condenserand is collected therefrom.

In one embodiment, fluid that is provided to a crystallizerexperiences a first cold mode (typically 200° F. to 230° F.) wherein sulfur vapor solidifies, and then a hot mode (typically about 275° F. to about 300° F.), whereby the solid Sliquifies and flows as described above into crystallizer condenserand is collected therefrom. In one embodiment, gas exiting the crystallizer(s)is routed to the quench towerand processed as described above to remove residual SOcontained therein.

In various embodiments (not shown), partially and/or substantially desulfurized fluid streams may be obtained from any or all condensers within any or all desulfurization zonesof a desulfurization system. Similarly, back-end systemsand/orA may be employed with any or all desulfurization zonesof a desulfurization system.

An exemplary method utilizing an embodiment of a desulfurization system of the present invention comprises:

A Desulfurization System Provision Step, comprising providing a desulfurization system, such as desulfurization system, comprising a mixing vessel, such as mixing vessel, and one or more desulfurization zones, such as desulfurization zones, each comprising, in sequence, a reheater, such as reheater, a reactor, such as reactor, and a condenser, such as condenser;

A Fluid Mixing Step, comprising mixing a hydrocarbon fluid stream, such as hydrocarbon input stream, with a sulfur dioxide stream, such as SOinput stream, in the mixing vessel;

A Desulfurization Step, comprising flowing the mixed stream output from the mixing vessel though at least one desulfurization zone; and

A Sulfur Removal Step, comprising removing sulfur at least one desulfurization zone condenser.

Optionally, one or more of the following steps may be performed:

The foregoing methods are merely exemplary, and additional embodiments of utilizing a floating oil absorption apparatus of the present invention consistent with the teachings herein may be employed. In addition, in other embodiments, one or more of these steps may be performed concurrently, combined, repeated, re-ordered, or deleted, and/or additional steps may be added.

The foregoing description of the invention illustrates exemplary embodiments thereof. Various changes may be made in the details of the illustrated construction and process within the scope of the appended claims by one skilled in the art without departing from the teachings of the invention. The present invention should only be limited by the claims and their equivalents.