Exhaust gas processing system and method

Abstract

A system that may treat a gas stream includes a sulfur removal unit that may remove sulfur from the gas stream and generate a first treated gas stream; an oxides of nitrogen removal unit disposed downstream from and fluidly coupled to the sulfur removal unit; and a heat exchange system disposed between the sulfur removal unit and the oxides of nitrogen removal unit. The heat exchange system includes a first heating element that may heat the first treated gas stream and generate a first heated gas stream having a first temperature, and a second heating element disposed downstream from and fluidly coupled to the first heating element. The second heating element may receive and heat the first heated gas stream and generate a second heated gas stream, and the second heated gas stream has a second temperature that is greater than the first temperature.

Description

SP3063- 1 -EXHAUST GAS PROCESSING SYSTEM AND METHODBACKGROUND OF THE DISCLOSURE

[0001] The present disclosure generally relates to abating exhaust gas emissions from natural gas engines. More specifically, the present disclosure relates to a system having a heat exchange system that recovers and transfers heat from exhaust gas to activate one or more catalysts used for abating emissions in an exhaust gas.

[0002] Natural gas is an abundant and economical alternative to oil-derived fuels such as gasoline, kerosene and diesel. Accordingly, manufactures of engines used in stationery and transport applications / service are shifting their attention and efforts from oil-derived fuels to compressed natural gas (CNG) or liquefied natural gas (LNG) as fuels. Both CNG and LNG are less expensive and burn cleaner than oil-derived fuels. However, exhaust gas generated from the combustion of natural gas contains undesirable components (i.e., emissions). For example, the exhaust gas emissions may include pollutants such as oxides of nitrogen (NO and NOX), carbon dioxide (CO2), methane (CH4), sulfur dioxide (SO2), and volatile organic compounds (VOC) among others. Levels of these pollutants in exhaust emissions are regulated and there are continuous efforts to remove them from the exhaust gas. Techniques for the removal of these pollutants include catalytic processes that decompose the pollutants into nitrogen (N2), hydrogen (H2), carbon monoxide (CO), and water vapor.

[0003] U.S. Application No. 2012 / 0209342 describes a process for removing nitrous oxide (N2O) from a gas stream. This is a low energy input process that provides a high heat recovery and over 75% nitrous oxide destruction removal efficiency by using multiple interconnected heat transfer and reaction zones. The process includes passing the gas stream through the heat transfer zones where heat is transferred to the gas stream prior to contacting a denitrogenation (deNOx) catalyst. However, this process does not reduce nor remove other pollutants found in exhaust emissions such as CH4 and other VOCs. As such, additional processing of denitrified exhaust gas may be required to meet regulatory requirements. Accordingly, there is a current need for an exhaust emission abating system that reduces and / or eliminates not only NOx, but also in generalSP3063- 2 - gaseous hydrocarbons including methane, ethane and VOCs in exhaust emissions in an effective and efficient manner.SUMMARY

[0004] In one embodiment, a system that may treat a gas stream includes a sulfur removal unit that may remove sulfur from the gas stream and generate a first treated gas stream; an oxides of nitrogen removal unit disposed downstream from and fluidly coupled to the sulfur removal unit; and a heat exchange system disposed between the sulfur removal unit and the oxides of nitrogen removal unit. The heat exchange system includes a first heating element that may heat the first treated gas stream and generate a first heated gas stream having a first temperature, and a second heating element disposed downstream from and fluidly coupled to the first heating element. The second heating element may receive and heat the first heated gas stream and generate a second heated gas stream, and the second heated gas stream has a second temperature that is greater than the first temperature.

[0005] In another embodiment, a process for treating a gas stream, comprising providing a first treated gas stream to a heat exchange system disposed between a sulfur removal unit and an oxides of nitrogen removal unit. The heat exchange system includes a first heating element and a second heating element, and the first treated gas stream is generated from the gas stream in the sulfur removal unit. The process also include heating the first treated gas stream in the first heating element to generate a first heated gas stream having a first temperature; providing the first heated gas stream to the second heating element; heating the first heated gas stream in the second heating element to generate a second heated gas stream having a second temperature that is greater than the first temperature; and providing a third heated gas stream having a third temperature to the first heating element. The third heated gas stream heats the first treated gas stream to generate the first heated gas stream, the third temperature is greater than the second temperature, and the third heated gas stream is generated from the second heated gas stream.

[0006] In a further embodiment, a system that may treat a gas stream includes a heat exchange system disposed between a sulfur removal unit and a oxides of nitrogen removal unit. The heat exchange system includes a first heating element that may heat a first treated gas streamSP3063- 3 - output from the sulfur removal unit and generate a first heated gas stream having a first temperature; and a second heating element disposed downstream from the first heating element and that may heat the first heated gas stream and generate a second heated gas stream having a second temperature greater than the first temperature.

[0007] Additional features and advantages of exemplary implementations of the disclosure will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of such exemplary implementations. The features and advantages of such implementations may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features will become more fully apparent from the following description and appended claims or may be learned by the practice of such exemplary implementations as set forth hereinafter.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Advantages of the disclosure may become apparent upon reading the following detailed description and upon reference to the drawings in which:

[0009] FIG. 1 is a block diagram of a reactor system that includes a heating system positioned between a desulfurization unit and a devolatization unit, whereby the heating system includes a first heating element and second heating element, in accordance with an embodiment of the present disclosure;

[0010] FIG. 2 is a block diagram of a reactor system that includes a first heat exchange system positioned between a desulfurization unit and a devolatization unit and a second heat exchange system positioned downstream of the first heat exchange system and the devolatization system, in accordance with an embodiment of the present disclosure; and

[0011] FIG. 3 is a flow diagram of a method for treating a gas stream using the systems of FIGS. 1 and 2, in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION

[0012] One or more specific embodiments of the present disclosure will be described below.These described embodiments are examples of the presently disclosed techniques. Additionally,SP3063- 4 - in an effort to provide a concise description of these embodiments, not all features of an actual implementation may be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions will be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0013] When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. fOM4] — The terms “approximately,” “about,” and “substantially” as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of a stated amount.

[0015] As used herein, the terms “exhaust gas,” “untreated exhaust gas,” and “raw exhaust gas” are intended to denote an exhaust gas that has not be treated for removal of exhaust emission components. The term “treated exhaust gas” as used herein is intended to denote an exhaust gas that has undergone treatment to remove one or more exhaust emission components. The term “desulfurized exhaust gas” as used herein is intended to denote an exhaust gas that has undergone treatment for the removal of sulfur species. The term “devolatized exhaust gas” as used herein is intended to denote an exhaust gas that has undergone treatment for the removal of VOCs.SP3063- 5 -

[0016] As discussed above, exhaust gas generated from combustion of natural gas contains undesirable emissions such as oxides of nitrogen (NO and NOX), carbon dioxide (CO2), methane (CH4), sulfur dioxide (SO2), and volatile organic compounds (VOC). Exhaust emission regulatory standards require that unreacted CH4 in exhaust gas resulting from engine slip be reduced. Certain existing exhaust emission abating systems do not remove CH4. One approach to removing CH4 from exhaust gas is to treat the exhaust gas with a devolatization catalysts. However, devolatization catalysts are sensitive to sulfur. The exhaust gas includes sulfur species that poison the devolatization catalysts. In addition, devolatization reactions occur a temperatures higher than denitrogenation and desulfurization reactions. Therefore, heat is required to activate the devolatization catalysts. Due, in part, to the lower heat requirement for activation of denitrogenation and desulfurization catalysts, existing systems use the raw exhaust gas to provide heat. However, using the raw exhaust gas limits the operating temperature of catalysts used in these processes and, for devolatization catalysts, the raw exhaust gas temperature is not sufficient. As such, the emission removal efficiency of the devolatization catalyst may be undesirable. The system disclosed herein removes CH4 and other exhaust emissions components effectively and efficiently by arranging desulfurization, denitrogenation, and devolatization reactors in a manner that allows for recovering and transferring heat generated in the system and mitigating sulfur poisoning of catalysts. As such, the exhaust gas may be treated for CH4 slip and the longevity of sulfur-sensitive catalysts may be improved.

[0017] With the foregoing in mind, FIG. 1 is block diagram of a system 10 that may be used to remove undesirable components generally found in gas streams generated from hydrocarbon refining and combustion processes. In the illustrated embodiment, the system 10 includes a power generator 12, a desulfurization or sulfur removal unit 14, a devolatization unit 18, a deNOx or oxides of nitrogen removal unit 20, and a heating system 26. The power generator 12 includes one or more combustion devices that are used to generate power and operate machinery and / or equipment (e.g., irrigation and other agricultural systems, power plants, waste incineration plants, marine vessels, turbines, and the like). For example, the power generator 12 includes one or more engines, incinerators, furnaces / bumers, boilers, fired heaters, or any other combustion devices and combinations thereof that combust a fuel source to generate power for operating machinery and / or systems. In addition to providing power and operating machinery, the powerSP3063- 6 - generator 12 may also be used to compress gas in, for example, the natural gas value chain. The power generator 12 may use natural gas (e.g., CNG and / or LNG, RNG) as a fuel source. However, other fuels such as gasoline or diesel may be used, without departing from the scope of the present disclosure. In operation, the power generator 12 combusts the fuel source and generates an exhaust gas 30. The exhaust gas 30 includes undesirable components generated as a result of combustion. For example, the exhaust gas 30 may include sulfur species (e g., sulfur oxides (SOX)), volatile organic compounds (VOC), methane (CH4), ethane (C2H6), carbon monoxide (CO), oxides of nitrogen (NOX), and other undesirable components, and combinations thereof.

[0018] As shown in the illustrated embodiment, the desulfurization unit 14 receives the exhaust gas 30 via a raw exhaust gas conduit extending between the power generator 12 and the desulfurization unit 14, where sulfur species are removed from the exhaust gas 30 to generate a desulfurized exhaust gas 36. As discussed above, sulfur species may deactivate certain catalysts used for removing pollutants from exhaust emissions. Therefore, it is desirable to desulfurize the exhaust gas 30 before contacting with, for example, deNOxcatalysts. The desulfurization unit 14 includes one or more sulfur guard beds having a desulfurization adsorption catalyst that removes the sulfur species from the exhaust gas 30 to generate the desulfurized exhaust gas 36. The desulfurization adsorption catalyst may include any suitable catalyst that removes sulfur from the exhaust gas 30. By way of non-limiting example, the desulfurization adsorption catalyst may include materials such as, for example, metal-oxides supported on an inorganic carrier. By way of non-limiting example, the metal oxide includes oxides of vanadium, calcium, magnesium, nickel, and / or iron. In certain embodiments, the desulfurization adsorption catalyst is supported on a carrier such as, for example, alumina or titania. In certain embodiments, the one or more sulfur guard beds may include sorbents instead of, or in combination with, the desulfurization catalyst that adsorb the sulfur species, thereby removing them from the exhaust gas 30 and generating the desulfurized exhaust gas 36.

[0019] Prior to feeding into the desulfurization unit 14, the exhaust gas 30 may be mixed with air 38 in the raw exhaust gas conduit. For example, the air 38 may be injected into the raw exhaust gas conduit before, after, or at the same time the exhaust gas 30 is fed into the raw exhaust gas conduit. The air 38 may cool the exhaust gas 30 to a temperature that is suitable for optimalSP3063- 7 - desulfurization in the desulfurization unit 14. For example, the exhaust gas 30 may exit the power generator 12 and flow into the raw exhaust gas conduit at a temperature of between 315 °C and 535 °C. While some heat may be lost to tubing of the raw exhaust gas conduit between the power generator 12 and the desulfurization unit 14, the temperature of the exhaust gas 30 may still be too high (e.g., approximately 800 °C or more) for effective and efficient desulfurization and may impact performance of the desulfurization catalyst. Therefore, the air 38 is mixed with the exhaust gas 30, thereby cooling it to optimal desulfurization temperatures between 390 °C and 580 °C.

[0020] In addition to cooling the exhaust gas 30, the air 38 may be used to increase the oxygen content of the exhaust gas 30, which may improve oxidation of gaseous hydrocarbons such as methane, ethane, and volatile organic compounds. The air 38 may also be used as a diluent. For example, in certain embodiment, and undesirable amount of unreacted methane (i.e., methane slip) may remain in the exhaust gas 30. The unreacted methane may result in undesirable temperature increases across catalyst beds in certain downstream reactions (e.g., in the devolatization unit 18). By diluting the concentration of unreacted methane in the exhaust gas 30, the undesired temperature rise may be mitigated. The air 38 may also dilute the sulfur species in the exhaust gas 30, thereby improving the longevity of the desulfurization catalyst in the desulfurization unit 14.

[0021] In certain embodiments, the air 38 is used to bring the system 10 to temperature at start-up, as discussed in further detail below. Briefly, during start-up, the air 38 may circulate through the system 10 until the temperature of the system 10 reaches a target operating temperature. By way of non-limiting example, the target operating temperature of the system 10 may be between 350 and 700 °C, more preferably between 400 and 650 °C, and most preferably between 450 and 600 °C. During start-up, the exhaust gas 30 does not enter the system 10.

[0022] Following desulfurization, the desulfurized exhaust gas 36 is fed to the heating system 26 via a desulfurized exhaust conduit extending between the desulfurized unit 14 and the heating system 26 and heated in the heating system 26. As discussed above, the exhaust gas 30 has VOCs that need to be removed to meet emission regulatory requirements. Devolatization reactions occur at temperatures in excess of 535 °C. Therefore, it is desirable that the exhaust gasSP3063- 8 - entering the devolatization unit 18 be at or near the devolatization reaction temperature for effective and efficient devolatization. While the exhaust gas 30 exiting the power generator 12 may have a temperature of 535 °C, heat loss occurs as the exhaust gas 30 flows to the desulfurization unit 14. Moreover, when mixed with the air 38, the temperature of the exhaust gas 30 is reduced such that its temperature is below 535 °C. Therefore, after desulfurization of the exhaust gas 30, the resultant desulfurized exhaust gas 36 is heated in the heating system 26.

[0023] The heating system 26 includes a first heating element 42 and a second heating element 48. The first heating element 42 may include one or more heat exchangers that transfer heat to the desulfurized exhaust gas 36 and generate a first heated desulfurized exhaust gas 50. The one or more heat exchangers may be any suitable regenerative or recuperative heat exchanger that transfers heat from one fluid to another. By way of non-limiting example, the one or more heat exchangers may be a recuperative shell -and-tube heat exchanger, plate heat, plate-fin heat exchanger, or regenerative ceramic heat exchanger, and the like. As illustrated in FIG. 1, the first heating element 42 receives a heat transfer fluid (e.g., devolatized exhaust gas 56) and indirectly transfers the heat of the heated fluid to the desulfurized exhaust gas 36, thereby heating it and generating the first heated desulfurized exhaust gas 50 and a cooled exhaust gas 58. The desulfurized exhaust gas 36 may be heated to between 482 °C and 537 °C by the first heating element 42.

[0024] By using the heat generated by other system processes, in this instance the heat from the devolatized exhaust gas 56, the overall efficiency of the exhaust gas decontamination process is improved and optimization for a self-sustaining process may be achieved. For example, without being bound by theory, catalytic materials in certain reactors of the system 10 (e.g., the devolatization unit 18) may initially act as heat sinks and, once the reaction(s) begin, as heaters by releasing energy which is applied to heating system 26 ^hereby pre-heating the devolatized exhaust gas 56. The amount of internal heat release from hydrocarbon catalytic oxidation and the required fuel consumption to generate that heat may be reduced by betweenl-99% compared to existing systems. Certain existing systems may require 100% of the heat to come from external sources. In contrast, the system of the present disclosure utilizes heat generated within the system, which reduces the amount of external heat and the overall fuel consumption for system. Consequently,SP3063- 9 - the carbon footprint of exhaust emission removal processes resulting from fuel usage is reduced compared to existing systems. For example, the disclosed heating exchange system 26 reduces the carbon footprint of the system 10 by between 10% and 50%, preferably between 20% and 45%, and more preferably between 20% and 40%.

[0025] While in the illustrated embodiment, the desulfurization unit 14 is positioned upstream of the heat exchange system 26, the desulfurization unit 14 may be positioned downstream of the heat exchange system 26. For example, in certain embodiments, the temperature of the exhaust gas 30 may be lower than an optimal temperature for effective and efficient desulfurization to occur. As such, the exhaust gas 30 may be heated in the heat exchange system 26 to increase its temperature to the optimal temperature for desulfurization. However, it is preferred that the desulfurization unit 14 be positioned upstream of the heat exchange system 26. An advantage of desulfurizing the exhaust gas 30 before feeding to the heating system 26 is that fouling of the heating element 42 may be mitigated. For example, the sulfur species in the exhaust gas 30 may deposit on surfaces of the heating element 42, thereby causing fouling and reducing the heat exchange efficiency over time. Therefore, by desulfurizing the exhaust gas 30 before heating in the heating system 26, the heat exchange efficiency of the heat exchange system 26 may be maintained.

[0026] As discussed above, the devolatization unit 18 provides the heat transfer fluid used by the first heating element 42 to heat the desulfurized exhaust gas 36. For example, the system 10 includes a heat transfer fluid conduit extending between the devolatization unit 18 and the first heating element 42 that provides the heat transfer fluid to the heat exchangers of the first heating element 42. The amount of heat the heat transfer fluid transfers to the desulfurized exhaust gas 58 is limited by the reaction temperature of the devolatization unit 18. In certain instances, the heat from the devolatization unit 18 may not be sufficient to heat the desulfurized exhaust gas 36 to the desired temperature (e.g., equal to or greater than 535 °C) for effective and efficient devolatization. For example, the first heated desulfurized exhaust gas 50 may be at a temperature that is approximately 15 °C to 95 °C lower than the desired temperature. As the first heated desulfurized exhaust gas 50 may not be at the desired temperature, the second heating element 48 is used to provide additional heat to the first heated desulfurized exhaust gas 50. The second heating elementSP3063- 10 -48 may be a burner, electric heater, or any other suitable heating device that may be used to provide heat to the first heated desulfurized exhaust gas 50. In a preferred embodiment, the second heating element 48 includes a burner that receives and bums a fuel 64 to generate heat that is transferred to the first heated desulfurized exhaust gas 50, resulting in a second heated desulfurized exhaust gas 68. For example, the resultant product of burning the fuel 64 is mixed with the first heated desulfurized exhaust gas 50 and directly heats it. As should be appreciated, the amount of the fuel 64 that may be required to heat the first heated desulfurized exhaust gas 50 to the desired temperature is significantly less than what would be required if the desulfurized exhaust gas 36 was not first heated by the first heating element 42.

[0027] The fuel 64 may be any suitable fuel that may be burned to generate heat. For example, the fuel 64 may be natural gas, propane, and the like. In certain embodiments, an alternative energy source such as, for example, steam may be used to provide heat. In a preferred embodiment, the fuel 64 is natural gas. The fuel 64 may be treated to remove one or more contaminants (e.g., pollutants) prior to feeding to the second heating element 48. For example, the fuel 64 may contain sulfur species. Accordingly, the fuel 64 may be treated in a sulfur guard bed, or desulfurization unit, to remove these undesirable sulfur species. As the fuel 64 is burned in the second heating element 48, the resultant gas may contain undesirable emissions (e.g., NOXand VOCs). These undesirable emissions are removed in the devolatization unit 18 and the deNOxunit 20 along with those present in the second heated desulfurized exhaust gas 68.

[0028] The second heated desulfurized exhaust gas 68 is heated to a temperature of greater than or equal to approximately 535 °C by the gas resulting from burning of the fuel 64. Therefore, once heated to the desired temperature, the second heated desulfurized exhaust gas 68 is fed to the devolatization unit 18 via a heated exhaust gas conduit extending between the second heating element 48 and the devolatization unit 18 for removal of VOCs. The devolatization unit 18 includes one or more reactors having a devolatization catalyst such as, for example, a methane oxidation catalyst (MOC) that removes the VOC and CF from the second heated desulfurized exhaust gas 68 to generate the devolatized exhaust gas 56 that is used as the heat transfer fluid in the first heating element 42. By way of non-limiting example, the devolatization catalyst may be precious metal (Pt, Pd, Ag, Ru, etc.) and / or base metal (Cu, Ni, etc.) catalyst with the addition ofSP3063- 11 - promoters and binders. In certain embodiments, the devolatization catalyst is supported on an alumina or titania carrier.

[0029] Devolatization of the second heated exhaust gas 68 releases heat that may be utilized by the system 10 to heat exhaust gas streams flowing through the system. The heat released by the devolatization of the second heated exhaust gas 68 heats the resultant devolatized exhaust gas 56 to a temperature of approximately 593 °C. The heat from the devolatized exhaust gas 56 may be recovered in the first heating element 42 and used to heat the desulfurized exhaust gas 36, as discussed above. This in turn cools the devolatized exhaust gas 56 to generate the cooled exhaust gas 58, which is at a suitable temperature of between approximately 150 °C and 550 °C for undergoing denitrification in the deNOxunit 20.

[0030] Once cooled, the cooled exhaust gas 58 is fed to the deNOx unit 20 via a cooled gas conduit extending between the first heating element 42 and the deNOx unit 20. The deNOx unit 20 includes several features that facilitate removal of the NOXfrom the cooled exhaust gas 58. For example, the deNOx unit 20 may include one or more reactors having a deNOx catalyst that converts NOXinto nitrogen and water and generates a treated exhaust gas 70. The treated exhaust gas 70 meets regulatory emission levels and may be released as an on-spec exhaust gas from the system 10. For example, following deNOx in the deNOx unit 20, the treated exhaust gas 70 may be fed to a stack that releases the treated exhaust gas 70 from the system 10. A fan positioned between the deNOx unit 20 and the stack may be used to facilitate release of the treated exhaust gas 70. The deNOx catalyst may be any suitable denitrogenation catalyst that has a high activity and selectivity at low temperatures (e.g., between approximately 100 °C to approximately 400 °C) and pressures between 0 kilopascals (kPa) to 1200 kPa. Under the deNOx conditions, the deNOx catalyst removes greater than 98% of NOx present in the cooled exhaust gas 58. The deNOx catalyst may be any suitable NOx reduction catalyst having catalytically active metals such as, for example, vanadium (V) and / or tungsten (W), metal oxides of aluminum (Al), copper (Cu), iron (Fe), cobalt (Co), tin (Sn), chromium (Cr), nickel (Ni), manganese (Mn), titanium (Ti), silver (Ag), platinum (Pt), rhodium (Rh), palladium (Pd), and mixtures thereof supported on a carrier (e.g., titania, alumina, silica, and the like). Examples of catalyst that may be used to remove NOXfrom the cooled exhaust gas 58 include those described in U.S. Patent No. 6,419,889.SP3063- 12 -

[0031] In certain embodiments, the deNOxunit 20 may include an ammonia injection grid (AIG) that injects ammonia into a stream of the cooled exhaust gas 58 before it contacts the deNOx catalyst. As discussed above, removal of NOXoccurs at temperatures between 100 °C and 400 °C. The devolatized exhaust gas 56 that is directed to the deNOxunit 20 is at a temperature of approximately 593 °C, which is too hot for the deNOxcatalyst. Such temperatures are not suitable for the selective reduction of NOXand may undesirably impact catalyst performance and activity. However, the configuration of the system 10 disclosed herein, recovers and transfers the heat from the devolatized exhaust gas 56 to the desulfurized exhaust gas 36, thereby cooling the devolatized exhaust gas 56 to generate the cooled exhaust gas 58 that is at a temperature suitable for effective and efficient deNOx in the deNOx unit 20. As discussed above, recovering the heat from the devolatized exhaust gas 56 reduces the amount of external heat required to heat the desulfurized exhaust gas 36 (or in some embodiments, the exhaust gas 30) to the temperature suitable for devolatization in the devolatization unit 18, thereby reducing the overall carbon footprint of the system 10. It also cools the devolatized exhaust gas 58 to a temperature suitable for deNOxin the deNOx unit 20.

[0032] In one embodiment, heat from the treated exhaust gas 70 may be recovered prior to releasing from the system 10. For example, FIG. 2 illustrates a system 80 having a second heating system 82 positioned downstream of the deNOx unit 20. The second heating system 82 receives the treated exhaust gas 70, cools it, and generates a cooled treated exhaust gas 90 and steam 92. The second heating system 82 may include one or more heat exchangers that remove and recover heat from the treated exhaust gas 70 by indirect heat exchange with a heat transfer fluid (e.g., water). The treated exhaust gas 70 transfers its heat to the heat transfer fluid, thereby heating the heat transfer fluid to generate the steam 92. The steam 92 may be used to heat other system process and / or external equipment. For example, in one embodiment, the second heating system 82 may include a boiler that provides the heat transfer fluid used to indirectly recover heat from the treated exhaust gas 70. The steam 92 generated by heating the heat transfer fluid with the treated exhaust gas 70 may be directed to peripheral equipment or systems and used to provide heat. The heat from the steam 92 is released to the heat the peripheral equipment or system, thereby cooling the steam 92 and generating cooled water. The cooled water may be recirculated to the boiler, which provides the cooled water as the heat transfer fluid to the second heating system 82.SP3063- 13 -

[0033] Returning to FIG. 1, the system 10 includes a controller 96 to govern operation of the system 10. As should be appreciated, the system 80 of FIG. 2 also includes a similar controller. The controller 96 may independently control operation of the system 10 by electrically communicating with sensors, control valves, pumps, and other flow adjusting features throughout the system 10. The controller 96 may be any device employing a general purpose or application specific processor 98, both of which may include memory circuitry 100 for storing instructions such as system parameters such as, for example, desulfurization conditions, devolatization conditions, deNOxconditions, fluid temperatures, system pressure, and exhaust emission levels among others. The processor 98 may include one or more tangible, non-transitory, machine- readable media collectively storing instructions executable by the processor 98 to control actions described herein. In certain embodiments, the controller 96 may use information provided via input signals 104 to execute instructions or code contained on a machine-readable or computer- readable storage medium (e.g., the memory circuitry 100) and generate one or more output signals 108 to the various control devices (e.g., valves, pumps, etc.) to control a flow of fluids throughout the system 100.

[0034] In one embodiment, the controller 96 may operate control devices (e.g. valves, pumps, etc.) to control amounts and / or flows between different system components. It should be noted that there may be valves throughout the system 10 used to adjust different amounts and / or flows between system components. For example, the controller 96 may govern operation of valves to control an amount or adjust a flow of the exhaust gas 30, the air 38 and the fuel 64. As discussed above, during start-up the exhaust gas 30 may not be circulated through the system 10. The system 10 includes one or more valves the control the flow of the exhaust gas 30 from the power generator 12 to the desulfurization unit 14. The controller 96 may close these valves to block a flow of the exhaust gas 30 from flowing to the desulfurization unit 30 and redirect the flow away from the system 10 and open an air valve that allows the flow of the air 38 into the system 10. In addition, during start-up, the controller 96 may open a fuel valve that allows a flow of the fuel 64 into the second heating element 48 to provide heat for heating the air 38. Once the various components of the system 10 are heated to the desired operating temperature, the controller 96 may open the valves that direct the exhaust gas 30 into the system 10. Following start-up, the controller 96 may adjust any one of the valves to control an amount of the exhaust gas 30, the air 38, and / or the fuelSP3063- 14 -64 that enters the system 10 to control the temperature of the exhaust gas 30, 36, 50, 56, and 68, thereby providing for efficient and effective removal of exhaust gas emissions.

[0035] The unique arrangement of the units 14, 18, and 20 and the heating system 26 provide for a system that efficiently and effectively removes multiple exhaust emission components at a lower carbon footprint compared to existing systems that do not recover heat and remove multiple exhaust emission components. Moreover, the second heating element 48 may be used to control the heat provided to the system 10. For example, if the first heated exhaust gas 50 is at or near (e.g., ± 10 °C) the desired temperature for devolatiztion, it may not be necessary for the second heating element 48 to heat the first heated exhaust gas 50. Therefore, the second heating element 48 may be bypassed or turned off so as not to heat the first heated exhaust gas 50 further. However, in embodiments in which the first heated exhaust gas 50 is below the desired temperature for devolatization, the second heating element 48 provides the necessary heat to raise the temperature of the first heated exhaust gas 50 to the required temperature for effective and efficient devolatization. The system 10 includes a plurality of temperature sensors that measure the temperature of the various exhaust gas streams (e.g., the first heated exhaust gas 50) and communicate with the controller 96 via the output signal 104. Based on the measured temperature, the controller 96 may provide the output signal 108 to the fuel value and control the amount of fuel 64 provided to the second heating element 48 such that the temperature of the first heated exhaust gas 50 is at the desired temperature.

[0036] In certain embodiments, the activity of one or more of the catalysts used for removal of exhaust emission components may decrease over time. One way to increase the activity of a spent catalyst without removing and replacing with fresh catalyst is to increase the reaction temperature. The second heating element 48 may be used to increase the temperature of, for example, the second heated exhaust gas 68 to the temperature required to increases the activity of the deactivated catalyst in the devolatization unit 18. In doing so, the overall longevity of the catalyst in the devolatization unit 18 may be increased, thereby reducing the overall cost of the system operation that may be incurred for having to shutdown the system and replace the spent catalyst. For example, sensors (e.g., methane sensor) that measure exhaust emission levels may provide information to the controller 96 via the input signal 104 with information about the amountSP3063- 15 - of exhaust emissions in the devolatized exhaust gas 56. The controller 96 determines whether the measured exhaust emissions are within the desired levels. If the exhaust emission is outside the desired level, the controller 96 provides the output signal 108 to the heating system 26 with instructions to increase the temperature of the second heated exhaust gas 68. The second heated exhaust gas 68 may be raised to temperature that is sufficient to increase the activity of the deactivated catalyst in the devol atizati on unit 18.

[0037] Embodiments of the present disclosure also include a method for removing multiple exhaust emission components form an exhaust gas. FIG. 3 is a block diagram of a method 120 that may be used by the system 10, 80 to effectively and efficiently remove exhaust emission components from an exhaust gas. The method 120 includes providing a gas stream to a sulfur removal unit (block 124) and removing sulfur species from the gas stream to generate a first treated gas stream (block 126). For example, an exhaust gas (e.g., the exhaust gas 30) containing exhaust emission components is generated in a power generator (e.g., the power generator 12) from burning of natural gas. The exhaust gas includes sulfur species that undesirable impact the activity of certain catalysts used in removing exhaust emission components from the exhaust gas. For example, catalysts such as devolatization catalysts (e.g., methane oxidation catalysts) and deNOxcatalyst are sensitive to sulfur species. Therefore, prior to treating the exhaust gas with devolatization and / or deNOx catalysts, the exhaust gas is fed to a desulfurization unit (e.g., the desulfurization unit 14) that removes the sulfur species from the exhaust gas and generates a first treated exhaust gas (e.g., the desulfurized exhaust gas 36).

[0038] The method 120 also includes providing the first treated gas stream to a heating system (block 130) and heating the first treated gas stream to generate a heated gas stream (block 132). The heating system (e.g., the heating system 26) includes multiple heating elements (e.g., heating elements 42, 48) that heat the first treated gas stream (e.g., the desulfurized exhaust gas 36) to a temperature that is suitable for devolatization. Devolatization reactions, in particular for removing methane, in the presence of the devolatization catalyst occur at temperatures of approximately 535 °C or more. In contrast desulfurization reactions in the presence of a desulfurization catalyst occur at a temperature range of between approximately 315 °C and 482 °C. Therefore, it is desirable to heat the first treated gas stream to a temperature that is at or nearSP3063- 16 - the reaction temperature for devol atizati on occur in a devolatization unit (e.g., the devolatization unit 18). As discussed above, heat from an output (e.g., the devolatized exhaust gas 56) generated in the devolatization unit may be used to heat the first treated gas stream. For example, the devolatization unit output may be fed into a heating element (e.g., the first heating element 42) having one or more heat exchangers that recover and transfer heat from the output to heat the first treated gas stream via indirect heat exchange and generate a heated treated gas stream (e.g., the first heated exhaust gas 50). For example, the heating element may increase a temperature of the first treated gas stream from approximately 315 °C to 426 °C to approximately 357 °C to 482 °C, thereby generating the heated treated gas stream.

[0039] Additional heat provided by a second heating element (e.g., the second heating element 48) may be used to increase the temperature of the heated treated gas stream further if needed. For example, the second heating element may combust a fuel (e.g., the fuel 64) to generate a gas having a temperature of between approximately 482 °C and 538 °C. This gas is injected into and mixed with the heated treated exhaust gas, thereby increasing its temperature to generate the heated gas stream (e.g., the second heated exhaust gas 68). In other embodiment, the second heating element is an electric heater and does not combust a fuel to generate heat. By heating the treated gas stream in the heating system disclosed herein, the heated gas stream may be at a temperature suitable for effective and efficient devolatization in the devolatization unit. In addition, the overall efficiency of exhaust emission removal systems having the heating system and emission removal units (e.g., the units 14, 18, 20) arranged in the manner disclosed herein is improved by recovering and transferring heat from certain system processes to others, thereby reducing the external heat requirement of the system. In addition, catalyst run time / longevity is improved by the combination of removing sulfur species that deactivate catalysts from the exhaust gas prior to heating and treating with sulfur sensitive catalysts. For example, even in the absence of sulfur, the activity of the devolatization catalyst decreases over time. One way to increase the activity of a deactivated catalyst and extend its catalytic lifespan is to raise the temperature across the catalyst bed. The second heating element may be used to increase the temperature of the heated gas stream to the required temperature for reactivation of the deactivated catalyst. This reduces the frequency of having to shutdown the system to replace the deactivated catalyst. That is, the deactivated catalysts may be reactivated in situ by increasing the reaction temperature across theSP3063- 17 - catalyst bed with the heated gas stream, thereby extending the amount of time the catalyst may be used before having to be replaced.

[0040] Following heating of the treated gas stream, the method 120 also includes providing the heated gas stream to the devolatization unit (block 140) and removing volatile components from the heated gas stream to generate a devolatized gas stream (block 142). As discussed above, volatile organic compounds (VOCs) including methane (CH4) and ethane (C2H6) are present in exhaust gas generated in combustion engines. The level of VOCs present in exhaust need to be below a certain regulatory limit before the exhaust may be released from the system. The heated gas stream (e.g., the second heated exhaust gas 68) is fed to the devolatization unit (e.g., the devolatization unit 18) where CH4, C2H6, and other VOCs are removed from the heated exhaust gas in the presence of a devolatization catalysts, thereby generating a devolatized gas stream (e.g., the devolatized exhaust gas 56).

[0041] The devolatized gas stream exiting the devolatization unit is at a temperature of greater than or equal to 593 °C. Heat from the devolatized gas stream may be recovered and transferred to other processes in the system. Accordingly, the method 120 further includes providing the devolatized gas stream to the heating system to generate a cooled gas stream and a portion of the heated gas stream (block 146) and providing the cooled gas stream to a deNOxunit to remove NOXand generate a second treated gas stream (block 150). For example, as discussed above, the first treated gas stream (e.g., the desulfurized exhaust gas 30) is not at a suitable temperature for devolatization. Therefore, heat from the devolatized gas stream (e.g., the devolatized exhaust gas 56) is used to heat the first treated gas stream in the heating system (e.g., the heating system 26) to generate the heated treated gas stream (the first heated exhaust gas 50). Using heat from the devolatized gas stream to heat the first treated gas reduces the amount of external heat required to increase the temperature of the first treated gas to the desired temperature for efficient and effective devolatization to occur. Unlike the system and method of the present disclosure, existing systems use heat from exhaust gas exiting the engine (e.g., untreated exhaust gas) to heat system components and fluids circulating through the system. Therefore, the temperature to which system component and fluids circulating therethrough are heated to is limited to the temperature of the untreated exhaust gas output by the engine. Consequently, operatingSP3063- 18 - temperatures of catalyst used for treating exhaust gas are limited to the maximum temperature of the untreated exhaust gas (e.g., less than 538 °C). That is, the untreated exhaust gas temperature may be less than the optimal temperature for the catalyst to efficiently and effectively remove exhaust emissions. Moreover, when using the untreated exhaust gas as the heat source, in situ thermal regeneration of deactivated catalyst cannot occur due to the limited maximum temperature of the untreated exhaust gas.

[0042] The technical effects of the system and method disclosed herein is the arrangement of a combination of multiple exhaust emission removal unit and a heating system that enables removal of multiple exhaust emission components and utilizes heat recovered from certain process in a manner that improves the overall effectiveness and efficiency of exhaust emission removal systems. For example, the system and method disclosed herein removes sulfur species from exhaust gas generated from combustion of natural gas, which mitigates fouling of system surfaces and deactivation of sulfur sensitive catalysts caused by the deposition of the sulfur species on surfaces of the system and sulfur sensitive catalysts. In addition, the disclosed system and method use a heating system that recovers and transfers heat from a devolatized exhaust gas to a desulfurized exhaust gas, thereby heating the desulfurized exhaust gas to a temperature suitable for devolatization reactions. For example, desulfurization and deNOxreactions occur at temperatures lower than devolatization reactions. Therefore, devolatizing the exhaust gas after desulfurization and before deNOxallows for the heat generated in the devolatization reaction to be recovered and transferred from the devolatized exhaust gas to the desulfurized exhaust gas in the heating system, thereby raising the temperature of the desulfurized exhaust gas. Additional heat may be provided to the heated desulfurized exhaust gas in the disclosed heating system to further raise the temperature of the desulfurized exhaust gas to a suitable temperature for devolatization. In addition to heating the desulfurized exhaust gas, the heating system of the present disclosure cools the devolatized exhaust gas to a temperature that is suitable for deNOx.

[0043] In addition to recovering and using the heat generated by devolatization of the desulfurized exhaust gas, the system and method of the present disclosure improve the longevity of certain catalyst used for the removal of exhaust emission. For example, the second heating element of the disclosed heating system may apply additional heat to the desulfurized exhaust gasSP3063- 19 - such that the desulfurized exhaust gas is heated to a temperature that thermally regenerates a deactivated catalyst (e.g., deactivated devolatization catalyst) in situ. Without in situ thermal regeneration of the catalyst, system shut down may be required to replace the deactivated catalyst resulting in undesired downtime and increased costs. Therefore, not only does the system and method disclosed herein improve the effectiveness and efficiency of exhaust emission removal systems, it also reduces the amount of external heat required for system processes and enable in situ thermal regeneration of deactivated catalysts.

[0044] The present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

SP3063- 20 -CLAIMS1. A system configured to treat a gas stream, comprising: a sulfur removal unit configured to remove sulfur from the gas stream and to generate a first treated gas stream; an oxides of nitrogen removal unit disposed downstream from and fluidly coupled to the sulfur removal unit; and a heat exchange system disposed between the sulfur removal unit and the oxides of nitrogen removal unit, wherein the heat exchange system comprises: a first heating element configured to heat the first treated gas stream and to generate a first heated gas stream having a first temperature; and a second heating element disposed downstream from and fluidly coupled to the first heating element, wherein the second heating element is configured to receive and heat the first heated gas stream and to generate a second heated gas stream, and wherein the second heated gas stream has a second temperature that is greater than the first temperature.

2. The system of claim 1, comprising a first conduit positioned downstream of the heat exchange system and extending between the second heating element and a gas devolatization unit, a second conduit positioned downstream from the first conduit and extending between the gas devolatization unit and the first heating element, and a third conduit positioned downstream from the second conduit and extending between the first heating element and the oxides of nitrogen removal unit, wherein the first conduit is configured to provide the second heated gas stream to the gas devolatization unit, the second conduit is configured to provide a third heated gas stream output by the gas devolatization unit to the first heating element, and the third conduit is configured to provide a cooled gas stream output by the first heating element to the oxides of nitrogen removal unit, and wherein a temperature of the third heated gas stream is greater than the second temperature.SP3063- 21 -3. The system of claim 1, comprising a gas devolatization unit disposed between the heat exchange system and the oxides of nitrogen removal unit and configured to output a third heated gas stream, and wherein the third heated gas stream is configured to heat the first treated gas stream in the first heating element.

4. The system of claim 1, wherein the first heating element comprises one or more recuperative heat exchangers.

5. The system of claim 1, wherein the first heating element comprises one or more regenerative heat exchangers.

6. The system of claim 1, wherein the second heating element comprises a burner or an electric heater.

7. The system of claim 1, comprising one or more combustion engines configured to generate the gas stream, wherein the gas stream comprises one or more of a sulfur species, oxides of nitrogen, volatile organic compounds, and methane.

8. The system of claim 1, comprising a second heat exchange system disposed downstream from the oxides of nitrogen removal unit, wherein the second heat exchange system is configured to remove heat from a second treated gas stream output from the oxides of nitrogen removal unit and to generate a cooled treated gas and steam.

9. A process for treating a gas stream, comprising:SP3063- 22 - providing a first treated gas stream to a heat exchange system disposed between a sulfur removal unit and an oxides of nitrogen removal unit, wherein the heat exchange system comprises a first heating element and a second heating element, and wherein the first treated gas stream is generated from the gas stream in the sulfur removal unit; heating the first treated gas stream in the first heating element to generate a first heated gas stream having a first temperature; providing the first heated gas stream to the second heating element; heating the first heated gas stream in the second heating element to generate a second heated gas stream having a second temperature that is greater than the first temperature; and providing a third heated gas stream having a third temperature to the first heating element, wherein the third heated gas stream heats the first treated gas stream to generate the first heated gas stream, wherein the third temperature is greater than the second temperature, and wherein the third heated gas stream is generated from the second heated gas stream.

10. The process of claim 9, comprising providing the second heated gas stream to a devolatization unit disposed between the second heating element and the oxides of nitrogen removal unit and removing incomplete combustion products from the second heated gas stream in the devolatization unit to generate the third heated gas stream.

11. The process of claim 9, wherein heat from the third heated gas stream is removed during heating of the first treated gas stream to cool the third heated gas stream and generate a cooled gas stream.

12. The process of claim 11, comprising providing the cooled gas stream to the oxides of nitrogen removal unit and removing oxides of nitrogen from the cooled gas stream to generate a second treated gas stream.SP3063- 23 -13. The process of claim 12, comprising providing the second treated gas stream to a second heat exchange system disposed downstream from the oxides of nitrogen removal unit and heating a fluid in the second heat exchange system to generate a cooled treated gas stream and steam.

14. The process of claim 9, comprising combusting a hydrocarbon fuel in an engine disposed upstream of the sulfur removal unit to generate the gas stream, wherein the gas stream comprises one or more of a sulfur species, oxides of nitrogen, volatile organic compounds, and methane.

15. A system configured to treat a gas stream, comprising: a heat exchange system disposed between a sulfur removal unit and a oxides of nitrogen removal unit, wherein the heat exchange system comprises: a first heating element configured to heat a first treated gas stream output from the sulfur removal unit and to generate a first heated gas stream having a first temperature; and a second heating element disposed downstream from the first heating element and configured to heat the first heated gas stream and to generate a second heated gas stream having a second temperature greater than the first temperature.

16. The system of claim 15, wherein the first heating element comprises one or more recuperative heat exchangers.

17. The system of claim 15, wherein the first heating element comprises one or more regenerative heat exchangers.SP3063- 24 -18. The system of claim 15, wherein the second heating element comprises a burner or an electric heater.

19. The system of claim 15, comprising a first conduit positioned downstream of the heat exchange system and extending between the second heating element and a gas devol atizati on unit, a second conduit positioned downstream from the first conduit and extending between the gas devolatization unit and the first heating element, and a third conduit positioned downstream from the second conduit and extending between the first heating element and the oxides of nitrogen removal unit, wherein the first conduit is configured to provide the second heated gas stream to the gas devolatization unit, the second conduit is configured to provide a third heated gas stream output from the gas devolatization unit to the first heating element, and the third conduit is configured to provide a cooled gas stream output from the first heating element to the oxides of nitrogen removal unit, and wherein a temperature of the third heated gas stream is greater than the second temperature.

20. The system of claim 19, a second heat exchange system disposed downstream from the oxides of nitrogen removal unit, wherein the second heat exchange system is configured to remove heat from a second treated gas stream output from the oxides of nitrogen removal unit and to generate a cooled treated gas and steam.

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