Classifications

• • 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
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/54—Nitrogen compounds
  • B01D53/56—Nitrogen oxides
  • B01D53/565—Nitrogen oxides by treating the gases with solids
• • 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
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
  • B01D53/8621—Removing nitrogen compounds
  • B01D53/8625—Nitrogen oxides
  • B01D53/8628—Processes characterised by a specific catalyst
• • 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
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9404—Removing only nitrogen compounds
  • B01D53/9409—Nitrogen oxides
  • B01D53/9413—Processes characterised by a specific catalyst
  • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/20—Reductants
  • B01D2251/208—Hydrocarbons
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20715—Zirconium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/209—Other metals
  • B01D2255/2092—Aluminium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/01—Engine exhaust gases
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/02—Other waste gases
  • B01D2258/0283—Flue gases
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)

Definitions

• the presently disclosed subject matter relates to methods and systems for removing pollutant gases from the exhaust gas stream formed by a combustion process, such as internal combustion engines, furnaces, power plants, and so forth.
• a combustion process such as internal combustion engines, furnaces, power plants, and so forth.
• the disclosed subject matter is related to the use of zeolite catalysts loaded with various of metals for selective catalytic reduction of nitrogen oxides (NOx) from the exhaust gases resulting directly or indirectly from a combustion process in the exploration, production, refining, manufacture, supply, transport, formulation or blending of petroleum, petrochemicals or the direct products thereof.
• NOx nitrogen oxides
• Combustion devices in commercial applications such as those in the petroleum and petrochemical processing field, which includes the exploration, production, refining, manufacture, supply, transport, formulation or blending of petroleum, petrochemicals, or the direct products thereof, are a source of NOx emissions.
• a continuing effort has been made over the years to develop methods and systems to remove pollutant gases from exhaust gases produced by combustion unit operations.
• NOx nitrogen oxides
• Nitrogen oxides are produced, for example, when nitrogen reacts with oxygen within a combustion chamber under high temperature and pressure conditions. NOx can also be produced, for example, in fluid catalytic converters (FCCs) and furnaces due to combustion of nitrogen from FCC feeds, heating oil, and/or fuel oil. Such nitrogen oxides can include either one or a combination of nitrogen monoxide and nitrogen dioxide.
• FCCs fluid catalytic converters
• Such nitrogen oxides can include either one or a combination of nitrogen monoxide and nitrogen dioxide.
• SCR selective catalytic reduction
• SCR is a catalytic technique to convert NOx to diatomic nitrogen, N 2 , and water, H 2 0.
• a fluid reductant— such as anhydrous ammonia, aqueous ammonia or urea— is added to a stream of exhaust gas and absorbed onto a catalyst.
• a method for selective catalytic reduction of NOx includes providing an exhaust stream containing an amount of NOx from a combustion operation.
• a portion of the exhaust stream and a reductant stream including a low molecular weight hydrocarbon are introduced to a first catalytic reactor, which comprises a first catalyst including alumina loaded with silver.
• the reductant stream and the portion of the exhaust stream being introduced to the first catalytic reactor are at suitable operating conditions to reduce the amount of NOx in the exhaust stream.
• the NOx-reduced exhaust stream from the first catalyst is then directed to a second catalyst including zirconia loaded with at least one metal.
• the low molecular weight hydrocarbon is propylene. In various embodiments as discussed below, for purpose of illustration and not limitation, propylene is used as an example of the low molecular weight
• the first catalytic reactor includes a vessel or similar structure
• the second catalyst is within the structure of the first catalytic reactor.
• the second catalyst is in a second catalytic reactor located downstream of the first catalytic reactor.
• the source of the exhaust stream can be a refinery component, selected from the group consisting of a combustion furnace, a boiler, a heater turbine, and a fluid catalytic cracking unit.
• the first catalytic reactor can be located near a flue of the at least one refinery component to maintain the first catalytic reactor at an operating temperature between about 300 °C and 400 °C. Alternatively, the first catalytic reactor can be maintained at an operating temperature between about 300 °C and 400 °C by heating or cooling the exhaust stream.
• the exhaust stream can include about 0.1% to about 20% oxygen, e.g., about 2%> to about 9%> oxygen, and about 1% to about 10%> water, e.g., about 5% water.
• Molar ratio of propylene to NOx in the reductant stream can be between about 0.5 to 2 .
• the operating temperature of the first catalytic reactor can be between about 300 °C and about 400 °C, for example, at about 400 °C.
• hydrogen is provided in the reductant stream, for example, at a concentration of up to 5000 ppm.
• the reductant stream and the at least a portion of the exhaust stream collectively can have a gaseous hourly space velocity of between 30K cc per hour and 120K cc per hour through the first catalytic reactor.
• the first catalyst comprises 2 wt. % silver loaded on alumina.
• the loaded metal of the second catalyst is selected from the group consisting of copper, cerium, and tungsten.
• the second catalyst includes Cu/W/Zr0 2 and/or Ce/Zr0 2 .
• the loaded metal can be present in metal oxide form, depending on the preparation methods of the second catalyst.
• a system for selective catalytic reduction of NOx includes a conduit in fluid communication with a source of an exhaust stream from a combustion operation, the exhaust stream containing an amount of NOx; a source of a reductant stream including a low-molecular weight hydrocarbon; a first catalytic reactor in fluid communication with the conduit and the source of the reductant stream, the first catalytic reactor comprising a first catalyst including alumina loaded with silver; an outlet in fluid communication with the first catalytic reactor to direct the NOx-reduced exhaust stream from the first catalytic reactor; and a second catalyst including zirconia loaded with at least one metal, the second catalyst in fluid communication with the first catalyst.
• the first catalytic reactor includes a vessel or similar structure
• the second catalyst is within the structure of the first catalytic reactor.
• the second catalyst is in a second catalytic reactor located downstream of the first catalytic reactor.
• Fig. 1 is a flow diagram of a method for NOx reduction according to an embodiment of the disclosed subject matter.
• Fig. 2A is a schematic diagram of a system for NOx reduction according to an embodiment of the disclosed subject matter.
• Fig. 2B is a schematic diagram of a system for NOx reduction according to an alternative embodiment of the disclosed subject matter.
• NOx refers generally to a compound consisting of nitrogen and at least one oxygen molecule, and particularly to one or more of nitrogen monoxide, nitrogen dioxide and di-nitrogen or nitrous oxide.
• NOx-reduced stream includes a fluid stream having a reduction of such nitrogen monoxide, nitrogen dioxide, and nitrous oxide.
• combustion operation refers to any process wherein an energy-storing material is burned to produce energy or other byproduct.
• a “combustion operation” can include a unit operation within a commercial operation or the like in which NOx is emitted as the result of a combustion reaction.
• a combustion operation can include, but is not limited to, the operation of a combustion engine, furnace, boiler, heater and a turbine.
• a combustion operation can further include a fluid catalytic converter (“FCC”) regenerator operation, in which NOx is found in a FCC regenerator exhaust stream.
• FCC fluid catalytic converter
• GHSV gaseous hourly space velocity
• the term "commercial operation” refers to any operation in which a commodity (e.g., electricity), chemical, petroleum or other article of commercial interest (including a chemical intermediate to an article of commerce interest) is manufactured, produced or otherwise provided.
• a commodity e.g., electricity
• chemical, petroleum or other article of commercial interest including a chemical intermediate to an article of commerce interest
• commercial operation can include the exploration, production, refining, manufacture, supply, transport, formulation or blending of petroleum, petrochemicals, or the direct products thereof.
• the article of commercial interest can be manufactured, produced or otherwise provided in an industrial scale.
• the term "provided in an industrial scale” refers to a scheme in which, for example, gasoline or other product of commercial interest is produced on a generally continuous basis (with the exception of necessary outages for plant
• a method for selective catalytic reduction of NOx includes providing an exhaust stream from a combustion operation, the exhaust stream containing an amount of NOx.
• a portion of the exhaust stream and a reductant stream including a low molecular weight hydrocarbon introduced to a first catalytic reactor, which comprises a first catalyst including alumina loaded with silver.
• the reductant stream and the portion of the exhaust stream being introduced to the first catalytic reactor are at suitable operating conditions to reduce the amount of NOx in the exhaust stream.
• the NOx-reduced exhaust stream from the first catalyst is then directed to a second catalyst including zirconia loaded with at least one metal.
• a system for selective catalytic reduction of NOx includes a conduit in fluid communication with a source of an exhaust stream from a combustion operation, the exhaust stream containing an amount of NOx; a source of a reductant stream including a low-molecular weight hydrocarbon; a first catalytic reactor in fluid communication with the conduit and the source of the reductant stream, the first catalytic reactor comprising a first catalyst including alumina loaded with silver; an outlet in fluid communication with the first catalytic reactor to direct the NOx-reduced exhaust stream from the first catalytic reactor; and a second catalyst including zirconia loaded with at least one metal, the second catalyst in fluid communication with the first catalyst.
• the low molecular weight hydrocarbon is propylene.
• the second catalyst is within the first catalytic reactor. In other embodiments, the second catalyst is in a second catalytic reactor located downstream of the first catalytic reactor.
• an exhaust stream 220 containing NOx is provided (step 110) from a combustion operation 210.
• the combustion operation 210 can be any combustion operation that produces an exhaust stream containing NOx.
• the combustion operation can be, for example, a combustion operation in a refining operation involving a refinery component.
• Such refinery component can include a combustion furnace, a boiler, a heater turbine, or a fluid catalytic cracking unit among others.
• the combustion operation generally has a flue or similar outlet, such that the exhaust stream 220 exits the combustion operation via the flue outlet.
• the exhaust stream 220 can include other gases in addition to NOx.
• the exhaust stream can include an amount of oxygen, water, and other byproducts of the combustion operation.
• the exhaust stream can also contain trace amounts of hydrocarbons.
• the exhaust stream can include about 0.1% to about 20% oxygen, e.g., about 2%> to about 9%> oxygen, and about 1% to about 10%> water, e.g., about 5% water.
• the exhaust stream 220 is introduced (step 120) to a first catalytic reactor 230.
• the first catalytic reactor 230 includes a vessel of suitable construction for the intended operating conditions, and is in fluid
• the conduit 231 can be attached to the first catalytic reactor by suitable means and provided with a suitable inlet adapter as needed for flow of the exhaust stream to the first catalytic reactor 230.
• the conduit 231 can be threaded, welded, or otherwise attached to a port in the first catalytic reactor 230.
• the first catalytic reactor 230 is located proximate a refinery flue outlet of the at least one refinery component to maintain the first catalytic reactor at an operating temperature between about 300 °C and about 400 °C, as described further below.
• the exhaust stream 220 can first pass through one or more valves or treatment devices 270 prior to the first catalytic reactor 230.
• the exhaust stream can pass through a heat exchanger to control the temperature of the exhaust stream.
• a pump can be used to provide a desired flow rate to the first catalytic reactor.
• a reductant stream 265 is also introduced (step 130) to the first catalytic reactor 230.
• the reductant stream 265 includes an effective amount of low molecular weight hydrocarbon, such as propylene, to reduce NOx.
• the amount of propylene in the reductant stream 265 can be an amount sufficient to provide about a 0.5 to 2 molar ratio of propylene to the NOx in the exhaust stream 220. For example, if the amount of NOx in the exhaust stream 220 is 1000 ppm, the amount of propylene in the reductant stream 265 can be between about 500-2000 ppm.
• the reductant stream can be provided by a reductant stream source 260, such as a storage vessel for storing propylene.
• a reductant stream source 260 such as a storage vessel for storing propylene.
• propylene can be stored as a liquid, and can be first vaporized before being introduced to the first catalytic reactor.
• the first catalytic reactor 230 can have a port 234 in fluid communication with the reductant stream source 260 to receive the reductant stream 265.
• the port 234 can include a valve, or a plurality of valves to regulate the flow rate of the reductant stream.
• the first catalytic reactor 230 includes a first catalyst 240 including alumina loaded with silver.
• the first catalyst 240 can be structurally arranged, for example, on catalyst beds or the like within the first catalytic reactor 230.
• the first catalyst 240 can be in a variety of suitable structural or solid forms, such as powders, pellets, particles, washcoated or formed monoliths such as a honeycomb structure and the like, to allow the exhaust stream to contact the catalyst.
• the first catalyst 240 can be prepared using procedures known in the art. For example, ⁇ -alumina substrate can be prepared by a complexing agent-assisted sol gel method, followed by calcination.
• Silver can be loaded onto the ⁇ -alumina via incipient wetness impregnation techniques, for example, using silver nitrate or silver sulfate solution to impregnate alumina, followed by calcination at appropriate temperature to obtain the target level of loading.
• This is a conventional wet impregnation technique.
• silver can be loaded at about 2 wt. % based on the total weight of the first catalyst.
• the reaction product in this phase can include nitrous oxide (N 2 0).
• the NOx reduced stream containing the reaction product of this phase and any unreacted NOx can be directed to a second catalyst, thereby converting the NOx to N 2 , as will be further described below.
• the second catalyst 340 can include zirconia loaded with at least one metal.
• the second catalyst 340 can be structurally arranged, for example, on catalyst beds or the like in the second catalytic reactor 330, and can be in the form of powders, pellets, particles, washcoated or formed monoliths such as a honeycomb structure, and the like.
• the loaded metal of the second catalyst can be copper, cerium, tungsten, or mixtures thereof.
• the second catalyst includes Cu/W/Zr0 2 and/or Ce/Zr0 2 .
• the second catalyst can be prepared by permeating into the zirconia an amount of a salt containing the selected metal.
• the metal-modified catalyst is then calcinated in air to obtain a predetermined weight loading of the metal or metals loaded into the substrate.
• a catalytic reactor is a structural element that includes one or more catalyst.
• a catalytic reactor can include a vessel or similar structure of suitable construction containing the desired catalyst.
• the first catalyst and the second catalyst can be in a first catalytic reactor and a second catalytic reactor, respectively (Fig. 2A), or in the same catalytic reactor, i.e., the first catalytic reactor (Fig. 2B).
• the second catalytic reactor 330 can be located downstream from the first catalytic reactor 230, for example, at a distance downstream from the first catalytic reactor 230 such that the operating temperature of the second catalytic reactor 330 can be cooler than that of the first catalytic reactor.
• the NOx-reduced exhaust stream 250 can flow through a heat exchanger to achieve a desired temperature at the second catalytic reactor 330.
• the second catalyst is in the second catalytic reactor as illustrated in Fig. 2A, additional reductant stream can be introduced upstream of the second catalytic reactor. If the first catalyst and the second catalyst are both in the first catalytic reactor as illustrated in Fig. 2B, the two catalysts can be arranged with the second catalyst in a relative downstream position. The first catalyst and the second catalyst can be stacked directly against each other, or have a gap therebetween.
• the operating temperature can be varied.
• the operating temperature of the first catalytic reactor 230 can be between about 250 °C and about 550 °C.
• the operating temperature for each of the catalytic reactors can be same or different.
• a narrower range of suitable temperature can be determined in which the activity of the catalyst(s) used exhibits a maximum, e.g., by measuring NOx percent conversion at different temperatures.
• the operating temperature of the first catalytic reactor can be about 500 °C when only the first catalyst is loaded therein, and about 400 °C when both the first catalyst and the second catalyst are loaded therein.
• the desired operating temperature of the first catalytic reactor can be obtained in various ways. Combustion operations, such as in refinery equipment, often produce flue gas in the temperature range above 500 °C. As such, and in one embodiment, the operating temperature of the first catalytic reactor 230 can be maintained at the desired range or value by locating the first catalytic reactor 230 downstream from the combustion operation 210 at a location where the exhaust stream 220 is expected to have such a temperature range or value. For example, this location can be somewhere downstream of the combustion operation 210, with the exhaust stream 220 exiting the combustion operation 210 and flowing through the conduit 231 to the first catalytic reactor 230 after the exhaust stream has lost certain amount of thermal energy.
• the desired operating temperature can be maintained with the use of a heat exchanger 270 or the like.
• the heat exchanger 270 can be located downstream from the exhaust flue source (i.e., the flue of the combustion operation 210) and upstream from the first catalytic reactor 230.
• Various mechanisms and devices for modulating the temperature of a flue gas are known.
• an air heater or economizer can be disposed in the stream.
• the heat exchanger uses byproduct heat or thermal energy from the refinery for increased efficiency.
• Other suitable devices and techniques can also be suitable to maintain the operating temperature.
• the system and method disclosed herein can achieve NOx reduction of greater than 90%.
• the flow rate of the exhaust stream 220 through the first catalytic reactor 230 (and/or the second catalytic reactor, if present) therefore can be controlled or maintained at a desired level through the first catalytic reactor 230 to utilize or maximize the capacity of the first (and/or the second) catalytic reactor.
• flow regulators and/or pumps or the like such as an induced-draft fan can be disposed in fluid communication with the system disclosed herein to maintain a desired flow rate through the first catalytic reactor 230.
• the GHSV can be, for example, between about 30K cc per hour and about 120K cc per hour based on catalyst provided in powder form. Likewise, the GHSV can be least 5000 cc per hour, for example where the catalyst is provided on washcoated or bulk monoliths.
• the further reduced NOx-reduced exhaust stream 350 (in Fig. 2A, or 250, in Fig. 2B) can be directed away from the second catalyst through the outlet conduit 332 (in Fig. 2A, or 232 in Fig. 2B).
• the further reduced NOx-reduced exhaust stream can then be released into the atmosphere, for example through a stack.
• a gas mixture consisting of about 1000 ppm of NO, about 2% to about 9% 0 2 , and about 5% H 2 0 is treated with a catalyst system as described above.
• the first catalyst is 2% Ag/ Alumina and the second catalyst is tabulated in Table 1 below.
• the first catalyst and the second catalyst are stacked in series in a same catalytic reactor, with the first catalyst positioned relatively upstream of the second catalyst.
• the reductant stream includes propylene at 1000-2000 ppm, and hydrogen at 2000 ppm.
• the total flow rate is such that the GHSV ranged from 30K to 120K cc per hour.
• the operating temperature is about 400 °C.
• the first catalyst and the second catalyst were prepared with standard wet impregnation technique as described above.
• Table 1 provides observed NO conversions of the gas mixture referenced above for the different operating conditions as summarized below.

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• Engineering & Computer Science (AREA)
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• Health & Medical Sciences (AREA)
• Biomedical Technology (AREA)
• Analytical Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Chemical Kinetics & Catalysis (AREA)
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• Exhaust Gas Treatment By Means Of Catalyst (AREA)
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• 2013
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