Hydrocabon cracking furnace with steam addition to lower mono-nitrogen oxide emissions
원문보기
IPC분류정보
국가/구분
United States(US) Patent
등록
국제특허분류(IPC7판)
B01J-019/00
C10G-009/00
C10G-009/20
F23C-006/04
F23C-005/08
출원번호
US-0066211
(2011-04-08)
등록번호
US-8703064
(2014-04-22)
발명자
/ 주소
Payne, David C.
출원인 / 주소
WPT LLC
대리인 / 주소
Schultz & Associates, P.C.
인용정보
피인용 횟수 :
0인용 특허 :
35
초록▼
An apparatus and method is presented for reducing mono nitrogen oxide emissions in a hydrocarbon processing furnace. A preferred embodiment hydrocarbon cracking furnace includes a firebox with a set of wall burners and a set of floor burners, the floor burners comprising secondary burner tips burnin
An apparatus and method is presented for reducing mono nitrogen oxide emissions in a hydrocarbon processing furnace. A preferred embodiment hydrocarbon cracking furnace includes a firebox with a set of wall burners and a set of floor burners, the floor burners comprising secondary burner tips burning a fuel-rich mixture and positioned below primary burner tips burning a fuel-lean mixture. A portion of flue gases are recirculated from the primary burner combustion area to the secondary burner combustion area and back to the primary burner combustion area. The floor burners further comprise a set of steam injection ports that inject steam into a conical flow to contact flames at the primary burner tips, reducing flame temperature and thereby reducing thermal NOx. The steam injection ports are positioned in the firebox above the primary burner tips.
대표청구항▼
1. A method for reducing mono-nitrogen oxide emissions from a hydrocarbon cracking furnace having a firebox with a floor, two side walls, two end walls and a roof with an exhaust stack for exhausting flue gases, the method including the steps of: providing a set of floor burners disposed on the floo
1. A method for reducing mono-nitrogen oxide emissions from a hydrocarbon cracking furnace having a firebox with a floor, two side walls, two end walls and a roof with an exhaust stack for exhausting flue gases, the method including the steps of: providing a set of floor burners disposed on the floor adjacent to the two side walls;providing a set of hybrid radiant tubes near a vertical central plane bisecting each of the two end walls;providing a source of fuel gas;providing a source of steam;providing an adjustable source of fresh air;providing the set of floor burners with a set of primary burner tips, connected to the source of fuel gas, and a set of secondary burner tips, connected to the source of fuel gas, where the secondary burner tips are positioned at a height below the set of primary burner tips and fixed between the set of primary burner tips and the vertical central plane;providing a set of steam injection ports, connected to the source of steam, placing the set of steam injection ports between the set of secondary burner tips and the primary burner tips;flowing a first fuel gas flow from the source of fuel gas to the set of primary burner tips at a flow rate F1;flowing a second fuel gas flow from the source of fuel gas to the set of secondary burner tips at a flow rate F2 resulting in a combined flow rate F=F1+F2;flowing steam from the source of steam at a flow rate S to the set of steam injection ports to create a set of conical steam flows;adjusting the flow rate S to between about one-fourth of the combined flow rate F to about equal to the combined flow rate F;adjusting a fresh air flow from the source of fresh air to the set of primary burner tips;mixing the first fuel gas flow with the fresh air flow as a first mixture which is sub-stoichiometric with respect to fuel gas;burning the first mixture to create a first set of flames and a first flue gas;contacting the first set of flames with the set of conical steam flows;recirculating a portion of the first flue gas to mix with the second fuel gas flow as a second mixture containing a sub-stoichiometric amount of oxygen;burning the second mixture at the secondary burner tips to create a second set of flames and a second flue gas;burning the second flue gas along with the first mixture at the primary burner tips to contribute to the first flue gas;adjusting the first and second sets of flames to deliver a total heat flux through a horizontal cross-section of the firebox at between about 250,000 and about 400,000 BTU/ ft2; and,exhausting the first flue gas, the second flue gas, and the portion of the first flue gas through the exhaust stack as a combined flue gas whereby the combined flue gas has a reduced mono-nitrogen oxide concentration. 2. The method of claim 1 including the steps of: providing a set of wall burners disposed along the two side walls;flowing a third fuel gas flow from the source of fuel gas to the wall burners at a flow rate F3;burning the third fuel gas flow to create a third set of flames and a third flue gas;adjusting the first, second and third sets of flames to deliver a total heat flux through a horizontal cross-section of the firebox at between about 250,000 and about 400,000 BTU/ft2; and,exhausting the first flue gas, the second flue gas, the third flue gas and the portion of the first flue gas through the exhaust stack as a combined flue gas whereby the combined flue gas has a reduced mono-nitrogen oxide concentration. 3. The method of claim 1 including the additional steps of: providing a source of feedstock for hydrocarbon cracking, connected to the hybrid radiant tubes;providing a heat exchanger, connected to the hybrid radiant tubes;flowing the feedstock into the hybrid radiant tubes;heating the hybrid radiant tubes with the total heat flux;cracking the feedstock molecules into a desired hydrocarbon product in a cracking process;flowing the desired hydrocarbon product into the heat exchanger;quenching the cracking process; andflowing the desired hydrocarbon product away from the firebox. 4. The method of claim 3 including the step of selecting an olefin as the desired hydrocarbon product. 5. The method of claim 4 including the additional step of selecting at least one olefin for the hydrocarbon product from the group of ethylene, propylene and butadiene. 6. The method of claim 3 including the step of selecting an aromatic as the desired hydrocarbon product. 7. The method of claim 6 including the additional step of selecting benzene as the aromatic. 8. The method of claim 3 including the additional step of selecting at least one of the groups of ethane, butane, propane, naphtha and gas oil as the feedstock. 9. The method of claim 1 including the additional step of adjusting the set of conical steam flows to a height of between 12 inches and 18 inches above the primary burner tips. 10. A method for reducing mono-nitrogen oxide emissions from a hydrocarbon cracking furnace having a firebox with a floor, two side walls, two end walls, a roof and an exhaust stack for exhausting flue gases, the method comprising the steps of: providing a set of N floor burners disposed on the floor adjacent to the two side walls;providing a set of M wall burners disposed along the two side walls;providing a set of hybrid radiant tubes near a vertical central plane bisecting each of the two end walls;providing a source of fuel gas;providing a source of steam;attaching a set of 3N primary burner tips, connected to the source of fuel gas, to the set of N floor burners;attaching a set of 3N secondary burner tips, connected to the source of fuel gas, to the set of N floor burners at a height below the set of 3N primary burner tips and at a position between the set of 3N primary burner tips and the vertical central plane;attaching a set of 2N steam injection ports, connected to the source of steam, to the set of N floor burners between the set of 3N secondary burner tips and the 3N secondary tips;delivering a combined fuel gas flow into the firebox with a combined flow rate F;delivering a steam flow into the set of 2N steam injection ports with a flow rate S of between about one-fourth and about equal to the combined flow rate F;dividing the combined fuel gas flow into a first flow to the set of M wall burner burners with flow rate F1 and into a second flow to the set of N floor burners with flow rate F2, where F1/F2 is between zero and about 0.25;subdividing the second flow into a third flow to the set of 3N primary burner tips with flow rate F3 and a fourth flow to the set of 3N secondary burner tips with flow rate F4, where F3/F4 is between about 0.1 and about 0.2;delivering a fresh air flow to the N floor burners by adjusting an air intake baffle connected to ambient air;mixing the fresh air flow with the third flow;burning fuel gas from the first flow to create a first set of flames and a first flue gas;burning fuel gas from the third flow to create a second set of flames and a second flue gas;burning fuel gas from the fourth flow to create a third set of flames and a third flue gas;recirculating a portion of the second and third flue gases as a recirculating flue gas;spraying the steam flow from the 2N steam injection ports into a set of 2N conical steam flows which make contact with the second set of flames thereby reducing the mono-nitrogen oxide emissions into the first, second, third and recirculating flue gases; and,exhausting the first, second, third and recirculating flue gases through the exhaust stack. 11. The method of claim 10 including the step of selecting M=0 wherein there are no wall burners included in the firebox. 12. The method of claim 10 including the additional step of adjusting the conical steam flows to a height of between 12 inches and 18 inches above the primary burner tips. 13. The method of claim 10 including the additional step of adjusting the combined fuel gas flow into the firebox to between about 0.25 lb/hr and about 0.35 lb/hr per cubic foot of volume of the firebox. 14. The method of claim 10 including the additional step of delivering the total heat flux through a horizontal cross-section of the firebox of between 250,000 and 400,000 BTU/ft2. 15. The method of claim 10 including the steps of: further subdividing the third flow into a left primary burner flow with flow rate PL, a right primary burner flow with flow rate PR, and center primary burner flow with flow rate PC, where PL is about the same as PR and PC/PL is between about 1.1 and 1.3; and,further subdividing the fourth flow into a left secondary burner flow, a right secondary burner flow, and a center secondary burner flow with about equal flow rates. 16. The method of claim 10 including the additional steps of: providing a source of feedstock for hydrocarbon cracking, connected to the hybrid radiant tubes;providing a heat exchanger, connected to the hybrid radiant tubes;flowing the feedstock into the hybrid radiant tubes;heating the hybrid radiant tubes with the total heat flux;cracking the feedstock molecules into a desired hydrocarbon product in a cracking process;flowing the desired hydrocarbon product into the heat exchanger;quenching the cracking process; andflowing the desired hydrocarbon product away from the firebox. 17. The method of claim 16 including the additional step of selecting at least one of the groups of ethane, butane, propane, naphtha and gas oil as the feedstock. 18. The method of claim 16 including the additional step of selecting an olefin as the hydrocarbon product. 19. The method of claim 18 including the additional step of selecting at least one olefin from the group of ethylene, propylene and butadiene as the hydrocarbon product. 20. The method of claim 16 including the additional step of selecting an aromatic as the hydrocarbon product. 21. The method of claim 20 including the additional step of selecting benzene as the aromatic. 22. A method for upgrading an existing hydrocarbon cracking furnace to reduce mono-nitrogen oxide emissions where the hydrocarbon cracking furnace has a firebox with a floor, two side walls, two end walls and a roof with an exhaust stack for exhausting flue gases, a set of floor burners attached to the floor adjacent to the two side walls, a source of fuel gas, and a set of hybrid radiant tubes situated near a vertical central plane bisecting each of the two end walls, the set of hybrid radiant tubes attached to a feedstock source at a first end and a heat exchanger on a second end, the method comprising the steps of retrofitting and operating the hydrocarbon cracking furnace according to the sub-steps: providing a set of primary burner tips on the set of floor burners above the level of the floor, connected to the source of fuel gas;providing a set of secondary burner tips on the set of floor burners at about the level of the floor, fixed between the set of primary burner tips and the vertical central plane, connected to the source of fuel gas;providing an adjustable source of fresh air;providing a source of steam;adding a set of steam injection ports to the set of floor burners, between the set of secondary burner tips and the primary burner tips at about the height of the primary burner tips,connecting the set of steam injection ports to the source of steam;flowing fuel gas into a first fuel gas flow from the source of fuel gas to the set of primary burner tips at a flow rate F1;flowing the fuel gas into a second fuel gas flow to the set of secondary burner tips at a flow rate F2;flowing steam from the source of steam at a mass flow rate S to the set of steam injection ports to create a set of conical steam flows, where the mass flow rate S is between about one-fourth and about equal to the combined flow rate F=F1+F2;adjusting a fresh air flow to flow from the source of fresh air to the set of primary burner tips;mixing the first fuel gas flow with the fresh air flow as a first mixture containing a sub-stoichiometric amount of fuel gas;burning the first mixture to create a first set of flames and a first flue gas;contacting the first set of flames with the set of conical steam flows;recirculating a portion of the first flue gas as a recirculating flue gas;mixing the second fuel gas flow with the recirculated fraction of first flue gas as a second mixture containing a sub-stoichiometric amount of oxygen;burning the second mixture to create a second set of flames and a second flue gas;burning the second flue gas along with the first mixture at the primary burner tips to contribute to the first flue gas; and,exhausting the first flue gas, second flue gas, third flue gas and recirculating flue gas through the exhaust stack as an exhausted flue gas with reduced mono-nitrogen oxide emissions. 23. The method of claim 22 further comprising the steps of: providing a set of wall burners attached to the two side walls,flowing the fuel gas into a third fuel gas flow into the wall burners at a flow rate F3;burning the third fuel gas to create a third set of flames and a third flue gas; and,exhausting the first flue gas, second flue gas, third flue gas and recirculating flue gas through the exhaust stack as an exhausted flue gas with reduced mono-nitrogen oxide emissions. 24. The method of claim 22 including the step of adjusting the first and second sets of flames to deliver a total heat flux through a horizontal cross-section of the firebox of between about 250,000 and about 400,000 BTU/ft2. 25. The method of claim 23 including the step of adjusting the first, second and third sets of flames to deliver a total heat flux through a horizontal cross-section of the firebox of between about 250,000 and about 400,000 BTU/ft2. 26. A hydrocarbon cracking furnace producing low mono-nitrogen oxide emissions comprising: a firebox with a floor, two side walls, two end walls and a roof;an exhaust stack connected to the roof for exhausting flue gases from the firebox;a set of floor burners attached to the floor adjacent to the two side walls;a set of hybrid radiant tubes positioned near a vertical central plane bisecting each of the two end walls and further attached to a feedstock source at one end and a heat exchanger on the other end;a source of fuel gas;a source of steam;the set of floor burners including a set of burner tiles having a top tile surface adjacent to the side wall, a lower surface positioned between the top tile surface and the vertical central plane, a beveled surface connecting the lower surface to the top tile surface where the top tile surface is between about 4 inches and about 9 inches above the floor and the lower surface is at the level of the floor;the set of burner tiles further including a chamber;a set of primary burner tips attached to the set of burner tiles inside the chamber at a height of between about 3 inches below the top tile surface and about the level of the top surface, and connected to the source of fuel gas;an air intake baffle connected between ambient air and the chamber;a set of secondary burner tips attached to the set of burner tiles at the lower surface and extending to a height of between about 3 inches above the lower surface and about the level of the lower surface, the set of secondary burner tips connected to the source of fuel gas;a set of steam injection ports, connected to the source of steam, and further attached to the set of burner tiles between the set of primary burner tips and the set of secondary burner tips at a height about the same as the set of primary burner tips;a first fuel gas flow from the source of fuel gas to the set of primary burner tips having a flow rate F1;an ambient air flow to the set of primary burner tips from the ambient air sufficient to enable a fuel-lean combustion at the primary burner tips;a second fuel gas flow from the source of fuel gas to the set of secondary burner tips having a flow rate F2;a steam flow at a flow rate S from the source of steam to the set of steam injection ports and emerging from the set of steam injection ports into the firebox as a set of conical steam flows, where the flow rate S is between about one-fourth and about equal to the combined flow rate F=F1+F2;a recirculating flue gas flow from the combustion of the first and second fuel gas flows, recirculated to the set of secondary burners;a set of pilot burners attached to the set of floor burners in proximity to the primary burner tips and the secondary burner tips and attached to the wall burners, the set of pilot burners connected via a set of pilot valves to the source of fuel gas;a feedstock flow from the feedstock source into the hybrid radiant tubes;a hydrocarbon product flow from the hybrid radiant tube into the heat exchanger;a set of primary flames generated by fuel-lean combustion at each of the set of primary burner tips;a set of secondary flames generated by fuel-rich combustion at each of the set of secondary burner tips; and,wherein each conical steam flow of the set of conical steam flows is in contact with at least two primary flames in the set of primary flames. 27. The hydrocarbon cracking furnace of claim 26 wherein each conical steam flow of the set of conical steam flows has a cone aperture of between about 50 degrees and 70 degrees. 28. The hydrocarbon cracking furnace of claim 26 wherein the set of conical steam flows spray upwards to a height of between about 12 inches and 18 inches above the set of steam injection ports. 29. The hydrocarbon cracking furnace of claim 26 where the heat exchanger is a transfer line heat exchanger. 30. The hydrocarbon cracking furnace of claim 26 where the proportion of the number of steam injection ports to the number of primary burner tips is between 1:4 and 2:1. 31. The hydrocarbon cracking furnace of claim 30 where there are two steam injection ports for every three primary burner tips. 32. The hydrocarbon cracking furnace of claim 26 further comprising: a set of wall burners attached to the two side walls;a third fuel gas flow from the source of fuel gas to the wall burners having a flow rate F3;a steam flow at a flow rate S from the source of steam to the set of steam injection ports and emerging from the set of steam injection ports into the firebox as a set of conical steam flows, where the flow rate S is between about one-fourth and about equal to the combined flow rate F4=F1+F2+F3; and,a set of wall burner flames generated by fuel gas combustion at each of the set of wall burners. 33. The hydrocarbon cracking furnace of claim 32 wherein: the floor and roof each have an area of between about 650 ft2 and 800 ft2;the volume of the firebox is between about 30,000 and about 40,000 ft3;the combined flow rate F4 is between about 8,500 lb/hr and about 11,000 lb/hr; and,the flow rate S is between about 0.25 F4 and 1.0 F4. 34. The hydrocarbon cracking furnace of claim 33 wherein the set of wall burners includes between 40 and 50 wall burners;the set of floor burners includes between 15 and 20 floor burners; and,each floor burner in the set of floor burners includes three primary burner tips, three secondary burner tips and two steam injection ports. 35. The hydrocarbon cracking furnace of claim 32 wherein: the floor and roof each have an area of between about 600 ft2 and about 800 ft2;the volume of the firebox is between about 30,000 and about 40,000 ft3;the floor burners and wall burners combine to produce between about 200 MMBTU/hr and about 250 MMBTU/hr; and,the flow rate S is between about 0.25 F4 and about 1.0 F4. 36. The hydrocarbon cracking furnace of claim 35 wherein the set of wall burners includes between 40 and 50 wall burners;the set of floor burners includes between 15 and 20 floor burners; and,each floor burner in the set of floor burners includes three primary burner tips, three secondary burner tips and two steam injection ports. 37. The hydrocarbon cracking furnace of claim 32 wherein the set of wall burners comprise multiple rows of wall burners. 38. The hydrocarbon cracking furnace of claim 37 wherein there are three rows of wall burners on a first side wall of the firebox and two rows of wall burners on the opposing side wall of the firebox. 39. The hydrocarbon cracking furnace of claim 32 where the set of wall burners are distributed so that there are five wall burners for every two floor burners.
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이 특허에 인용된 특허 (35)
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Schwartz Robert E. (Tulsa OK) Waibel Richard T. (Broken Arrow OK) Rodden Paul M. (Sand Springs OK) Napier Samuel O. (Sapulpa OK), Methods and apparatus for burning fuel with low NOx formation.
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