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WO2002090829A1 - Procede et arrangement pour la reduction des emissions d'oxyde d'azote en combustion sur lit fluidise - Google Patents

Procede et arrangement pour la reduction des emissions d'oxyde d'azote en combustion sur lit fluidise Download PDF

Info

Publication number
WO2002090829A1
WO2002090829A1 PCT/FI2001/000445 FI0100445W WO02090829A1 WO 2002090829 A1 WO2002090829 A1 WO 2002090829A1 FI 0100445 W FI0100445 W FI 0100445W WO 02090829 A1 WO02090829 A1 WO 02090829A1
Authority
WO
WIPO (PCT)
Prior art keywords
fluidized bed
combustion chamber
circulating gas
secondary air
combustion
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/FI2001/000445
Other languages
English (en)
Inventor
Pia Salokoski
Jari Alin
Marko Fabritius
Pia Kilpinen
Edgardo Coda Zabetta
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fortum Oyj
Valmet Power Oy
Original Assignee
Fortum Oyj
Kvaerner Power Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fortum Oyj, Kvaerner Power Oy filed Critical Fortum Oyj
Priority to PCT/FI2001/000445 priority Critical patent/WO2002090829A1/fr
Publication of WO2002090829A1 publication Critical patent/WO2002090829A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
    • F23L7/00—Supplying non-combustible liquids or gases, other than air, to the fire, e.g. oxygen, steam
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C10/00—Fluidised bed combustion apparatus
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C9/00—Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
    • F23L2900/00—Special arrangements for supplying or treating air or oxidant for combustion; Injecting inert gas, water or steam into the combustion chamber
    • F23L2900/07002—Injecting inert gas, other than steam or evaporated water, into the combustion chambers

Definitions

  • the invention relates to a method according to the preamble of claim 1 and to an arrangement according to the preamble of claim 11 for reducing nitrogen oxide emissions in fluidized bed combustion.
  • the fuel is combusted and partially gasified in a fluidized bed which resides above a diffuser located in the bottom portion of the combustion chamber of the fluidised bed boiler and is formed by parti culate matter bed material and the fuel mixed therewith.
  • the bed material is sand.
  • the bed is maintained in a fluidized state by way of injecting fluidizing air upwards into the bed from nozzles located in the grid.
  • Boilers utilizing fluidised bed combustion may be categorized on the basis of their bed type into two main types: boilers with a bubbling fluidized bed and boilers with a circulating fluidized bed.
  • a bubbling fluidized bed In a bubbling fluidized bed, the velocity of the fluidizing air injected into the fluidized bed is so low as to allow the fluidized bed to form in the bottom portion of the combustion chamber. In contrast, a circulating fluidized bed uses a much higher velocity of the fluidizing air, whereby a fraction of the bed material can rise with the fluidizing air to the upper portion of the combustion chamber, wherefrom it is circulated back to the bottom portion of the combustion chamber.
  • a bubbling fluidized bed generally also uses a coarser bed material than that used in a circulating fluidized bed. In a circulating fluidized bed boiler, the fuel, combustion air and bed material become effectively mixed with each other, whereby the combustion chamber is operated at an equalized temperature and the occurrence of local temperature peaks is avoided.
  • the goal of the invention is achieved by means of feeding circulating gas to the bottom portion of the combustion chamber of a fluidized bed boiler, to above the fluidized bed.
  • the circulating gas is fed into the region remaining between the inlet point of the secondary air and the top level of the fluidized bed or, alternatively, at the level of the secondary air inlet; however, so as to prevent the circulating gas from becoming mixed with the secondary air either before being discharged into the combustion chamber or immediately after entering the same.
  • Such a mixing would be detrimental because it counteracts the object of establishing reactions in which nitrogen oxides are reduced.
  • the circulating gas can be flue gas taken from the fluidized bed boiler proper or from a combusting system operating external to the boiler.
  • the oxygen and nitrogen oxides contained in the circulating gas react with nitrogen compounds emerging from the fluidized bed thus forming molecular nitrogen N 2 .
  • the invention is only suited for use in fluidized bed boilers operating with a bubbling fluidized bed.
  • the arrangement according to the invention is suited not for use in circulating fluidized bed boilers because in these the boiler construction, flow conditions and temperature distributions are essentially different from those prevailing in boilers operating with a bubbling fluidized bed.
  • the invention offers significant benefits.
  • An essential reduction in the nitrogen oxide emissions of a fluidized bed boiler can be attained by way of admitting circulating gas into the bottom portion of the combustion chamber of the boiler, at a level above the fluidized bed.
  • the arrangement according to the invention has a very simple construction inasmuch it only needs piping for the circulating gas with feed means connected thereto for passing the circulating gas into the combustion chamber of the boiler, as well as control devices connected thereto for adjusting the flow of the circulating gas. Accordingly, the assembly according to the invention is easy to adapt to existing boilers, too.
  • the walls of the combustion chamber 2 of a fluidized bed boiler 1 are in a conventional manner lined with boiler tubes containing flowing water or steam into which the heat released by the combustion of the fuel is transferred.
  • the bottom portion of the combustion chamber 2 is formed by a air grid 3 via which ash formed in the combustion is removed from the combustion chamber 2.
  • the air distribution is provided with nozzles wherefrom fluidizing air 4 is injected upward into the combustion chamber 2.
  • the fluidizing air 4 also serves as the primary combustion air for the fluidized bed 5 formed by paniculate matter.
  • the velocity of the fluidizing air 4 is adjusted such that the fluidized bed 5 is formed in the bottom portion of the combustion chamber 2 and no substantial loss of the bed material from the combustion chamber 2 along with the gas flow will take place, thus generally disposing with the need for circulating the bed material particles back to the bed 5.
  • This type of fluidized bed is also known as a bubbling fluidized bed. Although a fraction of the bed material particles can rise with the flow of the primary air 4 up to the middle portion of the combustion chamber 2, a bubbling fluidized bed 5 has a clearly discernible top level.
  • the infeed rate of the primary air 4 is about 35 % of the total air feed required for complete combustion.
  • the fuel is introduced at a distance above the fluidized bed 5 via fuel feed means 6 such as openings provided on the walls of the combustion chamber 2.
  • secondary air inlet means 7 To above the fuel feed means 6 into the combustion chamber 2 is fed secondary air via secondary air inlet means 7 at an infeed rate typically representing about 35 % of the total air feed into the combustion chamber 2.
  • the secondary air inlet means 7 are adapted on the walls of the combustion chamber 2 displaced at a distance above the top level of the bubbling fluidized bed 5. Additionally, tertiary air is admitted into the combustion chamber 2 at an infeed rate of about 30 % of the total combustion air feed into the boiler.
  • the tertiary air inlet means 8 are adapted on the walls of the combustion chamber 2, at a distance above the secondary air inlet means 7.
  • the arrangement according to the invention may also be used in such fluidized bed boilers in which the fuel feed means 6 are located above the secondary air inlet means 7.
  • Fuel fed to above the fluidized bed 5 falls into the bed material wherein it is dried and partially gasified. Pyrolysis gases formed in the gasification of the fuel react with the oxygen of the primary air and simultaneously rise upward in the combustion chamber 2. The ungasified fraction of the fuel is combusted both in the fluidized bed 5 and, with a continuous diminishing size of fuel particles, also above the bed 5.
  • a fraction of the pyrolysis gases rising from the fluidized bed 5, as well as the ungasified portion of the fuel introduced into the bed, typically coke, and the carbon monoxide generated in the combustion reactions of coke are combusted in a burning zone created at the level of the secondary air inlet means 7.
  • the possibly still combustable fraction of the flue gases after passing the secondary air inlet means 7 is brought to complete combustion with the help of the tertiary air 8.
  • the flue gases rise above the tertiary air inlet means 8 they meet a superheater 9 located in the upper portion of the combustion chamber 2. After passing the superheater 9, the flue gases flow past heat recovery panels comprising a feed water preheater 10 and a combustion air preheater 11.
  • a cleaning device such as an electrostatic filter 13.
  • circulating gas is injected to the bottom portion of the combustion chamber 2.
  • Separate means 14 for injecting the circulating gas are adapted on the walls of the combustion chamber 2 or on the boiler walls at a point between the secondary air inlet means 7 and the top level of the bubbling fluidized bed 5.
  • the circulating gas injection means 14 and the discharge point of the circulating gas may be located at the same level with the secondary air inlet means 7 with the provision that the circulating gas is prevented from becoming mixed with the secondary air either before being discharged into the combustion chamber 2 or immediately after entering the combustion chamber 2.
  • the circulating gas can be generally taken from the flue gases formed by the combustion process in the combustion chamber 2 by way of passing a fraction of the flue gases, advantageously taken via a duct connected to a point between a flue gas blower 15 and the smoke stack 12, with the help of a blower 16 back to the combustion chamber 2.
  • the dust content of the circulating gas is low, since the gas is first purified in a cleaning device 13.
  • the oxygen content of the circulating gas is typically 1.5 to 10 vol.%, most advantageously 2 to 5 vol. and the gas temperature is 120 to 200 °C.
  • the mass flow rate of the circulating gas is advantageously 5 to 40 %, most advantageously 10 to 30 % of the total air flow rate required in combustion.
  • the circulating gas injection means 14 may be placed, e.g., on opposite walls of the combustion chamber 2. In this manner, the circulating gas can be injected tangentially into the combustion chamber 2.
  • the oxygen and nitrogen oxides contained in the circulating gas injected into the combustion chamber 2 react with the nitrogen compounds rising from the fluidized bed 5 so as to form molecular nitrogen N 2 .
  • the fluidized bed 5 is operated in a reducing state.
  • the temperature and steam content of the circulating gas affect the reaction rates and paths of the chemical processes taking place. The reactions are sensitive to both of the above-mentioned parameters.
  • the injection of the circulation gas lowers the temperature of flue gases in the combustion chamber 2 in the region between the secondary air inlet means 7 and the tertiary air inlet means 8 to about 1100 °C. Without the injection of the circulating gas, this temperature would typically be in the order of 1200-1300 °C.
  • the circulating gas injection also improves the mixing of flue gases in the region above the fluidized bed 5 thus preventing bundling of the gas flows rising from bed. Resultingly, a homogeneous gas flow is created in the secondary air inlet zone.
  • the oxygen imported by the circulating gas promotes combustion in the bottom portion of the combustion chamber 2 thus compensating for the temperature decrease due to the imported circulating gas in the circulating gas injection zone.
  • the fuel to be combusted in the fluidized bed boiler 1 must be relatively dry and have a high heat value in order to obtain the desired outcome from the injection of the circulating gas.
  • the fuel shall advantageously have a heat value greater than 6 MJ kg, most advantageously greater than 7 MJ/kg.
  • the term circulating gas refers to any type of flue gas formed in conjunction with combustion so that the gas has a sufficiently low oxygen content and contains nitrogen oxides.
  • the circulating gas may be taken from an external combustion process, such as that of a combustion engine, if the exhaust gas delivered by the same has a sufficiently low oxygen content.
  • the temperature of the admitted gas may be higher than that mentioned above, even up to 600 °C.
  • the exhaust gas of a combustion engine contains a plurality of uncombusted components: hydrocarbons, soot and carbon monoxide.
  • the exhaust gas is rich with nitrogen oxides and, if the engine is run using a sulfur-containing fuel, oxides of sulfur.
  • the uncombusted components of the exhaust gas will bum in the combustion chamber 2 and the nitrogen oxides can thereby interact with the above-mentioned chemical reactions.
  • the oxides of sulfur are removed in the sulfur removal system of the fluidized bed boiler 1.
  • the exhaust gas of a gas turbine is not suitable for use as the circulating gas inasmuch its oxygen content due to the high air/fuel ratio is greater than 10 vol.%.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Fluidized-Bed Combustion And Resonant Combustion (AREA)

Abstract

L'invention concerne un procédé et un arrangement pour chambre de combustion (2) d'appareil de combustion en lit fluidisé (1), à lit fluidisé bouillonnant (5) opérationnel dans la partie inférieure de l'appareil. Le procédé considéré permet de réduire les émissions d'oxyde d'azote en combustion: on injecte un air primaire (4) dans la chambre de combustion (2), depuis le bas (3) vers le haut, puis on injecte le combustible (6) dans le lit fluidisé (5), et on injecte ensuite de l'air secondaire (7) à une certaine distance au-dessus du lit fluidisé (5). Enfin, du gaz de circulation est injecté dans la chambre de combustion (2), plus précisément dans une partie restante, entre le dessus du lit fluidisé (2) et le point d'entrée de l'air secondaire (7) ou bien au niveau de ce point d'entrée, mais séparément de lui.
PCT/FI2001/000445 2001-05-09 2001-05-09 Procede et arrangement pour la reduction des emissions d'oxyde d'azote en combustion sur lit fluidise Ceased WO2002090829A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/FI2001/000445 WO2002090829A1 (fr) 2001-05-09 2001-05-09 Procede et arrangement pour la reduction des emissions d'oxyde d'azote en combustion sur lit fluidise

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/FI2001/000445 WO2002090829A1 (fr) 2001-05-09 2001-05-09 Procede et arrangement pour la reduction des emissions d'oxyde d'azote en combustion sur lit fluidise

Publications (1)

Publication Number Publication Date
WO2002090829A1 true WO2002090829A1 (fr) 2002-11-14

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PCT/FI2001/000445 Ceased WO2002090829A1 (fr) 2001-05-09 2001-05-09 Procede et arrangement pour la reduction des emissions d'oxyde d'azote en combustion sur lit fluidise

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102966945A (zh) * 2012-11-02 2013-03-13 阳光凯迪新能源集团有限公司 降低生物质循环流化床锅炉氮氧化物排放的方法
CN104006377A (zh) * 2014-03-04 2014-08-27 郭继会 燃煤烟尘实现大气零排放治理方法
CN107327839A (zh) * 2017-08-16 2017-11-07 华能白山煤矸石发电有限公司 一种循环流化床锅炉降氧抑氮系统及控制方法

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5664203A (en) * 1979-10-26 1981-06-01 Babcock Hitachi Kk Low nox fluidized bed type incinerator
JPS5952106A (ja) * 1982-09-20 1984-03-26 Babcock Hitachi Kk 流動層ボイラ
EP0237712A1 (fr) * 1986-02-05 1987-09-23 Ishikawajima-Harima Heavy Industries Co., Ltd. Procédé de combustion pour un incinérateur à lit fluidisé
US4766851A (en) * 1985-05-23 1988-08-30 Kraftwerk Union Aktiengesellschaft Combustion chamber for a fluidized-bed furnace
DE3814314C1 (fr) * 1988-04-28 1989-06-22 Deutsche Babcock Werke Ag, 4200 Oberhausen, De
WO1993005340A1 (fr) * 1991-09-12 1993-03-18 Imatran Voima Oy Procede et dispositif de refroidissement des matieres circulantes dans une chaudiere a lit fluidise

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5664203A (en) * 1979-10-26 1981-06-01 Babcock Hitachi Kk Low nox fluidized bed type incinerator
JPS5952106A (ja) * 1982-09-20 1984-03-26 Babcock Hitachi Kk 流動層ボイラ
US4766851A (en) * 1985-05-23 1988-08-30 Kraftwerk Union Aktiengesellschaft Combustion chamber for a fluidized-bed furnace
EP0237712A1 (fr) * 1986-02-05 1987-09-23 Ishikawajima-Harima Heavy Industries Co., Ltd. Procédé de combustion pour un incinérateur à lit fluidisé
DE3814314C1 (fr) * 1988-04-28 1989-06-22 Deutsche Babcock Werke Ag, 4200 Oberhausen, De
WO1993005340A1 (fr) * 1991-09-12 1993-03-18 Imatran Voima Oy Procede et dispositif de refroidissement des matieres circulantes dans une chaudiere a lit fluidise

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102966945A (zh) * 2012-11-02 2013-03-13 阳光凯迪新能源集团有限公司 降低生物质循环流化床锅炉氮氧化物排放的方法
WO2014067405A1 (fr) * 2012-11-02 2014-05-08 阳光凯迪新能源集团有限公司 Procédé pour la réduction du rejet d'oxyde d'azote d'une chaudière à biomasse à lit fluidisé circulant
CN102966945B (zh) * 2012-11-02 2016-03-02 阳光凯迪新能源集团有限公司 降低生物质循环流化床锅炉氮氧化物排放的方法
CN104006377A (zh) * 2014-03-04 2014-08-27 郭继会 燃煤烟尘实现大气零排放治理方法
CN107327839A (zh) * 2017-08-16 2017-11-07 华能白山煤矸石发电有限公司 一种循环流化床锅炉降氧抑氮系统及控制方法
CN107327839B (zh) * 2017-08-16 2023-08-18 吉林大学 一种循环流化床锅炉降氧抑氮系统及控制方法

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