WO1989006334A1 - Procede de combustion servant a reduire la formation d'oxydes d'azote dans un processus de combustion et appareil de realisation dudit procede - Google Patents

Procede de combustion servant a reduire la formation d'oxydes d'azote dans un processus de combustion et appareil de realisation dudit procede Download PDF

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Publication number
WO1989006334A1
WO1989006334A1 PCT/FI1988/000203 FI8800203W WO8906334A1 WO 1989006334 A1 WO1989006334 A1 WO 1989006334A1 FI 8800203 W FI8800203 W FI 8800203W WO 8906334 A1 WO8906334 A1 WO 8906334A1
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WO
WIPO (PCT)
Prior art keywords
air
gases
combustion
stage
furnace
Prior art date
Application number
PCT/FI1988/000203
Other languages
English (en)
Inventor
Jouko Laine
Original Assignee
Oy Tampella Ab
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 Oy Tampella Ab filed Critical Oy Tampella Ab
Publication of WO1989006334A1 publication Critical patent/WO1989006334A1/fr

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Classifications

    • 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 
    • F23C7/00—Combustion apparatus characterised by arrangements for air supply
    • F23C7/02—Disposition of air supply not passing through burner
    • 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 
    • F23C6/00—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion
    • F23C6/04—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection
    • F23C6/045—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection with staged combustion in a single enclosure

Definitions

  • a method of combustion for the reduction of the forma ⁇ tion of nitrogen oxides in a combustion process and an apparatus for applying the method
  • the invention relates to a method of combustion for the reduction of the formation of nitrogen oxides in a combustion process, wherein the combustion is carried out by introducing air required for the burn ⁇ ing of fuel into a furnace in at least two stages so that in the first stage the introduction of air is carried out understoichiometrically in relation to the fuel, preferably with a coefficient of air ranging from 0.90 to 0.97, and in at least one stage overstoi- chiometrically so that the total coefficient of air exceeds the value one.
  • the invention is also concerned with an apparatus for applying the method, which ap ⁇ paratus comprises at least first and second air supply means for introducing air into the furnace of a boiler in at least two stages.
  • Nitrogen oxides are hazardous to the environ ⁇ ment. Great amounts of them are formed in industrial processes and in power plants and other boilers, and one of the most important objects of environmental protection is to reduce the emission of nitrogen oxides into the atmosphere.
  • the object of the present invention is to pro ⁇ vide a method by means of which the formation of nit ⁇ rogen oxides at the combustion stage can be reduced to a minimum and in which the formation of oxides can be constantly controlled without any expensive catalyst solutions difficult to control and the like solutions used in the methods described above.
  • the invention is characterized in that the gases formed in the combus ⁇ tion in the first stage are cooled from a temperature obtained during the combustion, preferably as high as possible, to a lower temperature, and that more air is introduced among the gases at the earliest during the cooling of them so that substantially within the entire furnace the amount of air introduced among the gases is at each particular point at the most such as would be required for the formation of a predetermined concentration of nitrogen oxides at the temperature which the gases have at this particular point.
  • An essential idea of the invention is that the introduction of air into the combustion process is controlled so that the formation of nitrogen oxides at a temperature at different points in the furnace and with a corresponding ratio of air to fuel, remains be ⁇ low a sufficiently low level, that is, below a pre- determined concentration level, which is achieved by carrying out the combustion in a stepwise manner so that in the first stage air is introduced under- stoichiometrically while allowing the temperature to rise so as to improve the coefficient of efficiency to the highest possible value, whereafter the formed gases are cooled to a temperature such that the con ⁇ centration level of nitrogen oxides at this particular temperature remains sufficiently low when air is introduced in the second stage so that the total coef- ficient of air increases to a value at least 1.
  • a further object of the invention is to provide an apparatus for applying the method, the apparatus being characterized in that it comprises a cooler, preferably a superheater which is mounted in the fur ⁇ nace of the boiler after the first air supply means in the direction of flow of the gases contained in -the furnace, so that the gases formed in the first under- stoichiometric combustion stage are forced to flow through the cooler, and that the second air supply means are arranged to introduce more air into the fur ⁇ nace at the earliest at the cooler in the direction of flow of the gases.
  • a cooler preferably a superheater which is mounted in the fur ⁇ nace of the boiler after the first air supply means in the direction of flow of the gases contained in -the furnace, so that the gases formed in the first under- stoichiometric combustion stage are forced to flow through the cooler, and that the second air supply means are arranged to introduce more air into the fur ⁇ nace at the earliest at the cooler in the direction of flow of the gases.
  • An essential idea of the apparatus according to the invention is that the first superheater of the boiler is positioned in the furnace after the first combustion stage but nevertheless no further than in the second combustion stage so that the superheater separates the space for the combustion stage to be carried out under understoichiometric conditions from the rest of the furnace space, whereby the flue gases flow through the superheater, being simultaneously cooled according to the invention to a desired tem ⁇ perature, and more air is introduced into the super- heater or after it, whereby the flue gases are at the desired temperature after the introduction of air.
  • the temperature of the gases in the superheater or after it can be adjusted by introducing more air, and thereby it is possible to keep the temperature of the boiler at a value suitable for the kinetics of the formation of nitrogen oxides by adjusting the coefficient of air so that the forma ⁇ tion of nitrogen oxides can be kept on the allowed level or even below it.
  • Figure 1 illustrates the dependance between the temperature occurring in the method according to the invention and the coefficient of air in relation to one level of nitrogen oxides, and schematically the dependence between the coefficient of air and the tem ⁇ perature when applying the method according to the in ⁇ vention; and
  • Figure 2 illustrates schematically an apparatus applied in the method according to the invention.
  • the curve A illustrates schema ⁇ tically the influence of the dependance between the temperature in the furnace and the mole ratio between fuel and air, i.e. the coefficient of air, on the for ⁇ mation of nitrogen monoxide at a NO level of 100 ppm.
  • the maximum concentration of nitrogen monoxide in flue gases with a coefficient of air of 0.99, for instance, and within the temperature range from 700 to 1,500°C, is about 65 ppm, and correspondingly with a coeffi- cient of air of 0.95 only 10 ppm.
  • the low concentra ⁇ tion of nitrogen monoxide is due to the fact that as there is only little oxygen present, carbon monoxide and hydrogen are formed in the combustion, and the nitrogen oxide possibly occurring is reduced by them through reactions approximately such as the following. NO + CO -> 1/2 N2 + C02 NO + H2 -> 1/2 N2 + H2O
  • concentration of nitrogen monoxide in the combustion carried out understoichiometrically in a manner known per se can be kept at a low value, and one faces with problems only when more air is intro ⁇ quizd into the boiler for completing the combustion process. This is because at a high temperature even a small excess of air results in rapid formation of nitrogen monoxide in an amount hazardous to the envi ⁇ ronment?
  • the maximum con ⁇ centration of nitrogen monoxide is about 400 ppm and with a coefficient of air of 1.05 about 800 ppm.
  • the concentra ⁇ tion of nitrogen monoxide in a combustion process carried out at a low temperature is very low irrespec ⁇ tive of the coefficient of air (ranging from 0.9 to 1.3) to be used in a practical case.
  • the maximum concentration of nitrogen monoxide is about 120 ppm, which requires a high coefficient of air; at 700°C, the corresponding nitrogen monoxide value is as low as 10 ppm.
  • these prin- ciples can be connected in one and the same combustion means in such a manner that the air required for the combustion is fed in at least two stages so that in the first combustion stage the coefficient of air is below 1, preferably from 0.90 to 0.97, whereby the amount of nitrogen monoxide formed at a high tempera ⁇ ture, typically 1,400°C, is insignificant. Thereafter the gases are cooled to a low temperature, preferably below 1050°C with the concentration of 100 ppm as a limit value, whereby more air is introduced among the gases either after the cooling or simultaneously with the cooling process, the formation of nitrogen monox ⁇ ides remaining insignificant all the time.
  • FIG. 1 shows schematically by way of example the curve A representing the nitrogen monoxide concentration of 100 ppm as a function of the tempera ⁇ ture and the coefficient of air, and the different combustion stages of the method according to the in- vention in such a manner that the nitrogen monoxide concentration in the gases always remains below the value indicated by the curve A.
  • Figure 2 shows schematically an apparatus suited for applying the method according to the inven- tion, comprising a combustion means such as a boiler 1 or the like comprising a furnace 2.
  • Fuel 3 is intro ⁇ quizd into the furnace 2 by means of one or more feed ⁇ ing means 4, and primary air 5 is fed into the same portion of the furnace 2 by means of first air supply means 6.
  • first air supply means 6 When the ratio of the primary air to the ture of the gases after the superheater is preferably below 1050°C when a concentration of 100 ppm is used as a limit value.
  • These combustion stages are illus ⁇ trated in Figure 1, in which the line B-C represents understoichiometric combustion, the line C-D cooling without introduction of air, and the line C-E cooling by introducing secondary air 8.
  • Secondary air and tertiary air can, of course, be introduced at more than two points, or air can be introduced in connection with the cooling or after it at a single point, whereby the introduction of air is adjusted so that the principle represented by the tem ⁇ perature/coefficient of air nomogram B-F in Figure 1 will be followed.
  • the apparatus can be constructed by means of inexpensive construction technical alterna ⁇ tives known from the prior art and no expensive cata ⁇ lysts or pressure chambers are required.
  • the method according to the invention is easy to real- ize and can be controlled in a simple manner by apply- 8 amount of air theoretically required for complete com ⁇ bustion is below one, that is, the coefficient of air is preferably in the range from 0.90 to 0.97, there is a constant small undersupply of oxygen in that portion of the furnace with a resultant abundant formation of carbon monoxide and hydrogen. These substances prevent the formation of nitrogen monoxide, or if nitrogen monoxide should be formed, it is immediately reduced to nitrogens by these substances.
  • the temperature of the gases in the furnace may drop to a value as low as 650°C, whereby the sulphur dioxide contained in the flue gases is possibly at least partially reduced to hydrogen sul ⁇ phide.
  • the temperature of the gases drops to such a low value that the formation of nitrogen monoxide is nevertheless insignificant in a later combustion stage, i.e., when the coefficient of air rises to an overstoichiometric value.
  • the addi ⁇ tion of secondary air 8 may also be carried out in connection with the superheater 7, whereby the amount of secondary air is adjusted so that when the coeffi- cient of air is one or slightly higher, the tempera- ing the principles of the method and the apparatus de ⁇ signed accordingly by measures and means connected with the operation of a conventional boiler.
  • the desired maximum value of nitrogen monoxide 5 can be estimated in advance, and the combustion pro ⁇ cess can be effectively modified so that a prede ⁇ termined limit value will not be exceeded.
  • the final temperature of flue gases as such does not have any decisive importance if only the temperature/coeffi-
  • the cooling can be effected by some other method, such as a thermodynamic process.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)

Abstract

La présente invention se rapporte à un procédé de combustion et à un appareil servant à réduire la formation d'oxydes d'azote dans un processus de combustion. Dans ledit procédé, l'air requis pour la combustion est introduit dans un fourneau (2) en deux étapes au moins, de sorte que dans la première étape le cofficient de l'air est compris de préférence entre 0,90 et 0,97 pendant que la combustion est effectuée dans des conditions sous-stoechiométriques, et en une étape au moins de sorte que le cofficient total de l'air dépasse la valeur 1. Selon ledit procédé, les gaz s'étant formés dans la première étape de combustion sont refroidis à une température inférieure, pendant qu'on introduit davantage d'air dans les gaz au plus vite en connexion avec l'opération de refroidissement. L'introduction d'air est effectuée de sorte que le coefficient total de l'air en chaque point particulier dans le fourneau (2) est au maximum tel que cela est requis par la température des gaz en ce point particulier pour une concentration de monoxyde d'azote qui ne dépasse pas une valeur prédéterminée devant se former dans les gaz. L'appareil comprend un surchauffeur (7) qui effectue l'opération de refroidissement dans le fourneau (2) de la chaudière (1) après la première étape de combustion et à travers lequel les gaz s'étant formés pendant la première étape sont amenés à s'écouler sous pression. On introduit davantage d'air pour la combustion finale au niveau du surchauffeur (7) et/ou en aval de celui-ci.
PCT/FI1988/000203 1988-01-04 1988-12-29 Procede de combustion servant a reduire la formation d'oxydes d'azote dans un processus de combustion et appareil de realisation dudit procede WO1989006334A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI880002A FI87013C (fi) 1988-01-04 1988-01-04 Braenningsfoerfarande foer minskande av bildning av kvaeveoxider i samband med foerbraenning samt anordning foer tillaempande av foerfarandet
FI880002 1988-01-04

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Publication Number Publication Date
WO1989006334A1 true WO1989006334A1 (fr) 1989-07-13

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FI (1) FI87013C (fr)
WO (1) WO1989006334A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1991010864A1 (fr) * 1990-01-08 1991-07-25 Transalta Resources Investment Corporation Procede de combustion
US5215455A (en) * 1990-01-08 1993-06-01 Tansalta Resources Investment Corporation Combustion process
WO1998000675A1 (fr) * 1996-06-28 1998-01-08 Imatran Voima Oy Procede et dispositif de combustion de gaz dans un foyer

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3048131A (en) * 1959-06-18 1962-08-07 Babcock & Wilcox Co Method for burning fuel
US3228451A (en) * 1957-06-25 1966-01-11 Urquhart S 1926 Ltd Method of burning fuels
US3911083A (en) * 1972-02-24 1975-10-07 Zink Co John Nitrogen oxide control using steam-hydrocarbon injection
US3914091A (en) * 1973-03-01 1975-10-21 Tokyo Gas Co Ltd Combustion method for hydrocarbonic fuels with low emission of nitrogen oxides
DE2534841C2 (de) * 1974-12-11 1983-12-01 Energiagazdálkodási Intézet, 1027 Budapest Feuerungsanlage
WO1987001790A1 (fr) * 1985-09-20 1987-03-26 Oy Tampella Ab Procede pour diminuer les emissions d'oxydes d'azote et d'oxydes de soufre lors du brulage de combustibles contenant de l'azote et du soufre
US4704084A (en) * 1979-12-26 1987-11-03 Battelle Development Corporation NOX reduction in multisolid fluidized bed combustors

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3228451A (en) * 1957-06-25 1966-01-11 Urquhart S 1926 Ltd Method of burning fuels
US3048131A (en) * 1959-06-18 1962-08-07 Babcock & Wilcox Co Method for burning fuel
US3911083A (en) * 1972-02-24 1975-10-07 Zink Co John Nitrogen oxide control using steam-hydrocarbon injection
US3914091A (en) * 1973-03-01 1975-10-21 Tokyo Gas Co Ltd Combustion method for hydrocarbonic fuels with low emission of nitrogen oxides
DE2534841C2 (de) * 1974-12-11 1983-12-01 Energiagazdálkodási Intézet, 1027 Budapest Feuerungsanlage
US4704084A (en) * 1979-12-26 1987-11-03 Battelle Development Corporation NOX reduction in multisolid fluidized bed combustors
WO1987001790A1 (fr) * 1985-09-20 1987-03-26 Oy Tampella Ab Procede pour diminuer les emissions d'oxydes d'azote et d'oxydes de soufre lors du brulage de combustibles contenant de l'azote et du soufre

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1991010864A1 (fr) * 1990-01-08 1991-07-25 Transalta Resources Investment Corporation Procede de combustion
US5085156A (en) * 1990-01-08 1992-02-04 Transalta Resources Investment Corporation Combustion process
US5215455A (en) * 1990-01-08 1993-06-01 Tansalta Resources Investment Corporation Combustion process
WO1998000675A1 (fr) * 1996-06-28 1998-01-08 Imatran Voima Oy Procede et dispositif de combustion de gaz dans un foyer

Also Published As

Publication number Publication date
FI87013B (fi) 1992-07-31
FI880002A0 (fi) 1988-01-04
FI880002A (fi) 1989-07-05
FI87013C (fi) 1992-11-10

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