(19)
(11) EP 1 621 599 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
01.02.2006 Bulletin 2006/05

(21) Application number: 05106709.8

(22) Date of filing: 21.07.2005
(51) International Patent Classification (IPC): 
C10B 21/10(2006.01)
C10B 5/02(2006.01)
C10B 21/20(2006.01)
(84) Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU LV MC NL PL PT RO SE SI SK TR
Designated Extension States:
AL BA HR MK YU

(30) Priority: 30.07.2004 IT GE20040071

(71) Applicant: Paul Wurth Italia S.p.A.
16149 Genova (IT)

(72) Inventor:
  • Pivot, Stefano
    16156 Genova (IT)

(74) Representative: Porsia, Attilio et al
c/o Succ. Ing. Fischetti & Weber Via Caffaro 3/2
16124 Genova
16124 Genova (IT)

   


(54) Method for reduction of nitrogen oxides in coke-oven flue gases and coke oven combustion chamber therefor


(57) Method of controlling combustion in coke ovens for reduction of nitrogen oxides in coke-oven gases, characterized in that, in the combustion chambers of the oven, between the two air inlets, a wall is constructed which rises in said chambers to a reduced height between about 1/3 and 1/5 of the height of said chambers, said walls being provided with a hole near their base, and being provided to correspond to the upper limit of said hole, on one side of the said wall housing the nozzle for supply of the combustion gas, with a diverting element for diverting a proportion of the combustion air supplied to said chamber onto the other side of said wall. Said diverting element comprises a plate projecting from said wall. Preferably said wall has a height of about 1 metre.




Description


[0001] The present invention relates to the control of combustion in coke ovens for reduction of nitrogen oxides in coke-oven gases, to render said gases less polluting when they are discharged to atmosphere. More particularly, the invention relates to equipment that provides said control, and hence reduction of the nitrogen oxides in coke-oven gases, at far lower cost than the conventional equipment. The systems generally used for reduction of the nitrogen oxides in coke ovens are: (a) reduction of flame temperature by recirculating a proportion of the flue gases so as to dilute the fuel gas so as to lower the combustion temperature somewhat and (b) admission of the combustion air in various zones along a suitable pipe in order to "stagger" the flame along the pipe so that a reduction of the temperature of the flame itself is also achieved in this way, by breaking it up into several flamelets with consequent reduction of the production of nitrogen oxides.

[0002] A third system is also known for the reduction of nitrogen oxides in coke-oven gases, described for example in patent US-A-5,017,270 of Krupp Koppers GmbH, which relates substantially to a combination of these two arrangements. In accordance with this patent it is proposed to adopt, in combination, a system for circulation, which in itself is already known, with a system for distribution of air at various levels, again in itself already known.

[0003] According to this known technology, the two channels leading to one combustion chamber of the coke oven both become air ducts and no longer flue gas ducts and moreover the two channels leading to the adjacent chamber become flue gas ducts and extend downwards to a regenerator which, alternately, in a first time segment, for example in the first 20 minutes, accumulates the heat of the flue gases and in the next, gives up this heat to the air. This prior patent envisages outlets at various levels and so combines the effect of recirculation with the effect of distribution of the air at several levels.

[0004] According to the present invention, the problem of reduction of nitrogen oxides is solved with a combustion system in which the flame is not staggered physically but is fractionated owing to an aerodynamic shape. This system has the advantage that it is simpler than the known systems, since it does not involve the ad-hoc construction of a channel, made of refractory bricks, which would make the oven design more complicated. It only requires the construction of a wall in the combustion chambers of the oven, positioned between the two air inlets, rising to a height of only about one metre in the oven, and with a hole near its base equipped with a diverting plate, made of a refractory material, causing the air to go more in one direction than another.

[0005] For a better assessment of the scope of the present invention, it has to be borne in mind that 600-700 different brick moulds are required for constructing a coke oven plant of this type. With the present system, about ten shapes of bricks are eliminated, because it is no longer necessary to build a long, high channel with several small holes for outlet of the secondary air streams. This constitutes a definite economic advantage in oven construction, in view of the considerable simplification of oven design.

[0006] A further advantage of the design according to the present invention relates to supply of these ovens with gas mixture. It is known that the problem of nitrogen oxides does not exist when the oven is supplied with gas mixture, whereas the problem does exist when the oven is supplied with rich gas. For most of the time, coke oven batteries operate on gas mixture, not on rich gas. Since the gas mixture has low calorific value, it must be preheated, for which it follows the fate of the air. If a simple wall is built in the middle of the combustion chamber, the result is that the air leaves on one side and the gas on the other and in the lower part there is no flame so that this part is poorly heated. We are therefore faced with the problem of finding how to carry air from the gas and vice versa to make it burn at the bottom as well otherwise the device that worked well for the rich gas since there were two air streams, is limiting when operating on gas mixture. The device according to the invention which causes diversion of the gas flow meets this objective. The ovens consume 1/3 of gas for heating and 2/3 for exporting. Since the rich gas is a high-value gas (4000 or more kilocalories), at iron and steel works the aim is to supply the oven with low-value gas from the blast furnace, which is called gas mixture or lean gas, so that all the gas produced by the oven is exported, instead of consuming 1/3. Therefore the coke ovens at iron and steel works, where there is production of gas mixture of low calorific value (about a quarter compared to rich gas, i.e. approx. 1000 kcal), are operated on gas mixture.

[0007] Further aims and advantages of the present invention will become clearer from the following description of one embodiment of the invention, illustrated as a nonlimiting example in the appended drawing, in which a portion of a coke oven battery is shown schematically in longitudinal section.

[0008] Referring to the drawing, it shows the combustion chambers or channels 1, and a distillation chamber 2. Refractory walls 3 separate the distillation chamber 2 from the combustion channels 1, and the heat is transmitted through said walls 3 to the coal charge contained in the distillation chambers. To achieve optimum distillation with minimum production of nitrogen oxides, it is necessary for the vertical temperature distribution on walls 3 to be perfectly uniform. For this purpose, according to the present invention, a central wall 4 is erected in the combustion chambers 1, extending to a relatively small height, of about one metre, and dividing the base of chambers 1 into two zones 101, 201 respectively. Near its base, this wall has a through-hole 5, and a plate 6 is arranged corresponding to the top edge of said hole 5, and projects from said wall into zone 101 of chamber 1. A pipe for admission of combustion air is labelled 7, and a manifold for feed of fuel gas is labelled 8, and communicates with nozzle 9 with its opening in section 101 of chamber 1. As shown by the dashed-line arrow F, a portion of the air from pipe 7 is diverted by plate 6 through hole 5 in chamber 201, whereas another portion of the air continues on its way (arrow F1) in chamber 101, meeting the gas coming from nozzle 9, so that a portion of the gas is caused to burn in chamber 101 i.e. in the bottom part of combustion chamber 1, whereas another portion of the gas moves upwards, beyond wall 201, where it meets the air diverted by plate 6, and burns in the top part of chamber 1. Owing to this arrangement, uniform heating of the whole of combustion chamber 1 is obtained, and owing to the staggering of the combustion flame the emission of nitrogen oxides in the exhaust gases is greatly reduced.

[0009] The exhaust gases flow into the regenerators 108 (arrow F2), heating the air fed to the oven in countercurrent to them, and then to the smokestack.

[0010] Of course, the present invention is not limited to the embodiments that have been illustrated and described, but comprises all variants and modifications within the wider scope of the inventive concept, substantially as claimed hereunder.


Claims

1. Method of controlling combustion in coke ovens for reduction of nitrogen oxides in coke-oven gases, characterized in that, in the combustion chambers of the oven, between the two air inlets, a wall is constructed which rises in said chambers to a reduced height between about 1/3 and 1/5 of the height of said chambers, said walls being provided with a hole near their base, and being provided to correspond to the upper limit of said hole, on one side of the said wall housing the nozzle for supply of the combustion gas, with a diverting element for diverting a proportion of the combustion air supplied to said chamber onto the other side of said wall.
 
2. Method according to Claim 1, in which said diverting element comprises a plate projecting from said wall.
 
3. Coke oven for carrying out the method of Claim 1 or 2, in which said wall has a height of about 1 metre.
 
4. Coke oven according to Claim 3, for carrying out the method according to either one of the Claims 1 or 2, substantially as described, illustrated and for the purposes explained above.
 




Drawing







Search report