Coke oven and method of operating the same

Details Coke oven and method of operating the same Coke oven and method of operating the same

2000-03-03

2004-09-28

Caldarola, Glenn (Department: 1764)

Distillation: apparatus

Apparatus

Systems

C202S124000, C202S125000, C202S126000, C202S127000, C202S138000, C202S142000, C202S242000, C202S248000, C202S267100, C201S041000

Reexamination Certificate

active

06797122

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a coke oven having improved combustion chambers and a method of operating the same. The coke oven of the present invention allows uniform combustion to be achieved in the direction of the height of the combustion chambers, thereby reducing the No
x
(nitrogen oxides) in the waste gas generated as a result of combustion.
BACKGROUND OF THE INVENTION
The basic performance required of a coke oven is to produce high-quality coke, to reduce fuel consumption, and to achieve these objects at a low cost. In addition to such basic performance, what has been called for in recent years is less No
x
contents in the waste gas.
Requirements for preventing environmental pollution have become increasingly severe year by year. The regulated NO
x
emission standards, specified by law for newly installed coke ovens, are quite stringent compared with those for existing coke ovens, and thus it is likely that new coke ovens cannot be constructed based on the prior art.
The NO
x
content in the waste gas increases with increasing combustion temperature. Therefore, No
x
in the waste gas of a coke oven can be reduced by decreasing the combustion temperature in the combustion chambers. However, the combustion temperature must be higher than a predetermined value for the purpose of producing coke, and inevitably increases with higher operation rates. Therefore, the most realistic NO
x
reduction measure would be to eliminate localized, abnormal high temperature by achieving uniform combustion in the direction of oven height of the combustion chambers. However, since each combustion chamber of a coke oven has a slender, grooved structure (i.e., it is remarkably high in the vertical direction with respect to its horizontal cross-sectional area), it is difficult to achieve uniform combustion due to it's a structure. The difficulty increases particularly with tall coke ovens.
The combustion temperature can be reduced locally by increasing flame lengths, e.g., by decreasing the calorific value of a fuel gas while diluting the fuel gas with the waste gas. The following methods are available as the specific measures:
(1) A method in which the waste gas in the combustion chamber is circulated, thereby increasing flame lengths and hence decreasing flame temperatures. This method is accomplished in Koppers circulation type coke ovens;
(2) A method in which combustion is scattered by partially supplying both the combustion air and a lean gas or only combustion air from a plurality of heightwise arranged ports partially (see Japanese Unexamined Patent Application Laid-Open Nos. 61-133286(1986) and 1-306494(1989), and Published Japanese Translation of PCT International Publication No. 4-501876(1992). This method is adopted in Carl Still coke ovens, Otto coke ovens, and Nippon Steel Corporation coke ovens as a multistage supply system for only combustion air, particularly when a rich gas in used as fuel. This method is called “the multistage combustion method.”
Here, fuel gases used for coke ovens include not only a high calorific gas, such as a coke-oven gas called a rich gas, but also a gas called a lean gas. The rich gas means a fuel gas whose calorific value ranges from 14700 to 20160 kJ/Nm
3
(3500 to 4800 kcal/Nm
3
), and the lean gas means a blast-furnace gas or a mixed gas of a blast-furnace gas and a coke-oven gas whose calorific values range from 3360 to 5460 kJ/Nm
3
(800-1300 kcal/Nm
3
).
Therefore, (a) rich gas combustion and (b) lean gas combustion take place in a coke oven. An oven that can handle either (a) or (b) is called a single combustion coke oven, and an oven that can handle both (a) and (b) is called a compound combustion coke oven.
The method in (1), described previously, is aimed at accomplishing the slowing down of the combustion progress in the direction of oven height by reducing the oxygen content and the calorific value of the fuel gas while circulating the waste gas, and thus is effective for controlling the amount of NO
x
generated. However, in this method the amount of waste gas increases, and energy losses also increase when the amount of circulated waste gas is increased. Further, in the waste gas circulation method based on the Koppers coke oven circulation system, it is difficult to increase the waste gas circulation rate greatly due to the restricted cross-sectional area of a circulation port. The rate can be increased to about 20% at most. In addition, the amount of waste gas circulated cannot be varied as desired, either.
The method of reducing NO
x
by multistage combustion in (2), described previously, requires adjustment of the distribution ratio of the combustion air or lean gas, in the direction of oven height during the operation of the coke oven when the amount of fuel gas is greatly varied. However, in the actual coke oven operation, not only such an adjustment entails much time, but also the place to be adjusted is limited mainly to the ports at the uppermost stage and at the bottom, imposing difficulty adjusting the apertures of intermediate ports, and thus a satisfactory effect on NO
x
reduction cannot be obtained.
An exemplary bottom structure of the combustion chamber of a coke oven is disclosed in the previously described Published Japanese Translation of PCT International Publication No. 4-501876(1992) and Cokemaking International, Vol. 4-2, pp.71-83 (1992). As shown in FIG.
9
(
a
), a rich-gas port
2
is arranged near an oven wall
6
of a coke oven, and a lean-gas port
7
and an air port
3
are arranged side by side in the middle. Further, Japanese Publication of Examined Patent Application No. 5-29678 (1993) discloses a drawing in which a lean-gas port and an air port extend in the direction of coke pushing (i.e., direction of oven length), side by side, almost in the middle of a combustion chamber. However, no description is made as to the arrangement and structure of the lean-gas port and the air port, for achieving a uniform combustion temperature in the direction of oven height and for reducing NO
x
in the waste gas.
SUMMARY OF THE INVENTION
The basic object of the present invention is to provide a coke oven and a method of operating the same that forms a waste gas containing less NO
x
.
A specific object of the present invention is to provide a coke oven, having a combustion chamber that can eliminate localized high-temperature combustion by achieving uniform combustion in the direction of oven height, even if the oven is of a tall, large-sized structure.
Another specific object is to provide a coke oven having a combustion chamber that can achieve the above-described uniform combustion independently of the combustion type, i.e., either single combustion in which either a rich gas or lean gas is used as fuel, or compound combustion in which both are used alternately.
Still another specific object is to provide a method of in operating a coke oven that allows NO
x
in the waste gas to be reduced by achieving uniform combustion within the combustion chamber.
The present invention pertains to a coke oven such as shown in FIG.
1
. In
FIG. 1
, reference numerals I, II, III . . . denote arrays of combustion chambers, and i, ii, . . . , denote carbonization chambers. The combustion chamber arrays and the carbonization chambers are arranged alternately in the direction of oven battery (Y direction). Each combustion chamber array consists of many combustion chambers
1
-
1
,
1
-
2
,
1
-
3
,
1
-
4
. . . that extend in the direction of coke pushing (X direction). What is to be improved by the present invention are the structure of these combustion chambers and the combustion method applied to such combustion chambers.
Here, the direction of oven battery means the direct ion in which many combustion chambers (specifically, a plurality of combustion chambers divided by flue partition walls, or so-called an array of flues) and carbonization chambers extend alternately in parallel. Further, the direction of coke pushing means the direction at right angles to the direction of oven battery, and i

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