JPS6038435B2 - Method for removing nitrogen oxides from coke oven combustion exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing nitrogen oxides from coke oven combustion exhaust gas.

In a coke oven, a heating chamber is provided adjacent to the carbonization chamber to heat the carbonization chamber, and hydrocarbon fuel is combusted here.

The combustion gas produced by this combustion is concentrated and exhausted, but since this exhaust gas contains nitrogen oxides (usually referred to as NOx), in order to prevent pollution, NOX is removed, which means that NOx is rendered harmless. After being converted into components, it must be released into the atmosphere. As a method for removing NOx in the gas, for example, in the presence of ammonia, under heating,
A method is known in which a /x-containing gas is brought into contact with a catalyst such as a metal or a metal oxide, or a method in which selective reduction is carried out with ammonia at a temperature in a specific range, which is higher than the above-mentioned contact method without using a catalyst.

However, in the case of coke oven exhaust gas, there is a characteristic that the exhaust gas temperature and the /x concentration in the exhaust gas are not constant and change over time. In other words, heating in a typical horizontal coke oven is carried out in individual heating chambers that are installed in parallel across a carbonization chamber, with burners installed in each section across the side wall of the heating flame path, and heated for a certain period of time. This is done by burning fuel gas alternately in a burner at intervals. Immediately after the burner is switched, the exhaust gas temperature is low and the NOx concentration is low, but as the combustion progresses in the burner, both gradually rise until a certain period of time, and then decrease when the burner is switched. Because of this change over time, when coke oven exhaust gas is deoxed using the catalytic contact method described above, ammonia is first injected into the exhaust gas, but if the amount of ammonia added is kept constant, the following problems occur. That is, when the /x concentration is low, excessive ammonia is released into the atmosphere and causes secondary pollution, and when the nox concentration is high, the reduction of nox cannot be carried out sufficiently.

Furthermore, since the temperature of the exhaust gas is not constant, the activity of the catalyst is not effectively quenched, resulting in a difference such that, for example, when the temperature is low, the removal rate of /x is low, and when the temperature is high, the removal rate of nox is high. Such disadvantages also occur in the method of selectively reducing Nox with ammonia without a catalyst. The present inventors have completed the present invention through extensive research in order to solve such inconveniences. The purpose of the present invention is to provide a method for efficiently removing NOx by reducing changes over time in the temperature and NOx content of flue gas discharged from a coke oven. In the operation of a coke oven, which has a large number of individual heating chambers and burns and heats by switching the burners in each heating chamber alternately, the entire heating chamber of the coke oven is divided into a plurality of coarse sections. The switching of the burners is carried out substantially simultaneously, but the switching of the burners between the silks is staggered, so that the respective exhaust flue gases are introduced into a common flue gas conduit and merged before being converted into nitrogen oxides. The present invention relates to a method for removing nitrogen oxides from coke oven combustion exhaust gas, which is characterized by subjecting it to removal treatment.

The present invention will be described in detail below in conjunction with the accompanying drawings. Examples of coke ovens to which the method of the present invention is applied include common horizontal coke ovens such as the Otto type, Koppers type, Kuroda type, Nippon Steel type, and Karl Steel type.

That is, for example, in a heating chamber, two burners, one on the combustion side and one on the idle side through which the exhaust gas passes (sometimes there are two in each side of the heating chamber, or a total of four burners), are used to heat the heating chamber at regular intervals. Any type of furnace may be used that employs a heating method in which combustion is performed by switching combustion burners. In the following explanation, an automatic coke oven will be used as an example. FIG. 1 is a schematic plan view of an example of a coke oven in which the method of the present invention is carried out, FIG. 2 is a schematic side view of the same, and FIG. 3 is a schematic partial cross-sectional view showing an example of a burner in a heating chamber. In the figure, 1
is the heating chamber of the coke oven, 2 is the carbonization chamber, 3 is the waste heat valve, 4 is the air valve, 5 is the switching winch, 6a and 6b are the wire ropes for switching the valves, 7 is the bonito path, 8 is the chimney, 9, 9 ' is the burner for the longest flame, 10,10' is the burner for the short flame, 11
12 is an air supply port, 12 is an exhaust port, 13 is a heating flame path side wall forming a heating flame path, and 14 is a /x removal device. 1st
As shown in the figure, in the furnace, a large number of heating chambers 1 are provided in parallel at positions sandwiching the carbonization chamber, and the inside of each heating chamber 1 is divided into one for long flames and one for short flame, as shown in FIG. Flame burners 9, 9' and 10, 10' are arranged.

The burners 9, 9' and 10, 10' are switched at regular intervals to perform combustion alternately. That is, what is shown here is one unit of heating chamber, with one burner for the longest flame and one burner for shortest flame in each section separated by the heating flame path adjacent wall 13, and the total number of burners for one unit of heating chamber. There are four burners. For example, when the heating chamber is continued for a certain period of time with the longest flame burner 9, the switching is sequentially performed to the long flame burner 9', then to the short flame burner 10, and then to the short flame burner 10'. It is possible. These burners are switched by waste heat valve 3 and air valve 4.
This is carried out by simultaneous operation, and the combustion exhaust gases enter the common bonito pipe 7 via the individual waste heat valves 3 and are discharged from the chimney 8. When the burners are switched, for example, when one burner 9 starts combustion, the Knox concentration in the exhaust gas gradually increases, but when the combustion of the burner 9 is stopped after a certain period of time, the Knox concentration rapidly decreases.

When the other burner 10 is then used, the nox concentration begins to rise again. The temperature of exhaust gas also shows a similar trend. In the present invention, the entire heating chamber of the furnace is divided into several lines.

The number of heating chambers 1 for each silk is preferably the same. Usually, the division unit of the coke oven gate is 2 to 5 units. The entire heating chamber may be divided sequentially into equal numbers from one end of the furnace group to the other, or may be divided into every other heating chamber, or every two or more heating chambers. In the method of the present invention, the burners in the same group are switched substantially simultaneously, but the burners are switched at different times in other groups.

For example, if the burner is changed over every two powders, and if the heating chamber is divided into four groups, that is, there are four sets of silk, it is sufficient to provide a 5-minute interval difference between the sets. When this is done, the concentration of Knox results as shown in FIG. 4. FIG. 4 shows the Knox concentration as the vertical axis and the passage of time (20 minute intervals) as the axis. 1,0,m,W is 4
This is the Nox concentration curve in the gas discharged from each pipe of the set, and the Nox concentration curve is shown in the same shape at 5 minute intervals, and when introduced into a common exhaust gas pipe, the Nox concentration curve is shown as T. is averaged.

Similar results are obtained for the temperature of the exhaust gas. To specifically illustrate the operation of carrying out the above method, the furnace gate of a coke oven is divided into a plurality of groups A, B, C, etc., and each group of gates has a waste heat valve 3 and an air valve. Wire ropes 6a, 6b, etc. for switching 4 are provided independently,
The structure is such that one wire rope is operated and the waste heat valve and air valve attached to the same set of heating chambers connected to it can be switched at the same time as the burner is switched.

Then, when the switching winch 5 operates, for example, the wire rope 6a, by the operation of the timer, the coarse air valve and waste heat valve of A open or close, and after a certain period of time, the wire rope 6b is activated to open the coarse heating chamber of B. Air valves and waste heat valves open or close. Burner switching is also performed in synchronization with this. The above cycle may be repeated. Further, by providing each air valve and waste heat valve with, for example, a solenoid valve timer, the opening and closing times can be staggered. As described above, the exhaust gas discharged from each set is mixed in the bonito dish, the NOx concentration is averaged, and the exhaust gas is discharged without any significant difference over time.

A nox removal device 14 is provided near a location where the exhaust gas is sufficiently mixed and at an appropriate temperature, and there removes nox, that is, converts it into harmless components. Any type of nox removal device can be used, such as a catalytic type as described above, a non-catalytic type, and an ammonia selective reduction type. Since the /x concentration and temperature of the exhaust gas are said to have extremely small changes over time, extremely efficient nox removal can be carried out. Although preferred embodiments of the method of the present invention have been described above, the present invention is not limited to these examples, and various modifications other than those described above can be made within the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of an example of a coke oven in which the method of the present invention is carried out, FIG. 2 is a schematic side view of the same, FIG. This is a diagram for explaining the action and effect of the invention method, in which the vertical axis represents the Knox-containing soil and the axis represents the route time. In the figure, 1 is a heating chamber, 2 is a carbonization chamber, 3 is a waste heat valve, 4 is an air valve, 5 is a switching winch, 6a and 6b are wire ropes for switching valves, 7 is a flue, 9, 9', 10 10' is a burner, 11 is an air supply port, 12 is an exhaust port, and 14 is a nox removal unit. Fig. O2 Fig. O' Fig. O3 Fig. O4 Fig.

Claims (1)

[Claims] 1. In the operation of a coke oven that has a large number of individual heating chambers and burns and heats by alternately switching the burners in the individual heating chambers, the heating chambers of the entire coke oven are divided into a plurality of groups. , the burners within each set are switched substantially simultaneously, but the burners between sets are switched at different times, so that each exhaust gas discharged is introduced into a common exhaust gas conduit. A method for removing nitrogen oxides from coke oven combustion exhaust gas, which comprises subjecting the flue gas to nitrogen oxide removal treatment after the amalgamation. 2. The method according to claim 1, in which the heating chambers of the entire coke oven are divided into 2 to 5 sets.