JPS5852010B2 - Denitrification method for sintering furnace exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for denitrating sintering furnace exhaust gas, in which the temperature of sintering furnace exhaust gas is raised using carbon monoxide, and at the same time, the gas is purified and then denitrified.

In the denitrification method using ammonia catalytic reduction of sintering furnace exhaust gas, it is necessary to raise the temperature of the exhaust gas to a predetermined temperature before the reaction, but the fuel cost required for raising the temperature is a major problem.

For this reason, a denitrification method has been proposed in which carbon monoxide contained in sintering furnace exhaust gas is oxidized by a catalyst and the heat generated at the time is effectively utilized.

The denitrification method shown in Fig. 1 is an example of this method. In this method, the exhaust gas after denitrification is heated through a heat exchanger 1, then further heated in a heating furnace 2, and ammonia 3 is added as a reducing agent to cause the denitrification reaction. The exhaust gas was denitrated in layer 4, and then passed through carbon monoxide oxidation layer 5, which was made of a synthetic catalyst synthesized by impregnating an alumina carrier with noble metals such as platinum and palladium, to oxidize carbon monoxide and raise the temperature of the exhaust gas. After that, the heat exchanger 1 is returned to the heat exchanger 1, and the temperature is lowered and discharged.

However, the synthetic catalyst used in this method must be heated to a high temperature of 300° C. or higher in order to increase the oxidation rate of carbon monoxide, is expensive, and has problems in disposing of the catalyst after it has deteriorated.

Moreover, the heat of oxidation of carbon monoxide is used through the heat exchanger 1, which has the drawback of poor utilization efficiency.

Another method of denitration is shown in FIG.

In this method, the exhaust gas after denitrification is heated through a heat exchanger 11, then heated in a heating furnace 12, ammonia 13 is added thereto, and this is put into a denitrification reaction layer 14 containing iron ore, where NOx At the same time, carbon monoxide is also oxidized by iron ore, and then passed through the heat exchanger 11.

However, with this method, as with the one in Figure 1, it is impossible to expect an improvement in the oxidation rate unless the temperature is above 300°C, and if the oxidation rate is increased to increase the temperature raising efficiency, there is a risk that the denitrification rate will decrease. be.

In addition to denitrification treatment of sintering exhaust gas, purification of automobile exhaust gas is also mentioned as a treatment technology for carbon monoxide.

This method uses a synthetic catalyst, but like the example shown in FIG. 1, the cost is high and there are problems in disposing of the catalyst whose activity has decreased.

The present invention was made in view of the above circumstances, and its purpose is to create a sintering method that can effectively utilize oxidation heat, use an inexpensive catalyst, and use it as a resource even if the activity decreases. The present invention provides a method for denitrifying furnace exhaust gas.

That is, the present invention improves the efficiency of utilizing the heat of oxidation of carbon monoxide gas by oxidizing carbon monoxide gas before denitrification treatment, instead of oxidizing it after or simultaneously with denitrification treatment as in the conventional method. It is something.

In this case, the temperature of the sintering exhaust gas before denitration treatment is 100 to 2
50°C, and therefore it is necessary to select a catalyst that is highly active in this temperature range.

The present invention focuses on the fact that naturally occurring manganese ore is effective as a carbon monoxide oxidation catalyst, and that this catalyst is highly active at temperatures below 300°C. This made it possible to oxidize carbon monoxide gas.

Moreover, since this manganese ore is used as a resource in steel mills, even if it deteriorates, it can be effectively used as a resource.

The present invention will be described in detail below with reference to the drawings.

The main sintering exhaust gas is first transferred to the heat exchanger 21 as shown in FIG.
After passing through, it is desulfurized by a desulfurizer 22.

In this case, it is preferable that SOx be desulfurized to several ppm or less.

The chemical composition of the exhaust gas after desulfurization is as shown in Table 1, for example.

The dust is removed by a wet dust collector 23, and then passed through a booster 24 and the heat exchanger 21 to a moving bed type carbon monoxide oxidation layer 25.
be guided by.

This oxidized layer 25 is filled with manganese ore, such as manganese ore or iron-manganese ore, which acts as a carbon monoxide oxidation catalyst.

An example of its chemical composition is shown in Table 2.

Here, the sintering exhaust gas flowing into the carbon monoxide oxidation layer 25 is
The temperature is preferably 300°C or less, particularly preferably in the range of 100 to 250°C.

This was revealed in a pilot experiment of 20ONrrl'/hr.

Figure 4 shows the relationship between the temperature ('C') of the sintering exhaust gas flowing into the carbon monoxide oxidation layer 25 and the oxidation rate (%) of carbon monoxide. Using manganese ore with the composition of A61 shown in Table 2, 5V = 5000h
The experimental result when r-' is shown.

In addition, using manganese ore with a composition of /162,
When V = 5000 hr-', curve C is manganese ore with composition 3, and when S V = 3000 hr-1, curve d is manganese ore with composition A3 and 5V = 5000 h.
The case of r-1 is shown respectively.

In this experiment, manganese ore sized to 8 to 25 mm was used, the oxide layer 25 was 400 mm in diameter x 2000 mm, and the thickness of the manganese ore filling was SV = 30.
530 in 00 hr-1, 32 in SV Ni5000-1
0i! It is i.

From this experimental result, /461 and A62 have high activity, with an oxidation rate of about 50% at 60°C and about 99% at 100 to 200°C.

Also, even with A3, the oxidation rate is about 40% at 200 to 300°C.

Therefore, a sufficient oxidation rate cannot be obtained at temperatures above 300°C, resulting in
It can be seen that temperatures of 100 to 250°C are particularly preferable for those with a temperature of 162 to 162.

In this way, carbon monoxide in the sintering exhaust gas is oxidized in the carbon monoxide oxidation layer 25, but this exhaust gas is heated to a predetermined temperature in the heating furnace 27 through the heat exchanger 26, and after adding ammonia 28, it is denitrified. After denitration in the reaction layer 29, the heat exchanger 2
6 and is discharged to the outside.

As described above, in the present invention, carbon monoxide is oxidized before denitrification, and the heat of oxidation is directly used for the denitrification reaction, so that the efficiency of using the heat of oxidation can be improved and fuel costs can be saved.

Moreover, since manganese ore is used as a reaction catalyst, it is inexpensive and has remarkable effects such as being able to be used effectively as a resource in steel plants even if the activity decreases.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams showing the different denitrification methods previously proposed, Figure 3 is a block diagram showing the denitrification method according to the present invention, and Figure 4 is a block diagram showing the denitrification method according to the present invention. FIG. 5 is a characteristic diagram showing the relationship between the average temperature of inflowing exhaust gas and the oxidation rate of carbon monoxide, and FIG. 5 is a characteristic diagram showing the relationship between the oxidation rate of carbon monoxide and the rising temperature of the exhaust gas. 21... Heat exchanger, 22... Desulfurizer,
23... Wet type dust collector, 24... Booster, 25... Carbon monoxide oxidation layer, 26...
... Heat exchanger, 27 ... Heating furnace, 28 ...
... Ammonia, 29 ... Denitrification reaction layer.

Claims (1)

[Claims] 1. Carbon monoxide gas coexisting in the sintering furnace exhaust gas is
A method for denitrating sintering furnace exhaust gas, which comprises oxidizing the exhaust gas using manganese ore as a catalyst at a temperature of 0.degree. C. or lower, and then denitrating the exhaust gas. 2 The oxidation temperature conditions for carbon monoxide gas are 100 to 250
The method for denitrating sintering furnace exhaust gas according to claim 1, wherein the temperature is 0.degree.