JPS5841894B2 - Method for denitrifying sintering exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When denitrating the sintering exhaust gas, the present invention oxidizes CO contained in the sintering exhaust gas using a denitration catalyst, and uses the heat obtained thereby to oxidize the CO contained in the sintering exhaust gas. The present invention relates to a method for denitrating sintering exhaust gas, which reduces the amount of fuel required for a heating furnace used to raise the temperature of the sintering exhaust gas to the denitrification reaction temperature.

As a denitration method for sintering exhaust gas, the sintering exhaust gas is passed through the low-temperature side of a heat exchanger, then passed through a temperature raising furnace to raise the temperature to the temperature required for denitration, and then heated in a reactor equipped with a denitration catalyst. A method is known in which the nitrogen is removed by catalytic reduction with ammonia and then passed through the high temperature side of the heat exchanger.

However, the amount of sintering exhaust gas to be processed is large, so in order to raise the temperature of the sintering exhaust gas to the denitrification reaction temperature, it is necessary to
Huge amounts of fuel must be consumed.

For this reason, CO in the sintering exhaust gas is catalytically oxidized and burned in a reactor separate from that for denitrification, and the heat obtained at this time is used as part of the heat source to obtain the denitrification reaction temperature. Therefore, a method has been proposed to reduce the amount of fuel used to obtain the denitrification reaction temperature, but this method requires the use of extremely expensive platinum as a catalyst for denitrification, and is not suitable for industrial use. No catalyst has yet been discovered, and even if one were discovered, another reactor would have to be installed for this purpose (CO oxidation), and the catalyst would also be very expensive. is expected.

Therefore, the present inventors conducted research to solve the above problems, and as a result, the sintering exhaust gas was passed through the low-temperature side of the heat exchanger, and then passed through a temperature raising furnace to raise the temperature necessary for denitrification. In the denitrification method of sintering exhaust gas, the temperature is raised to 100%, and then denitrified by catalytic reduction with ammonia in a reactor having a denitrification catalyst, the sintered exhaust gas is passed through the high temperature side of the heat exchanger, wherein the catalyst has crystals in the X-ray diffraction line. α-Fe2 with 110 plane peak intensity/104 plane peak intensity of lattice of 0.6 or more
03, and if the heat obtained by bringing CO in the pre-sintering exhaust gas into contact with the α-Fe203 and oxidizing it is applied to raise the temperature of the sintering exhaust gas, the α-Fe203 will produce ammonia NOx due to
reduction and oxidation of CO can be carried out simultaneously,
At that time, since the CO oxidation rate of α-nee Fe2O3 decreases over time during use, multiple reactors are connected in parallel.
By making it possible to selectively use a reactor and replacing a catalyst with a reduced CO oxidation rate as appropriate, heat from CO oxidation can be obtained stably, there is no need to newly install another reactor, and the above-mentioned It was discovered that the amount of fuel used in the heating furnace can be reduced by an amount equivalent to the amount of heat obtained by CO oxidation.

This invention has been made based on the above findings, and will be described below based on embodiments with reference to the drawings.

FIG. 1 is a schematic diagram of the denitrification equipment for sintering exhaust gas,
As shown in the figure, the sintering exhaust gas that has passed through the low-temperature side of the heat exchanger 1 and has been heated passes through the booster 2 and then the temperature-raising furnace 3, where it is mixed with ammonia and connected in parallel. The heat exchanger 1 passes through a plurality of reactors 4 in which
It is designed to pass through the high temperature side of the

The reactor 4 contains α-Fe203 as a denitrification catalyst, and the peak intensity of the 110 plane of the crystal lattice plane in the X-ray diffraction line/the peak intensity of the 104 plane is 0.6 or more. Below, NOx in the sintering exhaust gas is reduced by ammonia, and at the same time, CO, which is normally contained in the sintering exhaust gas at about 1% by volume, is oxidized by the catalyst.

The catalyst mentioned above was used as a denitrification catalyst.
This is because iron oxide containing Fe203 can be obtained in large quantities at low cost, and when the aforementioned 110 plane peak intensity/104 plane peak intensity is 0.6 or more, an extremely excellent denitrification rate can be obtained.

Examples of the iron oxide containing α-Fe203 include various iron ores, dust and scale generated in steel mills, and iron oxide recovered from sintered slag pickling solution.

As mentioned above, such a material is extremely inexpensive and can be used as a raw material for iron manufacturing after denitrification treatment, so the denitrification cost can be kept extremely low even if it is frequently replaced and used for a short period of time as described later.

Then, in the reactor 4, CO in the sintering exhaust gas is
The heat obtained by the oxidation of the sintered gas by the catalyst increases the temperature of the sintering exhaust gas.

Therefore, in the temperature rising furnace 3, the sintering exhaust gas temperature at the inlet of the reactor 4 is at least as low as the denitrification reaction temperature.
Combustion is controlled so that the temperature is obtained by subtracting the temperature increased by the heat obtained by CO oxidation in the reactor 4.

A reactor (using iron ore as a catalyst) is equipped with denitrification equipment configured like this.

The solid line in Figure 2 shows the relationship between the SV and the denitrification reaction rate of the sintering exhaust gas in the reactor whose inlet temperature was 340°C (for comparison, CO oxidation was not caused). The dotted line in the figure shows the relationship between the SV and the denitration reaction rate when denitration was performed under the same conditions as described above except that a conventional catalyst was used.

The same applies to the dotted line in Figure 3. ). Further, FIG. 3 shows the relationship between the sintering exhaust gas temperature at the inlet of the reactor and the denitrification reaction rate in the reactor when the SV of the sintering exhaust gas in the reactor was maintained at 3000 Hr-1.

Furthermore, when used in a reactor as a denitrification catalyst,
The initial oxidation rate of CO in the sintering exhaust gas (SV: 3000 Hr) of iron ore (reactor population CO concentration: 1%),
The relationship between the sintering exhaust gas and the reactor inlet temperature is shown in Figure 4. Figure 5 shows the oxidation rate (solid line) and denitration rate (dotted line) of CO (concentration at reactor inlet: 1%) over time, as well as the oxidation rate over time (dotted line) of CO (reactor inlet concentration: 1%). The rising temperatures of the sintering exhaust gas are shown below.

In other words, the temperature rise of the sintering exhaust gas in the reactor is Day 1: 46℃, 2nd day = 34℃, 3rd day = 28℃, 4th day: 25℃, Met.

In this way, the CO oxidation rate of iron ore decreases over time as denitrification occurs, and the rising temperature of the sintering exhaust gas in the reactor also decreases accordingly (note that at the beginning of denitrification, the 5th
As shown in the figure, the temperature inside the reactor is high due to the high CO oxidation rate, and therefore the denitrification rate shows a high value at the beginning of denitrification, but as the CO oxidation rate decreases, the temperature in the reactor increases. As you can see, it converges to about 70%.

As described above, the denitrification rate of iron ore does not decrease even with long-term use, but the CO oxidation rate decreases, so it must be replaced after short-term use in order to recover heat through CO oxidation.

). Therefore, if a plurality of reactors 4 connected in parallel are selectively used, and for example there are four reactors 4 as shown in Fig. 6, three reactors are always operated and the other one is stopped. The reactors will be used for 3 days, and on the 4th day, the reactors will be stopped and the other reactors that have been stopped will be restarted. Do it like this.

By doing this, of the three reactors in operation, one reactor is operated on the first day after the start of operation, and the other reactor is operated on the second day after the start of operation.
One reactor is on the third day, so for example, if the S in each reactor is 3500 Hr' and the inlet temperature is 340°C, the treated gas from three reactors will be The temperature in the mixing section becomes as shown in FIG. 7, and a stable temperature can be maintained.

Furthermore, by operating the three units in parallel, energy savings of about 10% could be achieved.

As mentioned above, if the reactor population temperature is the same,
The higher the value of S■, the less the temperature rise of the sintering exhaust gas within the reactor.

Therefore, when trying to increase the temperature rise of the sintering exhaust gas in the reactor, when trying to increase S The reactor inlet temperature may be lowered.

As explained above, in this invention, a specific α-Fe203 is used as a denitrification catalyst, and a plurality of reactors are connected in parallel so that the reactors can be appropriately selected and used. Since the reduction of NOx in the reactor with ammonia and the oxidation of CO in the same gas are simultaneously and stably carried out, the amount of fuel for the heating furnace can be reduced by an amount equivalent to the amount of heat obtained by the CO oxidation. Moreover, since the catalyst can be provided at low cost, denitration can be performed at low cost.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a sintering exhaust gas denitrification equipment to which the present invention is applied, Figure 2 is a diagram showing the relationship between S of sintering exhaust gas in a reactor and the denitration reaction rate, and Figure 3 is a diagram showing the relationship between the reactor and the denitrification reaction rate. A diagram showing the relationship between the sintering exhaust gas temperature at the inlet and its denitrification reaction rate, FIG. 4 is a reactor. The relationship between the initial oxidation rate of CO in the iron ore sintering exhaust gas and the reactor inlet temperature of the same gas is shown in Figure 5.
The figure shows the CO oxidation rate and denitrification rate of the same iron ore over time, Figure 61 is a diagram of the parallel connection of reactors, and Figure 7 shows the change in outlet temperature of four reactors connected in parallel. It is a diagram. 1... Heat exchanger, 2... Booster, 3.
...Temperature rising furnace, 4...Reactor.

Claims (1)

[Claims] 1. The sintering exhaust gas is heated to the temperature required for denitrification by passing it through the low-temperature side of a heat exchanger and then passing through a heating furnace, and then heated in a reactor having a denitrification catalyst. In the denitrification method of sintering exhaust gas, which is denitrated by catalytic reduction with ammonia and then passed through the high temperature side of the heat exchanger, the catalyst has a crystal lattice peak intensity of 110 plane/104 plane peak intensity of 0.6 in an X-ray diffraction line. α−F e
20 g, and a plurality of the reactors are connected in parallel between the temperature raising furnace and the low temperature side of the heat exchanger,
The plurality of reactors are selectively used to bring CO in the sintering exhaust gas into contact with the α-Fe203 to oxidize it, and the heat obtained thereby is applied to raise the temperature of the sintering exhaust gas. Characteristic denitrification method for sintering exhaust gas.