JPS6330056B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for denitrating sintering exhaust gas (exhaust gas generated in the process of manufacturing sintered ore), etc. by oxidizing carbon monoxide contained in the exhaust gas using a catalyst and raising the temperature of the exhaust gas. When denitrating the sintering exhaust gas, it is necessary to heat the sintering exhaust gas to the reaction temperature by burning M gas or the like. On the other hand, a method has been proposed that focuses on unburned carbon monoxide contained in sintering exhaust gas and burns it to raise the temperature. In this method, exhaust gas is passed through a rotary regenerative heat exchanger incorporating a carbon monoxide oxidation catalyst to oxidize carbon monoxide, and the exhaust gas is heated by the heat of oxidation, thereby reducing the basic unit of M gas. This is a method that allows long-term operation by regenerating the catalyst when the lowered and heated gas returns to the heat exchanger (Japanese Patent Application Laid-Open No. 168827-1982). However, in this method, the heating temperature changes when the concentration of carbon monoxide in the exhaust gas changes. If the heating temperature is too high, there is a risk of equipment destruction or a decrease in the denitrification rate, while if the temperature is too low, it may become impossible to regenerate the catalyst. In order to solve this problem, various temperature control methods have been proposed in the past. For example, as shown in FIG. 1, exhaust gas 1 containing carbon monoxide is transferred to a heat exchanger 2,
When the exhaust gas is denitrified by sequentially passing through the catalyst 3, blower 4, denitrification reactor 5, and the heat exchanger 2, there is a method in which a water spray cooling device 6 is provided before and after the catalyst 3 to cool the exhaust gas by spraying water or the like. . However, this method
There are problems such as clogging of the water spray nozzle and condensation, and there are also problems in terms of effective use of heat since it is cooled. Another method is to connect the bypass line 7 to the catalyst 3.
There is a method of controlling this amount of bypass by providing a bypass amount (Japanese Patent Application Laid-open Nos. 151558-1982, 37035-1980, 40420-1980). However, with this method, some of the carbon monoxide is bypassed and is not oxidized, so there is a problem in making effective use of heat.Furthermore, the exhaust gas after treatment contains carbon monoxide, so it is important to prevent pollution. There's a problem. Furthermore, if the temperature difference before and after the catalyst is small, the bypass amount will be large and the equipment cost will be high. The present invention was made in view of the above circumstances, and
The purpose is to provide a method for oxidizing carbon monoxide in exhaust gas, which can control the temperature increase to a constant temperature without impairing the heat utilization efficiency of exhaust gas. That is, the present invention passes exhaust gas containing carbon monoxide through a rotary regenerative heat exchanger incorporating a carbon monoxide oxidation catalyst to raise the temperature by oxidizing carbon monoxide, and then passes it through a denitrification reactor to denitrify the gas. Then, when the denitrified exhaust gas is passed through the heat exchanger to regenerate the catalyst, an outgoing bypass passage is provided for the exhaust gas containing carbon monoxide to bypass the rotary regenerative heat exchanger and the catalyst, and the denitrified exhaust gas is is provided with a return bypass path for bypassing the heat exchanger and the catalyst, and a portion of the exhaust gas is bypassed to one or both of the bypass paths based on the carbon monoxide concentration in the exhaust gas and the exhaust gas temperature. The bypass flow rate is adjusted to control the temperature of the exhaust gas flowing into the denitrification reactor, the heating temperature of the exhaust gas flowing into the heat exchanger after denitrification, and the carbon monoxide concentration in the treated exhaust gas. . The present invention will be explained below with reference to the embodiment shown in FIG. A blower 12 blows the exhaust gas 11 containing carbon monoxide.
is guided to the rotary regenerative heat exchanger 13 by suction. This heat exchanger 13 incorporates a carbon monoxide oxidation catalyst 14 such as an iron ore catalyst, which oxidizes carbon monoxide in the exhaust gas 11 to raise the temperature of the exhaust gas 11.
The heated exhaust gas 11 is led to the denitrification reactor 15 to be denitrated, and then led to the heat exchanger 13 to be heated to the catalyst 14.
is regenerated and exhausted as clean gas 16. In this denitrification system, if the denitrification reaction temperature and catalyst regeneration temperature are insufficient, the temperature raising device 17 may be used as an auxiliary device. Therefore, the present invention provides bypass paths 18 and 19 that bypass both the heat exchanger 13 and the catalyst 14 on the outward and return paths of the exhaust gas 11, respectively, and controls the flow rate of the exhaust gas flowing through the bypass paths 18 and 19 using the bypass valves 20 and 21. By controlling the heating temperature, the heating temperature is controlled. In this case, either a method of bypass-circulating the exhaust gas only through the forward bypass passage 18 or a method of bypass-circulating the exhaust gas through both the reciprocating bypass passages 18 and 19 is effective. Note that in the case of only the forward bypass path 18, the ratio of the amount of low temperature gas to the amount of high temperature gas to the heat exchanger 13 changes, and the heat exchanger efficiency changes. Alternatively, the bypass flow rate may be controlled by measuring the carbon monoxide concentration, exhaust gas temperature, and flow rate, and automatically controlling the bypass valves 20 and 21 based on the resulting numerical data alone or in combination. However, according to this lever method, the exhaust gas 11 comes into contact with the catalyst 14 installed in the heat exchanger 13 again on the return trip, so the temperature rises on the return trip as well, increasing the final temperature of the exhaust gas, which increases the effective use of heat. It is advantageous from Furthermore, since the low temperature gas before the heat exchanger 13 is bypassed, a small amount of bypass flow is required, and equipment costs can be reduced. Furthermore, this method is highly reliable as it is free from problems such as nozzle clogging and dew condensation unlike water spray cooling. Next, one example of temperature balance in the method of the present invention will be explained. Using the system shown in Figure 3, calculate the temperature at point F.
Under the condition of keeping it constant at 430℃, the gas inflow temperature at point A is 130℃, and the temperature rise at the catalyst is
Assuming that the temperature was 100°C, the temperature etc. of each point (A to I) was investigated. This result is shown in Table 1 (No. 1, No. 2)
Shown below. In order to compare with this, the temperature etc. of each point (A to I) were similarly investigated for the one in FIG. 1 (No. 3) and the one in FIG. 2 (No. 4, No. 5). The results are also listed in Table 1. Here, No. 1 is, in the case of reciprocating bypass flow control,
No. 2 shows the case of flow control only for the forward bypass. Further, No. 5 shows a case in which a catalyst is also provided on the return trip (indicated by a broken line) in the case of FIG. 2. The reason why the temperature at point F is kept constant at 430°C is to take into account the heat resistance of the equipment, ensuring the denitrification reaction temperature, and the catalyst regeneration temperature.

【table】

[Table] * Heat exchanger efficiency tends to change like this when the amount of low-temperature gas flowing in is smaller than the amount of high-temperature gas. (Since only the forward direction is bypassed, the amount of low-temperature gas is relatively small.)
As is clear from the above table, the final exhaust gas temperature (point I) of the example is lower than that of the comparative example (conventional method).
It can be seen that the temperature is 30 to 40°C higher, which is advantageous in effectively utilizing waste heat. Furthermore, the bypass flow rate is less than half that of the case where only the catalyst is bypassed. Also, the amount of carbon monoxide released into the atmosphere is reduced, especially in No.
1 becomes zero. Note that in Table 1, when the carbon monoxide concentration changes, the temperature rise due to the catalyst changes. For this reason F
In order to maintain the temperature at the point at 430°C, the amount of reciprocal bypass is changed, but the same tendency as above occurs even in the changed state. As described above, according to the present invention, there is a remarkable effect that the temperature increase of exhaust gas can be controlled while effectively utilizing exhaust heat.

[Brief explanation of the drawing]

1 and 2 are system diagrams of a conventional method for oxidizing carbon monoxide in exhaust gas, and FIG. 3 is a system diagram of a method for oxidizing carbon monoxide in exhaust gas, showing an embodiment of the present invention. 11... Exhaust gas, 12... Blower, 13... Rotating regenerative heat exchanger, 14... Catalyst, 15... Denitration reactor,
16... Clean gas, 17... Temperature raising device, 18... Outbound bypass path, 19... Return bypass path, 20, 21... Bypass valve.

Claims (1)

[Claims] 1 Exhaust gas containing carbon monoxide is passed through a rotary regenerative heat exchanger incorporating a carbon monoxide oxidation catalyst to raise the temperature by oxidizing carbon monoxide, and then passed through a denitrification reactor to be denitrified. When the exhaust gas is passed through the heat exchanger to regenerate the catalyst, the exhaust gas containing carbon monoxide bypasses the rotary regenerative heat exchanger and the catalyst, and the exhaust gas after denitration is passed through the heat exchanger. and a return bypass path for bypassing the catalyst and the catalyst, and a part of the exhaust gas is bypassed to one or both of the bypass paths based on the measured carbon monoxide concentration in the exhaust gas and the exhaust gas temperature, and the bypass path is An exhaust gas characterized in that the temperature of the exhaust gas flowing into the denitrification reactor, the heating temperature of the exhaust gas flowing into the heat exchanger after denitrification, and the carbon monoxide concentration in the treated exhaust gas are controlled by adjusting the flow rate. Carbon monoxide oxidation method.