JPH022607B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a denitrification treatment apparatus, and particularly to a denitrification treatment apparatus that prevents temperature rise due to reaction heat when the concentration of nitrogen oxides (NO _x ) in the gas to be treated is high.

As a conventional dry flue gas denitrification system, the ammonia catalytic reduction method is widely known, and has many achievements in removing _NOx from boiler flue gas, for example. The _NOx concentration in this boiler flue gas is about several hundred ppm,
Temperature increases due to the heat of reaction can usually be ignored. However, in cases such as the removal of _NOx from dissolved waste gas from spent nuclear fuel reprocessing, _NOx
The concentration changes over time in the range from about 1000 ppm to about 8%, and the gas temperature rise due to reaction heat is expected to range from about 10°C to 800°C. For this reason,
Conventional through-flow type denitrification equipment has the problem of temperature rise in the catalyst layer, for example, when the temperature exceeds 400°C, the porous surface of the catalyst becomes clogged, resulting in a reduction in catalyst performance. Measures such as cooling the inside of the catalyst device with water have been considered in response to the temperature increase in the catalyst layer, but this method is not desirable because the internal structure of the device becomes complicated.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to suppress the temperature rise due to reaction heat in the catalyst layer of a denitrification catalyst device for removing _NOx from spent nuclear fuel reprocessing waste gas, and to achieve a suitable catalytic reaction. It is an object of the present invention to provide a denitrification treatment device that is controlled within a temperature range.

The present invention relates to a denitrification catalyst device that denitrates gas to be treated with a nitrogen oxide concentration in the range of 0.1 to 8%, which is generated during spent nuclear fuel dissolution and reprocessing, by an ammonia catalytic reduction method, and A gas preheater and a gas cooler provided on the gas inlet side and the gas outlet side, respectively, an ammonia injection means provided in the gas flow path between the used gas preheater and the denitrification catalyst device, and A processing gas recirculation piping system that recirculates the processing gas to the inlet side of the gas preheater, an inert gas supply means that introduces an inert gas from the outside into the processing gas recirculation piping system, and a denitrification catalyst device. and a gas circulation flow rate control device that controls the amount of gas circulated through the treated gas circulation piping system so that the temperature of the catalyst layer is within a certain range, and the temperature of the denitrification catalyst device is controlled by a gas preheater and a cooler. A denitrification treatment device used for denitrification of spent nuclear fuel reprocessing waste gas, characterized in that it is heated when there is a shortage of denitrification reactor and cooled when the temperature of the denitrification reactor rises above a predetermined value due to the denitrification reaction. be.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 2 is a system diagram of a denitrification catalyst device showing one embodiment of the present invention. In the figure, this device includes a preheater 1 that preheats exhaust gas in an exhaust gas supply line 7 to a predetermined temperature, and a catalyst tower 2 filled with a denitrification catalyst, such as a catalyst supporting an oxide of a transition metal such as molybdenum or vanadium. , a cooler 4 and an exhaust blower 10 provided on the outlet side of the catalyst tower 2, a line 6 and a blower 5 for recirculating the outlet exhaust gas of the catalyst tower 2 to the entrance side, and a An outside air (inert gas) supply line 12 and an air supply blower 8 provided on the inlet side, a three-way control valve 11 that adjusts the amount of recirculated gas and the amount of outside air supplied, and a thermometer that measures the temperature of the catalyst layer of the catalyst tower 2. 2A control system 1 for detecting and adjusting the opening degree of the three-way control valve 11;
It consists of 3. The gas to be treated is in the ventilation line 7.
If the exhaust gas temperature is below a predetermined temperature, the exhaust gas enters the preheater 1, where it is preheated, and then ammonia is injected and mixed from the ammonia injection line 3, and introduced into the catalyst tower 2. The treated gas denitrified in the catalyst tower passes through the cooler 4, and part of it is discharged to the outside by the exhaust blower 10, but the other part is sent back to the inlet side of the catalyst tower 2 ( It is returned to the preheater 1). At this time, an appropriate amount of ammonia is injected from the ammonia injection line 3 at a stoichiometric ratio or higher relative to the amount of _NOx contained in the gas to be treated that has been preheated by the preheater 1.
While passing through the catalyst tower 2 together with the gas to be treated, _NOx in the exhaust gas is catalytically reduced and decomposed into nitrogen and water. After the treated gas leaving the catalyst tower 2 is cooled by the temperature rise in the cooler 4 and the catalyst tower 2, a part of it passes through the recirculation line 6 to the preheater 11.
is recirculated to the inlet side. When circulating exhaust gas from other systems when the amount of exhaust gas circulation is insufficient or when the _NOx concentration is particularly high at the start of operation, adjust the three-way control valve 11 and introduce inert gas from line 12. Bye. The temperature of the catalyst layer of the catalyst tower 2 is adjusted by adjusting the opening degree of the three-way control valve 13 so that the temperature detected by the catalyst layer thermometer 2A is within a constant temperature range. By recirculating the exhaust gas (or inert gas) in an amount corresponding to the temperature of the thermometer 2A, the _NOx concentration in the gas to be treated that is supplied to the catalyst tower 2 is diluted, and the rise in reaction temperature is suppressed. Ru. For example, when _{the NO} Rise to about 100℃
can be suppressed to Furthermore, if the inlet temperature of the catalyst tower (denitrification catalyst device) 2 drops too much due to exhaust gas circulation, it is of course possible to heat it with the preheater 1. Further, as described above, the cooler 4 at the outlet of the catalyst tower 2 is cooled by the temperature rise due to the reaction heat of the catalyst tower 2, and temperature adjustment that cannot be controlled by the exhaust gas circulation alone is performed.

In the above embodiment, the thermometer 2A and its control line 13 are for automating temperature control; of course, such a control line is not provided, and the valves are manually adjusted as appropriate according to the temperature rise. Good too.

In addition, as an operating method for recirculating exhaust gas,
There are cases where it is always recirculated and cases where it is only recirculated when _{the NO} It is necessary to make a decision on the safe side regarding the relationship between removal efficiency and SV value, as well as the relationship between gas linear velocity and which design should be adopted.

According to the above embodiment, an appropriate amount of exhaust gas is recirculated according to the temperature of the catalyst bed of the catalyst tower 2, and the gas temperature is adjusted by the gas preheater and cooler provided at the inlet and outlet sides of the denitrification catalyst device. By doing so,
By doing so, the temperature rise of the catalyst layer is suppressed,
It is possible to maintain a predetermined temperature and maintain high catalyst performance.

As described above, according to the present invention, by recirculating the denitrified exhaust gas, it is possible to control the temperature rise due to the reaction heat of the catalyst layer to below a certain value without providing a complicated cooling means to the catalyst device.

[Brief explanation of drawings]

Figure 1 is a system diagram of a conventional flue gas denitrification system;
The figure is a system diagram of a flue gas denitrification device showing one embodiment of the present invention. 1... Preheater, 2... Catalyst tower, 2A... Thermometer, 3... Ammonia injection line, 4... Cooler, 5... Recirculation blower, 6... Recirculation line,
7... Ventilation line, 8... Air supply blower, 10...
Exhaust blower, 11...3-way control valve.

Claims (1)

[Claims] 1. A denitrification catalyst device that denitrates gas to be treated with a nitrogen oxide concentration in the range of 0.1 to 8% generated during spent nuclear fuel dissolution and reprocessing by an ammonia catalytic reduction method, and A gas preheater and a gas cooler each provided on the outlet side, an ammonia injection means provided in a gas flow path between the gas preheater and the denitrification catalyst device, and a treated gas exiting the gas cooler. a process gas recirculation piping system that recirculates the gas to the inlet side of the gas preheater;
an inert gas supply means for introducing an inert gas into the treated gas recirculation piping system from the outside; and a gas circulating in the treated gas circulation piping system so that the temperature of the catalyst layer of the denitrification catalyst device is within a certain range. and a gas circulation flow rate control device for controlling the amount, and the gas preheater and cooler heat the denitrification catalyst device when the temperature is insufficient, and raise the temperature of the denitrification reactor to a predetermined value or higher by the denitrification reaction. A denitrification treatment device used for denitrification of spent nuclear fuel reprocessing waste gas, characterized in that it is cooled when it is heated.