JPS6221703A - Nitric acid plant having exhaust gas denitrizer - Google Patents

Abstract

PURPOSE:To carry out the denitration reaction at optimum gas temperature, by placing two-stage exhaust gas heater after an ammonia oxidizer, and attaching an ammonia catalytic reduction denitration apparatus to the outlet channel of the former stage heater. CONSTITUTION:NH3 evaporated by the evaporator 1 is mixed with air supplied through the compressor 3 and the air heater 5, and oxidized in the oxidizer 3. The produced nitrogen oxide is passed through the heater 5, the first exhaust gas heater 7A and the second exhaust gas heater 7B to effect the heat-exchange, condensed in a condenser cooler 9, introduced into the absorption column 11, and absorbed in water to obtain nitric acid. The exhaust gas exhausted from the absorption column 11 is introduced into the heater 7A through the line 15 to effect the heat-exchange and to control the gas temperature to 310-350 deg.C and gas pressure to 6-7kg/cm<2>G at the outlet-side line D. The conditioned gas is supplied to the ammonia catalytic reduction denitration apparatus, denitrated by ammonia reduction, and supplied through the heater 7B to the steam turbine 13 to recover the energy.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a nitric acid plant having a flue gas denitrification device, and more specifically to a method for catalytic reduction of nitrogen oxides in flue gas discharged from a nitric acid plant in the presence of ammonia. This invention relates to a VJ acid plant having a flue gas denitrification device.

(Prior art) When using a flue gas denitrification device using the dry ammonia catalytic reduction method to denitrify flue gas discharged from a nitric acid plant, the equipment configuration of the conventional nitric acid plant does not have a gas temperature zone suitable for the denitrification reaction. For this reason, there is a problem that the denitrification device does not function sufficiently.

That is, FIG. 2 is a flow sheet showing the schematic configuration of a conventional nitric acid plant. Ammonia is vaporized in the evaporator 1, oxidized in the oxidizer 3 to produce nitrogen oxide, and the air heater 5 and After exchanging heat with exhaust gas heating I51, it is condensed in a condensing cooler 9, and nitrogen oxide is absorbed into water in an absorption tower 11 to obtain nitric acid.The oxidizer 3 is pressurized with a compressor 6. After the air is preheated by the air heater 5, it is mixed with ammonia from the generator 1 and introduced into the oxidizer 3.The exhaust gas discharged from the absorption tower 11 passes through the exhaust gas heater 7. After being heated, the energy is recovered by the steam turbine 13 and discharged as exhaust gas.The ammonia catalytic reduction device has an ammonia introducing means and a part filled with a nitrogen oxide reduction catalyst such as vanadium or titanium. It is installed in the exhaust gas pipe 15 from the tower 11, but when installed at position A in front of the exhaust gas heater 7, the exhaust gas temperature is 20
~3Q'C1 pressure is as low as 6-7 kg/cIIIG, and a new temperature raising device is required. Moreover, if it is installed at the outlet position B of the exhaust gas heater 7, the temperature will be too high at 500-550"C (pressure 6-7 kg/col G), so the reaction rate will decrease. On the other hand, at the outlet 1c of the turbine 13, the reaction rate will decrease. If provided, exhaust gas temperature 220-260℃, pressure 0.0
The temperature is too low at 2kg/cot G. In such conventional nitric acid plants, the temperature at the set position of the denitrification device is either too low or too high to perform ammonia reduction denitrification, so there is a problem in that a sufficient denitrification rate cannot be obtained.

(Problems to be Solved by the Invention) An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a nitric acid plant having a suitable equipment configuration for performing ammonia reduction and denitrification in the nitric acid plant. .

(Means for Solving the Problems) The present invention provides a nitric acid plant that has an exhaust gas heater downstream of an ammonia oxidizer and an exhaust gas denitrification device using ammonia catalytic reduction in the exhaust gas pipe of an absorption tower. The present invention is characterized in that exhaust gas heaters are provided in two stages, and an ammonia catalytic reduction and denitrification device is provided on the exit side of the exhaust gas pipe line passing through the first stage exhaust gas heater.

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

FIG. 1 is a flow sheet showing the equipment configuration of the nitric acid plant of the present invention. Evaporator l in this nitric acid plant,
Oxidizer 3, air heater 5, condensing cooler 9 and absorption tower 1
1 is a conventionally known one. For example, as the oxidizer 3, a platinum mesh catalyst or one filled with a catalyst mainly composed of iron oxide is used. This plant differs from the conventional system shown in FIG. The gas containing the exhaust gas passes through the first exhaust gas heaters 7A and 7B to exchange heat with the exhaust gas passing through the exhaust gas pipe line 15, and an ammonia catalytic reduction denitrification device is provided in the outlet pipe line of the first exhaust gas heater 7A. . However, the total capacity of the first and second exhaust gas heaters 7A and 7B is approximately equal to that of the original exhaust gas heater 7. By providing the first and second exhaust gas heaters 7A and 7B in this manner, the gas temperature in the outlet side pipe line to the heater 7 can be adjusted to the optimal temperature and pressure for the denitrification reaction, for example, 310 to 3
It can be set at 50°C and the pressure is 6 to 7 kg/cj Q, and the function of the denitrification reactor installed there can be maximized.

(Example) As shown in Figure 1, two exhaust gas heaters of a nitric acid plant were installed.
An ammonia injection pipe was provided on the exhaust gas outlet side of the first exhaust gas heater 7A, and a denitrification reactor was provided downstream thereof. The denitration reactor used was one filled with a TiO2 base metal catalyst as a catalyst. The temperature of the exhaust gas introduced into the denitrification reactor is 310-350℃, and the pressure is 6-7K.
g/cIIIG. As a result of the denitrification experiment, the denitrification rate was 9.
It was 8%.

For comparison, a denitrification reactor similar to that shown in Fig. 1 was installed in the outlet side pipe B of the exhaust gas heater 7 shown in Fig. 2, and a denitrification experiment was conducted. 7
kg/col G, and the denitrification rate was 50%.

(Effects of the Invention) According to the present invention, the exhaust gas heater of the nitric acid plant has two stages, and the denitrification reaction can be performed at the optimal gas temperature by providing the denitrification reactor in the outlet pipe line in the previous stage. Furthermore, since the pressure is high, the amount of catalyst used can be reduced, and the diameter of the reaction column can also be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic flow of a nitric acid plant to which the present invention is applied, and FIG. 2 is a diagram showing a schematic flow of a conventional nitric acid plant. Agent Patent Attorney Takeshi Kawakita HNO3 HNO3

Claims (1)

[Claims] (1) Having an exhaust gas heater downstream of the ammonia oxidizer,
In a nitric acid plant that has an exhaust gas denitrification device using ammonia catalytic reduction in the exhaust gas pipe of the absorption tower, exhaust gas heaters are installed in two stages, and the ammonia catalytic reduction denitrification device is installed on the exit side of the exhaust gas pipe that passes through the first stage exhaust gas heater. A nitric acid plant having a flue gas denitrification device, characterized in that the device is provided with a flue gas denitrification device.