JPH01232297A - Retreated off-gas treatment equipment - Google Patents

Abstract

PURPOSE:To hold concentration of recovered nitric acid constant by grasping the amount of NOX removed from off gas by detecting the flow rate of supply oxygen, the flow rate of oxygen at the exit of an absorption system, and the flow rate of NOX at the exit of the suction system, and controlling the flow rate of supply absorp tion liquid, etc. CONSTITUTION:The reprocessed off gas processor is equipped with an oxygen supply flow rate detector 31 between a dissolving tank 3 and an NOX suction tower 6. Further, an oxygen flow rate detector 32 and an NOX detector 35 are provided in the exit gas line of the absorption tower 6, and an absorption liquid supply pump 43 and an absorption liquid drain pump 44 are provided with a liquid flow rate controller 33. In this constitution, the absorption amount of NOX absorbed by the absorption tower 6 is estimated by the detector 31 provided on the entrance side of the absorption tower 6 and the detectors 32 and detector 35 provided on the exit side of the absorption tower 6 according to variation in the concentration of NOX produced in the dissolving tank 3. The absorption liquid supply pump 43 which sends the absorption liquid from the absorption liquid tank 42 and the absorption liquid drain pump 44 are controlled according to the estimated value. Consequently, the recovered nitric acid concentration is held constant.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a reprocessing off-gas processing device, and in particular, to a reprocessing off-gas treatment device, and in particular, a method for treating recovered nitric acid recovered in an iodine re-entering column in an off-gas processing facility from a nuclear fuel reprocessing plant, etc. The present invention relates to a reprocessing off-gas processing apparatus suitable for keeping the concentration of recovered nitric acid returned to the dissolving tank constant regardless of NOx fluctuations in the off-gas in an apparatus equipped with a line returning to the dissolving tank for reuse.

[Conventional technology]

At nuclear fuel reprocessing plants, spent fuel is dissolved in concentrated nitric acid to recover substances such as uranium and platonium that can be reused as fuel. Off-gas, which is the main component, is generated, and volatile FP (fission products) such as iodine in the spent nuclear fuel is also released together with this gas.

FIG. 6 is a system diagram of a conventional off-gas treatment apparatus of this type. This device consists of a dissolution tank 3 for dissolving spent fuel with concentrated nitric acid, an iodine expulsion tank 4 for expelling iodine dissolved in the solution in the dissolution tank 3, and an iodine expulsion tank 4 for expelling iodine from the dissolution tank 3 and the iodine expulsion tank. A condenser 5 that condenses most of the water vapor in the generated off-gas, an N08 absorption tower 6 that absorbs and removes NOx in the off-gas, an absorption acid liquid storage tank 7 that stores the absorbed acid liquid from the condenser 5, and an absorption acid liquid. A Tatsumoto re-expelling tower 9 that expels iodine in the absorbed acid liquid from the storage tank 7, a recovered acid liquid storage tank 10 that stores the acid liquid recovered in the iodine re-extracting tower 9, and an adsorbent for removing iodine. Iodine removal tower 1 for adsorption removal
It consists of 3.

The NOx absorption tower 6 is of a tray type, as shown in the detailed cross-sectional view of FIG. It consists of a cooling coil 52 inserted into a shelf 50 to suppress temperature rise and increase NOx absorption drop.

In such an apparatus, the off-gas 18 generated from the dissolution tank 3 and the iodine expulsion tank 4 is sent to the condenser 5, where most of the water vapor is condensed.

This condensate is used as an absorption liquid in the NOo absorption tower 6. The gas from which water vapor has been removed in the condenser 5 is supplied to the lower part of the NOx absorption tower 6, and NOx in the gas is absorbed and removed by the absorption liquid supplied from the upper nozzle of the NOx absorption tower 6. Since a large amount of iodine is mixed in the condensate from the condenser 5 and the absorption acid liquid from the NOxM absorption tower 6, these are stored in the absorption acid liquid storage tank 7 and then transferred to the iodine re-expulsion tower 9. , heated to 80-90°C and N
The iodine is driven out by the two gases. The absorbed acid liquid from which iodine has been removed is stored in the recovered acid liquid storage tank 10, then cooled, the concentration is adjusted in the recovered nitric acid adjustment tank 53 for reuse as a dissolving liquid, and then sent to the dissolution tank 3.

On the other hand, the gas discharged from the Noe absorption tower 6 and the iodine re-expulsion tower 9 was mixed, preheated to 150°C in a preheater 12 to lower the relative humidity in the gas, and filled with an adsorbent. The iodine is sent to the iodine removal column 13, where most of the iodine flowing into the off-gas system is removed. The gas from which iodine has been removed is cooled by a cooler 16, passes through a filter 14, is transferred to the exhaust stack 1 by a blower 15, and is discharged.

[Problem to be solved by the invention]

In the conventional reprocessing off-gas treatment method described above, NO.
In the x absorption tower 6, NOx in the off-gas is removed using nitric acid (
HNOx), and this recovered nitric acid is returned to the dissolution tank 3.
It is used in HNOx in the melting tank 3 is heated to 6 to 7 in order to melt the spent nuclear fuel. It is necessary to set the concentration of N.

However, the spent nuclear fuel supplied to the melting tank 3 is
These include cut fuel rods as shown in Figure 4.
The components are non-uniform at the axial end (section A) and the axial middle section (section B) of the fuel rod.

For this reason, the concentration of NO in the off-gas gas components from the dissolution tank 3 becomes non-uniform, and the concentration of NO in the off-gas gas components from the dissolution tank 3 becomes non-uniform.
HN in the recovered acid solution stored in the recovered acid solution storage tank 10 through
O*fl=degrees fluctuate.

Therefore, conventionally, the concentration of recovered nitric acid returned to the dissolution tank 3 was set at 6 to 7N.
A recovered nitric acid adjustment tank 53 is installed to adjust the amount of nitric acid.

The recovered nitric acid adjustment tank 53 has a relatively large device structure, and the off-gas processing equipment becomes large.

It is an object of the present invention to provide a reprocessing off-gas treatment device that can solve the problems of the prior art described above, keep the concentration of recovered nitric acid constant even when the NOX concentration in the off-gas fluctuates, and omit the recovered nitric acid adjustment tank 53. Our goal is to provide the following.

[Means to solve the problem]

The above object is achieved by controlling the flow rate of the supplied absorption liquid and the flow rate of the extracted absorption liquid according to the amount of NOx removed from the off-gas.

That is, the present invention grasps the amount of NOx removed from the off-gas by detecting the supplied oxygen flow rate, the oxygen flow rate at the absorption system outlet, and the NOx flow rate at the absorption system outlet, and controls the supplied absorption liquid flow rate and the extracted absorption liquid flow rate. By doing so, the concentration of recovered nitric acid is kept constant.

[Effect]

FIG. 2 shows the relationship between the amount of NOx absorbed from the off-gas to the absorption liquid side in the NOx absorption tower and the amount of reduction in oxygen in the gas at the inlet and outlet of the NOx absorption tower. It can be seen from the figure that there is a correlation between the amount of oxygen reduction and the amount of NOX absorption. The reason for this is thought to be as follows.

The absorption rate of NO and NO□, which are the main components of NOx, into the absorption liquid is relatively high for NO2, but negligibly small for NO. Therefore, in order for NO to be absorbed into the liquid, it needs to be oxidized to NO□ according to the following reaction.

NO+ K O2→NO□・・・・・・(1) NO□
The absorption of into the liquid occurs according to the following equation.

2NO□10HzO→HNOz +HNOff・・・・・・
-(2) Here, HNO□ becomes NO again according to the following equation.

3HNO□→HNOx+2NO10Hz O・・・・・・
(3) This NO becomes NO□ again according to reaction formula (1), and is absorbed into the liquid again.

As described above, in the absorption of N08, oxygen is necessary for the oxidation of NO, and it is thought that oxidizing No promotes the absorption of NOx.

From this, it can be seen that there is a correlation between the amount of NOx absorbed in the NOx absorption tower and the low 1dffi of oxygen.

Therefore, it is possible to adjust the recovered nitric acid concentration to a constant level by understanding the NOx absorption amount from the amount of oxygen reduction in the above-mentioned Nox absorption system and controlling the absorption liquid supply flow rate to the NoX absorption tower and the absorption liquid withdrawal amount. can.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a system diagram showing an embodiment of the reprocessing off-gas treatment apparatus according to the present invention. In FIG. 1, the same components as those in FIG. 6 are given the same reference numerals, and a description of the structure will be omitted. In the figure, the difference from the conventional apparatus shown in FIG. 6 is that an oxygen supply flow rate detector 31 is provided in the oxygen supply line 41 between the dissolution tank 3 and the No. An oxygen flow rate detector 32 and a NOx detector 35 are provided in the absorbing liquid supply pump 43 and an absorbing liquid extracting pump 44 are provided with a liquid flow rate controller 33.

In such a configuration, N generated from inside the dissolution tank 31
In response to changes in O and concentration, the amount of NO□ absorbed in the NOx absorption tower 6 is transferred to the oxygen supply flow rate detector 31 installed on the side of the NOx absorption tower 6 and the outlet gas line of the NOx absorption tower 6. Oxygen flow detector 32 and NOx provided
It is estimated by the detector 35, and the absorption liquid tank 4 is
By controlling the absorption liquid supply pump 43 and the absorption liquid extraction pump 44, which feed the absorption liquid from 2, the concentration of recovered nitric acid can be kept constant.

The optimum location for installing the oxygen flow rate detector 32 and the NOx detector 35 provided in the outlet gas line of the NoX absorption tower 6 is a location where iodine in the system is removed. Therefore, it is desirable to provide the gas line after the outlet gas line of the iodine removal column 13 which adsorbs and removes iodine from the gas. The reason for this is that if the detector is installed in a gas line containing iodine, normal operation of the detector cannot be maintained for a long period of time due to corrosion caused by the iodine gas.

To understand the amount of NOx absorbed into the liquid in the NOx absorption tower 6, it is necessary to
Installing a detector may be considered, but since the off-gas contains highly corrosive iodine gas, reliability cannot be maintained over a long period of time. Furthermore, NOx absorption tower 6
Since artificial gas contains saturated water vapor at around 90°C, if the temperature is lower than this temperature, condensed water will be generated, and NO will be added to this condensed water.
x is partially absorbed and the exact NOxI in the gas? ! Gives an error to I1 degree detection. However, in the embodiment described above, such a problem does not occur.

In this way, by the operation of the absorption liquid supply pump 43 and the absorption liquid extraction pump 44, the amount of absorption acid liquid supplied to the absorption acid liquid storage tank 7 and the amount of absorption acid liquid extracted from the NOx absorption system and supplied to the iodine re-extraction tower 9. By controlling the amount of absorbed acid liquid, for example, as shown in FIG.
x When the concentration fluctuates, the recovered acid concentration can be kept constant as shown by the broken line in FIG. 3, and the change in the recovered nitric acid concentration that occurs in the method using the conventional apparatus shown by the solid line in FIG. 3 can be avoided.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to maintain the recovered nitric acid concentration constant despite changes in the NOx concentration in the off-gas, eliminating the need for the conventional recovered nitric acid concentration adjustment tank, etc., and reducing equipment costs. Driving and operability can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of the reprocessing off-gas treatment device of the present invention, and FIG. 2 is a diagram showing the relationship between the amount of oxygen reduction and the amount of NOx absorbed in the NOx absorption tower of the reprocessing off-gas treatment device. Figure 3 is a graph showing changes in recovered nitric acid concentration in relation to changes in NOx concentration in off-gas, and Figure 4 is a graph showing changes in recovered nitric acid concentration in relation to changes in NOx concentration in off-gas.
An explanatory diagram showing the parts of the fuel rod that affect the change in Ox concentration. Figure 5 is a graph showing the 11 degree change in NOxi in the off-gas depending on the part of the fuel rod shown in Figure 4. Figure 6 is the conventional reprocessing. System diagram of off-gas treatment equipment, Figure 7 is NO.
FIG. 2 is a schematic cross-sectional configuration diagram of an x-absorption tower. 3...Dissolution tank, 4...Iodine expulsion tank,
5...Condenser, 6...NoX absorption tower, 7...Absorbing acid liquid j tank, 9...
Iodine re-extraction tower, 10... Recovery acid liquid storage tank, 13
...Iodine removal tower, 14...Furukyu 18.
...Off gas, 31...Oxygen 2M amount detector 32...Oxygen 2M amount detector, 33.Old...Liquid flow rate control bolt 35...NOx detection Vessel, 42...
... Absorption liquid tank, 43 ... Absorption liquid supply pump, 44 ... Absorption liquid extraction pump. Agent Patent Attorney Masaru Nishimoto −

Claims (1)

[Claims] (1) A dissolution tank that dissolves spent fuel, etc., an NO_x absorption tower that absorbs and removes NO_x in the off-gas from the dissolution tank, etc., and an iodine repurifier that drives out iodine from the absorption acid liquid generated in the NO_x absorption tower. an oxygen supply flow rate detector that detects the flow rate of oxygen supplied upstream of the NO_x absorption tower; and an oxygen supply flow rate detector that detects the flow rate of oxygen supplied on the upstream side of the NO_x absorption tower; An oxygen flow rate detector that detects the flow rate and an NO_x flow rate detector that detects the NO_x flow rate of off-gas on the downstream side of the NO_x absorption tower are provided, and based on the signals from each of these detectors, the oxygen flow rate is 1. A reprocessing off-gas treatment apparatus characterized by being provided with a controller that controls the flow rate of the absorption liquid supplied and the flow rate of the absorption liquid extracted from the NO_x absorption system.