JPS6361062B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for controlling the backwash development rate of ion exchange resins, and in particular, it is possible to always obtain a predetermined backwash development rate even when there are changes in temperature and piping resistance, and to achieve stable separation of anion and cation exchange resins. and a method by which the separation of scrubbing cruds may be carried out. There are various methods for purifying water using ion exchange resins, such as the mixed bed method and the multi-bed method, as well as methods that combine these methods with each other. Water can be purified to a high degree by this method, so it is widely practiced. In this mixed bed method, there are two methods: using granular ion exchange resin and regenerating the ion exchange resin repeatedly, and forming a mixed bed of powdered ion exchange resin, and when the ion exchange capacity of the mixed bed reaches its limit, all the powder is removed. There are methods for disposing of ion exchange resins, and the former method is better than the latter from the point of view of effective use of the resin. However, even in the former method of recycling ion exchange resins, that is, the mixed bed method using granular ion exchange resins, increasingly high purity water quality is required, and the particle size of the ion exchange resins used accordingly tends to become smaller. By the way, in the mixed bed method in which anion and cation exchange resins are mixed together, in order to regenerate these resins, there must be a means for separating the mixed anion and cation exchange resins from each other. In the conventional method, water is passed from below the mixed bed by utilizing the difference in terminal velocity caused by the difference in specific gravity between anion and cation exchange resins (usually an anion exchange resin). The resin (usually a cation exchange resin) with a high terminal velocity is separated upward and the resin with a high terminal velocity (usually a cation exchange resin) is separated downward, or the resin on the upper side is transferred to another container and each is treated with a chemical solution. It was to be recycled. However, in this mixed bed method, if the particle size of the ion exchange resin is reduced, the terminal velocity of the resin in water decreases, and even slight fluctuations in water flow make it difficult to separate the anion and cation exchange resins. The particle size of the resin that can be used in the mixed bed method is determined by whether or not it is possible to separate the anion and cation exchange resins.
To explain this in detail with reference to Figure 1, Figure 1 shows the terminal velocity distribution of the ion exchange resins shown in Table 1 in water at 30°C.
The particle size distribution of the ion exchange resin is a lognormal distribution.

[Table] The anion/cation exchange resin widely used in the conventional mixed bed method has a particle size of 760 μm in mode value. This anion/cation exchange resin is made by further reducing this particle size and setting the mode value of each resin to 550 μm. It has become something that has been made possible. However, the horizontal axis in Figure 1 is on a logarithmic scale with terminal velocity (cm/sec), so if the fluctuations in water flow during backwashing and separation are the same, it will be more difficult to separate the anion and cation exchange resins. Become something. Furthermore, the backwash development rate of ion exchange resin in water varies depending on not only the particle size and density of the resin but also the temperature of the water.For example, the lower the temperature, the more viscous the water becomes. will increase. This is illustrated in FIG. 2, and it can be seen that even if the flow rate is the same, the backwashing development rate changes significantly due to changes in temperature. In the mixed bed method, it is important to always maintain the backwash development rate of the resin layer at an appropriate value, especially to ensure that the resin layer is developed to the vicinity of the backwash water outlet at the top of the tower.
This increases the degree of mutual separation during regeneration of anion and cation exchange resins, and also reduces the amount of suspended solids (referred to as cladding) adsorbed on the ion exchange resin.
This is extremely important because it physically separates the ion exchange resin from the ion exchange resin by scrubbing (air supply operation) and further ensures that the ion exchange resin flows out above the ion exchange resin layer using backwash water. However, in the conventional method, the backwash expansion rate fluctuates depending on the temperature change of the water, so it was necessary to set the amount of backwash water taking into account this margin. An object of the present invention is to provide a method that always maintains a constant backwash development rate even when the water temperature changes when developing an ion exchange resin with backwash water. The method for controlling the backwash expansion rate of the present invention is to control the backwash expansion rate in a backwash operation in which backwash water is supplied from the lower part of the ion exchange resin layer and backwash water is extracted from above the ion exchange resin layer. In the method, the flow rate and temperature of the inflow pipe of backwash water are measured, and the set flow rate value is corrected so as to have a preset expansion rate based on the temperature, and the flow rate of backwash water is set to be corrected. A control valve is used to control the flow rate. According to the present invention, since the flow rate during backwashing is corrected depending on the temperature, the desired backwashing development rate can always be obtained, and the separation of anion and cation exchange resins or the removal of crud after scrubbing can be easily achieved. The operation can be carried out under optimal conditions. The present invention will be further explained based on FIG. Figure 3 shows the main parts of a regeneration tower for ion exchange resin from a double water desalination tower in a BWR type (boiling water type) nuclear power plant. A backwash water supply pipe is provided at the bottom of the regeneration tower 1, and an overflow pipe 5 is provided at the top for extracting backwash water from above. Further, the water for backwashing is led from the backwash water header 6 to the backwash water supply pipe 4 via the backwash water inflow pipe 7, and the inflow pipe 7 includes a thermometer 8, a flow meter 9, Control valve 10 and auto-on 9
An off valve 11 is provided. On the other hand, regarding the backwash water extraction side, the backwash water flowing out from the overflow pipe 5 is transferred to the extraction pipe 1.
2 and flows into the waste liquid storage tank 13. In the figure, 14 is an automatic on/off valve. Further explaining the flow rate control in this system, the water temperature signal from the thermometer 8 is sent to the regulator 15, and the regulator 15 adjusts the flow rate to achieve a preset backwash development rate of the ion exchange resin layer at that temperature. Perform calculations (or find from a table),
On the other hand, it is compared with the flow rate signal from the flow meter 9, and the difference is corrected by adjusting the control valve 10 to make it zero. Therefore, the expansion rate of the resin in the regeneration tower 1 can be kept constant no matter how the water temperature changes. In addition, since the length of the pipe from the regeneration tower 1 to the waste liquid storage tank called RadWest is generally more than 100 m, the pipe resistance changes greatly over time, but the method of the present invention Since the flow rate is always adjusted to achieve the desired backwash expansion rate, all disturbances can be eliminated and stable operation can be performed. In the present invention, a thermometer, a flow meter, and a control valve are provided in the backwash water inflow pipe to increase operational stability. On the outlet pipe 12 side, the operation will not be stable at the beginning of backwashing, and furthermore, equipment with important functions such as thermometers, flow meters, control valves, etc. will be further contaminated. Therefore, this cannot be said to be desirable. When the ion exchange resin in the regeneration tower 1 is developed based on the present invention, the backwash development rate is set such that the top surface of the developed ion exchange resin reaches the vicinity of the backwash water outlet. desirable. In this way, even when anion and cation exchange resins are to be separated, the spread layer has the maximum layer height that the apparatus allows, making separation easier. Furthermore, even when separating and removing the detached crud from the ion exchange resin by scrubbing, if the upper surface of the ion exchange resin reaches below and near the extraction port, the terminal velocity of the ion exchange resin is lower than the final velocity of the ion exchange resin. This is because even if the crud has a slightly small terminal velocity, it will be discharged from the extraction port to the outside of the system, allowing efficient backwashing.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between terminal velocity and particle size distribution during backwashing of ion exchange resin, Figure 2 is a graph showing the relationship between flow rate and backwash expansion rate with temperature as a parameter, and Figure 3 is a graph showing the relationship between flow rate and backwash expansion rate with temperature as a parameter. 1 is a block diagram showing an apparatus for implementing the present invention. FIG. 1... Regeneration tower, 8... Thermometer, 9... Flow meter,
10...Control valve, 11...Automatic on/off valve, 15
...Adjuster.

Claims (1)

[Claims] 1 Supply backwash water from the bottom of the ion exchange resin,
In a method for controlling the backwash expansion rate in a backwash operation in which backwash water is extracted from above an ion exchange resin layer, the temperature and flow rate of the backwash water inflow pipe are measured, and the flow rate is set in advance based on the temperature. Control of the backwash expansion rate of ion exchange resin, characterized in that the flow rate that gives the backwash expansion rate is determined, and the measured flow rate is adjusted by a control valve so as to become the desired temperature-corrected flow rate. Method.