JPS6345615B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to the control of a granulator for compressing and granulating powder, and for example, a granulator suitable for compressing and granulating radioactive waste powder whose composition varies greatly. Related to machine control. [Background of the Invention] The main types of waste generated in nuclear power plants are concentrated waste liquid containing iron oxide (Fe ₂ O ₃ ) caused by corrosion, used ion exchange resins, used supercharging materials, etc. There are recycled waste liquids that are mainly composed of sodium sulfate and waste liquids that are mainly composed of boric acid, which are generated as a result of the regeneration process of used ion exchange resins. Japanese Patent Laid-Open Publication No. 1983-1999 proposed a method in which these wastes are mixed individually or in advance, dried and powdered using the same equipment, and then granulated using a granulator to form pellets.
This is shown in Publication No. 15079, etc. FIG. 2 shows a schematic structure of this granulator and a conventional control method thereof. The powder 5 held in the powder hopper 1 is pre-compressed by a screw feeder 2 and transferred to a pair of forming rolls 4 which are pressed together by a spring 3.
The pellets are fed in between and granulated into pellets 6. The pellets 6 are required to have a certain mechanical strength so as not to be damaged during handling during subsequent transportation and storage, and during final processing. In order to satisfy such requirements, conventionally the rotation speed of the roll 4 is kept constant, and the rotation of the screw feeder drive machine 8 is adjusted so that the torque of the roll drive machine 7, for example, the power consumption if the drive machine is a motor, is constant. A control method was used to change the number. In FIG. 2, 9 is a roll torque detector for detecting the torque of the roll drive machine 7, 10 is a torque setting device for the roll drive machine, and 11 is a screw feeder rotation speed regulator, which performs the above control. It constitutes a control system for However, the powder supplied to the granulator has completely different physical properties, ranging from dried powder of concentrated waste liquid mainly composed of mirabilite (Na ₂ SO ₄ ) to used ion exchange resin. . When powders with different physical properties are granulated using the same granulator, the conventional control method described above, which changes only the rotational speed of the screw feeder, will cause the screw feeder to The screw feeder rotation speed may have to be lowered below the screw feeder rotation speed at which the roll torque suddenly decreases to an extremely low value, or the roll torque may not be able to reach a predetermined value. Even if the rotational speed of the feeder is increased, the screw feeder and the powder rotate together, causing the so-called "slip" phenomenon in which the powder cannot be pushed in, making it impossible to control the granulator. A situation like this occurs. This will be explained in detail below. Now, let us consider the case where a waste liquid with a high solid content concentration as shown in A in Table 1 is dried and powdered and then applied to a granulator. FIG. 3 shows the characteristics of a conventional control method in which, in the above case, the roll rotation speed of the granulator is kept constant and the roll torque of the granulator is controlled to be constant only by controlling the screw rotation speed. Curve a shows the roll rotation speed, b shows the screw rotation speed, and curve c shows the roll torque, and the value shown by the dotted line in the figure B is the control torque setting value.
As the screw rotation speed (curve b) increases, the roll torque (curve c) also increases, and when this exceeds the set value, the granulator control device reduces the screw rotation speed and brings the roll torque closer to the set value. However, even if the screw rotation speed is reduced, the roll torque hardly decreases and does not return to the set value easily. For this reason, the control device operates to extremely reduce the screw rotation speed, and as a result, the ability to supply the powder in the hopper to the rolls is lost, and the roll torque sharply decreases. In this way, since the machine cannot be operated with a predetermined torque, pellets with sufficient strength cannot be produced.

[Purpose of the invention]

The purpose of the present invention is to provide a control method for a granulator that can stably supply pellets having a constant mechanical strength under an appropriate pellet forming pressure even if the composition and object of the treated powder change. and equipment. [Summary of the Invention] The present inventors believe that the reason why the rotational speed of the screw feeder is not easily reflected in changes in roll torque is that
Thinking that this is due to the flow characteristics of the powder in the hopper of the granulator, we measured the relationship between roll rotation speed and roll torque using the screw feeder rotation speed as a parameter. The measurement results are as shown in FIG. 7, and it is clear that the roll torque can be increased by lowering the rotational speed of the roll. Therefore, if the desired roll torque cannot be obtained by simply increasing the screw feeder rotation speed, the desired roll torque can be obtained by lowering the roll rotation speed, which will prevent "slip". By appropriately lowering the roll rotation speed when the screw rotation speed approaches the screw rotation speed at which the phenomenon occurs, a predetermined roll torque can be ensured without lowering the set value of the roll torque as in the prior art. In addition, if the roll torque becomes excessive and cannot be reduced to the specified roll torque by simply lowering the screw feeder rotation speed, it is possible to reduce the roll torque to the specified value by increasing the roll rotation speed. can. [Embodiment of the Invention] An embodiment of the present invention is shown in FIG. The powder 5 supplied from the dryer is received in the granulator hopper 1, and the screw feeder 2 in the hopper is rotated by the screw feeder drive machine 8, and the powder is transferred between the rolls 4 rotating at a constant torque. When the pellets are fed, pellets 6 connected in a plate shape are formed. The plate-shaped pellets are introduced into a pellet sizer 15 and separated into individual granular pellets 16. The rolls 4 are pressed by springs 3 to maintain an appropriate pressing load and roll spacing so that pellets with a constant shape can be produced. The roll 4 is driven by a roll drive machine 7. The roll torque detector 9 detects the torque of the roll by detecting the power consumption of the roll driving machine 7, etc., and sends the detection signal to the calculator 13, which then controls the roll torque setting device 10 and the roll rotation speed setting device. In combination with the signal from 14, a calculation output signal is sent to the roll rotation speed regulator 12 and the screw feeder rotation speed regulator 11 so that the roll torque is constant, and the screw feeder is controlled by the signals from the respective regulators. The drive device 8 is controlled to drive the screw feeder to supply powder to the rolls, and at the same time, the roll drive device 7 is controlled to drive the rolls to granulate pellets with a constant roll torque. The control system of the above embodiment will be described in further detail below. FIG. 8 shows the configuration of the arithmetic unit 13 mentioned above. The calculator 13 receives a comparison signal between the signal from the roll torque detector 9 and the signal from the roll torque setting device 10, and also calculates a predetermined speed increase gradient and upper and lower limit rotation speeds of the screw corresponding to the powder composition respectively. Program function d to memorize and command so that it does not deviate; Switch function a to switch between screw feeder rotation speed control and roll rotation speed control; Holding function b to keep the screw rotation speed at a value close to the lower limit; when the roll is automatically controlled through switch a with a signal from the roll torque detector, and roll rotation speed setting device 1
It is equipped with a roll control switch function c that switches from 4 to automatic control that controls the rotation speed to a constant rotation speed from a preset rotation speed. Here, the upper limit rotation speed of the screw feeder means the rotation speed of the screw feeder above which "slip" occurs, and the lower limit rotation speed of the screw feeder means the rotation speed above which "slip" occurs. It means the rotational speed of the screw feeder below which the roll torque suddenly decreases to an extremely low value. FIG. 9 is a sequence diagram when the calculator 13 automatically controls the rotation speed of the screw feeder to keep it at a constant set value in response to roll torque fluctuations while the roll rotation speed is constant. Then, signals are transmitted to the screw feeder rotation speed regulator 11 and the roll rotation speed regulator 12 through paths shown by thick lines, respectively. FIG. 10 shows signal transmission in bold lines when the computer 13 maintains the rotational speed of the screw feeder constant and automatically controls the roll rotational speed so that the roll torque becomes a constant set value. The above control system is configured such that the variation in roll torque is controlled by adjusting the screw feeder rotational speed in a range between its upper and lower rotational speed limits.
As long as the roll torque can be sufficiently converged to the set value, the circuit state shown in Fig. 9 is adopted and the roll torque is controlled to be maintained at the set value by adjusting the screw feeder rotation speed. When the roll torque fluctuation is large and the screw feeder rotation speed reaches a rotation speed close to the lower limit or upper limit rotation speed, the circuit state shown in Fig. 10 is switched to reduce the screw feeder rotation speed to the lower limit. The roll torque is controlled to be kept constant at a set value by increasing or decreasing the roll rotation speed. The circuit switching as described above is performed by a command from the program function section d. An example of the operation of this control system including the arithmetic unit 13 will be explained with reference to FIGS. 11 and 12. 11th
The figure shows the control characteristics when the waste liquid with a high solid content concentration shown in A of Table 1 is dried and powdered and applied to a granulator. (Curve b) increases, and accordingly, the roll torque (Curve c) also increases, and when the set value of the roll torque is exceeded, the screw feeder rotational speed is automatically reduced. However, when the screw feeder rotation speed decreases to a rotation speed just before the screw feeder rotation speed (lower limit rotation speed) at which the roll torque suddenly increases, the screw feeder changes to the circuit state shown in FIG. The rotational speed of is maintained at this rotational speed, and the roll rotational speed (curve a) is a deviation signal between the signal from the roll torque detector 9 and the setting signal from the roll torque setting device 10 from the constant rotational speed control up to that point. In response to this, automatic control is switched to increase the roll rotation speed, and the roll torque (curve c) is controlled to the set value without sudden torque fluctuations. FIG. 12 shows the control characteristics when the waste liquid with a low solid content concentration shown in C in Table 1 is applied to a granulator. In this case, when the screw rotation speed reaches a rotation speed just before the rotation speed at which the slip phenomenon occurs (upper limit rotation speed), the circuit state is switched from Figure 9 to Figure 10 to maintain the screw feeder at that rotation speed. At the same time, the roll rotation speed is controlled to be lowered, thereby controlling the roll torque to a set value. As mentioned above, the ability to keep the roll torque constant by controlling the screw rotation speed and roll rotation speed is due to the powder supply characteristics of the screw feeder.
This is because it has the characteristics shown in the figure. In addition,
In the embodiment described above, the roll rotation speed is adjusted only when the screw feeder rotation speed approaches its upper limit or lower limit rotation speed.
Not only this, but also within the range between the upper and lower limits of the screw feeder rotation speed, the roll torque can be controlled to a constant set value by adjusting both the screw feeder rotation speed and the roll rotation speed in combination. It is clear from FIG. 7 that this is possible. In this embodiment, control is also performed to restrict the speed increase gradient when the screw feeder speeds up, such as during startup. This is because if the speed increase gradient of the screw feeder is large, the roll torque setting value may be exceeded when starting the screw feeder, or the screw feeder may speed up to a high rotation speed that enters the powder sliding region. This is to prevent this from happening. To explain this, the 13th
The figure shows the mechanical characteristics of the granulator when the screw speed-up gradient is set to various values.Figure a shows the change in rotational speed when starting the screw, and figure b shows the change in the rotation speed when the screw is started. This figure shows the changes in roll spacing and roll load when the granulator is started with a screw speed increase gradient. The range below the dotted line in Figure b is the permissible range for the granulator, and if the roll spacing or roll load exceeds this, there is a risk of mechanical damage to the granulator, so the drive of the screw and rolls will be automatically stopped. The protective device is now working. By the way, when the screw is started at a high acceleration gradient K ₁ in figure a, the rotational speed of the screw becomes curve a _1. In this case, as shown by curve b ₁ in figure b, the roll distance (tolerable value is 5 mm or less) or the roll load ( (The permissible value is 90 tons or less), the granulator will stop (trip) if the permissible value is exceeded. Therefore, in the embodiment of the present invention, the screw is started at a smaller screw acceleration gradient _K2 in FIG. a. As a result, the screw rotation speed becomes curve a ₂ , and the roll spacing or roll load becomes b ₂ in figure b, which can be kept within the allowable value. The relationship between the screw speed increase gradient described above and the roll spacing and roll load movement of the granulator changes depending on the composition of the waste liquid as shown in Table 1. Therefore, in the embodiment of the present invention, the predetermined speed increase gradient of the screw is selected depending on the composition of the material to be granulated. The smaller the ramp-up gradient, the fewer the granulator stops, but the longer it takes to reach a predetermined roll torque, the less the amount of pellets with a predetermined strength. Therefore, it is necessary to select the optimum value for the speed increase gradient of the screw feeder for each waste liquid composition. In the program function section in FIG. 8, several acceleration gradients to be selected are stored as schematically illustrated. FIG. 14 is an example showing the operating time of one batch (nine batches are operated in one day) and the change in roll torque during that time. If the speed increase gradient of the screw feeder is large, the time 2 will be as shown by the curve 1 in the same figure.
The roll torque stabilizes at the set value in minutes, but if the acceleration gradient is small, it takes more than twice as long, 5 minutes, as shown by the curve 2 in the figure, until the roll torque stabilizes. Pellets made while the roll torque is not stable are easily damaged and cannot be stored safely, so they must be collected and granulated again. The throughput of the granulator will be low. Therefore, it can be seen that in order to increase the throughput and operate the granulator without tripping, it is necessary to select an appropriate acceleration gradient depending on the composition of the waste liquid. Figure 15 is a flow sheet of a radioactive waste liquid volume reduction and solidification treatment facility that processes radioactive waste liquid generated from nuclear power plants by turning it into dry powder and supplying it to a granulator.
This is suitable for applying the present invention. The radioactive waste liquid from the power plant is concentrated to a predetermined concentration by the concentrating equipment 17 and stored in the concentrated waste liquid storage tank 18 . The main component of radioactive waste liquid is iron oxide produced by corrosion, but this iron oxide is converted into radioactive metals by fission products such as iodine produced by nuclear fission in the reactor or by radiation irradiation. It is integrated with corrosion products such as aged cobalt metal.
These are guided to a dryer 21 by a supply device 20 and dried to form a powder. This powder is introduced into a granulator 22 and granulated into pellets 16 having the necessary strength for safe storage and processing. When pelletizing with the granulator 22, the strength of the pellets changes depending on the composition and physical properties of the waste liquid, so in the implementation of the present invention,
The concentrated waste liquid is introduced into the analyzer 19 in advance and analyzed. Based on the analysis data, the control system of the granulator is adjusted as described above, and the dried powder is applied to the granulator and granulated into pellets having a predetermined strength. Table 1 shows an example of analytical data for waste liquid containing iron oxide as a main component. [Effects of the Invention] According to the present invention, not only can powder be granulated by controlling only the rotation speed of the screw feeder in the past, but also powder can be granulated to a predetermined strength with such conventional control. Powders with different physical properties can be granulated into pellets having a predetermined strength. Furthermore, the granulation pressure can be set by changing the set value of the roll torque, and granulation can be performed under a roll torque commensurate with the granulation pressure, which has the effect of reducing the power consumption of the granulator.

[Brief explanation of the drawing]

FIG. 1 is a schematic overall configuration diagram of an embodiment of the present invention;
Fig. 2 is a schematic configuration diagram of the conventional example, Fig. 3 A, B and Fig. 4 A, B are diagrams showing the control according to the conventional example, and Figs. 5 and 6 show the relationship between roll torque and pellet forming pressure. FIG. 7 is a diagram showing the relationship between the pellet forming pressure and pellet strength, FIG. 7 is a diagram showing the relationship between roll rotation speed and roll torque, FIG. 8 is a schematic diagram of the computing unit in the embodiment of the present invention, and FIGS. FIG. 10 is a diagram showing the operation of the arithmetic unit, FIGS. 11 and 12 are diagrams of control characteristics according to the embodiment of the present invention, and FIGS. 13a and 13b are diagrams showing the acceleration gradient of the screw feeder and the granulator. FIG. 14 is a diagram showing the relationship with mechanical factors, FIG. 14 is a diagram showing changes in roll torque over time, and FIG. 15 is a schematic diagram of radioactive waste liquid granulation equipment. 1...Hotsupa, 2...Screufeeda, 3
... Roll pressure spring, 4 ... Roll, 5 ... Powder, 6 ... Plate pellet, 7 ... Roll drive machine,
8... Screw feeder drive machine, 9... Roll torque detector, 10... Roll torque setting device, 1
1... Screw feeder rotation speed regulator, 12...
...Roll rotation speed regulator, 13...Arithmetic unit, 14...
... Roll rotation speed setting device, 15 ... Pellet sizing machine, 16 ... Granular pellet, 19 ... Analyzer.

Claims (1)

[Claims] 1. The roll torque of a granulator, which uses a rotating screw feeder to force powder between a pair of mutually pressurized rolls to granulate it, is defined as the screw feeder rotation speed and the roll rotation. A control method for a granulator in which the screw feeder rotation speed is controlled to a set value by adjusting the number of screw feeders, and when the screw feeder rotation speed falls below the lower limit rotation speed, the roll torque suddenly decreases to an extremely low value. When the rotation speed decreases to a value close to the maximum rotation speed (the screw feeder rotation speed above which slipping of the screw feeder occurs), the rotation speed increases to a value close to the upper limit rotation speed (the screw feeder rotation speed above which slipping of the screw feeder occurs). At that time, the screw feeder rotational speed is maintained at the rotational speed before the corresponding one, and
A method for controlling a granulator, characterized by increasing or decreasing the number of roll rotations. 2. The method of controlling a granulator according to claim 1, wherein only the screw feeder rotation speed is adjusted in the range between the rotation speeds of the two front sides. 3 The roll torque of the granulator, which uses a rotating screw feeder to force the powder between a pair of mutually pressurized rollers for granulation, is adjusted to the set value by adjusting the screw feeder rotation speed and roll rotation speed. A control device for a granulator to be controlled, which includes a computing unit that receives a comparison signal between roll torque and roll torque set value and a roll rotation speed set value signal, and a screw feeder rotation speed that receives input from the computing unit. It consists of a regulator and a roll rotation speed regulator, and the computing unit stores and commands the upper and lower limit rotation speeds of the screw feeder, and the program function section allows the screw feeder rotation speed to reach the upper limit rotation speed according to instructions from the program function section. When the rotational speed is between the nearest rotational speed and the lower limit rotational speed, input the above comparison signal and roll rotational speed setting value signal to the screw feeder rotational speed controller and roll rotational speed controller, respectively. and a switch function section that inputs the comparison signal to the roll rotation speed regulator when the screw feeder rotation speed reaches the rotation speed before either of the above values, and a switch function section that switches to the latter state. 1. A control device for a granulator, comprising a holding function section that holds an input to a screw feeder regulator at that time.