JPH0150441B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a control device for a concentrator that uses steam as a heating source.

(Prior Art) FIG. 3 shows a conventional control device. 1 is an evaporator with a heat exchanger 2 inside. A stock solution is sent from the bottom of the evaporator 1 through a stock solution inlet pipe 3, and heating steam is sent from a steam inlet pipe 4 at the top. The liquid at the bottom of the evaporator 1 is circulated by a pump 5 through a circulation line 6, flushed at the top of the heat exchanger 2, and heated within the heat exchanger 2. The generated steam is discharged through a discharge pipe 7 at the top of the steam can. The liquid concentrated by evaporation is taken out from the bottom of the evaporator 1 through a take-out pipe 8.

9 is a level controller that detects the solution level at the bottom of the evaporator with a level meter 10 and connects the raw solution inlet pipe 3.
This controls the flow control valve 11 on the inlet side, which is disposed at the inlet side.

On the other hand, 12 is a concentration controller which detects the concentration of the concentrated liquid with a concentration meter 14 provided in the take-out pipe 8 and controls the outlet side flow rate control valve 13.

As described above, a concentrating device is generally provided with a concentration control system using the outlet side flow rate as the manipulated variable and a level control system using the inlet side flow rate as the manipulated variable. However, the causal relationship between various quantities such as concentration is as shown in FIG. 4, and concentration control operates through level control. For this reason, the performance of concentration control also depends on the performance of level control, making it difficult to improve the performance of concentration control.

(Problems to be Solved by the Invention) In view of the problems of conventional devices, it is desirable to suppress hunting in concentrated liquid concentration control and improve responsiveness of concentrated liquid concentration control in a solution concentrator that uses steam as a heating source. This is what we are trying to achieve.

(Solving Means by the Invention) In a concentrating device that flashes a stock solution supplied to the bottom of an evaporator equipped with a heat exchanger on the heat exchanger via a circulation pipe and evaporates, the concentration of the solution on the outlet side is detected. , a concentration control system that controls the solution flow rate on the inlet side using a concentration controller, and a level control system that detects the solution level in the evaporator and controls the solution flow rate on the outlet side using a level controller. The system can now be controlled without going through the level control system.

(Example) An explanation will be given based on FIG. 1. The evaporator itself has the same structure as shown in FIG. That is, 1 is an evaporator, and a heat exchanger 2 is located inside. The undiluted solution is sent from the bottom of the evaporator 1 through the undiluted solution inlet pipe 3, and then into the vapor inlet pipe 4 at the top.
Heating steam is sent from The liquid at the bottom of the evaporator 1 is circulated through a circulation line 6 by a pump 5.
The heat exchanger 2 is flashed at the upper part of the heat exchanger 2.
heated inside. The generated steam is discharged through a discharge pipe 7 at the top of the steam can. The liquid concentrated by evaporation is taken out from the bottom of the evaporator 1 through a take-out pipe 8.

Now, in the present invention, the outlet concentration D in the take-out pipe 8 is detected by the concentration meter 14, and the concentration controller 12 operates the inlet side flow rate control valve 11 so that the manipulated variable becomes the inlet side solution flow rate Fi. Configure the control system. In addition, a level control system is constructed in which the weight W of the solution in the can is detected as the solution level by a level meter 10, and the outlet side flow rate control valve 13 is operated by the level controller 9 so that the manipulated variable becomes the outlet side flow rate Fo.

The causal relationship between various quantities due to the above two control systems is the second
It will look like the figure. At this time, the controller
Use a PID controller.

Note that when cleaning the take-out pipe 8 during operation, the solution in the evaporator 1 may not be able to escape. At that time, the signal may be switched so that the configuration as shown in FIG. 3 is obtained, and the concentration controller 12 is not operated, and the level controller 9 is operated on the entrance side to perform level control.

(Function) As shown in FIG. 2, the concentration control controller 12 is operated using the deviation between the concentration setting value Dref and the detected concentration D as input, and the inlet side flow rate control valve 11 is operated by the output thereof. As a result, the inlet side flow rate Fi becomes the manipulated variable. Inlet side flow rate Fi
directly affects the concentration and is not affected by the outlet flow rate Fo.

Solution level set value Lref and detected solution level L
The controller 9 for level control is operated using the deviation from the output as input, and the outlet side flow rate control valve 13 is operated based on the output thereof, and as a result, the outlet side flow rate Fo becomes the manipulated variable. The amount of solution in the can is moved by the effect of integrating the difference between the inlet flow rate Fi and the outlet flow rate Fo, which is detected as the solution level. In this level control system, the inlet flow rate Fi appears to move like a disturbance.

(Effects) Since the level control system is not interposed in the concentration control system, it has become possible to improve the performance of concentration control without depending on the performance of the level control system. This makes it easy to improve responsiveness while suppressing hunting in concentration control.

Incidentally, FIG. 5 shows a time-weight (wt) % diagram for an apparatus equipped with the control system according to the present invention, and it can be seen that the concentration of the concentrated liquid is extremely stable.
Figure 6 shows the time for a device equipped with a conventional control system.
It is a weight (wt)% diagram. It is easy to understand that the concentration of the concentrate is hunting.

[Brief explanation of drawings]

FIG. 1 is a piping control circuit diagram of the device of the present invention. FIG. 2 is also an explanatory diagram of the control system. Figure 3 is a piping control circuit diagram of a conventional device. FIG. 4 is also an explanatory diagram of the control system. FIG. 5 is a time-weight (wt) % diagram in the device of the present invention. Figure 6 shows time in conventional equipment.
Weight (wt)% figure. In the figure, 1... evaporator, 2... heat exchanger, 3...
Stock solution inlet pipe, 4... Steam inlet pipe, 5... Pump, 6...
Circulation pipe, 7...Discharge pipe, 8...Takeout pipe, 9...Level controller, 10...Level meter, 11...Flow rate control valve, 12...Concentration controller, 13...Flow rate control valve, 14...Concentration meter.

Claims (1)

[Claims] 1 In a concentrating device where the stock solution supplied to the bottom of an evaporator equipped with an internal heat exchanger is flashed onto the heat exchanger via a circulation pipe and evaporated, the concentration of the solution on the outlet side is detected and the concentration controller A heating device characterized by comprising a concentration control system for controlling the solution flow rate on the inlet side, and a level control system for detecting the solution level in the evaporator and controlling the outlet side solution flow rate using a level controller. Control device in a solution concentrator using steam as a source.