JPH0410361B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to improvement of controllability when changing the flow rate of heated steam in a concentration control device using a multi-effect can.

<Prior Art> The configuration and problems of a conventional device will be explained using an example of instrumentation of a multi-effect can shown in FIG. 1,
2 and 3 are the first to third evaporators connected in a cascade; 101, 201, and 301 are the heat exchangers of the first, second, and third evaporators, respectively; 4 is the heat exchanger for the heated steam S to the first evaporator; A pipe line supplying the heat exchanger 101 of No. 1, 1
02 transfers the evaporated steam V ₁ from the first evaporator to the second evaporator 2
A pipe line 202 supplies the heat exchanger 201 to the second heat exchanger 201.
A conduit 302 is a conduit for supplying the evaporated vapor V ₂ of the steam can 2 to the heat exchanger 301 of the third evaporator 3 , and a conduit 302 is a conduit for guiding the evaporated vapor V ₃ of the third evaporator to the condenser 5 .
In the condenser 5, 501 is a connection pipe to a vacuum pump, and 502 is a bleed pipe to the atmosphere. 10
3,203,303 are heat exchangers 101,201,
301 drain.

Reference numeral 6 denotes a flow rate sensor that measures the flow rate F _s of the heating steam S, 7 a control valve that controls this flow rate, and 8 a control valve 7 that receives the output e _s of the flow rate sensor 6 and the set value Y _s of the heating steam flow rate. It is a controller that operates.

9 is a pipe line for supplying the feed liquid B to be concentrated into the third evaporator 3; 10 is a pump inserted into this pipe line; 11 is a control valve that controls the feed liquid flow rate _F3 ;
12 is a level sensor that measures the level _L3 of the supply liquid B in the evaporator 3, and 13 is the output of the level sensor.
This is a level controller that receives e _l3 and a set value Y _l3 and operates the control valve 11 to control the flow rate _F3 . 14 is a pipe line for transferring the feed liquid in the evaporator 3 to the evaporator 2, 15 is a pump inserted in this pipe, and 16 is a control valve that controls the flow rate _F2 of the feed liquid to the evaporator 2. ,
17 is a level sensor that measures the level _L2 of the supply liquid B in the evaporator 2, and 18 is the output of the level sensor.
This is a level controller that receives e _l2 and set value Y _l2 and operates the control valve 16 to control the flow rate _F2 . 19 is a pipe for transferring the supply liquid in the evaporator 2 to the evaporator 1; 20 is a pump inserted into the pipe; 21
is a control valve that controls the flow rate _F1 of fluid to the evaporator 1,
22 is a level sensor that measures the level _L1 of the feed liquid B in the evaporator 1, and 23 is the output of the level sensor.
This is a level controller that receives e _l1 and set value Y _l1 and operates the control valve 21 to control the flow rate F ₁ .

24 is a discharge pipe for discharging the concentrated supply liquid B', 25 is a pump inserted in this pipe, 26 is a control valve for controlling the flow rate F ₀ of the discharged supply liquid B', 27
28 is a concentration sensor that measures the concentration _D1 of the feed liquid in the evaporator 1, and 28 is the output e _d of the concentration sensor and the set value Y _d
This is a concentration controller that controls the discharge flow rate F ₀ by operating the control valve 26 in response to the flow rate F 0 .

29 is a pipe for bleeding air A into the pipe 302 to the concentrator 5, 30 is a control valve inserted into this pipe, and 31 is a pressure sensor for measuring the pressure P ₃ in the third evaporator 3. , 32 is a pressure regulator that receives the output e _p of the pressure sensor and the set value Y _p and operates the control valve 30 to control the amount of bleed air.

T ₁ , T ₂ , T ₃ are the temperatures inside the evaporators 1, 2, and 3;
P ₁ , P ₂ , and P ₃ are the pressures in each evaporator, L ₁ , L ₂ , and L ₃ are the feed liquid levels in each evaporator, and D ₁ , D ₂ , and D ₃ are the feed liquid concentration in each evaporator. It is.

In such a configuration, the pressure in each evaporator is P ₁
The pressure gradient is >P ₂ >P ₃ , the temperature is T ₁ >T ₂ >T ₃ , and the concentration is D ₁ >D ₂ >D ₃ .
Therefore, when the temperature of the feed liquid B to be concentrated is low, a backflow type configuration as in the embodiment is used in which the heated steam S is supplied from the third evaporator 3 side in the opposite direction to the flow.

The concentration D ₁ of the discharged supply liquid B' is maintained at a set value Y _d by controlling the discharge flow rate F ₀ from the discharge evaporator 1 . The flow rates F ₁ , F ₂ , and F ₃ of the liquid supplied to each evaporator are controlled so that the levels L ₁ , L 2 , and L ₃ of each evaporator are maintained at approximately constant levels Y _l1 , _{Y l2 ,} and Y _l3 . .

In the operation of such multiple effect canisters, it is important to maintain a constant concentration of concentrate within each evaporator without significantly varying the level of liquid within each evaporator. The control loop configuration shown in FIG _.
Y _s ) is constant and relatively small disturbances (feed liquid concentration,
(heating steam pressure, heating steam flow rate), it is possible to effectively maintain concentration control and level control in a steady state.

However, when the flow rate of the discharged supply liquid is changed significantly, there is a drawback that good concentration control and level control are difficult. That is, if F _s is significantly increased over a short period of time (changing the discharge feed liquid is done by changing the steam flow rate F _s ), the calorific value of the first stage evaporator begins to increase. To maintain a constant level in the can, the level controller 23 increases the feed flow rate F ₁ by an amount commensurate with the increase in evaporation. This keeps the level constant, but the concentration D ₁ in the can increases. This is the balance for the can F ₀ D ₁ = F ₁ D ₂ to D ₁
It is clear that =F ₁ ·D ₀ /F ₀ holds true, and as F ₁ increases, D ₁ also increases.

Therefore, in order to lower the concentration _D1 , the concentration controller 2
8 increases F ₀ . If F ₀ is increased, the level inside the can will drop, so F ₁ is increased again to keep the level constant. By repeating this process, D ₁ , F ₀ , and F ₁ fluctuate until they reach steady values, and this fluctuation affects the level fluctuations in the second and third evaporators, and at the same time the concentration in each evaporator increases. _D2 , _D3
also fluctuate significantly, and it takes a long time for these to settle down to new steady values.

<Problems to be Solved by the Invention> In order to solve the above-mentioned drawbacks, the present invention solves the above-mentioned drawbacks by providing a method in which the level and concentration of the liquid in each evaporator do not change significantly even if the flow rate of the discharged supply liquid is changed in a short period of time. The purpose of this invention is to realize a control device that can be stabilized in a short time.

<Means for Solving the Problems> The structural feature of the present invention is that a plurality of evaporators are connected in sequence and the steam generated in one evaporator is used to heat the next evaporator to heat the supply liquid. A control device for a multi-effect canister that sequentially condenses includes a steam flow rate controller that adjusts the heated steam flow rate based on a measured value and a set value of the heated steam flow rate supplied to the first evaporator, and a steam flow rate controller that controls the concentrated supply liquid. a concentration controller that adjusts the discharge flow rate of the discharged steam can based on the measured concentration value and set value of the feed liquid in the evaporator; A level controller that adjusts the supply flow rate of the supply liquid based on the value, and a feed forward means that adds a manipulated variable related to the heated steam flow rate to the manipulated outputs of the concentration controller and the level controller. That's the point.

<Function> The feed forward control loop adds the manipulated variable related to the heating steam flow rate to the manipulated output of the concentration controller and level controller, so that when the heating steam flow rate setting is significantly changed, the discharge flow rate F ₀ and the supply flow rate F ₁ can be increased before the concentration controller output and the level controller output increase, and level fluctuations and concentration fluctuations in each evaporator can be minimized.

<Example> An example of the apparatus of the present invention will be described with reference to FIG. Elements that are the same as those in FIG. 2 are given the same reference numerals and their explanations will be omitted. A dotted block C is a feed forward control loop which is a characteristic part of the device of the present invention. Numerals 31 to 34 are feed forward calculation circuits which receive the measurement signal e _s of the flow rate F _s of the heating steam S, and operate the control valve 2 in proportion to the increment in the flow rate of the heating steam S.
1, 16, 13, and 26 are operated as feed forwards. Outputs of arithmetic circuits 31, 32, 33, 34
e _f1 , e _f2 , e _f3 , and e _f4 are generally expressed by the following functions.

e _f1 = f _i (F _s ) = K _i (F _s − F _nio ) (1) where F _nio is the minimum flow rate of heating steam, i = 1 to 4
It is.

The setting method for K _i is as follows. First, the flow rates F ₁ , F ₂ , F ₃ of the supply liquid to each evaporator and the discharge flow rate F ₀ are determined by the opening degrees θ ₁ , θ ₂ of the control valves 21, 16, 11 and 26,
Assume that it is proportional to θ ₃ and θ ₀ . Only the method for setting K ₁ will be described below, but K ₂ to _{K 4} can also be set using a similar method.

When the opening degree of θ ₁ when the heating steam flow rate F _s is the minimum and maximum is θ _1nio and θ _1nax and the maximum value of the heating steam flow rate is F _snax , K ₁ = (θ _1nax − θ _1nio ) / (F _snax −F _snio ) (2).

Next, the operation of the feed forward control loop in the present invention will be explained.

First, if there is no feed forward control loop, after changing F _s by changing the set value Y _s , until the control valves 21, 16, 11, 26 settle to steady values, the As mentioned above, the fluctuations in concentration and level are large.

In such a case, in order to suppress fluctuations in concentration D ₁ and level L ₁ , the amount of evaporated vapor in evaporator 1 must be reduced.
When V ₁ , F 0 and F 1 should be manipulated in advance so that F ₀ · D ₁ = F ₁ · D ₂ (3 ₎ F ₁ −F ₀ −V ₁ = ₀ (4) .
The same applies to the evaporators 2 and 3. If the manipulated variables of F ₀ and F ₁ due to feed forward are set as equation (2), equations (3) and (4) will approximately hold, and it is possible to minimize concentration fluctuations and level fluctuations. Become.

The above-described embodiment is an example in which the present invention is applied to a triple-effect can, but it is not limited to triple-effect cans,
Can be applied to any multi-can configuration. Furthermore, when the temperature of the feed liquid is high, similar feed forward control can be applied to a forward flow type feed liquid that is fed from the first stage evaporator side.

The calculation of feed forward control has shown an example of proportional calculation, but in consideration of compensation of dynamic characteristics, a first-order lead/lag element (T _D s+1/Ts+1) is added, and f _i (F _s )=T _D It is also possible to set it as s+1/Ts+1·K _i (F _s −F _snio ) (5). Here, the optimum value of the coefficient of the primary lead/lag element may be determined by a trial run of the control system.

In the above embodiment, the object of feedforward control is the operation amount to the control valves 21, 16, 11, and 26, but the control valves 21 and 26 perform level control and concentration control of the evaporator 1 that discharges the feed liquid. It is effective even if it is limited to

<Effects> As explained above, according to the present invention, the following effects can be expected.

(1) When the discharge flow rate of the feed liquid to be concentrated is significantly changed in a short period of time, the level and concentration of the feed liquid in each evaporator can be stabilized in a short time without significantly changing the level and concentration of the feed liquid.

(2) In steady-state operation without changing the set value of the heating steam flow rate, the configuration is the same as the conventional control system, and the controllability of the conventional device is not lost.

(3) In conventional control systems, when changing the amount of heating steam, there is a large interference between concentration control and level control, and it is difficult to perform good control of both, but adding feedforward control as in the present invention As a result, interference between the two is reduced, and good controllability can be expected for both.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is a configuration diagram showing an example of a conventional device. 1, 2, 3... Evaporator, 4... Heated steam supply pipe line, 6... Heated steam flow rate sensor, 7, 11, 1
6, 21, 26, 30...control valve, 8, 13, 1
8, 23, 28...controller, 12, 17, 22...
... Level sensor, 21 ... Concentration sensor, 32 ...
Pressure sensor, S...heated steam, B...supply liquid,
B'...Drained fluid.

Claims (1)

[Claims] 1. In a control device for a multi-effect can which sequentially connects a plurality of evaporators and uses the steam generated in one evaporator to heat the next evaporator to sequentially concentrate the supplied liquid, a steam flow rate controller that adjusts the heated steam flow rate based on the measured value and set value of the heated steam flow rate; and a steam flow rate controller that adjusts the heated steam flow rate based on the measured value and set value of the heated steam flow rate; a concentration controller that adjusts the level of the feed liquid in the discharge evaporator based on the measured value and the set value; a level controller that adjusts the supply flow rate of the feed liquid based on at least the measured value and the set value of the level of the feed liquid in the discharge evaporator; A multi-effect tank control device comprising feed forward means for adding a manipulated variable related to the flow rate of heated steam to the manipulated outputs of the concentration controller and the level controller.