JP3091247B2 - Method and apparatus for controlling flow rate of circulating absorption liquid to absorption tower in wet exhaust gas desulfurization unit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a control apparatus for controlling the flow rate of circulating an absorbent to an absorption tower of a wet exhaust gas desulfurization apparatus. The present invention relates to a method and apparatus for controlling the flow rate of circulating an absorbent to an absorption tower of a wet exhaust gas desulfurization apparatus suitable for reducing pump power.

[0002]

2. Description of the Related Art As shown in FIG. 6, in a wet flue gas desulfurization apparatus, an inlet exhaust gas 22 is brought into gas-liquid contact with an absorbing liquid supplied from an absorbing liquid circulating line 24 in an absorbing tower 26, and SO _{2 in} the exhaust gas is discharged. Is fixed in the form of sulfite in the absorbing solution, and the exhaust gas is discharged from the chimney through the discharge line 23. S
The absorbing liquid having absorbed O ₂ flows down from the tower to the circulation tank 27. The circulation tank 27 has an absorbent slurry flow control valve 2
Absorbent is supplied through 8, and the liquid having recovered the absorption performance of SO ₂ is supplied to the absorption tower 26 by the absorption tower circulation pump 18. Part of the circulating liquid is discharged through the withdrawal line 25, and in a later step, the sulfite in the absorbing liquid is oxidized and recovered as gypsum.

[0003] As a control method of this type of wet flue gas desulfurization apparatus, for example, Japanese Patent Application Laid-Open No. Sho 60-110320 is disclosed.
Publication. In this control method, an optimal pH value signal 31 of the absorbing liquid circulating through the absorption tower 26 and an optimal operating number signal 32 of the absorption tower circulating pump 18 are set by the simulation model 30 in accordance with the load of the exhaust gas flowing into the absorption tower. Then, when the load is stable, a number obtained by subtracting 1 from the optimum operation number is set, and a certain increment is added to the above-mentioned optimum pH value to obtain a set value of the pH. Only when the condition (1) is satisfied, the supply amount of the absorbent and the number of pumps are controlled based on the changed set value.

However, in this control method, the simulation
That the simulation model can accurately reproduce the behavior of the actual machine.
And is essential. In desulfurization equipment, desulfurization performance
Is the exhaust gas flow rate, the inlet SO_TwoConcentration, absorption solution pH and solution
-Governed by the gas ratio, but at the same pH,
Oxidation state, ie, sulfites (eg, CaS
O _ThreeThe desulfurization performance differs depending on the concentration of ()).

FIG. 7 shows the relationship between the oxidation state and the desulfurization performance.
As is clear from the figure, in order to accurately predict the change in the desulfurization rate due to the change in operating conditions by a simulation model, the oxidation state, that is, the concentration of sulfite, is required. In consideration of the uncertainty of the salt oxidation rate, it is necessary to correct the data by manual analysis, which is complicated in driving operation. No consideration was given to the possibility of occurrence.

[0006]

In the above-mentioned prior art, the optimal number of operating absorber circulation pumps is determined by a simulation model. However, no consideration is given to the accuracy of the simulation model. If the desulfurization rate cannot be maintained, and if the operating condition changes drastically, it is necessary to correct the coefficients of the simulation model based on the manually analyzed values of the composition of the absorbing solution, thereby increasing the burden on the operator. There was such a problem.

An object of the present invention is to provide a control device capable of maintaining a desulfurization rate near a target value using only information that can be measured online.

[0008]

According to a first aspect of the present invention, an exhaust gas containing sulfur oxide (SOx) is introduced into an absorption tower, and is contacted with an alkaline absorbing solution to remove SOx. In the method for controlling the flow rate of circulating an absorbent to an absorption tower of a wet exhaust gas desulfurization apparatus, the SO introduced into the absorption tower is controlled.
x Calculate the leading value of the circulation flow rate demand based on the total amount and the pH value of the absorbent and the set value of the desulfurization rate, and determine the value between the desulfurization rate and the set value of the desulfurization rate determined from the measured SOx concentration values at the inlet and outlet of the absorber. A circulating flow correction amount is obtained by a self-adjustment type fuzzy inference corresponding to the deviation value and the rate of change of the deviation value, and the correction amount is added to the preceding value of the circulating flow demand prior to the absorption tower circulating pump. The present invention relates to a method for controlling a flow rate of circulating an absorbent to an absorption tower of a wet exhaust gas desulfurization apparatus, characterized in that the number is controlled.

In a second aspect, in the first aspect,
SOx is SO _2, and the SOx amount introduced absorption tower relates to an absorbent liquid circulating flow control method to the absorption tower of a wet flue gas desulfurization apparatus characterized by determining from the SO ₂ concentration in the absorption tower inlet gas and the exhaust gas flow rate . The third invention is an SO
Exhaust gas containing sulfur oxides such as ₂ is introduced into the absorption tower and brought into contact with an alkaline absorbing solution to absorb and remove the sulfur oxides. , Exhaust gas S at the inlet to the absorption tower
O ₂ concentration, the absorption solution pH value to the absorption tower, and flow demand prior value calculator for calculating an absorption liquid circulation flow rate demand preceding value of the absorption tower based on the desulfurization ratio setting value, the absorption tower inlet of the exhaust gas,
A device for calculating the desulfurization rate from the measured SO ₂ concentration at the outlet,
A deviation between the calculated desulfurization rate and the desulfurization rate set value and a fuzzy controller that calculates a demand correction signal of the absorption tower circulation flow rate using fuzzy inference that can self-adjust the control rule based on the change rate of the deviation; A device for determining a circulation flow rate of an absorber based on an output value of a demand leading value calculator and an output value of a fuzzy controller is provided. .

[0010]

The leading value of the demand for the circulation flow rate of the absorption tower based on the on-line measured quantity is operated so as to change the flow rate demand, which is the base for maintaining the desulfurization rate at the target value, in accordance with the change of the operation state. If the system is operated with the circulation flow rate of the absorption tower serving as the base, a deviation occurs between the desulfurization rate and the desulfurization rate set value.

Based on the deviation and the rate of change of the deviation,
Self-adjusting fuzzy inference, that is, the control response is evaluated in real time, and the control rule is automatically corrected based on this evaluation. , The desulfurization rate does not deviate from the target value.

[0012]

FIG. 1 shows a specific embodiment of the method for controlling the circulation flow rate of an absorption tower of a wet flue gas desulfurization apparatus according to the present invention. In the figure, reference numeral 6 denotes a flow rate demand leading value calculator, which is an exhaust gas flow meter 1, a pH meter 2, an inlet SO ₂ concentration meter 3, and a desulfurization rate setting device 4.
The following calculation is performed using the respective output signals of.
The desulfurization rate η is expressed by the following equation.

(Equation 1)

(Equation 2)

Here, BTU: constant, pH: pH value, S
O ₂ : inlet SO ₂ concentration, L / G: liquid-gas ratio, f ₁ ,
f ₂ , f ₃ : In order for the functional desulfurization rate η to become the desulfurization rate set value η _set , from the equations (1) and (2),

(Equation 3)

Here, L _d : leading value of flow demand,
G _g : Exhaust gas flow rate Accordingly, the flow rate demand preceding value signal 11 is obtained from the equation (3). On the other hand, the inlet SO ₂ concentration meter 3 and the outlet S
A desulfurization rate signal 9 is obtained from the output signal of the O ₂ concentration meter 5 using a subtractor 7a and a divider 8, and the desulfurization of the output signal of the desulfurization rate setting device 4 and the desulfurization rate signal 9 is performed by a subtractor 7b. Rate deviation signal 1
0 is obtained and input to the fuzzy controller 13.

As shown in FIG. 5, the fuzzy controller 13
It comprises a control performance evaluator 19, a control rule corrector 20, and a fuzzy correction signal calculator 21. The control performance evaluator 19 performs the following calculation based on the desulfurization rate deviation signal 10. The desulfurization rate deviation signal 10 is a deviation between the output signal η _set of the desulfurization rate setting device 4 and the desulfurization rate η, and is scaled as follows.

(Equation 4)

(Equation 5)

Here, η _set : set value of desulfurization rate, η _n : n
Calculated value of desulfurization rate at time point, Ke,

[Outside 1] : Scaling factor, e _n: n Time desulfurization rate deviation standard value at point, △ e _n: indicates a membership function of the change e _n and △ e _n desulfurization rate deviation standard value 2 in the n time point.
The meanings of the symbols in the figure are as follows. NB: negative and large (Negative Big), NS: negative and small (Negative Small), ZE: almost zero (Zero E)
qual), PS: Positive Small, P
B: large positive (Positive Big) Thus, the control performance evaluator 19, to quantify the control performance e _n and △ e _n in the membership functions.

The control performance evaluation is similar to a method which the operator is performing, e _n and △ e _n, namely to evaluate the control condition directly feeds back a correction amount of the control rules. FIG. 4 shows a control rule for determining the correction amount. How to read this figure, the situation of e _n and △ e _n, originally correction amount of the control operation that should have been added to the control output in the past, that is, the correction amount Q of the absorption tower circulating flow rate . In the figure, for example, if in e _n = NB, if △ e _n = NB, a control rule such as Q = NB.

Therefore, the control performance evaluator 19 creates a control rule for determining the correction amount of the circulation flow rate of the absorption tower based on the control characteristics of the desulfurization rate. Next, the control rule modifier 20 determines a control rule as follows. FIG. 3 shows a basic control rule. How to read this diagram
Is the same as that in FIG. 4, the status of e _n and △ e _n, determines the increment H of the absorption tower circulating flow to be corrected.

Here, based on the evaluation result by the control performance evaluator 19, a control rule considered to be responsible for the current control state is modified or newly created. The control state at sampling time k is caused by the combined effect of all control operations in the past. Therefore, the control rule R _kj that infers the control operation before j sampling is modified by the correction amount Q _k given by the control performance evaluator 19.

The rule R _kj is _defined as ｛e _kj , △ e _kj , H
_kj ｝. This is because, in the example of FIG. 3, if e _kj = NB, and if _{Δe kj} = NB, then H _kj = N
B. Therefore, the modified rule

[Outside 2] Is represented by the following equation.

(Equation 6)

The replacement of the control rules is performed by the following logic, where R is the set of the entire rules.

(Equation 7) here,

[Outside 3] _Denotes the complement of R _kj , and ∩ and ∪ denote the product and sum of the sets. In this way, the control rule corrector 20 automatically corrects the control rule. Next, the fuzzy correction signal calculator 2
In step 1, the following operation is performed. Control rule modifier 20
, And the created rule is R (M), M = 1, 2,..., N
And Here, N indicates the number of rules.

[0022] e _n, the fuzzy set for the value of △ e _n, the rules M, and A _M, B _M. The fuzzy set of the operation amount of the increment, which is determined from the rule M and C _M, the membership functions and μc _M. At this time, from rule M

(Equation 8) Using this WM, the membership function of the basic increment of the operation amount satisfying the rules 1 to _M

[Outside 4] Is

(Equation 9)

The coordinates of the center of gravity of

[Outside 5] Is calculated by the following equation.

(Equation 10)

This value (outside 5) is set as a basic increment P of the manipulated variable. Assuming that the correction amount of the circulation amount of the absorber at the time point n is △ ∪n, the correction amount △ ∪n + 1 at the next time point _{n + 1} is

[Equation 11] Here, G: control gain As described above, the fuzzy controller 13 performs the above-described calculation for each sampling time, and inputs the flow rate demand correction amount signal 14 to the adder 12. The adder 12 adds the flow rate demand leading value signal 11 and the flow rate demand correction signal 14 to output a flow rate demand signal 15, which is input to the pump number setting device 16. The number-of-pumps setting unit 16 obtains the required number of pumps that does not fall below the circulating flow demand, and uses this as the optimum operating number signal to determine the number of the absorption tower circulating pumps 18.

The present control system is basically based on a flow rate demand correction signal 14 which is a feedback correction signal obtained by subjecting a flow rate demand preceding signal 11 and a desulfurization rate deviation signal 10 to signal processing by a self-adjustment type fuzzy inference. The method is for calculating the circulating flow demand, and is characterized in that a flow demand advance value is obtained from an online measurement signal, and that a self-adjustment type fuzzy inference is used for feedback correction.

As for the control of the circulation flow rate of the absorption tower,
Here, control of the number of pumps is assumed, but a similar control method can be applied to flow rate control by pump rotation speed control using a fluid coupling or the like. In the present invention, the fuzzy controller 13 can self-adjust the control rules based on the controllability of the desulfurization rate, so that the desulfurization rate can be maintained near the target value in any operating state, and stable operation of the desulfurization device is ensured. In addition to this, it is possible to reduce the pump power cost at a low load.

[0027]

According to the present invention, by installing a self-adjusting fuzzy controller for correcting the demand for the circulation flow rate of the absorption tower, the circulation flow rate of the absorption tower or the number of operating circulation pumps can be determined while observing the change behavior of the desulfurization rate. As a result, it is possible to control the circulating flow rate of the absorption tower by a veteran operator who is familiar with the behavior of the plant, maintain the desulfurization rate at the target value in all operating conditions, secure stable desulfurization performance, and By the appropriate control, there is an effect that the power of the pump for circulating the absorption tower at a low load can be reduced.

[Brief description of the drawings]

FIG. 1 is a control system diagram showing one embodiment of a method for controlling a circulation flow rate of an absorption tower according to the present invention.

FIG. 2 is an explanatory diagram of a membership function used in the present invention.

FIG.

FIG. 4 is an explanatory diagram showing an example of a control rule in a fuzzy controller used in the present invention.

FIG. 5 is a block diagram showing a configuration of a self-adjusting fuzzy controller.

FIG. 6 is a control system diagram showing a conventional absorption tower circulation flow rate control method.

FIG. 7 is a diagram showing the relationship between pH, oxidation state and desulfurization rate.

[Explanation of symbols]

1 ... an exhaust gas flowmeter, 2 ... pH meter, 3 ... inlet SO ₂ concentration meter, 4 ... desulfurization rate setting device, 5 ... outlet SO ₂ concentration meter, 6 ... flow demand prior value calculator, 7a, 7b ... subtractor , 8 divider, 9 ... desulfurization rate signal, 10 ... desulfurization rate deviation signal, 11 ...
Flow demand advance value signal, 12 ... Adder, 13 ... Fuzzy controller, 14 ... Flow demand correction signal, 15 ... Flow demand signal, 16 ... Pump number setting device, 17 ... Optimum operation number signal, 18 ... Absorption tower circulation pump , 19: control performance evaluator, 20: control rule corrector, 21: fuzzy correction signal calculator.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁷ Identification code FI G05B 13/02

Claims (3)

(57) [Claims] 1. An exhaust gas containing sulfur oxide (SOx) is introduced into an absorption tower, and brought into contact with an alkaline absorbing solution to produce SOx.
In the method of controlling the circulation flow rate of the absorbent to the absorption tower of the wet exhaust gas desulfurization device for removing water, the leading demand value of the circulation flow rate of the absorption tower is determined based on the total amount of SOx introduced into the absorption tower, the pH value of the absorption liquid, and the set value of the desulfurization rate. , SOx at inlet and outlet of absorption tower
A circulating flow rate correction amount is determined by a self-adjusting fuzzy inference corresponding to a deviation value between the desulfurization rate obtained from the concentration measurement value and the desulfurization rate set value and a rate of change of the deviation value, and the correction amount is determined by the absorption tower. A method for controlling a circulation flow rate of an absorbent to an absorption tower of a wet exhaust gas desulfurization apparatus, wherein the number of absorption tower circulation pumps is controlled based on an overall flow rate demand added to a preceding value of a circulation flow rate demand. 2. The wet exhaust gas desulfurization apparatus according to claim 1, wherein SOx is SO ₂ , and the total amount of SOx introduced into the absorption tower is determined from the exhaust gas flow rate and the SO ₂ concentration of the exhaust gas at the inlet of the absorption tower. A method for controlling the flow rate of circulating absorption liquid to the absorption tower. 3. An exhaust gas containing sulfur oxides such as SO ₂ is introduced into an absorption tower and brought into contact with an alkaline absorption liquid to absorb and remove the sulfur oxides. In the control device, the flow rate of the exhaust gas, the concentration of SO _{2 at} the inlet of the exhaust gas to the absorption tower, the pH of the absorbing solution to the absorption tower
A flow rate demand advanced value calculator for calculating an absorption liquid circulation flow rate demand advance value to the absorption tower based on the value and the desulfurization rate set value;
Fuzzy absorption tower inlet of the exhaust gas, a device for calculating the desulfurization rate than SO ₂ concentration measurements of the outlet, the control rule based on the deviation and the change rate of the deviation between the computed desulfurization rate and the desulfurization ratio setting value can self-adjusting A fuzzy controller for calculating a demand correction signal for the circulation flow rate of the absorption tower using inference, and a device for determining the circulation flow rate of the absorption tower based on the output value of the flow rate demand advance value calculator and the output value of the fuzzy controller are provided. An apparatus for controlling the flow rate of circulating absorption liquid to an absorption tower of a wet exhaust gas desulfurization apparatus.