JPH0278420A - Method of supplying absorbent slurry to absorption column of wet type exhaust gas desulfurizer - Google Patents

Abstract

PURPOSE:To maintain pH at a target value in all operating states by installing a computing element which predicts the concn. of the absorbent in a liquid absorbent and can calculate the supply rate of the absorbent at which the pH can be maintained at the target value. CONSTITUTION:The predicted value 12 of the concn. of the absorbent in the liquid absorbent in an absorption column at the present point of time is calculated from the supply rate and withdrawal rate of the absorbent slurry and the absorption rate of the sulfur oxide in the absorption column and a dissolution rate constant 13 of the absorbent is determined in accordance with the sulfur oxide absorption rate and the concn. of the total Ca ions in the liquid absorbent in the absorption column and the predicted value 12 in the computing element 7. Further, the predicted value 14 of the concn. of the absorbent in the absorption column 14 after n-minutes is calculated from the sulfur oxide absorption rate calculated by the predicted load after n-minutes of the prescribed time and the predicted value 14 of the concn. of the absorbent in the absorption column necessary after n-minutes is calculated from the intensity of the hydrogen ions after n-minutes, the sulfur oxide absorption rate in the absorption column, the constant 13 and the concn. of the total Ca ions in the liquid absorbent are calculated in the computing element 11. The supply rate of the absorbent slurry to the absorption column is controlled in accordance with the deviation between the predicted values 14 and 15 in a coefft. device 17.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for supplying an absorbent slurry to a wet flue gas desulfurization device, and particularly to a method for maintaining the pH of an absorbent slurry in an absorption tower at a target value. The present invention relates to a method for supplying absorbent slurry to an absorption tower suitable for.

[Conventional technology]

As shown in FIG. 2, the conventional method of controlling a wet flue gas desulfurization equipment is to introduce exhaust gas into an absorption tower 23 from a duct 22, and circulate it there through the absorption tower 23, circulation pump 26, and circulation line 31. It is brought into gas-liquid contact with the absorption liquid 24. After the SO2 in the exhaust gas is absorbed by the absorption liquid, the exhaust gas is transferred to the exhaust line 3.
0 and is exhausted from the chimney.

On the other hand, the absorption liquid 24 that has absorbed SO2 flows down to the tank 25 from the bottom of the tower. Absorbent is supplied to the tank 25 from an absorbent slurry supply line 28, so that S0
The liquid that has recovered the absorption performance of No. 2 is supplied to the absorption tower 23 through the circulation line 31 by the absorption tower circulation pump 26. Incidentally, a part of the circulating fluid is discharged through the discharge line 27 and is oxidized into gypsum in a subsequent process.

In this SO2 absorber, the amount of absorbent supplied is conventionally controlled as follows. The pH value of the absorption liquid is detected by the pH meter 4 and inputted to the controller 19b.

The controller 19b inputs a signal to the adder 18b so that the pH value of the absorption liquid reaching the top of the column is constant.

On the other hand, the load detector 21 detects the load of 5o21 entering the system, that is, the load of the desulfurization plant, and inputs it to the adder 18b. Adder 1.8b adds the signal from controller 19b and the signal from load detector 21, and inputs the result to controller 19b as a set value signal.

Further, the flow rate of the absorbent slurry supply line 28 is detected by the absorbent slurry flowmeter 5 and inputted to the controller 1.9c. The controller 19c controls the absorbent slurry flow rate regulating valve 20 based on these signals.

However, in wet flue gas desulfurization equipment, the pH response to the addition of absorbent slurry is very slow (time constant is about 40 minutes), so by the time the pH reaches the set value,
It takes time equivalent to a time constant. Therefore, in order to maintain the pH at the set value, when changing the amount of absorbent supplied,
Accurate pH control is impossible unless you predict how much the pH will change after 0 minutes. In particular, conventional control systems that supply absorbent in accordance with pH deviations do not take into account the fact that pH controllability deteriorates when the load changes significantly.

As a control method to improve the controllability of this pH,
JP-A-61-97019, JP-A-62-204829
For example, the number etc.

JP-A No. 61-97019, as shown in Figure 3, p.
The pH future value prediction signal 4 is generated using the H prediction calculator (1) 42.
4 and the pH set value signal 40, the absorbent slurry supply amount is corrected. In this method, p
Since the predicted value of H greatly affects the amount of absorbent slurry supplied, the degree of pH prediction may become a problem.

Therefore, in Japanese Patent Application Laid-open No. 62-204829, as shown in FIG.
A control method has been devised in which the parameter correction signal 46 is input to the calculator 43 so that it matches the current value prediction signal 45, thereby improving the pH prediction accuracy. here,
41 is a desulfurization rate setting signal.

However, in these control methods, the absorbent is supplied based on the deviation between the set pH value and the measured value, so the oxidation state of the sulfite in the absorbent (e.g. total oxidation state, semi-total oxidation state) Depending on the oxidation state (oxidation state, partial oxidation state), the required amount of absorbent supply may vary significantly even for the same pH deviation. In particular, in a quasi-total oxidation state (the concentration of sulfite in the absorption liquid is almost zero and sulfite ions are present in a supersaturated state), the dissolution rate of the absorbent, that is, the neutralization reaction rate, is extremely reduced. In order to correct the necessary pH deviation, it may be necessary to add a large amount of absorbent in excess of several times the equivalent amount.

In this way, the conventional control method does not necessarily
There was a drawback that the pH of the absorption liquid could not be maintained at a set value.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into consideration the poor responsiveness of the absorbent pH to the addition of absorbent and the difference in the amount of absorbent required depending on the oxidation state of sulfite. In a quasi-total oxidation state, it is not possible to maintain the pH near the target value, so the absorbent is not properly supplied, the desulfurization performance is unstable due to pH fluctuations, and pH fluctuations promote scale formation. There was a problem with that.

The purpose of the present invention is to install a calculator that can calculate the amount of absorbent supplied to maintain the pH at the target value by predicting the concentration of the absorbent in the absorbent liquid, and to maintain the pH at the target value under all operating conditions. It is about maintaining.

[Means to solve the problem]

The above purpose is to introduce an absorbent slurry into an absorption tower of a wet flue gas desulfurization equipment in which flue gas is introduced into an absorption tower and brought into contact with an absorbent slurry in the absorption tower to absorb and remove sulfur oxides from the flue gas. A process of calculating the predicted value of the absorbent concentration in the absorption liquid in the absorption tower at the present time from the supply amount of absorbent slurry in the tower, the amount of extracted liquid and the amount of sulfur oxides absorbed, and the amount of sulfur oxides absorbed in the absorption tower. A step of determining the dissolution rate constant of the absorbent based on the total calcium ion concentration in the absorbent and the predicted value of the absorbent concentration, and the amount of sulfur oxide absorbed in the absorption tower calculated based on the expected load after a predetermined time of n minutes. , calculating a predicted value of absorbent concentration in the absorption tower after a predetermined time n minutes from the predicted value of absorbent concentration in the absorption tower at the current time and a dissolution rate constant of the absorbent; and p after a predetermined time n minutes. H
Based on the hydrogen ion strength determined from the set value, the amount of sulfur oxide absorbed in the absorption tower, the dissolution rate constant of the absorbent, and the total calcium ion concentration in the absorption liquid, the absorbent in the absorption tower required after a predetermined time of n minutes. and the amount of absorbent slurry supplied to the absorption tower based on the amount of deviation between the predicted absorbent concentration in the absorption tower after a predetermined time n minutes and the required predicted absorbent concentration. This is achieved by a method for supplying an absorbent slurry to an absorption tower of a wet flue gas desulfurization apparatus, which comprises a step of controlling.

〔Example〕

A specific embodiment of the absorbent supply amount control method of the present invention is shown in FIG. In FIG. 1, l is an exhaust gas flow strain meter, 2 is an inlet so2 concentration meter, and 3 is an outlet so2/lI! ! meter, 4 is p
H meter, 5 is an absorbent slurry flow meter, 6 is a flow meter for extracting slurry from the absorption tower 23 to the outside, 8 is a load request signal, 9 is a pulverizer, IO is a pH setting value, 11 is an absorbent concentration calculation Vessel (2
), 12 is an absorbent concentration signal, and 13 is an absorbent dissolution rate constant signal.

7 is an absorbent concentration calculator (1), which performs the following calculations. The absorbent concentration balance in the absorption liquid 24 in the absorption tower is as follows. Here, ■=tank volume (1), χ: absorbent concentration (mo A/n), t: time (h), y: absorbent slurry concentration (-), yp: absorbent purity (-), M a
: Absorbent molecule Wk (kg/mol), G
sl: absorbent slurry flow rate (kg/h), Rsoz
: S02 absorption M (mo/l/h), Gd: withdrawal flow Et (kg/h), γ: absorption liquid specific weight Ckg/
h) Gg: Exhaust gas flow M (N j! / h), 2
++20: Moisture in exhaust gas (-), Cso,
: Inlet SO2 concentration (ppm), ζ: Sulfur ratio ((Cso,
-C'so, ) /Cso, ), C'so,
: Outlet SO2 concentration.

Therefore, equations (1) and (2) are used for online measurement signal 1.
By solving based on 2.3.4.5.6, the predicted value χ (12 in FIG. 1) of the current absorbent concentration is obtained.

On the other hand, since the removed 5o21 and the absorbent removal REt are equal, Rsoz = V ・T a
= i3) γ β (Ca2'') where Ta ; absorbent consumption (moff/ε
・h), k: Absorbent dissolution rate constant, ()l''): Hydrogen ion concentration (mol/Il), (Ca''): Total calcium ion concentration in the absorption liquid (mol/'j2), α, β ,
T: Constant.

When equations (3) and (4) are solved using the current absorbent concentration χ determined from equations (1) and (2), the dissolution rate constant k of the absorbent can be fixed online. In a semi-slightly oxidized state, this dissolution rate constant becomes extremely small. Note that [Ca2+] can be easily estimated from pH and C1'bN degree. That is, CaSO4; Ca2” + 304CaS
Ca2+, which is present in the liquid in the form of O4, increases as pi-1 increases and then becomes saturated, and is determined by the pH. Also, CaCji2: Ca2” + 2(), 1
1- Since Ca2+ and C11- in the liquid exist in the form of the above formula, if Cji- is l mol / E, C
A total is 1/2 mol/il! becomes.

Therefore, (Ca”) represents CaSO4 and CaCA
'It becomes the sum of 2. Therefore, (Ca””)=f1 (pH)+f2 (Cji1
) In this way, the current absorbent concentration prediction signal (χ) 12 and the absorbent dissolution rate constant signal (k) 13 are determined by the absorbent concentration calculator (1) 7.

Next, 11 is an absorbent concentration calculation unit (2), which performs the following calculation using the online measurement signal 5.6.8, IO, and the output signal of the pulverizer 9. First, the operating conditions after n minutes are predicted using the following equation.

Here, L: load (%), R: over or under firing rate.

Based on this operating condition, the absorbent concentration prediction signal χ t+n14 after n minutes is determined from equations (1) to (4). At this time, the absorbent concentration signal 12 is used as the initial absorbent concentration. Note that k in equation (4) is the absorbent dissolution rate constant signal 13
Use.

When formula (1) is expanded into a difference, t+Δt t TV V Ma where, T, ■, Δt, Ma, y, Yp, Z H2O is known, and GdXGsg, Gg, C3O2, 77 can be found by online measurement.

By repeatedly calculating the above equation until iΔt=n, χ t+n is obtained from χt. In addition, the current values are used for the manipulated variables Gd, GQ, and GsQ, and Gg, C
5o2 is determined using equations (5) to (7) from the predicted load value.

η is pHt+Δ(, L/G <Glt/Gg t +
Δt), C5o2 t+Δt. here,
GQ is the amount of absorbent slurry sprayed in the absorption tower.

η −r (pH, L/c, c)t
+Δ1 1+Δt so2 t+Δ
t(3), From equation (4), pH=-j! ogto(H”)L+Δt
j+ΔtR=G
(1-χ)C・η・10-6/22
．． 4so2 L+Δt gt+Δt 1+2
0 5o2t+Δ11+Δt(Ca2+) =r1(
pH) +f2 (Cj'-')t+Δ1
The absorbent concentration prediction signal 15 required after 1+Δt n minutes is −pHs
et (H")-10...(8) (here, pH5et: pH setting value) (2), (
It can be calculated using equations 3) and (4).

t+n From the above equation, χ j+n5et is found. In addition, Rso2j
+n, (Ca2'') according to the procedure described above.

t+n Note that in the half-metal oxidation state, k in equation (4) becomes extremely small, and the required absorbent concentration prediction signal 15 becomes extremely large. In this manner, the absorbent concentration calculator (2) 11 can calculate the absorbent concentration prediction signal 14 after n minutes and the absorbent concentration prediction signal 15 necessary after n minutes.

The subtracter 16a calculates the deviation between the absorbent concentration prediction signal 14 after n minutes and the absorbent concentration prediction signal 15 required after n minutes, multiplies them by a constant coefficient in the coefficient unit 17, and adds them together.
In the conventional control system, the absorbent supply demand signal 29
is added, the subtractor 16b calculates the deviation from the output signal of the absorbent slurry flow meter 5, the controller 193 processes the signal, and the absorbent supply amount is adjusted by opening and closing the absorbent slurry flow rate regulating valve 20. Adjust.

Since the present invention has such a configuration, it is possible to predict the change in the concentration of the absorbent in the absorbent when the supply amount of the absorbent is manipulated, and the pH of the absorbent can be accurately controlled to a set value. The present invention is particularly effective when the load fluctuates significantly and when the half metal is in a single oxidation state.

FIG. 5 shows an example of pH control based on the control method of the present invention.

〔Test conditions〕

Exhaust gas amount: ~240 Nm/11, input so2
Concentration: 580 ppm, pH setting value: 5.7 In Fig. 5, the actual test is pH control using the control method of the present invention.
Compared to the conventional control shown by the dashed line, the pH is maintained close to the set value, and as a result, it becomes smaller even during changes in the desulfurization rate, ensuring stable desulfurization performance even during large load fluctuations. It has been obtained.

FIG. 6 shows the behavior when transitioning from a fully oxidized state to a half-metal oxidized state. With conventional control, the pH decreases and the desulfurization rate cannot be maintained constant, but with the control of the present invention, good pH controllability is obtained.

In addition, in the conventional control method, the focus is on the pH deviation, and it seems possible to deal with this deviation by increasing the amount of absorbent correction corresponding to this deviation, but it is not possible to automatically determine the oxidation state. , in cases other than the half-metal oxidation state, the pH deviates significantly from the set value.

〔Effect of the invention〕

According to the present invention, the future absorbent concentration in the absorbent liquid can be predicted in accordance with changes in the absorbent supply amount, resulting in the following effects.

(1) Even when the load fluctuates significantly, the pH of the absorbent liquid can be maintained near the set value, so stable desulfurization performance can be ensured.

(2) Since the pH fluctuation is reduced, the amount of scale produced in the absorption tower can be reduced. .

(3) Since the oxidation state is automatically predicted based on the dissolution rate constant, the absorbent pH can be maintained near the set value even when the activity of the absorbent decreases due to the half-metal oxidation state. As a result, stable desulfurization performance can be ensured.

[Brief explanation of the drawing]

Figure 1 is a detailed explanatory diagram of the present invention, Figures 2 and 4 are prior art system diagrams for controlling the supply amount of absorbent slurry to a wet exhaust gas desulfurization equipment, and Figures 5 and 6 are diagrams of the present invention. It is an explanatory diagram on the verification side of the effect of. ■...Exhaust gas flow meter, 2...Inlet SO2 concentration meter, 3
...Exit S○2i! ! 1 degree meter, 4... pH meter, 5.
...Absorbent slurry flow meter, 6...Absorbent slurry extraction flow meter, 7...Absorbent concentration calculator (1), 8...
- Load request signal, 9... Differentiator, 10... pH setting device, 11... Absorbent concentration calculator, 12... Current absorbent concentration signal, 13... Absorbent melting rate constant signal, 1
4...Absorbent concentration prediction signal after n minutes, 15...Absorbent concentration prediction signal required after n minutes, 16...Subtractor, 1
7... Coefficient unit, 18... Adder, 19... Controller, 2o... Absorbent slurry flow rate adjustment valve, 29... Absorbent supply demand signal. Agent Patent Attorney Takenaga Kawakita Figure 2: Load detector 22: Duct 23: Absorption tower 24: Absorption liquid 25: Tank 26: Absorption liquid circulation pump time (minutes) Figure 6

Claims (1)

[Claims] Absorption in the absorption tower is a method for supplying absorbent slurry to the absorption tower of a wet flue gas desulfurization equipment in which flue gas is introduced into the absorption tower and brought into contact with an absorbent slurry in the absorption tower to absorb and remove sulfur oxides in the flue gas. The process of calculating the predicted value of the absorbent concentration in the absorption liquid in the absorption tower at the present time from the supply amount and withdrawal amount of agent slurry and the amount of sulfur oxide absorbed, and the process of calculating the predicted value of the absorbent concentration in the absorption liquid in the absorption tower and A step of determining the dissolution rate constant of the absorbent based on the total calcium ion concentration and the predicted value of the absorbent concentration, the amount of sulfur oxide absorbed in the absorption tower calculated based on the expected load after a predetermined time of n minutes, and the amount of sulfur oxide absorbed at the above-mentioned current time. A step of calculating a predicted absorbent concentration in the absorption tower after a predetermined time n minutes from a predicted value of the absorbent concentration in the absorption tower and a dissolution rate constant of the absorbent, and a step of calculating from a pH setting value after a predetermined time n minutes. Based on the hydrogen ion strength, the amount of sulfur oxide absorbed in the absorption tower, the dissolution rate constant of the absorbent, and the total calcium ion concentration in the absorption liquid, the predicted value of the concentration of the absorbent in the absorption tower required after a predetermined time n minutes. and a step of controlling the amount of absorbent slurry supplied to the absorption tower based on the amount of deviation between the predicted absorbent concentration in the absorption tower after a predetermined time n minutes and the required predicted absorbent concentration. A method for supplying absorbent slurry to an absorption tower of a wet flue gas desulfurization apparatus, comprising: