JPS61259733A - Apparatus for controlling ph of absorbing tower - Google Patents

Abstract

PURPOSE:To rapidly perform the control of pH by corresponding to the high speed change in load, by mounting a treating gas flow amount detector, a pH detector, a pH deviation operator, a multiplier, a pH regulator, an absorbent flow amount detector and an absorbent flow amount regulator. CONSTITUTION:The treating gas flow amount signal S21 from a treating gas flow amount detector 21 is inputted to a multiplier 23 and the pH detection signal S14 from a pH detector 14 is inputted to an operator 22 to operate pH deviation while the output thereof is inputted to the multiplier 23 to output a proportional sensitivity signal S23 to a pH regulator 15. The pH regulator outputs the absorbent flow amount set value signal S15 calculated from the proportional sensitivity signal S23, the pH detection signal and a preset pH set value to an absorbent flow amount regulator 16 to adjust the opening degree of a flow control valve 11.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a desulfurization plant for removing sulfur dioxide gas (S O2) from treated gas, and in particular to improvement of an absorption tower PH control device that controls the PH of circulating fluid. It depends.

[Conventional technology]

The schematic structure of a desulfurization plant, for example a wet lime gypsum process waste smoke desulfurization plant using carbon dioxide as an absorbent, will be described with reference to the system diagram shown in FIG.

In FIG. 5, a processing gas 3 containing sulfur dioxide gas is introduced into the absorption tower 1 from above through a processing gas introduction duct 2. A circulating fluid 5 is contained in a tank 4 provided below the absorption tower 1, and this circulating fluid 5 is circulated within the absorption tower 1 by a circulation pump 6 and a circulation pipe 7. The processing gas 3 comes into contact with the circulating liquid 5 in the circulation tower 1, and the processing gas 3
The sulfur dioxide gas contained therein is removed. That is, SO2 in the processing gas 3 is converted to H2S by the reaction shown by the following formula CI).
O, is generated and flows down. A part of this H2so3 is oxidized by oxygen (02) in the processing gas 3, and becomes H2SO4 as shown by the following formula (■). Also, the remaining H2SO,
is oxidized to H, 304 in the tank 4 by oxygen in the air injected from the air pipe 8.

So2+H, O→H, SO,...-CI) H2SO,+
-02→H, So, (II) Then, the treated gas that has passed through the absorption tower 1 and from which sulfur dioxide gas has been removed is discharged into the atmosphere as a treated gas through the exhaust duct 9.

When the contact with the treated gas 3 continues in the absorption tower 1 as described above, a large amount of H2SO generated by the absorption reaction and oxidation reaction shown in (I) and (If) above is contained in the circulating liquid 5. Since it is included, it will be S0 unless some measures are taken.
2 becomes difficult to absorb. Therefore, an absorbent, such as calcium carbonate (Ca COs ), is supplied to the circulating fluid 5 in the tank 4 through an absorbent supply pipe 12 equipped with a flow rate detector 10 and a flow rate control valve 11, and the following formula (I[ As shown in I), the circulating fluid 5 is neutralized and regenerated so that sulfur dioxide gas can be easily absorbed.

H2SO4+CaCO3-+CaSO4+H20+C0
2j-(III) Ca produced by the above formula (I[I)
A part of the circulating fluid 5 containing 5O is transferred to another process (not shown) via the transfer piping 13.

As suggested by the above explanation, the 802 absorption capacity of the circulating liquid 5 has a great influence on the performance of the desulfurization plant.The pH of the circulating liquid 5 is an indicator of the S02 absorption capacity of the circulating liquid 5. be. That is, Ca COz in the circulating fluid 5
The higher the concentration and the higher the pH, the more the SO2 absorption reaction is promoted.

It is conceivable to simply supply a large amount of absorbent to maintain the pH of the circulating fluid high, but this is not preferable from the viewpoint of cost.

For these reasons, it is necessary to maintain a pH level that maintains the desired performance.
It is desired to operate a desulfurization plant in

This is the desulfurization rate within the absorption tower 1.

Sulfur dioxide in the treated gas that is eventually released into the atmosphere
□ Maintain the gas concentration stably at the specified value, and
□ This leads to being able to follow changes in load (S02 amount at the absorption tower inlet) with good responsiveness.

By the way, as described above, it is the increase in the H2S Oa concentration in the circulating fluid that lowers the pH of the circulating fluid, and on the other hand, it is the Ca COz concentration in the circulating fluid that increases the pH of the circulating fluid. Therefore, the pH of the circulating fluid is determined by the balance between the amount of absorbed S02 and the concentration of CaC0.

In the conventional desulfurization plant shown in FIG. 5, the pH control device for the circulating fluid is as follows.

That is, a pH detector 14 is attached to the circulation pipe 7, and an output signal S 1 from this pH detector 14
4 is input to the PH regulator 15. This PH regulator 15
Then, the preset pH value and the output signal from the pH detector 14 are compared to determine the absorbent flow rate set value signal SSS.
Output. This signal is input to the absorbent flow regulator 16 together with the output signal of the flow rate detector 10, and the flow rate regulating valve it
Adjust the opening. In this way, the pH of the circulating fluid 5 [Problem to be solved by the invention] In the conventional pH control device described above, the proportional sensitivity of the pH mm meter 15 is kept constant regardless of fluctuations in the desulfurization load. Further, the proportional sensitivity of this PH regulator 15 is set so as not to oscillate at low loads. For this reason, even if the proportional sensitivity is an optimal value at low loads, the proportional sensitivity is too small at high loads, and the rapid response to load changes is slow, causing a phenomenon in which the pH of the circulating fluid 5 fluctuates greatly. If such a phenomenon occurs, the SO2 absorption reaction will be affected, and the SO2 absorption reaction of the treated gas at the outlet of the absorption tower 1 will be affected.
2 concentration became unstable and there was a risk that it would deviate from the regulation value.

In addition, in order to prevent the So, 9 degrees of the treated gas from deviating from the regulation value, the pH value of the 1i reflux liquid 5 must be made higher than necessary in advance, which reduces running costs. There was a problem in that it caused the temperature to rise.

The present inventors found that the cause of the above phenomenon, ie, the amount of CaCO3 remaining in the system, is a function of the processing gas flow rate and the PH of the circulating fluid. An example of these relationships is shown in Figure 6, where the horizontal axis represents the processing gas flow rate and the vertical axis represents the residual C in the system.
The relationship between the two is shown as aCO3 using the pH of the circulating fluid as a parameter. From FIG. 6, it can be seen that when considering the increase in load, it is necessary to supply an extra amount of absorbent not only to increase the desulfurized SO2 equivalent but also to increase the amount of CaCO3 remaining in the circulating fluid.

Now, if the load increase rate is small (1 to 2%/min),
Since the rate of change in residual CaCO3 is small, even a conventional pH control device can follow the deviation between the pH of the circulating fluid and the pH set value before it becomes large. However, when the load increase rate is large (3 to 5%/min), the rate of change in the amount of residual CaCO3 is large, so conventional pHf control devices cannot keep up with it. Immediate response to load changes is slow.

In addition, the pH deviation is set to 0.1, for example, with respect to the flow rate of the processing gas.
change (e.g. from pH 5.3 to pH 5.4)
The amount of residual CaCO3 required for this purpose was investigated. As a result, the seventh
As shown in the figure, it was found that even if the pH deviation to be changed was the same as 0.1, the residual Ca CO3Ji had to be increased as the flow rate of the process gas increased. This causes further slowing down of immediate response to high-speed load changes.

The present invention has been made to solve the above problems, and is an absorption tower PR control that can quickly make the pH of the circulating fluid follow the set value even in response to rapid load changes, and can reduce running costs. The purpose is to provide a device.

[Means for solving problems]

In order to solve the above-mentioned problems, the present inventors developed pHW14
The present invention was developed by considering the use of a value proportional to the pH deviation and the flow rate of the processing gas for control as the ratio of the moderator. That is, regarding the pH deviation, the proportional sensitivity is set as an increasing function of the pH deviation, and the processing gas flow rate is also controlled so that the proportional sensitivity increases as the processing gas flow rate increases.

That is, the absorption tower pH control device of the present invention includes a processing gas flow rate detector that detects the flow rate of processing gas introduced into the absorption tower, a PH detector that detects the pH of the circulating liquid, and a pH detector that detects the pH of the circulating liquid.
Input the output signal of the H detector and check the difference (pH
a multiplier that multiplies the output signal of the processing gas flow rate detector by the output signal of the function calculator; and output the absorbent flow rate set value signal.
a regulator, an absorbent flow rate detector that detects the flow rate of absorbent supplied to the absorption tower, and an output signal of the pH adjuster and an output signal of the absorbent flow rate detector that are input to the absorbent control valve. It is characterized by comprising an absorbent flow rate regulator that adjusts the opening degree.

[Effect]

According to such an absorption tower pH control device, the proportional sensitivity of the pHtJRWH device can be controlled in proportion to the pH deviation and the flow rate of the treated gas, thereby changing the flow rate of the absorbent. Such control is shown in Figure 2, for example. Figure 2 shows the relationship between pH deviation (pH set value - circulating fluid pH) and proportional sensitivity x control deviation (control deviation = pH deviation / pH meter span). It is something. As can be seen from Fig. 2, the absorption tower PH control device of the present invention can perform gentle control when the pH deviation is small, and as the pH deviation increases or the processing gas flow rate increases, the correction by the conventional device is possible. Since a larger correction is performed than the above, it is possible to quickly make the pH of the circulating fluid follow the set value. As a result, there is no need to increase the supply amount of 6 absorbent more than necessary.
Running costs can be reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Note 1. 0 Absorption tower according to the present invention p
Newly provided devices in the H control device are a processing gas flow rate detector 21, a calculator 22, and a multiplier 23.

At tm-th, the processing gas flow rate signal S 21 detected by the processing gas flow rate detector 21 provided midway through the processing gas introduction duct 2 is input to the multiplier 23 .

On the other hand, pH detection signal S detected by pH detection @14
14 is input to the calculator 22 to calculate the difference from a preset pH setting value, that is, the pH deviation, and the output signal is input to the multiplier 23 .

The multiplier 23 calculates the product of the processing gas flow rate signal and the pH deviation, and outputs the resultant proportional sensitivity signal S23 to the PHH moderator 15.

The pH regulator 15 outputs an absorbent flow rate set value signal Sli determined from the proportional sensitivity signal S-, the pH detection signal, and a preset pH set value. That is, pH1ll
The ff unit 15 converts PI or PID (
P: proportional, I: integral, D: differential) control is performed, and the following formula (
ff) is performed.

ε= (pH setting value - pH)/pH, n where, Sts
: pH adjuster output signal (absorbent flow rate setting value signal) F : Absorbent flow rate maximum value la! S23: Proportional sensitivity @ - Control deviation pi (: pH meter span pn TK two integral time TD: Differential time This absorbent flow rate set value signal S1 @ is absorbent flow rate regulator 1
6 is input.

The absorbent flow rate regulator 1B adjusts the opening degree of the flow rate regulating valve 11 based on this set value signal S15 and the output signal of the flow rate detector 10.

According to such an absorption tower pH control device, the flow rate of the absorbent is changed by changing the proportional sensitivity of the pai1 regulator in proportion to the pH deviation and the flow rate of the process gas. It is possible to control the circulating fluid by making larger corrections than before even in response to high-speed load changes, and quickly adjusting the circulating fluid P.
H can be made to follow the set value. Therefore, it is not necessary to increase the amount of absorbent supplied more than necessary, and running costs can be reduced.

The results of actually desulfurizing the treated gas using the conventional pH control device and the pH control device of the above example are shown in the third table.
Figure and 4th rI! In both cases, the load change rate was 5%/min.

In the case of the conventional apparatus shown in FIG. 3, the pH deviation becomes temporarily large during a high-speed load increase, and as a result, the SO2 concentration in the treated gas at the outlet of the absorption tower also becomes temporarily large. On the other hand, in the case of the apparatus of the above embodiment shown in Fig. 4, the response is good even when the load increases rapidly, and the p)1 deviation is suppressed to a small value, and as a result, the S02 concentration in the treated gas is also below the regulation value. It can be seen that it can be maintained so as not to exceed.

In addition, in the absorption tower pH control device of the said Example.

Although the proportional sensitivity is changed by feedback control, the present invention is not limited to this, and can also be applied when feedforward control is involved or when changing the pH setting value. [Effects of the Invention] As detailed above, according to the present invention, the pH of the circulating fluid can be made to quickly follow the set value □ even in response to rapid load changes, and an excessive amount of absorbent is not used □
Absorption tower p that can reduce running costs
H control device can be provided.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an absorption tower pH control device according to an embodiment of the present invention, and Fig. 2 is a system diagram of an absorption tower pH control device according to an embodiment of the present invention and a conventional absorption tower p.
PH deviation and proportionality in H control device ゛Characteristic diagram showing the relationship between sensitivity x control deviation, Figure 3 shows the changes in circulating fluid pH and outlet SO2 concentration during high-speed load increase when using a conventional pH control device. Figure 4 is a characteristic diagram showing the changes in pH and outlet S02 concentration of the circulating liquid during a high-speed load increase when using the pH control device according to the embodiment of the present invention, and Figure 5 is a characteristic diagram showing changes in the pH and outlet S02 concentration of the circulating fluid when using the pH control device according to the embodiment of the present invention. System diagram of the PHH control device, Figure 6 shows the relationship between the process gas flow rate and the amount of residual Ca C03 in the circulating fluid using the PH of the circulating fluid as a parameter Characteristic diagram, Figure 7 shows the relationship between the process gas flow rate and the amount of residual Ca C03 in the circulating fluid It is a characteristic diagram showing the relationship with the amount of residual CaCO3 necessary to correct the deviation by 0.1. 1... Absorption tower, 2... Processing gas introduction duct, 3...
・Processing gas, 4...Tank, 5...Circulating fluid, 6...
・Circulation pump, 7... Circulation piping, 8... Air piping,
9...Exhaust duct, 10...Flow rate detector, 11...
・Flow rate adjustment valve, 12... Absorbent supply piping, 13...
Transfer piping, 14--PH detector, 15--pHm controller 6--absorbent flow rate regulator, 21--processing gas flow rate detector, 22--computer, 23-- - Multiplier. Applicant Sub-Agent Patent Attorney Supply Pressure Takehiko Figure 2 Figure 3 Time (MIN)

Claims (1)

[Claims] In a desulfurization plant that introduces a treated gas containing sulfur dioxide gas into an absorption tower and desulfurizes it by contacting it with a circulating liquid containing an absorbent that circulates within the absorption tower, the flow rate of the treated gas introduced into the absorption tower is a processing gas flow rate detector for detecting, a pH detector for detecting the pH of the circulating fluid, a calculator for inputting the output signal of the pH detector and calculating a difference from a pH set value, and the processing gas flow rate. a multiplier that multiplies the output signal of the detector and the output signal of the function calculator; and a pH multiplier that inputs the output signal of the pH detector and the output signal of the multiplier and outputs an absorbent flow rate set value signal. a regulator, an absorbent flow rate detector that detects the flow rate of absorbent supplied to the absorption tower, and an output signal of the pH adjuster and an output signal of the absorbent flow rate detector that are input to the absorbent control valve. An absorption tower pH control device comprising an absorbent flow rate regulator that adjusts the opening degree.