JPS6150618A - Ph controller of absorbing tower - Google Patents

Abstract

PURPOSE:To hold the SO2-concn. and desulfurization ratio of exhaust gas to predetermined values, by controlling the pH-value of the absorbing solution of a desulfurization apparatus. CONSTITUTION:The flow amount of treating gas is detected by a treating gas flow amount detector 10 and the signal S11 thereof is inputted to a function calculator 21 to obtain a proportional sensitivity signal S21 which is, in turn, inputted to a pH regulator 22 along with the signal of a pH detector 13 to obtain proportional sensitivity to output a flow amount setting value signal S14. This signal S14 and the signal from an absorbent supply flow amount detector 17 are inputted to an absorbent flow amount regulator 15 to regulate the opening degree of an absorbent flow amount regulation valve 16.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a desulfurization plant for removing sulfur dioxide gas (8(h)(r) from a process gas, and in particular an absorption tower pH control device for controlling the pH of a circulating liquid. Regarding.

In a conventional desulfurization plant, for example, a wet lime gypsum flue gas desulfurization plant using carbonate or calcium hydroxide as an absorbent, the concentration of sulfur dioxide gas (S02, In order to maintain the desulfurization rate in the absorption tower at a predetermined value, it is necessary to reduce the p of the circulating liquid that circulates throughout the absorption tower.
It is necessary to be responsive to the pH setting value when H is stable and in the entire load range.

Therefore, a conventional example will be explained with reference to FIG.

FIG. 3 is a system diagram showing a schematic configuration of a conventional desulfurization plant. A processing gas containing sulfur dioxide gas (SO, gas) is introduced into the absorption tower 1 from above through a processing gas introduction duct 2 . - In the absorption tower 1, the circulating liquid 3 is continuously circulated through the circulation pump 4 and the circulation piping 5, and this circulating liquid 3 and the treated gas are brought into contact in the absorption tower 1 to completely remove the sulfur dioxide gas from the treated gas. This is the configuration to be removed. In other words, is SO in the processing gas an erroneous reaction shown in the following equation? H into the liquid
2SO, is formed and flows down - A part of this H,SO3 is converted to oxygen (02) in the processing gas and undergoes a reaction shown by the following formula (I + 1), and is oxidized to become H2BO3. .1
However, the treated gas that has passed through the absorption tower 1 is discharged into the atmosphere as treated gas through the exhaust duct 6.

S O2+Th O? E28 C3...(1)
H2BO3-1--C2-÷I(! S L12...
([1) In the circulating fluid 3, a large amount of CV-generated H2 S C3 H, 804 is present in the absorption reaction and oxidation reaction shown in the above formulas (I) and (IT). As a result, the pH of the circulating fluid 5 decreases. Therefore, the absorbent,
For example, calcium carbonate (OaO03) (other alkaline substances such as calcium hydroxide Ca(OH)2)
Neutralize the sea urchin circulating fluid 3 by completely supplying it to the system shown in the first-order equation (■).
1. Regenerate the liquid to easily absorb SO2. ing.

H2BO3+CaO03→0aSO4+H,o+co,
↑ @---cm Note that a part of the circulating fluid 3 is transferred to another process (not shown) via W8.

Generally, in the S02 absorption reaction, the pH of the circulating ff3 has a great influence, and the higher the pl, the more the So2 absorption reaction is promoted. In order to maintain a high pHk, a large amount of absorbent must be completely supplied, which is not desirable from a cost standpoint. So, should we operate at a pH level that maintains the desired performance? It is hoped that C will be carried out. Also,
In the above-mentioned work, in order to decrease the pHk of the circulation W5, it is necessary to increase the H,803 concentration or the H2SO4 concentration in the circulating fluid 3, and to increase the pH value, it is 0aO.
Increase in the amount of neutralization due to 03, that is, 0a in circulating liquid 3
This is the O03 concentration. The pHId of the circulating fluid is determined by the balance between the absorbed S02 and the neutralization amount of Oa C03.

Therefore, pH control in the conventional desulfurization plant mentioned above will be explained.

A pH detector 13 is attached to the circulation pipe 5, and a detection signal from this pH detector 13 is sent to a pH regulator 14.
Entered into. In pH regulator 14, crotch? The detected pH value is compared with the detection signal, and an absorbent flow rate set value signal 814k is output. The absorbent supply flow rate regulator 15 adjusts the opening degree of the flow rate adjustment 5P16 inserted in the absorbent supply pipe 7 based on this set value signal 814 Kl''. Note that reference numeral 17 is a flow rate detector.

In the above pH control, the proportional sensitivity of the H and pH regulator 14 is constant regardless of changes in the desulfurization load.

The proportional sensitivity of the pH1liF1 moderator 14 is set so that it does not oscillate at low loads, so even if it is an optimal value at low loads, the proportional sensitivity is too small at high loads, and as a result, the pH linkage The response was slow, and a phenomenon in which the circulating ffpH fluctuated greatly occurred.

Does pH fluctuation have a great effect on 802 absorption reaction as mentioned above? If the above-mentioned troublesome phenomenon occurs, the SO2 concentration of the treated gas at the outlet of the absorption tower 1 will not be stable and will fluctuate, leading to unregulated conditions. value? There was a fear of deviating. ``Furthermore, in order to prevent this problem, the pH value of the circulating fluid 3 is made higher than necessary in advance, which has the disadvantage of increasing the cleaning cost.

The present inventors investigated the cause of the above-mentioned phenomenon and found the following li'Jk.

In other words, even though the absorbent supply flow rate varies between low and high loads, the proportional sensitivity in pH control remains constant, so the absorbent supply flow rate must be corrected by the same amount for the same pH deviation. This is because only one thing is done.

The inventors believe that if the proportional sensitivity in the pH control system is changed in accordance with the load and in proportion to the absorbent supply flow rate in steady state, the absorbent supply flow rate for the same pH deviation will be proportional to the load at that time. be proportional to the absorbent supply flow rate at steady state;
That is, it has been found that since the absorbent supply flow rate is corrected at the same ratio, stable pH responsiveness can be obtained over the entire load.

Furthermore, the present inventors have discovered the relationship shown in FIG. 2 between the processing gas flow rate and the constant absorbent supply flow rate. In Figure 2, the horizontal axis represents the processing gas flow rate [Nm3/H]', and the vertical axis represents the absorbent supply flow rate (lime slurry flow it) (m3/H).
'? and 9 are diagrams showing specific examples of processing gas flow rates and absorbent supply flow rates. There is a strong correlation between the processing gas flow rate and the absorbent supply flow rate as shown in FIG.

Problems to be Solved by the Invention The present invention has been made based on the above points.
The aim is to make the proportional sensitivity of the pH controller variable as a function of the total process gas flow rate, and to make the pH response nearly constant over the entire load range, thereby making it possible to An object of the present invention is to provide an absorption tower pH control device that is capable of stabilizing the SO2 concentration and reducing running costs.

Means for Solving the Problems The present invention provides a desulfurization plant in which a treated gas containing all sulfur dioxide gas is introduced into an absorption tower, circulated throughout the absorption tower, and brought into contact with a circulating liquid containing all absorbent to desulfurize. , a processing gas flow rate detector that detects the entire flow rate of the processing gas introduced into the absorption tower; a function calculator that inputs a signal from the processing gas flow rate detector and outputs a proportional sensitivity signal according to this signal; The pH detector that detects the entire pH of the circulating fluid and the proportional sensitivity signal are all inputted to the 7" LL total ratio, and an absorbent supply flowmeter set value signal is output in accordance with the detection signal from the pH detector. and an absorbent stream t? fed to the absorption column.
Absorbent supply flowmeter detects the absorbent flow rate, the signal from the pH adjuster, and the detection signal from the absorbent supply flow rate detector. The present invention relates to an absorption tower pH control device which is completely equipped with a reagent flow rate regulator.

The configuration of an absorption tower pH control device according to an embodiment of the present invention will be described below with full reference to FIG. Note that the same equipment and the like as those shown in FIG. 3 are designated by the same reference numerals, and the explanation thereof will be omitted.

The present invention newly includes a processing gas flow rate detector 10, a function calculator 21. and pI (regulator 22).

The processing gas flow rate signal f'L7j is detected by the processing gas flowmeter detector 10. , n are input to the function calculator 21.

As mentioned above, the function calculator 21 outputs all calculation signals proportional to the absorbent flow rate in a steady state corresponding to the processing gas flow rate, so the absorption coefficient shown in FIG. Signal total proportional sensitivity signal S equivalent to agent supply flow rate
Output as 21. The pH regulator 22 uses this proportional sensitivity signal sn b p ■ The detection signal from the detector 13 and the preset pH value EX absorbent supply flow rate. In other words, the pH regulator 22 uses the proportional sensitivity signal 1h+ and 9P (proportional) or P (proportional, integral)
, or 7 lines of control (proportional, integral, differential) from P,
A circulating fluid supply flow rate set value signal 814 k is outputted to the absorbent supply flow rate regulator 15 as shown in the following equation.

However, F; pH controller output (absorbent supply flow rate set value) Fm
ax; maximum absorbent flow rate pH5pn; pH meter span; proportional sensitivity TD; differential time gpH; pH deviation (pH set value - pH) Also, proportional sensitivity (K) U to be changed by adjusting the processing gas flow 1゛, in the integral, it was included in the '5 integrand.

The absorbent supply flow rate regulator 15 fully adjusts the opening degree of the flow rate regulating valve 16 based on this set value signal 814.

As described above, according to the absorption tower pH control device according to the present invention, since the proportional sensitivity (5) is changed according to the absorbent supply flow rate commensurate with the total processing gas flow rate, it is possible to maintain an approximately constant and stable pH over the entire load range. Not only can the tolerability be obtained, but also the 5o2I% level in the treated exhaust gas can be maintained completely stable.

-7. Is the So2 concentration in conventionally treated exhaust gas regulated? In order to prevent deviations from the pH value, measures were taken to keep the pH set point higher than necessary, but this measure can be completely eliminated and running costs can be reduced completely. becomes possible.

Since the present invention relates to proportional sensitivity in feedback control in a pH control system, it can be similarly applied to cases involving feedforward control or cases where the pH setting value is completely changed.

Effects of the Invention According to the absorption tower pH control device of the present invention, it is possible to obtain a substantially constant and stable pH response over the entire load range. Further, the concentration of So in the treated exhaust gas can be maintained at a completely stable level. Furthermore, since there is no need to raise the pH value more than necessary, there is no need to take any measures for this purpose.
Running costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of the absorption tower pH control device according to the present invention, and FIG. 2 is a diagram showing the entire relationship between the process gas flow needle and the absorbent supply flow rate in a steady state. FIG. 6 is a system diagram of a conventional absorption tower PU control device. Sub-agents 1) Meifuku agent Ryo Hagiwara -

Claims (1)

[Claims] Detects the flow rate of the treated gas introduced into the absorption tower in a desulfurization plant that introduces the treated gas containing sulfur dioxide gas into the absorption tower, circulates it within the absorption tower, and desulfurizes it by contacting it with the circulating liquid containing the absorbent. a processing gas flow rate detector that inputs a signal from the processing gas flow rate detector and outputs a proportional sensitivity signal according to the signal;
a pH detector that detects H; a pH regulator that inputs the proportional sensitivity signal to make it proportional sensitivity and outputs an absorbent supply flow rate set value signal according to the detection signal from the pH detector; An absorbent supply flow rate detector that detects the flow rate of absorbent supplied to the absorption tower, a signal from the pH regulator, and a detection signal from the absorbent supply flow rate detector are inputted to control the absorbent flow rate control valve. An absorption tower pH control device comprising an absorbent flow rate regulator that adjusts the opening degree.