JPH03213125A - Absorbent ph control apparatus of wet exhaust gas desulfurizer - Google Patents

Abstract

PURPOSE:To keep stable desulfurizing capacity by rapidly restoring the pH of an absorbent by the supply of an alkali agent when the activity of the absorbent is extremely lowered like a quasi whole quantity oxidation state. CONSTITUTION:An alkali agent supply line 67 having an alkali agent flow rate detector 49 and an alkali agent flow rate control valve 68 and an absorbent draw-out line 71 having an absorbent draw-out flow rate detector 47 are provided to a circulation tank 11 while an outlet SO2 concn. detector 45 and an absorbent activity operator 51 operating an absorbent activity estimation signal 52 on the basis of the detection signals from an exhaust gas flow rate detector 17, an inlet SO2 concn. detector 18, a pH detector 20, an absorbent slurry flow rate detector 19, the outlet SO2 concn. detector 45 and the detector 47 are provided to the outlet of an absorbing tower 7. Then, on the basis of the comparing result of the alkali agent demand signal 63 and absorbent demand signal 49 based on the signal 52, the alkali agent flow rate detection signal 50 from the detector 49 and the absorbent slurry flow rate detection signal 40 from the detector 19, either one of the valve 68 and an absorbent slurry flow rate control valve 16 is opened and closed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control device for a wet flue gas desulfurization equipment, and particularly to a PH control device for an absorbent slurry suitable for reducing the amount of absorbent used. .

[Background Art] In recent years, as the demand for power generation has increased, boilers that use fossil fuels as their main fuel have also become larger, and the impact of power generation boilers on air pollution is increasing.

Emission regulations for SOx, which accounts for a large proportion of the pollutants that increase air pollution, are becoming stricter year by year. Under these circumstances, since the second oil shock, Japan's power generation industry, which has been using oil as its main fuel, is switching to coal, which is cheaper and has ample supply.

However, as boilers have become larger, boiler startup and shutdown operations (hereinafter simply referred to as DS
(referred to as S operation) is repeated.

As a feature of recent electricity demand, with the growth of nuclear power generation, the difference between the maximum and minimum power loads has also increased, and there is a tendency to shift boilers for thermal power generation from base load use to load adjustment use. By changing the pressure of the boiler according to the load and performing variable pressure operation, the boiler is operated in a supercritical pressure region at full load and in a subcritical pressure region at partial load, which improves power generation efficiency at partial load. a few percent
This is because it can be improved.

However, because DSS operation is performed frequently on a daily basis, the amount of exhaust gas fluctuates due to load fluctuations.
Since the amount of soluble acid gas and the amount of fly ash differ depending on the type of coal, it is impossible to reduce the SOx value to below the target SOx value, for example, during a partial load such as a load to l'/213.

For example, wet flue gas desulfurization equipment installed at thermal power plants, etc.
Calcium carbonate (Ca CO2), calcium hydroxide [
Using an absorbent slurry made of slurry containing Ca (OHM)] or calcium oxide (CaO) as an absorbent,
Absorbs sulfur oxides (SOx) in exhaust gas from boilers, etc.
The most common method is to oxidize the obtained calcium sulfite and recover it as calcium sulfate, that is, gypsum.

A schematic system diagram of a conventional wet flue gas desulfurization apparatus using this limestone or lime is shown in FIG.

FIG. 4 is a control system diagram of the absorbent slurry in the wet flue gas desulfurization device.

In FIG. 5, exhaust gas from a boiler (not shown) is introduced into a cooling tower 2 through a flue 1, and in the cooling tower 2, the exhaust gas is brought into contact with an absorbent slurry supplied by a cooling tower circulation pump 3. The dust contained therein is removed, and a portion of the SOx is also absorbed and removed. Note that a mist eliminator 6 may be installed in order to remove mist in the gas sent to the absorption tower 7.

In the absorption tower 7, SOx in the exhaust gas is removed by gas-liquid contact between the absorbent slurry supplied from the absorption tower circulation pump 1o and the exhaust gas.
After the mist is absorbed and removed, the entrained mist is removed by the demister 8 and discharged from the flue 9 as a process gas.

SOx in the exhaust gas is stored in the absorption tower circulation tank 11 of the absorption tower 7.
The absorbent slurry 14 necessary to absorb
A part of the absorption liquid slurry in the absorption tower circulation tank 11 is transferred from the absorption tower circulation tank 11 to the cooling tower circulation tank 5 through the communication pipe 12.
Supplied by

A part of the absorbent slurry containing calcium sulfite produced by absorbing SOx in the cooling tower circulation tank is extracted by the cooling tower bleed pump 4.

It is recovered as gypsum in an oxidation tower (not shown).

In the figure, 17 is the exhaust gas flow rate detector, 18 is the inlet SOx
19 is an absorbent slurry flow rate detector, 20 is an absorption tower slurry PH detector, and 21 is a cooling tower slurry PH detector.

A conventional absorbent slurry control system diagram in this wet flue gas desulfurization apparatus is shown in FIG.

In FIG. 4, 16 is an absorbent slurry flow rate adjustment valve, 17
is an exhaust gas flow rate detector, 18 is an inlet SOx concentration detector, 1
9 is an absorbent slurry flow rate detector, 20 is an absorption tower slurry PH
Detector 22 is an absorbent slurry supply line identical to that shown in FIG.

23 is an exhaust gas flow rate detection signal, 24 is an inlet SO2 concentration detection signal, 25 is a multiplier, 26 is a total S○2 amount signal, 27 is a function generator, 28 is a PH setting signal, 29 is a slurry PH detection signal, 30 is a 31 is a PH deviation signal, 32 is a function generator, 33 is an absorbent slurry excess rate correction signal for the PH deviation, 34 is a function generator, 35 is a total SO2 amount signal 26
36 is an adder; 36 is an adder;
37 is an absorbent slurry excess rate signal, 38 is a multiplier, 39 is an absorbent slurry flow rate setting signal, 40 is an absorbent slurry flow rate detection signal, 41 is a subtracter, 42 is an absorbent slurry flow rate deviation signal, and 43 is a controller , 44 is an absorbent slurry flow rate control signal.

In such a structure, the amount of exhaust gas flowing into the cooling tower 2 of the wet flue gas desulfurization equipment is detected by the exhaust gas flow rate detector 17 and the SO2 concentration is detected by the inlet S02 concentration detector 18, respectively, and the exhaust gas flow rate detection signal 23 and the inlet SO□ concentration are detected. The detection signal 24 is input to a multiplier 25 to calculate a total S○2 amount signal 26.

The function generator 27 provides a PH setting signal 28 for the total S02 amount signal 26, and the actual absorption tower slurry PH detector 20
A subtracter 30 calculates the deviation from the slurry PH detection signal 29, and a function generator 32 calculates an absorbent slurry excess rate correction signal 33 corresponding to this PH deviation signal 31.

On the other hand, the function generator 34 provides an absorbent slurry excess rate advance signal 35 in correspondence with the total SO□ amount signal 26, and an adder 36 adds the absorbent slurry correction signal 33 to this signal. The output signal of the adder 36 is the absorbent slurry excess rate signal 37
Therefore, the total SO2 amount signal 26 is multiplied by the multiplier 38 to obtain the absorbent slurry flow rate setting signal 39. This absorbent slurry flow rate setting signal 39 and the absorbent slurry flow rate check signal 4 from the actual absorbent slurry flow rate detector 19
0 is calculated as an absorbent slurry flow rate deviation signal 42 by a subtractor 41, and ? The slurry flow rate of the absorbent slurry supply line 22 is adjusted by opening and closing the absorbent slurry flow rate control valve 16 via the A meter 43 in accordance with the absorbent slurry flow rate control signal 44 .

However, such slurry flow rate control does not take into consideration the fact that good control characteristics cannot be obtained under special operating conditions such as DSS operation.

In other words, the oxidation state of the absorbent varies between the total oxidation state (SO2 absorption amount (oxidation amount)) and the partial oxidation state (SO□
Absorption amount > oxidation amount).

The oxidation state will be explained below using FIG.

In FIG. 6, the solid line A indicates the fully oxidized state, the dashed line B indicates the partially oxidized state, and the broken line C indicates the semi-fully oxidized state.

- For boat fishing, the partially oxidized state is B at high loads, and the fully oxidized state is A at low loads.

However, when the operating conditions shift from low load to high load, such as during DSS operation, the oxidation state shifts from full oxidation state A to partial oxidation state B, but as this transition state, quasi-full oxidation state C Occur.

In this quasi-total oxidation state C, there is no solid sulfite produced by absorbing SO2 in the absorbent, so
Sulfite ions become difficult to crystallize, and the sulfite ions in the absorbent become supersaturated, and the S02 partial pressure in the absorbent increases, resulting in a decrease in desulfurization performance.

In other words, the reason why sulfite does not exist in semi-total oxidation state C is that in semi-total oxidation state C, if the amount of SO2 absorbed increases from that in full oxidation state A (e.g. due to an increase in load).
Occurs transiently.

In total oxidation state A, S O,"-+'/202-)5
By the oxidation reaction of 042-, sulfite (CaSOy
) are all present in the form of sulfate (Ca SO4).

If the amount of SO2 absorbed increases from this state, if the above oxidation reaction does not proceed, sulfite ions (
S○3'-) exists in a supersaturated state, but the crystallization reaction (C
a''+so,''=→CaS○,) is relatively slow, so the state where sulfite (CaSO,) does not exist is the quasi-total oxidation state C. In addition, the reason why sulfite ions are difficult to crystallize is
Crystallization reaction (Ca″1+ SO3″−+Ca SOl
) requires a sulfite nucleus (solid substance) to proceed, but in quasi-total oxidation state C, no solid substance exists, making crystallization difficult. Note that in the total oxidation state A, there are almost no sulfite ions, so crystallization of sulfite ions does not pose a problem.

On the other hand, the reason why the S02 partial pressure in the absorption liquid increases is that if the crystallization reaction does not proceed, the sulfite ions in the absorption liquid become supersaturated and the concentration increases. P5oz=k [S O,”
-] (P soz: SO2 partial pressure in the absorption liquid, k: constant)
From the above formula, Psoz is the sulfite ion concentration ([SO,”-
]).

In addition, supersaturated sulfite ions precipitate on the surface of the absorbent, causing 1. The dissolution reaction of the absorbent becomes sluggish, and a large amount of absorbent must be supplied in order to maintain the pH of the absorbent at which the necessary desulfurization performance can be maintained.

For example, the excess rate of absorbent in partial oxidation state B with high load and full oxidation state A with low load is at most 5%, but in the middle of the transition from full oxidation state A to partial oxidation state B, that is, in quasi-total oxidation state. In state C, the excess rate of absorbent is 200% (
The amount of absorbent in the wet flue gas desulfurization equipment reaches 3 times that amount, which is undesirable.

As described above, in the conventional PH control device, no consideration is given to the supply of the absorbent in the quasi-total oxidation state C.

[Problems to be Solved by the Invention] Conventional control devices have the disadvantage that the oxidation state of the absorbent shifts to a quasi-total oxidation state, resulting in a decline in desulfurization performance and the inability to secure the target desulfurization rate. There was a drawback that stable desulfurization performance could not be ensured in a fully oxidized state.

The present invention aims to eliminate such conventional drawbacks,
The purpose is to propose an absorbent PH control device that can ensure a target desulfurization rate even under special operating conditions, ie, quasi-total oxidation conditions.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides an alkali agent supply line having an alkali agent flow rate detector and an alkali agent flow rate regulating valve in a circulation tank, and an absorbent extraction flow rate detector. an absorbent extraction line having an outlet SO2 concentration detector at the absorption tower outlet, an exhaust gas flow rate detector, an inlet SO2 concentration detector, a PH detector, an absorbent slurry flow rate detector, an outlet SO□ concentration detector, and a withdrawal flow rate. An absorbent activity calculator is provided to calculate an absorbent activity prediction signal based on the detection signal from the detector, and an alkali agent demand signal, an absorbent demand signal, and an alkali agent demand signal based on the absorbent activity prediction signal from the absorbent activity calculator are provided. Opening at least one of the alkali agent flow rate adjustment valve and the absorbent slurry flow rate adjustment valve based on the comparison result between the alkali agent flow rate detection signal from the flow rate detector and the absorbent slurry flow rate detection signal from the absorbent slurry flow rate detector; It was designed to be closed.

[Operation] Since the activity of the absorbent changes depending on the oxidation state of sulfite in the absorbent, the absorbent activity calculator operates so as to be able to predict the activity of the absorbent based on the online detection signal. Thereby, the ratio between the amount of absorbent slurry and the amount of alkali agent added can be adjusted.

In other words, when the activity of the absorbent decreases, instead of adding a large amount of absorbent, the pH of the absorbent is adjusted by adding an alkaline agent. Even in the state.

The pH can be maintained at a set value, and although alkaline agents are consumed, the amount of absorbent used can be significantly reduced.

[Example] The present invention will be explained below using the drawings.

FIG. 1 is an absorbent PH control system diagram according to an embodiment of the present invention,
FIG. 2 is a schematic configuration diagram of FIG. 1, and FIG. 3 is a characteristic curve diagram of partition coefficient and absorbent activity.

In FIGS. 1 and 2, numerals 1 to 44 indicate the same parts as the conventional ones.

In Figures 1 and 2, 45 is an outlet SO2 concentration detector, 46 is an outlet 502a degree detection signal, 47 is an extraction flow rate detector, 48 is an extraction flow rate detection signal, 49 is an alkali flow rate detector, and 50 is an alkali flow rate Detection signal, 51 is an absorbent activity calculator, 52 is an absorbent activity prediction signal, 53 is a function generator, 54 is a distribution coefficient signal, 55 is a PH correction signal generator, 56 and 57 are PH correction signals on the alkali agent side, Absorbent side PH correction signal, 58 is a multiplier, 59 is an absorbent excess rate correction signal, 60 is a function generator, 61 is a PH deviation correction signal, 62 is a multiplier, 63 is an alkali agent demand signal, 6
4 is a subtracter, 65 is an alkali agent flow deviation signal, 66 is an alkali agent regulator, 67 is an alkali agent supply line, 68 is an alkali agent flow rate adjustment valve, 69 is an absorbent slurry demand signal, and 70 is an alkali agent flow rate control signal. , 71 are extraction lines.

Before explaining the control system diagram of FIG. 1 in such a structure, the absorbent activity calculator 51 will be explained.

The absorbent activity calculator 51 receives the exhaust gas flow rate detection signal 23 from the exhaust gas flow rate detector 17 and the inlet SO2'a degree detector 18.
Inlet 5o221 degree detection signal 24, PH detector 20
PH detection signal 29 from absorbent slurry flow rate detector 19
an absorbent slurry flow rate detection signal 40 from the outlet SO2 concentration detector 45, an outlet SO2 concentration detection signal 46 from the outlet SO2 concentration detector 45, and a withdrawal flow rate detection signal 48 from the extraction flow rate detector 47.
Perform the following calculations from .

The absorbent concentration balance in the absorbent is V''=Gst-y-yp/Mh R1+020a'!/
γ!・-・-(1)t R1102= G r(1-X hzo) C'110
2 ”l '10-'/22.L...(2) η= (C
'+5o2- C'go-)/ C'a-o2-- (
3) Here, ■; Circulation 7g9 agent concentration (moQ/Q), t: time (h), y: absorbent slurry concentration (), yp: absorbent purity (-), M: absorbent Molecular weight (kg/moQ), Gs (: Absorbent slurry flow rate (kg/h), R so-: SO z absorption amount (
moQ/h).

G,: Extraction flow rate (kg/h), γPa absorption liquid specific weight (
kg/Q), Gt: Exhaust gas flow rate (Q/h), X
N2O: Moisture in exhaust gas (-), C', o2: Inlet SO
2 concentration (ppm), η: desulfurization rate (-), c'so2
: Indicates outlet SO2 concentration (ppm).

Therefore, the above equations (1) to (3) can be used as the exhaust gas flow rate detection signal 2.
3. The predicted value of absorbent concentration is required.

On the other hand, since the amount of SO2 removed and the amount of absorbent consumed are equal, R goz = V ・Y a
""...(4) γ. =k[H”]'[x]
'/ [C a '']'' -===・(5)
Here, γA=absorbent consumption (IIlOQ/Q−h),
k: Absorbent activity, [H”l: Hydrogen ion concentration (moρ
HaD.

[Ca""]: Total calcium ion concentration in the absorption liquid (m
oQ/Q), α, β, γ: constants.

When equations (4) and (5) are solved using the absorbent concentration X found from equations (1) to (3), the activity k of the absorbent can be predicted from the above equation. Note that [Ca''] can be easily estimated from the PH and CQ-concentrations, and the absorbent activity calculator 51 can predict the absorbent activity.

Based on the absorbent activity prediction signal 52 which is the output of the absorbent activity calculator 51, a function generator 53 calculates a distribution coefficient signal 54 from the relationship shown in FIG. This distribution coefficient signal 54 is
It is input to the H correction signal generator 55 to obtain an alkaline agent side PH correction signal 56 and an absorbent slurry side PI (correction signal 57).

・In other words, the alkaline agent side PH correction signal 56 and the absorbent slurry side PH correction signal 57 are signals corresponding to the distribution ratio of absorbent and alkaline agent for PH feedback correction, and when the activity of the absorbent decreases, 1 , PH feedback correction mainly controls the alkaline agent.

On the other hand, the process up to calculating the PH deviation signal 31 in the subtracter 30 of the absorbent slurry control system is the same as the conventional method, but in the embodiment of the present invention, this PH deviation signal 31 is sent to the function generator 60, and , the absorbent slurry excess rate correction signal 33 calculated by the function generator 32 of the absorbent slurry control system is applied to the multiplier 5.
8 respectively.

Then, in the multiplier 58, the absorbent slurry excess rate correction signal 3
3 and the previously explained absorbent side PH correction signal 57 to obtain an absorbent excess rate correction signal 59, which is input to the adder 36.

The adder 36 adds the absorbent excess rate signal 35 and the absorbent excess rate correction signal 59 to obtain the overall absorbent excess rate signal 37, and the 1 multiplier 38 adds the S○2 amount signal 26 and the multiplication signal 59 to obtain the overall absorbent excess rate signal 37. A chemical slurry demand signal 69 is determined. The absorbent slurry flow rate deviation signal 42, which is the deviation between the absorbent demand signal 69 and the absorbent slurry detection signal 40 from the absorbent slurry flow rate detector 19, is processed by the controller 43, and the absorbent slurry supply line 22 absorbs The absorbent slurry flow rate adjustment valve 16 is opened and closed by the absorbent slurry flow rate control signal 44 to control the absorbent slurry flow rate of the absorbent slurry supply lines 2.

On the other hand, regarding the alkaline agent, the PH deviation signal 31 is processed by the function generator 60 as the PH deviation correction signal 61, and the multiplier 62 processes this PH deviation correction signal 61 and the alkali open side PH.
The correction signal 56 and the multiplication signal together form the alkaline agent demand signal 6.
3, and the alkali agent flow rate deviation signal 65, which is the deviation from the alkali agent flow rate detection signal 50 from the alkali agent flow rate detector 49, is processed by the controller 66 as an alkali agent flow rate control signal 70, and the alkali agent flow rate control signal 70 is The alkaline agent flow rate is controlled by opening and closing the alkali agent flow rate regulating valve 68.

As described above, the PH control device according to the present invention uses the absorbent activity calculator 51 to predict the absorbent activity online, and adjusts the absorbent slurry supply line 22 according to this activity.
The supply ratio of the absorbent slurry and the alkaline agent is controlled by opening and closing the absorbent slurry flow rate adjusting valve 16 and the alkaline agent flow rate adjusting valve 68 of the alkaline agent supply line 67,
This is to control the pH of the absorbent to a set value. Basically, an alkaline agent is used for pH deviation correction only when the activity of the absorbent decreases, and as for the absorbent.

This is to cut the PH deviation correction amount.

Since the present invention has such a configuration, even under special operating conditions such as a quasi-total oxidation state, the pH of the absorbent can be maintained at a set value using an alkaline agent, and the consumption amount of the absorbent can be reduced.

[Effects of the Invention] According to the present invention, when the activity of the absorbent is extremely reduced such as in a quasi-total oxidation state, the pH of the absorbent can be quickly restored by supplying an alkaline agent. Stable desulfurization performance can be maintained.

Further, when the activity of the absorbent decreases, it is possible to prevent the introduction of a large amount of absorbent, so the consumption of the absorbent can be reduced, which is more effective than the consumption of the alkaline agent.

[Brief explanation of drawings]

FIG. 1 is an absorbent PH control system diagram according to an embodiment of the present invention,
Figure 2 is a schematic configuration diagram of Figure 1, Figure 3 is a characteristic curve diagram with the vertical axis representing the partition coefficient and the horizontal axis representing absorbent activity, Figure 4 is a conventional PH control system diagram, and Figure 5 is a diagram of the conventional PH control system. Schematic configuration diagram of Fig. 4, No. 6
The figure is a characteristic curve diagram in which the vertical axis shows the desulfurization rate and the horizontal axis shows the pH of the absorption liquid. 7... Absorption tower, 11... Circulation tank,
16... Absorbent slurry flow rate adjustment valve, 17...
...Exhaust gas flow rate detector, 18...Inlet SO2
Concentration detector, 19... Absorbent slurry flow rate detector, 20... PH detector, 22... Absorbent slurry supply line, 23... Exhaust gas flow rate Detection signal, 24... Inlet SO□ concentration detection signal, 29.
... Slurry PH detection signal, 39 ... Absorbent slurry flow rate setting signal, 40 ... Absorbent slurry flow rate detection signal, 45 ... Outlet SO2 concentration detector , 47... Extraction flow rate detector, 49...
... Alkaline agent flow rate detector, 51 ... Absorbent activity calculator, 52 ... Absorbent activity prediction signal, 63
...Alkaline agent demand signal, 67...
- Alkaline agent supply line, 68... Alkaline agent flow rate adjustment valve, 69... Absorbent slurry demand signal, 71... Extraction line. 1st factor Figure 2 d Bow Figure 3 Figure 4rIA 115 Figure If6I! 1 --→-PH

Claims (1)

[Scope of Claims] An absorption tower that absorbs sulfur oxides in exhaust gas with an absorbent slurry, a circulation tank that stores this absorbent slurry, and an absorbent slurry supply line having an absorbent slurry regulating valve to the circulation tank. installed, exhaust gas flow rate detector at absorption tower inlet, inlet SO
_2 Due to the deviation between the absorbent slurry flow rate setting signal based on the detection signal from the concentration detector and the PH detector of the circulation tank and the absorbent slurry flow rate detection signal from the absorbent slurry flow rate detector of the absorbent slurry supply line. An alkali agent supply line having an alkali agent flow rate detector and an alkali agent flow rate adjustment valve in the circulation tank; An absorbent extraction line with a detector, an outlet SO_2 concentration detector at the absorption tower outlet, an exhaust gas flow rate detector, an inlet SO_2 concentration detector, a PH detector, an absorbent slurry flow rate detector, an outlet SO_2 concentration detector, and an extraction An absorbent activity calculator is provided that calculates an absorbent activity prediction signal based on the detection signal from the flow rate detector, and an alkali agent demand signal and an absorbent demand signal are calculated based on the absorbent activity prediction signal from the absorbent activity calculator. , at least one of the alkali agent flow rate adjustment valve and the absorbent slurry flow rate adjustment valve based on the comparison results with the alkali agent flow rate detection signal from the alkali agent flow rate detector and the absorbent slurry flow rate detection signal from the absorbent slurry flow rate detector. An absorbent PH control device for a wet flue gas desulfurization device, characterized in that it opens and closes.