JPS59225723A - Seed crystal slurry supply method in waste gas desulfurization apparatus according to wet lime gypsum process - Google Patents

Abstract

PURPOSE:To prevent scale adhesion in a washing apparatus, by measuring boiler load or a fuel flow amount, the O2-concn. in effluent gas from an oxidation apparatus, the flow amount of a washing liquid to the oxidation apparatus and the flow amount of a seed crystal slurry while manipulating the flow amount of the seed crystal slurry so as to make the operation result of the measured values constant. CONSTITUTION:A boiler load signal measured by a detector 24 is inputted to a function generator A23 while the O2-concn. signal in effluent gas from an oxidation apparatus 5 measured by an O2-densitometer 21 is inputted to a function generator B. The flow amount F of a washing liquid withdrawn to the oxidation apparatus 5 from a washing apparatus 3 and the flow amount F' of a seed crystal slurry supplied to the washing apparatus 3 from the oxidation apparatus 5 are measured by flow meters 27, 32 and the measured values are inputted to a subtractor A33. Operation shown by formula is performed and the flow amount of the seed crystal slurry in an arranged pipe 6 is manipulated so as to make a CaSO4-concn. constant by a regulator 29. The set value of the regulator 29 is set to a predetermined amount or more of the CaSO4-concn. generating no scale.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wet flue gas desulfurization device for removing sulfur oxides (hereinafter referred to as SOx) contained in flue gas using calcium carbonate (hereinafter referred to as CaCO3) and/or calcium carbonate (hereinafter referred to as CaCO3).

In the desulfurization method that uses Ca(OH)2 or CaCO3 scrubber to remove SOx from flue gas, the gypsum generated in the flue gas cleaning equipment (hereinafter referred to as scrubber) becomes scale inside the scrubber. There is a difficult problem of deposition, and countermeasures against scale problems are the most important technical factor. As a measure against this scale problem, by adding seed crystal gypsum of a certain poison or higher to the seed crystal supply, that is, to the scrubber cleaning liquid, the gypsum produced in the scrubber is deposited on the crystal surface of the seed crystal gypsum.

A scale prevention measure that prevents precipitation inside scrubbers by growing scale is an excellent measure that has been widely put into practical use.

The present invention relates to a method for supplying seed crystals, which is an important technical factor for preventing such scale troubles within the scrubber.

In the method of removing SOx in flue gas using Ca(OH)2 or CaCO3 slurry, the cleaning solution contains sulfite (hereinafter referred to as Ca5O3) and sulfate Cal/Rum (hereinafter referred to as C).
It is a well-known fact that a5O,) is produced, and since both have low solubility, most of them precipitate in the same phase and are suspended in the liquid.

The scale trouble in the conventional example will be explained in more detail below.

Figure 1 illustrates the flow of a conventional method.5 For example, exhaust gas from a coal-fired boiler is introduced into a scrubber 3 from an exhaust gas-containing rotaryde 1.

The inlet of the scrubber 3 is cooled by the cleaning liquid.

Dust is removed. Of course, there is also a conventionally known method in which the exhaust gas is cooled and dust removed using a separate cooling and dust removal device before entering the scrubber, and the present invention can be applied in the same manner. Due to the cooling of the exhaust gas, some of the water in the cleaning liquid evaporates, but it is replenished by the makeup water 2. Next, the exhaust gas is cooled and dust removed in the main body of the scrubber 3, and at the same time, SOx in the exhaust gas is absorbed into the cleaning liquid.

The reaction when CaCO3 is used as an absorbent is as follows.

Caso3+SO□+H2O-+Ca +2H803
(a) H8O3−+−>O□ →H+5O4−(b)
Ca +SO--+Ca5O(c) CaCO3+H8O3+H-+CaSO3+H20+C
O2(d)So3+H20-+ 2H-1-5Q42-
(e) That is, CaS generated by the scrubber
O3 is combined with absorbed S02 and Ca and Hso in formula (a);
However, some of the H8O3- in the exhaust gas becomes 0□
As shown in formula (b), H”+SO
It becomes 4”-.

In addition, H3O3- and H+ are neutralized by the absorbent, and as shown in equation (d), CaSO3, H20, and C
02 and CO2 is dissipated into the gas. Generated Ca
When the concentration of and 502- increases, it becomes CaSO4 as shown in equation (C) and precipitates in the solid phase like CaSO3.

Note that the production ratio of CaSO4 and CaSO3 depends on the amount of S04''- produced by 02 in the exhaust gas.

The cleaning liquid is supplied to the scrubber 3 through the circulation pipe 4 by the circulation pump 18, and is in contact with the exhaust gas. CaCO
An absorbent of Ca(OH)2 or Ca(OH)2 is constantly supplied to the pipe 13 to keep the concentration of CaCO3 in the cleaning liquid constant. A portion of the cleaning liquid is sent to the oxidizer 5 through a pipe 9. This amount of extraction is controlled by a level controller 11 and a control valve 12 so as to keep the cleaning liquid level in the scrubber 3 constant. In the oxidizer 5, air or a gas containing oxygen is supplied through a pipe 7, and oxidizes CaSO3 in the extracted cleaning liquid to generate CaSO4. At this time, oxygen in the air or oxygen-containing gas is consumed in proportion to the amount of CaSO3 in the extracted cleaning liquid. The flow rate of gas containing air or oxygen is controlled by a flow rate controller 19 and a control valve 20 so as to be constant. Also, used air or gas containing oxygen is taken out from the oxidizer 5 through a pipe 10.

CaSO3 in the slurry is oxidized in the oxidizer 5,
A portion of the slurry whose solid phase is mostly CaSO4 is supplied to the scrubber 3 through the pipe 6 as a seed crystal slurry to increase the CaSO4 concentration in the cleaning liquid. Note that the flow rate controller 14 is used to keep the seed crystal slurry flow rate constant. It is controlled by a control valve 15.

Further, the flow rate of the slurry extracted from the pipe 8 is controlled by the level controller 16 and the control valve 17 so that the slurry level in the oxidizer 5 is kept constant.

As mentioned earlier, in order to prevent scale adhesion in the scrubber, the concentration of seed crystals in the cleaning solution, that is, gypsum (CaSO4)
It is necessary to maintain the concentration above a predetermined concentration. Supplying the seed crystal slurry to the scrubber 3 has the effect of increasing the CaSO4 concentration in the cleaning liquid. However, in the conventional method, the seed crystal slurry flow rate is only supplied at a constant rate (7), but the CaSO4 concentration is not controlled, so there is no guarantee that the concentration will always be above the specified concentration, and in some cases it may fall below the specified concentration, causing the scrubber to fail. There was a risk that scale would build up inside. For example, 02 in exhaust gas
As the concentration decreases, the amount of 502- generated decreases, so the generation of Ca5O in the scrubber 3 decreases, and conversely, the amount of Ca502- generated decreases.
Production of SO3 increases. Therefore, the CaS in the scrubber 3
Since the O4 concentration decreases, it is conceivable that the concentration becomes lower than the predetermined concentration.

The present invention was devised for the purpose of correcting the above drawbacks of the conventional method, and by controlling the CaSO4 concentration in the cleaning liquid at a constant level and maintaining it at a predetermined concentration or higher under any operating conditions, it is possible to prevent scale from entering the scrubber. It can prevent adhesion.

FIG. 2 specifically shows one embodiment of the present invention.

First, regarding the principle of measuring the degree of CaSO3 in the cleaning solution (8) I will explain.

The amount of sulfur oxides absorbed from exhaust gas is expressed by the formula (1) (%). However, here, ΔS is the amount of absorbed sulfur oxides (K9mo
i/H), G is the amount of exhaust gas before introducing the scrubber (Kym
ol/H], ySO2 represents the sulfur oxide concentration in the untreated exhaust gas [-], and η8o2 represents the desulfurization rate [-].

In addition to formula (1), the sulfur compound supplied to the scrubber 3 is a seed crystal slurry supplied from the pipe 6.

Well, the cleaning liquid that is extracted from the scrubber 3 is only from the pipe 9, and the sulfur compounds that are extracted are C as mentioned before.
Since they are considered to be aSO4 and CaSO3, the relationship of equation (2) holds true from mass balance in a static state.

ΔS+F'(CaSO4)' = F'([:CaS
O4]+CCaSO3:] ) ・= 121[Ca5
O4)' = (CaSO4) ten (CaS03:l
・Where F is the flow rate of the cleaning liquid extracted from the pipe 9 (
,//)I).

[CaSO4] is the CaSO4 molar concentration V in the cleaning solution?
mol/m'].

[CaSO3] Molar concentration of CaSO3 in the cleaning solution (Kym
ol/? ? 11:].

F' is the seed crystal slurry flow rate (tr?/H) in pipe 6, CC
aSO4]' is the CaSO4 concentration (Kgm
ol/m', 1° Even when CaSO3 is oxidized in the oxidizer 5 and becomes CaSO4, the total amount as sulfur oxides does not change, so it can be seen that Equation C2)1 holds true.

Next, the following relationship exists between the 02 concentration in the air or oxygen-containing gas after the piping 10 of the oxidizer 5 has been used and the CaSO3 molar concentration in the cleaning liquid. The explanation will be given assuming that the oxidizing gas in the oxidizing device 5 is air.

CaS in the slurry flowing into the oxidizer 5 through the pipe 9
O3 molar concentration (CaSO3) (Kymol /rr?
)year.

Let the inflow flow rate be F(i/H), and Ca5o in the oxidizer 5
If the oxidation rate of 3 is α, it is oxidized in the oxidizer 5 and Ca
Amount Z of CaSO3 that becomes SO4 (Kfmol/H)
is (formula 31).

2=α・F・[CaSO3]... (
3) The amount of oxygen consumed at this time Z' (Kqm, ol /
, H) need only be half the amount of oxidized CaSO3 in terms of molar ratio, so the formula (41) is obtained.

Z′=! Z-! Salary α・F・(CaSO3:] =-t
4) 2 On the other hand, the air flow supplied from the piping 7 to the oxidizer 5 fits
Fair (Kqmol/H) roxygen concentration x, (
-), the amount of oxygen supplied A (Kfmol /
H) is expressed as equation (5).

A = Fair-x...(5)+4+
, +5+ formula, the oxygen meter A' (K
gmot/H) is expressed as equation (6).

A'= A -Z'=Fairax, -2*α・F・[
CaSO3]... (6) 1. Since the oxidizer 5 consumes only oxygen and not other gases, the amount C (KLimo +/H) of other gases other than oxygen is determined by the pipe 7. The amount is the same for piping 10.

C= Fair (1-x, )
-f71 O2 concentration x21-) at pipe 10 is (8
) is the formula.

A' X・-T same as -+81(6+
Substituting the +71 formula yields formula (9).

When formula (9) is transformed into a formula for calculating [CaSO3], (
10) Equation becomes.

In equation +11, O2 concentration in pipe 10 and Ca in cleaning liquid
The relationship between SO3 concentration was found.

il+ +21 +21' +IfI calculates the CaSO4 concentration in the cleaning liquid using the formula (11).

Since the desulfurization rate ηs02 is normally operated to be constant, it can be regarded as a constant.

1. When the sulfur content in the boiler fuel is constant, it can be assumed that the SOx concentration in the exhaust gas is constant. Although the exhaust gas flow rate varies depending on the boiler load,
There is a strong correlation between exhaust gas flow rate and boiler load.1Figure 3
There is a relationship as shown in Equation 02 expresses this relationship in the form of a function.

G = fo (w) ... (It is a suppressed type. Since the air flow rate Fair in the pipe 7 is controlled, it is regarded as a constant, and the oxidation rate α is also a constant. O2 concentration of air
Needless to say, 1 is constant.

From the above, when the constant parts are summarized, equation (11) becomes equation (1).

However, f2(W)=yS02・ηSO2・fo(w)
'...+1412F1air Xl-X2 "f(x2)= "-□...+151α 1-
X2 Therefore, from the +131 formula, boiler load W, piping 1
It can be seen that the CaSO4 concentration of the cleaning liquid can be determined by measuring the O2 concentration of the used air at 0. In the present invention, the flow rate of the seed crystal slurry is adjusted so as to keep the CaSO4 concentration constant.

This will be explained in detail with reference to FIG.

The boiler load in the boiler 30 is measured by the detector 24. Instead of the boiler load, the boiler fuel flow rate, which is proportional to the boiler load, may be measured and used. Here, a case using a boiler load will be explained. The boiler load signal measured by the detector 24 is input to the function generator 23.

It is assumed that the function generator 23 is set in advance to generate the function f2(w) shown in equation (141).

An O2 concentration meter 21 is installed in the pipe 10 to measure 02 concentration 1fX2, and this O2 concentration signal is input to the function generator 22. The function generator has a built-in function that generates f(x2) shown in equation +151. A flow meter 27 is installed in the pipe 9 to measure the extraction flow rate F, and a flow meter 32 is installed in the pipe 6.
and measure the seed crystal slurry flow rate F'. These two flow rate signals are input to the subtracter 33, and the function generator 23
The output signal of the subtracter ■33 and the output signal of the subtracter ■33 are divided by the divider ■3.
Enter 4. Furthermore, the output signal of the function generator 22 and the flow rate signal of the flow meter 27 are input to a divider 28. The output signal of the divider (2) 34 and the output signal of the divider (28) are input to the attenuator 26.

The output signal of the subtractor (2) 26 indicates the value on the right side of equation (13i).Therefore, the output signal of the subtractor (26) is equivalent to the Ca5O concentration of the cleaning liquid.The output of the subtractor (26) The signal is input as a control amount to the controller 28, and the output signal from the controller 28 is used to control the seed crystal slurry flow rate in the piping 6.When controlling the seed crystal slurry flow rate, the flow rate controller is used as shown in Fig. 2. 14 and a control valve 15 to control the seed crystal slurry flow rate, and the set value of the flow rate controller 14 is changed by the output signal of the controller 28, or the controller 2
Any method in which the control valve 15 is directly actuated by the output signal No. 8 may be used. If the setting value of the controller 28 is set to a concentration of Ca5O above a predetermined amount at which scaling is likely to occur.

Under any operating conditions, the CaSO4 concentration of the cleaning fluid is maintained at a predetermined level or higher, and scale does not occur.

Although the present invention has been specifically explained above based on one embodiment, the present invention is not limited to this embodiment. 00□Measure four items: concentration, flow rate of cleaning liquid extracted from the cleaning device and introduced into the oxidation device, and flow rate of seed crystal slurry supplied from the oxidation device to the cleaning device, perform calculations shown in formula f131, and control the calculation results to a constant value. Any device may be used as long as it controls the flow rate of the seed crystal slurry supplied from the oxidation device to the cleaning device.

For example, the calculation shown in the aJ formula may be performed by an electronic computer. In addition, although the first type crystal slurry flow meter 32 is separate from the seed crystal slurry flow rate controller 14, if the structure is such that a flow rate signal can be taken out from the second type crystal slurry flow rate controller 14, the first type crystal slurry flow meter 32 can be omitted. Good too.

With such a configuration, according to the present invention, the concentration of Ca2O3 in the cleaning liquid in the scrubber can be kept constant, and as a result, it is possible to prevent scale from accumulating and depositing inside the scrubber. .

[Brief explanation of drawings]

FIG. 1 shows a conventional method, and FIG. 2 shows an embodiment of the present invention. FIG. 3 shows an example of the relationship between boiler load and exhaust gas flow rate. 1...Exhaust gas inlet duct, 2...Make-up water. 3...Scrubber, 4...Circulation piping, 5...Oxidizer. 6.7,8,9. IO...Piping, 11. 16
...Level controller, 12. 15. 17. 2(
1. Control valve. 14.19...Flow rate controller, 18...Circulation pump. 13...Absorbent supply line, 21...O2 concentration meter,
22゜23...Function generator, 24...Boiler load detector. 26.33... Subtractor, 28; 34... Divider, 29... Controller, 30... Boiler,
27. 32...Flow meter. Figure 1

Claims (1)

[Claims] A wet flue gas treatment device that uses a slurry containing calcium hydroxide and/or 7-calcium carbonate to clean flue gas and remove sulfur oxides from the flue gas. Part or all of the cleaning liquid is removed from the cleaning device. The gypsum slurry is extracted and introduced into an oxidizing device by supplying air or oxygen-containing gas to oxidize the sulfur oxides absorbed by the cleaning liquid from the flue gas, and then a part of the gypsum slurry is used as a seed crystal slurry for the above-mentioned cleaning again. In the method of supplying to the device, the load or fuel flow rate of the boiler 2 that generates the exhaust smoke is measured, and the signal of the load or fuel flow rate is input to the function generator (2) that generates a preset function; Measure the oxygen concentration of the used air or gas containing spent oxygen coming out of the oxidizer, input the oxygen concentration signal to a function generator that generates a preset function, and then input the oxygen concentration signal from the cleaning device. Measure the flow rate of the cleaning liquid extracted and introduced into the oxidation device and the flow rate of the seed crystal slurry supplied from the oxidation device to the cleaning device, and input the cleaning liquid flow rate signal and the seed crystal slurry flow rate signal to a subtractor (2) to generate the function. The output signal of the function generator ■ and the output signal of the subtractor ■ are input to the divider ■, and the output signal of the function generator ■ and the cleaning liquid flow rate signal are input to the divider ■, and the output signal of the divider ■ is and the output signal of the divider ■ are input to the subtracter ■, the output signal of the subtractor ■ is used as a control meter, and the flow rate of the seed crystal slurry supplied from the oxidation device to the cleaning device is used as the operation number to output the subtractor. A method for supplying seed crystal slurry in a wet lime gypsum flue gas desulfurization equipment characterized by controlling a signal value to a constant value.