JP2583902B2 - Control device for wet flue gas desulfurization unit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet flue gas flow apparatus, and more particularly to a wet flue gas suitable for stably treating an exhaust gas containing an acid gas and a fly ash in addition to a sulfurous acid gas. The present invention relates to a control device for a smoke desulfurization device.

[Conventional technology]

In recent years, as the demand for power generation has increased, the size of boilers using fossil fuel as a main fuel has also increased, and the degree of influence of power generation boilers on air pollution has been increasing.

SOx emission regulations, which account for a large proportion of the pollutants that increase this air pollution, tend to become more stringent year after year. Under this circumstance, the power generation industry in Japan, which has been using oil as its main fuel since the Second Petroleum Shock, is switching to coal fuel, which is cheaper and has a sufficient supply.

However, in order to increase the size of the boiler and reduce the power generation cost, the boiler starts and stops on a daily basis to carry out frequent load fluctuations according to the power generation demand (Daily Start Stop or less). DSS) operation and weekend start / stop operation (WSS).

As a characteristic of recent power demand, the difference between the maximum and minimum power loads has increased with the increase in nuclear power generation, and there has been a tendency to shift thermal power boilers from base load to load adjustment. The boiler performs a variable-pressure operation by changing the pressure according to the load, so-called a variable-pressure operation boiler that operates in a supercritical pressure region for a full load and a subcritical pressure region for a partial load, thereby generating electricity at a partial load. This is because the efficiency can be improved by several percent.

However, since the DSS operation is performed frequently on a daily basis and the WSS operation is performed on a weekly basis, the amount of exhaust gas fluctuates due to the load fluctuation, and the amount of soluble acid gas or fly ash is also dependent on the type of coal. For example, 1/4, 1/2, 3 /
At the time of partial load such as 4 loads, it cannot be reduced below the target SOx value.

For example, a wet-type flue gas desulfurization device installed in a thermal power plant or the like includes calcium carbonate (CaCO ₃ ), calcium hydroxide [Ca
(OH ₂ )] or an absorbent slurry consisting of calcium oxide (CaO) as an absorbent, absorbs sulfur oxides (SOx) in the exhaust gas from boilers and the like, and oxidizes the resulting calcium sulfite. Most commonly, calcium sulfate is recovered as gypsum.

On the other hand, with the diversification of energy, coal is widely used as boiler fuel for power plants and factories. The fuel exhaust gas from this coal contains acid gas such as hydrogen fluoride (HF) and hydrogen chloride (HCI) and fly ash, which are several tens of times higher than those of heavy oil fired exhaust gas. Have various adverse effects. HCI and HF are
It reacts with the absorbent slurry to form calcium chloride (CaCl ₂ ), consumes the absorbent (CaCO ₃ ) supplied in proportion to the SOx, and reduces the dissolution rate of the absorbent (CaCO ₃ ) slurry. Further, when Furaiatsushiyu is mixed into the absorbent slurry, Al ^3+, heavy metals and dissolution of such Fe ^3+, in particular Al ³⁺ HF
And form a poorly soluble compound on the surface of the particles of CaCO ₃ which is the absorbent slurry, and extremely reduce the dissolution rate of the absorbent slurry.

FIG. 3 shows a schematic system diagram of a conventional wet flue gas desulfurization apparatus using this coal-fired exhaust gas.

In FIG. 3, exhaust gas from a boiler or the like (not shown) is introduced into a dust tower 2 by a flue 1, and is supplied to the dust tower 2 by a dust tower circulation tank 3 and a dust tower circulation pump 4. The dust contained in the exhaust gas is removed by the gas-liquid contact with the absorbent slurry and the SOx
Is 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 5.

In the absorption tower 5, the SOx in the exhaust gas is brought into contact with the exhaust gas by gas-liquid contact between the absorbent slurry supplied from the absorption tower circulation tank 7, the absorption liquid circulation pump 8 and the absorbent slurry circulation pipe 9.
After being absorbed and removed, the accompanying mist is removed by the demister 10 and discharged from the flue 11 as a processing gas.

Absorber slurry 12 necessary for absorbing SOx in the exhaust gas is stored in the absorber circulation tank 7 of the absorber 5.
13, supplied from an absorbent slurry supply pipe 16 via a pump 14, an absorbent slurry control valve 15.

A part of the absorbent slurry containing calcium sulfite generated by absorbing SOx in the absorption tower circulation tank 7 is extracted by the absorption tower bleed pump 17 and collected as gypsum in an oxidation tower (not shown). .

In the figure, 18 is an exhaust gas flow rate detector, 19 is an inlet SO ₂ agricultural degree detector, 20 is an outlet SO ₂ concentration detector, and 21 is an absorbent slurry flow rate detector.

FIG. 4 shows a typical diagram of a conventional absorbent slurry flow rate control system, which will be described. Detecting the outlet SO ₂ concentration detector 20 from the outlet SO ₂ concentration detection signal 22 to the inlet SO ₂ concentration detector 19 from the inlet SO ₂ concentration detection signal 23, the desulfurization ratio signal using the subtractor 24, the divider 25 Calculate 26. Further, a multiplier 28 multiplies the exhaust gas flow rate detection signal 27 detected by the exhaust gas flow rate detector 18 by a constant for moisture correction (converted to dry gas) to obtain a dry base exhaust gas flow rate detection signal 29 from which moisture in the exhaust gas has been removed. Calculate. The multiplier 30 multiplies the dry base exhaust gas flow rate detection signal 29 by the inlet SO ₂ concentration detection signal 23 to obtain a total SO ₂ amount signal 31. The total SO ₂ amount signal 31 and the desulfurization rate signal 26 are calculated by a multiplier 32 to calculate a removed SO ₂ amount signal 33. A function generator 34, while obtaining the absorbent slurry excess required for reaction with SO _2, generally is a so-called excess constant control to constant excess, whereas in this PH of absorbent slurry Although a method of correcting the excess ratio has been proposed, basically, the removal SO ₂
This is a control in which the absorbent slurry is added to the amount.

In the multiplier 35, the removed SO ₂ amount signal 33 and the absorbent excess ratio signal 36
An absorbent slurry flow rate setting signal 37 is further obtained and input to an absorbent slurry flow rate controller (calculator) 38.

On the other hand, the absorbent slurry flow detector signal 39 from the absorbent slurry flow detector 21 is input to a calculator 38, and the calculator 28 outputs a deviation signal 40 between the absorbent slurry flow setting signal 37 and the absorbent slurry flow detection signal 39. The deviation signal 40 causes the absorbent slurry control valve 15 of the absorbent slurry supply pipe 16 to open and close.

[Problems to be solved by the invention]

The control device of the prior art, by multiplying a constant excess ratio setting signal to remove SO ₂ amount supplied amount of absorbent slurry,
Since the absorbent slurry flow rate setting signal was set, the amount of the absorbent slurry corresponding to the amount of the acid gas was insufficient, and the desulfurization rate was reduced.

The present invention solves the drawbacks of the prior art, and the object is to control the amount of the absorbent slurry according to the amount of SO ₂ removed and the amount of the acidic gas, and to improve the desulfurization performance by consuming the absorbent slurry of the acidic gas. This is to prevent the drop.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an acid gas concentration setting device for setting an acid gas concentration according to the type of coal, an oxygen concentration signal from the acid gas concentration setting device, and an exhaust gas flow rate. A multiplier for calculating an acid gas neutralizing absorbent slurry flow setting signal from the dry base exhaust gas flow detecting signal from the detector, and adding the absorbent slurry flow setting signal and the acidic gas neutralizing absorbent slurry flow setting signal. Adder is provided,
An absorbent slurry flow rate setting signal is corrected by an acid gas neutralizing absorbent slurry flow rate setting signal.

〔Example〕

Hereinafter, a desulfurization reaction and an acid gas removal reaction in a wet flue gas desulfurization apparatus will be described before describing the embodiments of the present invention.

(1) Desulfurization reaction (when air is not blown) SO ₂ + Ag → H ₂ SO ₃ … (1) 1 / 2CaCO ₃ + H ₂ SO ₃ → 1 / 2Ca (HSO ₃ ) ₂ + 1 / 2CO ₂ + Ag (2) 1 / 2Ca (HSO ₃ ) ₂ + 1 / 2CaCO ₃ → CaCO ₃・ 1 / 2H ₂ O ＋ 1 / 2CO ₂ … (3) (OVERALL) SO ₂ + CaCO ₃ + Ag → CaSO ₃・ 1 / 2H ₂ O + CO ₂ (4) Thus, the reaction between the absorbent (O ₃ ) (CaCO ₃ ) slurry and SO ₂ in the desulfurization reaction is 1: 1. The amount of the absorbent slurry equivalent to the amount of SO ₂ removed in the system is 1: 1. Required, but in fact, SO ₂
To secure the absorbent in the slurry, it is necessary or more equivalents of the absorbent slurry and SO _2.

(2) acid gas removal reaction (a) HCl removal reaction ^{HCl + Ag → H + + Cl} - ...... (5) H + + Cl - + 1 / 2CaCO 3 → 1 / 2CaCl 2 + 1 / 2CO 2 + Ag ...... (6) (OVERALL) _{HCl + 1 / 2CaCO 3 + Ag} → 1 / 2CaCl 2 + 1 / 2CO 2 ...... (7) (b) HF removing reaction ^{HF + Ag → H + + F} - ...... (8) H + + F - + 1 / 2CaCO 3 → 1 / 2CaF 2 +1 / 2CO ₂ + Ag (9) (OVERALL) HF + 1 / 2CaCO ₃ + Ag → 1 / 2CaF ₂ + 1 / 2CO ₂ (10) For the removal reaction of acid gas, HCl is formula (5) and HF is (8)
As shown in the formula, unlike the reaction for removing SO ₂ dissolved in water by water, it can be fixed in the liquid without being diffused, and can be removed only with water. However, H ⁺
Since the concentration becomes high (that is, the PH becomes low), when removing the acidic gas with the desulfurization absorption solution, the PH needs to be at least 3.5 or more to absorb SO _{2. In} this case, HCl
In formula (6), the reaction of formula (9) is indispensable in HF, and an absorbent slurry is indispensable. In addition, this HCl, HF
And the reaction with the absorbent slurry is 1: 1/2,
/ 2 equivalents of absorbent slurry is required. Reaction of the acid gas and the absorbent slurry, so place relatively faster than the reaction of the absorbent slurry and SO _2, is no need to consider the excess as the SO _2, at most, with 2-3% good.

As described above, when exhaust gas containing a large amount of acid gas such as HCl and HF such as coal-fired exhaust gas is washed with the desulfurizing absorbent slurry, the use of the absorbent slurry in consideration of the consumption of the absorbent slurry by HCl and HF is considered. By controlling the supply amount, SO ₂ , HCl, HF
Therefore, since the slurry can always be supplied to the minimum necessary amount of the absorbent, there is no possibility that the desulfurization performance is deteriorated due to the insufficient supply of the absorbent slurry.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

In FIGS. 1 and 2, reference numerals 15 to 40 denote the same components as conventional ones.

41 is an acid gas concentration setting device for setting the acid gas concentration according to the type of coal, 42 is an acid gas concentration signal, 43 is a dry base exhaust gas flow signal 29 and an acid gas neutralizing absorbent slurry flow rate from the acid gas concentration signal 42. A multiplier for calculating the setting signal 44, 45 is
An adder adds the SO ₂ side absorbent slurry flow rate setting signal 37 and the acidic gas neutralizing absorbent flow rate slurry setting signal 44, and 46 is an absorbent slurry flow rate setting signal.

In FIG. 1, an exit SO ₂ concentration detector 20 detects an exit SO ₂ concentration detection signal 22 from an exit SO ₂ concentration detector 20, and an entrance SO ₂ concentration detector 19 detects an entrance SO ₂ concentration detection signal 23. The desulfurization rate signal 26 is calculated using the above. Further, a multiplier 28 (32) multiplies the exhaust gas flow rate detection signal 27 detected by the exhaust gas flow rate detector 18 by a constant for moisture correction to calculate a Doyer base exhaust gas flow rate signal 29 excluding moisture in the exhaust gas. The dry base exhaust gas flow rate signal 29 and the inlet SO ₂ concentration detection signal 23 and calculates the total SO ₂ double signal 31 multiplied by the multiplier 30. The obtained total SO ₂ amount signal 31 and desulfurization rate signal 26 are operated by a multiplier 32 to obtain a removed SO ₂ amount signal 33. The function generator 34 calculates the excess amount of the absorbent slurry required for the reaction with SO _2, and basically keeps the excess ratio constant. Multiplier 35 removes SO ₂ amount signal 33
And determine the SO ₂ side absorbent slurry flow rate setting signal 37 required than absorbent excess signal 36 to the absorption of SO _2.

On the other hand, the acid gas (HCl, HF) contained in the exhaust gas easily reacts with the absorbent slurry and consumes the absorbent slurry. Therefore, it is necessary to supply the absorbent slurry to this. An acid gas concentration setter 41 gives an acid gas concentration signal 42 in the inlet exhaust gas, a multiplier 43 multiplies this by a dry base exhaust gas flow rate signal 29 from which moisture has been subtracted, and the reaction between the absorbent slurry and the acid gas is 1 : Absorber slurry flow rate setting signal for neutralization of acid gas necessary to correct for (2 basically multiply by 0.5) and finally neutralize the amount of acid gas
Calculate 44.

Then, the SO ₂ side absorbent slurry flow rate setting signal 37 and the acid gas neutralizing absorbent slurry flow rate setting signal 44 are added by an adder 45 to become an absorbent slurry flow rate setting signal 46, and an absorbent slurry flow rate detection signal 39 and The absorbent slurry flow rate setting signal 46 is calculated by the calculator 38, and the deviation signal 40 causes the absorbent slurry control valve 15 of the absorbent slurry supply pipe 16 to open and close.

Since absorbent slurry flow rate setting signal 46 is by connexion corrected SO ₂ side absorbent slurry flow rate setting signal 37 and the acid gas neutralizing absorbent slurry flow rate setting signal 44 in this control device in the first view, The required minimum amount of absorbent slurry can be supplied to SO ₂ , HCl, and HF, and a decrease in desulfurization state can be prevented.

In addition, the absorbent slurry can be supplied during DSS operation, WSS operation, or even when the coal type is changed.

The control device shown in FIG. 2 is an effective control device when a soluble alkali is added for neutralizing acid gas.

1 is different from the control device of FIG. 1 in that a neutralizer flow rate detector 47 and a subtracter 48 are provided in the controller of FIG. 1 and a neutralizer flow rate detection signal 49 from the neutralizer flow rate detector 47 is provided. Input to the subtractor 48,
The acid gas-side neutralizing absorbent slurry flow rate setting signal 44 is reduced by the neutralizing agent flow rate detection signal 49 to obtain an acidic gas neutralizing absorbent slurry flow rate setting signal 44a. It is the same as the one.

Incidentally, a method for continuously measuring the concentration of acid gas such as HCl or HF in a gas is described in, for example, "Industrial Measurement Method Handbook", pages 539 to 542, published by Asakura Shoten on March 10, 1982, and JP-B-53-9877. JP-A-57-104853 and JP-A-60
It is widely known, for example, from JP-A-1114761.

〔The invention's effect〕

According to the present invention can always supply a predetermined excess absorbent slurry against exhaust gas containing acidic gases and SO _2, lowering of desulfurization performance due to lack of the absorbent slurry can be prevented.

Further, since the supply amount of the absorbent slurry required for neutralizing the acid gas can be controlled, the desulfurization performance can be followed even if the type of coal changes.

[Brief description of the drawings]

1 and 2 are control system diagrams of a wet flue gas desulfurization device according to an embodiment of the present invention, FIG. 3 is a schematic configuration diagram of the wet flue gas desulfurization device, and FIG. 4 is a conventional control system diagram. . 15 ... absorbent slurry control valve, 18 ... exhaust gas flow detector,
19 ...... inlet SO ₂ concentration detector, 20 ...... outlet SO ₂ concentration detector,
21 ...... absorbent slurry flow detector, 22 ...... outlet SO ₂ concentration detection signal, 23 ...... inlet SO ₂ concentration detection signal, 27 ...... exhaust gas flow rate detection signal, 29 ...... dry basis exhaust gas flow rate signal, 37 ...
... absorbent slurry setting signal, 38 ... calculator, 39 ... absorbent slurry flow rate detection signal, 40 ... deviation signal, 41 ... acid gas concentration setting device, 42 ... acid gas concentration setting signal, 43 ... Multiplier, 44 ... Absorbent slurry flow rate setting signal for acid gas neutralization,
45: Adder, 46: Absorber slurry flow rate setting signal.

Continuation of the front page (72) Inventor Toshio Katsube 6-9 Takara-cho, Kure City, Hiroshima Prefecture Inside the Kure Plant of Babkotsuk Hitachi Ltd. (56) References JP-A-63-224719 (JP, A) JP-A-56-105729 (JP, A) JP-A-59-32924 (JP, A) JP-A-64-47425 (JP, A)

Claims (1)

(57) [Claims] An absorbent slurry flow rate setting signal is calculated based on detection signals from an exhaust gas flow rate detector, an inlet SO ₂ concentration detector, and an outlet SO ₂ concentration detector. When the slurry flow rate detection signal is detected, the absorbent slurry setting signal and the absorbent slurry flow rate detection signal are input to a calculator to obtain a deviation signal, and the deviation signal is used to open and close the absorbent slurry control valve. Upstream of the computing unit, an acid gas concentration setting device for setting the acid gas concentration according to the type of coal, an acid gas concentration signal from the acid gas concentration setting device, and a dry base exhaust gas flow detection signal from the exhaust gas flow detector. A multiplier for calculating an acid gas neutralizing absorbent slurry flow rate setting signal from the controller and an adder for adding the absorbent slurry flow rate setting signal and the acidic gas neutralizing absorbent slurry flow rate setting signal. Controller of the wet flue gas desulfurization apparatus characterized by the flow rate setting signal so as to by connexion corrected to absorbent slurry flow rate setting signal for acid gas neutralization.