JPH0815531B2 - Control device for wet flue gas desulfurization unit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to control of an alkali compound in a wet flue gas desulfurization apparatus, and is particularly suitable for reducing utility when treating a flue gas from a quartz fired boiler. The present invention relates to a control device for a wet flue gas desulfurization device.

[Conventional technology]

In recent years, as the demand for power generation has increased, the size of boilers that use fossil fuels as the main fuel has also increased, and the degree of influence of the power generation boiler on air pollution is also 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, as the size of the boiler grows, the boiler is started and stopped on a daily or weekly basis in order to change the load frequently according to the power generation demand in order to reduce the power generation cost.
Start Stop, Weekly Start Stop Hereinafter, simply called DSS, WSS) operation is repeated.

As a feature of the recent demand for electric power, the maximum and minimum difference in electric power load has increased along with the growth of nuclear power generation, and there is a tendency to shift boilers for thermal power generation from those for base load to those for load adjustment. By changing the pressure of the boiler according to the load to perform a variable pressure operation, a so-called variable pressure operation boiler that operates in the supercritical pressure range at full load and in the subcritical pressure range at partial load is used to generate power at 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 as described above, the amount of exhaust gas fluctuates due to this load change, and the amount of soluble acid gas and fly-ashing also fluctuates depending on the coal species. Because the amount is different, for example 1 / 4,1 / 2,3 /
The target SOx value cannot be reduced below the partial load such as 4 loads.

For example, wet flue gas desulfurization equipment installed at thermal power plants, etc., includes calcium carbonate (CaCO ₃ ) and calcium hydroxide [Ca
(OH ₂ )] or calcium oxide (CaO) as a heat absorbing liquid slurry is used to absorb the sulfur oxides (SOx) in the exhaust gas of the boiler and oxidize the resulting calcium sulfite. The most common method is to recover calcium sulfate, that is, gypsum.

FIG. 5 shows a schematic system diagram of a conventional wet flue gas desulfurization apparatus using this limestone or lime.

In FIG. 5, the untreated gas 2 at the inlet of the absorption tower 1 is introduced into the absorption tower 1, and the sulfur-based sulfur contained in the untreated gas 2 is brought into gas-liquid contact with the calcium-based absorbent slurry in the absorption tower 1. Gas, dust, HCl and HF are removed. After the entrained mist is removed by the demister 3, the cleaned processing gas 4 is discharged to the atmosphere as the processing gas 4. On the other hand, the required amount of the absorption liquid slurry 5 is absorbed in the absorption tower circulation tank 6 of the absorption tower 1, and the absorption liquid slurry 5 is sent to the top of the absorption tower 1 by the circulation pump 7 to absorb the sulfurous acid gas.

Absorption liquid slurry 5 that has absorbed sulfurous acid gas into calcium sulfite in the absorption tower 1 and returns to the absorption tower circulation tank 6, but air 8 is supplied to the absorption tower circulation tank 6 to reduce calcium sulfite. , Become plaster. A part of the circulating absorbent slurry is withdrawn to the relay tank 10 through the withdrawal conduit 9. Here, sulfuric acid 11 may be added to convert unreacted limestone or the like into gypsum 17 described below, and high-purity gypsum 17 may be recovered. The slurry in the relay tank 10 is extracted to a shukuuna 14 via a slurry pump 12 and a conduit 13, and after being concentrated to a predetermined concentration, the gypsum 17 is dehydrated by a separator 15 and solidified as a gypsum 17 by a weighing machine 16. Be recovered. On the other hand, the clear water (superfluid) of the shukukuna 14 is stored in the supertank 19 via the superfluid conduit 18. Part of the perhydrogen is discharged from a blow water conduit 21 to a waste water treatment device (not shown) via the blow water control valve 20 in order to keep the concentration of impurities such as chlorine ions in the system below a certain value. The remaining excess water is returned to an absorption liquid slurry tank (not shown) and reused in the system. Further, in order to prevent the desulfurization performance of the absorbent slurry from being deteriorated by dust HCl and HF in the exhaust gas, alkali compounds such as alkali metal compounds and alkaline earth metal compounds are stored in the alkali compound supply tank 22 and the alkali compound supply pump is used. 23, alkali compound supply conduit 24,
A predetermined amount is supplied to the absorption tower circulation tank 6 via the alkali compound control valve 25.

That is, when the coal-fired untreated gas 2 is purified into the treated gas 4 by the wet flue gas desulfurization device, the soluble acidic gas and fly-ash which are mostly contained in the coal combustion gas are absorbed into the absorbent liquid slurry 5.
When it is contained therein, the concentrations of Cl ⁻ (chlorine ion), F ⁻ (fluorine ion) and fly ash are increased, which prevents the absorption slurry 5 from being dissolved and prevents the desulfurization performance from decreasing. In order to prevent the deterioration of the drainage performance in this way, an alkali metal compound (NaOH, Na ₂ SO ₄ , Na ₂ S) is added to the slurry 5 of the calcium compound (CaCO ₃ , Ca (OH) ₂ etc.).
O ₃ , KOH, K ₂ SO ₃ , K ₂ SO ₄ etc.) or an alkaline compound such as an alkaline earth metal compound (Mg (OH) ₂ , MgSO ₄ etc.) is added,
Increases the reactivity of calcium compounds such as limestone, and reduces dust and H
It is conventionally known to prevent interference such as Cl and HF.
However, the following method is used as a method for adding these alkaline compounds.

(1) Add a certain amount of alkali compound in proportion to the concentration of HCl and HF in the untreated gas.

(2) Add an alkaline compound so that the slurry pH of the tank (circulation tank of the absorption tower or cooling tower, or other tank) in the wet flue gas desulfurization device becomes a set value.

[Problems to be solved by the invention]

However, in the above-mentioned addition methods (1) and (2) of the prior art, the alkali metal concentration (eg Na) or alkaline earth metal concentration (eg Mg) in the system tends to be excessive. That is, according to the addition method of (1), it is necessary to accurately detect the concentration of HCl and HF in the untreated gas, but at present, the concentration of HCl and HF in flue gas can be continuously measured with high reliability. Since there is no measuring device, it is necessary to assume the HCl and HF concentrations in the exhaust gas from the analytical values of Cl and F in coal and input them as set values. Therefore, there is a margin in this setting value,
This will eliminate variations in coal analysis and add an excessive amount of alkaline compounds.

Further, according to the addition method of (2), since it is a method of adding so that the pH of the slurry in the tank of the wet flue gas desulfurization device is constant, it is possible to prevent the dust, HCl, and HF from interfering with the pH.
Is obtained empirically or experimentally, and the pH value is set. Therefore, the set value of this pH is also set to a higher value in consideration of variations in measuring instruments and safety, and an extra amount of alkaline compound is added.

As described above, in the conventional technology, it is possible to prevent or mitigate interference with the desulfurization performance of dust, HCl, and HF that occurs when treating sulfur dioxide gas in coal-fired boiler exhaust gas, but consideration is given to excess supply of alkaline compounds. However, there was a drawback that the chemical cost of the alkaline compound was high.

An object of the present invention is to provide a control device for a wet flue gas desulfurization device, which can prevent excessive supply of an alkali compound and can add the minimum necessary amount of the alkali compound even during DSS and WSS operation. .

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention provides an alkaline compound detector for detecting a flow rate of an alkaline compound in an alkaline compound supply pipe, a blow water detector for detecting a flow rate of blow water in a blow water conduit, and an alkali compound Alkali compound concentration setter that sets the concentration, a calculator that calculates the alkali compound setting signal from the blow water detection signal from the blow water detector and the concentration setting signal from the alkali compound concentration setter, the alkali compound setting signal and the alkali Providing a comparator that calculates the alkaline compound detection signal from the compound detector,
Control to close the alkaline compound control valve when the alkaline compound setting signal and the alkaline compound detection signal are larger than the alkaline compound setting signal, and open the alkaline control valve when the alkaline compound setting signal is larger than the alkaline compound detection signal. To do.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a control system diagram according to an embodiment of the present invention, FIG. 2 is a control system diagram according to another embodiment of FIG. 1, and FIG. 3 is a wet flue gas desulfurization device according to an embodiment of the present invention. It is a schematic block diagram.

In FIGS. 1 to 3, reference numerals 1 to 25 are the same as conventional ones.

26 is an alkaline compound detector provided in the alkaline compound supply pipe 24 for detecting the flow rate of the alkaline compound, 27 is a blow water detector provided in the blow water conduit 21 for flowing out the flow rate of the blow water, and 28 is an alkali metal compound concentration setting , 29 is a blow water detection signal, 30 is a concentration setting signal, 31 is an alkali compound setting signal, 32 is a calculator that calculates the alkali compound setting signal 31 from the blow water detection signal 29 and the concentration setting signal 30, and 33 is an alkali compound A detection signal, 34 is a comparator for comparing the alkaline compound setting signal 31 and the alkaline compound detection signal 33, and 35 is a control signal (deviation signal). Further, in FIG. 2, 36 is a blow water side alkaline compound setting signal, 37 is a gypsum weight detector, 38
Is a gypsum weight detection signal, 39 is a gypsum attached water setting device, 40 is an attached water setting signal, 41 is a multiplier, 42 is an attached water detection signal, 43 is a multiplier, 44 is a gypsum attached water side alkaline compound setting signal, 45 Is an adder for adding the blow water side alkaline compound setting signal 36 and the gypsum attached water side alkaline compound setting signal 44.

Before describing the embodiments of the present invention, dust, HCl, H in exhaust gas will be described from the characteristic curve diagram of FIG. 4 made by the inventors.
The concentration of the alkaline compound in the system of the wet flue gas desulfurization device, which is required to prevent the F interference, will be described.

The present inventors have conducted research and development on wet flue gas desulfurization equipment for treating diversified coal combustion exhaust gas, and in the process, in order to prevent and mitigate the interference of dust, HCl, and HF contained in coal-fired exhaust gas. The present invention was achieved after experimentally finding that the necessary minimum alkali compound concentration was present, and conducting further experimental research on this countermeasure.

That is, the test results are shown in FIG. Figure 4 shows
By varying the Na concentration in the slurry (inside the system), coal-burning exhaust gas (SO ₂ = 1000ppm, dust = 200mg / m ³ N, HCl = 80ppm, HF
(= 30 ppm) is examined. From this experimental result, it was found that the desulfurization rate can be maintained if the Na concentration in the system is maintained at a predetermined value or higher. Also,
It was found that even if the alkali compound was added at a predetermined concentration or higher, the effect was not obtained and the alkali compound was simply wasted. Therefore, it is important to keep the concentration of the alkali compound in the system constant, and in order to keep the concentration constant, it is necessary to replenish the system in the system in proportion to the amount discharged to the outside of the system. On the other hand, alkali metal compounds (compounds such as Na and K) or
Alkaline earth metal compounds such as Mg also generally have high solubility and are not discharged out of the system as solids such as gypsum. From this, as the amount of the alkaline compound discharged to the outside of the system, the amount of blown water from the blown water conduit 21 and the amount of gypsum 17
It is obvious that it is determined by the adhered water that adheres to and goes out of the system.

Also, looking at the ratio of the amount of blow water to the amount of gypsum attached water, SO ₂
= 1000 ppm, it is 10: 1, and the amount of the alkaline compound discharged out of the system together with the blow water is larger. First, it is understood that the alkaline compound may be controlled by the blow water amount. Further, when the SO ₂ concentration is as high as several 1000 ppm, the production amount of gypsum 17 is also increased, and the discharge amount of the alkaline compound due to the gypsum-adhering water is also large, and by controlling the alkaline compound by adding the amount, the desulfurization rate is increased. Can be maintained at a substantially constant value. In FIG. 1, an arithmetic unit 32 obtains an alkaline compound setting signal 31 based on a blowing water detection signal 29 from the blowing water detector 27 and a concentration setting signal 30 from the alkali metal concentration setting device 28, and the alkaline compound setting signal is obtained. The signal 31 is input to the comparator 34.

On the other hand, the alkaline compound detection signal 33 from the alkaline compound detector 26 is also input to the comparator 34, and its deviation is a control signal.
It is output as 35.

In this way, the alkaline compound control valve 25 is opened and closed so that there is no deviation between the alkaline compound setting signal 31 and the alkaline compound detection signal 33.

That is, when the alkali compound detection signal 33 is smaller than the alkali compound setting signal 31, the alkali compound conduit 24
When the alkaline compound detection signal 33 is opened to the alkaline compound control valve 25, the alkaline compound control valve 25 is closed.

FIG. 2 is a control system diagram showing another embodiment of FIG.

The difference between the control system diagram of FIG. 1 and the control system diagram of FIG. 2 is that in the control system diagram of FIG.
29 and the concentration setting signal 31, the alkali compound setting signal
Although 31 was calculated, in the control system diagram of FIG. 2, this alkaline compound setting signal 31 is changed to the blow water side alkaline compound setting signal 36 and the gypsum attached water side alkaline compound setting signal 44.
It is obtained by adding.

That is, the gypsum weight detection signal from the gypsum weight detector 37
38 and the attached water setting signal 40 from the gypsum attached water setting device 39 are input to the multiplier 41, and the multiplier 41 calculates the attached water detection signal 42.

Then, in the multiplier 43, the concentration setting signal 30 and the adhered water detection signal
42 is multiplied to obtain a gypsum-adhered water side alkaline compound setting signal 44, and an adder 45 blows water side alkaline compound setting signal 36.
And the gypsum-adhered water side alkaline compound setting signal 44 are added to obtain the alkaline compound setting signal 31.

Since the other explanations are the same as those in FIG. 1,
Description is omitted.

According to the embodiment of the present invention, the amount of the alkaline compound added to the system in order to prevent interference with the desulfurization performance peculiar to coal-fired exhaust gas can be controlled to a minimum, so that the operation can be performed with low utility.

Further, by individually determining the loss of the alkaline compound due to the blow water and the loss of the alkaline compound due to the gypsum-adhering water, it is possible to operate at a high desulfurization rate for a wide range of coal types.

〔The invention's effect〕

According to the present invention, the amount of alkali compound added can be controlled to a minimum depending on the type of coal, and high desulfurization performance can be obtained even when performing DSS operation or WSS operation.

[Brief description of drawings]

1 and 2 are control system diagrams according to the embodiment of the present invention, FIG. 3 is a schematic configuration diagram of a wet flue gas desulfurization device according to the embodiment of the present invention, and FIG. 4 is a desulfurization rate and slurry FIG. 5 is a characteristic curve diagram showing the relationship of Na concentration, and FIG. 5 is a schematic configuration diagram of a conventional wet flue gas desulfurization apparatus. 1 ... Absorption tower, 2 ... Untreated gas, 5 ... Absorption liquid slurry, 6 ... Absorption tower circulation tank, 17 ... Gypsum, 21 ... Blow water conduit, 22 ... Alkaline compound supply tank, 24 ... … Alkaline compound supply pipe, 25 …… Alkaline compound control valve, 26
…… Alkaline compound detector, 27 …… Blow water detector, 28
…… Alkali metal compound concentration setter, 29 …… Blow water detection signal, 30 …… Concentration setting signal, 31 …… Alkaline compound setting signal, 32 …… Calculator, 33 …… Alkaline compound detection signal, 34 …… Comparison vessel.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01D 53/34 ZAB

Claims (1)

[Claims] 1. An absorption tower for absorbing the sulfur oxides in the untreated gas with an absorption liquid slurry composed of a calcium compound, an absorption tower circulation tank for storing this absorption liquid slurry, and an absorption tower circulation tank for storing other than calcium. An alkaline compound consisting of an alkali metal or alkaline earth metal compound is supplied through an alkaline compound supply pipe and an alkaline compound control valve, and the absorbent slurry in the absorption tower is separated into gypsum and superfluid, and the superfluid is blown into a water conduit. In what is discharged to the outside of the system, an alkali compound detector that detects the flow rate of the alkali compound in the alkali compound supply pipe, a blow water detector that detects the flow rate of blow water in the blow water conduit, and the concentration of the alkali compound Alkaline compound concentration setter to set, blow water detection signal from blow water detector and concentration from alkali compound concentration setter An arithmetic unit that calculates the alkaline compound setting signal from the setting signal and a comparator that calculates the alkaline compound setting signal and the alkaline compound detection signal from the alkaline compound detector are provided, and the result of comparing the alkaline compound setting signal and the alkaline compound detection signal When the alkaline compound detection signal is larger than the alkaline compound setting signal, the alkaline compound control valve is closed, and when the alkaline compound setting signal is larger than the alkaline compound detection signal, the alkaline compound control valve is opened. A control device for a characteristic wet flue gas desulfurization system.