JPS59169523A - Control of wet waste gas desulfurization apparatus - Google Patents

Abstract

PURPOSE:To attain to reduce the power cost of an air compressor, by controlling the amount and pressure of air supplied to an oxidizing tower corresponding to the amount of calcium sulfite generated in an exhaust gas absorbing tower supplied to the oxidizing tower. CONSTITUTION:In a wet waste gas desulfurization by absorbing SOx in exhaust gas with a limestone slurry is supplied to an oxidizing tower 15 through an oxidizing tower supply tank 13 to be oxidized to calcium sulfate with air sent into said tower 15 from an oxidizing air compressor 21 while the reaction mixture is withdrawn to a gypsum thickener 16 to recover gypsum, the air amount sent to the oxidizing tower 15 is controlled corresponding to the amount of calcium sulfite supplied to said oxidizing tower 15 by a flow meter 105 and a control valve 111 or air pressure is controlled by a pressure controller 107 and a control valve 110. In parallel to this operation, a suction valve 113 and an air release valve 112 are opened and closed by the pressure switch 106 provided to an air tank 22 for storing oxidizing air to subject the air compressor 21 to repeated load and unload operations and the power reduction during low load is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling intoxicant fog in a crystal desulfurization apparatus, and particularly to a method for controlling an oxidation tower suitable for reducing the power cost of an oxidation air compressor.

Currently, flue gas desulfurization equipment used to treat flue gas from boilers, etc. uses limestone, lime, etc. as an absorbent (hereinafter referred to as limestone, lime, etc. as an absorbent, or as an absorbent supplied to an absorption tower). Calcium sulfite produced by absorbing sulfur oxides (SO,) in exhaust gas from boilers is oxidized to produce calcium sulfate,
That is, wet flue gas desulfurization equipment that recovers gypsum as gypsum is generally used.

Figure 1 shows a system diagram of a conventional wet flue gas desulfurization system. Exhaust gas from boilers, etc. is introduced into a dust removal tower 2 through a flue 1,
Here, through gas-liquid contact with the circulating fluid supplied from the scrubbing tower circulation tank 5 to the circulation pump 4, it is cooled to a saturation temperature and at the same time, the dust contained in the exhaust gas is removed. It is sent to absorption tower 7. After SO in the exhaust gas is absorbed and removed by gas-liquid contact with the absorption liquid slurry supplied through the circulation pump 10 through the pipe 40 in the absorption tower 7, the entrained mist is removed in the demister 8. , is discharged from the flue 9.

The absorption tower 71G is supplied with absorbent slurry from the absorbent slurry tank 25 to the pump 26 depending on the amount of SOo to be absorbed and removed from exhaust gas from a boiler or the like. On the other hand, S.O.
The slurry containing the produced calcium sulfite is extracted by the absorption tower extraction pump 11 in proportion to the amount of SOx absorbed, and is supplied to the oxidation tower supply tank 13. The slurry that entered the oxidation tower supply tank 13 is sulfuric acid 28
Due to the reaction with , the unreacted absorbent becomes gypsum and
After the pH is adjusted, the slurry is sent to the oxidation tower 15 by the pump 14, and the calcium sulfite in the slurry is oxidized by air supplied from the oxidation air compressor 21, and converted into gypsum. The gypsum slurry is stored in a gypsum slurry tank 17, and further sent to a dehydrator 19 by a pump 18, where it is dehydrated and recovered as gypsum 20. Further, the air supplied to the oxidation tower is extracted from the top of the tower and sent to the absorption tower 7. In addition, in the figure, 3 is a drainage pump, 6 is a mist eliminator, 12 is make-up water, 23 is a filtered water tank, 24 is a filtered water pump, and 27 is an absorbent.

Next, we will discuss the main reactions inside the desulfurization equipment.

In the absorption tower 7, the absorbed 8(h) reacts with the absorbent as shown in equation (1) and becomes calcium sulfite.
Furthermore, some of it is due to 02 contained in the exhaust gas, (z)
It is oxidized and becomes gypsum as shown in the formula.

CaCO5+ Sow + H20→Ca5Os ・
HzO+ COr...(1)2 CaSOt HzO102+ HzO-+CgSC
)4.2Hgcl...(2)2 2 2 Therefore, the composition of the slurry extracted from the absorption tower 7 consists of the above-mentioned calcium sulfite, gypsum, and unreacted absorbent. This slurry is sent to the oxidation tower supply tank 13, where it reacts with sulfuric acid to form gypsum. Next, in the oxidation tower 15, calcium sulfite is oxidized by the reaction of formula (2) above, and almost all of the calcium sulfite becomes gypsum.

In the device system as described above, conventional air was supplied to the oxidation tower 15 at a constant pressure and supply amount regardless of the amount and composition of the slurry flowing into the oxidation tower 15.

However, the amount of S08 flowing into the desulfurization device changes as the load on the boiler changes and the amount of 8 minutes in the fuel changes, so the amount of calcium sulfite extracted from the absorption tower also changes.

For example, if the 8 min at low load or in fuel is reduced, the amount of calcium sulfite produced will also be reduced. Also, depending on the O1 concentration in the inlet gas, the oxidation rate in equation (2) above changes,
0. The higher the concentration, the greater the oxidation rate of the absorption system, and the less calcium sulfite is extracted.

In this way, due to fluctuations in the operating conditions of the boiler, the oxidation tower 1
Even though the amount of calcium sulfite flowing into the air compressor 21 fluctuates, constantly supplying a constant amount of oxidizing air from the air compressor 21 will unnecessarily consume the power of the air compressor at low loads. Yes, it is extremely uneconomical.

The object of the present invention is to eliminate the drawbacks of the prior art described above, reduce the amount of air for oxidizing calcium sulfite supplied to an oxidation tower, and thereby reduce the power cost of an air compressor, etc. An object of the present invention is to provide a method for controlling a smoke desulfurization device.

The present invention is a wet exhaust system in which SOx in exhaust gas is absorbed using limestone or an absorption liquid slurry containing lime, etc., and the produced calcium sulfite is oxidized by air pressure in an oxidation tower and recovered as gypsum. The smoke desulfurization apparatus is characterized in that the amount of air and/or air pressure supplied to the oxidation tower is controlled in accordance with the amount of calcium sulfite supplied to the oxidation tower.

In the present invention, the method of adjusting the flow rate or pressure of the oxidation tower supply air includes: providing an air tank at the outlet of the air compressor of the supply air source, loading the air compressor according to the pressure setting value of the air tank; It is preferable to install a plurality of air compressors and select the number of air compressors to operate, in which unloading is repeated.

In addition, to determine the amount of calcium sulfite supplied to the oxidation tower, it can be calculated from the amount of exhaust gas flowing into the absorption tower, the SOf concentration, the 02 concentration, and the amount of slurry extracted from the absorption tower.
Another method is to calculate it based on the 02 concentration of the oxidation tower outlet air.

It is desirable that the amount of calcium sulfite supplied to the oxidation tower is corrected based on the pH of the slurry at the outlet of the oxidation tower.

Hereinafter, the present invention will be explained in more detail by rotation. FIG. 2 is a system diagram of an oxidizing tower circulation system showing the control method of the present invention, and FIGS. 3 and 3A are system diagrams of controlling the supply amount of oxidizing air in the present invention.

In this example, the inlet exhaust gas amount is 100 and the Soz concentration is 101.
Calculate the amount of calcium sulfite produced from the amount of absorption S (h) obtained by integrating the
By correcting the amount of calcium sulfite oxidized in the absorption system, which is determined by the concentration, and by taking into account the time delay factor, which is determined by the amount of liquid held in the absorption tower and the amount extracted from the absorption tower, the amount of calcium sulfite is extracted from the absorption tower. Calculate the amount of calcium sulfite, use this amount of calcium sulfite as a leading signal, and use pH 108 of oxidation bath loss 2 as a correction signal if necessary.
The amount of air flowing into the oxidation tower is controlled by a control valve 111.

First, in FIG. 2, the air supplied to the oxidation tower 15 is
The air is sucked into the air compressor 21 through the suction valve 113, and the air tank 2
After the air is stored in step 2, the oxidation tower inlet air pressure controller 10
7 and an air pressure control valve 110, the pressure is controlled to a constant value and supplied to the oxidation tower 15. Reference numeral 105 is an air flow meter, 106 is a pressure switch, 108 is a pH meter, 111 is an air flow control valve, and 112 114 is a blowoff valve, and 114 is a blowoff silencer. The air amount control method in this case is as shown in FIG.
The signal of 01 is processed by a multiplier 121 to obtain the amount of absorbed 80w, and this is multiplied by a constant to calculate the amount of calcium sulfite produced. 125 and a multiplier 121 to determine the amount of calcium sulfite oxidized in the absorption tower, an adder 122 to subtract it from the amount of calcium sulfite determined from the Box concentration in the exhaust gas, and further adder 122
By adding a time delay element determined from the amount of liquid retained in the absorption tower determined by the integrator 123 and multiplier 121 and the amount of liquid extracted from the absorption tower extraction flowmeter 103, the amount of liquid extracted from the absorption tower is calculated. The amount of calcium sulfite is determined, and this amount of calcium sulfite is used as a leading signal, and the function generator 126 sets a signal for the amount of air required to enter the oxidation tower 15. At this time,
The oxidation bath loss slurry Q pH value is detected by a pH meter 108 and compared with the preset value of the controller 120 as a guide for completion of the reaction, and the deviation is converted into an air amount signal by the function generator 124. Correct the rigid volume signal.

The value obtained by adding this air amount signal by an adder 122 is set as a set value, and the air flow rate control valve 111 is controlled via a Kpi moderator 127 so that the air amount detected by the oxidation tower air flow meter 105 approaches the set value. do.

Here, the oxidation tower inlet air pressure is controlled by the control valve 1 through the controllers 107 and 128 as shown in FIGS. 2 and 3A.
Furthermore, an air tank 22 is provided at the outlet of the oxidizing air compressor, and the air compressor 21 is loaded or unloaded by the pressure switch 106 of the air tank 22. Air compressor 2 during unload operation
The suction valve 113 and the discharge valve 112 of No. 1 are fully closed.

By implementing the control method described above, when the required amount of oxidizing air decreases during low load, it is possible to reduce the power consumption of the air compressor by increasing the unload time. . For example, when the present invention is implemented under the following conditions, the power of the air compressor is 3240K per day.
WH, can be reduced by 972,000 KWH per year.

Example (1) Desulfurization equipment conditions Inlet gas amount 1,628,000 OON/L SO
2 Concentration 550 Desulfurization Rate 90 Chi 02 Concentration 2.7 Chi (2) Operating Conditions Daily Operating Load Pattern 100 Chi Load 12 Hours 20 Chi Load 12 Hours Next, Fig. 4 shows another embodiment of the present invention. It is a control system diagram of the oxidation tower shown. This is to adjust the pressure of the oxidation tower according to load fluctuations, and uses the amount of calcium sulfite extracted from the absorption tower calculated in the same manner as in the above example as a leading signal to adjust the pH of the loss slurry from the oxidation tower 15. is used as a correction signal, and the oxidation tower pressure adjustment valve 109 and/or oxidation tower inlet air pressure adjustment valve 110 is controlled by changing the air pressure setting value of the pressure controller 104, 107, and this pressure setting is The air compressor 21 is loaded and unloaded by switching a pressure switch 106 which is provided with a plurality of pressure setting values for the air tank 22 at the outlet of the air compressor according to the pressure setting values. Since the unloading time of the compressor can be increased during low load, power consumption can be reduced.

In the above embodiment, as a signal for controlling the air amount,
The amount of calcium sulfite in the oxidation tower 15 was determined from the amount of gas at the inlet of the desulfurizer, the concentration of 80% in the gas, the 02 concentration, and the amount of liquid held in the absorption tower and the amount extracted (residence time). Install a 02 concentration meter on the oxidation tower outlet air piping,
The O2 concentration in the oxidizer outlet air can be used as the control signal.

This is because the amount of calcium sulfite oxidized in the monoxide tower is proportional to the amount of O2 consumed, so the same effect as in the above example can be obtained by maintaining the O2 concentration at the outlet of the oxidation tower at a set value. It is from.

Additionally, by installing multiple oxidizing air compressors and controlling the number of units in operation depending on the amount of calcium sulfite supplied to the oxidizing tower, it is possible to significantly reduce the power required for the oxidizing air compressors. .

As described above, according to the present invention, the power of the air compressor at low load is reduced by changing the pressure and/or flow rate of the oxidizing air according to the amount of produced calcium sulfite flowing into the oxidizing tower. can do.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a flue gas desulfurization equipment to which the present invention is applied;
FIG. 2 is a system diagram of an oxidation tower inlet showing an embodiment of the present invention;
3 and 3A are control system diagrams for the air supply amount to the oxidation tower, and FIG. 4 is a control system diagram for the air supply amount to the oxidation tower showing another embodiment of the present invention. 7... Absorption tower, 13... Oxidation tower supply tank, 15.
...Oxidation tower, 21...Oxidation air compressor, 25...
Absorbent slurry tank, 100...Exhaust gas flow meter, 10
1...SO concentration meter, 102...02 concentration meter, 1o
3... Absorption tower discharge flow meter, 104... Oxidation tower pressure regulator, 105... Oxidation tower air flow meter, 108...p
H meter, 111... Oxidation tower air. Agent Patent Attorney Takenaga Kawakita Figure 1 Figure 12 ◇ △20 Figure 2 Procedural Amendment June 8, 1981 Commissioner of the Patent Office Kazuo Wakasugi 1, Indication of Case 1981 Patent Application No. 41416 2. Title of the invention Control method for wet flue gas desulfurization equipment 3. Relationship with the case of the person making the amendment Patent applicant 4. Agent 103 Address 11-8 Nihonbashi Kayaba-cho, Chuo-ku, Tokyo (
Benimoe Building) Phone 03 (639) 5592 Name (7658) Patent attorney Kawakita Take Cho 5, Date of amendment order Voluntary 6, Subject of amendment Detailed description of the invention in the specification and drawings. 7. Contents of the amendment (1) “From the 4th line from the bottom of page 9 to the 4th line of page 10 of the specification”
The air amount signal is set by subtracting it from and correcting it. ” should be amended as follows. The amount of calcium sulfite extracted from the absorption tower q (mol/h) is corrected by subtracting from
h) is determined as (■) using the tank 01 time delay time constant - determined from the tank's liquid volume v <e> and the slurry volume Q (A/h) extracted from the absorption tower. This is an adder 130 as shown in this figure.
, an integrator 131, and a multiplier 132. Using the amount of calcium sulfite determined as described above as a preceding signal, the function generator 126 sets a signal for the amount of air required to enter the oxidation tower 15. (2) Figure 3 of the drawings has been revised as shown in the attached sheet. that's all

Claims (1)

[Scope of Claims] (1) Sulfur oxides (hereinafter referred to as SO) in exhaust gas are absorbed using an absorption liquid slurry such as limestone or slurry containing lime, etc., and the generated calcium sulfite is absorbed into an oxidation tower. In a method for controlling a wet flue gas desulfurization equipment that oxidizes calcium sulfite with air and recovers it as gypsum, the amount and/or air pressure of air supplied to the oxidation tower is controlled in accordance with the amount of calcium sulfite supplied to the oxidation tower. A method for controlling a wet flue gas desulfurization device, characterized in that: (2. In claim 1, as means for adjusting the flow rate or pressure of the air supplied to the oxidation tower, an air tank is provided at the outlet of the air compressor of the supply air source, and the pressure setting value of the air tank is adjusted to A method for controlling a wet flue gas desulfurization equipment, which comprises repeatedly loading and unloading an air compressor. A method for controlling a wet flue gas desulfurization equipment, which comprises installing a plurality of air compressors and controlling the flow rate depending on the number of air compressors in operation. (4) Any one of claims 1 to 3. In , the amount of calcium sulfite fed to the oxidation tower is
A method for controlling a wet flue gas desulfurization equipment characterized in that the method is calculated from the amount of exhaust gas entering the absorption tower, the SO concentration, the O2 concentration, and the amount of slurry extracted from the absorption tower. (5) In any one of claims 1 to 3, the amount of calcium sulfite supplied to the oxidation tower is
Oxidation tower outlet air O! 1. A control method for a wet flue gas desulfurization device, characterized in that the concentration is calculated based on the concentration. (6) #In claim 4 or 5,
A method for controlling a wet flue gas desulfurization apparatus, characterized in that the amount of calcium sulfite supplied to the oxidation tower is corrected according to the pH of slurry at the outlet of the oxidation tower.