JP3204691B2 - Exhaust gas desulfurization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a flue gas desulfurization process, an exhaust gas desulfurization process with reduced operating costs with particularly reduced equipment costs by reducing the height of the absorption tower.

[0002]

2. Description of the Related Art A system around an absorption tower of a conventional wet exhaust gas desulfurization apparatus will be described with reference to FIG. Exhaust gas from a boiler or the like is introduced from an inlet duct 1 into an absorption tower 2, desulfurized by gas-liquid contact with an absorbing liquid in the tower, and discharged from an outlet duct 3.
Is discharged from On the other hand, the absorbent for desulfurization is stored in an absorbent circulation tank 21 at the bottom of the absorption tower 2, pressurized by an absorption tower circulation pump 4, introduced into the tower by a circulation pipe 5, and sprayed from a spray nozzle 6. This absorbing liquid is generally a mixture of limestone or slaked lime with water, and is used in a slurry state having a solid concentration of about 10%. As a precaution for handling this slurry, it is necessary to keep the slurry flowing. When the slurry is stopped, solids settle, become clogged, and cause deposition. For this reason, a stirrer 18 is provided in the liquid storage tank portion of the absorption tower 2 to constantly stir the slurry. When the circulation pump 4 is stopped, the drain valves 7 and 8 are opened after the stop to prevent solid matter from accumulating in the pump 4 and the pipe 5, and the drain pipes 9 and 10 are connected to the drain pit 11. Discharge. The drain pit 11 is a storage tank having a small capacity enough to store a part of the absorption liquid contained in the absorption tower circulation pipe 5 and the pump 4. The drain pit 11 is drawn into the absorption tower 2 while extracting the absorption liquid from the pipe 5 and the pump 4. It is for doing. A level switch 13 is provided in the drain pit 11, and the slurry flows into the pump 4 and the circulation pipe 5 so that
When the pit level exceeds a specified value, the drain pump 14 is activated by a signal from the level switch 13 and the piping 1
5 to be collected in the absorption tower. The level of the drain pit 11 is reduced by the operation of the drain pump 14, and when the level of the drain pit 11 becomes equal to or less than the specified value, the level switch 13 is operated again, and the drain pump 14 is stopped. When slurry discharge in the circulation pump 4 and the circulation pipe 5 is completed by the above operation, the drain valves 7 and 8 are closed, and the drain discharge operation is completed. The above operation procedure is summarized in FIG.

As described above, in the prior art, the slurry in the circulation pump 4 and the pipe 5 is collected in the storage section of the absorption tower 2 via the drain pit 11. For this reason, when the absorption tower circulation pump 4 is stopped, the liquid storage level of the absorption liquid circulation tank 21 increases. An overflow pipe 19 is attached to the upper part of the liquid storage section of the absorption tower 2, but it is necessary to allow for the above-mentioned increase in the level h between the normal liquid level (N, L) and the overflow pipe level. This level rise is about 1
m, the height of the absorption tower needs to be increased by 1 m, and the total head of the absorption tower circulation pump also needs to be increased.

[0004]

In the above prior art, no consideration is given to a method of recovering the absorption liquid slurry retained in the circulation pump 4 and the pipe 5 when the absorption tower circulation pump 4 is stopped. There was a problem that the tower height was increased, the total head of the circulation pump was also increased, and both equipment costs and operation costs were increased.

[0005] It is an object of the present invention, lower the tower height of the absorption tower, lowering the total head of the circulation pump, this to save equipment costs, the operating costs
An object of the present invention is to provide an exhaust gas desulfurization method which can achieve the following.

[0006]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
The present invention has an absorption section having an absorption section at the top and a tank section at the bottom.
Exhaust gas containing sulfur oxides is introduced into the absorption section of the tower,
Circulation pump for absorbing the absorbent slurry stored in the tank
To the spray nozzle provided in the absorption unit via the circulation pipe
And spray contact with the above-mentioned exhaust gas in gas-liquid contact.
Absorb and remove the sulfur oxides and remove the absorbent after spraying
Exhaust gas desulfurization by wet exhaust gas desulfurization equipment contained in a tank
The method further comprises the step of:
The absorbent in the pipe is drained to the drain pit and
During the suspension period, this is retained and when the above desulfurization unit is restarted
After the liquid level in the absorption tower drops,
The absorption liquid held in the above-mentioned absorption tower tank
An exhaust gas desulfurization method characterized by the following .

[0007]

[0008]

After the absorption liquid circulation pump 4 stops, the circulation pump 4
The slurry in the pipe 5 is held in the drain pit 11 that can hold the entire amount of the absorbing liquid in the circulation pipe. After the circulation pump 4 is restarted with the restart of the desulfurization device, the drain pump 14 is started, and the slurry is discharged to the drain pit 11. Absorbing slurry from absorption tower 2
To be collected.

Thus, after the absorption liquid circulation pump 4 is started,
Since the circulation pump 4 and the pipe 5 are filled with the slurry held in the absorption tower storage section, the level of the absorption tower temporarily decreases. After that, slurry is collected from the drain pit 11 and the absorption tower level will be restored.
There is no need to allow for the level increase in the distance h from the liquid level in the absorption tower to the overflow seat.

The pump head of the absorption liquid circulation pump 6 for the spray nozzle 6 in the absorption tower is 25 to 30 m. If the height of the absorption tower tank 2 can be reduced by about 1 m according to the present invention, the pump head is 3 to 30 m. 4%, saving pump operating costs.

[0011]

FIG. 2 shows a drain blow collecting operation procedure when the circulation pump is stopped according to the present invention, which will be described in detail below.
After the circulation pump 4 is stopped, the operation is the same as that of the related art until the drain valves 7 and 8 are opened to blow the slurry in the pump 4 and the pipe 5.

A feature of the present invention is that the drain pump 14 is started after the circulation pump 4 is restarted. While the circulation pump 4 is stopped, the drain in the pump and the piping is held in the drain pit 11, and the drain is held. The pump 14 does not start. After the circulation pump 4 starts, the circulation pump 4 and the pipe 5
After the slurry in the bottom circulating tank 21 of the absorption tower 2 is sent to the inside, the liquid level of the absorption tower is lowered, and then the drain pump 14 is started to recover the slurry in the drain pit 11. When the collection is completed and the drain pit level falls below a specified value, the operation of stopping the drain pump is the same as in the related art.

As another embodiment of the present invention, the same effect can be obtained even if the start-up of the circulation pump 4 as the start-up condition of the drain pump 14 in the procedure shown in FIG. Yes, and of course, the same effect can be obtained when used in combination. Further, when the absorbing liquid contained in the drain pit is collected in the lower tank of the absorption tower, it may be supplied to the spray nozzle of the upper absorption section, and the absorbing liquid after spraying may be collected in the lower circulation tank of the absorbing tower.

According to this embodiment, since the liquid level in the absorption tower 2 does not rise, the tower height can be reduced, and the power of the circulating pump can be reduced by lowering the pump head.
For example, in a flue gas desulfurization device installed in a 1000 MW class thermal power plant, the total head of the absorption tower circulation pump is 30 m.
Pump with a 500 kW motor
About 5,000 KWH /
h. By reducing the total head of this pump by 1 m, the pump power can be reduced by about 3% or 150 KW.

[0015]

According to the present invention, since the liquid level in the absorption tower does not rise, the height of the tower can be reduced and the total head of the circulating pump can be reduced, so that the pump power can be saved.

[Brief description of the drawings]

FIG. 1 is a system diagram of an absorption tower and a drain pit of a desulfurization apparatus to which the present invention is applied.

FIG. 2 is a diagram showing an operation procedure of extracting and recovering a slurry in the absorption tower circulation pump and pipes according to the present invention.

FIG. 3 is a diagram showing an operation procedure for extracting and recovering slurry in the absorption tower circulation pump and circulation pipe according to the prior art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Absorption tower inlet duct, 2 ... Absorption tower, 3 ... Absorption tower outlet duct, 4 ... Absorption tower circulation pump, 5 ... Absorption tower circulation pipe, 6
… Spray nozzle, 7, 8 drain valve, 9, 10 drain pipe, 11 drain pit, 12 stirrer, 13 level switch, 14 drain pump, 15 pipe, 16…
Pump outlet valve, 17: Pump inlet valve, 18: Stirrer, 1
9: overflow pipe, 20: seal pot, 21: absorption liquid circulation tank.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yasuki Hashimoto 6-9 Takara-cho, Kure-shi, Hiroshima Pref. Inside the Kure Plant of Babcock Hitachi Ltd. (56) References JP-A-1-249127 (JP, A) JP-A Sho 60-147219 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/50 B01D 53/77

Claims (1)

(57) [Claims] 1. A absorbing portion at the top, introducing exhaust gas containing sulfur oxides to absorb part of the absorption tower having a tank portion at the bottom, the circulation piping absorbent slurry absorbing solution stored in the lower tank and the circulation pump A wet exhaust gas desulfurization that supplies and sprays the exhaust gas to the spray nozzle provided in the absorption section through the air, makes gas-liquid contact with the exhaust gas, absorbs and removes the sulfur oxides in the exhaust gas, and stores the absorbent after the spray in the lower tank. Discharge by device
In scan desulfurization process, the withdrawn absorption liquid of the circulation pipe during shutdown of desulfurizer the drain pit, during the stop period of the circulation pump to retain this, at the time of restart of the desulfurization apparatus, the absorption tower fluid level An exhaust gas desulfurization method, comprising: collecting the absorbent retained in the drain pit after the water has dropped into the absorption tower tank.