JPH11197450A - Wet desulfurization equipment and its operation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flue desulfurization equipment keeping the slurry concentration in an absorbing solution tank and also keeping the absorbing solution level in the absorbing solution tank within the given range when the operation of extracting intermittently an absorbing solution from the absorbing solution tank and also provide an operation method thereof. SOLUTION: An absorbing solution from an absorbing solution tank 1a containing a lime stone slurry storing the absorbing solution is brought into contact with boiler gas introduced into an absorption column 1 to remove sulfur oxide in gas, and the absorbing solution absorbing the sulfur oxide in exhaust gas is returned to the absorbing solution tank 1a. At that time, the specific gravity of the absorbing solution in the absorbing solution tank 1a is sensed by a specific gravity hydrometer 16, and the feed amount of reinforcing water from a reinforcing water feed line 10 into the absorbing solution is adjusted, and also the absorbing solution extraction amount out of an absorbing solution extraction line 9 of the absorbing solution tank 1a is adjusted based on the sensed value of a liquid level indicator 17 for the absorbing solution in the absorbing solution tank 1a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wet flue gas desulfurization apparatus and method suitable for removing sulfur oxides in boiler exhaust gas.

[0002]

2. Description of the Related Art FIG. 4 shows a system diagram of a flue gas desulfurization apparatus according to the prior art. The boiler exhaust gas 14 is introduced into the absorption tower 1. In the absorption tower 1, the absorption liquid containing limestone slurry in the absorption liquid tank 1 a at the lower part of the absorption tower is supplied to the spray nozzle 3 by the circulation pump 2, and from the nozzle 3. The exhaust gas introduced into the absorption tower 1 is removed and cooled by the sprayed absorbing liquid, and the sulfur oxides contained in the exhaust gas are absorbed.

[0003] Limestone used for removing sulfur oxides from the exhaust gas is supplied from a limestone slurry supply line 8 to a regulating valve 1.
By 1, the supply amount is adjusted and introduced into the absorption tower 1. The supply amount of the limestone slurry is controlled by the amount of sulfur oxide in the exhaust gas 14 introduced into the absorption tower 1.

[0004] The sulfur oxides absorbed in the absorbing solution react with limestone as an absorbing agent, and are further oxidized into gypsum by air supplied into the absorbing solution. The limestone slurry containing the generated gypsum is supplied to the absorption liquid extraction pump 4 from the absorption liquid tank 1a.
, And is dehydrated by the dehydrator 6 and collected as gypsum 7.

[0005]

Here, in order to maintain the desulfurization performance of the absorption tower 1, it is necessary to keep the concentration of limestone in the absorption tower 1 constant. In step 13, an amount of absorption liquid corresponding to the supply amount of limestone slurry is extracted.

[0006] Further, since the absorption liquid is evaporated by cooling the exhaust gas in the absorption tower 1, supply water is supplied by a regulating valve 11 provided in the supply water pipe 8 in accordance with the evaporation.

On the other hand, when a hydrocyclone (not installed in the flue gas desulfurization system shown in FIG. 4) is installed downstream of the absorption liquid (gypsum slurry) extraction line 9, the hydrocyclone is installed. It is necessary to keep the balance between the underflow and the overflow constant, and for this purpose, it is necessary to keep the flow rate of the absorption liquid containing the gypsum slurry from the absorption liquid extraction line 9 constant. Therefore, the adjustment of the amount of the absorbent to be withdrawn from the absorbent tank 1 a
The N-OFF control operation (discontinuous opening / closing control) must be performed.

In the ON-OFF control (non-continuous opening / closing control) operation of the regulating valve 12, if only the ON-OFF control based on the gypsum slurry concentration in the absorbent tank 1a is performed, if the gypsum slurry concentration becomes high, The absorption liquid in the absorption liquid tank 1a is withdrawn and replenishment water is supplied to the absorption liquid tank 1a. However, as described above, the absorption liquid withdrawal amount is affected by the amount of sulfur oxide flowing in. The withdrawal amount and the supply amount of make-up water to the absorbent cannot be set at a fixed ratio.

For example, when treating an exhaust gas having a sulfur oxide concentration lower than the sulfur oxide concentration in the exhaust gas of the hydrocyclone design value, the supply amount of limestone is reduced and the limestone in the absorption liquid tank 1a is reduced. In addition, in order to keep the gypsum slurry concentration constant, it is necessary to reduce the amount of makeup water supplied accordingly. Therefore, in this case, the absorbent tank 1
The absorption liquid level of “a” is decreasing.

In addition, when the ON-OFF control operation is performed to adjust the amount of the withdrawn liquid from the absorption tank 1a based on the level of the absorption liquid in the absorption tank 1a, the absorption liquid is removed if the absorption liquid level is higher than the reference value. Withdraw from the absorbent tank 1a,
Supply water is supplied to this, for example, when treating the exhaust gas having a lower sulfur oxide concentration than the sulfur oxide concentration in the exhaust gas of the hydrocyclone design value, the supply amount of limestone decreases, and the supply amount of limestone decreases. However, the amount of makeup water becomes excessive, and the slurry concentration decreases.

Adjustment of the amount of the absorbing liquid withdrawn from the absorbing liquid tank 1a is performed by controlling the concentration of the slurry in the absorbing liquid tank 1a. Adjustment of the supply amount of the replenishing water is controlled by controlling the level of the absorbing liquid in the absorbing liquid tank 1a. In this case, the slurry concentration in the absorbing solution is reduced when the level of the absorbing solution is restored by supplying makeup water to the absorbing solution after withdrawing the absorbing solution. In a balanced operation in which the absorption liquid level is reduced in a stopped state, the absorption liquid level is reduced before the slurry concentration is recovered, so that makeup water is supplied again, and the slurry concentration is further reduced. I will.

[0012] Further, in a balance in which the level of the absorbing liquid rises in a state where the extraction of the absorbing liquid and the supply of the makeup water are stopped,
When the make-up water is supplied until the liquid level recovers from the state in which the liquid level is lowered after the absorption liquid is withdrawn, the limestone slurry concentration decreases, but the absorption liquid level further increases until the limestone slurry concentration recovers. Will rise.

An object of the present invention is to maintain the concentration of the slurry composed of limestone and gypsum in the absorption liquid tank within a certain range even if the operation of intermittently extracting the absorption liquid from the absorption liquid tank is performed.
Another object of the present invention is to establish a wet flue gas desulfurization apparatus capable of maintaining the level of the absorbent in the absorbent tank within a certain range and a method of operating the same.

[0014]

The above object of the present invention is attained by the following constitution. That is, an absorption tower that contacts an absorption liquid containing limestone slurry with boiler exhaust gas to absorb and remove sulfur oxides in the exhaust gas, an absorption liquid tank that stores the absorption liquid that has absorbed sulfur oxides in the exhaust gas, Absorbent extraction line with extraction line automatic opening / closing valve for extracting the absorption liquid from the absorption liquid tank, and make-up water supply line with supply water supply line for supplying makeup water into the absorption liquid tank A line, a hydrometer for measuring the specific gravity of the absorbent in the absorbent tank or a slurry concentration meter in the absorbent and a liquid level meter for measuring the liquid level of the absorbent, and a hydrometer or the absorbent for the absorbent A control device is provided for controlling the opening and closing of the make-up water supply line automatic opening and closing valve based on the detection value of the slurry concentration meter therein, and for controlling the opening and closing of the extraction line automatic opening and closing valve based on the detection value of the liquid level meter for the absorbent. Wet The absorption liquid is supplied into the absorption tower from a smoke desulfurization device or an absorption liquid tank containing limestone slurry for storing the absorption liquid, and is brought into contact with the boiler exhaust gas introduced into the absorption tower to remove sulfur oxides in the exhaust gas. In a wet flue gas desulfurization method for absorbing and removing and absorbing the sulfur oxides contained in the exhaust gas and returning the absorbing solution to the absorbing solution tank, the replenishing water to the absorbing solution tank is determined based on the specific gravity of the absorbing solution in the absorbing solution tank or the slurry concentration. This is a wet type flue gas desulfurization method in which the supply amount of water is adjusted, and the amount of absorption liquid withdrawn from the absorption liquid tank is adjusted based on the level of the absorption liquid in the absorption liquid tank.

At this time, the liquid level at the start of the absorption liquid withdrawal in the absorption liquid tank, the liquid level at the stop of the absorption liquid withdrawal, and the specific gravity or slurry concentration of the absorption liquid at the start of the supply of make-up water to the absorption liquid in the absorption liquid tank. The specific gravity or the slurry concentration of the absorbing liquid when the supply of the replenishing water to the absorbing liquid in the absorbing liquid tank is stopped is set.

The wet type flue gas desulfurization apparatus of the present invention is not limited to the spray type in which the absorbent is sprayed from the spray nozzle, but the wet wall type in which the exhaust gas is brought into contact with the absorbent flowing through the wet wall, and the bubbling type in which the exhaust gas is bubbled in the absorbent. Can also be applied to those provided with an absorbing liquid. Further, the absorbing liquid tank for storing the absorbing liquid of the present invention may have either a structure provided below the absorption tower or a structure provided as a separate device from the absorption tower.

[0017]

[Action] Even after the absorption liquid is withdrawn to the liquid level at which the withdrawal is stopped, the replenishing water for the absorption liquid is supplied with a predetermined amount of limestone in the absorption liquid. It is not supplied until the specific gravity of the absorbing solution corresponding to the gypsum slurry concentration is reached. During this time, fresh limestone slurry and washing water around the absorption tower are being replenished, and the slurry concentration and the absorption liquid level in the absorption liquid in the absorption tank at the bottom of the absorption tower naturally rise. When the specific gravity of the absorbing liquid corresponding to the slurry concentration is obtained, the supply water is supplied when the supply water reaches the value corresponding to the supply start concentration.

Further, at the time when the level of the absorbing liquid to be started is reached, the extraction of the absorbing liquid is started again, and the concentration of the slurry (or the specific gravity of the absorbing liquid) is changed to the concentration at which the supply of the make-up water is stopped (or the specific gravity of the absorbing liquid). ), The supply water supply is stopped. With such an operation method, the liquid level of the absorbent in the absorbent tank and the concentration of the slurry composed of limestone and gypsum can be controlled within a certain range.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to a flow chart of a flue gas desulfurization apparatus shown in FIG. Although the flow of the flue gas desulfurization device shown in FIG. 1 is basically the same as that of the conventional technology shown in FIG. 4, it is characterized by a control device for operating the flue gas desulfurization device.

An absorption liquid tank 1a containing limestone slurry is disposed below the absorption tower 1, and the absorption liquid in the absorption liquid tank 1a is supplied to a spray nozzle 3 provided in an empty tower portion of the absorption tower 1 by a circulation pump 2. Absorbing liquid is being supplied. Therefore, the exhaust gas 14 introduced into the absorption tower 1 is sprayed by the spray nozzle 3
Gas-liquid contact with the limestone slurry in the absorbing liquid sprayed from the mist, the sulfur oxides in the exhaust gas are absorbed by the limestone slurry. The sulfur oxides absorbed in the absorbing solution react with limestone as the absorbing agent, and the air 15 supplied to the absorbing solution further reacts.
Is oxidized into gypsum. The limestone slurry containing the produced gypsum is withdrawn from the absorbing liquid tank 1a by the absorbing liquid extracting pump 4 to the absorbing liquid extracting line 9 and sent to the hydrocyclone 18 where it is concentrated. Will be collected as At this time, an absorption liquid extraction valve 13 is provided in the absorption liquid extraction line 9, and the opening / closing control of the absorption liquid extraction valve 13 adjusts the amount of the absorption liquid extracted.

The limestone used for removing sulfur oxides in the exhaust gas is supplied from the limestone slurry supply line 8 into the absorption tower. 14 is controlled in accordance with the amount of sulfur oxide.

The feature of the flow shown in FIG. 1 is that an absorption liquid specific gravity signal 16 and an absorption liquid level signal 17 in the absorption tower are provided, and the output signals of these two signals 16 and 17 are controlled respectively. The apparatus 20 enters the apparatus 20 and controls the opening and closing of the makeup water supply valve 11 and the feedwater discharge valve 13 based on the two output signals.

That is, the supply amount of makeup water supplied from the absorption tower makeup water supply line 10 is controlled by opening and closing the makeup water supply valve 11 from the absorption liquid (gypsum slurry) specific gravity signal 16. The amount of gypsum slurry withdrawn, that is, the amount of absorbent absorbed, is determined by controlling the level of the absorbed liquid in the absorption tower based on the signal from the level signal 17 to open and close the absorbent extraction valve 13.

The absorbing solution having absorbed the sulfur oxides is oxidized by the air 14 blown into the absorption tower tank 1a to produce gypsum.
Is sent to the hydrocyclone 18 as a gypsum slurry. The gypsum slurry concentrated in the hydrocyclone 18 is further dehydrated by the gypsum dewatering machine 6 and collected as the gypsum cake 7.

In the flow of the flue gas desulfurization apparatus shown in FIG.
FIG. 2 shows an operation simulation result of controlling the extraction amount of the absorbing liquid (gypsum slurry) by the signal of the level signal device 17 and controlling the supply amount of the makeup water by the absorbing liquid specific gravity signal device 16.

As shown in FIG. 2, the supply of make-up water is continued until the specific gravity of the absorbent reaches a predetermined value even after the absorbent is withdrawn to the stop level by controlling the level of the absorbent in the absorbent tank 1a. Do not start. During this time, the limestone slurry and the washing water around the absorption tower have been replenished.
The limestone slurry concentration in the absorbing solution and the level of the absorbing solution in a rise naturally. Then, when the slurry concentration of limestone and gypsum (specific gravity of the absorbing solution) becomes the value of the supply water supply start concentration (specific gravity of the absorbing solution), supply of the makeup water is started. Further, the withdrawal of the absorbing liquid is started again when the level of the absorbing liquid reaches the level of the absorbing liquid at the start of the withdrawal of the absorbing liquid, and the supply of the make-up water is stopped when the specific gravity of the absorbing liquid reaches the slurry concentration at which the supply of the make-up water is stopped. By repeating such an operation method, the liquid level and the slurry concentration of the absorbing liquid in the absorbing tower can be controlled within a certain range.

The embodiment shown in FIG. 3 is the same as the flow shown in FIG. 1 except that the hydrocyclone 18 used in the flow shown in FIG. 1 is not used. Thus, the main purpose is to intermittently withdraw the absorbing liquid (gypsum slurry) in the absorption tower, regardless of whether the downstream device of the absorption tower 1 is equipped with a hydrocyclone.
Further, the present invention is applicable regardless of the type of the gypsum dewatering machine.

According to the present invention, even if the absorption liquid (gypsum slurry) in the absorption liquid tank is withdrawn intermittently, the level of the absorption liquid in the absorption liquid tank and the gypsum slurry or limestone in the absorption liquid are maintained. The slurry concentration can be kept within a certain range.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow of a wet flue gas desulfurization device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a simulation result when the present invention is applied to the flow of FIG. 1;

FIG. 3 is a diagram showing a flow of the wet flue gas desulfurization apparatus according to the embodiment of the present invention.

FIG. 4 is a view showing a flow of a conventional wet flue gas desulfurization apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Absorption tower 2 Circulation pump 3 Spray nozzle 4 Absorption liquid extraction pump 6 Dehydrator 7 Gypsum cake 8 Limestone supply slurry line 9 Gypsum extraction line 10 Absorption tower supply water supply line 11 Supply water supply valve 12 Adjustment valve 13 Absorption liquid extraction valve 14 Exhaust gas 15 Air 16 Absorbent specific gravity signal 17 Level signal 18 Hydrocyclone 20 Controller

Claims (2)

[Claims] 1. An absorption tower for contacting an absorbent containing limestone slurry with boiler exhaust gas to absorb and remove sulfur oxides in the exhaust gas, and an absorbent tank for storing the absorbent absorbing the sulfur oxides in the exhaust gas. An absorption liquid extraction line with an extraction line automatic opening / closing valve for extracting the absorption liquid from the absorption liquid tank; and a makeup water supply line automatic opening / closing valve for supplying makeup water into the absorption liquid tank. A makeup water supply line, a hydrometer for measuring the specific gravity of the absorbent in the absorbent tank or a slurry concentration meter in the absorbent and a liquid level meter for measuring the liquid level of the absorbent, and a hydrometer for the absorbent. Or, control for opening / closing a make-up water supply line automatic opening / closing valve based on a detection value of a slurry concentration meter in an absorbing solution, and control for opening / closing control of an extraction line automatic opening / closing valve based on a detection value of a liquid level meter for the absorbing solution. Equipment Wet flue gas desulfurization apparatus characterized by. 2. An absorption liquid is supplied from an absorption liquid tank containing limestone slurry for storing the absorption liquid into an absorption tower, and brought into contact with boiler exhaust gas introduced into the absorption tower to absorb sulfur oxides in the exhaust gas. In the wet flue gas desulfurization method for removing and absorbing the sulfur oxides contained in the exhaust gas to the absorption tank, the replenishing water to the absorption tank is determined based on the specific gravity or the slurry concentration of the absorption tank in the absorption tank. A wet flue gas desulfurization method comprising adjusting the supply amount and adjusting the amount of the absorbing liquid withdrawn from the absorbing liquid tank based on the level of the absorbing liquid in the absorbing liquid tank.