JPS61245823A - Method for controlling liquid level of absorbing tower in flue gas desulfurization apparatus according to wet limestone/gypsum process - Google Patents

Abstract

PURPOSE:To constantly control the concn. of CaCO3 in a washing solution even if the flow amount of flue gas is varied, by calculating the level set value of a washing solution as the function of the flow amount of flue gas and operating the regulation valve of the washing solution withdrawing piping from an absorbing tower by a level regulator. CONSTITUTION:Flue gas is introduced into an absorbing tower 3 from an exhaust gas inlet duct 1 and cooled at the inlet part of the absorbing tower 3 by a washing solution to remove dust in said flue gas and SOx in the flue gas is further absorbed by the washing solution in the main body part of the absorbing tower 3. The washing solution is supplied to the absorbing tower 3 by a pump 5 through recirculation piping 6 and a part thereof is discharged out of the system through piping 8. The gas flow amount detection signal from the flowmeter 11 arranged to the inlet duct 1 is inputted to a function generator 12 and the output signal thereof is inputted to a level detection regulator 9 as the level set value thereof. A regulation valve 10 is operated by the level detection regulator 9 so as to adjust the level of the washing solution to said set valve to regulate the withdrawal amount of the washing solution.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention uses calcium hydroxide (Ca(OH)1) and/or calcium carbonate (0aOO1) to reduce sulfur oxides (hereinafter referred to as The present invention relates to an absorption tower level control method of a wet flue gas desulfurization equipment for removing oxidants (referred to as 80).

[Conventional absorption tower level control method]

Conventionally, as this type of control method, the method shown in FIG. 4 is known. For example, exhaust gas from a coal-fired boiler is introduced into the absorption tower 3 through the exhaust gas inlet duct 1.
At the inlet, the cleaning liquid cools and removes dust. Of course, a method is also known in which the exhaust gas is cooled and dust-removed using a separately arranged cooling and dust-removal device before entering the absorption tower 3.

Due to the cooling of the exhaust gas, some of the water in the cleaning liquid evaporates, but it is replenished by makeup water from the pipe 2. Subsequently, the exhaust gas is further cooled and dust removed in the main body of the absorption tower 3, and at the same time, 80X in the exhaust gas is reacted with and absorbed by the cleaning liquid.

When Ct a O03 is used as an absorbent in the cleaning solution, the following reaction occurs? ) 80X is absorbed.

Oa80g + BCh + TizO→Oa"+ 2
H80B-(1)H803"-1000! → H+
804"-(2)Oa"+ 804"--*0a
804 (3) OaO03+
2H-+ Oa”+ Hlo + Co-trim (4jOa”+ H80s
--+ 0a80B + a+ (5) That is, 〇 a 803 generated in absorption tower 3 is absorbed son
In equation (1), Oa”+ and H day 03− are obtained, but this H
A part of 803- is oxidized by 01 K in the exhaust gas and becomes H"+804"- as shown in equation (2).

In addition, Fi+ is neutralized by O a 003, which is an absorbent (
As in formula 41, Oa” and n, o and ool, and 00
2 is released as a gas from the outlet 4 shown in FIG.

When the concentration of the generated 17'2so-1 and R803- increases, it becomes (3L (4) Ca804.0a as shown in 2).
80B, it precipitates in the solid phase. In addition, 0a804 and C
The generation rate on day a 03 is determined by the amount of H042- produced by 02 in the exhaust gas.

The cleaning liquid is supplied to the absorption tower 3 through the circulation pipe 6 by the circulation pump 5 and comes into contact with the exhaust gas.

The cleaning liquid in the absorption tower 3 is supplied with caco3 (or 0
a(OB)1) slurry or absorbed 80. It is supplied in approximately the equivalent amount of SO2, and increases and decreases in proportion to the absorbed SO2.

A portion of the cleaning liquid is drawn out of the system through piping 8. This withdrawal amount is controlled by a level detection controller 9 and a control valve 10 so as to keep the cleaning liquid level in the absorption tower 3 constant.

[Problems to be solved by the present invention]

By the way, modern power generation boilers vary the amount of power generated and the load on the boiler depending on the power demand, so the amount of exhaust gas generated by the boiler also changes, and when the amount of exhaust gas changes, the amount absorbed by the absorption tower 3 increases. Also fluctuated, same 80! The flow rate of the absorbent supplied through the pipe 7 also fluctuates almost in proportion to the amount.

By the way, the reaction amount ti of the neutralization reaction of C a 00B, which is an absorbent shown in equation (4), is the total amount shown in equation 67.

R=KX[0aOOs]
6) R: Reaction amount (kpmol/Hr) K: Reaction rate constant (1/Hr) [Oa (!01]: O!LOO3 concentration (kpmol
/m') A: Cross-sectional area of the cleaning liquid reservoir in the absorption tower (vehicle 2) L: Cleaning liquid level (m) This reaction amount is 80. Equal to the equivalent of a quantity.

Suppose that the amount of exhaust gas increases and the amount of 802 gas absorbed by the absorption tower 3 increases.
When the amount increases, the reaction amount (R) shown in equation (6) also increases in proportion to this.

At this time, in equation (6), the reaction rate constant (K) and cross-sectional area (A) are constant, and the level (T#) is considered to be constant because it is level-controlled as described above.

Therefore, as the amount of reaction increases, C! The a003 concentration will increase. Also, 0a003 through piping 8
The cleaning liquid containing 803 is extracted from the system, and the O a C03 contained in this cleaning liquid is wasted without being used for 803 absorption.

In the conventional method of controlling the level at a constant level, when the exhaust gas flow rate increases, the Oa 003 concentration increases for the above-mentioned reason, resulting in a waste (!aoo1 amount increases).

[Means for Solving the Problems] The present invention has been made to solve the drawbacks of the above-mentioned conventional method.The present invention measures the flow rate of the exhaust gas introduced into the absorption tower, and sets the signal of this exhaust gas flow rate in advance. input the function into the function generator that generates the function, detect the cleaning liquid level of the -N direction absorption tower,
This level detection signal is input to the level controller as a control amount, and the output signal of the function generator is input to the level controller as a level setting value. The present invention aims to provide a method that can control O a 003 at a nearly constant level even if the flow rate of exhaust gas increases, without increasing the amount of wasted O a 003, by operating a control valve installed in a pipe that extracts O a 003. It is.

〔Example〕

Embodiments of the present invention will be described below with reference to FIG.

First, exhaust gas is introduced into the absorption tower 3 from the exhaust gas inlet duct 1, and is cooled and dust-removed by a cleaning liquid at the entrance of the absorption tower 3. Next, the exhaust gas is further cooled and dust removed in the main body of the absorption tower 5, and at the same time, the exhaust gas 80 reacts with and is absorbed by the cleaning liquid.

The cleaning liquid is supplied to the absorption tower 3 through the circulation pipe 6 by the circulation pump 5 and comes into contact with the exhaust gas.

In these steps, the gas flow rate is detected by a flow meter 11 installed in the exhaust gas inlet duct 1, and this flow rate detection signal is input to the function generator 12.

The function generator is set to generate a function f (X) representing the relationship between the exhaust gas flow rate and the level setting value, as shown in FIG.

This function f(x) is shown below.

However, a: Since the amount of reaction (6) in equation (6) and the amount of exhaust gas (resistance) are approximately proportional, the relationship R=a−x holds true. a represents this proportionality constant.

K: Caro1 reaction rate constant (same as K in equation (6)) (caco31o" target cleaning liquid 0aOO1 concentration M: cross-sectional area ((same as M in equation 6J) The function f (b) is input as the level setting value of the level detection controller 9.The level detection controller 9 controls the control valve 10 so that the level becomes the level setting value, that is, the function f (b) shown by equation (7). operating.

As a result, the Q a OOH concentration [Ca0O1
] becomes equation (87) from equation (63) and equation (7).

K.mu.&-X a*X Here, since the reaction amount (6) is R=a-z as described above, this is substituted.

a ・X = [0aOO1] @ ... (B) The present invention calculates the concentration of 0aO03 [0aCOs
l is the target cleaning liquid Oa 00B concentration [O
It is clear that a(!031o is constant.

As a result, the amount of O a OOH that is wasted can be reduced.

Further, in the above embodiment, the control valve 10 is directly operated by the output signal of the level detection controller 9, but the present invention is not limited thereto.

For example, as shown in FIG. 3, the output signal of the level detection controller 9 is used to operate the setting value of the flow rate detection controller 13 that detects the amount of pipe 8 to be extracted, and the flow rate detection controller 13 is used to adjust the level detection. The control valve 10 may be operated so that the flow rate is set by a total of nine output signals.

[Effects of the present invention]

As described in detail above, according to the present invention, the level of the absorption tower in the wet lime gypsum method flue gas desulfurization equipment can control the Oa003 concentration in the cleaning liquid to be almost constant without changing even if the flue gas flow rate fluctuates. A control method can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the absorption tower level control method of the flue gas desulfurization equipment of the present invention, FIG. 2 is a diagram showing the relationship between the amount of exhaust gas and the level setting value, and FIG. The figure is a schematic diagram showing another embodiment for explaining the absorption tower level control method of the present invention. Figure m4 is a schematic diagram for explaining a conventional absorption tower level control method of a flue gas desulfurization device. 1... Exhaust gas inlet duct, 3... Absorption tower, 4...
Exhaust gas outlet duct, 5... Circulation pump, 6... Circulation piping, 7... Absorbent supply piping, 8... Cleaning liquid extraction piping, 9... Level detection controller, 10...
・Control valve, 11...Gas flow meter, 12...Function generator, 13...Flow rate detection regulator L gas flow rate (1)

Claims (1)

[Claims] In an absorption tower level control method for a wet flue gas treatment device that cleans flue gas using a slurry containing calcium hydroxide and/or calcium carbonate to remove sulfur oxides in the flue gas,
The flow rate of the exhaust gas introduced into the absorption tower is measured, and the signal of the exhaust gas flow rate is inputted to a function generator that generates a preset function, while the cleaning liquid level in the absorption tower is detected, and the level of the cleaning liquid in the absorption tower is detected. Piping that inputs the detection signal as a control amount to a level controller, further inputs the output signal of the function generator to the level controller as a level setting value, and extracts liquid or slurry from the absorption tower according to the output signal of the level controller. 1. A method for controlling liquid level in an absorption tower in a wet lime-gypsum flue gas desulfurization equipment, the method comprising operating a control valve provided in a wet lime-gypsum flue gas desulfurization system.