JPS6161616A - Method for controlling desulfurization plant by wet lime and gypsum process - Google Patents

Abstract

PURPOSE:To follow up a rapid increase in desulfurization load by controlling the pH of a liquid absorbent and the concn. of calcium carbonate in a desulfurization plant by a went lime and gypsum process. CONSTITUTION:When the supply of an absorbent to the absorption tower of a desulfurization plant by a wet lime and gypsum process is controlled, the pH and the calcium carbonate concn. of a slurry in the absorption tower are measured by a pH detector 11 and a calcium carbonate concn. detector 18. When the calcium carbonate concn. exceeds a specified value, a requisite amt. of the absorbent for controlling the pH value is supplied, and an increased amt. of the absorbent is supplied to regulate the calcium carbonate concn. to more than a specified value, when the calcium carbonate concn. is lower than a specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for controlling a wet lime-gypsum desulfurization plant.

[Prior art]

A conventional wet lime gypsum desulfurization plant is constructed as shown in FIG. 2, and desulfurization is carried out in the following manner.

First, when the exhaust gas 1 is introduced into the absorption tower 3 from the duct 2, it comes into contact with the circulating absorption liquid 4. S in exhaust gas
Ol is Ht80s in the liquid by the absorption reaction of the following formula (1).
t-generates and flows down SO, 10 times 0 → H, 80,...
- (1) After this, the exhaust gas passes through the exhaust line 5f and is discharged from the chimney.

On the other hand, the liquid that has produced H,80, flows down into tank 6 from the bottom of the column. A neutralizing agent (calcium carbonate, other alkaline substances such as calcium hydroxide) is supplied to m6 from supply line 1, and this neutralizing agent neutralizes the liquid and produces Ca5O.
The neutralized liquid producing s is supplied to the absorption tower 3Vc through circulation 2in9t by a pump 8. In addition, a part of the circulating fluid is taken out and Ca80s is converted to CaS in the post-process.
Oxidized to O4.2H10 (gypsum).

The conventional control method for the above-mentioned S02 absorption device is carried out in an incomplete manner. pHfli! of the absorption liquid circulating in the pH detector 11! is detected and input to the controller 12. The controller 12 inputs a signal to the adder 13 so as to keep the pH value of the absorption liquid reaching the tower insects constant.

First, the load detector 14 installed in the duct 2 detects the SO of the exhaust gas entering the system! The load of the desulfurization plant (hereinafter referred to as desulfurization load) is detected and inputted to the adder 13. The signal and the signal from the load detector 14 are added together and input as a set value signal to the flow rate controller 15.
The flow rate is detected by the flow rate detection unit 16, and the flow rate controller 15
Enter. The flow rate controller 15 is 1. Based on these signals, the control valve 17 installed in the supply line 7 is controlled.

[Problem that the invention seeks to solve]

In the above-mentioned control method, maintaining the pH of the absorbing liquid at a predetermined value means constantly supplying the absorbent for iodine and tooth material to be harvested. However, when lucicum carbonate is used as an absorbent, the dissolution rate of calcium carbonate is very slow, so undissolved solid calcium carbonate must always be present in order to maintain absorption performance.

However, if the plant is shut down for a long time, such as late at night or on weekends, the supply of ions to the absorption tower will be stopped, while the absorbent remaining in the tank, such as calcium carbonate, will reach its saturated solubility. As it continues to dissolve, the pH value increases significantly compared to during normal operation. When the plant is operated under these conditions, the pH value is high using the conventional control method described above, so all of the absorbent is not injected. On the other hand, the solid calcium carbonate concentration is lower by the amount dissolved during the shutdown, so If a sudden increase in desulfurization load occurs, the absorbent cannot be added in time, making it difficult to maintain desulfurization performance.

The present invention provides a control method for a wet lime-gypsum desulfurization plant that can follow a sudden increase in desulfurization load and maintain desulfurization performance even when the plant is operated after being stopped for a long time at night or on weekends. This is what I am trying to do.

[Means for solving problems]

In the present invention, when controlling the supply location of absorbent to the absorption tower of a wet lime gypsum desulfurization agent, the pH value and calcium carbonate m degree of the slurry in the tank of the absorption tower are measured, and the calcium carbonate concentration is determined. If the pH value is above a predetermined value, the amount of absorbent necessary for pH control is supplied; on the other hand, if the calcium carbonate concentration is below a predetermined value, an increased amount of absorbent is supplied so that the calcium carbonate concentration is above the predetermined value. There are nine signs of f.

[Effect]

According to the above-mentioned method of the present invention, even if the plant is operated after being stopped for a long time at night or on weekends, the pH value in the absorption tower tank can always be controlled and the calcium carbonate concentration can be kept above a certain value. Since it can be maintained, it is possible to follow a sudden increase in desulfurization load well, and in turn, it is possible to maintain good desulfurization performance.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail with reference to FIG. Components similar to those shown in FIG. 2 already described are given the same reference numerals and their explanations will be omitted.

Reference numeral 18 in FIG. 1 is a calcium carbonate concentration detector that detects the calcium carbonate concentration of the circulating absorption liquid 4 and inputs the detection signal to the signal switching means 19. This switching means I9
A signal from the pH controller I2 is inputted to the pH controller 12, and a signal from the constant value generating means 20 is also inputted to the pH controller 12. Further, the switching means 19 inputs a signal to the adder 13. Next, the control method of the present invention will be explained.

First, the pH value of the circulating absorption liquid is detected by the pH detector 1 and inputted to the controller 12. Furthermore, the signal from the controller 12 is inputted to the signal switching means 19, and the calcium carbonate concentration detector 81B detects the pH value of the circulating absorption liquid. Detects the calcium carbonate concentration of the liquid,
The switching means 19Vc is input. In the signal switching means 19, if the calcium carbonate daughter force is equal to or greater than a predetermined value,
The signal from the controller 12 is output as is to the adder JJIC, and is sent to the control valve 1 of the supply line 7 via the flow rate controller 15.
Control 7.

On the other hand, when the carbonate concentration is less than the predetermined value, the signal switching means 19 outputs the signal from the constant value generating means 20 to the adder 13. At this time, in the adder 13, the supply amount of the absorbent is determined by the output of the constant value generating means and the load detector 14.
Since it is determined by the output of , the supply 2-in-7 control valve 17 is controlled via the flow rate controller 15't- so that the absorbent b corresponding to the load is supplied into the tank 6 on mass balance. Shif! : In response to an increase in the desulfurization load, the carbonate concentration in the tank 6 of the absorption tower 3 is maintained at a predetermined value or higher, and the desulfurization performance can be maintained. In addition, the signal switching means ;!
It is necessary to set a lower limit value for calcium carbonate concentration for OVC, but this can be determined by considering the plant design conditions and the properties of limestone.

〔Effect of the invention〕

As detailed above, according to the present invention, even when the plant is operated after being stopped for a long time at night or on weekends, it is possible to follow a sudden increase in desulfurization load and always maintain good desulfurization performance. A method for controlling lime-gypsum desulfurization gas can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a desulfurization plant used in the control method of the present invention, and FIG. 2 is a schematic diagram of a desulfurization plant used in the conventional control method. l...Exhaust gas, 3...Absorption tower, 4...Absorption liquid, 6
...paddle, 7...supply lie/, 9...circulation 2-in,
11... pH detector, 12... Controller, 13...
Adder, 14... Load detector, 15... Flow rate controller, 16... Flow rate detector, 17... Control valve, 18...
- Calcium carbonate concentration detector, 19... Signal switching means, 20... Constant value generating means. Applicant Sub-Agent Patent Attorney Takehiko Suzue Figure 1O Figure 2

Claims (1)

[Claims] In controlling the amount of absorbent supplied to the absorption tower of a wet lime gypsum desulfurization plant, the pH value and calcium carbonate concentration of the slurry in the tank of the absorption tower are measured, and if the calcium carbonate concentration is above a predetermined value, The method is characterized in that an amount of absorbent necessary for pH value control is supplied, and when the calcium carbonate concentration is below a predetermined value, the absorbent is increased and supplied so that the calcium carbonate concentration is equal to or higher than a predetermined value. Control method for wet lime gypsum desulfurization plant.