JPS62136229A - Apparatus for controlling concentration of so2 at outlet of wet waste gas desulfurization equipment - Google Patents

Abstract

PURPOSE:To keep the concn. of outlet SO2 constant regardless of the load of a boiler, by detecting the concn. an pH value of outlet SO2 and changing the pH of a recirculation liquid corresponding to the detected values and, at the same time, controlling the flow amount of an absorbent. CONSTITUTION:The concn. of outlet SO2 is detected by the outlet SO2 concn. detector 15 arranged to an exhaust duct 9 after SO2-removal and the output signal thereof is inputted to a SO2 concn. regulator 16 and compared with a preset outlet SO2 concn. value to perform feedback control. The control signal of the SO2 concn. regulator 16 is inputted to an amplifier 17 and, subsequently, the output of the amplifier and a pH lower limit value are inputted to an adder to output a pH set value. Further, the pH of a recirculation liquid is detected by a pH detector 14 and the detection signal is inputted to a pH regulator 10 and compared with the pH set value to perform feedback control and, by the output signal from said regulator 10, the opening degree of a flow control valve 11 is controlled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to sulfur dioxide gas (802) fjr in a processing gas.
80 in the desulfurized treated gas at K
2 concentration (hereinafter referred to as outlet 80.concentration) control.

[Conventional technology]

The schematic structure of a desulfurization plant, such as a wet lime gypsum process waste smoke desulfurization plant using calcium carbonate as an absorbent, will be explained with reference to the system diagram shown in FIG.

In FIG. 4, a processing gas 3 containing sulfur dioxide gas is introduced into the absorption tower 1 from above through a processing gas introduction duct 2. A circulating fluid 5 is contained in a tank 4 provided below the absorption tower 1, and this circulating fluid 5 is circulated within the absorption tower 1 by a circulation pump 6 and a circulation pipe 7. The treated gas 3 comes into contact with the circulating liquid 5 in the absorption tower 1, and the treated gas 3
The sulfur dioxide gas contained therein is removed.

That is, 802 in the processing gas 3 generates fi H2SO3'i by the reaction shown in the following equation (1) and flows down. This H
, SO8 is partially oxidized by oxygen (02) in the processing gas 3, and becomes H2SO4 as shown in the following formula (U).

In addition, the remaining H2SO3 is oxidized in the tank 4 by oxygen in the air injected from the air pipe 8, and becomes H,SO4.
becomes.

So2+ H20→H2So3 ・・・・・・・・・
(1) H2SO3+-o2→azSO4・・・・・・
...(...)Then, the treated gas that has passed through the absorption tower 1 and from which sulfur dioxide gas has been removed is discharged into the atmosphere as a treated gas through an exhaust duct) 91.

When the contact with the treated gas 3 continues in the absorption tower 1 as described above, the circulating liquid 5 contains a large amount of H2SO4 produced by the absorption reaction and oxidation reaction shown in (1) and (n) above. If some measures are not taken, SOz
becomes difficult to absorb. Therefore, an absorbent, such as calcium carbonate (CaC!03), is supplied to the circulating fluid 5 in the tank 4 through an absorbent supply pipe 12 equipped with a flow rate detector 10 and a flow rate control valve 11. ) As shown in K, the circulating fluid 5 is neutralized and regenerated so that it can easily absorb sulfur dioxide gas.

H2SO4+ CaCO3→0a804 +H20+
CO2↑... (■) A part of the circulating fluid 5 containing 0tLBO4 generated according to the above formula (III) is transferred to another process (not shown) via the transfer pipe 13.

As suggested from the above explanation, the SO2 absorption capacity of the circulating fluid 5 has a great influence on the performance of the desulfurization plant. The pH of the circulating fluid 5 is an indicator of the SO and absorption capacity of the circulating fluid 5. That is, the higher the concentration of CaCO3 in the circulating fluid 5 and the higher the pH, the more the SO absorption reaction is promoted.

It is conceivable to simply supply a large amount of absorbent to maintain the pH of the circulating fluid at a high level, but this is not preferable in terms of cost.

For these reasons, it is necessary to maintain a pH level that maintains the desired performance.
It is desired to operate a desulfurization plant in

This leads to stably maintaining the desulfurization rate in the absorption tower 1 and the sulfur dioxide gas concentration in the treated gas released into the atmosphere at a predetermined value.

In the conventional desulfurization plant shown in FIG.
The pi control device is as follows.

That is, a pH detector 14 is attached to the circulation pipe 7, and the output signal from this pg detector 14 is determined by the pH value.
is input to the regulator 10.

This pH regulator 10 compares a preset pH setting value with the output signal from the pH detector 14, and
Performs feedback control of ID (P: proportional, engineering: integral, D: differential). The opening degree of the flow rate regulating valve 11 is adjusted by the output signal of the pH regulator 10. In this way, the pH of the circulating fluid 5 is controlled to a predetermined value.

[Problems to be solved by the invention]

In recent years, in desulfurization plants, there has been a need to control the outlet 8029 degrees constant regardless of changes in boiler load. However, in conventional pH control devices, the amount to be controlled is pH, and there is no guarantee that the outlet SO2 concentration can be controlled to a predetermined value.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an outlet SO2 concentration control device that can control the outlet SO2 concentration to a predetermined value regardless of changes in the boiler load. be.

[Means for solving problems]

From the above explanation, the present invention was developed based on the idea of directly detecting the outlet SO2 concentration and changing the pH of the circulating fluid to increase or decrease the flow rate of the absorbent according to the detected amount.

That is, the outlet SO2 concentration control device of the present invention is used in a desulfurization plant in which a process gas containing sulfur dioxide gas is introduced into an absorption tower and is desulfurized by contacting with a circulating liquid containing an absorbent and circulating within the absorption tower. So detects the concentration of SO2 in the next-processed gas desulfurized in the absorption tower, S inputs the output signal of the concentration detector and the 5 oz degree detector as a control variable
an O2 concentration regulator, an amplifier inputting the output signal of the So2 concentration regulator, a pH detector detecting the pH of the circulating fluid, and an adder adding a preset pH lower limit value and the output of the amplifier; A pH control controller that inputs the output signal of the adder as a set value and the output signal of the pH detector as a control amount, and piping for supplying an absorbent to the absorption tower, and an output of the pH control controller. This is an outlet 802a degree control device in a wet flue gas desulfurization device, characterized in that it is equipped with a flow control valve whose opening degree is adjusted by a signal.

[Effect]

According to the present invention, when the outlet 502g degree is detected and the detected value is larger than the set outlet SO2 concentration, the circulating fluid pH is increased to promote the collection reaction to BO*'1 and the outlet 8
02 llij degree decreases and approaches the set value. Conversely, when the detected value is smaller than the set outlet SO and concentration, the circulating fluid p
By lowering H, SO and absorption reactions are suppressed, and the outlet S
As the O2 concentration increases, it approaches the set value.

However, if the circulating fluid pH is too low (e.g. 4 or less)
If absorption towers, piping, etc. are exposed to strong acids, corrosion will occur. Therefore, in the present invention, a reference value is given to the adder so that the output of the adder becomes the pH lower limit value when the output of the 802 controller is at its lowest, so that the pH set value of the circulating fluid does not become less than the specified value.

Furthermore, if the circulating fluid pH setting value becomes too high, it is said that when calcium carbonate is used as an absorbent, the pH will not rise above 6 even if a large amount is supplied to the absorption tower because it is a weak alkali. When the pH set value is 6 or more, even if the amount of absorbent is increased, the circulating FJpH will not increase at the set pHi, and a large amount of absorbent will be supplied forever. The amplifier gain is set so that the output of the adder becomes the upper limit of the pH set value when the SO2 controller output is at its maximum, which prevents excess absorbent from being supplied.

As described above, in the present invention, the first conditions are to prevent corrosion of absorption towers, piping, etc., and to prevent wasteful supply of absorbent, and the outlet So and concentration are determined within a range that satisfies these conditions. can be controlled to the value of

〔Example〕

Embodiments of the present invention will be described below with reference to FIG. Note that the same equipment and the like as the conventional apparatus shown in FIG. 4 are given the same numbers and the explanation thereof will be omitted.

Newly provided devices in the outlet 802a degree control device according to the present invention are an outlet SO2 concentration detector 15, an SO2 concentration controller 16, an amplifier 17, and an adder 18.

In FIG. 1, an outlet 8028 degree detector 15 installed in an exhaust duct 9 through which the processing gas from which sulfur dioxide gas has been removed passes.
The output SO and concentration are detected. The output signal of the outlet SO and the concentration detector 15 is input to the concentration controller 16 802. This SO2 concentration controller 16 compares the preset concentration value at the outlet 802 and the output signal from the outlet SO26 degree detector 15,
= integral, D: differential) feedback control is performed. S.O.
, the output signal of the concentration controller 16 is input to an amplifier 17. An example of the characteristics of the amplifier 17 is shown in FIG. The horizontal axis in FIG. 2 is the 802 eJ degree controller output, and the vertical axis is the amplifier output.The amplifier output is input to one end of the adder 18 in FIG. Enter at one end.

The output of the amplifier 17 in FIG. 2 is shown in FIG. 3. In FIG.
This value is obtained by adding pH4, which is the lower limit of the set value.

Furthermore, the circulating fluid pH' is detected by the rpH detector 14, and the detection signal is inputted as a control amount to the epH controller 10. This pH controller 10 compares the pH setting value inputted with the output signal of the adder 18 and the output signal of the H detector 14, and compares it with the output signal of the H detector 14, : 1 garment) feedback control is performed. The opening degree of the flow control valve 11 is adjusted by the output signal of the pH controller 10. In this way, the concentration at the outlet 802 is controlled to a predetermined value. However, if the circulating fluid pH is not lower than the lower limit,
When the outlet SO+ concentration cannot be controlled to a predetermined value, the outlet S
02 The concession system # is discontinued and the circulating fluid pH is controlled to the lower limit value. On the other hand, if the outlet SO□ concentration cannot be controlled to a predetermined value unless the circulating fluid pHk exceeds the upper limit value, the outlet So2 concentration control is stopped and the circulating fluid pH is controlled to reach the upper limit value.

〔Effect of the invention〕

As detailed above, according to the present invention, the first condition is to prevent corrosion of absorption towers, piping, etc., and to prevent wasteful supply of absorbent, and the concentration at the outlet 802 is adjusted within a range that satisfies these conditions. It can be controlled to a predetermined value.

[Brief explanation of drawings]

FIG. 1 is a system diagram of the exit 802 (1 degree control device) in an embodiment of the present invention, FIG. 2 is a chart showing the characteristics of the amplifier, FIG. 3 is a chart showing the relationship between the adder output and the amplifier output, and The figure is a system diagram of a conventional absorption tower pH control device. 502 concentration controller output Figure 3 Amplifier output PH Figure 4

Claims (1)

[Claims] In a desulfurization plant where a treated gas containing sulfur dioxide gas is introduced into an absorption tower and desulfurized by contacting with a circulating liquid containing an absorbent and circulating within the absorption tower, the treatment gas desulfurized in the absorption tower is an SO_2 concentration detector that detects the SO_2 concentration; an SO_2 concentration controller that inputs the output signal of the SO_2 concentration detector as a control amount; an amplifier that receives the output signal of the SO_2 concentration controller; and a pH of the circulating fluid.
a pH detector for detecting a pH value, an adder for adding a preset pH lower limit value and the output of the amplifier; and a pH value for inputting the output signal of the pH detector as a control amount using the output signal of the adder as a set value. A wet flue gas desulfurization device comprising a control controller and a flow rate control valve that is provided with piping for supplying an absorbent to the absorption tower and whose opening degree is adjusted based on the output signal of the pH control controller. outlet SO_2 concentration control device.