JPS62136228A - 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. and pH value of outlet SO2 and changing 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 SOx-removal and the output signal thereof is inputted to a SO2 concn. regulator 16 to be compared with a preset outlet SO2 concn. value and feedback control is performed. The output signal of the SO2 concn. regulator 16 is inputted to an upper and lower value limiter 17. Further, 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 set value from the upper and lower value limiter 17 to perform feedback control and, by the output signal from said detector 14, the opening degree of a flow control valve 11 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention aims to reduce the concentration of So, concentration (
This is related to control (hereinafter referred to as outlet SO2 concentration).

[Conventional technology]

The schematic structure of a desulfurization plant, for example, a wet lime gypsum process waste smoke desulfurization plant that has already absorbed calcium carbonate, will be described with reference to the system diagram shown in FIG.

In Fig. 5, the absorption tower 1 has a processing gas introduction duct) 2t
- A processing gas 3 containing sulfur dioxide gas is introduced from above. 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 sulfur dioxide gas contained in the treated gas 3 is removed.

That is, SO2 in the processing gas 3 generates H2SO3 through the reaction shown in the following equation (1) and flows down. This H2
A part of SO3 is oxidized by oxygen (C2) in the processing gas 5, and becomes H2SO4 as shown by the following formula (fl).

In addition, the remaining H2SO3 is oxidized in the tank 4 by the oxygen in the air injected from the air pipe 8, and becomes H2S C.
It becomes 4.

SO2+ H,O-→H2SO3・・・・・・・・・(
1) H2SO3+ -02-) H2SO4...
(If) 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 the exhaust duct 9.

As mentioned above, when the contact with the treated gas 3 is continued in the absorption tower 1, 7'CH4SO4 is generated in the circulating liquid 5 through the absorption reaction and oxidation reaction shown in 0) and (I[) above.
Since it contains a large amount of S
It becomes difficult to absorb O2. Therefore, an absorbent, such as carbonic acid A/sium (CaC03), 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, and the following formula ( If[)K
As shown, the circulating fluid 5 is neutralized and regenerated so that it can easily absorb sulfur dioxide gas.

H2SO4+ CaC! 03-+0aSO4+ H2O
+002↑...(Ill) A part of the circulating fluid 5 containing CaSO4 generated by the above formula (Ill) is transferred to the transfer pipe 13.
is transferred to another process (not shown).

As suggested by the above explanation, the SO of circulation W′M,S
2 Absorption capacity has a great influence on the performance of a desulfurization plant. The index of the EI02 absorption capacity of the circulating fluid 5 is:
This is the pH of the circulating fluid 5. That is, CaC in the circulating fluid 5
When the 03 concentration is high and the pH is high, the SO2 absorption reaction is promoted.

It is conceivable to simply supply a large amount of absorbent to maintain the pH of the circulating fluid 5 at a high level, but this is not preferable in terms of cost.

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

This leads to stably maintaining the desulfurization rate in the absorption tower 1 and, ultimately, 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. 5, the pH control device for the circulating fluid 5 is as follows.

That is, a pH detector 14 is attached to the circulation pipe 7, and an output signal qpH from this pH detector 14 is detected.
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
(P: proportional, engineering: integral, D=differential) feedback control is performed. 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, there has been a need in desulfurization plants to control the outlet SO2 concentration to a constant level regardless of changes in boiler load. However, with conventional pH control devices, the amount to be controlled is only the pH, and there is no guarantee that the outlet SO2 (a degree) can be controlled to a predetermined value.

The present invention has been made to solve the above-mentioned problems, and the outlet SO. It is an object of the present invention to provide a concentration control device that can control the concentration to a predetermined value.

[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 circulating fluid pHf in accordance with the detected amount to increase or decrease the absorbent flow rate.

That is, the outlet S02 concentration control device of the present invention is used in a desulfurization plant where 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 inside the absorption tower. , an SC2 concentration detector that detects the SO2 concentration in the treated gas desulfurized in the absorption tower, an SO2 concentration controller that inputs the output signal of the S(h concentration detector as a control amount), and the SO2 concentration controller an upper and lower limit limiter that receives an output signal as input, and a pH value of the circulating fluid.
A pH detector that detects the above, a pH control controller that uses the output signal of the upper and lower limiters as a set value and inputs the output signal of the pH detector as a control amount, and piping that supplies absorbent to the absorption tower are installed. This is an outlet SO2 concentration control device in a wet flue gas desulfurization device, characterized in that the present invention further comprises a flow rate control valve whose opening degree is controlled by the output signal of the pH control regulator.

[Effect]

According to the present invention, the outlet SO2 concentration is detected, and when the detected value is larger than the set outlet So2 concentration, the circulating fluid pa is increased to promote the SO2 absorption reaction and the outlet SO2 concentration is increased.
The lower the concentration, the closer it is to the set value.

Conversely, when the detected value is smaller than the set outlet SO20i degree,
By lowering the circulating fluid pH, the SO2 absorption reaction is suppressed, and the outlet SO2'a degree increases and approaches the set value.

However, if the circulating liquid pE is too low (for example, below 4), the absorption tower, piping, etc. will not be exposed to strong acids and corrosion will occur. Therefore, in the present invention, a lower limiter is provided to prevent the pH setting value of the circulating fluid from falling below a specified value to prevent corrosion.

Furthermore, it is said that if the pH setting of the circulating fluid is too high, when calcium carbonate is used as an absorbent, the pH will not rise above 6 even if it is supplied to a mass absorption tower because it is a weak alkali. ), when the pH setting value is 6 or higher, even if the amount of absorbent is increased, the circulating 31Jl pH will not increase until the installed PN, and a large amount of absorbent will be supplied forever. In order to prevent excessive supply of absorbent, upper and lower limiters for the pH setting value are provided in the present invention.

As described above, in the present invention, the first conditions are to prevent corrosion of the absorption tower, piping, etc., and to prevent wasteful supply of absorbent, and the outlet S02 concentration is set within a range that satisfies these conditions. It is controlled to a predetermined value.

〔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. 5 are given the same numbers and the explanation thereof will be omitted.

The newly installed devices in the outlet SO□ concentration control device according to the present invention are the outlet SO2 concentration detector 1s and the SO21
They are a percentage adjuster 16 and an upper and lower limiter 17.

In FIG. 1, an outlet SO2 concentration detector 15 installed in an exhaust duct 9 through which the processing gas from which sulfur dioxide gas has been removed passes.
The outlet SO2 concentration is detected. The output signal of the outlet SO2 concentration detector 15 is input to the SO2 concentration controller 16. This So, d degree controller 16 compares the preset outlet SO2 concentration set value with the output signal from the outlet SO□ concentration detector 15,
= integral, D = differential) feedback control is performed. S0
The output signal of the 2# degree controller 16 is input to the upper and lower limiter 17. An example of the characteristics of the upper and lower limiter 17 is shown in FIG.

The horizontal axis in Fig. 2 is the output signal of E302 # degree adjustment meter 16,
The vertical axis is the output of the upper and lower limiter 17.

As a result, the set value of the pH adjuster 10 is adjusted to the specified pH.
The permissible range will not be exceeded.

The output signal of the upper and lower limiter 17 is input as a set value of the pH controller 10. Furthermore, the pH of the circulating fluid is measured by the pH detector 14.
The detected signal t-p is inputted as the control amount of the controller 10. This pH controller 10 compares the pH setting value input by the output signal of the upper and lower limiter 17 and the output signal of the pH detector 14, : differential) feedback control. The opening degree of the flow control valve 11 is adjusted by the output signal of the pH controller 10. In this way, the outlet SO2 concentration is controlled to a predetermined value. However, if the outlet SO2 concentration cannot be controlled to a predetermined value unless the circulating fluid pH is lower than the lower limit value (40 in the example of the upper and lower limiters in FIG. 2), the outlet SO2 concentration cannot be controlled to a predetermined value. Concentration control is stopped and the circulating fluid pH is controlled to the lower limit value. On the other hand, if the outlet SO2 concentration cannot be controlled to a predetermined value unless the circulating fluid p)I is increased to or above the upper limit value (aO in the example of the upper and lower limiters in Fig. 2), the outlet SO2 concentration control is stopped and the circulating fluid is The pH is controlled to be at the upper limit.

Although one example has been described in the embodiment, the following configuration may be used without departing from the spirit of the present invention.

(1) In the above embodiment, the flow rate control valve 11 was directly adjusted by the pHtA moderation meter output, but as shown in FIG. The absorbent flow rate is adjusted by setting the flow rate controller 18 to a set value.

(2) In addition to the above flow rate controller 18, an inlet gas flow meter 19 and an adder 20 are added as shown in FIG. 4, and the output of the inlet gas flow meter 19 and the pH controller 1 are
The absorbent flow rate is adjusted by inputting the output of 0 to the adder 20 and inputting the output of the adder 20 as the set value of the flow rate controller 18.

〔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 outlet SO2 concentration is set to a predetermined range within a range that satisfies these conditions. can be controlled to the value of

[Brief explanation of drawings]

Fig. 1 is a system diagram of the outlet SO2 power control device in an embodiment of the present invention, Fig. 2 is a chart showing the characteristics of the upper and lower limiters, and Figs. 6 and 4 show other embodiments of the invention. System diagram, FIG. 5 is a system diagram of a conventional absorption tower pH control device. Sub-Agents 1) Meifuku Agent Ryo Hagiwara − Sub-Agent Atsuo Anzai Figure 1 1-
J (PH) Fig. 2 Input signal of upper and lower three vines Fig. 3 Knee --- 1-J Fig. 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 upper/lower limit limiter that inputs the output signal of the SO_2 concentration controller; a pH detector that detects the pH of the liquid; a pH control controller that uses the output signal of the upper and lower limiters as a set value and inputs the output signal of the pH detector as a control amount; and supplies an absorbent to the absorption tower. An outlet SO_2 concentration control device in a wet flue gas desulfurization device, characterized in that the device is equipped with piping and a flow rate control valve whose opening degree is adjusted based on the output signal of the pH control regulator.