JPS60110322A - Ph controller for absorbing tower - Google Patents

Abstract

PURPOSE:To make pH response characteristics substantially constant over the entire desulfurization load range and to stabilize SO2 concentration in a gas being treated, by a method wherein the proportional sensitivity of a pH adjustor can be varied in relation with desulfurization load. CONSTITUTION:The flow rate and the SO2 concentration of the gas being treated are detected by detectors 10, 9, are input into a multiplier 11, and a desulfurization load signal S11 by a constant on the basis of the relationship between the desulfurization load and the flow rate of an absorbing agent supplied, and outputs a proportional sensitivity signal S21 to the pH adjustor 22. The adjustor 22 outputs an absorbing agent supply flow rate correcting signal S22 to a coefficient adder 12, based on the signal S21, a detection signal from a pH adjustor 13 and a preset pH value. The adder 12 outputs an absorbing agent supply flow rate set point signal S12 to an absorbing agent supply flow rate adjustor 15, based on the signals S22 and S11, and the opening of a flow control valve 16 is adjusted on the basis of the signal S12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a desulfurization plant for removing sulfur dioxide gas (802) from a process gas, and particularly to an absorption tower door control device for controlling circulating fluid.

In a desulfurization plant, for example, in a wet lime gypsum flue gas desulfurization plant using calcium carbonate or calcium hydroxide as an absorbent, the concentration of sulfur dioxide gas (S02) in the treated gas released into the atmosphere or the desulfurization rate in the absorption tower is determined. In order to maintain this value, it is necessary that pl (+) of the circulating liquid circulating through the absorption tower is stable and that 14 follows the set value with good responsiveness in the entire load range.

Therefore, a conventional example will be explained with reference to FIG.

FIG. 1 is a system diagram showing a schematic configuration of a conventional desulfurization plant. Reference numeral 1 in the figure indicates an absorption tower, and sulfur dioxide gas (S02 gas) is supplied to this absorption tower 1 through a processing gas introduction duct 2.
A processing gas containing is introduced from above. On the other hand, circulating fluid 3 is circulating in absorption tower 1? The circulating liquid 3 and the treated gas are brought into contact with each other in the absorption tower 1 to remove sulfur dioxide gas from the treated gas. That is, s02 in the processing gas reacts as shown in the following formula (I) to generate H2SO3 in the liquid and flows down. A part of H2SO3 with is oxygen (02) in the processing gas
Then, it undergoes a reaction as shown in the following formula (II) and is oxidized to become H2SO4. The treated gas that has still passed through the absorption tower 1 is discharged into the atmosphere through the exhaust duct 6 as treated gas.

S02+H2o-1 → H2SO3・Curved surface (I) H2SO
3+ -! o -1→H2SO4・・・・・・・・・(
■)2 The circulating fluid 3 contains a large amount of H2SO3 and H2SO4 produced by the absorption reactions and oxidation reactions shown in formulas (1) and (II) above.
There is a risk that the Me1 value of Therefore, an absorbent such as calcium carbonate (caco3) (low calcium hydroxide Ca
(O) (2 iso-alkaline) is supplied and the following formula ω
As shown in υ, the circulating fluid 3 is neutralized and door control is performed as shown in figure S02.
It is regenerated into a liquid that is easily absorbed.

H2SO4+CaCO3→caso4+H2o+co2
↑...River (G) Note that a part of the circulating fluid 3 is transferred to another process (not shown) via piping 8.

Generally, the PII of the circulating fluid 3 has a great effect on the S02 absorption reaction, and the higher the PII, the more the S02 absorption reaction is promoted. In order to maintain a high pH, a large amount of absorbent must be supplied, which is not desirable from a cost standpoint. Therefore, it is desired to operate the vehicle with a voice that is loud enough to maintain the desired performance. In addition, as mentioned above, the circulating fluid 3
What lowers the 0 voice is an increase in the H2SO3 concentration or H2SO4 concentration in the circulating fluid 3, and what increases the male voice is an increase in the amount of neutralization by CaCO5, that is, the source level of CaCO3 in the circulating fluid 3. . The pH of the circulating fluid is determined by the balance between the amount of absorbed SO2 and the amount of CaCO3 neutralized.

Therefore, door control in the conventional desulfurization plant mentioned above will be explained.

A sulfur dioxide gas concentration detector 9 is installed in the processing gas introduction duct 2.
and a processing gas flow rate detector 1o are inserted, and these sulfur dioxide gas concentration detector 9 and processing gas flow rate detector 1
The output signal is sent to a multiplier 1, multiplied, and output as a desulfurization load signal 811 to a coefficient adder 12. On the other hand, a voice detector 13 is attached to the circulation pipe 5.
This detection signal from the detector 13 is sent to the tone tone generator 14. The tone generator 14 compares a preset portion with the detection signal and outputs a deviation signal S□4 to the coefficient adder 12. The coefficient adder 12 outputs a set value signal St2 to the absorbent supply flow rate regulator 15 based on the desulfurization load signal s0□ and the deviation signal S14. The absorbent supply flow rate regulator 15 adjusts the opening degree of the flow rate regulating valve 16 inserted in the absorbent supply pipe 7 based on this set value signal 81g. Note that the reference numeral 17 is a flow rate detector.

According to the above configuration, the neutralizing agent supply amount is adjusted by so-called feed pack control only by the pH deviation signal S14, and the proportional sensitivity of the pH regulator 14 is constant regardless of changes in the desulfurization load. and pH regulator 14
The proportional sensitivity of is set so as not to oscillate at low loads, so
Even if the value is optimal at low loads, the proportional sensitivity is too small at high loads, and as a result, the PH response is slow and a phenomenon of large waves occurs. As mentioned above, fluctuations in the voice have a great influence on the SO2 absorption reaction, and when the above-mentioned phenomenon occurs, the SO2 of the treated gas at the outlet of the absorption tower 1
□The yield was unstable and fluctuated, and there was a risk that it would deviate from the specified value. In addition, in order to prevent such a situation, the pli value of the circulating fluid 3 is made higher than necessary in advance, resulting in an increase in running costs.

The present invention has been made based on the above points, and its purpose is to improve the response by making it possible to change the proportional sensitivity of the cylinder as a function of the desulfurization load. It is an object of the present invention to provide an absorption tower PII control device that makes it possible to keep the temperature constant over the entire desulfurization load range, thereby stabilizing the 502 fA degree in the treated gas and reducing running costs.

That is, the absorption tower internal control device according to the present invention can be used in a desulfurization plant in which a process gas containing sulfur dioxide gas is introduced into the absorption tower, circulated within the absorption tower, and is brought into contact with circulating liquid containing an absorbent to desulfurize the absorption tower. A processing gas flow rate detector detects the processing gas flow rate introduced into the absorption tower, a sulfur dioxide gas concentration detector detects the sulfur dioxide gas temperature in the processing gas introduced into the absorption tower, and a signal from the sulfur dioxide gas concentration detector and A multiplier that inputs and multiplies the signal from the processing gas flow rate detector, a function calculator that inputs the signal from this multiplier and outputs a proportional sensitivity signal according to the signal, and detects the voice of the circulating fluid. a pH detector that inputs the proportional sensitivity signal and uses it as a proportional sensitivity, and outputs an absorbent supply flow rate correction signal according to the detection signal from the pi (detector); ) A coefficient adder that inputs the signal from the I regulator and the signal from the multiplier and outputs an absorbent supply flow rate setting value signal.

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. First, before explaining the configuration of the absorption tower P [1] control loading according to this embodiment, the relationship between the desulfurization load and the absorbent supply flow rate will be explained with reference to FIG. In Figure 2, the horizontal axis shows the desulfurization load (inlet S02 concentration of process gas flow rate) (Nm3/
H), the vertical axis shows the absorbent supply flow rate (lime slurry flow rate)
(m3//H) (approximately the same as the amount of neutralization (absorbent consumption) in the system) is a diagram showing the relationship between the desulfurization load and the absorbent supply flow rate. As is clear from FIG. 2, the absorbent supply flow rate is proportional to the desulfurization load because it is supplied in an amount equivalent to the desulfurization load.

Next, the configuration of the absorption tower pH control device according to this embodiment will be explained with reference to FIG. That is, a function calculator 21 is provided, and the desulfurization load signal S11 from the multiplier 11 is inputted to the function calculator 21.

The function calculator 2 multiplies the desulfurization load signal S8□ by a constant according to the relationship between the desulfurization load and the absorbent supply flow rate shown in FIG.

The tone cylinder 22 has a proportional sensitivity signal S21, - the detector 13.
The absorbent supply flow rate is adjusted based on the detection signal from the sensor and a preset binary value. That is, the PHH moderator 22 performs P (proportional), PI (proportional, integral), and PID (proportional, integral, differential) control using the proportional sensitivity signal S2□, and corrects the circulating fluid supply flow rate of the output as shown in the following equation. A signal 822 is output to the coefficient adder 12.

・・・・・・・・・・・・) However, F; pH controller pressure Fm1LX ``Maximum absorbent flow rate PH; PH meter span pn K; Proportional sensitivity T,; Integral time TD; Derivative time ε, H ; - deviation (pH setting value - 1 ()) Also, proportional sensitivity (because the odor changes depending on the desulfurization load, K is included in the integral in the integration.Then, the coefficient adder 12 uses this absorbent supply flow rate correction signal S0 and the above Desulfurization load signal St
An absorbent supply flow rate setting value signal S1.S is sent to the absorbent supply flow rate regulator 15 based on S1. Output. absorbent.

The supply flow rate regulator 15 adjusts the opening degree of the flow rate adjustment valve 16 based on this set value signal 811.

As described above, the absorption tower PI-1 control device according to this embodiment has a proportional sensitivity (lead can be changed as appropriate in proportion to the desulfurization load, and in steady state, the absorbent supply flow rate is proportional to the desulfurization load). Because of this relationship, it is possible to correct the absorbent supply flow rate at the same rate over the entire load range, which makes it possible to obtain almost constant voice response and maintain a stable SO2 concentration in the treated exhaust gas. In addition, conventional measures were taken to keep the pH setting value higher than necessary to prevent the SO2 concentration in treated exhaust gas from deviating from the specified value, but such measures are no longer necessary. This makes it possible to reduce running costs.

As detailed above, the absorption tower control device according to the present invention has the following features:
A process for detecting the flow rate of the treated gas introduced into the absorption tower in a desulfurization plant that introduces a treated gas containing sulfur dioxide gas into an absorption tower, circulates it through the absorption tower, and desulfurizes it by contacting it with a circulating liquid containing an absorbent. A gas flow rate detector, a sulfur dioxide gas humidity detector that detects the sulfur dioxide gas concentration in the treated gas introduced into the absorption tower, and a signal from this sulfur dioxide gas concentration detector and a signal from the above-mentioned treated gas flow rate detector are input. a multiplier that multiplies the signal, a function calculator that inputs the signal from the multiplier and outputs a proportional sensitivity signal according to the signal, a PH detector that detects P+1 of the circulating fluid, and a PH detector that detects P+1 of the circulating fluid; Input this as a proportional sensitivity and output an absorbent supply flow rate correction signal according to the detection signal from the voice detector p)
1 regulator, and a coefficient adder which inputs the signal from this leg cylinder and the signal from the multiplier and outputs an absorbent supply flow rate setting value signal.

Therefore, a nearly constant pH response can be obtained over the entire load range, making it possible to stabilize the SO2 concentration in the treated exhaust gas, and eliminating the need to unnecessarily increase the SO2 concentration. Running costs can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of the conventional absorption tower Pl (control device), Figs. 2 and 3 are diagrams explaining an embodiment of the present invention, and Fig. 2 shows the relationship between the desulfurization load and the absorption side supply flow rate. The diagram shown in FIG. 3 is a system diagram of the absorption tower pli control device. 1... Absorption tower, 2... Processing gas introduction duct, 3...
・Circulating fluid, 9...Sulfur dioxide gas concentration detector, 10...
Processing gas flow rate detector, 11... Multiplier, 12... Coefficient adder, 13...-detector, 14... pH regulator, 21... Function calculator, S□... Proportional sensitivity signal, S
! ! ...Absorbent supply flow rate correction signal, S, ...Absorbent supply flow rate setting value signal. 1st flash 'XgZ figure 0 200 400 600 80O

Claims (1)

[Claims] In a desulfurization plant that introduces a treated gas containing sulfur dioxide gas into an absorption tower, circulates it through the absorption tower, and desulfurizes it by contacting it with a circulating liquid containing an absorbent, detecting the treated gas flow fragments introduced into the absorption tower. A processing gas flow rate detector, a sulfur dioxide gas concentration detector that detects the sulfur dioxide gas concentration in the processing gas introduced into the absorption tower, and a signal from this sulfur dioxide gas concentration detector and a signal from the processing gas flow rate detector. a multiplier that inputs and multiplies; a function calculator that inputs a signal from the multiplier and outputs a proportional sensitivity signal according to the signal;
Jh A PH detector that detects the pH of the condensate; and a PH detector that inputs the proportional sensitivity signal and uses it as a proportional sensitivity; and a coefficient adder which inputs signals from the -1 regulator and the multiplier and outputs an absorbent supply flow rate set value signal. Device.