JPS6058229A - Control of flow amount of compressed air in oxidizing tower - Google Patents

Abstract

PURPOSE:To perform economical operation, in the oxidizing tower of a wet waste gas desulfurization apparatus, by detecting the amount of CaSO4 in a slurry withdrawn from an absorbing tower, and regulating the amount of compressed air supplied to the oxidizing tower corresponding to the detected value. CONSTITUTION:A slurry 2 based on CaSO3 and gypsum withdrawn from an absorbing tower is guided to an oxidizing tower 1 while compressed air 5 and sulfuric acid 4 are supplied to the slurry 2 and air oxidation is performed to prepare a gypsum slurry 3. In this case, the CaSO4-concn. of the withdrawn slurry 2 is detected by a CaSO4-concn. detector 20 and the flow amount thereof is detected by a flow amount detector 21 while both detected values are sent to a multiplier 22. This multiplier 22 multiplies both detected values to detect the CaSO3-amount of the withdrawn slurry 2. When this detected value is sent to a high selector 24, the high selector 24 controls the amount of compressed air 5 supplied to the oxidizing tower 1 by using the detection signal.

Description

[Detailed Description of the Invention] The present invention detects the amount of calcium sulfite in the slurry extracted from the absorption tower in the oxidation tower of a wet flue gas desulfurization equipment, and adjusts the flow rate of compressed air used in the oxidation tower according to this value. This invention relates to a control method for economical operation with excessive supply of compressed air flow.

Figure 1 shows the instrumentation flow in a conventional oxidation tower. In Figure 1, the slurry 2 drawn out from the tower in the suction 1 section, which is mainly composed of calcium sulfite, unregenerated J5 calcium compound, and gypsum, is guided to the oxidation tower 1 with a force ' -Neru.

In the oxidation tower 1, this absorption tower extraction slug IJ 2 r,
Air oxidation of calcium sulfite in il, gypsum and -1-
Compressed air 5 is supplied from the bottom of the column, and exhaust air 6 is discharged from the top of the column to the outside of the system. 7. Flow rate controller 8
is provided, and the flow rate is controlled by operating the valve 9 and supplying it to the oxidation tower 1.

In addition, during air oxidation, ρ11 of the gypsum slurry in the oxidation tower
In order to prepare the equation, a PH detector 1o, a pi (controller 11) are installed, and an operation valve 12 is operated to adjust the f flow rate 4 to the oxidation tower 1.
is supplied to.

The gypsum slurry 3 containing the gypsum precipitated in the oxidation tower is sent to a separation step and recovered as Mlj raw gypsum.

In this flow, calcium sulfite should be cultivated in the oxidation tower (supplied compressed air flow rate 5), but it increases depending on the amount of sulfur dioxide gas desulfurized in the absorption tower (always constant despite the increase and decrease). There was considerable waste in supplying the flow rate and reducing the pressure when the amount of calcium sulfite decreased.

The flow rate of compressed air supplied into the oxidation tower is determined by the oxygen utilization rate (i.e., the amount of oxygen absorbed by the slurry in the oxidation tower relative to the amount of oxygen in the amount of compressed air supplied to the oxidation tower) relative to the amount of calcium sulfite to be oxidized within the oxidation tower. Oxygen amount) is constant (usually 6o~50%)
It is always most efficient when

In order to eliminate the problems of the conventional method described above, the present invention detects the amount of calcium sulfite in the slurry extracted from the absorption tower, and uses this value to supply compressed air to the oxidation tower so that the oxygen utilization rate becomes a predetermined value. This was done to control the flow rate and save energy.

That is, in the process of the present invention, a slurry extracted from an absorption tower mainly composed of calcium sulfite and gypsum is led to an oxidation tower, and compressed air and @acid are cut off in the oxidation tower to perform air oxidation to form a gypsum slurry. A method for controlling the flow rate of compressed air in an oxidation tower in a wet flue gas desulfurization section, the method comprising: detecting the amount of calcium sulfite in the slurry taken out from the absorption tower, and using the detected signal to control the flow rate of air (pressure m) supplied to the oxidation tower. It is related to.

First, the principle of the method for continuously measuring calcium sulfite concentration according to the present invention will be explained.

A constant flow rate of slurry extracted from the absorption tower is introduced into a closed reaction vessel.
The liquid in excess of the amount held in the reaction vessel is discharged as overflow.

If sulfuric acid is supplied so that the concentration of the liquid in this reaction vessel is 5 or less, calcium sulfite in the slurry extracted from the absorption tower,
Calcium carbonate reacts with sulfuric acid to generate stoichiometrically equal amounts of 802 and C02 according to the reaction formula below, resulting in calcium sulfate.

CILS03+H2SO4→CaSO4+H20SO
2↑ (1) caco, −+−H2so4−+caso
4th edition, o+co2↑ (2) Supply a constant flow of carrier air to the reaction vessel, and reduce the S generated by fi+, +21 formula.
After extracting O2 and CO2 from the reaction vessel together with carrier air and dehumidifying them, if the SO2 and CO2 concentrations are detected using an SO2 concentration meter and a CO2 concentration meter, calcium sulfite in the slurry extracted from the absorption tower can be determined using the following equation (3). Concentration can be measured continuously.

Calcium sulfite concentration [mol/e] = where xl is C
02 concentration (ppm) y X2 is 502a degrees (ppm) +
F, carrier air flow rate (Nl/m1n−);

F2 is the slurry detection flow taken out from the absorption tower! -[#/min'l
l is shown respectively.

Next, a specific example of the present invention using the above-mentioned calcium sulfite detector will be described. An example of the instrumentation flow of the present invention is shown in FIG. In the figure.

1 to 12 are the same as in FIG. 1, and 20 to 25 are devices newly added according to the present invention.

The amount of calcium sulfite in the slurry extracted from the absorption tower is determined by the output signal of the aforementioned calcium sulfite concentration detector 20 and the flow rate detector of the slurry extracted from the absorption tower. A part of the output signal of the multiplier 22 is input to a delay device (a negative order lag filter is also possible) 23. The output signal of the delay device 23 and the output signal of the multiplier 22 are input to the high selector 24, and the high selector 24 selects and outputs the larger signal. As a result, the output signal of the high selector 24 is the same signal from the multiplier 22 when the amount of calcium sulfite in the slurry extracted from the absorption tower increases, and is the signal from the delay device 23 when the amount of calcium sulfite decreases.

The set delay time of the delay device 23 depends on the dissolution rate (PI) of calcium sulfite in the oxidation tower,
Although it varies depending on the process, it takes about 5 to 10 minutes.

Note that in a process in which the amount of calcium sulfite in the slurry extracted from the absorption tower does not decrease rapidly, the retarder 23 and the high selector 24 may not necessarily be necessary.

Further, the amplifier 25 amplifies the output signal of the high selector 24 when the oxygen utilization rate is constant, and uses the signal as the set value of the flow rate town section 8.

Here, the gain C is expressed by the following formula.

α@yo2 Here, α is the set oxygen utilization rate [%] Yo2 each indicates the oxygen concentration [%] in the supplied compressed air.

Now, a case will be explained in which the concentration of calcium sulfite in the slurry stream extracted from the absorption tower or the slurry extracted from the absorption tower becomes large, and the amount of calcium sulfite supplied to the oxidation tower increases. This increase in calcium sulfite is detected by the calcium sulfite concentration detector 2a and the absorption tower extraction slurry flow rate detector 21, and is expressed as an increase in the output signal of the 1 multiplier 22. The output signal of the multiplier 22 is sent to the NO1 selector 24.
After being selectively outputted by the amplifier 25 and amplified as the compressed air flow rate setting value, the flow rate is inputted to the flow rate n cylinder needle 8. As a result, the flow rate of compressed air supplied to the oxidation tower is increased by an amount commensurate with the increase in calcium sulfite.Conversely, when the amount of calcium sulfite in the slurry extracted from the water absorption tower decreases, 22 output signal decreases. In this case, the signal passing through the delay device 23 is selectively outputted by the high selector 24 during the set delay time of the delay device 23, and the flow rate of compressed air to be supplied is higher than the amount of calcium sulfite in the slurry extracted from the absorption tower. The flow rate before calcium sulfite reduction is supplied, and then the supplied compressed air flow rate is reduced so that the oxygen utilization rate becomes a predetermined value.

As a result, even if the amount of calcium sulfite in the slurry extracted from the absorption tower suddenly decreases, the supply air flow rate will not decrease suddenly, and even if calcium sulfite remains in the oxidation tower, it will not flow out unreacted. It never comes.

From the above, according to the method of the present invention, compared to the conventional operation in which the flow rate of supplied compressed air is constant, it is possible to perform a significantly more economical operation without causing unreacted calcium sulfite to flow out.

In addition, in the method of the present invention, if the amount of calcium sulfite in the slurry extracted from the absorption tower is small in the plant and the flow rate of compressed air supplied to the oxidation tower decreases too much, a lower limit value may be set for the flow rate of compressed air supplied.

[Brief explanation of the drawing]

FIG. 1 shows a conventional instrumentation flow. FIG. 2 is an instrumentation flow of one embodiment of the present invention. In FIG. 2, 20...calcium sulfite concentration detector 21...flow rate detector 22...multiplier 26...delay device 24...high selector 25...amplifier. Sub-agents 1) Meinoki agent Ryo Hagiwara - Figure 1

Claims (1)

[Claims] The slurry extracted from the absorption tower containing mainly calcium sulfite and gypsum is guided to the oxidation tower, and compressed air and sulfuric acid are supplied to the oxidation tower to perform air oxidation to form gypsum slurry. A method for controlling the flow rate of compressed air in an oxidation tower in a wet flue gas desulfurization apparatus, characterized by detecting the amount of calcium and controlling the flow rate of compressed air supplied to the oxidation tower using the detection (F4).