JPS6274436A - Wet type waste gas desulfurization apparatus - Google Patents

Abstract

PURPOSE:To obtain good oxidation capacity, by stabilizing the pH of a cooling part even if the start/stop operation of a boiler is repeated by providing absorbing solution slurry auxiliary supply piping for supplying an absorbing solution slurry from an absorbing solution slurry tank to the recirculation tank of the cooling part. CONSTITUTION:Exhaust gas from a flue 2 is guided to the cooling part 23 of the lower part of a desulfurization tower to perform dust removal, cooling and partial desulfurization while the treated exhaust gas is guided to an absorbing part 24 through a collector 25 and SOx in the exhaust gas is absorbed and removed by an absorbing solution slurry. The absorbing solution slurry is independently supplied to the recirculation tank 7 of the absorbing port 24 and the recirculation tank of a dust removing part from an absorbing solution slurry tank 10 through absorbing solution slurry supply piping 29 and absorbing solution slurry auxiliary supply piping 30. A part of the absorbing solution slurry in the recirculation tank 7 of the absorbing part 24 is withdrawn to the recirculation tank 5 of the cooling part 23 through a conduit 27 in the amount corresponding to the supply amount to the tank 7. Air is blown into the tank 5 from air supply piping 26 to oxidize sulfite to turn it into gypsum 20.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a wet flue gas desulfurization system 3'', and particularly relates to a wet flue gas desulfurization system that can supply absorbent slurry in response to load fluctuations. be.

[Background of the invention]

In recent years, as demand for power generation has increased, boilers that use fossil fuels as their main fuel have become larger, and the impact of power generation boilers on air pollution is also increasing.

Among the pollutants that increase air pollution, the emission regulations for SOx, which has a large impact on the Northern Army, tend to become stricter year by year. Under these circumstances, since the second oil crisis, Japan's power generation industry, which has been using oil as its main fuel, is switching to 5-carbon fuels, which are cheaper and have ample supply sources.

However, as boilers have become larger, boilers have to be started and stopped on a daily basis in order to frequently change load according to power generation demand in order to reduce power generation costs.
5tart 5top, Weekly 5tart 5
(hereinafter simply referred to as DSS and WSS) are repeated.

As a feature of recent electricity demand, with the growth in nuclear power generation, the difference between the maximum and minimum power loads has also increased, and there is a tendency to shift boilers for thermal power generation from base load use to load adjustment use. By using a variable pressure boiler, which operates in a supercritical pressure region at full load and in a subcritical pressure region at partial load, it is possible to generate electricity under partial load. Increase efficiency by a few percent
This is because it can be improved.

However, because DSS operation is frequently performed on a daily basis and WSS operation is performed on a weekly basis, exhaust gas l fluctuates due to fluctuations in fuel load, and soluble acid gas l and fly ash are produced depending on the coal content. Since the quantities are different, f, fl is /4
．． /2. Target SOx during partial force loading such as /4 load
The value cannot be below ℃.

For example, wet flue gas desulfurization equipment installed in thermal power plants etc. uses calcium carbonate (CaC0,), calcium hydroxide [
Ca(OH,) ] or calcium oxide (CaO
) is used as an absorption liquid slurry to absorb sulfur oxides (SOx) in exhaust gas from boilers, etc., oxidize the obtained calcium sulfite, and recover it as calcium sulfate, that is, gypsum. method is the most common.

A schematic system diagram of a conventional wet flue gas desulfurization apparatus using this limestone or lime is shown in FIGS. 5 and 6.

Currently, in a wet flue gas desulfurization system for a thermal power plant, as shown in Fig. 5, the exhaust gas is pressurized by a desulfurization fan 1 and sent from a flue 2 to a cooling tower 3, and is then fed into a cooling tower circulation tank 5 by a cooling tower circulation pump 4. The exhaust gas is brought into gas-liquid contact with the absorbent slurry to cool the exhaust gas humidity to saturated humidity, as well as to remove dust and partially desulfurize. The exhaust gas after cooling enters the absorption tower 6,
Here, SOx in the exhaust gas is absorbed and removed by gas-liquid contact with the absorption liquid slurry circulated from the absorption tower circulation tank 7 into the absorption tower 6 by the absorption tower circulation pump 8. It is discharged from outlet 9.

On the other hand, absorption liquid slurry of a specified amount is fed to the absorption tower 6 from the absorption liquid slurry tank 10 via the absorption liquid slurry pump 11° and the absorption liquid slurry supply pipe 29, and the SOx in the exhaust gas is
absorbs and produces calcium sulfite. A portion of the generated slurry containing calcium sulfite is extracted by an absorption tower extraction pump 12 and supplied to an oxidation tower supply tank 13. Thereafter, the slurry is reacted with sulfuric acid 14 to convert some of the unreacted limestone into gypsum, and at the same time adjust the pH to a level suitable for oxidizing calcium substite. Supplied oxidation tower 1
6, it is oxidized to gypsum by air. The obtained gypsum slurry was transferred to gypsum slurry tank 18.
It is dehydrated in a centrifuge 19.

Collected as gypsum 20.

How to use: Filtered water in the Gypsum Shirafuna 17 is supplied to the absorption liquid slurry tank 10 from a filtered water tank 2 and a filtered water pump 22. However, in recent years, the oxidation tower supply tank 13. Omitting the oxidation tower 16,
A one-tower type shown in FIG. 6 has been proposed.

1, 5 [The difference from the one in Fig. 5 is that the one in Fig. 5 is a two-unit type with a cooling tower 3 and an absorption tower 6, but the one in Fig. 16 is a single-tower type with a cooling section 23 and an absorption section 24. This is the point I made.

In other words, the dust removal that was performed in the Henchury type is changed to the Sugere method, and the cooling part 23 is incorporated in the lower part of the absorption part 24, and the bottom of the tower is used as the cooling part circulation tank 5, and the slurry supplied to the cooling part 23 is directly transferred to the cooling part circulation tank 5. drop it inside. cooling,
The exhaust gas after dust removal comes into gas-liquid contact with the slurry in the absorption section 24 at the top of the tower, and sulfur oxides are removed. The slurry after the gas-liquid contact is collected by the collector 25 and returned to the absorption section circulation tank 7 provided separately. Oxidizing air is supplied into the cooling section circulation tank 5 from the air supply pipe 26 to generate gypsum, and the dedicated oxidizing tower 16 shown in FIG. 5 is omitted. Limestone slurry as an absorbent is supplied to the absorption section circulation tank 7, and a part of the slurry in the absorption section circulation tank 7 is extracted through a conduit 27 and supplied to the cooling section circulation tank 5. As described above, in the conventional wet flue gas desulfurization equipment described in FIG. 5, since oxidation is not performed in the dust removal tower circulation tank 5, calcium sulfite coexists in the slurry, and this acts as a buffer to stabilize the cooling tower 30PH. Work but the 6th
In the wet flue gas desulfurization equipment described in the figure, the cooling section circulation tank 5
Since oxidation is forcibly carried out within the cooling section circulation tank 5 by oxidizing air from the air supply pipe 26, almost no calcium sulfite coexists in the slurry within the cooling section circulation tank 5, and the pH becomes unstable. In addition, since there is no blinding phenomenon covering the surface of limestone particles, the reactivity of limestone is improved, and C, r
CO- is absorbed by sulfur dioxide gas. As a result, there is almost no Cact in the slurry in the cooling section circulation tank 5, and the pH decreases.

Therefore, in order to operate the cooling section 23 at a high desulfurization rate and oxidation rate, it is necessary to stabilize the cooling section 230PH between 5.0 and 5.5. In order to supply fresh limestone slurry from the tank 10, the absorption section circulation tank 7 is a very large tank, and the fresh slurry flows into the cooling section circulation tank 5 and affects the pH of the cooling section circulation tank 5. I like that it takes a long time to do it.

In addition, the limestone slurry supplied to the absorption section circulation tank 7 reacts with SOx in the absorption section 23 and the pH has already decreased, so even if this slurry is supplied to the cooling section circulation tank 5, it has poor reactivity and is not suitable for DSS operation. This is not preferable for those that perform WSS operation and constantly fluctuate by 9 loads.

[Purpose of the invention]

The present invention aims to eliminate such drawbacks,
The purpose is to obtain a wet flue gas desulfurization device that can stabilize the pH of the cooling section and obtain good oxidation performance even when DSS operation or WSS operation is performed.

[Summary of inventions]

In order to achieve the above-mentioned object, the present invention is provided with an absorption liquid slurry sub-supply pipe for supplying absorption liquid slurry from an absorption liquid slurry tank to a cooling section circulation tank.

〔Example〕

Hereinafter, embodiments of the present invention will be explained using the drawings.

Figure 1 is a schematic system diagram of a wet flue gas desulfurization device according to an embodiment of the present invention, Figure #+2 is a control system diagram of Figure 1, and Figures 3 and 4 are the relationship between desulfurization rate and PH in the cooling section. , is a characteristic diagram showing the relationship between oxidation rate and PH.

In FIG. F1 and FIG. 2, numerals 1 to 29 indicate the same parts as the conventional ones.

30 is a connection from the absorption liquid slurry tank 10 to the cooling section circulation tank 5
31 is an SO1 concentration detector, 32 is an exhaust gas flow rate detector, 33 is a cooling unit PH detector, 34 is a cooling unit absorption liquid slurry flow rate control valve, 35 36 is the exhaust gas flow rate detection signal, 37 is the SOx Il
k degree detection signal, 38 is a multiplier, 39 is total SOx 34
Detection signal, 40 is a function generator, 41 is a cooling unit number liquid collection slurry flow I controller, 42 is a cooling unit PH setting signal, 43 is an absorption liquid slurry flow detection signal, 44 is an electro-pneumatic converter, 45 is a On the cooling unit PH adjustment side, 46 is a PH correction signal, and 47 is an adder.

u) In Figure 1, the exhaust gas is passed through the desulfurization fan 1. The gas is guided from the flue 2 to the cooling section 23 at the bottom of the desulfurization tower, where it is dust removed, cooled, and partially desulfurized, and then passed between the collectors 250 and guided to the absorption section 24 . Here, the sulfur dioxide gas in the exhaust gas comes into gas-liquid contact with the absorption liquid slurry, and after the SOx is absorbed and removed and the entrained mist is removed by the demister 28, the exit 9 of the desulfurization tower
is discharged from.

On the other hand, the absorbent slurry, which is an absorbent, is in the absorbent slurry tank 1.
0 to absorption liquid slurry supply pipe 29. The absorption number slurry sub-supply pipe 30 independently supplies the absorption part circulation tank 7 and the dust prevention part circulation tank 5.

The absorption liquid slurry in the absorption section circulation tank 7 is supplied to the absorption section 24 by the absorption section circulation pump 8, falls through the tower while coming into gas-liquid contact with the exhaust gas, is collected by the collector 25, and is sent down the downcomer pipe. It is returned to the absorption section circulation tank 7 for circulation and use. Further, a portion of the absorbent slurry is drawn out to the dustproof section circulation tank 5 through the conduit 27 in proportion to the amount of absorbent slurry supplied to the absorption section circulation tank 7. Fresh absorbent slurry is supplied to the cooling section circulation tank 5 by the absorption liquid slurry sub-supply pipe 30, and is sprayed in the cooling section 23 by the cooling section circulation pump 4 and comes into gas-liquid contact with the exhaust gas, thereby cooling, removing and removing the exhaust gas. Partial desulfurization is performed. In addition, the air supply pipe 26 provided in the cooling section circulation tank 5 is installed and air is blown into the tank 5 to oxidize the sulfite and turn it into gypsum 20.

In this case, in the present invention, fresh absorbent slurry is supplied to the cooling section circulation tank 5 through the absorbent slurry sub-supply pipe 30, so that even if DSS operation or WSS operation is performed, the cooling section 230PH remains stable. Good desulfurization and oxidation performance can be obtained.

In addition, the unloading rate and PH in the cooling section 23, the oxidation rate and PH
The relationship will be explained using FIG. 3 and ff4.

As shown in FIGS. 3 and 4, the relationship between the PH in the cooling section circulation tank 5 of the cooling section 23 and the desulfurization rate, and the oxidation rate and PH are contradictory, so the operation is performed at a high desulfurization rate and oxidation rate. In order to do this, it is necessary to operate the cooling part at a pH of around 5.0 to 55! It becomes.

However, in the conventional system shown in Figures W and 6, the absorption liquid slurry is supplied to the absorption section circulation tank 7, conduit 27. There is a time delay because it is supplied to the cooling section circulation tank 5, and the PH has already reacted with SOx in the absorption section 24.
It is not possible to operate stably at a pH of 5.0 to 5.5 because the pH is low and the reactivity is poor.

Therefore, in the present invention, a cooling section 2 is provided separately from the absorption section 24.
3. Fresh absorbent slurry is supplied from the absorbent slurry sub-supply pipe 30, and the pH is stabilized at 5.0 to 5.5.
This resulted in high desulfurization and oxidation rates.

Next, the control system of the present invention will be explained with reference to FIG. , the total SOx amount detection signal 39 is determined, and this total SOx f#, the detection signal 39 is set as the P H setting signal 42 of the cooling section absorption liquid slurry flow rate controller 41 with respect to the total SOx i detection signal 39 by the function generator 40, It is compared with the absorption liquid slurry flow rate detection signal 43 from the cooling part absorption liquid slurry flow rate detector 35, and after a proportional integral operation is performed, it is converted into an air signal by the electro-pneumatic converter 44, and the signal is sent to the cooling part of the absorption liquid slurry sub-supply piping 30. Absorbent slurry flow 'JK control valve 3
Operate 4.

Although the above circuit supplies a flow rate of the absorption liquid slurry that provides a stable pH at each load, if a disturbance such as a load change occurs, it is unlikely that VCP)T will fluctuate temporarily. The actual measurement signal from the cooling section circulation tank PH detector 33 is compared with the setting signal of the cooling section circulation PH controller 45,
After carrying out the proportional integral operation, this signal is added as a correction signal 46 by an adder 47 to correct the setting signal 42 for the supply flow rate of the cooling section absorption liquid slurry. In other words, since the load-to-time etc. are stable with almost no PH fluctuation, the correction signal 46 to the adder 47 becomes zero, and the output signal from the function generator 40 becomes the setting signal 42 as it is. On the other hand, when the load is being lifted or lowered, there is a possibility that the pH of the cooling section circulation tank 5 may fluctuate due to disturbances. In that case, a positive or negative correction signal 46 is input to the adder 47, and the setting signal 42 is corrected.

〔Effect of the invention〕

Since the present invention is provided with an absorption liquid slurry sub-supply pipe that supplies the absorption liquid slurry from the absorption liquid slurry tank to the cooling section circulation tank, even when DSS operation or WSS operation is performed, the cooling section P
H can be stabilized and desulfurization can be performed at high desulfurization and oxidation rates.

[Brief explanation of drawings]

FIG. 1 is a schematic system diagram of a wet flue gas desulfurization apparatus according to an embodiment of the present invention, FIG. 2 is a control system diagram of FIG. 1, and FIGS. 13 and 4 are desulfurization rates and PH in the cooling section. Characteristic diagrams showing the relationship between oxidation rate and P)T, Figure 5 and '
FIG. 6 is a schematic system diagram of a conventional wet flue gas desulfurization device. 5... Cooling section circulation tank, 7... Absorption section circulation tank, lO... Absorption liquid slurry tank,
23... Cooling section, 24... Absorption section, 3
0 absorption liquid slurry sub-supply piping. Figure 1 Figure 2 Figure 3 Figure 4 - PH(-) Figure 5 - [Two people

Claims (1)

[Claims] A cooling section that cools exhaust gas with an absorption liquid slurry, a cooling section circulation tank that stores this absorption liquid slurry, an absorption section that absorbs sulfur oxides in the exhaust gas with an absorption liquid slurry, and an absorption section that stores this absorption liquid slurry. In the wet flue gas desulfurization equipment which supplies absorbent slurry from the absorbent slurry tank to the absorption part circulation tank, the absorbent slurry supplies the absorbent slurry from the absorbent slurry tank to the cooling part circulation tank. A wet flue gas desulfurization device characterized by having a sub-supply piping.