JPH0536086B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a wet flue gas desulfurization system, and particularly to a wet flue gas desulfurization system that contains soluble acid gases such as hydrochloric acid (HCl) and hydrogen fluoride (HF) and fly ash in the flue gas. This relates to a wet type flue gas desulfurization equipment that fires coal containing a large amount of coal.

[Background of the invention]

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

Emission regulations for _SOx , which accounts for a large proportion of the pollutants that increase air pollution, are becoming stricter year by year. Under these circumstances, Japan's power generation industry, which has used oil as its main fuel since the second oil shock, is now switching to coal, which is cheaper and has ample supply.

However, as boilers have become larger, boilers have been started and stopped repeatedly on a daily basis in order to perform frequent load changes according to power generation demand in order to reduce power generation costs.

As a feature of recent electricity demand, as nuclear power generation grows, the difference between maximum and minimum loads also increases.
There is a trend to shift boilers for thermal power generation from base load to load adjustment, and these boilers are operated at variable pressure by changing the pressure according to the load.
By using a variable pressure boiler that operates in a so-called supercritical pressure region at full load and in a subcritical pressure region at partial load, the power generation efficiency at partial load can be improved by several percent.

However, due to the frequent load changes on a daily basis, the amount of exhaust gas fluctuates due to these load changes, and the amount of soluble acid gas and fly ash vary depending on the type of coal. , for example 1/
At partial loads such as 4, 1/2, and 3/4 loads, it is not possible to reduce the _SOx value below the target value.

For example, wet flue gas desulfurization equipment installed at thermal power plants, etc. uses an absorbent slurry containing calcium carbonate (CaCO ₃ ), calcium hydroxide [Ca(OH ₂ )], or calcium oxide (CaO) as an absorbent. The most common method is to use a slurry to absorb sulfur oxides (SO ₂ ) in exhaust gas from boilers, etc., oxidize the obtained calcium sulfite, and recover it as calcium sulfate, that is, gypsum.

A schematic system diagram of a conventional oil-fired wet flue gas desulfurization apparatus using this limestone or lime is shown in FIG. FIG. 2 is a system diagram showing a method for supplying absorbent slurry and a control system for the supply amount in a wet flue gas desulfurization apparatus.

In FIG. 1, exhaust gas 1 from a boiler (not shown) is pressurized at an inlet flue 2 by a desulfurizing fan 3, cooled by heat exchange with the process gas by a gas heater 4, and then cooled by an outlet flue 5. and is introduced into the cooling tower 6 of the wet flue gas desulfurization equipment.

In this cooling tower 6, the circulating liquid supplied from the cooling tower circulation tank 7 by the circulation pump 8 is cooled to the saturation temperature by gas-liquid contact, and after the dust contained in the exhaust gas 1 is removed, the absorption tower Sent to 9. In some cases, a mist eliminator 10 may be installed to remove mist in the exhaust gas 1 sent to the absorption tower 9.

In the absorption tower 9, _SOx in the exhaust gas is absorbed and removed by gas-liquid contact with the absorption liquid slurry supplied via the piping 12 by the circulation pump 11, and then the entrained mist is removed in the demister 13 to become a treated gas.
This processing gas is supplied to the mist eliminator 1 of the flue 14.
5, the gas is heated by the exhaust gas 1 by a gas heater 4, and released into the atmosphere while preventing white smoke from forming.

In addition, 16 is a make-up water piping to the mist eliminator 10 and the demister 13.

On the other hand, in the absorption tower 9, the absorption liquid slurry necessary to absorb _SOx in the exhaust gas is stored in the absorption liquid slurry tank 17.
from the absorption tower 9 by the pump 18, while from the absorption tower 9 by the absorption tower bleed pump 19.
A portion of the absorption liquid slurry containing calcium sulfite produced by absorbing _SOx is extracted and supplied to the oxidation tower supply tank 20. Oxidation tower supply tank 20
Then, the unreacted absorption liquid reacts with sulfuric acid 21 to become gypsum, and after the pH is adjusted, the pump 22
The calcium sulfite in the slurry is sent to the oxidation tower 23 by the air compressor 24 and oxidized by air supplied through the air tank 25, and the calcium sulfite in the slurry becomes gypsum. The obtained gypsum slurry is sent to a gypsum concentration tank 26, a slurry tank 27, a pump 28, and a dehydrator 2.
It is dehydrated through step 9, and gypsum 30 is recovered.

On the other hand, the overwater in the gypsum concentrating tank 26 is supplied to the absorbent slurry tank 17 from the overwater tank 31 and the overwater pump 32, added with an absorbent 33, and again supplied from the pump 18 to the absorption tower 9.

In addition, 34 is a pump, 35 is a drain, 36 is an absorption liquid slurry flow rate transmitter, 37 is an absorption liquid slurry flow rate control valve, 38 is a PH meter for the absorption liquid slurry, 39 is an exhaust gas flow rate transmitter, and 40 is a _SOx concentration meter. It is.

The method for supplying the absorbent slurry and the method for controlling the supply amount in this wet flue gas desulfurization equipment are as shown in Fig. ₂ . They are each detected by _{the SO}
Calculate the SO ₂ amount 44 and add a certain limestone excess rate (constant) 45 to it to obtain the set value 46 of the absorbent slurry.
This value is compared with the actual slurry flow rate value 47 detected by the absorbent slurry flow rate transmitter 36 in the calculator 48, and the limestone slurry flow rate electro-pneumatic converter 50 is opened and closed based on these deviation values 49. The absorption liquid slurry flow rate control valve 37 was controlled so that the amount was as small as possible.

In such a control method, the excess ratio of the absorption liquid slurry in the absorption tower 9 (absorption liquid equivalent/absorbed _SOx equivalent - 1) remains constant regardless of the amount of _SOx flowing in.

However, as a characteristic of the absorption tower 9 of a wet flue gas desulfurization equipment, the higher the pH of the absorption liquid and the lower the amount of inflow _SOx , the higher the desulfurization performance becomes. The higher the concentration and the lower the amount of inflow _SOx , the higher it will be. In other words, when a wet flue gas desulfurization equipment is operated at low load, the desulfurization performance decreases not only due to a decrease in _the amount of inflow _SO rises. This consumes more absorbent than necessary during low-load operation, and as a result, a large amount of sulfuric acid is consumed, increasing operating costs.

However, as mentioned above, the pH of the absorbent slurry in the absorption tower ₉ depends on the amount of _SOx absorbed and the absorbent concentration in the absorbent slurry. The absorbent concentration will decrease. Generally, the absorption tower 9 is about 20% of the amount withdrawn to the oxidation tower supply tank 20.
Because slurry for hours is stored, there is a delay in the change in liquid composition compared to the rate of change in load on the inflow gas side. If the load is increased from a state where the system is operating with slurry properties, the change in liquid composition will be delayed in response to the increase in load, resulting in a temporary drop in PH and a decrease in the desulfurization rate. This has the disadvantage that stable operation cannot be achieved, especially in wet flue gas desulfurization equipment installed in boilers and the like where the load fluctuates frequently.

As mentioned above, if the boiler load fluctuates greatly and low load operation continues for a long time such as on weekends or late at night, or if the boiler operation is stopped, the absorption tower 9
As the limestone slurry concentration in the absorption liquid slurry tank 17 becomes thinner and the PH becomes lower, the capacity of the absorption tower 9 and the absorption liquid slurry tank 17 becomes very large.
Once the slurry concentration is thin and the pH is low, it cannot follow a sudden increase in load, and as a result, the SO ₂ at the outlet of the wet flue gas desulfurization equipment tends to increase, making it impossible to meet environmental standards.

[Purpose of the invention]

The present invention aims to eliminate the drawbacks of such conventional technology, and its purpose is to have good followability to load fluctuations of boilers, etc., and to be able to cope with soluble acid gas and fly ash in coal-fired exhaust gas treatment. A wet flue gas desulfurization device is provided.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention makes gas-liquid contact between exhaust gas containing sulfur oxides (SO _X ) and absorption liquid slurry in a cooling tower and an absorption tower, and absorbs and removes SO _X from the exhaust gas. In the wet flue gas desulfurization equipment, a slurry circulation piping system provided in each of the cooling tower and the absorption tower, a connecting pipe connecting the slurry circulation piping systems, and an absorbent slurry supply piping having an absorbent slurry flow rate control valve. and the pH of the absorbent slurry in the cooling tower slurry circulation piping system.
a PH transmitter that detects the PH value, a PH signal setting device that sets a reference PH value, and a carbonate supply pipe having a carbonate flow rate control valve, and the actual PH value from the PH transmitter is the PH signal. If the PH signal is higher than the preset PH signal set value by the setting device, open the absorbent slurry flow control valve, close the carbonate flow control valve, and if the actual PH value is lower than the PH signal set value. ,
The absorbent slurry flow control valve and the carbonate flow control valve are configured to be opened.

[Example of the present invention]

FIG. 3 is a schematic system diagram of the wet flue gas desulfurization apparatus of the present invention, FIG. 4 is a control system diagram for limestone slurry flow rate, and FIG. 5 is a control system diagram for carbonate flow rate.

3 to 5, numerals 1 to 50 are the same as the conventional ones, and 51 is a slurry circulation piping system of the cooling tower 6, which is connected to the cooling tower 6, the cooling tower circulation tank 7, and the cooling tower circulation pump 8. and circulate the absorbent slurry.

52 is a slurry circulation piping system of the cooling tower 9, which includes the absorption tower 9, the absorption tower circulation tank 53, and the absorption tower circulation pump 1.
1.

54 is a connecting pipe connecting the slurry circulation piping system 51 of the cooling tower 6 and the slurry circulation piping system 52 of the absorption tower 9, and 55, 56, 57, 58 are PH transmitters provided in the slurry circulation piping system 51 of the cooling tower 6. , a carbonate flow rate control valve, carbonate supply piping for sodium carbonate, potassium carbonate, etc., and a carbonate flow rate transmitter, 59 is a PH adjustment tank, 60 is a drain tank, 61 is a drain pump, 62
62 is a sump mist eliminator that removes fly ash from the exhaust gas 1. Those that have this sump mist eliminator 62 are called soot separation systems, and those that do not have them are called soot mixing systems.

In such a structure, the difference between the conventional wet flue gas desulfurization system shown in FIG. 1 and the wet flue gas desulfurization system of the present invention shown in FIG. 3 is that in the cooling tower 6 of the conventional wet flue gas desulfurization system, In the wet flue gas desulfurization system of the present invention, the slurry circulation piping system 52 of the absorption tower 9 and the slurry circulation piping system of the cooling tower 6 are used to cool and remove dust by the circulating liquid from the cooling tower circulation tank 7. 51
The absorption liquid slurry is stored in a cooling tower circulation tank 7 and supplied to the cooling tower 6 from a circulation pump 8 to cool the exhaust gas and remove dust.

In other words, when treating coal-fired exhaust gas, if soluble acid gas and fly ash, which are abundant in coal exhaust gas, are included in the absorbent slurry, the concentrations of Cl ^- (chlorine ions), F ^- (fluorine ions), and fly ash will increase. This prevents the dissolution of the absorbent slurry from becoming high and the desulfurization performance from decreasing due to this inhibiting the dissolution of the absorbent slurry.

Therefore, in the embodiment shown in FIG. 3, the adverse effects caused by chlorine ions, fluorine ions, and fly ash in the absorbent slurry are ultimately caused by PH.
For example, the slurry circulation piping system 51 (cooling tower circulation tank 7) of the cooling tower 6 must remove, for example, sodium carbonate from the carbonate supply piping 57, before it is extracted to the oxidation tower supply tank 20 for treatment. The pH is controlled by supplying

In addition, both soda carbonate and absorbent slurry have desulfurization ability when the pH is increased, and since PH control interferes with each other, the role of the two is that the desulfurization performance itself is performed by the absorbent slurry, and the sodium carbonate The purpose of supplying is to prevent dissolution of the absorbent slurry from being inhibited by chloride ions, fluoride ions, and fly ash, and to prevent a decrease in the desulfurization performance of the absorbent slurry, and is not intended for desulfurization itself.

Therefore, the pH of the absorbent slurry is constantly controlled using limestone, and soda carbonate is only supplied when the pH falls below a specified value. In this way, a conventional oil-fired wet flue gas desulfurization device can be improved to a coal-fired wet flue gas desulfurization device by simple modification work.

An example of absorbent slurry flow rate control and soda carbonate flow rate control will be described below with reference to FIGS. 4 and 5.

4 and 5, an absorption liquid slurry flow rate transmitter 36, an absorption liquid slurry flow rate control valve 37, an exhaust gas flow rate transmitter 39, an _SOX concentration transmitter 40, an actual measurement value of exhaust gas amount 41, and an actual measurement value of _SOX concentration 42. , computing unit 4
3. SO ₂ amount 44, slurry flow rate actual value 47, calculator 48, deviation value 49, limestone slurry flow rate electro-pneumatic converter 50 are completely the same as the conventional one shown in FIG. 2, and PH transmitter 55, The carbonate flow rate control valve 56, the carbonate supply pipe 57, and the carbonate flow rate transmitter 58 are the third
It is the same as the one shown in the figure.

In FIG. 4, a PH conversion signal 64 at each load is programmed in advance from the SO ₂ amount 44 by a function generator 63, and a bias 66 is operated by an adder 65 to arbitrarily set the PH value during operation. Setting value 6
7 can be corrected.

On the other hand, the PH transmitter 55 of the cooling tower circulation tank 7
The measured PH value 68 and the set PH value 67 are calculated by a calculator 69, and the deviation value 70 is calculated by an adder 73 through a function generator 71 having nonlinear characteristics and a manual/automatic switch 72. Add the rate setting value 75 to get the total limestone excess rate setting value 76
and is multiplied by the amount of SO ₂ 44 in a multiplier 77 to obtain a limestone request signal value 78. The other explanations are the same as those in FIG. 2 and will therefore be omitted.

In other words, from the SO ₂ amount 44 by the function generator 63
A PH set value 67 and a limestone excess rate set value 75 are programmed in advance by a function generator 74, and the limestone excess rate is corrected using an actual PH value 68.

Next, soda carbonate flow rate control will be explained using FIG. 5.

PH signal setting value 80 from PH signal setting device 79
Then, the actual measured PH value 68 from the PH transmitter 55 is guided to a function generator 83 as a deviation value (excess rate PH correction) 82 by the arithmetic unit 81 .

On the other hand, the reference value 85 from the reference value setter 84 is guided to the function generator 83, and when the deviation value 82 is greater than or equal to the reference value 85, the function generator 83 does not operate; does not supply carbonated soda),
On the other hand, if the reference value is less than 85, the function generator 83
is activated and outputs the α signal 86.

In addition, the function generator 8 corrects the concentration settings of fluorine ions, crawl ions, and fly ash (mainly fluorine ions) based on the load (processing gas amount).
7 concentration correction signal 88 and concentration setting (setting the concentration of fluorine ions, etc. depending on the type of coal) 89
is multiplied by a multiplier 90, the corrected concentration 91 and the α signal 86 from earlier are multiplied by a multiplier 92, and a sodium carbonate excess rate (α' signal) 93 after PH correction is obtained.

Then, the processing gas amount 44 and the α' signal 93 are multiplied by a multiplier 9.
Multiply by 4 to obtain the required soda carbonate value of 95.

This required value of soda carbonate 95 and carbonate supply pipe 5
The sodium carbonate actual measurement value 96 from the carbonate flow transmitter 58 of 7 is outputted as a soda deviation value 98 by the carbonate soda flow rate controller 97, and the soda carbonate flow rate electro-pneumatic converter 9
9, the sodium carbonate flow rate control valve 56 is opened and closed to control the flow rate of sodium carbonate in the carbonate supply pipe 57.

Note that when soda carbonate is being supplied under the control shown in FIG. 5, the manual/automatic switch 72 shown in FIG. To prevent mutual interference, only the limestone excess rate set value 75 side is controlled by the function generator 74.

〔Effect of the invention〕

As described above, the present invention is a wet flue gas desulfurization method that absorbs and removes _SOx from the flue gas by bringing the flue gas containing sulfur oxides ( _SOx ) into gas-liquid contact with an absorption liquid slurry in a cooling tower and an absorption tower. In the apparatus, a slurry circulation piping system provided in each of the cooling tower and the absorption tower, a communication piping connecting the slurry circulation piping systems, an absorption liquid slurry supply piping having an absorption liquid slurry flow rate control valve, and a cooling tower. PH of absorbent slurry in slurry circulation piping system
a PH transmitter that detects the PH value, a PH signal setting device that sets a reference PH value, and a carbonate supply pipe having a carbonate flow rate control valve, and the actual PH value from the PH transmitter is the PH signal. If the PH signal is higher than the preset PH signal set value by the setting device, open the absorbent slurry flow control valve, close the carbonate flow control valve, and if the actual PH value is lower than the PH signal set value. ,
Since the absorption liquid slurry flow rate control valve and the carbonate flow rate control valve are configured to open, it has good followability to load fluctuations, and can be quickly applied even if soluble acid gas or fly ash changes in coal-fired exhaust gas treatment. Desulfurization performance can be followed.

[Brief explanation of the drawing]

Figures 1 and 2 show conventional wet flue gas desulfurization equipment. Figure 1 is a schematic system diagram of the wet flue gas desulfurization equipment, and Figure 2 is the absorption liquid in the wet flue gas desulfurization equipment shown in Figure 1. Slurry control system diagram, Figures 3 to 5
The figure shows a wet type flue gas desulfurization device of the present invention, and Fig. 3 is a schematic system diagram of the wet type flue gas desulfurization device of the present invention,
4 and 5 are control system diagrams for controlling the absorbent slurry flow rate and the carbonate flow rate in the wet flue gas desulfurization apparatus shown in FIG. 3. 6... Cooling tower, 9... Absorption tower, 51, 52... Slurry circulation piping system, 54... Connection piping, 55... PH transmitter, 56... Carbonate flow rate control valve, 57... Carbonate supply piping.

Claims (1)

[Claims] 1. Bringing the exhaust gas containing sulfur oxides (SOx) and absorption liquid slurry into gas-liquid contact in a cooling tower and an absorption tower,
In a wet flue gas desulfurization device that absorbs and removes SOx in flue gas, a slurry circulation piping system provided in each of the cooling tower and absorption tower, a connecting piping system that connects the slurry circulation piping systems, and an absorption liquid slurry flow rate adjustment system are provided. An absorption liquid slurry supply device with a valve, a PH transmitter attached to the cooling tower slurry circulation piping system to detect the PH of the absorption liquid slurry, a PH signal setting device to set a reference PH value, and a carbonate flow rate. and a carbonate supply pipe having a control valve, and when the actual pH value from the PH transmitter is higher than the PH signal setting value preset by the PH signal setting device, the absorption liquid slurry flow rate is adjusted. Open the valve and close the carbonate flow control valve, if the actual PH value is lower than the PH signal set value,
A wet flue gas desulfurization apparatus, characterized in that the absorbent slurry flow rate control valve and the carbonate flow rate control valve are configured to open.