JPH0131412B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wet flue gas desulfurization device that absorbs and removes sulfur oxides (SOx) contained in exhaust gas from a boiler or the like through gas-liquid contact with an absorbent slurry such as limestone. .

Conventionally, in a wet flue gas desulfurization apparatus, exhaust gas is pressurized by a desulfurization fan 1 and sent to a cooling tower 2.
In the cooling tower 2, the exhaust gas comes into gas-liquid contact with the slurry in the cooling tower circulation tank 5, which is supplied by the pump 3 via the cooling tower spray pipe 4, and the exhaust gas temperature is cooled to the saturation temperature, and dust removal and partial desulfurization are performed. It will be done.
The cooled exhaust gas enters the absorption tower 7, where it comes into contact with the absorbent slurry sent from the absorption tower circulation tank 8, through the absorption tower circulation pump 9, and the absorbent slurry piping 10 into the absorption tower 7, and becomes the exhaust gas. The SOx inside is absorbed and removed. The absorbent slurry sprayed by the sprayer 21 accumulates at the bottom of the absorption tower 7 and returns to the absorbent circulation tank 8 through the return pipe 11 that communicates the absorption tower 7 with the absorbent circulation tank 8 . Then, the absorbent slurry is sprayed by the spray 21 through the absorbent slurry pipe 10 again. That is, the absorbent slurry is circulated between the absorbent circulation tank 8 and the absorption tower 7 through the absorbent slurry piping 10 and the return piping 11. 22 is a stirrer, and the stirrer 22 constantly stirs the absorbent slurry or suspension in the absorbent circulation tank 8 to prevent solid-liquid separation.

Here, the amount of exhaust gas flowing into the desulfurization equipment and the SOx concentration in the exhaust gas vary from the rated value to about 1/4 of the rated value, depending on the boiler load and the properties of the fuel burned in the boiler. However, it is desirable for desulfurization equipment to operate at a constant desulfurization efficiency even if the exhaust gas conditions (gas amount, SOx concentration) fluctuate.

When the amount of absorbent slurry sprayed is constant, the desulfurization rate of the desulfurization equipment is higher as the amount of exhaust gas is lower and the SOx concentration in the exhaust gas at the entrance of the absorption tower is lower. The desulfurization rate increases as the amount increases. Therefore, it is theoretically possible to keep the desulfurization rate constant by varying the spray amount in response to variations in exhaust gas conditions. However, in such desulfurization equipment, the liquid-gas ratio [spray liquid volume (/
h)/exhaust gas amount (Nm3/h)] is usually 10(/N
m3) It is necessary before and after. Therefore, for example, the amount of exhaust gas
When processing 500000Nm3/h, the liquid gas ratio is 10
/Nm3, the amount of spray liquid will be a huge amount of 5000m3/h. When this huge amount of spray liquid is passed through a single absorbent slurry pipe, the pipe diameter is approximately 40B.
becomes.

However, since the absorbent is composed of acidic components and is in the form of a slurry, a large-diameter pipe with corrosion resistance and wear resistance is required. Therefore, it is actually difficult to provide a control valve for regulating the flow rate of the absorbent slurry in a large-diameter pipe, and conventionally, the system has been operated at a constant spray amount regardless of fluctuating exhaust gas conditions. Therefore, as is clear from Figure 2, which shows the relationship between inlet gas amount and desulfurization rate in conventional equipment, in an equipment designed with a processing gas amount of 500,000 Nm3/h, the processing gas amount is 200,000 Nm3/h.
When reduced to h, the desulfurization rate increases to 97%.
As a result, if the desulfurization rate is lower than the rated value, the desulfurization rate becomes too high, and not only limestone and sulfuric acid are consumed accordingly, but also a large amount of by-product gypsum is produced.

An object of the present invention is to provide a wet flue gas desulfurization device that can be operated at a constant desulfurization rate regardless of fluctuating exhaust gas conditions.

The present invention provides a gas flow rate detector and an SOx concentration detector as gas property detectors for the flue gas to be desulfurized in the line that introduces the flue gas into the absorption tower, and connects absorbent slurry piping to each detector. branched into at least two or more branch pipes, and each branch pipe communicated with the absorbent circulation tank side, and a detection signal from one of the two detectors, which is different from the other, is transmitted in the middle of each branch pipe. The absorption tower is equipped with a correction SOx concentration detector that measures the SOx concentration of the treated exhaust gas and corrects the opening degree of each valve based on the difference between this measured value and the set value. This is installed in the flow path for treated exhaust gas flowing out from the pipe. This not only makes it possible to adjust the amount of absorbent slurry sprayed according to the gas properties of the exhaust gas, but also allows each valve in each branch pipe to be adjusted based on the exhaust gas flow rate and SOx concentration of the exhaust gas properties. , it is possible to control the operation individually, that is, by only one factor, to reduce the range of flow rate control by each valve, making it possible to use valves for small diameter pipes, and to control the operation of valves by combining multiple factors. This prevents the problem of hunting that occurs during control, and also corrects the opening degree of the valve using a detection signal from the correcting SOx concentration to perform more appropriate flow rate control.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIGS. 3 and 4 are schematic configuration diagrams each showing an example of the present invention. In Fig. 3, the difference from the conventional example shown in Fig. 1 is that from the desulfurization fan 1 to the cooling tower 2.
A gas flow rate detector 12 and
A SOx concentration detector 13 is provided. That is, in this embodiment, the gas property detector is formed by the gas flow rate detector 12 and the SOx concentration detector 13. In this way, the gas flow rate of exhaust gas and SOx
If the concentration is detected individually, desulfurization treatment can be performed with extremely high precision. Further, two branch pipes 14 and 15 are provided which branch from the absorbent slurry pipe 10 and reach the absorbent circulation tank 8, and a flow rate regulating valve 1 is provided in each of the branch pipes 14 and 15.
6 and 17 are interposed. The flow rate adjustment valve 16 is controlled based only on the signal from the gas flow rate detector 12, while the flow rate adjustment valve 17 is controlled based on the signal from the SOx concentration detector 13.
It is designed to be controlled solely based on signals from the In Fig. 3, 18 is a correction SOx concentration detector that detects the SOx concentration in the exhaust gas at the outlet of the absorption tower 7, and the detector 18 is the difference between the measured value of the SOx concentration in the treated exhaust gas and the set concentration value. The valve 16,1
This is for correcting the opening degree of No.7. This detector 18 allows the desulfurization process to be performed with even higher precision. Other parts in FIG. 3 that are the same as those in FIG. 1 are designated by the same reference numerals.

Next, the operation of the above embodiment will be explained. The gas flow rate is set, the return flow rate of the absorbent slurry returned from the branch pipe 14 to the absorption tower circulation tank 8 is set by the flow rate detector 12, and the opening degree of the flow rate regulating valve 16 is commanded. Furthermore, this opening degree is corrected by the difference between the set value of the SOx concentration at the outlet of the absorption tower 7 and the measured value of the SOx concentration detector 18 for correction.

On the other hand, the opening degree of the flow rate regulating valve 17 is commanded based on the flow rate set based on the inlet SOx concentration detected by the SOx concentration detector 13. Furthermore, this opening degree is determined by the set value of the SOx concentration at the outlet of absorption tower 7 and the SOx for correction.
It is corrected based on the difference from the measured value of the concentration detector 18.

In addition, when the load is high and the flow rate of exhaust gas is high, the amount of absorbent slurry sprayed from the spray 21 increases by controlling the valves 16 and 17, so the amount returned to the absorbent circulation tank 8 through the return pipe 11 also increases. There will be more. Therefore, due to this large amount of return from the return pipe 11, the inside of the absorbent circulation tank 8 is violently agitated. On the other hand, when the load is low, the valve 16,
As the opening degree of the sprayer 17 increases, the amount of spray from the sprayer 21 decreases. Therefore, the amount returned from the return pipe 11 to the absorbent circulation tank 8 decreases, and the stirring force decreases. However, the interior of the absorbent circulation tank 8 is violently agitated due to the large amount of return from the branch pipes 14 and 15. That is, the inside of the absorbent circulation tank 8 is similarly vigorously agitated by the circulated absorbent slurry both under high load and under low load. Therefore, the stirrer 22 can be made smaller than conventional ones.

Here, if a flow meter is installed in each of the branch pipes 14 and 15, and the slurry flow rate is measured by each flow meter, and this measured value is fed back to the flow rate adjustment valves 16 and 17, the flow rate of the absorbent slurry can be controlled. This can be done more accurately.

According to this embodiment, the amount of absorbent slurry returned to the absorption tower 7 is varied in response to fluctuations in the flow rate of the exhaust gas introduced into the absorption tower 7 and the SOx concentration (gas properties) in the exhaust gas. The amount of spray can be varied. Therefore, by appropriately selecting the number of branch pipes and the number of flow rate regulating valves installed in these, it is possible to support large-capacity desulfurization equipment with large fluctuations in the amount of exhaust gas and the concentration of SOx in the exhaust gas. I can do it. For example, in a desulfurization equipment with an inlet gas amount of 500,000 Nm3/h, a liquid-gas ratio of 10/
Even if the desulfurization rate varies from Nm3 to 6/Nm3, a constant desulfurization rate can be obtained.

FIG. 4 is a schematic diagram showing another embodiment of the present invention, in which automatic valves 19 and 20 that can open and close fully are provided in place of the flow rate regulating valves 16 and 17 shown in FIG. Also in this device, the gas flow rate detector 12
The gas flow rate is detected, and when the gas flow rate falls below the set gas amount, the automatic valve 19 provided in the branch pipe 14 is fully opened, and the absorbent slurry is returned to the absorbent circulation tank 8.

On the other hand, the automatic valve 20 is fully opened when the SOx concentration detected by the SOx concentration detector 13 falls below the set SOx concentration. At this time, if the SOx concentration at the outlet of the absorption tower 7 becomes higher than the set value, the automatic valves 19, 20
It is desirable to provide an interlock that forces the terminal to be fully closed.

In this example, as shown in FIG. 5, since the amount of spray introduced into the absorption tower 7 changes discontinuously, the desulfurization rate also changes discontinuously, but within a constant range. According to this embodiment, although the absorbent is in the form of a slurry, since the automatic valve operates fully closed and fully open, there is an advantage that the valve wear is less compared to the case of the flow rate regulating valves 16 and 17.

As described above, according to the present invention, the desulfurization apparatus can be operated at a constant desulfurization rate regardless of changes in the inlet gas properties, and the consumption of limestone and sulfuric acid can be reduced. For example, in a desulfurization device with an inlet gas amount of 500,000 Nm3/h, an inlet SOx concentration of 1000 ppm, and a planned desulfurization rate of 90%, the conventional device achieved a desulfurization rate of 97% when operated at 200,000Nm3/h.

On the other hand, when the device of the present invention is operated at 200,000 Nm3/h with a desulfurization rate of 90%, the amount of limestone used can be reduced by approximately 65 kg per hour, and the amount of limestone used can be reduced by 200,000 Nm3/h.
If the operation is 8 hours a day at night and the desulfurization equipment is operated 300 days a year, the result is 65 x 8 x 300 = 156,000 kg, which means that the amount of limestone used can be reduced by 16 tons per year. Similarly, sulfuric acid can be reduced by approximately 6 kg per hour, or 14,400 kg per year.

As mentioned above, according to the present invention, the spray amount of the absorbent slurry can be adjusted according to the gas properties of the exhaust gas, and the operation can be performed at a constant desulfurization rate. Not only can the generation of SOx be reduced, but the operation of each valve in each branch pipe is controlled individually, based on only one factor, rather than a combination of the exhaust gas flow rate and SOx concentration among the exhaust gas properties. It becomes possible to reduce the flow rate control range of the valve, and therefore, it becomes possible to use a valve with a small diameter pipe, and the spray amount of the absorbent slurry can be easily and reliably adjusted. Furthermore, when one valve is controlled by a combination of multiple factors, there is a problem in that hunting occurs due to rapid fluctuations in multiple factors in contradictory directions, reducing durability.However, in the present invention, one factor, one valve control Therefore, this hunting problem does not occur. Furthermore, since the SOx concentration in the treated exhaust gas is detected and the valve opening degree is corrected and controlled based on the deviation from the set value, control can be performed with extremely high precision.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing a conventional flue gas desulfurization equipment, Fig. 2 is a diagram showing the relationship between inlet gas amount and desulfurization rate in the conventional equipment, and Figs. 3 and 4 are diagrams showing the implementation of the present invention, respectively. A schematic configuration diagram showing an example, FIG. 5 is a diagram showing the relationship between the spray amount, desulfurization rate, and load (gas flow rate, SOx concentration) in the embodiment shown in FIG. 4. 1... Desulfurization fan, 2... Cooling tower, 5... Cooling tower circulation tank, 7... Absorption tower, 8... Absorption tower circulation tank, 12... Gas flow rate detector, 13... SOx
Concentration detector, 14, 15...Branch pipe, 16, 17
...Flow rate adjustment valve, 18...SOx concentration detector for correction, 19,20...Automatic valve.

Claims (1)

[Claims] 1.Equipped with an absorption tower having one or more stages of spray in the tower, and connecting the spray to an absorbent circulation tank in which a suspension consisting of an absorbent slurry such as limestone is stored through absorbent slurry piping. Wet flue gas communicates with the absorption tower and the absorbent circulation tank, and removes sulfur oxides in the exhaust gas supplied into the absorption tower by contacting with the absorbent slurry sprayed from the spray. In the desulfurization equipment, a gas flow rate detector and an SOx concentration detector are provided as gas property detectors for the flue gas to be desulfurized in the middle of the line that introduces the flue gas into the absorption tower, and the absorbent The slurry piping is branched into at least two or more branch pipes, each branch pipe is connected to the absorbent circulation tank side, and one of the two detectors, which is different from the other, is connected to the middle of each branch pipe. A correction SOx concentration detector is equipped with valves that operate independently based on the detection signals of the SOx concentration detector, which measures the SOx concentration of the treated exhaust gas, and corrects the opening degree of each valve based on the difference between this measured value and a set value. A wet flue gas deflow device, characterized in that it is provided in a flow path of treated flue gas flowing out from an absorption tower.