JPH0579362B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for controlling the amount of limestone supplied in a wet limestone-gypsum method flue gas desulfurization equipment, and in particular, a method for controlling the amount of limestone supplied according to the boiler load change rate. It is about the method.

[Background of the invention]

In the conventional wet limestone-gypsum method flue gas desulfurization equipment,
A slurry containing a basic calcium compound as a main ingredient is circulated in an absorption tower, the circulating liquid and combustion exhaust gas containing sulfur dioxide are brought into gas-liquid contact, the sulfur dioxide is converted to calcium sulfite, and then the calcium sulfite is oxidized, It is collected as plaster. Limestone is used as the basic calcium compound. The absorption tower is operated with the amount of limestone supplied slightly larger than the chemical equivalent of sulfur dioxide in the combustion exhaust gas. At this time, there is a close relationship between the circulating liquid PH in the absorption tower, the sulfur dioxide concentration (desulfurization rate) at the outlet of the absorption tower, and the solubility of limestone, and the absorption tower is operated so that the circulating liquid PH becomes a predetermined value. The control system has been assembled and is being operated.

In these control systems, when the boiler load is constant and the limestone supply amount is adjusted to maintain the circulating fluid pH at a predetermined value, the sulfur dioxide concentration at the absorption tower outlet can be kept below the allowable value. can be held.

However, boilers in thermal power plants and the like are operated with varying loads depending on the daily power demand.
That is, at night when the demand for electricity is low, the boiler is operated at a low load, and the boiler load is increased as the demand increases. At this time, the boiler load is normally ramped up at a rate of 3 to 8%/min. Now 50 for maximum load amount
It takes 6 to 16 minutes to start up a boiler that is operated at The amount of sulfur also increases to 1.4-1.5. In response to such changes in the amount of treated gas and inflowing sulfur dioxide over a short period of time, the desulfurization apparatus performs control to supply the amount of limestone so that the desulfurization rate is always higher than the set desulfurization rate.

However, with the conventional constant control method for the circulating liquid PH of the absorption tower, the dissolution rate of the supplied limestone is slow, and it is not possible to cope with the increase in the amount of combustion exhaust gas and inflowing sulfur dioxide due to the rate of change in boiler load. decreases, making it impossible to maintain the set desulfurization rate. For this reason,
Control methods such as those described in Japanese Utility Model Application Publication No. 59-53832, Japanese Utility Model Application Publication No. 59-44533, and Japanese Patent Application Publication No. 59-36528 have been proposed. According to these methods, the rate of change in the boiler load is detected and the amount of limestone supplied is rapidly added to prevent a decrease in the desulfurization rate.

However, with these control methods, when the boiler load change rate is slow at startup, it is possible to respond to boiler load changes without reducing the desulfurization rate, but when the load change rate is large, these boiler load change rates Therefore, it was necessary to rapidly introduce an amount of limestone corresponding to the load change rate by increasing the capacity of the limestone supply pump.

[Purpose of the invention]

The purpose of the present invention is to maintain the set desulfurization rate when the boiler load changes daily, especially when the boiler load is rapidly ramped up from low load to high load, and to prevent the supply of excess limestone. - To provide a control method for a gypsum method flue gas desulfurization equipment.

[Summary of the invention]

The daily load on the boiler varies by starting up and shutting down the boiler in a planned manner depending on the amount of electricity demanded. When the boiler is brought down from high load to low load, it is controlled by the desulfurization rate and the slurry PH in the absorption tower circulation tank, and is operated at or above the set desulfurization rate.

On the other hand, when the boiler load suddenly increases from low load to high load, limestone slurry is rapidly added after detecting the boiler load. The solubility of limestone cannot be followed, and the desulfurization rate cannot be maintained at the set desulfurization rate for several minutes to several tens of minutes after the boiler load is started.

Generally speaking, when the relationship between the solubility of limestone and the PH (ion concentration index) of slurry is organized in terms of hydrogen ion concentration, there is a proportional relationship between the two. In addition, the solubility of limestone affects the hydrogen ion concentration, limestone concentration, calcium ion concentration, particle size, etc. of the slurry.

The present inventors have found that it is advantageous to aerate the slurry with air to reduce the apparent gas phase carbon dioxide concentration in order to increase the solubility of limestone. Figure 2 shows the results of a basic test showing the PH recovery effect of slurry when it is aerated with air (bubbling with air). Carbon dioxide gas (CO ₂ partial pressure 0.1 atm.) in an aqueous solution of limestone and calcium sulfite is bubbled, and air is bubbled into this slurry to bring the apparent gas phase CO ₂ partial pressure to approximately 0.05 atm. Shows the slurry PH recovery status. As is clear from Figure 2, by bubbling air into the slurry, the pH of the slurry is rapidly restored.

The present invention was achieved based on such knowledge, and it detects the boiler load amount from the combustion exhaust gas of the boiler and introduces air into the liquid retention part of the absorption tower circulation tank when the boiler load is started. At the same time, limestone slurry is supplied into the slurry bubbled with air in the absorption liquid circulation tank, increasing the solubility of limestone and speeding up the PH recovery rate of the slurry, thereby reducing the sudden load on the boiler. The system is designed to quickly respond to sudden start-ups, and to ensure stable operation without lowering the desulfurization rate below the set desulfurization rate.

[Embodiments of the invention]

FIG. 1 shows a control system of a wet limestone-gypsum flue gas desulfurization apparatus according to the present invention.

Flue gas 2 from a boiler is introduced into an absorption tower body 1 of a limestone-gypsum flue gas desulfurization apparatus. On the other hand, the circulating liquid 4 extracted from the absorption tower circulation tank 3 is sprayed from a spray nozzle 6 via a circulation pump 5, and comes into gas-liquid contact with the combustion exhaust gas 2 here.
The combustion exhaust gas 7 from which sulfur oxides have been removed at the gas-liquid contact portion is heated.

A slurry 10 of limestone 9 adjusted in a slurry adjustment tank 8 is sent to an absorption tower circulation tank 3 through a pump 11.
The limestone slurry is supplied after being adjusted by the limestone slurry supply amount adjustment valve 12 via the limestone slurry. On the other hand, a part of the slurry is removed from the absorption tower circulation tank 3 through the channel 13 and sent to a gypsum recovery device (not shown).

In this embodiment, the exhaust gas amount of the combustion exhaust gas 2 is detected by the exhaust gas amount detector 14, and then the sulfur dioxide concentration in the exhaust gas is detected by the sulfur dioxide concentration detector 1.
5, and the exhaust gas amount detection signal 16 and the sulfur dioxide detection signal 17 are input to the computing unit 18, respectively. Further, the PH value of the slurry in the liquid retention section in the absorption tower circulation tank 3 is detected by the PH detector 19, and a PH detection signal 20 is input to the calculator 18. In addition, the exhaust gas amount detector 14 detects information on the boiler load factor from the combustion exhaust gas amount, and when a start-up signal of a change in the boiler load is detected, the air amount adjustment valve operation signal 21 is output from the calculator 18 to adjust the air amount. The valve 22 is opened, air 25 is supplied to the channel 24 via the pump 23, and the slurry in the absorption tower circulation tank 3 is bubbled with air to perform decarboxylation.

In addition, the computing unit 18 calculates the required amount of limestone to be supplied from the combustion exhaust gas amount change rate, the sulfur dioxide concentration change rate, and the circulating fluid PH value in the absorption tower circulation tank 3. Based on this calculated value, the computing unit 18 supplies limestone slurry. A feed rate regulating valve actuation signal 26 is output, which causes limestone slurry 10 to be pumped through pump 11.
A predetermined amount of is supplied to the absorption liquid circulation tank 3.

Next, Figs. 3A to 3E show how to start up the boiler load change without bubbling the circulating liquid in the liquid retention part of the absorption tower circulation tank with air.
This figure shows changes in slurry pH and deflow rate of the absorption tower when limestone slurry is rapidly added.

On the other hand, as in the example shown in Fig. 1, Figs. 4A to 4F show air bubbling and rapid injection of limestone into the circulating liquid in the liquid retaining section of the absorption tower circulation tank in response to the start-up of boiler load changes, as in the embodiment shown in Fig. 1. The changes in the slurry PH and the desulfurization rate of the absorption tower are shown when these are performed in parallel.

From Figures 3 and 4, it can be seen that the PH recovery of the slurry is slow with only the rapid addition of limestone, and the desulfurization rate is unable to maintain the set desulfurization rate for a period of time and decreases, and then gradually in parallel with the PH recovery of the slurry. The desulfurization rate also shows a tendency to recover.

In response to this, the boiler load change rate is detected, air is bubbled into the slurry in the absorption tower circulation tank liquid retaining section to recover the pH, and limestone slurry is rapidly poured into the slurry that is being bubbled by air. As a result, the PH recovery speed of the slurry is faster than when only the limestone slurry is rapidly added as shown in Figure 3, and it has been found that the desulfurization rate can be maintained stably without decreasing.

〔Effect of the invention〕

As described above, according to the present invention, bubbling with air and rapid injection of limestone slurry are used in combination with the slurry in the liquid retaining section in the absorption tower circulation tank in response to load changes during boiler start-up. Therefore, the pH recovery rate of the slurry is increased, which is effective in maintaining a stable drainage rate. Furthermore, by bubbling the slurry in the liquid retention section in the absorption tower circulation tank with air, the pH recovery rate of the slurry is increased, which has the effect of preventing excessive supply of limestone slurry.

[Brief explanation of drawings]

Figure 1 is a system diagram showing one embodiment of the present invention, Figure 2 is a system diagram showing an embodiment of the present invention.
The figure is a graph showing the PH recovery status of the slurry when air is bubbled into the slurry.
C, D, and E are boiler load, processing gas amount, and
Graph showing a comparison of changes over time in limestone slurry flow rate, slurry PH, and desulfurization rate, Figure 4 A, B, C,
D, E, F are boiler load, processing gas amount,
It is a graph showing a comparison of changes over time in limestone slurry flow rate, slurry PH, desulfurization rate, and air blast amount. 1... Absorption tower main body, 2... Combustion exhaust gas, 3...
Absorption tower circulation tank, 10...Limestone slurry, 1
4... Exhaust gas amount detector, 15... Sulfur dioxide concentration detector, 18... Arithmetic unit, 19... PH detector, 2
5...Air.

Claims (1)

[Claims] 1 Detect a boiler load change, input the detection signal to a computing unit, and operate a regulating valve that supplies air to the slurry in the liquid retaining section of the absorption tower circulation tank when an increase signal of the boiler load amount is detected. While bubbling the slurry in the liquid retaining section with air, each detection signal of the amount of combustion exhaust gas, the sulfur oxide concentration, and the PH value of the slurry in the liquid retaining section of the absorption tower circulation tank is inputted to a computer to supply the required limestone. A limestone-gypsum method flue gas desulfurization device, characterized in that the limestone slurry is supplied into the slurry bubbled with air by calculating the amount and operating a limestone slurry supply amount adjustment valve based on a signal from a computing unit. control method.