JPS5836621A - Desulfurizing method for waste gas of pulverized coal firing boiler - Google Patents

Abstract

PURPOSE:To desulfurize the waste gas of pulverized coal firing boilers at high degrees with improved utilization rate of Ca and good economy by blowing the powder of a Ca-base alkali adsorbent into said boilers and using part of the powder of the adsorbent after adsorption of SOx cyclically. CONSTITUTION:The SOx produced by the combustion of pulverized coal in a pulverized coal firing boiler 1 is caused to react with the Ca-base alkali adsorbent supplied through an adsorbent supplying pipe 2 and a transfer pipe 3 for circulating powder in the boiler, whereby the concn. of the SOx in the waste gas is decreased. The waste gas is conducted to a high temp. electric dust precipitator 5 whereby the adsorbent powder and flyash powder in the waste gas are removed. After the gas is passed through a dry type denitrator 6 and an electric preheater 7, the pressure thereof is increased with an induced draft fan 8 and the pressurized gas is discharged through a chimney 10. The powder captured with the precipitator 5 is discharged through a removal pipe 11, and part thereof is blown through a piping 3 into the boiler 1. The remaining part is discharged through a discharging pipe 12 and is used for reclamation of land or for other effective applications.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a dry desulfurization method for exhaust gas from a Yihui pulverized coal-fired boiler. It is about the method.

At present, wet methods are generally used for desulfurization of exhaust gas from pulverized coal-fired boilers, and the limestone-gypsum method in particular has become an established technology. However, this method requires an expensive desulfurization equipment. It is necessary to secure a large amount of water. Wastewater treatment is required. It has drawbacks such as: Moreover, it is expected that securing water will become increasingly difficult and wastewater regulations will become stricter in the future, which is becoming a major problem in promoting new large-capacity pulverized coal-fired boilers. Under these circumstances, the dry method is attracting attention again, and the development of an economical dry desulfurization method is desired.

As one of the dry desulfurization methods, a method of injecting a Ca-based alkaline hydroxide absorbent made of calcium carbonate powder, calcium hydroxide powder, or a mixture thereof into a boiler is conventionally known. However, with this method, as shown in Figure 1,
In order to obtain high desulfurization performance, it is necessary to increase the Ca/S molar ratio (absorbent injection amount mo1/generated SO1 amount mat) (see the solid curve plotting the white circle with circulation ratio = 0), and a large amount of In addition to requiring an absorbent, the Ca utilization rate (
The rate of reaction with SOx (90a) was low (see the broken line curve plotted with white circles), and it was poor in economic efficiency, making it difficult to adopt it in practice. Note that FIG. 1 will be explained in detail later.

As a result of intensive research on the above dry desulfurization technology, the present inventors discovered that the Ca-based alkaline absorbent collected by a dust collector still has SOx absorption ability, and that It was discovered that a Ca-based alkaline absorbent and fly ash could be separated using a device, and an economically and technically superior desulfurization method was invented.

That is, the present invention provides a desulfurization method in which Ca-based alkali absorbent powder is blown into a WI pulverized coal-fired boiler, and then the Ca-based alkali absorbent powder that has absorbed sulfur oxide is collected together with fly ash by a dust collector. A desulfurization method that can increase the Ca utilization rate by blowing a part of the powder collected by this dust collector back into the pulverized coal-fired boiler and recycling the Ca-based alkaline absorbent. This is what we intend to provide. In addition, when the amount of circulation increases, the concentration of soot and dust inside the pulverized coal-fired boiler increases, making it more likely that troubles such as boiler tube wear and blockage will occur. The body is separated into coarse powder with high fly ash content using a classification device.
By separating it into fine powder with low fly ash content and blowing part of the fine powder back into the pulverized coal-fired boiler,
It is also an object of the present invention to provide a desulfurization method that can reduce the amount of fly ash circulation.

Hereinafter, the configuration of the present invention will be explained based on the drawings.

FIG. 1 shows an example of an apparatus for carrying out the method of the invention. Sulfur oxides generated by combustion of pulverized coal in the pulverized coal-fired boiler 1 are transferred to the absorbent powder supply pipe 2. Calcium carbonate powder supplied by circulating powder transfer pipe 3 - hydration power V
It reacts with a Ca-based alkali absorbent made of ium powder or a mixture thereof in the boiler 1, and the concentration of sulfur oxides in the gas is partially reduced. Exhaust gas from one boiler is led to a high-temperature electrostatic precipitator 5 through an exhaust gas flue 4, and powders such as absorbent and fly ash in the exhaust gas are removed.

The exhaust gas from which the powder has been removed is sent to a dry denitrification device6. After passing through the air preheater 7, the pressure is increased by the induction 7-amp 8, and the air is discharged from the chimney 10 through the clean gas flue 9. The powder collected by the high-temperature electrostatic precipitator 5 is extracted from the collected powder extraction pipe 11, a part of which is blown into the boiler 1 again through the circulating powder transfer pipe 6, and the remainder is used as treated powder. The body is extracted through the body extraction pipe 12 and disposed of in a landfill or put to effective use.

Next, another embodiment of the present invention will be described based on FIG. The powder collected by the high-temperature electrostatic precipitator 5 is extracted from the collected powder extraction pipe 11 and guided to a classification device 16 such as a wind classifier, where it is separated into coarse powder with a high fly ash content and fly ash. It is separated into fine powder with low ash content. The fine powder with a low fly ash content was extracted by the fine powder extraction pipe 14, a part of it was blown into the boiler 1 again through the circulating powder transfer pipe 6, and the remaining part was extracted from the coarse powder extraction pipe 15. Together with the coarse powder, it is extracted through the treated powder extraction pipe 12 and disposed of in a landfill or put to effective use. Other configurations are second
This is the same as the case shown in the figure.

Examples and comparative examples will be described below.

Example: Coal having an ash content of 15% by weight and a sulfur content of 1.2% by weight was combusted, slaked lime powder (average particle size 6 μm) was blown into the boiler as an absorbent, and part of the powder collected by the dust collector was blown into the boiler. The desulfurization test was then carried out by circulating the water again. The desulfurization tests were as follows: Ca/S molar ratio 8°, circulation ratio 1.1, no classification, Ca/S molar ratio 8°, circulation ratio 1.1, classification -
〇 a/S molar ratio 3. When the circulation ratio is 5.5 and no classification is performed, the Ca/S molar ratio is 3. This was carried out for the case of classification at a circulation ratio of 5.5. The results are shown in the table below: Test Na8. NcL
k IIJo, 5-N [shown in 1,6.

Note that the Ca/S molar ratio is the ratio of the number of moles of newly supplied calcium hydroxide to the number of moles of sulfur oxide generated from the boiler when calcium hydroxide is not blown into the boiler, and the circulation ratio is the ratio of the number of moles of calcium hydroxide that is newly supplied to the number of moles of sulfur oxide generated from the boiler when calcium hydroxide is not blown into the boiler. The desulfurization rate is the ratio of the number of moles of the compound to the number of moles of newly supplied calcium hydroxide. 10a Utilization rate refers to the proportion of newly supplied calcium hydroxide that reacts with sulfur oxide, and on Kino's side, a wind classifier was used as a classification device, and the diameter of one classification was 10μ. .

Comparative Example The same coal used in the example was burned, and slaked lime powder (average particle size 6μ) was blown into the boiler as an absorbent.
Desulfurization tests were conducted without circulating the powder collected by the dust collector. The results are shown in Test 2 in the following table. In addition, for test ceramics, 1 is the SO in exhaust gas when no absorbent is added.
, concentration and dust concentration at the dust collector inlet.

(The following is a blank space) FIG. 1 is a graph showing the relationship among the Ca/S molar ratio, desulfurization rate, and Ca utilization rate in the above table.

The curve plotting white circles is for circulation ratio = 0 (test N
112), and the curve plotting the half-filled white circle is for the circulation ratio -1,1 (test N11B,
4), and the curve plotting the black circle indicates the circulation ratio = 5
．． In the case of 5 (Tess) No, 5, 6) 0 indicates
As is clear from the table and FIG. 1, the method of the present invention can achieve a high desulfurization rate even if the Ca/S molar ratio is small compared to the conventional method that does not involve circulation, and can utilize Ca. It can be seen that the dust concentration at the entrance of the dust collector can be lowered when classifying with a classifier.

As explained above, according to the method of the present invention.

In addition to the advantages that high desulfurization efficiency can be obtained and no water is required, there is no need for wastewater treatment.

Since the absorbent is used repeatedly, a high Ca utilization rate can be obtained, and there is no need to particularly install a desulfurization device, which has the advantage of being excellent in economical efficiency. Furthermore, when classifying with a classifier, it is possible to reduce the soot and dust concentration within one boiler.

[Brief explanation of the drawing]

Figure 1 shows the results of Examples and Comparative Examples.
/S molar ratio, desulfurization rate, and Ca utilization rate graph '97
．． FIG. 2 is a systematic explanatory diagram showing one example of the apparatus for implementing the method of the present invention, and FIG. 3 is a systematic explanatory diagram showing another example of the apparatus for implementing the method of the present invention. 1...Pulverized coal-fired boiler, 2...Absorbent powder supply pipe. 3... Circulating powder transfer pipe, 4... Exhaust gas flue, 5...
Electrostatic precipitator, 6... Dry denitrification device, 7... Air preheater. 8... Induction fan, 9... Clean gas flue, 10...
chimney. 11... Collection powder extraction pipe, 12... Processed powder extraction pipe. 16...Classifying device-14...Fine powder removal pipe, 15...
Coarse powder removal pipe

Claims (1)

[Claims] Desulfurization in which Ca-based alkali absorbent powder is injected into a 1 gjt powder-fired boiler for 7 hours, and then the Ca-based alkali absorbent powder that has absorbed sulfur oxide is collected together with fly ash in a dust collector. A method for desulfurizing exhaust gas from a pulverized coal-fired boiler, characterized in that a part of the powder collected by the dust collector is blown into the pulverized coal-fired boiler again. 2. In a desulfurization method in which Ca-based alkali absorbent powder is injected into a pulverized coal-fired boiler and then the Ca-based alkali absorbent powder that has absorbed sulfur oxide is collected together with fly ash by a dust collector, this dust collector A method for desulfurizing exhaust gas from a pulverized coal-fired boiler, characterized in that the collected powder is separated into coarse powder and fine powder by a classifier, and a part of the fine powder is blown into the pulverized coal-fired boiler again.