JPS5938021B2 - Two-stage electrostatic precipitation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry dust collection method for exhaust gas from a borosilicate glass melting furnace, and particularly to a dry dust collection method suitable for recovering and utilizing boric acid separated and removed from the exhaust gas.

The dust contained in the above exhaust gas contains raw materials such as silica sand, lime, soda, potash, borax, etc., as well as gaseous alkali salts, boric acid, etc., but at the stage of introduction into the dust collector, The temperature of the exhaust gas has decreased to about 260°C.

At this temperature, most of the alkali salts are pulverized, so they can be sufficiently collected using, for example, an electrostatic precipitator.

However, boric acid has a high vapor pressure even at the above temperature, so
It was in a vaporized state and difficult to remove using dry dust collection.

For this reason, when the exhaust gas diffuses into the atmosphere at the exhaust port after passing through the dust collector, it is rapidly cooled and the boric acid is condensed into powder, causing white smoke generation.

In order to prevent such a situation, in some prior art methods, the exhaust gas is first subjected to dry dust collection in a high temperature state, and then the boric acid in a vaporized state is removed by a wet method.

However, in this method, the boric acid and the like are dissolved in the cleaning solution, and a device for separating and removing them is required.

Further, in the above-mentioned conventional technology, expensive boric acid had to be discarded, and a method for collecting dust from the exhaust gas that is effective and appropriate from the viewpoint of resource reuse has been desired.

In addition, in the dry dust collection method, for example, if the exhaust gas is cooled and the vaporized boric acid is condensed into powder, and then electrostatically collected, the generation of white smoke can be prevented, but the collected dust It contains boric acid of intermediate purity, so it is not worth collecting and reusing, and if it is shredded and thrown away, boric acid will contribute to pollution, so it is important to minimize the amount of boric acid in the collected dust. desirable.

The purpose of the present invention is to solve the above-mentioned problems of the prior art, to reliably and selectively separate and remove boric acid from the exhaust gas without using a wet method, and to provide an effective and appropriate dry method from the viewpoint of pollution prevention and resource reuse. Provides a dust collection method.

As a means to achieve the above object, the present invention first converts exhaust gas from a borosilicate glass melting furnace into a high temperature state (approximately 260°
C) is introduced into the first dust collector, and after removing most of the dust contained in the exhaust gas, the exhaust gas is
It is characterized in that after being forcedly cooled to 0° C. or lower, it is introduced into an electric precipitator, which is a second precipitator.

In the above method, a dry type precipitator is naturally used as the first precipitator, and a gravity sedimentation type precipitator, an inertial type precipitator, an electric precipitator, etc. are used depending on the processing conditions.

There are three reasons why the exhaust gas from which most of the dust has been separated and removed in the first dust collector is forcedly cooled to 100° C. or lower.

First, boric acid can be selectively recovered.

That is, when the exhaust gas is forcibly cooled on the inlet side of the first dust collector, boric acid is collected together with other dust, and even if this is collected and used, the purity of the boric acid will decrease. Its utility value is low.

Second, as is clear from various literatures, the vapor pressure of boric acid changes rapidly around 100°C, and a sufficient trapping effect cannot be obtained above 100°C.

The third problem is that boric acid itself has a high electrical resistance value, and even if an attempt is made to collect it with an electrostatic precipitator, a sufficient collection effect cannot be achieved due to the reverse ionization phenomenon.

That is, by keeping the exhaust gas at 100°C or lower, steam and sulfuric acid in the exhaust gas condense and provide moisture, so the electrical resistance value of the exhaust gas becomes relatively small and electrostatic precipitator Create conditions that make it easy to demonstrate performance.

In addition, in the present invention, the reason why an electric precipitator is used as the second precipitator is that when boric acid, which was originally in a gaseous state, is pulverized by rapid cooling, the particles are extremely fine. An electric precipitator is suitable as a dry precipitator for efficiently collecting boric acid particles.An embodiment of the present invention will be described below with reference to the drawings.

In the figure, the flue 1 is a flue for exhaust gas from a borosilicate glass melting furnace, and the exhaust gas passes through the flue 1 to the first
is introduced into an electric precipitator 2, which is a precipitator.

This electric precipitator 2 separates and removes dust mainly composed of alkali salts in the exhaust gas.

An air introduction pipe 4 is connected to the outlet flue 3 of the first electrostatic precipitator 2, and the air is introduced into the flue 3 through the pipe 4, and the temperature of the exhaust gas is cooled to 85°C.

As shown below, the vapor pressure of boric acid depending on the temperature decreases rapidly when the temperature drops below 100°C.

Temperature ('C) 20 43.5 66 79 1
00 128 Vapor pressure (im/Hg) 2 5
16 30 60 242 Therefore, most of the boric acid in the exhaust gas is solidified into powder, and the temperature of the exhaust gas is 85℃.
Since it is below, a part of the vapor in the exhaust gas is condensed, which has the effect of lowering the apparent electrical resistance value of the boric acid particles.

In the second electrostatic precipitator 5, dust mainly composed of boric acid is separated and removed, and the purified exhaust gas is discharged into the atmosphere from a flue 7 via a blower 6.

A comparison of the compositions of the dust collected by the first electrostatic precipitator 2 and the second electrostatic precipitator is as follows.

K2O5i02SO2AS203A1203PbONa
20B203 External 1st dust collector 13.2 tr
37.6 1. Otr 1.7 12.1
13.2 - Second dust collector 4.2 tr
10.8 tr tr tr
3.8 62.5 - As is clear from the above,
The dust collected by the second electrostatic precipitator has high purity boric acid,
It can be fully used for reuse.

However, the purity of the boric acid in the dust collected by the first electrostatic precipitator is relatively low, so there is a problem even if it is discarded as is, or it is discarded after being filtered or treated to prevent pollution. Less is.

In the above embodiment, direct cooling by introducing atmospheric air was used as a method of cooling the exhaust gas, but indirect cooling using a heat exchanger or the like may also be used.

Indirect cooling makes it possible to recover waste heat from exhaust gas,
Since the amount of exhaust gas does not increase, the capacity of the second dust collector at the subsequent stage can be reduced.

As described above, the present invention enables dry dust collection of the exhaust gas from the borosilicate glass melting furnace without producing white smoke, and the dust collected in the second dust collector can be collected and used by folding it. , has great effects from the viewpoint of pollution prevention and resource reuse.

Furthermore, since a wet dust collection method is not used, there is no need to install a water treatment device.

[Brief explanation of drawings]

The attached figure is a schematic system diagram showing one embodiment of the present invention. 1, 3... Flue, 2... First electrostatic precipitator, 4...
Air introduction piping, 5...second electrostatic precipitator.

Claims (1)

[Claims] 1. The exhaust gas from the borosilicate glass melting furnace is first introduced into the first dust collector to remove most of the dust contained in the exhaust gas, and then the exhaust gas is forcibly cooled to below 100°C. A dry dust collection method for exhaust gas from a borosilicate glass melting furnace, which is then introduced into an electrostatic precipitator, which is a second dust collector.