JPH11342314A - Treatment of chloride dust containing-exhaust gas and treating device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely prevent the clogging of a duct and a bag filter without increasing the volume of a duct collector and an exhaust fan and performing of insulation of the duct for preventing condensation. SOLUTION: Chloride containing exhaust gas discharged from a rotary hearth furnace 1 is caused to flow through a water cooling duct 2 to preheat it to temperatures near the boiling point of the chloride and higher than that. It a cooling column 3, cool air is fed to the exhaust gas which has passed through the cooling duct 2 to quickly cool the exhaust gas to temperatures lower than the melting point of the chloride dust to make the chloride dust in a solid phase. The chloride dust which has become in a solid phase is collected by a bag filter of a dust collector through an exhaust duct.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating exhaust gas containing chloride dust, and more particularly to a method and an apparatus for treating exhaust gas containing chloride dust which can effectively prevent clogging of ducts and bag filters. .

[0002]

2. Description of the Related Art The exhaust gas from a rotary hearth furnace for reduction, which aims to reuse iron dust by reducing it, contains Zn originating from charged materials.
This Zn is usually contained in the exhaust gas as dust and becomes ZnO. Further, since chlorine (Cl) is contained in the dust, ZnC12 is generated. ZnCl 2 has a melting point of about 400 ° C. and a boiling point of 700
It is about ° C., and in this temperature range, it exhibits a liquid phase and adheres to the exhaust duct and the bag filter to cause clogging.

[0003] Therefore, conventionally, the 1200
The exhaust gas of about ℃ is led to a cooling tower through a duct lined with refractory material, where it is mixed with cold air to rapidly cool the gaseous exhaust gas to the melting point of dust (ZnC12) or less to form a solid phase. ing. However, in this method, it is necessary to blow a large amount of cold air in order to rapidly cool the high-temperature exhaust gas, and the total amount of the exhaust gas increases, and the capacity of the dust collector and the exhaust fan provided at the subsequent stage becomes excessive. There's a problem. Further, there is also a problem that dust adheres firmly to the inner surface of the duct through which high-temperature exhaust gas flows due to seizure.

In order to suppress an increase in the total amount of exhaust gas, a method of directly spraying water or steam on the exhaust gas in a cooling tower to quench the exhaust gas by the latent heat of vaporization thereof has been attempted. However, ZnC12 in a solid phase is often used. The dust contains deliquescent so that it absorbs and fluidizes water, making it easy to clog ducts and bag filters.In addition, the dew point of exhaust gas is high, so dew forms unless the dust collector and the duct leading to it are kept warm. There's a problem.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art. In order to increase the capacity of a dust collector or an exhaust fan or to perform heat insulation of a duct for preventing dew condensation, an exhaust duct or a bug is prevented. An object of the present invention is to provide a method and an apparatus for treating exhaust gas containing chloride dust, which can completely prevent clogging of a filter.

[0006]

In order to achieve the above object, the method for treating exhaust gas containing chloride dust according to the present invention comprises:
The exhaust gas containing chloride dust is pre-cooled to a temperature close to the boiling point of the chloride dust and higher than the boiling point by heat exchange through a partition wall. It is characterized by rapid cooling to a temperature lower than the melting point of material dust.

[0007] In the method of the present invention, the temperature of the exhaust gas is previously reduced to near the boiling point of chloride dust by heat exchange through the partition before the cold air is mixed. Therefore, even if a large amount of cold air is not supplied as in the related art, the temperature of the exhaust gas quickly drops to a temperature lower than the melting point of chloride dust. As a result, the chloride dust quickly passes through the liquid phase to become a solid phase, thereby preventing clogging of the duct and the like. In this case, since the supply amount of the cool air can be reduced as described above, the capacity of the dust collector and the exhaust fan does not increase more than necessary. Furthermore, unlike the conventional case, water and steam are not directly mixed into the exhaust gas for rapid cooling.
Fluidization of chloride dust is prevented, which also prevents clogging of the duct and the like, and the dew point of the exhaust gas does not rise, so that it is not necessary to heat-protect the dust collector and the duct leading to the dust collector.

[0008] The above processing method can be realized by the following processing apparatus. That is, the apparatus for treating exhaust gas containing chloride dust circulates the exhaust gas containing chloride dust discharged from the industrial furnace (1), and exhausts the exhaust gas to a temperature close to and higher than the boiling point of the chloride dust. A cooling duct (2) for pre-cooling, and a cooling tower (3) for supplying cool air to the exhaust gas passing through the cooling duct (2) and rapidly cooling the exhaust gas to a temperature lower than the melting point of the chloride dust. I have it.

[0009] A heat exchanger (10) utilizing sensible heat of exhaust gas can be provided between the industrial furnace (1) and the cooling duct (2). According to this, the exhaust heat can be effectively used simultaneously with the cooling of the exhaust gas.

[0010] The reference numerals in parentheses indicate the correspondence with specific means described in the embodiment described later.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows an example of a processing apparatus for performing a processing method of the present invention. From the rotary hearth furnace 1 for reducing ironmaking dust, a water-cooled duct 2 is
And extends through the water-cooled duct 2 with ZnO and ZnCl
Exhaust gas containing 2 as dust is distributed. The inner peripheral surface temperature of the water cooling duct 2 is about 100 to 150 ° C.
Exhaust gas flowing out of the rotary hearth furnace 1 at a high temperature of about 200 ° C. radiates heat while flowing through the water cooling duct 2 and is pre-cooled,
When reaching the cooling tower 3, the boiling point of ZnCl2 (about 700 ° C)
The temperature drops to about 750 ° C., which is close to and slightly higher than this.

Cooling air of about 30 ° C. is supplied to the cooling tower 3 by an air duct 7 having an air damper 71 interposed therebetween. Cools rapidly. As a result, ZnCl2 in the exhaust gas quickly passes from the gas phase to the liquid phase to become a solid phase. In this temperature range, ZnO also becomes a solid phase.

The exhaust gas containing the solid phase of ZnO and ZnCl 2 reaches the dust collector 4 via the exhaust duct 8 and is collected and purified by the built-in bag filter.
Through the chimney 6. During this time, ZnO and Zn
Since Cl2 is a dry solid, the exhaust duct 8
Even if it adheres to the bag filter in the dust collector 4, it does not cause clogging or the like.

(Second Embodiment) As shown in FIG. 2, a radiant heat exchanger 10 having a small flow resistance is provided in a duct 9 immediately after exiting from a rotary hearth furnace 1, so that it can be connected to air. Heat exchange may be performed. That is, the air supplied to the heat exchanger 10 is heated by the heat of the exhaust gas discharged from the rotary hearth furnace 1 to be preheated air used in the rotary hearth furnace 1. During this time, the exhaust gas is deprived of heat and its temperature is lowered from about 1200 ° C. when flowing out of the rotary hearth furnace 1 to about 1000 ° C., and the exhaust gas whose temperature has dropped is introduced into the water cooling duct 2 leading to the cooling tower 3. . According to this, the water cooling duct can be shortened, and effective use of exhaust heat can be achieved.

It should be noted that the chloride dust to which the present invention is applied is not limited to dust containing Zn but can be applied to dust containing Pb, for example. Further, in each of the above embodiments, a water-cooled duct was used to lower the exhaust gas temperature to near the boiling point.However, as long as the refrigerant does not directly mix with the exhaust gas and exchanges heat through the partition, the water-cooled duct is limited. Absent.

[0016]

As described above, according to the present invention, it is possible to completely prevent the clogging of the duct and the bag filter due to the dust in the exhaust gas, and to increase the capacity of the dust collector and the exhaust fan and to prevent dew condensation. This eliminates the need for heat-retaining work for the duct, and can realize a significant cost reduction.

[Brief description of the drawings]

FIG. 1 is a system diagram of a processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a system diagram of a processing device according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Rotary hearth furnace, 2 ... Water cooling duct, 3 ... Cooling tower, 4 ... Dust collector, 7 ... Air duct, 8 ... Exhaust duct, 10 ... Heat exchanger.

Claims (3)

[Claims] 1. Exhaust gas containing chloride dust is pre-cooled to a temperature close to and higher than the boiling point of the chloride dust by heat exchange through a partition, and thereafter, cool air is mixed into the exhaust gas. A method for treating an exhaust gas containing chloride dust, wherein the exhaust gas is rapidly cooled to a temperature lower than the melting point of the chloride dust. 2. A cooling duct for pre-cooling exhaust gas containing chloride dust discharged from an industrial furnace to a temperature close to and higher than the boiling point of the chloride dust, and a cooling duct for cooling the exhaust gas. A cooling tower for supplying cool air to the passed exhaust gas to rapidly cool the exhaust gas to a temperature lower than the melting point of the chloride dust, and a cooling tower for treating the exhaust gas containing chloride dust. 3. An apparatus for treating exhaust gas containing chloride dust according to claim 2, wherein a heat exchanger utilizing sensible heat of said exhaust gas is provided between said industrial furnace and said cooling duct.