JP3177160B2 - Operating method of back pressure collapsible bag filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a bag filter, and more particularly, to a so-called counter pressure collapse type bag filter for collecting dust contained in a high-temperature gas such as blast furnace gas. Get involved.

[0002]

2. Description of the Related Art Gas generated from a blast furnace (hereinafter, referred to as blast furnace gas or B gas) is used as a fuel in a hot blast furnace, a coke oven, a billet heating furnace, a boiler, etc. in an ironworks, but is discharged from the blast furnace. 10-30 g as it is
/ Nm ³ of dust. Therefore, it is necessary to remove and clean to a dust content that does not interfere with use in the various furnaces and devices described above. Conventionally, as this gas purifying device, a device in which a venturi scrubber or a dry electric precipitator is arranged in series with a blast furnace gas discharge line in a sedimentation chamber type dust collector utilizing inertia of a gas flow has been used. .

[0003] Of these, dry electric dust collectors require too much initial investment at the time of construction, and when dust generated by the operation of blowing high-pulverized coal into a blast furnace in recent years, sufficient dust collection efficiency cannot be obtained. When wet dust arrives, there is a problem that it becomes difficult to separate collected dust from the dust collecting electrode. In addition, the enlargement of blast furnaces and the operation of high pressure became widespread,
In particular, at the present time when the furnace top pressure power generation has been implemented, it has become necessary to reduce the dust content as much as possible and to maintain the heat energy of the high-temperature gas at a high level. Therefore, instead of the electric dust collector and the wet-type venturi scrubber, a so-called bag-filter type dust collector having excellent dust removing performance and high dust removing efficiency has been adopted.

[0004] This bag-filter type dust collector (hereinafter referred to as "the dust collector")
The use of bags and filters) has certainly improved dust removal efficiency and performance. However, the problem of poor separation of wet dust exists in a different form from the electrostatic precipitator. It is necessary that the bag filter collects and periodically removes dust adhering to the filter cloth so that the dust does not excessively increase. Japanese Patent Laid-Open No. 57-20
No. 7523 discloses a method of vibrating a filter cloth by mechanical means. As shown in FIG. 2 (a), a reverse pressure is applied to the gas flow direction by air using a separate blower.
The so-called counter pressure collapse method (hereinafter referred to as counter pressure) described in JP-A-207522 and the method of spraying a pulse jet of high-pressure air from a nozzle (hereinafter referred to as pulse method) shown in FIG. 2B are generally used. A counter pressure method or a pulse method is frequently used for dust removal of blast furnace gas.

[0005] By the way, collected by a bag filter,
Conventionally, when the dust adhering to the filter cloth is peeled off by the reverse pressure, the blower has been operated with a flow rate-pressure characteristic uniquely determined. However, when the flow rate-pressure characteristic is uniquely defined, if the filter cloth is clogged, the pressure loss of the filter cloth becomes too large when applying a counter pressure, and there is a problem that the filter cloth itself is damaged. That is, the filter cloth used in the back-pressure bag filter generally has a thin porous polytetrafluoroethylene (hereinafter referred to as PTFE) membrane adhered to the filtration side of the woven cloth with an adhesive.
Since the direction of the reverse pressure is opposite to the direction of filtration, a force acts in the direction of peeling off the adhered film. When the film comes off, the woven fabric itself does not have the ability to collect dust and easily breaks.

Further, if the blower is operated with flow-pressure characteristics such that the back pressure applied to the filter cloth does not become excessive when clogged, dust can be removed due to the structure of this type of bag filter. There was also the problem of disappearing. That is, one type of bag filter of this type is formed by collecting four to six rooms (sections) provided with a large number of filter cloths, and switching between collecting dust and removing the dust by back pressure for each section. This is done at the same time. for that reason,
In some cases, the pressure raising (back pressure) capability of the blower becomes lower than the filter cloth differential pressure of the section performing the filtration, and the dust cannot be removed at all. This is because the filter cloth is durable against the differential pressure in the filtration direction (maximum allowable differential pressure during filtration: 400 m).
mAq) and weak against differential pressure in the reverse pressure direction (maximum allowable differential pressure at the time of reverse pressure: up to 200 mmAq). That is, if the filter cloth is clogged at the time of the reverse pressure, the differential pressure of the bag / filter immediately exceeds 200 mmAq, and the filter becomes unusable.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention has been developed to operate a collapsed bag filter capable of always smoothly removing dust when a reverse pressure is applied to the filter cloth to which dust is attached by air. It is intended to provide a way.

[0008]

Means for Solving the Problems The inventor of the present invention has made intensive studies to achieve the above object, and has set a maximum pressure increase capacity greater than a maximum allowable filtration pressure difference and a maximum allowable back pressure difference Pressure + the maximum permissible filtration differential pressure), and then focused on adjusting the differential pressure of the section during back pressure. That is, in the present invention, when dust adhering to the filter cloth of the bag / filter is blown back into the dust collecting chamber by applying a back pressure with air, the maximum pressure increasing capability of the blower for generating the back pressure has a maximum allowable filtration time difference of the filter cloth. Select a pressure greater than the pressure and less than (maximum allowable reverse pressure differential pressure + maximum allowable filtration differential pressure), and constantly measure the differential pressure generated in the filter cloth when the reverse pressure is applied. A method of operating a back pressure collapse type bag filter characterized by controlling the number of revolutions of a back pressure generating blower so as to be not more than a value.

Further, the present invention is a method of operating a back pressure collapse type bag filter characterized by controlling an opening degree of a damper attached to a back pressure generating blower instead of the rotation speed. Further, the present invention provides a filter fabric having a strength of 80.
kg / (5 cm width), a polytetrafluoroethylene membrane having an infinite number of pores having an average diameter of 2 μm is thermally fused to a surface layer on the filtration surface side of a felt base having a heat shrinkage of 0.5% or less. A method of operating a back pressure collapse type bag filter characterized by the fact that the target value when the back pressure is applied is set to 300 mmAq. It is also a driving method.

According to the present invention, the differential pressure in the filter cloth chamber when dust is removed is constantly monitored and maintained at the target value, so that the following effects can be expected. (1) Prevention of filter cloth damage due to excessive back pressure (2) Prevention of filter cloth clogging due to reduction of back flow (3) Ensuring stable dust peeling ability.

By employing a new filter cloth, the maximum allowable differential pressure at the time of back pressure can be increased to 300 mmAq, and by setting it to a target value, the above-mentioned effect can be further remarkable.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a flow of equipment for implementing a method of operating a back pressure collapse type bag filter according to the present invention. First, there are four filter cloth chambers 6 (No. 1 to No. 4) in which a large number of bag-shaped filter cloths 11 are arranged.
There, for ease of explanation, No. No. 3 filters and collects dust. 4 is assumed that dust 9 adhered to the filter cloth 11 is removed to the dust collecting chamber 10 by a reverse pressure.

The dust 9 is filtered and collected by using a dust-containing high-temperature gas as an untreated gas 8 via a dust collection chamber 10 and
o. The filtration is performed by filtering through the bag-like filter cloth 11 in the filter cloth chamber 6. At that time, most of the collected dust 9 is collected in the dust collection chamber 10.
And some of them adhere to the filter cloth 11. The processing gas 13 that has passed through the filter cloth 11 flows out of the system through the exhaust fan 12 as shown by the arrow.

On the other hand, the dusting off of the attached dust 9 to the dust collection chamber 10 is performed, for example, in No. As shown by 4 filter cloth chamber 6, the air is blown by the blower 1 for generating reverse pressure in a direction opposite to the filtration direction, and thereby dust 9 attached from the outside to the inside of the filter cloth 11 is dropped. Therefore, since the bag filter performs the filtration and the dust 9 removal at the same time, the exhaust fan 12 and the blower 1 for generating the back pressure are constantly operated.

According to the present invention, the blower 1 for generating a back pressure has a maximum pressurizing capacity which is larger than the maximum permissible differential pressure during filtration of the filter cloth and smaller than (the maximum permissible differential pressure at the time of the reverse pressure + the maximum permissible differential pressure at the time of the filtration). It is necessary to make a selection. In other words, a blower that satisfies the condition of the air volume-pressure characteristic is required for both the prevention of filter cloth breakage and the stable back pressure.
The woven fabric-based filter cloth currently in use has a maximum allowable differential pressure at the time of back pressure of 200 mmAq and a maximum allowable differential pressure at the time of filtration of 400 mm.
mmAq, and thus the target value at the time of back pressure in this case is 200 mmAq.

Next, in the present invention, the maximum allowable differential pressure at the time of back pressure is set to a target value so that the base and the PTFE film do not peel off when the filter cloth 11 is at a reverse pressure. To control. For this reason, a differential pressure measuring sensor 14 is attached to the filter cloth chamber 6, the value of which is constantly measured, and can be compared and calculated with a target value stored in the controller 4 via the differential pressure transmitter 5. . The control amount obtained as a result is obtained by changing the rotation speed of the blower 1 for generating the back pressure or by changing the suction control damper 3 (hereinafter, damper).
It is specifically adjusted by changing the opening degree. Normally, the flow rate-pressure characteristic curve of the back pressure generating blower usually has a surging occurrence area on the upper right side. However, when the damper 3 is squeezed, this area decreases, so that the filter cloth 11 Even when clogging occurs and the amount of air for back pressure decreases, generation of surging can be suppressed.

[0017] According to the present onset Akira, filter cloth life, what was a conventional one year, equal to or more than 3 years. In addition, the dust recovery rate was 99.99%, which was much better than the conventional operation method. In the present invention, as the control means other than the change of the opening degree of the damper and the rotation speed of the blower, it is possible to adopt an inlet / vane control which can further reduce the power consumption of the blower when the throttle is squeezed.

Further, the present invention includes a case where the type of the filter cloth 11 used is changed. The filter cloth 11
Converts a conventional woven fabric into a felt base having a strength of 80 kg / (5 cm width) and a heat shrinkage of 0.5% or less, and PTFE having innumerable pores having an average diameter of 2 μm in the surface layer on the filtration surface side. The film was manufactured by bonding by heat fusion.

Using this filter cloth 11, a counter pressure differential pressure of 200
The results obtained by operating the bag filter while changing the mmAq to 1000 mmAq are represented by the timing at which the PTFE film starts peeling, and are summarized in Table 1. From Table 1, the differential pressure at the time of back pressure was 3
When the rotation speed of the damper 3 or the blower 1 is controlled to be equal to or less than 00 mmAq, it is clear that the film does not peel even if dust removal exceeds 60,000 times (corresponding to use for about 3 years). Becomes Therefore, in the present invention,
The target value at the time of back pressure when using this filter cloth is 300 mm
Aq. In Table 1, if the target value of the back pressure is assumed to be 400 or 1000 mmAq, the peeling of the PTFE film is considerably accelerated.

[0020]

[Table 1]

[0021]

As described above, according to the present invention, when the dust contained in the high-temperature gas is treated by the back pressure collapsible bag filter, the dust collection efficiency can be improved without frequently changing the filter cloth. High smooth driving has become possible. In addition, a secondary effect of suppressing the power consumption of the blower for generating the back pressure to a minimum was obtained.

[Brief description of the drawings]

FIG. 1 is a flow chart showing an apparatus for implementing a method of operating a back pressure collapsible bag filter according to the present invention.

FIGS. 2A and 2B are diagrams for explaining a dust removal method of a bag filter, wherein FIG. 2A is a reverse pressure collapse method and FIG. 2B is a pulse jet injection method of high pressure air.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 back pressure generating blower 2 motor of above blower 3 motor of suction damper 4 controller 5 differential pressure transmitter 6 filter cloth chamber 7 suction damper (damper) 8 untreated gas 9 dust 10 dust collection chamber 11 filter cloth 12 exhaust Blower 13 Process gas 14 Solenoid valve 15 High pressure air piping

Claims (4)

(57) [Claims] When the dust adhering to the filter cloth of the bag / filter is blown back into the dust collecting chamber by applying a back pressure to the air, the blower for generating the back pressure has a maximum pressurizing capacity, and a maximum permissible differential pressure during filtration of the filter cloth. Select a larger one and smaller than (maximum allowable reverse pressure differential pressure + maximum allowable filtration differential pressure)
A reverse pressure collaps type bag characterized by constantly measuring the differential pressure generated in the filter cloth when a reverse pressure is applied, and controlling the rotation speed of the blower for generating the reverse pressure so that the measured value becomes equal to or less than the target value. How to operate the filter. 2. A method of operating a back pressure collapse type bag filter according to claim 1, wherein an opening degree of a damper attached to the back pressure generating blower is controlled instead of the rotation speed. 3. The filter cloth has a strength of 80 kg / (5 cm).
Width), and a polytetrafluoroethylene membrane having an infinite number of pores with an average diameter of 2 μm is thermally fused to the surface layer on the filtration surface side of the felt base having a characteristic of a heat shrinkage of 0.5% or less. 3. The method for operating a back-pressure collapsible bag filter according to claim 1, wherein: 4. A target value when the above-mentioned back pressure is applied is 300 m.
The method for operating a back pressure collapse type bag / filter according to claim 3, wherein the value is mAq.