JPH08173734A - Method for forming precoat layer of bag filter - Google Patents

Abstract

PURPOSE: To carry out the neutralization of harmful acidic gas and the filtration of soot and dust by passing combustion gas after a precoat layer being formed in a short time by conducting a brushing-off operation by a total unit dust collection mechanism and supplying a chemical reagent simultaneously when brushing-off conditions are met. CONSTITUTION: Whether brushing-off conditions are met or not is judged by a pressure difference and an average concentration per unit time. After a pure gas damper 55 being closed by the command of a controller 8, a pulse jet air current is jetted into filter cloth by a brushing device 54 to backflow pure gas 22 to carry out a brushing-off operation almost simultaneously by a total unit dust collection mechanism. Next, the damper 55 is opened, combustion gas is introduced, a powder pump 93 is actuated, a chemical reagent 91 is introduced into a flue 4 to be mixed with the combustion gas to make mixed gas 23. The gas 23 reaches an initial adhesion layer to form a precoat layer, and then the supply of the reagent 91 is interrupted until the next brushing-off operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bag filter device for separating and removing or recovering acidic harmful gas and dust, suspended matter and the like from a gas stream.

[0002]

2. Description of the Related Art Currently, the most widely used type of bag filter device in practical use is a filter cloth in which a combustion gas is accompanied by a chemical agent for neutralizing and filtering acid gas. It is a system that removes the dust layer consisting of chemicals and soot and dust accumulated on the filter cloth by adhering it on the top of the filter cloth as the operation continues, and using a pulse jet method, a multi-chamber structure applied to a refuse incinerator. This type of method will be described as a typical example of the prior art.

FIG. 8 is a diagram showing an outline of a bag filter device which has been conventionally used.

In FIG. 8, a high temperature combustion gas containing acidic harmful gas and dust produced in an incinerator (not shown) is cooled by a gas cooling device (not shown) and then enters the pre-absorption reaction section a. Inside the front-stage absorption reaction section a, a supply section b for injecting a drug that absorbs acidic harmful gas is installed.

The medicine is stored in the medicine storage tank c, cut out by a fixed quantity supply device d installed in the lower portion of the medicine storage tank c, and pneumatically transported to the supply section b by a blower e. .

Inside the pre-absorption reaction section a, the chemical continuously supplied from the supply section b reacts with the acidic harmful gas in the combustion gas to some extent, but most of the chemical remains unreacted in the bag filter device. Enter in f.

That is, the combustion gas entering the bag filter device f contains a part of the reaction products and most of the unreacted chemicals together with the acidic harmful gas and dust generated in the incinerator. .

The soot and dust in the combustion gas and the reaction product and the unreacted chemical are contained in the filter chamber f1 of a plurality of unit dust collecting mechanisms (only one chamber is shown in the figure) constituting the multi-chamber bag filter device f. It is filtered by a plurality of suspended filter cloths f2, adheres to the surface of the filter cloth f2 to form a dust layer, and gradually grows.

On the other hand, the acidic harmful gas contained in the combustion gas causes a post-absorption reaction with the unreacted drug in the dust layer,
Combining with the above-described filtering work, the combustion gas that has passed through the filter cloth portion becomes clean gas, and the draft fan g is drawn from the clean gas chamber f3.
Through the chimney h to the atmosphere.

When the above-mentioned operation is continued, the air flow resistance of the dust layer gradually increases due to the accumulation of chemicals and soot and dust that continue to fly, making it difficult for the combustion gas to pass through.

Therefore, for each row of the plurality of filter cloths f2 constituting the plurality of unit dust collecting mechanisms, the controller i gives a command in accordance with a fixed order and interval to the gas from the blow-off device j while passing the gas through. A common measure is to spray a jet stream to separate the dust layer.

In addition, the differential pressure detector k detects the differential pressure between the inside and outside of the filter cloth f2.
If the differential pressure exceeds the set value, the same as above.
There is also a method of starting intermittent withdrawal for each row of a plurality of filter cloths f2. In any case, the dust that has been separated and dropped, that is, collected ash, is discharged from the hopper f4 to the outside by the discharging device f5. It is done like this.

Further, the concentration of acidic harmful gas at the outlet of the clean gas chamber f3 may be detected by the analyzer m, and the amount of medicine supplied by the constant quantity supply device d may be adjusted by a command from the control device i.

[0014]

However, according to the above-mentioned conventional method, since the main force of neutralizing the acidic gas and filtering the dust is the dust layer formed by the continuously flying chemicals and dust, the bag filter device f is used. The processing performance of will gradually improve over time during operation.

Therefore, the unit dust collecting mechanism immediately after the removal is
Not only the dust layer is not formed, the neutralization / filtration capability is not provided, but also the ventilation resistance is low, so that a large amount of combustion gas flows in and a large amount of untreated gas is discharged.

That is, due to a partial lack of processing capacity, the processing capacity of the bag filter device f as a whole is lowered, causing pollution.
It was a general measure to continue spraying a large amount of chemicals such as 5 to form a dust layer at an early stage.

As a result, the increase of the dust layer due to the unreacted chemical agent is promoted, the air flow resistance is increased quickly, and the interval for removing the dust is shortened to shorten the life of the filter cloth f2.

The filtration rate on the surface of the filter cloth f2 is
Generally, since the flow velocity of gas in the flue is extremely slow, about 1/1000, when the amount of combustion gas decreases, a large amount of the entrained chemical becomes stalled as soon as it flows into the filtration chamber f1 and the induced draft fan is introduced. Even if suctioned by g, a part of the gas may separate from the combustion gas and fall into the hopper f4 before reaching the surface of the filter cloth f2.

Due to the above-mentioned excessive supply and the above-mentioned drop phenomenon,
Not only will drug costs increase, but the amount of collected ash (exhaust ash) designated as “specially controlled waste” will increase due to the inclusion of harmful substances such as heavy metals and dioxins. It was causing an increase.

Further, in the case of FIG. 8 in which the front absorption reaction section a is placed in advance in order to promote the neutralization reaction of the drug, although the amount of the drug used and the amount of ash discharged are reduced, the installation area is also increased. There was a problem that the equipment cost was high.

Further, since the stripping operation is carried out in the passing gas, the neutralized reaction stripped ash is re-scattered and re-attached to the surface of the filter cloth f2 to reduce the treatment efficiency and shorten the stripping interval. There was also the problem of bringing it.

Therefore, in order to solve these problems, a precoat type bag filter device in which a precoat layer is formed on the surface of the filter cloth before the filtration work is used, and its control method is as follows. Applicant's "Bag filter device control method (Japanese Patent Laid-Open No. 5-123515)"
(Hereinafter referred to as a prior application) has been proposed.

The outline of the prior application is shown in FIG. 9 below. The same members as those of the bag filter device described above are designated by the same reference numerals, and description thereof will be omitted.

This bag filter device f is also a multi-chamber type and is composed of a plurality of unit dust collecting mechanisms (only one chamber is shown in the figure), and the same as the above-mentioned one according to a predetermined system by the control device i. Perform drop-off and discharge operations.

However, the start of the removal of the first unit dust collection mechanism is also the time when both the internal and external differential pressure of the filter cloth f2 and the concentration of the acidic harmful gas exceed the set values, that is, when the neutralization reaction is completed, and each unit collection is started. After closing the damper s installed for each dust mechanism, all the filter cloth f2 rows in the mechanism are continuously blown off.

After the discharging operation is completed, the control valve v exclusively for the unit dust collecting mechanism is opened, the medicine is fed from the medicine storage tank c and blown into the hopper f4, and the surface of the filter cloth f2 in the filtration chamber f1 is discharged. After forming the precoat layer, the damper s is opened to return to the normal filtration operation, the next unit dust collecting mechanism is removed, and then the precoat layer forming operation is performed.

By the above-mentioned operation, since the precoat layer of the chemical is formed on the surface of the filter cloth f2 for each unit dust collecting mechanism from the beginning, the deterioration of the processing capacity immediately after the cleaning is not caused, and the pre-stage absorption. Even if the reaction part a is not installed, high efficiency can be constantly exhibited.

Further, since the precoat layer formed after the neutralization reaction is completed and the dust layer adhering thereto are removed, an increase in ash discharged due to the unreacted drug can be prevented, and it is not necessary to excessively supply the drug. Therefore, the increase rate of the ventilation resistance is reduced, and the cleaning interval is widened, so that the life of the filter cloth f2 can be extended.

However, since the drug transportation is not an exhaust gas entrainment method by blowing a flue but a method of directly air-feeding into each unit dust collecting mechanism, the apparatus similar to the conventional method lacks the transportation capacity, and the transportation is not performed. It was necessary to increase the amount of air used and the pressure, and to increase the amount of air blown into the drug accumulation site, which resulted in an unnecessary increase in the amount of exhaust gas.

Further, the low-temperature air for drug transport is blown directly into the hopper f4 of each unit dust collecting mechanism, and is accompanied by the combustion gas blown into the hopper f4 and rises to the filtration chamber f1. It cannot be mixed well, and the air reaches the surface of the filter cloth f2 without raising the temperature so much.

Therefore, the portion where the low temperature air is predominant causes the moisture in the medium temperature combustion gas to condense to fix the drug to the filter cloth f2, resulting in destabilization of the processing performance and increase in the number of times of removal. However, the service life of the filter cloth f2 was shortened.

[0032]

A method of forming a precoat layer for a bag filter device according to the present invention has a plurality of unit dust collecting mechanisms and forms a precoat layer on the surface of a filter cloth in advance before performing a filtering operation. A method for forming a precoat layer of an apparatus, wherein the operation of removing the precoat layer is performed at substantially the same time in all the unit dust collecting mechanisms, and the operation of forming the precoat layer is performed at the same time in all the unit dust collecting mechanisms, and the next time the removal is performed. The drug is not supplied until the operation.

[0033]

[Function] When the cleaning condition is reached, the combustion gas flowing into each unit dust collecting mechanism constituting the bag filter device is shut off and discharged, and this cleaning operation is carried out by all unit dust collecting mechanisms. At the same time, the chemicals are supplied to the entire filter cloth in the bag filter device to form the precoat layer in a short time, and then the combustion gas is passed to neutralize the contained acidic harmful gas and filter the dust.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a bag filter device in which the method for forming a precoat layer of the bag filter device according to the present invention is implemented.

In FIG. 1, reference numeral 1 is a gas cooling facility for cooling high-temperature combustion gas containing acidic harmful gas and dust generated in an incinerator (not shown), and the cooled intermediate-temperature combustion gas 21 is an induced draft fan 3 Is sucked by and passes through the main flue 4 and the branch flue 41, and individually flows into the plurality of unit dust collecting mechanisms constituting the bag filter device 5.

Each of these unit dust collecting mechanisms has a plurality of filter cloths 6.
A discharge chamber 53 and a hopper chamber 52 connected to the lower side of the filtration chamber 51, and a discharge device 54 inside and a clean gas damper 55 outside. A clean gas chamber 56 is provided.

The plurality of clean gas dampers 55 are connected to the induction fan 3 and a chimney (not shown) via the branch duct 71 and the common clean gas duct 7.

In the clean gas duct 7, an acidic and harmful gas concentration meter 81, a clean gas flow meter 82, and a bag filter device 5 are provided.
A differential pressure gauge 83 for measuring the differential pressure at the inlet and outlet of the device is provided, and each of the measuring instruments 81, 82, and 83 is connected to a control device 8 including various control instruments in addition to the timer device 84.

Reference numeral 9 is a harmful gas removing device, which is a chemical storage tank 92 for storing a chemical 91 for neutralizing acidic harmful gas, and a variable-operable powder pump 93 for discharging and transporting the chemical 91.
The medicine transport pipe 94 is connected to the middle of the flue 4.

Next, the operation control procedure when the precoat layer forming method of the present invention is carried out by the bag filter device having the above-described structure will be described from the precoat layer forming operation to the normal "acidic harmful gas neutralization and dust filtration". Each operation from the operation (hereinafter, simply referred to as a filtration operation) to the precoat layer forming operation after the removing operation is described.

FIG. 2 shows the state of adhesion on the surface of the filter cloth 6 during the filtering operation, FIG. 3 shows the procedure of the precoat layer forming operation, and FIG. 4 shows the procedure of the filtering operation and the removing operation.

First, the precoat layer forming operation is shown in FIG.
It will be described with reference to FIGS.

In step S1, when all the clean gas dampers 55 attached to the plurality of unit dust collecting mechanisms are opened, the medium-temperature combustion gas 21 containing acidic harmful gas and dust passes through the flue 4 and branches. It flows into each unit dust collecting mechanism of the bag filter device 5 via the flue 41, rises in the hopper chamber 52, and reaches the surfaces of the plurality of filter cloths 6 suspended in the filter chamber 51.

At the beginning of operation, the outer surface of the filter cloth 6 is sprayed with the chemical agent 91 in advance to form a bridge with the bulky yarn portion of the filter cloth body 61, so that the filter cloth 6 is not peeled off even if the following wiping operation is performed. It is covered with the initial adhesion layer 62 (see FIG. 2).

Here, the combustion gas 2 reaching the surface of the filter cloth 6
1 passes through the above-mentioned initial adhesion layer 62 and the filter cloth main body 61 (step S2) and is filtered to become the clean gas 22, and the clean gas chamber 56, the clean gas damper 55, and the branch duct 71.
Through the clean gas duct 7.

Therefore, the flow rate of the clean gas 22 is measured by the clean gas flowmeter 82 arranged in the clean gas duct 7 (step S3), and whether the flow rate is equal to or more than the amount (set value) sufficient to transport the medicine 91. If it is sufficient, the process proceeds to step S5, and if it is within the set value in step S4, in step S6, some of the clean gas dampers 55 among the plurality of unit dust collecting mechanisms are turned on. Block and return to step S3.

In step S5, the combustion gas 21 flows into each unit dust collecting mechanism in which the clean gas damper 55 is opened.

Then, in step S7, the powder pump 93 is activated to cut out the medicine 91 from the medicine storage tank 92 and send it into the flue 4 via the medicine transport pipe 94. This makes the drug 91
Is mixed with the medium-temperature combustion gas 21 to become a mixed gas 23, which is stirred and heated in the flue 4 and enters each unit dust collecting mechanism to reach the surface of the initial adhesion layer 62 of each filter cloth 6. (Step S8).

If this operation is continued, the mixed gas 23 becomes
It reaches the surface of the initial adhesion layer 62 in a dry state in which moisture is not condensed, and is filtered, and becomes a drug layer containing a small amount of dust and particles and grows to form the precoat layer 63 (step S9).

Next, in step S10, it is determined whether or not the precoat layer is formed on all the unit dust collecting mechanisms. This determination is made by the powder pump 9 corresponding to the delivery amount of the chemical agent 91 which is set in advance from the treatment gas amount, the acid harmful gas removal rate, and the like.
The operation time of No. 3 is measured by the timer device 84, and it is considered that the precoat layer is formed on all the unit dust collecting mechanisms when this time has elapsed. When a part of the clean gas damper 55 is closed in step S6, the situation is set in consideration of this situation.

When the precoat layer 63 is formed by all the dust collecting mechanisms in this way, the process proceeds to step S11.
The powder pump 93 is stopped.

Next, the filtration operation and the removal operation performed after the above-mentioned precoat layer forming operation will be described with reference to FIGS. 1, 2 and 4.

Filter cloth 6 on which the above-mentioned precoat layer formation is completed
The normal filtration work is performed by the combustion gas 21 passing through (step S12). Where the combustion gas 21
The soot and dust mixed therein are filtered and deposited on the surface of the precoat layer 63 to form the dust layer 64, and the acidic harmful gas also contained causes a neutralization reaction with the chemical agent 91 forming the precoat layer 63. (Step S13) It becomes neutral gas. That is, by passing through the filter cloth 6, the combustion gas 21 becomes the clean gas 22 and is discharged into the clean gas chamber 56.

If this ventilation gas is continued, the dust layer 64 gradually grows to increase the ventilation resistance of the combustion gas 21 and increase the load on the induction fan 3.

Therefore, the differential pressure gauge 83 detects the differential pressure before and after the bag filter device 5 (step S14), and compares whether the unit time average value of the differential pressure is within the set value (step S15). If it exceeds, the process proceeds to step S18, and if it is lower, the process goes to step S17 described below.

At the same time, the acidic harmful gas concentration meter 81
The unit time average concentration of the clean gas 22 is detected (step S16) and compared with the set value (step S17). If the concentration is low, the process returns to step S14 to continue the operation, but if it is high, the process proceeds to the next step S18.

Although not shown, in step S17, the density exceeds the set value, but in step S14
When there is a margin in the differential pressure due to, the powder pump 93 may be activated to additionally supply the chemical agent 91 to restore the neutralization ability, and the filtration operation may be continued.

Next, in step S18, it is judged whether or not the discharge condition is satisfied, that is, both the differential pressure and the unit time average value of the concentration exceed the set values,
When the removal condition is satisfied, the following removal operation is performed in order from the first unit dust collecting mechanism to the last unit dust collecting mechanism in accordance with a preset order by a command from the control device 8.

More specifically, first, after closing the clean gas damper 55 of the head unit dust collecting mechanism (step S1)
9), the jetting device 54 injects a pulse jet stream into the filter cloth 6 to cause the clean gas 22 to flow back into the filter cloth 6, thereby removing the precoat layer 63 and the dust layer 64 from the surface of the initial adhesion layer 62. Peel off (step S2
0). At this time, the clean gas damper 55 is closed,
Since the combustion gas 21 does not flow in, the separated ash falls into the hopper chamber 52 without being scattered again.

The exfoliated ash (collected ash) that has fallen is discharged by the discharge device 53.
By discharging the clean gas damper 55 of the top unit dust collecting mechanism while discharging from the outside (step S2
1), the top unit dust collecting mechanism is in the initial gas passing state (step S22).

Subsequently, the variable speed powder pump 93 is operated at a low speed to reduce the supply of the medicine 91 (step S2).
3) Then, in the unit dust collecting mechanism of the next stage, the wiping operation is performed in the same manner as in steps S19 to S23 described above (step S24), and thereafter, the wiping operation of the unit dust collecting mechanism is performed in the same manner (step S25). When the removal of all the dust collecting mechanisms in operation is completed (step S26), the process returns to step S3 described above, and the entire amount precoat forming operation is performed.

Here, the above-mentioned medicine amount reducing operation is a means for reducing the waste of discharging the medicine adhering to the unit dust collecting mechanism.

In this example, it is explained that each operation described above is compared with the detected value from the measuring instrument and the command is issued from the control device 8. However, when the operation is stable, the operation is performed by the measuring instrument. Instead of the control, the set period control by the timer device 84 may be performed, and each measuring instrument may be for alarm.

The chemicals 91 are supplied by the powder pump 93.
However, when the effect of raising the temperature of the chemicals and the carrier air by the combustion gas 21 is sufficiently obtained,
Instead of the powder pump 93, a conventional blower blower system may be adopted. [Comparison of Conventional Method, Prior Application Method and Present Invention Method] FIG. 5 is a diagram comparing the conventional method shown in the upper stage with the prior application method shown in the middle stage and the present application method shown in the lower stage. The chemical supply state (shaded area) and the stripping operation (black bar area) are shown, and the upper half shows the transition of the neutralization reaction rate average value of the chemical layers on all the filter cloths during the filtration operation. In addition, the numbers marked with a circle in the upper and middle rows indicate the number of each unit dust collecting mechanism in the case of the 6-chamber type.

Here, when the precoat layer is formed, in the conventional method, the chemical is continuously blown into the flue, and in the prior application method, the chemical injection is performed after the disinfection for each unit dust collecting mechanism. In the present application, all devices are supplied at once in the flue, whereas air supply is used. Further, in the method of the present application,
When the amount of gas is less than the specified value, the number of unit dust collecting mechanisms for supplying the drug is reduced and the precoat layer is formed, so that the drug adhesion efficiency can be improved.

The conventional method has a drawback that the number of times of the cleaning operation is extremely large because the cleaning operation is continuously performed for each row of the filter cloth group. In the prior application method, each unit dust collecting mechanism is used. The method of the present application is different from that of the present invention, in which all devices are removed in a series of operations.

Further, the neutralization reaction rate of the chemical in the whole filter cloth is equivalent to 3 to 5 in the conventional method, which is an excessive supply, so that the differential pressure increases rapidly, resulting in a short time. Inevitably about 30%,
The prior application method has a neutralization reaction rate of 10 for each unit dust collection mechanism.
Although it rises to almost 0%, it will be nearly 50% as a whole in order to pay off for each unit dust collection mechanism. On the other hand, in the method of the present application, all devices are removed at the same time,
In order to pre-coat all at once, the shape will rise to the right and approach 100%. [Experimental Example] FIGS. 6 and 7 show an example of the experimental results of the removal, precoat layer formation and filtration operations according to the method of the present invention.

HCl inlet concentration is 450 to 600 ppm
Occasionally, under the condition that the outlet concentration is reduced to 20 ppm or less, the cleaning is performed about 6 minutes after the start of the experiment, and
The precoat layer formation was completed in time. About 300 kg of the drug is supplied in about 1 hour required for forming the precoat layer, and 6 kg of the drug is supplied in the first 6 minutes and 294 kg of the remaining 54 minutes. This drug supply is about 1.5 in blow equivalent ratio.

In this state, the filtration operation was continued without additionally supplying the drug, but it could be left for 7 hours until the outlet concentration reached the target of 20 ppm (see FIG. 6).

Further, the differential pressure is steadily increased from 50 mmAq to about 175 mmAq only due to the adhesion of dust, demonstrating that the highly efficient performance of the present application is stable and continues for a long time.

[0072]

As described above, according to the present invention, since the precoat layer is formed on all the unit dust collecting mechanisms of the bag filter device substantially at the same time, the gas is passed through.
The performance is not deteriorated immediately after the removal operation, and even if there is no additional equipment such as a pre-absorption reaction device, high efficiency is demonstrated from the beginning with the amount of the drug which is about 1/2 to 1/4 that of the conventional method described above. Therefore, the harmful gas removal performance can be properly maintained for a long time.

Further, in the conventional system and the prior application system, the elapsed time after the drug is attached differs for each individual dust collecting mechanism,
The neutralization reaction rate was also low and unstable,
In the method of the present application, since the precoat layers are formed almost at the same time, the neutralization reaction is increased in the entire apparatus on average. Therefore, hunting due to measurement error and short-term fluctuation does not occur, and the drug used is effective because the injected drug is discharged when the neutralization reaction ends, and drug cost can only be saved. Since the amount of unreacted chemicals is reduced, the post-treatment cost of discharged ash can be reduced. In addition, the rate of increase in ventilation resistance is low, and the adhesion of chemicals and dust to the filter cloth due to moisture absorption is avoided,
It can be easily removed, its interval can be increased, and the life of the filter cloth can be extended.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a bag filter device in which a method for forming a precoat layer of a bag filter device according to the present invention is implemented.

FIG. 2 is a cross-sectional view showing a state of attachment on the surface of a filter cloth during a filtering operation.

FIG. 3 is a flowchart showing a procedure of a precoat layer forming operation.

FIG. 4 is a flowchart showing a procedure of a filtering operation and a removing operation.

FIG. 5 is a diagram comparing the conventional system shown in the upper stage with the prior application system shown in the middle stage and the present system shown in the lower stage.

FIG. 6 is a diagram showing an example of the experimental results of the removal, precoat layer formation, and filtration work according to the method of the present application.

FIG. 7 is a diagram showing an example of an experimental result of the removal and precoat layer forming work according to the method of the present application.

FIG. 8 is a diagram showing an outline of a conventional precoat type bag filter device.

FIG. 9 is a diagram showing an outline of a conventional bag filter system.

[Explanation of symbols]

 5 Bag filter device 6 Filter cloth 63 Precoat layer 8 Control device

Claims (1)

[Claims] 1. A method for forming a precoat layer of a bag filter device, comprising a plurality of unit dust collecting mechanisms, which preliminarily forms a precoat layer on the surface of a filter cloth before performing a filtering operation. The precoat of the bag filter device is characterized in that all the unit dust collection mechanisms are performed at the same time, the formation operation of the precoat layer is performed almost simultaneously in all the unit dust collection mechanisms, and the chemical is not supplied until the next cleaning operation. Layer forming method.