JPH05123515A - Control of bag filter apparatus - Google Patents

Abstract

PURPOSE:To reduce not only the use amount of a chemical agent but also installation cost by keeping the high capacity removing efficiency of acidic harmful gas and soot. CONSTITUTION:In a bag filter apparatus 3 of such a type that a precoat layer is formed to the surface of the filter cloth 4 arranged in the bag filter apparatus 3 before filtering work is performed, the differential pressure between the inside and outside of the filter cloth 4 is detected by differential pressure detector 31 and the concn. of the gas on the outlet side of the bag filter device 3 is detected by concn. detector 81 and, on the basis of these detection results, the thickness of the precoat layer and a shaking-off period are adjusted.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 6 shows a schematic example of a conventional industrial bag filter system.

A high temperature combustion gas containing dust and acid harmful gas generated in an incinerator or a combustion furnace (not shown) is cooled by the gas cooling device a to a temperature lower than the allowable temperature of the bag filter device b.

A neutralizing agent d such as slaked lime supplied from a harmful gas removing device (not shown) is continuously injected into the flue c connecting the gas cooling device a and the bag filter device b, The chemical agent d is mixed with the combustion gas cooled by the gas cooling device a to form the exhaust gas e, which is neutralized with the acidic harmful gas contained in the combustion gas while traveling through the flue c.
The surface of the filter cloth f suspended in the bag filter device b is reached.

During this period, a part of the drug d undergoes a neutralization reaction with the acidic harmful gas, but the rest remains unreacted and adheres to the surface of the filter cloth f to form a dust layer g.

The bag filter method is different from the reaction by stirring contact in the flue and the electric dust collector of the dry harmful gas removing method, and when the exhaust gas e passes through the dust layer g and the filter cloth f, the acidic harmful gas is generated. Since the reaction proceeds while contacting the unreacted drug d, the neutralization reaction is efficiently performed.

Further, since the dust contained in the exhaust gas e is also adsorbed on the surface of the dust layer g or in the voids formed in the dust layer g, the harmful substances in the gas which has passed through are removed by the dry harmful gas removing method 1. The treated gas h is removed to about / 10 and becomes harmless, which is sucked into the draft fan j and discharged into the atmosphere from a chimney (not shown).

When the operation is continued in this state, the dust layer g gradually grows due to the accumulation of the chemicals d and the dust accumulated in the exhaust gas e, the ventilation resistance increases, and not only the power cost is increased but also the filter cloth is used. The seams and the like of f are easily damaged.

Therefore, when the pressure loss due to the dust layer g exceeds the set value, the damper k provided in the flue c is closed, and the valve n connected to the backwash fan m is opened, whereby the filter cloth is closed. The processing gas h is sent back to the inside of f, the grown dust layer g is peeled off, and the dropped reacted chemicals and dust are discharged from the discharge device p to the outside.

After the dust layer g has been removed by backwashing the processing gas h, the backwash fan m is stopped, the valve n is closed, and the damper k is opened to restore the normal operating condition.

When the bag filter device is composed of a plurality of devices, it is a system for sequentially performing the above-mentioned removal work.

In addition to the above-described reverse pressure blow-off method, a mechanical vibration method used for a simplified type and a pulse jet method described later are also used as the blow-off method. It is common to go.

Further, there are an inner surface filtration type in which the dust layer g is attached and an outer surface filtration type in which the dust layer g is attached to the outer surface. Recently, however, the outer surface filtration type of the pulse jet blow-off system has become popular. It was

[0014]

However, according to the conventional method, the main force of filtration is the dust layer g formed by the drug d and the dust, and the filtration by the filter cloth f has an auxiliary role. The cloth f is merely a tool for forming the dust layer g.

Therefore, the filtration performance of the bag filter device b is gradually improved with the growth of the dust layer g formed during operation, and high performance is required from the beginning.
It is not possible to maintain a certain level of performance.

Here, the dust layer g is not formed only by the unreacted and reacted chemicals d, but since the dusts and water contained in the exhaust gas e are simultaneously adhered, the chemicals d and the dusts absorb moisture. As a result, not only does the binding force increase and the ventilation resistance is amplified, it is combined with the filter cloth f to make it difficult to remove it.
There was a problem of damaging itself.

Furthermore, since the entire dust layer g is peeled off due to the above-mentioned cohesive force at the time of brushing off, not only it takes a long time for regeneration, but also the ventilation resistance of the filter cloth f which has been brushed off is reduced at once. Therefore, the maximum amount of gas flows in the portion with the weakest filtration capacity.

Therefore, it is said that the concentration of dust in the treated gas h reaches 10 to 100 times immediately after the cleaning, compared with that before the cleaning. Since the removal rate and the trapping rate of soot and dust are low and may cause pollution, the equivalence ratio of 4 to 5
It is necessary to continue to eject a large amount of the drug, which results in not only an excessive amount of the drug used but also an expedited withdrawal cycle.

As a measure against the unstable performance at the time of removing, the bag filter device b is composed of a plurality of units,
A system is adopted to cover the required filtration area calculated from the planned amount of gas and acidic harmful gas removal rate, etc., by adding the removal capacity of the unit that is missing after the filter is removed, and to ensure the removal performance of the entire facility. Therefore, there is a problem that the equipment becomes large.

In addition, the filter cloth f is the exhaust gas e immediately after it is removed.
Since it was exposed to the inside, there was also a risk of burning due to unextinguished suspended matter flying with the exhaust gas e.

In order to solve the above-mentioned various problems, Japanese Patent Publication No. 52-29470 discloses a method of forming a precoat layer with a chemical agent before carrying out a filtering operation. Since it is due to an alarm when the differential pressure inside and outside the filter cloth increases, if the differential pressure rises regardless of the relationship with the exhaust gas concentration, that is, regardless of the presence or absence of unreacted chemicals, the chemicals with a certain layer thickness are There was a waste of paying off.

[0022]

A method of controlling a bag filter device according to the present invention is a bag filter device of a system in which a precoat layer is formed on the surface of a filter cloth installed in the bag filter device before performing a filtering operation. In addition to detecting the pressure difference between the inside and outside of the filter cloth, the gas concentration at the outlet side of the bag filter device is detected, and the layer thickness of the precoat layer is adjusted based on these detection results, and the timing of the removal is adjusted. Is.

[0023]

The pressure difference between the inside and the outside of the filter cloth suspended inside the filter device is detected to estimate the layer thickness of the adhesion layer composed of the precoat layer and the dust accumulation layer. When the pressure difference reaches the set value, the adhesion layer is reached. Get rid of.

Further, by detecting the concentration of acidic harmful gas at the outlet, the effective layer thickness of the unreacted drug is estimated, and the next drug injection amount is corrected based on the concentration when the adhering layer is removed. However, when only the outlet concentration reaches the set value, the additional injection of the medicine is repeated until the differential pressure reaches the set value.

[0025]

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

FIG. 1 shows a schematic configuration of a bag filter system for carrying out the method for controlling a bag filter according to the present invention. FIG. 2 is an enlarged view showing the state of adhesion and deposition on the surface of the filter cloth.

In FIG. 1, reference numeral 1 denotes an incinerator, in which high-temperature combustion gas containing dust and acid harmful gas generated in the incinerator 1 flows through a gas cooling device 2 and a flue 6 by a suction action of an attracting fan 9. After that, it is sent to the bag filter device 3.

The gas cooling device 2 cools the combustion gas below the allowable temperature of the filter cloth 4 suspended in the bag filter device 3, and the cooled combustion gas becomes exhaust gas 5 and the bag filter device. Sent to 3.

As described above, the filter cloth 4 is suspended in the bag filter device 3, and the exhaust gas 5 sent from the gas cooling device 2 permeates the filter cloth 4 from the outside to the inside to process gas. 8 and is configured to be sucked toward the induced draft fan 9 side.

A compressed air source 32 for injecting compressed air into the filter cloth 4 of the bag filter device 3 is connected via an opening / closing valve 33, and the compressed air The method of removing the bag deposits attached to the outer surface of the filter cloth 4 by the rush is called a pulse jet method.

Further, a damper 61 for controlling the flow rate of the exhaust gas 5 is installed in the flue 6 and an acidic harmful gas removing device 7 for supplying a chemical 72 for neutralizing the acidic harmful gas 7 is provided.
Are communicated with each other via the control valve 71.

The bag filter device 3 includes a filter cloth 4
A differential pressure detector 31 for detecting the differential pressure between the outside and the inside of the bag filter device 3 is provided, and the flue 82 that connects the bag filter device 3 and the induced draft fan 9 is provided with an acidic harmful gas on the outlet side of the bag filter device 3. A concentration detector 81 for detecting the gas concentration is provided, and the detection values detected by the differential pressure detector 31 and the concentration detector 81 are input to the control device 10, and the control device 10 is based on these detection values. The damper 61 and the control valve 71 are opened and closed.

Reference numeral 36 in FIG. 1 denotes a discharge device provided at the bottom of the bag filter device 3, which discharges the adhered substances to the outside when the adhered substances on the outer surface of the filter cloth 4 are removed. To do.

Next, a method of controlling the bag filter according to the present invention will be described.

First, when starting the initial operation, as shown in the flow chart of FIG. 3, the damper 61 is closed and the control valve 71 is opened, and a fresh air is blown by a blower (not shown) built in the acidic harmful gas removing device 7. By spraying the chemical agent 72 with the air, the chemical agent 72 collides with the surface of the fresh filter cloth 4 to form a bridge with the bulky thread portion of the filter cloth 4, and is strong so as not to be peeled off even if a wiping operation described later is performed. A primary adhesion layer 41 (see FIG. 2) is formed, after which the control valve 7
1 is closed (steps S1 to S4). The filter cloth 4 and the primary adhesion layer 41 serve as a permanent base.

Next, the control operation of the filtration work will be described with reference to the flow charts of FIGS.

First, the control valve 71 is opened, the fresh air is used to further inject the chemical 72 onto the surface of the primary adhesion layer 41 by the blower of the acidic harmful gas removing device 7, and one cycle of acidic harmful gas is discharged. After forming the precoat layer 42 (see FIG. 2) in charge of neutralization and dust filtration in a short time, the control valve 71 is closed (steps S11 to S1).
3). As a result, the precoat layer 42 becomes unreacted drug 72.
It will be formed by.

Thereafter, the damper 61 is fully opened and the exhaust gas 5
If it is passed through the bag filter device 3, the dust particles contained in the exhaust gas 5 are captured by the precoat layer 42 and deposited on the surface, and gradually form the dust accumulation layer 43 (see FIG. 2). Further, since the acidic harmful gas contained in the exhaust gas 5 passes through the voids of the unreacted precoat layer 42 having a sufficient thickness, the primary adhesion layer 41 and the filter cloth are subjected to almost complete neutralization reaction. After passing through No. 4, it becomes the processing gas 8, which is sucked by the induced draft fan 9 and discharged into the atmosphere from a chimney (not shown) (steps S14 to S16).

When the operation is continued in this state, the soot-and-dust accumulation layer 43 is gradually enlarged and the ventilation resistance is increased, and the unreacted portion of the precoat layer 42 is gradually decreased, so that the acidic harmful gas in the processing gas 8 is reduced. The concentration will increase.

The change in the ventilation resistance is detected in step S17 by the differential pressure detector 31 between the inside and outside of the filter cloth 4 of the bag filter device 3, and in step S18 the average value of this differential pressure is calculated. And proceeds to step S19.

In step S19, it is determined whether the differential pressure is greater than or equal to the set value. If the differential pressure is greater than or equal to the set value, step S2
0, the damper 61 is closed by the command of the control device 10 to stop the inflow of the exhaust gas 5, and then the opening / closing valve 33 communicated with the compressed air source 32 is opened to inject compressed air into the filter cloth 4. Let Due to the impact of this plunge, the precoat layer 42 that has undergone a neutralization reaction and the grown dust and dust layer 43
After peeling off the adhered substances, the on-off valve 33 is closed (steps S21 to S23).

In the case of the present invention, the surface of the precoat layer 42 absorbs moisture in the exhaust gas 5 to increase the cohesive force, but the cohesive force decreases toward the inner side, so only pulse air is jetted. Thus, only the deposit can be peeled off leaving the filter cloth 4 and the primary adhesion layer 41, and the filter cloth 4 is not damaged unlike other methods.

The adhering substances dropped by this removing operation are carried out to the outside by the discharging device 36.

When the operation for removing the adhering substances is completed, the damper 61 is closed in step S24 to stop the inflow of the exhaust gas 5 into the bag filter device 3, and the process returns to step S11 based on the command from the control device 10. The control valve 71 is opened only for a command time described later, and the blower blows the medicine 7
Similarly to the above, the precoat layer 42 having an appropriate layer thickness is regenerated by injecting 2 with fresh air in a short time, and then the damper 61 is fully opened to restart the filtering operation.

In this operation, the precoat layer 42 is formed immediately after the adhered substances are removed, and thereafter the chemical 7 is added to the exhaust gas 5.
Since 2 is not jetted, it is possible to prevent clogging of the filter cloth 4 due to moisture absorption, to stabilize the removal efficiency at all times, and to prevent a large amount of exhaust gas from locally concentrating at the time of cleaning.

The above-mentioned command time corresponds to steps S25 and S2.
6, the concentration detector 81 detects the concentration of acidic harmful gas in the processing gas 8 at the time of the previous removal, calculates the average value of the concentration and stores it in the control device 10, and based on the calculated value, the control device 10 Then, the injection time of the next medicine 72 is set. That is, the layer thickness of the precoat layer 42 is adjusted to an effective thickness corresponding to the acidic harmful gas concentration by changing the injection time of the next chemical agent 72 at any time according to the calculated acidic harmful gas concentration. For example, if the calculated acidic harmful gas concentration is low, the injection time of the chemical agent 72 at the next time is shortened, and the layer thickness of the precoat layer 42 is thinned so that an appropriate acidic harmful gas concentration is obtained.

When there is no large difference in the amount of treated gas and the removal rate of soot and acidic harmful gas differs depending on the customer, the layer thickness of the precoat layer 42 is adjusted so that the bag filter device 3 having the same capacity can be used. Can be dealt with.

On the other hand, if the differential pressure is within the set value in step S19, the process proceeds to step S27. In step S27, it is determined whether or not the concentration of the acidic harmful gas calculated in step S26 is equal to or higher than a preset value. If the concentration is within the preset value, the process returns to step S15 to continue the above-described filtration work.

If the concentration is equal to or higher than the set value, the process proceeds to step S28, the damper 61 is half-opened by the command of the control device 10, the control valve 71 is opened for a certain period of time, and the chemical 72 is sprayed on the upper layer of the dust accumulation layer 43. To form the additional adhesion layer 44, and then the control valve 71 is closed (steps S29 to S).
31), and returns to step S14 to continue the above-described filtration work. This additional operation is repeated until the differential pressure reaches the set value.

In this example, the bag filter device 3 has a structure of only one set, but in general, the bag filter is a combination of a plurality of units, and in that case, formation and removal of each layer on the filter cloth 4 are performed. The operation of is performed in the order in which the set value is reached according to a command from the control device 10.

Further, the primary adhesion layer 41 and the precoat layer 4
The chemical injection fluid for forming 2 is basically the blower built in the acidic and harmful gas removing device 7 as described above, but the compressed air source 32, the processing gas 8, or the additional adhesion layer 44 is formed. Exhaust gas 5 may be used according to the procedure of time,
In the case of forming the additional adhesion layer 44, either one may be used as described above.

Further, the adjustment of the injection amount of the medicine 72 is not limited to the adjustment of the injection time in this example, but may be the adjustment of the supply speed of the medicine 72.

The discharging operation is not limited to the pulse jet method of this embodiment, but may be a reverse pressure discharging method, a mechanical vibration method, or an inner surface filtration type or an outer surface filtration type.

[0054]

As described above, according to the method of the present invention, it is possible to remove the precoat layer based on the pressure difference between the inside and outside of the filter cloth installed in the filter device and the gas concentration on the outlet side, as well as the removal of the precoat layer. By adjusting the thickness, it is possible to always maintain proper filtration performance, and to effectively use up the sprayed drug, the amount of drug used, that is, the drug cost can be reduced, and the processing efficiency can be improved. Moreover, since it is not necessary to have a margin in the filtration area, the apparatus can be made compact and the facility cost can be reduced. Furthermore, by adjusting the thickness of the precoat layer,
Since it can handle a wide range of requirements, it not only requires a small number of models, but can also respond to changes in regulation values.

Therefore, it is a model equipped with an optimal control method even for countermeasures against heavy metals and dioxins, which are currently difficult to counteract.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of a bag filter system for carrying out a method of controlling a bag filter according to the present invention.

FIG. 2 is an enlarged view showing a state of adhesion / accumulation on the surface of the filter cloth.

FIG. 3 is a flowchart showing a flow at the start of initial operation.

FIG. 4 is a flowchart showing a control operation of filtration work.

FIG. 5 is a flowchart showing a control operation of filtration work.

FIG. 6 is a configuration diagram showing an outline of a conventional bag filter system.

[Explanation of symbols]

 3 Bag filter device 4 Filter cloth 42 Precoat layer 31 Differential pressure detector 81 Concentration detector

Claims (1)

[Claims] 1. A bag filter device of a type in which a precoat layer is formed on the surface of a filter cloth installed in a bag filter device before performing a filtering operation, wherein a differential pressure between the inside and outside of the filter cloth is detected and A method for controlling a bag filter device, which comprises detecting a gas concentration on the outlet side of the filter device, adjusting the layer thickness of the precoat layer based on these detection results, and adjusting the removal time.