JP2006326514A - Exhaust gas treating method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas treating method and apparatus for reducing the pressure loss of a bag filter without changing the components of bag filter catching dust. <P>SOLUTION: In the exhaust gas treating method for collecting dust included in the exhaust gas of a coke oven 14 by the bag filter 36, the dust is caught by the bag filter 36, and flocculated dust deposited in the hopper 50 of the bag filter 36 is partially taken out and supplied to the entrance smoke passage 14 of the bag filter 36. In this case, the dust to be caught can be flocculated on the surface of the bag filter 36 until it becomes larger than the particle size of scattering dust in the entrance smoke passage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas treatment method and apparatus for collecting dust contained in exhaust gas of a coke oven with a bag filter.

  A coke oven for producing coke by dry distillation of coal has a basic configuration of a carbonization chamber in which coal is charged and heating chambers provided on both sides of the carbonization chamber. The carbonization chamber and the heating chamber are separated by a brick wall. In the coke oven, the coal in the carbonization chamber is steamed by high-temperature heating from the heating chamber to produce coke or coke oven gas such as hydrogen gas and methane gas, which are each effectively used. In coke ovens, the sealability of the brick wall that separates the carbonization chamber from the heating chamber may deteriorate due to aging due to long-term operation. If it does so, a part of combustible gas which volatilized from coal will leak into a heating chamber. When this combustible gas leaks, it burns in the heating chamber, so that the heating chamber is in an oxygen-deficient state and soot is generated. For this reason, the heating efficiency of the carbonization chamber by a heating chamber will fall.

  As a device for removing dust in such exhaust gas, an electrostatic precipitator or a bag filter is used. The electrostatic precipitator that collects dust in the exhaust gas by corona discharge between the discharge electrode and the collection electrode has the advantage that the pressure loss is low and the running cost is low, while the discharge electrode is used for increasing the dust collection rate. Therefore, it is necessary to increase the size of the apparatus.

  Here, the pressure loss can be generally represented by a value obtained by correcting the difference in average total pressure of exhaust gas at the inlet and outlet of the apparatus with a difference in height. For example, a U-tube manometer connected to the filter inlet and the filter outlet is used to measure the upstream side static pressure (filter inlet pressure) and the downstream side static pressure (filter outlet pressure). The lower the measured value, the better the air permeability.

  On the other hand, a bag filter that passes exhaust gas through a filter and collects dust in the exhaust gas has a high dust collection rate and a high removal efficiency of a trace amount of harmful substances. In addition, the initial introduction cost is excellent in that it is inexpensive, but there are problems such as a large pressure loss and a high running cost.

Recently, bag filters are widely used to remove dust in various combustion exhaust gas from the dioxin problem caused by combustion and the cost of initial introduction.
The bag filter is required to stably reduce the pressure loss during operation in order to stably operate the entire dust collection equipment incorporating the bag filter. Bag filters for waste incinerators and aluminum melting furnaces have an average particle size of collected dust of several microns, and in this case, the pressure loss is usually operated at about 2 kPa or less in many cases.

  Therefore, the present inventor conducted an experiment by introducing the actual exhaust gas into the model bag filter in order to examine the applicability of the bag filter to remove soot in the coke oven exhaust gas. When the pressure loss of this experiment was evaluated, the pressure loss was 2.5 kPa or more. Therefore, when only the coke oven exhaust gas is introduced into the bag filter, practical operation of the dust collection facility becomes difficult.

  Also, as a result of investigating the scattering particle size in the entrance flue of this bag filter by the particle size distribution measurement method using an under sensor sampler, the average particle size of the dust is 0.5 to 1 μm, and also examined with an electron microscope The dust particle number distribution had a peak in the vicinity of 0.1 μm. The result was that there were more fine particles than the dust discharged from the waste incinerator and aluminum melting furnace.

In response to such an increase in pressure loss due to dust having a small particle size, a filter aid having a large particle size is supplied to the bag filter inlet to reduce the pressure loss of the dust collection equipment (for example, Patent Documents 1 to 3). The filter aid prevents dust from clogging by collecting dust having a small particle size, thereby reducing the pressure loss of the bag filter. For example, Patent Document 1 discloses that pearlite having a large particle size is used as a filter aid.
JP 2002-336692 A JP 2005-034695 A JP 2004-298744 A

However, when a filter aid as shown in the above-mentioned patent document is used in order to suppress an increase in pressure loss, other components derived from the filter aid, particularly inorganic, are contained in the dust in the coke oven exhaust gas mainly containing carbon When the system components are included, it becomes difficult to effectively use the fuel because it contains impurities. Therefore, it is desired that the filter aid used is the same component as the dust contained in the coke oven exhaust gas.
This invention is made | formed in view of such a situation, and it aims at providing the waste gas processing method and apparatus which reduce the pressure loss of a bag filter, without changing the component of bag filter collection dust.

  The inventor found that in the experiment in which the actual exhaust gas from the coke oven was introduced into the model bag filter, the dust that was collected on the filter cloth surface and then dropped into the hopper by backwashing aggregated to increase the particle size. I found. In particular, it was found that the particle size of the hopper-collected dust was influenced by the backwash interval at which the dust collected by the filter cloth was removed.

  In order to solve the above problems, an exhaust gas treatment method according to the present invention is an exhaust gas treatment method in which dust contained in exhaust gas of a coke oven is collected by a bag filter, wherein a part of the collected dust collected by the bag filter is collected. It supplies to the entrance flue of the said bag filter, It is characterized by the above-mentioned.

  In this case, the collected dust is preferably aggregated on the surface of the bag filter until it becomes larger than the particle size of scattered dust in the inlet flue. The supply amount of the collected dust may be supplied at a weight ratio of 1: 3 to 1:10 with respect to the amount of scattered dust in the inlet flue of the bag filter. In the bag filter, the collected dust may be attached to a filter cloth in advance.

  An exhaust gas treatment apparatus according to the present invention includes an inlet flue to which exhaust gas from a coke oven is supplied, a bag filter that collects dust contained in the exhaust gas, and an exhaust pipe that discharges the collected dust. In the exhaust gas treatment apparatus, a circulation path for branching the discharge pipe and connecting to the inlet flue, and a supply means for supplying a part of the collected dust of the bag filter from the circulation path to the inlet flue It is characterized by having.

  According to the present invention as described above, the collected dust collected by the bag filter, which is the same component as the dust contained in the coke oven exhaust gas, is supplied to the inlet flue of the bag filter. For this reason, other components are not mixed in the dust and can be effectively used as fuel.

  The collected dust is agglomerated on the bag filter surface until it becomes larger than the particle size of the scattered dust in the inlet flue. For this reason, the collected dust serves as a filter aid, and dust with a small particle size contained in the coke oven exhaust gas can be collected to suppress clogging of the filter. For this reason, the pressure loss of the bag filter can be reduced.

Further, the collected dust is supplied at a weight ratio of 1: 3 to 1:10 with respect to the amount of scattered dust in the inlet flue of the bag filter. For this reason, the pressure loss of the bag filter can be reduced efficiently, and the operating cost of the feeder can be reduced by introducing excessive collection dust.
In the bag filter, the collected dust can be attached to a filter cloth in advance. For this reason, it is not necessary to always operate the supply means. Further, the amount of collected dust supplied can be reduced.

Hereinafter, preferred embodiments of an exhaust gas treatment method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of an exhaust gas treatment apparatus of the present invention. As shown in the figure, the exhaust gas treatment apparatus 10 has a dust collector 12 as a basic configuration.
The dust collector 12 divides a lower dust-containing gas chamber 30 and an upper dust-free gas chamber 32 by a boundary surface 34. The boundary surface 34 is provided with a plurality of openings 40 in which the bag filter 36 is disposed.

  The bag filter 36 has a long cylindrical shape, and is formed of a cage for holding the shape and a filter cloth 38 covering the surface thereof. The upper end of the bag filter 36 has a flange shape, is fitted in the opening 40 and is closed at the lower end, and hangs down from the opening 40 to the dust-containing gas chamber 30. The dustless gas chamber 32 is connected to the exit flue 42.

  A hopper 50 in which the collected dust accumulates is formed at the lower part of the dust collector 12. The hopper 50 is connected to a dust discharge pipe 54 via a valve 52. A branch pipe 56 is connected to the dust discharge pipe 54, and the branch pipe 56 is connected to the inlet flue 16 through the feeder 26. As described above, the exhaust gas treatment apparatus 10 forms a circulation path for collected dust by the inlet flue 16, the dust collector 12, the dust discharge pipe 54, and the branch pipe 56. The supply device 26 serving as a supply means supplies a part of the collected dust collected by the bag filter 36 and deposited by the hopper 50 to the inlet flue 16, and for example, a blower or the like can be used.

  The exhaust gas dust collector 10 having the above-described configuration operates as follows. Exhaust gas discharged by heating the coal charged in the coal chamber of the coke oven 14 at a high temperature in an adjacent heating chamber from the inlet flue 16 connecting the coke oven 14 and the dust collector 12 to the dust-containing gas chamber 30 of the dust collector 12. be introduced. The exhaust gas introduced into the dust-containing gas chamber 30 collects dust in the exhaust gas on the surface of the filter cloth 38 formed into a cylindrical shape.

  The collected dust collected on the surface of the filter cloth 38 jets high-pressure air from a backwash nozzle (not shown) into the cylindrical filter cloth 38 from the dust-free gas chamber 32 side, and the lower end of the dust collector 12. The hopper 50 is wiped off. It should be noted that the compressed air blowing interval (backwash interval) of the backwash nozzle can be set at an arbitrary interval to be described later.

The collected dust accumulated in the hopper 50 is periodically discharged out of the system via the valve 52. Part of the discharged collected dust is supplied to the inlet flue 16 of the bag filter 36 by the feeder 26 connected to the dust discharge pipe 54.
On the other hand, clean gas from which dust has been collected is discharged from the dust-free gas chamber 32 through the exit flue 42 and can be effectively used because no other components are mixed in during the dust collection process. .

  FIG. 2 shows the relationship between the aggregated average particle size (μm) of collected dust collected in the hopper 50 by backwashing and the time (minutes) of the backwashing interval. Show. In the table, A indicates the coagulation average particle size of the coke oven dust, and B in the table indicates the coagulation average particle size of the waste incinerator dust.

  First, as shown in A in the table, when the backwash interval was 1 minute, the agglomerated average particle diameter was 9.5 μm. Further, the agglomerated average particle size of the dust tends to increase with the passage of the time of the backwash interval, and became almost constant when the backwash interval was 30 minutes or more.

  Here, in the inlet flue 16 of the dust collector 12, the average particle diameter of the scattered dust examined by an under-sensor pan was 0.5 to 1.0 μm. Therefore, it can be seen that the collected dust collected by the hopper 50 has an average particle size of about 10 times larger than the scattered dust in the inlet flue 16 with a backwash interval of 1 minute or more.

  Then, as a comparative example, the coagulation average particle size of dust collected from the waste incinerator dust by the hopper 50 of the dust collector 12 using the same type of device as the dust collector 12 for the coke oven is shown in Table B. When the backwash interval was 1 minute, the agglomerated average particle size was 6.5 and became almost constant after 15 minutes.

  Here, the average particle size of the dust scattered in the inlet flue of the waste incinerator bag filter was 5.2 μm as determined by an under-sensor pan. As a result, it can be seen that the collected dust collected by the hopper 50 has an agglomerated average particle size that is about 10 times smaller than the scattered dust in the inlet flue 16 even when the backwash interval is 60 minutes.

  As a result, it was found that the dust discharged from the coke oven tends to have a larger particle size in a shorter time than the dust discharged from the waste incinerator. The reason why the agglomerated average particle size of the collected dust discharged from the coke oven 14 is increased in a short time is that the coke oven has a smaller foreign matter mixing ratio and stronger agglomeration between particles than the waste incinerator. Can be considered. In this way, the collected dust according to the embodiment supplied to the inlet flue has a backwash interval set to a predetermined time, and the particle size of the dust collected on the surface of the bag filter 36 during that time is scattered dust in the inlet flue. It is made to aggregate so that it may become larger.

  FIG. 3 shows a case where the exhaust gas treatment apparatus 10 according to the embodiment is used and only the coke oven exhaust gas is introduced into the bag filter, and the collected dust collected in the hopper with a backwash interval of 30 minutes is used as a filter aid. The time-dependent change of the pressure loss at the time of supplying continuously from an inlet is shown. Here, the solid line in the figure shows the case with a filter aid, and the dotted line shows the case without a filter aid.

  The vertical axis of the graph indicates the pressure loss (kPa) of the bag filter, and the horizontal axis indicates the elapsed time (h). The experiment was conducted at a filtration speed of 1 m / min through the filter cloth. Moreover, the filter aid supplied the collection dust equivalent to 3 times in weight ratio with respect to the amount of scattered dust in the inlet flue before filter aid supply. The amount of scattered dust can be determined by measuring the concentration of scattered dust in the inlet flue and based on this measured value. As a result, the pressure loss after 1 hour was about 2.7 kPa without the filter aid, but it was 1.8 kPa or less with the filter aid. It became clear that pressure loss could be greatly reduced.

  In the above embodiment, as the filter aid, the collected dust (aggregation average particle size is 55 μm) collected in the hopper with a backwash interval of 30 minutes was supplied to the inlet flue, but the particle size of the collected dust in the hopper As shown in FIG. 2, if the backwash interval is 1 minute or more, it is larger than the floating dust in the inlet flue of the bag filter. For this reason, using collected dust for 1 minute or more has an effect of reducing the pressure loss of the bag filter. However, it is preferable to use agglomerated dust in the hopper with a backwash interval of 5 minutes or more, that is, a collected dust having an agglomerated average particle diameter of 15 μm or more.

In FIG. 3, x marks indicate that dust collected corresponding to the weight ratio of the scattered dust in the inlet flue is tripled in advance on the surface of the filter cloth 38, and the exhaust gas from the coke oven 14 is removed from the dust collector. 12 shows the pressure loss of the bag filter after one hour has elapsed after being introduced into the dust collector. As shown in the figure, the pressure loss of the bag filter is 2.0 kPa, and it can be seen that the pressure loss is reduced as compared to after 1 hour when no filter aid is supplied.
Thereby, it is not necessary to always operate the feeder 26, and the operating cost can be reduced by operating it regularly.

  In the present embodiment, an example in which aggregated dust corresponding to a three times weight ratio of the supply amount of the filter aid to the concentration of scattered dust in the inlet flue is supplied is shown, but the present invention is not limited to this. In the experiments in which the weight ratio of the filter aid to the scattered dust in the inlet flue was changed from 1: 1 to 1:20, the results of reducing the pressure loss were obtained. The pressure loss decreased as the weight ratio increased up to 1: 3. The pressure loss was almost the same at a weight ratio of 1: 3 to 1:10, and increased slightly at a weight ratio of 1:10 to 1:20.

  As described above, when the weight ratio of the filter aid to the scattered dust in the inlet flue is increased to 1:10 or more, the reduction of the pressure loss shows a significant change, and the operating cost of the feeder 26 is increased accordingly. become. For this reason, the supply amount of the collected dust is preferably set to a weight ratio of 1: 3 to 1:10.

It is a figure which shows the structure outline of the waste gas processing apparatus of this invention. It is a figure which shows the relationship between the aggregation average particle diameter of the collection dust wiped off in the hopper by backwashing, and the elapsed time of a backwashing interval. It is a figure which shows a time-dependent change of the pressure loss of a bag filter inlet_port | entrance.

Explanation of symbols

10 ......... Exhaust gas treatment device, 12 ......... Dust collector, 14 ......... Coke oven, 16 ......... Inlet flue, 26 ......... Supply machine, 30 ......... Dust-containing gas chamber, 32 ......... None Dust gas chamber, 34 .... Interface, 36 .... Bug filter, 38 .... Filter cloth, 40 .... Opening, 42 .... Exit flue, 50 .... Hopper, 52 .... Valve, 54 ... Dust discharge pipe.

Claims (5)

In the exhaust gas treatment method of collecting dust contained in the exhaust gas of the coke oven with a bag filter,
A part of the collected dust collected by the bag filter is supplied to an inlet flue of the bag filter.   The exhaust gas treatment method according to claim 1, wherein the collected dust is aggregated on the surface of the bag filter until it becomes larger than a particle size of scattered dust in the inlet flue.   The supply amount of the collected dust is supplied at a weight ratio of 1: 3 to 1:10 with respect to the amount of scattered dust in the entrance flue of the bag filter. 2. The exhaust gas treatment method according to 2.   The exhaust gas treatment method according to claim 1, wherein the collected dust is attached to a filter cloth in advance on the bag filter. In an exhaust gas treatment apparatus comprising an inlet flue to which exhaust gas from a coke oven is supplied, a bag filter that collects dust contained in the exhaust gas, and an exhaust pipe that discharges the collected dust,
A circulation path for branching the discharge pipe and connecting to the inlet flue;
Supply means for supplying a part of the collected dust of the bag filter from the circulation path to the inlet flue;
An exhaust gas treatment apparatus comprising:

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