JP2000107562A - Treating apparatus for exhaust combustion gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove harmful substances at a high efficiency with the min. amt. of an exhaust gas treating agent by installing a measuring means concerning the back wash cycle of a bag filter and by controlling the amt. of an exhaust gas treating agent according to the measured back wash cycle of a bag filter. SOLUTION: An alkaline powder 4 for neutralizing HCl and SOx from an exhaust gas treating agent supply apparatus 3 and an adsorbent powder 5 (e.g. active carbon) for adsorbing org. chloride compds. and heavy metals are fed, in a flue 1a, to an exhaust gas 2 discharged from an incinerator 1. The exhaust gas 2 is caused to pass through a bag filter 8 and a pile thereof to be filtered and discharged as a cleaning gas 2" through a chimney 13. In back washing the pile of the bag filter 8, the pressure difference between the upper and the lower side of the bag filter 8 is measured with a pressure difference measuring device 9 and when the measured pressure difference reaches a certain value, a back washing air pulse jet 10 is started. The pressure difference measuring device 8 also measures the back wash cycle to control the amt. of the powder supplied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas treatment apparatus for treating harmful substances in flue gas generated from various combustion devices such as municipal waste incinerators.

[0002]

2. Description of the Related Art Exhaust gas emitted from combustion devices such as municipal waste incinerators and various incinerators contains soot, hydrogen chloride,
It contains heavy metals including sulfur oxides, nitrogen oxides, and mercury, and harmful substances such as organic chloride compounds. Various treatment methods have been conventionally used to remove these harmful substances. .

[0003] That is, soot and dust is removed by a bag filter provided in the flue, and hydrogen chloride and sulfur oxides are removed by pouring alkaline powder into the flue upstream of the bag filter. And a neutralization reaction is caused on the surface of the bag filter. As for heavy metals such as mercury and organic chlorine compounds, an adsorption method of adsorbing and removing them with an adsorbent is mainly used. Also in this case, for example, as described in JP-A-4-15692 and the like,
An adsorbent powder such as slaked lime or activated carbon is injected into the flue upstream of the bag filter, and these harmful substances are adsorbed to the adsorbent powder in the flue and on the surface of the bag filter. I do. When the powder is blown upstream of the bag filter, a reaction aid for improving the removability of the powder from the filter is usually added in addition to the neutralizing agent and the adsorbent.

The amount of the alkaline powder to be charged needs to be 1 to 3 times the molar equivalent of the amount of an acidic substance such as hydrogen chloride. No control method of changing is employed, and a predetermined ratio of alkaline powder is continuously added. Also, about 50 to 300 mg of an adsorbent such as activated carbon is required for 1 Nm ^{3 of} exhaust gas amount, and in this case, a predetermined fixed amount of adsorbent is continuously blown.

Instead of continuously blowing a certain amount of alkaline powder or adsorbent into the flue, a differential pressure across the bag filter is detected, and the supply of the absorbent is controlled according to the detected value. Conventionally, a method for performing the above-described method has been proposed (Japanese Patent Application Laid-Open
No. 23530).

[0006]

SUMMARY OF THE INVENTION Among the above prior arts,
The method of continuously blowing a certain amount of alkaline powder or adsorbent into a flue has the following problems.

That is, it is considered that the neutralization reaction and the adsorption reaction slightly proceed in the flue, but mainly proceed when the exhaust gas passes through the deposited layer deposited on the surface of the bag filter.
Therefore, if the bag filter is backwashed to remove the deposits in order to restore the air permeability of the bag filter, the efficiency of removing harmful substances is reduced.

FIG. 4 shows the relationship between the operation time of the bag filter and the backwash cycle in the actual machine. In the present specification, the “backwash cycle” refers to a cycle in which one bag filter is backwashed. As is clear from this figure,
The backwashing cycle from the start of the operation of the bag filter to about 700 days changes between 80 and 180 minutes. Thereafter, the backwashing cycle is sharply shortened. Once a minute it is quite short. Generally, the backwashing of the bag filter is performed using the differential pressure (Δ
P), for example, when the differential pressure is 100 mmH ₂ O
Is reached, control is performed to execute the removal of the deposited layer by the backwash air pulse. Shorter backwash cycle means that clogging of the filter means that ΔP does not recover to the initial value even after the
When the amount of dust and the amount of powder to be added are constant, the shorter the backwash cycle, the more the deposit on the surface of the bag filter when the backwash is performed. The deposited layer becomes thinner than the initial one.

For example, if the gas amount at the bag filter inlet is 3000
0 m ³ N / h, dust amount including added powder is 8.0 g / m
^{When 3} N, the filtration area of the bag filter is 900 m ² , and the backwash cycle is 160 minutes, the amount of dust deposited on the surface of the bag filter is 4.6 g / m ² / min. The density of the ash is about 0.
7, the thickness of the deposited layer is 0.000066 m ³ / m
² / min, resulting in a deposition of 0.066 mm per minute. 10.56 mm (736 g / m
² ) and the literature (Mitsubishi Heavy Industries Technical Report 23 (4), pp90-
96, 1986-7) 10.5
This is consistent with the statement that dust was removed by backwashing after depositing about mm. On the other hand, the backwash cycle is 1
In the case of 5 minutes, the thickness of the deposited layer is only 1 mm.

Differential pressure Δ before and after the bag filter for controlling backwashing
The powder accumulation amount obtained from P and the backwash cycle is as follows. That is, the filtration speed LV =
At 0.6 m / min, the differential pressure ΔP = 13 mmH ₂ O, Δ
From the description that the relationship of P∝LV _0.8 (0.8 power) holds, ΔP = 18.6LV _0.8 (0.8 power) is obtained. When the gas is processed at a filtration speed LV = 1.2 m / min,
ΔP = 23 mmH for a blank without dust accumulation
₂ O. When 100mmH is backwashed with ₂ O and is controlled, increase of ΔP is 77MmH ₂ O, this is a deposition layer thickness corresponds to about 11 mm, substantially coincide with the values obtained from the dust amount calculated above .

When the deposition amount is 1 mm, the increase in ΔP is equivalent to only about 10 mmH ₂ O, and the increase in ΔP after dust removal is obtained.
P does not decrease only to 80~90mmH ₂ O about not recover to the initial value.

When 50 mg of powdered activated carbon is blown as an adsorbent for organochlorine compounds and heavy metals per 1 Nm ^{3 of} exhaust gas, a backwashing cycle of 160 min.
Toxic substances will be adsorbed by the 4 g adsorbent layer.
In the case of 5 minutes, it is 0.4 g / m ² , and with 50 mg, the same removal performance as in the initial stage cannot be obtained. However, in reality, even if the ΔP of the bag filter increases and the backwash cycle is shortened, the use continues without replacing the filter, so that the supplied powder such as an organic chlorine compound or heavy metal is used. The performance of removing harmful substances removed by the deposited layer on the bag filter surface is reduced.

That is, as shown in FIG. 5A, the backwash cycle of the bag filter is shortened, but FIG.
When the input amount of the activated carbon as the absorbent is kept constant as shown in FIG. 5, the concentrations of dioxins and heavy metals increase as shown in FIGS. 5 (c) and 5 (d).

On the other hand, in the method in which the supply amount of the absorbent is controlled by the differential pressure before and after the bag filter, the supply amount of the absorbent is increased in accordance with the increase in the differential pressure. The amount will increase and unnecessary absorbent will be charged.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for treating combustion exhaust gas which can eliminate such deficiencies of the prior art and can obtain a highly efficient harmful substance removing effect with a minimum amount of an exhaust gas treating agent.

[0016]

According to the present invention, in order to achieve the above-mentioned object, one or more kinds of exhaust gas treating agents are blown into a flue connecting a combustion device and a bag filter, thereby causing harmful substances in flue gas. A flue gas treatment apparatus for removing flue gas, comprising: means for measuring a backwash cycle of the bag filter, wherein the one or more kinds of exhaust gas treating agents are provided in accordance with the backwash cycle of the bag filter detected by the measurement means. The supply amount is controlled.

As described above, when the addition amount of the exhaust gas treating agent is controlled in accordance with the backwash cycle of the bag filter, even after the backwash cycle is shortened and the deposited layer on the bag filter surface becomes thin, the surface of the bag filter becomes thin. Since the thickness of the reaction layer formed on the substrate can be ensured, harmful substances can be removed with high efficiency. In addition, since one or more kinds of exhaust gas treating agents are supplied as needed, various harmful substances such as acidic substances, heavy metals and dioxins can be treated at the same time. Further, if a catalytic bag filter is used as a bag filter, denitration becomes possible.

The supply amount of the exhaust gas treating agent can be controlled by increasing the supply amount of the exhaust gas treating agent as the backwash cycle of the bag filter becomes shorter.

Further, the reference pressure difference for controlling the pressure difference in the backwashing of the bag filter can be arbitrarily set in the range of 30 mmH ₂ O to 150 mmH ₂ O.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a flue gas treatment apparatus according to the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram of a combustion exhaust gas treatment apparatus according to the present embodiment,
FIG. 2 is a graph showing a method for controlling the supply of an exhaust gas treating agent performed by the combustion exhaust gas treating apparatus according to the present embodiment and its effect.

As shown in FIG. 1, an exhaust gas 2 discharged from an incinerator 1 is converted into an alkaline powder 4 for neutralizing HCl and SOx from an exhaust gas treating agent supply device 3 in a flue 1a.
And an adsorbent powder 5 such as activated carbon for adsorbing organic chlorine compounds and heavy metals. In addition, in the adsorbent powder 5, a reaction aid for improving the removability of dust from the bag filter 8 can be added. The exhaust gas 2 ′ into which the neutralizing agent, the adsorbent, and the reaction aid have been introduced is introduced into the bag house 7 and passes through the bag filter 8. Since a deposited layer composed of a mixture of dust and the supplied powder is formed on the surface of the bag filter 8, the exhaust gas 2 'is filtered by passing through the bag filter 8 and the deposited layer, and the cleaning gas 2 " The cleaning gas 2 ″ is
It is discharged from the chimney 13.

To remove the backing layer deposited on the surface of the bag filter 8 (backwashing), a timer or a pressure difference between upstream and downstream of the bag filter 8 is measured by a differential pressure measuring device 9 and the value is set in advance. It is performed by activating the backwash air pulse jet 10 when the predetermined value is reached. The differential pressure measuring device 9 also measures the backwash cycle, and controls the amount of powder supply according to the value.

One of the adsorbents for adsorbing heavy metals and dioxins is activated carbon powder having a pore diameter of about 20 angstroms and a particle diameter of about 300 mesh. In addition, activated coke and diatomaceous earth used as a reaction aid can be used.

Inorganic substances such as alumina, diatomaceous earth and activated clay are effective as a reaction aid for improving the removability of dust from the bag filter 8. Furthermore, the diatomaceous earth is more effective when mixed with a metal halide, and can be effectively used as a reaction aid and an adsorbent.

The neutralization reaction between an acidic substance such as hydrogen chloride and an alkaline powder is a solid-gas reaction. Therefore, in order to increase the reaction efficiency, the frequency of contact between the two is important. As the alkaline powder, special lime slaked lime (particle size: about 6 μm) which is specified by JIS and used conventionally can be used.
It is more advantageous to use a material having a larger specific surface area (for example, “Tamacalc” manufactured by Okutama Kogyo). The specific surface area is about 15 m ² / g for the special name slaked lime,
Tamacalc is 35-40 m ² / g, and the latter is more than 2.5 times larger. Therefore, when it is put into the flue 1a, the contact frequency with the acidic substance increases, and even in a high temperature region, the neutralization reaction, which is an exothermic reaction, proceeds, and a high removal rate is obtained. In addition, slaked lime ("Eslime GC" manufactured by Ueda Lime Manufacturing Co., Ltd .; particle size of 5 to 6 μm) having a flat and petal-like particle shape has a specific surface area of about 35 m ² / g and a large reaction area. It is valid.

As apparent from FIG. 2A, the incinerator 1
As the operation proceeds, the backwash cycle sharply decreases. In this case, if the activated carbon as the adsorbent is introduced in the same amount as the initial amount, the thickness of the powder layer deposited on the surface of the bag filter 8 is reduced, and the contact time between the exhaust gas and the activated carbon is shortened.
The effect of activated carbon is weakened, and both dioxins and heavy metals cannot maintain their initial values.

Therefore, in this embodiment, as shown in FIG. 2B, the amount of activated carbon as an adsorbent is increased in accordance with the shortening of the backwash cycle of the bag filter 8. That is, the backwash cycle of the bag filter 8 is measured by the differential pressure measuring device 9, and when it is detected at the point A in FIG. The input amount of activated carbon is increased at the point B in FIG. Thereby, as shown in FIGS. 2C and 2D, both the dioxins and the heavy metals can maintain the initial values.

This control method can be applied to an existing refuse incineration plant without any problem, and can also be used for a newly installed refuse incineration plant in the same manner as before.

Hereinafter, the effects of the present invention will be clarified with reference to more specific examples.

(First Embodiment) The gas amount at the bag entrance is 3000
0~40000m ³ N / h, the amount of dust is 5~15g / m ³
N, HCl concentration is 200 to 400 ppm, mercury concentration is 0.1 to 0.5 mg / m ³ N, water content in exhaust gas is 18
-20%, NOx concentration 150-200 ppm, CO concentration 250-300 ppm, dioxin concentration 10
ngTEQ / Nm ³ of exhaust gas having a filter permeation speed of 1.2 m / min and a neutralizing agent addition amount of Ca (OH) ₂ / H
Under the conditions of a Cl molar ratio of 2.7, an addition amount of a reaction assistant and an adsorbent of 20 wt% with respect to a neutralizing agent, and a filter temperature of 160 ° C., the removal rates of HCl, mercury and dioxins were determined by a backwash cycle Were obtained for 90 minutes and 15 minutes. When the backwashing cycle was 90 minutes, powdered activated carbon was added as an adsorbent at 50 mg / Nm ³ , but when the backwashing cycle was shortened to 1/6 of 15 minutes, the amount of powdered activated carbon added was increased six times. It was 300 mgNm ³ . The amount of Ca (OH) ₂ , which is a neutralizer for acidic substances, was not controlled.

When the backwash cycle is 90 minutes, HCl
HCl removal rate of 95% or more at a concentration of 10 to 20 ppm,
The mercury concentration was 0.005 to 0.025 mg / m ³ N, the mercury removal rate was 95%, and the dioxin concentration was 0.1 ng TEQ / Nm ³ , which satisfied the new guidelines of the Ministry of Health and Welfare. On the other hand, when the backwash cycle is 15 minutes,
Since Ca (OH) ₂ as a neutralizing agent was not controlled, the HCl concentration was 10 to 40 ppm and the removal rate was 90% or more, but the amount of the adsorbent added was 300 mg / Nm.
^Because of the increase to ³ , mercury and dioxins can be efficiently removed, and the mercury removal rate is 95% and the dioxins are 0.1 ng TEQ / Nm ³ or less, respectively.

From these results, by controlling the addition amount of the adsorbent in accordance with the backwashing cycle, even after the backwashing cycle becomes short and the deposited layer on the filter surface becomes thin, the acidic substance and mercury can be efficiently obtained. It can be seen that simultaneous treatment of dioxins and dioxins has become possible. The dust removal did not affect the dust removal performance at all. In this embodiment, only the adsorbent is controlled, but it is needless to say that the addition amount of the neutralizing agent can also be controlled.

(Comparative Example) The control of the amount of powder supplied by the backwashing cycle was not performed. When the backwashing cycle was 90 minutes or 15 minutes, 50 mg / N was used as the adsorbent.
m ³ powdered activated carbon was added to treat the exhaust gas under the same conditions as in the first example. Other conditions were the same as in the first embodiment.

When the backwash cycle is 90 minutes, HCl
HCl removal rate of 95% or more at a concentration of 10 to 20 ppm,
The mercury concentration was 0.005 to 0.025 mg / m ³ N, the mercury removal rate was 95%, and the dioxin concentration was 0.1 ng TEQ / Nm ³ , which satisfies the new guidelines of the Ministry of Health and Welfare. On the other hand, when the backwash cycle was 15 minutes, the neutralization agent Ca (OH) ₂ was not controlled, so that the HCl concentration was 10 to 40 ppm and the removal rate was 90% or more. And dioxins have reduced removal performance, each having a mercury removal rate of 60
%, The concentration of dioxins is 0.5 ng TEQ / Nm ³
It became.

(Second Embodiment) FIG. 3 shows a configuration of a combustion apparatus provided with a combustion exhaust gas treatment apparatus according to a second embodiment. As is clear from this figure, the flue gas treatment apparatus of this example is characterized in that a catalyst bag filter 11 is used as a bag filter and a reducing agent adding device 6 for adding a reducing agent into the flue is added. I do.

The catalyst bag filter 11 is a slurry of a titanium oxide vanadium pentoxide-based catalyst for denitration, carried on a bag filter made of Tefair having an inner diameter of 15 cm and a length of 1.2 m, and dried to obtain a filter area of 1 m ^2. 480 per
A catalyst supporting g catalyst was used. On the other hand, the amount of the reducing agent added was an NH ₃ / NO molar ratio of 1 and the filter temperature was 20
0 ° C. Further, since the filter temperature was set to 200 ° C., slaked lime (Ca (OH) ₂ ) as a neutralizing agent was
Those having a specific surface area as large as 40 m ² / g were used. Other conditions were the same as in the first embodiment.

When the backwashing cycle was 90 minutes, powdered activated carbon was added as an adsorbent at 50 mg / Nm ³ , but when the backwashing cycle was shortened to 1/6 of 15 minutes, the amount of powdered activated carbon added was reduced. Six times, 300 mg / Nm ³ .
Also in the case of this example, Ca (OH) which is a neutralizer for acidic substances
The control of the addition amount of No. ₂ was not performed. 90 backwash cycles
Minute, the HCl concentration becomes 10 to 20 ppm,
The removal rate is 95% or more, and the mercury concentration is 0.005 to 0.02.
At 5 mg / m ³ N, the removal rate was 95%, and the dioxin concentration was 0.1 ng TEQ / Nm ³ , which satisfies the Ministry of Health and Welfare guidelines and satisfies the European standards. On the other hand, when the backwash cycle is 15 minutes, the neutralizer Ca
Since the control of (OH) ₂ is not performed, the HCl concentration is 10
Although the removal rate was ４０40 ppm and the removal rate was 90% or more, the amount of the adsorbent added was increased to 300 mg / Nm ³ , so that mercury and dioxins could be removed with high efficiency. Dioxins had a value of 0.1 ng TEQ / Nm ³ or less. The denitration effect of the catalyst bag filter 11 was not affected by the backwash cycle, and all exhibited high denitration performance of about 80%. Soot removal performance was also unaffected by the backwash cycle.

By controlling the addition amount of the adsorbent in accordance with the backwashing cycle in this manner, even after the backwashing cycle is shortened and the deposited layer on the filter surface becomes thin, the acidic substance, mercury and mercury can be efficiently treated. The use of dioxins and a catalyst bag filter also enabled denitration, enabling simultaneous processing of harmful components in exhaust gas.

[0039]

According to the present invention, since the amount of the exhaust gas treating agent to be added is controlled by grasping the thickness of the deposited layer from the bag filter backwash cycle, the bag filter backwash cycle is shortened. In addition to ensuring a preferable thickness of the reaction layer, unnecessary exhaust gas treating agents may be introduced at the time of back washing as in the case where the supply amount of the exhaust gas treating agent is controlled by the differential pressure before and after the bag filter. Absent. Therefore, the efficiency of removing harmful substances can be increased while the amount of the exhaust gas treating agent charged is kept to a minimum.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a combustion exhaust gas treatment apparatus according to an embodiment.

FIG. 2 is a graph illustrating a method of controlling the supply of an exhaust gas treating agent performed by the combustion exhaust gas treating apparatus according to the embodiment and the effect thereof.

FIG. 3 is a configuration diagram illustrating another example of the combustion exhaust gas treatment apparatus according to the embodiment.

FIG. 4 is a graph illustrating a relationship between an operation time and a bag filter backwash cycle.

FIG. 5 is a graph showing a conventional technique and its problems.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incinerator 1a Flue 2 Exhaust gas 2 'Exhaust gas which mixed neutralizer, reaction aid, reducing agent 2 "Processing gas 3 Powder supply device 4 Alkaline powder (neutralizer) 5 Reaction aid or adsorbent Or both 6 reducing agent 7 baghouse 8 bag filter 9 differential pressure and backwash cycle measuring device 10 backwash device 11 catalytic bag filter 12 exhaust fan 13 chimney

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 53/50 B01D 53/34 124Z 53/81 134A 53/68 136A 53/64

Claims (3)

[Claims] 1. A flue gas treatment apparatus for removing one or more harmful substances from flue gas by blowing one or more kinds of flue gas treating agents into a flue connecting a combustion device and a bag filter, wherein the bag filter is backwashed. A flue gas treatment apparatus, comprising: a cycle measuring means, wherein the supply amount of the one or more kinds of exhaust gas treating agents is controlled in accordance with a backwash cycle of the bag filter detected by the measuring means. . 2. The processing apparatus according to claim 1, wherein a supply amount of the one or more kinds of processing agents is increased as a backwash cycle of the bag filter is shortened. apparatus. 3. The processing apparatus according to claim 1, wherein a reference differential pressure at the time of performing differential pressure control on the backwashing of the bag filter is:
30mmH ₂ O ~150mmH ₂ O processor of flue gas and setting the range of.