JPH10337432A - Exhaust gas treatment and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas treating method and device therefor enabling to save the treatment cost and being more effective compared to a conventional method and device. SOLUTION: This treating method is constituted to treat exhaust gas discharged from a heat equipment. In this case, the exhaust gas is collected dust with a wet type dust collector 8, introduced into a gas cooler 10 together with circulation water cooled with a water cooler 12 to perform a cooling treatment against low temp. saturated gas, heats with a heating device 13 to a specified temp., introducing into a bag filter 4 to collect powder and dust.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a municipal solid waste incinerator,
The present invention relates to a method and an apparatus for treating exhaust gas discharged from a melting furnace or other similar heat equipment.

[0002]

2. Description of the Related Art Conventionally, exhaust gas discharged from municipal solid waste incinerators, melting furnaces, and other similar heat equipment has a high temperature and contains dust, hydrogen chloride (HCl), and dioxin. Must be released to the atmosphere after removal.

According to the current theory, the emission of dioxins is considerably suppressed by lowering the temperature of the gas to be treated to as low as possible, ideally 130 ° C. or less, and subjecting it to dust collection through a bag filter. I know. It has been found that a trace amount of dioxin which still remains can be removed by blowing activated carbon into the front stage of the bag filter and adsorbing it, and collecting the dust and dust with the bag filter.

On the other hand, with respect to hydrogen chloride in exhaust gas, a large amount of alkaline powder such as lime is blown into the gas to be adsorbed, and then treated by collecting it with a bag filter. .

[0005] For the above reasons, an exhaust gas treatment process currently generally planned is as shown in FIG. In FIG. 5, the high-temperature exhaust gas discharged from the incinerator 1 is cooled by a heat recovery device 2 such as a boiler. However, since the temperature is still high at several hundred degrees Celsius, the temperature of the water spray chamber 3 is further increased.
, And after flowing to about 150 ° C. to 200 ° C., it is allowed to flow into the bag filter 4. Before flowing into the bag filter 4, activated carbon and lime are blown in by the activated carbon supply device 5 and the alkali powder supply device 6, respectively. Are rendered harmless by a fly ash treatment device (not shown) and discarded.

This method has the following problems. (1) In the temperature drop method by water injection, the object cannot be achieved unless all of the sprayed water evaporates while floating. Therefore, the spray chamber 3 requires a very large space volume, and the apparatus becomes large.

(2) The exhaust gas cooled by such a method becomes extremely humid. For example, assuming that the temperature of the original gas is 500 ° C. and the humidity is 0.2 [kg water / kg dry gas], the humidity after the water is injected so that the temperature becomes 150 ° C. is 0.38 kg / kg. kg, and the dew point temperature of the gas becomes 75 ° C. to 80 ° C. This is because the operation condition of the bag filter 4 is quite severe, and if there is any local cooling, dew condensation or corrosion due to the acid dew point of hydrogen chloride occurs.
Further, calcium chloride present in a large amount in fly ash is hygroscopic and deliquesces depending on the temperature and humidity of the gas, and absorbs moisture when the temperature is lowered at the time of stoppage, causing bag cloth to be clogged. In order to prevent these dangers and to operate stably for a long period of time, it is usually limited to about 200 ° C., and at most to 150 to 180 ° C. even if a special stable operation is devised.

(3) Since the gas temperature is high, the reaction efficiency of the blown lime is poor, and it is necessary to blow lime several times the hydrogen chloride equivalent, and more than half of the collected dust reacts with hydrogen chloride. Or it is unreacted lime, which is uneconomical as a device. (4) The activated carbon injected is mixed with a large amount of dust and lime and collected.
Neither reproduction nor reuse is possible.

(5) A large amount of dust (fly ash 7) collected by the bag filter 4 requires a large cost for its treatment.

[0010]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and an apparatus for treating exhaust gas which can solve the above-mentioned problems and reduce the processing cost and are more effective than the conventional one. I have.

[0011]

According to the exhaust gas treatment method of the present invention, in an exhaust gas treatment method for treating exhaust gas discharged from a heat facility, the exhaust gas is introduced into a gas cooler and cooled by a water cooler. The circulating water is brought into contact with the circulating water to cool the saturated gas at a low temperature, heated to a predetermined temperature by a heating device, and introduced into a bag filter for dust collection.

Before the cooling process, the exhaust gas is subjected to dust collection by a wet dust collector.

The heat treatment is performed by mixing a part of the exhaust gas in a high temperature state.

[0014] In the dust collection process, cooled circulating water is introduced into a wet dust collector to perform the dust collection process.

Further, an alkali blowing process for blowing an alkali powder is performed between the heating process and the dust collecting process.

Further, an activated carbon blowing process for blowing activated carbon is performed between the heating process and the dust collecting process.

Further, heavy metals and water-soluble salts are removed from the dust collected in the dust collection process, and the residue is returned to a heat facility for re-incineration.

According to the exhaust gas treatment apparatus of the present invention, in an exhaust gas treatment apparatus for treating exhaust gas discharged from a heat facility, a wet dust collector is provided downstream of the heat facility, and the exhaust gas is cooled by a water cooler downstream of the heat facility. Provide a gas cooler to be brought into contact with the circulating water, further provided a bag filter via a gas heating device in the subsequent stream, provided an activated carbon supply device and an alkali powder supply device between the gas heating device and the bag filter,
A sludge treatment device is provided to remove heavy metals and salts from the collected dust and return the residue to heat equipment for re-incineration.

The present invention is configured as described above, and the exhaust gas discharged from the heat equipment is subjected to dust collection processing in a wet dust collector, where 90 to 95% of the dust contained in the exhaust gas is collected. Most of harmful gases such as hydrogen chloride and sulfurous acid gas in the gas are absorbed by controlling the pH of the circulating water. The exhaust gas that has passed through the wet dust collector is cooled by a gas cooler from a saturated state at the wet bulb temperature (about 75 to 80 ° C.) and dehumidified.
The heat is radiated from the water cooler. Then, the bag filter is heated to a temperature suitable for the bag filter, for example, 130 ° C. by the heating device, and then flows into the bag filter to be subjected to dust collection processing.

The amount of exhaust gas flowing into the bag filter is reduced due to a decrease in temperature and humidity, and the load on the filter is reduced. To decrease. Most of the hydrogen chloride in the exhaust gas is absorbed by the wet dust collector, and the amount of calcium chloride in the dust is small, and there is no danger of absorbing bag cloth. Therefore, it can be used safely even in a batch furnace where the operation is frequently stopped. Dioxin is also effectively treated with a bag filter at a temperature of 130 ° C. or less.

Since the dust is collected as a slurry by the wet dust collector, the pH of the circulating liquid can be freely adjusted. For example, the apparatus is operated at pH 2 to elute heavy metals in fly ash into the liquid while absorbing hydrogen chloride. It is also possible to make heavy metals,
Alternatively, it can be easily rendered harmless as a solid without water-soluble salts. Then, the residue can be re-input to the thermal equipment to thermally decompose dioxin.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a heat recovery device 2 such as a boiler is interposed in an exhaust gas line L1 from an incinerator 1 which is a heat facility, and is connected to a wet dust collector 8. In the dust collector 8, circulating water is circulated by a pump 9, and the circulating water is in the form of a slurry containing dust. Therefore, a known device such as a venturi rubber is used. The line L2 from the dust collector 8 is connected to a gas cooler 10, and the structure of the gas cooler 10 is, for example, a packed bed type. Then, circulating water is circulated to the cooler 10 by a circulating water pump 11, and cooling heat is
The heat is dissipated. If the water cooler 12 is, for example, a so-called cooling tower system and circulating water is brought into direct contact with the atmosphere, cold water of about 30 to 35 ° C. can be easily obtained even in summer. Although not shown in the circulating water system of the wet dust collector 8 and the gas cooler 10, each of them has a pH value.
Is provided.

A heating device 13 is interposed in the line L3 from the gas cooler 10 and communicates with the bag filter 4, and is discharged from the bag filter 4 to the atmosphere through the line L4. The heating device 13 may be any one of a heating process using a small-scale fuel combustion device, and heating through a heat exchanger upstream of the system. In addition, an activated carbon supply device and an alkali powder supply device are connected downstream of the heating device 13 in the line L3.

On the other hand, the collected liquid-phase sludge is sent from the wet dust collector 8 to the sludge treatment equipment 15 via the line L5, and is collected from the circulating water system of the gas cooler 10 and by the bag filter. Line L6 from fly ash 7,
It is collected in the sludge treatment device at L7. The sludge treatment apparatus 15 employs the above-described method. The residue after separation and extraction of heavy metals M and washing and removal of water-soluble salts S such as calcium chloride is returned to the incinerator 1 by a line L8. . The activated carbon remaining in the collected fly ash 7 is returned to the supply device 5 for reuse by the line L9.

With the above configuration, 90 to 95% of the dust contained in the exhaust gas that has exited the incinerator 1 and passed through the heat recovery unit 2 is subjected to dust collection in the wet dust collector 8. . In addition, harmful gases such as hydrogen chloride and sulfurous acid gas in exhaust gas can also be controlled by controlling the pH of circulating water.
Most of it is absorbed. The gas that has passed through the wet dust collector 8 is dehumidified by the gas cooler 10 from its saturated state at the wet bulb temperature (about 75 to 80 ° C.), and is again heated by the heating device 1.
In 3, the bag filter 4 is heated to an appropriate temperature, for example, 130 ° C., and flows into the bag filter 4.

For example, the flow rate of the inflow gas is 150 ° C. and the humidity is 0.38 kg / kg according to the conventional method.
Assuming that the temperature is 130 ° C. and the humidity is 0.037 kg / kg according to the present invention, (273 + 130) / (273 + 15)
9) = 0.95 (1 + 1.6 × 0.037) / (1 + 1.6 × 0.3) due to the humidity difference (assuming that the volume of water vapor is 1.6 times the dry gas volume).
8) = 0.66 The total reduction rate is 0.95 × 0.66 = 0.63. That is, even if the amount of gas generated in the furnace is the same, the amount of air processed by the bag filter is 63%.

Next, in the embodiment shown in FIG. 2, as another method of the heating device 13 shown in FIG. 1, a line L10 provided with a bypass valve 14 from a line L1 is provided downstream of the cooler 10 in a line L3. The exhaust gas is heated by a part of the high-temperature gas being mixed, and the temperature of the gas flowing into the bag filter 4 is increased.

The embodiment shown in FIG. 3 is an embodiment in which a water cooler 12 A is provided in the circulating water system of the wet dust collector 8. This configuration has the advantage that the load on the downstream gas cooler 10 can be reduced and the water cooler 12 can be small.

The embodiment shown in FIG.
In a form applicable to the case where the exhaust gas temperature is relatively low and the amount of dust is small, the wet dust collector of the above embodiment is omitted, and the exhaust gas flows directly from the heat equipment 1 into the gas cooler 10 through the line L1. ing.

[0030]

The present invention is configured as described above and has the following effects. (1) The wet type dust collector has a high gas passing speed inside, so that the size of the device can be made much smaller than that of the conventional spray chamber, and it is economical. (2) The humidity and temperature of the gas flowing into the bag filter are low, the amount of air to be processed is reduced, and the load on the bag filter is reduced. (3) Most of the hydrogen chloride in the exhaust gas is absorbed by the circulating fluid of the wet dust collector, and the amount flowing into the bag filter is small. Even if it is necessary to blow lime beyond the allowable value, The reaction of lime at 130 ° C. or less is good, and the amount of blowing is very small. (4) Since there is almost no calcium chloride in dust, moisture absorption of bag cloth does not occur. Also, since there is no remaining hydrogen chloride, there is no need to worry about an acid dew point, and safe operation is possible. (5) Dioxin does not exist in exhaust gas after the bag filter treatment at 130 ° C. or less. Even if activated carbon needs to be blown for residual dioxin in exhaust gas, the amount of fly ash collected is small. In addition, as long as the activated carbon content is high and the activity of the activated carbon remains, it can be reused. (6) The amount of fly ash collected by the bag filter is reduced to about one-tenth of the conventional one. Other dust is recovered as slurry of the wet dust collector and does not contain blown lime, so that it is less than half of the conventional dust. (7) The slurry collected by the wet dust collector is a liquid phase,
By adjusting the PH of the circulating flow, detoxification such as removal of heavy metals or removal of water-soluble salts is possible. . If fly ash from the bag filter is mixed into the sludge treatment, the generation of fly ash can be reduced to zero theoretically.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an embodiment of the present invention.

FIG. 2 is a view showing a difference between the second embodiment and FIG. 1;

FIG. 3 is a diagram showing a configuration of a third embodiment.

FIG. 4 is a diagram showing a configuration of a fourth embodiment.

FIG. 5 is a diagram showing a configuration of a conventional exhaust gas treatment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Incinerator 2 ... Boiler 3 ... Water spray chamber 4 ... Bag filter 5 ... Activated carbon blowing device 6 ... Lime blowing device 7 ... Fly ash 8 ... Wet dust collector 9, 11 ... pump 10 ... gas cooler 12, 12A ... water cooler 13 ... gas heating device 14 ... bypass valve 15 ... sludge treatment device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 50/00 502 B01D 50/00 502Z 53/68 53/34 134B 53/77 134E 53/70

Claims (8)

[Claims] In an exhaust gas treatment method for treating exhaust gas discharged from a thermal facility, the exhaust gas is introduced into a gas cooler, brought into contact with circulating water cooled by a water cooler, and introduced into a low-temperature saturated gas. An exhaust gas treatment method, comprising: performing a cooling treatment on a substrate, heating the mixture to a predetermined temperature with a heating device, and introducing the dust into a bag filter. 2. The exhaust gas treatment method according to claim 1, wherein the exhaust gas is subjected to dust collection by a wet dust collector before the cooling process. 3. The exhaust gas treatment method according to claim 1, wherein the heat treatment is performed by mixing a part of high-temperature exhaust gas. 4. The exhaust gas treatment method according to claim 1, wherein the dust collection is performed by introducing cooled circulating water into a wet dust collector. 5. The exhaust gas treatment method according to claim 1, wherein an alkali blowing process for blowing an alkali powder is performed between the heating process and the dust collecting process. 6. The exhaust gas treatment method according to claim 1, wherein an activated carbon blowing process for blowing activated carbon is performed between the heating process and the dust collection process. 7. The exhaust gas treatment method according to claim 1, wherein heavy metals and water-soluble salts are removed from the dust collected in the dust collection processing, and the residue is returned to a heat facility for re-incineration processing. . 8. An exhaust gas treatment apparatus for treating exhaust gas discharged from a heat facility, wherein a gas dust collector is provided downstream of the heat facility, and the exhaust gas is brought into contact with circulating water cooled by a water cooler in the downstream stream. An exhaust gas treatment device, comprising a gas filter and a bag filter provided downstream of the gas filter through a gas heating device.