JPH119962A - Waste gas treatment method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste gas treatment method and an apparatus for the method by which treatment is efficiently carried out at lowered treatment cost as compared with a conventional method and which is especially suitable when a countermeasure method for treating dioxins and hydrochloric acid gas is carried out after dust removal by an already existing apparatus comprising a dry dust collecting apparatus. SOLUTION: In a waste gas treatment method for treating waste gas emitted out of a heating facility, the waste gas is subjected to dust collecting treatment by a dry dust collecting apparatus 17, the resultant waste gas is introduced into a wet scrubber 8 for absorptive gas treatment, the treated waste gas is then introduced into a gas cooling apparatus 10 and cooled to be a saturated gas at low temperature by being brought into contact with circulated water cooled by a water cooling apparatus 12, and the saturated gas is dehumidified, the dehumidified gas is heated to a prescribed temperature by a heating apparatus 12, and the heated gas is introduced into a bag filter and filtered for powder dust collection and removal.

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. 4, the high-temperature exhaust gas discharged from the incinerator 1 is cooled by a heat recovery device 2 such as a boiler. However, the temperature is still high at several hundred degrees Celsius.
, 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. In addition, calcium chloride present in a large amount in fly ash is hygroscopic and deliquesces depending on the temperature and humidity of the gas. In addition, when the temperature is lowered at the time of stoppage, it absorbs moisture and causes clogging of bag cloth. 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, the present invention addresses the above problems and reduces processing costs and is more effective than in the prior art, especially when one already owns a dry dust collector and subsequently has dioxin. It is an object of the present invention to provide an exhaust gas treatment method and an apparatus suitable for taking measures against hydrogen chloride.

[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 subjected to dust collection by a dry dust collector and introduced into a wet scrubber. Gas absorption process
The exhaust gas flows into a gas cooler, contacts the circulating water cooled by a water cooler, cools down to a low-temperature saturated gas, performs dehumidification processing, heats it to a predetermined temperature with a heating device, and introduces it into a bag filter. And perform dust collection processing.

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

In the gas absorption treatment, circulating water cooled by a water cooler is introduced into a wet scrubber to perform a dust collection treatment.

An alkali blowing process for blowing an alkaline 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, an excess portion of the waste water discharged in the gas absorption process is returned to the heat equipment to perform a drying process.

According to the exhaust gas treatment apparatus of the present invention, in an exhaust gas treatment apparatus for treating exhaust gas discharged from a thermal facility, a dry dust collector and a wet scrubber are provided downstream of the thermal facility, and the exhaust gas is cooled by water in the subsequent stream. A gas cooler is provided for contact with the circulating water cooled by the vessel, and a bag filter is further provided in the subsequent stream via a gas heating device, and an activated carbon supply device and an alkali powder supply device are provided between the gas heating device and the bag filter. And a fly ash treatment device for treating the collected dust.

Note that the dry dust collector of the preceding stage does not necessarily require high dust collection efficiency, and may have a simple structure such as an electric dust collector or a cyclone which can select any efficiency.

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 dry dust collector, where almost all fly ash contained in the exhaust gas is collected. Then, in the wet scrubber, harmful gases such as hydrogen chloride and sulfurous acid gas in the gas are mostly absorbed by controlling the pH of the circulating water.
The flue gas that has passed through the wet scrubber has its wet bulb temperature (7
From the saturated state at about 5 to 80 ° C.), the gas is cooled by a gas cooler and dehumidified, and the heat is radiated from the water cooler. Then, the appropriate temperature for the bag filter in the heating device,
For example, it is subjected to a heating process at 130 ° C., then flows into a bag filter, and is subjected to a dust collection process.

The amount of exhaust gas flowing into the bag filter decreases due to a decrease in temperature and humidity, and the load on the bag filter is reduced. On the other hand, the amount of fly ash is reduced by several tens of minutes due to the dust collection of the dry dust collector 17. To about 1. And
Most of the hydrogen chloride in the exhaust gas is absorbed by the wet scrubber, and the amount of calcium chloride in the dust is low, and there is no danger of absorbing bag cloth. Therefore, it can be used safely in batch furnaces that are frequently shut down. Dioxin is also 1
At temperatures below 30 ° C., it is effectively treated with a bag filter.

The amount of waste water discharged from the wet scrubber is determined by the concentration of slurry and salt contained therein. In the case of the present invention, it is determined by the concentration of salt generated by absorption of hydrogen chloride, for example, calcium chloride, and when fly ash is contained. It is greatly reduced in comparison.

Since fly ash collected by the dry dust collector and the bag filter is both powder, it is subjected to a conventional dry treatment method, for example, heating to decompose dioxin, and then kneading with cement or a chemical and water. Such as stabilizing heavy metals
So-called fly ash solidification can be performed.

In that case, if the drainage of the wet slab is small, all of it is used as water for kneading during solidification,
No drainage to the outside. If the wastewater is excessive, it is returned to the previous heating facility as a liquid and sprayed in a high-temperature region, and the water is evaporated to a powder, which is collected by a dry dust collector together with other fly ash generated in the heating facility. Then, similarly to the above, it is possible to make no drainage to the outside.

[0024]

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 L <b> 1 from an incinerator 1, which is a heat facility, and is connected to a dry dust collector 17 and further to a wet scrubber 8. Circulating water is circulated in the wet scrubber 8 by a pump 9. And
The line L2 from the wet scrubber 8 is connected to the gas cooler 10
The structure of the gas cooler 10 is, for example, a packed bed type. Circulating water is circulated through the gas cooler 10 by a circulating water pump 11, and cooling heat is radiated by a water cooler 12. The water cooler 12 is, for example, a so-called cooling tower system, and if the circulating water is brought into direct contact with the atmosphere, the water cooler 12 can easily have 30 to 35 even in summer.
Cold water of about ° C is possible. Although not shown in the circulating water system of the wet scrubber 8 and the gas cooler 10,
Each is provided with a function of adjusting pH.

A heating device 13 is interposed in the line L3 from the gas cooler 10 and communicates with the bag filter 4, and the bag filter 4 discharges the air 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. The line L
An activated carbon supply device 5 and an alkali powder supply device 6 are connected to the downstream of the heating device 13 of FIG.

On the other hand, the wet scrubber 8 and the gas cooler 1
Wastewater from 0 is collected in lines L5 and L6, respectively, and the remainder used for fly ash treatment 16 is returned to the incinerator 1 by line L8 and dried. The fly ash 7 collected by the bag filter 4 is collected by a line L7, and the fly ash 7 collected by the dry dust collector 17 is collected by a fly ash processing device 16 via a line L9. 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-described configuration, most of the fly ash contained in the exhaust gas from the incinerator 1 and passing through the heat recovery device 2 is collected by the dry dust collector 17.
Further, in the wet scrubber 8, harmful gases such as hydrogen chloride and sulfurous acid gas in the exhaust gas are mostly absorbed by controlling the pH of the circulating water. The exhaust gas that has passed through the wet scrubber 8 has a wet bulb temperature (75 to 8).
From the saturated state at about 0 ° C.), the humidity is reduced by the gas cooler 10, and the bag filter 4 is again heated by the heating device 13 to a temperature suitable for the bag filter 4, for example, 130 ° C.
Flowed into. For example, the flow rate of the inflow gas is 150 ° C. and the humidity is 0.38 kg / k according to the conventional method.
g, and the above-mentioned temperature of 130 ° C. and humidity of 0.037 kg / kg according to the present invention, (2
73 + 130) / (273 + 159) = 0.95 Due to the difference in humidity (assuming that the volume of water vapor is 1.6 times the dry gas volume), (1 + 1.6 × 0.037) / (1 + 1.6 × 0.3)
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 after the cooler 10 in a line L3. The high temperature gas is mixed with the flow, the exhaust gas is heated, and the temperature flowing into the bag filter 4 is increased.

The embodiment shown in FIG. 3 is an embodiment in which a water cooler 12A is provided in the circulating water system of the wet scrubber 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.

[0030]

The present invention is configured as described above and has the following effects. (1) Since the wet scrubber has a high gas passage speed inside, the size of the apparatus 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 scrubber, and the amount flowing into the bag filter is small. Even if it is necessary to inject lime exceeding 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. The remaining dust is collected in the dry dust collector and does not contain blown lime, so that it is less than half of the conventional dust. (7) If the wastewater from the wet scrubber is re-introduced into an incinerator to be dried into powder and collected by the dry dust collector 17 together with other fly ash, no drainage can be made to the outside.

[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 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 scrubber 9, 11 ... pump 10 ... gas cooler 12, 12A ... water cooler 13 ... gas heating device 14 ... bypass valve 16 ... fly ash treatment device 17 ... dry dust collector

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 50/00 501 B01D 50/00 502Z 502 51/10 A 51/10 B 53/18 E 53/18 53/26 A 53 / 26 53/34 134B 53/68

Claims (7)

[Claims] 1. An exhaust gas treatment method for treating exhaust gas discharged from a heat facility, wherein the exhaust gas is subjected to dust collection by a dry dust collector, introduced into a wet scrubber to perform a gas absorption treatment, and the exhaust gas is subjected to a gas cooler. Into a circulating water cooled by a water cooler, cooled to a low-temperature saturated gas, dehumidified, heated to a predetermined temperature by a heating device, and introduced into a bag filter to collect dust. A method for treating exhaust gas, comprising: 2. The exhaust gas treatment method according to claim 1, wherein the heat treatment is performed by mixing a part of the exhaust gas in a high temperature state. 3. The exhaust gas treatment method according to claim 1, wherein the gas absorption treatment is performed by introducing circulating water cooled by a water cooler into a wet scrubber to perform the gas absorption treatment. 4. 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. 5. 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. 6. The exhaust gas treatment method according to claim 1, wherein an excess portion of the wastewater discharged in the gas absorption treatment is returned to the heat equipment to perform a drying treatment. 7. An exhaust gas treatment apparatus for treating exhaust gas discharged from a thermal facility, wherein a dry dust collector and a wet scrubber are provided downstream of the thermal facility, and the exhaust gas is contacted with circulating water cooled by a water cooler in the subsequent stream. An exhaust gas treatment device, comprising: a gas cooler for causing a gas to flow, and a bag filter provided downstream of the gas cooler via a gas heating device.