JP3826714B2 - Waste disposal method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a waste treatment method, and more particularly to a method for reducing the amount of condensed water discharged from a moisture condenser from the system.
[0002]
[Prior art]
When waste is burned at a high temperature in a gasification melting furnace and the exhaust gas temperature is set to 800 to 1400 ° C., dioxins in the exhaust gas are decomposed, and further, the exhaust gas is rapidly cooled to 200 ° C. or less by an exhaust gas cooling device to re-synthesize dioxins. Can be prevented. 200 ° C. The flue gas is quenched to below, are contained harmful gases such as solids or SO ₂ of dusts, to remove solids such as dust by a bag filter or the like, harmful gas ₂ such as SO Needs to be removed by desulfurization equipment. Further, the steam-saturated exhaust gas from which solid substances such as dust and harmful gases such as SO ₂ are removed is subjected to moisture removal by an indirect cooling type moisture condenser and supplied to a boiler or the like as a high calorie fuel gas.
[0003]
[Problems to be solved by the invention]
However, the condensed water discharged from the moisture condenser has a high ammonia concentration and cannot be discharged out of the system as it is for environmental conservation. For this reason, the water treatment equipment for draining condensed water out of a system is required, and there exists a problem that a water treatment equipment cost and a running cost rise.
[0004]
An object of the present invention is to provide a method for reducing the amount of condensed water outside the system.
[0005]
[Means for Solving the Problems]
As a result of examining the water balance of the waste treatment facility, the present inventors have obtained the following knowledge.
[0006]
(A) The water supplied to the waste treatment facility having the gasification melting furnace, the exhaust gas cooling device, the exhaust gas cleaning device, and the moisture condenser is the water contained in the waste and the water spray supplied to the exhaust gas cooling device. Water. On the other hand, the water | moisture content discharged | emitted out of the system is the water | moisture content in the exhaust gas from which the condensed water discharged | emitted from the water | moisture content condenser and water | moisture content were removed. Therefore, the water content in the exhaust gas from which water has been removed is balanced with the amount of water contained in the waste, and the condensed water discharged from the water condenser is reused as water for sprinkling supplied to the exhaust gas cooling device. If possible, there will be no extra drainage and no water treatment facility will be required. On the other hand, even if a situation occurs in which the amount of moisture contained in the waste is large and cannot be balanced with the amount of moisture in the exhaust gas from which moisture has been removed, only the excess condensed water needs to be treated. Thus, if only the excessive condensed water is water-treated, the load of the water treatment facility can be reduced. As a result, water treatment facility costs and running costs can be greatly reduced as compared with the conventional case.
[0007]
(B) In order to confirm the above idea, a test was conducted in a waste treatment test facility (waste treatment amount: 20 mass t / d scale). The test results are shown below.
(A) When condensed water is used as water for exhaust gas cooling, there is a concern about the concentration of salts and the like in the condensed water, but since the salts are removed by the exhaust gas purifier after cooling the exhaust gas, they are not concentrated in the condensed water. On the other hand, the ammonia content in the condensed water is concentrated, but the ammonia concentration in the condensed water is a constant concentration of about 2000 mg / l.
[0008]
(B) There was a concern that the concentration of nitrogen oxides in the exhaust gas when the gas whose moisture was adjusted by the moisture condenser was boiler-combusted was increased due to an increase in the ammonia content. However, the nitrogen oxide concentration in the exhaust gas showed an increasing tendency during the test, but it became a constant value at about 50 ppm, which is the target concentration of 100 ppm or less, and the concentration did not increase any more.
[0009]
The present invention has been made on the basis of the above knowledge, and the gist thereof is “a gasification melting furnace for gasifying and melting waste, and an exhaust gas cooling device for rapidly cooling the exhaust gas discharged from the gasification melting furnace,” , An exhaust gas cleaning device that removes dust and harmful gas in the exhaust gas rapidly cooled by the exhaust gas cooling device, and a moisture condenser that removes moisture in the exhaust gas from which dust and harmful gas have been removed by the exhaust gas cleaning device A waste treatment method using a waste treatment facility, wherein condensed water generated from the moisture condenser is used as cooling water for the exhaust gas cooling device, and partially condensed water in which ammonia content is concentrated is water treatment facility it is in the process method of processing waste which is characterized in that ".
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a process diagram showing an example of the waste treatment method of the present invention.
As shown in the figure, the waste is put into the gasification melting furnace 1 and incinerated in a high temperature environment. In addition, although not shown, the water content of waste to be input is also adjusted in advance by a drying device, a dehydrating device, or the like. Waste generated in the gasification melting furnace generates a gas by a thermal decomposition reaction, and the thermal decomposition residue becomes a molten state in a high temperature environment and is separated from the molten slag and the molten metal with specific gravity and discharged from the lower part 2 of the furnace. The produced gas is discharged from the gas discharge port 3 to the exhaust gas cooling device 4 in the next process as exhaust gas. The temperature of the exhaust gas before being discharged to the exhaust gas cooling device 4 is adjusted in the gasification melting furnace 1 so as to be a dioxin decomposition temperature of 800 to 1400 ° C. The exhaust gas is rapidly cooled by the sprinkling cooling type exhaust gas cooling device 4 and adjusted to a temperature of 200 ° C. or lower. The reason for adjusting to 200 ° C. or lower is to prevent resynthesis of dioxins.
[0011]
The sprinkling cooling type exhaust gas cooling device 4 used in the present invention is desirably used so as to control the amount of sprinkling so that drainage is not generated. The exhaust gas cooled to a predetermined temperature is dedusted by the bag filter 5 by adding slaked lime or the like to the exhaust gas. By adding slaked lime or the like in this way, salt, sulfur oxides, and the like are removed together with dust. Next, salt, sulfur oxide, etc. that could not be removed by the bag filter 5 are removed and further removed by the desulfurization device 6. In addition, the apparatus comprised from the bag filter 5, the desulfurization apparatus 6, etc. is named generically, and is also called the exhaust gas purification apparatus 10 below. The exhaust gas from which dust, sulfur oxides, and the like have been removed by the exhaust gas cleaning device 10 in this way, moisture in the exhaust gas is removed as condensed water by the moisture condenser 7. The exhaust gas from which moisture has been removed by the moisture condenser 7 is sent to an energy conversion device such as a boiler 8 and used as fuel gas.
[0012]
The ammonia concentration in the condensed water is as high as about 600 mg / l and cannot be drained out of the system as it is for environmental conservation. For this reason, the water treatment equipment for draining condensed water out of a system is required, and there exists a problem that a water treatment equipment cost and a running cost rise.
[0013]
In the present invention, this condensed water is temporarily stored in the circulation pit 9 or the like and used as cooling water for the exhaust gas cooling device 4. Thereby, the scale of the water treatment facility which processes condensed water can be made small. In general, many steps are required to treat the condensed water, and it is effective from the viewpoint of reducing waste treatment costs that the scale of the water treatment facility can be reduced. The main components to be treated among the components of condensed water are ammonia and cyan.
[0014]
FIG. 2 is a process diagram showing an example of a method for treating condensed water.
As shown in the figure, the condensed water is once received in the water storage tank 11 and the pH is adjusted to alkaline in the pH adjustment tank 12 with an aqueous NaOH solution. Heating is performed with steam in the stripping tank 13, deammonia (stripping) is performed with air, and the ammonia concentration is reduced to 12.1 mg / l. The ammonia gas generated here is collected as ammonium sulfate in a sulfuric acid aqueous solution by No. 1 scrubber 23. In this process, cyan in the condensed water is also removed from the condensed water, but it is not absorbed by the sulfuric acid aqueous solution of No. 1 scrubber 23 but is absorbed by the aqueous NaOH solution by No. 2 scrubber 24. The aqueous NaOH solution that has absorbed cyan is returned to the neutralization tank 14, and water containing cyanide is neutralized with an aqueous sulfuric acid solution, and the contact oxidation tank 15, No. 1 precipitation tank 16, sterilization tank 17 and No. 2 precipitation tank. 18 is bioprocessed. Water after biological treatment has a cyan concentration of 0.1 mg / l or less. The water after this biological treatment meets the drainage standards and can be discharged. Further, since it is necessary to reduce the salt concentration and COD for circulation in the system, in order to reduce COD, the sand filter 19 and the activated carbon tower 20 are passed through, the COD concentration is set to 5 mg / l or less, and the reverse osmosis membrane 22 is passed The salt concentration is lowered to a level at which the electric conductivity is 1 ms / cm or less. As described above, in order to use condensed water as circulating water, the water treatment process becomes complicated.
[0015]
Here, as shown in FIG. 1, when this condensed water is once stored in the circulation pit 9 and used as the cooling water of the exhaust gas cooling device 4, the ammonia content in the condensed water is concentrated. The ammonia concentration of the water becomes a constant concentration of about 2000 mg / l. The reason for this is not clear, but it is presumed that the ammonia concentration of the condensed water becomes a constant concentration of about 2000 mg / l by the following mechanisms (1) to (4).
[0016]
(1) Ammonia is generated during combustion in the gasification and melting furnace, with the nitrogen content in the waste put into the gasification and melting furnace. This ammonia content is condensed in the condenser and dissolves during the condensation of moisture.
[0017]
(2) When this condensed water is blown into the gas cooling facility, the condensed water evaporates in the gas cooling facility, and water vapor and ammonia gas become main components. Ammonia gas generated from the ammonia gas generated in the gasification melting furnace and the condensed water blown in is dissolved in the condensed water by the condenser, and a part of the ammonia gas remains in the product gas without being dissolved.
[0018]
(3) When the ammonia content in the product gas before condensation increases, the ammonia concentration in the condensed water also increases, but the ammonia content remaining in the product gas after moisture condensation also increases in a constant distribution.
[0019]
(4) The ammonia concentration in the condensed water becomes a constant value when the amount of ammonia that is constantly generated from the waste is equal to the amount of ammonia that is distributed and increased in the product gas after condensation.
[0020]
In addition, the nitrogen oxide concentration in the exhaust gas when the gas whose moisture was adjusted by the moisture condenser was boiler-combusted showed an upward trend during the test, but became a constant value at about 50 ppm, which is the target concentration of 100 ppm or less. The concentration does not increase. The reason for this is not clear, but it is estimated that the nitrogen oxide concentration in the exhaust gas becomes a constant value of about 50 ppm by the following mechanism.
[0021]
That is, the ammonia (NH ₃ ) remaining in the product gas has a constant value as described above, and is estimated to be decomposed by the reaction formulas ( ₁ ) and ( ₂ ) shown below in the combustion process of the product gas. Is done.
[0022]
2NH ₃ +7/20 ₂ → 2NO ₂ + 3H ₂ O ――――― ▲ 1 ▼
4NH ₃ + 3NO ₂ → 7 / 2N ₂ + 6H ₂ O ――――― ▲ 2 ▼
Nitrogen oxides increase in the oxidation reaction of (1), but some NH ₃ is decomposed into nitrogen at a constant rate by the decomposition reaction of (2), so that the nitrogen oxide becomes a constant value at a low level. Estimated.
[0023]
【Example】
The test was conducted in a waste treatment test facility (waste treatment amount: 20 mass t / d scale, equipment configuration: the same as in FIG. 1). The test method and test results are shown below.
[0024]
(Comparative example)
Waste is pre-dried to about 10% by mass moisture and then charged into the gasification melting furnace at a rate of 20 mass t / d. Industrial water is blown into the exhaust gas cooling device 4 at an average of 420 L / Hr, and the exhaust gas is about 1000 ° C. To about 150 ° C. Moreover, since the moisture in the outlet gas of the condenser was maintained at 30% by weight, an average of 420 L / Hr of condensed water was generated. The nitrogen oxide concentration in the exhaust gas after boiler combustion after 6.5 hours was as low as 17.3 ppm, but an average of 420 L / Hr of condensed water was generated, and this condensed water contained about 760 ppm of ammonia. In addition, water treatment was required to reduce the ammonia concentration below a predetermined value.
[0025]
(Invention Example 1)
The waste is pre-dried to a moisture content of about 10% by mass and charged into the gasification melting furnace at a rate of 20 mass t / d. Condensed water is blown into the exhaust gas cooling device 4 at an average flow rate of 420 L / Hr to reduce the exhaust gas Cooled from 1000 ° C to about 150 ° C. The condensed water flow rate was 420 L / Hr on average as a result of maintaining the water concentration in the outlet gas of the condenser at 30% by weight, which was consistent with the required cooling water flow rate in the exhaust gas cooling device 4.
[0026]
As a result of injecting condensed water into the gas cooling device at an average of 420 L / Hr and cooling the exhaust gas from about 1000 ° C to about 150 ° C, the nitrogen oxide concentration in the exhaust gas after boiler combustion was 53 ppm after 6.5 hours However, it did not increase after that, and the concentration was unnecessary for the denitration treatment of the exhaust gas. Moreover, since the amount of condensed water generated and the amount used in the gas cooling device were balanced, there was no surplus water of condensed water, so water treatment was unnecessary. In addition, the COD, suspended solids concentration (SS), potassium, calcium, magnesium concentration, etc. in the condensed water were the same as when industrial water was blown, and there was almost no influence of the use of condensed water. On the other hand, the sulfur oxide concentration and carbon dioxide concentration in the exhaust gas were the same as when industrial water was used in the gas cooling apparatus, and there was almost no influence of the use of condensed water.
[0027]
(Invention Example 2)
The waste is pre-dried to about 20% by mass of moisture and then charged into the gasification melting furnace at a rate of 20 mass t / d. As a result of a test cooled to about 150 ° C., 60 L / Hr of surplus water was generated on average. This excess water amount was 1/9 of the generation amount shown in the comparative example. Further, the ammonia concentration in the surplus water was about 2000 ppm, which was about 3 times the concentration of the comparative example. However, the scale of the water treatment facility was reduced to 1/9. On the other hand, the concentration of nitrogen oxides in the exhaust gas after boiler combustion increased to 49 ppm after 6.5 hours, but it did not increase after that, and was a concentration that did not require denitration treatment of the exhaust gas.
[0028]
【The invention's effect】
By this invention, it becomes possible to reuse the condensed water discharged | emitted from a water | moisture content condenser, and can reduce water treatment equipment cost and running cost.
[Brief description of the drawings]
FIG. 1 is a process diagram showing an example of a waste treatment method of the present invention.
FIG. 2 is a process diagram showing an example of a method for treating condensed water.
[Explanation of symbols]
1: gasification melting furnace,
2: Lower part of furnace,
3: Gas outlet
4: Exhaust gas cooling device,
5: Bug filter,
6: Desulfurization equipment,
7: Condenser,
8: Boiler,
9: Circulation pit,
10: Exhaust gas cleaning device,
11: Water tank
12: pH adjustment tank,
13: stripping tank,
14: Neutralization tank,
15: Contact oxidation tank,
16: No. 1 sedimentation tank,
17: Sterilization tank,
18: No. 2 sedimentation tank,
19: sand filter,
20: Activated carbon tower,
21: adjustment tank,
22: Reverse osmosis membrane,
23: No.1 scrubber
24: No.2 scrubber
25: Chimney.

Claims (1)

A gasification melting furnace for gasifying and melting waste, an exhaust gas cooling device for rapidly cooling the exhaust gas discharged from the gasification melting furnace, and removing dust and harmful gas in the exhaust gas rapidly cooled by the exhaust gas cooling device A waste treatment method using a waste treatment facility having an exhaust gas cleaning device and a moisture condenser for removing moisture in the exhaust gas from which dust and harmful gases have been removed by the exhaust gas cleaning device, the moisture condenser The waste water treatment method is characterized in that the condensed water generated from the exhaust gas is used as cooling water for the exhaust gas cooling device, and the partially condensed water enriched with ammonia is treated with a water treatment facility .

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