JP2002195544A - Cooling method for waste gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling method for waste gas in which dioxins can be prevented from being resynthesized and waste water is not produced without increasing the cost of a device and a running cost. SOLUTION: When the flow rate of waste gas from a waste combustion and treatment device is x m3 (normal state)/hr, the length of a waste gas introducing part is x/3 mm or more, the exhaust speed of waste gas in a cooling tower is 0.2 to 2 m/sec, a retention time of waste gas in the cooling tower is 3 to 20 seconds, the diameter of water droplet of water jetted from a water distributing nozzle is 150 μm or smaller and the temperature of a gas exhaust part is 120 to 200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas cooling method capable of preventing resynthesis of dioxins (hereinafter simply referred to as dioxins) and generating no waste water.

[0002]

2. Description of the Related Art Conventionally, exhaust gas from a waste combustion treatment apparatus is introduced from above a cooling tower, and the exhaust gas is cooled by spraying water.
The exhaust gas after cooling was discharged from below the cooling tower. In the cooling tower, an exhaust gas introduction part is arranged at an upper end, a water spray nozzle for spraying water downward is provided inside, and a drain collection part is formed at a lower end, and a drain collection part is formed. A gas discharge portion that opens downward is provided above. In such a conventional exhaust gas cooling device, since water is sprayed into the exhaust gas flowing downward, the falling direction of the water droplet and the direction of the exhaust gas flow are the same, the residence time of the water droplet in the exhaust gas is short, and the water droplet evaporates completely. Because of the lack of water, the generation of wastewater is inevitable. Furthermore, temperature unevenness in the cooling device due to gas drift is likely to occur, and cooling unevenness during water spray cooling is likely to occur, so that there is a high possibility that water droplets that cannot be completely evaporated are generated, and drainage is likely to occur. When wastewater is generated in this way, a water treatment facility is required, which leads to an increase in the facility cost and running cost, and improvement has been required.

[0003]

For example, Japanese Patent Application Laid-Open No. 2000-111
In the publication No. 018, as shown in FIG. 1, an exhaust gas introduction unit 2 for introducing exhaust gas into the cooling tower 1 is provided below the cooling tower 1,
By providing a gas discharge unit 3 for discharging the cooled exhaust gas to the flue above the cooling tower 1, the flow of exhaust gas in the cooling tower is formed upward, and the exhaust gas introduction unit 2 and the gas discharge unit 3 There is disclosed an exhaust gas cooling device provided with a water spray nozzle 4 between which water can be jetted upward.

However, in this apparatus, since the exhaust gas is once introduced downward into the tower, the temperature drop in the convection section before water cooling is about 100 ° C. or more, and thus the exhaust gas is first cooled slowly. Then, the resynthesis of dioxin easily occurs. Therefore, in this structure, there is a problem that dioxin removal by a catalyst or the like is indispensable in a subsequent process, which leads to an increase in equipment cost and an increase in running cost.

Japanese Patent Application Laid-Open No. 11-141856 discloses that FIG.
As shown in the figure, the cooling tower 1 has an inner tower 6 partitioned by a partition plate 5, and has an exhaust gas introduction unit 2 for introducing exhaust gas so as to collide with the partition plate 5. An exhaust gas cooling device having a water spray nozzle 4 between the gas discharge unit 3 is disclosed. In this cooling method, exhaust gas is introduced so as to collide with the partition plate 5, and while giving a swirling flow to the exhaust gas, the exhaust gas is introduced below the cooling tower 1 and guided upward of the cooling tower 1; Water is sprayed downward from a sprinkling nozzle 4 between the gas discharge section 2 and the gas discharge section 3 to cool the exhaust gas.

However, even in this cooling method, in the cooling tower 1, since the exhaust gas is once introduced downward into the tower, the temperature drop in the convection section before water cooling becomes about 100 ° C. or more. When the exhaust gas is first slowly cooled, re-synthesis of dioxin easily occurs. Therefore, in this structure, there is a problem that dioxin removal by a catalyst or the like is indispensable in a subsequent process, which leads to an increase in equipment cost and an increase in running cost. Further, since the structure of the cooling tower 1 becomes complicated, equipment costs are increased, and dust tends to adhere to the inner tower 6, so that there is a problem that maintenance for dust removal takes time.

An object of the present invention is to provide a method for cooling exhaust gas which can prevent re-synthesis of dioxin and does not generate wastewater without increasing equipment costs and running costs.

[0008]

Means for Solving the Problems The present inventor conducted a test using a flue gas cooling mini-plant apparatus and examined a method for minimizing the drift of flue gas as much as possible.

FIG. 3 is a conceptual diagram of an exhaust gas cooling mini-plant apparatus used for the test. As shown in the drawing, an exhaust gas introducing section 2 having a cooling tower 1 and having the same axis as the cooling tower 1 is provided at an upper part of the cooling tower 1, a water spray nozzle 4 is provided at an upper part of the cooling tower 1, and a lower part of the cooling tower 1 is provided. Using a flue gas cooling mini-plant apparatus (waste treatment amount: 2 mass t / d or 20 mass t / d scale) having a gas discharge section 3, the length of the exhaust gas introduction section (with the cooling tower excluding the curved section) The relationship between the length of the pipe on the same axis: hereinafter simply referred to as the length of the exhaust gas introduction section) and the exhaust gas drift index was investigated.

The prerequisites for this test are described below. FIGS. 4A and 4B are conceptual diagrams showing the position of the thermometer in the cooling tower when the exhaust gas drift index is obtained.
FIG. 4A is a side view, and FIG. 4B is a plan view.

As shown in FIG. 1A, the thermometer is located at a position () immediately above the water spray nozzle 4 of the cooling tower 1, at a substantially intermediate point position () just above the water spray nozzle 4 and immediately above the gas discharge part 3, and at a gas discharge part. At three positions immediately above (3), six positions (A to F) at circumferentially 60-degree intervals as shown in FIG.
Of about 50 mm was inserted into the inside of the cooling tower 1 and the measured values were expressed as TA, TB,..., TE, TF, and the exhaust gas drift index was obtained.

That is, the flue gas drift P is obtained from the following equation, and the value obtained by indexing the P value when the length of the gas introduction portion is １/3 as 1 is defined as the flue gas drift index for convenience. P = (maximum value of TA to TF) / (minimum value of TA to TF) × (maximum value of TA to TF) / (minimum value of TA to TF) × (maximum value of TA to TF) / (TA to (Minimum value of TF) FIG. 5 is a conceptual diagram showing the definition position of the superficial velocity of the exhaust gas.

That is, the superficial velocity V (m / sec) of the exhaust gas is obtained from the following equation based on the cross-sectional area of the maximum diameter portion shown in FIG. V = G / 3600 × (273 + T1) / 273 / (πD 2/4) However, G: exhaust gas flow rate of the cooling tower entry side (m ³ (standard state) / h), T1: cooling tower entry side exhaust gas Temperature (° C.), D: Maximum diameter of cooling tower (m).

Based on the above prerequisites, tests were conducted to determine the relationship between the length of the exhaust gas introduction section and the exhaust gas drift index.
(A) FIG. 6 is a graph showing the relationship between the exhaust gas introduction section length and the exhaust gas drift index. The test conditions at this time were as follows: the superficial velocity of the exhaust gas in the cooling tower was 1 m / sec, the residence time of the exhaust gas in the cooling tower was 10 seconds, and the water droplet diameter of the water jetted from the water spray nozzle was It is about 100 μm, and the outlet temperature of the cooling tower is 180 ° C.

[0015] As shown in FIG.
When it is less than / 3 mm, the exhaust gas drift index increases rapidly, but when it is χ / 3 mm or more, the exhaust gas drift index becomes almost constant regardless of the test scale.

(B) The relationship between the superficial velocity and the amount of waste water generated was investigated using an exhaust gas cooling mini-plant apparatus having a waste treatment amount of 20 mass t / d. FIG. 7 is a graph showing the relationship between the superficial velocity in the cooling tower and the amount of generated wastewater. The test conditions at this time were as follows: the length of the exhaust gas introduction section was constant at χ / 2 mm, the residence time of the exhaust gas in the cooling tower was 7 seconds, the water droplet diameter of the water ejected from the water spray nozzle was about 85 μm, The outlet temperature of the tower is 180 ° C.

As shown in FIG. 1, the superficial velocity is 0.2 to 2 m / se.
The amount of generated wastewater becomes zero in the range of c. The reason why drainage is generated outside this range of superficial superficial velocity is that if the superficial superficial velocity is less than 0.2 m / sec, the gas flow will not be unidirectional and the gas flow will be easily disturbed, It is presumed that the water comes into contact with the inner wall of the cooling tower and becomes wastewater without evaporating.If the superficial tower speed exceeds 2 m / sec, the gas flow is likely to be disturbed as well, This is presumed to be due to contact with the inner wall of the cooling tower, which is discharged without being evaporated.

(C) The relationship between the residence time of the exhaust gas and the amount of waste water generated was investigated using an exhaust gas cooling mini-plant apparatus having a waste treatment amount of 20 mass t / d scale. FIG. 8 is a graph showing the relationship between the residence time of exhaust gas and the amount of generated wastewater. The test conditions at this time were that the length of the exhaust gas introduction section was χ / 2 mm.
It is constant, the superficial velocity of the exhaust gas in the cooling tower is 1.2 m / sec, the water droplet diameter of the water jetted from the water spray nozzle is about 85 μm, and the cooling tower outlet temperature is 180 ° C.

As shown in FIG.
The amount of drainage generated becomes zero in the range of ~ 20 seconds. If the residence time of the exhaust gas is less than 3 seconds or more than 20 seconds, it is estimated that drainage is generated because the control of the watering amount becomes unstable.

(D) Using a flue gas cooling mini-plant apparatus with a waste treatment amount of 20 mass t / d, the relationship between the water droplet diameter of water spouted from the watering nozzle and the amount of drainage was investigated.
FIG. 9 is a graph showing the relationship between the water droplet diameter and the amount of generated wastewater. The test conditions at this time were as follows: the exhaust gas introduction section length was constant at χ / 2 mm, and the superficial velocity of the exhaust gas in the cooling tower was 1.2 m / sec.
The exhaust gas residence time is 7 seconds, and the outlet temperature of the cooling tower is 180 ° C.

As shown in the figure, when the water droplet diameter is 150 μm or less, the amount of drainage generated becomes zero. The present invention has been made based on the above findings, and the gist is as follows.

(1) A cooling system having a cooling tower, an exhaust gas introduction part having the same axis as the cooling tower at the upper part of the cooling tower, a water spray nozzle at the upper part in the cooling tower, and a gas discharge part at the lower part of the cooling tower. A method of cooling exhaust gas from a waste combustion treatment device sent from an exhaust gas introduction unit to a cooling tower using an apparatus, cooled by water jetted from a water spray nozzle, and then discharged from the cooling tower via a gas discharge unit In the above, when the flow rate of the exhaust gas from the waste combustion treatment device is χm ³ (standard state) / hr, the length of the exhaust gas introduction part is χ / 3 mm or more, and the superficial velocity of the exhaust gas in the cooling tower is 0.2 to 2 m / sec, the residence time of the exhaust gas in the cooling tower is 3 to 20 seconds,
A method for cooling exhaust gas, wherein a water droplet diameter of water spouted from a water spray nozzle is 150 μm or less, and a temperature of a gas discharge part is 120 to 200 ° C.

(2) The exhaust gas cooling method according to the above (1), wherein the water amount per hole of the water spray nozzle is 750 L / hr or less. (3) The exhaust gas cooling method according to the above (1), wherein the number of holes and the inlet water pressure of the water spray nozzle satisfy the following expression (1).

(Number of nozzle holes) × (Nozzle inlet water pressure (MPa)) ≧ 2.5 MPa (1) (4) Water and nitrogen, or
The exhaust gas cooling method according to the above (1), wherein a two-fluid nozzle for injecting water and air is used.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for reducing a water droplet diameter to 150 μm or less will be described below. First, the relationship between the amount of water sprayed per nozzle hole and the water droplet diameter was investigated using an exhaust gas cooling mini-plant apparatus having a waste treatment amount of 20 mass t / d.

FIG. 10 is a graph showing the relationship between the amount of water spray per nozzle hole and the diameter of water droplets. The test conditions at this time were as follows: the exhaust gas introduction section length was constant at χ / 2 mm, the superficial velocity of the exhaust gas in the cooling tower was 1.2 m / sec, the exhaust gas residence time was 7 seconds, and the cooling tower outlet temperature Is 180 ° C. Further, the test was performed with the value of (number of nozzle holes) × (nozzle inlet water pressure (MPa)) kept constant at 2 MPa.

As shown in the figure, a water droplet size of 150 μm or less can be obtained when the amount of water sprayed per nozzle hole is 750 L / hr or less. Next, the relationship between (number of nozzle holes) × (nozzle inlet water pressure (MPa)) and water droplet diameter was investigated using an exhaust gas cooling mini-plant apparatus having a waste treatment amount of 20 mass t / d.

FIG. 11 is a graph showing the relationship between (number of nozzle holes) × (nozzle inlet water pressure (MPa)) and water droplet diameter. Incidentally, the test conditions at this time, the exhaust gas introduction section length χ / 2mm constant, the superficial velocity of the exhaust gas in the cooling tower is 1.2m / sec,
Exhaust gas residence time is 7 seconds, cooling tower outlet temperature is 180 ° C
It is. In addition, the test was performed with a constant water spray amount of 750 L / hr per nozzle hole.

As shown in the figure, when (number of nozzle holes) × (nozzle inlet water pressure (MPa)) is 2.5 MPa or more, a water droplet diameter of 150 μm or less is obtained. Even if only water is used as the watering nozzle, if the above conditions are satisfied, no drainage from the cooling tower is generated. However, if a two-fluid nozzle of water and nitrogen (or air) is used, the water droplet diameter becomes larger. Because of the small size, no drainage occurs even if there is a sudden change in the amount of watering.

The amount of water spray may be controlled using feedback control or other control methods so as to reach a predetermined exhaust gas temperature, and is used in combination with the cooling tower operation method of the present invention.

[0031]

[Example] Waste treatment amount: Test result of cooling exhaust gas generated in a gasification and melting test furnace of a shaft furnace type of 20 mass t / d scale with a test cooling device (waste disposal amount: 20 mass t / d) Is described below.

All tests were conducted by controlling the amount of water sprayed so that the outlet exhaust gas temperature of the test cooling device was 120 to 200 ° C. In each case, three days were tested. Table 1 shows the test conditions and the results.

[0033]

[Table 1]

As shown in the table, when the exhaust gas flow rate was χm ³ (standard state) / hr, the length of the exhaust gas introduction section was 排 ガ ス / 3 mm or more using the test apparatus shown in FIG. Superficial superficial velocity is 0.2-2m / sec, residence time of exhaust gas is 3-20
Seconds, and the diameter of the water jetting from the watering nozzle is 150 μm
In the following examples of the present invention, no wastewater is generated, and the dioxin concentration in the exhaust gas is 0.03 ng-TEQ / m ³ (standard state).
It was below.

Further, even if the test apparatus shown in FIG. 3 is used,
As shown in Comparative Examples 1 to 7, wastewater was generated because the length of the exhaust gas introduction portion, the superficial velocity of the exhaust gas, the residence time of the exhaust gas, and the diameter of the water droplet jetted from the water spray nozzle were out of appropriate ranges.

On the other hand, in the conventional examples 1 and 2 using the test apparatus (waste disposal amount: 2 mass t / d) shown in FIGS. 1 and 2, no wastewater was generated, but the dioxin concentration in the exhaust gas was low.
0.2 ng-TEQ / m ³ (standard state) or more, which was higher than that of the present invention.

[0037]

According to the method for cooling exhaust gas of the present invention, not only no waste water is generated but also the dioxin concentration in the exhaust gas at the outlet of the cooling tower becomes extremely low, and dioxin removal equipment using a catalyst, an adsorbent, etc. in the subsequent stage. Becomes unnecessary.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing the configuration of the invention described in JP-A-2000-111018.

FIG. 2 is a conceptual diagram showing the configuration of the invention described in JP-A-11-141856.

FIG. 3 is a conceptual diagram of an exhaust gas cooling mini-plant apparatus used for a test.

FIG. 4 is a conceptual diagram showing the position of a thermometer in a cooling tower when an exhaust gas drift index is obtained. FIG. 4 (a) is a side view, and FIG. 4 (b) is a plan view.

FIG. 5 is a conceptual diagram showing a definition position of a superficial velocity of exhaust gas.

FIG. 6 is a graph showing a relationship between an exhaust gas introduction section length and an exhaust gas drift index.

FIG. 7 is a graph showing a relationship between a superficial velocity in a cooling tower and an amount of generated wastewater.

FIG. 8 is a graph showing the relationship between the residence time of exhaust gas and the amount of generated waste water.

FIG. 9 is a graph showing a relationship between a water droplet diameter and an amount of generated wastewater.

FIG. 10 is a graph showing the relationship between the amount of water spray per nozzle hole and the diameter of a water droplet.

FIG. 11 is a graph showing the relationship between (number of nozzle holes) × (nozzle inlet water pressure (MPa)) and water droplet diameter.

[Explanation of symbols]

 1: cooling tower, 2: exhaust gas introduction part, 3: gas discharge part, 4: water spray nozzle, 5: partition plate, 6: inner tower.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Ishida 3, Oaza Hikari, Kashima City, Ibaraki Prefecture Sumitomo Metal Industries Kajima Works F-term (reference) 3K070 DA05 DA37 DA83

Claims (4)

[Claims] 1. A cooling device comprising a cooling tower, an exhaust gas introduction part having the same axis as the cooling tower at the upper part of the cooling tower, a water spray nozzle at an upper part in the cooling tower, and a gas discharge part at a lower part of the cooling tower. In the cooling method of the exhaust gas, the exhaust gas from the waste combustion treatment device sent from the exhaust gas introduction unit to the cooling tower is cooled by water jetted from the water spray nozzle, and then discharged from the cooling tower via the gas discharge unit. , The flow rate of exhaust gas from the waste combustion treatment equipment is χm ³ (standard condition) / h
When r, the length of the exhaust gas introduction section is χ / 3 mm or more, the superficial velocity of the exhaust gas in the cooling tower is 0.2 to 2 m / sec, and the residence time of the exhaust gas in the cooling tower is 3 to 20 seconds. The water droplet diameter of the water spouting from the watering nozzle is 150 μm or less,
A method for cooling exhaust gas, wherein the temperature of the gas discharge section is 120 to 200 ° C. 2. The water amount per hole of said watering nozzle is 75
2. The method for cooling exhaust gas according to claim 1, wherein the cooling rate is 0 L / hr or less. 3. The number of holes of the watering nozzle and the inlet-side water pressure are:
The exhaust gas cooling method according to claim 1, wherein the following expression (1) is satisfied. (Number of nozzle holes) x (Nozzle inlet water pressure (MPa)) ≥ 2.5MPa (1) 4. Water and nitrogen as the watering nozzle,
The method for cooling exhaust gas according to claim 1, wherein a two-fluid nozzle for injecting water and air is used.