JP2000274654A - Method and system for desuperheating of exhaust gas utilizing hot water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect the wall face of a gas cooling chamber against damage due to adhesion of water drops by spraying pressurized hot water having temperature higher than the boiling point of water under atmospheric pressure into exhaust gas from a combustor during temperature lowering process thereby preventing spray water from adhering, as it is, to the wall face of the gas cooling chamber. SOLUTION: High temperature high pressure hot water Wt of 142.9 deg.C (saturated water at pressure of 3 kg/cm2G) is stored in a hot water tank 2 and steam S is introduced from a waste heat boiler, or the like, of an industrial waste incinerator into the hot water tank 2 thus raising the temperature of the hot water Wt and keeping the raised temperature. When the temperature of high temperature exhaust gas Gh from a combustor is lowered in a gas cooling chamber 1, hot water Wt in the hot water tank 2 is fed to a nozzle 4 y means of a pump 3 and sprayed into the high temperature exhaust gas Gh. Since the sprayed hot water Wt is high temperature high pressure water having temperature higher than the boiling point of water under atmospheric pressure, pressure reduced boiling takes place abruptly in the vicinity of the spray opening to produce steam instantaneously thus cooling the exhaust gas Gh efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for treating exhaust gas discharged from a combustion device such as a refuse incinerator or a boiler. It relates to a method and a device for reducing the temperature of exhaust gas, which can prevent damage to the chamber and exhaust gas duct, prevent operational troubles due to dust accumulation, etc., and also remove acidic gas in exhaust gas. is there.

[0002]

2. Description of the Related Art Exhaust gas discharged from a combustion device such as a refuse incinerator or a boiler is generally purified by a gas purification device and then released into the atmosphere. By the way, when purifying the exhaust gas, the temperature of the exhaust gas is adjusted to an appropriate temperature, for example, from about 120 ° C.
In some cases, the temperature must be reduced to about 0 ° C.
In such a case, generally, an exhaust gas temperature reducing device configured to spray water into exhaust gas and reduce the exhaust gas temperature using sensible heat and latent heat of evaporation of water is widely used.

FIGS. 9 and 10 show an example of a conventional exhaust gas cooling apparatus. In FIGS. 9 and 10, reference numeral 21 denotes a gas cooling chamber, 21a denotes an exhaust gas inlet, 21b denotes an exhaust gas outlet, and 21c denotes an exhaust gas outlet. Ash outlet, 22 is a desuperheated water tank, 23 is a pressurized pump, 24 is a desuperheated water nozzle, 25 is a temperature control device,
5a is a temperature detector, 26 is a temperature-reducing water flow control valve, 27 is an injection pump, 28 is an air compressor, 29 is a compressed air tank, 3
0 is a mixer, Gh is a high-temperature exhaust gas, Gl is a low-temperature exhaust gas, C
Is ash.

That is, in the exhaust gas cooling device shown in FIG.
First, the temperature-reduced water tank 2 pressurized by the pressure pump 23
2 is sprayed into the gas cooling chamber 21 through a desuperheated water nozzle 24 provided near the exhaust gas inlet 21a. The temperature of the sprayed water rises when it comes into contact with the high-temperature exhaust gas Gh, and when it reaches the boiling point, it evaporates to become steam.

On the other hand, the high-temperature exhaust gas Gh in the gas cooling chamber 21
Is cooled by the sensible heat of the sprayed water, the latent heat of vaporization, and the sensible heat of water vapor, is cooled to a predetermined temperature, becomes low-temperature exhaust gas Gl, and is led out from the exhaust gas outlet 21b. Further, the amount of water sprayed into the gas cooling chamber 21 is controlled by adjusting the opening degree of the temperature-reducing water amount control valve 26 via the temperature control device 25 according to the temperature detection signal from the temperature detector 25a. In addition, the temperature of the low-temperature exhaust gas Gl derived from the exhaust gas outlet 21b is maintained at a desired temperature by controlling the amount of water sprayed into the gas cooling chamber 21 by changing the amount of return water to the desuperheated water tank 22.

[0006] In the exhaust gas temperature reducing apparatus shown in FIG. 10, first, water supplied from a desuperheated water tank 22 by an injection pump 27 and high-pressure air from a compressed air tank 29 are mixed in a mixer 30. This causes the water to be atomized. Thereafter, the atomized water is sprayed from the mixer 30 into the gas cooling chamber 21 through the desuperheated water nozzle 24 provided near the exhaust gas inlet 21a.

[0007] The temperature of the sprayed water is high temperature exhaust gas Gh.
Rises by contact with the gas, and evaporates into steam when the boiling point is reached.
Is cooled by the sensible heat of the sprayed water, the latent heat of evaporation, and the sensible heat of water vapor. The amount of water sprayed into the gas cooling chamber 21 is controlled by the temperature controller 25 through the temperature controller 25 to adjust the opening degree of the temperature-reducing water amount control valve 26. That the temperature of the low-temperature exhaust gas Gl is maintained at a set value by adjusting the amount of spray water.
This is exactly the same as the case of FIG.

The conventional exhaust gas temperature reducing apparatus shown in FIGS. 9 and 10 can reduce the temperature of the high-temperature exhaust gas Gh to a desired temperature by using inexpensive water, and has excellent practical utility. It is. However, there are still many problems to be solved in the above-mentioned conventional exhaust gas cooling device. Among them, (a) water droplets directly hit the wall surface of the gas cooling chamber and flow down, which may cause breakage of the refractory material. It is important that dust adheres and accumulates on the walls to make stable operation of the gas cooling chamber difficult, and that (b) the gas cooling chamber becomes large and the exhaust gas temperature reduction device cannot be miniaturized. Is a serious problem.

That is, in the case of the one-fluid system using only water shown in FIG. 9, even if the pressure of the deheated water is increased or the deheated water nozzle 24 is devised, the deheated water is made to have a fine particle diameter. It is difficult to atomize into a spray body, the particle size of atomized desuperheated water is usually about 70 to 300 μm,
It is a relatively coarse value. Therefore, it is difficult to completely evaporate the atomized temperature-reduced water in a limited space, and water droplets directly hit the wall surface of the gas cooling chamber, thereby causing damage to the refractory material. Also, even if the refractory material is not damaged, dust and the like adhere to and accumulate on the surface of the refractory material wetted by the water droplets, and the deposited matter grows sequentially, so that the exhaust gas passage resistance in the gas cooling chamber greatly fluctuates,
Smooth operation of the gas cooling chamber may be difficult.

In the case of the two-fluid system using water and compressed air shown in FIG. 10, the particle size of the atomized temperature-reduced water is usually as small as about 30 to 100 μm. As compared with the case of the system, the frequency of occurrence of inconvenience due to the attachment of water droplets is relatively low. However, in this case, the initial cost and the running cost of the compressed air equipment are required, which is disadvantageous in terms of economy.

Further, it takes a considerable time for the temperature of the atomized desuperheated water to rise to the boiling point and for it to completely evaporate. Therefore, the residence time of the exhaust gas in the gas cooling chamber needs to be sufficiently long, and as a result, a large-volume gas cooling chamber is required. For example, in an industrial waste incinerator that incinerates about 300 T / D of industrial waste, the amount of exhaust gas is 90,000 Nm ³ /
H, when the high temperature exhaust gas Gh at the inlet exhaust gas temperature of 240 ° C is reduced to the low temperature exhaust gas Gl at the outlet exhaust gas temperature of 180 ° C,
When using the one-fluid exhaust gas temperature reduction device shown in FIG. 9, a gas cooling chamber having an inner diameter of about 4800 mmφ and a height of about 9000 mm is required, and an exhaust gas inlet 21 a and an exhaust gas outlet 21 are required.
b and the overall height of the exhaust gas temperature reduction device including the ash outlet 21c are:
It is about 180,000 mm.

Incidentally, in the design of the conventional exhaust gas cooling device, the heat load of the gas cooling chamber is usually 5,000 to 10,000.
0 kcal / m ³ · H (the unit volume of the gas cooling chamber, the amount of heat that can be removed from the exhaust gas per unit time). In this example, the heat load of the gas cooling chamber is 7000 k
cal / m ³ · H.

[0013]

SUMMARY OF THE INVENTION The present invention has the above-mentioned problem in the conventional exhaust gas temperature reducing apparatus, namely, (a) in the case of the one-fluid system, the particle diameter of atomized temperature-reduced water is large. ,
Water droplets directly hit the wall of the gas cooling chamber, damaging the refractory material, making it difficult to operate smoothly due to the deposition and accumulation of dust, etc. (b) In the case of the two-fluid system, compressed air equipment is required The equipment cost and running cost are high, and (c) it takes time to evaporate the atomized water particles, so that the gas cooling chamber cannot be significantly downsized. By making the particle size of the atomized water particles much smaller than before, it was possible to reduce the temperature of the exhaust gas efficiently and inexpensively with a very small exhaust gas temperature reduction device. It is an object of the present invention to provide an exhaust gas cooling method and an exhaust gas cooling device used for the method.

[0014]

Means for Solving the Problems The present inventor has designed, manufactured, and tested a large number of exhaust gas temperature reducing devices to use a deheated water nozzle in a one-fluid type exhaust gas temperature reducing device using only water. It is difficult to reduce the particle size of the atomized desuperheated water to about 100 μm or less, no matter how much the desuperheated water nozzle is improved or the pressure of the deheated water is increased, as long as the water is used to atomize the water. Therefore, it has been found that the volume of the gas cooling chamber cannot be reduced significantly.

Therefore, the inventor of the present invention has adopted a common sense practice in the design of this type of exhaust gas temperature reduction apparatus, that is, using sensible heat and evaporation of water using room temperature water of about 20 to 30 ° C. as the temperature reduction water. It departs from the practice of "Utilizes latent heat effectively for cooling high-temperature exhaust gas.""Gas-liquid two-phase flow containing pressurized hot water having a temperature equal to or higher than the boiling point of water or a part of pressurized hot water containing steam Is atomized and ejected from the conventional temperature-reduced water nozzle. "

When using pressurized hot water having a temperature equal to or higher than the boiling point of water under atmospheric pressure, the sensible heat component of water that can be utilized for cooling exhaust gas is used as compared with the conventional one-fluid system. The amount of water required will increase slightly due to a decrease in However, when the pressurized hot water is jetted from the desuperheated water nozzle into the gas cooling chamber, so-called reduced-pressure boiling occurs near the outlet of the desuperheated water nozzle, and the particle size of the atomized water is several tens μm.
This is because the particles have a fine particle size of about several μm and are rapidly evaporated in a short time in the gas cooling chamber, and there is a possibility of improving the cooling effect of the exhaust gas and reducing the size of the gas cooling chamber.

The invention of the present application has been created based on the above-mentioned idea which overturns the ordinary technical common sense or practice of the present inventors, and results of a number of exhaust gas temperature reduction tests based on the idea. The invention of Item 1 has a basic configuration of the invention in which pressurized hot water having a temperature higher than the boiling point of water under atmospheric pressure is sprayed as desuperheated water into exhaust gas.

A second aspect of the present invention is to spray the pressurized hot water having a temperature higher than the boiling point of water under the atmospheric pressure into the gas cooling chamber or the exhaust gas duct as desuperheated water. It is.

The third aspect of the present invention is the first or second aspect.
In the invention, hot water taken out of the deaerator or continuous blow water of a boiler is used as a part of pressurized hot water.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the pressurized hot water containing a part of the steam is used as the temperature-reducing water. .

[0021] The invention of claim 5 is the invention of claim 1 or claim 2.
According to the invention, the hot pressurized water containing the alkaline solution is used as the temperature-reduced water.

According to a sixth aspect of the present invention, in the fifth aspect, the heated alkaline solution is mixed into hot water.

[0023] The invention of claim 7 is the invention of claim 5 or claim 6.
In the invention, the alkaline solution is an alkaline aqueous solution or an alkaline slurry solution.

The invention of claim 8 is the invention of claim 7, wherein the alkaline aqueous solution contains sodium hydroxide (caustic soda) and the alkaline slurry solution contains calcium hydroxide (slaked lime). This was a slurry solution.

According to a ninth aspect of the present invention, there is provided a gas cooling chamber having a gas inlet, a gas outlet, and an ash outlet, and a hot water tank storing pressurized hot water having a temperature higher than the boiling point of water at atmospheric pressure. And a deheated water nozzle that sprays hot water from the hot water tank into the gas cooling chamber, a deheated water amount control valve that adjusts the amount of hot water supplied to the deheated water nozzle, and a temperature detector for low-temperature exhaust gas flowing out of the gas outlet The basic configuration of the present invention comprises a temperature control device that controls opening and closing of the dewatering water amount control valve based on a detection signal from the temperature detector.

According to a tenth aspect of the present invention, there is provided an exhaust gas duct through which exhaust gas flows, a hot water tank storing pressurized hot water having a temperature higher than the boiling point of water at atmospheric pressure, and a hot water tank from the hot water tank. Water nozzle for spraying water into the exhaust gas duct, a dewatering water amount control valve for adjusting the amount of hot water supplied to the deheated water nozzle,
The basic configuration of the present invention is that a temperature detector for the low-temperature exhaust gas flowing out from the outlet of the exhaust gas duct and a temperature control device that controls opening and closing of the dewatering water amount control valve based on a detection signal from the temperature detector are provided. is there.

According to an eleventh aspect of the present invention, in the ninth or tenth aspect of the present invention, hot water is supplied to the reduced temperature water nozzle by the internal pressure of the hot water tank.

According to a twelfth aspect of the present invention, there is provided a gas cooling chamber having a gas inlet, a gas outlet, and an ash outlet, and a hot water tank storing pressurized hot water having a temperature higher than the boiling point of water under atmospheric pressure. When,
An alkaline solution tank storing an alkaline solution, a mixer for mixing hot water from a hot water tank and an alkaline solution from the alkaline solution tank, and spraying hot water containing the alkaline solution from the mixer into the gas cooling chamber. A desuperheated water nozzle, a desuperheated water amount control valve that adjusts a flow rate of hot water containing an alkaline solution supplied to the deheated water nozzle, and an alkaline solution amount control valve that adjusts a flow rate of the alkaline solution supplied to the mixer. A temperature detector for the low-temperature exhaust gas flowing out of the gas outlet, an acid gas concentration detector for the low-temperature exhaust gas, a temperature control device that controls the opening and closing of the temperature-reducing water amount control valve based on a detection signal from the temperature detector, An acidic gas concentration control device that controls opening and closing of an alkaline solution amount control valve based on a detection signal from a gas concentration detector is a basic configuration of the present invention.

According to a thirteenth aspect, in the twelfth aspect, an alkaline solution heater for heating the alkaline solution is provided on the alkaline solution inlet side of the mixer.

According to a fourteenth aspect of the present invention, in the twelfth or thirteenth aspect, the alkaline solution tank is an alkaline solution tank storing an alkaline aqueous solution or an alkaline slurry solution.

The invention according to claim 15 is an exhaust gas duct through which exhaust gas flows, a hot water tank storing pressurized hot water at a temperature higher than the boiling point of water at atmospheric pressure, and an alkaline solution storing an alkaline solution. A tank for mixing hot water from the hot water tank with an alkaline solution from the alkaline solution tank; a desuperheater nozzle for spraying hot water containing the alkaline solution from the mixer into the exhaust gas duct; A dewatering water amount control valve for adjusting the flow rate of hot water containing the alkaline solution to be supplied to the hot water nozzle, an alkaline solution amount control valve for adjusting the flow rate of the alkaline solution to be supplied to the mixer, and flowing out of the outlet of the exhaust gas duct. A low temperature exhaust gas temperature detector, an acid gas concentration detector of the low temperature exhaust gas, and a temperature control for controlling opening and closing of a dewatering water amount control valve based on a detection signal from the temperature detector. Device and, by the detection signal from the acid gas concentration detector in which the basic structure of the invention and the acid gas concentration controller which controls the opening and closing of the alkaline solution amount control valve.

According to a sixteenth aspect, in the fifteenth aspect, an alkaline solution heater for heating the alkaline solution is provided on the alkaline solution inlet side of the mixer.

According to a seventeenth aspect of the present invention, in the invention of the fifteenth or sixteenth aspect, the alkaline solution tank is an alkaline solution tank storing an alkaline aqueous solution or an alkaline slurry solution.

The source of the high-temperature exhaust gas may be any combustion device such as a refuse incinerator or a boiler, and the present invention can be applied to all types of combustion exhaust gas. In addition, the temperature of the high-temperature exhaust gas Gh supplied to the gas cooling chamber can be set to 1000 ° C. to 150 ° C., and the temperature of the low-temperature exhaust gas Gl derived from the gas cooling chamber can be set to 100 ° C. or more. When used for so-called primary cooling of exhaust gas, the temperature of the high-temperature exhaust gas Gh is about 900 ° C to 1 ° C.
000 ° C, temperature of low temperature exhaust gas Gl is 150 ° C to 250 ° C
When used for secondary cooling of exhaust gas, the temperature of the high-temperature exhaust gas Gh can be set to about 200 ° C. to 400 ° C., and the temperature of the low-temperature exhaust gas Gl can be set to about 120 ° C. to 250 ° C.

The shape of the gas cooling chamber may be either vertical or horizontal, and its sectional shape can be freely selected from a circle, an ellipse, and a square. Similarly, the form of the exhaust gas duct may be either horizontally long or vertically long, and its sectional shape may be any of circular, elliptical, square, and the like.

The pressurized hot water Wt is water maintained at a temperature higher than the boiling point (100 ° C.) of water under atmospheric pressure, and is so-called high-pressure high-temperature water. The pressure of the hot compressed water Wt can be selected to a value of 1 kg / cm ² · G or more to 100 kg / cm ² · G position physician, considering the pressure resistance of the hot water tank 2 such 3~10kg / cm ^It is desirable to select between ² and G. Further, the pressurized hot water Wt may be in a state in which steam is partially contained therein (a so-called two-phase fluid), but it is desirable that the content of steam is small.

As a heat source for producing hot water, steam from a waste heat boiler is used in the case of an incinerator equipped with a waste heat boiler, and a part of evaporated steam is used in a boiler. Can be used. In an incinerator without a waste heat boiler, an exhaust gas heat exchanger is provided to use steam from the heat exchanger, or an independent small-capacity steam boiler or electric boiler is installed. In addition, when the deheater is attached to the waste heat boiler of the incinerator and the boiler,
The hot water generated in the deaerator can be used as it is as desuperheated water. In this case, only the piping equipment from the deaerator is required as the supply equipment for the hot water Wt, and the exhaust gas temperature reduction device can be configured at extremely low cost.

Further, when the combustion device is a boiler or an incinerator provided with a waste heat boiler, continuous blow water from the boiler can be used as a part of the hot water used as desuperheated water. In most of the boiler facilities, in order to prevent the concentration of the corrosion inhibitor and the like in the boiler water from rising and to exhibit a stable corrosion prevention function, one of the boiler water (hot water) is used. Part is discharged outside. The boiler water discharged to the outside usually has a pH of 8.5 to 11.8.
Since it is alkaline water, it has the effect of dechlorination and desulfurization in exhaust gas, and in the case where exhaust gas desalination / desulfurization equipment is attached, the amount of chemical used for this can be reduced.

When the gas cooling chamber is a vertical type, it is desirable to provide the desuperheated water nozzle for atomizing the pressurized hot water near the gas inlet of the high-temperature exhaust gas Gh above it. Is appropriately selected according to the configuration of the gas cooling chamber and the number of the dewatered water nozzles attached. The same applies to the case where hot pressurized water is jetted into the exhaust gas duct.

Further, the structure of the temperature-reducing water nozzle may be any structure, and for example, a well-known screw type or collision type water spray nozzle may be used.

Further, the number of nozzles to be cooled is appropriately selected depending on the shapes of the gas cooling chamber and the exhaust gas duct, the number of jet ports provided in one nozzle, the required amount of hot water jet, and the like. Conventional industrial waste incinerator [Incineration amount 300t
on / D, exhaust gas amount 90,000Nm ³ / H, exhaust gas 2
Next cooling (high temperature exhaust gas Gh temperature 240 ° C, low temperature exhaust gas G
1 temperature 180 ° C), hot water (temperature 142.9 ° C, pressure 3)
kg / cm ² G of saturated water)], one desuperheated water nozzle having three ejection ports is provided above the gas cooling chamber as described later.

According to the present invention, the hot water sprayed from the desuperheated water nozzle has a high temperature and a pressure considerably higher than the boiling point (100 ° C.) under the atmospheric pressure. As a result, when sprayed from the temperature-reduced water nozzle, it rapidly boils under reduced pressure near the outlet of the nozzle outlet to become fine particles, and evaporates instantaneously after being sprayed to become water vapor, so that water droplets do not evaporate. 。Do not directly hit the wall of the gas cooling chamber. As a result, the volume of the gas cooling chamber can be reduced, and equipment costs and equipment space can be reduced.
For example, in the exhaust gas cooling device provided at the waste gas boiler outlet side of the conventional industrial waste incinerator, when the temperature of the high temperature exhaust gas is reduced by 60 ° C. from 240 ° C. to 180 ° C., the heat load of the evaporating chamber becomes 50,000 to 150,000 kcal /
m ³ · H. That is, the heat load (5,000 to 10,000) of the gas cooling chamber in the conventional exhaust gas cooling device.
000 kcal / m ³ · H), the heat load of the exhaust gas temperature reducing apparatus of the present invention is 50,000 to 150,
000 kcal / m ³ · H, and the volume of the gas cooling chamber 1 could be reduced to 1/5 to 1/15. Further, in the present invention, in some cases, without providing a gas cooling chamber, a configuration may be adopted in which a desuperheated water nozzle is inserted into a high-temperature exhaust gas duct to spray hot water directly into the high-temperature exhaust gas duct. It is possible.

When hot water is used as the desuperheated water, the amount of spray water slightly increases compared to the case where conventional low-temperature water is used due to the sensible heat of the hot water. For example, the temperature of desuperheated water in a conventional exhaust gas desuperheater is 20 ° C., and the temperature of hot water in an exhaust gas desuperheater of the present invention is 142.9 ° C. (pressure 3 kg / cm 3
⁽ Saturated water at ² G), the required amount of hot water is about 1.2 times. However, with such an increase, it is not necessary to particularly increase the size of the piping of the hot water system, and the cost of equipment does not increase significantly.

When removing acidic gases such as hydrogen chloride (HCl) and sulfur oxides (SO ₂ ) in the exhaust gas, hot water mixed with an alkaline solution is jetted into the exhaust gas from a desuperheated water nozzle as desuperheated water. . Further, the alkaline solution,
It may be in the form of an alkaline aqueous solution or an alkaline slurry solution.

The temperature of the alkaline solution to be mixed into the hot water is particularly high when the temperature of the desuperheated water after mixing the alkaline solution is higher than the boiling point of water at atmospheric pressure. You don't have to. But,
If the temperature of the desuperheated water becomes lower than the boiling point of water at atmospheric pressure due to the mixing of the alkaline solution, it is necessary to heat the alkaline solution to the required temperature before mixing the alkaline solution into the hot water. desirable.

The alkaline agent in the alkaline solution may be any, but when used in the form of an alkaline aqueous solution, sodium hydroxide (caustic soda.
NaOH) and magnesium hydroxide (Mg (OH) ₂ ) are preferred. When used in the form of an alkaline slurry solution, calcium hydroxide (slaked lime / Ca (O
H) ₂ ), quicklime (CaO), calcium carbonate (CaC)
O ₃ ) sodium carbonate (Na ₂ CO ₃ ) and the like are preferred.

The total amount of the alkaline agent in the alkaline solution to be mixed into the hot water is appropriately adjusted depending on the type of the acidic gas in the exhaust gas to be removed, the amount of the acidic gas to be removed, and the temperature of the exhaust gas. An amount of the alkaline agent corresponding to 8 to 1.5 is mixed into the hot water.

[0048]

FIG. 1 shows an embodiment of a method and an apparatus for reducing exhaust gas according to the present invention.
1 is a gas cooling chamber, 1a is an exhaust gas inlet, 1b is an exhaust gas outlet, 1c is an ash outlet, 1d is an airtight holding device, 2 is a hot water tank, 3 is a pump, 4 is a reduced temperature water nozzle, and 5 is temperature control. The apparatus, 5a is an exhaust gas temperature detector on the outlet side, 5b is an exhaust gas temperature detector on the inlet side, 6 is a dewatering water amount control valve, Gh is high temperature exhaust gas, Gl is low temperature exhaust gas, S is heated steam, Wt is hot water, C is ash.

Referring to FIG. 1, gas cooling chamber 1 is formed in a so-called tower shape, and the wall surface is formed in a heat insulating structure using a known heat-resistant material. Further, an exhaust gas inlet 1a is provided above the gas cooling chamber 1, an exhaust gas outlet 1b is provided below the gas cooling chamber 1, and an ash outlet 1c and an airtight holding device (opening / closing damper) 1d are provided at the lower end of the inverted cone below. .

The shape of the gas cooling chamber 1 and its sectional shape may of course be other than the tower type shown in FIG. In the present embodiment, the high-temperature exhaust gas Gh (temperature of about 240 ° C.) discharged from the waste heat boiler (not shown) of the industrial waste incinerator into the gas cooling chamber 1 is used.
° C, and a flow rate of about 90,000 Nm ³ / H).
C. to 150.degree. Further, the exhaust gas to be cooled may be exhaust gas from any combustion device, and the flow rate thereof is not particularly limited.

The hot water tank 2 is formed of a metal heat-resistant and pressure-resistant tank having a required capacity, and is protected by a heat insulating material. In the hot water tank 2, water (pressurized hot water Wt) having a temperature higher than the boiling point (100 ° C.) under atmospheric pressure is stored. High-temperature, high-pressure hot water Wt of 0.9 ° C. (saturated water at a pressure of 3 kg / cm ² G) withstands a pressure of 10 kg / cm ²
Is stored in the hot water tank 2.

In the embodiment of FIG. 1, steam S for heating is introduced into a hot water tank 2 from a waste heat boiler (not shown) provided in an industrial waste incinerator, and the heated steam S The temperature of the hot water Wt is maintained at the value of 142.9 ° C. by the heat. As a heating source of the hot water Wt, in addition to the configuration utilizing the heat of the steam from the boiler as in the present embodiment, the heat of the combustion gas or the combustion exhaust gas, the heat of a separately provided heating burner or electric heater. It is also possible to adopt a configuration utilizing When boiler equipment is provided, so-called continuous blow water from the boiler is used as a part of hot water, or when the boiler equipment is provided with a deaerator, It is also possible to use the high-temperature and high-pressure water generated in the inside as the hot water Wt or a part of the hot water Wt.

The pump 3 converts the hot water Wt into a water nozzle 4
The pump 3 is provided only when necessary due to the pressure loss of the pipe between the hot water tank 2 and the deheated water nozzle 4 and the position head of the deheated water nozzle 4. .

The desuperheated water nozzle 4 is a known hollow cone type nozzle as shown in FIGS. 2 and 3, and in this embodiment, a nozzle provided with three jet ports 4a at an angular interval of 120 ° C. Are provided at the center of the upper part of the gas cooling chamber 1. In FIG. 2, 4b is a main body, 4c is a spiral, and 4d is a water guide hole. Further, the injection angle of each injection port 4a of the desuperheated water nozzle 4 is about 60 ° (the injection pressure is 3 kgf / cm).
² ), the flow rate is about 3.8 l / min (injection pressure 3 kg
f / cm ² ). Furthermore, in the present embodiment, a hollow cone type spray nozzle as shown in FIG. 2 is used as the desuperheated water nozzle 4, but the type and structure of the desuperheated water nozzle 4 may be any, The conventional room temperature water is heated to 190 to 3 kg under a pressure of ² to 3 kgf / cm ^2.
If it can be made into spray water with a particle size of about 00 μm,
The present invention can be used sufficiently.

The temperature control device 5 receives temperature detection signals from the exhaust gas temperature detector 5b on the inlet side and the exhaust gas temperature detector 5a on the outlet side, and controls the opening and closing of the dewatering water amount control valve 6 to thereby control the gas cooling chamber 1. The amount of hot water sprayed into the inside is adjusted, and the temperature of the low-temperature exhaust gas Gl discharged from the exhaust gas outlet 1b is maintained at a set value.

In this embodiment, a thermostat type temperature detector is used as the exhaust gas temperature detectors 5a and 5b, but any type of temperature detector may be used. In this embodiment, the dewatering water amount control valve 6 is provided in the hot water supply pipe line. However, as shown in FIG. 6, the dewatering water amount control valve is provided in the return pipe line of the hot water Wt. The valve 6 may be interposed, and any system may be used as long as the amount of hot water supplied to the temperature-reduced water nozzle 4 can be adjusted.

When the temperature of the high-temperature exhaust gas Gh from the combustion device is reduced, the hot water Wt in the hot water tank 2 is sent to the reduced temperature water nozzle 4 by the internal pressure in the hot water tank 2 and / or the pressurized water supply force of the pump 3. Is sprayed into the high-temperature exhaust gas Gh from the desuperheated water nozzle 4. Hot water Wt sprayed from nozzle 4
Is high-pressure water at a temperature considerably higher than the boiling point (100 ° C.) under atmospheric pressure.
b. rapidly boil under reduced pressure near the outlet of a.
It becomes fine particles of μm to several μm and instantaneously evaporates into water vapor, which is cooled by heat exchange with the high temperature exhaust gas Gh in the gas cooling chamber 1. The low-temperature exhaust gas Gl cooled to a predetermined temperature is attracted to the outside through the exhaust gas outlet 1b, and ash (dust or the like) C in the separated exhaust gas is discharged to the outside from the ash outlet 1c.

[0058]

Example 1 Exhaust gas flow rate 90,000 Nm ³ / H (exhaust gas from waste heat boiler of industrial waste incinerator), temperature 240
To reduce the high temperature exhaust gas Gh at 180 ° C to 180 ° C,
A tower-type cooling device having a cylindrical gas cooling chamber 1 was formed. Temperature of hot water Wt 142.9 ° C. (pressure 3 kg / cm ²⁾
When the amount of hot water to be sprayed is 2.5 ton / hr, the required volume of the gas cooling chamber 1 is 300
0 mm and a height of 6000 mm, and the high temperature exhaust gas Gh is sufficiently cooled to a predetermined temperature (180
° C).

The exhaust gas under the same conditions is passed through a conventional tower-type cooling device (2).
In the case of treatment with 0 ° C. water and the amount of sprayed water is about 2 ton / h), the required capacity of the gas cooling chamber is about 4800 mm.
φ × 9000 mmH, and in comparison with this, it is possible to greatly reduce the size of the gas cooling chamber 1 in the present invention.
Has been confirmed. In the present invention, the spray water amount of the hot water Wt is increased by about 20% as compared with the case where conventional water (20 ° C.) is used. Further, in the present invention, damage to the refractory material due to the adhesion of water droplets to the wall surface of the gas cooling chamber 1 and no trouble due to adhesion and accumulation of dust and the like do not occur at all, and a continuous reduction of the extremely stable high-temperature exhaust gas. Warm could be done.

FIGS. 4 and 5 show another embodiment of the method and apparatus for reducing the temperature of exhaust gas according to the present invention, and show a side surface of an exhaust gas duct 7 for deriving high-temperature exhaust gas Gh discharged from a waste incinerator. The mounting flange 7 for the nozzle 4
a, and the hot water Wt is sprayed from the desuperheated water nozzle 4 attached to the flange 7a into the high-temperature exhaust gas Gh in the duct 7. The embodiment shown in FIGS. 4 and 5 is different from the embodiment shown in FIGS. 1 and 2 only in that the gas cooling chamber 1 is replaced with a vertically long exhaust gas duct 7.
Other configurations of the apparatus are exactly the same as those in FIGS.

[0061]

Example 2 Hot water to be sprayed was 142.9 ° C., 3 kg / c
m ² · G saturated water, duct inner diameter 2000 mmφ, duct length L = 7000 mm,
By spraying the hot water Wt of 4 ton / h into the duct 7, the high temperature exhaust gas Gh of 90000Nm ³ / H and the temperature of 240 ° C. is continuously reduced to the low temperature exhaust gas Gl of about 180 ° C. at the duct outlet 7b. We were able to. Further, at this time, it was confirmed that no water droplets adhered to the inner wall surface of the duct 7, and therefore there was no adhesion or accumulation of dust or the like due to the water droplets.

FIGS. 6 and 7 show a third embodiment of the method and the device for reducing the temperature of exhaust gas according to the present invention. Injection into Gh removes (or neutralizes) acidic components in the exhaust gas at the same time as the temperature of the exhaust gas decreases
It is something to do.

In FIGS. 6 and 7, 8 is an alkaline solution tank, 8a is an alkaline agent supply device, 8b is a stirrer,
9 is an alkaline solution pump, 10 is an alkaline solution flow control valve, 11 is an alkaline solution heater, 11a is a drain discharge valve, 12 is a mixer of hot water Wt and alkaline solution Wp, 13 is an acid gas concentration control device, 13a the acid gas concentration detector of low exhaust gas Gl, S ₁ is heated for steam, P is an alkali agent, W ₁ is water, Wp is an alkaline solution,
Except for these components, the other components of the exhaust gas temperature reducing apparatus are exactly the same as those shown in FIGS.

[0064] That is, the In Figure 6, the hot water alkaline aqueous solution are used as alkaline solution Wp mixed into Wt, for example, an alkali such as sodium hydroxide (caustic soda · NaOH) in water W ₁ An alkaline aqueous solution in which the agent P is dissolved is stored in the alkaline solution tank 8.

Incidentally, an alkali forming an alkaline aqueous solution
As the agent P, if it is a water-soluble agent, the above-mentioned sodium hydroxide is used.
Other than magnesium, such as magnesium hydroxide
Um (Mg (OH)_Two) May be used. Also,
Alkaline agent in alkaline aqueous solution stored in ink 8
The concentration is water W ₁Temperature and water W of alkaline agent P used₁
Is appropriately selected depending on the solubility in
Is sodium hydroxide, the alkali agent concentration is 20
３０30%.

[0066] On the other hand, said In Figure 7, the alkaline slurry solution as alkaline solution Wp mixed into hot water Wt are used, for example, water W ₁ Calcium hydroxide (slaked lime · Ca (OH) ₂ ) Is stored in an alkaline solution tank 8 in which a solid-liquid mixture (slurry) in which an alkaline agent P such as) is suspended. In addition, alkaline agent P
The, as long as it is dispersed into the water W ₁ to form a slurry may be other than the calcium hydroxide, for example slaked lime (CaO) or calcium carbonate (CaC
O ₃ ) and sodium carbonate (Na ₂ CO ₃ ) can be used.

The mixing amount of the alkaline solution Wp in the hot water Wt is determined by the acid gas concentration detector 13 in the low temperature exhaust gas Gl.
is controlled by opening and closing the alkaline solution flow control valve 10 via the acidic gas concentration control device 13 in accordance with the detection signal from a, whereby the acidic gas concentration in the low temperature exhaust gas Gl is adjusted to a predetermined value. It is kept at the set value.
The mixing amount of the alkaline solution Wp in the hot water Wt is determined from the temperature of the low-temperature exhaust gas Gl, the type of the acidic gas to be removed, the target acid gas removal rate, and the like. The alkali agent P is mixed into the hot water Wt in an amount equivalent to 1.0 to 1.5 times the amount of the acidic gas to be removed in an equivalent ratio.

The alkaline solution heater 11 is provided with hot water W
The temperature of the alkaline solution Wp mixed into t is heated to a predetermined temperature to prevent the temperature of the alkaline temperature-reduced water flowing out of the mixer 12 from dropping significantly. When the mixing amount of the alkaline solution Wp is small, or when the temperature of the alkaline solution Wp is relatively high (for example, 80 ° C. to 90 ° C.), disturbance to the hot water Wt during mixing is relatively small. Therefore, in such a case, the installation of the alkaline solution heater 11 can be omitted.

In the embodiment shown in FIG. 6 and FIG. 7, the structure is such that the alkaline temperature-reduced water is injected into the gas cooling chamber 1, but the alkaline temperature-reduced water is injected into the gas cooling chamber 1. Alternatively, the exhaust gas duct 7 as shown in FIGS.
Needless to say, a configuration in which the fuel is injected into the inside may be adopted.

[0070]

Example 3 Exhaust gas flow rate of 90,000 Nm ³ / h (H in exhaust gas and exhaust gas from a waste heat boiler of an industrial waste incinerator)
Cl concentration 800 ppm), high temperature exhaust gas G at 240 ° C
In order to reduce the temperature of h to 180 ° C., a tower type cooling device having a cylindrical gas cooling chamber was formed. Hot water Wt temperature 1
42.9 ° C. (saturated water at a pressure of 3 kg / cm ² · G), temperature of alkaline solution (25% NaOH aqueous solution) Wp 25 ° C., supply amount of hot water Wt 1.9 ton / h, supply of alkaline solution Wp When the supply amount is 0.606 ton / h and the supply amount of the sprayed alkaline hot water is about 2.56 ton / h, the required volume of the gas cooling chamber 1 is 3000 m in inner diameter.
m and a height of 6000 mm, and the temperature of the high-temperature exhaust gas Gh was sufficiently reduced to a low-temperature exhaust gas Wl of a predetermined temperature (180 ° C.) using the gas cooling chamber 1.

At this time, the supply amount of the alkaline agent P to the amount of HCl in the exhaust gas is 1.0 in equivalent ratio, and the removal rate of HCl detected by the acid gas concentration detector 13a is:
When the temperature of the low-temperature exhaust gas Gl was 180 ° C, it was about 93%.

The calculation of the supply amount of the alkaline solution Wp is as follows. The amount of HCl in 90,000 Nm ³ / h of exhaust gas having an HCl concentration of 800 ppm is 9 × 10
⁴ × 800 × 10 ⁻⁶ = 72 Nm ³ / h. Also, 7
The equivalent number / h of 2Nm ³ / h HCl is 72 / 22.4
= 3.214 kmol / h. Since the equivalent ratio is 1, the number of equivalents / h of NaOH to be supplied is 3.214 kmo
1 / hr, and when this equivalent number / hr of NaOH is supplied by a 25% aqueous solution of NaOH Wp,
The supply amount of the aOH aqueous solution Wp is 40 kg / kmol ×
3.214 kmol / h × 100/25 = 606 kg /
h.

The removal of the acidic gas in the exhaust gas by spraying the NaOH aqueous solution is based on the following reaction formula. NaOH + HCl → NaCl + H ₂ O NaOH + SO ₂ + 1 / 2O ₂ → Na ₂ SO ₄ + H ₂ O The generated NaCl and the like are post-processed by an electrolysis method or the like, but since these processing methods are already known,
Here, the description is omitted.

The alkaline solution (2 ° C.) at room temperature (25 ° C.)
In the present embodiment, the alkaline solution Wp is heated to about 80 ° C. by the alkaline solution heater 11 in consideration of disturbance to the hot water Wt when the 5% NaOH aqueous solution (Wp) is mixed. Although the heater is supplied, even when the heater 11 is not used, the temperature of the alkaline hot water at the outlet side of the mixer 11 decreases, so that the amount of spray water from the desuperheater nozzle 4 slightly decreases. And there was no particular problem.

When the exhaust gas contains a high-concentration acidic gas, the temperature of the hot water Wt after mixing is further lowered by increasing the mixing amount of the alkaline solution Wt. It has been found that setting the temperature of the hot water Wt at a higher temperature can sufficiently cope with it without providing the heater 11.

FIG. 8 shows the state of the change of the acid gas (HCl) removal rate when the supply amount of the NaOH aqueous solution Wp supplied to the mixer 12 is changed in the third embodiment. A is the value when the temperature of the low temperature exhaust gas Gl is set to 180 ° C, and curve B is the value when the temperature of the low temperature exhaust gas Gl is 1
The values set at 50 ° C. are respectively shown. Note that the vertical axis of the curve is the acid gas removal rate%, and the horizontal axis is the supply amount represented by the equivalent ratio of NaOH.

As is clear from FIG.
The lower the temperature of 1 is, the higher the removal rate is. Table 1 below shows specific measured values of the embodiment shown in FIG.

[0078]

[Table 1]

[0079]

According to the present invention, since pressurized hot water is used as desuperheated water, the sprayed hot water suddenly boils under reduced pressure near the outlet of the desuperheated water nozzle. It becomes a fine spray having a particle size of about several μm and instantaneously evaporates into water vapor. This eliminates the possibility that the sprayed hot water directly collides with and adheres to the gas cooling chamber wall surface as it is as water droplets, completely preventing damage to the gas cooling chamber wall surface due to water droplet adhesion and trouble due to dust accumulation. Will be prevented.

Further, since the sprayed hot water is instantaneously evaporated, the cooling performance of the spray water is greatly improved, and the size of the gas cooling chamber can be significantly reduced. That is, in the conventional gas cooling chamber using ordinary temperature water as the temperature reducing water, the heat load of the gas cooling chamber is usually about 5,000 to 15,000 kcal / m ³ · H, whereas the temperature reduction according to the present invention is performed. In the gas cooling chamber of the apparatus, the heat load of the gas cooling chamber is 50,000 to 15
The gas cooling chamber can be increased to about 000 kcal / m ³ · H, and the size of the gas cooling chamber can be significantly reduced.

Further, when the pressure of the hot water tank is sufficient, a pressurizing pump is not required, so that the equipment can be configured very simply and the running cost can be greatly reduced.

When a deaerator is attached to the incinerator or the boiler equipment, the hot water of the deaerator can be used as it is. It is only necessary to have the plumbing equipment. As a result, the exhaust gas temperature reduction equipment can be configured at extremely low cost.

Further, since the hot water can be sprayed into the duct for high-temperature exhaust gas without reducing the gas cooling chamber itself or without providing the gas cooling chamber, the equipment cost can be greatly reduced. . Furthermore, in an incinerator equipped with a boiler and a waste heat boiler, the continuous blow water of the boiler can be used as a part of hot water for cooling water, and the blow water is alkaline with energy saving. In addition, the amount of chemicals in the exhaust gas desalination and desulfurization equipment can be reduced.

When the hot water supplied to the temperature-reducing water nozzle is alkaline hot water, the acidic gas in the exhaust gas can be removed at a high removal rate with a smaller amount of the alkali agent. It is possible to further reduce the size of the acidic gas removal equipment installed downstream of the apparatus and reduce the amount of chemicals used.

The alkaline solution to be mixed into the hot water does not need to be heated to a high temperature, especially by heating. By setting the temperature of the hot water to a slightly higher temperature, the alkaline solution at room temperature can be poured into the hot water. The stable operation of the exhaust gas temperature reduction device can be performed while mixing. As described above, the present invention has excellent practical utility.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of an exhaust gas temperature reduction method and apparatus according to the present invention.

FIG. 2 is a partial longitudinal sectional view of a desuperheated water nozzle used in the present invention.

FIG. 3 is a view as viewed in the direction of arrows in FIG. 2;

FIG. 4 is a front view showing another embodiment of the exhaust gas temperature reducing method and device according to the present invention.

FIG. 5 is a view as viewed along the line II in FIG. 4;

FIG. 6 is a view showing still another embodiment of the exhaust gas temperature reducing method and apparatus according to the present invention, and is an explanatory diagram in a case where an alkaline aqueous solution is mixed into hot water as an alkaline solution.

FIG. 7 is a view showing still another embodiment of the exhaust gas temperature reducing method and apparatus according to the present invention, and is an explanatory diagram in a case where an alkaline slurry solution is mixed into hot water as an alkaline solution.

FIG. 8 is a curve showing an acidic gas removal characteristic in an exhaust gas according to an example of the present invention.

FIG. 9 is a system diagram showing an example of a conventional exhaust gas cooling device.

FIG. 10 is a system diagram showing another example of a conventional exhaust gas cooling device.

[Explanation of symbols]

1 is a gas cooling chamber, 1a is an exhaust gas inlet, 1b is an exhaust gas outlet, 1c is an ash outlet, 1d is an airtight holding device, 2 is a hot water tank, 3 is a pump, 4 is a desuperheated water nozzle, 4a is a jet port,
b is a main body, 4c is a spiral, 4d is a water introduction hole, 5 is a temperature control device, 5a is an exhaust gas temperature detector on the outlet side, 5a is an exhaust gas temperature detector on the outlet side, 6 is a water reduction amount control valve, and Gh is a high temperature. Exhaust gas, Gl is low temperature exhaust gas, S is heated steam, C is ash, Wt
Is hot water, 7 is a duct, 7a is a flange for mounting a nozzle for reducing temperature water, 7b is a duct outlet, 8 is an alkaline solution tank, 8
a is an alkaline agent supply device, 8b is a stirrer, 9 is an alkaline solution pump, 10 is an alkaline solution flow control valve, 11
Is an alkaline solution heater, 11a is a drain valve, 12 is a mixer, 13 is an acid gas concentration control device, 13a is an acid gas concentration detector of low temperature exhaust gas, Wp is an alkaline solution, P
Alkaline agents, W ₁ is water, S ₁ is heated for vapor.

Claims (17)

[Claims] 1. A method for reducing the temperature of an exhaust gas using hot water in an incinerator or a boiler facility, which comprises spraying pressurized hot water having a temperature higher than the boiling point of water at atmospheric pressure into the exhaust gas as deheated water. Method. 2. Hot water in an incinerator or a boiler facility, wherein pressurized hot water having a temperature higher than the boiling point of water under atmospheric pressure is sprayed as de-cooled water into a gas cooling chamber or an exhaust gas duct. Exhaust gas cooling method using 3. The exhaust gas reduction using hot water according to claim 1, wherein the hot water taken out of the deaerator or the continuous blow water of the boiler is used as a part of the pressurized hot water. Warm method. 4. The pressurized hot water containing steam as a part thereof is used as desuperheated water.
A method for reducing exhaust gas temperature using hot water according to claim 1. 5. The method for reducing the temperature of exhaust gas using hot water according to claim 1, wherein the pressurized hot water containing the alkaline solution is used as temperature reducing water. 6. The exhaust gas temperature reducing method using hot water according to claim 5, wherein the heated alkaline solution is mixed into hot water. 7. The method for reducing exhaust gas temperature using hot water according to claim 5, wherein the alkaline solution is an alkaline aqueous solution or an alkaline slurry solution. 8. The hot water of claim 7, wherein the alkaline aqueous solution is an aqueous solution containing sodium hydroxide (caustic soda) and the alkaline slurry solution is a slurry solution containing calcium hydroxide (slaked lime). Exhaust gas cooling method. 9. A gas cooling chamber having a gas inlet, a gas outlet, and an ash outlet, a hot water tank storing pressurized hot water having a temperature higher than the boiling point of water under atmospheric pressure, and a hot water tank. A deheated water nozzle for spraying hot water from the nozzle into the gas cooling chamber, a deheated water amount control valve for adjusting the amount of hot water supplied to the deheated water nozzle, a temperature detector for low-temperature exhaust gas flowing out from a gas outlet, and the temperature detection. A temperature control device for controlling the opening and closing of a dewatering water amount control valve in accordance with a detection signal from a heater. 10. An exhaust gas duct through which exhaust gas flows, a hot water tank storing pressurized hot water having a temperature higher than the boiling point of water at atmospheric pressure, and hot water from the hot water tank into the exhaust gas duct. A desuperheated water nozzle to be sprayed, a desuperheated water amount control valve for adjusting the amount of hot water supplied to the deheated water nozzle, a temperature detector for the low-temperature exhaust gas flowing out of the outlet of the exhaust gas duct, and a detection signal from the temperature detector to reduce the temperature. An exhaust gas temperature reducing device using hot water, comprising: a temperature control device that controls opening and closing of a hot water amount control valve. 11. The method according to claim 9, wherein the hot water is supplied to the reduced-temperature water nozzle by the internal pressure of the hot water tank.
An exhaust gas temperature reducing apparatus using hot water according to item 1. 12. A gas cooling chamber having a gas inlet, a gas outlet, and an ash outlet, a hot water tank storing pressurized hot water at a temperature higher than the boiling point of water under atmospheric pressure, and an alkaline solution. A stored alkaline solution tank, a mixer for mixing the hot water from the hot water tank and the alkaline solution from the alkaline solution tank, and a temperature-reducing water spraying hot water containing the alkaline solution from the mixer into the gas cooling chamber. A nozzle, a temperature-reducing water amount control valve for adjusting the flow rate of the hot water containing the alkaline solution to be supplied to the temperature-reducing water nozzle, an alkaline solution amount control valve for adjusting the flow rate of the alkaline solution to be supplied to the mixer, and a gas outlet Temperature detector for low temperature exhaust gas flowing out of
An acid gas concentration detector of the low-temperature exhaust gas, a temperature control device that controls the opening and closing of a dewatering water amount control valve by a detection signal from the temperature detector, and an alkaline solution amount control valve by a detection signal from the acid gas concentration detector. An exhaust gas cooling device using hot water, comprising: an acid gas concentration control device for controlling the opening and closing of the exhaust gas. 13. The exhaust gas temperature reducing apparatus using hot water according to claim 12, wherein an alkaline solution heater for heating the alkaline solution is provided on the alkaline solution inlet side of the mixer. 14. The exhaust gas temperature reducing apparatus using hot water according to claim 12, wherein the alkaline solution tank is an alkaline solution tank storing an alkaline aqueous solution or an alkaline slurry solution. 15. An exhaust gas duct through which exhaust gas flows, a hot water tank storing pressurized hot water having a temperature higher than the boiling point of water under atmospheric pressure, an alkaline solution tank storing an alkaline solution, and a hot water tank. A mixer for mixing the hot water from the tank with the alkaline solution from the alkaline solution tank, a desuperheated water nozzle for spraying hot water containing the alkaline solution from the mixer into the exhaust gas duct, and supplying the deheated water nozzle A temperature-reducing water flow control valve for adjusting the flow rate of the hot water containing the alkaline solution, an alkaline solution flow control valve for adjusting the flow rate of the alkaline solution supplied to the mixer, and the temperature of the low-temperature exhaust gas flowing out of the outlet of the exhaust gas duct A detector, an acid gas concentration detector of the low-temperature exhaust gas, a temperature control device that controls the opening and closing of the temperature-reducing water flow control valve based on a detection signal from the temperature detector, An exhaust gas temperature reducing device using hot water, comprising: an acidic gas concentration control device that controls opening and closing of an alkaline solution amount control valve according to a detection signal from a gas concentration detector. 16. The exhaust gas temperature reducing apparatus using hot water according to claim 15, wherein an alkaline solution heater for heating the alkaline solution is provided on the alkaline solution inlet side of the mixer. 17. The exhaust gas temperature reducing apparatus using hot water according to claim 15, wherein the alkaline solution tank is an alkaline solution tank storing an alkaline aqueous solution or an alkaline slurry solution.