JPH09280540A - Heat exchanger and exhaust gas treatment equipment having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold a heat recovering part of a heat exchanger in a necessary minimum size, to suppress sticking of dust to fins in the heat recovering part and to avoid a rise in a pressure loss of passing air by a construction wherein fin pitches of a tube with the fins positioned in a specified area wherein the amount of condensed and sticking SO3 is large are set to be larger than ones in other areas in the heat recovering part. SOLUTION: In a heat recovering part 5, an exhaust gas inlet 103 into which exhaust gas passing through an electrostatic precipitator is introduced is provided on one end side of a housing 51 and an exhaust gas outlet 104 on the other end side thereof. A large number of fins 102 are fixed at prescribed pitches on the outer periphery of a tube 102 with the fins provided in a zigzag inside the housing 51 and a heat transfer medium such as water is made to flow through the tube. In the heat recovering part 5, the pitches of the fins 102 for the tube 101 are set to be larger in a specified area M of condensation and sticking wherein condensed dust of SO3 is apt to stick to the fins than in other areas. By setting the specified area M, it is made possible to suppress sticking of the dust efficiently, to make the heat recovering part 5 small in size and compact and to maintain a pressure loss of passing air to be low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger having a finned tube, and a flue gas treatment apparatus equipped with such a heat exchanger for recovering heat from exhaust gas containing SO ₃ .

[0002]

BACKGROUND OF THE INVENTION FIG. 3, the dust such as the exhaust gas from a coal combustion boiler, nitrogen oxides (NO _X), sulfur oxides (SO _X) of the processing system of a combustion exhaust gas containing air pollutants, such as A block diagram is shown.

In FIG. 3, the combustion exhaust gas discharged from the boiler 1 is introduced into a denitration device 2 filled with a catalyst,
Ammonia (NH ₃ ) 10 injected as a reducing agent reduces NO _{x in} the exhaust gas to water and nitrogen to render it harmless. Next, this combustion exhaust gas is introduced into the air preheater 3 and generally heat is recovered by heating the air to 120 to 150 ° C. The exhaust gas from which heat has been recovered is introduced into the electrostatic precipitator 4 to remove dust, and then further introduced into the heat recovery section 5 of the heat exchanger 11 for heat recovery, and generally from 120 to 150 ° C. Heat recovery up to ~ 100 ° C. The heat recovery unit 5 of the heat exchanger 11 is composed of a finned tube group, and exhaust gas flows outside the finned tube group, and a heat medium such as hot water, oil, or steam flows in the tube. The heat of the exhaust gas is recovered by directly exchanging heat between the exhaust gas and the heat medium.

The exhaust gas from which heat has been recovered in the heat recovery section 5 of the heat exchanger 11 is introduced into the wet desulfurization device 6, where it is cooled and wet treated with limestone as an absorbent.
As a result, SO _X in the exhaust gas is absorbed and removed, and gypsum is produced as a by-product. The exhaust gas at the outlet of the wet desulfurization device 6 is generally lowered to 45 to 55 ° C. Therefore, if this exhaust gas is released into the atmosphere as it is, it will be difficult to diffuse due to low temperature, and there will be problems such as white smoke.
This exhaust gas is introduced into the reheating unit 7 of the heat exchanger 11 to be heated, the heat recovery unit 5 recovers the heat, and the heating medium 9 whose temperature has risen is circulated, whereby the exhaust gas is reheated and the stack The temperature of the exhaust gas discharged from 8 is raised to a predetermined temperature or higher.

As the heat exchanger 11, like the Jungstrom type heat exchanger, the element whose temperature has risen due to the heat recovery due to the rotation of the heat storage element and the exhaust gas from the wet desulfurization device 6 are brought into contact with each other. There is provided a so-called heat storage type heat exchanger for exchanging heat. However, in this heat storage system, the dust attached to the element in the heat recovery section 5 is re-scattered at the time of reheating, and the dust concentration in the chimney increases. Moreover, in such a system, S
Since there is a problem that O _X leaks to the reheating section, a heat exchanger equipped with finned tubes has recently been put into practical use.

Details of the heat recovery section 5 of the heat exchanger having the finned tube as described above are shown in FIGS. 1 and 2.
In FIGS. 1 and 2, 51 is a housing, 101 is a finned tube through which a heat medium flows, and fins 102 for increasing the heat transfer area are fixed to the outer periphery of the tube 101. 103 is an exhaust gas inlet, 104 is an exhaust gas outlet, 105 is a heat medium inlet, and 106 is a heat medium outlet. Exhaust gas flows between the fins 102 to exchange heat with a heat medium flowing in the finned pipe 101 to heat it. .

That is, in FIGS. 1 and 2, in the heat recovery section 5, a finned pipe 101 through which a heat medium flows is provided.
Exhaust gas passes through the inter-fin passages 107 to perform heat exchange. The pitch e of the fins 102 is about 8 to 10 mm in consideration of the initial ventilation pressure loss, thermal efficiency, etc., and the effective height of the heat recovery section 5 in which the finned tubes 101 are arranged is
3-5 m, and in this range finned tube 101
20 to 50 stages are arranged.

1 to 3, the high temperature exhaust gas is introduced into the heat recovery section 5 of the heat exchanger 11 and exchanges heat with the heat medium flowing in the pipe 101 with the fins 102 to become low temperature exhaust gas. The exhaust gas is discharged from the exhaust gas outlet 104 and introduced into the downstream wet desulfurization device 6. Further, the heat medium is the heat medium inlet 1
It is introduced from 05, exchanges heat with the exhaust gas, and the heat medium outlet 106
Out of the exhaust gas and is circulated to the reheating unit 7 to be used for raising the temperature of the exhaust gas.

The fin pitch e of the finned tube 101
As the number of fins 102 is increased and the number of fins 102 is increased, the contact area with the exhaust gas is increased and the entire apparatus can be made compact. On the other hand, if the fin pitch e is too narrow, the ventilation pressure loss increases and the power cost increases. Also, it is not economical because dust is likely to be clogged. Therefore, the fin pitch e is usually set to 8
It is about 10 mm.

[0010]

The conventional heat exchanger 1 described above.
The heat recovery unit 5 of No. 1 heats the pitch e of the fins 102
Set a constant value (about 10 mm) over the entire area of section 5.
There is SO in the exhaust gas _ThreeIs the fin 102 of the heat recovery unit 5
Condensates and adheres to the air to generate adhered dust, resulting in short-term ventilation pressure loss.
Since it was easy for the phenomenon of rising in
When the collecting unit 5 is washed with water to remove dust that is firmly attached to it,
It was sometimes uneconomical and tedious.

The SO ₃ gas is contained in the exhaust gas from the coal-fired boiler 1 together with dust. This SO ₃
The gas is produced by oxidizing a part of sulfur contained in the fuel during combustion, and in the case where a denitration device is installed recently, sulfur dioxide (S
0.5 to 2% of O ₂ ) gas is oxidized to generate SO _3, which is added to the SO ₃ gas generated during combustion and contained in the exhaust gas. Therefore, the SO ₃ concentration reaching the inlet of the air preheater 3 is about 5 to 50 ppm, although it varies depending on the sulfur content in the fuel.

When the SO ₃ passes through the air preheater 3, the temperature of the exhaust gas falls and becomes lower than the acid dew point. Therefore, a part of the SO ₃ is sulfur mist (H ₂ SO ₂ ) due to the condensation reaction shown in the following formula (1). ₄ ), is attached to the entrained dust and is collected together with the dust in the downstream electrostatic precipitator 4.

SO ₃ + H ₂ O ← / → H ₂ SO ₄ ………………………… (1) Generally, if the temperature of the air preheater 3 is 120 to 140 ° C., SO ₃ It is said that the gas passes through 10% to 20% of the air preheater 3, and the SO ₃ gas concentration at the outlet of the air preheater 3 is in the range of 1 to 10 ppm. The dust concentration varies depending on the ash content in the fuel, but in the case of the exhaust gas of a coal-fired boiler, it is usually several g / m ³ N to several 10 g at the boiler outlet.
/ M ³ N, dust is collected by the electrostatic precipitator 4 and 300
It is generally less than mg / m ³ N.

Therefore, the exhaust gas at the inlet of the heat recovery section 5 of the heat exchanger 11 usually contains 1 to 10 ppm of SO ₃ gas and approximately 300 mg / m ³ N of dust. This SO ₃
When the temperature of the exhaust gas is lowered in the heat recovery section 5 of the heat exchanger 11 and the condensation reaction shown in the equation (1) is performed, it is converted into sulfuric acid mist (H ₂ SO ₄ ) and is heated together with the entrained dust. It adheres to the fin 102 of the recovery unit 5. The condensed sulfuric acid mist (H ₂ SO ₄ ) reacts with the iron content in the heat exchanger 11 constituent material and the iron content in the dust to produce iron sulfate crystals. This becomes a binder and becomes fixed dust, which is fixedly deposited on the fin 102.

Normal dust (soft-adhesion dust) is produced by so-called steel ball spraying, in which steel balls (usually 4 to 5 mmφ) are scattered from the upper part of the heat recovery section 5 of the heat exchanger 11 and the adhered dust is removed by the impact. Although it can be easily removed by attaching a dust removing device, it is extremely difficult to remove dust that is produced by iron sulfate and becomes a binder and is fixed. For this reason, such adhered dust may be removed by the fins 10 over time.
Thickly adheres to the surface of No. 2, which increases ventilation pressure loss. Further, a phenomenon in which the steel balls are clogged and cannot be dropped occurs at the same time, and in that case, the ventilation pressure loss rapidly increases, and finally the heat exchanger 11 needs to be washed with water. Further, also in the suit blower removing device, since the ventilation pressure loss increases due to the adhesion of the dust, it is necessary to wash with water.

On the other hand, if the pitch e of the fins 102 of the heat recovery section 5 is increased, a sudden increase in ventilation pressure loss can be avoided even if the dust adheres as described above. If it is increased, the heat recovery unit 5 is inevitably increased in size in order to obtain the required heat exchange performance, and an increase in the installation space of the device causes an increase in cost.

The object of the present invention is to keep the heat recovery part of the heat exchanger as small as possible and to prevent dust from adhering to the fins of the heat recovery part, thereby increasing the ventilation pressure loss. An object of the present invention is to provide a flue gas treatment device and a heat exchanger for the same which can be suppressed.

[0018]

Means for Solving the Problems The present invention is intended to solve the above-mentioned problems, and the gist of the means is that finned tubes through which a heat medium flows through exhaust gas containing SO ₃ are arranged in multiple stages. In the heat recovery section of the heat exchanger for recovering exhaust gas heat by exchanging heat with the heat medium, the heat recovery section has a fin located in a specific region where the amount of SO ₃ condensed and adhered is large. The heat exchanger is characterized in that the fin pitch of the attached tube is set to be larger than that in other regions, and a flue gas treatment apparatus provided with this heat exchanger and air preheater.

According to the above-mentioned means, in the heat recovery section, in the flow direction of the exhaust gas, the SO ₃
Because there is a specific area with a lot of adhered dust due to
By making the fin pitch of this specific region larger than that of the other regions, the fixation of SO ₃ condensed dust in the same region is suppressed to be lower than that of the other regions. As a result, the increase of the ventilation pressure loss in the specific region is suppressed, the fin pitch in the other region of the other heat recovery unit can be narrowed, and the heat recovery unit can be downsized.

Therefore, it is possible to obtain a heat exchanger in which the ventilation pressure loss is reduced for a long period of time and the size thereof is reduced, and a flue gas treatment apparatus using the heat exchanger.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. 1 is a block diagram of a heat recovery part of a heat exchanger to which the present invention is applied, FIG. 2 is an enlarged cross-sectional view of a main part of a finned tube of the heat recovery part, and FIG. 3 is the heat recovery part. A block diagram of a flue gas treatment device equipped with a heat exchanger having the above is respectively shown.

The flue gas treatment apparatus shown in FIG. 3 has the same construction as the conventional one described above, 1 is a boiler, 2 is a denitration apparatus,
3 is an air preheater, 4 is an electrostatic precipitator, 6 is a wet desulfurizer,
8 is a chimney. A heat exchanger 11 is composed of a heat recovery unit 5 and a reheating unit 7 to which the present invention is applied. The operation of the smoke emission processing device is the same as that of the conventional one, and therefore its explanation is omitted here.

In the heat recovery section 5 shown in FIGS. 1 and 2, reference numeral 51 is a housing, one end of which is an exhaust gas inlet 103 into which the exhaust gas passing through the electrostatic precipitator 4 is introduced, and the other end of which is an exhaust gas outlet 104. Is provided. 101 is a finned tube provided in the housing 51 in a meandering shape,
A large number of fins 102 are fixed to the outer periphery at a predetermined pitch e, and a heat medium such as water flows through the inside. 1
Reference numeral 05 is an inlet of the heat medium, and 106 is an outlet of the heat medium.

In the heat recovery section 5 according to the embodiment of the present invention, the pitch e of the fins 102 for the finned tube 101 is set to a specific area M (length Z) of condensation attachment where SO ₃ condensation dust is easily attached. Pitch e is larger than the other areas (lengths Z ₁ and Z ₂ ).

The details and the basis of setting will be described below. In the heat recovery unit 5, the condensation and adhesion region of SO ₃ can be obtained by an experiment, but in this embodiment, the gas flow rate of the heat recovery unit 5 is changed from the condensation rate of SO ₃ gas under normal operating conditions. The SO ₃ deposit amount distribution in the direction is estimated, and the range in which the SO ₃ condensation deposit amount is large is set as the condensation deposit region, that is, the designated region M, in this estimation result. Specifically, the average value of the SO ₃ condensate deposition amount in the gas flow direction is calculated from the estimation result of the SO ₃ condensate deposition amount distribution,
For example, the range in which the amount of SO ₃ condensed and adhered is larger than this average value is defined as the specific region M, and the fins 1 in this region M are
The pitch e of 02 is set to be larger than the other areas.

Therefore, the condensation rate of the SO ₃ gas is obtained by the following equation (2).

[0027] _{-G M · dy / dZ = kg} · a · p · (y-y 1) ..................... (2) where G _M: gas molar flow rate [kgmol / h] y: gas SO ₃ parts per [-] y _1: SO ₃ equilibrium fraction [-] Z: effective length of the heat recovery section (m) kg: mass transfer coefficient of the gas phase [kgmol / m ² · h · atm] a: unit Heat transfer area per height [m ² / m] p: Total pressure [atm] The above-mentioned y ₁ (SO ₃ equilibrium fraction) is usually calculated by a heat exchanger by a well-known method. The surface temperature is determined, and the dew point is used as the dew point to determine the relationship between the SO ₃ concentration and the dew point. Further, the above-mentioned kg (mass transfer coefficient of gas phase) takes a value of 5 kgmol / m ² · h · atm.

As described above, by setting the fin pitch e of the specific area M to be larger than that of the other areas, the dust adhesion is effectively suppressed, and the heat recovery section 5 is provided.
The air pressure loss can be kept low for a long time while maintaining the small size and compactness. That is, as described above, according to the study by the inventors, as shown in the cross-sectional view of FIG. 4, the adhesion area of the adhered dust to the finned tube 101 is uniformly adhered to the entire finned tube 101. Rather, the adhered dust adheres much to the finned pipe 101 in a certain specific region M, and the adhered dust adheres less to the other regions. That is,
The reason why the ventilation pressure loss rapidly increases is that the adhered dust is locally attached to the finned pipe 101 portion in a certain region.

Therefore, by expanding the fin pitch e in the specific region M to which the adhered dust adheres, it is possible to avoid a rapid increase in ventilation pressure loss, and further to uniformly expand the fin pitch e over the entire area of the heat recovery section 5. Compared with the case, the size of the heat recovery part 5 can be made significantly smaller. Conversely speaking, the fin pitch e of the portion other than the specific region M is
However, even if it is narrower than the conventional one, a rapid increase in ventilation pressure loss is unlikely to occur, and in this respect, the heat recovery section 5 can be downsized. If the generation of the adhered dust is suppressed, the dust removal operation such as washing with water may be carried out at the time of the periodic inspection of the boiler 1, and the long-term stable operation of the entire flue gas treatment system can be performed by easy maintenance work. This is possible.

Further, if an attempt is made to change the design of the existing heat exchanger 11 by simply expanding the fin pitch e of the specific region M or to modify it, in order to secure a constant heat transfer area, the heat recovery section is required. The size of 5 will be slightly increased. However, in this case, by changing the specifications of the fin pitch e in a region (a range other than the specific region M) in which the amount of adhered dust is small, the size of the heat recovery unit 5 is prevented from increasing and the overall size is improved. It is possible to prevent the generation of adhered dust that causes a rapid increase in ventilation pressure loss. That is, the fin pitch e in the area where the amount of adhered dust is small may be made slightly smaller than the current specifications. Thus, the specific area M
And the other area, the pitch e of the fins 102 is relatively
By differentiating, the problems of long-term stable operation and downsizing of the system, which could not be achieved at the same time in the past, are solved.

It should be noted that, based on the above-described idea, that is, the above-mentioned technical idea that the region M in which the amount of adhered dust is extremely large is specified and the fin pitch e of the specific region M is relatively increased by the estimation based on the experiment or the condensation. Is also effectively applied when heat is recovered from another high-temperature fluid containing a component other than SO ₃ , which condenses to form adhered dust or adhered scale as in the case of SO ₃ . [Examples] Examples of the above-described embodiment of the present invention will be described below with reference to FIGS.

First, the block diagram shown in FIG. 3 is used.
A coal-fired boiler is installed in the same test equipment as the flue gas treatment equipment used.
La exhaust gas 200m^ThreeN / h is supplied to heat the heat exchanger 11.
Figure 7 shows the adhesion test of adhered dust to the collecting part 5 (total length 5 m).
It carried out on the conditions shown. After the test, heat the heat exchanger 11
Opening inspection of the storage part 5 and sticking to each fin 102
Dust is sampled and soluble SO in the dust is sampled._Four
Is analyzed by ion chromatography and the SO_ThreeAdhesion amount
I asked. Figure 5 shows the SO based on the analysis results. _ThreeAdhesion amount
SO as 1_ThreeIt shows the distribution of adhered amount.
You. As is clear from FIG._ThreeAdhesion of heat transfer surface
It does not adhere uniformly to the whole, but SO in a certain range
_ThreeOften adheres to SO_ThreeDistribution is seen in the adhesion.

For example, the SO ₃ concentration of Run No. ₃ 10.3
At ppm, the SO ₃ deposition amount is large in the range of 1 to 2.5 m from the gas inlet side of the heat recovery section 5 of the heat exchanger 11. Therefore, by expanding the fin pitch e at this portion, it is possible to suppress an increase in ventilation pressure loss to a low level, which leads to long-term stable operation of the entire system of the smoke treatment apparatus. Further, the solid line in the figure is the result of the inventors of the present invention estimating the SO ₃ attachment amount distribution by the method described above, and the measured value and the estimation value of the SO ₃ attachment amount distribution are in good agreement. Therefore, the specific region M in which the fin pitch e should be relatively large can be set only by the above estimation.

Next, under the condition of Run No. 2 in FIG. 7, the heat recovery section 5 with fin pitch e = 10.16 mm in all stages
(A) and only the fins 102 within the range of 1.25 to 2.45 m from the inlet side of the heat recovery unit 5 are fin pitch e = 12.
Using the heat recovery part (B) having a length of 70 mm, the time-dependent change in ventilation pressure loss was investigated. FIG. 6 shows the result. As shown in the figure, the fin pitch e in the area where adhered dust is likely to adhere is set to 1
The rise in ventilation pressure loss in the heat recovery section (B), which was set to 2.70 mm, was extremely small, and long-term stable operation could be performed. The heat recovery unit (B) has a slightly lower heat exchange rate than the heat recovery unit (A), but this is not a problem, and the actual equipment may be slightly increased in size or adhered with adhered dust. It was a value that could be solved by slightly narrowing the fin pitch e in a small area.

The application of the present invention is not limited to the system shown in FIG. 3, but can be applied to the system shown in FIG. That is, FIG. 9 shows a system in which the heat recovery part 5 of the heat exchanger 11 is arranged on the downstream side of the air preheater 3, and then the electrostatic precipitator 4 is arranged.
In this system, the exhaust gas is cooled in the heat recovery section 5 of the heat exchanger 11 to lower its temperature, and the temperature flowing into the electric dust collector 4 is as low as 80 to 100 ° C., so that the dust collection efficiency is improved.
Since the temperature drop in the electrostatic precipitator 4 is small, the temperature of the heat recovery part 5 remains almost unchanged.

However, in this case, although the dust concentration is slightly increased, the adhesion of the adhered dust to the heat recovery section 5 is
This tends to be reduced. That is, SO in exhaust gas
_{Even if 3} is condensed and becomes sulfuric acid mist (H ₂ SO ₄ ), if the dust concentration is high, the sulfuric acid mist will adhere to a large amount of dust and the adhesiveness will not be so strong. And the amount of adhered dust on the surface of the fin 102 is rather reduced. Also in this case, it is clear that there is a distribution in the condensation rate of SO ₃ in the heat recovery section 5, and the application of the present invention is effective. Further, as described above, the present invention can also be applied to the heat exchanger 11 that recovers heat from another high-temperature fluid containing a fixed component other than SO ₃ .

[0037]

The present invention is configured as described above.
According to the present invention, the ventilation pressure loss of the entire heat recovery unit can be reduced by a simple means of increasing the fin pitch only in a specific region where SO ₃ condensed dust is often stuck in the heat recovery unit. It is possible to obtain a heat exchanger with suppressed ventilation pressure loss and a flue gas treatment device using the heat exchanger.

If the ventilation pressure loss is suppressed to a normal level, the fin pitch in other parts can be reduced,
A heat exchanger in which the heat recovery unit is downsized can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a heat recovery unit of a heat exchanger for a flue gas treatment system according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a finned tube of the heat recovery section.

FIG. 3 is a block diagram of a flue gas treatment device in the above embodiment.

FIG. 4 is an explanatory diagram showing a distribution of adhered dust in a heat recovery unit in the smoke exhaust processing system.

FIG. 5 is a diagram showing a SO ₃ attachment amount distribution in an example of the present invention.

FIG. 6 is a diagram showing a change over time in ventilation pressure loss in the above-mentioned embodiment.

FIG. 7 is a diagram showing test conditions in the above-mentioned embodiment.

FIG. 8 is a diagram showing the dew point of sulfuric acid (H ₂ SO ₄ ).

FIG. 9 is a block diagram of an exhaust gas treatment device according to another embodiment of the present invention.

[Explanation of symbols]

 1 Boiler 5 Heat Recovery Part 6 Wet Desulfurization Device 7 Reheating Part 11 Heat Exchanger 101 Finned Tube 102 Fin

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satomi Ochiai 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Haruhiko Kataoka 5007 Itozakicho, Mihara City, Hiroshima Prefecture Mitsubishi Heavy Industries In Mihara Manufacturing Co., Ltd. (72) Inventor Rei Sakai 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (72) Inventor Koichiro Iwashita 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanbishi Heavy Industries Within the corporation

Claims (2)

[Claims] The exhaust gas containing 1. A SO _3, finned tube heat medium flowing is led to the heat recovery of the heat exchanger arranged in multiple stages, the exhaust gas heat by the heat medium and the heat exchanger In the heat recovery section, the heat recovery section is characterized in that the fin pitch of the finned tube located in a specific region where the amount of SO ₃ condensed and adhered is large is set to be larger than that in other regions. Heat exchanger. 2. A flue gas treatment apparatus comprising the heat exchanger according to claim 1 and an air preheater for heating air with exhaust gas upstream of the heat exchanger.