KR100288398B1 - Waste heat recovery system - Google Patents

Abstract

PURPOSE: A waste heat recovery system is provided to maximize recovery rate of waste heat by preheating cold water and air by indirect heat exchange of working fluid. CONSTITUTION: A system includes a main heat exchanger(10); a high temperature condensed water heat exchanger(20); a fresh steam heat exchanger(30); and a preheated air return device(40). The main heat exchanger integrally comprises a vaporizing part and a condensing part to preheat cold water and air for combustion simultaneously using thermosiphon principle. The vaporizing part is where multiple heating pipes(11a), packed with working fluid, vaporized in cold temperature when heated under vacuum, are placed in a first cylindrical body to exchange heat with high-temperature exhaust gas. The condensing part comprises multiple fin pipes, storing working fluid vapor and placed in a second cylindrical body, and has a cold water pipe(14) spirally wound around the second cylindrical body to condensationally exchange heat with the air for combustion and the cold water supplied from outside. The high temperature condensed water heat exchanger makes high temperature condensed water exchange heat with a preheated air in a preheated air outlet of the main heat exchanger to lower the temperature of the high temperature condensed water to supply to a condensed water recovery tank(60). The preheated air return device passes preheated air in the preheated air outlet to an air inlet of the main heat exchanger so that high-temperature air is mixed with cold air to be blown.

Description

Waste heat recovery system {WASTE HEAT RECOVERY SYSTEM}

The present invention relates to a waste heat recovery apparatus for preheating cold water and combustion air supplied to a boiler by recovering waste heat contained in exhaust gases generated during combustion of a heat use facility, for example, an industrial boiler.

A waste heat recovery apparatus of an industrial boiler generally known in the art has a structure in which a water supply preheater 2 and an air preheater 3 are sequentially installed at an exhaust gas outlet 1a of the boiler 1 as shown in FIG. 1. It is. The water supply preheater 2 and the air preheater 3 are composed of a plurality of bundle tubes 2a and 3a, and the hot exhaust gas is discharged to the atmosphere via the bundle tubes 2a and 3a. .

The water supply pipe 4 is connected to the condensate recovery tank 5 via the water supply preheater 2. Therefore, the cold water supplied through the water supply pipe 4 is preheated by heat exchange with the hot exhaust gas in the water supply preheater 3. The combustion air supply pipe 6 is also connected to the boiler 1 via the air preheater 3. Therefore, the combustion air is heat-exchanged with the high-temperature exhaust gas in the air preheater 3 to be supplied to the boiler 1 in a preheated state.

On the other hand, high temperature condensate is generated during operation of the boiler, and the high temperature condensate is recovered to the condensate return tank 5 through the condensate pipe 7 and used for boiler feed water. At this time, a high pressure is applied due to the high temperature of the condensate, so that the condensate recovery tank 5 is generally configured in an open manner to prevent inoperation due to such a high pressure.

As described above, since the high temperature waste gas generated during the operation of the boiler is not discharged to the atmosphere as it is, the high temperature waste heat contained in the exhaust gas is recovered to preheat the water supply and air necessary for the operation of the boiler. Can be increased, and energy loss can be reduced.

However, the conventional waste heat recovery apparatus as described above has a problem that the waste heat recovery rate is low because the heat transfer effect is lowered because the heat transfer by the convection of the exhaust gas, the cold water, and the exhaust gas and the combustion air is performed.

In addition, the conventional waste heat recovery apparatus has low temperature corrosion caused by sulfuric acid dew point at the outlet portion of the air preheater where the low temperature air and the high temperature exhaust gas are in contact with each other, or the outlet portion of the water supply preheater where the exhaust gas and the cold water are in contact. There is a problem that cannot be avoided.

In addition, in the conventional waste heat recovery apparatus, in order to increase the waste heat recovery rate, the exhaust gas is refracted in two or three passes to avoid the occurrence of ventilation resistance, and since the water supply preheater and the air preheater are independent from each other, This is necessary, and therefore it is avoided to install an air preheater and a water feed preheater at the same time.

In addition, the conventional waste heat recovery apparatus has the following problems in recovering the condensed water. That is, since the condensate has a large amount of heat stored, the higher the condensate recovery rate, the lower the energy loss. However, conventionally, the condensate recovery tank is open, so that fresh steam is generated and discharged to the atmosphere according to the difference between the condensate discharge pressure and the atmospheric pressure, resulting in enormous energy loss, increased water treatment cost of the boiler feedwater, and the boiler. It is inevitable that scaling of irrigation occurs.

The present invention has been made in view of the above, and the thermosiphon principle of latent heat exchange through heat evaporation and condensation of working fluid, that is, cold water and air by indirect heat exchange of boiling and condensation by vacuum low temperature steam of working fluid The purpose is to provide a waste heat recovery apparatus that can maximize the waste heat recovery by preheating.

Another object of the present invention is to provide a waste heat recovery apparatus capable of preventing the low temperature corrosion phenomenon as in the prior art at the time of waste heat recovery.

It is still another object of the present invention to provide a waste heat recovery apparatus which can reduce the manufacturing cost by not requiring a large installation place because the air preheater and the water supply preheater are integrally formed.

It is still another object of the present invention to absorb high-temperature condensate heat generated during operation of a boiler as combustion air and recover the condensate below 100 ° C. where fresh steam is not generated. To provide a waste heat recovery apparatus that can reduce.

1 is a view schematically showing a conventional waste heat recovery apparatus,

2 is a view schematically showing a waste heat recovery apparatus according to an embodiment of the present invention,

3 is a cross-sectional view taken along the line A-A of FIG. 2 showing the configuration of the main heat exchanger, which is the main part of the present invention;

4 is a cross-sectional view showing the configuration of a high temperature condensed water heat exchanger (or fresh steam heat exchanger) constituting the waste heat recovery apparatus of the present invention, and

5 is a cross-sectional view taken along the line B-B in FIG.

<Explanation of symbols for main parts of drawing>

10: main heat exchanger 11, 12; First and second cylindrical bodies

11a: heating tube 12a: fin pipe

14: cold water pipe 15: steam heating tube

20: high temperature condensate water heat exchanger 22, 32: vertical fin tube

30 fresh flash heat exchanger 40 preheated air return means

41: return duct 42: air volume control damper

50: cold water tank 60: condensate recovery tank

70 press-fit blower 80 control unit

Waste heat recovery apparatus according to the present invention for achieving the above object, the main heat exchanger for preheating the cold water and the combustion air supplied to the boiler at the same time by using the thermosiphon principle of latent heat heat exchange through the evaporation and condensation of the working fluid And a high temperature condensate water heat exchanger that exchanges high temperature condensate generated during operation of the boiler with preheated air at the outlet side of the preheating air of the main heat exchanger, lowers its temperature, and supplies the condensate recovery tank to the condensate recovery tank. A fresh steam heat exchanger for exchanging fresh flash steam with cold intake air at the inlet side of the preheating air of the main heat exchanger and supplying the fresh steam back to the condensate recovery tank where no fresh steam is generated, and preheated air at the outlet side of the preheating air. Part of the gas is bypassed to the air inlet so that the hot air Is preheated mixture comprises return means for preheating the air to be blown.

The main heat exchanger includes an evaporator configured to heat-exchange with a high-temperature exhaust gas by arranging a plurality of heating tubes in which a working fluid that is evaporated at low temperature when heated under vacuum is disposed inside the first cylindrical body, and the operation generated by the evaporator. A plurality of fin pipes accommodating fluid vapor are disposed inside the second cylindrical body, and the cylindrical body is provided with a spirally wound cold water tube to integrally condense and heat exchange the combustion air and cold water supplied from the outside. It is composed. Therefore, it is possible to maximize the amount of waste heat recovery, minimize the ventilation resistance, reduce the installation place as well as reduce the manufacturing cost.

The high temperature condensate water heat exchanger is installed at the preheating air outlet side of the condensation unit, and a condensate inlet pipe is connected to one side and a condensate recovery pipe is connected to the other side. The condensate recovery pipe is connected to the condensate recovery tank.

The fresh steam heat exchanger is installed at the air inlet side of the condensation unit, one side is connected to the upper side of the condensate recovery tank through the steam inlet pipe, the other side is connected to the lower side of the condensate recovery tank through the condensate discharge pipe.

The preheated air return means is installed to reach the air inlet side from the preheated air outlet side of the condensation unit, and is composed of a return duct each having an air inlet and an air outlet, respectively, and an air volume control damper installed inside the return duct. .

The above objects and other features of the present invention will become more apparent by describing the preferred embodiments of the present invention in detail with reference to the accompanying drawings.

2 is a schematic view showing a waste heat recovery apparatus according to an embodiment of the present invention, Figure 3 is a cross-sectional view taken along the line AA of Figure 2 showing the configuration of the main heat exchanger that is the main part of the present invention, Figure 4 Sectional drawing which showed the structure of the high temperature condensed water heat exchanger (or fresh steam heat exchanger) which comprises the waste heat recovery apparatus of this invention, and FIG. 5 is sectional drawing taken along the BB line of FIG.

In the drawing, reference numeral 10 is a main heat exchanger, 20 is a high temperature condensed water heat exchanger, 30 is a fresh steam heat exchanger, and 40 is a preheated air return means.

The main heat exchanger 10 heat-exchanges the hot exhaust gas generated during combustion of the boiler and cold water and combustion air supplied from the outside to preheat the cold water and combustion air to a predetermined temperature so that the boiler is supplied. The main heat exchanger 10 includes an evaporation unit formed by arranging a plurality of heating tubes 11a in contact with a high temperature exhaust gas perpendicularly to the inside of the first cylindrical body 11, and a plurality of condensation heat exchangers with combustion air. The fin pipe 12a of the second cylindrical body 12 is vertically arranged in the condensation unit is arranged integrally assembled. Each heating tube 11a of the evaporation unit maintains a predetermined vacuum pressure, and each of the heating tubes 11a is filled with a working fluid which evaporates at low temperature when heated under vacuum. The cold water pipe 14 is spirally wound around the second cylindrical body 12 of the condensation unit. One side of the cold water pipe 14 is connected to the water supply tank 50 through the water supply pipe 14a, and the other side thereof is connected to the condensate recovery tank 60 through the hot water discharge pipe 14b. In addition, the evaporator is provided with a steam heating tube 15 installed along the longitudinal direction of the first cylindrical body 11.

The high temperature exhaust gas generated by the operation of the boiler is discharged while contacting each heating tube 11a of the evaporation unit, whereby the working fluid filled in the heating tube 11a is heated by heat exchange with the high temperature exhaust gas. Low temperature evaporation. The low temperature evaporated working fluid vapor is heat-exchanged with the combustion air passing through the fin pipe 12a on the side of the waste heat absorbing side and the cold water flowing through the cold water pipe 14, and then condensed and recovered to the heating pipe 11a of the evaporator. . As this process is repeated continuously, the cold water and combustion air supplied to the boiler are preheated simultaneously. Here, the steam heating tube 15 is for heating the working fluid arbitrarily and when the non-condensable gas or other gas is present to hinder the heat transfer, the steam heating tube 15 heats the working fluid to the non-condensable gas. Is used to achieve the required vacuum level by removing or using volumetric expansion and heat of condensation.

The high temperature condensate water heat exchanger 20 heats the condensed water of the high temperature generated during the operation of the boiler with the preheated combustion air to lower the temperature thereof and then sends the condensed water recovery tank 60. The high temperature condensed water heat exchanger 20 is installed at the combustion air outlet side of the evaporator, and has a structure in which a plurality of vertical fin tubes 22 are provided at predetermined intervals inside the first body 21. One side of the first body 21 has a connector 21a to which the condensate inlet pipe 23 is connected, and on the other side there is a connector 21b to which the condensate recovery pipe 24 is connected. The condensate recovery pipe 24 is connected to the condensate recovery tank 60, and a check valve 25 for preventing a backflow is installed in the condensate recovery pipe 24.

The flash steam heat exchanger (30) exchanges fresh flash steam re-restored in the condensate recovery tank (60) with low-temperature combustion air to lower the temperature to 100 ° C. or lower condensate that does not generate flash steam, and then condensate recovery tank. (60) to act. The flash steam heat exchanger (30) is installed at the combustion air inlet side in front of the press-fit blower (70), and similar to the high temperature condensate water heat exchanger (20) described above, a plurality of vertical fin tubes inside the second body (31). 32 consists of a structure installed at regular intervals. One side of the second body 31 has a connector 31a to which the steam inlet pipe 33 is connected, and the other end has a connector 31b to which the condensate recovery pipe 34 is connected. The steam inlet pipe 33 is connected to the upper side of the condensate recovery tank 60, the condensate recovery pipe 34 is connected to the lower side of the condensate recovery tank 60, this condensate recovery pipe 34 A check valve 35 for preventing backflow is provided.

The preheated air return means 40 is for bypassing a part of the preheated high-temperature combustion air, thereby preventing the excessively high temperature preheated air from being supplied to the boiler. The preheated air return means 40 is provided in the return duct 41 and the inside of the return duct 41 provided to reach the combustion air inlet side from the preheated air outlet side of the condensation unit of the main heat exchanger 10. The air volume control damper 42 is formed. Air inlets 41a and air outlets 41b having cutouts are formed at both sides of the return duct 41, respectively. A portion of the hot preheated air is introduced through the air inlet 41a of the return duct 41 and discharged to the air outlet 41b, where it is mixed with cold air and preheated and sucked back into the press-fit blower 70.

In the figure, reference numeral 71 denotes a water level sensor for detecting the level of the working fluid, 72 is a water supply pump, 73 is a condensate temperature sensor, 74 is a working fluid temperature sensor, and 75 to 78 are solenoid valves. In addition, the reference numeral 80 receives a signal from the water level meter 71, the condensate temperature sensor 73 and the working fluid temperature sensor 74, the water feed pump 72 and each of the solenoid valves (75, 76, 77, 78) Control unit to control.

Hereinafter, the effect of the waste heat recovery apparatus according to the present invention configured as described above will be described.

When the boiler is operated, the hot exhaust gas discharged from the boiler is exhausted through the evaporation part of the main heat exchanger 10. At this time, the working fluid is heated while the working gas of the exhaust gas and the heating tube 11a is exchanged. By heating the working fluid as described above, the working fluid in a vacuum is evaporated at a low temperature, and the working fluid vapor which has been evaporated at low temperature is the combustion air and the cold water pipe 14 passing through this place in the fin pipe 12a of the condenser. Cold water flowing through the condensation heat transfer and then liquefied to return to the heating tube (11a). By repeating this process, combustion air and cold water are preheated. In other words, the cold water supplied to the boiler is preheated at the same time as the combustion air, and also the latent heat exchange based on the thermosiphon principle maximizes the heat transfer effect, thereby increasing the waste heat recovery rate.

The high temperature condensate generated during operation of the boiler is exchanged with the preheated combustion air in the high temperature condensed water heat exchanger 20 installed at the preheated air outlet side of the main heat exchanger condensate to recover the condensed water in a state where the temperature is lowered. The tank 60 is recovered. Then, the flash steam re-evaporated in the condensate recovery tank 60 is condensed by heat exchange with the low temperature combustion air in the flash steam heat exchanger (30) located at the inlet side of the press-fit blower (70) and then condensate recovery tank (60). Is recovered. That is, the fresh steam generated by the difference between the steam condensate pressure and the atmospheric pressure is transferred to the combustion air and then lowered below 100 ° C. below the boiling point at atmospheric pressure to be recovered to the condensate recovery tank and reused in the boiler feed water. Therefore, unnecessary consumption of condensate can be reduced, and energy efficiency can be improved.

On the other hand, in the hot air for combustion heat-exchanged with the exhaust gas according to the present invention, the blowing amount needs to be adjusted due to the fact that the air volume of the press-fit blower 70 is excessively designed compared to the combustion amount. A portion of the preheated air having an excessively high temperature relative to the combustion amount is introduced through the air inlet 41a of the preheated air return means 40 installed adjacent to the hot condensed water heat exchanger 20 and bypassed through the return duct 41. The bypassed air is discharged through the air outlet 41b located at the combustion air intake side, where it is mixed with cold air and preheated and sucked into the blower. Here, the returned preheated air is appropriately controlled by the air volume control damper 42 provided in the return duct 41. This makes it possible to prevent low temperature corrosion and corrosion of the system under low load.

On the other hand, the working fluid encapsulated in the main heat exchanger of the present invention is at an appropriate level according to the ratio of the evaporator and the condenser, the type is selected according to the temperature of the exhaust gas (waste heat) and the preheating air to be preheated. It is used. The boiling point under atmospheric pressure of water is 100 ° C, ethyl alcohol is 78 ° C, and Dowsam A, the fruit oil, is around 258 ° C. Therefore, a waste heat recovery apparatus may be configured by using a fluid having a high boiling point when a high temperature is required and using a fluid having a low boiling point when a large amount of waste heat is recovered at a low temperature. The temperature of the preheated combustion air is determined by the steam temperature of the working fluid generated according to the boiling point of the working fluid and the internal vacuum degree. In addition, the internal vacuum degree can be controlled by the amount of air to endotherm and the number and discharge temperature of the cold water pipe spirally wound in the internal steam chamber. In the waste gas waste heat recovery where corrosion is not a problem, such as gas combustion, the working fluid in the part where hot exhaust gas is contacted uses a high boiling oil type, and the low temperature exhaust gas part uses alcohol having a low boiling point. If so, the exhaust gas temperature may be drastically lowered to maximize the amount of waste heat recovered.

According to the present invention as described above, since the parts corresponding to the conventional air preheater and the feed water preheater are integrated into one device, the installation place can be reduced and the manufacturing cost can be reduced.

In addition, according to the present invention, since the exhaust gas passes in one pass, the ventilation resistance is minimized. Furthermore, since the latent heat exchange is performed by the thermosiphon principle, the heat transfer effect is increased, thereby maximizing the waste heat recovery amount.

In addition, according to the present invention, the hot condensate is exchanged with the preheating combustion air at the preheating air outlet side to lower the temperature, and then recovered to the condensate recovery tank, and the fresh steam re-evaporated in the condensate recovery tank is used for combustion. Heat exchange with low temperature air at the air inlet to recover condensate below 100 ° C that does not generate fresh steam, thus minimizing energy loss.There is no fresh steam discharge, thus reducing refill water cost and boiler watering. Scale phenomenon can be prevented.

In addition, according to the present invention, since part of the preheated combustion air is bypassed and mixed and preheated with low-temperature air, the air is blown, so that low-temperature corrosion and corrosion of the system at low load can be prevented.

On the other hand, while the above has been shown and described with respect to preferred embodiments of the present invention, the present invention is not limited to the above-described embodiment, the field to which the invention belongs without departing from the spirit of the invention claimed in the claims below. Anyone of ordinary skill in the art that various modifications can be made, of course, such modifications are within the scope of the claims.

Claims (1)

A plurality of heating tubes enclosed with a working fluid that is evaporated at low temperature when heated under vacuum are disposed inside the first cylindrical body to receive an evaporator for heat exchange with high temperature exhaust gas, and a working fluid vapor generated by the evaporator. A plurality of fin pipes are disposed inside the second cylindrical body, and the second cylindrical body is provided with a spirally wound cold water pipe, and a condensation unit for condensing heat exchange with the air for combustion and cold water supplied from the outside is integrally formed with cold water and Main heat exchanger using the thermosiphon principle to preheat the combustion air at the same time; A high temperature condensed water heat exchanger for exchanging hot condensate generated during operation of a boiler with preheated air at the outlet side of the preheated air of the main heat exchanger to lower the temperature thereof and then supply the condensed water to the condensate recovery tank; A fresh steam heat exchanger for exchanging fresh flash steam re-evaporated in the condensed water recovery tank with a low temperature suction air at a preheating air inlet side of the main heat exchanger to supply the condensed water recovery tank to a condensed water recovery tank in which fresh steam is not generated; And return ducts having air inlets and air outlets respectively formed on both sides of the main heat exchanger from the outlet side of the preheated air to the air inlet side, and a flow rate control damper installed inside the return duct. And preheating air return means for bypassing a portion of the preheated air on the side to the air inlet side to allow the hot air to be mixed with the cold air to be preheated and blown.