KR20190027170A - Steam cycle-based heat engine for waste heat recovery and method for operating the same heat engine - Google Patents

Abstract

According to an embodiment of the present invention, provided is a steam cycle-based waste heat generation heat pump including a first heat exchanger for exchanging heat between exhaust gas discharged from a combustion device and a working fluid circulating through a steam cycle for heat energy supply to the working fluid; a turbine that mechanically works by the working fluid supplied from the first heat exchanger; a second heat exchanger for condensing the working fluid discharged from the turbine; and a pressurizing pump which pressurizes the working fluid discharged from the second heat exchanger and supplies the pressurized working fluid to the first heat exchanger. The evaporation temperature of the working fluid is set such that the system efficiency of the heat engine can have waste heat generation efficiency value within a predetermined range including a maximum value. At this time, the waste heat generation efficiency is defined as a value proportional to the product of the waste heat recovery efficiency of the heat engine and the cycle efficiency.

Description

TECHNICAL FIELD [0001] The present invention relates to a steam cycle-based heat pump and a method of operating the same,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam cycle-based waste heat power generation heat engine, and more particularly, to a heat engine system and method for operating the same, which can maximize water recovery while having optimum system efficiency.

BACKGROUND ART [0002] Generally, a power generation system using a steam cycle-based heat pipe is used in a power plant or the like. Recently, such a steam cycle-based heat engine is also used as a power generation system using various waste heat (exhaust gas). This power generation system converts power from thermal energy into mechanical power by means of a working fluid circulating between the heat exchanger, the turbine, the condenser, and the pump to obtain power. The high-temperature exhaust gas discharged from the combustion device is supplied to the heat exchanger to transfer thermal energy to the working fluid, and the working fluid receives the thermal energy and vaporizes it to drive the turbine.

In the waste heat power generation system, it is important to increase the efficiency of waste heat generation (power generation / waste heat). However, in the case of a steam cycle-based heat pipe, the efficiency of the waste heat generation varies depending on the temperature of the exhaust gas and the kind of the working fluid. Therefore, it is required to find the optimal waste heat generation efficiency for a given heat pipe system.

The waste heat of the exhaust gas can not be efficiently recovered in the conventional waste heat steam cycle, and in recent years, water (H2O) in the exhaust gas has been often discharged without being sufficiently recovered. In the case of power plants, water consumption is particularly high, and the exhaust gas temperature of the power plant is more than 100 ° C, and a large amount of water is discharged in the form of steam. Conventionally, absorbent materials or cooling water are used for water recovery. The dehumidifying devices using the absorbing material have a drawback in that a large amount of cooling water is circulated due to a small temperature difference when the exhaust gas is cooled by using cooling water.

Patent Document 1: Korean Patent Publication No. 2010-0044738 (published on Apr. 30, 2010) Patent Document 2: Korean Patent No. 10-1450660 (published on October 15, 2014)

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and provides a heat engine system having an optimal system efficiency.

Further, in one embodiment of the present invention, there is provided a heat engine system capable of maximizing the water recovery while having an optimum efficiency.

According to an embodiment of the present invention, there is provided a steam cycle-based waste heat power generation heat pipe comprising: a first heat exchanger for exchanging heat between exhaust gas discharged from a combustion apparatus and a working fluid circulating a steam cycle; A turbine that mechanically works by the working fluid supplied from the first heat exchanger; A second heat exchanger for condensing the working fluid discharged from the turbine; And a pressurizing pump which pressurizes the working fluid discharged from the second heat exchanger and supplies the pressurized working fluid to the first heat exchanger, wherein the operating efficiency of the heat pipe is set so as to have a value Wherein the evaporation temperature of the fluid is set so that the waste heat generation efficiency is defined as a value proportional to the product of the waste heat recovery efficiency of the heat engine and the cycle efficiency.

In one embodiment, the waste heat recovery efficiency is the amount of heat utilized in the steam cycle for the maximum amount of heat available when cooling the exhaust gas to room temperature, and the cycle efficiency is the net output of the steam cycle to the heat utilized in the steam cycle .

In one embodiment, the predetermined range of the waste heat generation efficiency may be a range having a value that is 90% or more of the maximum value of the waste heat generation efficiency.

In one embodiment, the pressurization pump may be configured to increase or decrease the evaporation temperature of the working fluid by regulating the pressure applied to the working fluid.

In one embodiment, a feedback path for branching a part of the working fluid discharged from the second heat exchanger and re-supplying the working fluid to the second heat exchanger; And a third heat exchanger for exchanging heat between the exhaust gas discharged from the first heat exchanger and the working fluid on the feedback path.

In one embodiment, in the third heat exchanger, the working fluid may receive thermal energy from the exhaust gas and evaporate, and the water vapor in the exhaust gas may condense and produce water.

In one embodiment, the flow control valve further comprises a flow control valve for regulating the flow rate of the working fluid that is branched through the feedback path, wherein the flow control valve is operatively connected to the working fluid Can be controlled.

According to another embodiment of the present invention, there is provided a method of operating a steam cycle-based heat engine, comprising: a first heat exchange step of heat-exchanging a working fluid circulating a steam cycle and exhaust gas discharged from a combustion device in a first heat exchanger; Performing the mechanical work with the turbine using a first heat exchange working fluid; A second heat exchange step of condensing the working fluid discharged from the turbine in a second heat exchanger; And pressurizing the second heat exchanged working fluid by a pressurizing pump, wherein the evaporating temperature of the working fluid is set so that the waste heat generation efficiency of the heat engine pipe has a system efficiency value within a predetermined range including a maximum value, Wherein the waste heat power generation efficiency is defined as a value proportional to a product of a waste heat recovery efficiency of the heat engine and a cycle efficiency.

In one embodiment, the waste heat recovery efficiency is the amount of heat utilized in the steam cycle for the maximum amount of heat available when cooling the exhaust gas to room temperature, and the cycle efficiency is the net output of the steam cycle to the heat utilized in the steam cycle .

In one embodiment, the predetermined range of the waste heat generation efficiency may be a range having a value of 90% or more of the maximum value of the waste heat power generation efficiency.

In one embodiment, the pressurization pump may be configured to increase or decrease the evaporation temperature of the working fluid by regulating the pressure applied to the working fluid.

In one embodiment, forming a feedback path for branching a part of the working fluid discharged from the second heat exchanger and re-supplying the working fluid to the second heat exchanger; And a third heat exchange step of exchanging heat between the exhaust gas discharged from the first heat exchanger and the working fluid on the feedback path.

In one embodiment, the third heat exchange step may include a step wherein the working fluid evaporates by receiving thermal energy from the exhaust gas and the water vapor in the exhaust gas condenses to produce water.

In one embodiment, controlling the flow rate of the working fluid flowing to the feedback path based on the temperature of the exhaust gas discharged from the first heat exchanger may be further included.

According to an embodiment of the present invention, by adjusting the pressure of the working fluid circulating the steam cycle to increase or decrease the evaporating temperature of the working fluid, it is possible to realize a heat engine having optimal cogeneration efficiency.

According to one embodiment of the present invention, the exhaust gas temperature is lowered simultaneously with the power generation through the exhaust gas cogeneration steam cycle system to condense the moisture in the exhaust gas, thereby recovering the water and utilizing it as the water. If the exhaust gas temperature is cooled to room temperature, the condensable fine dust which occupies 80% or more of the exhaust gas can be simultaneously recovered and removed.

1 is a view for explaining a steam cycle-based heat engine according to an embodiment,
2 is a view for explaining a TS diagram of a steam cycle-based heat engine,
3 is a view for explaining the TS diagram when the evaporation temperature of the working fluid is lowered,
4 is a view for explaining the efficiency of the heat engine according to the evaporation temperature of the working fluid,
5 is a view for explaining a steam cycle-based heat engine according to an alternative embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features, and advantages of the present invention will become more readily apparent from the following description of preferred embodiments with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments disclosed herein are provided so that the disclosure can be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In the present specification, the singular form includes plural forms unless otherwise specified in the specification. The terms "comprise" and / or "comprising" used in the specification do not exclude the presence or addition of one or more other elements.

Hereinafter, the present invention will be described in detail with reference to the drawings. In describing the specific embodiments below, various specific contents have been set forth in order to explain the invention in more detail and to aid understanding. However, to the extent that the present invention is understandable, It can be seen that it can be used without any specific contents. In some cases, it should be mentioned in advance that it is common knowledge in describing an invention, and that parts not significantly related to the invention are not described in order to avoid confusion in describing the invention.

1 is a view for explaining a steam cycle-based heat engine according to an embodiment. In the present specification, the term "heat pipe" is a system for converting thermal energy into mechanical energy through circulation between a high-temperature and low-temperature heat source. The heat engine can be used as a power source of a vehicle such as an automobile or a ship, a steam turbine of a power plant, etc. However, the use of the heat engine is not particularly limited in the present invention.

Referring to the drawings, a steam cycle-based heat engine according to an embodiment may include a first heat exchanger 10, a turbine 20, a second heat exchanger 30, and a pressurization pump 40. The first heat exchanger 10, the turbine 20, the second heat exchanger 30 and the pressurizing pump 40 constitute a steam cycle and are connected by the first to fourth pipelines L1 to L4 have. The first to fourth conduits L1 to L4 constitute a closed loop, and the working fluid flows in the conduit. In one embodiment, the working fluid may be water (H2O), but other working fluids known in alternative embodiments may be used.

The first heat exchanger 10 exchanges heat between the exhaust gas discharged from the combustion apparatus and the working fluid circulating the steam cycle to supply thermal energy to the working fluid. In the illustrated embodiment, the exhaust gas is supplied to the first heat exchanger 10 through the fifth conduit L5, cooled by heat exchange and then discharged through the sixth conduit L6, and the fourth conduit L4 The working fluid supplied to the first heat exchanger 10 is heated by the heat energy of the exhaust gas and discharged through the first conduit L1. In one embodiment, the exhaust gas may be a hot gas exiting any combustion device, and the combustion device may be any of a combustion device such as, for example, a gas turbine, a gas engine, a diesel engine, a combustor, an incinerator or the like.

The high temperature working fluid discharged through the first conduit L1 is supplied to the turbine 20 and the turbine 20 mechanically works by the working fluid and discharges the working fluid through the second conduit L2.

The second heat exchanger (30) receives the working fluid discharged from the turbine (20) to condense and cool it. That is, in one embodiment, the second heat exchanger 30 may be, for example, a condenser. At this time, a coolant (water-cooled or air-cooled) flows into the second heat exchanger 30 from the seventh conduit L7, receives heat energy from the working fluid, and is heated and discharged to the eighth conduit L8. The pressurizing pump 40 compresses the working fluid that has been condensed and cooled in the second heat exchanger 30, and then discharges the working fluid to the first heat exchanger 10 side through the fourth conduit L4.

In this way, in the steam cycle-based heat engine according to the embodiment, the working fluid circulates through the first heat exchanger 10, the turbine 20, the second heat exchanger 30, and the pressurizing pump 40, In one embodiment, the working fluid is set to have an evaporation temperature within a predetermined temperature range. In one preferred embodiment, the evaporation temperature of the working fluid can be set such that the waste heat generation efficiency of the heat engine shown has a maximum value. In another preferred embodiment, the evaporation temperature of the working fluid can be set so that the waste heat generation efficiency of the heat engine shown has a certain range of system efficiency values including the maximum value. Hereinafter, a preferable evaporation temperature range of the working fluid will be described with reference to FIGS. 2 to 4. FIG.

Figure 2 shows a T-S (temperature-entropy) diagram of the steam cycle-based heat engine of Figure 1; In the figure, the X-axis is the entropy and the Y-axis is the temperature, and the graph shows the temperature-entropy change of the working fluid with the steam cycle.

2 are the same as the numbers of the first to eighth pipelines L1 to L8 in Fig. 1, respectively. That is, when the working fluid supplied to the first heat exchanger 10 through the fourth conduit L4 is heated and vaporized and then discharged to the first conduit L1 in FIG. 1, Move along the line from point to point 1. That is, the temperature and entropy increase at point 4, and the evaporation starts at point 9, the temperature is kept constant and the entropy continues to increase.

The working fluid then moves from point 1 to point 2 while the working fluid passes through the turbine 20. Moving from point 2 to point 3 in FIG. 2 corresponds to cooling and condensing of the working fluid through the second heat exchanger 30 and moving from point 3 to point 4 in FIG. Which corresponds to being pressurized by the pressurizing pump 40.

The exhaust gas passing through the first heat exchanger 10 of Fig. 1 moves along the line from point 5 to point 6 in Fig. That is, when the exhaust gas passes through the first heat exchanger 10, it is cooled while transferring the heat energy to the working fluid, and the entropy also becomes small. Further, the refrigerant (water-cooled or air-cooled) passing through the second heat exchanger 30 of FIG. 1 moves along the line from point 7 to point 8 in FIG.

The thermal energy transferred from the exhaust gas to the working fluid in the first heat exchanger 10 is the heat amount Q _EG corresponding to the temperature difference in the temperature-entropy graph of the exhaust gas of FIG. 2 (that is, the graph from points 5 to 6) _in an exhaust gas in order to transfer thermal energy to the working fluid temperature of the exhaust gas in the first heat exchanger 10 is passed by the 2-entropy graph, the temperature of the operating fluid, and more entropy graph always be above, at this time, The minimum temperature difference for heat transfer is called the pinch temperature (ΔT1).

On the other hand, the efficiency of a steam cycle-based cogeneration system can be explained by waste heat recovery efficiency, cycle efficiency, and waste heat efficiency. The waste heat recovery efficiency (η _HR ) can be defined as the heat quantity (Q _{EG, in} ) utilized in the steam cycle for the maximum heat quantity (Q _{EG, max} ) available when cooling the exhaust gas to room temperature have.

η _HR = Q _{EG, in} / Q _{EG, max} --- Equation 1

The cycle efficiency (eta _cyc ) can be defined as the net output date (W _net ) of the steam cycle with respect to the heat quantity (Q _{EG, in} ) utilized in the steam cycle and expressed as Equation 2 below.

侶_cyc = W _net / Q _{EG, in} --- Equation 2

The system efficiency (η _sys ) of the waste heat generation system (η _sys ) can be defined as the _net output day (W _net ) of the steam cycle with respect to the maximum amount of heat that can be utilized when the waste heat is cooled down to room temperature, and is proportional to the product of the waste heat recovery efficiency and the cycle efficiency As shown in FIG. For example, the waste heat (system) efficiency can be expressed by Equation 3 below.

侶_sys = W _net / Q _{EG, max} --- Equation 3

Since it is important to maximize the output of the waste heat steam cycle from a given waste heat source in a steam cycle-based heat pump, it is important to improve the efficiency of the waste heat generation among the above three efficiencies.

According to an embodiment of the present invention, the evaporation temperature of the working fluid can be adjusted in order to increase the efficiency of waste heat generation of the heat engine. For example, by optimizing the waste heat recovery efficiency and cycle efficiency by raising or lowering the evaporation temperature of the working fluid, optimum waste heat generation efficiency can be achieved.

Fig. 3 shows a T-S diagram when the evaporating temperature of the working fluid is lowered. Compared with FIG. 2, it can be seen that the temperature at point 9 and point 1 in FIG. 3 is lowered. Therefore, in this case, the working fluid in the first heat exchanger 10 receives heat energy from the exhaust gas, so that the temperature and entropy increase at the fourth point, the evaporation starts at the point 9, and the temperature is constant And the entropy increases.

At this time, the temperature-entropy graph of the exhaust gas (i.e., the graph from points 5 to 6) and the temperature-entropy graph of the working fluid passing through the first heat exchanger 10 (i.e., 1), the temperature difference between the exhaust gas and the exhaust gas may be larger than that of FIG. That is, the slope of the temperature-entropy graph of the exhaust gas of FIG. 3 is more inclined than in FIG. Therefore, in this case, the waste heat recovery efficiency? _HR is increased as compared with FIG.

However, when the temperature of the exhaust gas (exhaust outlet temperature) at the time of passing through the first heat exchanger 10 is lowered, the cycle efficiency? _Cyc is decreased. Therefore, the waste heat that is proportional to the product of the waste heat recovery efficiency and the cycle efficiency The power generation efficiency may be rather reduced. On the contrary, when the evaporation temperature is increased, the cycle efficiency becomes higher, but the waste heat recovery efficiency is lowered because the exhaust outlet temperature becomes higher. Therefore, it can not be guaranteed that the waste heat generation efficiency necessarily increases.

In other words, there is a trade-off relationship between waste heat recovery efficiency and cycle efficiency, and FIG. 4 schematically shows a trade-off between these two efficiencies. Referring to FIG. 4, as described above, as the evaporation temperature of the working fluid is lowered, the waste heat recovery efficiency is increased but the cycle efficiency is lowered. As the evaporation temperature of the working fluid is increased, the waste heat recovery efficiency is lowered and the cycle efficiency is increased. Thus, the efficiency of the waste heat system (proportional to the product of the two efficiencies) has a maximum value (η _MAX ) at any given evaporation temperature, as shown, but at a lower or higher evaporation temperature, the system efficiency drops. Therefore, it is desirable to maintain the evaporation temperature of the working fluid within a certain range so that the system efficiency is a maximum value (? _MAX ) or a system efficiency value within a predetermined range including this maximum value (? _MAX ).

For example, when the system efficiency is a maximum value (? _MAX ) or at least 90% of the maximum value, the evaporating temperature of the working fluid is set within a temperature range between T1 and T2 . In the illustrated embodiment, it is assumed that the optimum system efficiency is equal to or greater than 90% of the maximum value eta _MAX , and thus the evaporation temperature of the working fluid is set to T1 to T2. However, according to the specific embodiment, The evaporation temperature range of the working fluid can be varied.

In one embodiment, as a method of adjusting the evaporation temperature of the working fluid, a method of controlling the pressure applied to the working fluid (determined by the flow rate of the refrigerant and the number of revolutions of the turbine) can be used. For example, the pressure applied to the working fluid by the pressurizing pump 40 may be adjusted to control the pressure of the working fluid flowing into the first heat exchanger 10, and the pressure of the working fluid flowing into the first heat exchanger 10 When the pressure of the working fluid is lowered, the evaporating temperature of the working fluid is lowered, and when the pressure of the working fluid flowing into the second heat exchanger 10 is increased, the evaporating temperature is increased.

According to the embodiment described with reference to FIGS. 1 to 4, the pressure of the working fluid can be controlled by controlling the pressurizing pump 40 to increase or decrease the evaporating temperature of the working fluid, It is possible to implement a heat engine having a heat exchanger.

1, the temperature of the exhaust gas supplied to the first heat exchanger 10 is generally between about 100 and 200 degrees Celsius, and is about 70 degrees Celsius when passing through the first heat exchanger 10. In this case, And is discharged to the outside through, for example, a stack (chimney). However, the discharged exhaust gas still contains a large amount of water, and in order to maximize the water recovery, it may be desirable to lower the outlet temperature of the exhaust gas to 50 ° C or less. An alternative embodiment for increasing the water recovery of the exhaust gas as described above will be described with reference to Fig.

5 is a steam cycle-based heat pipe system according to an alternative embodiment, showing a heat engine configuration capable of maximizing water recovery by condensing moisture in the exhaust gas.

Referring to the drawings, a steam cycle-based heat engine according to an alternative embodiment includes a first heat exchanger 10, a turbine 20, a second heat exchanger 30, a pressurizing pump 40, a third heat exchanger 50 ), And a circulation pump (60). The steam cycle constitution of the first heat exchanger 10, the turbine 20, the second heat exchanger 30 and the pressurizing pump 40 is the same as or similar to the steam cycle of the embodiment shown in FIG. 1, do.

Compared with FIG. 1, FIG. 5 differs from the first and second embodiments in that the third heat exchanger 50, the circulation pump 60, and the tenth to twelfth conduits L10 to L12 for connecting the circulation pump and the circulation pump 60 are further included. The tenth to twelfth conduits L10 to L12 form a feedback path for branching a part of the working fluid discharged from the second heat exchanger 20 and re-supplying the working fluid to the second heat exchanger 20, The third heat exchanger (50) and the circulation pump (60) are arranged.

In the illustrated embodiment, the exhaust gas discharged from the first heat exchanger 10 is supplied to the third heat exchanger 50 without being discharged outside the heat engine. Therefore, in the third heat exchanger (50), the exhaust gas supplied from the first heat exchanger (10) and the working fluid on the feedback path perform heat exchange. By this heat exchange, water vapor in the exhaust gas is condensed, and the working fluid can be injected into the second conduit (L2) after being vaporized by receiving thermal energy. The condensed water vapor in the third heat exchanger 50 is discharged as water and the remaining components of the exhaust gas can be discharged in a separate path.

The circulation pump 60 operates so that the working fluid circulates along the feedback path. Unlike the pressurizing pump 40, the circulating pump 60 does not apply any additional pressure to the working fluid and serves to pump the working fluid to circulate.

How much of the working fluid discharged from the second heat exchanger 20 is circulated through the feedback path may vary depending on the specific embodiment. In one embodiment, for example, 1:10 may be cycled to the feedback path, but this ratio may vary depending on the embodiment.

The number of revolutions of the circulation pump 60 may be adjusted to control the flow rate of the working fluid to be circulated to the feedback path, or a flow control valve (not shown) may be provided on the feedback path, for example. In one embodiment, the flow control valve may increase or decrease the flow rate of the working fluid to be circulated to the feedback path depending on the temperature of the exhaust gas supplied to the third heat exchanger (50). For example, a higher temperature of the exhaust gas may require more working fluid to condense steam, thereby increasing the flow rate of the circulating working fluid to the feedback path and vice versa. Although not shown in the drawings, this flow rate control is performed by, for example, generating a flow rate control signal based on a temperature sensor for measuring the temperature of the exhaust gas supplied to the third heat exchanger 50 and a sensed value of the temperature sensor, And a control unit for transferring the flow rate to the flow control valve.

According to this heat pipe system, for example, when the exhaust gas supplied to the first heat exchanger 10 is at a temperature between approximately 100 and 200 degrees centigrade, the exhaust gas is discharged from the first heat exchanger 10, And is discharged at a temperature of at least 50 degrees, preferably at a temperature of 30 to 40 degrees Celsius when discharged from the third heat exchanger 50, and then discharged.

According to the above-described alternative embodiment, the exhaust gas that has passed through the first heat exchanger 10 can be supplied to the third heat exchanger 50 to condense moisture in the exhaust gas to achieve water recovery. Further, in this process, since no additional refrigerant or working fluid is used, a portion of the working fluid circulating the existing steam cycle can be branched and recirculated, and the exhaust gas can be cooled through the phase change of the recirculated working fluid, System configuration maximizes water recovery.

It will be apparent to those skilled in the art that various modifications and variations may be made to the present invention without departing from the spirit or scope of the invention. Therefore, the scope of the present invention should not be limited by the described embodiments, but should be determined by the scope of the appended claims, as well as the appended claims.

10: first heat exchanger
20: Turbine
30: Second heat exchanger
40: Pressure pump
50: Third heat exchanger
60: circulation pump

Claims (15)

CLAIMS 1. A method of operating a steam cycle-
A first heat exchange step of exchanging heat between the exhaust gas discharged from the combustion device and the working fluid circulating the steam cycle in the first heat exchanger;
Performing the mechanical work with the turbine using a first heat exchange working fluid;
A second heat exchange step of condensing the working fluid discharged from the turbine in a second heat exchanger; And
And pressurizing the second heat exchanged working fluid by a pressurizing pump,
Setting the evaporation temperature of the working fluid so that the waste heat generation efficiency of the heat engine has a maximum value and a waste heat generation efficiency value of a predetermined range including the maximum value, wherein the waste heat generation efficiency is a product of a waste heat recovery efficiency of the heat engine and a cycle efficiency Wherein the steam cycle is defined as a proportional value. The method according to claim 1,
The waste heat recovery efficiency is the amount of heat utilized in the steam cycle for the maximum amount of heat available when the exhaust gas is cooled to room temperature,
Wherein the cycle efficiency is a net work of steam cycles for the heat utilized in the steam cycle. The method according to claim 1,
Wherein the predetermined range of the waste heat generation efficiency is a range having a value of 90% or more of the maximum value of the waste heat power generation efficiency. The method of claim 3,
Wherein the steam pump is configured to increase or decrease the evaporation temperature of the working fluid by adjusting a pressure applied to the working fluid by the pressure pump. The method according to claim 1,
Forming a feedback path for branching a part of the working fluid discharged from the second heat exchanger and re-supplying the working fluid to the second heat exchanger; And
And a third heat exchange step of exchanging heat between the exhaust gas discharged from the first heat exchanger and the working fluid on the feedback path. 6. The method of claim 5,
Wherein the third heat exchange step includes the step of the working fluid being evaporated by receiving heat energy from the exhaust gas and the water vapor in the exhaust gas being condensed to produce water. 6. The method of claim 5,
And controlling the flow rate of the working fluid flowing to the feedback path based on the temperature of the exhaust gas discharged from the first heat exchanger. As a steam cycle-based cogeneration heat engine,
A first heat exchanger (10) for exchanging heat between the exhaust gas discharged from the combustion apparatus and a working fluid circulating the steam cycle to supply thermal energy to the working fluid;
A turbine (20) mechanically operated by the working fluid supplied from the first heat exchanger;
A second heat exchanger (30) for condensing the working fluid discharged from the turbine; And
And a pressurizing pump (40) for pressurizing the working fluid discharged from the second heat exchanger and supplying the pressurized fluid to the first heat exchanger,
Setting the evaporation temperature of the working fluid so that the waste heat generation efficiency of the heat engine has a maximum value and a waste heat generation efficiency value of a predetermined range including the maximum value, wherein the waste heat generation efficiency is a product of a waste heat recovery efficiency of the heat engine and a cycle efficiency Wherein the steam-cycle-based heat exchanger is defined as a proportional value. 9. The method of claim 8,
The waste heat recovery efficiency is the amount of heat utilized in the steam cycle for the maximum amount of heat available when the exhaust gas is cooled to room temperature,
Wherein the cycle efficiency is a net work of steam cycles for the heat utilized in the steam cycle. 9. The method of claim 8,
Wherein the predetermined range of the waste heat generation efficiency is a range having a value of 90% or more of a maximum system efficiency value. 11. The method of claim 10,
Wherein the steam pump is configured to increase or decrease the evaporation temperature of the working fluid by regulating a pressure applied to the working fluid by the pressure pump. 9. The method of claim 8,
A feedback path for branching a part of the working fluid discharged from the second heat exchanger (30) and re-supplying the working fluid to the second heat exchanger (30); And
And a third heat exchanger (50) for exchanging heat between the exhaust gas discharged from the first heat exchanger (10) and the working fluid on the feedback path (50). 13. The method of claim 12,
Wherein the working fluid in the third heat exchanger receives thermal energy from the exhaust gas to evaporate, and the water vapor in the exhaust gas condenses to generate water. 13. The method of claim 12,
Further comprising a flow control valve for regulating the flow rate of the working fluid branched through the feedback path,
Wherein the flow control valve controls the flow rate of the working fluid based on the temperature of the exhaust gas discharged from the first heat exchanger (10). 13. The method of claim 12,
The temperature of the exhaust gas discharged from the first heat exchanger 10 is 70 to 80 degrees,
Wherein the temperature of the exhaust gas discharged from the third heat exchanger (50) is 50 degrees or less.

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