Power System Driven By A Low-Temperature Heat Source

Abstract

A power system driven by a low-temperature heat source includes a power cycling unit and a heat pump unit. The power cycling unit includes a turbine, a condenser, a pump, a first heat exchanger, and a second heat exchanger. The turbine, the condenser, the pump, the first heat exchanger, and the second heat exchanger are connected in sequence. The heat pump unit includes a condenser and an evaporator. The condenser of the heat pump unit is connected to the second heat exchanger. The evaporator is connected to the condenser of the heat pump unit. The evaporator absorbs heat of a working fluid in a waste heat pipe.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power system and, more particularly, to a power system driven by a low-temperature heat source.

2. Description of the Related Art

In petrochemical or steel industries, low-temperature heat sources can be obtained from working fluids at 80-90° C. in waste heat pipes through use of heat regenerators that recycle heat energy during processes. The energy can be saved if the low-temperature heat sources are recycled.

As an example, FIG. 1 shows a conventional power system 9 including a pump 91, a boiler 92, a turbine 93, and a condenser 94 that are connected to each other by pipes filled with a working fluid, forming a closed circulating piping system. The pump 91 compresses the working fluid to increase the pressure and temperature of the working fluid entering the boiler 92. Heat Q_in is inputted to the boiler 92 by burning natural gas or kerosene to heat the temperature increased working fluid into steam through phase change. The steam drives the turbine 93 to output work W_out.

However, although the low-temperature heat source is used as a portion of the heat source for the conventional power system 9, the heating effect provided by the low-temperature heat source is limited. As a whole, the work W_out. outputted by the turbine 93 can not reach the ideal value, because the low-temperature heat source generated during the processes is directly introduced into the conventional power system 9 through single-stage heat exchange. As a result, the heat efficiency of the conventional power system 9 is reduced. Thus, improvement to the conventional power system 9 is required.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a power system driven by a low-temperature heat source. The temperature of the low-temperature heat source is increased to an ideal value and then introduced into the power system to increase the effect of the power system and to fully utilize a large amount of low-temperature heat source with low enthalpy.

The present invention fulfills the above objective by providing a power system driven by a low-temperature heat source including a power cycling unit and a heat pump unit. The power cycling unit includes a turbine, a condenser, a pump, a first heat exchanger, and a second heat exchanger. The turbine, the condenser, the pump, the first heat exchanger, and the second heat exchanger are connected in sequence. The heat pump unit includes a condenser and an evaporator. The condenser of the heat pump unit is connected to the second heat exchanger. The evaporator is connected to the condenser of the heat pump unit. The evaporator is adapted to absorb heat of a working fluid in a waste heat pipe.

Preferably, the heat pump unit includes a compressor and a throttle valve. The compressor, the evaporator, the throttle valve, and the condenser are connected to each other. The compressor is connected to the turbine of the power cycling unit. By such an arrangement, the shaft work outputted by the turbine drives the heat pump unit to save the energy consumed by the compressor.

The present invention will become clearer in light of the following detailed description of illustrative embodiments of this invention described in connection with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The illustrative embodiments may best be described by reference to the accompanying drawings where:

FIG. 1 shows a schematic diagram of a conventional power system.

FIG. 2 shows a schematic diagram of a power system driven by a low-temperature heat source of a first embodiment according to the present invention.

FIG. 3 shows a temperature-entropy diagram of a power cycling unit of the first embodiment.

FIG. 4 shows a schematic diagram of a power system driven by a low-temperature heat source of a second embodiment according to the present invention.

FIG. 5 shows a temperature-entropy diagram of a power cycling unit of the second embodiment.

All figures are drawn for ease of explanation of the basic teachings of the present invention only; the extensions of the figures with respect to number, position, relationship, and dimensions of the parts to form the preferred embodiments will be explained or will be within the skill of the art after the following teachings of the present invention have been read and understood. Further, the exact dimensions and dimensional proportions to conform to specific force, weight, strength, and similar requirements will likewise be within the skill of the art after the following teachings of the present invention have been read and understood.

DETAILED DESCRIPTION OF THE INVENTION

The term “low-temperature heat source” referred to hereinafter means a working fluid having a temperature below 100° C. after absorbing industrial waste heat.

With reference to FIG. 2, a power system driven by a low-temperature heat source of a first embodiment according to the present invention includes a power cycling unit 1 and a heat pump unit 2 connected to the power cycling unit 1.

The power cycling unit 1 can output shaft work for an intended use as well as the power for the heat pump unit 2. Specifically, the power cycling unit 1 includes a turbine 11, a condenser 12, a pump 13, a first heat exchanger 14, and a second heat exchanger 15 that are connected in sequence by pipes receiving a first working fluid. Namely, the first working fluid flows through the turbine 11, the condenser 12, the pump 13, and the first and second heat exchangers 14 and 15 and then flows back to the turbine 11. The turbine 11 can output shaft work W_out and can drive the heat pump unit 2 to operate. The condenser 12 releases heat from the first working fluid at a constant pressure, converting the first working fluid from a gas state into a saturated liquid state. The pump 13 compresses the first working fluid to increase the temperature and pressure of the first working fluid. The first heat exchanger 14 absorbs heat Q1 from a working fluid in a waste heat pipe 8 to preheat the first working fluid of the power cycling unit 1. The second heat exchanger 15 absorbs heat Q2′ released by the heat pump unit 2, increasing the temperature of the first working fluid of the power cycling unit 1 to an ideal value. The heat pump unit 2 is connected to the second heat exchanger 15 of the power cycling unit 1 to absorb the heat Q2 from the working fluid in the waste heat pipe 8 and to release the heat Q2′ to the second heat exchanger 15. When the working fluid flows through an area covered by the first heat exchanger 14, the temperature of the working fluid drops due to absorption of the heat Q1 from the working fluid by the first heat exchanger 14. Thus, it is not easy to recycle and reuse the working fluid in the waste heat pipe 8. By provision of the heat pump unit 2 according to the present invention, heat can be guided from a lower temperature position to a higher temperature position. Namely, the heat Q2′ released by the heat pump unit 2 can be larger than the heat Q2 absorbed from the waste heat pipe 8. By such an arrangement, the temperature reduced working fluid can be used again to effectively and fully utilize a large amount of low-temperature heat source having low enthalpy. This saves the energy and increases the shaft work W_out of the turbine 11 while enhancing the heat efficiency of the power cycling unit 1.

In this embodiment, the heat pump unit 2 includes a compressor 21, a condenser 22, a throttle valve 23, and an evaporator 24. The compressor 21, the condenser 22, the throttle valve 23, and the evaporator 24 are connected to each other by pipes to form a closed circulating system. A second working fluid, such as a coolant, is filled in the pipes. The compressor 21 is connected to the turbine 11 of the power cycling unit 1, such that the shaft work W_out outputted by the turbine 11 drives the compressor 21, saving the work required for driving the compressor 21 and saving the energy. The compressor 21 compresses the second working fluid. After compression, the temperature of the second working fluid is lower than that of the working fluid in the heat waste pipe 8. Thus, when the second working fluid flows to the evaporator 24, the second working fluid absorbs the heat Q2 from the working fluid in the waste heat pipe 8. The throttle valve 23 is used to convert high pressure/low temperature second working fluid into low pressure/high temperature second working fluid during an iso-enthalpy process, such that the temperature of the second working fluid is higher than that of the first working fluid of the power cycling unit 1. This allows transmission of the heat Q2′ into the second heat exchanger 15 to increase the temperature of the first working fluid.

Operation of the power system driven by a low-temperature heat source of the first embodiment according to the present invention will now be described with reference to FIG. 2 and further to FIG. 3 showing a temperature-entropy diagram of the power cycling unit 1. When the first working fluid flows through the pump 13, the first working fluid is isentropically compressed, and the temperature of the first working fluid is increased to T_o (see a→b in FIG. 3). When the first working fluid flows through the first heat exchanger 14, the temperature of the first working fluid is increased from T₀ to T₁ by the heat Q1 absorbed by the first heat exchanger 14 (see b→c in FIG. 3). When the first working fluid flows through the second heat exchanger 15, the temperature of the first working fluid is increased from T₁ to T₂ by the heat Q2′ released by the heat pump unit 2, heating the first working fluid to an overheated steam state (see c→d in FIG. 3). Thus, when the first working fluid having a temperature of T₂ flows through the turbine 11, the turbine 11 outputs shaft work W_out (see d→e in FIG. 3). Then, the first working fluid flows to the condenser 12 to release low-quality waste heat, completing a cycle (see e→a in FIG. 3).

The main feature of the power system driven by a low-temperature heat source according to the present invention is that the heat of the working fluid in the waste heat pipe 8 can be absorbed in advance to preheat the first working fluid in the power cycling unit 1. Since the temperature of the working fluid in the waste heat pipe 8 drops, the power system driven by a low-temperature heat source according to the present invention utilizes the heat pump unit 2 to further absorb heat from the temperature reduced working fluid in the waste heat pipe 8 and to covert it into heat with a higher temperature to the second heat exchanger 15. Thus, the first working fluid can be in an ideal overheated steam state before entering the turbine 11, increasing the shaft work W_out of the turbine 11. Furthermore, the shaft work W_out of the turbine 11 can be used to drive the compressor 21 of the heat pump unit 2. As a result, in addition to effective recycling and reuse of the low-temperature heat source (the working fluid in the waste heat pipe 8), the power system driven by a low-temperature heat source according to the present invention can enhance the heat efficiency of the power cycling unit 1 and can effectively save energy.

With reference to FIG. 4, a power system driven by a low-temperature heat source of a second embodiment according to the present invention includes a power cycling unit 1, a heat pump unit 2, and an auxiliary heat pump unit 3. The power cycling unit 1 is connected to the heat pump unit 2 and the auxiliary heat pump unit 3. The heat pump unit 2 of the second embodiment is substantially the same as that of the first embodiment and is, therefore, not described in detail to avoid redundancy.

In this embodiment, the power cycling unit 1 includes a turbine 11, a condenser 12, a pump 13, a first heat exchanger 14, a second heat exchanger 15, and a third heat exchanger 16. The functions of and connections between turbine 11, the condenser 12, the pump 13, the first heat exchanger 14, and the second heat exchanger 15 are substantially the same as those in the first embodiment and, therefore, not described in detail to avoid redundancy. In this embodiment, the third heat exchanger 16 is mounted between the turbine 11 and the second heat exchanger 15 to absorb heat Q3′ released by the auxiliary heat pump unit 3, heating the first working fluid for the third time.

The auxiliary heat pump 3 is connected to the third heat exchanger 16 of the power cycling unit 1 to absorb heat Q3 from the working fluid in the waste heat pipe 8 and to release the heat Q3′ to the third heat exchanger 16. When the working fluid flows through an area covered by the first and second heat exchangers 14 and 15, the temperature of the working fluid significantly drops due to absorption of heat from the working fluid by the first and second heat exchangers 14 and 15. By provision of the auxiliary heat pump unit 3 according to the present invention, the heat can be guided from a lower temperature position to a higher temperature position. Namely, the heat Q3′ released by the auxiliary heat pump unit 3 can be larger than the heat Q3 absorbed from the waste heat pipe 8. By such an arrangement, the temperature reduced working fluid can be effectively used to save the energy and to increase the shaft work W_out of the turbine 11 while enhancing the heat efficiency of the power cycling unit 1.

In this embodiment, the auxiliary heat pump unit 3 includes a compressor 31, a condenser 32, a throttle valve 33, and an evaporator 34. The compressor 31, the condenser 32, the throttle valve 33, and the evaporator 34 are connected to each other by pipes to form a closed circulating system. A third working fluid, such as a coolant, is filled in the pipes. The compressor 31 is connected to the turbine 11 of the power cycling unit 1, such that the shaft work W_out outputted by the turbine 11 drives the compressor 31, saving the energy. The compressor 31 compresses the third working fluid. After compression, the temperature of the third working fluid is lower than that of the working fluid in the heat waste pipe 8 that has passed through the first heat exchanger 14 and the heat pump unit 2. Thus, when the third working fluid flows to the evaporator 34, the third working fluid absorbs the heat Q3 from the working fluid in the waste heat pipe 8. The throttle valve 33 is used to convert high pressure/low temperature third working fluid into low pressure/high temperature third working fluid during an iso-enthalpy process, such that the temperature of the third working fluid is higher than that of the first working fluid entering the third heat exchanger 16 of the power cycling unit 1. This allows transmission of heat Q3′ into the third heat exchanger 16 to increase the temperature of the first working fluid for the third time.

Operation of the power system driven by a low-temperature heat source of the second embodiment according to the present invention will now be described with reference to FIG. 4 and further to FIG. 5 showing a temperature-entropy diagram of the power cycling unit 1. When the first working fluid flows through the pump 13, the first working fluid is isentropically compressed, and the temperature of the first working fluid is increased to T₀ (see a→b in FIG. 5). When the first working fluid flows through the first heat exchanger 14, the temperature of the first working fluid is increased from T₀ to T₁ by the heat Q1 absorbed by the first heat exchanger 14 (see b→c in FIG. 5). When the first working fluid flows through the second heat exchanger 15, the temperature of the first working fluid is increased from T₁ to T₂ by the heat Q2′ released by the heat pump unit 2, heating the first working fluid to an overheated steam state (see c→d in FIG. 5). When the first working fluid flows through the third heat exchanger 16, the temperature of the first working fluid is increased from T₂ to T₃ by the heat Q3′ released by the auxiliary heat pump unit 3, heating the first working fluid for the third time (see d→e in FIG. 5). Thus, when the first working fluid having a temperature of T₃ flows through the turbine 11, the turbine 11 outputs shaft work W_out (see e→f in FIG. 5). Then, the first working fluid flows to the condenser 12 to release low-quality waste heat, completing a cycle (see f→a in FIG. 5).

In addition to providing the same function and effect of the first embodiment, the power system driven by a low-temperature heat source of the second embodiment according to the present invention provides additional auxiliary heat pump unit(s) 2, 3 corresponding to the number of additional heat exchanger(s) 15, 16 to effectively use a large amount of working fluid with low enthalpy and to heat the first working fluid in the power cycling unit 1 multiple times.

In view of the foregoing, the power system driven by a low-temperature heat source according to the present invention includes at least two heat exchangers in which the first heat exchanger 14 is used to initially heat the first working fluid, and subsequent heat exchanger(s) 15, 16 cooperate with corresponding heat pump unit(s) 2, 3 to further effectively use the temperature reduced working fluid in the waste heat pipe 8. Thus, a large amount of working fluid with low enthalpy can be effectively used while saving energy.

Thus since the invention disclosed herein may be embodied in other specific forms without departing from the spirit or general characteristics thereof, some of which forms have been indicated, the embodiments described herein are to be considered in all respects illustrative and not restrictive. The scope of the invention is to be indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Claims

1. A power system driven by a low-temperature heat source comprising:

a power cycling unit including a turbine, a condenser, a pump, a first heat exchanger, and a second heat exchanger, with the turbine, the condenser, the pump, the first heat exchanger, and the second heat exchanger connected in sequence; and

a heat pump unit including a condenser and an evaporator, with the condenser of the heat pump unit connected to the second heat exchanger, with the evaporator connected to the condenser of the heat pump unit, with the evaporator adapted to absorb heat of a working fluid in a waste heat pipe.

2. The power system driven by a low-temperature heat source as claimed in claim 1, with the heat pump unit including a compressor and a throttle valve, with the compressor, the evaporator, the throttle valve, and the condenser connected to each other, with the compressor connected to the turbine of the power cycling unit.

3. The power system driven by a low-temperature heat source as claimed in claim 1, further comprising: a third heat exchanger mounted between the second heat exchanger and the turbine, with the third heat exchanger connected to an auxiliary heat pump unit.

4. The power system driven by a low-temperature heat source as claimed in claim 3, with the auxiliary heat pump unit including a compressor connected to the turbine of the power cycling unit.