Jet boosting two-stage organic Rankine cycle power generation system and method thereof

Abstract

The invention relates to the technical field of low-grade heat utilization, in particular to an injection boosting two-stage organic Rankine cycle power generation system and method, and the system comprises a condenser, a working medium pump, a first evaporator, a first expansion machine, a first power generator, a supersonic vapor-liquid two-phase flow injector, a second evaporator, a second expansion machine and a second power generator. Two stages of organic Rankine cycles are coupled through the supersonic speed vapor-liquid two-phase flow ejector, dead steam at an outlet of the first expansion machine is ejected through a high-pressure liquid working medium, the pressure of the outlet of the first expansion machine can be reduced while part of working medium pump power consumption is saved, dead steam waste heat of the first expansion machine can be recycled, and the working medium pump power consumption is reduced. Therefore, the technical economy of the organic Rankine cycle power generation system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of low-grade heat utilization, and in particular to a jet-boosted two-stage organic Rankine cycle power generation system and a method thereof. Background Art

[0002] As energy and environmental issues become increasingly prominent, the organic Rankine cycle (Rankine cycle using low-boiling-point organic matter as the working fluid) power generation system has received more and more attention as one of the technical means to develop and utilize low-grade thermal energy such as solar energy, geothermal energy and industrial waste heat. However, due to the limitation of the temperature level of the heat source, the efficiency of the organic Rankine cycle power generation system driven by low-grade thermal energy is relatively low.

[0003] Existing studies have shown that increasing the heat source temperature or lowering the condensation temperature can effectively improve the thermal efficiency of the organic Rankine cycle. However, when the temperature difference between the heat source and the cooling medium increases, in order to make the cycle work at a better operating point and ensure a suitable expansion ratio, a two-stage or multi-stage organic Rankine cycle technology is generally required. Although this technology improves the thermal performance of the organic Rankine cycle to a certain extent, it also increases the complexity of the system, especially increasing the number of heat exchangers and working fluid pumps, resulting in low technical and economic efficiency of the system. Therefore, the existing related technologies need to be further improved and developed. Summary of the invention

[0004] The purpose of the present invention is to solve the problems existing in the prior art. The present invention provides a jet-boosted two-stage organic Rankine cycle power generation system and method thereof.

[0005] To achieve the above objectives, the first objective of the present invention is to provide a jet-boosted two-stage organic Rankine cycle power generation system, comprising a condenser, a working fluid pump, a first evaporator, a first expander, a first generator, a supersonic vapor-liquid two-phase flow ejector, a second evaporator, a second expander, and a second generator;

[0006] Wherein, the outlet of the condenser is connected to the inlet of the working fluid pump;

[0007] The outlet of the working fluid pump is divided into two branches, the first branch is connected to the first evaporator, the first expander and the ejection fluid inlet of the supersonic vapor-liquid two-phase flow ejector in sequence;

[0008] The second branch is connected to the working fluid inlet of the supersonic vapor-liquid two-phase flow ejector, and the outlet of the supersonic vapor-liquid two-phase flow ejector passes through the second evaporator and the second expander in sequence, and is connected to the inlet of the condenser;

[0009] The first expander is connected to the first generator via a coupling, and the second expander is connected to the second generator via a coupling.

[0010] As an improvement of the technical solution of the injection boost two-stage organic Rankine cycle power generation system of the present invention, the supersonic vapor-liquid two-phase flow ejector uses high-pressure liquid working fluid as the working fluid, and the organic working fluid exhaust steam of the first expander is used as the ejection fluid.

[0011] As an improvement on the technical solution of the jet-boosted two-stage organic Rankine cycle power generation system of the present invention, the condenser, the first evaporator and the second evaporator are falling film heat exchangers, shell and tube heat exchangers or plate heat exchangers, or other forms of heat exchangers, and their heat transfer tubes can be ordinary tubes or enhanced tubes.

[0012] As an improvement of the technical solution of the jet-boosted two-stage organic Rankine cycle power generation system of the present invention, the first expander and the second expander are turbine expanders, screw expanders or scroll expanders, and may also be other forms of expanders.

[0013] As an improvement of the technical solution of the injection-boosted two-stage organic Rankine cycle power generation system of the present invention, the first generator and the second generator may be synchronous generators or asynchronous generators.

[0014] As an improvement to the technical solution of the jet-boosted two-stage organic Rankine cycle power generation system of the present invention, the working fluid pump may be a shielded pump or a magnetic pump.

[0015] As an improvement to the technical solution of the jet-boosted two-stage organic Rankine cycle power generation system of the present invention, the connection between the components of the system is a metal pipe connection.

[0016] Another object of the present invention is to provide a jet-boosted two-stage organic Rankine cycle power generation method, using the jet-boosted two-stage organic Rankine cycle power generation system as described above, comprising the following steps:

[0017] The organic working medium exhaust gas of the second expander is cooled into liquid working medium by an external cooling medium such as natural water or air in the condenser;

[0018] The liquid working medium is pressurized by the working medium pump to form high-pressure liquid working medium, and enters two branches respectively;

[0019] In the first branch, the high-pressure liquid working medium enters the first evaporator of the first-stage cycle, is heated to saturated steam or superheated steam by the low-grade heat source, and then enters the first expander, performs work in the first expander, and drives the first generator to operate and generate electricity through the coupling;

[0020] In the second branch, the high-pressure liquid working medium enters the supersonic vapor-liquid two-phase flow ejector as the working fluid, and forms a supersonic jet after passing through the supersonic nozzle. The exhaust steam of the first expander enters the variable-section mixing chamber of the supersonic vapor-liquid two-phase flow ejector under the induced action of the supersonic jet. The two fluids directly contact therein to form a supersonic vapor-liquid two-phase flow, and a condensation shock wave is generated in the case of flow obstruction, achieving a sudden change in pressure, and obtaining a high-pressure subcooled liquid working medium with a pressure exceeding the working fluid and a medium temperature.

[0021] The high-pressure liquid working medium flowing out of the supersonic vapor-liquid two-phase flow ejector enters the second evaporator in the second-stage cycle, is heated to saturated steam or superheated steam by the low-grade heat source, and then enters the second expander, performs work in the second expander, and drives the second generator to operate and generate electricity through the coupling;

[0022] Subsequently, the exhaust steam from the second expander enters the condenser to complete the system cycle.

[0023] Beneficial effects of the present invention:

[0024] 1. The present invention utilizes a supersonic vapor-liquid two-phase flow ejector to couple a two-stage organic Rankine cycle, which not only saves part of the power consumption of the working fluid pump of the organic Rankine cycle power generation system, but also acts as a regenerator to recover the waste heat of the exhaust steam of the first expander, and can more fully develop and utilize low-grade heat sources.

[0025] 2. The present invention uses a supersonic vapor-liquid two-phase flow ejector to use high-pressure liquid working fluid to inject the exhaust steam at the outlet of the first expander, thereby reducing the outlet pressure of the first expander and effectively increasing the inlet and outlet pressure difference of the first expander, which is beneficial to improving the technical and economic performance of the organic Rankine cycle power generation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the present invention.

[0027] Explanation of the reference numerals: 1-condenser; 1a-condenser inlet; 1b-condenser outlet; 2-working fluid pump; 2a-working fluid pump inlet; 2b-working fluid pump outlet; 3-first evaporator; 3a-first evaporator inlet; 3b-first evaporator outlet; 4-first expander; 4a-first expander inlet; 4b-first expander outlet; 5-first generator; 6-supersonic vapor-liquid two-phase flow ejector; 6a-working fluid inlet of the supersonic vapor-liquid two-phase flow ejector; 6b-injection fluid inlet of the supersonic vapor-liquid two-phase flow ejector; 6c-outlet of the supersonic vapor-liquid two-phase flow ejector; 7-second evaporator; 7a-second evaporator inlet; 7b-second evaporator outlet; 8-second expander; 8a-second expander inlet; 8b-second expander outlet; 9-second generator. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and beneficial effects of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0029] Example 1

[0030] like Figure 1 As shown, an embodiment of the present invention provides a two-stage organic Rankine cycle power generation system with jet boosting, comprising a condenser 1, a working fluid pump 2, a first evaporator 3, a first expander 4, a first generator 5, a supersonic vapor-liquid two-phase flow ejector 6, a second evaporator 7, a second expander 8 and a second generator 9;

[0031] The outlet 1b of the condenser 1 is connected to the inlet 2a of the working fluid pump 2;

[0032] The outlet 2b of the working fluid pump 2 is divided into two branches, the first branch is connected to the first evaporator 3, the first expander 4 and the ejection fluid inlet 6b of the supersonic vapor-liquid two-phase flow ejector 6 in sequence;

[0033] The second branch is connected to the working fluid inlet 6a of the supersonic vapor-liquid two-phase flow ejector 6, and the outlet 6c of the supersonic vapor-liquid two-phase flow ejector 6 passes through the second evaporator 7 and the second expander 8 in sequence, and is connected to the inlet 1a of the condenser 1;

[0034] The first expander 4 is connected to the first generator 5 via a coupling, and the second expander 8 is connected to the second generator 9 via a coupling.

[0035] In some embodiments, the condenser 1 , the first evaporator 3 and the second evaporator 7 may be falling film, shell and tube or plate heat exchangers, or other forms of heat exchangers.

[0036] In some embodiments, the first expander 4 and the second expander 8 may be turbine expanders, screw expanders, scroll expanders, or other forms of expanders.

[0037] In some embodiments, the first generator 5 and the second generator 9 may be synchronous generators or asynchronous generators.

[0038] In some embodiments, the working fluid pump 2 may be a shielded pump or a magnetic pump.

[0039] In some embodiments, the various components of the present invention are connected by pipes, preferably metal pipes.

[0040] The present invention utilizes a supersonic vapor-liquid two-phase flow ejector 6 to couple the two-stage organic Rankine cycle, which not only saves the power consumption of the working fluid pump 2 of a part of the organic Rankine cycle power generation system, but also recovers the exhaust steam waste heat of the first expander 4 as a regenerator, and can more fully develop and utilize low-grade heat sources. In addition, the present invention uses a supersonic vapor-liquid two-phase flow ejector 6 to use a high-pressure liquid working fluid to eject the exhaust steam at the outlet 4b of the first expander, which can reduce the pressure of the outlet 4b of the first expander, effectively increase the inlet and outlet pressure difference of the first expander 4, and is conducive to improving the technical and economic performance of the organic Rankine cycle power generation system.

[0041] Example 2

[0042] The present invention also provides a jet-boosted two-stage organic Rankine cycle power generation method, using the jet-boosted two-stage organic Rankine cycle power generation system as described above, comprising the following steps:

[0043] Step 1: the organic working medium exhaust gas of the second expander 8 is cooled into liquid working medium by an external cooling medium such as natural water or air in the condenser 1;

[0044] The liquid working medium is pressurized by the working medium pump 2 to form a high-pressure liquid working medium, and enters two branches respectively;

[0045] In the first branch, the high-pressure liquid working medium enters the first evaporator 3 of the first-stage cycle, is heated to saturated steam or superheated steam by the low-grade heat source, and then enters the first expander 4, performs work in the first expander 4, and drives the first generator 5 to operate and generate electricity through the coupling;

[0046] Step 2: In the second branch, the high-pressure liquid working medium enters the supersonic vapor-liquid two-phase flow ejector 6 as the working fluid, and forms a supersonic jet after passing through the supersonic nozzle. The exhaust steam of the first expander 4 enters the variable-section mixing chamber of the supersonic vapor-liquid two-phase flow ejector 6 under the induced action of the supersonic jet. The two fluids directly contact therein to form a supersonic vapor-liquid two-phase flow. When the flow is blocked, a condensation shock wave is generated to achieve a sudden pressure change, and a high-pressure subcooled liquid working medium with a pressure exceeding the working fluid and a medium temperature is obtained;

[0047] Step 3: The high-pressure liquid working medium flowing out of the supersonic vapor-liquid two-phase flow ejector 6 enters the second evaporator 7 in the second-stage cycle, is heated to saturated steam or superheated steam by the low-grade heat source, and then enters the second expander 8, performs work in the second expander 8, and drives the second generator 9 to operate and generate electricity through the coupling;

[0048] Subsequently, the exhaust steam from the second expander 8 enters back into the condenser 1 to complete the system cycle.

[0049] The organic working fluid can be selected from one or more of R245fa (pentafluoropropane), R1233zd (E) (trans-1-chloro-3,3,3-trifluoropropene), R1234ze (E) (trans-1,3,3,3-tetrafluoropropene) and R1234ze (Z) (cis-1,3,3,3-tetrafluoropropene), and other low-boiling-point organic working fluids can also be used.

[0050] As a preferred example, the working principle of the present invention is described below using R245fa as the working fluid of the organic Rankine cycle:

[0051] The R245fa exhaust gas in the second expander 8 is cooled by an external cooling medium such as natural water or air in the condenser 1 to form liquid R245fa, and then pressurized by the working fluid pump 2 to form high-pressure liquid R245fa;

[0052] The high-pressure liquid R245fa flowing out of the working fluid pump 2 is divided into two streams, one of which flows into the first evaporator 3 along the first branch, and the other flows into the supersonic vapor-liquid two-phase flow ejector 6 along the second branch as the working fluid;

[0053] The high-pressure liquid R245fa entering the first evaporator 3 is heated to saturated vapor or superheated vapor by an external low-grade heat source and then enters the first expander 4 to expand and perform work, thereby driving the first generator 5 connected to it through a coupling to operate and generate electricity.

[0054] The high-pressure liquid R245fa entering the supersonic vapor-liquid two-phase flow ejector 6 as the working fluid forms a supersonic jet after passing through the supersonic nozzle. The R245fa exhausted gas of the first expander 4 enters the variable-section mixing chamber of the supersonic vapor-liquid two-phase flow ejector 6 under the induced action of the supersonic jet. The two fluids directly contact therein to form a supersonic vapor-liquid two-phase flow. When the flow is obstructed, a condensation shock wave is generated to achieve a sudden pressure change, thereby obtaining a supercooled liquid R245fa with a pressure slightly higher than the outlet pressure of the working fluid pump 2.

[0055] The high-pressure subcooled liquid R245fa flowing out of the supersonic vapor-liquid two-phase flow ejector 6 enters the second evaporator 7. The high-pressure subcooled liquid R245fa in the second evaporator 7 is heated to saturated vapor or superheated vapor by an external low-grade heat source and then enters the second expander 8 to expand and do work, thereby driving the second generator 9 connected to it through a coupling to operate and generate electricity; subsequently, the exhaust steam of the second expander 8 enters the condenser 1 to complete the system cycle.

[0056] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

Claims

1. A jet-boosted two-stage organic Rankine cycle power generation system, characterized in that: It includes a condenser, a working fluid pump, a first evaporator, a first expander, a first generator, a supersonic vapor-liquid two-phase flow ejector, a second evaporator, a second expander and a second generator; Wherein, the outlet of the condenser is connected to the inlet of the working fluid pump; The outlet of the working fluid pump is divided into two branches, the first branch is connected to the first evaporator, the first expander and the ejection fluid inlet of the supersonic vapor-liquid two-phase flow ejector in sequence; The second branch is connected to the working fluid inlet of the supersonic vapor-liquid two-phase flow ejector, and the outlet of the supersonic vapor-liquid two-phase flow ejector passes through the second evaporator and the second expander in sequence, and is connected to the inlet of the condenser; The first expander is connected to the first generator via a coupling, and the second expander is connected to the second generator via a coupling.

2. The jet-boosted two-stage organic Rankine cycle power generation system according to claim 1, characterized in that: The supersonic vapor-liquid two-phase flow ejector uses a high-pressure liquid working medium as a working fluid, and the organic working medium exhaust steam of the first expander is used as an ejection fluid.

3. The jet-boosted two-stage organic Rankine cycle power generation system according to claim 1, characterized in that: The condenser, the first evaporator and the second evaporator are falling film heat exchangers, shell and tube heat exchangers or plate heat exchangers.

4. The jet-boosted two-stage organic Rankine cycle power generation system according to claim 1, characterized in that: The first expander and the second expander are turbine expanders, screw expanders or scroll expanders.

5. The jet-boosted two-stage organic Rankine cycle power generation system according to claim 1, characterized in that: The first generator and the second generator are synchronous generators or asynchronous generators.

6. The jet-boosted two-stage organic Rankine cycle power generation system according to claim 1, characterized in that: The working fluid pump is a shielded pump or a magnetic pump.

7. A jet-boosted two-stage organic Rankine cycle power generation method, characterized in that: The use of the jet boost two-stage organic Rankine cycle power generation system as claimed in any one of claims 1 to 6 comprises the following steps: The organic working medium exhaust gas of the second expander is cooled into liquid working medium by an external cooling medium such as natural water or air in the condenser; The liquid working medium is pressurized by the working medium pump to form high-pressure liquid working medium, and enters two branches respectively; In the first branch, the high-pressure liquid working medium enters the first evaporator of the first-stage cycle, is heated to saturated steam or superheated steam by the low-grade heat source, and then enters the first expander, performs work in the first expander, and drives the first generator to operate and generate electricity through the coupling; In the second branch, the high-pressure liquid working medium enters the supersonic vapor-liquid two-phase flow ejector as the working fluid, and forms a supersonic jet after passing through the supersonic nozzle. The exhaust steam of the first expander enters the variable-section mixing chamber of the supersonic vapor-liquid two-phase flow ejector under the induced action of the supersonic jet. The two fluids directly contact therein to form a supersonic vapor-liquid two-phase flow, and a condensation shock wave is generated in the case of flow obstruction, achieving a sudden change in pressure, and obtaining a high-pressure subcooled liquid working medium with a pressure exceeding the working fluid and a medium temperature. The high-pressure liquid working medium flowing out of the supersonic vapor-liquid two-phase flow ejector enters the second evaporator in the second-stage cycle, is heated to saturated steam or superheated steam by the low-grade heat source, and then enters the second expander, performs work in the second expander, and drives the second generator to operate and generate electricity through the coupling; Subsequently, the exhaust steam from the second expander enters the condenser to complete the system cycle.

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