AU2021101183A4

AU2021101183A4 - Closed Ocean Thermal Energy Conversion System

Info

Publication number: AU2021101183A4
Application number: AU2021101183A
Authority: AU
Inventors: Shimiao HUANG; Bin Li; Minghai Xu; Li Zhang
Original assignee: China University of Petroleum East China; Southern Marine Science and Engineering Guangdong Laboratory Zhanjiang
Current assignee: China University of Petroleum East China; Southern Marine Science and Engineering Guangdong Laboratory Zhanjiang
Priority date: 2021-01-28
Filing date: 2021-03-05
Publication date: 2021-05-06
Anticipated expiration: 2029-03-05
Also published as: CN112664418B; CN112664418A

Abstract

Disclosed is a closed ocean thermal energy conversion (OTEC) system, including a warm seawater transportation mechanism, an evaporator, a steam turbine, an exhausted steam fluid pipeline, a liquid fluid pipeline and a heat exchange coil. The heat exchange coil is provided in a deep cold seawater area, one end of the heat exchange coil is connected to one end of the exhausted steam fluid pipeline, another end of the exhausted steam fluid pipeline is connected to the steam turbine, another end of the heat exchange coil is connected to one end of the liquid fluid pipeline, another end of the liquid fluid pipeline is connected to the evaporator, the evaporator is connected to the steam turbine, the superheated steam is configured to work in the steam turbine to form the exhausted steam, and the evaporator is connected to the warm seawater transportation mechanism. 1/3 112 3 4 T M 1 12 P' 2 13 PI warm seawater on the deep cold ocean surface 8 5 6 FIG. 1

Description

1/3

112 3 4 T M 1 12 P' 2

13 PI

deep cold warm seawater on the ocean surface

8 5 6 FIG. 1

CLOSED OCEAN THERMAL ENERGY CONVERSION SYSTEM TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of ocean thermal energy conversion (OTEC), in particular to a closed OTEC system.

BACKGROUND

[0002] Since the 1920s, people have begun to explore the development and utilization of ocean thermal energy, and have conducted experimental tests and actual production of OTEC systems of different scales based on the principle of the Rankine cycle. According to the different fluids and processes, there are three main forms of OTEC systems, namely, an open cycle system, a closed cycle system and a mixed cycle system. The most commonly used system at present is the closed cycle system.

[0003] In the closed cycle system, the cycle of fluid is still based on the Rankine cycle. However, the fluid is changed from water to a low boiling point fluid such as R134a, and the high temperature heat source and low temperature heat source are respectively replaced with deep and cold seawater at a certain depth of the sea. The warm seawater on the ocean surface is boosted by the warm seawater pump and enters the evaporator through the warm seawater pipeline, where it exchanges heat with the fluid R134a. R134a absorbs heat at a constant pressure in the evaporator S, and changes from the compressed liquid state to the saturated liquid state, further to the saturated steam state and finally to superheated steam. The superheated steam expands adiabatically in the steam turbine T to output work. The exhausted steam discharged from the steam turbine releases heat to the cold seawater at a constant pressure in the condenser and condenses into the saturated liquid state. This process is a constant pressure process and also a constant temperature process. The cold seawater is obtained at a depth of about 1000m of the sea, and passes through the cold seawater pipeline with an insulation layer, and is pumped by the cold seawater pump to the condenser to exchange heat with the exhausted steam at a constant pressure. The condensed fluid undergoes an adiabatic process in the fluid pump, and the compressed liquid after the pressure rises enters the evaporator again to complete the cycle.

[0004] Since the temperature difference between warm seawater and cold seawater is small, the thermal efficiency of the cycle is low. In order to increase the thermal efficiency of the cycle, it is necessary to increase the temperature difference. In order to achieve this goal, the OTEC system is usually installed in areas with high ocean surface temperature, and obtains cold seawater from a deeper ocean depth as far as possible within the allowable range of the equipment, and sends it to the condenser on the sea surface through the pipeline with the insulation layer. Obtaining cold seawater from a considerable depth under the sea requires a long enough pipeline and a booster pump that can provide enough energy. The deeper the depth is, the longer the cold seawater pipeline will be, which means the greater the resistance loss along the way the seawater flows through the pipeline. This leads to the need to consume a considerable amount of electricity generated by the power generation system to obtain cold seawater, which greatly reduces the power generation efficiency of the OTEC system.

SUMMARY

[0005] The objective of the present disclosure is to provide a closed OTEC system, which reduces the pump power required for system circulation and improves power generation efficiency.

[0006] In order to achieve the above objective, the present disclosure provides a closed OTEC system, including a warm seawater transportation mechanism, an evaporator, a steam turbine, an exhausted steam fluid pipeline, a liquid fluid pipeline and a heat exchange coil, wherein the liquid fluid pipeline is provided with an insulation layer, the heat exchange coil is provided in a deep cold seawater area, one end of the heat exchange coil is connected to one end of the exhausted steam fluid pipeline, another end of the exhausted steam fluid pipeline is connected to the steam turbine, the exhausted steam after work is transported to the heat exchange coil through the exhausted steam fluid pipeline to exchange heat with cold seawater to form a saturated liquid fluid, another end of the heat exchange coil is connected to one end of the liquid fluid pipeline, a fluid pump is provided on the liquid fluid pipeline, another end of the liquid fluid pipeline is connected to the evaporator, a unsaturated liquid fluid after being boosted by the fluid pump exchanges heat with warm seawater in the evaporator to form superheated steam, the evaporator is connected to the steam turbine, the superheated steam does work in the steam turbine to form exhausted steam, and the evaporator is connected to the warm seawater transportation mechanism.

[0007] In an embodiment, the warm seawater transportation mechanism includes a water intake pipe, a drainage pipe, and a warm seawater pump, the warm seawater pump is provided on the water intake pipe, and both the water intake pipe and the drainage pipe are connected to the evaporator.

[0008] In an embodiment, the fluid is the organic fluid R134a.

[0009] In an embodiment, a diameter of the liquid fluid pipeline is smaller than a diameter of the exhausted steam fluid pipeline.

[0010] Therefore, the present disclosure adopts a closed OTEC system with the above-mentioned structure. The heat exchange coil replaces the condenser for the heat exchange between the fluid and the cold seawater. The arrangement position is moved from the original position above the sea surface to the corresponding depth below the sea surface. The arrangement of condensers, cold seawater pumps and pipelines are eliminated, which reduces the pump power required for system circulation and improves the power generation efficiency of the OTEC system.

[0011] The technical solutions of the present disclosure will be further described in detail below through the accompanying drawings and embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a schematic structural diagram of a closed OTEC system according to the present disclosure.

[0013] FIG. 2 is a T-s diagram of an R134a Rankine cycle according to the present disclosure.

[0014] FIG. 3 is a schematic structural diagram of a traditional OTEC system.

[0015] Reference signs

[0016] 1. Warm seawater transportation mechanism; 11. Water intake pipeline; 12. Drainage pipeline; 13. Warm seawater pump; 2. Evaporator; 3. Steam turbine; 4. Exhausted steam fluid pipeline; 5. Liquid fluid pipeline; 6. Heat exchange coil; 7. Insulation layer; 8. Fluid pump.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] Embodiment

[0018] FIG. 1 is a schematic structural diagram of a closed OTEC system according to the present disclosure. FIG. 2 is a T-s diagram of an R134a Rankine cycle according to the present disclosure. The closed OTEC system includes a warm seawater transportation mechanism 1, an evaporator 2, a steam turbine 3, an exhausted steam fluid pipeline 4, a liquid fluid pipeline 5 and a heat exchange coil 6. The warm seawater transportation mechanism 1 includes a water intake pipe 11, a drainage pipe 12, and a warm seawater pump 13. The warm seawater pump 13 is provided on the water intake pipe 11, and both the water intake pipe 11 and the drainage pipe 12 are connected to the evaporator 2. The liquid fluid pipeline 5 is provided with an insulation layer 7. The fluid in this embodiment is an organic fluid R134a. The viscosity of R134a is about 10 times that of water, and R134a is latent heat exchange, and seawater is sensible heat exchange, so that a required flow rate of R134a is less than that of seawater, which greatly reduces the transportation resistance. The heat exchange coil 6 is provided in a deep cold seawater area, one end of the heat exchange coil 6 is connected to one end of the exhausted steam fluid pipeline 4, another end of the exhausted steam fluid pipeline 4 is connected to the steam turbine 3, the exhausted steam after work is transported to the heat exchange coil 6 through the exhausted steam fluid pipeline 4 to exchange heat with cold seawater to form a saturated liquid fluid, another end of the heat exchange coil 6 is connected to one end of the liquid fluid pipeline 5, a fluid pump 8 is provided on the liquid fluid pipeline 5, and another end of the liquid fluid pipeline 5 is connected to the evaporator 2. Since temperature and pressure affect the intensity of molecular motion, under the same other conditions, the higher the temperature, the more intensity the molecular motion, and the lower the pressure, the more intensity the molecular motion. Saturated liquid means that the rate at which molecules change from liquid to gas is equal to the rate at which the molecules change from gas to liquid. It can be understood that the intensity of molecular thermal motion is at a fixed value, so saturation pressure and saturation temperature should have a one-to-one correspondence. After the saturated liquid is pressurized by the fluid pump 8, the temperature remains almost unchanged. At this time, the molecular thermal motion slows down due to the increase in pressure. Therefore, the rate at which molecules change from liquid to gas is less than the rate at which they change from gas to liquid, which is an unsaturated liquid. The unsaturated liquid fluid after being boosted by the fluid pump 8 exchanges heat with warm seawater in the evaporator 2 to form superheated steam. After the fluid is pressurized by the fluid pump 8, due to the increase in pressure, the subsequent evaporation process needs the fluid to be saturated at a higher temperature, that is, the fluid evaporates at a higher temperature. Therefore, after the fluid is pressurized, the evaporation temperature can be increased correspondingly, the heat exchange temperature difference of the entire cycle can be increased, and the thermal efficiency of the cycle can be increased. The evaporator 2 is connected to the steam turbine 3, the superheated steam works in the steam turbine 3 to form exhausted steam, and the evaporator 2 is connected to the warm seawater transportation mechanism 1. When the fluid flows downwards, it is the exhausted steam after work, and needs to be condensed in the heat exchange coil 6. The exhausted steam fluid pipeline 4 has low requirements for thermal insulation performance, and exchanges heat with seawater during the exhausted steam transportation. The heat exchange between the fluid in the heat exchange coil 6 and the cold seawater can be reduced, and the heat exchange area and length of the heat exchange coil 6 can be reduced. The fluid is in a saturated liquid state when it flows upwards. To avoid cavitation of the fluid pump 8 and reduce the thermal efficiency of the cycle, the liquid fluid pipeline 5 has high requirements for the insulation layer 7, for reducing the heat exchange between the fluid and the surface warm seawater before it flows through the fluid pump 8 and enters the evaporator 2. A diameter of the liquid fluid pipeline 5 is smaller than a diameter of the exhausted steam fluid pipeline 4.

[0019] FIG. 3 is a schematic structural diagram of a traditional OTEC system. The traditional OTEC system is usually installed in areas with high ocean surface temperature, and obtains cold seawater from a deeper ocean depth as far as possible within the allowable range of the equipment, and sends it to the condenser on the sea surface through the pipeline with the insulation layer. Obtaining cold seawater from a considerable depth under the sea requires a long enough pipeline and a booster pump that can provide enough energy. The deeper the depth is, the longer the cold seawater pipeline will be, which means the greater the resistance loss along the way the seawater flows in the pipeline. This leads to the need to consume a considerable amount of electricity generated by the power generation system to obtain cold seawater, which greatly reduces the power generation efficiency of the OTEC system.

[0020] Taking a 1MW OTEC system as an example, the diameter of the liquid fluid pipeline 5 is 30 cm, and the diameter of the exhausted steam fluid pipeline is 60 cm. The larger the pipe diameter, the slower the fluid flow in the pipe under the same flow rate, and the along-the-path resistance of the fluid transported along the pipe will be greatly reduced. After calculation, the pump power required to pump cold seawater in the original scheme is 94124W, while the pump power required to pump the fluid in this scheme is 37909W. Compared with the original technical solution using a 65cm diameter cold seawater pipeline for pumping water, which is also set at a position of 1000m below the sea, the pump power consumption for pumping cold seawater of this technical solution is only 40.3% of the original solution. It can be seen from this that when the diameter of the liquid fluid pipeline 5 in this solution is small, the expected effect can be achieved, that is, the pump power consumption for system operation is saved.

[0021] Therefore, the present disclosure adopts a closed OTEC system with the above-mentioned structure. The heat exchange coil replaces the condenser for the heat exchange between the fluid and the cold seawater. The arrangement position is moved from the original position above the sea surface to the corresponding depth below the sea surface. The condensers, cold seawater pumps and pipelines thereof are eliminated, which reduces the pump power required for system circulation and improves the power generation efficiency of the OTEC system.

[0022] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure rather than limiting them. Although the present disclosure has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present disclosure, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present disclosure.

Claims

CLAIMS What is claimed is:

1. A closed ocean thermal energy conversion (OTEC) system, comprising a warm seawater

transportation mechanism, an evaporator, a steam turbine, an exhausted steam fluid pipeline, a

liquid fluid pipeline and a heat exchange coil, wherein the liquid fluid pipeline is provided with

an insulation layer, the heat exchange coil is provided in a deep cold seawater area, one end of

the heat exchange coil is connected to one end of the exhausted steam fluid pipeline, another

end of the exhausted steam fluid pipeline is connected to the steam turbine, exhausted steam

after work is transported to the heat exchange coil through the exhausted steam fluid pipeline to

exchange heat with cold seawater to form a saturated liquid fluid, another end of the heat

exchange coil is connected to one end of the liquid fluid pipeline, a fluid pump is provided on

the liquid fluid pipeline, another end of the liquid fluid pipeline is connected to the evaporator,

an unsaturated liquid fluid after being boosted by the fluid pump exchanges heat with warm

seawater in the evaporator to form superheated steam, the evaporator is connected to the steam

turbine, the superheated steam is configured to work in the steam turbine to form the exhausted

steam, and the evaporator is connected to the warm seawater transportation mechanism.

2. The closed OTEC system of claim 1, wherein the warm seawater transportation

mechanism includes a water intake pipe, a drainage pipe, and a warm seawater pump, the warm

seawater pump is provided on the water intake pipe, and both the water intake pipe and the

drainage pipe are connected to the evaporator.

3. The closed OTEC system of claim 1, wherein the fluid is organic fluid R134a.

4. The closed OTEC system of claim 1, wherein a diameter of the liquid fluid pipeline is

smaller than a diameter of the exhausted steam fluid pipeline.