GB2395754A

GB2395754A - Ocean thermal energy conversion system with low level condenser

Info

Publication number: GB2395754A
Application number: GB0227861A
Authority: GB
Inventors: Dominic Michaelis
Original assignee: Dominic Michaelis
Priority date: 2002-11-29
Filing date: 2002-11-29
Publication date: 2004-06-02
Anticipated expiration: 2022-11-29
Also published as: GB2395754B; GB0227861D0

Abstract

The Ocean Thermal Energy Conversion (OTEC) system comprises a condenser 20, eg formed of radial finned-tube heat exchangers, which is located in deep cold waters, to which the vaporised working fluid (eg ammonia) vapour, having driven a surface-mounted turbo-generator 11, is transferred down an insulated conduit 12. The condensed fluid runs into a sump 21 from which it is pumped up by a pump 22 back to the surface, where heat exchangers 15, eg on a platform 10, expose it to surface water heat. The vapour drives the turbo-generator 11 and is returned again to the condenser, to complete the cycle. The condenser may be located at the lower end of a tube containing linking pipework and machinery serving as access and as guide to raise the condenser to the surface for maintenance. In a modification, fig.4, the condensed working fluid is pumped up via a series of pumps 22 and a series of break tanks linked by an air pipe 40, avoiding the huge pressure of the whole column. The deep location of the condenser obviates the cost and inefficiency of the convention long cold water pipe and causes less environmental disturbance.

Description

OCEAN THERMAL ENERGY CONVERTER

CONDENSER

This invention relates to condensers used in Ocean Thermal Energy Conversion systems.

Ocean Thermal Energy Conversion (OTEC) systems are a well known and researched form of power generation based on exploiting the difference of temperature of bodies of water at the surface heated by the sun and those at lower levels which remain cold. Normally, in these systems, there is provided a surface land-based or floating energy conversion device comprising an electricity generating turbine driven, in "closed cycles", by a fluid cyclically vaporised by the hot surface water and returned to its fluid state by a condenser cooled by colder waters pumped up through a very long cold water pipe (COOP) extending down to lower depths. In "open cycle" OTEC systems, the surface water itself is the working fluid, vaporizing in a vacuum chamber, the expanding vapour driving a low pressure turbine which generates electricity. The condenser fluid is again the cold water drawn from the depths, as in the closed cycle, and the water, condensed from the vapour having lost its salt and impurities, can be used for drinking, or for irrigation. "Hybrid" systems incorporating both cycles have also been experimented. OTEC systems have proved expensive and inefficient due in large part to the high cost of the cold water pipe, and to the important quantities of energy required to pump large volumes of cold water from great depths to the surface.

According to the present invention, there is provided an ocean thermal energy conversion (OTEC) condenser located at great depth, to which the working vapour is transferred, being pumped down a connecting tube and exposed to coolth as it is condensed back by heat exchangers into its working fluid state in the low level condenser. The liquid condensate is recovered at the base of the condenser elements in a sump from which it is pumped back in an insulated tube to the surface. The working fluid, possessing a low boiling point such as ammonia, for example, is then ready for its next cycle, to be vaporised by warm surface waters, driving a turbo-generator, in the "closed cycle" mode, or to be expanded to cool vaporised sea water in the "open cycle" mode, the vapour being then pumped down to the low level condenser, to be returned again into its liquid state.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows, in diagrammatic form, the low level condenser system.

Figure 2 shows a plan view of the low level condenser, and a section through the connecting tubes. Figure 3 shows a sectional elevation of the low level condenser.

Figure 4 shows an alternative system for the pumping of a fluid from great depths.

Referring to Fig 1, the OTEC low level condenser system comprises an "upper station" consisting of a floating or shore-mounted platform 10 on which is located a turbine linked to an electric generator 11. The turbine, in the "closed cycle" mode is activated by a low temperature boiling point working fluid which is pumped from the depths through an insulated pipe 12 and which is vaporised in an annular sealed expansion chamber 13 heated by the warm surface water 14 pumped through a peripheral heat exchange chamber 15 linking the warm water inlet 16 to the cooled water outlet 17. In the "open cycle" mode, the working fluid is vaporised within a sea-surface sealed evaporator, as in a refrigeration cycle, condensing the vaporised sea water with adequate heat exchange systems, thereby effecting the condensation cycle, returning the sea water vapour to its liquid state, the liquid recovered being "distilled" water suitable for drinking and irrigation purposes..

Linking the "upper station" to the "lower station" is a grouping of pipes, principally the conduit taking the vaporised working fluid 18 which is pumped or blown down by a pump or turbine 19 to the "lower station" and the working fluid insulated conduit 12 which can either be grouped together, or be disposed co-axially, with the working fluid conduit at the centre.

Electric cables and any other necessary pipework can run in this grouping.

The lower station comprises an array of radial finned tube heat exchanger vanes 20 in which the vaporised working fluid is condensed back to its liquid form, running down into a sump 2 l, from which it is pumped back to the "upper station" by a pump. 22 Referring to Fig 2, there is shown a section through the co-axial links between the two "stations", the working fluid pipe 12 being at the core, and carrying the working fluid upwards, surrounded by a layer of insulation 23 within which other smaller pipework and cables can run, these being located at the centre of the working fluid vapour pipe 24 carrying the vapour downwards to the low level condenser.

Below this section shown in Fig 2 is a plan view of the low level condenser, which consists of finned tube heat exchangers, the tubes 25 running vertically between top and bottom manifolds 27, the tubes being at the centre of finned surfaces 26 increasing their heat exchange capacity with the cold surrounding water, resulting in the vapour condensing back to its liquid state, in which it runs down to a centrally located sump 28, the working liquid being then pumped into the central pipe 12 by a pump. 29. The condenser can be planned as a single unit, or as a cluster of juxtaposed units.

In another embodiment, the pump or pumps in series can be cylindrical and can be lowered down the central working fluid pipe, and raised by connecting cables or integrated moles for servicing. The plan shows a helical ramp 30 around the pipe assembly, which allows a motor 31, by gripping to its surface, to induce a circular upwards motion to the whole condenser assembly, so that it can be unlocked from gasket ports and wound up gently to the surface for repairs and servicing, and lowered back to lock into its working position. Alternatively, vertical guides alongside the deepwater pipe can also be used to raise the condenser.

Although thermosyphon would cause water movement over the hotter fins, a set of water impellers 34 may move the water over the fins and increase the condenser efficiency.

Referring to Fig 3, a section is taken through the central pipe array, showing the working fluid vapour pathway down the outer central tube 24 into the upper manifold 27 of the radial fins 32, through the finned tubes 25, the vapour condensing back into its fluid state 33 which runs down into a sump 28, the whole assembly being sealed and designed to resist external deep water pressures. The working fluid is then pumped to the surface by a single pump 29 through the central working fluid pipe t 2, or by a series of pumps 22. The section also shows the water impeller blades 34.

Referring to Fig 4, in a further embodiment of this invention, because of the very great heights through which the working fluid has to be pumped, an air pipe 40 opened, when and as necessary to a pressurization accumulator, 43 at its surface end, set to the working pressure of the fluid (4 atmospheres for ammonia), accompanies the working fluid pipe, being linked to a series of chambers with air at their top end, 41, and thus forming a series of break tanks, each pump 22 acting on the fluid at the bottom of the lower end of the chamber, 42, and pumping it through the interrupted working fluid pipe 44 to the chamber directly above, thus only pumping the height between each chamber, so that the pressure opposed by each pump corresponds to the height between the chambers. The huge pressure of the whole column is thus avoided, and pumps can be selected for their optimum efficiency enabling considerable energy savings to be achieved. A system of interrelated sensors 45 ensure that the working fluid level in each chamber remains between fixed points, determining the regime of each different pump to achieve optimum upward flow, the lowest pump acting on the working fluid recovered from the condenser in the sump 28, the rate of condensation so dictating the overall upward flow.

Although for clarity, Fig 4 shows the pumps and pipework running alongside each other, it is possible to use cylindrical pumps acting on the working fluid in a central conduit, the break tanks and air pipe placed either within or in an annular fashion around the central conduit in a co axial manner. An eccentric outer tube could provide space for a maintenance lift alongside vertically disposed pumps, pipes and break tanks.

This disposition of pumps and break tanks applies generally to the pumping of any fluids through great heights, and in particular from great depths.

Whereas in conventional OTEC systems, huge quantities of cold water are pumped from great depths to effect the necessary working fluid condensation on the surface, the low level condenser system and related pumping arrangement, as described herein with reference to Figures 1 to 4, can increase the overall efficiency of OTEC power generation and help in making it viable in comparison with other energy sources.

Because the low level condenser system does not take large quantities of deep level seawater to the surface, it causes less environmental disturbance than its conventional counterpart.

Claims

1 An ocean thermal energy conversion (OTEC) condenser located at great depth, to which the working vapour is transferred, being pumped down a connecting tube and exposed to coolth as it is condensed back by heat exchangers into its working fluid state in the low level condenser. The liquid condensate is recovered at the base of the condenser elements in a sump from which it is pumped back in an insulated tube to the surface. The working fluid, possessing a low boiling point such as ammonia, for example, is then ready for its next cycle, to be vaporised by warm surface waters, driving a turbo-generator, in the "closed cycle" mode, or to be expanded to cool vaporised sea water in the "open cycle" mode, the vapour being then pumped down to the low level condenser, to be returned again into its liquid state.

2 An ocean thermal energy conversion (OTEC) condenser, as claimed in claim 1, that can be used in " closed cycle" systems in which the low boiling point fluid, is evaporated in a sealed chamber heated by warm surface sea water, the vapour driving a turbine before being returned to the low level condenser to be liquefied and pumped upwards to effect its next cycle. It can also be used with "open cycle" systems, in which sea water under partial vacuum is the working fluid, vaporised by the warm sea surface waters, driving a turbo-

generator. To condense the vapour, a heat exchanger, at sea level, within which the working fluid is expanded, as in a refrigeration cycle, is used to provide coolant surfaces, thereby producing as the condensate valuable "distilled" water which can be used as drinking water, for irrigation and other applications, the vaporised fluid being returned to the low level condenser to be liquefied and pumped up to the sea surface again.

3 An ocean thermal energy conversion (OTEC) condenser, as claimed in claim 1 and 2, comprising an "upper station" consisting of a floating or shore based platform on which is located a turbine linked to an electric generator, the turbine being activated, in a "closed cycle" system, by a working fluid pumped from great depths which is vaporised in a sealed expansion chamber heated by the warm surface waters. The vapour having powered the turbo-generator is then transferred through a conduit to a "low level" station which houses the condenser heat exchangers within which the vapour is returned to its liquid state

4 An ocean thermal energy conversion (OTEC) condenser, as claimed in claim 1 and 3, situated at great depth receiving from above the working fluid vapour, and constituted of an array of finned manifolds and heat exchangers, planned radially or otherwise, through which the vapour is passed to be cooled into a liquid condensate, which runs down to a sump, from which it is pumped back to the surface through an insulated pipe. Optionally, the vapour conduit and the insulated working fluid pipe can be grouped co- axially with the latter at the centre, electric cables and other necessary conduits possibly running through the insulating jacket. The fins are cooled by cold deep sea water running across their surface either by thermosyphon effect, or moved by water impellers. The condenser can be a single unit or a cluster of juxtaposed units.

S An ocean thermal energy conversion (OTEC) condenser, as claimed in claim 4, designed as a mobile unit, locked in its lowest position to all gasket ports, but able to be raised to the surface, for repairs and servicing, either by an upward rotation along a helical guide surrounding the co-axial tubes, or following vertical guides running up the tubes along their length so that the condenser unit can be raised either by its own motor, or by cables allowing it to be winched up to the floating or land based surface platform.

6 An ocean thermal energy conversion (OTEC) condenser, as claimed in claim 1 and 4, located at a great depth in cool waters returning the working fluid vapour to its liquid state, the condensate being pumped back to the surface either by a single high pressure pump located at the level of the condenser sump, or by a number of pumps acting in series, these pumps possibly being cylindrical and lowered down the working fluid pipe to different predetermined levels.

7 An ocean thermal energy conversion (OTEC) condenser, as claimed in claim 6, and shown in Fig 4, which, because of the very great heights through which the working fluid has to be pumped, is provided with an air pipe fitted as and if necessary with a pressurization accumulator at its surface end, adjusted to the vapour pressure of the working fluid in its cooled liquid state, for example 4 atmospheres for ammonia at 5 C. The air pipe which accompanies the working fluid pipe is linked to a series of tubular chambers with air at their top end, under comparatively low pressure, thus forming a series of break tanks, each pump acting on the fluid at the bottom end of each chamber and pumping it to the chamber directly above, thus only pumping the height between each chamber, so that the pressure opposed by each pump corresponds to the height between the chambers, and the huge pressure of the whole column is avoided. A system of interrelated sensors ensures that the liquid level in each chamber is correct, and governs the regime of the series of pumps to ensure optimum efficiency and energy savings.

This arrangement can be used in any application requiring liquid pumping through great heights and from great depths.

8 An ocean thermal energy conversion (OTEC) condenser, as claimed in claim 7, comprises linking pipes, pumps and chambers between the surface and the low level submerged condenser either planned to run vertically alongside each other, or planned co-

axially, running within a single principal tube. A further external eccentric tube can allow for the passage of a lift for maintenance.

9 An ocean thermal energy conversion (OTEC) condenser, as claimed in claim 1 and claim 4, which effects the condensation of working fluid without pumping cold water to the surface from great depths, as occurs in conventional OTEC, and thus avoids this pumping and the possible risk of environmental damage that it entails.

10 An ocean thermal energy conversion (OTEC) condenser system substantially as described herein with reference to Figures 1-4 of the accompanying drawings.