GB2444731A - Ocean thermal energy conversion - Google Patents

Abstract

An open cycle ocean thermal energy conversion (OTEC) plant generates electricity and desalinated water. The plant comprises an inner chamber (shell) 2 surrounded by an outer chamber 1, one of the chambers containing a vacuum. Relatively warm ocean water is pumped into the vacuum containing chamber where it is evaporated, the vapour passing through a turbine 20, which generates electricity, to the other of the chambers where it is condensed into desalinated water using relatively cold ocean water. The chambers 1, 2 may be spherical in shape. Part of the generated electricity maybe used to produce hydrogen. The plant is located on a floating platform 3 which is supported by pressure ballasted hollow columns 4 which allow it to rise and fall as required. A pipe (50, figure 2) supplying the relatively cold ocean water is separately buoyed and moored, and is linked to the platform 3 by telescopic flexible tubing (57, figure 2). A plankton control device may be fitted to the plant which allows plankton to be brought to the ocean surface for fish farming.

Description

OCEAN THERMAL ENERGY CONVERSION PLANT

This invention relates to the design of Ocean Thermal Energy Conversion Plants.

At the end of the nineteenth century, a French engineer, D'Arsonval, suggested generating energy by using the differential between tropical ocean temperatures at around 28 C and water pumped from great depths at 5 C, a system experimented by his successor Claude, and now generally known as OTEC, or Ocean Thermal Energy Conversion.

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 long cold water pipe (CWP) 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, is desalinated water which can be used for drinking, or for irrigation. "Hybrid" systems incorporating both cycles have also been experimented.

According to the present invention, there is provided an Ocean Thermal Energy Conversion Plant consisting of a floating or shore based platform, on which is located the plant, generating, in the "open cycle" both electricity and desalinated water, the platform being fitted with air pressure ballasted underwater columns so that the platform can be raised in high seas to avoid being submerged, and lowered in fairer weather so that ships can come alongside it to service the plant and take on board hydrogen created from part of the electricity generated and desalinated water, the columns fitted with hydrodynamic cowls pivoting to face high seas to minimise drag, the columns being fitted with air pumps to allow their height to be adjusted, and a water duct taking warm surface water, even in high seas, to the surface by water pumps located on the platform, pumping the hot water required for the OTEC cycle to work to the bottom of the evacuated evaporative chamber, the same pump powering arrays of perforated pipes, which release water under pressure to form droplets of water that immediately vaponse in the vacuum created in the outer spherical chamber and in the inner spherical chamber by a vacuum pump, the nesting spheres having 3 dimensional curvature shells that are best suited to resist a uniformly applied force, the space between the inner and outer shells under vacuum forming the Evaporator, the vapour rising to the top where it enters a turbogenerator located at crest of the inner sphere, containing the evacuated condensation chamber or Condenser, the warm vapour being forced through an array of condensation hollow flat part circular twin plated thin effective heat exchangers, because the cold water at 5 C is pumped to the pipes feeding their upper parts, the cold water then running down inside the condensation plates by gravity, allowing them to be very effective, thin hanging membranes, to a collecting manifold and from there pumped back into the sea, the vapour, losing its salt content when vaponsed, having been in contact with the condensation plates, condenses to create desalinated water, which runs down the plates to fall into a sump from which it is pumped away, uncondensed vapour and dry air being blown away by the vacuum pump to make way for incoming vapour, the inner sphere acting as the condenser necessary for the operation of the turbine, the cold water having been pumped from deep cold waters up a cold water pipe (CWP) which is independantly moored and bouyed below the plant, which is subject to the movement of the waves, and is linked to the CWP by telescopic flexible tubing that can absorb differential movement and be brought up in storm conditions to disassociate the plant from its CWP, or by flexible tubing that can take up vertical and horizontal movement, the cold water pumps being located in a chamber below the inner sphere, protected also by a hydrodynamic cowl, pumping the water from the depths to the top of the condensing plates, cold water pumped up the CWP whose walls need to be kept smooth by regular automated cleaning, the base of the CWP fitted with aerating equipment to help in giving an upward movement to the water column in the CWP, a plankton control device being fitted when necessary, all plant components being readily accessible for servicing, a central lift shaft being used to take any component that needs outside servicing or replacement to the top of inner sphere, the plant being closed down and the turbine being designed to move sideways, the components taken to areas below the top outer sphere openings from where they can be craned away, the electricity generated being cabled from the outer sphere superstructure, above which is the systems control room, accessible by a separate lift and fire escape stairway, the electricity cabled to land or hydrolysed to create hydrogen, the desalinated water being pipelined or tankered away, the OTEC plant platform being able to link up to other platforms, for staff housing, plant servicing, hydrogen production and treatment, electricity transformation, fish farming, harbour facilities for tankers, a helipad, associated leisure facilities and other requirements.

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 a section taken through an OTEC power and desalination plant, illustrating two nesting part spherical shells forming the main structure, the space between the two shells acting mainly as the evaporator, the space within the inner shell designed as the condenser, a turbine between the two producing electricity, the condensate desalinated water being pumped away as a valuable by product, the base of the inner shell fitted with pumps that draw cold water from the depths up to cool the condenser, the shells resting on a platform ballasted to adapt to different weather conditions, and housing the ocean surface hot water pumps leading to the evaporator.

Figure 2 shows diverse junctions between the independantly moored and buoyed Cold Water Pipe (CWP) and the OTEC plant Figure 3 shows an aerating system at the base of the CWP, as well as a helical water flow inducer designed to centrifuge plankton away from the water entering the CWP. A plan view of the bailast column hydrodynamic cowl is included.

Fig 4 shows a number of linked platforms creating a complex around the OTEC plant.

Fig 5 shows an overall view of the OTEC plant at sea.

Referring to Figure 1, The OTEC plant structure consists principally of an outer part spherical shell, 1, and an inner spherical shell, 2. The spherical shells are supported by a floating platform, 3, which is in turn supported by a number of immersed hollow columns, 4, into which air is pumped by compressors, 5, which allow variations of overall bouyancy, over and above that given by the bottom of the inner sphere, 2, and the cylindrical structure, 7, housing the cold water pump room, 8, the whole structure floating in fair weather just above the water line, 9, so that large and small vessels can board, and being able to rise higher when large waves, 10, occur, the immersed columns and the spherical pump room being equiped with hydrodynamic cowls, 11, to reduce the drag and the forces exerted on the mooring cables, 12, the columns fitted with base flanges, 41, to increase their resistance to overturning moments exerted on the platform structure in heavy seas.

Warm water from the ocean surface is drawn in through ducts, 13, in the immersed columns by a series of pumps, 14, driving the water to a thin moving water plane, 15, from which water is evaporated under the vacuum established in the duct created between the inner and outer spherical shells by a vacuum pump, 16, the water also being pumped through pipework equiped with spray creating nozzles, 17, to increase water evaporation, the expanding water vapour created between the shells rising to the upper part of the evaporative duct, 18, towards the turbine, 20, located at the top of the inner sphere, 2.

The turbine is powered by the high pressure in the evaporative duct, the Evaporator, 18, and the draw created by vapour condensation in the inner sphere designed as the Condenser, 19.

The condenser uses cold ocean water drawn from great depths, such that the difference of temperature between the warm surface water and the cold deep water is at least 20 C.

The cold water is drawn up the Cold Water Pipe (CWP), 40, shown in Fig 2, arriving up to a CWP linking tube receptor, 54, and the cylindrical pump room, 8, where are located a number of pumps, 23, that pump the cold water from the receptor into the bottom of the inner sphere, 2, and into manifold tubes, 24, that feed the the top condenser plate feeder tubes, 25, the cold water reaching the condenser plates, 40, through which it flows at a speed related to vapour condensation rates, the used cold water being collected by a manifold tube, 26, and pumped back into the ocean by pumps, 27.

The warm vapour is blown by the turbine, 20, partly into suitably perforated ductwork, 21, above the condenser plates and partly downwards being deflected into the voids between the condenser plates by aerofoils, 22, that force the vapour to enter the array of condenser plates.

The evaporated water has left its saline components in the evaporator, so that, as the vapour is condensed, it is desalinated water which, by gravity, runs down the condenser plates, fitted with horizontal ledges which, every few metres, direct the condensate to the centre of the space between the condenser plates, this to prevent the running condensate from interfering with the condenser plate efficiency, where it falls to the base of the inner sphere, 2, to be collected as valuable desalinated water, running into a sump, 23, from which it is pumped away by a pump, 24, to a desalinated water outlet tube, 25. Remaining uncondensed vapour and dry air is removed by the air vacuum pump, 16.

The turbogenerator, 20, can be winched Out for servicing and left in position, 30 to give access to a central service shaft, 31, and lift platform 32 from which aerofoils and any readily displaced obstructions can be removed, able to lift all components or parts of components needing to be serviced or replaced, on a platform, 32, to the service gallery, 33, and serviced or taken to the space below a sliding roof panel, 34, from which it can be craned away by a mobile crane.

The electrical cabling, 35,from the turbogenerator leaves the OTEC plant from the crown of the outer sphere, 1. The electricity can either be cabled to shore, or hydrolised to create hydrogen, which can be pipelined or tankered to shore.

Above the servicing gallery is the control and communications centre, 36, with its antennae and radar facilities above, reached by an external lift and stair tower, 37.

Ships can berth alongside the OTEC plant, and a helipad, 38, is provided.

Staff housing and facilities, 39, are planned on the platform.

Referring to Figure 2, the cold water pipe, (CWP), 50, descending to great ocean depths, and therefore having great weight and inertia, is considered as an independant structure, with its own underwater bouyancy ring, 51, restrained from upward movement by its own mooring cables, 52, either totally independant, or linked to the main OTEC plant mooring cables, 58, at a depth sufficient to be minimally affected by the movement incurred by the plant in heavy seas, the top of the CWP fitted with a funnel structure to receive and lock into position the linking tube, 53, the tube made up of telescopically nesting elements, 57, having some flexibility in their joints or the material from which they are constructed, fitting, when retracted, into its receptor unit, 54, and so totally protected from heavy seas, or the linking tube being made of a flexible material to accomodate lateral movement, 55, the funnel, 53, and the receptor, 54, being designed to take up any vertical movement.

Referring to Figure 3, at the base of the cold water pipe, compressed air is taken from the platform down a tube, 60, which enters a circular pipework array, 61, fitted with nozzles discharging compressed air into the water entering the CWP, the array being located below the CWP to allow water to enter the CWP unimpeded.

Where plankton depletion is undesirable, or needs to be controlled, the CWP is fitted at its base with a length of pipe fitted with a spiral flange, 62, inducing a spiral water motion, the heavier plankton being centrifuged to the outer wall, which is provided, in its upper part, with a number of thin slits, 63, allowing a small amount of plankton rich fluid to escape, this length being of a slightly larger diameter, 68, so as not to increase friction at the CWP lower inlet, 65, The ballasting columns, 4, as well as the cylindrical pump room shell, 7, are fitted with hydrodynamic cowls, II, made of stiff thin sheet material, 79, stiffened by a frame, 76, with a central circular rotating flange, 77, allowing it to take the position of least resistance, water being on both sides of the plate, to reduce forces exerted by heavy weather on the OTEC plant structure. These cowls also reduce stresses induced on the mooring cables, 12.

They make possible the towing by tugs of a very heavy shore made structure to a distant ocean location.

Referring to Figure 4, an assembly of floating platforms is shown added to the OTEC Plant, comprising two hexagonal platforms and filler pieces to form a straight quayside for mooring, many such assemblies being able to answer different requirements, electricity transformation, hydolysis equipment and hydrogen handling, a helipad, staff housing, leisure, and other facilities necessary to the proper functioning of the OTEC Plant.

Referring to Figure 5, an illustration is given of an OTEC plant shown alone in its marine environment. The computer graphics program did not allow the hydrodynamic cowls to be simulated.

Claims (9)

1. I An Ocean Thermal Energy Conversion Plant consisting of a floating or shore based platform, on which is located the plant, generating, in the "open cycle" both electricity and desalinated water, the platform being fitted with air pressure ballasted underwater columns so that the platform can be raised in high seas to avoid being submerged, and lowered in fairer weather so that ships can come alongside it to service the plant and take on board hydrogen created from part of the electricity generated and desalinated water, the columns fitted with hydrodynamic cowls pivoting to face high seas to minimise drag, the columns being fitted with air pumps to allow their height to be adjusted, and a water duct taking warm surface water, even in high seas, to the surface by water pumps located on the platform, pumping the hot water required for the OTEC cycle to work to the bottom of the evacuated evaporative chamber, the same pump powering arrays of perforated pipes, which release water under pressure to form droplets of water that immediately vaponse in the vacuum created in the outer spherical chamber and in the inner spherical chamber by a vacuum pump, the nesting spheres having 3 dimensional curvature shells that are best suited to resist a uniformly applied force, the space between the inner and outer shells under vacuum forming the evaporator, the vapour rising to the top where it enters a turbogenerator located at crest of the inner sphere, containing the evacuated condensation chamber or condenser, the warm vapour being forced through an array of condensation hollow flat part circular twin plated thin effective heat exchangers, because the cold water at 5 C is pumped to the pipes feeding their upper parts, the cold water then running down inside the condensation plates by gravity, allowing them to be very effective, thin hanging membranes, to a collecting manifold and from there pumped back into the sea, the vapour, losing its salt content when vaporised, having been in contact with the condensation plates, condenses to create desalinated water, which runs down the plates to fall into a sump from which it is pumped away, uncondensed vapour and dry air being blown away by the vacuum pump to make way for incoming vapour, the inner sphere acting as the condenser necessary for the operation of the turbine, the cold water having been pumped from deep cold waters up a cold water pipe (CWP) which is independantly moored and bouyed below the plant, which is subject to the movement of the waves, and is linked to the CWP by telescopic flexible tubing that can absorb differential movement and be brought up in storm conditions to disassociate the plant from its CWP, or by flexible tubing that can take up vertical and horizontal movement, the cold water pumps being located in a chamber below the inner sphere, protected also by a hydrodynamic cowl, pumping the water from the depths to the top of the condensing plates, cold water pumped up the CWP, whose walls need to be kept smooth by regular automated cleaning, the base of the CWP fitted with aerating equipment to help in giving an upward movement to the water column in the CWP, a plankton control device being fitted when necessary, all plant components being readily accessible for servicing, a central lift shaft being used to take any component that needs outside servicing or replacement to the top of inner sphere, the plant being closed down and the turbine being designed to move sideways, the components taken to areas below the top outer sphere openings from where they can be craned away, the electricity generated being cabled from the outer sphere superstructure, above which is the CLAIMS (cont) systems control room, accessible by a separate lift and fire escape stairway, the electricity cabled to land or hydrolysed to create hydrogen, the desalinated water being pipelined or tankered away, the OTEC plant platform being able to link up to other platforms, for staff housing, plant servicing, hydrogen production and treatment, electricity transformation, fish farming, harbour facilities for tankers, a helipad, associated leisure facilities and other requirements.
2. 2 An Ocean Thermal Energy Conversion Plant, as claimed in Claim I, consisting of two nesting principally spherical volumes, but being able to be of different close geometries, such as ovoid, the inner volume able to be varied to achieve the highest energy and desalination yields, the principal functions taking place between, below and around the said volumes.
3. 3 An Ocean Thermal Energy Conversion Plant, as claimed in Claim I and 2, where the location of the Evaporator and the Condenser are inversed, the turbine being still at the top of the inner volume, but the evaporator being located in the inner volume, whilst the condenser is located in the outer volume, cold water and warm water ducts being adapted accordingly.
4. 4 An Ocean Thermal Energy Conversion Plant, as claimed in Claim 1 and 2, in which the cold water coolant is pumped to the top of the condensing plates, in rigid pipes supported by the main structure, the plates being hanging membranes through which the coolant runs by gravity, being of very thin materials forming more effective heat exchangers.
5. An Ocean Thermal Energy Conversion Plant, as claimed in Claim 1, from which the salt brine left after the evaporative process has taken place can be passed through a drier powered by the plant, or dehydrated in floating beds exposed to solar radiation, to provide valuable ocean salt.
6. 6 An Ocean Thermal Energy Conversion Plant, in which the Cold Water Pipe is independantly buoyed and moored, below the water level affected by heavy seas, and linked flexibly to, and separable from the main floating structure, the pipe provided with automated brushing equipment to keep its walls as smooth as possible to maintain its efficiency.
7. 7 An Ocean Thermal Energy Conversion Plant, as claimed in Cl;aim 1, that can be the core platform for a series of linking platforms to create a floating island which can accomodate functions directly linked to the plant, but can grow to include industrial and leisure facilities, provisions being made for safety of hydrogen production, storage, and transport, hydrogen facilities located in underwater caissons, and underwater hydrogen pipelines insuring safety.
8. 8 An Ocean Thermal Energy Conversion Plant, as claimed in Claim 1, whose Cold Water Pipe is fitted at its base with a larger diameter tube to which is fixed a spiral flange inducing a helical water motion, the heavier plankton being centrifuged to the outer wall, which is provided, in its upper part, with a number of thin slits allowing a small amount of plankton rich fluid to escape. This system can be replaced by a grid of smaller centrifuges below the CWP inlet, rejecting the plankton. Plankton depletion is an imortant criticism of CLAIMS (Cont) OTEC by environmentalists. The device would allow different quantities of plankton to be brought to the surface for fish farming, the rest being left in place.
9. 9 An Ocean Thermal Energy Conversion Plant substantially as described herein with reference to figures 1-5 of the accompanying drawings