WO1995028567A1

WO1995028567A1 - Ocean thermal energy conversion (otec) system

Info

Publication number: WO1995028567A1
Application number: PCT/US1995/004305
Authority: WO
Inventors: Robert J. Flynn; George J. Cicchetti; Jonathan D'e. Coony
Original assignee: Otec Developments
Priority date: 1994-04-15
Filing date: 1995-04-14
Publication date: 1995-10-26
Also published as: GT199500016A; NL1000149C2; NL1000149A1; AU2380795A

Abstract

An improved ocean thermal energy conversion (OTEC) system which performs desalination by receiving warm sea water, flash evaporating a portion of the warm sea water to produce steam, and condensing the steam with cold sea water to produce fresh water. The improved ocean thermal energy conversion (OTEC) system also generates energy by receiving a warm sea water, evaporating a working fluid at a natural depth of the received warm sea water to produce a working vapor, generating energy from the working vapor, and condensing the working vapor with the cold sea water at a natural depth of the cold sea water.

Description

OCEAN THERMAL ENERGY CONVERSION (OTEC) SYSTEM

The present invention relates to an improved ocean thermal energy conversion (OTEC) system.

BACKGROUND OF THE INVENTION Conventional ocean thermal energy conversion (OTEC) systems generally fall into three categories; first, a closed-cycle OTEC system 100 for generating electricity as illustrated in Figure 1; second, an open-cycle OTEC system 200 for generating electricity as a primary product and fresh water as a secondary product as illustrated in Figure 2; and third, a hybrid-cycle OTEC system 300 for generating electricity as a primary product and desalinated water as a secondary product, illustrated in Figure 3. Each of these conventional OTEC systems will be discussed below in detail.

As illustrated in Figure 1, a working fluid, which is contained within the closed cycle, is pumped by a liquid pump 102 into evaporator 104, where heat from a warm water intake is transferred from the warm water to the working fluid to generate a working fluid vapor. The warm water exiting the evaporator 104 is discharged to the sea. The working fluid vapor enters a turbogenerator 106 in order to generate electricity by conventional techniques. The working fluid vapor exits the turbogenerator 106 and is condensed in condenser 108 utilizing cold sea water as a heat sink. The condensed working fluid is then fed back to the feed pump in order to complete the closed cycle.

The open-cycle OTEC system 200 illustrated in Figure 2 includes a flash evaporator 202 for receiving a warm sea water intake and outputting steam. Further, a pump 204 pumps a warm sea water discharge out of the flash evaporator 202. The steam output from the flash evaporator 202 is input to turbine 206 which is connected to generator 208 in order to generate electricity by conventional techniques. Steam exits the turbine 206 and is input to condenser 210. The conventional open-cycle OTEC system 200 utilizes a surface condenser and a direct contact condenser. A surface condenser keeps the two fluids (sea water and pure water) separate while a direct contact condenser does not. A majority of the steam exiting the turbine 206 is provided to a direct contact condenser in the conventional open-cycle OTEC system 200, in order to generate electricity. The conventional open-cycle OTEC system 200 utilizes a surface condenser to condense a small percentage of the steam generated by the turbine 206 into fresh water utilizing cold sea water as a heat sink. A cold sea water discharge is pumped out of the condenser 210 by a pump 212. The non-condensible exhaust system 212, removes non-condensible gases and a portion of the steam from the steam output from the turbine 206. In the open- cycle OTEC system 200 described above, the generation of electricity by the turbine 206 and generator 208 is the primary product and the fresh desalinated water output from the condenser 210 is the secondary product.

The hybrid-cycle OTEC system 300 illustrated in Figure 3 includes an evaporator system 302 into which warm sea water is input, of which a small fraction, vaporizes in a vacuum flash evaporator 304. The vapor condenses on an ammonia evaporator 306, which contains ammonia liquid, pumped from pump 308. The vapor from the flash evaporation system 302 condenses on the ammonia evaporator 306, producing desalinated water. The ammonia vapor is input to an ammonia turbine/generator 310 in order to generate electricity by conventional techniques . The ammonia vapor is then condensed in an ammonia condenser 312. The recondensed ammonia is recycled to the pump 308 to complete the closed portion of the hybrid-cycle OTEC system 300.

Both the closed cycle and open cycle OTEC systems discussed above utilize separate evaporators and condensers. Further the hybrid cycle OTEC system discussed above utilizes a conventional evaporator system 302. The improved OTEC system of the present application includes a novel combined evaporator/condenser in contrast to the three above- identified systems. The combined evaporator/condenser further includes a plurality of evaporator spouts and a mist eliminator. The OTEC system of the present application further maintains a constant low pressure over each of the plurality of evaporator spouts. The OTEC system of the present application also generates fresh water as a primary product. The OTEC system of the present application generates only enough electricity, as a secondary product, to operate the OTEC system itself.

SUMMARY OF THE INVENTION One object of the present invention is to provide an improved ocean thermal energy conversion (OTEC) system. It is a further object of the present invention to provide an improved ocean thermal energy conversion (OTEC) system which evaporates a working fluid at a natural depth of the received warm sea water to produce a working vapor, generates energy from the working vapor, and condenses the working vapor with cold sea water at a natural depth of the cold sea water. It is a further object of the present invention to provide an improved OTEC system which receives the warm sea water and evaporates the working fluid to produce the working vapor, wherein the evaporation takes place at the natural depth of the warm sea water.

It is a further object of the present invention to provide an OTEC system which condenses the working vapor with the cold sea water, wherein the condensation occurs at the natural depth of the cold sea water. These objects of the present invention are fulfilled by providing an improved ocean thermal energy conversion (OTEC) system comprising desalination means for receiving warm sea water, flash evaporating a portion of the warm sea water to produce steam, and condensing the steam with cold sea water to produce fresh water; and energy generation means for receiving the warm sea water, evaporating a working fluid at a natural depth of the received warm sea water to produce a working vapor, generating energy from the working vapor, and condensing the working vapor with the cold sea water at a natural depth of the cold sea water.

These objects of the present invention are further fulfilled by providing an OTEC system including energy generation means including, evaporation means for receiving the warm sea water and evaporating the working fluid to produce the working vapor, said evaporation means being located at the natural depth of the warm sea water, turbine means for generating the energy from the working vapor, and condenser means for condensing the working vapor with the cold sea water, said condenser means being located at the natural depth of the cold sea water. These objects of the present invention are further fulfilled by providing a method of generating fresh water comprising the steps of (a) receiving warm sea water and flash evaporating a portion of. the warm sea water to produce steam;

(b) condensing the steam with cold sea water to produce fresh water; - (c) receiving the warm sea water and evaporating a working fluid at a natural depth of the warm sea water to produce a working vapor; and

(d) generating energy from the working vapor and condensing the working vapor with the cold sea water at a natural depth of the cold sea water.

These and other objects of the present invention will become more readily apparent from the detailed description given hereafter. However, it should be understood that a detailed description and specific Examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention and wherein:

Figure 1 illustrates a conventional closed-cycle OTEC system;

Figure 2 illustrates a conventional open-cycle OTEC system; Figure 3 illustrates a conventional hybrid-cycle OTEC system;

Figures 4 (a) and 4 (b) illustrate the improved OTEC system of the present invention, in a preferred embodiment; Figure 5 (a) illustrates the platform which supports the improved OTEC system illustrated in Figures 4(a) and 4 (b) ;

Figure 5 (b) illustrates the platform and the evaporator/condenser from an evaporator perspective;

Figure 5(c) illustrates the platform and the evaporator/condenser from a condenser perspective;

Figures 6(a) illustrates one embodiment of the novel combined evaporator/condenser for the OTEC system illustrated in Figures 4 (a) and 4 (b) ;

Figures 6 (b) through 6 (d) illustrate three alternatives for collecting seed bubbles for evolving non-condensible gases;

Figures 7 illustrates another embodiment of the novel combined evaporator/condenser for the OTEC system illustrated in Figures 4 (a) and 4 (b) ; Figures 8 illustrates a reservoir system for use in the OTEC system illustrated in Figures 4 (a) and 4 (b) ;

Figure 9 illustrates a mist eliminator of Figure 4 (a) in one embodiment of the present invention;

Figure 10 illustrates an alternative embodiment of the energy generation system illustrated in Figure 4 (b) ;

Figure 11 illustrates .an evaporator template of the ammonia evaporator sub-system;

Figures 12 and 13 illustrate an individual evaporating component of the evaporator template of Figure 11;

Figures 14 and 15 illustrate the electric generation sub-system of the energy generation system illustrated in Figure 10;

Figure 16 illustrates a buckling resistor reinforcement;

Figure 17 illustrates a condenser template of the ammonia condenser sub-system; and

Figures 18 and 19 illustrate an individual condensing component of the condenser template of Figure DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The improved ocean thermal energy conversion (OTEC) ^■ system 400 of the present invention, in a preferred embodiment, is illustrated in Figures 4(a) and 4(b) . This OTEC system 400 generates three million gallons of water per day and 2.0 megawatts of gross electricity. These 2.0 megawatts of electricity are utilized to power the OTEC system 400 illustrated in Figures 4 (a) and 4(b) , and as a result, the net electricity generated by the OTEC system 400 of the present application is zero megawatts. The various components of the OTEC system of the present application are sized such that the number of gallons of fresh water is maximized and the amount of electricity generated is sufficient enough to power the OTEC system 400.

As illustrated in Figures 4 (a) and 4 (b) , the OTEC system 400 of the present application comprises warm sea water pumping system 402 for pumping 2,500,000 pounds of warm sea water per minute. The warm sea water pumping system 402 is fed by six 4.83 foot ID pipes, which are each 300 feet in length. The 80°F warm sea water exiting the warm sea water pumping system 402 is split. 1,780,000 pounds per minute flows to flash evaporator 406 and 720,000 pounds per minute flows to ammonia evaporator 412. The warm sea water enters evaporator/condenser 404 at flash evaporator 406 which is maintained at a pressure of 0.325 psi. The warm sea water is flash evaporated through several flash evaporator spouts 408. A warm water discharge at a temperature of 69.6°F and steam at a pressure of less than or equal to 0.325 psi exit the flash evaporator 406. The steam is input to a mist eliminator 410 at a rate of 17,500 pounds per minute and the steam exiting from the mist eliminator 410 exits at a pressure of greater than or equal to 0.275 psia. This steam is input to a fresh water condenser 412 having 500,000 sq. ft. of surface area. Entering tubes of the fresh water condenser 412 is cold sea water at a rate of 1,260,000 pounds per minute at a temperature of 42.9°F. This cold sea water is provided by cold sea water pumping system 414 which receives 1,920,000 pounds of cold sea water per minute via six 4.83 foot ID pipes, each of which are 7,000 feet in length. The fresh water condenser 412 generates fresh desalinated water at a rate of 17,500 pounds per minute at a temperature of 61°F and a cold sea water discharge flow at a temperature of 58.6°F. The fresh water exiting the fresh water condenser 412 is the primary product of the improved OTEC system 400 of the present application.

As discussed above, Figure 4(a) illustrates each of the elements necessary to generate fresh desalinated water from the OTEC system 400 of the present application. In contrast, Figure 4(b) of the present application illustrates the components necessary to generate sufficient electricity to power the OTEC system 400.

The warm sea water pumping system takes in 2,500,000 pounds of warm sea water per minute and outputs 1,780,000 pounds of warm sea water per minute to the flash evaporator 406. The remaining 720,000 pounds of warm sea water per minute at a temperature of 80°F is input to an ammonia evaporator 418.

Similarly, the cold sea water pumping system 414 receives cold sea water at a rate of 1,920,000 pounds per minute and outputs 1,260,000 pounds of cold sea water per minute to the fresh water condenser 412.

The remaining 660,000 pounds of cold sea water at a temperature of 42.9°F is input to an ammonia condenser 416. The warm sea water from the warm sea water pumping system 402 is input to the ammonia evaporator 418, which has 170,000 sq. ft. of surface area.

The warm sea water heats liquid ammonia pumped by an ammonia pump 420 at a pressure of 129.5 psia to produce ammonia vapor and a warm water discharge at a temperature of 74.1°C. The ammonia vapor is input to a turbine 422 at a rate of 7,160 pounds of ammonia vapor per minute in order to produce a gross power generation of 2.0 megawatts. The ammonia vapor exiting the turbine 422 is input to the ammonia condenser 416, which also has 170,000 sq. ft. of surface area.

The cold sea water from the cold sea water pumping system 414 is also input to the ammonia condenser 416, which outputs a cold water discharge at a temperature of 48.7°F and liquid ammonia at a pressure of 94 psia. This ammonia is recycled back to the ammonia pump 420 in order to complete the closed cycle ammonia path.

The OTEC system 400 described in Figures 4 (a) and 4(b) is supported by the platform 500, illustrated in Figure 5(a) . The platform 500 includes two decks 502 and 504, and further includes a jacket 506 which includes all of the structure below the deck 504. The jacket 506 extends approximately 30 feet above the water surface. The jacket 506 has six legs, two of which are shown in Figure 5(a) as legs 508 and 510. The legs, which may house the 4.83 foot ID pipes, which provide the cold sea water pumping system 414 with cold sea water from a depth of 2700 feet. Figure 5(a) further illustrates four evaporator/condensers 400, although this number may vary depending on the desired amount of fresh water. Warm sea water intake pipes 512 extend down less than 100 feet and feed the four evaporator/condensers 404. Figure 5(b) illustrates the platform 500, the warm sea water pumping system 402, an evaporator/condenser 404 (from an evaporator perspective) , a warm sea water discharge system 514, and a non-condensible removal system 516. As illustrated in Figure 5(b) , each flash evaporator 406 includes fifteen flash evaporator spouts 408. Figure 5 (b) further illustrates a seed bubble generation system 518. Figure 5(b) further illustrates two alternative energy recovery turbines 520 and 522, each of which include a turbine blade system 524 for the extraction of power from the discharged warm sea water.

In the energy recovery turbine 520, the warm water discharge turns a turbine shaft 526 and the shaft 526 turns a right angle gear box 528, which is connected to a pump of the warm sea water pumping system 402, thereby providing auxiliary power to the pump. In the energy recovery turbine 522, the warm water discharge turns a turbine shaft 530, which is connected to a generator

532. The electricity produced by the generator 532 is used as needed anywhere in the OTEC system 400 to reduce the energy consumption.

Figure 5 (c) illustrates the evaporator/condenser 404 from a condenser perspective and the cold sea water pumping system 414. The cold sea water enters a pump 531 of the cold sea water pumping system 414. The cold sea water is then pumped to an inlet manifold 533 which distributes the cold sea water through a plurality of condenser tubes 538 of the fresh water condenser 412. The cold sea water exits the fresh water condenser 412 through an exit manifold 534 and a cold sea water discharge pipe. An energy recovery turbine 522 is located in the cold water discharge and performs the same function as the energy recovery turbine 522 of Figure 5 (b) . Steam condenses on an exterior of the plurality of condenser tubes 538. The condensed steam is routed into funnel-shaped collection ports 536, which is then pumped to shore. Non-condensible gases and a portion of uncondensed steam are input to vacuum system 540, which compresses the mixture to condense the previously uncondensed steam and expel the non- condensible gases to the atmosphere or to the warm or cold water discharges. A portion of the cold sea water is input to the vacuum system 540 via pipe 542 to help cool this process.

The evaporator/condenser 404, illustrated in Figure 4(a), will now be described in further detail, as illustrated in Figures 6(a) . The flash evaporator 406, the mist eliminator 410, the fresh water condenser 412, and a predeaeration chamber 602 are housed within evaporator/condenser shell 600. The warm sea water from warm sea water pumping system 402 is input to the predeaeration chamber 602. Within the predeaeration chamber 602, non-condensible gases are separated from the warm sea water and the non-condensible gases are either returned in the warm water discharge pipe 622 or returned to the ocean or the atmosphere by the vacuum system 540.

The warm sea water passes from the predeaeration chamber 602 to the flash evaporator 406 via a flash evaporator spout 408 thereby producing water vapor and mist within the flash evaporator 406. Flow control valve 710 controls the flow of warm sea water into the flash evaporator 406. The mist eliminator 410 is physically attached to the evaporator/condenser shell 600 and a separation wall 606, and separates the flash evaporator 406 from the fresh water condenser 412. The mist eliminator 410 traps mist on the flash evaporator side and only allows water vapor to pass through such that the water vapor may be condensed in fresh water condenser 412. The fresh water condenser 412 includes the plurality of condenser tubes 538 and the condensed water vapor is collected at a rate of 17,500 pounds per minute, as discussed above with respect to Figure 4 (a) .

In an effort to reduce the quantity of non- condensible gases revode by the vacuum system 540, a predeaeration chamber 602 is employed. Seed bubbles provide a catalyst for the further evolution of non- condensible gases in the predeaeration chamber 602. These seed bubbles may be collected from the warm sea water intake, the warm sea water discharge, or from the atmosphere. These three alternatives are illustrated in Figure 6 (a) . In order to collect the seed bubbles from the warm sea water intake, the warm sea water passes through a choke segment 612 and then enters the predeaeration chamber 602. At the choke segment 612, the pressure is decreased due to the restriction in diameter and the seed bubbles of the non-condensible gases are generated. In addition to the production of seed bubbles, the choke segment 612 provides for a greater evolution of non- condensible by creating a low pressure point in the warm sea water intake flow. The seed bubbles can also be supplied by providing a pipe with a check valve 642 to the atmosphere.

The seed bubbles can also be supplied from the warm sea water discharge using the three techniques illustrated in Figures 6 (b) - (d) . In Figure 6 (b) , the diameter of the warm sea water outlet flow pipe 610 is reduced from D₀ to Dj to create a stagnant region immediately downstream of Dl to separate the seed bubbles of the non-condensible gases from the warm water discharge. The seed bubbles are carried by the seed bubble pipe 614 and the seed bubble injection system 618 to the predeaeration chamber 602.

In another preferred embodiment as illustrated in Figure 6 (c) , a baffle 702 is placed in the warm sea water inlet flow pipe 610 to create a stagnant region due to the obstruction of the baffle 702 and the enlarged diameter of the pipe in this region. The separated seed bubbles of the non-condensible gases are input to predeaeration chamber 602 via the seed bubble pipe 614 and the seed bubble injection system 618. In another preferred embodiment as illustrated in Figure 6 (d) , a region of zero vertical velocity 702 is created by horizontal pipe section 704, wherein the natural buoyancy of non-condensible gases allow separation from the warm sea water discharge to occur, generating seed bubbles, which are collected in region 706. The seed bubbles are then input to the predeaeration chamber 602 via the seed bubble pipe 614 and the seed bubble injection system 618.

The predeaeration chamber 602 functions to remove as much of the non-condensible gases (NGC) from the warm sea water prior to introduction to the flash evaporator 406. The percentage of the non-condensible gases which are removed from the warm sea water is a function of three parameters : the pressure in the predeaeration chamber 602, the length of time the warm sea water spends in the predeaeration chamber 602, and the cross sectional area of the predeaeration chamber 602.

The predeaeration chamber 602 illustrated in Figure 6(a) further includes baffle 616, which routes the warm sea water in an indirect fashion to the flash evaporator spouts 408. This extends the period of time the warm sea water is in the predeaeration chamber 602. As a result, the warm sea water has a greater residency time in the predeaeration chamber 602 and is more heavily seeded with bubbles, which triggers a higher percentage of non-condensible gases to be evolved and carried away at the top of the predeaeration chamber 602.

The non-condensible gases which have gathered at the top of the predeaeration chamber 602 are then removed by the NCG removal pipes 620. The warm sea water discharge is then utilized to compress the non- condensible gases so that they may be either discharged at atmospheric pressure or reabsorbed into the warm sea water discharge released back into the ocean or atmosphere.

The NCG removal pipes 620 which remove the non- condensible gases from the predeaeration chamber 602 are extended down the warm water discharge pipe 622 with a vertically-movable extension 624 to such a depth that the pressure in the warm water discharge pipe 622 is incrementally less than the desired pressure in the predeaeration chamber 602. In this way, the removed condensible gases will flow from the predeaeration chamber 602 into the warm water discharge pipe 622. This extension 624 can be moved vertically up and down so that this pressure can be regulated. The velocity of the vertical bubble rise in the warm sea water is less than the velocity of the warm sea water discharge in the down pipe 622 so that the bubbles will be forced down with the discharge flow and become compressed as the pressure in the water increases.

Figure 7 illustrates an alternative embodiment of the evaporator/condenser 404 of Figure 6 (a) . Figure 7 and Figure 6(a) include numerous common elements, which have been given the same numerals, and whose description is omitted here. The predeaeration chamber 602 is placed outside the shell 600 and above the evaporation spouts 408. This configuration increases NCG removal because the warm sea water spends more time in the predeaeration chamber 602. The larger volume of the predeaeration chamber 602 and its elevation above the evaporator spouts 408 provides additional control over the pressure inside the flash evaporator 406. In order for the OTEC system of the present application to continuously produce fresh water from fresh water condenser 412, it is important that the pressure within the flash evaporator 406 be controlled near 0.3 psia. Since the flash evaporator 406 includes multiple flash evaporator spouts 408, it also is necessary to maintain a constant pressure at each of the flash evaporator spouts 408. If the pressure in the flash evaporator 406 is too far above 0.3 psia, then not enough steam will be generated. If the pressure is too far below 0.3, the steam can not reach the last condenser tube 412 and the steam begins to accumulate and cause the removal of the non-condensible gases to cease. The OTEC system of the present application typically operates with a pressure of 0.3 psia + 0.05.

The evaporator\condenser 404 of the present application requires relatively steady flow rates and pressures. In order to maintain control over the pressure within the flash evaporator 406 and across each of the flash evaporator spouts 408, a configuration such as the one illustrated in Figure 8 is utilized. The warm sea water inlet pipe 610 carries warm sea water into pumps 402. Were pumps 402 directly connected to each of the flash evaporators 404, voltage variations in the pumps 402 would directly and adversely affect the amount of water vapor being generated within the flash evaporator 406. These variations could cause the pressure within the flash evaporator 406 to vary too far from 0.3 psia, which would result in the generation of too much or too little steam, as discussed above.

Therefore, in one embodiment of the preferred invention, the output of warm sea water from each of the pumps 402 is fed together in pipe 1004, which feeds each flash evaporator 406. A static reservoir 1006 and compressed air source 1008 finely regulate the pressure in the flash evaporators 406.

In one preferred embodiment, as illustrated in Figure 9, the mist eliminator 410 is a three pass chevron-style mist eliminator wherein each wall element 802 is 9.68 inches in length and 1.5 inches apart. The water vapor and mist from the flash evaporator 406 are input to the flash evaporator side of the mist eliminator 410. As the combined water vapor and mist flows across the chevron-shaped wall elements 802 of the mist eliminator 410, the larger droplets of mist contact the wall elements 802 of the mist eliminator 410 and fall to the bottom of the flash evaporator 406, where they become part of the warm water discharge. The mist eliminator 410 allows the water vapor to pass through such that the water vapor may be condensed in the fresh water condenser 412.

Figure 10 illustrates an energy generation system which is an alternative embodiment of the energy generation system of Figure 4 (b) . The energy generation system illustrated in Figure 10 may be utilized in conjunction with the desalination system of Figure 4 (a) , where warm sea water pumping system 402 and cold sea water pumping system 414 are not required, as will be discussed below.

As illustrated in Figure 10, an ammonia evaporator sub-system 418 is located at a depth of approximately 75 feet from the ocean surface. This depth is selected depending on a natural depth and desired temperature of the warm sea water which is required as a warm sea water heat source. The warm sea water enters the ammonia evaporator sub-system 418 and heats liquid ammonia delivered by liquid ammonia transport 4201 of ammonia transport sub-system 420 to produce ammonia vapor and a warm water discharge. The ammonia vapor is input to electric generation sub-system 422 in order to produce electricity. The electric generation sub-system 422 is located above the ocean surface. The ammonia vapor exiting the electric generation sub-system 422 is input to the ammonia condenser sub-system 416 via vapor ammonia transport 4202 of ammonia transport sub-system 420, which is located at a natural depth of the desired cold sea water heat sink. In a preferred embodiment of the present invention, the ammonia condenser sub-system 416 is located at a depth of 2700 feet from the ocean surface.

The cold sea water at a depth of 2700 feet is input to ammonia condenser sub-system 416 as a cold sea water heat sink and the ammonia condenser sub-system 416 outputs a cold seawater discharge and liquid ammonia. This liquid ammonia is recycled back to the ammonia evaporator sub-system 418 via the liquid ammonia transport 4201 of the ammonia transport sub-system 420 in order to complete the closed cycle ammonia path.

Locating the ammonia evaporator sub-system 418 at a natural depth where the desired warm sea water intake is available, alleviates the need for deployment of numerous large sea water pipes and reduces the energy cost required to pump the warm sea water to the ammonia evaporator sub-system 418. Instead of pumping water from a different depth, the warm water at the proper depth is merely pumped through the ammonia evaporator sub-system 418. Similar reductions in piping and energy costs are realized by locating the ammonia condenser- sub-system 416 at a natural depth where the required cold sea water intake is readily available. In the embodiment illustrated in Figure 10, only the ammonia is pumped to different depths, not the warm and cold sea water. ^* Since the mass flow rate of the ammonia vapor/liquid is much smaller than either of the mass flow rate of the warm sea water or the cold sea water, significant energy is saved by only pumping the ammonia vapor/liquid to different depths.

As illustrated in Figure 10, the ammonia condenser sub-system 416 is located in deep water. The ammonia condenser sub-system 416 must be properly anchored to withstand the pressure at such a depth.

As illustrated in Figure 10, the ammonia evaporator sub-system 418 is located near the surface of the ocean, in shallow warm water, and the electric generation sub- system 422 is located above the ocean surface. Since the electric generation sub-system 422 generates electricity, it must be connected to on shore power distribution centers via power lines.

The ammonia evaporator sub-system 418 receives liquid ammonia from the liquid ammonia transport 4201 of the ammonia transport sub-system 420, distributes the liquid ammonia among a plurality of evaporator templates 1100, illustrated in Figure 11. In a preferred embodiment, the ammonia evaporator sub-system 418 includes four evaporator templates 1100. Further, as illustrated in Figure 11, each evaporator template 1100 includes six individual evaporating components 1102, into which the liquid ammonia is distributed. An individual evaporating component 1102 is illustrated in Figure 12. Each individual evaporating component 1102 chlorinates entering warm sea water to deter biofouling inside the tubes 1202. The ammonia evaporator sub¬ system 418 collects and delivers the vaporized ammonia to the electric generation sub-system 422. The ammonia evaporator sub-system 418 receives 102,000 lbs/min of liquid ammonia from the liquid ammonia transport 4201 of the ammonia transport sub-system 420 and distributes the liquid ammonia among the 24 individual evaporating components 1102.

The individual evaporating components 1102 are of the shell and tube type with ammonia on the shell side and naturally occurring warm sea water on the tube side. Each individual evaporating component 1102 is aligned vertically in such a way that the warm sea water flows in the direction of gravity. This serves two purposes. One, the warm sea water inlet is closer to the ocean surface, i.e. in more shallow water, this makes the sea water temperature slightly higher than it would be for a horizontally inclined unit. Second, the warm sea water discharge will be slightly cooler than the ambient sea water, and, as a result, will have a higher density and a consequent tendency to sink. Since it is desirable to move the discharge such that it does not contaminate further inlet sea water with thermal cooling, it is advantageous to force the cooler water down in accordance with its natural physical movements. A vertical alignment ensures this occurs.

Each of the 24 individual evaporating components 1102 has a tube 1202 inner diameter of 0.715 inches and a tube 1202 outer diameter of 0.75 inches, includes 19,000 tubes 1202 in the cylinder with a pitch of approximately 1.25, and has a tube length of 18 feet. Further, the shell 1204 is 18 feet long with an inner diameter of 11.2 feet, a wall thickness of greater than 1 inch, and an outer diameter of approximately 11.4 feet.

The sea water enters the tubes 1202 via an inlet cone 1206, situated at an upper end of each individual evaporating component 1102. The inlet cone 1206 is 60 inches in diameter and extends uniformly at a 30 degree angle to reach the 134.4 inch diameter of the shell 1204. There is no sea water outlet cone or manifold, as discussed above, the sea water discharge simply exits downward into the ambient environment.

In order to facilitate adequate rates of heat transfer by assuring sufficient water side convective heat transfer coefficients, sea water pumps 1208 are employed. Reliance on natural convention or irregular sea water currents to continually move and displace the sea water would result in heat transfer coefficients which are both unpredictable and considerably lower than the forced convection design of Figure 12. Since the overall heat transfer coefficient is inversely proportional to evaporator surface area, the sea water pumps 1208 are crucial to keeping the number of tubes 1202 to a reasonable level.

Each individual evaporator component 1102 requires a warm sea water flow rate of 815,000 lbs/min. The water enters at a temperature of approximately 80°F and exits 1208 at a temperature 3.6°F cooler or approximately 77.4°F. The sea water pumps have a large diameter, are axial, have a low head, and a high-flow rate, and are situated directly in front of the inlet cone 1206. Each sea water pump 1208 includes a motor connected to the electric generation sub-system 422 by appropriate electric cabling. The entering warm sea water may be chlorinated in one of two ways. The first includes a molecular chlorine reservoir 1210 located at the ocean surface or at the evaporation depth, which feed chlorine injection ducts 1212, located circumferentially around the sea water inlet cone 1206. In this manner, the entering warm sea water flowing through the tubes 1202 has sufficient rates of chlorination to resist the growth of biological organisms. The chlorine injection may occur intermittently, i.e. one hour per day, at moderate rates i.e., 100 parts per billion (ppb) , or continuously at lower rates such as 35 to 50 ppb. These injection rates depend on the type of tube material, site location, and time of year. A second method of chlorinating the entering warm sea water is illustrated in Figure 13 and includes an electrolytic system 1302 utilizing platinized titanium anodes 1304 and titanium cathodes 1306 to electrolyze a percentage of dissolved salt in the sea water to form sodium hypochlorite, which is as effective as molecular chlorine in deterring biofouling. Such an electrolytic system 1302 may also be employed continuously or intermittently, as discussed above.

The vaporized ammonia exits each individual evaporating component 1102 and is carried via a network of steel tubes and pipes 1004 to one of four (4) five foot inner diameter steel pipes 1106. These pipes 1106 transport the ammonia vapor above the ocean surface to the electric generation sub-system 422. The electric generation sub-system 422 illustrated in Figures 14 and 15, includes seven ammonia vapor turbine expanders 1402, seven corresponding generators 1404, an inlet manifold system 1406, an outlet manifold system 1408, a control center 1410, and electric transformers (not shown) . The turbine expanders 1402 take thermodynamic energy from the ammonia vapor and transform it into mechanical energy. The ammonia vapor enters each turbine expander 1402 as a high pressure, high enthalpy, completely vaporized yet saturated vapor and exits at a lower pressure, a lower temperature, and a lower enthalpy. The extracted energy is transferred into rotational force of a shaft leading to one of the corresponding generators 1404. Each generator 1404 transforms this mechanical energy into electricity in a conventional manner. The electric transformers alter the generated electricity to such a voltage and frequency that it can be supplied to a local grid and to parts of the OTEC system which require electricity, namely the sea water pumps 1208 and liquid ammonia pumps 1704 (to be described later) . The saturated exit vapor from the seven ammonia vapor turbine expanders 1402 enters an outlet manifold system 1408 which distributes the saturated exit vapor to the vapor ammonia transport 4202 of the ammonia transport subsystem 420. As discussed above with respect to Figure 10, the ammonia transport sub-system 420 includes two sets of pipelines, the vapor ammonia transport 4202 and the liquid ammonia transport 4201.

The vapor ammonia transport 4202 carries vaporous ammonia from the electric generation sub-system 422 to the ammonia condenser sub-system 416. The vapor ammonia transport 4202 includes four separate pipelines each transporting an equal one fourth of the 102,000 lbs/min flow of ammonia vapor. The inner diameter of each pipeline is five feet and the pipelines are made of carbon steel. The pressure inside the pipelines remains nearly constant at approximately 95 psia. Because the vapor ammonia transport pipelines extend to depths of almost 3,000 feet, the net external pressure is very large. In order to resist buckling, the pipewall thickness must become gradually larger as the pipe extends deeper and the external hydrostatic pressure becomes greater. The range of wall thicknesses and segment lengths for these pipelines varies from one inch and 40 feet at the ocean surface to 2.25 inches and 10 feet at the ammonia condenser sub-system 416 depth. In addition, a buckling resistor reinforcement 1600, illustrated in Figure 16, is included on each of the carbon steel pipe segments 1602.

The liquid ammonia transport includes a single pipeline 4201 extending from the ammonia condenser sub¬ system 416 in the cold seawater region to the ammonia evaporator sub-system 418 in the warm sea water region. The single pipeline 4201 has a constant inner diameter of 2.5 feet and is also made of carbon steel . Like the vapor ammonia transport 4202 pipelines, the single liquid ammonia transport 4201 pipeline wall thickness and segment length vary as a function of depth, in this case from 1.00 inch and 15 feet at the ammonia condenser sub-system 416 depth to 0.25 inches and 40 feet at the ammonia evaporator sub-system 418 depth.

The ammonia condenser sub-system 416 receives vaporous ammonia from the vapor ammonia transport 4202 of ammonia transport sub-system 420, distributes the vaporous ammonia among a plurality of condenser templates 1700 illustrated in Figure 17. In a preferred embodiment, the ammonia condenser sub-system 416 includes four condenser templates 1700. Further, as illustrated in Figure 17, each condenser template 1700 includes five individual condensing components 1702, into which the ammonia vapor is distributed. A individual condensing component 1702 is illustrated in Figure 18. Each individual condensing component 1702 chlorinates the entering cold sea water to deter biofouling inside tubes 1802 of the individual condensing components 1702. The ammonia condenser sub¬ system 416 collects the liquid ammonia and returns the liquified ammonia to the ammonia evaporator sub-system 418 via the ammonia transport system 420. The ammonia condenser sub-system 416 receives the 102,000 lbs/min of ammonia vapor from the vapor ammonia trar.sport 4202 of ammonia transport sub-system 420 and distributes it among the 20 individual condensing components 1702. These individual condensing components 1702 are of the shell and tube variety with ammonia on the shell side and naturally occurring cold sea water on the tube side. Each individual condensing component 1702 is aligned vertically in such a way that the cold sea water flows against the direction of gravity. This serves two purposes, as discussed above with respect to the individual evaporating components 1102. The first is .hat the sea water inlet is further from the ocean surface, i.e. in deeper water. This makes the inlet cole sea water temperature slightly lower than it would be for a horizontally inclined unit. Second, the sea water discharge is slightly warmer than the ambient sea water and as a result, will have a lower density and consequent tendency to rise. Since it is desirable to remove the cold sea water discharge and assure it does not contaminate further inlet sea water with thermal warming, it is advantageous to force the discharge cold sea water up in accordance with its natural physical movements. The vertical alignment assures this occurs. Each of the 20 individual condensing components 1702 has a tube 1802 inner diameter of 0.695 inches and a tube 1802 outer diameter of 0.75 inches, 18,000 tubes 1802 in the cylinder with a pitch of approximately 1.25, and a tube length of 18.0 feet. The shell 1804 is also 18 feet long with an inner diameter of 10.8 feet and an outer diameter of approximately 11.8 feet.

The cold sea water enters the tubes 1802 via an inlet cone 1806 situated at a lower end of each of the individual condensing components 1702. The inlet cone 1806 is 60 inches in diameter and extends uniformly at a 30° angle to reach the 130.8 inch diameter of the shell 1804. There is no sea water outlet cone or manifold, as discussed above, the cold sea water discharge simply exits upward into the ambient environment.

In order to facilitate adequate rates of heat transfer by ensuring sufficient sea water side convective heat transfer coefficients, sea water pumps 1808 are employed. Reliance on natural convection or the irregular sea water currents to continually move and displace the sea water results in heat transfer coefficients which are both unpredictable and considerably lower than the forced convention design illustrated in Figure 18. Since the overall heat transfer coefficient is inversely proportional to condenser surface area, the sea water pumps 1808 are crucial to keeping the number of tubes 1802 to a reasonable level.

Each individual condensing component 1702 requires a cold sea water flow rate of 742,700 lbs/min. The water enters at a temperature of approximately 43.9°F and exits at a temperature of 3.9°F warmer or approximately 47.8°F. The sea water pumps 1808 have a large diameter, are axial, have a low head, a high flow rate, are submersible, and are situated directly in front of the inlet cone 1806. Each sea water pump 1808 includes a separate motor connected to the electric generation sub-system 422 by appropriate electric cabling.

The ammonia condenser sub-system 416 does not suffer from the same rates of biofouling as the ammonia evaporator sub-system 418. This is due the colder temperature and different chemical content of the seawater at the deeper depth. However, biofouling control is still needed to ensure a consistent rate of heat transfer. As discussed above with respect to the ammonia evaporator sub-system 418, two options exist for the chlorination of the incoming cold sea water. The first option includes a molecular chlorine reservoir 1810 located at the ocean surface or at the ammonia condenser sub-system 416 depth which feed chlorine injection ducts 1812, located circumferentially around the entrance to the sea water inlet cone 1806. In this manner, the cold sea water is flowing through the tubes 1802 at a sufficient rate of chlorination to resist the growth of biological organisms. As discussed above, the chlorinating injection may occur intermediately (such as one hour per day) at moderate rates (100 ppb) or continuously at lower rates 35-50 ppb) . These values are dependent on the choice of tube material, site location, and time of year.

As also discussed above, the second method includes an electrolytic system 1902, illustrated in Figure 19 with platinized titanium anodes 1904 and titanium cathodes 1906 which deter biofouling by electrolyzing a certain percentage of dissolved salt in the cold sea water to form sodium hypochlorite, which is as effective as molecular chlorine in deterring biofouling. This system may also be employed continuously or intermittently.

The liquid ammonia exits each individual condenser component 1702 and is carried via a network of steel tubes and pipes to a liquid ammonia pump 1704 for each condenser template 1700. The liquid ammonia pumps 1704 include a number of centrifugal pumps acting in parallel or series. Casings protect the centrifugal pump motors situated at the ammonia condenser sub-system 416 depth and connected to the electric generation sub-system 422 by underwater electric cable. The liquid ammonia pumps 1704 pump the liquid ammonia into the liquid ammonia transport 4201 of the ammonia transport sub-system 420 and the closed cycle is completed. As illustrated in Figure 10 and discussed above, by locating the ammonia evaporator 418 at a natural depth where the desired warm sea water intake is available and locating the ammonia condenser 416 at a natural depth where the required cold sea water is available alleviates the need for pumping large quantities of warm and cold sea water. Since only the ammonia vapor/liquid is pumped, significant energy is saved.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention and all such modifications which would be obvious to one of ordinary skill in the art are intended to be included within the scope of the following claims.

Claims

What is claimed:

1. An ocean thermal energy conversion (OTEC) system, comprising: desalination means for receiving warm sea water, flash evaporating a portion of the warm sea water to produce steam, and condensing the steam with cold sea water to produce fresh water; and energy generation means for receiving the warm sea water, evaporating a working fluid at a natural depth of the received warm sea water to produce a working vapor, generating energy from the working vapor, and condensing the working vapor with the cold sea water at a natural depth of the cold sea water.

2. The OTEC system of claim 1, wherein said desalination means is an open-cycle desalination system and wherein said energy generation means is a closed- cycle energy system.

3. The OTEC system of claim 1, wherein a primary product of said OTEC system is the fresh water produced by said desalination means.

4. The OTEC system of claim 1, wherein said energy generation means generates enough energy to operate said OTEC system.

5. The OTEC system of claim 1, said desalination means including, flash evaporation means for receiving the warm sea water and flash evaporating the portion of the warm sea water to produce the steam, a mist eliminator for removing mist from the steam, and condenser means for condensing the steam with the cold sea water to produce the fresh water.

6. The OTEC system of claim 1, said energy generation means including, evaporation means for receiving the warm sea water and evaporating the working fluid to produce the working vapor, said evaporation means being located at the natural depth of the warm sea water, turbine means for generating the energy from the working vapor, and condenser means for condensing the working vapor with the cold sea water, said condenser means being located at the natural depth of the cold sea water.

7. The OTEC system of claim 5, further comprising: a single housing for housing said flash evaporation means, said mist eliminator, and said condenser means.

8. The OTEC system of claim 1, further comprising: a predeaeration chamber for removing non- condensible gases from the warm sea water.

9. The OTEC system of claim 5, said flash evaporation means including a plurality of evaporation spouts for flash evaporating the portion of the warm sea water to produce the steam.

10. The OTEC system of claim 9, further comprising: vertical static head pressure regulation means for controlling a pressure at each of said plurality of evaporation spouts.

11. The OTEC system of claim 8, further comprising: seed bubble injection means for injecting seed bubbles into said predeaeration chamber to facilitate evolution of the non-condensible gases.

12. A method of generating fresh water, comprising the steps of:

(a) receiving warm sea water and flash evaporating a portion of the warm sea water to produce steam;

(b) condensing the steam with cold sea water to produce fresh water; (c) receiving the warm sea water and evaporating a working fluid at a natural depth of the warm sea water to produce a working vapor; and

13. The method of claim 12, wherein a primary product of said method is the fresh water produced in said step (b) .

14. The method of claim 12, wherein the energy generated in said step (d) is sufficient to operate an

OTEC system which performs said method.