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Pitch

Thermonuclear fusion power has provide energy for the earth for more than 4 billion years. It is time to convert more to electricity.


Description

Summary

The closest continuously operating thermonuclear reactor (the sun) is also the primary energy supplier for the world. The large reactor core (10,000 time earth volume) at low energy generation density is at around 15 million degrees Celsius. The material used to confine the reactor core also scatter the generated fusion power and about 170,000 years is required for the fusion energy to reach the surface of the sun. From there at about 6000 C, the time to reach earth is about 8.5 minutes. The energy delivered to earth is initially stored as ocean thermal energy, with quantity greater than two years of intercepted energy, at the rate of 5000 times human need. OTEC (ocean thermal energy conversion) can divert more than 0.2 % of the delivered energy into electricity and completely solve global energy problem.

Human has been able to use thermonuclear fusion energy for destructive purpose (hydrogen bomb). There is effort to sustain fusion reaction so that the converted energy can possibly be put to productive use, the ability to capture the energy for productive use is not yet under serious development. There is no chance that human can imitate the fusion energy converter of the sun on earth. OTEC is the proper energy converter.

This proposal uses the existing fusion reactor (the sun), receiver (the global ocean) and add OTEC (ocean thermal energy conversion) plant in area with more than 1000 meter ocean water depth to convert the fusion energy into useful energy form (electricity). The generated electricity price should be less than 2 cents for each kilo-watt-hour (kwh). The original OTEC proposal (by French physicist Arsnoval) is 135 years old, but cost effective design concept and hardware implementation is still under development. This proposal provide initial analysis of possible OTEC plant site, Rankine cycle analysis, power plant capacity, material mass and buoyancy estimate, fluid flow requirement, thermal transfer estimate and other design information.


Category of the action

Reducing emissions from electric power sector.


What actions do you propose?

I am taking the initial action of providing the theoretical analysis to show OTEC is feasible, cost effective and has enough electricity generating capacity to meet global energy demand. Electrical energy can be converted into other forms and meet all human energy need.

For any interested people or organization with funding, construction of lab model and generate more extensive design and analysis details (cost less than one million dollars) is the first step. Small scale ocean OTEC model (20 or 140 kilo-watt capacity) can be built and tested with approximately 2 million dollars. Intermediate demonstration model (7 MW power) and production models (50 MW) will cost 30 and 200 million dollars. The cost for the production 50 MW plant should gradually approach 100 million dollars each. Mass production of the evaporator, condenser, turbine and inductor should make material cost dominate the production plant construction cost. With 400,000 production OTEC power plant distributed in tropical ocean areas, global energy requirement can be satisfied with this renewable, reliable (24/7 availability) technology. The sun has been sending energy to earth at a rate 5000 times human need. Tropical ocean covering more than 30 % of global surface. Converting 1 % of the solar energy in tropical oceans would have electricity generating capacity 15 times human need.

The basic design steps for this OTEC proposal is the following.

Select the initial ocean OTEC demonstration site. This proposal use surface temperature of 27 C and 1000 meter depth temperature of 5 C (difference of 22 C) for the Rankine cycle analysis. This temperature range existed for many locations on earth during the summer time. During the winter, the temperature difference may be reduced to 18 C, and the OTEC plant can generate 75 % of the peak electricity. Temperature and motion data to reveal possible strain/stress affecting the OTEC plant reliability should be collected. Anchored steel cable with 3D sensors to record motion (displacement, acceleration) and temperature from surface to 1000 meter depth with depth increments of 10 meter steps (relaxed at greater depth with slower change) throughout the year can provide reliable data for robust OTEC plant design, construction and operation.

Using high ocean water flow rate through the hot and cold heat exchangers, with surface to at depth temperature difference of 22 C, it is possible to achieve Rankine cycle working fluid temperature range of 16 C. Readily available ammonia is chosen as the working fluid. The ocean water and working fluid range are approximately 7.3 and 5.4 % of the ocean water absolute temperature (278 to 300; 282.5 to 298.5 Kelvin). The Carnot conversion efficiency limit for ideal gas operated in the working fluid temperature limit would be 5.4 %. The proposal Rankine cycle analysis indicate the theoretical upper limit for conversion efficiency is 5 %. There has never been any practical Carnot heat engine because ideal gas has no liquid to vapor phase transition. Without condensation, it is not practical for transfer of working fluid from the thermal energy rejection side to the thermal energy input side to complete a real cycle. Rankine cycle is the theoretical foundation for realistic heat engine analysis.

At 4 % net power conversion efficiency, circulation of each gram of ammonia through the Rankine cycle can convert 50 joules of thermal energy into electricity. The required ammonia circulation rate for the 50 MW plant is 1 million grams per second (1000 kg). The required cold and hot water flow rates are respectively 110 and 400 cubic meter per second. The input thermal energy at the hot heat exchanger is 1620 MW and the discarded thermal energy at the condenser is 1570 MW.

7 submerged cylindrical blocks (70 meter diameter, 20 meter height) with 2352 evaporator and condensing cells in each block can circulate the ammonia working fluid and turn 3 or more sets of turbine/inductor generators installed in each block to generate electricity. The generation capacity for each turbine/inductor set is from 2.5 to 4 MW. Two sets of the turbine can generate the rated power. The third turbine/inductor (or additional) set are redundant spare that can be put into operation if one of the primary generator set fail. The 50 MW production OTEC plant has 16464 evaporator and condenser cells.

Cold water from 1000 meter depth move along the vertical pipe to the cold water distribution block under the central cylindrical block. Cold ocean water flow through 7 distribution channels into each of the evaporator/condenser housing block and the condenser cells. Hot water from ocean surface surrounding (and at the same depth of) the generator blocks are pumped through the evaporator cells.

The complete OTEC plant diameter is around 250 meters. The 7 generator blocks are connected through flexible truss structures. Each generator block has buoys reaching ocean surface and ballast tanks to adjust buoyancy so that the slight positive buoyancy of the surface buoys and flexible cables can control the depth of the blocks. The 7 generator blocks and the cold water distribution blocks can be fabricated inside protected harbors with 20 meter (or more) water depth. These blocks can be towed to the assembly site with more than 1000 meter water depth for final assembly, including cold water pipe attachment. The completely assembled OTEC plants can be towed to sites where previously installed anchors can keep the OTEC plants from drifting way from the assigned location. Any failed generator block can be detached from the other good blocks and return to the harbor for repair.

Mass and displacement calculation for all OTEC plant components can be made to achieve the required buoyancy. For OTEC plant operation, ballast tanks filled with ocean water and air can adjust the operational buoyancy. The preliminary material use estimate is 1700 tons of aluminum (5086 marine grade, at 5000 dollars a ton is 8.5 million dollars), 10,000 tons of steel (at 1000 dollars a ton is 10 million dollars), 82,000 tons of steel reinforced concrete (at 300 dollars a ton is 25 million dollars). The raw material/fabrication cost for most of the construction mass is less than 45 million dollars. With technology maturity, another 55 million dollars is sufficient for all other installed components.

The heat exchanger (evaporator and condenser) wall thickness of 0.06 cm is strong enough for 12 cm diameter heat exchanger tubes in water depth of up to 100 meters (with a factor of 2 safety margin). Both evaporator and condenser (in 16464 cells) heat transfer areas are more than 560,000 square meter. The calculated heat transfer capacity at temperature drop of 0.5 C across the heat exchanger wall is 30 times the required heat transfer rate.

Pumping power required to move ocean water, working fluid can be calculated using the Moody diagram. The pressure drop (proportional to pumping power) for a pipe with circular cross section is a function proportional to fluid density, pipe length, fluid velocity squared and inverse diameter. Large diameter, low cost, flexible, vertical cold water pipe is best. The fluid flow velocity is below 2 meters per second. For the 50 MW OTEC plant, the pumping power for all the fluids (cold and hot ocean water, working fluid) is less than 2 % of the generated electricity. On shore OTEC plants will need much longer ocean bottom terrain following cold water pipes. Longer pipe need more material and pumping power so that both the plant construction and operating cost would increase substantially. Some initial OTEC demonstration/test (in Hawaii and Okinawa) use shore based OTEC plants, but most future cost effective designs have adopt the vertical cold water pipe.

10 meter diameter, 1000 meter long main cold water pipe with the enclosed ocean water will have inertia of 80,000 ton. Rigid cold water pipe cannot be expected to survive induced strain/stress of the ocean. Flexible cold water pipe able to tolerate multiple bending in different direction has been included in this OTEC proposal. The proposed power plant also use submerged main structure which will not be forced to move up and down with surfaces waves.

Three anchors reaching ocean bottom can keep each OTEC plants from drifting. The adjustable length anchor cables can pull the OTEC plant into deeper calm water during passage of storms. At OTEC plant locations with stronger ocean current, the mass of the anchor and anchor cable may need to be higher.

Initial laboratory test with one set of evaporator/condenser (a reduction factor of 16464 from the 50 MW production OTEC plant) should be able to generate 3000 watt of electricity. The test data can validate thermal transfer capabilities of the evaporator and condenser at simulate ocean temperature. This laboratory set up is about 6 meter tall and 2 meter across.

Initial ocean OTEC plants will be located at less than 25 miles from the shoreline. Generated electricity can be transmitted to shore using HVDC (high voltage direct current) technology. Upon reach shore, the land electricity delivery grid can be used. Production OTEC plant within 50 or 100 mile from shore line can also use HVDC technology for power delivery. For users unable to connect to the OTEC power line delivery system, the electrical energy can be converted into different form. Ammonia is selected after preliminary analysis as the convert energy delivery form. Ammonia tankers can be used like crude oil tankers to transport energy to all users in the world. All major ocean of the world (Pacific, Atlantic and Indian) have locations suitable for OTEC so that there is no need for the ammonia tankers to pass through narrow ocean channel or places like the southern ends of Africa or South America.

Solar energy delivered to earth has maximum density of 1.35 kw per meter square. The rotation of the earth make the maximum average energy density over a 24 hour period to be 400 watt per meter square. The 1630 MW thermal energy required for the 50 MW OTEC plant need 4 square kilometer area to collect. There are some discussion of grazing OTEC plants so that more surface thermal energy from larger area can be used. My proposal is to keep the OTEC plant from drifting. To avoid cooling the ocean surface temperature too much and reduce OTEC plant power output, 50 MW OTEC plant should be 2.5 or more km from its neighbor. The basic ocean thermohaline circulation mechanism is intrinsically able to make the ocean surface uniform by moving surface warm water to any area that may be cooled by natural or man made cause. The ocean water circulation can make OTEC plant able to concentrate solar power from an area much greater than the OTEC plant cross sectional area to the OTEC plant site. The effective solar energy concentration factor can be a factor of 500, much higher than most photovoltaic solar energy concentrator. In a 1997 paper by Kiehl and Trenberth, the average solar energy input to earth is 342 watt per square meter (other following numbers have the same unit but the units are not written to save key strokes). 67 and 77 are absorbed by atmosphere, 77 are reflected by clouds, aerosol and atmosphere. the 198 that reached surface are divided into 168 surface absorption and 30 surface reflection. The average energy absorption in the tropical ocean should be higher than the 168 global average.

Even if there is one million (when 400,000 is enough for the whole world) 50 MW OTEC plants, the ocean area required is on the order of 6 million square km. The world with total ocean area of 360 million square km has more than enough room for the one million OTEC plants.

OTEC is the global warming solution. It may take a miracle to get sufficient attention for this technology, but there is no doubt the subsequent implementation will be successful. 


Who will take these actions?

Government, business or other organizations can take action.

The first step for interested organization is to evaluate the technical merit with proper personnel. This proposal (with more information beyond the character limit of this contest) and revised plans can guide follow up actions. The second step is to test the 3000 watt lab model with one evaporator cell and one condenser cell. Simulated ocean water heated to realistic ocean water temperature at potential OTEC electrical plant site can be used to validate the evaporator and condenser performance. The proposed 50 MW rate OTEC plant would be the lab set up multiplied by a factor of 16464. Ocean demonstration models at 150 kw (kilowatt) and 1 megawatt may preced the 7 MW final proof model and 50 MW production model. More precise cost analysis for each of the proposed steps can be developed. It is most desirable that the interested organization can provide more than 100 million dollars to build and operate OTEC plant with more than 7 MW electricity generation capacity.

I am hopeful that successful demonstration of the 7 MW OTEC plant can attract more investors and fund to build the 50 MW production OTEC plant and 400,000 more production OTEC plant. with the total demand of 9 million turbine/inductor generator sets, the unit turbine/inductor design cost should be less than 100 dollar. For the 7 MW demonstration plant, relatively crude turbine/inductor design may be held below 5 million dollars. Construction of the 50 MW OTEC plant probably should include 100 million dollars for better turbine/inductor.

ClimatColab reviewer and judges should contact me for more details. I hope the contest organizer will alert government , business and other organizations about OTEC. The Paris agreement didn't reduce GHG emission enough to have any hope of keeping global temperature rise to less than 2 C in 50 years.


Where will these actions be taken?

The extensive analysis and OTEC lab model can be tested anywhere in the world. The ocean models will be placed at tropical ocean areas with minimum depth of 1000 meters where the surface water temperature is more than 20 degrees Celsius warmer than the water temperature at 1000 meter depth.

Hawaii, Guam and other US ocean territories have suitable sites for production OTEC electricity plants. The Hawaii renewable energy laboratory has some OTEC research facility for more than 30 years. Unfortunately, The Hawaii group may shift the focus away from marine thermal energy into marine kinetic energy. European Union (EU) countries cannot use OTEC plants in Europe, but many members of EU can use OTEC at their tropical territories (possessions). A small part of the South China sea can use OTEC. China access to OTEC is limited in the contested region. Western Pacific ocean (Solomon Islands, Philippines, Taiwan, Okinawa (Japan) is the best OTEC location. Some countries in Africa and South American can use OTEC. Australia, Indonesia and India also has access to good OTEC locations. All three major oceans (Pacific, Atlantic and Indian) have good OTEC sites so that tanker transport to energy users all over the world can always use deep ocean routes without constraints such as Suez or Panama canal.

Korea Research Institute of Ships and Ocean Engineering organization (KRISO) recently plan a 1 MW plant near Kiribati (central Pacific Ocean) in ocean with 1300 meter depth. South Korea apparently elects to try OTEC outside of its territorial waters and can become an OTEC technology supplier.


How much will emissions be reduced or sequestered vs. business as usual levels?

If 400,000 50 MW OTEC plants are in operation, the global electricity demand will be satisfied. Electricity generation will be accomplished without any green house gas (GHG) emission. The carbon emission reduction is 10 billion tons a year. The technology demonstration years will reduce no more than 1 million tons of carbon emission. A 50 MW plant can reduce emission by 25,000 ton a year. From the fifth to fifteen years, the average emission reduction can be more than 10 million tons a year. If all 400,000 OTEC plants are built in the next 40 years, the yearly carbon emission reduction increase is 250 million tons a year.

OTEC is not a direct GHG sequestering technology. The electricity generated can be used to operate equipment of sequestering technology.

Converting ammonia synthesis from using fossil fuel as hydrogen source (and discharge residual carbon content as emission) to OTEC powered atmospheric nitrogen and water hydrogen synthesis process, there are more emission reduction.


What are other key benefits?

OTEC electricity can be used to synthesize ammonia. Ammonia is a key ingredient for agricultural production.

The dominant natural fresh water generation process is evaporation/ condensation distillation. The most energy efficient desalination technology is reverse osmosis (RO). RO is able to get cubic meter of fresh water with 11 MJ (megajoule) of electricity. The OTEC hot heat exchanger can be used as evaporator and the cold heat exchanger can be used as condenser. OTEC like ocean thermal desalination plant is more cost effective than RM desalination plant. Ocean thermal energy represented by the evaporator and condenser ocean water temperature difference can provide more than 100 MJ of energy to generate one cubic meter of fresh water, using less than 1 MJ pumping power to move the ocean water through the heat exchangers (for each cubic meter of fresh water). There is no need to suffer the low thermal to electricity conversion efficiency.


What are the proposal’s costs?

The cost for convincing technology demonstration (operate 7 MW OTEC electrical plant) should be less than 100 million dollars. The cost of building 400,000 50 MW OTEC plant to meet global electricity demand is 40,000,000,000,000 dollars (40,000 billion dollars). Not bad for totally converting global electricity supply structure to renewable energy.

Earlier development steps cost much less money. shore based lab model that can be used to validate design heat exchanger performance can be tested with less than one million US dollars. Subsequent development steps with increasingly more money will be supported by increasing improved test data.

OTEC will make ocean a much more valuable resource. The Island building effort in Philippine Sea (Japan) and South China Sea (China) and the resultant challenge to the international ocean law will be more acute with OTEC development and deployment. Many OTEC plants will be placed more than 12 nautical miles from the shores of disputed islands, within the 200 nautical miles economic exclusion zone. The most significant economic benefit for the disputed islands is beyond the territorial water.

There has been some concern about OTEC plant discharging colder ocean water and harm marine life. This concern may be more relevant for shore based OTEC plant. At location with water depth of 1000 meter, there isn't much marine life. The colder water will also quickly sink toward the depth corresponding to the water temperature. The thermohaline circulation mechanism will always make ocean temperature distribution is proper equilibrium.

Interested reader can provide input for possible OTEC induced environmental harmful effect and I will respond. 


Time line

The short term goal is convincingly demonstrate the benefits of OTEC. 5 years may be sufficient. There is apparently no global coordinate effort to completely review OTEC theory and make design selections from many possible options. It is my opinion that cost effective OTEC plant must use low cost, vertical, flexible main cold water pipe in water with more than 1000 meter depth. The OTEC power plant should be practically of neutral buoyancy so that the main structure is below the ocean surface and is able to get into greater depth where there is less water motion and stress/strain during severe weather. Flexible connection to surface structure can also greater reduce the transmission of surface strain/stress to the main OTEC structure.

The medium term time of 15 to 50 years should be sufficient to convert global electricity generation system to OTEC. Users with shore lines located less than 100 miles from OTEC plants can use energy in the form of electricity. Additional energy distribution system to deliver converted OTEC energy to all the world need to be established. Ammonia with higher energy density than hydrogen (for the same volume) can be transported by tankers from the OTEC plant ocean site to users all over the world.

The long term effort is maintain global OTEC electricity supply system. 40 years OTEC plant replacement schedule is probably adequate. Some system improvements can be incorporated with the OTEC plant replacement schedule. OTEC related distribution system will also need maintenance. The replacement of the fusion power plant (the sun) is beyond the scope of this proposal.


Related proposals

An earlier entry in the 2015 Climate CoLab contest (MIT alumni).

There are some other proposal of using ocean energy. I want to mention that the most abundant energy resource in the ocean is thermal energy. Almost all other forms of ocean energies are insignificant when compared against thermal energy. The basic thermal mechanical conversion factor clearly indicates 1 C temperature increase in water has as much energy as water of 410 meter height or 90 meter per second (200 mph) kinetic energy. The kinetic energy available in ocean current, tide or wave is no where close to 200 mph so that these technologies cannot hope to compete with ocean thermal energy. Energy island with OTEC as an element may seems to be able to add to OTEC, but there is no good reason to encumber OTEC with ideas of questionable value.

US patent 8,484,972 B2 is a less cost effective OTEC design without cold water pipe. The introduction of low cost flexible main cold water pipe make cold water pipe better.


References

Contact me at jameslau2@gmail.com for more complete information.

Since the 1881 initial proposal, there has been many OTEC publications. Some organizations with OTEC information are the following. These sites have published papers ready for download.

www.otecnews.org

nelha.hawaii.gov

www.ioes.saga-u.ac.jp

hinmrec,hnei.hawaii.edu

The following papers are available for view and download at the hawaii.edu site.

LM-OTEC-Mini-Spar-Design-December-2-11.pdf. This floating design use vertical cold water pipe. Anchors are used to prevent the OTEC plant from drfiting.

OTEC history with Vega Bias. Old design without updates to include recent knowledge.

At one time, this site also provide a 2015 paper which is a Makai report to Vega citing good corrosion test result for using marine grade 5086 aluminum as heat exchanger material. contact me if you want to read the Makai report.