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Unleashing the Renewable Energy Potential of Oil Fields

The 2011: IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation – Ocean Energy, states, “The resource potential for OTEC is considered to be much larger than for other ocean energy forms . . . Among ocean energy sources, OTEC is one of the continuously available renewable resources that could contribute to base-load power supply.”

It then cites a 2007 article, A Preliminary Assessment of Ocean Thermal Energy Conversion Resources, by Gérard Nihous, University of Hawaii, that calculated the steady-state OTEC power potential at about 44,000 TWh/yr or 5 terawatts (TW).

In 1998 a team of NYU researchers lead by physicist Martin Hoffert concluded, the Earth’s atmospheric carbon dioxide content cannot be stabilized without a tenfold increase in carbon-emission-free power generation over the next 50 years.

In 1998 the world produced 1.5 TW of carbon-emission-free power and 15 years later that output has barely increased to just over 2 TW; far short of Hoffert’s goal of 15 TW and increasing at a pace that assures his goal will go unattained.

Dr. Hoffert stated in an email to this writer, he is a fan of OTEC but considers its potential too small to meet his objective.

The 2007 analysis of Nihous was based on a simple one-dimensional time-domain model of the thermal structure of the ocean. In more recent work he has used a three-dimensional approach that has upped his estimate to 30 TW, though he suggests the environmental effects at that level would probably be unacceptable. Taking the environment into account he suggests less than 10 TW is probably the limit.

Professor Hoffert identified one of the environmental effects as a potential to overturn the Thermohaline circulation due to the dumping of massive amounts of heat to the depths with OTEC on a massive scale.

Dr. Rod Fujita, of the Environmental Defense Fund has pointed to two others, “Using large amounts of cold, nutrient rich water from the deep ocean in order to produce energy could have some very negative impacts, like killing sea life by sucking it into the intake pipe or creating algal blooms by discharging nutrient rich sea water into warm, nutrient-poor surface water.”

When algal blooms die they eutrophy the water column to produce a dead zone.

About one-third of all human-generated carbon emissions have dissolved in the ocean. If nutrient-and carbon dioxide rich cold water is brought to the surface to produce OTEC power some of the gas will come out of solution and return to the atmosphere as the pressure drops.  

The final problem with conventional OTEC is cost, which is driven by the large diameter of the pipes required to move large masses of water.

The Ocean Thermal Energy Conversion Counter-Current Heat Transfer System addresses each of these issues.

First by reducing the size of the piping required to move heat by one order of magnitude. The system uses a heat pipe design, similar to a Liebig condenser. A heat pipe is the most efficient way to move heat by phase changes of the working fluid and the Liebig condenser is one of the oldest and simplest forms of laboratory condenser. It consists of a glass tube down which vapor flows surrounded by a glass envelope through which cooling water flows to induce condensation of the vapor in the internal tube.

In the Counter-Current Heat Transfer System a heat pipe of 1000 meters is the means of conveyance of the vapor and the 800 meters of ocean beneath the Thermocline is the cooling medium.

   

            Heat Pipe                                                                      Liebig Condenser

This is a closed system requiring minimal pumping of water therefore the impact on marine life is negligible.

The perceived shortcoming with the heat pipe design has been the thickness of the pipe required to withstand a pressure of 1000 meters of water acting on a cavity containing essentially a vacuum as the vaporized working fluid condenses. The thicker the pipe the slower heat transfers through its wall.

The proposed system overcomes this problem with two coil condensers within the vapor channel, which not only strengthen the pipe wall, similar to an inflated bicycle tube acting on a tire, they facilitate condensation by introducing the condensing medium into the column. The bottom coil circulates cold water within the condensed working fluid to reduce its temperature to that of the surrounding water – 4oC.  The chilled working fluid is then pumped through the second coil, above, which condenses the descending working fluid and warms the ascending fluid by absorbing the latent heat of condensation. This warmed fluid then enters segmented sections surrounding the vapor channel to be returned to the surface in a break tank arrangement. These sections not only strengthen the pipe, they induce counter-current heat flow which maximizes the heat transfer of the system.

 

Coil Condenser

This counter-current flow limits the impact on the Thermohaline circulation and maximizes the oceans potential to produce power.

By overcoming OTEC’s capacity, environmental and cost issues the Ocean Thermal Energy Conversion Counter-Current Heat Transfer System realizes the renewable energy potential of five times the output of the world’s producing oil fields.

Jim Baird's picture

Thank Jim for the Post!

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I K's picture
I K on July 24, 2013

You have posted about otec many times but have not addressed any of the questions that come up which makes the idea seem difficult in not impossible. 

I’ve asked many times how large the heat exchangers on both ends need to be and you never answer. 

 

 

A 100MW CCGT working at 60% efficency only needs to move 170MW of heat and importantly it does this via a temp gradient of a thousand kelvin

 

 

A hypothetical 100MW otec working at 3% efficency needs to move about twenty times as much heat via a twmp gradient fifty times lower.

 

 

 

 

 

 

To try and put this probleminto perspective if you jump into the sea your body surface area will be moving about 150watts of heat at a temp gradient probably similar to otect. So if you want to move 3300000000 watts whoch toy need to generate just 100MW of eletrocoty ot would be like 22 million humans in water.  So how are you going to construct a heat exchanger that has a surface area of about twnety million humans at an affordable price? 

 

To try and put a rough fogure on it. if yoy could move 1000 watts of heat per square meter of surface area yoy woild need a heat exchanger of 3.3 million square meters which is a an absurdly large figure. Even if somehow you could get ypur heat exchanger to work at 10k watts per square meters yoi would still need a ridiculously large 330000 sqiare meter heat exchanger. 

 

And this is before you consider the practicalities of hige heat exchangers in contact with non ideal sea water. I’ve worked woth air heat exchangers and they always need cleaning and maintenance or dust and crap clog them up and they become less and less efficient.  The samw qill happen to these sea heat exchangers. Crabs will ceap on them sword fish will puncture holes in them squids will lay theor eggs onto them and whales will vomit on them and sea weed will clog them.  You will need daily maintenance both on tje sirface and the bottom.

 

Engineering in the real word has a lot more tp overcome than just looking at two heat sinks and doing a heat engine equation to give you a figure

I K's picture
I K on July 24, 2013

So the two heat exchangers are to be 34 meters length 13 meters width and 16 meters height for a 16MWe unit

Some calcs show you would need to move about 100 tonnes of water per second. That’s doable for a heat exchanger that size in that you can move that much water through it but my gut feeling the heat transfer would not be possible at the rate you need it. You would either need to build and test models or do some advanced CFD simulations but I can’t see it.

For my two pence with air heat exchangers to move 1KW of heat needs a heat exchanger of roughly one cubic foot but these operate at temp differences of 50 centigrade not 1 centigrade. and as noted they need very frequent cleaning and maintenance or the dust and other things sucked in clog them up the same will be true of these ocean heat exchangers.  They will need to be cleaned often to remove the dead jelly fish and sea weeds.

Thanks for the post. I would agree thay the volume of the heat exchangers you posted are probably in the right ballpark. So any Idea how much two of the 

 

7000 cubic metres heat exchanger with an active pumping system able to move 100 tonnes per second of water would cost? 

 

 

Remember you need to construct these 16MW units for only about $20million each. Two 7000 cubic meter heat exchangers. A km long insulated heat pipe and a turbine and generator and transformer and an offshore cable link all built and installed for $20m…..likely?

 

 

Also this monster will weigh how much? I’m thinking about 10000 tonnes? 

 

 

 

I K's picture
I K on July 24, 2013

Heat pumps are a good comparison as otec is effectively a reverse heat pump. However it is somewhat misleading as heat pumps operate at higher temp differentials and only need to move a kw or so heat vs 400,000 tomes as mich for jist a 16MW otec system

donough shanahan's picture
donough shanahan on July 25, 2013

Here goes using a simple method

Equation Q=UAdt

Where Q is the heat load, U is the overall heat transfer coefficient, A is area of heat exchanger and dt is temperature difference between ho and cold.

The system is cold water on one side and ‘hot vapor under vacuum on the other side.

dt = 3K, U = 1000 W/m2K, Q =100MW

Area required = 33333 m2

In reality it will be much more. Also the size of the vacuum generating equipment would be prohibitive.

I K's picture
I K on July 25, 2013

Thanks this helps a lot

those who had no real idea of how otec works roughly speaking a 10MW unit will need 

 

 

A structure 1km tall with two office block  sized (5000 cubic meters) heat exchangers on either end moving 100 tonnes of water per second through them.

 

 

 The whole thing tethered down to the sea floor a few km down with some sort of bouncy aid to stop the metal structure sinking.

 

 

And this contraption connected to a dc line buried into the sea floor a few km down and all the way onshore maybe 200km away.

 

 

All for a sum not much more than $20m

 

 

Is it possible?  I doubt it very much considering shallow sea cables are about $1.5/watt that doesn’t leave much ($0.50/watt to construct your otec devise). Or just $5million to produce the devise as its share of the link already takes up $15million.

 

 

My advise to those excited about otec would be to try and cost the various parts. how much is the connecting line going to cost seeing as you need to bury it in very deep sea beds. how much is the foubdation and tethering system going to cost. What about the bouncy system to keep it afloat. What about the two huge 5000cubic meter heat exchangers. and then what is the install cost going to be.  You cant make a 1km high structure and toe it into place youe going to have to fabricate at least parts on site

 

 

 

 

I K's picture
I K on July 25, 2013

Jim the biggest problem from the outset before you even consider the devise is the hvdc cable to these devises. 

Undersea cables are not cheap. Here in Europe they seem to be building in shallow water for about $1.5 per watt. So a 1GW cable for 1.5 billion dollars.

And that is in waters only a few meters deep (typically 30 meters and rarely over 60 meters. How costly is it going to be to lay a cable in the sea floor 3000 meters down?  Has it even ever been done?? Even if you could do it for the same price as shallow water which is doubtful it nakes the projectvirtually un viable. A base load alternative to fossil fuels like nuclear or otec needs a cost of no more than $2/watt or its not going to work unsubsidised and if it needs subsidy its never going to replace FF.

And worh otec before you evwn start you may well have spent $1.50 of your $2.00 draging a line to location. id like itto work but far offshore deep water low ddensity devises are going to have a hell of a time competing wirh $1 a watt ccgts

Rick Engebretson's picture
Rick Engebretson on July 26, 2013

Thanks Jim, for contributing in 2 important ways.

First, you offer some new ideas for new energy resources. If there are others offering anything plausible, I sure haven’t seen it on TEC. Kind of like computer programming, there is always lots of debugging. Sounds like you’ve been debugging your OTEC notion.

Secondly, you are proposing an adaptation to a growing climate problem; the oceans will change. This approach is very important to a “landlubber” who can’t keep up with faster biomass growth rates plausibly due to climate change. Nobody seems to care where CO2 goes, so talking about the ocean and biomass seems more relevant than many postings.

However, the people who really deserve our sympathies are the forest fighters. They’ve been telling us they need some more consideration for years now. Instead we cut their budget and keep them fighting for their lives. So keep your chin up, it could be worse.

Rick Engebretson's picture
Rick Engebretson on July 26, 2013

I’ve been “debugging” in 2 different ways.

My frantic outside work has really gotten to me this year. The heat is dangerous enough. But the gnats, mosquitoes, and deerflies rattle my nerves. Wait until fall when all the flies feeding on livestock manure want to come indoors.

So I try recover indoors playing with programming an Arduino Uno microcontroller. I prefer the old rubber ball mice instead of the sensitive LED mice because my hands shake from insect neurotoxins. But those old mice don’t work on new Linux, anymore.

The Arduino is quite an impressive system, connecting to a USB type serial port. And I’m using an embedded version of the ancient Basic. Quite a network of real-time clocks, switches, sensors, motor controls, etc. can be managed from a PC.

We are of a different generation, Jim. People could enjoy imperfection as an opportunity to make things a little better. I do know the more you swat at deerflies, the more you attract.

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