Showing posts with label capture. Show all posts
Showing posts with label capture. Show all posts

Saturday, December 24, 2011

Can we capture methane from the Arctic seabed?

Can we capture methane from the Arctic seabed?

Stephen H. Salter, School of Engineering, University of Edinburgh, Scotland. 

Prepared for the John Nissen Methane Workshop, Chiswick 15,16 October 2011.

DRAFT 3 November with pressure ridge addition.

Methane is a greenhouse gas more than 100 times more effective than carbon dioxide in the short term.  It is stored in the form of clathrates which are unstable if pressure is lower or temperature is higher than a line on a pressure versus temperature graph. Figure 1 shows that the slope of the atmospheric concentration has sharply increased since 2007.  Previous high levels of methane were associated with the Permian mass extinction, 250 million years ago.

Figure 1. Anomalies of CH4 mean volume mixing ratios for Northern and Southern hemispheres courtesy Leonid Yurganov.  Updated mixing ratios (Dlugokencky et al., 2009) were subtracted from the seasonal cycles averaged over 2003-2007. The right scale shows the anomaly of total mass of CH4 in the tropospheric layer of each hemisphere. The growth has been continuing in 2010-2011, according to the updated satellite data by Frankenberg et al. 2011.


This note discusses the design problems of a system to deploy kilometre-sized areas of plastic film to collect methane from suitable areas of the sea bed.  The gas can be flared off at sea to convert it to less damaging carbon dioxide or perhaps, if there are very high flow rates, recovered by a gas carrier and used ashore.

There seem to be solutions to what appeared initially to be an insoluble problem.



The difficulties

When John Nissen first raised the problem of Arctic methane my initial reaction was that capture at the sea bed would be impossible.  But trying to design for the impossible can be interesting.  It seemed a useful exercise to identify the reasons for impossibility. We can list difficulties as follows:

  1. Methane release at very low flow rates over too wide an area.
  2. Release at very high rates over a small area such as a well blow-out.
  3. Rough seas during deployment.
  4. The presence of obstructions such as wreckage, rock outcrops, munitions or steep slopes.
  5. Fast, variable-direction or unpredictable currents.
  6. Equipment sinking into very soft ooze on the seabed.
  7. Hydrogen sulphide toxicity.
  8. Unacceptable biological consequences due to the presence of equipment.
  9. The need to recover everything at some date in the future.
  10. The pressure ridges shown by Peter Wadhams at the Chiswick workshop.

I now believe that despite these problems methane can be captured in quite large quantities from areas of several square kilometres of plastic film in a single installation. 

The design

The film sheet is packed into a pair of left and right-handed rubber trough cases [1] and [2] with a rectangular inner section as shown in figure 2. Each trough case carries two steel cables [3].  The trough cases would be produced by a continuous moulding/extrusion machine in lengths of several kilometres using plant similar to that used for electrical cables. The left and right handed pair are connected at the centre by two thin isthmus strips of material [4] [5] above and below a rectangular section passage.  The passage contains a rectangular section runner [6] with two blades [7] [8] which can be pulled through the full length of the extrusion by a steel cable. [9].   If the steel cable is pulled the two blades will cut the connection strips and the trough case halves will be separated. 

The underside of the   trough case extrusion has a moulded tread with a pattern of saw-tooth section ridges [10] lying at an angle of about 30 degrees to the length of the extrusion. This ridge angle is an important design parameter.  At the outer corners of the bottom of the insides of the trough cases are recesses [11] into which a bead on the edge of an extruded plastic sheet can be pushed.  The outer walls of the trough are much thicker than the inner walls and contain galleries [12] along which methane can be transported to riser pipes. They connect to the higher points of the saw-tooth moulding. A high-density filler is added to the rubber to make sure that it is heavier than cold sea water but not heavier than the ooze on the sea bed. The outer edges of the extrusion [13] are sloped like the front of a sledge.

At the bottom of figure 2 the troughs are shown filled with a zig-zag stack of flexible plastic with a density just greater than cold sea water and a thickness of about 200 microns.  The zig-zag stacks on each side a joined at the top [14].  The lower edges with a bead are pushed into the recesses in each trough.  This plastic would be produced by a second extrusion machine consisting of interdigital plates to be described later.  If the width of each trough is one metre and the trough depth is 150 mm there will be space for 750 layers of zig-zag plastic, giving an extended width of 1.5 kilometres when the zig-zags on the two sides are unpacked.  The stacks of plastic film can be packed securely by lid flaps [15] retained by a vacuum maintained through pipes [16]. 

The length of plastic and rubber would be wound in a single scroll on the drum of a pipe-laying vessel such as the Stena Apache.  A drum diameter of 35 meters could take a width of 1.5 kilometres and length of 3 kilometres, giving a capture area of 4.5 square kilometres.

Figure 2. Empty and filled extruded rubber trough cases with 4 times enlarged views of end and centre. 

Deployment.

Survey vessels with side-scan sonar and methane detection sensors would look for suitable sites with no large obstructions, suitable current velocities and comfortable methane emission rates.

Small obstructions can be levelled with robotic sea bed vehicles such as the one described at the 2011 EWTEC conference.

The pipe-laying vessel would take station well downstream of the target area and pay out the scrolled material to the sea bed as if it were oil pipe.  The extreme flexibility of the trough case (relative to 12 inch steel pipe) would allow wave tolerant J-lay rather than an S-lay release.

Once the full length of the package is on the sea bed (figure 3) it would be towed along the seabed by ropes attached to the fore end of the rubber extrusions until it reached a point before the start of the target area equal to the string length divided by the cosine of the ridge angle.  If possible the tow direction should be perpendicular to current and swell.

The central cable with knife blades would be pulled through the rubber extrusion to separate the two troughs.

The vacuum retaining the lid flaps will be released.

Towing to increase the width of the film can now begin. Towing from the pipe-laying vessel would mean lifting the leading edge of the pack and there might be disturbance by waves.  It is preferable to use a horizontal force from a sea bed walking vehicle.  There might sometimes be an advantage in raising and lowering the leading edge in the way used for aligning carpets.  The tow force would depend on the weight of the package in water and the coefficient of friction to the sea bed. This is expected to be about 250 kN.  This will set the size of the steel cables embedded in the rubber extrusions which transmit the tow force along the length of the rubber and the bollard pull of the tow vehicles.

The tow vehicles will keep the tow lines pointing along the line of the package but the angled ridges would make the two troughs move apart from each other and so the tow vehicles will take diverging courses. The layers of plastic film will be pulled away from the zig-zag stack, as shown in figure 3, with the weight of the retaining lids providing a gentle resisting force.. GPS systems will be used to keep the advance rate of the tow vehicles matched.

The small density difference between plastic and sea water will mean that the drag friction between plastic and sea bed will be very low with a factor of safety of several hundred relative to the plastic strength.

The ridges in the rubber extrusion will leave furrows on the surface of the seabed.  When the furrows are covered by the plastic sheet they will form passages for the removal of gas through galleries in the outer walls of the trough.

The outward movement of the trough cases will build up material from the sea bed at the front of the outer sledge faces.  Water moving through eductor jets [17] can move some of the sea bed material over the film.

The gas pipe connection from below the film to the surface will bring its pressure closer to atmospheric.  Eventually several bars of water pressure will clamp the film and trough casings firmly to the sea bed.


Figure 3. Deployment of the film using the side force from the inclined ridges at the bottom
of the trough cases. Proportions are grossly distorted.


Tooling

Thermo-plastic films can be made by heating pellets of the feed stock to their melting point, pumping the liquid material through fine gaps in an extrusion tool and progressively cooling the downstream section of the tool to a temperature at which the film can be handled. The energy requirement is the sum of melting heat and pumping pressure.  Much of the heat can be recycled back to the incoming feed stock. The product is easier to handle if the pumping is in a downward direction.

The tool will consist of one inner and two outer stacks of plates each of which consists of two half plates which have been machined with a zig-zag coolant channel and then riveted and spot-welded back together as shown in figure 4.   The key problem is maintaining an accurate gap, probably 200 microns, between inner and outer plates.  Gravitational sag will be avoided if plates are vertical.  At the top of the tool where the film material is still liquid the gap can be defined by streamlined shims but in the cooler regions it must be actively controlled with no physical blockage.

Material from a rolling mill usually has quite large flatness errors and a skin under compression.  The first step will be stress relief by raising the plate temperature to 650 C for an hour and cooling it slowly.

Toolroom surface grinders can work to a flatness better than 3 microns but if curved parts are held flat on a magnetic chuck the curvature will be restored when the magnetic flux is removed.  It will be necessary to hold the plates on a hot wax chuck as used in the optical industry.  It might be useful to consider a low-force cutting technique such as spark erosion.

Figure 4.    A grossly distorted plan view of the topology of the extrusion tool with exploded parts. A 1500 metre width would require 750 plates rather than eight.  Maintaining a gap for the film thickness is a challenging problem but may be done with differential temperature control. The tool for a 1500 metre width of film would weigh about 200 tonnes.  If the differential temperature idea is not feasible, smaller tools could be used but a way to store and join kilometre lengths edge to edge would be needed. Temporary coiling looks difficult.



Gap control

We can use an array of capacitance transducers to measure the gap between plates of an assembled stack.  We can cover the surfaces of plates with resistive heating elements either side of the cooling channels.  By differential control of the heating currents we can control the local curvature of a plate.  The coefficient of thermal expansion of stainless steel is 17 part per million per C degree.  A temperature difference of 1C across a 15 mm plate will induce a radius of curvature of 440 metres.  If the width of the heating element is 100 mm this means a deflection of 11 microns.

A neat way to provide plate deflection control is to divide the plate surfaces into 100 mm squares with a resistive layer filling most of the area.  The squares would be connected in series and driven with a constant current from a high impedance source rather than a constant voltage.  The current would be diverted around the heating element by a parallel, high-frequency switch operated for a variable fraction of the time.  A small fraction of the surface with a grounded guard backing would be given a high-frequency excitation to measure the capacitance to the adjacent plate.

Cold heat exchanger fluid will be pumped into the bottom of the vertical tooling plates and emerge from the top at nearly the melting temperature of the plastic film.  After some extra heating the fluid will then move downwards through a vertical-tube heat-exchanger to melt the incoming plastic.

Solidified film coming out of the bottom of the tool will be further cooled by an upward flow air which will then be directed down through a bed of rising feed pellets and shredded plastic being recycled.  Air can flow easily through gaps between pellets or shredded feed stock.  The surface area of pellets is large even if heat transfer per unit area is low. Heat can flow more easily between liquids.  However there will be an awkward gap between solid but nearly molten pellets in the air in the pellet heat exchanger and liquid in the one above it.  Although the temperature difference might be quite small the amount of latent heat of fusion might be substantial. 

Gas flow rates

A slide (number 34) from the Shakova - Semiletov paper given at the November 30 2010 DoD workshop in Washington, gives a figure for methane flux of 44 grams per square metre a day over half a 500 metre transect, shown below.   This is well above other observations.   The calorific value of methane is 55 MJ per kilogram so this would be a thermal power of 28 MW per square kilometre.  These conditions might well not apply to the full film area and, at this rate, it would probably not be worth collecting methane on a ship.  In future the rate, and gas prices, might increase. However the power level should be enough to drive a mechanism with chain saws and heat transfer pipes to keep a clear hole for a flaring stack in a moving winter ice field if methane release in winter was thought to be a problem.  

Size of release plumes

This paper has described what I believe to be the largest possible collector area using present technology.  We need to know more about the size and spacing of release plumes to decide if the area has to be as large as this.  One example of the kind of data needed is given in figure 5.  

Figure 5. An echo sounder image giving the size of methane plumes from Shakhova et al.. This shows a transect of about 500 metres in the Laptev sea showing bubble plume return features
and also zooplankton other non-bubble scatterers such as fish.


Material quantities

The Shakhova presentation also mentioned total areas of methane hot spots of 210,000 square kilometres, the area of a square of side 460 kilometres.  The proposed design needs about 200 tonnes of plastic film per square kilometre. Total world consumption of plastics in 2010 was about 300 million tonnes and forecast to rise to 538 million in 2020.  Protecting the Shakova area with coverings which lasted 10 years would take about 1.5% of total present world plastic production.

Recovery

Maintenance would be very difficult and is not planned. But anyone putting anything into the sea has an ethical duty to plan for its recovery.  The proposal is to make structures of two cutting discs about 2 metres in diameter separated at 12 metres which can roll along the length of the film to cut it into 12 metre wide strips.  The ends of the cut can be gripped with a vacuum plate, lifted to the surface and wound round a drum.  The area of the long side of a 3 km length sheet of clean film is only 0.6 square metres.  Over a period of years it will probably have acquired biological growths, some of which can be removed by pulling it between contra-rotating brushes.  It is desirable that growth thickness can be reduced to the level at which film can be packed into 2.2 metre diameter for movement in a sea container.  For a film length of 3 kilometres this means a thickness of film plus growth of 1.25 mm.   The extruded rubber trough cases would be wound on the drum of a pipe-laying vessel.

Comments on the feasibility of this proposal, however critical, would be welcome.

Conclusions.

There is a wide range of estimates for the rates of methane release from Arctic seabeds but the higher ones are alarming enough for all defensive measures to be carefully examined.

Initial design work for the manufacture and deployment of kilometre-sized areas of plastic film to capture methane suggests that that this may be possible for a range of emission rates provided that the areas of the sea bed are clear of obstructions. This conclusion should be checked with people from the plastic and rubber industries.

Deployment and recovery will require pipe-laying vessels from the oil industry , such as the Stena Apache, and specialised seabed crawlers which have been designed for wave and tidal-stream installation.

Unless methane emission rates are even higher than suggested it will not be economical to recover methane for use on land and so flaring off at sea is more likely.  However there may be enough energy to drive ice-cutting equipment to keep the water round a flare stack clear of drifting ice in winter.

The extrusion tool for a 1500 metre width will require about 200 tonnes of very flat stainless steel sheet. The critical problem is maintaining an accurate gap in the extrusion tool.  This can be done with differential temperature control of opposite surfaces of a stack of interdigital plates with central cooling channels. 

The separation of halves of a film package can be done by the force generated from angled saw-tooth ridges on the underside when the package is dragged over the sea bed.  This allows very wide film coverage from an easily transported package and leaves tracks for methane flow.

If the underside of the film has a pipe connection to the atmosphere the pressure from water above it will clamp it firmly to the sea bed.

Work on long-term biological testing of candidate film materials should begin as soon as possible.

It is necessary to have credible techniques to recover all materials from the sea bed.  The proposed method must be critically checked by experienced offshore engineers.

A 4.5 square kilometre area of 200 micron sheet will need about 930 tonnes or 25 railway trucks of plastic but this is small compared with world production.  Energy consumption in the present plastics industry is about 10 MJ a kilogram compared with 2.25 MJ for the latent heat of steam.  If the film extrusion velocity is 10 mm a second we will need 3.5 days for one pack and a power of 35 MW.  Heat pump technology could give a very large reduction in energy consumption and must be carefully investigated.

We may have to avoid deployment in water depths less than the deepest pressure ridges. The leading ice authority, Peter Wadhams, says that these can reach down to 34 metres below the surface.

Actions

Resolve the three-order of magnitude dispute about methane release rates and investigate sea bed methane release rates and their variability in space and time.

Check design assumptions with the plastic film and rubber extrusion industry. 

Choose the best candidate film materials with density just greater than cold sea water (1028.4 kg/m3) and establish stress capability in working conditions.  A large strain length is more important than tensile strength.

Place specimens of the various film types in suitable test site in northern Norway and observe biological results especially recolonization rates.  The earlier this begins the better.  Albert Kallio has warned about anoxic conditions below the film.  The area of test film must be large enough to replicate this.

Measure tow forces on 5-metre sized blocks and establish the best ridge angle for a range of sea bed conditions from gravel to sand to ooze.

Place blocks of various shapes and densities fitted with accelerometers on the sea bed and measure how many roll or slide.

Carry out a sonar side-scan survey to identify obstructions in suitable areas.  Some, such as bullion cargoes, may be removable.

Collect information on depth and occurrence of pressure ridges in methane release areas.

Pray that the continual underestimation of the potential climate risks by people who are responsible for defending us against them does not continue.

Links

World plastic production

Shakhova PowerPoint presentation link.

Shakhova Semiletov paper


Pipe-laying vessels

Other collected papers

References

Dlugokencky, E. J., L. M. P. Bruhwiler, J. W. C. White, L. K. Emmons, P. C. Novelli, S. A. Montzka, K. A. Masarie, P. M. Lang, A. M. Crotwell, J. B. Miller and L. V. Gatti (2009), Observational constraints on recent increases in the atmospheric CH4 burden, Geophysical Research Letters, 36, L18803, 10.1029/2009GL039780.
Frankenberg, C., I. Aben, P. Bergamaschi, E. J. Dlugokencky, R. van Hees, S. Houweling, P. van der Meer, R. Snel P. Dol (2011), Global column-averaged methane mixing ratios from 2003 to 2009 as derived from SCIAMACHY: Trends and variability, Journal of Geophysical Research-Atmospheres, 116(D04302), 1-12, 10.1029/2010JD014849.
Montzka, S. A., E. J. Dlugokencky and J. H. Butler (2011), Non-CO2 greenhouse gases and climate change, NATURE, 476, 43-50, 10.1038/nature10322.

Thursday, October 23, 2008

Removing carbon from air - Discovery Channel

 David Keith works to remove CO2 directly from ambient air Professor David Keith of the University of Calgary is working on a device that removes carbon dioxide directly from ambient air.

Keith has built a tower, 4 feet wide and 20 feet tall, with a fan at the bottom that sucks air in. Keith expects the air coming out at the top to have approximately 50% less carbon dioxide than the air coming in.

The tower features in an episode of Discovery Channel’s new “Project Earth” series on TV. The series has the largest budget of any in Discovery Channel’s history, and it may eventually attract a global viewership of more than 100 million.

The episode on Keith’s research has already aired in the U.S. - if you're missed it, you can watch it on Discovery Channel’s website, at: http://dsc.discovery.com/tv/project-earth/project-earth.html - click on “Episodes.”

If the program hasn't aired in your country, you may not get access to the online episode, but you can read more at: http://dsc.discovery.com/tv/project-earth/lab-books/fixing-carbon/guide1.html - also click on the links under "MORE CARBON".

The picture below describes the Big Picture of recycling, in which I envisage aviation to fund CO2 air capture. When talking about recycling, most people think about recycling of industrial products only. They may also see composting of organic waste as a (second) way of recycling. Instead of composting, I actually envisage organic waste to be burned by means of pyrolysis, in order to produce agrichar and hydrogen. I also envisage a third way of recycling that includes removing CO2 from the air. This CO2 could also be used for the production of agrichar and for commercial purposes such as to enrich greenhouses and for the production of building material, carbon fiber, etc. Furthermore, this CO2 could be used as fuel for aviation.

To tackle emissions by aviation, we can switch to airplanes and helicopters that are powered by batteries and hydrogen, or switch to fuels other than fossil fuel. Growth of algae could be assisted by such captured CO2, which could also be turned directly into fuel.

By financially supporting air capture of CO2 and the use of such CO2 to produce fuel, aviation could close the circle of this third way of recycling. This could make aviation environmentally sustainable. Since government is such a large user of aviation (both the military and civil parts of government), it makes sense for the government to start funding such air capture as soon as possible. An international agreement, to be reached in Copenhagen in 2009, could further arrange for the proceeds of environmental fees on commercial flights to fund such air capture and its use for fuel.

 Recycling, the Big Picture - by Sam Carana

Further links:
http://dsc.discovery.com/tv/project-earth/explores/carbon.html - Discovery Channel

http://www.ucalgary.ca/news/september2008/keith-carboncapture - David Keith

http://www.ucalgary.ca/~keith/AirCapture.html - David Keith

http://www.ucalgary.ca/~keith/Misc/AC%20talk%20MIT%20Sept%202008.pdf - M.I.T.

views.blogspot.com - by Sam Carana



The post below is added for archival purposes. It was originally posted by Sam Carana at knol in 2009, which has meanwhile been discontinued by Google. The post received 4513 views at knol.


Funding of Carbon Air Capture


HOW CAN CO2 CAPTURE FROM AMBIENT AIR BEST BE FUNDED?

FEES ON JET FUEL CAN HELP FUND THE DEVELOPMENT OF CARBON CAPTURE FROM AMBIENT AIR.


AIR CAPTURE of CO2 (carbon dioxide) is an essential part of the blueprint to reduce carbon dioxide to acceptable levels. Fees on Air Capture Fundingconventional jet fuel seems the most appropriate way to raise funding to help with the development of air capture technology.

Why target jet fuel? In most other industries, there are ready alternatives to the use of fossil fuel. Electricity can be produced by wind turbines or by solar or geothermal facilities with little or no emissions of greenhouse gases. In the case of aviation, though, the best we can aim for, in the near future at least, is biofuel or synthetic fuel, produced from CO2 captured from ambient air. As discussed below, development of these two forms of renewable energy can go hand in hand. 
Carbon air capture and production of synthetic fuel and bio fuel can go hand in hand
Technically, there seems to be no problem in powering aircraft with bio fuel. Back in Jan 7, 2009, a Continental Airlines commercial aircraft (a Boeing 737-800) was powered in part by algae oil, supplied by Sapphire Energy. The main hurdle appears to be that algae oil is not perceived as price-competitive with fossil fuel-based jet fuel.

Additionally, the aviation industry can offset emissions, e.g. by funding air capture of carbon dioxide. The carbon dioxide thus captured could be partly used to produce fuel, which could in turn be used by the aviation industry, as pictured on the top right image. The carbon dioxide could also be used to assist growth of biofuel, e.g. in greenhouses and in algae bags, as described below.
Algae can grow 20 to 30 times faster than food crops. As the CNN video on the right mentions, Vertigro claims to be able to grow 100,000 gallons of algae oil per acre per year by growing algae in clear plastic bags suspended vertically in a greenhouse. Given the right temperature and sufficient supply of light, water and nutrients, algae seem able to supply an almost limitless amount of biofuel.
The potential of algae has been known for decades. As another CNN report describes, the U.S. Department of Energy (DoE) had a program for nearly two decades, to study the potential of algae as a renewable fuel. The program was run by the DoE's National Renewable Energy Laboratory (NREL) and was terminated by 1996. At that time, a NREL report concluded that an area around the size of the U.S. state of Maryland could cultivate algae to produce enough biofuel to satisfy the entire transportation needs of the U.S.
Apart from growing algae in greenhouses, we should also consider growing them in bags. NASA scientists are proposing algae bags as a way to produce renewable energy that does not compete with agriculture for land or fresh water. It uses algae to produce biofuel from sewage, using nutrients from waste water that would otherwise be dumped and contribute to pollution and dead zones in the sea.

algae yieldThe NASA article conservatively mentions that some types of algae can produce over 2,000 gallons of oil per acre per year. In fact, most of the oil we are now getting out of the ground comes from algae that lived millions of years ago. Algae still are the best source of oil we know.

In the NASA proposal, there's no need for land, water, fertilizers and other nutrients. As the NASA article describes, the bags are made of inexpensive plastic. The infrastructure to pump sewage to the sea is already in place. Economically, the proposal looks sound, even before taking into account environmental benefits.

Jonathan Trent, lead research scientist on the Spaceship Earth project at NASA Ames Research Center, Moffett Field, California, envisages large plastic bags floating on the ocean. The bags are filled with sewage on which the algae feed. The transparent bags collect sunlight that is used by the algae to produce oxygen by means of photosynthesis. The ocean water helps maintain the temperature inside the bags at acceptable levels, while the ocean's waves also keep the system mixed and active.

algaeThe bags will be made of “forward-osmosis membranes”, i.e. semi-permeable membranes that allow fresh water to flow out into the ocean, while preventing salt from entering and diluting the fresh water inside the bag. Making the water run one way will retain the algae and nutrients inside the bags. Through osmosis, the bags will also absorb carbon dioxide from the air, while releasing oxygen. NASA is testing these membranes for recycling dirty water on future long-duration space missions.

As the sewage is processed, the algae grow rich, fatty cells that are loaded with oil. The oil can be harvested and used, e.g., to power airplanes.
In case a bag breaks, it won’t contaminate the local environment, i.e. leakage won't cause any worse pollution than when sewage is directly dumped into the ocean, as happens now. Exposed to salt, the fresh water algae will quickly die in the ocean.
The bags are expected to last two years, and will be recycled afterwards. The plastic material may be used as plastic mulch, or possibly as a solid amendment in fields to retain moisture.
A 2007 Bloomberg report estimated that the Gulf of Mexico's Dead Zone would reach more than half the size of Maryland that year and stretch into waters off Texas. The Dead Zone endangers a $2.6 billion-a-year fishing industry. The number of shrimp fishermen licensed in Louisiana has declined 40% since 2001. Meanwhile, U.S. farmers in the 2007 spring planted the most acreage with corn since 1944, due to demand for ethanol. As the report further describes, the Dead Zone is fueled by nitrogen and other nutrients pouring into the Gulf of Mexico, and corn in particular contributes to this as it uses more nitrogen-based fertilizer than crops such as soybeans.
The Louisiana coast seems like a good place to start growing algae in bags floating in the sea, filled with sewage that would otherwise be dumped there. It does seem a much better way to produce biofuel than by subsidizing corn ethanol.
Not Millions, but Billions of Dollars!
Carbon air capture could produce a form of renewable synthetic fuel that could be used to power aviation. Carbon air capture could also help produce biofuel to power aviation. It would therefore make sense to encourage development in carbon air capture by imposing fees on conventional jet fuel and by using the proceeds of those fees to help fund air capture of carbon dioxide.
According to zFacts.com, corn ethanol subsidies totaled $7.0 billion in 2006 for 4.9 billion gallons of ethanol. That's $1.45 per gallon of ethanol (or $2.21 per gallon of gas replaced). As zFacts.com explains, besides failing to help with greenhouse gases and having serious environmental problems, corn ethanol subsidies are very expensive, and the political backlash in the next few years, as production and subsidies double, will damage the effort to curb global warming.
On 15 May, 2009, U.S. Secretary of Energy Steven Chu announced that $2.4 billion from the American Recovery and Reinvestment Act will be used to expand and accelerate the commercial deployment of carbon capture and storage (CCS) technology.
At UN climate talks in Bonn, the world's poorest nations proposed a levy of about $6 on every flight to help them adapt to climate change. Benito Müller, environment director of the Oxford Institute for Energy Studies and author of the proposal, said that air freight was deliberately not included. The levy could raise up to $10 billion per year and would increase the average price of an international long-haul fare by less than 1% for standard class passengers, but up to $62 for people traveling first class.
In the light of those amounts, it doesn't seem unreasonable to expect that fees imposed on conventional jet fuel could raise billions per year. Proceeds could then be used to fund rebates on air capture of carbon dioxide, which could be pumped into the bags on location to enhance algae growth. Air capture devices could be powered by surplus energy from offshore wind turbines. With the help of such funding, the entire infrastructure could be set up quickly, helping the environment, creating job opportunities, making the US less dependent on oil imports, while leaving us with more land and water to grow food, resulting in lower food prices.
Cost of Carbon Air Capture
As to the cost of carbon air capture, GRT puts the current cost to harvest one ton of CO2 at $200 andestimates that, 2-3 years from now, it will cost about $150, while the price will come down to $30 to $20 as the technology is fully mature. 
Currently, carbon air capture isn't more expensive than to capture CO2 from smokestacks. The coal industry wants politicians to subsidize "clean coal", but current cost of capture (i.e. excluding transport and storage) is estimated at $100-150/tCO2 initially, possibly reducing to one third of that as the technology matures. That would price coal out of the market, while it doesn't even cover the cost of transporting the CO2 away from the plant and the subsequent sequestration, policing and monitoring all this over many years, etc.
Carbon air capture can be done at off-peak hours when cost of electricity needed for capture is low. Carbon capture from ambient air can also be done anywhere, meaning that it can take place on location, i.e. where the carbon is to be sequestered, which would save on the cost of transport. Or, even better, carbon capture can take place where the carbon is to be used for industrial or agricultural purposes, such as in greenhouses, algae bags or as soil supplements. By mixing carbon with hydrogen, the carbon can also be used to produce carbohydrates, i.e. synthetic fuel that could be used to power shipping and aviation. Such usage can help pay for the cost of carbon air capture.
 David Keith and his team are working to capture CO2 from ambient air Professor David Keith (left) of the University of Calgary is working on a tower, 4 feet wide and 20 feet tall, with a fan at the bottom that sucks air in. The tower looks like it's made mainly of plastic, which could be made with carbon produced by such a tower. Inside the tower, limestone or a similar agent is used to bind the CO2 and to split CO2 off by heating it up. The limestone is recycled within the tower, although it does need to be resupplied at some stage. Anyway, the main cost appears to be the electricity to run it. Keith and his team showed they could capture CO2 directly from the air with less than 100 kilowatt-hours of electricity per ton of CO2. At $0.10/kWh, that would put the electricity cost at $10 per ton.
In the U.S., each person emits about 20 tons of CO2 annually. In other words, each person in the U.S. could remove as much CO2 from the air with such a device, with annual operational costs of $200 for 2 Megawatt-hours of electricity. By comparison, a refrigerator consumes about 1.2 Megawatt-hours annually [2001 figures]. Of course, the additional cost of carbon disposal will make it more attractive to use large facilities at places where there's demand for carbon and where the associated economies of scale would facilitate lower operational costs. 

Towards a Sustainable Economy

The following comments were posted by Sam Carana under this knol:

Jul 19, 2010

There are several efforts under development to produce a carbon-neutral fuel. Two of them were recently described in article in New Scientist, entitled: Green machine: Cars could run on sunlight and CO2.
http://www.newscientist.com/article/dn18993-green-machine-cars-could-run-on-sunlight-and-co2.html
See also Sandia
https://share.sandia.gov/news/resources/releases/2007/sunshine.html

Whereas many may think that this is a good way to power cars, I agree with you that it makes more sense to have electric cars. However, aviation is a bit more difficult to clean up, that's why aviation in particular can benefit from such technology, and that would justify that aviation made financial contributions to fund such developments.

As air capture technology matures with financial assistance funded by fees on aviation, it will be in a better position to develop into a more general technology used to reduce CO2 in the atmosphere to more acceptable levels.
Jul 19, 2010
In my above reply, I referred to the use of concentrating solar power (CSP) plants to produce temperatures high enough to split water vapor into hydrogen and oxygen, and ambient carbon dioxide into carbon monoxide and oxygen. A team led by Athanasios Konstandopoulos has successfully managed to also split carbon dioxide into carbon monoxide and oxygen in this way. The hydrogen and carbon monoxide can subsequently be combined into hydrocarbons, i.e. synthetic oil.
http://www.newscientist.com/article/dn19308-the-next-best-thing-to-oil.html

Aug 27, 2010
An article in Nature describes the use of a solar cavity-receiver reactor to heat up non-stoichiometric cerium oxide to a temperature at over 1,500 °C, forcing the release of oxygen. Then, to re-oxidize it with H2O and CO2 at below 900 °C to produce H2 and CO – known as syngas, the precursor of liquid hydrocarbon fuels.
http://www.sciencemag.org/content/330/6012/1797

Jan 28, 2011

Milking algae

Instead of harvesting algae for processing into biofuel, there is prospect for "milking" the algae, i.e. extracting oil from the algae without killing them.

This method is followed by Joule Unlimited.
http://www.theglobeandmail.com/news/opinions/opinion/a-brave-new-world-of-fossil-fuels-on-demand/article1871149/

And also by Algenol, Synthetic Genomics (Craig Venter’s venture) and BioCee
http://theenergycollective.com/tyhamilton/50300/joule-cool-not-alone-quest-sunlight-fuel-game-changer

Jul 5, 2011

British company set to make renewable jetfuel

British company Air Fuel Synthesis plans to capture carbon dioxide from the air, and mix it with hydrogen extracted from water through electrolysis, in order to make liquid hydrocarbon fuels for transport, including for aviation.
http://www.airfuelsynthesis.com/technology.html
http://www.airfuelsynthesis.com/technology/technical-review.html
http://www.airfuelsynthesis.com/faqs.html