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Tag Archives: carbon dioxide

Facts and fiction

By Dave Elliott

Is the truth out there? An extended Xmas Whimsy

It’s usual for there to be a spread of viewpoints on most issues, and it’s always worth looking at a range views, including ‘outlier’ ones! On that, this is fun: www.xonitek.com/press-room/company-news/the-stone-age-didnt-end-because-they-ran-out-of-stones/

However at times you can get weary of obsessive time wasters and yearn for clarity! Sadly that may not be easy to achieve.

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Carbon concerns

cow.jpg
How much carbon is coming out?

By Michael Banks, Physics World, in Washington, DC

“Carbon is the most important element, but we are deeply ignorant of its effect on the Earth,” says Robert Hazen from the Carnegie Institution of Washington.

Hazen is the principal investigator of the deep carbon observatory – a 10-year programme funded by the Alfred Sloan Foundation to better understand the Earth’s carbon cycle.

It’s a wide-ranging study and speaking at the 2011 American Association for the Advancement of Science meeting in Washington, DC, Hazen spelled out the many questions that remain unanswered about carbon. These include how much of the element is stored in the Earth, especially in the core, and how much of the material is released when a volcano erupts.

In the case of a volcanic eruption, Hazen says some scientists conclude carbon makes up around 2% of the material ejected, while others say it is more like 75% – a big discrepancy that the programme will hope to reduce.

The programme only started in 2009 so Hazen is issuing a call to arms for scientists of different backgrounds to come together and join the project.

You will have to be quick as proposals for research activities must be submitted by 11 March.

Read more about the programme here.

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The Algebra of Algae … to Biodiesel

Over three decades ago the US government, through the then-known and newly-established Solar Energy Research Institute (SERI), established a Biofuels Program that included the Aquatic Species Program (ASP) to explore the ability to develop biofuels from microalgae. Today, SERI is known as the National Renewable Energy Laboratory (NREL), and in 1998 they concluded the ASP as the progress had slowed and there was a belief that advances in biological control and genetic engineering of algae were required to create a valid algae-based biofuel industry. Aside from carbon sequestration, NREL reports that: “Algal biodiesel is one of the only avenues available for high-volume re-use of CO2 generated in power plants. It is a technology that marries the potential need for carbon disposal in the electric utility industry with the need for clean-burning alternatives to petroleum in the transportation sector.” [Sheehan et al., 1998]

Furthermore, NREL states: “…we believe that biodiesel made from algal oils is a fuel which can make a major contribution to the reduction of CO2 generated by power plants and commercial diesel engines.” [Sheehan et al., 1998]

Finally, the NREL closeout report reads: “When compared to the extreme measures proposed for disposing of power plant carbon emissions, algal recycling of carbon simply makes sense.” [Sheehan et al., 1998]

If we combine these statements made in 1998 with proposed legislation in 2009 for greenhouse gas (GHG) reductions, we can pose the question regarding the viable size of an algal-based biofuel industry in the United States. The most popular climate bill in the current Congress is the American Clean Energy and Security Act of 2009 (ACES Act) by Henry Waxman and Edward Markey, and it discusses reducing GHG emissions by 83% of 2005 levels by 2050.

In 2005, the US carbon dioxide (CO2) emissions were 6,030 million metric tons (MtCO2). The electricity sector accounted for 2,510 MtCO2 and the transportation sector accounted for 1,980 MtCO2. In accordance with popularly discussed proposed legislation, 17% of 2005 US CO2 emissions are approximately 1,000 MtCO2. For simplicity of this analysis, we’ll assume that total CO2 emissions, rather than more generally all GHG, will need to be reduced to the target 17% by 2050.

Algae production requires CO2. And because algae and grow in aquatic environments instead of on land, the surface area of the algae that are exposed to the air, which contains CO2, is more limited than terrestrial biomass. Therefore, to grow algae biomass on industrial scales (e.g. profitable scales) CO2 is pumped into the algae-bearing water at much higher concentrations than in the atmosphere. Estimates for the amount of CO2 that are required for making biodiesel from algae are approximately 0.02 +/- 0.004 tons of CO2 per gallon of biodiesel (tCO2/gal). For example, NREL reports an example that 60 billion gallons (Bgal) of biodiesel would require 900 – 1,400 MtCO2. This quantity of CO2 is 36%-56% of total US power plant emissions.

So to get a maximum limit of how much biodiesel could be produced per year under the carbon restriction of the ACES Act, we can assume that all CO2 emissions come from transportation only. The figure below plots a simplified trajectory of US CO2 emissions (left axis) under the ACES Act, along with emissions from the electricity and transportation sectors. On the right axis, I’ve plotted the amount of biodiesel from algae that can be produced assuming that 100% of power plant emissions are captured and used for growing algae to make biodiesel (clearly an over estimate). This inherently assumes that (1) there will be absolutely no net CO2 emissions from any other industrial process, industry, or combustion of any hydrocarbon aside from burning the biodiesel in vehicles and (2) that no technology will feasibly exist for re-capturing the CO2 from combustion of biodiesel in the vehicle itself.

AlgebraOfAlgae_image.jpg
AlgebraOfAlgae_image.jpg

The plot shows that in 2050 50 Bgal/yr of biodiesel from algae would be the maximum amount allowed. Compare this to the 2008 US consumption of approximately 138 Bgal of gasoline and 61 Bgal of diesel. About half of the diesel was for freight trucks. Therefore, in 40 years, for the US to meet the ACES Act carbon reductions, we could produce 50 Bgal of biodiesel from algae, with 1,000 MtCO2 coming from fossil fueled power plants (assumed) if and only if no other fuel or economic sector had a net emission of CO2. Thus, if the CO2 supplied for algae came from coal power plants, then we would essentially be producing electricity from coal with CO2 capture, but not geologic or other storage systems, in the quantity of approximately 1,000 TWh or 50% of today’s coal powered generation. This does not mean that additional coal or natural gas power plants could not operate, but each would have to capture and sequester 100% of the CO2 emissions – a practical impossibility, but a sufficient assumption for this back-of-the-envelope analysis.

So what are some implications or conclusions from this quick analysis?

To drive as many miles as we do today (2.7 trillion/yr by cars and light trucks only) on 25%of current liquid fuels consumption, we need our transportation sector to be 400% more “liquid fuel” efficient in the range of 80 MPG of biodiesel to leave 16 Bgal for freight (about half the fuel for today’s freight)

This is not entirely difficult to imagine for light duty vehicles that currently have a fleetwide average of approximately 21 MPG. By creating plug-in hybrids and making cars lighter, the capability of meeting this fuel economy has been demonstrated. Imagining the implications for freight trucks may be more difficult, as they would still have to get over twice as efficient as today, and increasing freight travel by rail could help get goods around the country with less fuel. There are other possibilities, but knowing what we have to work for in terms of a carbon balance can prevent a “algae to biodiesel” bubble while still moving us to a lower-carbon future.

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