Carbon-negative energy

[yop]

If we combined biomass-to-electicity production with carbon-capture-and-storage, we would have an energy supply that actually scrubbed CO2 out of the air. And any inefficiencies in transmission or at the point of use would just mean more CO2 removed. The more more we wasted energy, the better for the environment!

Why don't we convert the middle of our country to this kind of energy production? Add windmills to the mix, and how far could we get our country towards the goals of becoming carbon-neutral and energy independent?

[yop]

1. Prairie restoration

Prairie is perhaps our most endangered ecosystem. The Great Plains was once the Earth's greatest grassland, but today nearly all prairie land has been taken for human uses such as agriculture or ranching- activities that would not be viable in many locations without government handouts. Without a doubt, we should restore the natural balance of plants and animals in such locations.

Beyond the value of a restored ecosystem, natural prairie flora provides an opportunity. Prairie grasses are eminently suitable for biomass energy production. Switchgrass is the best-known prairie grass.

These grasses evolved in response to an environment with irregular rainfall and frequent fires. As a result, they need little irrigation and have evolved strategies for conserving or replenishing nutrients, such as nitrogen, that would be lost to burning.

These grasses evolved to burn. We would simply be tapping the energy of that natural process for human use.

Prairie grasses possess some other very valuable qualities as well. They are champions at preventing soil erosion, and they help to fertilize the soil through symbiotic relationships with nitrogen-fixing bacteria. The combination of these two traits mean that prairie grasses naturally build up the soil, increasing its depth and fertility. Improved soil is a benefit for its ability to support future crops. It also represents a giant carbon sink. The added soil mass is largely composed of carbon that was pulled from the atmosphere as CO2.

[yop]

7. Humble grasses may be the best source of biofuel

Humble grasses may be the best source of biofuel

* 14:20 08 December 2006
* NewScientist.com news service
* Catherine Brahic

Humble grasses may be the best source of biofuel, say researchers, who estimate grasses could provide 19% of global electricity needs at the same time as soaking up carbon dioxide from the atmosphere.

David Tilman and his colleagues, at the University of Minnesota, US, say grasslands could be used to produce biofuel and would yield more energy than the traditional biofuel crops of corn and soya per hectare. What is more, the process is "carbon negative" – meaning it captures more CO2 than it releases into the atmosphere.

By contrast, corn-based biofuel has come under attack for requiring large amounts of fossil fuels to run the tractors, fertilise the fields and convert the crop into fuel (see Fuels gold: Big risks of the biofuel revolution).
Wild lupine and goldenrod

Tilman and his team focussed on fields left fallow after years of degradation by agriculture, as these already exist and would not need to created. The plots they planted were home to up to 16 different wild prairie grasses, including wild lupine, goldenrod, Indian grass, big blue stem and switchgrass.

They found that those plots with more species yielded more energy. Plots with 16 species generated on average 2.4 times more than plots that had just one type of plant.

When they compared the fuel yields of grasslands with corn fields, they found they could obtain over 50% more energy from the grasslands per hectare.

But the key advantage was revealed when they calculated how much CO2 was released by the entire process. This involves planting the wild grasses, harvesting and transporting them to the biofuel facility, and operating that facility.

The use of fossil fuels to power the process releases 0.3 tonnes of CO2 per hectare per year - but the growing grasses store 4.4 tonnes of CO2 in the roots and soil, meaning the net result is 4.1 tonnes removed from the atmosphere. The stems, leaves and flowers of the grasses also absorb CO2 but this is then released again when the grassland biofuel is burned later on – meaning no net gain or loss of CO2.
Global needs

In the US, there are already substantial areas of agricultural land left fallow and planted with prairie grasses in the Great Plains. Tilman estimates that converting those grasslands to biofuel, would meet 6% of that region's transportation fuel needs and 10% of its electricity needs.

He adds that these areas already store CO2 equivalent to that released by about 12% of the petroleum used for transportation in the region.

Globally, Tilman says, "we estimate that biofuels produced on the degraded lands of Earth could 13% of global needs and simultaneously produce electricity that met 19% of global needs".

Journal reference: Science (vol 314, p 1598)

http://environment.newscientist.com/article/dn10759-humble-grasses-may-be-the-best-source-of-biofuel-.html

[eppur_se_muova]

2. HOW are you proposing to "capture" carbon ?

:shrug:
Plan lacks specifics, and the suggestion that waste will lead to greater efficiency is thumbing your nose at thermodynamics -- wasted energy will just mean less CO2 is removed from the environment for the same energy turnover.

[XemaSab]

3. CO2 can be injected into underground geologic formations

or pumped into oil fields in order to help extract oil.

[yop]

4. Exactly

Plants use CO2 and sunlight to grow. We harvest the plants and burn them to produce electricity. This process also regenerates the CO2 in a convenient, concentrated, localized form. We collect the CO2 and pump it underground where it stays safely out of the atmosphere for millenia. The overall net effect is that CO2 is removed from the atmosphere and stored underground.

There is a slight risk that the containment at a CO2 storage site could fail. To minimize the risk to human life of such an occurance, you would want to put your storage locations in sparsely populated areas that are wide open with lots of wind to allow the escaping CO2 to quickly be diluted to safe levels. The Great Plains are ideal for this reason as well.

[Porcupine]

6. Extract hydrocarbons and plow in the resulting charcoal........

thereby improving the soil, sequestering carbon and allowing you to harvest more hydrocarbons next cycle. In essence you would have an agricultural, low-tech, way to sequester carbon in a positive feedback loop.

Or somebody could wait for the magic wand.

Terra Preta

[GliderGuider]

8. Terra Preta. Exactly.

One of the nicest little ideas to come along recently. I'm pretty excited about it, and I'm a depressed, doomsday-loving apocaphile :-)

[yop]

5. Research

JS Rhodes and DW Keith, "Engineering economic analysis of biomass IGCC with carbon capture and storage," Biomass and Bioenergy 29 (2005) 440-450

www.ucalgary.ca/~keith/papers/67.Rhodes.2005.BiomassCCS.e.pdf

If the costs to society of emitting CO2 are high enough that it makes sense to replace natural gas power plants with biomass, then adding carbon capture and storage to the biomass power system more than pays for itself.