How Green is Your Favorite Biofuel?

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Correspondence from an AG reader stimulated the series. The main example was biomass as the feedstock. Pyrolysis yielded Syngas; part of the product went toward drying of the incoming biomass then carbonization. As the idea was submitted, conversion of the remainder went toward DME.



Gasification of biomass has shown some potential, particularly when the feedstock is forestry waste or municipal solid waste.

Furthermore, a byproduct of the pyrolysis is char. To increase process efficiency, conversion in a fluidized bed reactor of the char plus pulverized coal went toward synthetic natural gas. The technology can make use of many different types of coal, petroleum coke, several sewage and industrial sludges, oils, slurries, liquid production wastes and biomass unsuited as feedstock for pyrolysis.

As part of Coal / Biomass to Synthetic Natural Gas step, the main example of integrated biofuel development also included diversion of the waste into agriculture processes. Agri-char is gaining acceptance as a low-tech form of carbon capture and storage.

Rather than synthetic natural gas, this blog, albeit reluctantly, tended toward the use of ethanol blends as a preferred alternative to diesel and gasoline. Reasons for this preference included:



The Idaho National Laboratory compared GHG emissions for various alternatives to conventional low-sulfur diesel transportation fuel. Their calculations resulted from modeling transportation fuels using the Argonne National Lab GREET (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation) model.

A Dutch economic analysis rated gasification of biomass as the most cost effective, even more so than cellulosic ethanol. Thus, building on the each cycle, in some cases applying co-generation strategies, would seem to make sense.

Unfortunately, such suppositions, from start to finish, focus upon efficiency and economy, omitting a consideration of emissions produced by the various processes. “While nearly all crop-derived biofuels emit less greenhouse gases than fossil fuels,” notes Matt Ford1, “whether or not they are better for the environment is still open for debate.”

In the AG reader’s proposal, DME is a cleaner burning fuel than diesel. Yet absent was any consideration of GHG emissions resulting from conversion of the biomass to Syngas or use of Syngas as a fuel, much less consideration of the inputs for harvesting and transport of the biomass.

Nor was there any consideration of GHG emissions from production of the synthetic natural gas. “At least that will be better than burning coal in a coal-fired power plant because the sulfur and heavy metals in the coal will be removed during the Syngas production process, which is another reason for fuel-less electrical power. Realistically, coal will probably be used.” While it would be a good thing if all GHG emissions were part of the consideration, at least knowing the expected miles per pound of carbon equivalent should be part of any “game changing” proposal of an alternative transportation fuel.



Adapted from (S1).

Greenhouse-gas emissions are plotted against overall environmental impacts of 29 transport fuels, scaled relative to gasoline. The origin of biofuels produced outside Switzerland is indicated by country codes: Brazil (BR), China (CN), European Union (EU), France (FR), and Malaysia (MY). Fuels in the shaded area are considered

advantageous in both their overall environmental impacts and greenhouse-gas emissions.

In an article for Ars Technica, Ford relays information from a recent study that was carried out at the behest of the Swedish government. The Swiss researchers examined the total environmental impact from various types of biofuels,

Zah, et al compared 26 different ones plus gasoline, diesel, and natural gas.

21 out of the 26 biofuels examined emitted less greenhouse gases than gasoline when burned. However, almost half—12 out of 26—had a greater composite environmental cost than fossil fuels.

Of those biofuels that had a greater (negative) impact were many economically important ones, including corn ethanol, sugarcane ethanol, and soy diesel. The biofuels that fared the best were those produced from residual products, such as biowaste or used cooking oil.

On a first pass, the results from the new study seem consistent with another comparison of GHG from various biofuels. Environmentalists count the diversion of biodegradable waste into anaerobic digestion and / or capture of bio-gas as a plus; it is less polluting than coal-fired generation.



Advocates claim that the optimized diversion of manure to bio-gas production by means of anaerobic digestion results in a negative value for production and is the only alternative fuel to do so.

What for me increased the credibility of the study by Zah and colleagues was recognition of the complexity of any such analysis. For instance, EBAMM (ERG Biofuel Meta-Analysis Model) shows us that “ethanol derived from corn, but distilled in a facility powered by coal was, in fact, on average worse, than gasoline.”

To their credit, the authors acknowledged the “apples and oranges” problem that one often encounters when trying to compare different biofuels. Nonetheless, Zah and coauthors were able to construct an objective evaluation method that used two criteria: greenhouse-gas emissions relative to gasoline, and overall environmental impact—an aggregated measure of natural resource depletion and damage to human health and ecosystems.

The study authors somewhat naively suggest the necessity of accepting alternative transportation fuels with lower EROEI if their environmental impact is significantly less. Still, the challenge, as Vinod Khosla observed in an interview with David Rotman2, remains to make any switch to an alternative transportation fuel scalable.

As AG commentator Jacque has noted:

While burning corn for CHP (Combined Heat and Power) is more efficient than using it to produce ethanol, the question is where are we going to get liquid fuels to power our current generation of vehicles?

As oil depletes, we need more liquid fuels, for which ethanol is especially suited. As ethanol production gets more efficient it can supply perhaps 30% of our transportation fuels.

Conservation could save another 20%to 30%. The combination of these two along with some electric vehicles should be able to keep up with decreasing supplies of oil.

Several ethanol plants have been built using methanol produced in a waste (manure) digester to supply heat for their distillation columns. This is a good, distributed energy source. Other people generated electricity with this methanol. As far as I recall no one is co-generating in these facilities, but that would be a great improvement.



Because of the amounts of nitrous oxides associated with cultivation and released into the atmosphere, Paul Crutzen and colleagues question3 whether growing and burning many biofuel crops actually may raise, rather than lower, greenhouse gas emissions. Crutzen’s work highlights the importance of establishing correct full life-cycle assessments for biofuels.

Co-generation, for Jacque and others, then, is an indicator of better EROEI. As yet, there would seem to be the absence of a simple indicator of better life cycle GHG emissions. And, the last word, is a caution about such analyzes that comes from Gristmill commentator GreyFlcn:

The problem being that it’s still based off of Michael Wang’s / Argonne Lab’s GHG projections.

http://greyfalcon.net/lca.png

The same Michael Wang that cuts out most emissions from land use, nitrogen, and soil disruption.

http://greyfalcon.net/n2o.png

http://greyfalcon.net/n2ostudy

http://greyfalcon.net/landuse

http://greyfalcon.net/soy2

http://www.treehugger.com/files/2007/12/ocean_bacteria_ni …

The same Michael Wang which makes some really crazy off the wall comments like “Oil produces less energy than Corn Ethanol”

http://i-r-squared.blogspot.com/2006/09/postscript-with-w …

The same Michael Wang, that after he was found to be bullshitting his study inputs, and their impacts skyrocketed, he miraculously made the emissions from ethanol go down even further than the previous study.

http://i-r-squared.blogspot.com/2006/03/how-reliable-are - …

Reference

S1. R. Zah et al., Okobilanz von Energieprodukten: Okologische Bewertung von

Biotreibstoffen (Empa, St. Gallen, Switzerland, 2007).

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