26 May 2006

Closed-loop Biodiesel

I think Robert Rapier has made it explicitly clear that switching to biofuels with our current gas guzzling enterprise is largely a non-starter. I have said this in the past, "that we should not dismiss biofuels simply because their lobby groups are stupid." Biofuels provide very high utility due to the fact that they are high-density liquid fuels, ideal for long distance transportation. However, the paradigm needs to change: we need to get serious about both conservation and efficiency. We need smaller, lighter cars that incorporate all the efficiency advantages of hybrids and diesels. We also need to offset load to electricity rather than liquid fuels through the plug-in concept.

Over at the Oil Drum, Heading Out wonders why the big emphasis on ethanol from the USA corn farmers? You mean aside from their money-grubbing mendacity? As he points out biodiesel is a much better idea. The problem with ethanol obviously lies in distillation. I am not very high on cellulose ethanol either due to this simple problem. Separating the product from the water requires a whole lot of heat input.

Biodiesel is fatty acids which have been esterified by the addition of an alcohol, typically methanol. This greatly improves the flow properties of biodiesel compared to straight vegetable oil (triglycerides). Vegetable oil is relatively easy to separate from the plant. The most common method is to basically squeeze it out mechanically. This requires vastly less energy than distillation.

There is still the problem of the methanol input. My potential solution to this problem was to run an anaerobic reactor with the remaining material (i.e. cellulose) in order to produce methane. Methane production by anaerobic bacteria requires some very low grade heat inputs that could certainly be supplied by passive solar if the system was well designed and insulated. Producing methane is this fashion is relatively wasteful of the carbon you've managed to sequester -- the output is roughly half CH4 and half CO2.

However, the key point is that through this integrated approach there is no destruction of the soil nutrients. From an energy perspective it makes more sense to simply burn the dry biomass but then all your fertilizer becomes fly ash. In a methane reactor, the fixed nitrogen, phosphorous, and potassium will still be in the sludge left over once the bacteria are done with it. The sludge can be used as a fertilizer (with some soil issues). Overall it is a much more 'permaculture' solution than anything else I've seen.

The biodiesel/biogas approach is nearly a closed-loop. It produces diesel fuel and methane to power the farm machinery needed to grow the crop, and it also preserves the majority of the nutrients in the soil. Ethanol is constantly hammered because it essentially transforms natural gas into ethanol. It should be clear to everyone that if the integrated biodiesel/biogas approach isn't energy positive it simply won't be able to run.

In the past I haven't been able to find sufficient information to analyze this problem. I hope to take a second look at the issue and see if a reasonable back of the envelope approximation can be done now that there's so much more ethanol information out there.

7 comments:

Robert Schwartz said...

Here are some useful links on Biodiesel:

Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus

Bioenergy Feedstock Information Network (BFIN)

Biomass as Feedstocks for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply

UNH Algae group

Kind of Hippie, but lots of information

Robert McLeod said...

Thanks that 2005 report from EERE is new.

Robert Schwartz said...

CIA Factbook:
US Land Area 9.2*10^8 ha

Arable Land in US 18% or 1.7*10^8 ha

Table 822 Cropland:
In Crops 1.4*10^8 ha

Census Bureau:
Land in Farms 2002 3.8*10^8 ha (1953 4.9 10^8 ha)


Annual fuel consumption 6.7*10^11 liters


Hippy Dippy Web site:

Crop liters oil/ha

corn (maize) 172
oats 217
cotton 325
hemp 363
soybean 446
pumpkin seed 534
rice 828
sunflowers 952
peanuts 1059
rapeseed (canola) 1190
olives 1212
jatropha 1892
avocado 2638
coconut 2689
oil palm 5950

==========================================

If we could increase the land in crops by about 20%, we could devote about 3*10^7 ha to oil crops. If we could average 1,000 l/ha*, we would have 3*10^10 of oil. That is about 5% of our current use. In order to run our transportation system on bio-diesel, we must bridge a gap of at least 4 doublings.

Could we bridge the gap? Pushing as hard as we can on automotive technology, we could certainly double fleet efficiency. We might even be able to quadruple it.

1,000 l/ha is not a stretch. But, of the crops with good oil yields, the only ones on the list above that have any promise and which are not tropical or sub-tropical, are rapeseed and sunflower. However, we have increased corn yields by over 8 times in the modern era. So we might be able to close the gap that way.

*1l of raw oil=~800ml of bio-diesel

Clearly, the algae approach, if it does not interfere with agriculture would be preferable to plowing up that much additional land.

Robert McLeod said...

As I've said before, getting down to 5 % will require offseting load to electricity; we won't get there through efficiency gains alone:

http://entropyproduction.blogspot.com/2005/09/rational-case-for-biofuels.html

It means plug-in vehicles for moving people and electrified trolly lines for trucks and trains.

Canola (rape) varies greatly in its yields, as does every other crop. 1000 L/ha is probably on the low side but appopriate for most Canadian production. European production seems to be about twice as high. Canola needs quite a lot of water and sulfur apparently.

I'm not sure where you found that the density of biodiesel was 1.25 times that of vegetable oil? This source gives a density of 0.91 kg/L for vegetable oil and 0.86 kg/L for biodiesel. While you lose a gylcerol molecule (C3H8O3) you gain three methanol molecules (CH3O) in the transesterfication process so there's a tiny net gain in mass.

Robert Rapier said...

There is still the problem of the methanol input.

Petrobas recently developed a process that eliminates the alcohol input. The oil is directly hydrogenated:

Petrobas Hydrogenation Process

RR

Hemant Thite said...

The Entropy Production concept is perfect. We have made it work. We generated methane from deoiled cakes of Jatropha and it has worked great. So much that we are fulltime into generation of Biogas from all types of deoiled cakes. This is the most sustainable approach and Biodiesel and Biogas must always go hand in hand.
I can provide support for methane generation from Biodiesel waste.

regards
Hemant
hrthite at vsnl.net

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