pstarr wrote:isgota wrote:pstarr wrote:Graeme, haven't I already lectured you on the fallacy of "renewable" biogas?
Conversion of landfills, sewage, farm waste and food waste into fuel is at best a waste-mitigation strategy, a way to avoid garbage disposal costs. The energy collection/processing btus are greater than output btus. Zero energy returned.
More carbon is released into the atmosphere than before. And no energy remains to drive Mom, Dad, Biff, and Babs on their shopping trips to the Mall. It is a GREEN LOSER.
Any sources? Because a quick "biogas EROEI" search yields
this paper showing exactly the opposite.
Same problem with the paper. The paper sited is very detailed explaining the energy costs for processing, transporting, and digesting various farm products (grasses, residue, and manure) but fails to include the very important cost of methane collection, compression, and distribution. Methane is not like diesel. You can not just simply pour it into a red jerry can, or a big shiny fuel truck. One must build the digester/pipeline infrastructure and compressing system.
The study is correct in one simple aspect; there is plenty of agriculture waste, especially manure, that requires disposal. Disposal by digestion makes sense, it is a simple perfected methodology that is mostly self-operational . . . the stuff rots and gives off stinky gas. However the gas must be trapped.
Here's a though experiment. We already collect animal manure in vast quantities and convert it into methane. The collection/transport exists, is maintained. The methane digestors are operational, have been for generations, the energy-cost (in expensive concrete/steel) amortized decades ago. No need to study or quantify the EROEI for the resulting methane because it is FREE. Yet we continue to power the digestors with expensive fossil-fuel electricity. WHY? We continue to flare off the methane daily. WHY? We don't use the methane to run our cars. WHY?
We must be NUTZ.
Do we hate the environment? Have the evil oil companies poisoned our minds? Should we rise up and destroy the evil oil companies? Graeme, help me here. Do they control our minds?
Though experiments are nice, but don't beat doing actual math.
You think compressing biogas is energetically expensive? Let's calculate it. CNG for fuel consists of compressions from 1 atm to about 250 atm. I will use the most inneficient way to compress a gas,
an isentropic compression.R is the gas constant ( about 8.3 J/mol K)
T1 is taken as 25 ºC (about 298 K)
and
Cp/Cv = k taken at 300 K and 0.1 MPa (about 1 atm) with
the data on page 636. The value is about 1.3
Inserting all the above in the equation of isentropic compression, the work (energy) necessary for compression equals to about 28,000 J/mol of methane.
But how much energy a mole of methane release at burning?
about 800,000 Joules. So compression only consumes about 3.5% of the methane (biogas) fuel. And reduces the final EROEI in the same magnitude. It's almost irrelevant.
Many of these "WHYS?" you are asking are based in economic constraints, not physical constraints. And the last one it's starting to happen more and more in many places around the world, it's North America the one is lagging.
http://www.iangv.org/current-ngv-stats/