Re: Energy Cost of Ethanol
- From: "cnctut" <cnctutwiler@xxxxxxxxxxxxx>
- Date: 4 Jul 2006 09:54:33 -0700
cnctut wrote:
cnctut wrote:
cnctut wrote:
cnctut wrote:
cnctut wrote:
cnctut wrote:
Greg Hansen wrote:
cnctut wrote:
Greg Hansen wrote:
Reviving the topic of Habshi's subject line, and hoping to avoid the
topic of the content, what is the energy cost of producing ethanol?
Does anyone have some solid references?
Greg
Do you wish to start at--I just bought one bushel of shelled corn at
the elevator for $2 now let's make some ethanol--or here, plant these
seeds and grow a bushel of corn-- then we'll make some ethanol. ;-))
Tut
Starting with the seeds, of course. Bushels of shelled corn don't
appear out of nowhere.
OK--here's some data estimates in KCALS for one acre of corn
production--
Labor 49000
Machinery 420000
Gas 797000
Nitrogen 940800
Phosphorus 47100
Potassium 63000
Seeds 68000
Irrigation 34000
Incecticides 11000
Herbicides 11000
Drying 120000
Electricity 330000
Transportation 70000
Total Inputs 2,896,800 Kilocalories per acre
For ethonal production corn need not be dried/Iowa farmers don't
irrigate/electric fans unnecessary saving 484,000KCAL---bringing the
total inputs to 2,412,800KCAL per acre of corn.
To be continued
Some may disagree with the 2,412,800 KCAL per acre figure--and they may
be correct. The farmer for example may say--I alternate inoculated
legumes (soy beans) with corn every year. This practice fixes about
100 lbs or more usable nitrogen per acre. Also, fertilizer requirements
are diminished by returning everything back to the soil except the
seed.
To be continued
So now we have the approx energy expended (2,412,800 KCALs) to plant
and harvest one acre of corn with some variance.
How many bushels of corn can be produced on this acre?
Numbers vary--record yield is over 300 bushels per acre--average is
near 150 bushels in 2005--up from 71 in 1970.
One bushel of shelled corn weighs 56 pounds--so one acre produces
150x56=8400lbs of corn--therefore the energy expended to produce one
pound of corn is 2,412,800KCAL/ 8400 or 287KCAL.
To be continued
To be continued
To sum to this point--it takes 287KCAL to produce one pound of corn--or
it can be purchased at the elevator for 200/56=3.57 cents
Now, how many gallons of ethyl alcohol C2H5OH (C2H60) can be made from
one bushel of corn?
Iowa State University (ISU) studies suggests that 2.5 gallons per
bushel could be produced under reasonable conditions. Recent studies
have also suggested that by treating ground corn with ultrasound, 30%
more sugar could be attained by improving the brake up of carb
molecules in the corn. For this example though, let's stick with 2.5
gallons per bushel but remember that 2.74 gallons per bushel would be
the probable limit from corn seeds only.
If one bushel of corn (56lbs) produces 2.5 gallons of ethanol--then
56/2.5= 22.4 lbs of corn will produce one gallon.
Before we start fermentation/distillation our energy/$ cost for the
corn necessary to produce one gallon of ethanol is/are:
22.4 lbs corn x 287KCAL per lb= 6428.8 KCALs (corn planted and
harvested)
or
22.4 lbs corn x 3.57 cent per lb= 79.96 cents (corn purchased at
elevator)
To be continued
Now let's take a look at actual ethanol production process. One method
that has work successfully for years ( perhaps not the best ref energy
costs but should work for our calculations)
Finely grind the corn seeds and heat at 212 F in water for 30 minutes
to form a gelatine (or mash). The starch in the mash is cooled then
malted at 152 F(addition of ground sprouted corn--the sprouted material
contains the enzyme diastase which converts the starch to sugar.) After
the material cools to around 70 F the yeast is added--the holding
vessel is capped and fermentation begins.
Chemically, for glucose.... C6H1206----->Enzyme--->2C2H50H (2C2H60)
In 7-10 days the yeast has coverted the sugars to ethanol and
distillation can begin.
Energy calculations remaining:
Grinding/crushing 20.9 lbs of corn (1.5 lb used for malting)
Heating solution to 212F and holding for 30 minutes
Malting (sprouting 1.5 lb of corn)
Grinding/crushing 1.5 lb of sprouts
Distillation of water and ethanol mixture
Misc--manpower, movement of fluids, etc.
To be continued
Please note the correction to the chemical equation posted in message
31.
It's easy to see at this point that the "devil" is in the distillation
process. Factors that will schew the outcome and resultant decision on
cost effectiveness--can be driven in a variety of directions based on
purity of the final ethanol product, the energy source used for
distillation, and the type of distillation method used (batch,
fractional, etc.)
Statements in a variety of writings suggest that an energy input
anywhere from 32,000 BTU's per gallon to---"a large industrial still
will use only one steam horsepower hour to produce twenty gallons of
alcohol"--ie 33,445.7BTUs/20 = 1672.28 BTUs per gal exist.
Note: 1672 BTUs per gal would suggest that Timo's figures are possible
regarding ethanol costs per liter.
We'll attempt to box in a BTUs/gal figure in upcoming posts--however,
if anyone would like to walk down to their University Chem Dept and ask
the following question, it would be appreciated.
Given a 6.6gal solution of 15% ethanol and water--how many BTU's would
be required to distill the ethanol to a 95% purity level using current
distillation technology--assuming continuous processing and reuse of
the latent heat of fusion for the mixture?
Please post the answer--thanks.
To be continued--
Before we start on the distillation energy calculations let's consider
what purity of ethanol we need. The following are a few statements
clipped from sources in 1979.
Alcohol fuel must be over 100 proof (50% ethanol/water) to burn
150 proof (75% ethanol/water) is desirable for heating purposes
170 proof (85% ethanol/water) is desirable for automotive use
Another source:
There is no difference in power and mileage between 160 proof (80%
ethanol/water) and 200 proof (100% ethanol)...additionally, at 160
proof the 20% water appears to cool the exhaust valves...
(Tuts note: It would seem that some water in the combustion process
might be beneficial under certain conditions as in this
example---"Water injection is also featured on the record setting
Spyder coupe owned byTom Keosababian of Whittier, California. The car
turned 133 MPH at the 1964 Bonneville Nationals." )
Side note: Oil companies use 200 proof ethanol to mix with their
product.
However, for those of you in cold country--what do you add to your auto
gas if you suspect water in the tank----Heet----which
is.....yup...alcohol. ;-))
Finally--what is the highest percentage of ethanol/water mixture we can
expect after the fermentation process.
Alcohol tolerance of the yeast used for fermentation and the amount of
sugar available in the solution determines the ethanol percentage.
Yeast will continue to convert sugar into ethanol as long as there is
sugar to digest and the alcohol in solution is diluted enough so that
it doesn't kill the active yeast.
Each yeast strain has a slightly different acholol tolerance--brewers
books document various strains and their probable ethanol percentage.
"It is important to understand that yeast cannot live in a solution
containing more than 14% alcohol by volume. This is the usual amount
that will destroy the yeast...but under certain circumstances, and with
suitable yeast the percentage might be as high as 18%. On the whole an
amateur is unlikely to produce more than 16%, because he is unlikely to
be able to carry out his ferment under conditions with constantly
favourable temperatures and a scientifically balanced must."
Point being--ferment to the highest possible percentage (our example
uses 15%.) Distillation of higher percentages of ethanol/water requires
less energy for any given product proof.
To be continued
.
- Prev by Date: Re: about electric potential
- Next by Date: Re: If someone paid me, I'd write code/theories for them, not me.
- Previous by thread: Re: Energy Cost of Ethanol
- Next by thread: OT: WHAT'S NEW Robert L. Park Friday 30 Jun 06 Washington, DC
- Index(es):
Relevant Pages
|
