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Digester design and construction info

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saving the world and other fun stuff...

Postby nathan_lamothe » Sun Sep 22, 2002 6:09 pm

Is anyone out there aware of research into the use of anaerobic digesters for crop residue? (straw / chaff).
Some of my grade 12 chemistry students did an interesting project last year looking at a farm energy production system that...well... could be incredible. I'll pass on more if your interested, but at this point the only hitch is how effective anaerobic digestion is with straw and chaff.... could even use high protien feeds etc...

If someone is aware of some numbers etc could you please post.

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H2 from agwaste

Postby Bob » Tue Sep 24, 2002 12:47 pm

Most interesting idea, Nathan. With your permission, I'm taking the liberty of cross-posting your email (with links attached), that fleshes out the idea.

===========================================
Bob,
Here is a simple hypertext outline of the idea I mentioned in the forum post. I had two goals in writing it up this way, to present the idea as simply as possible with as much backup research as possible without being intimidating.. and to experiment with the hypertext medium for expression (something I am working on with the English teacher at the school for a poetry unit, so some of the links are for creating combined experience rather than actual research.)

Anyway, have a look at 'er and let me know what you think -- to start with, if you think it is even remotely feasible, you have my permission to cross post this email to the forum in your discussion.

An experiment in transferring content:

Last spring I, with the assistance of four grade twelve students at Gronlid School in Gronlid Saskatchewan developed the following project for AITC s Youth Vision for Agriculture.

The goal of the project was to reduce greenhouse gas emissions from a hypothetical farm in the Vanscoy area of Saskatchewan.

The Proposal: If the farmer removes all the crop residue along with the crop, and uses it as feedstock for an anaerobic digester,

The digester will produce methane gas which can be decomposed thermally into a high quality carbon black and hydrogen.

The hydrogen can be used to fuel all the farms energy needs safely and cleanly.

The carbon can be sold.

The heat for thermal decomposition can be produced with an inexpensive solar furnace. The sludge from the digester is returned to the field as fertilizer but can have nutrients added as necessary and under ideal conditions before spreading on the fields.

Note: -all nutrient content removed from the field is returned except for the crop seed, which is removed anyway. -there are now three (crop, carbon, hydrogen) marketable commodities with (thus far) independent prices which improves both the economic viability and stability of the farm. As farms develop this process it removes the need for large scale hydrogen
distribution infrastructure: every farm will have a tank of hydrogen for sale -- you can pull into the yard and buy a tank when your car is low just like you can with gas now. Farms immediately surrounding urban centers will likely produce enough H<sub>2</sub> to supply the city, with the only exceptions being larger urban mage cities like LA and New York

-with conservation tillage the carbon sequestration is difficult to quantify. With this proposal it is simple to measure the amount of carbon removed from the atmosphere. Thus carbon credits from the Kyoto agreement will be easy to administer. (This is a fourth possible source of income for the farmer so long as the carbon black is sold only for stable, non combustive uses.)

-remember that unlike other environmentally
friendly practices being looked at for farm diversification (ethanol etc) this is the only one which results in a net negative carbon dioxide production, a self sufficient farm, and a clean fuel source for the nation/world and no nutrient loss to the farm soil (pyrolosis).

-the amount of hydrogen and carbon produced is enormous & much larger than you think, I guarantee it. Try the math yourself but assuming a worst case scenario:

--35 pounds of residue per bushel of crop (lowest number from this site)

--20 bushels per acre yield for the crop (lowest average yield from this site)

--50% of the biomass converted to biogas (85% yield should be possible but this is a
guess?)

--50% of the biogas methane (98% yield should be possible &lost this link& will recover soon)

--50% conversion of the methane to hydrogen and carbon (98% should be possible)

--2.21 pounds to the kilogram

--1 kg hydrogen equal to 1 gallon gasoline (BTU equivalent anyway)

--a 2,000 acre farm, entirely cropped (assumption from AITC competition guidelines)

-- the production of 79,185 kg of Methane (19,796 kg of Hydrogen (equivalent BTU s to 20000 gallons of gasoline), 59,389 kg of Carbon should be possible.

Under ideal conditions (top end of the numbers sourced above) the yields become
84,378 kg CH4, 1,033,630 kg H2, 31,00,891 kg C.

--even given $0.10/kg for these commodities
(very low), they come to between $15,850 and $421,890 in extra revenue for the farm & surely enough to justify research and development into such a venture?

--this extra farm income could be applied to reducing the environmental impact of other areas of the farm & solar & wind generation of electricity would for example become affordable, further freeing resources for other purposes (income).

Yours in Saving the World,

Nathan Lamothe
Sr. Science Teacher
Gronlid Central School

Other interesting related reading:

http://www.ncga.com/research/pdfs/Energy_and_Oil_Consumption_in_Beef_Production.pdf

http://www..eap.mcgill.ca/MagRack/SF/Fall%2095%20G.htm

http://www.iowaagopportunity.org/ethanolmanual/integrat.pdf

http://www.eagle.ca/~gcowan/boron_blast.html


[This message has been edited by Bob (edited 09-24-2002).]

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Postby nathan_lamothe » Tue Sep 24, 2002 3:38 pm

Thought you might like it. Its the sort of thing you wonder if you'd be better to spread because it is so far out of the envelope that it might just stimulate ideas in the right direction... or if you should bottle it up with patents and stuff until you are sure it works... but I figure I can spread it around...If someone else gets rich off it, my daughter will still live in a better world right?

Anyway, everyone I have presented it to has liked the idea, impressed with the possibility, and leaves it at that. My only real uncertainty is the anaerobic digester, though I would want to do some research into the effect on soil quality if all the digestion/rotting/composting occurs remotely (does it affect the fiber content? does it affect the temperature? does it affect the flora and fauna in the soil? etc. etc. etc.)

Any info or input that anyone has on the idea.. inculding extra reading I could do would be much appreciated... The grade twelve students have, with graduation, for the most part left this behinf (though one is building solar furnaces to produce heat / steam / electricity.. which is great)but I am still very interested in developing the idea further and getting it into hands that can do something with it...

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Postby Bob » Tue Sep 24, 2002 4:25 pm

(reply cross-posted from email)

Most interesting. On the surface, it seems like a viable idea. I believe it would be quite feasible to digest straw & chaff (wihout actually having done so). The lignin content could be problematic, but the C/N ratio should be excellent -- at least with the addition of small amounts of N, perhaps. Certainly worth pursuing further, I would think.

(end of cross-posted reply)

I'm still working my way through some of the papers & info -- (I particularly like the INFINITELY LARGE SOLAR FURNACE. I want to make one.)

I'm guessing that the economics of H2 would change somewhat when you factor in the cost/energy of compressing it, but it still might pencil out. Fun!

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Postby nathan_lamothe » Tue Sep 24, 2002 5:44 pm

Bob,

feel free to pass it on to whomever you like...

I thought about the compression costs as well, but figured with the volumes of H2 available, cost would be mediated by scale...If you read through the two pdf files from the DOE on thermal decomposition they include some of the economics near the end... my real fear would be oversupply driving down the price of H2 and high grade C... assuming it works that is...

Also, the easier solar furnace is a mylar lined satalite dish... Ryan (one of my graduated grade twelves) brought in an old starchoice one that he made up Friday... we were ignigting tar paper in under 4 seconds... on a day where the temperaure was 10C at the high and this was after school...

he has one at home with about 2/3's of an eoght foot dish covered in mylar... don't want to put your hand in that apparently...

people think they look dangerous when you start burning stuff with them... but the you step in front to show them your an idiot.. and you block the sun so nothing happens.. tada... instant safety net Image

just don't try it with a dish bigger than you are...

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Nathan

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Postby nathan_lamothe » Tue Sep 24, 2002 5:48 pm

BTW... this could make a lot of farmers rich right? But the way I see it the richest will be the guy who goes on the lecture circuit talking about how he got it all going...

or the farmer who stops farming and starts doing inservices (how can you tell I am a teacher) and seminars on how to set up your own...

Image

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Postby nathan_lamothe » Thu Sep 26, 2002 4:09 pm

Cross Post from an email conversation with Duane C. Johnson [mailto:redrok@redrok.com] of http://www.redrok.com/main.htm fame:

=============================================
You mentioned the use of satelite dishes for the concentrator. These are very easy to make. However they have a problem. The receiver is out in front and moving up in the air. This is not a very convenient place to have the pyrolytic equipment.

Here's my suggestion:
1. Use a satellite dish as the concentrator, but instead
of having it track the sun mount it in a stationary
location facing north and at ground level.
2. Use cheaper heliostat mirrors and reflect light at
the dish.

The beauty of the system is the lowered cost of the
solar collection. Flat mirrors are very cheap to make
and the dish does dos triple or quadruple duty.
You may even be able to use a smaller dish.

There is also a safety aspect. Since the dish is stationary
the hot spot is in a fixed location. Even if the trackers
for the heliostats quits working the hot spot won't move
onto a location where a fire could result. Neat huh!

I make some trackers that can drive the heliostats.
Pretty cheap to!

A technical note, adding more primary mirrors doesn't increase the concentration ratio in the secondary. What happens is each heliostat reflects light onto a different portion of the receiver.

What you do get is greater delivered power at a lower cost.


Duane

--
Home of the $35 LED solar tracker.
http://www.redrok.com/electron.htm#led3
CUL8ER \ \ \ \ \ \\ \ \ Receiver
Powered by\ \ \ \ \ \\ \ \ [*]
Thermonuclear \ \Solar\Energy\from the Sun \ /////|
Energy(the Sun) \ \ \ \ \\ \ / / /\/ / /|
\ \ \ \ \ /\ / \/ / / / |
WA0VBE \ \ \ \ / /\ \/ / / \/ /|
Ziggy \ \ \/ / / \ \/ \/ /\ |
\ / \ \/ / /\ \\ / \ / / |
"Red Rock Energy" === ===\ / \ / \ === \ / ===
Duane C. Johnson, Designer=== === \ \ === / |
1825 Florence St Mirrors,Heliostats,Controls & Mounts|
White Bear Lake, Minnesota \ \ / |
USA 55110-3364 \ \ |
(651)635-5O65 work \ \ / |
(651)426-4766 home \ \ |
(413)556-659O Fax copyright \ / |
(651)583-2O62 Red Rock Energy Site (C)980907 ===\ |
redrok@redrok.com (my primary email: address) \ |
redrok2@hotmail.com (Hotmail address) \ |
duane.johnson@unisys.com (Unisys address) \ | http://www.redrok.com/index.htm (My New Web site) \|
These are my opinions, and not that of Unisys Corp. ===

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Postby nathan_lamothe » Thu Sep 26, 2002 4:10 pm

hmmm cutting and pasting that signature didn't work.... it looks much cooler when it's right...

Sorry Duane.

Nathan Lamothe

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Postby nathan_lamothe » Tue Oct 01, 2002 4:06 pm

Hey Bob,

I think have some students interested in experimenting with an anaerobic digester... and perhaps testing diffrent straws / chaffs etc (easy to come by here in Sakatchewan). How simple can this be?
Could we just get some airtight 5 gallon pails with a spiggot to a baloon to capture gas for the container?
How do we insure anaerobic rather than aerobic processes? Is there something we could use as microbial starter or do we just seal in a candle or something that will consume the oxygen initally?

and all the other simple questions we haven't come up with in 10 minutes today...

Thanks Again,
Nathan

BTW... couple of students at the grade 7 level, and a couple of 12's have expressed interest...

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Postby Bob » Fri Oct 04, 2002 10:32 am

How simple can this be? Could we just get some airtight 5 gallon pails with a spigot to a balloon to capture gas for the container?

How about using some 2-liter plastic soda bottles? Put them in a heated water bath -- cheap styrofoam cooler filled with water with aquarium heater set to 95degF. At the simplest, slip uninflated balloons over the neck. But, better,

How do we insure anaerobic rather than aerobic processes?

Don't worry about it. Fill bottles with water, any available O2 will be soon depleted via microbial action.

Is there something we could use as microbial starter

Yes. Cow manure. Get it as warm & fresh as possible -- methanogens are quite fragile, easily killed. (I can just hear your students on their field trip now... :-)

or do we just seal in a candle or something that will consume the oxygen initally?

Shouldn't be necessary -- as noted above.

BTW... couple of students at the grade 7 level, and a couple of 12's have expressed interest...

That's great.

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Postby Bob » Fri Oct 04, 2002 11:21 am

What are your goals, Nathan? I can think of so many possibilities, ranging from basic interest in anaerobic digestion in general, to rigorous testing & measurement of specific feedstocks, feedrates (retention times), design geometry (e.g. single vs. 2-stage) etc.

If you are specifically interested in answering the question posed in your initial post above -- i.e. what quantity of CH4 can be extracted from a given quantity of a specific feedstock, it would take more than the simple bottle & balloon design. On the other hand, that could still be a good starting place, then modify, improve on and add to the design as basic information & understanding is gained.

When you figure out what you want to do, I'd be glad to participate -- or at least offer my $0.02, fwiw.

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Postby nathan_lamothe » Sat Oct 05, 2002 5:24 pm

Bob,

yah, I want to answer all the questions, but I am not independently wealthy, so for right now I am getting kids to do some of the experimenting with the very basics as part of the science courses I am teaching.

However, I am becomming obssesed, an will likely make an attempt at doing some involved experimentation into the feasibility of the digestion process for different feedsstocks over the next couple years...so any ideas you have, whenever you have them, and about whatever you happen to think of, I am interested.

BTW, for the overall process to work, the closer to pure the methane the better, and the two most problematic gases in biogas are H2S and CO2 right?... I just found some stuff on the DOE pages on thermal decomposition of H2S... more hydrogen, and elemental sufur...

(And if that tells you anything it should be that I have given up on finding info on the vegetation as feedstock and will have to rely on experimentation...fun)

Thanks again, and I am starting to refer people here rather than trying to retype everything in email questions...so maybe some of em'll post?

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Postby Bob » Sun Oct 06, 2002 7:41 am

OK, it sounds like what you want to do is to determine the ultimate digestibility of your feedstock -- leaving aside digester design questions for now.

That would lend itself to a batch feed process, where you take a measured quantity (& analysis) of feedstock, put it in your reactor (e.g. 2 liter bottle?) with some inoculum, then measure the quantity and quality of gas produced over the entire digestion period. After gas production has stopped, then again measure and analyze the remaining sludge to determine VS reduction.

Plot it out on a graph with time (days) on the X-axis, and volume of biogas & methane on the Y-axis. A simple way to remove CO2 from the biogas is to bubble it through some limewater (CaCO3 solution). If you measure the volume of gas both before & after, you can see how much is methane (or at least how much is not CO2). To remove H2S, filter the gas through some steel wool (e.g. a length of 2" PVC pipe packed with it). With your feedstocks (i.e. close to ideal C/N ratio) the biogas should be virtually all CO2 and CH4, with only trace amounts of other gases (e.g. H2S, H2).

WRT costs, the experimental setup itself (i.e. the reactors, & tubing, etc.) could be virtually nil. The more significant costs would be the test & measurement apparatus. Do you have, or have access to, gas analysis equipment? COD reactor?

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Postby Bob » Sun Oct 06, 2002 8:27 am

Further thoughts...

1. WRT limewater, I think that should have been Ca(OH)2 above, right?

2. I wouldn't be surprised if the digestibility of wheat straw & chaff has been already well researched. I know that bagasse (sugar cane residue), rice straw and other agricultural "waste" fibers are favored feedstocks in certain areas of the world. (But, even so, it might still be a great student project.)

3. You could have different teams of students each set up reactors, varying things like temperature, C/N ratio, effect of different amounts of buffering, etc. and compare the different shapes of the curves at project's end. Have them compete with each other to see whose design produced the most methane the soonest.

4. Back to the "big picture" -- re feasibility of individual farmers producing marketable hydrogen & carbon black, after reading some of the papers you provided links to above, it appears that the capital investment would need to be in the $million$. I wonder if the technology could either be scaled down so as to be feasible for smaller family farms, or perhaps it would lend itself to operation by a local co-op. The home-built solar furnace idea is fascinating. I wonder what it would take to build the prototype described in the "aerosol method" paper, and actually produce H2 & C from the CH4 generated. That would be another great fun follow-up experiment.

[This message has been edited by Bob (edited 10-06-2002).]

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Postby nathan_lamothe » Sun Oct 06, 2002 9:17 am

Bob,

I have access to a high school chem lab that was complete 20 years ago... lime water and glassware is no problem, but gas analysis and COD reactor... I'm not even sure what I'd be looking for.

I have wondered about the co-op aspect to managing the capital costs, and think it may be the best way, but I am still trying to get my head around the volumes we are talking about here. I do not see anything in the technologys presented that is not easily scaled up or down, with gas compression and transportation of feedstock, residue etc. seeming to be the largest operating costs?

Capital outlay for the complete system will be large no matter what scale you work with, but if my estimates for saleable output are even somewhat reasonable, almost any capital invested could be recovered?

The only problem I see with the co-op approach is the added cost of employees... but that may be more than mitigated by the possibility of having trained technichians operating the system to ensure maximum efficiancy?

I have no experience with these sorts of large scale questions, so it is all by guess and by golly for me...

BTW 2 things on the solar furnace idea... first, the NREL facility in the paper is god-like compared to what we'd actually need... it is overkill even for the experiment they were doing.... we'd never manage that... but..

The other TD paper lowers the temerature requirement significantly, so the level of solar furnace required becomes manageable. and the excess heat from the solar furnace, or cooling the exhaust (H2) from the TD unit is used to heat the farmhouse/shop/Anaerobic Digester...

Second, if you are really interested in the solar furnace stuff, Duane's site is the starting place... www.redrok.com/main.htm

Also, here is the best resource I've found on various feedstocks for AD http://www.ad-nett.org/assets/images/Feednw1.pdf

I think I'm gonna email them...see what they think....maybe if enough people have at least read about the idea...

:wink:

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Postby Bob » Mon Oct 07, 2002 9:24 am

... water and glassware is no problem, but gas analysis and COD reactor... I'm not even sure what I'd be looking for.

Well, I guess quantity of biogas and methane for starters. Probably the easiest way to do that would be to bubble it up under an inverted bottle with markings on it (or graduated cylinder?) placed in another water-filled container & measure the displaced volume as it rises. Measuring before & after bubbling through limewater could give the % of methane. Another idea might be to burn the biogas inside a home made "calorimeter" where you could measure the amount of heat generated.

Then, to determine degree of VS (volatile solid) reduction, measure oxygen demand of feedstock, and again, of remaining material after digestion. BOD (Biochemical oxygen demand) is pretty standard in the wastewater treatment industry, but is more difficult & time consuming. COD (chemical oxygen demand) can be done in 2 hrs using kits from, e.g., Hach Co.. You probably already have a lab oven & furnace, for determining moisure content (weigh sample, heat it to 105degC & weigh again) & VS content (heat to 600degC & weigh). IMO, delta-COD can tell you everything BOD can, as what you are measuring is the difference between before & after a biochemical process.

I do not see anything in the technologys presented that is not easily scaled up or down

I'd like to build a lab scale prototype of this:
Image


mounted at the focal point of one of those home made solar concentrators.

[This message has been edited by Bob (fixed image link 10-07-2002).]
Last edited by Bob on Fri Feb 17, 2006 3:46 pm, edited 3 times in total.

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Postby nathan_lamothe » Mon Oct 07, 2002 6:55 pm

Bob,

When I said I wasn't sure what I'd be looking for I meant what gas analysis equipment of COD test equipment would look like, rather than what I should be testing...but thanks.

Someday I'll read COD and not have to think for 10 minutes to remember what it means...

and the picture isn't loading here? a lab scale prototype of what?

thanks for the Hach link... I read the stuff on COD etc... very nice summary...

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Postby nathan_lamothe » Mon Oct 07, 2002 7:06 pm

Ok so I lied....

I am still reading the COD & BOD stuff... more than a summary huh?

Nathan

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Postby Bob » Tue Oct 08, 2002 7:02 am

Hmmm... I don't know why the image wouldn't display, Nathan. It works ok on mine. Maybe try reloading the page. (I did have to edit the image, so maybe you loaded the page before it was fixed and the broken version is in your cache). Anyway, in case you can't see it, it is Figure 4. Schematic of Solar-thermal Aerosol Flow Reactor, from the THERMAL DISSOCIATION OF METHANE USING A SOLAR COUPLED AEROSOL FLOW REACTOR paper.

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Postby nathan_lamothe » Mon Oct 14, 2002 9:39 am

Bob,

Anaerobic digestion is an endothermic process?

Nathan


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