Calculator questions

Digester design and construction info

Moderator: Bob

Post Reply
jacquay
Posts: 7
Joined: Mon Oct 17, 2005 2:53 pm
Location: Lethbridge, Alberta, Canada

Calculator questions

Post by jacquay » Mon Oct 17, 2005 2:57 pm

Hi Bob,

I am involved with Agriculture and Agri-Food Canada and we are starting to research methane production from anaerobic digestion for use in greenhouse gas calculator with mitigation. I am using your calculator to compare with our estimates here and see where North American communities compare. We are based on average farms with assorted livestock and crops.

Our calculator uses the Intergovernmental Panel on Climate Change (IPCC) guidelines. Do your base equations also make use international guidelines?

Can you tell me how you came upon the slurry concentration numbers from the amount of manure? Or can you share any of the other of the equations?

Also, can share your references that were used to come upon these estimates?

I can send you my direct email, if that would be better.

Thank you,
Jacquay :D

User avatar
nathan_lamothe
Posts: 58
Joined: Sat Sep 21, 2002 11:01 pm
Location: Joussard, Alberta, Canada

Post by nathan_lamothe » Wed Oct 26, 2005 4:17 pm

Jacquay,

Posting this mostly just so it pings for Bob. He's had some problems with the site lately and I'm not sure how often he's letting it pull him away from paying work...

If I recall correctly the calculator is based on numbers from a book he has... he's mentioned it before in this forum, but it was a couple years ago I think and I can't find the reference.

I'll see what I can rustle up.

Nathan

jacquay
Posts: 7
Joined: Mon Oct 17, 2005 2:53 pm
Location: Lethbridge, Alberta, Canada

Post by jacquay » Thu Oct 27, 2005 8:18 am

Nathan,

Thanks for the help! If you give me a range of years I can look in, I can search it out. But if you find that would be great!

Thanks again,
Jacquay

User avatar
Bob
Posts: 631
Joined: Tue Jul 03, 2001 11:01 pm
Location: Willow, Alaska USA
Contact:

Post by Bob » Fri Oct 28, 2005 8:30 am

Hi Jacquay,

Thanks for the question. (And thanks for the ping, Nathan.) Sorry about taking so long to respond. I was waiting until I had time to give a proper answer, then let it slip away.

Anyway, you are correct. The gas production calculations are (or were originally -- see below) based on data and methodology given in Other Homes and Garbage by Leckie, Masters, Whitehouse and Young. The composition data is still from that source (the book cites Anaerobic Digestion of Solid Wastes (Klein) and Methane Digesteres for Fuel Gas and Fertilizer (Merrill and Fry). However, the gas production calculations have since been revised, based on work done on two-phase digestion by Sam Ghosh. They now consist of a simple lookup based on data published in two papers: Improved Sludge Gasification by Two-Phase Anaerobic Digestion, Ghosh, S. 1987, and Pilot-Scale demonstration of Two-Phase Anaerobic Digestion of Activated Sludge, Ghosh, S. 1990.
Our calculator uses the Intergovernmental Panel on Climate Change (IPCC) guidelines. Do your base equations also make use international guidelines?
No. I am not familiar with them, but would be most interested in knowing more. My calculator has been intended only as a preliminary sizing tool for end users. However, it is somewhat aged (like the rest of this site) and could use an update.
Can you tell me how you came upon the slurry concentration numbers from the amount of manure?
The slurry concentration is adjusted (by adding water, as necessary) to provide an HRT of 3 days, and organic loading rate of 18.5 kg VS/m3-d in the acid-phase reactor, and an HRT of 9 days and loading rate of 6.2 kg VS/m3-d in the methane-phase reactor. These retention times and loading rates were selected as a best compromise between gas yield and tank size and cost.

jacquay
Posts: 7
Joined: Mon Oct 17, 2005 2:53 pm
Location: Lethbridge, Alberta, Canada

Post by jacquay » Fri Oct 28, 2005 9:56 am

Hi Bob,

Thanks for the reply, your information is looking helpful. I am looking into your references, it seems that I am using some of them already!

For the slurry concentrations (dilutions): The loading rates and the HRT's are pretty standard (in literature there are alot of comparisions) but dilution ratios are harder to find. Do you come upon these numbers in the literature or are these from your own experiance?

Also Another question: Do you find that most farms store their manure first in another area, or do they directly dilute it and add it to the digester fresh from the fields or pits? in other words, does the Manure normally need to be stored between land pickup and loading to the digester?

Thank you for your help,
Jacquay

User avatar
Bob
Posts: 631
Joined: Tue Jul 03, 2001 11:01 pm
Location: Willow, Alaska USA
Contact:

Post by Bob » Sun Oct 30, 2005 4:35 pm

For the slurry concentrations (dilutions): ... dilution ratios are harder to find. Do you come upon these numbers in the literature or are these from your own experiance?
Actually both. I assume that the moisture content numbers given in the literature (including values given in the sources referenced above and built into the calculations) are average values for fresh manure as it leaves the animal (assuming the animal in question does not have diarrhea on the day the sample was taken, etc :-)).

But in actual practice, moisture content has far more to do with collection method, i.e. whether it is dry scraped from the barn floor, flushed into a gutter with a water hose, or dry cow pies collected from a pasture by rural peasants, etc. Same thing with human feces. If pumped from a water flush toilet (even a < 1 liter/flush model) there is no need to add additional water for dilution. But if collected from a dry toilet with urine separation, there is.

So, basically the goal has been to add water as required to make a slurry that is easily pourable and pumpable without clogging pumps and pipes. Along that line, I have come across literature sources that describe a 6-8% slurry as being the consistency of thick cream.

That said, I have been working (so far only on paper) on a high-solids design that uses digester supernatant as dilutant to make a pumpable slurry. This has several advantages, including smaller tank size (obviously), but also lower and simpler heating requirements (less volume exchanged), and pre-mixing of bacteria with incoming raw waste in a fixed media environment.
Also Another question: Do you find that most farms store their manure first in another area, or do they directly dilute it and add it to the digester fresh from the fields or pits? in other words, does the Manure normally need to be stored between land pickup and loading to the digester?
I don't know the answer to that. My own direct experience is limited to smaller scale systems, but reviewing sources such as USEPA agSTAR program and looking through their demonstration projects I find various systems in use, and don't know if one method is predominant. I would guess that it depends on size of herd, and other site specific conditions.

jacquay
Posts: 7
Joined: Mon Oct 17, 2005 2:53 pm
Location: Lethbridge, Alberta, Canada

Post by jacquay » Mon Oct 31, 2005 9:44 am

Hi Bob,

Usefull info, thanks. I am using large and small sources for manure that include large cattle farms and crop farms with few animals that reuse the sludge for fertilizer. So I will give the agstar a try for manure handling procedures.

Your new system sounds interesting, will it have to use more power for mixing overall then? Do your other designs not have a continous mixing reactor?
Is this a batch process?
and pre-mixing of bacteria with incoming raw waste in a fixed media environment.

or are you refering to the fixed composition?

anyway, thanks again for your input and sorry to take you away from your work.

jacquay
Posts: 7
Joined: Mon Oct 17, 2005 2:53 pm
Location: Lethbridge, Alberta, Canada

Post by jacquay » Mon Oct 31, 2005 10:06 am

Is the 6-8% slurry a % of total solids or % volitile solids?
in manure? :D

User avatar
Bob
Posts: 631
Joined: Tue Jul 03, 2001 11:01 pm
Location: Willow, Alaska USA
Contact:

Post by Bob » Tue Nov 01, 2005 11:52 am

Your new system sounds interesting, will it have to use more power for mixing overall then?
No. Mixing is entirely passive, using rising gas bubbles to recirculate slurry.
Do your other designs not have a continous mixing reactor?
If you mean an open tank w/ free-swimming bacteria (vs plug flow) yes. But if you mean some form of continuous mechanical mixing process, no.
Is this a batch process?
No. It is continuous feed.
So I will give the agstar a try for manure handling procedures.
Check out the "farmware" design software and associated handbook in particular. As I recall, it has inputs for type of manure collection methods
...anyway, thanks again for your input and sorry to take you away from your work.
No problem. I appreciate the interest. :-) (Actually, I am currently traveling, in Florida helping my elderly parents pack and move to a new home, then off to Costa Rica for 2 weeks, checking in here as I can find internet access. It might be spotty after this week.)
Is the 6-8% slurry a % of total solids or % volitile solids?
Total solids. When I get back home, I'll post a copy of the composition data tables (including moisture content, TS and VS) for the various feedstocks included in the calculator.

jacquay
Posts: 7
Joined: Mon Oct 17, 2005 2:53 pm
Location: Lethbridge, Alberta, Canada

Post by jacquay » Wed Nov 09, 2005 1:29 pm

Total solids. When I get back home, I'll post a copy of the composition data tables (including moisture content, TS and VS) for the various feedstocks included in the calculator.
That sounds great; thanks. :D

If I get a chance somtime soon I will post something about the equations I am working on and the international guidlines.

Jacquay

User avatar
Bob
Posts: 631
Joined: Tue Jul 03, 2001 11:01 pm
Location: Willow, Alaska USA
Contact:

Post by Bob » Thu Nov 24, 2005 12:09 pm

I'm back. It was a great trip, but hard to come back to freezing temperatures and a foot of new snow on the ground. Here's the waste composition data table used in the calculator, as promised. (adapted from page 196 of Other Homes and Garbage)

Image

jacquay
Posts: 7
Joined: Mon Oct 17, 2005 2:53 pm
Location: Lethbridge, Alberta, Canada

Post by jacquay » Thu Nov 24, 2005 1:58 pm

Thanks for you help bob,

I am off to montreal for a few weeks so I wont have a chance to look at it till I get back.

thanks again,
Jacquay

Post Reply