Please teach me about ad

Hi,

as a dairy farmer (500) I’m acutely aware of the need to look at be better all the time, ridiculously not really to do with the food we produce but more how we do it.
inevitably we produce quite a bit of waste, [email protected], reject feed, feed waste from silos etc, we also use a fair bit of electric, milk cooling etc and whilst I think we are probably in the top 25% for efficiency kWh in vs food out etc surely ad is an obvious fit?
so I’d like to understand the detail of the process as well as the economics, so starting at the beginning

I currently separate my slurry as part of a sand bedding separator, does the gas come from the dm portion or the liquid? Do I need to put the solids back in?

we get a beating for generating methane, if we put it through a digester does this reduce the methane emissions in long term storage?

when the gas is burnt it generates co2, what would have been the fate of this without digestion? Presumably it would be emitted as methane then broken down in the atmosphere? I need to be sure I’d be making a reduction not a substitution.

does ad reduce the Dm of the digestate vs the in feed?

what kind of retention time do I need for slurry only?

is any n,p or k carried in the biogas? Ie lost?

how are the economics of such a system now if I use all the heat and power myself and reduce inputs to pay capital and running costs?

thanksfor any input

matt
 

rollestonpark

Member
Arable Farmer
Location
Burton on trent
Last time I heard, the ofgem ROC scheme for payments for electric production finished in 2017.
If that is still the case, without the subsidy payments for the electric production, AD is a none starter.

Think RHI finishes next March, so new installs from then wouldn't get this payment either.
Making it even more of a none starter.

However, methane is a much much worse gas for climate change than CO2.
So burning it in an engine and generating electric and hot water (and CO2) would be much better for climate change, than just letting it go...

Someone else will probably have more info than me, but AD setups can be difficult and unreliable if not done properly.
Also requires a lot of work (and investment) just to keep them going (when they are working).
You'll need (very) deep pockets, from what I can understand.
 

sjt01

Member
Mixed Farmer
Location
North Norfolk
@sjt01 is the man to ask, if you look through the threads he has a blog on his experiences. I think it is difficult to make it stack up without subsidy. Also I understand they don’t run well on just waste
I had not been commenting, hoping that @Chippy would come in. He has a slurry plant installed, and it was discussed in the thread Micro AD for slurry from June 2019. I have seen that type of plant at a cheesemaker in Somerset. As with all AD plants, there were installation and commissioning problems, but these can be overcome.
For AD to work without subsidy, you need:
1. A low cost or zero cost feedstock - dairy slurry, top of the maize clamp, whey from small scale cheesemaking.
2. A good use for the electricity on site, saving buying it in.
3. A good use for the heat from the CHP, such as heating farmhouse, cottages, dairy hot water, grain drying, workshop heating, cheesemaking heat, warm drinking water for cows.
4. An installation that the supplier allows you to modify without restrictions, combined with an owner/operator capable of appropriate use of feedstock, timely maintenance, and the ability to modify the plant when it does not work as required or needs too much maintenance.

We have quite a complex setup, feeding maize, slurry, whey, lucerne (replaced chopped beet), and I have extensively modified the plant. I have the advantage of an engineering background. I am happy to show people around, and talk about how it works. I think if I was in the OP's position, I would design a plant myself. Possibly start with second hand milk silos - insulated stainless tanks that are reasonably priced - as big as can be transported to farm.
 

Cowslip

Member
Mixed Farmer
We have a small ad plant on site but I'm sure we were told not to put slurry from sand cubicle dairy as the sand is very corrosive on the pumps etc. We take slurry from a local dairy but they are loose housed on straw. As one or the above comments ok when working, expensive when it goes wrong.
 
Matt, before you go down that road you need to be speaking to a number of your neighbours and friendly farmers to find out if you could get rid of the digestate over a sensible area. You can't tank liquid very far economically and as you know in our part of the world there is often no shortage of slurry.

You won't want sand anywhere near an AD unit, if it settles out in the main vessel you will have to shut the plant down, open the lid, ventilate it and be going in with shovels or mini loaders to get the stuff out.
 

sjt01

Member
Mixed Farmer
Location
North Norfolk
We have a small ad plant on site but I'm sure we were told not to put slurry from sand cubicle dairy as the sand is very corrosive on the pumps etc. We take slurry from a local dairy but they are loose housed on straw. As one or the above comments ok when working, expensive when it goes wrong.
To cope with the grit in our slurry (not sand beds) and from soil attached to beet, we had our tank designed with a hopper bottom, and flush the grit out once a month. Some operators have to shut down and take the lid off the tank to degrit, which is not a good option. I have spoken to people who ended up with a metre or so of grit after only a year (feeding poultry layer litter).
 

Cowlife

Member
I had not been commenting, hoping that @Chippy would come in. He has a slurry plant installed, and it was discussed in the thread Micro AD for slurry from June 2019. I have seen that type of plant at a cheesemaker in Somerset. As with all AD plants, there were installation and commissioning problems, but these can be overcome.
For AD to work without subsidy, you need:
1. A low cost or zero cost feedstock - dairy slurry, top of the maize clamp, whey from small scale cheesemaking.
2. A good use for the electricity on site, saving buying it in.
3. A good use for the heat from the CHP, such as heating farmhouse, cottages, dairy hot water, grain drying, workshop heating, cheesemaking heat, warm drinking water for cows.
4. An installation that the supplier allows you to modify without restrictions, combined with an owner/operator capable of appropriate use of feedstock, timely maintenance, and the ability to modify the plant when it does not work as required or needs too much maintenance.

We have quite a complex setup, feeding maize, slurry, whey, lucerne (replaced chopped beet), and I have extensively modified the plant. I have the advantage of an engineering background. I am happy to show people around, and talk about how it works. I think if I was in the OP's position, I would design a plant myself. Possibly start with second hand milk silos - insulated stainless tanks that are reasonably priced - as big as can be transported to farm.
Would you have a very rough drawing of such a system?
 
Matt, before you go down that road you need to be speaking to a number of your neighbours and friendly farmers to find out if you could get rid of the digestate over a sensible area. You can't tank liquid very far economically and as you know in our part of the world there is often no shortage of slurry.

You won't want sand anywhere near an AD unit, if it settles out in the main vessel you will have to shut the plant down, open the lid, ventilate it and be going in with shovels or mini loaders to get the stuff out.
aaah, as they say I’m not half as green as I am cabbage looking! In the last yr we’ve installed a sand separator so slurry is sand and free before going to storage, it’s made a few things viable that previously weren’t,this being one of them.

this is exactly where I think ad was wrong, surely if I only put in my cow slurry plus waste silage why do I need land to spread on, 40 tankers and all that nightmare, I take a product thats already here, make something I need out of it and then haul it away exactly as I would have done to the same places I would have done.

I had not been commenting, hoping that @Chippy would come in. He has a slurry plant installed, and it was discussed in the thread Micro AD for slurry from June 2019. I have seen that type of plant at a cheesemaker in Somerset. As with all AD plants, there were installation and commissioning problems, but these can be overcome.
For AD to work without subsidy, you need:
1. A low cost or zero cost feedstock - dairy slurry, top of the maize clamp, whey from small scale cheesemaking.
2. A good use for the electricity on site, saving buying it in.
3. A good use for the heat from the CHP, such as heating farmhouse, cottages, dairy hot water, grain drying, workshop heating, cheesemaking heat, warm drinking water for cows.
4. An installation that the supplier allows you to modify without restrictions, combined with an owner/operator capable of appropriate use of feedstock, timely maintenance, and the ability to modify the plant when it does not work as required or needs too much maintenance.

We have quite a complex setup, feeding maize, slurry, whey, lucerne (replaced chopped beet), and I have extensively modified the plant. I have the advantage of an engineering background. I am happy to show people around, and talk about how it works. I think if I was in the OP's position, I would design a plant myself. Possibly start with second hand milk silos - insulated stainless tanks that are reasonably priced - as big as can be transported to farm.
im very glad you said this, we started on this conversation as there is some benefit to kiln drying our recycled sand before reuse, so much so that it may actually stack up to use diesel to do it, if I can use excess heat to do it then great, but I’m also aware that I can’t go spunk millions on kit to do it, I started looking into it watching a long haired Australian on YouTube making digesters from ibcs, so I completely get where you are coming from
 

Winch Farming

Member
Mixed Farmer
Location
Hampshire
Hi,

as a dairy farmer (500) I’m acutely aware of the need to look at be better all the time, ridiculously not really to do with the food we produce but more how we do it.
inevitably we produce quite a bit of waste, [email protected], reject feed, feed waste from silos etc, we also use a fair bit of electric, milk cooling etc and whilst I think we are probably in the top 25% for efficiency kWh in vs food out etc surely ad is an obvious fit?
so I’d like to understand the detail of the process as well as the economics, so starting at the beginning

I currently separate my slurry as part of a sand bedding separator, does the gas come from the dm portion or the liquid? Do I need to put the solids back in?

we get a beating for generating methane, if we put it through a digester does this reduce the methane emissions in long term storage?

when the gas is burnt it generates co2, what would have been the fate of this without digestion? Presumably it would be emitted as methane then broken down in the atmosphere? I need to be sure I’d be making a reduction not a substitution.

does ad reduce the Dm of the digestate vs the in feed?

what kind of retention time do I need for slurry only?

is any n,p or k carried in the biogas? Ie lost?

how are the economics of such a system now if I use all the heat and power myself and reduce inputs to pay capital and running costs?

thanksfor any input

matt

Aardvark Energy would be a good company to talk to :
Energy | Aardvark Environment Matters (aardvarkem.co.uk)

Good luck
 

sjt01

Member
Mixed Farmer
Location
North Norfolk
How much of the different feedstocks are you using in your system per day? How much ability do you have to vary the proportions of the different feedstocks?
Thanks.
We feed all the slurry we have, all the whey, between 1/2 and 1 tonne of lucerne (more brings H2S levels too high). Then we top up with maize so it has a full hopper overnight. We have a feed algorithm that adjusts feed to maintain gas level at 65-80% fill.
 

sjt01

Member
Mixed Farmer
Location
North Norfolk
With the terrible events at a waste water plant at Avonmouth ,what safe gaurds are followed with AD plants as gas is what their about?
As it is mixed almost 50% with carbon dioxide, the fire extinguisher gas, it is quite difficult to burn at a farm AD. Sewage works tend to have a multi-stage process, where the CO2 comes off earlier and there is a much higher concentration of methane in the later stages. Also, if you are doing gas to grid, you purify it even further and add butane and propane.
On all AD sites, there should be risk assessments and suitable precautions. The bigger risk is hydrogen sulphide which just kills. We all wear monitors for H2S when working near the AD. This will also give indications of flammable gas escape.
The use of H2S monitors on farms should be compulsory when mixing slurry under slatted sheds, or similiar. It would save many deaths.
 

sjt01

Member
Mixed Farmer
Location
North Norfolk
@sjt01 could that plant be shrunk down much further ?

What is the limit on through put for an operational system ?
If it was pure slurry with no straw or pure maize (very short chop) then the wet feed loop could be eliminated which would be much simpler and less prone to failure.

The absolute limit on performance is the tank size, and therefore residence time. We work at about 50 days. Some feedstocks (e.g. pure whey) can be digested in hours but most about 50 days gets the most gas.
 
Presumably when you refer to the wet feed loop you mean the hopper, mixer, macerator and pump?

why do most have several tanks and you only have one? Is that just a capacity thing?

do you have gas scrubbers in there somewhere?

matt
 

sjt01

Member
Mixed Farmer
Location
North Norfolk
Presumably when you refer to the wet feed loop you mean the hopper, mixer, macerator and pump?

why do most have several tanks and you only have one? Is that just a capacity thing?

do you have gas scrubbers in there somewhere?

matt
Yes, we recirculate digester contents to mix with the feed, and push it through the macerator. It works well now but needed a lot of development to get it where it is now.
Some digesters work as a two stage process, with a primary tank where mostly acetogenesis happens - breaking down feed materials into volatile fattty acids, and a second methanogenesis stage where the methane is produced. In reality it is never as clear cut as that. Also, some digesters such as those used by Future Biogas have a main digester, then secondary tanks which are mainly for digestate storage but can capture a small amount of gas. These tanks are not heated unlike the main one.
Other big sites can have several systems running in parallel.
We do not have gas scrubbers, these are normally only used when exporting the gas into the gas grid, quite an expensive excercise. We burn our gas in a CHP to give electricity and heat. Some CHPs require an activated carbon filter to remove hydrogen sulphide, but ours does not. We do add ferric hydroxide and run a small amount of oxygen (0.1 to 0.4%) in the tank to reduce the H2S.
We have gas mixing, so instead of mechanical stirrers in the tank, we take some of the gas, compress it and bubble it up through each of 36 pipes in the base of the tank in turn.
 

AGCO reports sales increase of 43.5% compared to 2020 figures

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Written by Agriland Team from Agriland

The tractor manufacturer AGCO, which consists of brands such as Challenger, Fendt, GSI, Massey Ferguson and Valtra, reported its results for the second quarter ending June 30, 2021.

Net sales for the second quarter were approximately $2.9 billion, an increase of approximately 43.5% compared to the second quarter of 2020.

AEM

Reported net income was $3.73/share for the second quarter of 2021, and adjusted...
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