Slurry deal with a digester

Kingofgrass

Member
I’ve had my slurry tested etc and I’m clueless on working out what’s it worth to a digester does anyone on here know how to work it out roughly if I pm you the results over ? TIA
 

Kingofgrass

Member
Not very much, probably not worth transport off site. Very worthwhile in an on-site digester though. Our design calculations gave 30 m3 biogas from a tonne of slurry and 200 m3 from a tonne of maize silage.
Thanks for the reply,53m3 it’s come back on the test,transport isn’t an issue as it would be technically going there on return loads.as they deliver digestate free is there a rough figure per m3 of gas =£??
 
In this area, the best you could hope for would be a free swap, with the digester hauling it both roads. Slurry isn't worth much, I have never ever heard of money changing hands

At our plant we take it in for free if we are offered, I wouldn't even pay to transport it
 

Kingofgrass

Member
In this area, the best you could hope for would be a free swap, with the digester hauling it both roads. Slurry isn't worth much, I have never ever heard of money changing hands

At our plant we take it in for free if we are offered, I wouldn't even pay to transport it
I know a farmer getting £25 a ton for his slurry :eek: I was shocked aswel :eek:
 
Northern Ireland is coming down with slurry, if you can accept it during the closed period you are everyone's best friend.

But from a biogas perspective, dairy slurry really isn't worth a lot.
 

sjt01

Member
Mixed Farmer
Location
North Norfolk
Thanks for the reply,53m3 it’s come back on the test,transport isn’t an issue as it would be technically going there on return loads.as they deliver digestate free is there a rough figure per m3 of gas =£??
Dependent on a lot of factors, but for a rule of thumb a cubic metre of gas could yield 1.5 kWh of electricity and 2 kWh of heat in very round numbers. Out of that there is maintenance of digester and CHP before any profit.
 
53m3 sounds incredibly high. Who did the test? Slurry is normally thought to be in the region of 20m3 per ton, quite often less (depends on water content).

If you compare that against a good whole crop silage, which is over 200m3 gas and can be bought for say £40 a ton, it leaves the slurry worth at most £4 a ton. It also takes 10x as much slurry to achieve the same gas output, so you have 10x as much digestate to store and handle. Add the high transport costs for road hauling, and you will see that slurry is pretty worthless unless produced and digested on farm.
 

Kingofgrass

Member
7A898439-BED9-4256-9F5D-FB5C432CF1EF.jpeg
53m3 sounds incredibly high. Who did the test? Slurry is normally thought to be in the region of 20m3 per ton, quite often less (depends on water content).

If you compare that against a good whole crop silage, which is over 200m3 gas and can be bought for say £40 a ton, it leaves the slurry worth at most £4 a ton. It also takes 10x as much slurry to achieve the same gas output, so you have 10x as much digestate to store and handle. Add the high transport costs for road hauling, and you will see that slurry is pretty worthless unless produced and digested on farm.
Sorry 51,not 53 nrm did the test
 

thesilentone

Member
Livestock Farmer
Location
Cumbria
Slurry on average is about 8% DM of which around 80% is VS (80% of 8% - not the overall total)

The slurry VS will produce around 200 M3/CH4/ton

So, 80% of 8% = 6.4% of the overall total is available to produce Biogas

The next calculation is based on the efficiency of the Biogas Plant and level of biodegrading, at best you could expect around 15m3 CH4/ton which will be around 60% of the total Biogas production.

However, lets not undervalue slurry.

Slurry is the No1 feedstock for any biogas plant as it will liquidize the system, add nutrient to feed the bacteria, and carry the nutrient as a fertilizer. So, it should have a value.

Your sample clearly shows a gas production figure of 51 m3/ton, and a DM of 11.6%, this increases the VS to 9.3%, and CH4 to around 20m3/ton/VS if this represents 56.7% of the total Biogas (as per your sample) then my calculations = around 34m3 Biogas/ton.

You gave them a good sample, and if consistent, I would be checking the feed mix and digestibility of you cows diet :)
 

Kingofgrass

Member
Slurry on average is about 8% DM of which around 80% is VS (80% of 8% - not the overall total)

The slurry VS will produce around 200 M3/CH4/ton

So, 80% of 8% = 6.4% of the overall total is available to produce Biogas

The next calculation is based on the efficiency of the Biogas Plant and level of biodegrading, at best you could expect around 15m3 CH4/ton which will be around 60% of the total Biogas production.

However, lets not undervalue slurry.

Slurry is the No1 feedstock for any biogas plant as it will liquidize the system, add nutrient to feed the bacteria, and carry the nutrient as a fertilizer. So, it should have a value.

Your sample clearly shows a gas production figure of 51 m3/ton, and a DM of 11.6%, this increases the VS to 9.3%, and CH4 to around 20m3/ton/VS if this represents 56.7% of the total Biogas (as per your sample) then my calculations = around 34m3 Biogas/ton.

You gave them a good sample, and if consistent, I would be checking the feed mix and digestibility of you cows diet :)
Their on about 70% maize,more than normal,I get what your saying about checking the mix and digestibility of the cows but mucks about perfect coming out the cows,milking well,getting in calf well.as for the sample I scraped up into a pile and took to random samples,parlour washings are diverted into a tank no roofs/gutters go into the lagoon.i do struggle with muck to thick in the summer.thanks for the reply hazard a guess to what’s it worth in £££/ton ? (n) And I’ll see what they offer me
 

thesilentone

Member
Livestock Farmer
Location
Cumbria
Their on about 70% maize,more than normal,I get what your saying about checking the mix and digestibility of the cows but mucks about perfect coming out the cows,milking well,getting in calf well.as for the sample I scraped up into a pile and took to random samples,parlour washings are diverted into a tank no roofs/gutters go into the lagoon.i do struggle with muck to thick in the summer.thanks for the reply hazard a guess to what’s it worth in £££/ton ? (n) And I’ll see what they offer me


This calculation is complex and site specific, however in simple terms the cost should equal the cost v alternative cost of liquefying the plant. This can be achieved by re-circulation, however this system cannot be used indefinitely as the overall TAN level would become to high and alternative liquids would need to be added.

In addition, without slurry, a maize plant ' gets sick ' and the efficiency drops off as the bacteria become lethargic, this can be off-set by adding purchased nutrient and enzymes, for this there is a cost, this can also be used to add value to slurry.

But, the big negative is transport costs, which in most cases are similar to any value the product has.

So, the only alternative (as happens is many other Countries) is a local pipeline network.
 

Jim Pace

Member
All the man asked for was a value. Poor chap has had a lecture on analysis, granted a good lecture and explanation.

Depending on the plants needs and own feed and assuming they are not too tight on lagoon and digester capacity, between £4 and £7 per tonne delivered. Personally I would say nearer £4.
 

thesilentone

Member
Livestock Farmer
Location
Cumbria
All the man asked for was a value. Poor chap has had a lecture on analysis, granted a good lecture and explanation.

Depending on the plants needs and own feed and assuming they are not too tight on lagoon and digester capacity, between £4 and £7 per tonne delivered. Personally I would say nearer £4.


Well Jim Pace, if only life was that simple.

If you are sitting in the middle of Devon, Cornwall, Cumbria etc or NI Slurry for AD has very little to no value as a feed-stock, for obvious reasons.

However, if you are sitting in the middle of Holbeach or Boston, slurry has a value -simple supply and demand. However the other benefits slurry brings to AD (as detailed in what you found as a rather boring 'lecture on analysis' ) means it should have a market value. But, of course unless we know how to arrive at that value, we could do as you suggest and pull a number out of the air that is irrelevant. perhaps that is why cow slurry has little value.

As you may know, if any digester is suffering a fall-off or serious biological breakdown, the first thing any process/commissioning engineer will look for is cow slurry to help quickly establish a healthy culture, however this level of information is maybe to much lecturing.

So I assume what you require for the future from posts is less fact and more ' finger in the air ' information?
 

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