Is it too late for AD
- Thread starter mawleymoos
- Start date
What system are you looking at?
Mucktogold
Member
- Location
- Suffolk
Duncan Peters
New Member
theirs one on the market of which we are looking hard at to lease, that,s green you can have orange if you want you can have a different colour for the reactor and for the roof its new but very reliable it can use all sorts of waste materials at the front end you don,t have to be strict in what you feed it.
talking about bio-lectric, from what i have seen re the ones that have been in for a while is that they are braking down, three i know of, have stopped working the engineering seams to be at fault and with no help coming from the sellers or the manufacturers to boot because they did not take up the very expensive after sales package, forget the fit for purpose bit or the fact they only been in for nine or ten months, i wonder what trading standards would say
talking about bio-lectric, from what i have seen re the ones that have been in for a while is that they are braking down, three i know of, have stopped working the engineering seams to be at fault and with no help coming from the sellers or the manufacturers to boot because they did not take up the very expensive after sales package, forget the fit for purpose bit or the fact they only been in for nine or ten months, i wonder what trading standards would say
I know the biolectric plants are constantly being adapted for the UK market. We seem to have things over here that the Belgians don't have and so it wasn't until they started getting installed over here that these issues arose. They have changed a bit even from when mine was built late last year. I'm confident the biolectric plants are having less problems as time goes on. I know one thing I needed which know one realised was a soft start thing for the engines because when the motor goes from star to delta it would trip the engine out because of the drop in voltage in one of the phases. They now have soft start as standard
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Duncan Peters
New Member
sound like there getting on top of those things then,....................... a friend who has a client with one, not sure if its a 33 or 44 was told to stop feeding his herd too rich a feed stock as there was an issue with proteins causing high levels of hydrogen sulfide of which the engines can t cope with he still has the issue and is not getting anywhere with the developers, the system needs a gas scrubber and there not go to pay for the upgrade hes well and truly pee'd off and he had his slurry tested three times
- Location
- North Norfolk
What H2S levels are they getting? We were running at 5000 ppm at 0% oxygen. With an air bleed to give us 0.5% oxygen we are around the 100 ppm level which most engines can cope with.
- Location
- Cumbria
There appears to several risks to cover here:
1) Mono digestion does not work long-term without the addition of micro nutrient / enzymes. What is the annual cost of these ?
2) Of course H2S will be to high without some cleaning (should be below 250 ppm). I assume you have primary cleaning in the tank ?
1) Mono digestion does not work long-term without the addition of micro nutrient / enzymes. What is the annual cost of these ?
2) Of course H2S will be to high without some cleaning (should be below 250 ppm). I assume you have primary cleaning in the tank ?
- Location
- North Norfolk
Mixed digestion should work without trace elements but found out to my cost that Ni, Se and Co are necessary. Feeding dairy slurry, maize silage, energy beet and whey.
What do you mean by tank cleaning? Presume you don't mean draining down periodically.
- Location
- Cumbria
No, I mean primary gas cleaning by O2 injection.
Given the CH4 from slurry averages around 50%, by adding O2 to clean down the H2S, the CHP will be operating on fairly low % CH4.
I wonder what the actual % is, and how it affects the CHP efficiency ?
- Location
- North Norfolk
Running around 0.5% oxygen has no noticeable effect on methane %, but let it go above 1% and you do get methane depression. Our feedstock in a single tank CSTR gives us about 54-55% methane, and with oxygen at 0.5% then hydrogen sulphide is normally well below 150 ppm. Rising hydrogen sulphide at constant oxygen concentration is an early indicator of trouble.
- Location
- Cumbria
The amount of O2 required really depends on what level the H2S is at, all you are doing by adding O2 is diluting the overall volume. To run above 250ppm costs - allot, however once methane drops below 50%, then the CHP suffers through poor burning efficiency. (some are better than others)
So, if H2S is high due to the feed-stock, and the addition of O2 in the digester drops the CH4 below 50% (to help reduce the H2S levels), then a secondary cleaner is required, or (in the case of low cost plants) the addition of salts.
On low cost plants adding secondary cleaning can kill the IRR, however on larger plants (250kw+) it is a luxury worth adding, as you will be paid back by reduced CHP maintenance and oil costs.
So, if H2S is high due to the feed-stock, and the addition of O2 in the digester drops the CH4 below 50% (to help reduce the H2S levels), then a secondary cleaner is required, or (in the case of low cost plants) the addition of salts.
On low cost plants adding secondary cleaning can kill the IRR, however on larger plants (250kw+) it is a luxury worth adding, as you will be paid back by reduced CHP maintenance and oil costs.
- Location
- North Norfolk
Its not a dilution effect. At low oxygen levels a population of bugs develops which use the oxygen to convert hydrogen sulphide into elemental sulphur and water. Occasionally we have to clean the sulphur off the digester high level probe in the roof when the wet sulphur shorts it out.
- Location
- Cumbria
I agree with you comment, however the sulphur itself is not such an issue, its the sulphur in the gas that is the problem for the CHP unit, as you correctly say, O2 improves the environment for the bacterial growth, however it also dilutes the % methane content.
Digester Man
Member
A simple air injection fan would not cost much and would surely fix that. Air injection at 0.3% gets my plant down to about 30ppm, without it it would be around 2000 ish
Edit: read this, you don't need the fancyness of this particular one but it explains what a little air can do for your h2s. All you need is a simple blower and a way of measuring the air flow - http://www.allison.co.uk/wp-content/uploads/2013/05/Desulphurisation.pdf
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Digester Man
Member
Here's the little blower on my own plant which blows air into the primary and secondary tanks for desulphurisation, incredibly cheap and simple by biogas standards! It's connected to a little flow meter for each tank so you can inject the correct amount of air - and adjust with some trial and error to find the best % for your application.
Mucktogold
Member
- Location
- Suffolk
Looks much better and cheaper than those scrubber or strippers sold at the ABDA show. No having to buy iron absorption stuff as well, every few months.
- Location
- Cumbria
These fans are pretty much standard on all AD Plants, Scrubbers and Salt is used in addition to this.