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Discussion in 'Renewable Energy' started by Chippy, Apr 12, 2018.
There is your problem
Yeh I suspected temp would be a main reason. Will get oil boiler hooked up
Out of interest how bad is it to put formalin in the slats which will eventually enter the digester? Im talking 40 litres/week into a slatted tank that’s got 150,000 gallon of slurry in roughly ?
Great to hear from someone with experience, some questions.:
1) Was gas mixing part of the original design?
2) Is it a landia system?
3) What are the annual maintenance costs?
4) What is the annual energy consumption?
When you say Gas mixing has worked well for us for 9 years what do you actually mean ?
Chippy, before you do anything, get rid of the floating layer, it is pointless re-energising the bugs until this is done.
Possible inhibiting limits for formaldehyde are 100-400 mg/ltr, toxic around 500-100 mg/ltr.
Given your volumes of slurry, it should be OK... BUT !!!!!! how can you guarantee it is mixed perfectly ?
It is the original Greenfinch design
This is the base of the tank being poured. When the concrete had gone off, the pipes were trimmed to just above the concrete level.
This is maintenance records since installation in 2009 (I increased pulley size so they no longer eat Vee belts)
Apart from the Mikuni oiling pump, spares costs were trivial (<£20 a time), and that pump just needed cleaning up so the old one is now a spare.
Running costs - normally run for gas mixing about 20 minutes in the hour, but also use the compressed biogas as gas lift in the heating circuit so run 60 mins in the hour when heating. Compressor motor is 3 kW drawing about 6 A, rotary valve motor 0.14 kW drawing 0.5A all three phase
I visited the Ludlow Plant in 2009, which was working well on food-waste (from Somerset I believe). My only real concern for this type of mixing is when slow digested material is added such as grass and chopped straw and the risks of a floating layer.
What are your views.
We feed 30-50% slurry from cubicles bedded with straw, its generally chopped better than in the photo. The only time we had issues with a floating mat was at startup when the total solids level was too low. We started on dirty water with added slurry, but this did not work so had 15 tanker loads from the local Anglian Water AD Monsal stage,
What temp do you operate at ?
Normally 39-41°C, although when the pipes froze up recently we dropped to 33. It did not appear to hit gas production as much as I had feared, down about 1/3 but hard to estimate as we stopped feeding slurry when it was frozen.
Operating temp and HRT have a bearing on the ' speed of incorporation ' into the digestion process. Shock-loading (cold feed-stock) also has an impact on gas production. Prior to feeding, I think pre-heated well homogenised feed-stock is the best solution, and contributor to fast incorporation. But for this, the technology requires economy of scale.
This also reduces parasitic loading for the process agitators.