When a Bio-Gas Digester Bag is Fully inflated the pressure will be 0.33 Bar =33Kpa (4 psi), anything over that pressure will automatically be released the biogas into the Atmosphere by the Digesters Low pressure relief Valve, fitting one obviously will stop any damage/bursting of the digester Bag.
For all premises & facilities with an old Cave-Man Off-Grid Chemical Septic Tank System looking to better contribute towards slowing down Climate Change, it's a Lot Smarter to Re-plumb the existing Black-Water (sewerage), Grey-Water and ALL Organic Material into a Bio-Digester, that in turn produces Clean Green Bio-Gas straight from the digester bag, instead of Releasing all the Methane into the Atmosphere !
Only when the Top of the Digester-bag or Bio-Gas-bag is Full & Not being used, it will be automatically & slowly released into the Atmosphere by the system's Low pressure relief valve, that is a standard inbuilt safety feature on all our Digesters, or they would eventually burst.
If you find you are producing more Bio-Gas than your consuming, that opens up a Great opportunity to Start Storing excess bio-gas in another Storage Bag or Start Compressing it into LPG gas tanks for consuming when there may be times in Cold Weather when Digestion Slows, commonly during Colder periods if you don't have or want to use a Heater to warm the Digester liquid, we suggest you invest in a second Bio-Gas storage Bag & simply Plumb them together, there is virtually no limit to the size of a Bio-Gas Storage bag, as they come in large sizes that fill the inside a 6mt (20') Shipping Container, and even Larger for Industrial applications, where they are Commonly housed is very Large Digester Housings.
It is a lot smarter to secure longer term supply of bio-gas, by Compressing Bio-Gas into LPG Gas bottles!
As once the digester bladder is full, the gas would otherwise be released & wasted, due to the low pressure release valve automatically venting the bio-gas (Methane) into the atmosphere to stop the bladder/bag from being damaged.
Compressing your Bio-Gas enables you to better manage & secure your resource’s, and get you through times when you may not have enough organic matter to produce bio-gas.
Read this document on Bottling Biogas into Cylinders as Sustainable Energy Source to Mitigate Climate Cycling.
The process of compressing Bio-Gas/methane (Natural Gas) is relatively simple and can be done by a competent handy person, all that is needed is an Hi-Pressure Air compressor and the knowledge from the above Document.
These steps should be followed for your Safety;
- If your LPG Tank is Totally Empty, e.g. No gas escaping when the tap is opened, the tank will have Air in it.
- To remove the Air, connect the Hose from the Bio-gas Bag too the compressor.
- Start the Compressor for a minute or two, so there is approx 20~30 psi in the Tank, Stop the Compressor.
- Disconnect the filler hose, take the Tank Outside & open the Tap & let Gas out for 10~15 seconds, that will purge trapped Air.
- Reconnect, Fill up the Tank to about 50psi, and repeat Step 4 for about 30 seconds, now there should only be Gas in the Tank.
- Reconnect and Fill the Tank to 350 Psi or less, now you have Compressed Bio-gas when needed.
If you are looking to Compress Bio-Gas (CNG) to operate a Generator or Vehicle, you can use a Standard Air Compressor, but they are limited to Low pressure, it is better to Purchase a New Compressor capable of 1'250kpa (180psi) Pressure, we can supply this Hi-pressure Air Compressor for approx. $450 inc. Delivery, you can Order Here.
DANGER: LPG bottles are NOT recommended to hold above 25 Bar or 2'585Kpa or 375 Psi. So, using this type of Air Compressor, you need to make sure you DON'T let the Pressure go above 25 Bar pressure!
IMPORTANT WARNING: Anything above 25 Bar pressure becomes VERY Dangerous, especially with Old LPG Bottles, even though LPG Bottles have a 2585 Kpa or 375 Psi SAFTY Relief Valve, it may/will blow-out & decanter Gas !
Pre-filtering: If your Digester system does Not yet have any Bio-Gas Filtering, we recommend purchase Three 25cm (10") Water Filter housings, firmly pack the First housing with Steel Wool (H2S scrubber, removes the Sulphur), the Second housing fill with Carbon & the 3rd housing use Silica Gel (to remove Moisture), then you will be Compressing Clean & Dry Bio-Gas.
EXTREAM CARE: You should also make sure the Compressor does NOT Overheat, and that there is NO Air in the LPG Tank or Lines during Compressing as it can be Very Dangerous, as a Spark can cause an Explosion !
The manufacturers recommend NOT using this Air Compressor if the Temperature exceeds 60°C, and they recommend letting the Compressor Cool down for 30 minutes before proceeding.
As this Compressor is Not recommend for Bio-Gas, You should apply even MORE CAUSION if compressing Bio-Gas. We recommend installing a Flash-back arrestor before the compressor, and a lower operating Temperature can be assisted by using a larger volume of Cold Water that is Pumped through the Cylinder head, and possibly putting ICE in the Water if the Temperature rises too quickly.
As previously mentioned, to avoid Air Entering a LPG Tank that has been totally Emptied, you could reverse connect a compress to the Tank to draw as much Air out of the Tank as possible, Closing the Relief valve before stopping the compressor, or start filling the Tank for a few Minutes with Bio-gas, then remove it from the Compressor, take it OUTSIDE and Open the Relief Valve & let Gas escape for approx. 5 seconds, then go back Pressurise more Bio-gas & Repeat again for approx. 10 seconds, that should totally release any Air in the Tank.
If confident you have removed all the Air from the tank, now Fill up the Tank to no more than 350psi (as mentioned above), for an older Tank that have Not been tested, we recommend using a lot Lower Pressure for better Safety!
Aluminium & Galvanised LPG Tanks are the best to use, as they don't corrode like chipped painted Steel Tanks !