Well I finaly goten serious about going to stage two, a more percicely engineered system, goal is sto store enough methane to use it with out interuption or running out. To do this I am going to compress it into storage tanks.
So lets start with the digester:
1,000L tank, wast goes into the upper side, the digested slurry leaves the bottom (Flow through system) the slurry exits to a final tank befor being discharged to the green house (When it is finaly built)
Inside the tank there is a roll of oxigen barrier pex, it is used to heat the tank.
Gass is drawen off the top lid to the surface (Grade level)
The scrubber:
Stage 1 the gas is bubbles through a soda water mix to remove any contaminants and or organic acids, this now cleaned gas is passed through a colecent filter.
Stage 2 it passes into a refrigerated drier system, 2 feet of 4" white pvc with end caps. Inside the pvs the top half has a coil of 1/4 copper that is packed with copper scrubbies the lower half has nothing, this upper part is the active drying system using a bar fridge compressor.
The condensate is drained via gravity back to the digester tank through a check valve, the raw gas enters just below the center and the dried gas out the top.
Gas seperator:
This is a simply a 100 pound propane tank the gas enters the center, the top goes to the compressor, the lower drain is to purg the co2 (Still trying to figure an automated way to do this)
Compressor:
the gas flows through a silica bed to remove any traces of possible moisture that got through the scrubbing phase. The compressors are a matched set of deep freeze units.
Stage one the dried and filtered gas enters the comressors suction, it then flows out the discharg into an oil seperator*, then to a plate heat exchanger**
the gas then continues to the next compression stage, it to goes through an oil seperator^
then to a larg fan air coil unit for cooling befor proceeding to the storage tanks.
* & ^ The seperated oil flows through a air coil unit to cool down, it then flos through the compressors oil cooling loop befor being dumped into the suction line through a metering tube
** water is circulated through the inter cooler then directed to heat the digester, as is the waste heat from the refrigerated gas drying system
The dried and cooled high pressure gas then discharges through a catylitic oxigen scavenger and routed through 316SS Low carbon pipe to 6 propane tanks (100pounders) stored in a second isolated pit to keep a steady temp.
The Math:
127Cubic feet of ch4 contains 20,268 BTU
To cram 127 cubic feet into a space of 7.05 cubic feet (3 100 pound tanks) we need to bring the pressure up, when we do this we 1 generate heat, and 2 we squeeze out any heat the gass all ready had!
Step one we need to know the pressure P1*V1 =P2*V2 > P1:24.7*V1: 127Cubic feet = V2: 7.05*P2: ?
P2= V1: 127*P1: 24.7 / V2: 7.05 = 264psia (This will be the tank pressure at 20c (68f))
Compression ratio : P2/P1 264.7psiA / 24.7psiA = 10.7 (Idealy for good compressor life we want to keep it to 5 or lower hence the 2 compressors)
heat rise is P1*V1/T1 =P2*V2/T2
T2= P1*V1*T1/P2*V2
T2= T1 528rankin *P1: 24.7psia * V1: 127cf^3 / P2: 264.7 * 7.05 = 887.55rankin - 460 to get F = 427.55 degrees (This is why we need the intercooler as simply to much heat for the compressor valves to handle, by using 2 stages and an inter cooler we lower the heat to a safe level!) This is why we need a final cooling stage befor puting it into the tanks, it will only cool off more as it travels improving the storage system
since for a decent amount for cooking or a shower we need more so for now I just decided to add a second row of tanks, idealy I'd like some 2000L tanks say 3 of them in perallel but for now as a prototype system it will do.
Methane digesters produce the most gas when heated so by recycling the waste leat I can keep the digester at a perfect temp for high production.