Wanted to get your suggestions for the ideal fat pit size and shape. Our palm oil mill capacity is 30t/h and current fat pit size is 24m x 3m x 2,2m. Current observation is oil is not forming in fat pit, but some is forming in pond #2.
What is the ideal retention time for oil formation? Am i right to suggest a bigger fat pit size?
Is there a certain shape that is better for fat pit?
Looking forward for your inputs or feedbacks
The oil in your Pond#2 could be free oil or cellular oil. Free oil can be recovered at the Fat Pit by static separation with sufficient retention time. Cellular oil cannot be separated by static separation or mechanical separation (sludge centrifuge, decanters, etc). You can read more about this at http://poeb.mpob.gov.my/nature-of-oil-in-sludge-discharge/. Oil accumulation in Cooling Ponds after sometime is unavoidable. The challenge for millers is to eliminate the loss of free oil from the mill.
C.S.Tan is spot on with the recommendation of having two Fat Pits. One for the heavy phase (final discharge) from the Sludge Separators and Decanters and the other for the streams of liquid with free oil, like the Sterilizer Condensate, flushing from the Sand Cyclones, overflows from Crude Oil Tanks, etc. It make no sense to mix the waste sludge strams from the Sludge Separator and Decanters, which usually has less than 1% oil on sample, with the free oil from the other streams, and then try to recover the oil from the mixture in the Fat Pit.
The primary purpose of Fat Pit for the heavy phase sludge from the centrifuges and decanters is to ensure the centrifuges and decanters are not bypass during operation. Presence of free oil in this pit will indicate problems with the machines or operator apathy. I have come across operators running centrifuges minus the nozzles.
The Fat Pit for the other streams is the one from which the mill can easily recovery free oil. Excessive oil in this pit, will alert the mill supervisory staff of operational issues like repeated overflows from tanks, sterilization cycles or FFB quality issues all leading to higher oil losses.
I also concur with C.S.Tan, the monitoring of oil losses should be on Oil/DM or OIl/NOS instead of oil on sample. Excessive dilution will show lower oil loss on sample but the net oil loss will be higher.
Dear Kelvin, apart from further recovery of oil at fat pit, I am of the opinion that the primary function of fat oil pit is to monitor and control “spillages losses”. 1) I wish to define spillages looses as oil lost ex-fat oil pit (dry matter basis) nett off oil lost ex-centrifugal machines and steriliser condensate. 2) Usually oil lost ex-fat pit is higher than weighted average of ex-centrifugal machines and steriliser condensate which indicates that there are other sources of oil losses to fat oil pit. Other sources already pointed out by Mr. Wee. 3) To monitor and control spillages losses, I am of the opinion that 2 separate fat oil pits are needed, one (a)for centrifugal machines discharge and the other for (b) steriliser condensate, drain pipe discharge from various oil tanks, de-sanding cyclones, purifier discharge and other overflow pipes. 4) Fat oil pit for (a) centrifugal machines - under flow sludge has gone through 1,000 g so oil lost ex-fat pit (a) is unlikely to be higher than its inlet. 5) Fat oil pit (b) which received various sources and it’s ex-fat pit oil losses is very likely to be higher than steriliser condensate discharge. This figure will allow management to put various process control in place. 6) As regard to the capacity of fat oil pit, I concur with Mr. Wee’s suggestion. Thanks.