by Espana » Sun Jul 06, 2008 2:43 pm
Sorry for the delay, 10 days here in Spain can be a very long time - perhaps I have caught the manana attitude at last! I have some good news on the re-addition issue and something of a problem on the oil settlement / filtration system that I use for cleaning the initial supply of the wvo. First the good news.
The oil that I collect is passed through a series of settlement tanks, the first one taking out the vast majority of water and the heavier fats plus a small amount of oil. The final tanks (2) reduce the level of lighter fats to a negligible amount. The cleaned oil is then stored in a 1000 litre tank, the oil being drawn of in small quantities and blended as required. The average waste quantity is approx five lts. which after re-settlement over a 3 day period yields 11/2 liters of oil which is reintroduced back into the filtration system. The remaining waste is disposed of at our local re-cycling plant, this consists of approx 1 ltr of water - 21/2 ltrs of fats. It is this remnant of 21/2 ltr of fats that interest me as a source of fuel, as an addition to the blend, for my vapourising pot burner.
First I heat the fat in an old deep fat fryer until the fat liquifies and boils. At this point I reduce the temperature of the fryer until the fat boils at a soft boiland continue to boil for a further 5 minutes to drive off excess water. The hot fat is then drained off via a drain point in the base of the fryer and passed through a cloth filter until finally being collected in a 5 litre heavy duty plastic bottle. The fat is the allowed to cool to ambient room temp.
If I compare this refined fat to a sample of fat straight from the first settlement tank there is a marked difference. The refined fat is smoother and a little lighter in colour. The 'veins' seen in unrefined fat (water) have gone completly. It is this refined fat that I used in tests to determine the amount of fat that I can reintroduce back into the blend, but at what percentage?
The normal blend that I use in the vapourising pot is 74.5% cleaned wvo, 17% synthetic turpentine and 8.5% heating oil. This gives a good clean blue flame on all settings of the carb. It is the blue flame that is crucial to the burning of the blend but other equally important considerations have to be taken into consideration. With all vapourising pot burners the chimney air pressure is vital as this dictates the flow of air into the burner. Too little air - very dirty flame with sticky deposits - too much air and a run away burner situation occurs and if allowed to continue a major fire hazard will result. On the military pot burner which I use as my test rig, the burner was designed for a 4'' dia flue at 6 metre height. On my test rig I get the required air pressure on a 3 metre height. (Sorry for the digression, but the burner set up is very important .) Using the above blend, I mixed in total 5 ltr. of fuel i.e. 3.725 lts of cleaned wvo, .850lts of syn. turps. and .425ltr. of heating oil, this gives me the basic blend which is proven. I then went on to mix percentages of fat to the blend to determine if the burner would continue to burn clean i.e. blue flame. The percentages were 5, 10, 15, 20%
The results are as follows:-
5% - no noticeable difference in burning, at completion of burn deposit in base of pot loose and flakey, easy to clean.
10% - no noticeable difference in burning, still a blue flame, at completion of burn deposit in base of pot loose and flakey.
15% - flame showing sign of yellow at tip, on completion of burn deposit is greasy.
20% - some blue in flame but mainly yellow, also flame appears to be 'lazy', on completion deposit is very greasy and there is a very noticeable amount of soot beggining to form in the pot and burner unit.
As you can see from the above, 10% addition of refined fat (that is 10% of 5lts of initial blend bringing the total amount to 5.5lts) burns in the pot with no noticeable problem. There was the usual smoke on initial lighting which lasted for a period of less than 1 minute, after that, smokless. No smell during burn period. It must be noted that the blend including the addition of fat was burnt shortly after mixing. Now that I have a new blend with the addition of fat, I must look into the situation of settlement as my proposed 'day' tank is in the region of 40lts, approx 40 hours at high setting or 120 hrs on low.
To-day a problem occured in the settlement of fats in the last 2 tanks. The oil in these tanks is normally reasonably clear but this morning (06.07.08)
after pouring 18lts into the system the oil in the 2 tanks in question became 'milky' - contaminated with light fats. Each tank has a drain valve in the base which I regulary use to drain off deposits. The system has been running for some 8 months with no problem but temperatures here for the last 4 days have constantly been in the mid 30s C during the day and 25 C at night and last night we had a weather depression pass over us with a thunder storm. Any ideas out there?