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Waste plant oil as fuel
Waste plant oil (WPO) or waste vegetable oil (WVO), is pure plant oil that has already been used for frying food. It can be used to as a heating or cooking fuel or as a fuel for use in piston steam engines, internal combustion engines (diesel), Stirling engines, steam and fuel-powered turbines.
As the ethics of burning perfectly good oil (from human consumable plants) for transportation purposes are questionable, WVO is a good alternative to PPO. It can also be used in animal food or cosmetics.
Pre-filtering and purification
Depending on the purpose the WVO is to be used for, it must be "cleaned" before use. This can be as simple as days to weeks of gravity settling, or it might be pumped through filters. Using cleanable, reusable filters eliminate the waste of replaceable filters.
Pre-filtering when using the oil as a heating or cooking Fuel
The oil can be absorbed using a special but inexpensive absorbent pad. The soaked pad can then be placed in a receptacle and burned. It can be used as cooking fuel in lieu of firewood or charcoal. It can also be used as a Firestarter for bonfires and fireplaces.
See also: Soak and Burn Pad
Pre-filtering when using the oil in diesel engines
Particles (e.g. of food that was cooked in the oil) and water in the WVO will damage a diesel engine—particles will create buildup in the engine, and water in the fuel can destroy the engine. Repairs to the engine can cost more than the price of the vehicle. Therefore WVO must be filtered and water must be removed before it can be used as fuel. Some people allow the oil to stand (e.g. in barrels) for about a week to allow water to separate from the oil; it can then be drained off through a spout at the bottom of the barrel. Standing also allows particles to separate out from the oil and drift to the bottom of the barrel; this is a first step in filtration. One method is to install two drains on the barrel: one that drains from the bottom, to drain off water and particles, and another higher up, to drain off (hopefully) clean oil. That way, clean oil can be drained off without disturbing it and mixing the contaminants back in.
The barrels must be left alone while the oil is standing—jostling will mix some of the water and particles back into the oil.
After standing, the oil is filtered, first through a large filter and then through filters with progressively smaller holes in order to get out small particles that would collect in the engine and damage it. The oil can be filtered multiple times.
The oil can also be heated to boil off water. One way to test whether standing has gotten rid of the water is to heat up frying pan on the stove until it is very hot and a drop of water skitters in the pan, then take a cup of the oil after it has been stood and pour it into the pan—if it boils and spurts and makes a fuss, there is still water in it.
Use in vehicles
Diesel vehicles can be converted to run on vegetable oil. However, vegetable oil is thicker than diesel fuel and may not burn efficiently in the engine, leaving burnt residue in the engine that will eventually break it. Vegetable oil is thinner and less viscous when it is hot. In order for vegetable oil to burn efficiently, it must be hot when it enters the fuel injectors. Conversions employ various strategies to ensure this.
Often, waste cooking oil is discarded by restaurants and other businesses and consumers can obtain them for free. In other cases, they can only be obtained for a sum, yet this sum is often very small. The sum probably depends on the region where it is obtained (as local petrofuel prices dictate the price of biofuels in part) and also depends on the type of straight vegetable oil it was before being used to fry food (ie canola, peanut, ...). Finally, the freshness (freshly used, old, or rancid) will also be another factor determining the price. Since it is a recycled -or rather downcycled- product the price will be much lower than the local market price of the type of SVO it was made from (typically 1/3 or less.
Some restaurants have to pay to have their grease hauled off, and they may be willing to let you take it away for them. Sometimes you'll be required to take all or nothing. Some restaurants are willing to put used oil back into the containers it came in, which makes it convenient for hauling away. Oil is discarded into barrels or large, rectangular grease traps usually located behind the restaurant, often near the dumpsters or the back door of the kitchen.
See also: Negotiating For Waste Vegetable Oil
Determining which oil is good to use
Grease from restaurants that fry red meat is not good to use in a vehicle—it is thick and will form solids, reducing flow and creating clogging. Asian and Mexican restaurants and vegetarian restaurants are better sources because they frequently fry vegetable products. Chicken is also ok. A way to test whether oil is of good quality is to dip a piece of cardboard into it and watch it drip off—is it smooth and runny? Or is it thick and clumpy?
It is important to check to see whether water has gotten into the oil—if the containers were not closed, water may have gotten in.
Rancid oil can not be used for fuel.
- VWO collection service in cities: collection of VWO for burning it at a central electricity production plant