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Waste not, want not: Burning waste oil

October 11, 2010
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Buying waste/used oil heating equipment is a smart move, but it is an investment that requires research and thought.

A steady supply of waste oil is almost as valuable as gold in today's economic and energy-strained environment.

Operators fortunate enough to have either a conjoined quick lube operation or access to a reliable supply of waste oil are in an enviable position considering the constant flow of spent crankcase oil, transmission and hydraulic fluids drained and routinely replaced in motor vehicles.

Multi-purpose resources

For most carwash businesses, the greatest value derived from waste oil heating equipment is frequently based on the low cost supply of hot water that a good used-oil-fired boiler system can provide.

The hot water supplies carwash systems and can also be used to heat inside spaces through baseboard heat exchangers.

For example, in Northern areas it is sometimes used to operate in-pavement de-icing systems.

Burning used oil for heat recovery not only means free heat for the smart operator, but is also an environmentally-sound recycling practice, as well as a perfect way to help avoid encounters with the government's cradle-to-grave liability for the safe handling of waste oil.

With the right equipment, one gallon of waste oil has the same value as a gallon of high priced heating oil — in terms of British Thermal Unit (BTU) heating capacity, as well as replacement cost — and contains the heating capacity equivalent to 1.5 CCF (hundreds of cubic feet) of natural gas.

When compared to liquid propane, which is used in some remote locations for heating purposes, the value of waste oil as a fuel source for heating is close to $2-per-gallon.

Some quick lube operations sell their used oil for around 10-cents-per-gallon, but when it comes time to purchase used oil from recyclers it can cost up to 80-cents or more for a gallon, depending on the area. Therefore, access to freshly generated used oil has a high value.

Feeding the fire

Once an owner has decided to take the plunge and make the investment in equipment, a basic understanding goes a long way toward making the right decision on what type of used-oil heating equipment to purchase.

Used oil contains a range of variables that standard fuel oil furnaces never encounter. These variables include oils of different viscosities, synthetic oils and natural oils in various mixtures and concentrations, with mixtures of transmission and hydraulic fluids mixed in for good measure. Suffice it to say, no two batches of use oil are alike.

The equipment necessary to burn these brews reliably and efficiently must be properly engineered for the challenge, making the first concern for equipment the engineering of the equipment itself.

Some used-oil heating equipment is actually fuel oil equipment converted to burn used oils. The difference will be in how "heavy duty" the equipment is.

For example, weight is a good indicator. In a used-oil furnace, more weight indicates more mass, and may reveal what is called a multi-pass system.

A well-oiled machine

A key indicator of efficiency is what is called stack temperature. This is simply the temperature of the exhaust through the chimney.

The lower the temperature, the greater the heat exchange and the greater the system efficiency.

Higher stack temperatures indicate heat loss and lower efficiency. In used-oil heating systems, stack temperatures can range from 650-1,000 degrees Fahrenheit.

For boiler systems, look for a coil tube boiler as opposed to what is sometimes called a jacketed system. The coil tube design is efficient and effective for providing large amounts of hot water.

The coil tube design is just like it sounds: a thick steel tube wrapped in coil inside the combustion chamber. Water

travels through a steel tube, which forms a coil surrounding the flame, and is heated by simple heat transfer through the steel tube.

One pass through the tube raises the water temperature to a predetermined temperature — typically 120 degrees.

The advantage of a coil tube design is that the water is heated so quickly that the boiler does not need to double as a hot water storage unit, such as with a jacketed cast iron boiler design where water is held in reserve and constantly re-heated if the temperature drops.

For used-oil boilers, the coil tube design is therefore doubly effective: it is fueled by a free fuel source, and provides very efficient operation.

Taking a maintenance moment

When shopping for used-oil equipment, ask about maintenance intervals. A unit should provide a large opening and easy access to all internal surfaces.

The reason that cleaning is important is that a large amount of ash is produced in the combustion of used oils. That might not be so bad if it were not for the fact that this ash build-up reduces the efficiency of the heating equipment.

The ash serves as a temperature insulator, and makes the transfer of heat from the combustion chamber to the water (in the case of a boiler) or air (in the case of a furnace) much more difficult.

Other questions to ask include:

  • Do you have sufficient quantities of used oil to justify the investment? You will generally need access to about 1000 gallons of used-oil per year to have the investment make economic sense.

  • Do you have personnel who can take responsibility for overseeing the operation, including routine cleaning?

  • Like any high performance equipment, the better you take care of it, the better the results will be in terms of reliability, efficiency and long service life.

  • Can you find a reliable organization to service your system and back you up with responsiveness, expertise and parts on short order?

Used-oil heating equipment is not new. Industry estimates are that approximately 100,000 units have been installed since the early 1980s.

Some of those early units, especially well-built and well-maintained, are actually still in service. But the point is that there are enough used-oil heating units in the field that you should easily be able to find a peer with experience in these systems.

Thom Elmire is a service manager for Clean Burn, a manufacturer of used-oil heating equipment. He has over 34 years experience in the HVAC field, and can be contacted at thom@cleanburn.com.