Wildcatting In Wastewater
Record high oil prices are causing manufacturers to seek profitable ways to extract oil from their wastewater
- By Tom Hobson
- Oct 01, 2006
Since last year, when crude oil prices soared and gasoline topped $3 per gallon,
requests for skimmers to be used for recycling oil from plant wash water, municipal
wastewater, machine shop coolant, and contaminated groundwater have increased
25 percent according to one major supplier of oil skimming equipment. Usually,
the generator pays for the oil to be disposed of, but an emerging trend is to
sell the recovered oil to a recycler or burn the oil to lower heating bills.
In the past, manufacturers have been motivated to clean oily wastewater either
by regulatory compliance or by a desire to reduce disposal costs. Now industry
is broadening its narrow focus on pollution control and cost reduction to include
a realization of the profit hidden in its wastewater.
Experts are looking at the increasing demand for oil in Asia and cautioning
that prices could stabilize at $100 per barrel for crude oil, which ultimately
translates into higher energy bills. According to a recent survey of plant and
maintenance managers at manufacturing plants, machine shops, and other industrial
facilities, more plant managers are considering recycling waste oil as a way
to fight rising energy costs. The results show that 78 percent of respondents
are struggling to find ways to reduce plant energy costs, and in the face of
record-high fuel oil prices, 35 percent of respondents said they would consider
burning waste oil to heat their plants.
Now that President George W. Bush has called for new ways for Americans to reduce
their addiction to oil, the findings suggest that companies could be doing more
to reduce winter heating bills. Although 75 percent of the respondents said
their companies skim oil from wastewater, only 8 percent said that their plants
already burn waste oil for heat.
Additionally, the survey uncovered a widely held misperception: 70 percent of
respondents thought U.S Environmental Protection Agency (EPA) regulations for
plants burning their own used oil were more stringent than regulations for waste
oil disposal. In fact, the regulations are more relaxed. EPA supports the onsite
burning of used oil because it prevents oil from entering the watershed and
eliminates the risk of spills during transportation.
Oil skimming uses the difference in specific gravity and surface tension between
oil and water to pick up oil, grease, and other hydrocarbon liquids as a belt
passes through the water. It is a cost-effective means of cleaning industrial
wastewater prior to disposal or discharge.
Oil skimming is the lowest-cost way to remove oil from water. Oil skimmers remove
from one to 40 gallons of oil per hour, and when combined with an oil concentrator,
water in the reclaimed oil can be reduced to as little as 1 percent.
Burning waste oil is an environmentally sound alternative that prevents oil
from entering the watershed, which is why EPA supports it. Technically the EPA
term is "used oil" rather than "waste oil" (a term reserved
for hazardous waste), but most people call it waste oil.
Oil recycling is more common than people think. After it is collected, nearly
89 percent of used motor oil from vehicles is recycled for use as industrial
fuel or for space heating. Because it usually has a thicker viscosity, used
oil possesses more energy than #2 fuel oil. A typical gallon of waste oil contains
163,000 to 240,000 BTU -- more than twice the energy value of LP gas or coal.
Of course, not all oil is collected for recycling, and waste oil finds its way
into sewers, streams, and landfills. One quart of waste oil creates a two-acre
slick on surface water, and a gallon of waste oil contaminates 1 million gallons
of drinking water. Companies that skim their wastewater and recover their oil
for burning or recycling are helping the environment at the same time they are
reclaiming a valuable resource.
Concentrate Oil Before Recycling
Whether the reclaimed oil is to be burned for free heat or sold to a recycler,
it is important to remove as much water as possible. For example, if a salvage
firm wants to recycle the oil as a lubricant, then low water content eliminates
a separate step and reduces refining costs.
Under most operating conditions, a good oil skimmer will pick up oil with less
than 5 percent water. But as surface oil is reduced to a thin layer (1/16 to
1/8 inch thick), more water or coolant may also be picked up along with the
oil. When used in tandem with an oil skimmer, an oil concentrator will solve
this problem by providing virtually complete oil/water separation.
An oil concentrator (also called a decanter) is a secondary reservoir for the
skimmed product that allows removal of water below the surface while oil flows
off the top. Based on the principle of gravity separation, an oil concentrator
uses no electricity, timers, sensors, pumps or other moving parts. Typically
it is mounted on or near the skimmer and receives its discharged oil. For thicker-viscosity
oils and low-temperature applications, a thermostatically controlled heater
may be available as an option.
Reclaimed oil flows from the oil concentrator into a 55-gallon drum or large
storage tank. The 55-gallon drums are economical and easy to handle. If selling
the oil to a recycler, the recycler will remove the drum and leave an empty
drum in its place. If saving the oil to burn for heat in the winter, then many
plant managers store the oil in 250-gallon polypropylene tanks, called totes,
that can be moved with a tow.
Heat Your Plant with Your Wastewater
Waste oils that can be burned for heat include almost any oil up to 50 S.A.E.:
metal cutting oils, lube oil, crankcase oil, transmission and hydraulic fluid,
#1 and #2 diesel fuel, vegetable oils, and grease. After the oil is reclaimed
from the wastewater, the facility needs a properly designed furnace, boiler,
or heater to burn it for free heat. Several manufacturers and distributors may
be found by searching online.
Skimmed oil can be supplemented with used oil from other sources within an industrial
plant or even from outside sources. Companies can accept free waste oil from
other businesses that will be happy to avoid more costly means of disposal.
Yet another source of waste oil is the recycler, who sells it for a fraction
of the cost of fuel oil.
Waste oil furnaces are engineered specifically to burn used oil, but most can
burn standard fuel oil as well. Models range from small units used to heat automotive
service garages to units that produce up to 500,000 BTUs per hour (the EPA limit
without a special permit). A conventional furnace with a combustion chamber
may be converted to a waste oil furnace, or a separate unit may be installed.
In addition, waste oil boilers are used to supply hot water for radiant floor
heating, greenhouses, truck and car washes, and industrial processes.
The conversion/installation is relatively inexpensive, and it pays for itself
in recovered energy savings. In addition, because burning waste oil for heat
is considered recycling, the cost of the heater may qualify the company for
tax credits. Contact your state EPA office for information.
For burning waste oil, there are three main types of equipment. Which type is
used for oil recovered from skimming depends on the particular situation and
the amount of remaining trace water.
Vaporizing-type heaters are small, simple, and inexpensive. Often there is no
thermostat control. Atomizing heaters use compressed air and preheat the oil,
providing more complete, cleaner combustion. combustion incineration system
(CIS) heaters will burn oils that other heaters cannot, including ethylene glycol
and non-flammable liquids like water.
Selecting an Oil Skimmer
Oil skimmers help make oil recycling profitable because they offer a low initial
cost, are easy to install, and operate reliably with minimal maintenance. Oil
sticks to an oil-attracting medium and is removed as the medium is pulled through
wiper blades or scrapers by a motorized drive system. The skimmed product is
discharged through collection trays and drain channels into an external container.
Belt, disk, drum, mop, and tube types each have their advantages, so consult
the manufacturer for selection assistance.
Also, the water collection system must be set up properly in order to get maximum
performance from the skimmer. Because skimming requires the oil or other hydrocarbon
to be floating, the water must be in a reservoir where separation can occur.
The reservoir should have quiet areas and sufficient volume to allow adequate
This article originally appeared in the 10/01/2006 issue of Environmental Protection.