By John Davis
There are many ways asphalt storage tanks can be made more environmentally-friendly and energy-efficient through heating, insulation, annual monitoring, prudent construction and management.
Other advances include the use of greener heat transfer fluids in tank heating systems, reduced emissions into the atmosphere and the use of recycled steel for tank construction.
The grounds around asphalt storage tanks have become eco-friendly and more pleasing to the eye. We are seeing grass, shrubs, trees and flowers around asphalt tank farms. But a significant part of becoming more environmentally efficient is what we don’t see. A big part of the process for asphalt storage tanks equates to operational efficiency. Seat of the pants operations are out and careful management is in.
“There are certain things a good terminal operator will do to ensure his operation is as efficient as possible,” says Al Meitl of Asphalt Operating Services, LLC (AOS) in St. Louis.
“Terminals and asphalt storage facilities use energy, and the more energy you conserve, the more profitable you will be,” says Meitl. “We want to know how many BTUs are coming in and how many are going out.”
To manage the BTU count, operators must monitor their tanks and terminals regularly.
“That goes especially for older terminals—they need to be monitored regularly for maintenance and efficiency,” says Meitl.
Meitl and other terminal owners and managers say that an annual check-up for the tanks, both old and new, is a good investment. The check list includes:
- Proper insulation
- Monitoring leaks of all kinds, especially steam leaks
- Monitoring leaking coils or a clogged line
- Proper flow of heat transfer fluid.
A significant aspect of efficiently heating asphalt storage tanks is the selection of heat transfer fluid. There are a range of fluids, from new and used motor oil to mineral oil. Used motor oil may be the least expensive transfer fluid, but it may not do the most efficient job.
“Mineral oil is expensive but it has definite benefits,” says Butch Kirk of International Tank Service, Inc. (ITS) in Lima, Ohio.
“Mineral oil doesn’t break down like other oils or clog up the pipes like some heating oils do. It is an effective transfer fluid and requires fewer BTUs than other oils,” says Kirk.
High efficiency heaters
Many managers think that heating efficiency equates to a greener operation. Efficiency can be accomplished in a number of ways. New high efficiency heaters translate into lower heating costs. They reduce the amount of natural gas or fuel oil that is required to create the heat needed to keep tanks warm. High efficiency heaters also reduce the emissions released to the atmosphere. Switching from a low to high efficiency heater can save 10 percent on fuel costs and lower emissions by 10 percent as well.
If the terminal operation requires steam for rail car unloading, a steam generator using hot oil from the existing high efficiency hot oil heater is another saving. The hot oil is used as the energy source for the steam generator instead of using a boiler, which would require an additional energy source.
High pressure condensate systems
The use of railcars to transport asphalt to terminals and storage facilities requires the use of steam. And that is accomplished by a steam generator or a boiler. Currently, there are more boiler systems than steam generator systems. A steam generator system doesn’t need a boiler or often a boiler operator. Eliminating the boiler operator will add to the cost efficiency of the operation.
A high pressure condensate system, which uses a high pressure condensate with the steam generator or boiler, increases the efficiency of the steam system by 15 to 30 percent.
“Keeping the condensate under pressure does not allow the steam to flash off before re-entering the steam generator or boiler,” says Matt Corry of American Heating Company. “Thus, there is minimal condensate leaving the system as steam in comparison to a standard flash tank condensate system.”
This reduces the make-up water needed, as well as the amount of chemical required for new make-up water when condensate flashes. Also, less energy is needed to increase the temperature of the condensate from ambient to 150 psig pressure.
External exchangers boost asphalt temperatures when loading rail cars. The boost allows the operator to keep the temperature of the larger tanks at lower levels and decrease the heat loss in large tanks. This lowers fuel demand and reduces emissions. External exchangers are also valuable when material must be heated quickly.
Another efficient heating system is electric heating—using direct immersion. With electric heating all the energy is in direct contact with the heated material.
Manufacturers and users of electric heating agree that electric energy is 99 percent efficient. The electric heating elements are inside the sheath or the pipes, which are in direct contact with the liquid asphalt. According to one manufacturer with a national market, electric heating is 99 percent efficient the day you install it and ten years later it is still 99 percent efficient.
“Electric heat is reliable,” says Rick Jay, president of Process Heating Company in Seattle, Washington. “It’s virtually maintenance free—no weekend outages or shutdowns.”
Another positive aspect of electric heat, according to manufacturers, is low density or low watt density. Low watt density means keeping the material at an acceptable low temperature. Coking of the asphalt is unlikely to occur when the sheath temperatures are on the low side.
Another way to maintain a constant heating temperature in the asphalt tank is sufficient use of insulation around the tank. Additional insulation, or the proper amount of insulation at the time of constructing the tank, is a cost effective way to maintain proper tank temperature. Whether mineral wool or fiberglass, tank insulation sometimes gets wet and causes moisture to build up between the insulation and the tank. Wet insulation is like a saturated sponge and can compromise the effectiveness of the insulation.
“If we find moisture between the tank walls and the insulation when making repairs, we pull off the old and install new insulation,” says ITC’s Butch Kirk.
Upgrading the construction of the storage tank can minimize leaks and ensure a longer life. One efficient and safety-related development in the asphalt storage tank industry is secondary containment or double bottoms. Installing a second bottom contains possible leaks from the first bottom. There is usually four inches of sand between the two steel floors.
It’s called “interstitial space,” says Kirk and “resembles an ice cream sandwich.” Some erectors install a screw pipe coupling beneath the first floor to monitor possible leaks.
Another development that further improves asphalt tank farms involves the use of recycled steel. The used steel is re-melted in the kiln. Kirk says “the steel we use for the tank shelf and the roof is all recycled.” He says that the recycled steel meets all ASTM standards.
Clean water discharge
With earthen tanks, or tanks embedded in the earth, the operator must ensure that accumulated water after a rain is clean before it can be discharged into a stream or pond. The accumulated rainwater has to go through an oil/water separator before it can be discharged into the environment. In most operations, the water is tested before it is discharged — another way to ensure an environmentally safe, green operation.
Whether it’s through high-efficiency heaters, heating oils, proper insulation or recycled construction materials, tank owners and managers want to maximize their return on investment.
“Good management, efficiency and greening your operation all lead to profitability,” says Al Meitl. “And maintaining profitability is the bottom line.”