S. Schraeyen, Owens Corning, Beringen, Belgium; and J. VAN LOO, Owens Corning, Ghent, Belgium
Hot storage tanks in petrochemical facilities, terminals and industrial sites globally house valuable and often volatile products, including organic liquids, raw materials, intermediate fuels and byproducts. Properly insulating the base of hot storage tanks helps ensure the energy efficiency and operational economics of these industrial assets, while supporting safety. While insulating a tank's sides and roof is common practice, the base has traditionally been overlooked regarding insulating tanks in North America.
Unlike other parts of the tank (e.g., the walls or roof), the base of a hot storage tank is constantly exposed to hot contents. This sustained exposure means that the base is continually subject to thermal loss and should be considered a prime area to mitigate thermal loss. As companies come under environmental scrutiny and energy prices remain volatile, attention is focusing on opportunities to help improve thermal performance and curb carbon dioxide (CO2) emissions in every area of operations.
Considering the massive size, structure and high temperatures of the contents inside storage tanks, insulating the base area can provide an efficient strategy for reducing thermal loss and, consequently, CO2 emissions. Hot storage tanks come in various shapes and sizes, but the most common structure is typically a vertical, cylindrical storage tank. The gross capacities of these tanks can range from 100 bbl to more than 1.5 MMbbl, while their diameters can range from about 3 m to > 125 m. Industrial materials in hot storage tanks are stored across various temperatures (50°C–550°C) (FIG. 1).
While this article will touch on several benefits of insulating hot tank bases, insulation’s ability to reduce thermal loss from heat transfer generally represents the largest payoff. Concrete is a notoriously poor thermal insulator, and heat lost through the tank base and underlying concrete results in reduced energy efficiency and increased CO2 emissions. Depending on the thickness of the insulation and the temperature of the stored contents, an insulating strategy that uses cellular glass insulation to insulate the tank base may pay for itself in less than a year.
Identifying the optimal insulation thickness to defend against heat loss can help support the operational economics of the hot tank base. In addition to calculating the heat loss of the internal contents through the bottom of the tank, the author’s company can calculate the carbon emissions savings and the reduction in emissions taxes via energy efficiency improvements. Data informing the calculations includes historical increases in energy prices, global inflation data and CO2 allowances. Collectively, this data can allow asset owners to assess the payoff of insulating the tank base over its service life (FIG. 2).
Beyond the economics. Insulating the base makes sense for reasons that go beyond the financial payoff. As noted earlier, insulating the tank’s base reduces energy loss and can also reduce CO2 emissions. Additionally, selecting an impermeable material with high compressive strength to insulate the tank base can help make it easier to control processes, limit viscosity control reduction and help avoid possible solidification of the stored contents. Remarkably stable, cellular glass insulationa offers almost zero deflection, comparable to concrete.
Cellular glass is a 100% closed-cell material that is completely composed of glass. The impermeable nature of glass keeps moisture from migrating up through the ground. It also keeps stored liquids from passing through a breach in the tank into the external environment. Because it is vapor impermeable, cellular glass will not permit moisture to infiltrate the system in vapor form. As tanks are often used for different purposes and under varying cyclical conditions, cellular glass helps to protect the metal base against corrosion caused by water and vapor.
Structural integrity is yet another factor to consider when insulating the tank base. High temperatures and the load of contents inside the tank can stress the underlying concrete. As the cellular glass insulation reduces the heat flow to the concrete, the concrete experiences lower temperatures. Insulating with cellular glass may even reduce the rebar material added to the concrete.
Safety is always the highest priority in petrochemical environments, given the abundance of fuels, stored oils and other agents. Depending on the insulation material used, contents stored inside the tank could present a combustion risk if a leak occurs and volatile contents interact with a flammable insulating material. The composition of cellular glass means it is completely incombustible and unable to serve as a wick for any flammable liquids that might spill near its location.
Building a tank base insulating system. FIG. 3 shows the build-up for two tank base insulating systems—one designed to work for temperatures up to 150°C and the other for systems operating up to 250°C. Higher temperature environments require a multilayer system, although all systems start with the same build-up.
Retrofitting existing assets. While specifying an insulating system during the initial design process is generally advised, retrofitting tank bases is a common practice. There are generally two methods to retrofit the base of a hot tank.
The first method requires cutting a hole into the side of the tank’s steel wall after it is completely emptied and degassed and regulatory protocols have been followed. The hole should be high enough for workers (2 m) and wide enough for a wheelbarrow. After the hole is cut, the bottom of the tank is cleared and prepped to achieve a reasonable flatness before a layer of compacted sand is installed. Furthermore, an interleaving layer of a modified bituminous compound, reinforced with a polyester baseb, is added. Finally, a layer of cellular glass is added, followed by an interleaving layer with an overlap of 10%, topped with lean concrete. At this point, the new tank bottom can be welded in place.
A more common path for retrofitting a tank base relies on lifting the tank with jacks after it is emptied and degassed, following regulatory protocols. Once lifted, the tank can be inspected, and any metallurgical repairs can be made. With this approach, the previous build-up can be used. Depending on the tank’s temperature, a one or multilayer system can be installed, and the assembly can be capped with fine sand. Once these steps are completed, the tank can be lowered on top of the newly insulated tank base.
Takeaway. As energy prices remain volatile and asset owners are under increasing pressure to minimize the footprint of their operations, insulating tank bases can offer a strategy for boosting energy efficiency, curbing CO2 emissions and improving operational economics. HP
NOTES
a FOAMGLAS®
b PITTCOURSE® 100 DPC
STEFFEN SCHRAEYEN is a Technical Product Lead for the Industrial FOAMGLAS® business at Owens Corning. Schraeyen is a certified technical insulation performance check expert and earned a BS degree in chemical engineering from the University of Leuven in Belgium.
JOSEPH VAN LOO is the Director of Technical and Customer Services for the Industrial FOAMGLAS business at Owens Corning. Van Loo has more than 30 yr of experience in industrial insulation and is a member of several insulation working groups in Europe.