Controlling fluid viscosity in tank heating applications with electric heatersMay 03, 2019
Maintaining fluids at precisely controlled temperatures is a critical task in a wide range of industrial processes. Whether it is ensuring chemical reactions occur at the optimal temperature, preventing liquids from undergoing phase change to solids (freezing) or regulating fluid viscosity to guarantee smooth flow, precise fluid-temperature control is crucial to industrial operations. Commonly, fluids are stored in tanks during primary or intermediate stages of processing. In these cases, tank heaters maintain fluids at the desired temperatures.
Tank heating spans industries
Tank heating plays an important role in a variety of industries. In the oil and gas industry, crude oil as well as refined products like heavy fuel oils, diesel, lubricating oils, waxes and bitumen are kept warm in storage tanks to maintain ideal flow properties for conveyance through pipelines or other means of transport. In the shipping business, bunker oil is heated to ensure its free flowability, thereby providing propulsion and electricity to the vessel.
The chemical and petrochemical industries store refined petroleum products like olefins and aromatics in tanks for the production of solvents, adhesives, plastics and elastomers. And in the food and beverage industry, tank heaters regulate the temperatures of vegetable oils, liquid sugar and syrups, and chocolate and dairy products. Many other fluids are also heated in tanks, including demineralized water and other heat transfer fluids, lubrication oils, hydraulic oils, mineral oils and chemicals of all sorts.
The importance of controlling fluid viscosity
One of the principal reasons for using a tank heater to control the temperature of fluid stored in a tank is to regulate its viscosity. A fluid’s viscosity — or its resistance to flow — depends on its chemical composition and its temperature. As fluid temperature falls, its viscosity rises and the fluid flows more sluggishly. Conversely, as fluid temperature rises, its viscosity falls and the fluid flows more readily.
This relationship is particularly important for fluids with naturally high viscosities, like heavy fuel oil, or those stored in cold environments, such as tanks exposed to below-freezing winter temperatures. The elevated viscosities of fluids in unheated tanks in these circumstances can make it impossible to extract fluid from the tanks.
When an oil’s temperature falls to a certain level known as the cloud point, wax molecules within the oil will begin to crystallize, causing the oil to take on a cloudy appearance and raising its viscosity. If the temperature drops far enough, the oil will no longer flow due to gravity alone, which occurs at the oil’s pour point. Oil in this state has poor flow properties and will tend to block pipes, nozzles and filters, bringing industrial operations to a halt.
This situation can be avoided by deploying tank heaters to maintain the oil’s temperature, and thus its viscosity, within an optimal range. Electric heaters are highly effective at performing this function. Compared to alternatives like steam or natural gas heaters, electric heaters are safer, more efficient and offer more precise temperature control. Wattco offers immersion, circulation, flanged, screw plug and over the side electric heaters to fulfill the needs of any tank heating application.
Accurate heater control is essential
Accurate regulation of fluid temperature (and viscosity) can only be accomplished if the heater receives the right amount of power. The heater control panel governs this based on control signals it receives from the process temperature controller. The purpose of the temperature controller is to calculate the control signals that bring the current temperature of media in the tank to the desired setpoint.
Wattco’s heater control panels are available with silicon controlled rectifiers (SCR). These solid-state power regulators deliver an optimal flow of electricity to the heater. SCRs offer a number of advantages compared to mechanical contactors. SCRs contain no moving parts, resulting in lower operating and maintenance expenses. In addition, SCRs offer finer control, enabling shorter cycle times for improved temperature stability, reduced thermal shock to the heater and prolonged heater life.
The fluid determines heater power ratings
Just as important as an accurately powered heater is one that is properly sized. A tank heater’s power specifications must be closely matched to the fluid to be heated. This includes both the power density, or watts per square inch of heater element, as well as the overall power, or wattage, of the heater.
A tank heater with improper power specifications can have harmful consequences. If the heater’s wattage or power density are too high, the fluid stored in the tank can suffer damage. This is because every fluid has a different thermal conductivity. For example, water’s thermal conductivity is higher than that of oil, so water conducts heat away from a heater faster than oil. If a tank heater that was specified to heat water is immersed in oil, the heater could build up excessive heat, causing the oil to thermally fail and crack into light and heavy hydrocarbon components. If the temperature of the heating elements surpasses the flash point or fire point of the oil, there is a greater risk of ignition or explosion.
Trusted heater supplier
Tank-heating challenges are easily resolved with Wattco as the chosen electric tank heater supplier.
Wattco works with customers to custom design heaters with optimal specifications tailored to their application. In addition, Wattco heaters and control panels are available with safety features like temperature-limiting controls and explosion-proof and moisture-resistant enclosures. With over 50 years of experience as a manufacturer of electric heating elements and controls, Wattco uses only the highest-quality raw materials in fabrication and provides extremely quick turnaround, with custom-designed heaters delivered in days.
Contact Wattco today for more information on any tank-heating application or questions.