Using Electric Heaters to Provide Process Heat
Each application that requires heat has unique characteristics which will determine the best heating solution. Understand what must be heated — and to what temperature, for how long.
Heat is required in applications to prevent media freezing or to provide viscosity control in fluids like oil. Heat also can be used to prevent condensation on an electrical control box or a camera lens mounted outdoors. Additionally, heat will prevent gases in chemical vapor deposition (CVD) and semiconductor processes from condensing. From just these few applications, it is clear that heated tanks, pipes, vessels and other structures are common applications in the industrial world.
Many types of heating devices can meet these diverse applications’ process requirements. For instance, heat-trace cable and heating tapes work well heating pipes and valves to temperatures above 752°F (400°C). Heated blankets applied to the outside of tanks heat the contents. Immersion heaters mounted to a flanged feedthrough can heat the contents of a tank or the liquid flowing through a pipe. Removable heating jackets can provide both heat and insulation. Inductive heating also is an option for large, remote pipe-heating applications.
Each application that requires heat has unique characteristics that help determine the best heating solution. Application requirements include:
- Ambient conditions.
- The size of the vessel or pipe.
- Required insulation.
- The initial temperature of the material.
- The temperature to which the material must be heated or maintained.
They can be used as heat-loss variables in a heat loss calculator to determine the necessary wattage.
The wattage requirements for an application to heat material from one temperature to a higher temperature are vastly different from those for an application to maintain a material at the same temperature. The former is known as a heatup application while the latter is called a temperature-maintenance application. Knowing if there will ever be a requirement for a heatup is critical to the success of a heating system design.
Heatup Applications Demand More Wattage
When an application requires a heatup, the length of time the process requires to reach the desired temperature also will affect the wattage requirement. The faster the heatup requirement, the more wattage that is required.
The use of thermal insulation helps improve heating system efficiency. Using insulation reduces the wattage required to reach the desired temperature. In some cases, insulation that is 1” thick can reduce the wattage requirements by more than 75 percent (compared to same application without insulation). This is the same concept as a well-insulated home: It requires less energy to keep the interior warm in the winter.
The amount and type of power available must be considered during system design. If a heating system is large, the amp draw could exceed the available power at the site, and new power drops will be needed. Working with electrical and mechanical contractors when designing a system is important to ensure the proper amount of power is available. Also, controlling the temperature of the process should be investigated to specify the best control solution for an application.
The environment in some applications should be reviewed to determine if it is a hazardous or flammable-rated area. For example, for a gas-field application, any electrical heating product must be designed to prohibit electrical arcing. Overtemperature protection — preventing the heater from getting above the temperature at which a gas or vapor dust particle would auto-ignite if it were to make contact with a heated surface — guards against thermal hazards. High temperature protection devices are given T ratings (table 1). Such devices provide a fail-safe mechanism to prevent the heaters from overheating in the event of a controller or sensor failure.
Having an understanding of the options to heat tanks, pipes, vessels and other structures helps ease the task of specifying electric heaters. Take into account such factors as the required heat profile, heating characteristics (heatup or maintenance process) and environmental conditions to help ensure success.