Circulation Heater

Construction

Typical circulation heaters are manufactured using the following major components, designed to ensure reliable performance, operational flexibility, and safe operation under various industrial process conditions.

Terminal Enclosures

The design of the terminal enclosure varies depending on whether the heater is installed in a safe or hazardous area. The terminal enclosure is designed to protect the terminals of individual heating elements from external impacts such as dust, moisture, and harsh environmental conditions, while also facilitating safe and reliable connection of the incoming power supply to the heater bundle.

Marathon flameproof circulation heaters are certified for installation in hazardous areas classified as Zone 1 and Zone 2, suitable for Gas Group IIC, and are provided with IP66 protection to ensure maximum safety and durability.

Heater Bundle

The heater bundle consists of a number of U-pin heating elements that are adequately supported by a system of baffles and tie rods. The bundle is engineered to deliver the specified outlet temperature while maintaining element skin temperature and pressure drop within safe operating limits.

Heating elements may be fixed to the heater flange using standoff sleeve pipes with brazing, direct welding, or threaded couplings depending on design requirements. The total heat duty of the heater bundle can be divided into multiple subgroups or banks based on process conditions, which allows better control, enhanced flexibility, and optimized operational efficiency.

Pressure Vessel

The pressure vessel, also referred to as the heater housing, is a fabricated shell designed and manufactured in accordance with ASME or equivalent international standards. The vessel is provided with inlet and outlet nozzles to ensure smooth and controlled flow of the process fluid through the heater.

For maintenance and safe operation, the vessel is also equipped with drain and vent nozzles. The heater vessel can be designed for either horizontal or vertical installation and may be configured as a single-stage or multistage unit based on application requirements.

It is recommended that the vessel be externally insulated to minimize heat loss, improve energy efficiency, and protect the equipment from thermal shock during operation.

Temperature Sensors

The heater bundle is equipped with element skin temperature sensors to continuously monitor and regulate the element temperature within permissible operating limits. Depending on the application, additional sensors such as tube sheet temperature sensors, terminal box temperature sensors, vessel body temperature sensors, and process fluid temperature sensors may also be provided on a case-to-case basis.

The temperature sensors used in the system are typically RTDs or thermocouples and are certified in accordance with the classification of the installation area. A simple heater bundle can also be controlled using thermostat protection for both element skin temperature and process temperature monitoring.

For applications involving high operating pressure, it is recommended to install a Pressure Safety Valve (PSV) within the heater vessel as an additional safety measure to protect the system.

Control Panel

Heater control panels are designed to monitor and control the operation of the heater bundle while ensuring complete safety of both equipment and personnel. The control logic can be based on ON/OFF control using contactors, regulated control using thyristors, or a combination of both methods integrated within a single control panel.

Control panels can be installed in either safe or hazardous areas by following applicable design guidelines and certification requirements. The panels are provided with various indication systems such as Power ON, Heater ON/OFF status, Trip indication, and High Temperature alarms to ensure ease of operation and process awareness.

Temperature values of heating elements, process fluid, and other monitored zones are displayed on the control panel for effective monitoring. The panel is also equipped with essential safety interlocks such as high element temperature protection, earth fault detection, process over-temperature protection, and an emergency stop function to ensure safe and controlled operation at all times.