Selecting Air Heaters for Your Industrial Environment

Air Heating Systems (AHS) are used simultaneously in different processing units across industries. The use of such systems provide major benefits of significant reduction in the operational cost, as these systems function to increase furnace heating rate and the temperature of the product to be heated. Most of the industrial heating systems have an average life of 5,000 hrs, if used properly. Selecting a right air heaters for heating furnaces in the industrial environment with limited product knowledge is a tough job.


You may refer to the following technical guidelines in order to select an appropriate air heating system for your industrial setting.

Air Sources
In general, the air heater uses compressed air and air from regenerative blowers to heat the furnaces. The source of air should always be clean and dry. Dirt, grease, oil or vapors and reactive gases may cause damage to the heaters. It is recommended to use air or inert gas only.

Regenerative Blowers
Regenerative blowers are compact source for the clean air. These blowers are capable of producing low-pressure air for the heating system. Size of the blower is based on the maximum amount of airflow (CFM or LPM), it can produce without any external restrictions. When heater is attached to the blower, the flow of air decreases. If the blower is completely restricted, it may result in the failure of the system as the motor may overheat and cease to function.

So always choose a heating system with minimum air restriction, and opt for the blower that can overcome the backpressure generated by the heater, flare and associated piping. Regenerative blowers have a compact size, hence it is not recommended to use with industrial air heaters that are driven by heavy motors.

Compressed Air
Compressed air are the essential components of most of the industries. It is a high pressure regulated air, which often contains oil for lubricating pneumatic valves and equipment. It is recommended to filter these oils at regular basis to prevent fouling and damage of the air heating system.

Controls
An active control is the prerequisite for long heater life. Remember before switching to your control system, you must have sufficient air flow through the heater. This is applicable for heaters without over-temperature protection. Follow all applicable codes referred in the manual and use proper wiring for installation. Installation of the system should be done by experts.

Open-Loop (Manual) Control
System with open-loop control features a manually operated power controller used to apply fixed voltages to the heating element. This system allows the user to manually adjust the heater temperature. Always remember that if the air-flow is suddenly interrupted, it would result in system failure.

Closed-Loop (Feedback) Control
Close-loop heater control system comprises of power controller, temperature controller, and thermocouple. These components together provide a constant output temperature, regardless of changes in airflow. The control system also provides convenient display of the temperature.

Temperature Controller
It is advised to use digital temperature controls with type-K thermocouple inputs. The temperature control output should match the input of the power control.

A standard PID-type control with a wide proportional band setting will efficiently work to minimize temperature overshoot. The temperature may be auto tuned, but the temperature should not exceed the maximum of the heater. If the temperature rises at high speed during the auto tune, immediately turn off the power.

If you are using a solid state relay power control, the controller cycle time should be set for 100ms or less.

Thermocouple
The thermocouple should have (.030" max wire dia.), exposed-junction, type-K thermocouple for accurate temperature readings. Other thermocouple configurations, or varying distance from the heater may result in temperature measurement errors/or failure of the heating system.