Heated Gas Sample Lines and Umbilicals for Emissions Monitoring
eated sample lines are used in stack testing and emission monitoring to prevent the formation of moisture and acid gas condensation during sample extraction and transport, preserving the integrity of the gas sample for accurate measurement. Umbilicals generally consist of PFA or FEP tubing and a heat tracing element, imbedded in fiberglass insulation with a weatherproof jacket. A heat-traced sampling umbilical is often used in direct extractive CEMs for either hot/wet measurement or CEMs employing some method of dew point reduction prior to sample gas analysis. Two types of heat tracing are available for heated sample lines: Constant Wattage and Self-limiting.
Constant wattage or constant power density heat tracing allows higher operational temperatures to be maintained than self-limiting sample lines. They are used in applications requiring temperature maintenance above about 250 degrees F or where temperature must be more closely controlled and monitored. These sample lines require a thermostatic power controller and a thermocouple or other temperature feedback device. Constant watt sample lines are specified in watts per foot and the controller sized by the appropriate total power output.
Self-limiting sample lines feature the same basic construction as constant wattage lines, but the heat tracing becomes more resistive as its temperature rises, effectively limiting power delivery. This type of sample line requires no external controller and is suitable for many gas monitoring applications requiring temperature maintenance up to about 250 degrees F.