This vessel complies with the B149.3 Legislation, and the efficiency gains could pay for the upgrade in as little as 2 months.


When a customer in Alberta contacted an energy services company in Calgary in 2008, looking for an oil heater upgrade, a combustion controls challenge was presented. The customer wanted to increase the efficiency and reliability of their natural draft utility heater.

Fortunately for the Alberta processor, by combining its systems’ expertise with the benefits offered by advanced electronic switch technology from United Electric Controls (UE), the energy services company was able to deliver the kind of improved performance they were seeking.

At the Alberta facility, the system was having difficulty maintaining process temperature. Measurement of the burner orifice sizes and fuel gas pressures revealed a 3.5 million BTU/hour input each.

As an integral part of the upgrade process, an electronic temperature control from United Electric Controls, the One Series, was installed. The results of the upgrade include:
  • The vessel now maintains process temperature of 522°F (272°C) with only one firetube running at 68 percent combustion efficiency.
  • The total volume of air that is now being heated by the one firetube is approximately 105,000 SCF/hour. This notable reduction in air volume translates to more heat into the process and less into the atmosphere.
  • The second firetube has a live pilot and will ignite only if the process temperature drops to below 513°F (267°C).
  • This increase in efficiency is producing savings for the customer of approximately $574 per day in fuel costs.


The system that was installed created immediate added value for its customer – the increase in efficiency is producing savings of approximately $574 per day in fuel costs.

The upgrade was accomplished by utilizing United Electric's programmable RTD temperature switch with independent solid-state relays, which allowed mechanics to separate the control points for each tube and set a tight "deadband" for each setpoint. Along with an included field-scalable 4 to 20 mA analog output (providing a trending function tied back to a PLC), the electronic temperature control can effectively replace a switch, gauge and transmitter using a single process connection.

Accordng to United Electric Controls, the end results are measurably improved operating functions for the vessel. The primary firetube has slightly more net heat input than the vessel requires; therefore, its “on” time in the heating cycle is more efficient. The secondary tube can provide additional heat if required but does not come on during normal operation.

If for any reason the primary firetube experiences a flameout, the secondary tube will provide a backup and maintain a process temperature of 514°F (268°C). The new internals also allow the customer to switch the control of each tube, allowing for the operation of one tube as the primary for 6 months and then the other for the other 6 months. These high-efficiency burner internals also provide even heat distribution, further reducing stress on the fire tube.

United Electric Controls is headquartered in Watertown, Mass.

Links