Upgrading the controls on an existing industrial thermal fluid heater to a linkageless control system will increase efficiency and thereby maximize the return on investment. Updating an outdated combustion controls system is an excellent way to optimize a burner to perform at its maximum design capacity.

Most industrial burners in operation today are designed and installed with multiple linkage arms, rotating shafts, springs, cams, rotary joints, fixed joints and actuators. No matter the quality of installation or yearly maintenance, a linkage control system is limiting. It is not able to get a burner to perform to its design capability throughout its entire firing range. Linkageless control technology can.

Linkageless controls allow for independent control of the combustion air and fuel through the use of servo control motors attached to valves that react separately of one another. Additionally, a fuel curve can be defined in a controller to instruct each servo at what distance to open and close based on given process variables.

Overview of Combustion Controls Using Linkage Technology

Limitations exist for combustion controls using linkage technology.

Hysteresis. Linkages always have some hysteresis due to the connecting joints and limitations within those joints throughout their movement. Hysteresis is seen in the inability to return to the exact points to which the burner was tuned. Repeatability is a problem and will greatly affect combustion, thermal fluid heater efficiency and system reaction time. There is hysteresis with an actuator and driving direction with linkage systems because with poor repeatability, the actuator will actually reach two different points if it is traveling upward versus traveling downward.

Combustion Efficiency. Typically, a burner is tuned to be most efficient at high fire. As the burner moves down the firing curve, the burner becomes less and less efficient because the air and fuel flows are locked in proportion: the linkage rods and cams drive the air/fuel volumes together.

Parts. Some combustion systems may require up to 15 parts, including cams, springs, set screws, ball joints or multiple linkage rods, all of which must be adjusted during commissioning and tuning. Also, all of these different parts require spare parts that must be stocked and kept up with by a technician.

Overview of Combustion Controls Using Linkageless Technology

Upgrading to linkageless technology offers several features.

Independent Servo Motors. A linkageless system has independent servo motors with valves — one on the combustion air, one on each of the fuels and one on the FGR line if present. With these servos acting independently of each other for each position on the fuel curve, the air and fuel flow are set independently to achieve the highest combustion at each point. The controller takes position feedback constantly and maintains accurate return position, typically with less than 0.1 percent error. A positioning error of any kind will send an error code to the controller and alert the operator to the problem.

Combustion Curve. Being able to accurately set the combustion curve at each point on the firing curve — independently from previous points — allows the burner to fire at below 5 percent O2 throughout the firing curve, saving 3 to 5 percent on fuel. Some servo linkageless controls and burner systems will allow the excess oxygen to be as low as 3 percent O2 throughout the firing range. Having low O2 also ensures a hotter flame and provides quick reaction time to process changes.

Multiple Fuel Curves. Some controllers with servo capability will allow multiple fuel curves. The two curves can be set up at one time by a technician, and then the user can automatically switch from natural gas to oil with a button, without any further tuning requirements.

Maximum Outputs. Linkageless controls allow the burner to be fired at the maximum efficiency the burner was designed for throughout the firing range.

Monitored Operation. Linkageless control systems also can communicate with the plant system without the need for PLC control systems. End users have the ability to monitor the operation of a heating or process system in real time from different locations.

Features Possible with Linkageless Controls

More sophisticated controllers allow for other benefits — increased turndown capability, returning to pilot for very low turndowns, different setpoints and curves for process restraints, and ability to allow for more process feedback to provide greatest combustion efficiency with little increase in cost. In addition, updating combustion controls to linkageless technology will result in an immediate return on investment through the following benefits:

  • Increased performance.
  • Fuel savings.
  • Simplified system operation.

Linkageless controls will continue to be added to thermal fluid systems and other fired systems because of the benefits they offer. The immediate and measurable savings generated through the upgrade to a linkageless system will pay for itself rapidly, then continue generating a better overall return on investment. This makes linkageless systems a suitable option for high efficiency and control. Quite simply, knowledge of the fuel costs and accurate burner firing conditions will generate fuel and, therefore, hard dollar savings. Increasing fuel prices will force the industry to leverage new technology to ensure the most efficiency from existing equipment. Nearly any burner will benefit from a linkageless system.