Fully modulating burners with modulating controllers provide optimum fuel usage and the longest heater life.
Combustion controls play a significant role in the efficiency of fired heaters such as thermal fluid heaters or process heaters. Controls range in complexity from simple on/off switches to more advanced software programs known as profilers. The right controls for your system will be determined by your needs and goals.
Combustion is a chemical reaction in which rapid oxidation occurs. Three elements are required for combustion to happen: energy, fuel and oxygen. Maintaining the optimal mixture of those elements is the job of controllers. Three types of burners and controls are commonly used on thermal fluid heaters: 1. Fully modulating, 2. Low/ high/low and 3. On/off.
Fully modulating burners with modulating controllers provide optimum fuel usage and the longest heater life. They closely match the burner output with the changes in heat demand. They work a lot like cruise control works in a vehicle. If you encounter a hill while driving with cruise control engaged, the controls in your vehicle will automatically increase the fuel to maintain the determined speed as you ascend the hill. Similarly, the heater controls will automatically increase or decrease the burner output to maintain determined temperatures of the thermal fluid or liquid passing through the coils. This avoids temperature under- and overshooting, which is inherent in nonmodulating burner systems. Moreover, optimum temperature controls, along with safety limit devices, ensure the heater will operate within the design limits.
Modulation is controlled by mod motors. In some cases, only one mod motor is needed to control the ratio of oxygen and fuel mixture. Linkage is used to connect the mod motor shaft to the air damper and fuel valve. Since there is only one mod motor, the air and fuel cannot be controlled individually. This means you have to set the optimum ratio for high fire and the optimum ratio for low fire. Efficiency may suffer when it's not firing at one of those optimal firing rates. It's also important to readjust the linkage settings when the weather changes, because the optimal ratio during summer months may not be the optimal ratio during winter months.
The advantages of a single mod motor with linkage are simplicity of use and significantly lower costs, compared to more complex systems. But what if you have stringent emissions requirements and you need to add a flue gas recirculation system or another system to your heater? In this case, a single mod motor and linkage system is not going to be enough.
When you add multiple pieces to a burner system that requires multiple mod motors, which need to be controlled individually, this is called a parallel positioning system. A parallel positioning system is typically controlled by a valve profiler, a computer program designed to achieve maximum burner efficiency at virtually any firing rate. With Heatec's Omni⢠Combustion Controller System, for example, you can set up to 20 optimal firing points in a profile instead of only being able to set the optimal ratios at high fire and low fire. You can also save multiple profiles that you can easily switch between when the weather changes.
In today's world, simple low/high/low and on/off controls are virtually nonexistent. Fully modulating controls are far more efficient. And when meeting strict emission standards is paramount, a profiler is essential.
For more information about combustion controls and fired heaters, visit www.heatec.com or call (423) 821-5200.
