Controlling industrial combustion-based units such as boilers, heaters and furnace has historically relied on the use of fuel-to-air curves. These curves represent the amount of fuel and air required for a given load.
In this 4:28 video, Patented Combustion Solution From Emerson Improves Performance, Emerson’s Bob Sabin describes how stoichiometric, math-based control approach from common measurements typically found on a combustion unit provides more precise control versus fuel-to-air curve-based control.
Bob describes how the fuel-to-air curve approach dates back to the 1920s with control based on the use of mechanical cams to represent the fuel-to-air curves. While control technologies advanced from mechanical cams to analog to electronic to computerized digital controllers, these fuel-to-air curves have remained in use. Instead of mechanical cams, the values along the curves are stored in registers in the controller.
He notes that these curves are a compromise as they are set assuming certain operating conditions. These conditions, such as ambient air conditions, fuel properties, and the process unit itself can all change over time. Even the most consistent fuel source, natural gas, can have its energy content by volume change up to 10%. Other fuel sources such as waste fuels vary by much greater amounts.
Bob explains that improvements include better thermal efficiency, improved response to load changes and turndown, reduced emissions and overall better unit stability and reliability.