In a Power magazine article, Gas Chromatographs Offer New Technology for Power Plant Burner Control, Emerson’s Bonnie Crossland describes how the energy content can be monitored to improve overall energy efficiency.
For natural gas burners, variations in gas composition can have a direct impact on the ability to maintain burner control and desired combustion characteristics, especially if the variations are rapid or transient. The magnitude of the impact can be severe, including unstable combustion, ignitability problems, increased emissions, and burner noise.
Gas chromatographs (GCs) have been widely used in the upstream and downstream oil and gas industry at custody transfer points to measure natural gas component concentrations and other physical properties. This same information can be used in control strategies to optimize natural gas combustion in real time.
Feed-Forward Control. The typical air/fuel ratio controller uses carbon dioxide and oxygen concentrations from flue gas analyzers to control the air/fuel ratio within an optimum combustion region. The emissions in the flue stack are monitored and fed back into the air/fuel ratio controller as a feedback loop. When the natural gas composition changes, emissions change. The controller then adjusts the air/fuel ratio appropriately.
However, a GC allows feed-forward control because it can provide the ratio controller with information on gas compositional changes before gas combustion, and therefore, before emissions are adversely affected. This provides a method to adjust the air/fuel ratio before increased emissions or hydrocarbons are detected in the flue stack…
Not only is energy efficiency increased, but also emissions are reduced:
GCs can provide early warning of heavier liquid hydrocarbons in the natural gas stream. These natural gas liquids (NGLs):
Accurate determination of fuel gas composition allows for optimal adjustments of the air/fuel ratio, enabling the combustion turbine to operate at its most cost-effective efficiency point, while reducing NOx emissions.
…can cause flashback, which can severely damage turbines.
The temperature of the stream can be adjusted to help prevent the formation of liquids.
Bonnie describes how advances in gas chromatograph technology has simplified ongoing maintenance:
The software assistants in the local operator interface can literally walk the technician through the process of changing calibration gases, optimizing valve timing, and replacing the analytical module in the GC. New models also include built-in diagnostic functions that provide fast support for common tasks and can automatically gather diagnostic data.
Read the article for more on how to address changing natural gas energy density to optimize combustion, improve energy efficiency and reduce emissions.