Multi-point Thermal Meter Improves Combustion in Furnace Application

BP Oil converts crude oil to gasoline and jet fuel by heating the crude to 1800 F in large furnaces that incorporate 12 natural gas fired burners. To ensure proper operation, the operator must maintain a 10 to 1 fuel-to-air ratio at air mass flow rates of 1 to 1.3 million standard cubic feet per hour. Forced draft fans deliver combustion air mass flow rates in two or more ducts with multiple flow obstructions.

The refinery needed a system that could deliver an accurate mass flow measurement of ambient air in an application that presented the challenges of varying temperatures, varying loads and difficult flow profiles. Sierra's Multipoint mass flow meters are specified because flow averaging was determined to be the best solution to this monitoring problem. Louvers in the 5' x 6' ducts, directly upstream from the best flow monitoring location, create an irregular flow profile. Sierra modeled the application and recommended a flow straightening system in the ducts to reduce the number of mass flow sensing points required.

The metering system consists of two or more four-point averaging arrays, mounted vertically, in equal-area segments of each duct. All of the arrays are connected to Sierra Collector-Box electronics which averages the mass flow signal from each of the points in the array. The total air mass flow rate in each of the ducts is measured and outputted to the control system. By measuring oxygen in the furnace, fuel flow and combustion airflow, the operator is able to improve combustion control and reduce fuel waste. By providing a total flow solution that included both flow straightening and flow measurement, Sierra has helped BP engineers achieve improved combustion control and reduce fuel costs by more than $1,000,000 per year! The multi-point arrays give them a direct measurement of total mass flow at varying loads, and their no-moving parts design virtually eliminates maintenance procedures.