Simulation Helps Reduce Pressure Drop On Gas Turbine Inlet Duct By 50%+

Duke Energy uses a GE Frame 5 gas turbine to drive a compressor used in a natural gas pipeline. The intake system required retrofitting with a silencer to meet current regulations and the need also existed to reduce particle contamination. The pressure drop in the initial design was found to be 8.5 inches of water, much higher than the design specification which was 5.3 inches.

Mueller Environmental Designs Inc. which provides air filtration, noise control, evaporative cooling, mist extraction, and emissions control products to the oil and gas transmission industry, worked with consultants from ANSYS, Inc. to simulate flow in the inlet duct and identified variations in flow velocity across the cross-section of the inlet and a large recirculation zone. They made a series of design changes including modifying the inlet scroll configuration, adding radii to the ductwork, and adding guide vanes to the outlet region of the duct. Then they evaluated the effects of these changes by re-running the simulation. The changes reduced the pressure drop to just 4.2 inches water.

Updating The Duke Intake System

The four Duke Energy compressor stations with a total of eight compressors were installed in the 1960s and originally equipped with intake systems using single-stage fiberglass filters. Recently, Duke Energy decided to update these intake systems. The primary objective was to reduce inlet pressure differential. Other objectives included improved inlet air cleanliness and reduced inlet air noise. The filters in the old intake systems had to be cleaned frequently to protect the turbine blades from being eroded, corroded or deformed due to dirt.

The design specification mandated limits on the pressure drop of the intake system because additional fuel must be burned by the engine to overcome the pressure drop. At the same time, the intake system had to make several sharp turns to get into the compressor building. Space considerations placed severe limitations on the overall allowed length of the intake system, creating a substantial design challenge.

Mueller engineers designed a new intake system that includes a silencer and state-of-the-art filters. But they were concerned about the amount of pressure drop generated by the new design. The geometry of the intake system was far too complex to calculate the pressure drop using engineering calculations.

The standard approach for addressing this sort of problem begins after the equipment is installed. Then, if performance does not meet specifications, physical measurements of airflow are taken at various locations along the ductwork. Based on these measurements, engineers attempt to determine what is causing the problem. Based on this diagnosis, some type of flow control device is installed within the ductwork. Then the measurements are repeated to see if the device actually solved the problem.