Two gas turbine exhaust silencers for a Middle East petrochemical plant

The challenge

At a petrochemical plant in the Middle East, gas turbine exhaust passes through a waste heat recovery unit (WHRU) before it reaches the stack. The silencing had to sit in the duct between the gas turbine and the WHRU, in the full hot gas stream. Across six operating cases the flue gas runs from 45.2 to 96.4 kg/s at 470 to 565 °C, and the turbine exhaust carries a sound power level of 144 dB(A).

A silencer in that position has three jobs at once. It has to survive the exhaust temperature without distortion, keep its pressure drop small so it does not cost the turbine output or the WHRU heat, and meet a guaranteed noise level outside the duct.

Our approach & engineering

Axces designed two round silencers with a Ø3,800 mm shell and an overall length of 4,100 mm including the inlet and outlet cones. The cones connect the silencer to duct openings of 3,594 × 2,174 mm at the inlet and about 2,971 × 2,754 mm at the outlet.

Concentric annular baffles

Inside, the gas flows through concentric annular passages formed by baffles with perforated facings, held by radial stiffeners. The open annular passages keep the predicted pressure drop to 2 to 7.5 mbar across the operating cases, within the 100 mm water column allowed, while the baffles bring the noise down to a guaranteed 85 dB(A) at 1 m.

Built for 600 °C

The shell and cones are SA-387 Gr. 22 chrome-molybdenum steel, chosen for strength at high temperature. The silencers are designed for 600 °C and 0.05 bar(g), with a 3 mm corrosion allowance.

• Concentric annular baffles for low pressure drop
• Chrome-molybdenum shell and cones, designed for 600 °C
• Cones matched to the rectangular duct openings at both ends
• Guaranteed 85 dB(A) at 1 m

Scope of supply

• 2 × gas turbine exhaust silencers, Ø3,800 mm × 4,100 mm overall, with inlet and outlet cones
• Saddle supports
• Inspection and test plan, manufacturing data record, and installation, operation and maintenance manual
• Fabrication at Axces Production in Poland, delivered to a port in Germany for shipment

Results

Both silencers were fabricated at Axces Production in Poland and shipped in 2018, with their manufacturing data record.

• Guaranteed 85 dB(A) at 1 m
• Designed for exhaust gas up to 565 °C and 96.4 kg/s
• Predicted pressure drop of 2 to 7.5 mbar
• Delivered with inspection and test plan, data record and manual

Related reading

• Gas turbine silencer design for power generation sites: exhaust and inlet silencing for gas turbines
• Exhaust silencers explained: absorptive, reactive and combination designs
• Understanding dB(A) reduction targets: how to specify acoustic performance