Energy Systems

2007GT Exhaust Systems Seminar - StavangerMark Wickham/Andy Dyson/Paul Kingston

Energy Systems

Company History

Energy Systems

Relevant Experience

Operational Units Worldwide –

140 Fired Heaters – Designed to API560

126 GT WHRU’s – Cold Casing, Pressure parts designed to API 560

49 GT WHRU’s – Hot Casing, Designed to mostly NORSOK

Total WHRU’s in design, build or operation - 213

Energy Systems

Design Basis

The cost, weight and size of a WHRU system has a direct relationship to exhaust gas velocity. The higher the velocity the smaller the WHRU.

Traditionally flow has been assumed as average across the duct – 45m/s max on hot casings and 35m/s max on cold casings (internally insulated)

Energy Systems

Component Failures

Silencers – Baffle disintegration/insulation erosion

Diverters - Cracked hot casings

Casings - Cracked hot casings

Pressure Parts – external tube wall damage/header tube welds failure/tube leaks

Energy Systems

Hammerfest Design

Heat Exchanger

Heat Exchanger Valve

Silencer

Bypass Valve

Energy Systems

Causes of Failure

Development work with Statoil and Dresser over the past year on Sleipner, and with Statoil on Hammerfest has revealed two probable causes:-

•Vibration

•Overstressing of hot casings

Energy Systems

Typical Velocity Profile – LM6000 Outlet from Silencer

Energy Systems

Velocity Profile – LM2500+ Oseberg

Energy Systems

Velocity Profile – LM2500+ Sleipner

Vibration calculations

Energy Systems

Sleipner Findings

Development of the replacement Sleipner WHRU with Dresser and Statoil has highlighted the need for a velocity profile to be provided to WHRU suppliers with the enquiry

Transient FEA analysis has established that hot casings are more difficult to design than cold casings due to high stresses caused by thermal gradients, particularly during start up

Energy Systems

Sleipner Findings

Energy Systems

Conclusions

Failures can be prevented if the interface point between GT and WHRU is fully defined

It is more simple and effective to correct the velocity profile in the WHRU system where velocities are lowest

Hot casing designs need detailed transient stress analysis of all significant casing attachments

Energy Systems

Recommendations

Ensure vibration does not occur

• Reduce velocity to acceptable levels as soon as possible after the GT flange

•Ensure heat exchanger support system is designed for the maximum velocity plus good margin and support on fins rather than pressure parts

•Ensure silencer design considers maximum velocity plus a good margin

Energy Systems

Recommendations

Include the following in the enquiry specification

•Velocity profile at GT/WHRU interface point (max flow)

•Requirement for CFD modelling

•Requirement for vibration analysis

•Requirement for Transient FEA analysis on hot casings

•Make the design and supply of all components downstream of the GT outlet flange the responsibility of one company (including silencer)

Energy Systems

Recommendations

Consider the use of cold casings (internally insulated) in areas requiring extensive external stiffening – coil casings, support points, flanges, rectangular sections

Minimise the number of corners – circular ducts are ideal

Radius corners

Avoid corner welds