While the guidelines provided are specific to GE frames, they apply, in general, to exhaust systems offered by all frame OEMs. Sidebars provide checklists for inspection of ductwork, frames, and diffusers. Knowing where to survey for damage and what type of wear and tear to look for are critical to success. Important to maintaining your exhaust system in the condition required to achieve safety and dispatch goals are periodic inspections and follow-up repairs or replacement of components as necessary. Overheating also is known to cause turbine bearing issues, high lube-oil temperatures and resultant varnishing, and instrumentation failures. Years of demanding duty, frequent cycles, and/or overheating contribute to degradation conducive to early failures and costly forced outages. It is in direct contact with turbine exhaust and not protected by insulation like the downstream exhaust plenum and ductwork. An expansion joint is located just upstream of the HRSG’s transition piece.įor GE machines, the exhaust frame is a structural part of the turbine and supports the aft bearing. A so-called exhaust manifold bolts to the cylinder on one end and to the round (GT exit configuration)-to-square (HRSG inlet configuration) transition on the other. GTs made by Siemens Energy are characterized by an exhaust cylinder bolted to the outlet flange of the engine. Exhaust then flows to the stack via ductwork, which is connected to the plenum and any associated ductwork by an expansion joint.įocus here is on exhaust systems for GE frames 5, 6, and 7, which are similar in design.For GE frames serving in cogeneration and combined-cycle systems, the expansion joint at the back end of the plenum connects to the transition piece for the HRSG. Hot gas exits the GT via the exhaust frame and is distributed in the plenum by the diffuser. To illustrate: Frame engines manufactured by GE Energy for simple-cycle service typically are arranged as illustrated in Fig 1. Today’s offerings are much improved over those available only a few years ago, assuring users of longer operating lifetimes and a higher degree of personnel safety.Įxhaust systems are comprised of several components and vary depending on the turbine OEM. Equipment interfaces and site and owner requirements may impact the physical design, but most important is the thermal design, which depends on the insulating system.Īrrangement of the insulating system has evolved over time. Purpose of this article is threefold: Help you assess the condition of your plant’s exhaust system, catch up on the latest designs which can help eliminate many of your recurring repair jobs, and gain from one plant’s experience in replacing the exhaust systems on its GTs.Ī good exhaust system is defined here as one that can be used on any OEM’s gas turbine and has a quality insulating system. Consider yourself lucky to get 15 years out of an exhaust system. While most issues identified can be corrected at least temporarily with weld material and insulation, the wear and tear on these systems-particularly those at plants in cycling service-is considerable and their lifetimes are limited. There are inspections you should make before and during an outage to evaluate the condition of system components. However, exhaust systems are not something to forget when an outage approaches. These relatively simple systems essentially consist of metal components and insulation arranged to direct nominal 1000F gas exiting an engine to a heat-recovery steam generator (HRSG), or stack, while protecting personnel.Įxhaust systems usually are ignored on rounds, rarely getting more than a passing glance unless an operator hears gas whistling out of a hole, crack, or tear in the ductwork, expansion joint, or between mating faces of adjacent flanges. You don’t have to visit many generating facilities powered by gas turbines (GTs) or attend many user-group meetings to realize that exhaust systems get little or no respect. By David Clarida, Integrity Power Solutions LLC
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