Patent Application
20090074589
The invention relates to a structure and method for enhancing turbine performance and, more particularly, to a cooling circuit that diverts compressor discharge air to supplement the total required purge flow and cool critical turbine components.
The compressor discharge air leaking past the high pressure packing (HPP) of a gas turbine is typically returned to the primary gas path via the first forward wheelspace, between the first stage nozzles and first stage buckets. This secondary flow path is referred to as the HPP circuit. This air is used for two purposes: (1) it is used as purge flow in the first wheelspace to prevent hot gas ingestion; and (2) it cools critical components in the HPP circuit. Some of the critical components in the HPP circuit include the compressor tie bolts, marriage joint, nozzle support ring and first stage wheel.
In some designs, the flow level in the HPP circuit is higher than the wheelspace purge requirement because of component temperature requirements. Therefore, an ideal solution should reduce the total circuit flow to a level that satisfies the wheelspace purge requirements while keeping all critical components in the circuit under desired temperature requirements. Furthermore, a preferred solution may also be able to handle robustly varying ambient and turbine operation conditions. Finally, the solution should be able to retrofit in the existing hardware.
In a previous General Electric turbine design (the 9H turbine), an HPP circuit utilized a cooled cooling air bypass system. The circuit used a heat exchanger to cool the extracted compressor discharge air and bring the cooled cooling air to the front of the HPP circuit to not only cool the last stages of the compressor components but also prevent a later stage flow from coming into the HPP circuit. This system uses conventional sealing that the HPP and makes no attempt to regulate the purge flow required beyond conventional angel wing seals. The cooled cooling air is not adjustable.
Brush seals have been implemented in other turbine designs to reduce the purge flow. No cooled cooling air is needed there, however, because of lower compressor discharge temperatures and consequently lower temperatures in the HPP circuit resulting in adequate wheelspace temperature margins.
In an exemplary embodiment, a cooling circuit in a gas turbine serves to augment flow in a high pressure packing (HPP) circuit of the turbine. The cooling circuit includes an inlet pipe that receives compressor discharge air, and at least one cooled cooling air pipe in fluid communication with the inlet pipe via a pipe manifold. The pipe manifold distributes the discharge air across the at least one cooled cooling air pipe. An upstream seal is disposed upstream of an entrance to the HPP circuit, and a downstream seal is disposed downstream of the HPP circuit.
In another exemplary embodiment, a method of improving turbine performance using a cooling circuit by augmenting flow in a high pressure packing (HPP) circuit of the turbine includes the steps of receiving compressor discharge air in an inlet pipe; distributing the discharge air across a plurality of cooled cooling air pipes; and disposing an upstream seal upstream of an entrance to the HPP circuit to regulate air entering the HPP circuit and disposing a downstream seal downstream of the HPP circuit to regulate a need for wheelspace purge air.
In still another exemplary embodiment, the cooling circuit includes an inlet pipe that receives compressor discharge air; at least one cooled cooling air pipe in fluid communication with the inlet pipe via a pipe manifold, the pipe manifold distributing the discharge air across the at least one cooled cooling air pipe; a cooling source in direct contact with one of the at least one cooled cooling air pipe and the diverted air; a valve disposed between the inlet pipe and the at least one cooled cooling air pipe, the valve adjusting mass flow and a temperature of the diverted air based on a temperature of the HPP circuit; an upstream seal disposed upstream of an entrance to the HPP circuit; and a downstream seal disposed downstream of the HPP circuit.
With reference to
The seal 12 is placed upstream or adjacent the HPP circuit entrance before all critical components and the existing honeycomb seal. As noted, the seal can be a conventional brush seal, an adjustable seal with an actuating system, or the like.
An inlet tube or pipe 14 is positioned to receive compressor discharge air. Preferably, the circuit includes two inlet tubes or pipes 14 of about 3″ diameter.
Diverted air in the inlet pipe 14 is flowed to a plurality of cooled cooling air pipes 16 via a pipe manifold 18. The pipe manifold 18 distributes the discharge air from the inlet pipes 14 across the cooled cooling air pipes 16. The cooled cooling air pipes 16 direct the compressor discharge air to the HPP circuit.
In a preferred arrangement, the cooling circuit includes 12 cooled cooling air pipes that penetrate at the compressor discharge case vertical flange and run along the compressor discharge case strut at trailing edges. The cooled cooling air pipes are preferably ¾″ or 1″ in diameter. The positioning via the compressor discharge case struts serves to minimize the aerodynamic impact on the main gas flow. A computational fluid dynamics analysis has been conducted to ensure that the added tubing system has a negligible impact on the main gas flow. The tubes 16 further penetrate the compressor discharge casing inner barrel flange via suitable apertures.
The circuit preferably additionally includes a cooling source in communication with either or both of the inlet pipe 14 and the cooled cooling air pipes 16. In one arrangement, the cooling source comprises ambient air that serves to cool the air flow as it travels through the cooled cooling air pipes 16. Alternatively, the cooling source may comprise a heat exchanger 20 such as a tube-shell type heat exchanger or the like.
Still another alternative for the cooling source is an atomizer 22 that sprays water droplets in contact with either the diverted air or the cooled cooling air pipes 16. The atomizer 22 preferably generates micro-level water droplets that are sprayed directly to cool the extracted air. The amount of water required to cool the flow by 150° F. will elevate the main gas path flow moisture level by only 2%. Locally in the HPP circuit, the specific humidity will typically be 4-5 times compared to the condition at the inlet. This higher humidity in general is harmless to the circuit components.
The exit temperature and mass flow can be tuned by a valve 28 disposed between the inlet pipe 14 and the cooled cooling air pipes 16. An additional valve may be provided to control water mass when using the atomizer 22. The two valves can be operated either manually or automatically by control signals. Preferably, the valves can be automatically adjusted for desired mass flow and temperature of cooled cooling air based on a temperature measurement at the HPP circuit. Such valves can be used to regulate the CCA circuit regardless of the cooling mechanism used. These valves should be controlled based on temperature measurements made in the HPP circuit; these are typically made at several locations in the wheelspace, but can also be made at any critical location in the HPP circuit. Temperature measurements can be used to both determine that the cooling air is adequately cool, and to identify the hot gas ingestion into the wheelspace.
The cooled cooling air pipes 16 deliver the cooling air at various locations relative to the HPP circuit. As shown in
The system and method described endeavor to save the amount of compressor discharge air required in the HPP circuit and redirect it back to the main flow path to enhance turbine performance. This can be achieved robustly by introducing a secondary flow system to bring cooled cooling air in the circuit. The amount of the total flow required in the circuit is dictated by the wheelspace purge requirement. The difference between the wheelspace purge requirement and current flow is significant enough to justify the implementation of the secondary cooled cooling air circuit. A seal limits the air entering the HPP circuit to the minimum possible so that as much of the required purge air as possible is supplied by the cooled cooling air circuit. Improved sealing at the wheelspace via abradable angel wing seals reduces the amount of purge air required. The mixed compressor discharge air and cooled cooling air should be sufficient to prevent the wheelspace hot gas ingestion while keeping the critical components in the circuit under temperature limits.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
