ACTIVE TUB COOLING USING IMPELLER DISPOSED ON ROTOR SURFACE
Publication Date: 2013-Apr-22
The IP.com Prior Art Database
AbstractA technique of active cooling of a tub region in a double flow steam turbine is proposed herein. The technique cools the tub region using a fan or impeller blades. The fan or impeller blades are placed radially or axially over a rotor in tub region to create active flow through the rotor and tub region. The fan or impeller blades use shaft rotation to create pumping effect in order to cool the tub region.
The present invention relates generally to steam turbines, and more particularly to a technique of cooling an inlet region of a double flow steam turbine.
Double-flow steam turbines typically include two parallel flow turbine ends arranged on a common shaft. The two ends are a forward end and an aft end of the turbine. A tub diaphragm is located between the turbine ends and disposed around the shaft. Steam flows into the steam turbine radially inward and towards the tub. Subsequently, the steam flow divides, turns axially, and flows in opposing directions to enter simultaneously each of the forward and aft ends of turbine.
Steam flow becomes stagnant between the rotor and the tub of the double-flow steam turbine, typically in a region below the tub. As a result, a high temperature is built up on the rotor due to windage heating of the stagnant steam. High rotor temperature potentially shortens the useful life of the rotor and results in failure of the steam turbine.
Several conventional techniques are known for cooling the double flow steam turbine.
A conventional technique involves cooling a tub region of steam turbine. The technique utilizes an external cooling arrangement for all intermediate pressure (IP) dual flow turbine. The arrangement includes a pipe inserted through an inlet bowl section of high pressure (HP) turbine. According to an embodiment of the arrangement, a mixture of flow is extracted from the leakage flow in HP bowl section packing region and HP exhaust. Finally the flow is dumped at front of first stage wheel space of dual IP through the pipe. However, such cooling technique requires additional hardware for cooling arrangement. Also, inserting a pipe in main flow path in bowl affects the aero dynamics of flow before the first stage tub diaphragm.
Another conventional technique includes holes drilled in tub diaphragm. Typically, four holes are drilled each at 90 degrees angle circumferentially of 0.5 inch diameter in tub diaphragm. Further, wheel space/steam balance holes are removed from first stage wheel space. The cooling flow moves out from a main inlet steam and passes through very small holes. As a result, a throttling effect is generated which considerably reduces temperature and pressure of steam.
However, in the above technique root seal clearances do not have significant effect on the steam temperature of tub region. Also, there is very little change in cross flow with increase in the gap between rotor and tub diaphragm surface.
Another conventional technique includes different negative root reactions at each side of the tub region. The negative root reaction allows cooling flow through the wheel hole/steam balance hole of first stage bucket and cools the tub region. Due to different root reactions at both sides of the tub region, there is substantial amount of pressure difference on both the side of the tub which...