Steam Turbine Exhaust Hood Temperature

Because less power is being transferred to the electrical or mechanical load that is now missing.

Redfred is pretty much right on-

Steam turbines extract the thermal energy from the steam to do work- if there is little or no work to be done, you still have to spin the turbine so "some" work is being done- just not beneficial work.

If a fully loaded turbine with 600 PSIG, 600F inlet steam was exhausting steam at, say 5 PSIG saturated when fully loaded, the steam was giving up 1288-1156 or 132 BTU per pound and leaving at 227F.

Partially loaded, say 10% just to spin the turbine, you only use (132 x 0.1) or 13.2 BTU per pound. The steam will still be superheated but maybe 580 PSIG at 575F superheat which is about 1288-13.2. Guess why your hood is getting hot.

Energygod,

thanks for the explanation...

Can we just say that since the turbine is running out of the best conditions (when loaded), it will be running less efficiently and therefore more of the steam energy is converted to heat rather than to drive the turbine?

thanks

During low steam flow condition, the velocity and density of the steam is greatly reduced. This produces 2 effects:

First, windage losses increase. Windage is essentially friction which occurs when the turbine blades contact the near-stationary steam. The windage losses cause heating of the blades in the last few stages of the turbine.

Second, there is insufficient steam to absorb the heat from the blades. During higher flow conditions, the steam provides a cooling medium for the blades. That heat is carried by the steam into the condenser. The lower density and lower mass flow rate of the steam results in less heat transfer capacity. The temperature in the exhaust hood rises as less heat is removed to the condenser and more stays in the hood area.

The Heat Drop from the Steam, is very less due to very low load. Hence the temperature of steam flowing through the turbine is higher and hence the hood is having more temperature, wich in turn depends upon the surface radiation level also.

DHAYANANDHAN.S