hotwell temperature

[kchiguvari]

for improvement of boiler efficiency the hotwell temperatures should be a bit high enough for reduction in coal consumption to be realised. what is the maximum temperature allowable considering the use of multistage pumps whose impellers can be affected by heat and obviously a poor life .

 

[yogibear1]

The thing to consider with pumping of a heated liquid is the decrease in vapor pressure which will cause cavitation. The speed of the pump and the shape of the impeller have a direct bearing upon the dgreee of cavitation. The degree of cavitation depends upon the inlet tip speed of the impeller. The slower pumps (nominal 800 to 1700 rpm) are less susceptible. Tests have shown cavitation to be a maximum when condensate is between 100F to 120F.

 

[rmw]

The situation with the hotwell temperature is trying to balance two considerations against each other. You want the hotwell temperature to be as hot as possible, up to saturation temperature for the condenser, but you want the condenser pressure to be as low as possible, in order for the steam expanding through the turbine to deliver more useful work, and dump as little heat as possible to the condensate. The saturation temperature of the condenser sets the upper limit on how "hot" the hotwell temperature will be.

The reason you want the hotwell to be "hot" is that what ever temperaure is lost to sub-cooling must be made up by burning fuel, coal in your case.

However, in any case, the hotwell temperature is not going to be "hot" enough to have any detrimental effects on pump metallurgy. Some condensate systems heat the feedwater as high a 3-400F before the multistage BFP's ever see it. Obviously, they are designed to live in that service.

There have been some interesting threads on "condensate sub-cooling," and condenser problems. A search of this site using those words should turn up something.

One helpful thread to read would be 391-81838.

rmw