Closing Steam Turbine Bleeds

[mfdoom]

Hi,

I have a set of 3 steam turbines placed in tandem, having 7 bleed points used for heating feedwater. If I decide to close any one of these bleeds, and want to maintain the nameplate capacity and not increase power output, what performance and operational issues should I investigate to determine the feasibility of such an action?

 

[racookpe1978]

For best efficiency and safest long-term life, operate the turbine at its design conditions. Why do you believe the bleeds are reducing efficiency?

The feedwater preheat amounts increase overall plant efficiency.

 

[byrdj]

You NEED to look at your heat balances and WARNINGs provided by the turbine manufacture.

When you close a feed, you will be passing more steam in the latter sections that may not be design to take the loading and thus break turbine blades.

the units I worked provided instructions for the reduction in load based upon which heaters were removed. the closer to the HP inlet, the more reduction required.

That being said, during initial commissioning, the full load test was first go to CVWO, then go 5% overpressure and lastly take out the top heater for MAXIMUM generation. that was if the boiler had the capacitance

my next post is a matrix for a particular unit...

 

[byrdj]

http://files.engineering.com/getfil...-4245-4609-abdb-80891121ccb3&file=heaters.JPG

 

[stgrme]

In general, when you remove all feedwater heaters from service, a turbine manufacturer will advise not to operate at greater than the nameplate rating of the turbine. A turbine manufacturer will advise that a reduction in output below the nameplate rating is required if you remove a heater from service, but higher pressure heater(s) remain in service. In addition, a turbine manufacturer will also advise that a reduction in output below the nameplate rating is required if you remove non-adjacent heaters from service. The amount of reduction must be determined according to a particular manufacturer's recommendations.

Please note that as each high pressure feedwater heater is removed from service in sequence, starting with the highest pressure heater, the final feedwater temperature will be reduced. As the final feedwater temperature decreases, it will become more difficult for the boiler to produce the full (design) steam temperature. Operating at less than design steam temperature will result in increased moisture in the turbine exhaust, and consequently, a higher rate of erosion of the LP last stage blades. There may be other detrimental effects of operation at reduced steam temperatures depending on the configuration of the turbine.

Also remember that removing any feedwater heater from service will result in lower turbine efficiency.

Best of luck!