Multistage Turbines

Most multistage steam turbines are engineered to suit each application. There are two main types - impulse stages and reaction stages. In the impulse type, all pressure drop is taken across the stationary nozzle diaphragms whereas the reaction

Additional steam consumption if load less than normal max.

Additional steam consumption if load less than normal max.

Output power

Figure 8.12 Effect of turbine auxiliary valves.

I Max power with

1J/^ auxiliary valves open

Max power with auxiliary valves closed

Output power

Figure 8.12 Effect of turbine auxiliary valves.

the reaction type shares pressure drop equally between the moving and stationary rows of blades. Both types usually have an impulse 'control stage', mainly to limit axial thrust, but also to allow for multi-valve operation whereby steam is fed progressively to sections of the nozzle ring as the valves open in sequence. Reaction turbines have higher isentropic efficiency than impulse machines, but 'pure' impulse is rare and impulse blading with a degree of reaction is nearly as good for medium sized machines. Manufacturers' catalogs rarely quote efficiency and when buying new this should be investigated.

One potential problem with multi-valve machines is a dip in efficiency when a valve starts to lift off its seat. The initial steam flow is insufficient to generate high nozzle velocity and so contributes little power from the control stage. Operating at 'valve points' is therefore to be avoided if possible.

Was this article helpful?

0 0
Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment