Question of the Month – 2018

Question of the Month for April 2018

QUESTION:

What are the cold clearances on an average steam turbine?

ANSWER:

Steam turbine clearances are comparatively small.  Radial clearances are 0.180″ to 0.250″, which is the distance between the top moving blades and casing.  Axial clearances are 0.100″ to 0.200″, which is the distance between the nozzle exits and the leading edge of the blade.  Diaphragm gland clearances are 0.002″, which is the distance between the shaft and the bottom of the diaphragm.  Bearing clearances are 0.001″ per inch of diameter of shaft, with a minimum of 0.005″.  A 4″ shaft would rotate in a bearing with an inner diameter of 4.005″, whereas a 10″ shaft would have an inner diameter of 10.010″.

Question of the Month for March 2018

QUESTION:

How should horizontal steam lines be pitched? 

ANSWER:

Horizontal steam lines must always be pitched in the direction of the steam flow and have traps installed at the end of the run so condensate can be removed.  If the lines were piched back toward the boiler, the steam would pick up the condensate and cause water hammer and possible line rupture.

Question of the Month for February 2018

QUESTION:

Can plant efficiency be increased if a closed feedwater heater is used? 

ANSWER:

Yes, it is possible to increase plant efficiency when heating feed water in a closed feed water heater.  A good example of this is when steam is extracted or bled from a high-pressure stage of a steam turbine and used in a closed feed water heater.  The latent heat of the steam is recovered in the feed water instead of being lost in the condenser.

 

Question of the Month for January 2018

QUESTION:

What is the difference between a flush-front and an extended-front horizontal return-tubular boiler?

 ANSWER:

In the extended-front type horizontal return-tubular boiler the front tube sheet is set in line with the front of the boiler setting.  The lower part of the shell extends beyond the tube sheet.  This extension forms part of the smoke box and is known as the dry sheet.

The shell of the flush-front type horizontal return-tubular boiler does not extend beyond the front tube sheet.  The front of the boiler is set back from the front of the setting to allow a space which forms the smoke box.  An arch at the front of the furnace prevents the gases from entering this space and going directly to the stack.