Lesson 5 - Steam Technology SAQ
This lesson allows you to test yourself on the material covered in the Steam Technology lesson and determine the level to which you have met the learning outcomes.
Suggested Response - Q1
* Explain the difference between:
a) Shell (fire-tube) and water tube boilers
b) Pressurised and vented condensate recovery
c) Direct acting and pilot operated control valves
d) Process steam traps and drainage steam traps
Response:
a) With shell boilers, the ‘fire’ is kept in tubes that are passed through a shell with water.
With water tube boilers, the water is in the tubes and the ‘fire’ is on the outside of them. Water tube boilers are able to produce high outputs and high pressures, but their efficiencies are typically lower than those of shell boilers.
b) With a pressurised system, the condensate is kept pressurised and is pumped back to the boiler house without flashing. With a vented system, the condensate is collected into a vented condensate tank. This means that the condensate will release flash steam.
c) With a direct acting valve, the downstream pressure acts directly on the valve diaphragm in order to control the pressure. With a pilot operated control valve, the downstream pressure does not act directly on the diaphragm, but instead does so via a pressure sensing pipe, which together with a pilot diaphragm activates the control pressure in a pilot loop.
d) Process steam traps are fitted to process equipment in order to remove condensate.
Drainage steam traps are fitted to steam lines in order to drain the condensate that forms as the lines cool down.