Hi there
DN stands for nominal diameter and the number is the pipe diameter in mm. 200DN pipe is therefore 8" pipe
The economiser heats boiler feed water by using heat in the combustion gas which has left the evaporator/superheater tube bundles. The water flow normally goes from the boiler feed pumps through the economiser then sometimes through a preheater (which I think is your pre-evaporator) and then into the drum. Normally, but not always, no steam is formed in the economiser. The water circulates between the evaporator and the steam drum normally by natural convection. Steam is formed, by boiling, in the evaporator tubes and disengages from the feedwater in the steam drum, or drums. The purpose of the evaporator is to make steam from hot water. The evaporator is the "wall" of tubes that you see when you look inside the furnace of a water tube boiler. Some of the many purposes of the steam(s) drum are to separate water and steam, to provide a reservoir of steam to accommodate small, short term demand fluctuations, to act as a reservoir for water in the boiler, using a water level control system and to provide something for the evaporator tubes to connect to. Superheaters are used to raise the temperature of the steam above saturation temperature, and are normally a bundle of tubes with steam passing through the tubes and partly cooled combustion gas passing over the outside; the gas having been partly cooled by some or all of the evaporator. Superheaters often come in pairs(or even more); the first one heats the steam to higher than the required temperature, then water is sprayed into the steam to reduce its temperature slightly (called attemperation) then the second superheater heats up the steam to the final required temperature. The point of all this is to control the steam temperature very precisely, which is required if the user is a steam turbine. Reheaters are sometimes called superheaters. A reheater takes partly expanded steam from a turbine, heats it up and returns it to the next lower stage in the turbine. The point of this is to improve efficiency by adding heat, and to prevent condensation in the turbine which would damage it. A reheater looks and acts like a superheater.
The above is a gross simplification of the actual picture.
If you can locate a copy of the book "Steam" by Babcock and Wilcox, it will give you a better idea of the form and function of the things that make up a boiler.
Cheers
Steve McKenzie
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From: e-Engineer [mailto:segip@tm.net.my]
Sent: Tuesday, April 30, 2002 11:44 AM
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Subject: [PipingDesign] Boiler Piping System
Anybody fimiliar with boiler piping system?
What is DN? i.e. 200DN is it referring to the diameter?
We have a component which includes the followings;-
What is the flow like? Anybody knows of the function of thesecomponents?
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Received on Mon Apr 29 23:46:00 2002
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