Posted by Harold Kestenholz on July 10, 2001 at 15:33:32:
In Reply to: location of feed watewr regulator valve posted by zaib on July 10, 2001 at 09:41:46:
*** a feed water regulator valve be installed between the feed water pump & economiser
A description of the direction of flow may help:
http://www.fas.org/man/dod-101/navy/docs/swos/eng/62B-203I.html
"Knowing the water/steam flow through the boiler is critical to understanding the interrelationships of the boiler components. A summary follows:
The flow begins when feedwater enters the economizer inlet header and flows through the economizer tubes to the outlet header picking up approximately 100-200° F of sensible heat to about 350°F.
Feedwater leaving the economizer enters the steam drum via the internal feed pipe. The feed pipe distributes the water evenly along the length of the steam drum. "
An economizer is subject to a potentially variable flue tamperature depending on the service of the generator. Changing flow rates may cause varying water temperatures within the economizer. At times boiler water is circulated through the economizer to temper economizer water content. The economizer is considered part of the pressure vessel. A feedwater regulator provides water to the pressure vessel(s).
http://www.va.gov/facmgt/consulting/economizer.asp
"The economizers are located in the boiler stack close to the stack gas outlet of the boiler. They may be supported from overhead or from the floor. A feedwater line, which serves the boiler, is piped to the unit. No additional feedwater control valves or stack gas dampers are required. "
The feedwater pumps maintain a pressure 100 pounds or higher than the boiler pressure. The feedwater regulator permits this pressurized water to drop to boiler pressure in the economizer.
*** or between economiser & boiler drum and WHY.
The daerating condensate tank removes oxygen from feed water before the regulator so it will not enter and corrode an economizer. A question relating to an economiser piped before a regulator feeding water to a boiler drum could be: Why use a set of pumps to push water through an economiser, then raise the feedwater pressure using another set of pumps to make the pressure 300 psig higher than the boiler - when one set of pumps can do the job pushing water into the economiser which passes the water on to the boiler drum? Or - why would one possibly require the pumps to regulate against pressures due to economizers in the flue gases?
There are other types of economizing units that would be before the regulator, such as blowdown heat recovery, so these may make the question more complex.