FULTON RBC1250 - Feedwater Disperser

RB-RBC-IOMM-2015-1
Fulton Ltd
Page 39
MAINTENANCE - 4
Feedwater
Mounting Flange
Disperser Holes
Feedwater
Valve
4.9 FEEDWATER DISPERSER
CAUTION
DO NOT use unheated or untreated feedwater which can result in premature tube failure by oxygen
corrosion.
!
RBBoilersarettedwithafeedwaterdisperser,removableforcleaning.Theholesinthe
disperseraresizedtogiveanexitvelocitysufcienttoensurerapidmixingoftheboilerwaterand
the cooler feedwater, reducing temperature gradients within the water to a minimum.
In order to reduce oxygen corrosion to the tubes and prevent thermal shock, it is imperative
that feedwater entering the boiler is heated to 80 °C - 85 °C. (The solubility of oxygen in water
reduces to a minimum at 85 °C), on initial start-up this may not be possible.
As part of the water treatment programme chemicals will be dosed into the boiler feedwater line
and/or the boiler feedwater tank. The nature of many of these chemicals is that they react when
there is a rapid rise in temperature such that dissolved solids are precipitated and fall out of
solution as a sludge.
Therstmajorchangeintemperaturetothefeedwaterisasitentersthefeedwaterdisperser,as
a result some solids will be precipitated within the disperser, the majority will be washed through,
however some may remain as deposits.
The disperser should therefore be removed, inspected and cleaned at each inspection interval
i.e.6monthlyorbeforeifthefeedwaterpumphasdifcultyinmaintainingtheboilerwaterlevel.
To reduce the problems of possible disperser blockage, chemical dosage should always be
applied as a slug into the feedwater pipe rather than into the feedwater tank.
By chemical slug method, precipitation of solids only takes place from the water either side and
mixed with the dose.
By dosing the feedwater tank all of the feedwater becomes saturated with chemical causing all
of the feedwater entering the boiler to release precipitates/sludge. The exceptions are Sulphite
compounds used for oxygen scavenging which can be dosed directly into the feedwater tank.
Figure. 27 - Feedwater Disperser