Page 84 - Boiler_Operators_Handbook,_Second_Edition

Boiler Plant Operations 69

signal winds back into the normal control range. is ready to go into service. The data should be collected
Modern microprocessor based controls have anti- as soon as possible and, when necessary, before per-
windup features and procedureless, bumpless transfer formance testing. The following list is not necessarily
(manual to auto and vice versa) features that eliminated complete. You may note certain things about your new
the problems with earlier pneumatic and electronic con- boiler that are not indicated or documented and choose
trols. It’s possible the system designer didn’t properly to record those as well. The more data you collect the
configure those features and you can still experience more likely you will be able to detect problems with the
bumps on transfers. boiler during its life.
A fuel control valve should be positioned at a mini- Data should be collected at each firing rate (each
mum (mechanical) stop where fuel flow after ignition is screw on a jack shaft cam as shown in Figure 2-4 or each
more than the controller’s set point. If it isn’t, the con- 10% interval of control signal) and include much more
troller would wind up to maximum output (and it has than readings of all boiler mounted instruments, pressure
lots of time to do it before a main flame starts) so the fuel gauges, thermometers, etc. On steam boilers the drum
valve would suddenly swing open when the controls are level using either a signal level, a temporarily mounted
released to automatic. If the flow is a little higher than ruler, or simply the number of nuts at the side of the gage
the controller’s set point, reset windup (in this case it glass should be recorded. For hot water boilers the water
would wind down), there’s simply a delay in response. level in the expansion tank should be recorded even if it
However, there may not be sufficient time between main is adjusted automatically. I have seen many new boilers
flame ignition and transfer to automatic for the controls supplied without any pressure gauges on the fuel supply
to wind down and excessive fuel feed could still occur. system. Despite that you should find that required test
If the controls do wind down before transfer they ports permit connection of a gage to collect that data. This
will have to recover and once the fuel valve starts to is especially important when you have multiple boilers
open it swings open more than it should. To overcome or other equipment using a fuel gas supply which would
those strange actions the interface between Burner Man- prohibit taking fuel meter readings. If the boiler does not
agement and combustion controls should actually adjust have a fuel meter I would recommend purchasing one
the set points to achieve purge and light-off conditions and installing it right away so that data could be recorded
so the controls are controlling all the time. The ramping and collected continually.
controls should help overcome that problem with reset Not all boilers are fitted with draft gages but that
wind-up on light-off. Bumps off low fire and maximum should not stop you hooking up a manometer, measur-
fire can occur during normal firing and are discussed in ing, and recording the draft (sometimes a pressure read-
the section on controls. ing) at the fan discharge, the burner wind box or burner
head, in the furnace, at intermediate points within the
Collect Performence Data convection bank (where accessible), the boiler outlet,
Among the many things that don’t need a “break economizer outlet (when equipped with an economiz-
in period” a boiler should top the list. From the moment er), the air heater outlet (when equipped with an air
the first fire lights in the furnace a boiler begins breaking
down. So, collecting performance data on a new boiler
as soon as possible is essential. It gives you a record
of what the boiler was capable of when it was new,
completely clean, and not broken. While I know some
examples of where problems with a new boiler had to
be corrected before it was accepted a boiler is normally
at its best when it’s new. Should it happen that changes
have to be made in a new boiler this data should be col-
lected once the boiler is accepted. This data provides a
basis for comparison to actual operating conditions dur-
ing the life of the boiler and is very helpful in detecting
the source of problems such as inefficient operation.
Given some time to think about this since the first
edition of this book was published I have come up with
a list of data that should be collected once a new boiler Figure 2-4. Adjustment screw on control valve