POWER September 2014 - 43

WATER
house builder doesn't mean you are qualified
to build a multi-story office tower.
Cleaning vendors also have expertise in
helping you select the solvent or solvents
(with copper deposits) that will clean the
boiler. They should ask for a tube sample to
test in their small cleaning rig (in their lab)
and prove that the cleaning program you have
agreed on really does the job.
Solvent costs are a significant portion of
the cost of the cleaning job. There is no way
to accurately predict the amount of solvent
that will be required to clean a boiler. There
are some general rules of thumb, but remember
that these estimates are often based
on a single tube sample. The deposit in any
boiler is not uniform from top to bottom or
even from tube to tube, so the estimate of the
amount of deposit (and amount of solvent required)
is really more of a guess. Past cleaning
history and years since the last cleaning
often provide a better guide than the current
tube sample (or at least should be a factor in
the decision of how much solvent to bring).
When comparing prices from multiple vendors,
select an amount and base all the bids
on the same amount of solvent. This is particularly
the case with EDTA. After awarding
the bid, be sure that the vendor has extra solvent
(50% extra is common) either on-site or
very close to the plant, so that it can be used
if needed. Many a cleaning has been delayed
hours, if not days, while waiting for more
chemical to arrive from the supplier.
Get Some Help
Particularly as the time between chemical
cleanings increases (because you are taking
better care of the boiler chemistry-right?),
and with normal turnover, your plant staff
may have little or no experience with a
chemical cleaning. There are a number of
consulting engineers who either specialize
in, or offer as one of their services, support
of the chemical cleaning process, acting as
the owner's engineer and project manager.
Their help can be invaluable in keeping the
communication channel open between the
cleaning vendor and your operations, maintenance,
and management staff and in helping
at critical decision points in the process.
A Good Procedure
There are few things more important to
a smooth chemical cleaning than a wellthought-out
and well-documented cleaning
procedure. This will require the time and effort
of the plant's operation and engineering
staff to customize and prepare a cleaning procedure
for each unit.
Cleaning vendors can provide a general
outline of the cleaning process, and a consulting
engineer can help also, but your operators
know where the valves are and which
leak-by and which don't. There will be three
classes of valves: those that stay closed the
entire cleaning process, those that must stay
open the entire process, and those that need
to be opened and closed, depending on where
you are in the cleaning process.
There are also valves that the cleaning
vendor will be responsible for opening and
closing, such as those going to the waste
disposal (frac) tanks and chemical injection
points. Each valve that comes in contact
with the solvent (or potentially could come
in contact with the solvent) needs to fall into
one of these groups and be tagged accordingly.
Be on particular lookout for possible
contamination routes where the solvent can
get to a place where it was not designed to
go. If a contamination route would be very
serious, can a blank flange be installed? If
not, can a telltale be set up to provide early
detection of contamination?
One more aspect of deciding when to
clean is the actual scheduling-determining
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