Blowdown
The purpose of boiler blowdown is to regulate the amount of total
solids, dissolved and suspended, contained in the boiler water.
Added feedwater carries dissolved solids that are left behind
in the boiler as it is evaporated. Chemicals also add to the solids
concentration. Since evaporation is continuous, the accumulation
is also continuous. BLOWDOWN to waste a part of the concentrated
water and replacing it with feedwater is the only way the total
solids concentration can be held in check.
Failure
to remove sediments and sludge accumulation may result in
premature boiler failure such as cracked boiler plates,
low water cutoff failures or pressure controller failure.
Failure to control dissolved
and suspended solids in the boiler water may result in
foaming and priming. This in turn results in a wetter
steam and poor fuel economy.
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Steam boilers used solely for heating and where practically all
of the condensate is returned to the boiler, blowdown only as
often as the concentration of solids require.
Steam boilers used for process steam requiring high quantities
of make-up water should be blown down as required to maintain
desired chemical concentration levels and to remove precipitated
sediments.
Boilersmith Ltd. boilers are supplied with three types of blowdown
connections; BOTTOM BLOWDOWN, LOW WATER CUTOFF/WATER COLUMN BLOWDOWN
and SURFACE BLOWDOWN.
- Bottom
Blowdown and/or Drain
The bottom blowdown permits the removal
of sediment and sludge accumulation from the bottom of
the boiler.
If your boiler is supllied with two blowdown valves (a
quick-opening and a slow-opening valve) always
open the quick-opening valve first followed by the slow-opening
valve. This reduces stress on the pipe and fittings.
- Low
Water Cutoff and/or Water Column
All boilers are supplied with ball valves on the low-water
cutoffs for blowdown purposes of these devices. In addition
to removing sediment, blowing down while the burner is
running ensures that the low water cutoff is functioning.
The burner should shut off during the blowdown.
- Surface Blowdown
Continuous blowdown allows dissolved and suspended solids
to be removed continuously near the water surface. There
are three types of Surface Blowdown.
Intermittent
Blowdown manually at a pre-determined time schedule and
water testing schedule.
Continuous
Blowdown continuously while the boiler is steaming. A
throttling valve is installed to permit a controlled flow
to drain. The amount of flow is determined by periodic
testing.
Automatic
A solenoid valve and flow control valve are installed.
Based on conductivity or the amount of boiler feed water
the solenoid valve is energized.
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