 Boiler
Monitoring Equipment by Gestra
As a major distributor for Gestra, Valutech has been providing
boiler monitoring equipment for the heat and process fluid
control industry for well over a decade.
For efficient boiler operation with a high degree of safety the
following points are most important.
1. A modern water-treatment plant, designed to meet the specific
requirements of the plant.
2. TDS (total dissolved solids) control by continuous measurements
of the boiler water conductivity, continuous and intermittent blowdown
control.
Depending on the type of water-treatment a certain percentage of
salts remain in the feed water. Some of these salts (in particular
calcium and magnesium salts) form, together with other impurities,
the hardening constituents in the water.
As a result of the evaporation process the salt content in the
boiler water increases continually. To avoid deposits and carryover
of salts into downstream equipment caused by "foaming and priming",
the salt content must be kept within the permissible limits. The
easiest and most reliable method is by continuous blowdown.
Some hardening constituents may form suspended matter that drops
to the bottom of the boiler. Together with other foreign matter
they form a sludge layer which has to be purged to prevent corrosion,
reduced heat transfer etc. For this purpose intermittent blowdown
has proved successful.
Continuous and intermittent blowdown are complementary. To ensure
an optimum TDS level in the boiler water as a rule, both processes
are required. This holds true even for boilers provided with a complete
demineralization of plant.
Separate monitoring of the boiler water density provides additional
safety and should be used when boilers are operating without constant
supervision. In boiler plants equipped with manually operated continuous
and intermittent blowdown valves boiler-water conductivity monitoring
is essential for signaling when the conductivity limit value is
exceeded.
Boiler-Water Density Limitation
The boiler-water density (TDS-level) increases with the operating
time of the boiler. As the conductivity of the boiler water depends
on the TDS level, it increases to the same extent as the water density
and can effectively be used for monitoring the boiler-water density.
The boiler-water density limiter is a combination of a conductivity
electrode type ERL 16, LRG 17 or LRG 19 and the conductivity
limit switch type LRS 1-5b or LRS 1-6b or the conductivity
transmitter type LRT 1-5b or LRT 1-6b. The conductivity
is measured by the electrode and compared with the limit value preselected
on the conductivity limit switch. As soon as the preselected conductivity
limit value is exceeded, a relay contact is released in the limit
switch. The output current of the conductivity transmitter may be
monitored by the max-min limit switch URS-2b.
Continuous Blowdown
The Gestra automatic continuous blowdown system ensures that the
boiler-water density (TDS-level) is kept within the permissible
limit values. The system consists of a conductivity electrode, the
corresponding electronic control units and the intermittent blowdown
valve with electric actuator.
The boiler-water is monitored for its conductivity by the electrode
type ERL 16, LRG 17 or LRG 19, the continuous blowdown
controller type LRR or the conductivity transmitter type
LRT. As soon as the preselected conductivity limit value is
exceeded, e.g. increase in boiler-water density as a result of larger
steam consumption, the actuator will motor the continuous blowdown
valve type BAE to its HIGH flowrate position. When the density (TDS)
is back to normal, the valve is motored to its LOW flowrate position
ensuring continuous and economic blowdown.
Intermittent Blowdown
Besides continuous blowdown intermittent blowdown contributes to
boiler safety and trouble-free operation.
Intermittent blowdown ensures that precipitated solids and sludge
are cleared from the boiler so that they cannot accumulate in the
bottom of the boiler. A programme-controlled blowdown system with
rapid-action intermittent blowdown valve is used for this purpose.
The system consists of a cycling timer type PRS-7b, a
three-way solenoid valve, a strainer and blowdown
valve. The blowdown interval can be adjusted on the cycling
timer within a range of 0.5 to 31.5 hours and the blowdown pulse
(duration) within a range of 1 … 63 s (optimum value = 2 s) A manual
push button override permits manual blowdown to test the operation
of the system.
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