GESTRA SPECTORcontrol II, Оригинальная инструкция по установке

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Important notes
Terms and definitions
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Continuous boiler blowdown
As the boiler water evaporates, the concentration of non-volatile dissolved solids (TDS) left behind in
the boiler increases over time as a function of steam consumption. If the TDS (= total dissolved solids)
concentration exceeds the limit defined by the boiler manufacturer, foaming and priming occurs as the
density of the boiler water increases, resulting in a carry-over of solids with vapour into steam lines and
superheaters.
As a consequence, the operational safety is impaired and severe damage to boiler and tubes may
occur. To keep the TDS concentration within admissible limits, a certain portion of boiler water must be
removed continuously or periodically (by means of a blowdown valve) and fresh make-up water must
be added to the boiler feed to compensate for the water lost through blowdown.
Electrical conductivity - here as a result of the TDS content of boiler water - is measured in
microSiemens/cm (μS/cm). However, in some countries ppm (parts per million) is used for conductivity
readings. Conversion: 1µS/cm = 0.5 ppm.
Intermittent boiler blowdown
During the evaporation process fine sludge deposits settle on heating surfaces and in the lowest part
of the steam boiler. Boiler sludge is caused e. g. by oxygen-scavenging agents. Sludge deposits can
form an insulating layer that retards the flow of heat and cause the boiler walls to become dangerously
overheated.
To perform a bottom blowdown the intermittent blowdown valve must be opened abruptly.
The resulting suction effect occurs only at the moment when the valve is being opened, the opening
time should therefore not exceed 3 seconds. Longer blowdown periods will merely waste boiler water.
The timed pulse/interval control of the intermittent blowdown valve optimises sludge removal while
minimising loss of boiler water. The interval between the intermittent blowdown pulses and the duration
of the boiler blowdown can be set accordingly .
Large boilers often require more frequent boiler blowdowns. In this mode the frequency and the interval
between the pulses can be adjusted.
Operating position of the continuous blowdown valve
To keep the TDS concentration within certain limits a small quantity of boiler water is discharged con-
tinuously via the top blowdown valve. To ensure continuous blow-off the valve is always slightly open
(= operating position).
This operating position can be adjusted accordingly. For the corresponding amount of boiler blowdown
refer to the capacity charts of the continuous blowdown valve.
Compensation for steam bubbles (conductivity control)
The presence of steam bubbles can lead to greatly fluctuating conductivity readings. An attenuator will
damp the oscillations in the measurements.
Switching hysteresis (conductivity control)
If the controller is configured as 2-position controller, the valve will OPEN if there is a positive deviation
(X > w). The conductivity must then decrease until a new value that is lower than the setpoint minus the
adjusted hysteresis is reached. Once this value is reached the valve will be motored into the operating
position.
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