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LRR 1-50, LRR 1-51 - USA - Installation & Operating Manual -
850702-01
Specialist terms, abbreviations
Here, we explain some abbreviations, specialist terms, etc., which are used in this Manual.
NRGT .. / NRR.. / NRS.. / URS .. / URB .. / SRL .. / etc.
Equipment and type designations of GESTRA AG.
SELV
Safety Extra Low Voltage
Operating point (of the plant)
The operating point describes the operating parameters within which a plant or boiler is operated
in its nominal range. In a steam boiler, for example, these parameters would be output, pressure,
and temperature.
The design data may be a lot more stringent, however.
A boiler that is operated at 145 psi (10 bar) and 356 °F (180 °C) may be designed to withstand a
pressure of 870 psi (60 bar) and a temperature of 527 °F (275 °C), for example, which is therefore
not necessarily its operating point.
Continuous blowdown
As the boiler water begins to evaporate, the concentration of non-volatile total dissolved solids (TDS)
increases over time as a function of steam consumption. If the TDS concentration exceeds the limit
defined by the boiler manufacturer, foaming occurs as the density of the boiler water increases,
which is carried over into steam pipes and superheaters. The consequences are adversely affected
reliability and severe damage to steam generating units and pipes. To keep the TDS concentration
within admissible limits, a certain portion of boiler water must be removed continuously or period-
ically (by means of a continuous blowdown valve) and fresh feedwater must be added to the boiler
feed to compensate for the water lost through blowdown. To determine the total dissolved solids in
the boiler water, its electrical conductivity is measured in μS/cm, although some countries also use
ppm (parts per million) as the unit of measurement. Conversion 1 µS/cm = 0.5 ppm.
Operating position of the continuous blowdown valve
It is common practice to use the continuous blowdown valve to remove a certain amount of water
from the boiler in order to keep the TDS within the desired limits. This means that the valve must
always be slightly open during operation so that this quantity of water can be discharged (valve in
OPERATING position). This operating position can be adjusted and the blowdown volume can be
determined using the capacity charts of the valve.
Switching hysteresis
The controller is a 2-position controller, i.e. the continuous blowdown valve moves to the OPEN
position when the set point is reached. The conductivity must then decrease, and when it reaches a
value that is lower than the set point by the set hysteresis HySt, the valve moves into the OPERATING
position.
Temperature compensation
The conductivity of water changes as the temperature falls or rises. To obtain meaningful readings,
it is therefore necessary to base the measurements on the reference temperature of 77 °F (25 °C)
and to correct the measured conductivity using the temperature coefficient tC.
Cell constant and correction factor
The geometric variable (cell constant) of the conductivity electrode is taken into account when calculating
the conductivity. However, this constant may change during operation, e.g., due to dirt deposits on the
measuring electrode. Correction is achieved by changing the correction factor CF.
Flushing the continuous blowdown valve
The continuous blowdown valve can be flushed automatically to prevent it from sticking. In this
case, the continuous blowdown valve is actuated at intervals (flushing interval Si) and opens for
a certain time (flushing time Sd). After the flushing time, the valve is moved into the OPERATING
position or into the required control position.
