Electricity + Control October 2015

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STANDBY + BACK-UP ROUND UP
Data logger measures level,
conductivity and temperature
Keller, manufacturer of measuring technology such as iso-
lated pressure transducers and transmitters - represented
in southern Africa by Instrotech – has on offer the new
data logger, CTD (conductivity, temperature, depth) - a
version of the high precision DCX level data loggers for
depths of up to 200 m. It’s a highly integrated, complete
pressure measurement solution for water management.
This data logger for longterm monitoring, stores over
50 000 time-stamped level measurements, as well as
the associated conductivity and temperature readings
in each case. The multipurpose probes have a diameter
of 22 mm, making them suitable for all sounding tubes
with a nominal diameter of 2,5 cm or greater.
Conductivity crucial as standard process value
Water conductivity is a measure of purity, making it
an important standard process measurement in the
water and sewerage sector as well as in the beverage
and pharmaceutical industries. Changes in conductivity
are a clear indicator of contamination, for example with
particles or salts (chlo-
rides, nitrates, etc.). Typi-
cal values lie between
>50 mS (salt water) and
<5 μS (pure water). Kel-
ler supplies conductivity
probes combined with
level probes based on
pressure sensors. These
integrated measuring
systems are ideal for
checking the ingress of
seawater, slurry or ferti-
lizer into groundwater, rivers and lakes, or for performing
observation tasks relating to building projects or localized
water pollution. The Series DCX22 CTD level probes with
integrated data logger are available with a robust 316L
stainless steel housing or other materials, if necessary,
for enhanced chemical compatibility.
Level measurement: a core competency
Keller is a leading supplier of maintenance free, battery
operated level probes with remote data logger for ob-
servations at depths of up to 200 m and optional GSM
module for remote access. With level measuring toler-
ances of ± 0,02%FS, Keller’s extensive portfolio ranges
from data loggers with conventional relative pressure
sensors to level probes featuring two isolated absolute
pressure sensors that compensate for ambient pressure
deviations electrically or using software. All Series DCX-
22 products are now available as CTD level probes with
integrated conductivity and temperature sensor. At a
rate of one measurement per hour, the integrated lithium
battery has a life of up to eight years.
Enquiries:Tel. 010 595 1831 or
email
Guided radar level transmitters improve
reliability at UK power station.
Marchwood Power operates a £380 M natural gas-fired combined cycle
(CCGT) power station on Marchwood Industrial Park, adjacent to the River
Test near Southampton in the United Kingdom (UK).The station generates
842 MW of electricity for the national grid, enough to supply nearly one
million homes.
It is currently one of the most efficient power stations in the UK.The under-
slung condenser vessel sits directly under the steam turbine in Marchwood
Power station, condensing the exhausted steamand returning it to an aqueous
state, which is then circulated for reuse in the generation cycle. A reliable, ac-
curate level control is critical in this part of the process; if the vessel gets too
high, it could impinge on the turbine itself causing untold damage and loss
of generation.The correct condensate level needs to be maintained to ensure
the condenser back pressure is at the optimumvalue, lowering the flash point
of water and preventing wet steam from contacting the low pressure turbine
blades, assisting steam flow through the turbine and increasing efficiency.
When originally designed and commissioned, the plant installation con-
sisted of three differential pressure transmitters, using two out of three voting
method and a single magnetic float gauge on a bypass chamber. However,
there were ongoing issues with differential pressure measurement, mainly
due to the condensate filled impulse lines and vacuumwithin the condenser,
whichmeant they often had an unreliable level measurement on at least one,
increasing the risk of nuisance trips.A differential pressure-based level system
for this type of measurement is complex and requires a lot of interconnecting
pipe work, valves and condensate pots.
VEGA recommended that Marchwood opt for additional interconnecting
pipe work where the magnetic level gauge is installed, so that they could fit
three VEGAFLEX GWR transmitters into bypass tubes, using the same two
out of three voting method, which would give them reliable accurate level
measurement and control. VEGAFLEX use guided wave microwave pulses
which are virtually unaffected by temperature, pressure, vacuum to detect the
level.There were no issues with the Guided radar level transmitters improve
reliability at bypass tubes sharing the same vessel connection ‘manifold’, as it
is a ‘clean’ process.The units weremounted to the side of the boiler, alongside
the existing MLG, where there was plenty of head room for installation.The
measuring range required was over 1,7 m and the temperatures were much
lower than the process at 40 ºC, (even though VEGAFLEX can go to 450 ºC
and 400 Bar if needed).
Marchwood installed each GWR in a 50 mm diameter bypass tube con-
figuration, with isolation valves at the top and bottom. Once in place, it just
needed the GWR units to be cabled
and they were ready to commission.
Marchwood Power engineers carried
out the set-up themselves using
PACTware software, so they could
have a full configuration back-up
and calibration record. As well as
reducing maintenance costs, the
installation of the new sensors was
a more reliable, simpler system and
the cost was much lower than the
original arrangement.
Since installation, no outages
due to unreliable levels have been
recorded.
Enquiries: Chantal Groom.
Tel. 011 795 3249 or email
PRESSURE + LEVEL MEAS REMENT
Electricity+Control October ‘15 40