Electricity + Control October 2015

STANDBY + BACK-UP PRESSURE + LEVEL MEAS REMENT

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

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

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.

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 chantal.groom@vega.com

Enquiries:Tel. 010 595 1831 or email sales@instrotech.co.za

Electricity+Control October ‘15

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