Page 24 - EngineerIT September 2021

MEASUREMENT

Selecting the right pressure

transmitter for the best

desalination plant performance

Roberto Parapetti, global pressure market manager for ABB Measurement & Analytics,
highlights some of the key factors to consider when selecting pressure measurement
equipment for desalination applications.

lthough the vast majority of the the size of the plants, as well as the pipe network distributing the treated water, have
Earth’s surface is covered by greatly increased to keep pace with rising demand. This has introduced a need to
Awater, most of it is sea water. Only increase pressure levels in order to transport the water, requiring instruments that can
three percent is freshwater and most of handle the operating conditions. These increased pressures put additional strain on
that is locked away as ice in glaciers or pipelines, as well as increasing the risk of fractures and bursts that could lead to leakage.
at the poles. The future will see even this All these challenges, as well the processes and chemistry involved in turning sea
small percentage come under increasing water into drinkable water, need to be considered when selecting pressure measurement
stress as demand grows due to greater devices for desalination applications.
industrial production, changing lifestyles
and dietary habits, and the growing wealth Material of construction
of an increasingly urban population. In the desalination process, the material the pressure transmitter is made from is critically
Meeting the accelerating demand for important. The transmitter needs to be able to resist the highly corrosive saline nature
water will need new techniques to of sea water, sometimes at elevated pressures and temperatures. As these conditions
supplement existing supplies. can vary between plants, different levels of resistance will be required for each plant.
Sensor bodies will be protected by using either AISI 316L stainless steel or Hastelloy for
Alternative supplies of fresh applications that need a higher level of protection.
water Central to any pressure transmitter is the pressure sensor diaphragm, which
One of the techniques holding out needs special protection. This is most often made from Hastelloy C but some extreme
the promise of new water sources circumstances might require something different. For example, in the case of mixed
is desalination. Essentially, the
process involves sifting out unwanted
components of sea water or brackish
water, such as minerals and salt. The
result is potable water available for
drinking or for use in agriculture.
Despite the removal of the salt
and dissolved minerals, the recovered
water still needs to go through the
conventional processes used in treating
ordinary potable supplies to achieve
the required quality. These processes
include such stages as aeration and
filtration. To ensure all the necessary
parameters are controlled throughout
the desalination process, instruments
and analysers are used to measure
values such as pH and conductivity as
well as flow, pressure and temperature.
Pressure is an especially important
parameter to measure. This is because Desalination plant

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