DHA Cogen Power & Desalination Project
An Overview of Fine Filtration System
By M. Samiuddin Mirza, Senior Project Manager DHA
The water and electricity
shortage have been some major issues in our city and to
overcome such insufficiencies a high quality desalinated
water and power technology has been set up in collaboration
with DHA Cogen Ltd. and Siemens to provide quality potable
water to DHA residents. An update on this Hi-tech plant
is described below:
To ensure the provision of safe, reliable,
efficient and affordable potable water and electric power
for the comfort of the prestigious residents of Defence
Officers Housing Authority, Karachi is in unison with the
broad economic and social policy objectives of the Government
It is time again to give our dear readers
an update on the progress of Pakistan's first sea water
Desalination Project. The major site activities related
to civil engineering discipline and works of the foundations
to place the prime equipment of water production is reaching
Next stage is the mechanical erection and
preliminary activities are in full swing. Heat Recovery
Steam Generator mechanical erection is in progress under
the supervision of foreign OEM expert from Japan. The progress
of work from off shore piling for seawater intake structure
to on shore works is monitored continuously on a daily basis.
It must be appreciated that what is to follow is a concise
overview of some of the major activities that are taking
place at project location.
Here DCL shares the technical knowhow with
its readers expressing the importance of the feed (sea)
water quality to be maintained and continuously supplied
to the desalination plants required to produce WHO recommended
quality potable water for the residents.
Feed water (sea water) quality is of prime importance in
selecting the design parameters for a Desalination Plant.
The feed water quality varies from location to location
in the sea. Various samples of sea water are collected for
complete chemical analysis prior to establishing the best
possible location of sea water intake to desalination plant.
The feed water quality is analyzed for presence of various
salts (TDS) chemical elements, total suspended solids (TSS),
microbiological organisms and traces of metals.
The analysis decisive factor for the type
and design of feed water pre. treatment for desalination
units to avoid scaling/fouling of desalination plants and
equipment. This is very important from operational point
of view to minimize the down time of the plant. The sea
water samples taken for DHA Cogen Plant showed high TSS
values i.e. up to 60 ppm (parts per million) which requires
special pre-filtration system titled as "Fine Filtration
system" mesh size 30 microns, to supply quality sea
water as feed water to desalination plants for processing.
Fine Filtration System
Fine Filtration of sea water is achieved by carrying out
micro filtration, which is suitable for the filtration of
pollutant (suspended solids) mechanically through micro-screen
drum type filters especially manufactured by a reputable
foreign company. The fine filtration unit consists of a
rotation drum sieve through which the sea water feed passes.
The micro sieves stop and control the presence of suspended
solids by filtration to micron level.
The feed water from the intake system passes through the
rotating drum leaving the intercept solids on the inner
surface of the screen sieve basket. The screen baskets are
made up of fabric of high tension resistant polyester fiber
with high durability measuring mesh size from 5 micron to
200 micron. The micron giant filters are also provided with
back wash system to clean the collected suspended solids
by spraying water through pump and jet pipe mounted on the
top of screen baskets. The debris are collected by scrappers
and flushed into lateral water collecting channel. The filtered
water is discharged over an effluent over flow weir to a
pump pit for further pumping it to the plant. Penstocks
and stand by arrangements are also provided to avoid shut
downs during maintenance of the equipment.
DHA Cogen Ltd., has made all necessary arrangements for
timely procurement of the F.F. plant, designed and manufactured
by M/s Passavant of Germany with performance guarantee on
expected sea water inlet worst condition of TSS 100 ppm,
grain size 500 micron to achieve the filtered water outlet
condition of 28 micron TSS less than 30 ppm acceptable conditions.
This F.F. plant is in addition to the seawater intake system.
DCL will continue to remain in touch with dear readers
of "DHA NEWS” updating them with Process, Progress,
& Project (PPP).