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Abstract There is clear trend for high-pressure trains of a larger size. For a given plant size it reduces the number of trains with the corresponding savings in installation costs. Furthermore, fewer, larger Irains generally mean less capital than more, smaller trains. Larger units have, inherently, higher efficiency. There is a preference amongst plant designers and operators for la'ains capable of operating reliably without pressure lubrication. Today this limits the train size to, approximately, 10,000m3/d, considering a 40-45% conversion rate. Reliability, availability, dependability are paramount. Metallurgy with proven track record, adequate material combination, reasonable cost and ease of processing is the key to the success of the installation. 21094
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Keywords." High-pressure pump; Alloy 885; Materials; RO train
I. Description
In an analogy between a reverse osmosis
plant and the human body we could say that the
membranes are the lungs of the system and that
the feed pumps are the heart.
The main feed pumps, also known as the high-
pressure trains, are, undoubtedly, one of the
critical components of the plant. As such, every
effort should be made to ensure this equipment is
most reliable, dependable and efficient. This brief
paper focuses on trains of mid to large size, i.e.
trains for production of 2,500 mVd and larger.
The high-pressure train on today's plants
typically consists of a high-pressure pump, driven
by an asynchronous electric motor, and an energy
recovery turbine (ERT). The pump increases the
feed water pressure to that required by the membranes; the brine, rejected at high pressure,
is past through the ERT, which recovers that
energy. The electric motor provides the net
power.
The most common configuration is that in
which the electric motor, featuring a double
extended shaft; is placed between the pump and
the ERT, three separate elements -- pump, motor
and turbine, for much improved reliability, avail-
ability and maintainability.
2. Equipment configuration
On seawater plants, the high-pressure pump is
of the centrifugal type, horizontal configuration
and with multiple stages. The pump casing could
either be axially, also referred to as horizontally,
split or radially split of the segmental ring type.
It is not the intention of this paper to compare
both designs, however, an analysis of the in-
stallations yields the following results (Table 1).
Table 1
High-pressure pump - construction
Train size, Segmental, Axially Number of
m3/d radially (horizontally) trains
split, % split, % considered
2,500-4,000 67 33 90
4,000-5,500 32 68 75
Greater than 7 93 130
5,500
In the smaller segment, 2,500-4,000, the
trend is to install segmental radially split pumps.