daily operating costs, energy represents
about half of total expenses.
Reverse osmosis has grown in favor
over thermal desalination processes
(multistage flash and multi-effect distillation) because of relatively lower capital costs and significantly lower energy
costs. Moreover, the SWRO process can
readily incorporate ERDs into its system
Broadly speaking, there are two
types of ERDs:
1. Energy recovery turbines using
impulse rotary technology, and
Both technologies recover substantial
amounts of energy stored in the brine
waste stream to drive the high-pressure
membrane pumps. These ERDs can
reduce the energy consumption/cost of
the pumps by as much as 60%.
ERDs have limited valve applications, although there are some control
valves and several highly engineered,
special-purpose valves installed on these
systems. Most importantly, because
reducing overall energy costs in SWRO
plants is of paramount importance,
those charged with designing and specifying ERDs are seeking ways to incorporate valves, actuation and controls that
enhance flow efficiency and reduce energy costs.
The SWRO industry is growing at a
rapid pace. A substantial core of funda-
mental application experience and
expertise is continuously cataloged to
meet this need. Yet SWRO is still a
young and developing industry that will
require new and adaptive technologies
to fully exploit its potential.
BEN LEE is a product manager at Flowserve Corporation ( www.flowserve.com). He has 32 years of
experience working with Flowserve in various
roles. Reach him at firstname.lastname@example.org.
1. Pitting Resistance Equivalent Numbers
(PREN) indicate the relative resistance of
stainless steel- and nickel-based alloys to pitting corrosion. PREN are calculated as follows: PREN = Cr + 3. 3(%Mo) +
16(%N). The higher the value, the greater an
alloy’s expected resistance.