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Two-Cell Conductivity Analyzer Applied to Reverse Osmosis
Continuously Monitor
Your Process Efficiency
Background
When solutions of
different concentrations are separated by a semipermeable membrane,
the natural flow of the more dilute water to the more concentrated
side of the membrane is called "osmosis". In water
purification by reverse osmosis (RO), sufficient pressure is applied
to the concentrated side to force the water to flow through the
membrane in the other direction. The water is purified since
dissolved solids cannot easily pass through the membrane. Reverse
osmosis can remove 85% to 98% of dissolved salts in one pass, and
multiple passes can further improve purity. The purified water is
called "permeate" or "product". A continuous
flow of the concentrated water is discharged to prevent an excessive
buildup; this discharge is called "concentrate" or
"reject".
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Application
Efficiency of
reverse osmosis operations is usually monitored by comparing inlet
and outlet conductivity (sometimes reported in terms of ppm
TDS¾ total dissolved solids). Calculations of percent passage
or percent rejection used for this comparison can be provided and
displayed directly by a two-cell 9782 Analyzer.
Individual cell
temperature compensation for salts, with either conductivity or TDS,
and percent passage or percent rejection readouts provide a flexible
RO monitoring system. Temperature readout is also available for
normalized performance comparisons.
With direct conductivity or TDS, low percent
passage or high percent rejection indicates good system efficiency.
Alarms can be set accordingly. From operating experience and flow
rate data, abnormal readings can be interpreted as membrane fouling,
incorrect flow rate, membrane failure, etc.
Resistivity ratios can also be used to
calculate the percentages. In that case, Cell 1 and Cell 2 are
interchanged for the calculation, since resistivity is the
reciprocal of conductivity.
A special note: Many membrane materials and
water compositions also require pH adjustment of the feedwater to
prevent membrane deterioration or fouling.
Honeywell's Conductivity Solution
Using industry-accepted algorithms,
the 9782 Analyzer accurately compensates
for conductivity changes with temperature, making it ideal for a
broad range of water treatment applications. The superior electronic
design ensures reliable signals from the cells over the full display
range, allowing separation of cell and analyzer by as much as 1,500
feet without reduction of accuracy. A wide variety of conductivity
cells with cell constants specified for individual processes allows
reliable, continuous measurements.
Features
- High-purity water temperature compensation for neutral salts
- Computed, calculated variables (% passage, % rejection, ratio, difference)
- Large digital display showing conductivity, resistivity, or total dissolved solids and temperature
- Up to two independent cell inputs
- Multiple outputs for transmitting up to three measured or calculated variables
- Up to four relays available
- Ruggedly constructed cells withstand pressures up to 250 psig and temperatures up to 285° F (140° C)
Benefits
- Temperature compensation specific to high-purity water applications for improved accuracy
- Rugged materials of construction, reducing cell replacement costs
- Flexible mounting assemblies, reducing installation costs
- Automatic math computations for improved process analysis
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