PRODUCT NEWS

   
    
New TDS system promises major improvement
in boiler water quality and energy saving.

Demonstrating new levels of accuracy and reliability,
Emerson Process new Total Dissolved Solids Control
System, the TDS 880, offers a significant advance in
boiler blowdown management.

Benefits to steam boiler operators include more efficient use
of fuel, savings in water treatment chemicals, and less water
carryover in steam. Key to the superior performance of the
TDS 880 is an innovative design for the self-contained probe,
which functions independently of any boiler components and
eliminates a major cause of measurement drift. Integral
temperature compensation further improves measurement
accuracy and stability.

The total amount of dissolved solids (TDS) in boiler water is
assessed from the conductivity of the water. Uniquely, the TDS
880 performs this measurement entirely within the calibrated
probe tip. This yields excellent long-term accuracy and stability
by avoiding the problems associated with using part of the boiler
structure as the second electrode, such as unpredictable changes
in the electrical circuit through scaling and oxide build-up.
Measurement integrity is enhanced further by the use of titanium
and a high frequency AC signal to minimise electrode contamination.
The probe tip is also equipped with an integral platinum resistance
thermometer (PRT) to ensure close tracking of any changes to
water temperature, enabling accurate conductivity readings to be
made from a cold start up to 300°C.

Manufactured using techniques and materials developed over
25 years for Mobrey's renowned Hydrastep and Hydratect
products, the TDS 880 probe is designed to provide unsurpassed
reliability in the highly aggressive environment of a steam boilers.
The glandless, all-welded construction uses zirconia, titanium and
stainless steel components which negates the use of glands and
any possible leak. The probe is also fully adjustable during installation
and can be mounted both horizontally and vertically. 

A separate microprocessor-based control unit provides full
configuration facilities and control outputs for blowdown systems.
The unit, which is available for panel mounting or within an IP66
enclosure, provides a direct, high visibility readout of TDS or water
conductivity. Readings of water temperature, TDS setpoint, alarm
points and mA output are available via a secondary display, and
LEDs are used to indicate current alarm conditions and blowdown
valve status. The unit is easy to set up using the intuitive, menu-based
configuration facility, which is password protected for security.
Two fully independent TDS setpoints can be configured to operate
volt-free relay contacts for blowdown valve control, using on/off,
time proportioning, pulse proportioning or band operating modes.
 A separate 4-20mA output can be allocated to either TDS
(configurable for neutralised or raw water) or to water temperature,
enabling the TDS 880 to be easily incorporated into a plant DCS
or SCADA system.

Blowdown is an essential process for maintaining the efficiency
of steam boilers. As boiler water evaporates, the concentration
of suspended and dissolved solids increases. This can lead to
adverse conditions such as sludge build-up, surface foaming,
and increased water carryover into the steam, resulting in damage
to turbine blades and inline instruments or damage to valves and
process equipment through water hammer. Blowdown is the
controlled drainage of water containing dissolved solids and
sludge; the introduction of cleaner top-up water consequently
reduces the level of contaminants. Draining water from the
bottom of the boiler at regular intervals reduces sludge deposits,
and dissolved solids are normally removed by taking water from
near the surface in a continuous blowdown process.  This can
result in unnecessary loss of both energy (from the discarded
hot water) and expensive water treatment chemicals if the process
is not carefully and accurately controlled. The TDS 880 system,
with its enhanced accuracy and stability, enables blowdown to
be optimised to maintain TDS at an acceptable level while
minimising wastage. 

Mobrey can supply all the components necessary to
implement a TDS Control System, including blowdown valves
and a dedicated T-piece that provides a boiler attachment for
the probe with the blowdown connection in a single unit.
Alternatively, the TDS 880 system can be used to enhance
existing installations.
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November 2004
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