Solids control system benefits steam boilers

Demonstrating claimed new levels of accuracy and reliability, Solartron Mobrey's new total dissolved solids control system, the TDS 880, offers an advance in boiler blowdown management.

Demonstrating claimed new levels of accuracy and reliability, Solartron Mobrey's new total dissolved solids control system, the TDS 880, offers an 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 the 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 said Solartron.

The total amount of dissolved solids (TDS) in boiler water is assessed from the conductivity of the water.

The TDS 880 performs this measurement entirely within the calibrated probe tip.

This yields 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 degrees C claimed Solartron.

Manufactured using techniques and materials developed over 25 years for Solartron Mobrey's Hydrastep and Hydratect products, the TDS 880 probe is designed to provide 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 said the manufacturer.

Two fully independent TDS setpoints can be configured to operate volt-free relay contacts for blowdown valve control, using on and off, time proportioning, pulse proportioning or band operating modes.

A separate four-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 enables blowdown to be optimised to maintain TDS at an acceptable level while minimising wastage added Solartron.

Solartron Mobrey said it 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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