Skip to main content

Temperature control in a steam line

For injecting hot de-ionised water into a turbine steam line, an Austrian steel plant chose Hydra-Cell seal-less pumps.  Compared with the multi-stage centrifugal units originally intended, they were smaller, almost 40% less expensive to buy, more energy efficient and cheaper to run.  They were also easier to control, simpler to maintain and potentially more reliable on this application, carrying no risk of seal failure.

The steel plant needed to install a temporary pumping system to control the temperature of superheated steam in a turbine.  The task was to supply the steam line with hot de-ionised water at temperatures up to 105ºC  (220°F) and pressures to 45 bar (650 psi).  Service would be continuous - 24 hours a day, 7 days a week - over a 3 month period while the permanent steam conditioning plant was re-furbished.

De-ionised water is a difficult liquid to pump.  It does not have lubricating properties - so any pump that relies on the pumped liquid to lubricate its seals is vulnerable to rapid wear and likely to need frequent seal replacements.  On the other hand, most types of seal-less pump could not match the output pressures needed for injecting water into the steam line.

The original intention was to use two multi-stage centrifugal pumps, alternating one week in operation with one week on standby or maintenance.  But the pump specialists consulted by plant engineering, proposed a different solution, and on their recommendation a system based on the Hydra-Cell G-25 seal-less pump went into operation.

Two G-25 pumps were installed, as had been planned for the centrifugal pumps.  In the event, only one Hydra-Cell unit was needed and the second acted simply on standby duty.  The required flow and pressure were well within the capability of the G-25, and in virtually all other respects the Hydra-Cell unit had a clear advantage over the pumps originally envisaged.

With its simple build and high performance in relation to size, the Hydra-Cell pump/motor package, which included an oil cooler to compensate for high liquid temperatures, was almost 40% less expensive than the centrifugal alternative.

Part of this was down to lower motor costs.  Hydra-Cell pumps operate at more than 80% efficiency, as against maximum efficiencies of 45% for the multi-stage centrifugal pumps under consideration.  The G-25 pumps on this duty could be fitted with 11 kW (15 hp) motors, compared with the 55 kW (75 hp) motor needed to achieve comparable performance with centrifugal pumps.  So ongoing energy costs would also be considerably lower.

Another important consideration for this application was the Hydra-Cell’s capability as a metering pump.  Pump speed governs output flow - in a constant linear relationship which is not affected by pressure changes in the outlet line.  Flow could be easily and accurately controlled (with a turndown ratio of 10:1 or better) via a frequency inverter, with the pump responding fast on signal when a rise or fall in steam temperature needed correcting by adjusting the flow of DI water.

A centrifugal pump would have been more difficult to control because the flow/pressure relationship is not linear - rising pressure progressively reduces output flow.  Performance through time would also change if seals were allowed to wear.

The performance of the Hydra-Cell unit stayed consistent throughout the specified 3 month service period, and the pump ran as planned until the temporary steam conditioning system was de-commissioned.  Little maintenance had been needed, no problems were reported and both pumps were retained by the steelworks against any future requirement.

Model: G-25
Flow:  4000 l/hr (1060 gph)
Pressure:  45 bar (650 psi)

Liquids:

Deionised Water, Hot Deionised Water,