New desuperheater
February 2013
Valves, Actuators & Pump Control
PSV Mitech has launched a new type of desuperheater, which may also be used as an attemperator, with high turndown, good controllability and no moving parts in the steam flow. No additional control valves, steam assist or instrument air are required, only water, power and position signal. The eSteam desuperheater is a low maintenance and low cost solution for cooling superheated steam to within a few degrees of setpoint. It is designed for steam with flow rates up to 100 t/h at temperatures up to 500°C and pressures to 40 barg.
With five to seven nozzles, the unit can cover a wide range of requirements. Fine temperature control of ±1°C is achieved by controlled pulsing of the solenoid valves, each of which feeds high pressure water to a spray nozzle. This is the primary advantage of this system – the full available water pressure is applied across the nozzles when they are operating. In a conventional desuperheater an upstream globe control valve controls the water flow rate so that when a low water flow rate is required, the globe control valve closes and increases the pressure drop across the valve. This results in a low pressure drop across the nozzle which means that the water does not spray properly. In the eSteam design, low flow rates are achieved by reducing the amount of time the nozzles spray. A water turndown of 20:1 is achieved by varying the number of nozzles in use and the proportion of the sample time that one of these is open. Typically, downstream steam temperature is cooled to within 2–5°C of the saturation temperature.
The eSteam desuperheater can be used with water flows up to 12 t/h with up to 140°C water injection temperature at 20 to 40 barg pressure. The nozzles are sized according to the required water flow rate needed for the given steam parameters.
PSV Mitech’s custom designed microprocessor controller allows for smooth transitions across the turndown range and also monitors the number of cycles completed by each solenoid, spreading the load across all five and thereby increasing the overall lifespan of the unit.
The system components include nozzles, sparger, solenoid valves, manifold and controller enclosure. Temperature feedback is via the control room in the form of a 4–20 mA position signal to the desuperheater.
For more information contact Greg Walker, PSV Mitech, +27 (0)11 657 6000, [email protected], www.mitech.co.za
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