Desalination / Water
The increasing need for safe, reliable and consistent supply of fresh water has made many manufacturing industries look for efficient desalination plants.
Desalination is an artificial process by which saline water (generally seawater) is converted to fresh water. There are various technologies which can be divided into membrane-based (e.g. reverse osmosis) and thermal-based (e.g. Multiple Effect Desalination, Multistage Flash Distillation) methods. Multistage Flash Distillation (MSF) and reverse osmosis (RO) are the two most common desalination methods.
High-Pressure Membrane Feed (SWRO)
Sea-water Reverse Osmosis (SWRO) desalination removes salt and other chemical and biological contaminants, by passing seawater through partially permeable membranes. The process requires applied pressures higher than the osmotic pressure of the saline water, to push water through the membrane. Operating pressures range from 55 to 80 bar for seawater, to about 25 bar for brackish water treatment. The pressure control valve must be designed to break high differential pressure levels combined with high flow rates, and under conditions of severe cavitation.
Parcol’s 1-2480 series flanged control valves with drilled wings make the valve suitable for flow control in cavitating services on liquids and for low noise flow control on compressible fluids. With a double eccentric disc design, torque requirements and seal ring wear are reduced by minimizing its contact with the disc. Additional torque reduction is obtained by the profiled drilled integral wings.
Due to the eccentric design of the disc, these valves can provide a stable flow control with limited negative gradients and excellent shut-off in closed position. Also, the flow characteristic is improved and it is close to an equal percentage shape for low openings.
The reduction of flow coefficients due to the wings is balanced by higher values of factors FL, xT and xFZ which allow the use of this valves for high pressure drop and angular travel up to 80° on liquid and gas services. For more critical service a special execution with extended wings and angular travel up to 100° is available.
The highly saline environment is very corrosive, and extremely resistant valves are needed to regulate it. The 1-2480 series is available with body in A216 WCB, AISI 316, AISI 316L, A890 4A duplex stainless steel, with sizes up to 80 inches.
Steam to Brine Heaters
In Multistage flash desalination (MSF) plants, brine is heated in the brine heater until the top brine temperature (TBT). The TBT is a very important controlled variable, above which scaling will occur in the interior of the brine heater tubes, affecting plant performance.
Brine is heated in the brine heater using steam, via means of heat exchange. In order to ensure that the brine does not exceed the TBT, a desuperheater unit reduces the steam temperature to the required steam temperature.
Parcol’s 1-4442 series Spraysat multiple nozzle desuperheaters (variable area) are designed to provide optimum performances and high rangeability. The independent spray nozzles progressively activated by the throttling piston, provide a good water atomization down to minimum flow conditions. To improve the quality of atomization and accuracy of temperature control, several sizes of spray nozzles are available. The built-in control system is very compact, reliable and easy to operate. The split body design allows to change easily the orientation of water connection versus the steam piping, and greatly facilitate the seat replacement.
Brine Recirculation Valve
In Multistage flash desalination (MSF) plants, brine is heated in the brine heater until the top brine temperature (TBT). The brine recirculation valve plays a very important role in ensuring plant performance. Changes in the flow of the recirculation valve affects the control of the top brine temperature (TBT). The TBT is a very important controlled variable, above which scaling will occur in the interior of the brine heater tubes, affecting plant performance.
The brine recirculation valve is required to throttle excessive pump pressure from upstream. As one of the most severe services in the plant, the recirculation valve is subjected to full feed pump pressure on the inlet and a low outlet pressure.
VeGA is the most Versatile control valve for General Applications ever designed by Parcol. VeGA is a straight body single seat control valve with cage guided balanced plug designed to withstand the most severe process conditions.
The special plug design allows improving valve rangeability by reducing minimum controllable flow and plug erosion. The high pressure recovery factor value compared with conventional contoured plug control valves ensure higher flow rates on compressible fluid service and reduces cavitation risk and effects on liquid service. All versions have quick change trim.
Together with the standard high capacity trim, low noise trims and double cage trims are available respectively for critical service on compressible fluids (gas and vapor) and for high differential pressures or for cavitating service where higher pressure recovery factor values are required.
Balanced Plug with Pilot execution allows to comply with IEC sealing class V up to 566°C for compressible fluids service. “Flow to close” configuration improves seat ring protection and increases seating force making this solution particularly reliable.
Contoured unbalanced plugs are available for dirty fluids service.
A special material configuration is available to comply with NACE MR0175 and MR0103 standards.
VeGA control valves are usually equipped with Parcol diaphragm spring return pneumatic actuators 1-X-210 and 1-X-250 series (pneumatic cylinders 1-X-400 series for DN 16″ and over). Electrical or hydraulic actuators are also available on request.