WRITE UP ON COMBINED PRDS STSTION These PRDS Stations are manufactured at our Pune works in joint venture collaboration with Arca Regler, Germany who have more than 75 years experience in this field. We are the leaders in manufacturing PRDS in India and have an extensive reference list covering reputed clients. Our major users are Shyamnur Sugars Davangere, Samson Distillery, Gramox Paper Mysore, SIPM , Mysore, National Rayon, Hindalco, Tisco, Durgapur Steel Plant, IOCL Haldia, various NTPCs, Indal, ICI, Rishra, Many Sugar Plants etc. Moreover we are also approved by all major consultants like EIL, DCL, M N Dastur, Desin, Udhey, Toyo etc. The innovative technology of Combined Pressure Reducing and Desuperheating involves pressure reduction as well as desuperheating in the single valve. Unlike separate systems, here, the Spray water is sprayed immediately after the pressure reduction in the vena Contracta Region. This being a very turbulent zone mixing of steam and water is excellent and atomization takes place immediately. Thus a steam free from water is obtained. This reduces the chance of any water carryover which normally is predominate in separate PRV and Desuperheating System, resulting in leakage down the line and wear and tear of downstream valves. One million stroke life and the field reversibility are the major features of actuator being offered and the same is being supported by a strong Arca Positioner which works on a force balance principle. 10 g vibration proofness, field reversibility an change of valve characteristic by using cam are some of the product advantages of this Positioner. Same Positioner can be used for20 mm to 100 mm valve lift. We also have the pleasure in informing you that our Principals as well as Forbes Marshall Arca, India are ISO 9001 organizations. Being a Control and Instrumentation Company we are fully equipped with providing you turnkey solutions for complete PRDS Stations. The full fabrication design and testing of such stations are done at our works in Pune as per our QAP. Since most of the instruments required for controlling pressure and temperature are manufactured in-house by us, we are able to provide complete system guarantee for full system and after sales service thereafter. Our Bangalore office is equipped with Service Engineer who is trained to commission such PRDS Station. This is backed up by centralized Customer Support Division at Pune having 20 trained Engineers who cater to emergency needs. TECHNICAL SPECIFICAITONS FOR “ARCA” COMBINED PRDS VALVE PRDSH VALVE Type Body Trim Rangeability Trim Type Trim Design : Combined Pressure Reducing and Desuperheating in the single Unit : Alloy Steel / Carbon Steel : SS 410 Nitrited (Nitriting is much harder – 60 Rockwell compared to stelliting – 40 Rockwell, and hence Nitritin last much longer : 40 : 1 (high operational range for wide flow variation) : 2-Step Perforated (ensures stepwise pressure reduction resulting in longer life of trim and generation of low noise – below 85 dBA) : Pressure Balance ensures low thrush force requirement at very High differential pressure resulting in tight sealing ACTUATOR Type Reversability Actuator Stroke Life : Spring Diaphragm type : Field Reversible (From air to open to air to close) : 1 million strokes POSITIONER Model Type Interchangeability Valve Characteristic : Model 820 : Force balance : For any size of Arca Vena : Field changeable by cam TECHNICAL ADVANTAGES OF COMBINED PRDSH VALVE OVER SEPARATE PRV AND DESUPERHEATER Working Principal of Combined PRDSH Valve and its Advantages In an Arca combined PRDSH valves as steam passes through the valve. It gets reduced by an adiabitic process, just as in an normal pressure reducing valve. The steam momentorily looses its pressure and temperature after throttling but before it recovers both pressure and temperature, as it passes out through the valve. The adiabitically cooled steam at the vena contracta region is in a highly turbulent state and with high velocity as it is the region of the smallest diameter. At this point the spray water is injected in the valve.the state of steam helps in spontaneous evaporation of water, hence immediately reducing the steam temperature to the desired set point. Sl. No. 1a. 1b. 2. 3. 4. 5. 6. 7. 8. Combined PRDSH Valve Separate PRV and Desuperheater Compact Single Unit – saving in spaces and piping requirement. Compact Single Unit – less maintenance as single unit to be maintained. High turndown of 40:1 – can cater to wide flow and pressure variation Separate Unit – needs extra space and more piping. Separate PRV and DSH – Two separate units and hence higher maintenance requirement. Low turndown – operational problem at low flow condition and at high differential pressure. Looses controllability of pressure and temperature. Multiple nozzles – possibility of choking resulting in problem in temperature control Low accuracy for temperature control as mixing of steam & water takes place after recovery of pressure at steady flow profile zone. Noise level – relatively higher requiring replacement of valve trim earlier. No nozzles – no possibility of choking. High accuracy of 1C for control of temperature as steam & water mixes in highly turbulant zone (Vena Contracta Region). Noise level – low noise due to formation of mist when water is sprayed at Vena Contracta – longer life of valve internals. No possibility of water carryover under ideal conditions due to excellent evaporation of spray water into steam. Immediate evaporation of water inside the PRDS eliminates the needs for long straight lengths after the PRDSH valve. Low downtime for maintenance. High chances of water carryover as mixing of steam & water is not proper, resulting in wet steam. Thus leakage and damage to downstream valves / bends is envisaged. Evaporation of water only takes place after desuperheater resulting in long straight length requirement. Longer downtime maintenance.
