b'Process Industries | Engineer Innovationcharacteristic gets blamed for this. TheThe characteristic of the system pipe + valve isleft diagram in figure 10 shows thecompletely different from valve characteristic!characteristic of a ball valve in terms ofSystem ow rate vs. valve positionthe dimensionless loss coefficient . Due80 m3/h valve pipe k v,Valve k v,Pip70% of ow rate to the singularity ofat the completelyalone valve reduction happen in last closed state, the interpretation of the60 m3/h 20% of valve movementimage is difficult. still 70% of effective closure timeFlow rate40 m3/h initial ow t close,eff t closeTherefore, in the right diagram the same characteristic is shown, but in terms of20 m3/h valve 80%closedthe flow coefficient k(which is vanalogous to Cin imperial units). Again,0 m3/hvthe red line represents the ball valve. In0 %20 %40 %60 %80 %100 %this diagram it gets clear, that the ballclosed Valve openingvalve near the closed stat has a reallyFigure 11: Comparison of characteristics of pipe + valve and valve alonesmooth characteristic. So this does not explain the weak effect of the closing time elongation. Stage 1: fast movement to a specied position (case-dependent) in 1 s to position 13 percent openThe behavior is completely different, Stage 2: slow movement until valve is completely closedwhen we look at the system "pipe + in further 9 s to fully closed position - 10 s overallvalve(figure 11): 100 %Valve Closing PathsFigure 11 shows the flow rate versus the80 %Valve openingvalve opening. The blue line represents the complete system for the case of the60 %barge loading example. The dashed red line represents the ball valve alone (with40 %the same pressure source). It can be observed now that the strongest effect20 %of the valve closing occurs near the closed state, since during the first 800 %percent of the valve closing, the capacity0 s2 s4 s6 s8 s10 sof the ball valve is still so high, that theClosure timepressure loss of the pipe strictlyFigure 12: Two stage valve closuredominates. With this information, we try anotherClosure time increased by x10 to 10 sclosing profile that also closes the valveP maxreduced by 2.8 to 15.5 bargin 10 seconds but in a phased manner as shown in figure 12. Static Pressure Upstream of Ball ValveStratied uniformThe results for the status quo, staged24 barg t closure= 10s t closure= 10sclosure and hydraulic damper are shown Static pressurein figure 13. It can be observed that thewith damperobjective can also be met with a slower16 barg t closure= 1svalve closing, if the closing profile is optimised. Nevertheless, this is not in8 bargany case the best solution. For example, in case of line rupture due to ship drift, the amount of medium spilled during0 barg0 s2 s4 s6 s8 s10 s12 s 14sthe valve closing process is of coursetimehigher compared to fast valve closureFigure 13: Comparison of different surge mitigation methods combined with a hydraulic damper.As a result of this exercise, we get all necessary information about the behavior of the system by simulatingeffectiveness. Taking into account all the with Simcenter Flowmaster. Applicationreal life practical constraints, the solution of multiple mitigation techniques canthat is most convenient for the customer easily be assessed concerning theircan be obtained and delivered. n55'