【正文】 and the Surge Limit Line (SLL) ? Calculate Cv,calc (or equivalent) for point A ? Select standard valve size using the following criteria: . Cv, calc Cv,selected . Cv, calc Rc Qvol A Sizing the antisurge control valve 169。 2022 Compressor Controls Corporation Menu Fwd Prev Rew ? The speed of approaching surge is high ? The transmitter type and brand should be selected based on two major factors: – Reliability – Speed of response ? Desired rise time for Dp (flow) transmitters is 200 ms or less – Pressure step is 100% – The first order response (63%) is less than 200 ms ? Desired rise time for pressure transmitters is 500 ms or less Response time of the FMD transmitter In only 400 ms, DPO dropped by 14%, with a 2% change in DPc 100% 0 100% 0 100% 0 1 SEC. DPo A C D B Pd A C D B DPc A C D B Time Actual pressure Transmitter output 63% response 1 (1/e) t1 is less than 200 ms 169。 2022 Compressor Controls Corporation Menu Fwd Prev Rew ? Main selection criteria for FMD in antisurge control system: – Repeatability – Sufficient signaltonoise ratio ? Accuracy of the FMD is not critical ? FMD delays must be absolutely minimal ? Present stateoftheart limits the choice of FMD to head flow meters or to other devices that are based on the principle of velocity measurement: – Orifice plates – Venturi’s – Pitot tubes – etc. ? Remended flow range for FMD and transmitter is maximum pressor flow ? Remended Dp corresponding to Qmax, pressor is 10” WC (250 mmH2O) or more Flow Measuring Device (FMD) selection criteria 169。 2022 Compressor Controls Corporation Menu Fwd Prev Rew Process 1A UIC VSDS Section 1 VSDS Section 1 Suction Header A LSIC out RSP Serial work RSP B LSIC 1 MPIC Serial work Serial work Section 2 Section 2 2A UIC 1B UIC 1B UIC Serial work Serial work out Train B Train A ? How to operate equidistant from the Surge Control Line (SCL) when there is more than one section per machine ??? Select per train in the loadsharing controller the section closest to the SCL By selecting the section closest to the SCL it is guaranteed that the other section on the same train is not in recycle Equidistant Loadsharing for multisection pressors Share the load equal DEV’s for both trains on the section closest to SCL169。 2022 Compressor Controls Corporation Menu Fwd Prev Rew Loop Decoupling FA Mode PI Loop Decoupling + Analog Inputs + DEV To antisurge valve To performance control element PID Load balancing PV PV SP Primary response DEV DEV DEV DEV from other loadsharing controllers Primary response Average SP The load balancing response Loadsharing Controller Antisurge Controller Master Controller ? The fast master controller controls the primary process variable by directly manipulating the final control elements In order to balance the machines they need to be kept at the same DEV antisurge controller reports the actual DEV to the load balancing block in the loadsharing controller ? This reported DEV bees the Process Variable (PV) for the load balancing PID loop loadsharing controller reports thisPV also to the master controller Other loadsharing controllers also report their DEV PV to ter master controller calculates the average of all reported DEV PV’sThis average DEV is sent out to all loadsharing controllers to bee the SP for all load balancing blocks ? The load balancing block is a slow controller that will equalize all DEV’s for all parallel pressors ? Its output is added to the total output to the performance control element RT 169。 2022 Compressor Controls Corporation Menu Fwd Prev Rew ? Machines operate at same Rc since suction and discharge of both machines are tied together PICSP The DEV is a dimensionless number representing the distance between the operating point and the Surge Control Line ? Lines of equal DEV can be plotted on the performance curves as shown DEV = 0 Machines are kept at the same relative distance to the Surge Control Line (SCL) ? This means in practice the same DEV for both machines DEV1 DEV2 Recycle will only start when all machines are on their SCL Since DEV is dimensionless all sorts of machines can be mixed: small, big, axials, centrifugals The DEV will be the same for all machines but they will operate at different speeds and flow rates SCL = Surge Control Line Rc,1 qr,1 2 Rc,2 qr,2 2 Compressor 1 Compressor 2 Dev1 = Dev2 Q1 = Q2 N1 = N2 Notes: ? Maximum turndown (energy savings) without recycle or blowoff ? Minimizes the risk of surge since all machines absorb part of the disturbance ? Automatically adapts to different size machines