【正文】 off ? Minimizes the risk of surge since all machines absorb part of the disturbance ? Automatically adapts to different size machines ? CCC patented algorithm Equidistant Loadsharing Parallel Compressor Control 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 Section 1 Section 2 ? The piping layout for section 2 is excellent for surge protection ? Minimum volume between the three flanges Small volume ? The piping layout for section 1 is not ideal ? Large volume to be depressurized decreases ability of the control system to protect the machine against surge ? Result Poor surge protection Large surge margins Energy waste Process trips because of surge Sharing recycle coolers degrades surge protection 169。 2022 Compressor Controls Corporation Menu Fwd Prev Rew 100% 0% 100% 0% Time Time Controller output Operating point ? Response of CCC digital controller nearly identical to the analog controller ? Adding specialized response algorithm to PI control will allow even smaller surge margins Analog vs. digital controller at 25 executions per second Digital controller (25 executions per second) SLL SCL Analog controller SLL SCL 0% 100% 0% Tuning same as analog controller 169。 2022 Compressor Controls Corporation Menu Fwd Prev Rew Simplified Pamp。 2022 Compressor Controls Corporation Menu Fwd Prev Rew Controller output Operating point 100% 0% 100% 0% Time Time ? Compressor surged ? Large process upset would have resulted Analog vs. digital controller at 3 executions per second Digital controller (3 executions per second) SLL SCL Analog controller SLL SCL 0% 100% 0% Tuning same as analog controller 169。 2022 Compressor Controls Corporation Menu Fwd Prev Rew ? Piping layout influences the controllability of the the total system ? The primary objective of the antisurge controller is to protect the pressor against surge ? This is achieved by lowering the resistance the pressor is feeling ? The resistance is lowered by opening the antisurge valve ? Deadtime and timelag in the system needs to be minimized ? This is achieved by minimizing the volume between three flanges – Discharge flange of the pressor – Recycle valve flange – Check valve flange VSDS Compressor 1 volume to be minimized Piping layout consideration when designing an antisurge control system 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 Q2 Rc N1 N3 N2 ? In a typical masterslave control scheme the slave needs to be approx. 5 times faster than the master A The machine is operating in point A ? This is the intersection of 4 lines: ? Resistance line R1 ? Performance curve N1 ? PICSP ? FICSP = Output of PIC R1 PICSP FICSP Process disturbance causes the resistance to change from R1 to R2 R2 As a result the machine moves to point B B Since the PIC is slow it does not move its output yet which is the FICSP The FIC reacts fast and will try maintain its SPThe FIC will speed up the machine to point C at speed N3 C The disturbance is amplified Positive feedback system Only as the PIC starts to reduce its output to control pressure the FICSP es down and the pressure is restored D Notes ? Causes instability near surge ? Poor pressure control due to positive feedback in contr