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1、,负荷分配控制,在压缩机网络中，压缩机通常并联运行，有时也有串联运行 形成网络运行的目的包括： 备份 灵活操作 增加额外的能力 通常注重单元机组的运行而忽略网络的优化控制 压缩机制造商通常集中于单元机组的控制。 从“网络”的观点来看，应实现优良的喘振保护和网络的负荷分配优化控制。,压缩机网络,并联机组控制系统的目标是： 保持主性能变量稳定（压力或流量） 将负荷优化分配到网络中的各台机组上，同时： 发生喘振的机率最低。 最低的能耗 在启动或停开单一机组时将所带来的工艺扰动降到最低。,压缩机网络,Process,PIC,1,1,UIC,VSDS,Compressor 1,2,UIC,VSDS,Co
2、mpressor 2,HIC,1,Suction header,用于调节负荷的压缩机,满负荷运转的压缩机,注： 所有控制系统均为独立运行 变送器未标明。,基本负荷法,Rc,1,Rc,2,Compressor 1,Compressor 2,Machines operate at same Rc since suction and discharge of both machines are tied together,Base load one or more compressors and let the other(s) absorb the load swings,Swing machin
3、e,Base machine,Base machine is fully loaded and runs without recycle,Swing machine can be running with recycle,where: QP = Flow to process QC= Total compressor flow QC - QP = Recycle flow,Load could be re-divided to eliminate recycle,QP,1 + QP,2 = QP,1 + QP,2,注： 基本负荷法效率较低。 基本负荷法增加了#1压缩机组发生喘振的危险性，这是由
4、于#1压缩机将独立承担调整任何扰动。 基本负荷法需要操作人员的经常干预。 基本负荷法并不是推荐的方式,基本负荷法控制,Process,PIC,1,1,UIC,Compressor 1,Compressor 2,Suction header,Notes Performance controllers act independent of antisurge control Higher capital cost due to extra Flow Measurement Devices (FMD) Higher energy costs due to permanent pressure los
5、s across FMDs,1,FIC,2,FIC,2,UIC,out,out,RSP,RSP,RSP,out,RSP,Equal Flow Division Loadsharing Flow Diagram for Control Process,Machine 2 operates with recycle while machine 1 still has turn down,Machines operate at same Rc since suction and discharge of both machines are tied together,Equal flow divis
6、ion might work if both machines are identical,Machines are never identical except by coincidence,Bias relay on remote setpoint would only work if curves have same steepness,Notes: Requires additional capital investment in FMDs Requires additional energy due to permanent pressure loss across FMDs Poo
7、r pressure control due to positive feedback in control system (see next) Equal flow division is NOT recommended,Rc,1,Rc,2,QP,1 = QP,2,Equal Flow Division Loadsharing Parallel Compressor Control,Compressor 1,Compressor 2,where: QP = Flow to process QC= Total compressor flow QC - QP = Recycle flow,Q2,
8、Rc,N1,N3,N2,In a typical master-slave 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 PIC-SP FIC-SP = Output of PIC,Process disturbance causes the resistance
9、 to change from R1 to R2,As a result the machine moves to point B,Since the PIC is slow it does not move its output yet which is the FIC-SP,The FIC reacts fast and will try to maintain its SP The FIC will speed up the machine to point C at speed N3,The disturbance is amplified Positive feedback syst
10、em,Only as the PIC starts to reduce its output to control pressure the FIC-SP comes down and the pressure is restored,Notes Causes instability near surge Poor pressure control due to positive feedback in control system,Dynamic Response / Pressure To Flow Cascade,Notes All controllers are coordinatin
11、g control responses via a serial network Minimizes recycle under all operating conditions,Equidistant LoadsharingFlow Diagram for Control Process,Machines operate at same Rc since suction and discharge of both machines are tied together,The DEV is a dimensionless number representing the distance bet
12、ween 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,Recycle will only start when all mach
13、ines 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,Rc,2,Compressor 1,Compressor 2,Notes: Maximum turndow
14、n (energy savings) without recycle or blow-off Minimizes the risk of surge since all machines absorb part of the disturbance Automatically adapts to different size machines CCC patented algorithm,Equidistant LoadsharingParallel Compressor Control,Loadsharing Controller,Loop Decoupling,FA Mode,PI,RT,
15、Loop Decoupling,+,Antisurge Controller,Analog Inputs,+,DEV,To antisurge valve,To performance control element,Primary response,Primary response,Compressors in Parallel the primary response,Master Controller,Master controller controls the main Process Variable (PV) via its PID control block,The output
16、 of the master controller PID goes to the primary response block in the loadsharing controller,In the primary response block the controller checks if the machine is close to the SCL: Yes: dont reduce capacity - keep output constant No: reduce capacity as necessary Apply loadsharing gain M0 The output of the master controller goes via the prim
