Anti-surge control system

Flow control by recycle of process gas is used to maintain the minimum flow requirements of the anti-surge control system. Inputs from the pressure and speed transmitters are used to compute the required minimum flow setpoint, based on an anti-surge control line relationship, as shown in Figure 3.29. The anti-surge... 

As with many consumer goods, compressors cannot be purchased without accessories. Some of the accessories are essential to the basic operation of the compressor, such as lubrication systems and couplings. Other accessories, such as the anti-surge control equipment, are optional in order to enhance operation but are not essential. The accessories may be purchased from the equipment vendor or they may be purchased from another party—a decision open to the purchaser. Generally, the accessories essential to the operation are purchased from the equipment vendor as part of the original purchase. The lubrication system and couplings are classic examples of this option. Intercoolers, while essential, are not normally purchased from the equipment vendor if the application is a process compressor. 

The best anti-surge control is the simplest and most basic that will do the job. The most obvious parameter is minimum-flow measurement, or if there is a relatively steep pressure-flow characteristic, the differentia pressure may be used. The latter parameter allows for a much faster response system, as flow measurement response is generally slow however, the speed of response need only be fast enough to accept expected transients. One major problem with the conventional methods of measurement and control is the need to move the set point for initiation of the control signal away from the exact surge point to allow some safety factor for control response time and other parameters not directly included... 

Having said so much in favor of separation of control and safety functions there are always going to be situations where the control system also performs a safety role or where an integrated package is needed. An example would be a large turbo compressor set where anti surge control and load control are integrated into one scheme. 

---