Anti-Surge Control

For variable speed machines surge is a fine, not a single point The next group of schemes are based on developing an equation for this fine — either from the compressor manufacturer s data or from plant testing. 

The surge fine can usually be represented by a quadratic function 

Fg is measured by an orihce plate type meter and is related to the pressure drop (dp) across the orihce. 

If we assume the discharge coefficient (c ), the pipe diameter (d) and the fluid density (p) are all constant then building in the 15 % margin gives 

if m is gradient of the minimum flow line and c the intercept on the polytropic head axis, then 

---

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. 

There seems to be one problem with anti-surge control, which is its name. Both surge control and anti-surge are used. Anti seems to be what the control is supposed to do, so it will be used here. 

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... 

Brown, Royce N., An Experimental Investigation of a Pneumatic Closcrt Loop Anti-Surge Control for Centrifugal and Axial Flow Compressors Master s Thesis, University of Wisconsin, Madison, Wisconsin, 1966,... 

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... 

The Foxboro Company, Turbo Compressor Anti-Surge Control, Application Engineering Data 000-25, June, 1965. 

Some local controls are assumed to be in place, such as anti-surge control for the compressors. In addition, some valves are fiilly open or fixed, as shown in Fig. 35.1. The selection of controlled variables is strongly related to the goals that are set for operation of the fluid catalytic cracker. There are numerous constraints that all have to be met. Moreover, two main objectives should be met maximization of the total feed rate and dismtbance rejection. 

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. 

Gas compressor anti-surge (GM-OFF) control circuit, comprising transmitters, computers and pneumatic control valve Reverse flow protection (on axnal compressors only) as supplementary protection device against surging, working independently of the control circuit Expander emergency stop valve with pneumatic actuator and solenoid valve... 

Dimitrios, D. and George, R Industrial compressor anti-surge computer control. Int. J. Corn-put. Inform. Eng. 2007, 1, 220. 

Effectiveness of Internals in Controlling foam. Originally, the separators contained limited internals—an inlet disengaging device, surge baffles, an anti-foam baffle, and a demister at the outlet. After severe foaming occurred, however, a bank of parallel plates (Dixon plates) was filled in each separator on one of the Ninian and one of the Brent trains The plates provide a large surface area and are sloped so that the separated oil flows dow n to the surface of the liquid. The installation is illustrated m Ftg S. The parallel plates arc 4 in. apart and extend from near the top of the vessel in the vapor space down to the normal liquid level. 

Anti-Fertility Activity - At a dose of 2 mg in rats, A -THC suppressed the cyclic surge of luteinizing hormone secretion and also suppressed ovulation (a characteristic shared by other CNS-active drugs). However, mating and fertility indices were similar for control and all treatment groups in a study of the effect of A -THC on reproduction in rats. At doses of 2 and 3 mg/kg, A -THC caused a deterioration in the sexual performance of male rats (interpreted as reflecting a decreased motivation to copulate)... 

---