Surge control line

In most cases, closed-loop control can be improved by moving the surge control line to a more conservative position in response to disturbances. When the flow measurement is sufficiently stable (good signal-to-noise ratio), the controller can calculate the time derivative of the compressor map. 

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... 

In order to avoid surge occurrence in compressor, axial or radial one, antisurge valve is used usually. Various mechanisms have been presented for these valves which all of them are based on reduction of compressor downstream pressure and according to surge control line (to avoid surge occurrence). We use this line to compensate uncertainly in the measurements and delay in valve performance. There are some descriptions for this parameter that one of them has been shown in Eq. (3.8). 

FIGURE 3.9 Compressor characteristic curve of turbocharger GT35 and surge control line... 

A compressor surges at certain conditions of low flow, and the compressor map, a plot of head versus flow, has a surge line defining the limits. Surge controls help the machine avoid surge by increasing flow. For an air compressor, a simple spill to the atmosphere is sufficient. For a hydrocarbon compressor, recirculation from discharge to suction is used. 

Figure 12-61D. Centrifugal compressor surge control schematic diagram shows instrumentation required when primary flow-measuring device is located in centrifugal compressor discharge line. Symbols T = temperature P = pressure A = differential across compressor outlet to inlet. See Reference 89 for a detailed discussion. (Used by permission White, M. H. Chemical Engineering, p. 54, Dec. 25,1972. McGraw-Hill, Inc. All rights reserved.)...

Fig. 4. Selection of fan size where the soHd line represents a typical setting and the dashed lines the operating extremes, (a) Desirable sizing. The system resistance curve intersects the fan curve near its maximum efficiency. Changes in system resistance from a flow-control element also intersect the fan curve at desirable points for good flow control. The dashed curves also intersect system resistance curves at desirable locations, (b) A fan essentially too large for the system. The intersection of the system curve near the peak of the fan curve results in poor system flow control and perhaps surging.

The vertical position is preferred if the plot space is tight. Horizontal vessels are easier to support and are preferred when large Hquid surge volumes are required. The Hquid level displacement height for a unit volume is much less for a horizontal vessel than for a vertical vessel, which makes the control range shorter than for a vertical vessel. The displacement height per unit volume is only approximately linear on horizontal vessel when the level is near the center line, however. This can be a problem if the normal Hquid level is too low or too high and the instniments are not tuned for quick response. 

Progestins thicken cervical mucus, delay sperm transport, and induce endometrial atrophy. They also block the LH surge and thus inhibit ovulation. Estrogens suppress FSH release, which may contribute to blocking the LH surge, and also stabilizes the endometrial lining and provides cycle control. 

Pressure surge can be controlled by the use of surge vessels connected to the pipeline with a gas space above the liquid. If a pressure surge passes along the pipeline, liquid flows into the vessel through a check valve and the gas is compressed. Another valve then lets out the liquid at a controlled rate. This type of arrangement is used in large hydraulic lines. 

Since the liquid must be cooled if it is sent to the surge tank and then reheated in the vaporizer, there is an energy cost penalty associated with sending more material to the surge tank than is absolutely necessary. Your level control system shonld therefore hold both levels and also minimize the amount of material sent t o the surge lank. (Hint One way to accomplish this is to make sure that the valves in the lines to and from the surge tank cannot be opened simultaneously.)... 

A) Compressor surge is prevented by using a low flow controller that opens the valve in the spill-back line from compressor discharge to compressor suction. 

---