Surge system operation

For FCC applications, a rigorous analysis typically involves transient evaluations of expander coupling failures, generator load drops, compressor and surge system operation, and control valve malfunctions. The results of these evaluations permit optimum selection of control valves and control strategies. 

This chapter summarizes the disturbances experienced in Japan, including the disturbed equipment, incoming surge routes, and characteristics of the disturbances [1,10]. Results of these disturbances in power system operations, such as countermeasures and costs, are also explained, and some case studies are presented. 

Consider the liquid surge system shown in Figure 10.5. A high-level alarm is used to prevent tank overflow. After a high alarm sounds, the operator has ten minutes to respond before the ESD system turns off the pumps on the inlet streams. The tank is 6 ft in diameter, 8 ft tall, and half-full at the nominal conditions. The density of the liquid is constant. The nominal values and ranges of the flow rates are shown as follows ... 

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.

Other Selection Problems. Additional considerations can arise when fans must handle soHds or gases of low density, or must be operated in parallel or series. A compHcated flow system involving several fans in parallel, all of which are ia series with a common exhaust fan, can lead to surging and vibration unless selected carefully. Maximum tip speed, bearing types, single- and double-inlet fans, and wheel and shaft natural frequency and rigidity must also be considered. 

Voltage surges, caused by system disturbances or switching operations (for HT motors). 

In actual operation, disturbances on a power system, causing sudden changes in the system parameters, are quite frequent and may generate temporary overvoltages and voltage surges, as summarized above. The system disturbances may be of two types, external or internal, as explained below. 

Valve or non-linear resistor In this version, a nonlinear SiC resistance is provided across the gap and the whole system works like a preset valve for the follow current. The resistance has an extremely low value on surge voltages and a very high one during normal operations to cause a near-open circuit. It is now easier to interrupt the follow currents. 

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