Load drop

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. 

Figure 4-77. Speed changes during instantaneous load drop event calculated and experimental values.

Figure 4-83. Speed versus time plot during generator full load drop (PRS string).

A generator load drop of 100% is shown in Figure 4-89. For a valve elosure time of 1 see, a 5% overspeed is predieted. Note the eompari-son to the power reeovery string in Figure 4-83, where a 10% overspeed was predieted with a 10 see valve elosure. The mueh larger rotor inertia of the full power reeovery string allows the use of a slower and less expensive valve. 

Crane load drop ltr3 to i0"4/iift 1 x 10"4(/lift)... 

In Eq. (4.103), it is assumed that the influence of the instantaneous fiber displacement relative to the matrix due to the sudden load drop after instability is negligible. 

Turning the wheel at the back end of the cylinder counterclockwise, pulls back a large internal plug in the head. Now, when the piston starts to withdraw toward the crank end of the cylinder, there is more gas left inside the cylinder to expand. The greater the volume of gas inside the cylinder when the piston is at bottom dead center, the closer the piston is to top dead center before the intake valve opens. The delay in the opening of the intake valve reduces the amount of gas drawn into the cylinder. This reduces the number of moles of gas compressed by the piston. Compression work also diminishes and the driver horsepower or amp load drops. 

Vaporization controls depend on the operating pressure. If vacuum is required to vaporize the process fluid and if steam jets are used to create that vacuum, it is recommended that a pressure controller be installed on the steam inlet to maintain the optimum pressure required by the ejector. For processes in which load variations are expected, the operating costs can be lowered by installing a larger and a smaller ejector and automatically switching to the small unit when the load drops off, thereby reducing steam demand. 

The savings generated by variable-speed pumping increase as the load drops off. 

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