Shutdown sequences

If left on turning gear, it will continue until the turbine exhaust temperature decreases to 150 °F (66 °C), and a suitable amount of time (up to 60hrs) has elapsed. At this point, the turning gear and auxiliary lube oil pump will stop and the shutdown sequence is complete. On recognition of a shutdown condition, various contact status and analog values are saved (frozen) for display, if desired. 

A more normal shutdown sequence would first flush the fuel cell, reformer, and scrubber with nitrogen or C02 (if it is safe for the cell design). This step is followed by a slow bleed of air and nitrogen to repassivate the fuel cell and reformer under temperature control. If this is not done gradually, the reformer can reach temperatures high enough to violate its containment (meltdown) and become unrecoverable. The reformer performance does decrease after this treatment, but over 90% of its capacity can be retained. Similar problems are present when reforming the fuel cells themselves. 

Synchro-Self-Shifting ( SSS ) Clutches The automatic freewheel action of an SSS clutch simplifies plant startup and shutdown sequences. It is, of course, receiving its power input from a gas turbine or similar driver, while its output is connected to a driven machine. The drive disengages automatically when the driven machine speed exceeds that of the driver. Since large gas turbines are usually brought up to speed with either a startup gear motor or a helper turbine, thousands of SSS clutches (Fig. 29-77) are finding application here. 

Most fuel cell units have an error code display alert that will tell you what is wrong with the system if it is not working properly, and an automatic shutdown sequence if there are gas leaks or other problems that require immediate action. 

Many operating procedures are to be used as part of an overall start-up or shutdown sequence. In order to minimize the chance of a procedure being overlooked, forward and backward links to other procedures can be provided as shown at the bottom of Figure 6.29. 

Foss of Nitrogen External Coordination Other Facilities in the Area Equipment Suppliers Fire Department Police Department Regulatory Agencies Emergency Shutdown When to Shutdown Sequence of Actions Responsibility for Emergency Shutdown Post-Emergency... 

Interlocks are commonly used safety devices. The function of an interlock is to prevent the occurrence of an event in the piesraice of certain conditions. Some interlocks prevent action or motion, others send signals to other devices that prevent the action or motion. They automatically reconfigure or interrupt final control devices if monitored variables deviate significantly from specifications. Typical process variables monitored are flow, pressure, level, and temperature. Typical machine variables monitored are coolant level and temperature, lubricant level and temperature, vibration, speed, etc. Interlocks allow equipment to start and operate only when monitored variables are within designed specifications. Interlocks inhibit unanticipated actuation of equipment and ensure correct startup/shutdown sequences are followed. A permissive interlock will not allow a process or equipment to startup unless certain conditions are met. There ate two types of interlocks—safety and process interlocks. Each serves a different function. 

A demonstration was given of a reactor trip from full power using the emergency trip button with the automatic initiation of the Reactor Shutdown Sequence... 

Corrosion rates estimated for three shutdown sequences are illustrated in Fig. 14.24. 

SIS provides proper alarm including diagnostic alarm and display Proper shutdown sequence activated... 

SIS documentation consistent with installed system SIFs perform as specified with invalid process variables Proper shutdown sequence activated Proper alarm and display by SIS Correct computations included in SIS Bypass and manual shutdown function correctly Reset of SIS functions as per SRS Proof test interval included in maintenance procedure Diagnostic alarm performs as required SIS performs as required in case of loss of power SIS goes to desired state on power resumption SIS EMC immunity as per SRS... 

The principal operating cycle of the NPR is the startup - equilibrium shutdown sequence Analyses of reactor inlet and outlet piping... 

With regard to BWR type reactors, the single risk-dominant initiator is the cold over-pressurisation. There is potential for cold over-pressurisation during filling the reactor at the end of a Shutdown sequence. The status and proper actuation of safety and relief valves were found very important for BWR type reactors during shutdown state. 

SIS commimications to external networks or BPCS SIS components perform to SRS Trip set points Proper shutdown sequence... 

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