Common standby pump

EXHIBIT 8 22 Two Primary Pumps and One Common Standby Pump... 

Exhibit 8-22 iliu-strates how a common standby pump is used for two primary pumps this is the ideal layout, with flexibility loops added as reciuired. Exhibit 8-23 shows how the suction line for service B is tied into the suction line for. service A below or down-strearn from the block valve and up.stream from the strainer. The discharge line for service B is tied in downstream from the check valve. 

This applies when a functionally identical element is held permanently available to take over the duties of the foulted element. Such a case is illustrated by the very common arrangement of standby pumps, shown in Figure 6, where, in the event of hiilure of PI, P2 can be used as a replacement by re-configuring the valves and starting the spare pump, P2. 

Driver. If steam is available, a common choice is a steam turbine driver for the main pump and an electric motor for standby. Some plants prefer two electric motor-driven pumps. Give the minimum steam condition. Give the expected voltage drop on the electric system if more than 10% is expected, especially on large systems. 

Errors that resulted in the component being unavailable when needed—For example, equipment not restored to full operability following maintenance, testing, or inspection. Valves left closed, actuation or protective systems not reconnected, slip-blinds left in the line, or failing to return pump selector switches to the standby auto-start position are common examples. 

Chemical treatment consists of three weU-known treatment processes for ensuring rehable operation of RO membranes. First, a 20% sodium bisulphite (SBS) solution is injected by the chemical dosing pump (one pump is on standby). The iiyection rate is proportional to the RO feed water flow rate and is controlled by the PLC based on the chlorine concentration monitored by a chlorine analyser downstream of the in-line mixer. SBS like sodium sulphite and sodium metabisulphite is a reducing agent commonly used to dechlorinate RO feed or lower the chlorine concentration to less than 0.05 mg/1 in RO plants that use polyamide aromatic membranes. It takes 7.33 mg/1 of 20% NaHS03 solution to remove 1 ppm of residual chlorine in water on a stoichiometric basis. 

This group of characteristics specifies components of a standby feedwater system that is started if the main feedwater system is not available because of a failure. These systems should have an independent power source available after loss-of-ofifsite-power events. The auxiliary feedwater pumps are usually connected to the main feedwater tank and may also be used as normal start-up feedwater pumps at low reactor power (see above). The emergency feedwater system is usually designed for use in case of a catastrophic failure of the main feedwater system, e.g. if a common feedwater pipeline ruptures, making both main and auxiliary feedwater pumps unavailable. The emergency feedwater pumps and flowpaths should be different to those of the main and auxiliary feedwater. 

The general plant arrangement is for a duty dosing pump to inject the liquid chemical into a water transfer main, most commonly proportional to flow to ensure consistent dosing. A standby dosing pump should also be available, preferably with automatic switch-over if the duty pump fails. 

The common issue in both accidents was impulsive behavior by relatively non-senior people when faced with a (minor) crisis. In the case of Piper Alpha, it was the rapid decision to re-instate the standby condensate pump without checking its status properly. In the case of Mumbai High, it was the rapid decision to transfer the injured cook from MSV Samundra Suraksha to the Mumbai High North platform, despite adverse weather, the unavailability of the leeward crane, and the exposed design of the gas riser on the windward side. 

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