Venting startup/shutdown

When carrying out a rigorous profitability analysis, some design teams adopt the convention of reducing the process yield by a small amount, such as 2%, to account for the loss of raw materials and products during startups, shutdowns, and periods when there are malfunctions. Often, raw materials are vented or flared during startup. In other cases, one part of the plant shuts down while the remainder continues to operate, with small amounts of intermediate products vented when they are nontoxic and not easily stored, until the idle portion of the plant is restarted. 

The TMI accident demonstrated the continued need for dependable containment isolation after an accident as well as during startup, shutdown, and normal operation (when systems such as the containment purge and vent systems are used). There are three areas of concern for isolation of containment building penetrations, which are (1) fluid systems piping, (2)... 

Most state laws and safe practice require a safety relief valve ahead of the first stop valve in every positive displacement compressed air system. It is set to release at 1.25 times the normal discharge pressure of the compressor or at the maximum working pressure of the system, whichever is lower. The relief valve piping system sometimes includes a manual vent valve and/or a bypass valve to the suction to facilitate startup and shutdown operations. Quick line sizing equations are (1) line connection, (i/1.75 (2) bypass, ii/4.5 (3) vent, dl63 and (4) relief valve port, cU9. 

Device used to vent noncondensable gases from a boiler during startup and shutdown procedures. 

These activities may introduce many hazards, such as contaminants, materials of repair corrodible, combustible or catalytic in the given environment, blocked vents, open valves etc. into the restarted plant, while shutdown and startup are, in any event, the most dangerous periods. Many examples of reactive hazards thus introduced are to be found in [1], Mutatis mutandis, this is also true of the laboratory this Handbook contains many incidents consequent upon stopping a reaction and/or its agitation to sample, change cooling bath, etc. 

Absorption of a component of a gas stream into a liquid is a common practice in the chemical industry to affect cleanup of vent gases, conduct chemical reactions, purify products, or to recover products from process streams. The enhanced mass transfer capability of RPBs provides the opportunity to perform absorption processes in smaller equipment, to lower inventories, to shorten startup and shutdown times, and to lower pressure drop (48). Figure 8 provides a visual comparison of the size of a conventional absorber tower next to three RPBs that handle the equivalent gas and liquid flows (9). 

The SGS, which provides decay heat removal capability during shutdown operations by delivery of startup feedwater flow to the steam generator and venting of steam from the steam generators to the atmosphere via the power-operated relief valves. See subsection 6.3.6 for a description of the operation of the CVS. 

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