Security factors

Again, it is also important to remember that chemical emergency situations can easily reach beyond the boundaries of any industrial plant. This is to be expected, especially in this age of population explosion with its characteristic urban sprawl. It is not unusual to find, for example, a chemical industrial plant site or other industrial plant that originally was isolated from city dwellers but later became surrounded on all sides by neighbors. The point is that when a chemical spill or chemical disaster occurs in an isolated area there may be no cause for general alarm however, when such a deliberate disaster occurs in the plant site as described in the sugar plant incident, it should be clear that the purpose of PSM, RMP, the Patriot Act, Homeland Security directives, OSHA s Combustible Dust NEP, and other safety/security factors is far-reaching—and absolutely critical to the survival of a free society. 

Predicting losses is difficult, particularly losses through and around doors, jamb, sills, tramp air, cooling losses, and losses through conveyor equipment and gaps around it. Assigning safety factors or security factors to cover these matters requires experience and careful judgment. 

If it is then decided to add an air preheater to accomplish heat recovery, the required gross heat input to the furnace will equal required available heat or heat need (%available heat/100) = 13 625 000 h- (48%/10) = 28 400 000 gross Btu/hr. A security factor of at least 25% should be used therefore, the design input should be (28.5 kk Btu/hr) (1.25) = 35.6 gross kk Btu/hr. 

For abnormal conditions, a security factor of 1.2 is advised, or perhaps 1.4 for extra wall heat for a cold startup. 1.4 x 10.6 kk = 15 kk Btu/hr. ( Rules of thumb may be very case specific or overly safe, but can be assuring ballpark guides thus coauthor Reed prefers to call them thumb guides. One such is 80 000 Btu/hr ft of hearth for large high-temperature car furnaces, which gives 80 0(X) x 20 x 10 = 16 kk Btu/hr for the job in this example). 

Q13. When designing a flue system, what security factor should be used to make future productivity adjustments possible ... 

A13. A security factor of 1.3 is suggested, applied to the maximum burner firing rate and with flue gas exit temperatures 200°F (111°C) above the furnace running temperature at maximum rates. Some furnace designers may be irritated by these specifications, but they are needed to recover a furnace s normal temperature profile quickly. These specifications are more necessary for a mill with many delays to provide the versatility needed. It is important to be aware of different goals—furnace designers want to build an inexpensive furnace so that they can get the order, but operators want versatility to be able to heat and roll as many tons as possible. 

Ignoring the need for design security factors to allow for abnormal situations such as additional air from infiltration. 

Particularly someone trying to establish a low price for a proposed new unit. See the glossary, under safety factors, about security factors and margins. 

Coauthor Shannon designed a system considering all the normal deficiencies and with a 20% security factor, but he found that the system was just large enough to control the flue gas temperatiue entering the recuperator. This emphasizes the need to play it safe with expensive long-term equipment design and selection. 

See the glossary, under safety factors, about security factors and margins. 

The used carrier gases are nitrogen, hydrogen and helium. For a given GC system, best results, i.e. higher separation efficiency, are achieved with hydrogen. However, due to security factors, helium is commonly the choice. Modern equipment has electronic pneumatic controller (EPC) to maintain a constant flow during the analysis in former systems a pressure controller is usually installed. 

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