Duty/duties

DUTY DUTY DUTY DUTY DUTY DUTY DUTY... 

Book Bond is not just Byronic in his brooding Book Bond is full of self-loathing. He hates his job, hates the lack of honor and fair play in the world. He also hates the constant betrayal he faces, from the world around him and from his own emotions. For him, the only guiding darkness is duty. Duty tmmps everything. Book Bond does what he does because he must do it. For Queen and country, he must. There is no one else. It s all on him. Everybody else is going to fail in one way or another, therefore... 

F d Cone Revry r Feed F 8ottm Prod 8 Reflux Ratio R Ovhd Vapor I, Boil- Up Liquid Reflux Cond Rebt Duty Duty 0, 0, Bottm Temp Vapor Vel at Top y m/s... 

There are three levels or types of duty imposed by statute, which allow different responses to hazards. These are absolute duty, duty to do what is practicable, and duty to take steps that are reasonably practicable. Over the years, a body of case law has built up which gives guidance on the meaning of these duties in practice. Mostly, the cases have been decided in common law, in the course of actions for personal injuries which were based on alleged breach of statutory duty. 

Latent heat of vaporization decreases i.e., reboiler and condenser duties become lower. 

Consider the simple flowsheet shown in Fig. 6.2. Flow rates, temperatures, and heat duties for each stream are shown. Two of the streams in Fig. 6.2 are sources of heat (hot streams) and two are sinks for heat (cold streams). Assuming that heat capacities are constant, the hot and cold streams can be extracted as given in Table 6.2. Note that the heat capacities CP are total heat capacities and... 

After maximizing heat recovery in the heat exchanger network, those heating duties and cooling duties not serviced by heat recovery must be provided by external utilities. The outer-most layer of the onion model is now being addressed, but still dealing with targets. 

Taking the heat capacity of water to be 4.3 kJ kg K , heat duty on boiler feedwater preheating is... 

A refrigeration system is a heat pump in which heat is absorbed below ambient temperature. Thus the appropriate placement principle for heat pumps applies in exactly the same way as for refrigeration cycles. The appropriate placement for refrigeration cycles is that they also should be across the pinch. As with heat pumps, refrigeration cycles also can be appropriately placed across utility pinches. It is common for refrigeration cycles to be placed across a utility pinch caused by maximizing cooling water duty. 

In general, the final network design should be achieved in the minimum number of units to keep down the capital cost (although this is not the only consideration to keep down the capital cost). To minimize the number of imits in Eq. (7.1), L should be zero and C should be a maximum. Assuming L to be zero in the final design is a reasonable assumption. However, what should be assumed about C Consider the network in Fig. 7.16, which has two components. For there to be two components, the heat duties for streams A and B must exactly balance the duties for streams E and F. Also, the heat duties for streams C and D must exactly balance the duties for streams G and H. Such balemces are likely to be unusual and not easy to predict. The safest assumption for C thus appears to be that there will be one component only, i.e., C = 1. This leads to an important special case when the network has a single component and is loop-free. In this case, ... 

Thus, for a given exchanger duty and overall heat transfer coefficient, the 1-2 design needs a larger area than the 1-1 design. However, the 1-2 design offers many practical advantages. These... 

The heat duty on the heating/cooling medium is given by... 

The preceding appropriate placement arguments assume that the process has the capacity to accept or give up the reactor heat duties at the given reactor temperature. A quantitative tool is needed to assess the capacity of the background process. For this purpose, the grand composite curve can be used and the reactor profile treated as if it was a utility, as explained in Chap. 6. 

The gaseous reactor product is cooled first by boiler feedwater before entering a cooling water condenser. The cooling duty provided by the boiler... 

The dominant heating and cooling duties associated with a distillation column are the reboiler and condenser duties. In general, however, there will be other duties associated with heating and cooling of feed and product streams. These sensible heat duties usually will be small in comparison with the latent heat changes in reboilers and condensers. 

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