Start-up Period

In practice, an empty conventional batch column is started up in the following sequence  

1) The reboiler is charged with the material to be processed and heat is applied to it to bring the material to its boiling point temperature. 

2) Depending on the reboiler duty, a part of the material is vaporised and the vapour travels upward both through the plate holes and downcomers and almost instantly reaches the condenser. 

3) At this time, the coolant valve is opened and the condensed liquid is stored into a reflux drum. The reflux valve is opened when the liquid fills the condenser holdup tank. At this point some product may also be collected simultaneously. 

4) The liquid begins to flow into the top plate and collects on the plate because of the retention made by the vapour flow. When the liquid level passes the weir height (thus filling the holdup), the liquid begins to fall to the plate below and the same phenomenon is repeated until the reboiler is reached. In practice some liquid also trickles down from the plate holes when the flows are initially established. 

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As desired up to 5-6 times the T,. through field forcing (i.e. by raising the field voltage during the start up period)... 

You will have to investigate and apply trial and error field tests to resolve some of these problems. When new equipment are installed, it is wise to spend time during a shake-down and start-up period to explore the operational limitations of the process and train operators on how to handle these types of problems. 

It should be appreciated that a steam flow must be maintained through the elements at all times to prevent them burning away. If a single boiler is used then provision to flood the superheater during start-up periods may be required. 

The required warm-up time will vary with ambient conditions, being longer in cold weather and least in warm. Optimum-start controllers are now in general use which are programmed for the building warm-up characteristics and sense the inside and ambient conditions. They then transduce the required start-up period and set the heating plant going only when needed. This, and the previous scheme, will save fuel. 

As described in Section 7.3.1 when the derivative method is used, the specific MAb production rate at any time t during the batch start-up period is determined by... 

As described in Section 7.3.2 when the integral method is employed, the average specific MAb production rate during any time interval of the batch start-up period... 

Figure 17.11 Dialyzed Che most at Estimated values of specific MAb production rate versus time during the initial batch start-up period. A 5% standard error in raw data was assumed for data smoothing.

Araki, N., and Harada, H., Population Dynamics of Methanogenic Biofilm Consortium during a Start-Up Period of Anaerobic Fluidized Bed Reactor, Wat. Sci. Tech., 29(10-11) 361 (1994)... 

In this section we deal with perhaps the most conceptually difficult of all the responses observed in linear viscoelastic materials. This is the response of a material to an oscillating stress or strain. This is an area that illustrates why rheological techniques can be considered as mechanical spectroscopy. When a sample is constrained in, say, a cone and plate assembly, an oscillating strain at a given frequency can be applied to the sample. After an initial start-up period, a stress develops in direct response to the applied strain due to transient sample and instrumental responses. If the strain has an oscillating value with time the stress must also be oscillating with time. We can represent these two wave-forms as in Figure 4.6. 

Once this initial operating discipline is put into usable form, it must be communicated to the people who will use it. This means a series of training sessions before plant start up, training that continues through the start up period. 

Flow near a Wall Suddenly Set in Motion Set up the parallel-plate drag flow problem during its start-up period t < ttr, when vx =f(t) in the entire flow region, and show that the resulting velocity profile, after solving the differential equation vx/V = 1 — erf(y/pt/p), if H is very large. 

Table I shows the results of the class separation of residuum with absolute and percent recovery for each of the four fractions for day 1, 14 and 25. In general, the concentration of the less polar (hexane and toluene) fractions decreased or remained constant with time while, the more polar (CHCl and THF) fractions increased in percentage. This is best noted from data for days 14 and 25. Data from day 1 are somewhat variant from this trend. This is probably due to the inconsistency in operating conditions that occurred during the start-up period. Such assumptions should be viewed cautiously since the percent weight recovery from day 14 and 25 is not constant.

The start-up period is ended when the desired distillate purity is reached. Product take off is started and the product is collected at constant composition by varying the reflux ratio until a specified amount of distillate has been collected. This type of operation is known as variable reflux... 

The total reflux start-up period is ended when the unit reaches its steady state. Product is collected at some constant finite reflux ratio until the accumulated product composition reaches its desired purity. This type of operation is very common in practice and is known as constant reflux operation. Under this operation mode the column is operated using a fixed reflux ratio for the whole operation (cut), producing better than specification material at the beginning and below specification material at the end of the fraction (Barolo and Botteon, 1997 Greaves et al., 2001)... 

In the third cycle the pH-control of the DTPA-lactic acid solution is critical. A pH-value which is too low anywhere will lead to deposition of DTPA-crystals in the settlers near that point. These crystals are quite large and dissolve only very slowly. The largest danger for DTPA-crystallization seems to be during the start-up period before proper circulation of the DTPA-solution through the 3B and 3D batteries has been established. 

Figure 3 shows the evolution of the temperatures in this experience. During the starting-up period, wich last over 100 minutes, air and water were heated in an electrical heater. Initial flowrates were low and they were increased as the reaction temperature began to raise. When the reaction temperature was high enough, the electrical heater was switched off and water flowrate was fixed at 16.1 L/h. Then, the system evolved to its steady state. Air was finally fed at 120 °C due to the temperature increase produced in the compression stage. 

The New England Document Conservation Center, or NEDCC, was founded six years ago by the New England Library Board, with the help of start-up funds from the Council on Library Resources. The purpose was to provide paper conservation services to libraries, historical organizations, and public records offices that could not afford in-house laboratories. The idea was that a shared resource could eliminate wasteful duplication of equipment and make available on a regional basis the skills of professional paper conservators. It was expected that after a start-up period, the Center would be self-supporting through fees for its services. 

If, as is often the case, the stress reaches a steady value only after a transient period of steady shearing starting from a state of rest, then the instantaneous stress steady shear rate y, is the transient start-up... 

One special property of the process waters discussed is the broad heterogeneity in concentration of the dissolved and dispersed molecules. This is due to different products manufactured using the same machine and also due to shut down and start-up periods. Several authors have shown that the concentrations of organic and inorganic compounds vary even tenfold in process waters [18,27,28]. This means that when using membrane technology the membranes should be resistant to big fluctuations in the feed stream. 

The kinetics of coking for the reforming process has been investigated in a gravimetric reactor. Coking after the initial start-up period obeys the following rate law ... 

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