Control over residence time

The consecutive reaction will be triggered by too long exposure of already chlorinated product in an environment with a high density of chlorine radicals. Accordingly, controls over residence time, concentration profiles and efficient heat transfer have the potential to cope with such a problem. 

Flaked meats are delivered at a constant flow rate to the top kettle by means of a conveyor. The meats remain in the top kettle to cook for a predetermined time (controlled by the hnkage in the bottom gate) before dropping to the kettle below. The meats then remain in the second kettle before dropping into the third, and so on through the cooker. The gates governing the flow of meats from one kettle to another are opened and closed automatically by a mechanism that is tripped by the meat level in each kettle. The mechanism for each kettle is adjustable. This permits control over residence time in each kettle. The cookers are made in different sizes, with different numbers of stacks, and are supplied by several equipment manufacturers. 

In a continuous system, two essential elements are absolute control over residence time and residence time distribution. The residence time must be short and uniform during compounding to minimize heat history. Machine design, screw rpm, and throughput generally determine residence time. Continuous machines do not have an exact residence time but a residence time spectrum. Uniformity of a continuous operation is determined by the type of spectrum obtained. 

Table 8.2 Control over residence time by varying reagent flow rate.

Performing plasma processes in a continuous-flow microreactor leads to precise control of residence time and to extreme quenching conditions, therewith enabling control over the composition of the reaction mixture and product selectivity. In a nonequilibrium microplasma reactor, low-temperature activation of hydrocarbons and fuels, which is difficult to obtain in conventional thermochemical processes, can be achieved at ambient conditions. 

Films of TaaOs have been deposited by LPCVD at temperatures in the ranges of 340-400°C [118], and 470-650°C [119], with growth rates in the range of 40 Amin". The precise control of residence time of the precursor, temperature, pressure, and the Ta(OEt)s/02 ratio each was found to be an important factor in controlling conformality and uniformity. Film uniformity can be obtained that is better than 1.5% (SD lo) over a single 15 cm wafer and better than 4.5% (SD 3o) from wafer to wafer, run to run. 

The butene conversion level is highly dependent on its initial concentration. For instance, today commercial Dimersol-X technology achieves 80% conversion of butenes with up to 85% octene selectivity. A process flow diagram is depicted in Figure 1. The reaction takes place at low temperature (40-60 °C) in three or four consecutive well-mixed reactors. The pressure of 1.5 MPa is sufficient to maintain all reactants and products in the liquid state. Mixing and heat removal are ensured by an external recirculation loop over a heat exchanger system. The two components of the catalytic system are injected separately into this reaction loop under precise flow control. The residence time is between 5 and 10 h. 

The heated polymer solution emerges as filaments from the spinneret into a column of warm air. Instantaneous loss of solvent from the surface of the filament causes a soHd skin to form over the stiU-Hquid interior. As the filament is heated by the warm air, more solvent evaporates. More than 80% of the solvent can be removed during a brief residence time of less than 1 s in the hot air column. The air column or cabinet height is 2—8 m, depending on the extent of drying required and the extmsion speed. The air flow may be concurrent or countercurrent to the direction of fiber movement. The fiber properties are contingent on the solvent-removal rate, and precise air flow and temperature control are necessary. 

In the fixed catalyst method, the residence time in the reactor may be easily controlled to generate fibers of selected length and diameter, both dimensions which can vary over several orders of magnitude. Most of the physical properties which have been measured for VGCF have been made on this type of fiber. 

The present sources to the ocean are the weathering of old evaporites (75% of river flux) and CP carried by atmospherically cycled sea-salts (25% of river flux). Loss from the ocean occurs via aerosols (about 25%) and formation of new evaporites. This last process is sporadic and tectonically controlled by the closing of marginal seas where evaporation is greater than precipitation. The oceanic residence time is so long for CP ( 100Myr) that an imbalance between input and removal rates will have little influence on oceanic concentrations over periods of less than tens of millions of years. 

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