Pump-around

In an excimer laser the mixture of inert gas, halogen gas, and helium, used as a buffer, is pumped around a closed system consisting of a reservoir and the cavity. 

The first reactor in series in the Arco, lEP, and Phillips processes is adiabatic (vessel filled with catalyst). The exothermic heat of reaction is removed in a pump-around loop where a portion of the reactor contents are taken from the reactor, pumped through an external exchanger, cooled, and returned to the reactor. 

Distillation appHcations can be characterized by the type of materials separated, such as petroleum appHcations, gas separations, electrolyte separations, etc. These appHcations have specific characteristics in terms of the way or the correlations by which the physical properties are deterrnined or estimated the special configurations of the process equipment such as having side strippers, multiple product withdrawals, and internal pump arounds the presence of reactions or two Hquid phases etc. Various distillation programs can model these special characteristics of the appHcations to varying degrees and with more or less accuracy and efficiency. 

As shown in Fig. 13-92, methods of providing column reflux include (a) conventional top-tray reflux, (b) pump-back reflux from side-cut strippers, and (c) pump-around reflux. The latter two methods essentially function as intercondenser schemes that reduce the top-tray-refliix requirement. As shown in Fig. 13-93 for the example being considered, the internal-reflux flow rate decreases rapidly from the top tray to the feed-flash zone for case a. The other two cases, particularly case c, result in better balancing of the column-refliix traffic. Because of this and the opportunity provided to recover energy at a moderate- to high-temperature level, pump-around reflirx is the most commonly used technique. However, not indicated in Fig. 13-93 is the fact that in cases h and c the smaller quantity of reflux present in the upper portion of the column increases the tray requirements. Furthermore, the pump-around circuits, which extend over three trays each, are believed to be equivalent for mass-transfer purposes to only one tray each. Bepresentative tray requirements for the three cases are included in Fig. 13-92. In case c heat-transfer rates associated with the two pump-around circuits account for approximately 40 percent of the total heat removed in the overhead condenser and from the two pump-around circuits combined. 

FIG. 13-92 Methods of providing reflux to crude units, a) Top reflux, (h) Pump-back reflux, (c) Pump-around reflux. 

See Table opposite for what is happening inside the pump around the internal volute wall. 

For a fired reboiler, a pump-around system is used with an FRC to maintain constant flow. There will be a low flow alarm plus fuel shutoff. There will also be a high flow alarm plus fuel shutoff, since a tube rupture would reflect itself in a high flow. 

Chimneys (risers) blocking flow to draw sump forcing liquid to overflow prematurely. Flooding of trayed section below pump around. Lack of response to pump around flow changes. Design error. 

Reduetion in top reflux permits a reduction in the tower diameter in the section above the pump-around, thereby reducing investment. However, the reduction in reflux requires the addition of more fractionating plates to maintain the same separation efficiency. 

Figure 3-1. Flow diagram of atmospheric and vacuum distillation units (1,3) heat exchangers (2) desalter, (3,4) heater (5) distillation column, (6) overhead condenser, (7-10) pump around streams, (11) vacuum distillation heater (12) vacuum tower.

Interelectrode Gap The relative electrolyte volume available per unit surface area of the electrodes is determined by the distance (gap) between the electrodes. This distance is between fractions of a millimeter and some 10 cm. The ohmic losses in the electrolyte increase with the distance between the electrodes. On the other hand, when the electrolyte volume is too small, the reactant concentrations will change rapidly. Often, the electrolyte volume in a reactor is increased by providing space for the electrolyte not only between the electrodes but also above or below the block of electrodes. Sometimes the electrolyte is pumped around in an external circuit, including an additional electrolyte vessel. 

Group 3 Loss of pump around flow. This grouping comprises malfunctions associated with the circulation of fluids through and around the main fractionator. The loss of one or more pump flows (slurry, light cycle oil, naphtha, and heavy cycle oil) leads to the loss of some of the fractionator heat sink. 

The mathematical model is based on the superstructure shown in Fig. 11.2. The heat transfer fluid in heat storage remains in the storage vessel during heat transfer with only the process fluid pumped around. The superstructure also shows that each unit is capable of receiving external heating or cooling in addition to direct and indirect heat integration. 

Following are some examples of passive safety systems to reduce the likelihood of explosions in storage units. The use of baffles in a high-pressure storage vessel can cool the tank wall above the liquid surface via liquid pumped around by vapor bubbles, extending the time for fire fighting. Fire resistant tank insulation is also effective in delaying a BLEVE. 

A stirred tank reactor with a pump-around heat exchanger is arranged as on the sketch. The first order reversible reaction, A B, is to be carried to 80% conversion. The reaction temperature is to be kept at the value at which equilibrium conversion would be 90%. Temperature drop across the exchanger is to 60 K. Reaction in the exchanger circuit is neglected. Operating data are shown on the sketch and other data are k = exp(17.2-5800/T), 1/hr... 

Pump and treat hazardous waste management, 25 845 Pump-around streams, 13 223 Pump calculation worksheet, 21 56 Pump energy level, 14 695 Pump head, total developed, 21 57-58 Pumping, 14 658-659... 

The excess of chlorine thus favours formation of HOC1 which in turn accelerates the alternative route to chlorates. The reaction given by Equation 26.3 is significantly faster than that of reaction 26.1, and is strongly exothermic and thus presents runaway potential. This has been avoided historically by providing cooling within the caustic recycle or pump-around loop and by providing an excess of caustic. 

Dynamic simulations of a batch-operated scrubber with pump-around will be presented showing the effect of process configuration on destruction demands, where the method of hypochlorite destruction is a fixed-bed catalytic reactor. 

This type of traveling wave tube with cold cathode has been developed and met reasonable performance. However, a good system pumping around the cathode was difficult to achieve in the small enclosed spaces. 

Cycle Oil. Heavier, distillate range compounds formed during FCC processing can accumulate within the FCC fractionator. The primary fraction is called light cycle oil (LCO) and contains high percentages of monoaromatic and diaromatic compounds plus olefins and heavier branched paraffins. Unhydrotreated LCO is often quite unstable and has a very low cetane number. For this reason, it is blended into diesel fuel in controlled amounts. Heavy cycle oil and heavy naphtha are additional side cuts that can be produced. These streams can be pumped around to remove heat from the fractionator, used to supply heat to other refinery units, or used as low-quality blendstock component. 

The immobilization of hyroxynitrile lyase from Sorghum hicolor on a porous membrane incorporated in a standard pump-around reactor was patented by Andruski and Goldberg [80]. A solution of aldehyde and HCN in different organic... 

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