Tower pressure reduction

The large-scale plants which have so far been realized for the decaffeination of tea and coffee and for the extraction of hops and spices are now established. These are in general one-stage plants in which the extract is separated by adsorption on activated carbon or by pressure reduction. The tendency now is to replace adsorption by absorption in washing towers. 

The carrier gas used was argon or nitrogen. The flow rate was adjusted by a pressure reduction valve and kept constant, as indicated by a rotameter. The carrier gas was then passed through adsorption towers to remove H2O and CO2. The volume of the carrier gas was measured by a gas-flow meter. The reproducibility in the measured gas volume was of the order of 0.1%. 

Often there are significant differences in the phases that exit from one process operation and enter another. For example, hot effluent gases from a reactor are condensed, or partially condensed, often before entering a separation operation, such as a vapor-liquid separator (e.g., a flash vessel or a distillation tower). In process synthesis, it is common to position a phase-change operation, using temperature- and/or pressure-reduction operations, such as heat exchangers and valves. 

A significant drop in benefits can be seen for July. This was due to poor operation of the DIP tower, caused by a high butane content in the tower feed from the cmde unit stabilizers. The C4 s caused the DIP tower pressure to increase up to its safe operating limit, and the reboiler duty was cut back to avoid overpressuring the tower. This resulted in a reduction in fractionation efficiency and profitability during part of July, and represented one of the challenges encountered in sustaining the improved DIP performance. 

A small, slow reduction in tower pressure reduced fractionation efficiency. 

If, on the other hand, the equilibrium solute concentration C is very low, leading to a correspondingly low value for Cj in equation (10.1), the energy and capital costs associated with the recompressor can become major factors in determining the separation cost. This will be seen to be the case, for example, in the hypothetical process for extracting crushed rape seed with subcritical carbon dioxide which is considered in section 10.6. It would also be true of the extraction of caffeine from coffee beans if pressure reduction was used to recover the caffeine. In cases such as these the most economic flow conditions and tower dimensions will be such that Ct is quite close to the equilibrium value C. ... 

Example 16-14. Fractionation of Gasoline and Kerosene. The crude oil shown in Fig. 16-27 is to be fractionated into gasoline, kerosene, and other products. The top five plates of the tower, which separate gasoline from kerosene, operate at an equivalent pressure of 1,000 mm including the partial-pressure reduction of steam. The gasoline is to have an end point of about 380°F, and the kerosene is to have a gravity of 46 API. 

The background for the development of VK69 was a need for reduction of S02 emissions from double-absorption plants by installing a more active catalyst at low temperature downstream from the intermediate absorption tower. Clearly, the catalytic solution should be more competitive than the alternatives, e.g. tail gas scrubbing or triple-absorption layout, in terms of capital and operating costs. In the following, the required technical performance of the catalyst with respect to S02 oxidation activity, mechanical strength and pressure drop is discussed, and input from the literature and from practical experience in the field is presented. Reviews of the extensive literature published on sulphuric acid catalysts can be found in [2-5],... 

The pressure inside the deaerator started to drop, as there was not enough steam flow to keep the water in the drum at its boiling point. The reduction in the deaerator pressure increased the volume of steam flow through the bottom tray of the stripping tower. Why ... 

Static Pressure Drop—The reduction of air movement through the tower resulting from resistance of internal components such as air-intake louvers, fill packing, water distribution system, internal supporting beams, drift eliminators and fan stack configuration. 

Flooding is an excessive accumulation of liquid inside a column. Flood symptoms include a rapid rise in pressure drop (the accumulating liquid increases the liquid head on the trays), liquid carryover from the column top, reduction in bottom flow rate (the accumulating liquid does not reach the tower bottom), and instability (accumulation is non-steady-state). This liquid accumulation is generally induced by one of the following mechanisms. 

The first fraction consisting of benzene, chlorobenzene and phenyltrichlorosilane is separated in two stages. First, when the temperature of the tower top is 60-80 °C and residual pressure is 210 GPa, the distillation gives low-boiling components, benzene and chlorobenzene then, with the pressure increased to 80 GPa and the temperature on top increased to 195 °C the distillation produces high-boiling components, phenyltrichlorosilane and to some extent diphenyl. The end of the separation of low-boiling substances is determined by the reduction in chlorine content [to 26-25% (mass)] and the fraction density [to 1.200 g/cm3]. 

The primary factors that affect pressure drop in packed towers are (1) fluid-flow rates, (2) density and viscosity of the fluids, and (3) size, shape, orientation, and surface of the packing particles. Figure 16-17 illustrates the effects of fluid rates at constant operating pressure, and Fig. 16-19 shows how increased gas velocity due to reduction in operating pressure can affect the pressure drop. 

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