Double effect

Figure 14.4 Double-effect distillation. (From Smith and Linnhoff, Trans. IChemE, ChERD, 66 195, 1988 reproduced by permission of the Institution of Chemical Engineers.)...

RoUer-top cards have five to seven sets of workers and strippers to mix and card the fibers carried on the cylinder. The multiple transferring action and re-introduction of new groupings of fibers to the carding zones provides a doubling effect which enhances web uniformity. Stationary-top cards have strips of metallic clothing mounted on plates positioned concavely around the upper periphery of the cylinder. The additional carding surfaces thus estabhshed provide expanded fiber alignment with minimum fiber extraction. 

There are a number of ways to provide the heating or cooling medium at temperatures closer to the optimum level. One is by use of double-effect distillation, which uses the overhead vapor from one column as the heat source for another column such that the second column s reboiler becomes the first column s condenser. This basically cuts the temperature differential in half, and shows up as an energy saving because external heat is suppHed to only one of the units. 

Fig. 12. The relative energy input for removal of 1 kg of water relative to heat of vapori2ation is 0.7 in A, the double-effect crysta11i2er 0.015 in B, the...

Sindlady, heating surface area needs are not direcdy proportional to the number of effects used. For some types of evaporator, heat-transfer coefficients decline with temperature difference as effects are added the surface needed in each effect increases. On the other hand, heat-transfer coefficients increase with temperature level. In a single effect, all evaporation takes place at a temperature near that of the heat sink, whereas in a double effect half the evaporation takes place at this temperature and the other half at a higher temperature, thereby improving the mean evaporating temperature. Other factors to be considered are the BPR, which is additive in a multiple-effect evaporator and therefore reduces the net AT available for heat transfer as the number of effects is increased, and the reduced demand for steam and cooling water and hence the capital costs of these auxiUaries as the number of effects is increased. 

Figure 11-19. Lithium bromide hermetic absorption refrigeration system, double effect, liquid chiller/heater. As shown in chilling mode, water is the refrigerant under low absolute pressure (boiling at 40°F) (Used by permission Cat. 521-606, form 16DF-1 PD, 1994. Carrier Corporation, a United Technologies Company.)...

The 16DF direct-fired, double effect, absorption chiller/heater can also be operated in a non-simultaneous heating (only) mode to provide 140 F (60 C) hot water for-space heating or other purposes without any additional components. In this mode, the cycle follows a different vapor flow path than that undertaken for cooling and does not use the absorption process. ... 

Frequently, coil data will he available for a design air flow, hut the system resistance reduces this flow to a lower value. There is a double effect the lowering of the In MTD and the lower heat transfer from the coil by convection. 

The chiral catalyst 142 achieves selectivities through a double effect of intramolecular hydrogen binding interaction and attractive tt-tt donor-acceptor interactions in the transition state by a hydroxy aromatic group [88]. The exceptional results of some Diels-Alder reactions of cyclopentadiene with substituted acroleins catalyzed by (R)-142 are reported in Table 4.21. High enantio- and exo selectivity were always obtained. The coordination of a proton to the 2-hydroxyphenyl group with an oxygen of the adjacent B-0 bond in the nonhelical transition state should play an important role both in the exo-endo approach and in the si-re face differentiation of dienophile. 

Fidelis IK, Mioduski T (1981) Double-Double Effect in the Inner Transition Elements. 47 27-51... 

Bansal V, Ross R, Perkins JD, Pistikopoulos EN (2000) The Interactions of Design and Control Double Effect Distillation,... 

In Example 21.1, consider introducing a double-effect column to replace Column 2 for the backward heat integration arrangement. Assume an equal split of flowrate into the doubleeffect column. Is there any benefit from the arrangement ... 

Czech workers have examined displacements in substituted malononitriles in which the double bond transmits the double effect of the cyanide groups... 

A forward-feed double-effect evaporator, having 10 m2 of heating surface in each effect, is used to concentrate 0.4 kg/s of caustic soda solution from 10 to 50 per cent by mass. During a particular run, when the feed is at 328 K, the pressures in the two calandrias are 375 and 180 kN/m2 respectively, and the condenser operates at 15 kN/m2. For these conditions, calculate ... 

A forward-feed double-effect standard vertical evaporator with equal heating areas in each effect is fed with 5 kg/s of a liquor of specific heat capacity of 4.18 kJ/kgK, and with no boiling-point rise, so that 50 per cent of the feed liquor is evaporated. The overall heat transfer coefficient in the second effect is 75 per cent of that in the first effect. Steam is fed at 395 K and the boiling-point in the second effect is 373 K. The feed is heated to its boiling point by an external heater in the first effect. 

A double-effect climbing-film evaporator is connected so that the feed passes through two preheaters, one heated by vapour from the first effect and the other by vapour from the second effect. The condensate from the first effect is passed into the steam space of the second effect. The temperature of the feed is initially 289 K, 348 K after the first heater and 383 K after the second heater. The vapour temperature in the first effect is 398 K and in the second effect 373 K. The feed flowrate is 0.25 kg/s and the steam is dry and saturated at 413 K. What is the economy of the unit if the evaporation rate is 0.125 kg/s ... 

A double-effect forward-feed evaporator is required to give a product which contains 50 per cent by mass of solids. Each effect has 10 m2 of heating surface and the heat transfer coefficients are 2.8 and 1.7 kW/m2 K in the first and second effects respectively. Dry and saturated steam is available at 375 kN/m2 and the condenser operates at 13.5 kN/m2. The concentrated solution exhibits a boiling-point rise of 3 deg K. What is the maximum permissible feed rate if the feed contains 10 per cent solids and is at 310 K The latent heat is 2330 kJ/kg and the specific heat capacity is 4.18 kJ/kg under all the above conditions. 

Double-cell system, in soil and ground water treatment, 25 835 Double crucible technique, 11 135-136 Double-deck kiln, 15 530 Double-drum dryers, 9 134 Double-drum separator, 15 446 Double-effect distillation, 10 153 Double end point titration method,... 

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