Distillation specifications

For the atmospheric tower shown in Fig. 13-90, suppose distillation specifications are as follows ... 

The values of overhead composition can be varied from X3 of Figure 8-33 to other values as the drawoff percentage changes. As the drawoff percentage decreases, the distillate specification can be better maintained as the distillation operation continues for a fixed number of plates. For further discussion see References 129, 130, 131,133. 

The Pharmacopea and the Essential Oil Association of the United States require the following analyses as an index of oil purity refractive index, optical rotation, refractive index and optical rotation of a 10% distillate, specific gravity, aldehyde content, evaporation residue and ultraviolet absorption spectrum (Kesterson et al. 157 and Sale 29). 

Establish a mol percent heavy key component in distillate specification and a light key specification in the bottoms product ... 

The deentraining device of Fig. 5.7-11 may not be needed if the "contaminated overhead vapor meets distillate specifications. Entrainment data for sieve and bubble-cap trays have been correlated by Fair and coworkers 10 as shown in Fig. 5.7-12. The sieve tray data are for trays with small (less than 7 mm) diameter. Visual dsla of FRI. released as a movie.11 show that uuder distillation conditions 3 mm holes enlmin sigaificantly less than 12.7 mm boles, with hole areas and gross vapor rales being equal,... 

Use the Naphtali-Sandholm SC method with the Chao-Seader correlation for thermodynamic properties to calculate product compositions, stage temperatures, interstage flow rates and compositions, reboiler duty, and condenser duty for the following distillation specifications. 

The two bottoms specifications are the required product purities. The two distillate compositions are design optimization variables to be established by economics. As the distillate specifications get closer and closer to the corresponding azeotropic compositions, the separations in each column become more difficult and more trays are required (higher capital investment). However, the flow rates of the recycle stream D and D2 decrease as the difference between the two distillate compositions increases, so energy consumption... 

In the first column, the toluene impurity in the distillate benzene product is controlled by manipulating reflux, and the benzene impurity in the bottoms is controlled by manipulating reboiler heat input. Any benzene that drops out of the bottom of the first column ends up as an impurity in the distillate of the second column, and nothing can be done in the second column to affect this situation. The distillate specification is 1 mol% toluene. The bottoms specification is 0.3 mol% benzene, which gives a distillate impurity in the second column of 0.6 mol% benzene. 

For organometallic species, the analytical challenge involves quantitative extraction of the species from the solid phase without appreciable transformation to other forms. Various liquid extractants have been used such as methanolic hydrochloric acid (extraction of organotins). Strong alkali digests (KOFI or tetramethylammonium hydroxide) will dissolve most tissue without breakdown or transformation of arsenic species. As an alternative to liquid extraction, methylmercury species may be extracted from solids using steam distillation. Specific reaction conditions will affect the recovery of various species and rigorous validation of extraction procedures is therefore recommended. 

Heater Outlet Temperature This temperature can affect the lift of diesel out of UCO. A too low heater outlet temperature would cause a slump of diesel into UCO, which degrades the value of diesel into fuel oil. Too high of a heater outlet temperature will cause unnecessarily high reflux rate at the expense of extra heater duty. The heater outlet temperature is mainly a function of the hydrocarbon partial pressure in the flash zone because the distillation cut point is a function of the diesel distillation specification and fractionation efficiency. An optimal heater outlet temperature could be determined by the fractionation overflash, which measures the internal reflux rate. 

Figure 13.3 shows an example of the calculation that might be performed on a very high purity LPG splitter. The distillate specification is 0.05 mol% C4 in propane. The material sold from storage has a concentration very close to this specification and so there would appear little benefit to be obtained from better controlling it. However the rundown... 

FRACTIONAL DISTILLATION Specific heat Btu/CLb)(DegF) Pcu/(Lb fDegC)... 

We apply this method to the feed specified in Table 5.1 using the ASTM D-86 distillation, specific gravity and individual PNA composition. We convert the ASTM D-86 distillation curve to a TBP curve and estimate the molecular weight (using standard API correlations). We then optimize the parameters to match the EP, 90% and 70% of the TBP curve, molecular weight and specific gravity. We compare the calculated and measured values in Figure 5.12 and Table 5.9. 

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