J

voiume peice nt over

Figure 3.4. Whole crude TBP temperature—yield curve, lube—asphalt operation.

The owner specified the requirement to make three specification products off the tower.

1. Asphalt having a specification of 80 pen. as measured at 77 degrees F.

2. A heavy lube cut having a mid-volume viscosity of 700 SSU as measured at 100 degrees F and a yield on whole crude of 6.0 volume percent.

3. A light lube cut having a mid-volume viscosity of 100 SSU as measured at 100 degrees F and a yield on whole crude of 4.0 volume percent.

4. The required distillation ranges for the lube cuts were specified.

The overall system material balance is established by the following sequence.

1. Total distillate yield is set by analysis of the portion of the crude assay covering asphalt properties. From Fig ure 3.5, it is seen that an 80 pen. asphalt requires a residuum yield of 23.9 volume percent on whole crude. Thus, the whole crude cut volume between vacuum distillates and residuum occurs at 76.1 volume percent.

2. From Figure 3.6, it is determined that the mid-volumes of heavy lube and light lube, respectively, are 71.0 and 57.0 volume percent of whole crude. From these points and their respective yield requirements, it is determined that the heavy lube will occupy the whole crude range of 71.0 ± 3 volume percent and that the light lube will occupy the whole crude volume range of 57.0 ± 2 percent.

3. From Figure 3.4, it is seen that the TBP cut volume between atmospheric distillates and reduced crude is 52.5 percent. Thus, the tower will also yield the following three product streams.

a. A light vacuum gas oil (LVGO) over the range 52.5 to 55.0 volume percent.

Figure 3.5. Crude assay data. Asphalt yield versus penetration.

b. A medium vacuum gas oil (MVGO) over the range 59.0 to 68.0 volume percent.

c. A heavy vacuum gas oil (HVGO) over the range 74.0 to 76.0 volume percent. This cut may also be thought of as condensed overflash, even, though it is somewhat greater in volume than would normally be designed as overflash.

Thus, the yields of all products have been set. Product properties are determined as follows.

4. From the distillation ranges of the lube cuts, fractionation requirements are established by assuming that the TBP cut point is the mid-point of the total IBPjayerlap. betvvecnj? roduc ts.

5. From the TBP distillations of the products, ASTM and atmospheric EFV^curves are calculated and plotted. Note that the EFV curves are extrapolated to minus_20 percent for estimating the front end of the unstripped liquids which exist on the draw trays.

6. Stream gravities are obtaingcTfrom the whole crude properties, and molecular weights are calculated.

Fuels-Pitch Operation

The final material balance superimposed on the whole crude TBP curve is shown by Figure 3.7. This is for a typical operation producing maximum distillates and minimum residuum from a reduced crude feed. „The following procedures were used to develop the overall material balance.

The owner specified two requirements for the design of the system.

1. The TBP cut point between the distillates and the residuum was set at 1,100 degrees F.

2. The light vacuum gas oil (LVGO) was set at 30 volume percent of the total vacuum gas oils.

The overall system material balance is established by the following sequence.

1. Item 1 above sets the total distillate yield at 812 volume percent of whole crude.

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