Mid per cent curve

Curves of the proi>erties of the fractions vs. per cent distilled (mid per cent curves) or the average properties of a series of fractions vs. percentage yield (yield curves), by which realizations of yields can be prepared. Among common property curves are... 

Mid Per Cent Curves. The physical properties of an oil are found to vary gradually throughout the range of compounds that constitute the oil. Distillation is a means of arranging these chemical compounds in the order of their boiling points. The properties such as color, specific gravity, and viscosity are found to be different for each drop or fraction of the material distilled. The rate at which these properties change from drop... 

Example 4-2. Use of Gravity Mid Per Cent Cuorve. Compute the specific gravity of a 41.4 API (0.8183 sp gr) mixed-base crude oil from the specific-gravity mid per cent curve. Figure 4-15 is the gravity mid per cent curve as determined in the laboratory. 

Although viscosity is not an additive property, it is a fortunate coincidence that the viscosity of a wide fraction from a crude oil is almost exactly the same as the viscosity at the mid-point of the fraction. Apparently the curvature exhibited by vi osity mid per cent curves is just right to compensate for the lowering of viscosity by blending, so that the mid-point can be used. 

Abbreviated T.B.P. analyses of more than 150 crude oils are tabulated in Appendix B. Distillation curves may be plotted from the percentages given in the tabulation for temperatures of 80,300,400,450,550,700, and 900 F. Gravity mid per cent curves can also be plotted by using the Characterization Factors with the instantaneous temperatures just enumerated. 

This data shows that 85 per cent of production is from plants with direct operating costs within the range of 160 to 350/t of lead produced. The first quartile boundary is 195/t, and the third quartile upper boundary is 320/t. The above estimate for the sinter plant-blast furnace technology is around the average mid range of the curve, whereas the direct smelting technologies fall close to the first quartile boundary. 

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