درخواست كمك از مهندسان نفت براي توضيح دو پاراگراف در ارتباط با كارايي جداسازي برج تقطير نفت خام..
سلام.
لطفا دوستان كمك كنن .
توي اين متن من دقيق متوجه نمي شم كه چطور ميزان كارايي برج تقطير نفت خام رو مي تونن از خصوصيات نفت خام تشخيص بدن.
به نظر مياد كه ابتدا منحني TBP از نفت خام تهيه ميشه و بعد از خطوط 5% و 95%ميان يك سري توجيهاتي مي كنن كه من دقيق متوجه نميشم.
مهمترين سوال من اينه كه مگه منحني TBP يك منحني پيوسته نيست؟ پس چطور در اين متن هر كدوم از محصولات رو بصورت جداگانه رو يك منحني ترسيم كردن و مي گن با هم اورلپ داره يا نداره.. و بعد ميگن كارآيي جداسازي خوبه يا خير.
لطفا كمك كنين..
The boiling ranges of the different fractions and the topping operating conditions must be established a
priori. To do this a number of combinations of yields are provided for, for which the plant must allow a
certain degree of flexibility, such as to enable adjustments to be made quickly in line with the quality
of the crude oil and/or the products demanded by the market. The starting point for determining the
provisional quantity and characteristics of the products is the distillation TBP (True Boiling Point); based on
the specifications of the finished products and experience, the yields and the principal characteristics
of the fractions can be calculated by making an arbitrary assumption about the final boiling points of the products
that could be obtained from the crude. These products are found between boundary zones which
represent fractions common to two adjacent products.The boundary zones allow, when necessary, for the final
points originally specified to be shifted, subtracting all or a part of a certain border fraction from this or that
product and adding it to the adjacent product. Once the characteristics of the desired products
have been established, it remains to establish the efficiency with which the fractions are to be separated
from each other; in the refining industry this is done using conventional methods, given the complexity of
the composition of the mixtures involved. In practice, the starting point is the ASTM D 86 curve of the fractions, noting the difference between the temperature at which 5% of a fraction has distilled and that at which 95% of the fraction with a
boiling point immediately below it has distilled; if this difference is positive there is a gap and the
fractionating is considered to be good, whereas if it is negative there is an overlap and the fractionating is
deemed to be unsatisfactory.

By way of an example, Fig. 6 shows that heavy naphtha and kerosene are well
fractionated, that is, they are well separated from one another given that there is a gap of +13°C; on the
other hand, light gas oil and heavy gas oil are not well separated, as there is an overlap of -42°C, since the
light gas oil contains about 30% of product which should be part of the heavy gas oil, while the latter
contains about 20% of product which should be part of the light gas oil.
Based on the value of the internal reflux ratio, which depends on other processing variables
(characteristics of the fractions, overflash, intermediate refluxes), the number of theoretical trays
necessary is defined so as to achieve the value of the product of the internal reflux ratio by the number of
trays, which is, in turn, determined on the basis of the deviation from the ideal fractionating (Fenske, 1932;
Gilliland, 1940; Colburn, 1941). The number of actual trays is determined by dividing the number of
theoretical trays by an efficiency coefficient which depends on both the physical characteristics of the
fluid in question and the typology of the trays selected