The curve was produced from experimental results using a normal accepted pressure drop profile across the heater. For simplicity, the curve is related to temperature versus the factor K t /K 800
F .
The Soaking Volume Factor
The soaking volume factor is related to product yields and the degree of conversion.
The definitions of these items are discussed in the following sections.
The Degree of Conversion
The relationship of the soaking volume factor to the degree of conversion is given in
Fig. 7. These curves were the result of experimental data from the laboratory
cracking of many feedstocks. The family of curves given in Fig. 7 demonstrates
the comparative ease of cracking the large molecular structure of short residue to
that of increasing wax distillate content. Conversion is measured by the result of gas
and gasoline (to an end point of 257
F) produced.
Product Yields
A family of curves given in Figs. 8 and 9 shows the relationship of the soaking
volume factor to the yield of products of thermal cracking. Figure 8 shows the
yields when cracking wax distillate 662–1,022
F portion of the feed. Figure 9
shows the yields when cracking the bitumen portion of the feed. Both series of
curves relate to the soaking volume factor.
The Zone of Critical Decomposition
Experimental data show that cracking and stability of the cracked product varies
with the characteristics of the crude source material and boiling range. Figure 10
demonstrates this criterion as a relationship with the Watson characterization factor
“K” of the feedstock.
The shaded area of the figure is the range in which the major portion of cracking
occurs. Above this area, the cracked residue becomes unstable and precipitates
sediment when stored. It is undesirable to operate above this zone in most cases
where a cracked residue is required.
Discussion of the Concept
This is not a new concept for it has certainly been accepted as a basis for
design since the late 1950s. To date, there are at least six visbreakers and/or
thermal crackers to the author’s knowledge that were designed using these
parameters and are still in commercial use. In evaluating this concept, it is
540
D.S.J. Jones
F .
The Soaking Volume Factor
The soaking volume factor is related to product yields and the degree of conversion.
The definitions of these items are discussed in the following sections.
The Degree of Conversion
The relationship of the soaking volume factor to the degree of conversion is given in
Fig. 7. These curves were the result of experimental data from the laboratory
cracking of many feedstocks. The family of curves given in Fig. 7 demonstrates
the comparative ease of cracking the large molecular structure of short residue to
that of increasing wax distillate content. Conversion is measured by the result of gas
and gasoline (to an end point of 257
F) produced.
Product Yields
A family of curves given in Figs. 8 and 9 shows the relationship of the soaking
volume factor to the yield of products of thermal cracking. Figure 8 shows the
yields when cracking wax distillate 662–1,022
F portion of the feed. Figure 9
shows the yields when cracking the bitumen portion of the feed. Both series of
curves relate to the soaking volume factor.
The Zone of Critical Decomposition
Experimental data show that cracking and stability of the cracked product varies
with the characteristics of the crude source material and boiling range. Figure 10
demonstrates this criterion as a relationship with the Watson characterization factor
“K” of the feedstock.
The shaded area of the figure is the range in which the major portion of cracking
occurs. Above this area, the cracked residue becomes unstable and precipitates
sediment when stored. It is undesirable to operate above this zone in most cases
where a cracked residue is required.
Discussion of the Concept
This is not a new concept for it has certainly been accepted as a basis for
design since the late 1950s. To date, there are at least six visbreakers and/or
thermal crackers to the author’s knowledge that were designed using these
parameters and are still in commercial use. In evaluating this concept, it is
540
D.S.J. Jones