617
Hydrocracking
In the related Tervahl-T process (a thermal process but covered here for convenient comparison
with the Tervahl-T process), the feedstock is heated to the desired temperature using the coil heater
and heat recovered in the stabilization section and held for a specified residence time in the soaking
drum. The soaking drum effluent is quenched and sent to a conventional stabilizer or fractionator
where the products are separated into the desired streams. The gas produced from the process is
used for fuel.
22.3.19 t-stAr ProCess
The T-Star process is an ebullated-bed process that can acts as a pretreater for fluid catalytic cracking feedstock or as a hydrocracker. In the mild hydrocracking mode, the T-Star process can reach
conversions up to the 60% v/v and an advantage of operating the T-Star unit in mild hydrocracking
mode is that the T-Star catalyst is not sensitive to sulfur and nitrogen levels in the feed and will
provide constant conversion, product yields, and product quality.
The T-Star is based upon the residuum H-Oil process and the Texaco’s fixed-bed hydrotreating/
hydrocracking technology. The process is ideally suited for hard-to-process feedstocks and T-STAR
reactors can be used in-line as hydrotreaters/hydrocrackers within an H-Oil unit (Johns et al., 1993).
22.3.20 unICrACkIng ProCess
Unicracking is a fixed-bed catalytic process that employs a high-activity catalyst with a high
tolerance for sulfur and nitrogen compounds and can be regenerated (Reno, 1997). The design is
based upon a single-stage or a two-stage system with provisions to recycle to extinction (RAROP,
1991, p. 79).
In the process, a two-stage reactor system receives untreated feed, makeup hydrogen, and a
recycle gas at the first stage, in which gasoline conversion may be as high as 60% by volume. The
reactor effluent is separated to recycle gas, liquid product, and unconverted oil (Table 22.12). The
second-stage oil may be either once-through or recycle cracking; feed to the second stage is a mixture of unconverted first-stage oil and second-stage recycle. The process operates satisfactorily for a
variety of feedstocks that vary in sulfur content from about 1.0% by weight to about 5% by weight.
The rate of desulfurization is dependent on the sulfur content of the feedstock as is catalyst life,
product sulfur, and hydrogen consumption (Speight, 2000 and references cited therein).
In the process, the feedstock and hydrogen-rich recycle gas are preheated, mixed, and introduced
into a guard reactor that contains a relatively small quantity of the catalyst. The guard chamber
removes particulate matter and residual salt from the feed. The effluent from the guard chamber
flows down through the main reactor, where it contacts one or more catalysts designed for the
removal of metals and sulfur. The catalysts, which induce desulfurization, denitrogenation, and
hydrocracking, are based upon both amorphous and molecular-sieve containing supports. The product from the reactor is cooled, separated from hydrogen-rich recycle gas, and either stripped to meet
fuel oil flash point specifications, or fractionated to produce distillate fuels, upgraded vacuum gas
oil, and upgraded vacuum residuum. Recycle gas, after hydrogen sulfide removal, is combined with
makeup gas and returned to the guard chamber and main reactors.
The most commonly implemented configuration is a single-stage Unicracking design, where the
fresh feed and recycle oil are converted in the same reaction stage. This configuration simplifies the
overall unit design by reducing the quantity of equipment in high-pressure service and keeping highpressure equipment in a single train. The two-stage design has a separation system in each reaction
stage. However, the optimum flow scheme depends on feedstock capacity and product slate objectives.
The high efficiency of the process is due to the excellent distribution of the feedstock and hydrogen that occurs in the reactor where a proprietary liquid distribution system is employed. In addition, the process catalyst (also proprietary) was designed for the desulfurization of residua and is
not merely an upgraded gas oil hydrotreating catalyst as often occurs in various processes. It is a
Hydrocracking
In the related Tervahl-T process (a thermal process but covered here for convenient comparison
with the Tervahl-T process), the feedstock is heated to the desired temperature using the coil heater
and heat recovered in the stabilization section and held for a specified residence time in the soaking
drum. The soaking drum effluent is quenched and sent to a conventional stabilizer or fractionator
where the products are separated into the desired streams. The gas produced from the process is
used for fuel.
22.3.19 t-stAr ProCess
The T-Star process is an ebullated-bed process that can acts as a pretreater for fluid catalytic cracking feedstock or as a hydrocracker. In the mild hydrocracking mode, the T-Star process can reach
conversions up to the 60% v/v and an advantage of operating the T-Star unit in mild hydrocracking
mode is that the T-Star catalyst is not sensitive to sulfur and nitrogen levels in the feed and will
provide constant conversion, product yields, and product quality.
The T-Star is based upon the residuum H-Oil process and the Texaco’s fixed-bed hydrotreating/
hydrocracking technology. The process is ideally suited for hard-to-process feedstocks and T-STAR
reactors can be used in-line as hydrotreaters/hydrocrackers within an H-Oil unit (Johns et al., 1993).
22.3.20 unICrACkIng ProCess
Unicracking is a fixed-bed catalytic process that employs a high-activity catalyst with a high
tolerance for sulfur and nitrogen compounds and can be regenerated (Reno, 1997). The design is
based upon a single-stage or a two-stage system with provisions to recycle to extinction (RAROP,
1991, p. 79).
In the process, a two-stage reactor system receives untreated feed, makeup hydrogen, and a
recycle gas at the first stage, in which gasoline conversion may be as high as 60% by volume. The
reactor effluent is separated to recycle gas, liquid product, and unconverted oil (Table 22.12). The
second-stage oil may be either once-through or recycle cracking; feed to the second stage is a mixture of unconverted first-stage oil and second-stage recycle. The process operates satisfactorily for a
variety of feedstocks that vary in sulfur content from about 1.0% by weight to about 5% by weight.
The rate of desulfurization is dependent on the sulfur content of the feedstock as is catalyst life,
product sulfur, and hydrogen consumption (Speight, 2000 and references cited therein).
In the process, the feedstock and hydrogen-rich recycle gas are preheated, mixed, and introduced
into a guard reactor that contains a relatively small quantity of the catalyst. The guard chamber
removes particulate matter and residual salt from the feed. The effluent from the guard chamber
flows down through the main reactor, where it contacts one or more catalysts designed for the
removal of metals and sulfur. The catalysts, which induce desulfurization, denitrogenation, and
hydrocracking, are based upon both amorphous and molecular-sieve containing supports. The product from the reactor is cooled, separated from hydrogen-rich recycle gas, and either stripped to meet
fuel oil flash point specifications, or fractionated to produce distillate fuels, upgraded vacuum gas
oil, and upgraded vacuum residuum. Recycle gas, after hydrogen sulfide removal, is combined with
makeup gas and returned to the guard chamber and main reactors.
The most commonly implemented configuration is a single-stage Unicracking design, where the
fresh feed and recycle oil are converted in the same reaction stage. This configuration simplifies the
overall unit design by reducing the quantity of equipment in high-pressure service and keeping highpressure equipment in a single train. The two-stage design has a separation system in each reaction
stage. However, the optimum flow scheme depends on feedstock capacity and product slate objectives.
The high efficiency of the process is due to the excellent distribution of the feedstock and hydrogen that occurs in the reactor where a proprietary liquid distribution system is employed. In addition, the process catalyst (also proprietary) was designed for the desulfurization of residua and is
not merely an upgraded gas oil hydrotreating catalyst as often occurs in various processes. It is a