175
Recovery of Heavy Oil and Tar Sand Bitumen
products has become a major focus of operations with new concepts evolving into new processes
(Speight, 2007, 2011). Even though they may not be classed as conversion processes per se, pretreatment processes for removing asphaltene constituents, metals, sulfur, and nitrogen constituents are
also important and can play an important role in selecting a suitable wellhead processing option.
Conceivably, heavy oil could be upgraded at the wellhead and sent through a pipeline to a refinery for further upgrading. However, this is not to be construed that heavy oil upgrading will always
involve a coking step as the primary upgrading step. Other options, including some presented elsewhere (Speight, 2007), could well become predominant methods for upgrading in the future.
7.4.1.1 Thermal Cracking Processes
Thermal cracking processes offer attractive methods of feedstock conversion at low operating pressure
without requiring expensive catalysts. Currently, the widest operated residuum conversion processes
are visbreaking, delayed coking, and fluid coking that are still attractive processes for refineries from
an economic point of view (Dickenson et al., 1997). The visbreaking process offers wide potential
because of the mild nature of the process (Radovanović and Speight, 2011; Speight, 2012).
Visbreaking (viscosity reduction and viscosity breaking) is a mild form of thermal cracking,
insofar as the thermal reactions are not allowed to proceed to completion and are interrupted by
quenching. Process conditions range from 455°C to 510°C (850°F to 950°F) at a short residence time
and from 50 to 300 psi at the heating coil outlet. It is the short residence time that brings to visbreaking the concept of being a mild thermal reaction in contrast to, for example, the delayed coking
process where residence times are much longer and the thermal reactions are allowed to proceed to
completion. Liquid-phase cracking takes place under these low-severity conditions to produce some
naphtha, as well as material in the kerosene and gas oil boiling range. The gas oil may be used as
additional feed for catalytic cracking units, or as heating oil.
Hydrovisbreaking, a noncatalytic process, is conducted under similar conditions to visbreaking
and involves treatment with hydrogen under mild conditions (RAROP, 1991, p. 57). The presence
of hydrogen leads to more stable products (lower flocculation threshold) than can be obtained with
straight visbreaking, which means that higher conversions can be achieved, producing a lower viscosity product.
Visbreaking and variants, and the recently demonstrated ORMAT process, are examples of bulk
thermal processes that convert residues without progressing all the way to solid coke. These processes have significant potential integrated with deasphalting to produce varying yields of residua
to meet future alternative energy and hydrogen production needs.
A recent variant of the visbreaking process is the aquaconversion process (Marzin et al.,
1998), which is a catalytic visbreaking process that operates in the presence of steam. The visbreaking technology is limited in conversion level because of the stability of the resulting product because one process requirement is that the product has to be stable; standard visbreaking
allows only an approximate 2°–6°API upgrading of the heavy crude and only a limited viscosity
reduction, which does not ensure its transport without external diluent. The process pushes this
maximum conversion level within the stability specification by adding a homogeneous catalyst in
the presence of steam.
Other variants of the visbreaking that may find use at the wellhead could be the Tervahl T process and the Tervahl H process.
In the Tervahl T process (LePage et al., 1987; RAROP, 1991, p. 25), 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.
In the Tervahl H process, the feedstock and hydrogen-rich stream are heated using heat recovery
techniques and fired heater and held in the soak drum as in the Tervahl T process. The gas and oil from
Recovery of Heavy Oil and Tar Sand Bitumen
products has become a major focus of operations with new concepts evolving into new processes
(Speight, 2007, 2011). Even though they may not be classed as conversion processes per se, pretreatment processes for removing asphaltene constituents, metals, sulfur, and nitrogen constituents are
also important and can play an important role in selecting a suitable wellhead processing option.
Conceivably, heavy oil could be upgraded at the wellhead and sent through a pipeline to a refinery for further upgrading. However, this is not to be construed that heavy oil upgrading will always
involve a coking step as the primary upgrading step. Other options, including some presented elsewhere (Speight, 2007), could well become predominant methods for upgrading in the future.
7.4.1.1 Thermal Cracking Processes
Thermal cracking processes offer attractive methods of feedstock conversion at low operating pressure
without requiring expensive catalysts. Currently, the widest operated residuum conversion processes
are visbreaking, delayed coking, and fluid coking that are still attractive processes for refineries from
an economic point of view (Dickenson et al., 1997). The visbreaking process offers wide potential
because of the mild nature of the process (Radovanović and Speight, 2011; Speight, 2012).
Visbreaking (viscosity reduction and viscosity breaking) is a mild form of thermal cracking,
insofar as the thermal reactions are not allowed to proceed to completion and are interrupted by
quenching. Process conditions range from 455°C to 510°C (850°F to 950°F) at a short residence time
and from 50 to 300 psi at the heating coil outlet. It is the short residence time that brings to visbreaking the concept of being a mild thermal reaction in contrast to, for example, the delayed coking
process where residence times are much longer and the thermal reactions are allowed to proceed to
completion. Liquid-phase cracking takes place under these low-severity conditions to produce some
naphtha, as well as material in the kerosene and gas oil boiling range. The gas oil may be used as
additional feed for catalytic cracking units, or as heating oil.
Hydrovisbreaking, a noncatalytic process, is conducted under similar conditions to visbreaking
and involves treatment with hydrogen under mild conditions (RAROP, 1991, p. 57). The presence
of hydrogen leads to more stable products (lower flocculation threshold) than can be obtained with
straight visbreaking, which means that higher conversions can be achieved, producing a lower viscosity product.
Visbreaking and variants, and the recently demonstrated ORMAT process, are examples of bulk
thermal processes that convert residues without progressing all the way to solid coke. These processes have significant potential integrated with deasphalting to produce varying yields of residua
to meet future alternative energy and hydrogen production needs.
A recent variant of the visbreaking process is the aquaconversion process (Marzin et al.,
1998), which is a catalytic visbreaking process that operates in the presence of steam. The visbreaking technology is limited in conversion level because of the stability of the resulting product because one process requirement is that the product has to be stable; standard visbreaking
allows only an approximate 2°–6°API upgrading of the heavy crude and only a limited viscosity
reduction, which does not ensure its transport without external diluent. The process pushes this
maximum conversion level within the stability specification by adding a homogeneous catalyst in
the presence of steam.
Other variants of the visbreaking that may find use at the wellhead could be the Tervahl T process and the Tervahl H process.
In the Tervahl T process (LePage et al., 1987; RAROP, 1991, p. 25), 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.
In the Tervahl H process, the feedstock and hydrogen-rich stream are heated using heat recovery
techniques and fired heater and held in the soak drum as in the Tervahl T process. The gas and oil from