Faced with falling demand for low-value products such as residue fuel oil, operators are seeking proven, cost-effective technologies to help increase the value of their residue streams by revamping and debottlenecking existing units.
Shell Global Solutions’ thermal conversion processes enable refiners to upgrade a range of hydrocarbons. The base level is provided by our soaker–visbreaking technology: a low-cost conversion method for hydroskimming refineries. Operators can upgrade their thermal conversion units to the more advanced deep thermal residue conversion (DTC) process. DTC provides an attractive alternative for the bottom stream and creates products suitable for bitumen manufacture and power generation. Beyond this, our thermal gas oil process combines residue and thermal distillate conversion.
About the technology
Thermal conversion techniques have been around for more than 50 years, and the Shell Group (“Shell”) has been at the forefront of developing and optimising the technology. Shell accounts for about 40% of all worldwide thermal conversion capacity and has licensed more than 115 units, mostly for the visbreaker process.
The soaker–visbreaking process reduces the viscosity of vacuum and atmospheric residues in refineries.
The DTC process helps to maximise distillates by converting vacuum residue feed and then vacuum flashing the cracked residue.
The thermal gas oil process combines residue and waxy distillate conversion. Soaker–visbreaking technology is used for residue conversion, and an integrated recycle heater system is used to convert waxy distillate. The typical feedstock is atmospheric residue, which eliminates the need for an upstream vacuum flasher.
The yield for these conversion processes depends on feed type and product specifications.
- Figure 1: The preheated vacuum residue is charged to the visbreaker heater (1) and from there to the soaker (2). Conversion takes place in both the heater and the soaker. The operating temperature and pressure are controlled to reach the required conversion level and/or unit capacity. The cracked feed is then charged to an atmospheric fractionator (3) to produce the desired products, for example, gas, liquefied petroleum gas (LPG), naphtha, kerosene, gas oil, waxy distillate or cracked residue.
- Figure 2: The preheated short residue is charged to the heater (1) and from there to the soaker (2) where the DTC takes place. The conversion is maximised by controlling the operating temperature and pressure. The cracked feed is then charged to an atmospheric fractionator (3) to produce the desired products, for example, gas, LPG, naphtha, kerosene or gas oil. The fractionator bottoms are then sent to a vacuum flasher (4) that recovers additional gas oil and waxy distillate. The residual liquid coke is routed for further processing.
- Figure 3: The preheated atmospheric (or vacuum) residue is charged to the heater (1) and from there to the soaker (2). The conversion takes place in the heater and the soaker, and is controlled by the operating temperature and pressure. The soaker effluent is routed to the cyclone (3). The cyclone overheads are charged to the atmospheric fractionator (4) to produce the desired products, including a light waxy distillate. The cyclone and fractionator bottoms are routed to the vacuum flasher (6), where waxy distillate is recovered. The combined waxy distillates are fully converted in the distillate heater (5) at elevated pressure.
Typical examples are shown below.
|Feed: Vacuum residue of typical Middle East crude|
|Viscosity, cSt at 100°C||615|
|Product yield with vacuum flasher||wt%|
|Gasoline (ECP 165°C)||4.8|
|Gas oil (ECP 350°C)||13.6|
|Waxy distillate (ECP 520)||23.4|
|Residue (ECP +520°C)||56.0|
The JSC Salavatnefteorgsintez refinery at Salavat in Bashkortostan, the Russian Federation, has licensed a 1.5-Mt/y visbreaker unit. It incorporates our latest soaker–visbreaker and vacuum-flasher designs, and will produce cracked vacuum gas oil for use in a fluidised catalytic cracking unit (also licensed from Shell Global Solutions). The visbreaker unit plays a key role in helping to reduce the refinery’s residue fuel oil production and increase the yield of lighter, higher-value products.
The main products from the soaker–visbreaking technology are distillates and stable visbroken residue. A vacuum flasher can be used to recover additional gas oil and waxy distillates for catalytic cracker or hydrocracker feed from the cracked residue. This can provide a cost-effective revamp option for existing units.
Our DTC technology delivers high distillate yields, while still producing a stable liquid residual product (liquid coke) that can be used for specialty products and gasification or combustion (for example, to generate power or hydrogen).
The thermal gas oil process offers an attractive, low-cost conversion system for hydroskimming refineries in gas-oil-driven markets or for complex refineries with constrained waxy distillate conversion capacity.
Our thermal conversion capabilities are based on profound knowledge of hydrocarbon feedstocks and detailed understanding of thermal conversion gained through continuous R&D in pilot plants and commercial units.