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Converting the bottom of the barrel into valuable products.
Traditionally, crude-oil residues have been sold as marine bunker fuel or used on-site as furnace fuel. However, with changing legislation, refineries are under pressure to reduce both their emissions and the sulphur content of their products; in addition, the market for fuel oil is shrinking.
The Shell gasification process can be combined with other upgrading and treating technologies to convert a wide range of low-value heavy residues and asphaltenes into synthesis gas (syngas). After treating, this gas can be used as clean fuel for high-efficiency combined-cycle power generation (with optional carbon dioxide capture); as a hydrogen source for hydrocrackers (combined with the water–gas shift reaction); or it can be converted into high-value products such as synthetic hydrocarbons.
By drawing on its experience, Shell Global Solutions provides business, operational-support and project-execution services from design and engineering* through to commissioning and start-up, experience transfer, master planning and training.
Shell Technology Gas Value Chain
About the technology
The Shell Group’s (“Shell”) experience in gasification dates back to the 1950s, and more than 100 Shell gasification units have been developed or are at the planning stage.
Figure 1: A typical Shell gasification process scheme.
The non-catalytic partial oxidation of hydrocarbons takes place in a refractory-lined reactor. The syngas is cooled in the syngas effluent cooler, which is directly connected to the reactor, and high-pressure saturated or superheated steam is produced. The low level of soot in the syngas is removed when it passes through a quench, a separator and a scrubber. The process has an automated heat-up, start-up and shutdown system, which provides reliable plant operation.
Shell Pernis refinery
In the late 1980s, Pernis refinery was faced with tight environmental requirements and stringent product quality specifications. The gasification unit was integrated with a new hydrocracking unit and a cogeneration plant. A thermal cracker was revamped into a deep thermal cracker, which now produces 1,650 t/d of heavy residue as feed for the gasification process. The syngas produced is used in making 285 t/d of pure hydrogen for the hydrocracker and as a clean fuel for power generation in a 117-MWe integrated gasification combined-cycle plant.
This project demonstrates the benefits of integrating a polygeneration plant into a refinery where power, steam and hydrogen are all required for upgrading light products.
OPTI Canada Inc. and Nexen Inc.
The Long Lake project in Alberta, Canada, is a joint venture between energy company Nexen and OPTI Canada, a developer of integrated bitumen and heavy oil projects.
The project involves extracting 72,000 bbl/d of bitumen from the Athabasca oil sands. OPTI’s OrCrude™ primary upgrading process converts the raw bitumen into a partially upgraded product and a heavy asphaltene by-product. A distillate hydrocracking unit upgrades the product further into a premium-quality synthetic crude. The heavy asphaltene by-product feeds a 3,600-t/d Shell gasification unit, which generates hydrogen for the hydrocracker and process steam. Excess syngas is used to generate steam and power for bitumen extraction.
The Shell gasification process offers several technical advantages. It helps provide a high syngas yield, which is provided by special burner and reactor designs that enable operation at low oxygen consumption and low soot formation. Key features include:
- feed: high ash, sulphur content and viscosity;
- typically >2,600 Nm³ (CO + H2)/(t feedstock); and
- <1 mg soot/Nm³ in raw syngas. It also helps enhance thermal efficiency through the syngas cooling process.
Shell’s gasification technology is highly flexible and can be tuned to a variety of configurations, depending on customers’ needs.
The gasification process provides an intermediate product and does not operate in isolation; it is integrated into an existing (refinery) complex. Therefore, Shell’s gasification technology is highly flexible and can be tuned to a variety of configurations, depending on customers’ needs. The use of gasification can help in:
- improving product quality while simultaneously reducing plant emissions;
- producing sufficient hydrogen for producing today’s clean fuels;
- adapting processing facilities as demand for fuel oil diminishes;
- reducing demand for natural gas; and
- converting low-value products into high-value products.