Application of gasification technology has been gaining popularity in the refining industry in recent years. The successful startup and operation of several refinery bottoms-based gasification projects over the past year will provide the incentive for more refiners to consider gasification as a bottoms destruction option.
Gasification, coupled with deregulation of the global power markets, offers an excellent opportunity to convert the low value refinery bottoms to high value products like syngas, power, hydrogen, etc, and eliminate the production of residual fuel oil.
Widespread commercialisation of gasification in the refining industry is dependent on several factors. One that will play a key role is the ability of the refiner to provide a low value feed to the integrated gasification combined cycle (IGCC) complex. The solvent deasphalting process offers a refiner the ability to not only produce a low cost gasifier feedstock but also to generate additional conversion feedstock for the refinery. One such project is the ERG Petroli/ISAB Energy project in Italy, which processes visbroken residue in a ROSE solvent deasphalting unit and feeds the asphaltenes to an IGCC plant to produce electrical power.
In Italy, governmental regulations (Law 9/91 and Ordinance CIP 6/92) give priority to electricity produced through gasification of refinery bottoms because of its environmental and economic benefits. The Italian government has also created a favourable climate for the development of independent environmentally friendly power-producing stations through tariff incentives.
At the same time, the Italian National Power Producer (ENEL) has restricted sulphur content of fuel oil with a trend aimed to be below 1 per cent, along with severe limitations on Conradson carbon and metals.
These changes have encouraged the commercialisation of several refinery-based IGCC projects.
Upgrading issues
Gasification offers an opportunity to convert low value refinery bottoms to high value products like syngas, power, hydrogen, etc, in an environmentally friendly manner. The production of hydrogen, steam, power, and syngas from a gasification based plant is defined as integrated gasification polygeneration complex (IGPC).
The refinery-based IGPC market is projected to be over 5000MW over the next five years. Widespread commercialisation of gasification in the refining industry is primarily dependent on the ability of the refiner to provide a low value feed to the gasification complex.
Upgrading options
Analyses of different refinery bottoms processing schemes to identify configurations that not only produce the lowest cost feedstock for IGPC but also maximise the profitability of the refinery are critical to the development of these projects.
Residue upgrading technologies have generally been classified as either a carbon rejection process or a hydrogen addition process. Solvent deasphalting, visbreaking, thermal cracking, co*king, and catalytic cracking are carbon rejection processes, while catalytic hydrodemetallisation, hydrocracking, and hydrodesulphurisation are typical hydrogen addition processes.
The use of hydrogen addition and catalytic cracking processes for upgrading petroleum residue is restricted by the quality of the feed to the process. Solvent deasphalting, visbreaking, thermal cracking, and co*king processes are generally applied to a wider range of residues. Thermal cracking and visbreaking processes have been used in the refining industry since about 1910.
Visbreaking is a viscosity reduction process and can be applied to atmospheric or vacuum residue. Visbreaking typically reduces the fuel oil production by about 10 to 25 per cent. Thermal cracking and visbreaking processes have been widely used outside the United States. co*king is a severe thermal cracking process that converts all the feed to lighter products and solid co*ke. co*king minimises the yield of residual fuel oil in the refinery and is widely used in North America, South America and Asia.
Solvent deasphalting is a well-established, highly reliable upgrading process which has been commercially practised since the 1930s. The process involves the contacting of a heavy residue stream with a lighter hydrocarbon solvent in order to recover valuable deasphalted oils with dramatically improved quality. The process rejects highly aromatic, condensed asphaltenic molecules, which normally contain substantial quantities of co*ke precursors, metals, sulphur, and nitrogen.
Kellogg Brown & Root’s proprietary ROSE (Residuum Oil Supercritical Extraction) is a solvent deasphalting process that recovers the solvent at supercritical conditions [Nelson and Goodman, ROSE: The energy efficient bottom of the barrel alternative; Spring AICHE meeting, 1985. Northup and Sloan, Advances in solvent deasphalting technology; NPRA annual meeting, 1996].
Typical capital cost of the refinery bottoms upgrading processes:
Refinery unit Capital cost, US$/bpd
Supercritical SDA 800–1250
Visbreaking 1000–1400
co*king 2000–4500
Residuehydroprocessing 3000–7000
Residue catalytic cracking 3000–4000
