Securing fuel supply and reducing GHG emissions
Six strategic options are available to refiners to satisfy future energy and environmental requirements in the light of surging oil prices and public concerns over global warming, including refinery upgrades and revamps and the production of green fuels
A M Blume, T B Garrett, B P Goldhammer, E J Mace, M W Wunder and T W Yeung
Hydrocarbon Publishing Company
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To refiners, changes and challenges are constant. After overcoming the obstacles of fuel reformulations and dismal profit margins in the 1990s, the global refining industry is now under rising pressure from government energy policies to provide a steady supply of affordable fuels to the market and, at the same time, to comply with increasingly stringent environmental requirements regarding fuel cleanliness and plant emissions. This looming pressure is compounded by surging oil prices and public concerns over global warming, which has been partly attributed to the burning of fossil fuels. Additional difficulties and uncertainties lie in the need to increase product supply when mandates require that a portion of the supply be displaced by alternative fuels. Furthermore, operations at existing plants and future expansions to produce ultra-clean fuels must emit less CO2. The combination of these interdependent factors indicates that a “perfect storm” may be in the offing for petroleum refiners over the next decade.
Figure 1 best delineates the two primary objectives refiners must meet in their future operations in the near and intermediate terms: fuel supply security and compliance with environmental requirements. Achieving these objectives can be reached via six options, including refinery upgrades and revamps, refinery-petrochemical plant integration, non-traditional petrochemicals production, production of green fuels and chemicals in refineries, energy management and cogeneration of heat and power.
Upgrades and revamps to produce high volumes of ultra-clean fuels
Mandates for ultra-low-sulphur motor gasoline and diesel, plus surging fuel demand throughout the world, especially in China and India, have forced global refiners to undertake unprecedented construction work in terms of upgrades, new unit additions and, in some cases, grassroots refineries.
As countries around the world continue to revise their fuel standards, the future will see clean, high-performance transportation fuels in most developed regions. Although it is not apparent in current figures, fuel-exporting regions, such as the Middle East and Latin America, will be forced to tailor product quality to match higher regional customer specifications. Greater economic and political ties with Western Europe will compel countries in the Commonwealth of Independent States (CIS) and Central and Eastern Europe to comply with West European fuel standards. Some analysts project that the Pacific Rim and the Middle East will adopt 50–80% of the US clean-fuels regulations in the near future. Table 1 illustrates the projections for sulphur and aromatics contents of gasoline and on-road diesel for the period of 2005–2010.
To meet ultra-low-sulphur diesel (ULSD) requirements, many refiners have chosen to revamp their existing hydrotreaters, primarily because of the lower investment cost of revamps compared to the construction of new units. Furthermore, with the supply of light sweet crudes dwindling, the current trend in hydroprocessing is the treatment of heavy sour feeds that contain compounds such as sulphur, nitrogen, aromatics, iron and other undesirable components. These compounds pose significant problems with catalyst poisoning. However, new developments are allowing refiners to keep pace with increased demand. Many refiners are now introducing LCO into their ULSD units, and feeds such as these are typically high in heavy metals. The addition of metal traps upstream of the hydroprocessing unit has resolved most of these problems. To prevent organic nitrogen poisoning, many refinery configurations employ a pretreating unit using Ni-Mo-based catalysts upstream of the hydrocracker for maximum hydrogenation and denitrogenation.
Although it takes a backseat to ULSD projects, revamping hydrotreaters around the FCCU is another important focus. Half of all FCCUs incorporate pretreaters to meet their gasoline sulphur requirements, and improvements to these units make up the majority of ultra-low-sulphur gasoline (ULSG)-orientated revamps.
Five of the most common approaches to revamping hydrotreaters for clean-fuels production (in order of increasing capital costs) are to upgrade feedstock and integrate processes, implement a higher-activity catalyst, replace reactor internals for increased efficiency, add reactor capacity, and increase H2 partial pressure by installing an amine scrubber or a pressure-swing adsorber (PSA). Refiners also have the option to implement advanced process control (APC) and simulations to optimise operations.
Hydrocracking process licensers and catalyst manufacturers now focus on cost-effective technology to broaden the range of feeds, shift product distribution, improve product quality, reduce hydrogen consumption and increase energy efficiency. Hydrocracking catalysts have been receiving at least as much attention as the processes. The rate of commercialisation of new catalysts has accelerated recently, thanks to a better understanding of the process chemistry and the advent of sophisticated tools. Improvements in catalyst performance have allowed refiners to process lower-quality feeds and still enhance product quality. Catalysts designed for upgrading light-cycle oil (LCO) in a hydrocracker can now produce diesel containing 5 ppm sulphur or less with a 15-point increase in cetane index.
The development of the high-activity, acid-cracking-based formulations of hydrocracking catalysts has added flexibility in the operation of hydroprocessing units. This acid-cracking ability is inherent in an amorphous silica-alumina or highly acidic zeolite carrier. Combinations of both types of carriers are available. Typically, there has been a trade-off between catalyst activity and stability. New formulations that employ amorphous silica-alumina supports and dealuminated Y-zeolites are available and offer high activity with high stability. In addition, these designs allow for lower operating pressures, increased run lengths and higher diesel yields. New geometrical shapes of carriers allow higher void fractions, increased diffusion and lower pressure drop across the bed. One of the most important objectives with increased performance is the elimination of non-active zones within the bed. Catalyst and third-party suppliers are now offering such products as distributor trays, quench systems, advanced control systems and other proprietary hardware to resolve this problem.
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