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HYDROTREATING AND XTL (QUARTERLY ISSUES)
Publication date:2Q 2011
By mixing hydrogen and the feedstock under controlled conditions in the presence of a catalyst, contaminants in the form of sulfur-, nitrogen-, and oxygen-containing compounds, as well as metals, can be removed. When the catalyst is designed to remove a specific class of compounds, that fact is reflected in the name of the process, e.g., hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodenitrogenation (HDN), and hydrodearomatization (HDA)/hydrogenation (HYD). Hydrotreating is suitable for removing contaminants from feedstreams and product streams. For the feedstocks intended for other refinery processes—catalytic cracking, hydrocracking, catalytic reforming—hydrotreating serves two purposes: (1) it improves the quality of the products of those processes (especially quality specifications mandated by law, e.g., benzene reduction in motor gasoline), and (2) it protects the sensitive (and costly) catalysts from contamination. Hydrotreating is not without drawbacks: the capital investment is significant; operating costs (catalysts and hydrogen) can be high; and product quality may be adversely affected by the potential saturation of aromatics and olefins.
As oil becomes more difficult to access and process, the supply of energy may struggle to keep pace with demand. Primary drivers for the expansion of hydrotreating capacity include growing transportation fuel demand, the worldwide trend towards dieselization, increasingly stringent product specifications, and the increased levels of contaminants found in crude and intermediate refinery streams. Furthermore, efforts reduce the quantity of CO2 emitted from refineries and impede the growth of the oil industry's carbon footprint have led refiners to seek improvements in hydroprocessing technologies in a number of ways. Efficient utilization of hydrogen in hydrotreating processes will be a significant focus. Additionally, extending the length of catalyst cycles, especially when processing highly contaminated feeds, has emerged as a method to improve process economics and more efficiently execute routine maintenance activities, catalysts change-outs, and more intensive schedules turnarounds. Beyond conventional applications, hydrotreaters will help refiners cope with this changing market, as these units offer the ability to upgrade unconventional (resid and renewable) feeds to produce more diesel while helping meet stricter environmental regulations. Additionally, the use of hydrotreating technology to upgrade whole crude streams in heavy oil upgrading applications has been a topic of recent research and development work, particularly in areas that are exploring the processing of heavy crude resources for the first time.
Hydrotreating technology is not new, and many of the well-established hydrotreating systems, no longer patent-protected, are off-the-shelf systems that are provided by engineering firms. Nevertheless, novel flow schemes have been developed to enhance reactions while newly-designed reactor internals (e.g., trays and quench systems) squeeze out more activity from a given catalyst. The application of interstage separation and interstage strippers allows refiners to reduce the recycle ratio of hydrotreating processes, effectively expanding capacity and debottlenecking product fractionation equipment. New catalysts with higher activity allow the refiner to optimize product quality, throughput, and catalyst lifetime, while dealing with problems such as pressure drop build-up and excessive hydrogen consumption. Auxiliary equipment to optimize catalysts loadings and restore catalyst activity are provided. Furthermore, efforts to tailor catalyst loadings to achieve stringent product specifications in single reactor with multiple beds or in a series of catalyst reactor are noted. Integrated processing schemes with an aim towards improving process efficiency are also common.
Hydrotreating is also used for processing resid and renewable feeds. Resid hydrotreating allows for the conversion of heavy residual refinery streams while providing simultaneous HDM, HDN, HDS, Conradson Carbon removal, and asphaltenes conversion. Renewable feed hydrotreating is largely oriented towards technology developments that will allow refiners to upgrade highly-oxygenated, biologically derived feeds to high-quality transportation fuels. A focus on the development of novel processing schemes and catalyst technologies is clear, though much work is needed to determine the logistical feasibility of potentially attractive renewable feeds prior to wide scale commercial implementation of the technology. Additionally, the hydrotreating section features the latest trends and technology offerings, including:
Interest in XTL (biomass- and gas-to-liquids) technology continues to grow worldwide as energy demand increases, driven by non-OECD nations. New fuel sources will be needed as light sweet crude deposits continue to dwindle around the world. Heavier "opportunity crudes" are available, but these reserves are more expensive to upgrade due to higher contaminant levels, equating to more processing capacity and intensity being needed to transform these heavy reserves into high-quality transportation fuels. Also, with pending GHG emissions regulations being put in place by numerous countries and regions, these opportunity crudes are also coming under scrutiny in terms of environmental impact. A number of areas (i.e., the state of California) are implementing low carbon fuel standards which may result in penalties for processing high carbon intensity crude oils in refineries.
Biomass- and gas-to-liquids processes are able to yield high-quality products (e.g., middle distillates, naphtha) with improved properties (higher cetane number, improved pour point, lower sulfur content) when compared to petroleum-derived fuels. These processes also offer energy security to countries that have abundant supplies of natural gas and/or biomass feeds. From a refinery perspective, existing hydroprocessing equipment can be utilized to upgrade Fischer-Tropsch (F-T) derived synthetic crudes into high-quality products. Oil firms may look into joint ventures with companies that can reform the natural gas and process it through a F-T reactor to yield a synthetic crude, which can then be shipped to a refinery for further upgrading.
However, these technologies have not been utilized on a wide-scale, as only four gas-to-liquid (GTL) plants—Sasol's 45K-b/d Mossel Bay, South Africa and 34K-b/d Oryx in Ras Laffan Industrial City, Qatar facilities and Shell's 14.7K-b/d Bintulu, Malaysia and 140K-b/d Pearl in Ras Laffan Industrial City, Qatar plants—are currently in commercial operation; no commercial-scale biomass-to-liquid (BTL) complexes have been installed. A number of factors have contributed to the lack of widespread implementation, including economics of construction and operation, regulatory directions, and technology development and demonstration. Companies are continuing to focus on process and catalyst improvements to make these processes more attractive and competitive with traditional upgrading equipment. Going forward, XTL technologies may be an attractive alternative route for companies looking to supplement fuel production and/or expand operations into new markets. As countries around the world look to curb GHG emissions, BTL is an option for producing diesel with a low carbon intensity, as BTL-derived diesel has been estimated to have life cycle CO2 emissions of 3 gCO2e/MJ.
Continued XTL technology developments have focused on improving catalyst design and syngas quality to ensure a high-quality Fischer-Tropsch (F-T) product is yielded that can be used as a "drop in" replacement for conventional transportation fuels. Utilization of dry reforming to upgrade a mixed feed of natural gas and CO2 into syngas for further processing in F-T reactors is also disclosed. The installation of modular GTL technologies to capture economic opportunities related to stranded and/or flared gas is described. R&D work related to XTL was mostly focused on F-T technologies, specifically F-T reactor designs and cobalt- and iron-based catalysts. Additionally in the XTL section, new products and topics covered include:
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