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HYDROTREATING AND ENVIRONMENTAL CONTROLS
Publication date:2Q 2012
Hydrotreating and Environmental Controls
Hydrotreating is a process that has become synonymous with removing impurities from petroleum feedstocks. 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 product streams or feedstreams. 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 lead 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 technologies, 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. Further, a focus on the composition and formulation of the catalyst support material and the impact of various promoters located in either active phase or in the carrier has emerged in both commercial and R&D work. 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 technologies for processing resid and renewable feeds are relayed in pilot-scale studies and R&D work. 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 number of established oil majors have turned their attention to the production of bio-derived diesel streams for use as "drop-in" fuel while other innovations are oriented towards producing bio-based crudes to be fed or co-fed into refinery conversion units. 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:
Flue gas from industrial sources is known to contain a large amount of compounds (e.g., CO, NOX, SOX, PM) that are considered harmful to the environment. Government agencies have set standards to control the amount of these compounds that are released to the atmosphere with western nations imposing increasingly stringent limits on the amount of these pollutants that are permitted to be discharged from stationary sources. As a result, refiners in areas like Europe and the US must now install pollution control technology to ensure that they are in compliance with these tougher standards or risk being fined for non-compliance.
There are a number of environmental control technologies that are available to refiners looking to comply with local emissions standards, and most of these technologies can be implemented as either a stand alone unit or as a retrofit to an existing unit. Flue gas scrubbing systems (both wet and regenerable) that control refinery SOX and PM emissions are a popular technology choice for refiners. The application of older, well developed electrostatic precipitator (ESP) technology is seeing a resurgence as refineries work to meet particulate emissions requirements. Selective Catalytic Reduction (SCR) and Selective Non-catalytic reduction (SNCR) process and catalyst technologies are offered to limit NOX emissions along with low and ultra-low NOX burners. Clean burn flaring equipment is being installed to minimize the release of volatile organic compounds (VOCs) to the atmosphere. Unit specific hardware and additive technology is also available to reduce emissions from individual processes. FCC feed injection systems, third and fourth stage separators, and low NOX regenerators along with NOX and SOX reduction additives and CO combustion promoters are all available to mitigate emissions from the FCC regenerator. Finally, various sulfur plant units (i.e., acid gas removal, Claus, tailgas treater) are available to reduce refinery emissions.
However, because environmental control technologies represent a compliance cost and do not add any real value to a refiner's bottom line, plant management must take into account installation and operating costs to determine which technology will allow them to meet an emissions reduction goal at the lowest cost possible. For example, a refiner who had installed a wet flue gas scrubber downstream of a FCCU to mitigate SOX emissions was likely seeking an alternative solution to control SOX circa 2005-2006 following a spike in the price of lime and limestone. In light of the higher lime and limestone prices, a number of refiners switched to SOX reduction additives to lower costs. Subsequently, a spike in the price of rare earth metals that occurred in 2010-2011 created a situation where the use of SOX reduction additives that incorporated rare earths was no longer seen as the most cost-effective means to mitigating SOX emissions from refinery FCCUs. Constant monitoring of emissions control technology performance and costs are necessary to ensure that refiners remaining in compliance at the lowest cost possible. Additionally, the environmental controls section features the latest trends and technology offerings, including:
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hydroprocessing catalyst, hydrotreating catalysts, guard bed, graded bed, diesel production, ULSD production, ULSG production, ultra low sulfur, sulfur specifications, LCO upgrading, hydroupgrading, middle distillate, renewable hydrotreating, coprocessing, biofuels, resid hydrotreating, ebullated-bed, bunker fuel, heavy crude, heavy oil, opportunity crudes, hydrogenation, hydrodesulfurization, HDS, hydrodenitrogenation, HDN, hydrodemetallization, HDM, hydrodearomatization, HDA, coker naphtha, gas oil, VGO, distillate, FCC pretreat, post-treat, FCC gasoline, sulfidation, presulfiding, catalyst loading, aromatics saturation, benzene, Co, Mo, Ni, W, reactor internals, quench, mixing, distributor, hydrofining, advanced process control, fouling control, deactivation, catalyst management