Utilizing biofeeds in the FCCU

Many countries around the world are promoting the increased use of biofuels through government mandates and tax incentives. As a general term, biofeeds (a.k.a. renewable feeds, biorenewable feedstocks) include vegetable oils and animal fats, as well as carbohydrates (cellulosic materials, starches, sugars). The first generation of fuels derived from biofeeds comprises ethanol, made from corn and sugar cane by fermentation, and biodiesel, produced from fatty acids via transesterification with methanol. Subsequent generations of fuels and chemicals may be produced via several pathways, which are attracting the interest of companies associated with petroleum refining.

From a strategic point of view, refiners should not try to compete with biofuels producers, but rather try to use renewable feedstocks in traditional petroleum refining processes and make products that are compatible with conventional hydrocarbon fuels.

The implementation of biofeed processing techniques in petroleum refineries can result in a competitive advantage for both refiners and society at large. First, the processes provide refineries with alternative feeds that are renewable and could be lower in cost than petroleum. Second, they can reduce the costs of producing fuels and chemicals from biofeeds by utilizing the existing production and distribution systems for petroleum-based products and avoiding the establishment of parallel systems. Third, they offer refiners a way to compete with non-refining processors of biofeeds. Fourth, they provide a production base for fuels and chemicals that is less threatened by changes in government policies toward fossil fuel feeds and renewable energies. Last, but not least, it is thought that global CO₂ emissions can be reduced by up to 60% through the use of renewable energy sources, including biofuels.

Biofeeds that are able to be processed in the FCCU can essentially be categorized as biomass-derived oils (both lignocellulosic materials and free carbohydrates) or triglycerides and their free fatty acids. The operating conditions and catalysts used for each type of feed to achieve a desired product slate vary, and each feed comes with inherent advantages and disadvantages. Most of the research work completed to date has been performed on relatively pure biofeeds as opposed to blends of bio-based materials with traditional FCC feeds. Of course, practical implementation in a refinery will be accompanied by blending with VGO or resid. This Report present comprehensive and detailed information on feeds, catalysts, and operating conditions based on current research.

Biomass-derived oils are generally best upgraded by HZSM-5 or ZSM-5, as these zeolitic catalysts promote high yields of liquid products and propylene. Unfortunately, these feeds tend to coke easily, and high TANs and undesirable byproducts such as water and CO₂ are additional challenges. Waxy feeds obtained from biomass gasification followed by Fischer-Tropsch synthesis (BTL waxes) are especially suited for increasing LCO production in the FCCU, due to the high-paraffinicity, low-sulfur content, and low-aromatics yield of the feed. A major disadvantage for BTL waxes is the intrinsically low coke yield that can disrupt the FCCU heat balance. In terms of processability, triglycerides are the best-suited biofeed for the FCCU. These materials generally produce high-quality diesel, high-octane gasoline, and are low in sulfur. Triglycerides are compatible for processing with VGO, and thus, the capital cost to crack such feeds in an existing FCCU is estimated to be small (~$5MM). Regarding biorenewable feeds in general, FCC catalysts or blends thereof achieve acceptable product yields and selectivities. As biofeed use in the FCCU continues toward commercialization, the market potential will begin to allow catalyst manufacturers to allocate resources for more tailored catalyst development, greatly improving the yield and quality of desired products.

This Report devotes a complete section to the latest advances in fluid catalytic cracking of bio-oil from lignocellulosic material and carbohydrates, F-T BTL waxes, and triglycerides. Commercial works undertaken by various refiners and biofuels firms are carefully examined for potential breakthroughs. The goal is to assess what technologies are economically viable for refiners in the near and intermediate terms.

CO₂ reduction and carbon capture from the FCCU

In Europe, Conservation of Clean Air and Water in Europe (CONCAWE) recently reported on the trends and mitigating options for CO₂ emissions from EU refineries. As demand has moved toward lighter, cleaner fuels, refineries have become increasingly complex, requiring greater energy consumption. Currently, burning fuel for energy comprises around 90% of EU refinery carbon emissions, on average, while the remaining 10% is "chemical" carbon emitted during hydrogen production for desulfurization processes. As the EU continues to mandate lower sulfur levels in fuels, the percentage of chemical CO₂ could rise as high as 15% by 2020. Also, Europe's growing preference for diesel as a transportation fuel over gasoline has raised refiners' hydrocracking requirements, which in turn creates more CO₂ because of the increase in hydrogen demand. US refiners face the unique dilemma of balancing GHG emissions with the production of more ultra-clean fuels, while processing increasingly heavier and sourer crudes. Refiners looking to capitalize on heavy Canadian oilsands will have to decide the price they are willing to pay for the unavoidable increases in CO₂ associated with the processing of oilsands-derived synthetic crude. Refinery LPs must now incorporate CO₂ as a utility to reach profitable solutions.

Excluding the combustion of fuel in furnaces and steam boilers, the fluid catalytic cracking unit is the largest emitter of CO₂ in the refinery. Regenerator flue gas is almost exclusively the source and can comprise anywhere from 15-50% of refinery CO₂ emissions. The following chart, adapted from a report by Brazilian oil firm Petrobras, shows the distribution of CO₂ emissions in the refinery.  

The fluid catalytic cracking unit takes precedence in light of carbon taxation, cap-and-trade programs, and the impending emergence of carbon-capture technologies. Methods to reduce emissions from the FCCU and other refinery operations lend themselves to two conflicting categories: those that hinder the formation of CO₂ and those that aim to produce a pure CO₂ stream for capture. Improving unit energy efficiency, reducing coke yields, and shifting VGO to the hydrocracking unit belong to the former category, while carbon-capture methods typically comprise the latter. As refiners continue to develop a comprehensive strategy to reduce CO₂ emissions, a balance between these two categories must be found. This happy medium will be influenced greatly by the FCCU heat balance, which determines the amount of coke burned in the regenerator in present FCCU designs. Carbon-capture technologies tend to be compatible with maintaining current coke yields, while those that reduce CO₂ formation necessitate reduction in coke yield. Although FCCU convention says that the heat balance must be met through coke yield, it is possible that other, lower-carbon solutions can help meet the energy demands of the unit economically (e.g., heating the regenerator gas feed with combustion turbine flue gas). This Report identifies and analyses detailed solutions to reduce CO₂ emissions from the FCCU.

Carbon-capture methods are commonly categorized into three groups: pre-comb­­­­­­ustion, oxyfiring, and post-combustion, all of which offer potential emissions-lowering solutions for the FCCU. The majority of carbon-capture technologies are still far from industrial commercialization, with most solutions focused on coal-fired power generation facilities and natural gas production. However, these technologies can potentially be applied to the FCCU and/or refinery flue gas in general. The aim of this Report is to present FCCU GHG emissions-reduction strategies, with their advantages and disadvantages, in order to better equip refiners in choosing an economical route to adhere to GHG legislation.

Ultra-clean gasoline with low RVP

Environmental regulations to mitigate air pollution and acid rain problems have mandated gasoline reformulation—i.e., the removal of sulfur, benzene, and light olefins. In addition, global mandates to blend high-RVP ethanol into gasoline while minimizing VOC emissions are creating RVP challenges in FCC gasoline that must be addressed. Many options are available to reduce these undesirable components, but only a few of them are economical, as indicated in this Report.

When addressing gasoline sulfur content, the key to profitability is choosing the appropriate removal method. This is particularly true for FCC gasoline, since it accounts for most of the sulfur in the gasoline pool. Two solutions are: (a) hydrotreating or hydrocracking the FCC feed, and (b) post-treating the FCC gasoline. However, these methods are generally high-capex and high‑opex solutions. Other solutions that lower the load placed on hydroprocessing are addressed, including changing unit operating conditions, utilizing the latest advances in catalysts and additives, and capitalizing on the sulfur-reducing effects of different feeds. Developments in vanadium-, zinc-, zirconium-, gallium-, and manganese-promoted additives and modified kaolins are presented, among others. On the process side, inventions typically recycle naphtha back to the riser, or they introduce a second reactor where naphtha can further be upgraded. Work in this area is supported by a significant number of patents, especially in China.

A global trend toward lower benzene levels in gasoline is taking place. The majority of benzene-removal solutions currently focus on the catalytic reforming unit, since its product reformate contributes about 80 vol% of the benzene in the blending pool. This Report focuses on the technologies relevant to the FCCU, the second-largest contributor of benzene, with levels around 15 vol%. Naphtha benzene levels are chiefly affected by feedstock characteristics, operating conditions, and catalytic factors.

Because photochemically-reactive olefin VOCs are a major contributing factor to the smog problem, the California Air Resources Board (CARB) has controlled total gasoline olefin content—a 6 vol% flat limit or a 4 vol% average limit with a 10 vol% cap—in its Phase II regulations since 1996. The US EPA does not place a specific limit on total olefins in gasoline. Nowadays, with the increased blending of high-RVP ethanol into the gasoline pool, refiners need to lower olefins content chiefly to meet the overall RVP requirement. This Report compares and contrasts solutions for reducing olefins content and RVP in FCC gasoline. Specifically, patent and research results show that olefins-reduction process technologies are similar to those intended to reduce gasoline sulfur. Refiners have the option to employ pre and posttreatment methods such as feedstock and/or naphtha hydrotreating and fractionation. Like sulfur removal, FCC-related patent and peer-reviewed work focuses almost exclusively on recycling a product stream and specific reactor designs  The use of ZSM-5 and certain metals is mentioned several times in catalyst compositions designed to reduce gasoline olefins, as are rare-earth-containing zeolites.   

Meeting changing demand by increasing gasoline and diesel make

Record crude prices in mid-2008 prior to the current global economic crisis reflect a fundamental shift in fuel demand around the world. Refiners are forced to find ways to meet growing gasoline demand in spite of biofuels mandates that are designed to reduce gasoline consumption. Diesel fuel production is also being raised to meet the growing trend of dieselization in many parts of the world.

Historically, the fluid catalytic cracking unit (FCCU) has taken the role of the refinery's top gasoline producer. The global economic recession that began in late 2008, however, has recently kept gasoline demand low. The result is a gasoline overcapacity—most pronounced in the US—along with a deficit of middle distillates, mostly diesel. Prior to the current downturn, refiners were forced to find ways to meet growing gasoline demand, particularly in the gasoline-centric US market and in China and India, where unprecedented vehicle purchases continue. To complicate the gasoline situation, ethanol mandates implemented by many nations are sending mixed signals to refiners, making it difficult to set gasoline production rates and implement refinery planning.

Despite the global slide in gasoline demand, increasing gasoline yield and quality from the FCCU is still garnering attention from technology providers. Besides the use of optimized operating conditions, the Report identifies the importance of changing catalyst formulations (like additives modifying traditional USY zeolites), process configurations (e.g., reaction zones), and hardware options (e.g., novel riser reactors, feed injectors, and termination devices) that can increase both the yield and the quality of FCC gasoline. It should be noted that many of these technologies are broad improvements to the unit and can also address the quality and production of propylene and diesel, assist in the cracking of lower-quality feeds, and reduce unit emissions.

Diesel is a fast-growing transportation fuel in terms of demand. A recent study by consultancy Booz & Co. reported that dieselization is a worldwide phenomenon, and that the gasoline-to-diesel demand ratio will shift from 50:50 last year to 45:55 in 2030. The consultancy also expects regional imbalances in fuel supply to be magnified over the next several years as a result. It would therefore be advantageous for many refiners to achieve a level of flexibility in the FCCU, producing varying amounts of gasoline and LCO as the market changes. The FCCU contributes about 30% of the US's LCO supply, but this percentage is much higher in Europe, Asia, and Latin America, where middle distillates are in higher demand. Furthermore, Europe, China, and Brazil are known to be short of diesel.

FCCU LCO production can be increased by modifying feedstock composition, introducing improved catalysts and additives, and modifying operating conditions (i.e., recycle ratio, temperature, cat-to-oil ratio, etc.). The addition of an active alumina matrix is a common feature to help refiners increase LCO production when cracking heavy feeds. A comprehensive survey of patent literature in the Report found the use of an inorganic additive to occur more than once in catalyst formulations, and metal-doped anionic clays and amorphous silico-alumino-phosphates (SAPO) are cited, among other inventions. There is some overlap in catalysts tailored for LCO production and those tailored for resid feeds. Consequently, refiners looking to produce more diesel may want to consider heavier feeds to their FCCU. Process/hardware technologies to improve FCCU LCO yield include proper feed injection systems and risers/reaction zone designs as claimed by Petrobras, Shell, and Sinopec in their latest commercial processes. Finally, the use of biofeeds in the FCCU to produce a large volume of high-quality LCO has also received some attention. These feeds, namely animal fats and vegetable oils, not only increase LCO yield, but also provide high-quality products in terms of cetane number. This Report focuses on the latest developments in boosting FCC LCO yields, especially technologies that offer aromatics reduction and cetane improvement.

Capitalizing on light olefins demand

Prior to the global financial crisis beginning in mid-2008, the propylene market had experienced a large demand increase due to polymer-grade propylene usage and higher production of refinery alkylate and isooctane. As a result, a need for alternative production sources outside of steam pyrolytic cracking had developed. Despite some economic uncertainty, many refiners continue to leverage their existing FCCUs to produce more propylene.

This Report compares current propylene-production commercial process/hardware solutions with developments in patents and research papers to uncover emerging technologies. Feed injectors, feed distributor, and reaction zone designs have been the focus of improvements in commercial processes and latest inventions. For instance, the secondary feed acts as a quench and the location of the feed injection creates different severity zones in the riser, as disclosed in one invention. In regard to catalyst developments, continued improvements have been noted in ZSM-5 additives, which are available in different grades of activity, giving refiners more flexibility to meet their light olefins goals without affecting base catalyst activity. Additional progress in base catalysts are discussed and presented in a way that facilitates decision-making for the refiner. Emerging compositions involving phosphoric acid, zirconium, modified rare-earth zeolites, and more are included. 

Resid catalytic cracking

Refineries equipped to process heavy crudes have, so far, have reported high refining margins because they can take advantage of less-expensive heavy oils. Resid fluid catalytic cracking is an important component in the upgrading of such crudes, with unit profitability depending upon the extent to which heavy hydrocarbons in the feed are cracked into valuable products. The product slate, in turn, depends upon the feed characteristics, the catalyst, the hardware, and the operating conditions. Exemplifying a trend toward heavier feeds, 70% of the new FCCUs scheduled to start up between 2006 and 2015 are expected to process HVGO or resid feeds. This Report includes detailed discussions of technology advances in both catalyst and hardware for improving resid FCC operations.

Feed characterization is the first area of improvement. Although it is likely the lowest-impact option, predicting unit dynamics caused by feed changes is important in optimizing unit operation, especially for high-impact feeds like resids.  Complete RFCC process technologies are the most comprehensive approach to improve resid processing operations, but the offerings are also the most expensive. Product recycle and multiple reaction sections seem to be the most prevalent technology trends. Improving feed injectors, riser termination and catalyst separation devices, strippers, and regenerator components are good revamp options for existing units. As feeds get heavier, the trend toward a higher stripper residence time and, consequently, increased mass transfer between entrained hydrocarbons and steam will continue. Moreover, the role of the regenerator continues to evolve because of CO₂ reduction requirements.

Catalyst upgrades are relatively easy, efficient, and economical methods to improve RFCC operation. Commercially-available formulations can generally be organized by the dominant functionality: bottoms upgrading, coke selectivity, multi-functional (combined bottoms and coke selectivity), and product selectivity (propylene, gasoline, etc.). Matrix mesoporosity is known to play a major role in bottoms upgrading, and is a common theme in recent R&D works. The high accessibility to the zeolite created by such matrix materials can, however, create overcracking issues leading to higher coke make. Nevertheless, some catalysts seem to strike a balance between low coke make and improved bottoms conversion. Expect continued developments in multi-functional catalysts as refiners look for a cost-effective, simple, all-encompassing RFCC catalyst. Also, several bulk resid catalysts are tailored for propylene production and increased LCO yield.

Additives offered can be organized as possessing metals passivation, bottoms upgrading, or propylene functionalities. Look for additive development to follow a similar trend as bulk resid catalysts; i.e., additives that include bottoms upgrading, metals trapping, etc. in a single formulation. Of course, a market for more functionally-specific catalysts and additives should continue to exist since they offer greater flexibility and control. Furthermore, the emphasis in the patent literature on metals mitigation and resistance can leave refiners looking forward to continued improvements in commercial products addressing elevated vanadium, nickel, iron, calcium, and sodium levels in resid feeds.

Abatement of NO_X, SO_X, and particulate matter emissions

The FCCU regenerator flue gas—containing sulfur oxides, nitrogen oxides, and particulate catalyst finesľrepresents the largest source of air pollution in most refineries. The US EPA has set target emissions goals for the FCCU of 25 ppm SO₂ and 20 ppm NO_X, and is developing new standards for CO, particulate matter (PM), and volatile organic compounds (VOCs). Failure to meet strict stationary pollution controls, especially in the FCCU, can sink a refiner's bottom line. Several years ago, three different US refiners were required to spend about $1 billion to upgrade emissions-control technologies at their refineries, according to consent decrees they signed with the EPA. In Europe, the Integrated Pollution and Prevention Control directive compels refineries to implement best-available techniques to minimize airborne emissions. Many of the countries involved are also extending responsibilities to regional and local bodies, making for numerous emissions standards specific to geographic locations. In Asia, too, countries have limitations on industrial SO_X emissions that are often set by local communities.

According to the techno-economic assessments in this report, both catalyst and hardware solutions exist for reducing emissions. The economic feasibility of each method to reduce NO_X, SO_X, and PM is evaluated. These methods include improvements in base catalyst and catalyst additives, improvements in regenerator design, post-regeneration removal methods, and synergies achievable by combining different technologies. Some R&D developments presented include fluoro-structured copper and/or zinc-doped cerium oxide additives, bi- and tri-metallic additives, iron-magnesium-aluminum hydrotalcites, ferrierite zeolites, and more.

Several process-oriented technologies are commercially offered to give refiners flexibility in controlling unit emissions. These technologies include improved regenerator designs, flue gas scrubbers, and third-stage separators. Regenerator designs are generally oriented towards NO_X/CO mitigation, and address improvements to the spent catalyst distributor, the air distributor, or to the catalyst conduit between two regeneration stages/zones. One can expect continued improvements in two-stage designs to reduce emissions as refiners continue to process challenging feeds requiring such configurations. The variety of flue gas treatment developments suggests continued room for innovation in that area. Commercial scrubbers and third-stage separators are available. Developments in the patent literature to reduce flue gas NO include injecting a variety of reducing agents or using two CO boilers in series. Some technologies (e.g., wet gas scrubbers) are designed to allow for the removal of multiple pollutants, such as NO_X, SO_X, and PM. While these technology options typically present high up-front capital costs, they can reliably control more than one pollutant.

Both commercial and potential catalyst solutions to reduce emissions are compared in this Report to identifying future technologies. NO_X additives and CO combustion promoters are closely linked because CO promoters traditionally contain Pt, which, along with oxidizing CO, also enhances the oxidative formation of NO. Plus, CO promoters inhibit the reduction of NO to N₂, as this reaction requires CO as the reducing agent. Companies are taking these competing factors into account and offer additives to address both NO_X and CO emissions. The role of non-platinum promoters is the subject of over a dozen studies and the high price of platinum and other precious metals should prompt more R&D efforts in that direction. Rh and Ir are commonly-cited promoters of interest, as are Pd, Ru, and Ag. Mg-Al hydrotalcite-like compounds—also important in SO_X reduction formulations—are mentioned as support materials, and otherwise the use of amorphous alumina/aluminosilicates is generally reported. Finally, there are increasing interests of removing both SO_X and CO₂ in flue gas based on recent announcements by Shell and UOP as the world grows increasingly concerned over greenhouse gas emissions.

Increasing productivity and improving energy efficiency

Minimizing operating costs will also be paramount to FCCU profitability. Installing advanced process control, modeling, and simulation techniques will allow refiners to run the FCC at optimized operating conditions, limiting operational costs. These technologies can also help improve economics by optimizing maintenance activities and monitoring catalyst activity. Additionally, implementing a spent catalyst recycle will help limit fresh catalyst consumption in the FCCU, resulting in an improvements in operating costs.

Most of today's FCCUs were built in the 1970s, when efficient energy use was not of primary concern. These units were designed to be installed with minimal capital investment, and therefore, a great deal of room for energy performance improvement exists today. The coke yield of the FCCU is dictated by the energy needs of the unit. The heat of reaction from catalyst coke combusted in the regenerator is used to heat and vaporize fresh and recycle feed, heat atomizing steam, provide the heat required for endothermic cracking reactions, heat the combustion air up to regenerator flue gas temperature, make up for lost heat to surroundings, and produce stripping steam. Therefore, improving the utilization of the regenerator heat will serve to increase the unit's energy efficiency. As an additional benefit, maximizing the energy efficiency of the unit can reduce CO₂ emissions by combusting less coke.

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