V. Scalco, General Atomics Electromagnetic Systems, San Diego, California
The global pandemic, economic slowdown and instability caused by regional conflicts have significantly impacted the approximately 735 petroleum refineries worldwide. Today’s highly complex and competitive refining environment—coupled with eroding profits and difficulty maintaining a positive bottom line—is forcing more than half of these refineries to seek new market opportunities from the bottom of the barrel to remain competitive. Additionally, compliance with tougher climate regulations is further taxing refineries’ ability to invest in technology innovations to help keep pace with changing market demands while maintaining profitability.1
Refining management’s balancing act between new technology investment and increasing revenue potential is driving a trend toward utilizing severe catalytic cracking technology to increase profits while taking advantage of the existing crack spreads. More than 18 MMbpd of crude oil are processed through fluidized catalytic cracking (FCC) systems, along with ~75% of global gasoline production. FCC systems have become the refinery’s most versatile operating units to improve the bottom line. With the increase in crude prices, environmental compliance cost and current International Maritime Organization (IMO) 2020 regulation enforcement, the spread between lighter, less severe crudes and heavier, opportunistic crudes will become a bigger part of the refining sector’s economics. The FCC unit’s (FCCU’s) capability to convert heavy atmospheric gasoils, vacuum gasoils (VGOs) and atmospheric resids into more valuable gasoline and middle distillates can be exploited to support more positive profit margins.2
Heavier, opportunistic crudes are pushing the limits of catalytic cracking. Refiners are increasingly considering the utilization of more complex technologies for deeper conversion of challenging feedstocks arising from the processing of opportunistic crudes. Licensors such as Axens, UOP, KBR and others offer a suite of technologies designed for residual conversion and opportunistic feedstock upgrading. These technologies are tailored for processing heavier crudes and producing high-quality final products. As the future of refining has the industry moving toward the use of higher severity conversion units and synthetic crudes, the FCCU will remain the workhorse of the refinery.
Asia joins the race. In Japan, roughly 30 petroleum refining companies are utilizing FCCUs or resid FCCUs (RFCCUs) to produce propylene, liquefied petroleum gas (LPG), gasoline and light oil. S-Oil Korea has installed its first high-severity FCCU, and PERTAMINA Indonesia is investing in new RFCCUs to increase overall international market supply. India is expanding its ability to produce polypropylene through RFCCUs as petrochemical feedstock production is in high demand. New products generated from these RFCCUs can be consumed in the global market for transportation, power generation, petrochemical supply or shipped as a product blended for marine fuel. With years of operation in the RFCC market, Asia must now generate increased profits in a competitive environment and address applications for the bottom of the barrel streams from these units ladened with concentrated catalyst.1
The challenge. While the FCC system is one of the most productive and versatile technologies among refining processes, creating greater profits from an FCCU comes with a cost. Driving FCC technology into higher severity for increased propylene demand for petrochemical feedstocks is a growing trend. Along with fuel gas, C3S and C4S, FCCUs also produce as a byproduct a > 650°F heavy aromatic oil known as slurry oil. Slurry oil nomenclature refers to the catalyst fines carried over from the FCC reactor that end up in these bottoms. Because catalyst fines must be separated or be allowed to settle out of the oil, the product is more correctly referred to as main column bottoms (MCB), decant clarified oil (DCO), clarified oil (CO) or clarified slurry oil (CSO).2
Slurry oil is the lowest-value stream produced by an FCCU, representing only 3 vol%–7 vol% of the total products. A typical 50,000-bpd FCCU would produce as a byproduct 2,000 bpd (125,000 tpy) of slurry oil. The quality varies according to numerous factors including crude oil origin, FCC design and fractionation equipment. The two most important factors affecting quality are catalyst type and conversion level. Quality may also vary for marketing reasons by dilution in the FCC fractionator with heavy cycle gasoil. TABLE 1 shows the typical concentration range of catalyst in marketable slurries.3
Meeting market demands. Severe FCC feed hydrodesulfurization can reduce the sulfur content of slurry oil to less than 0.5 wt%; however, the hydrotreating would result in decreased slurry aromaticity unless conversion is greatly increased. Presently, ~40% of U.S. FCC feed is hydrotreated primarily at mild conditions so that slurries contain 0.5%–1.5% sulfur. Refiners do not desulfurize FCC feed just to lower the slurry oil sulfur content—they have other objectives, such as lowering gasoline sulfur, reducing sulfur emissions from catalyst regeneration, improving product yields and quality, or meeting new market requirements. Efforts to meet the IMO 2020 marine fuel regulation entail a joint process of hydrodesulfurization to less than 0.5% and fines removal to comply at < 50-ppm catalyst fines required by MARPOL IV.3,4
Sediments are composed of large particles greater than 20 µm, while filterable solids are composed of smaller particles typically in the range of 20 µm–submicron level. The sources of the solids are iron sulfide, silica, clays, scales, ash, coke and catalyst fines. Feedstock contamination starts upstream after the desalter, reaching downstream of the catalytic cracking unit. New catalysts, co-catalyst and additives, while benefitting the process, are at the same time adding more sediments, solids and poisoning metals to the bottom of the barrel, creating more challenges to removing these contaminants. Severe catalytic cracking activities come with the challenge of producing a higher concentration of these sediments and filterable solids within the slurry oil stream.5
Ash, or catalyst fines, are a particular problem for slurry, especially for heavy and viscous oils that need long residence time to allow for catalyst settling. Obtaining low ash (< 0.05 wt%) requires dedicated techniques, such as specialized catalyst selection, heating, chemical additives, separation technology, electrostatic precipitators, centrifuges and cyclones. The selection of an attrition-resistant catalyst helps significantly, and a few refiners buy higher-priced hard catalysts to alleviate ash problems in slurry oil. If a higher-priced catalyst or the idea of a new upper cyclone system is not an option, the challenge of catalyst fines separation and the recovery of lost profits can be efficiently addressed by adopting the right (MCB) separation technology.6
The race for profits. Higher severity FCCUs operate at critical conditions and concentrations in the production of higher ends for petrochemical feedstock supply. This makes the process more challenging, especially at the bottom of the barrel where high concentrations of solids, contaminants and catalysts are undermining the possibility of upgrading the slurry oil stream. Upgrading the catalytic cracking technology must coincide with increasing efficiency, reducing maintenance cost and improving the catalyst equilibrium cycle. Removing solids and ultimately increasing the lifespan of the FCC system is part of this equation and is directly related to incrementing the bottom line in refining.
The success of higher severity production relies on providing clarified slurry oil at < 50 ppm to maintain a marketable DCO. Several different filtration and separation technologies have been reviewed to find the most suitable solution capable of upgrading the challenging DCO stream. Many refiners "de-ash" with chemical aids to accelerate ash settling in storage. These chemicals are polymeric compounds that adhere to the catalyst surface, causing agglomeration of the fine particles to accelerate separation.7
For some time, refiners have found it economical to cat crack increasing quantities of > 1,000°F boiling material. Current analysis shows that approximately 40% of the industry is cracking some resid. Cracking an un-hydrotreated resid might result in a heavier, more viscous slurry oil with low aromaticity and high metals content. When resid is added to an existing FCCU, ash separation might be more difficult because the catalyst-removal system must handle a greater volume of more viscous slurry.8
Settling tanks for decanting slurry oil, like those shown in FIG. 1, have been in use for more than 40 yr and remain the most popular separation process for removing catalyst in slurry oil. Today, more than 61% of refineries use settling tanks to separate catalyst and other contaminates from slurry oil. The settling process is lengthy and creates a larger challenge once the tank is full of sediment. Refineries must resort to using settling agents to assist in speeding up the process. This creates sludge, hazardous waste and increases cost over time. One tank per year can cost a refinery $40,000 in settling agent, $500,000 in cleaning and maintenance, and $150,000 in land fill and waste disposal fees. This represents approximately $690,000 in increased costs to accomplish a bunker fuel at 500 ppm. DCO resulting from the settling tank process will continue to experience rising costs as environmental laws direct the handling of hazardous waste and as the decline in construction causes stockpiles of dried catalyst to collect at concrete kilns.7
In addition to recovering profits eroded by tank settling and installing catalyst fines separation technology at the outlet of the FCC slurry oil rundown, most of the fines can be collected and sent back to the riser. With this technology in place, the returned catalyst fines would support fresh catalyst reactivity while utilizing more acceptable avenues of escape via gas scrubbers, electrostatic precipitators, spent catalyst collection hoppers and, ultimately, through the flue stack. Additional profit recovery occurs from fines being removed that escape through the bottoms circuit and rundown to tank settling. By keeping the fines out of this process, the refiner can realize additional profit by adding the now retired settling tank to a refinery’s marketable inventory tank list. This is an added benefit to any refinery and could be worth as much as a $1 MM/yr in revenue.8
World demand for refined products is unique to the domestic market and international demand for each region. North American FCCUs operate at high severity to maximize gasoline and polypropylene. The result is a very heavy, aromatic decant oil. Due to low fuel oil production and specific-gravity limits, U.S. refineries can only blend low quantities of decant oil in resid, allowing the excess to be sold for other uses, such as carbon black feedstock.9
The quality of clarified slurry oil CSO for carbon black feedstock can generate as much as $18/bbl of increased revenue and increase middle distillate inventory (FIG. 2). With separation technology in place, a refiner can increase annual revenue by avoiding heavy cycle oil (HCO) or light cycle oil (LCO) as cutter stock with the CSO to meet lower concentration specifications, and more middle distillate can be used to produce lighter products, such as diesel. With the use of LCO, mechanical filtration is limited in backwash mediums and costly HCO/LCO is required for back washing the filters. Electrostatic separation, however, provides an economic advantage over other processes. Electrostatic separation technology uses raw feed from the FCCU/RFCCU for back flushing and does not decrease the overall production of the reactor or rob valuable lighter products. Middle distillate production is therefore increased along with profitability.2
The current market for CSO as carbon black feedstock carries the best value for a refiner. Installing efficient separation technology to ensure the quality of CSO and the reliability of the fines removal system is critical to increasing profits from this market. The properties of MCB make it difficult to find a solution without understanding the downsides of each technology. Centrifuges have been found to be unsafe and inefficient over time. Decanting or settling can only provide bunker grade products with long residence time. With the heavy asphaltene and coke content in severe RFCC or FCC operation, mechanical filtration solutions become blocked or severely eroded, requiring the complete disassembly or replacement of costly cartridges to continue operation. Other technologies are susceptible to plugging or blocking due to the inherent plugging properties.5,6
One of best technologies found to work in concentrated slurries without plugging or blockage is the author’s company’s electrostatic separator systema. The electrostatic separatora for slurry oil operates continuously without plugging or blockage from asphaltenes with an efficiency at the outlet averaging < 10-ppm catalyst fines after separation. To successfully increase refinery profits from the bottom of the barrel, proven robust technologies like electrostatic separator technologies are needed to handle the challenges accompanying high-severity processing while driving the FCCU to increase propylene yield.3
Active response. Three factors should be considered when determining the feasibility of separation applications to downstream refinery processes. The first is refinery economics: not all refineries with an FCC or RFCC process have the economic parameters needed to justify the installation of a catalyst fines removal system. The second is the severity of the fines. Controlling the quality of the slurry oil produced can influence the refinery’s marketable products and downstream maintenance. The third is to remove catalyst fines and particulates from the settling tank and the cost associated with the environmental impact of this process.
Not all refineries using FCCUs/RFCCUs have a market or economic requirement for producing CSO of < 100 ppm. Slurry oil is typically 6% of the overall production of the FCCU when the focus is on making transportation feedstock. If an FCCU is smaller than 30,000 bpd, the economic driver to upgrade a small amount of slurry is not beneficial and it becomes more economical to blend cutter stock to meet desired specifications. Larger complex refineries processing > 30,000 bpd are in the best economical position to increase profits from departiculating process streams such as slurry oil.9,10
Outside the profitability of increased production and middle distillates, consideration should also be given to decreasing downstream maintenance and downtime. With > 60% of the fines in slurry oil’s distribution being < 15 microns, it is very difficult for mechanical filtration or centrifuges to capture smaller fines. Instead, these processes allow them to pass through. The corrosive element of catalyst passing downstream erodes valves and other critical piping systems.
Taking control. A reactor running at 80,000 bpd can produce 5,600 bpd of slurry. At this production level, > 16 tons (t) of new catalyst is added to the FCCU. With constant unit operation, cyclones in the reactor release fines and, over time, larger catalyst can escape through this process. With the proper separation technology in place, lost catalyst—especially in older FCCUs—can be recovered and sent back to the riser. This adds greater attrition to the life of the catalyst equilibrium cycle in the FCCU and assists in better production and operation of the unit. With the recovery of 1,900 tpy, a savings of > $1.6 MM could be recovered just in catalyst loss and environmental savings. The example detailed in the next section will illustrate the total profit recovery that can be realized with the proper separation technology in place.
Example. Refinery A operates an FCCU with a throughput of 80,000 bpd. The FCCU has a slurry oil product flow of 6 vol% of feed, or 4,800 bpd at 0.0 API. The FCCU uses an electrostatic separatora to remove fines from 3,000 ppm to < 20 ppm—this is equivalent to 3 tpd of fines. Assuming there are 2 tpd of sludge for every tpd of fines, a total of 6.5 tpd of sludge and fines would have accumulated in the storage tank. In one year, the accumulation would be approximately 2,372 t.
The electrostatic separatora adds value by upgrading the slurry oil quality for high-grade coke production. Assuming a product value increase of $4/bbl of slurry oil: Profit = 4,800 bpd of slurry oil product x 365 d x $4 bpd = ~$7 MM/yr.
The only meaningful process cost for the electrostatic separatora is recycle. For this scale, the recycle flowrate would be 2 vol% of the effluent, or 100 bpd. At a cost of $1/bpd, this cost is: 100 bpd recycle x 365 x $1/bpd = $36,500.
Ignoring the labor and material costs of tank cleaning, consider the cost of land filling the sludge removed. Assuming landfill is $1/lb., the cost is: 1,600 tpy x $2,000/t = $3.2 MM/yr.
The annual revenue increase is: $7 MM – $400,000 + $3.2 MM = $9.8 MM/yr.
Takeaways. The evolution of the refining industry is racing toward more severe catalytic cracking technologies capable of processing heavier opportunistic crudes and meeting the profitable petrochemical demand. Refining improvements and petrochemical integrations are leading the way for refineries to find increased profits from every barrel processed. Implementing more severe catalytic technologies is an important step toward improving refinery flexibility. However, as licensors begin to develop new innovative processes and the demand for new synthetic pyrolysis oil blended crudes becomes more of a reality, the need to select the correct separation technology is critical.
Regardless of the separation path chosen, spent catalyst removal and waste management will remain one of the most difficult refining processes. Settling is expensive in lost time and reduced profits. Mechanical separation processes are limited and come with costly downtime and maintenance schedules. The refining industry has evolved away from centrifuges and filtration technology is becoming harder to operate in the more concentrated slurries. Electrostatic separation is a proven solution for trouble-free separation of high-severity FCC and RFCC slurries. Today’s technology can increase profits from new markets or recover profits from lost revenue for every refinery with an FCCU or RFCCU. It is now up to each refiner to take advantage of this solution. HP
NOTES
a Gulftronic® Electrostatic Slurry Separator
LITERATURE CITED
Since 1997, VICTOR SCALCO has been an integral part of process design and developmental downstream solutions for hydrocarbon recovery. Working in support of key players in the industry, his current position allows for new development of filtration and separation systems. He is principally involved in the technical development and training with engineering, procurement and construction (EPC) and FCC/RFCC licensors worldwide. His experience includes program development for commercial applications, scoping studies and commissioning. Scalco holds an MA degree from San Diego State University (U.S.) and has worked for more than 20 yr in the design and implementation of hydrocarbon filtration systems.