Academician Hou – Strategies for Processing Low-quality Crude Oil

Is this what you want to post: Discussion on measures to deal with low-quality crude oil? The overall trend in global crude oil extraction is toward heavier crude oils; there is an increase in low-quality crude oils that are high in sulfur and acid content, and crude oil prices remain at high levels. Due to processing capacity constraints, the price gap between low-quality crude oil and high-quality, low-sulfur crude oil widens. Domestically, the prices of refined oil products have long been lower than those of crude oil. Sinopec processes over 70% of its total crude oil input at high prices, resulting in losses for all oil refining companies. This article mainly discusses the technical measures that Sinopec should adopt to process low-quality crude oil in order to reduce its crude oil procurement costs and improve the efficiency of its refining plants, for reference. 　　1 Processing low-quality crude oil is a major strategic initiative. 1.1 Scope of low-quality crude oil 1) The NPRA in the United States classifies crude oil based on its density: crude oil with an API value greater than 38 is considered light crude, those with an API value less than 22 are heavy crude, and those with an API value between 22 and 38 are medium crude. However, there are some conventional classifications in the trade of crude oil, such as the API gravity of Arab heavy crude being 27.9, etc. Therefore, it is also feasible to classify crude oil as light crude when its API value is greater than 36, as heavy crude when the API value is less than 27, and as medium crude when the API value is between 27 and 36. 　　2) Crude oils containing sulfur are generally classified as follows: those with a sulfur content of less than 0.5% are low-sulfur crude oils, those with a sulfur content greater than 1.5% are high-sulfur crude oils, and those with a sulfur content between 0.5% and 1.5% are medium-sulfur crude oils. 　　3) Crude oil with a total acid number (TAN) of less than 0.5 mgKOH/g is considered low-acid crude oil; those with a TAN greater than 0.5 mgKOH/g are acidic crude oils, while those with a TAN greater than 1.0 mgKOH/g are high-acid-number crude oils. 　　It can be concluded that crude oils that meet any one of the criteria of an API degree of less than 27, a sulfur content of more than 1.5%, or a TAN value of more than 1.0 mgKOH/g can be classified as low-quality crude oils. 　　1.2 Oil will remain the primary energy source until 2030 In the last decade of the 20th century, the proven remaining reserves of conventional crude oil were around 140 billion tons per year on average. Entering the 21st century, the world’s crude oil production was around 3.6–3.7 billion tons per year. Thanks to advances in crude oil exploration technology, the world’s proven remaining reserves of crude oil have shown an upward trend in recent years: they exceeded 160 billion tons in 2002, surpassed 170 billion tons in 2003, and reached 177 billion tons by 2005 (all figures are based on data as of January 1 of that respective year). The global supply and demand for crude oil are roughly in balance. According to the projections of various international agencies, world oil resources will be more than sufficient to meet future consumption needs over the next 25 years, and oil will remain one of the world’s main energy sources until 2030. 　　1.3 Refining will remain the core business of Sinopec until 2030. In 2005, China’s crude oil processing volume reached 295 million tons, while the country’s total oil consumption was 327 million tons, accounting for 8.5% of the world’s total oil consumption. By 2030, the world’s total oil consumption is expected to be around 6.25 billion tons. The China Energy Research Society predicts that by 2030, China’s oil consumption will be 630 million tons, accounting for 10% of the world’s total oil consumption. Assuming China’s oil production remains at 200 million tons per year, its dependence on oil imports is 68%. On the premise that global crude oil supply and demand are roughly in balance, and in the absence of major international events, China should be able to obtain the necessary oil through international trade. In 2005, Sinopec’s crude oil processing capacity reached 172 million tons per year, with actual crude oil processed that year amounting to 149 million tons. Sinopec has become the fourth-largest oil refining company in the world, and it is expected that, through continued development over the next 15 to 25 years, it will rank among the largest oil refining companies in the world. Therefore, in the first few decades of the 21st century, the refining business will remain the core business of Sinopec. 　　1.4 The refining industry faces the severe challenge of high international oil prices. After the 1970s, three oil crises occurred due to the Middle East wars, the Iran-Iraq War, and the Gulf War, which led to a sharp rise in oil prices, though these prices later dropped again. Entering the 21st century, international crude oil prices experienced fluctuations, with continuous increases starting in 2003. The average price of WTI crude oil was 41.45 dollars per barrel in 2004, rising to 56.71 dollars per barrel on average in 2005. In January 2006, it exceeded 60 dollars per barrel, surpassed 70 dollars per barrel in April, and reached a peak of 78.4 dollars per barrel for New York futures in mid-July. As the situation in the Middle East eased and inventories increased, prices started to decline from October, with crude oil falling below $60 per barrel. OPEC adopted a measure to cut crude oil production by 1 million barrels per day in order to raise oil prices, which were fluctuating around $60 per barrel in early November. Analyzing the background of this rise in oil prices, most believe that the recovery of the world economy and economic growth driving up demand for oil are the main factors. It is not expected to drop significantly, and it will continue to remain at a high level of around 60 dollars per barrel. High oil prices have created a very severe situation for Sinopec’s refining business. 　　1.5 Widening price gap between low-quality crude oil and low-sulfur light crude oil As international crude oil prices rise, the price gaps between high-sulfur and low-sulfur crudes, as well as between heavy and light crudes, and between crudes containing acid and those without acid, also widen. For example, the price difference between low-sulfur Brent crude and sulfur-containing (Dubai + Oman)/2 crude was 4.26 dollars per barrel in 2004, and 4.51 dollars per barrel in 2005. According to data from relevant departments at Sinopec, for every 0.1 percentage point increase in the sulfur content of crude oil, the price decreases by $0.15 per barrel (8.8 yuan per ton) ； For every 1-unit decrease in the crude oil API grade, the price decreases by $0.27 per barrel (15.8 yuan per ton) ； For every increase of 1.0 mgKOH/g in the acid value of crude oil, the price decreases by $2.5 per barrel (146 yuan per ton). Currently, crude oil costs account for over 90% of the total raw material costs for refineries. Processing heavy crude oils that are high in sulfur and acid at lower purchase prices can significantly reduce refining costs, making it an important way to improve the profitability of refineries. For Sinopec, processing lower-quality crude oil is undoubtedly a major strategic move. 　　2 Technical strategies for processing low-quality crude oil: In 2005, Sinopec’s processing capacity for high-sulfur crude oil accounted for one-quarter of its total crude oil processing capacity; with a high proportion of capacity dedicated to processing residue oil, it has the necessary conditions to process more low-quality crude oil. However, looking at the crude oil used for processing in 2005, crude oil with an API gravity of less than 27 accounted for only 19%, while 81% was medium-grade and light-grade crude oil ； Crude oils with a sulfur content of over 1.5% account for only 19.5% of the total processed crude oil; low-sulfur crude oils make up 37.7%, while medium-sulfur crude oils account for 42.8%. Crude oils with a TAN value of over 0.7 mgKOH/g constitute only 22.4%, and high-acid crude oils with a TAN value of over 1.0 mgKOH/g are even rarer. It is evident that Sinopec has considerable potential to increase the processing of low-quality crude oil. 　　The key technical aspects for improving the processing capacity of low-quality crude oil are, first, controlling the corrosion caused by sulfur- and acid-containing crude oils on the equipment, especially in atmospheric and vacuum distillation units ； Second, there must be sufficient supporting residue processing capacity to process all the heavy residue ； Third, it is necessary to strengthen desulfurization and sulfur recovery during the product processing stage, to promote the development of refined oils with lower sulfur content, while simultaneously controlling SOx emissions and improving environmental protection. 　　2.1 Controlling equipment corrosion The corrosion of equipment caused by sulfur- and acid-containing crude oils affects distillation units first and foremost. The corrosion of distillation equipment can be divided into two main categories: low-temperature areas and high-temperature areas. 　　2.1.1 Controlling corrosion in the low-temperature areas of distillation units 2.1.1.1 Corrosion mechanisms Corrosion tends to occur easily in the overhead condensation systems when processing normal crude oil, and it becomes even more likely when dealing with high-sulfur, high-acid crude oil. The main reasons for corrosion in areas with low temperatures are as follows. 　　1) HCI corrosion. The electrodesalination of crude oil is ineffective; the inorganic and organic chlorides present in the crude oil enter the distillation system, where they undergo hydrolysis to form HCl. This acid enters the initial distillation column and the top of the atmospheric pressure column in gaseous form, and near the dew point it dissolves in water to form concentrated hydrochloric acid, thereby causing dew point corrosion. When it reacts with iron metal, it produces FeCl2 that is soluble in water, resulting in an orange-peel-like surface covered in rust, or causing pitting. 　　2) H2S corrosion. When processing sulfur-containing crude oil, H2S is present in the crude oil, as well as H2S generated by the pyrolysis of sulfides. Gaseous H2S is generally non-corrosive in the upper part of the tower, but when H2S dissolves in water, corrosion is most severe at temperatures below 75°C. H2S reacts with metals to form metal sulfides such as FeS, and the degree of corrosion depends on the concentration of H2S in the water. At the same time, HCl and H2S react with the corrosion products to produce more HCl. 　　3) Organic acid corrosion. When processing acid-containing crude oil, naphthenic acids crack to form various low-molecular-weight volatile organic acids, ranging from formic acid to heptanoic acid, which are readily soluble in the condensate at the top of the tower, causing dew point corrosion. 　　4) Ammonium salt corrosion. As the ammonia and chlorine concentrations at the top of the tower increase, ammonium salts are formed at a certain temperature, leading to corrosion beneath the scale in the equipment. 　　2.1.1.2 Control of corrosion in low-temperature areas Traditional one removal and three injections remains the most effective measure for controlling corrosion in the low-temperature areas at the top of the tower. 　　1) Use an efficient desalting agent to improve the desalting effect, reducing the salt content in the crude oil after desalting to below 3 milligrams per liter; this helps to minimize dew point corrosion caused by HCl generated through hydrolysis entering the tower top. 　　2) An efficient organic amine neutralizer is used to replace traditional ammonia water; the dosage is determined based on dew point and pH value, and it reacts with HCl to form organic ammonium chlorides. 　　3) Inject a highly effective oil-soluble film-forming corrosion inhibitor to reduce the metal corrosion rate. 　　4) When using a water-soluble corrosion inhibitor, an appropriate amount of water must be added to dilute NH4Cl and prevent corrosion under ammonium salt scale. 　　5) The performance criteria for one separation and three injections are based on the \"Top Condensate Specifications\" issued by Sinopec: Fe2+ levels should be less than 3 milligrams per liter (with advanced international standards requiring levels below 1 milligram per liter); chlorine content should be less than 30 milligrams per liter (with advanced international standards requiring levels below 20 milligrams per liter). When an organic amine is used as the neutralizing agent, the pH value should be between 5.5 and 7.5; when ammonia water is used as the neutralizing agent, the pH value should be between 7 and 9. The corrosion rate should be less than 0.2 millimeters per year. 　　6) It is recommended that for large-scale distillation units, whether through the adoption of existing technologies or through independent development, an online corrosion monitoring system should be installed at the top of the tower in order to better control corrosion in the low-temperature areas there. 　　2.1.2 Controlling corrosion in the high-temperature areas of distillation units Sulfur and acids in crude oil cause corrosion in the high-temperature areas of distillation units. 　　2.1.2.1 Various types of corrosion in high-temperature areas 1) Sulfur corrosion Active sulfides such as H2S, thiols, and elemental sulfur present in sulfur-containing crude oils can react with metals, causing corrosion. Inactive sulfides such as thioethers, polysulfides, and thiophenes also decompose at high temperatures to produce H2S and elemental sulfur. Therefore, corrosion in the high-temperature areas of sulfur-containing crude oil processing is mainly caused by H2S and elemental sulfur. When the sulfur content in crude oil is 0.2%, it causes severe corrosion of carbon steel at high temperatures ranging from 230 to 455°C; as the Cr content in the steel increases, the corrosion rate decreases significantly. 　　2) Naphthenic acid corrosion At high temperatures of 240–400°C, naphthenic acid reacts with iron metal to form oil-soluble iron naphthenate. As the corrosion products fall off or dissolve, or are stripped away by impact forces, the exposed metal surface undergoes further corrosion. Through repeated cycles, the equipment gradually thins until it eventually breaks due to perforation. 　　Corrosion is more severe due to the erosion caused by eddies and turbulence on fittings such as elbows. Taking crude oil with an acid value of 1.5 mgKOH/g as an example, when the flow rate of the crude oil increases from 8 meters/second to 22 meters/second, the corrosion rate of carbon steel rises from 6 millimeters/year to 12 millimeters/year, a doubling. 　　The corrosion rates of various steel grades vary greatly. For example, when the acid value of crude oil is 3 mgKOH/g, the corrosion rate of 316 steel at a high temperature of 377°C is only 0.06 mm/year; the corrosion rate of 410 steel is 360 times higher than that of 316 steel, while that of carbon steel is 800 times higher. 　　3) Sulfur/acid interaction corrosion High-sulfur, high-acid crude oils exhibit greater corrosivity due to the interaction between sulfur and acid. In some sulfur-resistant alloy steels, such as those with 12Cr or higher alloying levels, the presence of acid can destroy the sulfide film formed on their surface, accelerating corrosion. Corrosion is more severe in areas where the fluid flow changes direction, where the pipe diameter changes, and where there is significant erosion, such as elbows, valves, tees, erosion guards, and the feed section of towers. 　　2.1.2.2 Measures to control corrosion in high-temperature areas The control of corrosion in high-temperature areas primarily involves improving the material used in equipment and adopting appropriate anti-corrosion steel materials. 　　1) The corrosion rate of steel at different temperatures for high-sulfur, low-acid crude oils can be determined using McConomy curves ； For the selection of specific steel materials used in distillation units for processing high-sulfur crude oil, reference can be made to SH/T 3096-2002 \"Guidelines for the Selection of Materials for Key Equipment in Units for Processing High-Sulfur Crude Oil\" and SH/T 3129-2002 \"Guidelines for the Selection of Materials for Key Pipelines in Units for Processing High-Sulfur Crude Oil\". In accordance with the guidelines, when processing high-sulfur crude oil, the shells and bottom heads of distillation columns and flash towers with temperatures below 240°C can be made of carbon steel; whereas the shells and trays of atmospheric towers, vacuum towers, stripping towers, etc. are preferably made of carbon steel lined with OCr13 (OCr13Al) ； For parts of the heating furnace such as the furnace tubes where the temperature is above 240°C, Cr5Mo or Cr9Mo is recommended; for the oil transfer lines, lining materials such as Cr5Mo, Cr9Mo, 18-8, and OCrl3Al are suitable. 　　2) When processing high-acid crude oils (including those with high sulfur and high acid content), the selection of steel materials is also guided by the two standards SH/T 3096-2002 and SH/T 3129-2002. For the columns of the initial distillation tower and flash tower, as well as their trays, carbon steel lined with OCr13 (OCr13Al) can be used when the operating temperature is above 240°C ； For the shells of atmospheric and vacuum distillation columns, carbon steel lined with 316L is recommended; the trays should be made of 316L or 317L. The furnace tubes in heating furnaces are made of Cr5Mo or Cr9Mo. However, experience shows that the last 4 groups of furnace tubes at the outlet of the radiant furnace should be made of 316L, while oil transfer lines require a composite material of carbon steel and 316L. 　　3) Investigations conducted by Sinopec’s Science and Technology Committee together with relevant departments on distillation units have shown that the materials used in many units designed for processing high-sulfur and high-sulfur-high-acid crude oils are not yet suitable; oil refineries located along the rivers need to process crude oils containing sulfur and acids, and the materials in many of these units are inadequate. To enhance Sinopec’s capacity to process low-quality crude oil, facilities that fall short of requirements should be put into use in a timely manner, and renovations should be scheduled as early as possible, in order to further improve Sinopec’s flexibility in processing high-sulfur and high-acid crude oils. 　　2.2 Making full use of residue processing technologies to increase the degree of processing 2.2.1 Sinopec has a large capacity for residue processing, with a high degree of processing of heavy oils. Through years of development, by 2005 the capacity for processing residues (converted to VR) accounted for a significant proportion of Sinopec’s total crude oil processing capacity (see Table 1). 　　As can be seen from Table 1, in 2005 the ratio of China Petrochemical’s processing capacity for various vacuum residues to its overall crude oil processing capacity reached 30%, while the yield of light oils was 73.5%. Its capacity to process coker residue far exceeds that of heavy oil catalytic cracking for blending with vacuum residue, making it the leading unit for the in-depth processing of residue at Sinopec. 　　The proportion of residue processing in the United States has always been high. According to the 2005 statistics from the U.S. NPRA, the share of various residue processing methods in the total crude oil processing capacity is as follows: coking accounts for 15.1%, solvent deasphalting for 2.5%, residue hydrocracking (including residue hydrotreating) for 3.4%, and heavy oil catalytic cracking accounts for 15% of the total catalytic cracking capacity, based on the global capacity for residue catalytic cracking ； It can be inferred that the capacity of the United States to catalytically crack vacuum residue accounts for about 2.5% of its total processing capacity, bringing the overall figure to 23.5%. It can be seen that the proportion of coking units at Sinopec is roughly comparable to that in the United States, and Sinopec’s overall proportion of residue processing is among the highest in the world. 2.2.2 Continued strain in deep processing Although China Petrochemical has a high proportion of deep processing of heavy oil, there is still a shortage in the capacity for processing such oil. This is mainly because, on the one hand, most refining companies expand their capacity through upgrades; some of their facilities have incompatible structures, and some bottlenecks have not been resolved ； Secondly, the production and operation technical level of the heavy oil processing units has not been fully utilized, and there is still great potential ； Third, it mainly processes crude oil with a moderate to high density, containing a large amount of residue. To this end, it is necessary to process lower-quality crude oil more extensively, as well as further improve the level of processing heavy oil. 　　2.2.3 Delayed coking has become the most crucial unit for the deep processing of heavy oil in Sinopec. 1) International experience: Developing coking units to adapt to heavier crude oils. Looking at the development of heavy oil processing capacity in the United States, as the proportion of medium and heavy crude oil imports has increased, the average API value of the crude oil processed there has dropped from 32–33 in the 1980s to 30.5–31 at present. To address the trend of increasingly heavier crude oil, the United States accelerated the development of coking, with coking capacity increasing by 56% particularly between 1987 and 2001. 　　According to the U.S. Energy Information Administration (EIA), when the API gravity of crude oil at a group of 4 refineries was reduced from 33.1 to 25.7 (a decrease of 7.4 in API gravity), by increasing the coking capacity and raising its proportion to the total processing capacity from 7.5% to 23.1%, along with appropriate enhancements to processes such as hydrocracking, it was still possible to achieve a yield of light oil products of 84.1%. 　　2) Sinopec has mastered the technology for scaling up delayed coking. Sinopec’s engineering design department possesses this technology; by using double-sided radiant heating furnaces and coke towers with a diameter of 9.4 meters, a single set of delayed coking units with two towers can achieve an annual production capacity of 1.6 million tons, providing technical support for the renovation of existing facilities and the construction of new ones. Compared with other heavy oil processing units, delayed coking equipment is simpler, requires lower investment, has a shorter construction period, and offers greater flexibility regarding the feedstock residue oils. It can process various types of residue oils with high sulfur and acid content, as well as those with high levels of heavy metals and residual carbon. The low-sulfur coke produced by coking serves as raw material for electrodes, while high-sulfur coke can be used as CFB fuel; it is expected to see further development in the future. 　　3) Further improve the technical level of delayed coking production. Opt for low circulation ratio operations to enhance the plant’s processing capacity and reduce the rate of coke formation. Shorten the coking cycle and fully utilize the production potential of the coking unit. Achieve automatic disassembly and assembly of the upper and lower caps of the coke tower, enabling remote-controlled safe operation. Develop gasification technology to produce syngas using high-sulfur coke as raw material. 　　2.2.4 Appropriate development of the combined technology for residue hydroprocessing/catalytic cracking of heavy oil 1) Hydroprocessing of residue leads to significant effects in desulfurization, denitration, demetallization, and removal of residual carbon; the hydrogen content increases. The residue after hydroprocessing can meet the requirements for RFCC feedstock, which helps to improve the product profile, raise the quality of gasoline to European standards, and effectively control the emission of NOx and SOx in the flue gases from catalytic cracking. The combined process can maximize the yield of light oils, and it represents the optimal solution for improving the utilization rate of crude oil resources. 　　2) Sinopec has mastered the fixed-bed residue hydrogenation technology using AR and VR as raw materials. The hydroprocessing units at Maoming Petrochemical, with a capacity of 2 million tons per year using VR as raw material, and those at Hainan Refinery, with a capacity of 3.2 million tons per year using AR as raw material, are both capable of producing hydrogenated atmospheric residue suitable as feed for RFCC. To this end, when the heavy metal content in the residue is less than 200 ppm, the combined technology of residue hydroprocessing/catalytic cracking is the preferred method for processing high-sulfur residues, provided that the conditions permit. 　　3) Some heavy residue oils have high levels of heavy metals; for example, the heavy metal content in Tahe heavy residue oil exceeds 300 ppm. Fixed-bed hydrogenation is not capable of handling such high levels of metals, so boiling-bed hydrogenation processes such as LC-Fining or H-Oil must be used. However, the process technology and equipment are complex, the investment is high, and China does not yet possess this technology; thus it is necessary to introduce it. It can also be considered in areas with cheap hydrogen sources, but a thorough evaluation should be carried out. 　　2.2.5 Development of vacuum deep drawing technology 1) In the atmospheric and vacuum distillation units of Sinopec, the vacuum cut point is generally around 540°C; in the residue oil, fractions with temperatures below 520°C account for over 10%. There is significant potential to improve the extraction rate and increase the yield of fractionated oils. 　　According to foreign reports, the decompression cutting temperature can reach up to 620–630°C, and the distilled oil obtained can meet the requirements of downstream processing. 　　Reduced-pressure deep distillation offers significant economic benefits, especially since the total amount of residue removed through decoking accounts for half of the total residue removed in Sinopec’s operations. Based on the 75 million tons of crude oil processed for residue removal and decoking in 2005, the use of deep distillation technology can increase the VGO yield by 3%-5%, resulting in considerable increases in both VGO production and economic benefits. 　　2) The reduced-pressure deep pulling technique involves numerous engineering technologies. 　　The residual pressure at the top of the tower should be low, and the vacuum pumping system should be efficient. To raise the vacuum cutting point, it is necessary to increase the evaporation temperature and the outlet temperature of the heating furnace. The design of the oil transfer line must be closely coordinated with the residual pressure at the top of the tower, in order to minimize cracking and coking inside the vacuum distillation tubes. The pressure difference between the feed flash section and the tower top should be less than 10 mmHg; this is difficult to achieve with some types of packing, so highly efficient regular packing with low pressure drop is required. To improve the quality of deeply extracted VGO, the washing section uses composite fillers such as structured and grid types to enhance the oil washing efficiency. Optimize the structure, ensure uniform atomization of stripping steam, improve the efficiency of the stripping section, and adopt mid-section reflux spraying technology, etc. 　　3) International experience in decompression deep drilling. 　　ConocoPhillips carried out a vacuum deep drawing modification on Unit 1 of one of its refineries. The vacuum tower has a diameter of 6.7 meters and operates using a packed wet process ； Reduced-pressure cutting point design 565.5℃ ； The pressure in the evaporation section is 37 mmHg, while the residual pressure at the top of the tower is 27 mmHg; the pressure difference between these two values is 10 mmHg ； Outlet temperature of the vacuum furnace: 415.6℃ ； After the expansion of the oil transfer line, it divides into 4 streams; 2 of these streams enter the tower from the opposite side of the flash section, with a maximum flow velocity of 0.8 Mach ； The average heat intensity of the radiant tubes in the vacuum furnace is 31.5 kilowatts per square meter, with a maximum of 55 kilowatts per square meter. As a result of the modification, in addition to an increase in capacity and a higher density of the crude oil, when the crude oil cut point increases by 7%–9% compared to before the modification, the yield of HVGO from the crude oil rises by 60%–70%. The fraction in the residue with a boiling point below 565.5°C decreases by 54%–56%, the Coulson residue value of HVGO drops by 40%, and the content of heavy metals (Ni+V) is reduced by 85%. The color of HVGO changes from black or dark green before the modification to a transparent dark amber color; as a feedstock for catalytic cracking, its quality improves significantly. 　　4) Based on the above results, Sinopec should intensify the development of vacuum deep drawing technology, and gradually raise the vacuum cutting temperature used as coking feed from the current 540°C to 565.5°C in the first step, in order to increase the amount of vacuum distillate oil. 　　2.3 Desulfurization and sulfur recovery technologies for low-quality crude oil 2.3.1 Desulfurization and sulfur recovery are key to controlling environmental pollution and improving the quality of refined products 1) The current standards for sulfur content in refined products in China are relatively low, and it is an urgent and inevitable trend to achieve ultra-low sulfur levels in gasoline and diesel (sulfur content below 10 ppm); thus, the task of desulfurizing high-sulfur crude oil is even more challenging. 　　2) The atmospheric emission standards for SOx are becoming increasingly strict. In China, the allowable emission concentration of SOx from catalytic cracking flue gas is still 550–700 milligrams per cubic meter, and a 140-meter-high chimney can be used to accommodate higher emission levels. The New Source Performance Standards (NSPS) introduced by the U.S. EPA in December 2000 require an annual average SOx emission level in catalytic cracking flue gases to be less than 25 ppm, and 13 refiners representing over half of the United States’ refining capacity have signed commitments to comply with these standards. 　　3) The proportion of high-sulfur crude oil processed by Sinopec is increasing year by year. The share of imported crude oil with a sulfur content of over 1.5% rose from 20.65% in 2004 to 24.56% in 2005, an increase of 3.91 percentage points, which increases the processing difficulties for refineries. 　　4) In modern refineries, during the processing of sulfur-containing crude oil, desulfurization and sulfur production processes are employed, allowing an overall sulfur recovery rate of over 75%; the remaining 25% remains in the petroleum products or is released into the atmosphere and wastewater. 　　Therefore, the use of advanced technologies for desulfurization and sulfur recovery during crude oil processing is a key technique for processing low-quality crude oil. 　　2.3.2 Important desulfurization technologies in the processing of sulfur-containing crude oil 1) In catalytic cracking and coking processes, as well as in gas and distillation units dealing with light hydrocarbons, amine solutions are used to absorb H2S, so that these substances can be further utilized as low-sulfur fuels, liquefied gas, or raw materials for hydrogen production. Many refineries use untreated distillation tower overhead gas as fuel for heaters, which often causes dew point corrosion of the furnace tubes. In hydrogenation units for processing sulfur-containing crude oil, the circulating hydrogen also needs to have H2S removed. 　　2) Sulfur-containing VGO in catalytic cracking feed and coking CGO require hydrogen pretreatment to reduce their sulfur content to 0.1%–0.2%, so as to directly produce gasoline or blending components that meet Euro III and Euro IV standards, while also reducing SO2 emissions from catalytic cracking flue gas. 　　3) Catalytic cracking gasoline with excessive sulfur content requires post-treatment techniques such as selective hydrogenation or hydrodesulfurization to reduce its sulfur content to Euro III or higher levels. 　　4) Hydrorefining technology is widely used to reduce the sulfur content in coker naphtha, LCGO, catalytic cracking LCO, and sulfur-containingAGO to specified levels. 　　5) As mentioned above, sulfur-containing residue with a metal content of less than 200 ppm can be treated via hydrogenation to remove impurities such as sulfur, allowing the sulfur content in the residue fed into the RFCC to be controlled at 0.2%–0.4%, thereby producing gasoline that meets or exceeds Euro III standards. 　　6) In light of the demand for chemical raw materials such as high-octane gasoline components, naphtha for BTX aromatics, and ethylene cracking residues, it is necessary to develop hydrocracking of sulfur-containing VGO to a moderate extent in order to achieve thorough desulfurization of the products and produce fuels with ultra-low sulfur content. 　　7) Hydrodesulfurization under various hydrogen environments is the main process technology for desulfurization. To improve the desulfurization rate, it is necessary to develop new catalysts for various hydrogenation processes with higher desulfurization activity. 　　8) Processing sulfur-containing crude oil requires various hydrogenation processes that consume large amounts of hydrogen; therefore, it is necessary to vigorously explore hydrogen resources. Such as increasing the severity of catalytic reforming to produce more hydrogen ； Collect resources from coking, hydrocracking, catalytic reforming, and the distillation of light hydrocarbons to increase hydrogen production raw materials ； Hydrogen in catalytic cracking dry gas and ammonia synthesis off-gases is purified and recovered using technologies such as pressure swing adsorption and membrane separation ； Petroleum chemical plants that produce synthetic ammonia can use coal and asphalt to generate syngas as a source of hydrogen, and in areas near natural gas sources, hydrogen can be produced taking advantage of lower costs ； At the same time, further explore the technology of using high-sulfur coke gasification to produce syngas. 　　9) CFB boilers use high-sulfur coking fuel, and limestone is employed to fix sulfur as well as for further desulfurization of the flue gas, in order to meet the local regulations regarding flue gas emissions. 　　10) Develop new technologies for flue gas desulfurization in catalytic cracking, including sulfur transfer agents and amine liquid absorption for flue gas. 　　11) Improve the stripping technology for sulfur-containing wastewater. Processing processes such as catalytic cracking, hydrogenation, and coking generate large amounts of sulfur-containing wastewater, with concentrations exceeding 20 grams per liter; wastewater stripping technology is required to remove substances such as H2S. Wastewater stripping can be carried out in either single-tower or double-tower configurations. The acidic gas containing H2S that is removed is used for sulfur recovery, and ammonia can also be recovered to prevent the formation of ammonium hydrosulfide, which could clog the pipes in the sulfur recovery system. After stripping, the sulfur-containing wastewater is required to have an H2S level of less than 20 milligrams per liter and an NH3 level of less than 50 milligrams per liter. 　　2.3.3 Preferred sulfur recovery technologies The sulfur recovery of H2S-containing acidic gases in the processing of sulfur-containing crude oil generally employs the classical Claus process. Under strict control of the H2S:S02 ratio at 2:1, sulfur recovery rates of up to 95% can be achieved through thermal reaction conversion in a incinerator and secondary catalytic conversion in a Claus process. The exhaust gas is hydrogenated to be reduced to H2S, which is then absorbed by an amine solution; the regenerated H2S is returned to the Claus system, allowing a total sulfur recovery rate of 99.8%-99.9%. The remaining exhaust gas containing trace amounts of sulfur is incinerated and released into the atmosphere as SO2. Both the SSR sulfur recovery technology independently developed by Sinopec, and the technology introduced, adapted, and absorbed by Zhenhai Petrochemical of Sinopec, employ the aforementioned method. 　　To increase the processing of sulfur-containing or high-sulfur crude oil, refineries need to expand or build new sulfur recovery units based on the amount of sulfur to be recovered, and the technologies for this purpose can be those developed independently by Sinopec. 　　3 Summary The countermeasures for processing low-quality crude oil are briefly summarized as follows. 　　1) World crude oil prices have remained high for a long time, resulting in an increasing price gap between low-quality and high-quality crude oil. Processing more low-quality crude oil can significantly reduce crude oil costs, bringing substantial economic benefits to refining companies. 　　2) The criteria for low-quality crude oil are as follows: Crude oil that meets any one of the following conditions – API grade less than 27, sulfur content greater than 1.5%, or TAN greater than 1.0 mgKOH/S – can be classified as low-quality crude oil. 　　3) For distillation units, when processing low-quality crude oil, it is necessary to enhance the process of separation and injection, control the levels of iron and chloride ions in the condensate at the top of the tower, and keep the corrosion rate in the lower temperature areas below 0.2 millimeters per year. 　　4) For the high-temperature parts of the distillation units used in processing high-sulfur and high-acid crude oils, selecting appropriate steel grades can help control corrosion; the material selection criteria can be referred to the two guidelines SHT3096—2002 and SHT3129-2002. When processing high-sulfur, low-acid crude oils, materials such as OCrl3, Cr5Mo, Cr9Mo, or linings are generally used in the high-temperature areas ； When processing high-acid crude oils (with low or high sulfur content), 316L alloy steel or lining is generally required in the high-temperature areas. 　　5) Heavy crude oil with a low API value contains large amounts of residue, requiring an expansion of residue processing capacity. Since Sinopec has mastered the technology for scaling up delayed coking units, and given that coking features simple equipment, low investment costs, a short construction period, and high processing efficiency, delayed coking has become Sinopec’s primary method for the deep processing of residue in recent years. However, it is still necessary to improve technical capabilities in order to further unlock the processing potential of coking. 　　6) The combined unit of residue hydroprocessing/catalytic cracking is a technology that can optimize the utilization of crude oil resources and maximize the production of light petroleum products. Depending on the heavy metal content in sulfur-containing crude oil, moderate development can be pursued if conditions permit. 　　7) Develop deep vacuum distillation technology for vacuum residue, raising Sinopec’s crude oil distillation vacuum cut point from the current 540°C to 565.5°C in the first step, and apply this technology first in crude oil distillation units equipped with residue-decoking functions. As a result, Sinopec will be able to use deep vacuum distillation on half of its crude oil, which will significantly improve the profitability of its refining plants. 　　8) Desulfurization and sulfur recovery during crude oil processing are key to controlling pollution and improving the quality of oil products. 　　9) Develop a series of new desulfurization technologies for processing processes. Given that the hydrogenation process is the primary desulfurization technique, it is necessary to further develop catalysts with higher desulfurization activity. 　　10) Expand the sources of hydrogen production. In addition to making full use of the hydrogen resources available within the refining plants for hydrogen production and purification, petrochemical companies that produce fertilizers can make use of the hydrogen generated from coal or bitumen gasification. 　　11) Improve the stripping technology for sulfur-containing wastewater to fully recover sulfur from acidic gases. 12) Utilize independently developed sulfur recovery technology to achieve a sulfur recovery rate of 99.8%–99.9%.

Mr. Hou provided a summary and definition of low-quality crude oil, including parameters such as sulfur content, acid content, and API value. As a result, everyone now has a clearer understanding of low-quality crude oil, sulfur-containing crude oil (high-sulfur, low-sulfur, medium-sulfur), acid-containing crude oil (high-acid, low-acid, medium-acid), and heavy crude oil (heavy, light, medium). This is excellent – it clarifies the concepts and defines the ranges. I also came across this information in other conference materials, so I’d like to share my insights with you all. 1) The US NPRA classifies crude oil based on its density: crude oil with an API value greater than 38 is considered light crude oil, those with an API value less than 22 are heavy crude oil, and those with an API value between 22 and 38 are considered medium crude oil. However, there are some conventional classifications in the trade of crude oil, such as the API gravity of Arab heavy crude being 27.9, etc. Therefore, it is also feasible to classify crude oil as light crude when its API value is greater than 36, as heavy crude when the API value is less than 27, and as medium crude when the API value is between 27 and 36. 　　2) Crude oils containing sulfur are generally classified as follows: those with a sulfur content of less than 0.5% are low-sulfur crude oils, those with a sulfur content greater than 1.5% are high-sulfur crude oils, and those with a sulfur content between 0.5% and 1.5% are medium-sulfur crude oils. 　　3) Crude oil with a total acid number (TAN) of less than 0.5 mgKOH/g is considered low-acid crude oil; those with a TAN greater than 0.5 mgKOH/g are acidic crude oils, while those with a TAN greater than 1.0 mgKOH/g are high-acid-number crude oils. 　　It can be concluded that crude oils that meet any one of the criteria of an API degree of less than 27, a sulfur content of more than 1.5%, or a TAN value of more than 1.0 mgKOH/g can be classified as low-quality crude oils.