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As the trend toward heavier and lower-quality crude oil becomes increasingly apparent, the price differences between different types of crude oil force refineries to process more heavy and sulfur-rich crude oil. At the same time, society’s demand for petroleum products is also changing, with an increase in demand for light and medium-grade oils, while demand for heavy-grade oils is decreasing. Therefore, in recent years, the lightening of heavy oil has received attention in order to improve the economic efficiency of crude oil processing. In the current environment of high oil prices, there is even greater pressure to lighten heavy oil; many countries around the world are competing to develop cost-effective advanced processing technologies to convert heavy oil into high-value light oils or petrochemical feedstocks. The deep processing of heavy oil mainly refers to the processing of residue, which is one of the most complex systems in the world. The vast majority of impurities in crude oil, such as sulfur, nitrogen, metallic nickel, metallic vanadium, and asphaltenes, are concentrated in the residue. In particular, sulfur-containing crude oils often have high levels of metals (such as vanadium and nickel) as well as asphaltenes, which makes the further processing of these residues more difficult and complex. Residue is a hydrogen-deficient system. To convert residue oil with a low hydrogen content into light oil products with a high hydrogen content, either external hydrogen must be added or excess carbon must be removed. Therefore, deep processing technologies for residue can be divided into two main categories of processes: hydrogenation and decarburization. Hydrogenation processes include residue hydrogenation and residue hydrocracking, while decarburization processes include solvent deasphalting, coking, visbreaking, residue catalytic cracking, gasification, etc. Deep processing of residue is an important way for refineries to improve their economic efficiency. In the construction of new refineries and the renovation or expansion of existing ones, the selection of residue processing technologies and the optimization of the processing processes are often the most critical steps. Experience has shown that due to the great variability in the properties of residue, no single residue processing technique can address all issues. Finding the most economical and effective way to utilize all residue resources is also the driving force behind the continuous improvement of heavy oil processing technologies. Different residue processing processes have varying requirements regarding the properties of the feedstock; therefore, the choice of residue processing process depends to a large extent on the properties of the residue. Different residue processing technologies have distinct characteristics in terms of raw material requirements and suitability, product distribution and quality, as well as process flow. The current technical approaches and process characteristics for heavy oil processing are as follows: 1. Characteristics of the delayed coking-hydrogenation-catalytic cracking combined process: High-sulfur residue oil is fed into the coking unit, while high-sulfur wax oil and coking wax oil undergo desulfurization and denitration in the hydrogenation unit before being used as feedstock for catalytic cracking ； The slurry produced by the heavy oil catalytic cracking unit is used as feed for delayed coking; the coked naphtha is fed into catalytic cracking to increase gasoline production, or it is refined and desulfurized using hydrogenation units before being used as a raw material for ethylene cracking. High-sulfur coke can be used as a feedstock for CFB boilers to generate steam and electricity for the entire plant. 2. Characteristics of the solvent deasphalting-catalytic cracking combined process: All or part of the oil slurry is extracted and mixed with vacuum residue as feed to the solvent deasphalting unit, which improves the yield of deasphalted oil; this deasphalted oil is then sent to the heavy oil catalytic unit for blending. 3. Characteristics of the residue hydrogenation–heavy oil catalytic cracking combined process: Poor-quality residue is subjected to residue hydrogenation treatment to produce some light petroleum products. The hydrotreated atmospheric residue is used as a feedstock for heavy oil catalytic cracking, while the heavy recycle oil produced by the heavy oil catalytic cracking unit can be used as feed for residue hydrotreatment. The high content of aromatics in the heavy recycle oil can effectively improve the solubility of resins and asphaltenes in the residue, thereby increasing its conversion rate, reducing catalyst fouling, and extending the catalyst’s lifespan. 4. Characteristics of the combined process flow of residue solvent deasphalting – asphalt gasification – deasphalted oil hydrogenation – catalytic cracking: This process makes use of solvent deasphalting to concentrate metals, sulfur, and carbon residue in low-quality residues; thereafter, the deoiled asphalt is fed into a gasification unit to produce electricity, steam, and syngas. The deasphalted oil is then sent either for hydrocracking or, after hydrogenation, for further conversion in catalytic cracking. 5. Characteristics of the residue hydrogenation-delayed coking combined process: Poor-quality residue is subjected to mild hydrogenation treatment via residue hydrogenation to reduce its sulfur content ； Residues with low sulfur content are fed into the delayed coking unit ； Light oil products are produced through decarburization via coking; the light oil products obtained from this combined process require minor refining before they can be sold as finished products. Meanwhile, the low-sulfur petroleum coke produced has good market demand and a wide range of applications. 6. Characteristics of the catalytic cracking – solvent deasphalting – delayed coking combined process: Based on the catalytic cracking – solvent deasphalting combined process, the solvent deasphalting – delayed coking combined process is further applied. The catalytic unit incorporates deasphalted oil, and tries to remove as much slurry as possible for use in the solvent deasphalting unit, thereby increasing the slag incorporation rate in the catalytic unit and boosting its processing capacity. The coking unit processes deoiled asphalt, solving the problem of where to dispose of this material that previously hindered the continuous operation of the solvent deasphalting unit; it also increases the processing capacity of that unit and provides more feedstock for catalytic cracking. Coking wax oil is as well sent to the catalytic cracking unit for further processing. 7. Characteristics of the catalytic cracking – delayed coking and solvent deasphalting – delayed coking combined process: It is a combination of the catalytic cracking – delayed coking combined process and the solvent deasphalting – delayed coking combined process. The biggest difference between this combined process and the catalytic cracking–solvent deasphalting–delayed coking combined process is that in this process, the oil slurry is sent to the feed of the coking unit for blending, rather than being sent to the solvent deasphalting unit for blending. 8. Characteristics of the hydrotreating process for residue: Depending on the degree of conversion achieved through hydrotreatment, residue hydrotreatment can be divided into residue hydrotreating and residue hydrocracking. During the hydrotreatment of residue, reactions to remove impurities primarily occur, including desulfurization, denitration, demetallization, and the reduction of residue carbon; the conversion rate of heavy fractions into light fractions (or the degree of lightening) is less than 50%. In residue hydrocracking, reactions to remove impurities also occur, but the lightening rate is higher than 50% in this case. Based on the type of residue hydrogenation reactor, residue hydrogenation can be divided into 4 types: fixed-bed hydrogenation, fluidized-bed hydrogenation, suspended-bed hydrogenation, and moving-bed hydrogenation. 9. Characteristics of the residue IGCC technology process: IGCC technology is an integrated gasification and cyclic power generation technology. This technology includes the production of syngas, the purification of syngas, and combined-cycle power generation. The gasification technology for residue oil utilizes the partial oxidation method, and the main patent holders for this technology are Texaco and Shell. The crude syngas must undergo dust removal and desulfurization to meet the requirements of the equipment downstream of IGCC as well as emission standards. Syngas purification technologies are divided into normal-temperature wet purification (that is, cooling the gas first before purifying it) and high-temperature dry purification. Each purification method includes two steps: dust removal and desulfurization.