Carry out pressure reduction and deep drawing to optimize the operation of heavy oil units to achieve energy conservation and emission reduction in refining

Thread Content

"Energy conservation and emission reduction" is not only a concrete practice to implement the scientific outlook on development and build a harmonious society, but also an intrinsic need to tap the internal potential of oil refining and enhance international competitiveness. In recent years, under the guidance of the Party Committee of Sinopec Group Corporation, the refining segment has been adhering to the work policy of "optimizing efficiency, increasing energy, saving energy and reducing emissions", and has carried out comprehensive and in-depth technical services and comprehensive research, and carried out special energy-saving and emission reduction work such as "hydrogen resource management", "reducing deep drawing", and "coking to increase operating load". Refining energy consumption is being reduced year by year in accordance with the requirements of the "11th Five-Year Plan" development plan formulated by the party group. 　　In recent years, various companies have made effective efforts to pay close attention to the three basics and strengthen energy-saving management. By breaking down energy consumption indicators step by step and implementing energy-saving responsibilities at all levels, they have achieved gratifying energy-saving results. Sinopec's refining energy consumption has dropped from 78.25 kg of standard oil/ton at the beginning of the "Tenth Five-Year Plan" to less than 67 kg of standard oil/ton now. However, it is still relatively difficult to achieve the energy-saving goals of the “11th Five-Year Plan” simply by strengthening management. Combining the experience of technical services in the past few years, the Refining Division felt the need to strengthen the overall refining process management from a macro perspective and optimize the operating structure between units. ； Realize the concept of molecular management from a micro perspective, and do a good job in heavy oil management, light hydrocarbon management, hydrogen management and energy flow management. That is to say, relying on the existing unit structure and optimizing the overall process processing method, the operating efficiency of the refining unit can be further improved to achieve the goal of energy conservation and emission reduction. From the analysis of the demand for heavy crude oil, the top priority is to deeply process the purchased heavy crude oil, reduce or eliminate the production of fuel oil, and fully realize the benefits of the purchased heavy crude oil. On the one hand, the optimization of heavy oil processing equipment is to shorten the coking cycle of the delayed coking equipment, reduce the circulation ratio, and improve the residual oil processing capacity. On the other hand, it is necessary to optimize the operation of atmospheric and vacuum distillation, implement vacuum deep drawing, and minimize the generation of heavy oil. The basic idea of ​​vacuum deep drawing operation is to use a model to cut crude oil into very narrow fractions on the basis of conventional decompression, and then synthesize the narrow fractions according to the requirements of each cutting point. Appropriate fillers (height) are added according to the simulated oil properties after synthesis, and steam is injected into the bottom of the vacuum furnace and the vacuum tower. That is, the technical requirements for "decompression deep drawing" oil products are achieved through the combination of software and hardware. The core of the decompression deep drawing technology is the calculation and selection of the medium flow rate, vaporization point, oil film temperature, furnace tube wall temperature, steam injection amount (including furnace tube steam injection and tower bottom blowing), etc. in the decompression furnace tube to prevent coking in the furnace tube and ensure a production cycle of more than four years and safe production. In the design, modification and operation optimization calculation of decompression deep drawing, a strict correlation-based dynamic model (such as crude oil evaluation database and management system CADB/CAMS) is needed to evaluate the inflection point between input and benefit. Various economically feasible operation plans can be calculated based on different cutting point targets to improve operational flexibility to meet the changing requirements of the market and raw oil. The decompression deep drawing technology can reduce furnace tube coking by adjusting steam injection into the decompression furnace tube. The furnace outlet temperature can reach 430°C, and the cutting point temperature of wax oil/resid oil can reach 580~630°C (with a small amount of investment, the cutting point temperature of wax oil/resid oil in the distillation unit can also be increased by 25~50°C), which is different from the usual cutting point of wax oil/resid oil of 530~540°C. Compared with the temperature, a higher total extraction rate can be obtained. The amount of cracked gas generated is less than 0.3% of the raw material. The steam injection amount is 1% to 2% of the raw material (newly built equipment). The temperature difference of the oil transfer line is 10 to 20°C. Tube-by-tube modeling of the heating furnace tubes can provide an analysis of the state of the fluid in the furnace tube and cracking/coking tendency, and propose an operation plan or transformation strategy to delay coking. 　　Application status of vacuum deep drawing technology at home and abroad 1. Current situation of vacuum pulling rate of joint-stock companies In the context of relatively high crude oil prices, purchasing high-sulfur heavy crude oil is an effective measure to reduce crude oil procurement costs. The API degree of Sinopec's imported crude oil dropped from 32.99 in 2004 to 30.83 in 2006. The optimization of crude oil procurement effectively reduced refining costs. However, judging from the production and operation in the first half of 2007, the heavy crude oil has brought about an increase in fuel oil yield. The processing capacity and processing load of heavy oil processing equipment such as delayed coking have not fully realized the economic benefits of purchasing heavy crude oil. At present, the outlet temperature of the joint-stock company's vacuum furnaces is mostly below 400°C. Only three sets of units have outlet temperatures between 400 and 405°C. The content of components in the vacuum residue oil before 500°C is generally more than 5%. Seriously, More than 10%, the cutting point temperature of vacuum wax oil is generally below 530°C, and the highest is below 560°C. When the cutting point temperature of the German MIRO decompression wax oil reaches 605°C, the residual carbon still maintains a level of 1.7%. It can be seen that there is great potential to improve the pull-out rate of the pressure reducing device. The decompression systems of the 58 atmospheric and vacuum distillation units currently operated by the joint-stock company have the following common problems:: First, the decompression and deep drawing process is imperfect. The extraction temperature of the earlier distillation unit was considered to be below 530°C, and the operation plan for deep decompression and extraction was not considered during the design. The decompression tower did not have a bottom-reducing quenching oil process, and there was no good control method for the bottom-reduction temperature. When the bottom temperature of the tower increased, it was easy to cause the bottom-reducing pump to be evacuated, and in severe cases, it led to coking accidents at the bottom of the decompression tower. Some devices do not design a steam injection point at the entrance of the radiant section, and the oil film temperature of the decompression furnace tube is difficult to control. The hanging material grade of the furnace tube is designed to be lower than the furnace tube material, which limits the furnace temperature to no higher than 800°C. Second, the device operating load matching is unreasonable. The outlet temperature of the atmospheric pressure furnace is low, the extraction rate under normal pressure is low, and the components of diesel and wax oil overlap. After the diesel component enters the pressure reduction system, the first-line reduction ratio is large, and the diesel content of the second-line reduction component is high, which increases the load of the pressure reduction heating furnace. ； The load of the decompression furnace is tight, the decompression extraction rate is insufficient, and the components of wax oil and residual oil overlap. The third is the lack of technical support and card-side operation. Since there are no strict calculations for specific crude oil types and heating furnace structures, if we just rely on experience to further increase the heating furnace outlet temperature, we will inevitably worry about coking of the decompression heating furnace. In actual operation, the decompression furnace outlet temperature is more than 10°C lower than the design value. 　　2. Progress of international decompression deep drawing technology At present, the two companies with independent decompression deep drawing technology in the world are Shell and KBC. Shell's pressure reduction deep-drawing technology relies on the empty tower design of the pressure reduction tower, which has a small pressure drop and is more suitable for the design of new atmospheric and vacuum distillation units. KBC's pressure reduction deep drawing technology can provide coking curves of different crude oils and tube-by-tube calculations of heating furnace tubes through its software simulation calculation function, which is suitable for operation optimization and partial modification of equipment. The application of decompression deep drawing allows the decompression furnace to operate safely at an outlet temperature of 430°C, and the cutting point temperature of wax oil/residual oil reaches above 580°C, or even 630°C. Specific Measures for Implementing Decompression and Deep Pulling Based on the actual situation of decompression and deep pullout this year, we feel that the following aspects need to be done to carry out decompression and deep pullout:: 1. Optimize the normal and vacuum operation, reasonably distribute the operating load of the device, and avoid transferring the load of normal pressure distillation to vacuum distillation. Appropriately increase the outlet temperature of the atmospheric pressure furnace to lower the extraction rate under normal pressure, reduce the overlap of diesel and wax oil components, and reduce the operating load of vacuum distillation. 2. Improve the pressure reduction and deep drawing process. It mainly includes the following aspects of transformation:: Set up a steam injection point at the entrance of the radiant section of the decompression heating furnace to control the oil film temperature of the decompression furnace tube and prevent the furnace tube from coking. Check the hanging material of the furnace tube of the pressure reducing heating furnace to make sure that the hanging material grade matches the furnace tube. Set up a quenching oil process at the bottom of the vacuum tower, and use the cold cycle of part of the residual oil to control a reasonable temperature at the bottom of the vacuum tower to avoid pump evacuation at the bottom of the vacuum tower and coking at the bottom of the vacuum tower. Modify the internal structure of the pressure reduction tower to maximize the extraction of the second reduction line to meet the demand for hydrocracking raw materials ； Minimize the extraction of the third-line reduction line. The third-grade reduction line is used as a means to adjust the quality and quantity of hydrocracking raw materials. The remaining third-grade reduction lines are used as raw materials for hydrotreating or directly enter catalytic cracking processing to reduce the catalytic cracking slag ratio and improve the distribution of catalytic cracking products. 3. Relying on technical support and combining model calculations with experience to improve the severity of existing decompression operations. In order to avoid coking due to decompression furnace tubes, decompression deep drawing should be carried out scientifically. By drawing on foreign experience and calculating the heating furnace operating curve and coking curve, a safe operating zone for decompression and deep drawing is proposed to achieve long-term decompression and deep drawing. Specific steps include: In the first step, the model is used to simulate, calculate and evaluate the original design, equipment and other parameters of the device and the processed crude oil, including the heating furnace, oil transfer line, vacuum fractionation tower, vacuum system, coking curve, etc., to find the bottleneck problem of deep drawing. The second step is to simulate and analyze the current operating conditions of the device, and evaluate the potential and options for adjusting the deep drawing operation. The third step is to put forward suggestions to improve the current operating conditions and test procedures to improve the wax oil/resid oil cutting point, implement and maintain them. 　Case analysis of vacuum deep drawing operation 1. Effect of vacuum deep drawing: A domestic refinery has an 8 million tons/year normal pressure and vacuum distillation unit with a design capacity of 22,800 tons/day. The outlet temperature of the vacuum furnace is 405°C. Since there is no quenching oil facility at the bottom of the vacuum tower, the outlet temperature of the vacuum furnace is greater than 396°C and the vacuum residue pump appears to be evacuation. The actual outlet temperature of the decompression furnace is controlled not to exceed 395°C, the device processing capacity can only be maintained at 19,800 tons/day, and the wax oil cutting point temperature is below 530°C. After the decompression system was appropriately modified this year, a residual oil quenching facility was added to effectively control the temperature at the bottom of the decompression tower. Through simulation calculations of the decompression system, the outlet temperature of the decompression furnace was increased to 406°C, and the cutting point temperature of the wax oil was increased to 560°C. Achieving the minimum extraction of the third line and the maximum extraction of the second line not only meets the quality requirements of hydrocracking raw materials, but also ensures the raw material needs of the wax oil hydrotreating unit. Due to the improvement of the dry point of straight-run diesel, the extraction rate of the atmospheric tower is better, which accordingly reduces the operating load of vacuum distillation, increases the operating flexibility of the vacuum tower, and improves the processing capacity of the device. During the decompression and deep drawing operation, a new quenching oil process at the bottom of the decompression tower was put into use. Steam injection measures were used in the decompression furnace tube and the bottom of the decompression tower to increase the temperature of the outlet branch of the decompression furnace from 395°C to about 405°C. 　2. Energy consumption analysis: In the decompression and deep pulling operation mode, the energy consumption of the normal and decompression device increases by 0.20 units. The total contribution to the increase in the entire plant is 4,560 kg of standard oil per day. The yield of vacuum residual oil decreased by 3 percentage points, and the total residual oil volume decreased by 684 tons/day. Calculated based on the average energy consumption of the delayed coking unit of 24 kg of standard oil/ton, the contribution to the reduction in energy consumption of the entire plant is 16,416 kg of standard oil/day. After comprehensive consideration of the two items, the comprehensive energy consumption of refining decreased by 11,856 kg of standard oil/day, equivalent to 0.52 kg of standard oil/ton of crude oil. Since vacuum deep drawing improves the treatment mode of residual oil, the yield of light oil increases. According to the simulation calculation results of the entire plant process, the outlet temperature of the vacuum furnace increases by 10°C, which generates an annual economic benefit of 9.7 million yuan, and the energy consumption of refining per 10,000 yuan of output value is also reduced. The economic benefits of vacuum deep drawing are significant. The vacuum deep drawing operation can effectively reduce the yield of residual oil, increase the carbon residue and density of vacuum residual oil, give full play to the operating capacity of the coking unit, increase the yield of light oil, reduce the yield of fuel oil, and increase the yield of high value-added products. As crude oil prices continue to remain high, optimizing the processing mode of the heavy oil system through decompression and deep drawing operations can not only achieve the purpose of energy conservation and emission reduction, but also maximize the economic benefits of purchasing lower-priced high-sulfur heavy crude oil.