The impact of anti-reaction schemes on catalytic energy consumption

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The impact of reactive regeneration schemes on the energy consumption of catalytic cracking units. Energy conservation is an eternal theme in human industrial activities, as it relates to the consumption of non-renewable resources and pollution of the living environment. Energy conservation is also an economic issue, as it is a significant component of production costs that cannot be ignored ； With soaring world energy prices today, this deserves our utmost attention. The catalytic cracking unit is an important secondary processing unit in refineries; in 2004 alone, the catalytic cracking capacity of Sinopec Corporation and PetroChina Corporation combined exceeded 90 Mt/a. Sinopec Corporation’s share of catalytic cracking processing is even higher, at 34.41%; therefore, the energy consumption of catalytic cracking units has a significant impact on the energy savings of refineries. 1. Current energy consumption status of domestic units: Through years of efforts, the energy consumption of catalytic cracking units has been reduced to relatively low levels. Statistics from 2004 show that the average energy consumption per ton for the catalytic cracking units of Sinopec Corporation and PetroChina Corporation was 2759.1 MJ/t and 2734 MJ/t respectively. The performance metrics of the two units with the lowest energy consumption are particularly advanced; Unit II (wax oil catalysis) at Sinopec Zhenhai Refining & Chemical Co., Ltd. achieved 1918 MJ/t, while Unit IV (heavy oil catalysis) at CNPC Dalian Petrochemical Co., Ltd. reached 1962.8 MJ/t – both of which are at the world’s advanced level. However, it is also necessary to recognize the imbalance in development; among the plants of the two major companies with a processing capacity of ≥0.6 Mt/a, the highest energy consumption levels reached 3651.3 and 3794 MJ/t, indicating that there is still much room for improving energy efficiency. There are many factors that affect the energy consumption of catalytic cracking units, such as product specifications, weather conditions, unit configuration, utility supply conditions, design quality, operational level, and management level. We cannot simply judge the efficiency of a device in terms of its energy consumption figures. These conditions result in the incomparability of energy consumption in catalytic devices. In the energy-saving efforts for existing installations, following the principle of achieving high output with minimal investment, there are many energy-consuming factors related to the hardware configuration of these installations; these factors cannot be improved without significant technical upgrades. Energy-saving measures related to such factors require substantial investment, resulting in poor technical and economic indicators, and thus may not be feasible. Therefore, the most favorable time for energy-saving efforts is at the initial stage of plant construction; making rational choices regarding the type of equipment and the configuration of the units can reduce the plant’s energy consumption from the outset. This paper analyzes the energy consumption characteristics of different reaction regeneration schemes and their impact on the energy consumption of the device. 2. Classification of catalytic units from the perspective of energy consumption 2.1 Domestic catalytic cracking units can be divided into the following four categories: Type I: Units with rapid-bed and turbulent-bed regeneration arranged side by side; examples of this type include Unit IV (3.5 Mt/a) at Dalian Petrochemical Company of China National Petroleum Corporation, and Unit II (3.0 Mt/a) at Zhenhai Refining & Chemical Co., Ltd. of Sinopec, both of which utilize technology developed independently in China. Type II: Units with single-stage regeneration arranged coaxially or side by side; examples of this type include Unit III (1.4 Mt/a) at Shanghai Gaqiao Petrochemical Company of Sinopec, and Unit I at Jiujiang Branch of Sinopec. Type III: Counter-current two-stage regeneration with high and low columns side by side; this type is represented by the Lanzhou Petrochemical Branch of CNPC (3.0 Mt/a) and Unit II of the Jinan Branch of Sinopec (1.4 Mt/a). Type IV: Two-stage regeneration with three columns arranged side by side; this type features three columns placed side by side, as seen in Unit III of the Yanshan Branch of Sinopec in Beijing ； The regenerator is arranged in parallel with the settler, as in the 0.8 Mt/a catalytic unit of Sinopec Shanghai Petrochemical Co., Ltd ； There are settlers that are coaxial with each other or arranged side by side, such as the Liaohe Petrochemical Branch of China National Petroleum Corporation and the Qiange Petrochemical Branch of China National Petroleum Corporation ； A coking tank can be added below the second stage; for example, the 3.0 Mt/a catalytic unit of Dalian West Pacific Petrochemical Co., Ltd. can also be classified under this category. 2.2 Foreign catalytic cracking units can also be included in the above classification. Type I: UOP’s coking drum falls under this category ； Type II: Kellogg’s HOC process, Shell’s high-low tandem configuration, and Rums’ high-low tandem configuration can be classified under this category ； Type III: UOP’s RCC can be included in this category ； Type IV: S.W Company’s three-in-line devices can be classified under this category ； 3. Energy consumption data of domestic catalytic cracking units: First, we selected four units of the same scale based on the aforementioned classification to conduct a simple comparison of their energy consumption. Table 1 Comparison Table of the Four Types of Units Type Manufacturer Item I II III IV JL G JN F Scale, Mt/a 1.4 1.4 1.4 1.4 Actual processing volume, Mt/a 1.45 1.37 1.17 1.69 Production scheme Conventional MIP Conventional Conventional Liquefied gas yield, wt% 14.02 16.54 16.44 20.87 Dry gas yield, wt% 3.91 3.86 5.46 4.41 Coke yield, wt% 8.28 8.49 8.86 6.82 Energy consumption, MJ/t 2471.47 2458.49 2704.25 2924.48 * Data sourced from the annual statistical reports of the two major companies for 2004. Next, we select the energy consumption data of the four largest domestic plants with a capacity of ≥3.0 Mt/a in 2004 for comparison. Table 2: Comparison of energy consumption for large-scale plants. Type, Manufacturer, Project: IV, I, II, III, X, Z, D, L. Plant capacity, Mt/a: 3.0, 3.0, 3.5, 3.0. Plant load factor, %: 88.24, 93.69, 101.99, 88.73. Feed carbon residue, wt%: 4.78, ~1.5, 4.55, 5.12. Energy consumption in 2004, MJ/t: 2744.03, 1917.97, 1962.77, 2737.75. * Data sourced from the annual statistical reports of the two major companies for 2004. The table data show that the energy consumption of Types I and II is significantly lower than that of the other two types. The data for a particular year may be due to random factors; presenting the statistical data for the device over various years in Table 3 will provide a clearer picture. Table 3: Energy consumption data over the years for the four types of devices. Type, Plant Name: IIIIIIIVZGJF; Scale, Mt/a: 3.0, 1.4, 1.4, 1.4. Energy consumption in MJ/t in 1999: 2787.57, 733.72, 893.13, 633.59. Energy consumption in MJ/t in 2000: 2542.64, 2619.68, 3740.91, 3135.49. Energy consumption in MJ/t in 2001: 2195.14, 2548.09, 3010.31, 3035.85. Energy consumption in MJ/t in 2002: 2150.34, 2610.47, 2809.76, 3189.92. Energy consumption in MJ/t in 2003: 1858.10, 2433.79, 2754.08, 3053.43. Energy consumption in MJ/t in 2004: 1917.97, 2458.49, 2704.25, 2924.48. Average annual energy consumption: 2132.76, 2576.14, 3065.16, 3078.97. * Data sourced from the annual statistical reports of Sinopec Corporation. We further merged and classified the data on similar units from Sinopec Corporation for 2003 and 2004 (excluding units with special production schemes such as ARGG/DCC), among which there were 5 units of type I, 5 units of type II, 4 units of type III, and 10 units of type IV. The average values are listed in Table 4. Table 4 Average energy consumption of classification units. Type, Year: Headquarters average. I, II, III, IV. Energy consumption in MJ/t for 2003: 2900.20, 2257.94, 2731.47, 3165.64, 2804.32. Energy consumption in MJ/t for 2004: 2788.83, 2294.79, 2651.08, 2931.60, 2693.37. * Data sourced from the annual statistical reports of Sinopec Corporation over the years. By comparing from the various perspectives mentioned above, a consistent conclusion can be drawn: Type I has the lowest energy consumption, Type II is slightly higher, while Types III and IV have much higher energy consumption. Next, we will conduct detailed calculations to determine which factors result in the lowest energy consumption for Type I. 4. Energy simulation analysis: To reduce the impact of factors such as design level, management level, and operational level on the energy consumption of the plant, we conduct simulation calculations for the regeneration and downstream systems using the same raw material properties, product specifications, and steam consumption. This approach helps to eliminate various factors that make direct comparison difficult, thereby enabling an assessment of the impact of different regeneration schemes on energy consumption. The conditions for the simulated comparison use an annual processing capacity of 1.4 Mt/a ； The main fan unit uses three units ； The outlet pressure of the main fan is 0.4 MPa(A) ； The compressor is driven by a medium-pressure backpressure turbine ； Calculations were performed under the condition where the char formation rate was set at 8 wt%, and the results of the simulation are listed in Table 5. Table 5 Simulation and comparison results of various reaction regeneration schemes. Type, Item: I, II, III, IV. Electricity consumption for the main fan unit/compressor, MJ/t: Benchmark, +28.05, +93.78, +177.94. Energy consumption for CO and waste heat boilers, MJ/t: Benchmark, 0.00, -4.61, -39.77. Low-temperature heat energy consumption for the distillation column overhead vapor, MJ/t: Benchmark, +34.75, +80.39, +8.79. Energy consumption for the air compressor, MJ/t: Benchmark, +12.14, +60.71, +6.28. Total, MJ/t: Benchmark, +74.94, +230.27, +153.24. It can be seen from the data in Table 5 that the differences in energy consumption among the various types correspond to the same order as observed in the actual statistical data. The data in the table above also show that the impact of the two-device approach on energy consumption is quite significant; once this approach is chosen, the future energy consumption level of the device is determined as well. Moreover, the difference in energy consumption between different types of devices cannot be eliminated by any energy-saving measures. Given that the results of this simulation were calculated using the most conservative parameters, it is normal for the difference in energy consumption observed in actual data to be higher than theoretically predicted. 5. Conclusions (1) Although there are many factors that affect the energy consumption of catalytic cracking units, the impact of the reaction-regeneration scheme is decisive and inherent; the differences in energy consumption resulting from different configurations of these two units cannot be reduced through improved management, better operating practices, or general energy-saving modifications. For this reason, whether it is a new design or a renovation to update the two devices, extreme caution should be exercised, and a thorough comparison should be carried out. (2) From an energy consumption perspective, coking tank regeneration (Type I) is the most efficient; coaxial and stacked high-low types (Type II) are next; two-stage regeneration with three units in parallel (Type IV) has higher energy consumption, while counter-current two-stage regeneration (Type III) has the highest energy consumption. A regular principle of energy use can also be observed, namely that single-stage regeneration is superior to two-stage regeneration ； Complete combustion of CO is superior to incomplete combustion of CO, and an equal-height arrangement of the two devices is better than a high-low arrangement. This post was last edited by zjx1973 on 2008-1-15 08:56.]