Catalytic energy-saving approaches I have worked on

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Ways and measures for energy conservation (I) Ways of energy conservation For heavy oil catalytic cracking units, the energy consumption is primarily concentrated in three areas: one of these is the energy required for coking； The second is utility consumption ； The third is the heat recovery section. The size of the coke produced plays a decisive role in the energy consumption of the facility; the key to saving energy is ① to reduce the amount of coke produced ； ②Improve coke utilization rate. For fixed installations, given a certain raw material supply and production plan, the energy consumption of heavy oil catalytic units mainly depends on the energy recovery process. (II) Energy-saving measures 1. Rational design is a prerequisite for energy savings. 1) Reducing coke formation: In the design of the 3.5 million tons/year heavy oil catalytic cracking complex, taking into account the high proportion of slag in the feedstock and the high rate of coke formation, efficient feedstock nozzles and a technology for rapidly terminating reactions at the outlet of the riser were employed to reduce coke production, lower the yield of catalytic cracking dry gas, and improve the utilization rate of hydrogen in the feedstock. On this basis, an efficient stripping section design was adopted to focus on reducing the yield of steammable tar. By using molecular sieve catalysts and novel metal passivators, the yield of catalytic coke and contaminated coke is reduced. 2) Maximum recovery of flue gas pressure energy: On the basis that the regeneration scheme facilitates the recovery of flue gas pressure energy, an appropriate regeneration pressure is selected, and through optimization of the design of the main air and flue gas system processes as well as their layout, the pressure and temperature drops in these systems are reduced, thereby ensuring, through proper design, maximum recovery of flue gas pressure energy. 3) Increase the power recovered by the exhaust turbine by raising the back-pressure, which increases the enthalpy drop of the exhaust turbine and accordingly boosts the power recovered by it. 4) Make full use of heat sources at high temperatures to generate steam; utilize external circulation heat exchangers to produce medium-pressure steam in order to recover the excess heat from the regeneration system, use waste heat boilers to recover as much heat as possible from the regenerated flue gas, and employ the oil slurry circulation system as well as the secondary circulation system in the distillation tower to generate medium-pressure steam by recovering heat from high-temperature sources. 5) Recovery of low-temperature heat: By utilizing hot water circulation, the low-temperature heat from the vapor at the top of the distillation tower, the circulating oil at that location, light diesel, and stabilized gasoline is captured for use in insulation and heating of other equipment or pipelines, as well as for winter heating. 6) Reduce the consumption of circulating water: Arrange the heat exchange processes reasonably, make use of air coolers and seawater coolers as much as possible, in order to reduce the amount of circulating water used. 7) Utilization of scale effects: The processing capacity of this unit is 3.5 Mt/a, which is relatively large; this facilitates energy recovery and optimization. Moreover, a larger scale results in lower heat dissipation costs, as well as higher efficiency for pumps and other equipment. 2. Stable and efficient operation is the guarantee for energy savings and consumption reduction. 1) Operation status of the flue gas compressor-main fan unit: The flue gas compressor is the most important energy recovery device in the plant; its efficient and stable operation is key to reducing the plant’s energy consumption. Therefore, ensuring the long-term operation of the flue gas compressor-main fan unit is a priority in efforts to save energy in catalytic plants. The 3.5 Mt/a heavy oil catalytic unit encountered problems with fouling of the exhaust fan; frequent switching between the main and backup fans due to high fan vibration had a significant impact on the unit’s energy consumption. Taking advantage of the downtime for maintenance, the workshop installed online laser analyzers for catalyst particles at the inlet and outlet of the three cyclones, in order to monitor in real time the concentration of catalyst dust in the flue gas at the inlet of the flue gas extractor. Targeted improvements were made to the first and second stage cyclone systems as well as the third cyclone, thereby completely resolving the technical problem of fouling in the flue gas extractor. This ensured the long-term operation of the flue gas extractor and main fan units, playing an important role in the plant’s energy-saving efforts. 2) Operation status of the waste heat boiler: The operation status of the waste heat boiler has a significant impact on the energy consumption of the catalytic unit. The steam production of a boiler is primarily influenced by the boiler load and its operating cycle. Due to issues such as vibration in the waste heat boiler and leaks in the economizer, some of the flue gas has to be routed through a bypass, which significantly impairs the recovery of heat from the flue gas and greatly increases the energy consumption of the facility. During the shutdown for maintenance of the unit, technical modifications were carried out on the boiler economizer, which completely resolved the vibration problem associated with it. This allowed all of the flue gas to flow into the waste heat boiler, and with the bypass valves fully closed, it contributed significantly to reducing the unit’s energy consumption. If the waste heat boiler can operate at full load for extended periods, significant energy savings can be achieved. 3) Operation status of the slurry system: The operation of the slurry system not only directly affects the thermal balance of the distillation system and the energy consumption of the plant, but also has a direct impact on the long-term operation of the plant. Blockages in the heat exchangers and pipelines of the slurry system not only lead to a significant decrease in steam production but may also result in an emergency shutdown, severely affecting the operation of the plant. 3. Careful operation and optimized management are the key to saving energy and reducing consumption. 1) Optimize the addition of additives to reduce coking volume and ensure the plant operates at full capacity. The operating load of the plant directly affects its energy consumption levels. A high load rate, with the device operating near its design conditions, results in lower energy consumption. With a low load factor, the actual operating point deviates significantly from the design point, and all parts of the device operate at lower efficiency, which increases energy consumption per unit. With **the petrochemical company’s 20 million tons per year crude oil processing capacity being realized, the diversification, heaviness, and inferior quality of raw materials have become more severe. Due to changes in the feedstock, the 3.5 million tons per year heavy oil catalytic cracking unit has gradually encountered difficulties in cracking heavy oil; the contents of the heavy metals Ni and V in the balance agents have reached over 12,000 ppm and 6,000 ppm respectively, resulting in severe contamination of the catalyst by these heavy metals and a gradual decline in its activity. The yield of slurry oil, dry gas, and coke from the unit increased significantly. This results in a lower load on the device. To improve catalyst activity, increase cracking depth, and raise the plant load, the LB-5 catalyst and a cracking additive for the bottom oil of the Converter tower were successively employed, and a bimetallic passivator was used in place of a monometallic passivator. Tests have shown that by adding various additives, the micro-reactivity of the catalyst can be increased by 2–5 units, while the oil slurry yield can be reduced by about 2%; this effectively increases the degree of cracking and enhances the processing capacity of the plant. In addition, catalysts and additives affect the reaction heat that contributes to energy consumption; meanwhile, by influencing the yields of dry gas and hydrogen, they also affect the energy consumption of the plant. The effect of the catalyst on the one-pass conversion rate influences energy consumption through changes in the reprocessing ratio, while the pore structure and pore size of the catalyst affect energy consumption by impacting the stripping efficiency. Therefore, optimizing the addition of catalysts and additives plays a crucial role in reducing the energy consumption of the facility. 2) Optimize the operation of the reaction system to reduce coking. ① Adjust the distribution of steam in the stripping section in a timely manner according to changes in raw materials and operational requirements, thereby improving the stripping efficiency. Optimizing the steam flow rate for material atomization ensures both good atomization of the material and low steam consumption. For a 3.5 Mt/a heavy oil catalytic unit, controlling the atomization steam at around 3% is sufficient to meet the requirements for raw material atomization; in practice, it is strictly maintained at ≤4%. In addition, through technical modifications, the anti-coking steam has been changed from 1.0 MPa as originally designed to 3.5 MPa, with a controlled flow rate of 1.5 t/h, effectively reducing coking at the top of the settler. ②Control the appropriate reaction temperature. If the reaction temperature is controlled too low, it will not be possible to effectively crack the heavier components in the feed oil; this can result in unvaporized oil adhering to the catalyst and causing coking. Excessively high reaction temperatures can lead to intensified thermal cracking and condensation reactions; therefore, controlling the reaction temperature at an appropriate level is crucial for reducing coking. The reaction temperature in a 3.5 Mt/a heavy oil catalytic unit is generally 500–512°C. ③In operation, strive to minimize the reprocessing ratio, keeping it at no more than 0.1, and stop the reprocessing of oil slurry. A lower reprocessing ratio is equivalent to reducing the content of heavy aromatics in the total feed, thereby decreasing the raw materials for the condensation coking reaction. 3) Make good use of the CO combustion aid to ensure complete regeneration, and strictly control the release of CO along with the regenerated flue gas into the atmosphere. The 3.5 Mt/a heavy oil catalytic unit uses a method of adding the material at regular intervals and in fixed quantities; it is specified that at least 8 kg should be added per shift, with the possibility of adding more depending on operational conditions. 4) Increase the steam generation rate from external heat extraction. Timely adjustment of the external heat exchanger to generate as much steam as possible is key to reducing energy consumption. The two external heat exchangers of the 3.5 Mt/h heavy oil catalytic unit are always operated at full capacity, resulting in a total output of medium-pressure steam exceeding 200 t/h, which is crucial for reducing the energy consumption of the entire unit. 5) Adjustment of the opening degree of the flue gas fan inlet butterfly valve and the double-acting slide valve: During normal operation, the opening degree of the double-acting slide valve is kept at its minimum to reduce the exhaust volume through the flue gas fan bypass, thereby recovering as much of the pressure energy of the flue gas as possible. For the 3.5 Mt/a heavy oil catalytic unit, it is specified that as long as a stable regeneration pressure can be maintained, the opening degree of the double-acting slide valve shall not exceed 1%; the power consumption of the exhaust fan is kept as low as possible by adjusting the butterfly valve at the exhaust fan inlet and the main air volume. In winter, the smoke engine can generate 2,000–3,000 kW/h of power, while in summer the power consumption is less than 2,000 kW/h. 6) Operate the waste heat boiler properly to ensure its long-term, full-load operation and to control the flue gas temperature. The flue gas temperature is constrained by sulfur corrosion of the equipment; generally, 180°C is considered an appropriate value for the flue gas temperature. The flue gas temperature of a 3.5 Mt/a heavy oil catalytic unit is generally controlled at 180–200°C. After the vibration problem of the waste heat boiler was resolved, operational measures were taken to ensure that the bypass valve of the waste heat boiler remained fully closed, so that all flue gas flowed into the waste heat boiler. Currently, the superheated steam output of the waste heat boiler is greater than 200 t/h, and the temperature of the superheated steam has increased from 395–400°C to 420–425°C (an increase of 25°C). This allows Unit 1 of the thermal power plant to generate an additional 25.2 million kW of electricity per year, resulting in energy savings of 7,560 tons of standard oil per year. 7) Improve the utilization of heat at low temperatures: By utilizing desalinated water and hot water circulation, the low-temperature heat from the oil and gas at the top of the distillation tower, the recycle oil from that same location, light diesel, the recycle oil from intermediate stages, the product slurry, condensed water, and stabilized gasoline is captured and made available for use by users such as gas distillation units, thermal power plants, and storage and transportation tank areas. This heat can also be used for pipeline insulation and heating in winter. The 3.5 Mt/a heavy oil catalytic unit currently supplies over 900 tons of low-temperature hot water at around 105°C, reducing the unit’s energy consumption by nearly 8 kgEO per ton of feedstock. Having effective low-temperature heat users outside the device is key to the utilization of low-temperature heat. The efficiency of low-temperature heat utilization is an important factor affecting the energy consumption of the system. 8) Make good use of steam; strictly control the use of medium-pressure steam at reduced pressures. It is beneficial for energy consumption to minimize, or even avoid, the use of temperature reducers. For the operation of the air compressor within the unit, its consumption of medium-pressure steam should be minimized, for example by reducing the backflow in the plant. Steam consumption at 1.0 MPa is an important part of the plant’s energy consumption; reducing the amount of steam used can effectively lower the plant’s energy use. For example, by using pre-heated dry gas while ensuring product quality, 4 to 5 tons of steam can be saved per hour, which plays a significant role in reducing the energy consumption of the facility. Strengthen management of steam leaks, emissions, drips, and seepages; additionally, reduce steam waste during anti-freezing measures. 9) Optimization of the slurry system operating conditions: Maintaining a maximum slurry circulation rate allows for an increase in the amount of vapor generated from the slurry, thereby reducing the energy consumption of the plant ； Secondly, it can increase the linear velocity inside the heat exchanger tubes, preventing scaling and blockage in the heat exchanger. Based on the properties of the raw materials and the slurry, maintain a reasonable amount of slurry discharge, and strictly control the slurry density to be no more than 1050 kg/m3. It is necessary to ensure that the temperature at the bottom of the fractionation tower does not exceed 350°C, to control the low liquid level at the bottom of the tower, and to reduce the residence time of the slurry. 10) Recovery of saline condensate: The 3.5 Mt/a heavy oil catalytic unit recovers the wastewater from various steam drums in its thermal system, and sends it to the power plant as saline condensate, at a rate of about 30 tons per hour. This not only reduces the energy consumption of the equipment but also lowers the fresh water usage throughout the plant. 11) Reducing the consumption of circulating water and seawater: The amount of circulating water and seawater used as cooling media within the equipment must be adjusted promptly in response to changes in temperature and operating conditions, in order to maintain the temperature of the return water, control the temperature difference at the inlet and outlet of the cooling equipment, and thereby reduce water consumption. The workshop has established a maintenance record sheet for circulating water and seawater heat exchangers, urging operators to inspect these heat exchangers and take temperature measurements at designated points; any discrepancies in the temperature difference between the inlet and outlet are adjusted promptly. The device’s water seals are all filled with reclaimed water to reduce freshwater consumption. 12) Strengthen the management of desalinated water. First and foremost, it is necessary to control the amount of wastewater discharged from each steam drum; not a single drop of water should be wasted, while at the same time ensuring that the quality of the water in the steam drums remains satisfactory. In addition, all the recovered oil-containing condensate and salt-containing condensate are sent back to the power plant for reuse. 13) Proper use of variable-frequency motors: Due to the variability in raw materials and processing methods, some process parameters can vary significantly; using variable-frequency motors can help reduce power consumption effectively. The 3.5 Mt/a heavy oil catalytic unit is equipped with 11 variable-frequency motors. While making every effort to use variable-frequency pumps, the workshop also strengthens the maintenance of these pumps; should a variable-frequency motor fail and stop operating, it is repaired immediately and put back into use as soon as possible. Although the 3.5 Mt/a heavy oil catalytic unit has low energy consumption, there is still some energy that can be utilized, such as the recovery of turbine exhaust steam, and further optimization is needed. The effort to save energy and reduce consumption is endless; **petrochemical companies will actively employ new catalytic technologies and processes, vigorously promote energy-saving projects, and continue to work towards further improving energy conservation efforts and the level of catalytic cracking technology in our country.