Problems with the catalytic cracking MIP process

You have already explained what MIP is; the process flow isn’t complicated either – it simply involves adding a widened secondary reaction zone to the original lift pipe, with the catalyst slurry from the stripping section being used to maintain a certain level of catalyst in that secondary reaction zone. In the secondary reaction zone, lower reaction temperatures and longer reaction times are primarily used to enhance hydrogen transfer and isomerization reactions, while secondary cracking reactions are moderately controlled. Under the combined action of secondary cracking and hydrogen transfer reactions, the olefins in gasoline are significantly reduced, while the octane rating of gasoline remains unchanged.

The original post was posted by shd163207 on 2009-1-15 at 12:53. Due to the increasing attention paid to air pollution, China’s Environmental Protection Bureau issued the \"Standards for Controlling Toxic Substances in Automotive Gasoline\" on June 1, 1999; these standards specify the requirements for automotive gasoline. This standard was implemented in Beijing, Shanghai, and Guangzhou starting from July 1, 2000, and across the country on January 1, 2003. The quality specifications for this gasoline stipulate that its olefin content shall not exceed 35 v%, its aromatic content shall not exceed 40 v%, its benzene content shall not exceed 2.5 v%, and its sulfur content shall not exceed 0.08 m%. In China, catalytically cracked gasoline accounts for over 80% of the total finished gasoline, and the olefin content in catalytically cracked gasoline is between 40% and 65%, which results in an olefin content in the finished gasoline that is significantly higher than the requirements set by the new standards for gasoline. Therefore, reducing the olefin content in catalytic cracking gasoline is an urgent and challenging research task for the catalytic cracking process. Therefore, the 1.2 million tons per year catalytic cracking unit at the Yongping Refinery of the Refining and Chemicals Company of China National Petroleum Corporation (Limited) was designed to utilize the mature and reliable engineering technologies of LREC, as well as the new catalytic cracking process for increased isomer production (MIP) developed by the Research Institute of Petrochemical Science (RIPP). This unit combines the advantages of various domestic and international technologies; its main process design is based on the characteristics of the feedstock and the requirements regarding the desired products. It employs a new type of riser reactor to carry out cracking, hydrogen transfer, and isomerization reactions, thereby reducing the content of light hydrocarbons and increasing the content of isoparaffins. The main function of its first reaction zone is to rapidly and thoroughly crack the hydrocarbon mixture to produce light hydrocarbons; therefore, the operation mode in this zone is similar to that of conventional catalytic cracking, namely high temperature, short contact time, and a high oil-to-catalyst ratio ； The main function of the second reaction zone is to convert light hydrocarbons into isoparaffins. Both parallel and sequential reactions occur, and a low reaction temperature facilitates this conversion. Therefore, the operating conditions of this second reactor differ from those used in conventional catalytic cracking processes, namely low reaction temperatures and long reaction times, which help to promote the conversion of light hydrocarbons into isoparaffins and aromatics. Figure 1 Schematic diagram of the new reactor. To achieve reactions in separate reaction zones, the design of the riser includes a conventional reactor and a wider second reactor (as shown in Figure 1). The second reactor is controlled using forced balance regulation; the bed density in the second reaction zone is controlled by adding recycled catalyst outside this reactor and introducing quenching medium to regulate the temperature. The quench medium (crude gasoline or acidic water) system was basically completed by the end of 2003, and successful commissioning took place in 2004. During the trial production while driving the plant, the fluidization in the second reactor of the riser exhibited the following issues: A. At the start of fluidization, the inventory and density in the second reactor increased sharply; the catalyst remained in this reactor, making it extremely difficult to achieve fluidization. B. After material cutting, when the system operates in single-container fluidization mode, the lift pipe experiences severe vibration. Through analysis of the problems that arise during actual operation, as well as through practical mitigation measures, it was determined that there was a gas-solid transport issue in the second reactor. Measures such as adding fluidization rings to this reactor were implemented, which improved its fluidization conditions and eliminated the severe vibration of the lift pipe during single-container fluidization after material cutting. 2.1.1 Existing problems: (1) After multiple cutting operations, once fluidization begins in a single reactor, fluidization occurs in two reactors as well. After the catalyst flows from the first reactor to the second reactor, its density and amount increase significantly, reaching an upper limit of 8.5 tons; meanwhile, no amount is detected in the stripping section, indicating that there is insufficient driving force for catalyst fluidization, causing it to remain in the second reactor. (2) On May 10, 2004, after the material was cut off by the device, the lift pipe experienced severe vibration accompanied by noise. 2.1.2 Cause analysis: (1) Reason for vibration: The total weight of the lift pipe and the secondary reactor is 100–200 tons; such significant vibration cannot be caused by thermal stress or internal forces from systems such as the reactor grids. Upon careful observation on site, it was found that the steam pressure at 1.0 Mpa dropped to 0.35 Mpa due to material cutting, and the steam pressure gauge located at the bottom of the lift pipe fluctuated between 0.1 and 0.35 Mpa as the lift pipe vibrated ； Furthermore, analyzing the sounds inside the reactor: there was first a loud noise, followed by a sound similar to that of water falling, along with vibrations. Since there was only catalyst inside the lift pipe, it can be inferred that the cause of the vibrations was the impact of the catalyst. Why could it cause such severe vibrations? As shown in Figure 2, due to the improper sealing of the external circulation plug valve, the dense-phase bed in the secondary reactor gradually accumulates catalyst. There are 120 DN80 holes in the grating of the secondary reactor; as the catalyst becomes increasingly compacted, the steam pressure used for lifting drops to 0.35 Mpa. With insufficient lifting force, it is not possible to break through the dense-phase bed. Once the steam pressure at the lower level reaches 0.35 Mpa, it manages to break through the dense-phase bed, resulting in a “**” phenomenon. After the catalyst is lifted, the steam pressure drops rapidly to 0.1 Mpa, causing the fluidization to stop and the catalyst to fall back onto the grating of the secondary reactor. This repeated process of lifting and falling leads to the occurrence of vibrations and noises. The specific analysis is as follows: P1 remains at 0.35 Mpa, while P2 rises to 0.35 Mpa; the catalyst on the baffle in the second reactor breaks through the material seal. P3 becomes 0 Mpa due to the cessation of fluidization (at this point, fluidization occurs only within a single container). Once the catalyst is displaced, P2 drops rapidly, and the catalyst settles back inside the second reactor; this process generates vibrations and noises. After the catalyst settles back, a new material seal is formed on the baffle of the second reactor, and P2 goes through another pressure buildup process. This results in periodic P3 vibrations. (2) Reasons for the failure of fluidization in the second reactor: After material cutting or bed clogging, external heat removal and the decrease in vapor generation from the oil slurry lead to a reduction in the total steam pressure to 1.0 Mpa. When attempts are made to restart fluidization, there is no upward flow of feed oil and gas. The catalyst, accelerated by the pre-elevation section, overcomes the resistance posed by the grid in the second reactor; as a result, V3 drops to 0 m/s, preventing the formation of a linear flow. This leads to backmixing within the second reactor, with the catalyst falling back onto the grid, thereby increasing its density and volume. In the end, fluidization in V1 becomes impossible. Figure 3 Schematic diagram of pressure and flow velocity distribution. 2.1.3 Solution: Due to insufficient lifting force, a remedial plan was proposed during the major maintenance of the unit in September 2004, which involved adding a steam fluidization ring at the lower part of the second reactor in order to increase the force for fluidizing the catalyst within that reactor. Based on calculations, the designed flow rate of steam for fluidizing the second reactor is 0–5 t/h. To ensure proper fluidization and prevent coking when the unit is operating normally, orifice plates (Φ10 mm) are used to maintain unobstructed flow. The steam used is superheated steam at a pressure of 1.0 Mpa and at a temperature of 400–500°C. The designed process flow and the fluidization mechanism for the second reactor are shown in Figures 4 and 5. Figure 4: Process flow diagram. Note: The pipeline has a diameter of Φ89×4.5 mm, and the flow rate can be adjusted between 0–5 t/h. The orifice plate is installed in a pipeline with a diameter of Φ45×3.5 mm; the orifice plate itself has a diameter of Φ10 mm, and the flow rate through it is 500 kg/h. There are 12 nozzles distributed evenly, as detailed in Figure A. Figure 5: Diagram showing the fabrication of the fluidization ring. Note in Figure A: (1) The nominal diameter of the ring pipe is DN80, with a wall thickness of 4.5 mm. (2) The material is 0Cr18Ni9Ti. (3) All butt welds shall be subject to radiographic inspection in accordance with JB4730—94, and no defects are allowed. (4) This diagram is a schematic; the unit of measurement is mm. (5) Process it into two sections and assemble them on-site during installation. 3. Effects
3.1 This fluidization ring was installed during the major maintenance of the unit in September 2004, and it was put into operation on September 23, 2004. When fluidization of the two reactors began, two tests were conducted; the results are shown in Table 1:
Table 1: Comparison Table of Fluidization Tests
First Test Second Test
Reagent valve opening percentage % 30 30
Steam for lifting, t/h 5.6 5.3
Steam for raw material atomization, t/h 9.8 9.5
Steam for fluidizing the second reactor, kg/h 800 2000
Density of the second reactor, kg/m³ 316 186
Capacity of the second reactor, t 8.5 2.35
Outside valve opening percentage % 0 0
Pressure difference between the two reactors, Mpa 40 40
Effects Non-fluidization Fluidization
3.2 After the unit began to fluidize properly, the steam flow rate through the orifice plate was 500–600 KG/H, and this did not affect the fluidization of the lift pipe nor the quality of the product. The comparison of the effects is shown in Table 2 (data from “Calibration Report for the Second Set of Atmospheric Pressure Catalytic Cracking Units”, Engineering Research Institute of Sinopec Luoyang Petrochemical Engineering Company, November 15, 2004):
Table 2: Comparison of Fluidization and Product Quality
Before renovation After renovation
Outside valve opening percentage % 22 18
Density of the second reactor, kg/m³ 153.8 143.1
Capacity of the second reactor, t 2.5 1.87
Outlet temperature of the second reactor, °C 485.6 489.6
Pressure drop in the lift pipe, kPa 83 73.7
Hydrocarbon content in gasoline, v% 34 38.5
Octane number of gasoline, RON 90.6 91.7
4. Conclusions
Through this technical renovation (the design process was guided and approved by Jin Changyou from the Engineering Research Institute of Sinopec Luoyang Petrochemical Engineering Company), the problems of difficult fluidization when the second reactor started operating and vibration in the lift pipe during single-reactor operation were resolved. This renovation had no negative impact on the fluidization of the lift pipe or the quality of the product. The technical improvements met the expected goals, and these findings can serve as a reference for similar MIP systems.

Upvote for floor 3, it’s very comprehensive. The specific advantages and disadvantages of each process depend on the conditions of the original equipment and the overall objectives of the refinery.

The main goal is to increase the production of liquefied gas and raise its yield, which can generally reach around 20%.

The design is good, but the olefins in gasoline decrease; the olefins in liquefied gas also drop, and even the yield of liquefied gas decreases as a result. In practice, there is more coking, overall losses increase, and the liquid yield declines. The only advantage is that the gasoline has a higher octane rating

Goals of the MIP-CGP process: 1. Reduce the olefin content in gasoline to <18%； 2. Increase the LPG yield to over 20% ； 3. Increase the propylene yield to 8% ； 4. Reduce the sulfur content in gasoline by about 30%.

Our company’s heavy oil catalytic cracking uses MIP

Put simply, it’s similar to stir-fried pork with return-to-the-pan technique. In the past, the old FCC method was like simply boiling plain pork; now, on top of that, the temperature is lowered and the pork is stir-fried, which naturally results in a better taste compared to plain boiled pork. It’s particularly suitable for the taste of Chinese people. The process is simple and effective. The dual lift pipes are remnants discarded by UOP, deemed to have no future, and were picked up by people in China (from the Petroleum University). It’s like taking the pig skin from pork that has been boiled until it’s tender, and then boiling it separately for a while. Cut it off along with the white meat. Of course, this process takes a lot of firewood and time. So, domestic manufacturers find it costly and troublesome. So, if Zhuge Liang exists, what’s the need for Zhou Yu?

The characteristic of the MIP reactor is that it divides the reactor into two reaction zones. The first reaction zone is primarily for cracking and lightening, while the second one involves processes such as translocation, isomerization, and aromatization ； The olefin content in gasoline can be reduced by 10–20 percentage points, with the octane rating remaining essentially unchanged.

Many advantages of MIP have been mentioned; the use of MIP or MIP-CGP technology increases the production of liquefied gas and gasoline, but it reduces the production of dry gas and diesel. In particular, the quality of diesel is very poor, with a very low cetane number, and the diesel produced through hydroprocessing does not meet the requirements of National Standard 3 or National Standard 4, so it can only be used in blended fuels.

What was said on the 2nd floor is concise and to the point; I agree.