In catalytic reactions such as catalytic cracking and hydrocracking, the fine catalyst powder in the product slurry will not only cause corrosion and blockage of downstream equipment but also limit and reduce its application fields and economic value directly as products and by-products.
For the low-temperature Fischer-Tropsch synthesis reaction, separating the Fischer-Tropsch synthetic wax from the gas-liquid-solid three-phase slurry-bed reactor is one of the technical difficulties and key points of the entire Fischer-Tropsch synthesis process.
It can be seen that the selection of oil slurry separation and purification technology is related to the stable operation of the above catalytic reaction and product quality.
Oil slurry is a product with high relative density and high viscosity produced in the chemical production process such as petroleum refining and chemical production. Since most of the production uses catalytic reactions, the oil slurry has a large solid content (mainly fine catalyst particles), which leads to corrosion of downstream equipment And clogging, to a large extent, also limits and reduces the application field and economic value of oil slurry directly as products and by-products.
Application Advantages Of Slurry Filtration Technology
At present, the separation of oil slurry can generally adopt the methods of sedimentation, filtration, electrostatic and centrifugal separation.
Gravity sedimentation and centrifugal separation are the original traditional liquid-solid separation methods, but they have problems such as poor separation effect, small processing capacity, and large equipment investment.
Among them, gravity sedimentation requires a large number of storage tanks, which increases equipment and operating costs, although it is possible to consider adding sedimentation aids to improve sedimentation efficiency.
However, the addition of additives will increase the cost of cleaning and subsequent re-separation.
Therefore, the above two separation methods are not suitable for large-scale industrial applications and are currently often used in the liquid-solid separation process in laboratories.
Although electrostatic separation has a better separation effect in foreign applications, its equipment is complicated to operate, large in investment, high in operation and maintenance costs, and poor in adaptability and stability.
In addition, the operating temperature of electrostatic separation is low, and the catalytic cracking oil slurry is mostly 280-320°C. The raw oil slurry needs to be cooled before separation, which causes energy waste and loss.
This technology has the characteristics of the small size of separable solids, high separation efficiency, simple equipment and operation, low investment, low operating cost, compact equipment, and small area.
Due to its outstanding separation performance and economic advantages, filtration technology has been successfully applied to the separation of oil slurry in the refining and chemical processes such as catalytic cracking and hydrocracking. It is currently the most widely used oil slurry separation method in the world.
In addition, filtration technology also has industrial applications in the gas-liquid-solid separation of Fischer-Tropsch synthesis reactors.
Industrial Application Of Oil Slurry Filter Element
The filtration separation method uses a wedge wire screen to intercept and separate the solid catalyst particles in the oil slurry. By changing the size of the gap, it is possible to filter fine powders with different particle size requirements.
Choosing effective filter materials and backwashing methods are the key to filtration. According to the different materials of filter elements currently used in industrial applications, the filtration technology can be divided into sintered metal powder filtration and wedge wire filter.
The wedge wire filter adopts a continuous slit structure, which has good thermal conductivity and toughness.
It also has good processing and welding performance, can be used under high temperature and high-pressure conditions, has good thermal shock resistance, is easy to clean and regenerate, and the gap is usually 10 to 1000 μm.
The research and development of these two types of filters have been quite mature, and they have been used in processes such as catalytic cracking oil slurry, coking heavy wax oil, hydrocracking, low-temperature Fischer-Tropsch synthetic oil slurry separation, and fixed-bed reactor protection worldwide. Continuously try to apply it to other slurry filtration systems.
The HyPulse filter was developed by the American MOTT company, using AISI 316 porous sintered metal powder with a pore size of 0.5 μm as the filter element, and the filter material was provided by the American Bekaert company.
The filter has two models, HyPulseLSI and HyPulseLSM. The difference lies in the flow direction of the filtered slurry in the metal tube bundle. The HyPulse LSM filter is more suitable for the recovery and filtration of nickel-based and other high-density, expensive catalysts.
The first industrial HyPulse LSI filter was used in high-temperature slurry filtration in the carbon fiber production process in 1985, and since the 1990s has been widely used in catalyst filtration in catalytic cracking process.
The gas-assisted flushing filtration technology developed by the Dutch Dahlman Industrial Group uses sintered metal as the filter element, and the entire device is skid-mounted. The main equipment of the system includes 2 to 3 sets of filters, backwash liquid receiving tanks, and gas storage tanks.
The filter realized industrial application in 2004, and the first industrial unit was used for the separation of FCC slurry to protect the catalyst bed in the downstream LC-Fining hydrocracking process. It has been successfully applied to the oil slurry separation process of large refineries such as Axens, CLG, UOP, Shell, ConocoPhillips, etc.
The system adopts a cross-flow filtration method from the inside to the outside. The filter cake is formed on the inner wall of the pipe during filtration. When the filter pressure difference reaches the set value, the raw material inlet and the filtrate valve are closed, and the gas from the gas buffer tank pressurizes the filter. , After the pressure is over, quickly open the discharge valve at the bottom of the filter to form a reverse flow from outside to inside in the filter, so as to achieve the effect of cleaning the filter cake
Sintered Wire Mesh Filter
Sintered metal wire mesh is made of multilayer metal woven wire mesh as raw materials and prepared through special laminate design, composite pressing, and vacuum sintering processes.
The traditional sintered wire mesh has only one fine filter, which will be worn and damaged after long-term use. In order to improve the filtering effect and prolong the service life of the filter, several layers of wire mesh can be laminated together, which is divided into a protective layer and a filter layer. , Support layer and other functional layers.
By fusing and bonding at the weaving point of the warp and weft of the wire mesh, its rigidity and strength are increased, the anti-deformation ability of the filter element is improved, and the shortcomings of ordinary wire mesh such as low filtration accuracy and easy abrasion are also improved.
The Dynapore filter in the United States adopts the design concept of a gradual increase in weaving density. Multilayer wire meshes that can achieve different functions such as filtration, fluid distribution, and support are forged together, which effectively intercepts solid particles and reduces the risk of clogging.
Currently, the filtering technologies that have successfully implemented industrial applications include the American Pall filter, the ReactoGard filter, and the Italian ACR filter. These manufacturers have made innovations in filter element design, layout, and technology in combination with specific processes.
The backwash filtration technology developed by the Pall Company of the United States was used in the hydrogenation process at the beginning of its research and development. Since the 1980s, it has been used for the separation of catalytic cracking slurry and has been widely recognized. It has been successfully applied to protect the fixed-bed catalytic Reactor and improve other refining and chemical processes such as hydrocracking reactions.
Pall filters can meet the filtration requirements of different solid content by selecting different filter media. The filter element used in the catalytic cracking process is a multi-layer Rigamesh K woven sintered stainless steel mesh, a woven mesh sintered in a high-temperature vacuum furnace, and the filter holes are firm. It is not easy to deform, the filter pores are evenly distributed, and a more uniform filter cake can be formed. The filtration efficiency is high. The void ratio and filtration areas are 7 times and 2 times that of wedge filtration, respectively.
Pall filter adopts cross-flow filtration from outside to inside and gas pulse backwashing process. The viscosity of the imported oil slurry is required to be 0.8×10–3～4×10-3Pa·s, and the solid content in the backwash filtrate can be as high as 30% ( Mass fraction). Because the oil slurry contains asphaltenes, it is necessary to add solvent soaking during the backwashing process to fully regenerate it.
The ACR (automatic counter-wash refining) filter is developed and manufactured by the Italian FILTREX company. It is currently used in large refineries in the United States, Italy, India, and other regions, and is mainly used for coking heavy wax oil filtration and vacuum wax oil filtration.
The filter adopts a cross-flow filtration and liquid backwashing system from inside to outside, and the washing liquid can be filtered slurry or introduced into the external liquid.
Eaton and UOP jointly developed the ReactoGard filter system. At the beginning of its research and development, it was used for the filtration of catalytic cracking feed oil to protect the fixed-bed catalyst bed from being blocked. It was the first in the world to be used for feed oil filtration. The automatic backwash filter has been developed for the fifth generation and has been successfully used in more than a hundred separation processes such as fixed bed catalyst protection, catalytic cracking oil slurry filtration, and atmospheric and vacuum residue filtration.
The filter is composed of multiple filter tubes. The upper ends of all filter tubes are fixed by tube plates. There are 3 configurations of 8, 19, and 28. The filter surface area provided by each configuration is 0.6m2, 1.4m2, and 2.0. m2.
According to customer needs, the filter element can be selected from 2-40μm metal woven mesh or 23-50μm slot wedge wire mesh. Slot wedge wire screens are suitable for filtering high solids, heavy and corrosive materials, and are used to filter solid particles that block the catalytic bed of the fixed bed during the hydrogenation process.
Due to the severe damage of the catalyst and the relatively high residue, the relatively high content of colloid and asphaltene in the oil slurry of domestic petrochemical plants results in poor quality of the oil slurry.
Therefore, even if the foreign mature filtration technology is used, there will still be frequent filter switching and reduced filter life, and the clogging problem has not been fundamentally solved.
At present, to solve the problem of filter clogging, one method is to add a pre-filter on the basis of the original process. After adding a pre-filter with a wedge wire as the filter element, the solids removal rate can be maintained at about 98%, which effectively reduces the second The filtering load of the level filter.
Another method is to install a cyclone before the filter as a pre-separator.
After the catalytic cracking oil slurry is separated by filtration, it can be further processed through delayed coking, hydrocracking, thermal cracking, solvent extraction, and other processes to produce chemical products with high added value.
Such as carbon black, needle coke, asphalt and modifiers, rubber softeners and fillers, thermal oil, and so on.