Typical applications of cyclone separation technology in the petrochemical industry
⑴ Oily wastewater cyclone separation technology
Domestic petrochemical companies generally still use the "old" method for sewage treatment "Three sets of" technologies, namely "sedimentation, oil separation - flotation - biochemistry". The advantage of this technology is that the cost is low; the disadvantage is that it occupies a large area, has poor oil-water separation effect, and cannot effectively remove dissolved oil, emulsified oil and dispersed oil in sewage. As the blending ratio of heavy and inferior crude oil continues to increase and the degree of emulsification of oily sewage intensifies, this facility can no longer meet the requirements for clean production.
Oil-water cyclone separation technology is a high-efficiency and energy-saving separation technology developed in the 1980s. The key part is the hydrocyclone, which can separate oil-water mixtures of several microns or more. Compared with other oil removal equipment, hydrocyclones have the advantages of compact structure, small size, light weight, high oil removal efficiency, no moving parts, long service life, closed process and no pollution. Under the same conditions of processing capacity and oil removal performance, its weight is only 1/10 of other oil removal equipment, and its volume is 1/15 of other equipment. The investment in engineering construction is reduced by about 50%. Compared with secondary air flotation, The one-time investment is only 50% of the secondary air flotation (including scum treatment equipment), and the area occupied is only 1/25 of the secondary air flotation. It can be widely used in oily sewage treatment projects in oil fields, refineries, chemicals, machinery and other industries.
Table 7 Comparison between cyclone oil removal technology and other oil removal technologies. Type of oil remover. Cyclone separation API PPI CPI TPI Residence time (min) 2-3 seconds 30 60 90 90 Removal min. Oil droplet size (μm) 5 150 60 30-60 30-50 Import oil content (ppm) 500 1000 1000 1000 1000 Minimum export oil content (ppm) 10 30 10-20 10 10 Floor area (based on API) 1/25 1 1/2 1/3 1/3 Oil removal method Automatic oil draining oil skimming pipe Oil collection pressure difference Automatic oil skimming pipe Automatic oil skimming pipe Automatic plate cleaning No need for regular cleaning Regular cleaning Regular cleaning Fire protection safety measures Fully sealed, Safe with oily smell and fire hazard, water seal, safe plastic cover, safer plastic cover
Safer Note: API: advection grease trap; PPI: parallel plate grease trap; CPI: Corrugated plate type grease trap;
TPT: inclined plate type grease trap, etc.
① Oily sewage from electric desalination device
The oil composition in electric desalination oily sewage is relatively It is complex and its main component is inferior and heavy crude oil that is seriously emulsified. Crude oil is an organic mixture with very complex composition, polarity and phase state. According to the theory of colloidal chemistry, crude oil droplets in sewage are usually divided into four categories: floating oil, dispersed oil, emulsified oil, and dissolved oil according to the size and stability of the crude oil droplets.
From the analysis of the oil morphology of the electrically desalted oily sewage, it is difficult to effectively separate the oily electrically desalted sewage by gravity sedimentation, so a more effective cyclone separation method must be used. The influence of the properties of oily wastewater on cyclone performance includes oil droplet size distribution, wastewater viscosity and temperature, oil-water density difference and other factors.
Figure 11 is a picture of the installation site of sewage cyclone separator equipment for an electric desalination unit in a refinery in our office. Figure 12 is a schematic diagram of the separation process.
Figure 12 Schematic diagram of the cyclone separation process of sewage in electrical desalination equipment
Table 8 Relevant operating parameters and performance index parameters of cyclone separation of electrical desalination oily sewage Parameter numerical operating parameters Inlet pressure Pi MPa >0.40 Inlet temperature t ℃ 30~80 Sewage oil concentration Ci mg/l ~200000 (20%v/v) Oil-water density difference Δρ g/cm3 >50 Performance index processing capacity Q t/h 3~500 (designed as needed) Operating pressure MPa reduction 0.25~0.35 Purified water oil concentration Cu mg/l When inlet Ci <5000: Cu <500
When inlet Ci >5000: separation efficiency >90~95 Waste oil recovery rate % >90 Other structures Materials are selected according to requirements. ② Catalytic cracking unit wastewater treatment
When the wastewater from the catalytic unit exceeds the standard, it will carry a large amount of dirty oil into the raw water tank. Although it has been separated by sedimentation, some of the dirty oil will still enter the sewage stripping device, causing the stripping tower to The operation is disordered and the vapor-liquid phase balance is difficult to restore, which causes the quality of purified water, acid gas, and ammonia to deteriorate, directly affecting the production of downstream devices. Therefore, consider adding oil-water separation facilities to the sewage pipeline to reduce the amount of dirty oil entering the raw water tank.
Process flow and supporting equipment
The basic process flow is shown in Figure 12 and Figure 13.
When the cyclone separation system is working, the liquid from the oil-water separator of the device is pressurized by the centrifugal pump and enters the inlet of the hydrocyclone. The purified water after cyclone treatment is measured by the flow meter and then discharged to the sewage gas. lifting device; the oil-rich liquid coming out of the overflow port flows through the flow meter and returns to the upper part of the oil-water separator of the device. The processing capacity of the cyclone oil-water separator is controlled by the frequency conversion speed regulation of the pump according to the liquid level of the oil-water separator of the device. In addition, the system can also realize a bypass process without using a cyclone.
Figure 12 Sewage separation flow chart with pump 13 Sewage separation process without pump
Technical indicators:
Processing capacity: designed according to needs;
< p>Separator pressure drop ΔP<0.4MPa;Purified water oil concentration <300mg/l or separation efficiency>95.
③ Delayed coking cold coke water (circulation) cyclone degreasing
The coking cold coke water is treated with the cyclone as the center. The basic principle process is shown in Figure 18. The overflow part (dirty oil) returns to the cold coke water tank for cyclic oil removal, and the underflow (water) is cooled to 50°C by the air cooling system and then enters the cold coke water tank.
Technical indicators: The processing capacity can be designed according to needs, the separator pressure drop ΔP<0.4MPa, the oil concentration of purified water <300mg/l or the separation efficiency>90.
④ Pretreatment of overhead water in atmospheric and vacuum units (Figure 15)
Figure 15 Schematic diagram of overhead oil-water cyclone separation process
⑵ Liquid-solid cyclone Separation technology
① Catalyst removal from catalytic cracking oil slurry (liquid-solid separation)
In response to the technical problem of oil slurry catalyst separation, since 1993, China University of Petroleum (East China) has The phase flow separation laboratory has successively carried out research on catalytic oil slurry filtration technology and oil slurry cyclone separation technology. The research results show that for the online separation of FCC oil slurry, hydrocyclone separation is a feasible technical route. Hydrocyclone separation technology is used to separate the catalyst in the oil slurry. The separation efficiency can reach 90%~97%. The separated oil slurry can be used as fuel oil; if the oil slurry needs to be made into high value-added products (such as needle coke, Carbon fiber, etc.), it is necessary to increase the filtration and separation process. The manufacturers with more successful filtration technology mainly include Mott and Pall. However, for oil slurry with high solid content, it is extremely necessary to adopt pre-separation means before the filter. Using hydrocyclone separation technology to pre-separate the oil slurry can greatly extend the backwash cycle of the filter and improve the separation effect of the filter. Extend filter media life.
Figure 16 is a schematic diagram of the hydrocyclone separation process of catalytic oil slurry.
Figure 16 Schematic diagram of FCC oil slurry hydrocyclone separation process scheme
② Residual oil decoking
The heavy oil suspended bed processing technology developed by China University of Petroleum (East China) The new hydrogen technology has reached the world's advanced level. However, it was found from domestic and foreign tests that during operation, the colloid gradually generates coke using fine catalyst particles and other mechanical impurities as carriers. Due to untimely discharge, coke blocks the reactor, which affects the normal operation of the reactor and can Whether solid particles such as coke can be discharged from the system in a timely manner has become a key factor affecting the industrialization and long-term safe operation of the process.
Based on the characteristics of high temperature, high pressure, large flow rate, high solid content, high colloidal asphaltene content and small density difference between the liquid and solid phases of the tail oil of the heavy oil suspended bed hydrogenation cycle, comparative analysis of petroleum Liquid-solid separation methods such as gravity sedimentation, cyclone separation, filtration separation, and electrostatic separation are commonly used in chemical production. The cyclone separation method has the advantages of simple equipment structure, simple process flow, and easy control. In particular, it has good process adaptability and operation The advantage of stability makes it the simplest and feasible technical route. Figure 17 is a picture of the installation of a cyclone (levels 1 and 2) for tail oil decoking in a suspended bed hydrogenation cycle.
a. First-level installation diagram b. Second-level installation diagram
Figure 17 Installation diagram of cyclone for tail oil decoking of heavy oil suspended bed hydrogenation cycle (levels 1 and 2)< /p>
③ Decoking of ethylene quenching oil
The quenching oil slurry produced by the HCC industrial test contains a high content of solid impurities such as catalyst particles. If it cannot be removed in time, the quenching oil slurry system will The solid concentration will continue to increase, which will lead to solid deposition and pipeline blockage, thus affecting the long-term operation and economy of the entire process. Therefore, using appropriate separation technology to remove solids from the oil slurry and reduce the solid content is of great practical significance to ensure the long-term operation of the HCC process. Due to the particularity of the environment in which HCC oil slurry is located: high temperature, high pressure, flammability, and the high viscosity of the oil slurry itself, separation is very difficult.
Figure 18 is the on-site installation diagram of the cyclone separator used for quenching oil, liquid and solid system separation in the "heavy oil contact cracking to directly produce ethylene" process (industrial test)
Figure 18 Heavy oil contact Installation diagram of the cyclone separator for quenching oil decoking in the industrial test of direct pyrolysis to ethylene
④ Used in the pump seal flushing system
Use the hydrocyclone to separate part of the pump outlet The liquid is purified and impurities are removed, and the purified liquid is used in the seal flushing system of the pump. As shown in Figure 19.
Figure 19 Cyclone for pump seal flushing system
⑤Separation of solid and gas-liquid in offshore oil and gas wells
Offshore oil and gas are generally compressed by a compressor. High-pressure transport to land, but because the produced oil and gas will contain some fine sand particles and liquid droplets, it is necessary to set up a gas-liquid or gas-solid separator in the compressor to remove these sand particles and liquid droplets. Its design indicators are:
●Basically remove particles or droplets above 5 μm, and 100% removal of particles larger than 10 μm;
●The total separation efficiency is greater than 98.5%;
●The total pressure drop is not greater than 50kPa.