Ma Qilin (Daiqing Petrochemical Company Plastics Factory, Daqing 163714, Heilongjiang)
The low-pressure polyethylene plant of Daqing Petrochemical Company Plastics Factory is a complete set of equipment imported from Japan. It has three production lines and was put into production in 1986. Each production line produces 70,000 tons of polyethylene per year. The centrifuge is the key equipment on the device. Its function is to separate the plastic powder generated by the polymerization reaction from the hexane. After the plastic powder is dried, it is put into the artificial particle system to produce plastic granules, which are recycled and reused. The centrifuge is a horizontal structure with mechanical seals and a short service life. To solve this problem, our factory cooperated with Chengdu Yitong Technology Co., Ltd. to change the double-end mechanical seal to dry gas seal and achieve success. The effect is very good.
1 Centrifuge working principle The working principle of the centrifuge is shown in Figure 1.
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The mixture of plastic powder and hexane continuously enters the machine through the feed pipe 7, and enters the drum through the discharge port of the inner cylinder of the screw conveyor 5. Under the action of centrifugal force, the mixture forms a ring flow in the drum, plastic The powder settles on the inner wall of the drum 4 under the action of centrifugal force. Due to the differential action of the differential 2, a relative movement between the screw conveyor and the drum is formed, and the plastic powder is pushed to the small end of the drum. The outlet is discharged; the liquid phase hexane forms an inner ring, and the depth of the annular liquid layer is adjusted by the overflow baffle at the big end of the drum, and the separated liquid is discharged through the overflow hole, and the sediment (ie, plastic powder) and the hexane liquid are separately collected. In the powder and liquid compartments in the casing 3, the casing is unloaded by gravity.
2 Improvement of mechanical seal The centrifuge adopts the traditional mechanical seal. The advantage of mechanical seal is that the structure is simple, the technology is mature, and the processing precision is not high. The disadvantage is that the service life is short, the power consumption is large, and the liquid medium must be used to lubricate the sealing surface. Cooling, the fluctuations in the parameters of the production process have a great impact on the seal. Since the centrifuge was put into production, the service life of the mechanical seal has been very short, and the length of the Zui is only 5 months. It takes 28 hours to replace the mechanical seal, which seriously affects the output. Moreover, the mechanical seal (referred to as the machine seal) leaks after the hexane liquid, hexane is a flammable, explosive medium, not only has significant safety hazards, but also causes serious pollution to the environment. Based on this, we decided to change it to dry gas seal to improve economic efficiency and eliminate safety hazards. Dry gas seal is a kind of non-contact seal form advanced by Zui. It consists mainly of rotating ring, static ring, sealing ring, spring, spring seat and bushing.
The rotating ring sealing surface is ground and polished, and a fluid dynamic pressure groove is machined thereon, as shown in Fig. 2. When the dry gas seal rotating ring rotates, the sealing gas is sucked into the dynamic pressure groove. Due to the throttling action of the sealing weir, the gas entering the sealing surface is compressed, and under the action of the gas pressure, the sealing surface is pushed away, and the flowing gas A thin film is formed between the two sealing faces, and the thickness is 3~5um. When the combined force of the gas static pressure and the spring force is equal to the gas film reaction force, the film thickness is very stable, thus ensuring the seal. Reliability.
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Through the analysis of the structure of the centrifuge, we decided not to change the structure of the equipment, and adopted a double-face dry gas seal. The size is the same as the original seal size, and the structure is similar and easy to install, as shown in Figure 3. Considering that the process medium has plastic powder, the sealed chamber is cleaned with clean hexane. The dry gas-tight dynamic pressure groove is processed on the end face of the moving ring, and the moving ring is made of tungsten carbide (WC) material, which has the advantages of high surface hardness, good wear resistance and large thermal conductivity; the static ring is made of impregnated graphite material, which has High strength, good self-lubricating performance and high temperature resistance.
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The sealing gas is nitrogen, which is supplied by the external network. The high pressure of Zui is 0.7MPa, the normal working pressure is 0.5-0.6MPa, the low pressure of Zui is 0.4MPa, and the nitrogen flow rate is greater than l0 standard m3/h.
The nitrogen gas of 0.7 MPa passes through the filtration unit, is depressurized to 0.5 MPa, and enters the sealed chamber through the flow meter. In order to prevent the nitrogen pressure fluctuation in the pipe network, a nitrogen gas bottle is used as an emergency backup gas source, and the standby gas source is available for gas for 2 hours. The dry gas seal leakage is indicated by the flow meter. During normal operation, the nitrogen leakage is kept within a stable range. If the leakage amount continues to increase, the pressure in the sealed chamber will decrease. When the pressure åž drops to 0.3 MPa, the interlock will stop. To ensure the safety of the centrifuge. From the actual operation situation, when the nitrogen pressure is 0.5MPa, the good operation can be guaranteed. At this time, the nitrogen consumption is 0.48 standard m3/h, which is smaller than the designed standard m3/h.
3 Installation Precautions We installed the dry gas seal on the centrifuge for the first time in May 2002. After 15 days of operation, the seal failed and leaked. The machine seal was removed and found to be intact on the feed side, while at the discharge end (differential speed) The side of the device is very worn. The reason is that the machine seal is installed at normal temperature, generally around 20 ° C, and the temperature is 80 ° C in the production process. Due to the temperature difference of 60 ° C, a thermal expansion of 1.5 mm is generated in the axial direction, and the shaft is on the feed side. Positioned, there is axial displacement on the discharge side, and the dry gas seal is fixed on the shaft, thus causing the dry gas seal of the end face to fail. The solution is to reserve 1.5mm of the machine seal first, and when it reaches 80 °C, it just compensates for the amount of thermal expansion. After solving the effects of thermal expansion, it worked well and there has been no problem since June 2002.
4 Summary In general, dry gas seals are applied on clean media and dry gas seals are applied to centrifuges. This is the first time in our country and has been successful, providing good dry gas seals for other similar process conditions. Learn from. In June 2004, we changed the other two centrifuges into a thousand gas seals, which worked well and achieved good economic benefits.
The low-pressure polyethylene plant of Daqing Petrochemical Company Plastics Factory is a complete set of equipment imported from Japan. It has three production lines and was put into production in 1986. Each production line produces 70,000 tons of polyethylene per year. The centrifuge is the key equipment on the device. Its function is to separate the plastic powder generated by the polymerization reaction from the hexane. After the plastic powder is dried, it is put into the artificial particle system to produce plastic granules, which are recycled and reused. The centrifuge is a horizontal structure with mechanical seals and a short service life. To solve this problem, our factory cooperated with Chengdu Yitong Technology Co., Ltd. to change the double-end mechanical seal to dry gas seal and achieve success. The effect is very good.
1 Centrifuge working principle The working principle of the centrifuge is shown in Figure 1.
The mixture of plastic powder and hexane continuously enters the machine through the feed pipe 7, and enters the drum through the discharge port of the inner cylinder of the screw conveyor 5. Under the action of centrifugal force, the mixture forms a ring flow in the drum, plastic The powder settles on the inner wall of the drum 4 under the action of centrifugal force. Due to the differential action of the differential 2, a relative movement between the screw conveyor and the drum is formed, and the plastic powder is pushed to the small end of the drum. The outlet is discharged; the liquid phase hexane forms an inner ring, and the depth of the annular liquid layer is adjusted by the overflow baffle at the big end of the drum, and the separated liquid is discharged through the overflow hole, and the sediment (ie, plastic powder) and the hexane liquid are separately collected. In the powder and liquid compartments in the casing 3, the casing is unloaded by gravity.
2 Improvement of mechanical seal The centrifuge adopts the traditional mechanical seal. The advantage of mechanical seal is that the structure is simple, the technology is mature, and the processing precision is not high. The disadvantage is that the service life is short, the power consumption is large, and the liquid medium must be used to lubricate the sealing surface. Cooling, the fluctuations in the parameters of the production process have a great impact on the seal. Since the centrifuge was put into production, the service life of the mechanical seal has been very short, and the length of the Zui is only 5 months. It takes 28 hours to replace the mechanical seal, which seriously affects the output. Moreover, the mechanical seal (referred to as the machine seal) leaks after the hexane liquid, hexane is a flammable, explosive medium, not only has significant safety hazards, but also causes serious pollution to the environment. Based on this, we decided to change it to dry gas seal to improve economic efficiency and eliminate safety hazards. Dry gas seal is a kind of non-contact seal form advanced by Zui. It consists mainly of rotating ring, static ring, sealing ring, spring, spring seat and bushing.
The rotating ring sealing surface is ground and polished, and a fluid dynamic pressure groove is machined thereon, as shown in Fig. 2. When the dry gas seal rotating ring rotates, the sealing gas is sucked into the dynamic pressure groove. Due to the throttling action of the sealing weir, the gas entering the sealing surface is compressed, and under the action of the gas pressure, the sealing surface is pushed away, and the flowing gas A thin film is formed between the two sealing faces, and the thickness is 3~5um. When the combined force of the gas static pressure and the spring force is equal to the gas film reaction force, the film thickness is very stable, thus ensuring the seal. Reliability.
Through the analysis of the structure of the centrifuge, we decided not to change the structure of the equipment, and adopted a double-face dry gas seal. The size is the same as the original seal size, and the structure is similar and easy to install, as shown in Figure 3. Considering that the process medium has plastic powder, the sealed chamber is cleaned with clean hexane. The dry gas-tight dynamic pressure groove is processed on the end face of the moving ring, and the moving ring is made of tungsten carbide (WC) material, which has the advantages of high surface hardness, good wear resistance and large thermal conductivity; the static ring is made of impregnated graphite material, which has High strength, good self-lubricating performance and high temperature resistance.
The sealing gas is nitrogen, which is supplied by the external network. The high pressure of Zui is 0.7MPa, the normal working pressure is 0.5-0.6MPa, the low pressure of Zui is 0.4MPa, and the nitrogen flow rate is greater than l0 standard m3/h.
The nitrogen gas of 0.7 MPa passes through the filtration unit, is depressurized to 0.5 MPa, and enters the sealed chamber through the flow meter. In order to prevent the nitrogen pressure fluctuation in the pipe network, a nitrogen gas bottle is used as an emergency backup gas source, and the standby gas source is available for gas for 2 hours. The dry gas seal leakage is indicated by the flow meter. During normal operation, the nitrogen leakage is kept within a stable range. If the leakage amount continues to increase, the pressure in the sealed chamber will decrease. When the pressure åž drops to 0.3 MPa, the interlock will stop. To ensure the safety of the centrifuge. From the actual operation situation, when the nitrogen pressure is 0.5MPa, the good operation can be guaranteed. At this time, the nitrogen consumption is 0.48 standard m3/h, which is smaller than the designed standard m3/h.
3 Installation Precautions We installed the dry gas seal on the centrifuge for the first time in May 2002. After 15 days of operation, the seal failed and leaked. The machine seal was removed and found to be intact on the feed side, while at the discharge end (differential speed) The side of the device is very worn. The reason is that the machine seal is installed at normal temperature, generally around 20 ° C, and the temperature is 80 ° C in the production process. Due to the temperature difference of 60 ° C, a thermal expansion of 1.5 mm is generated in the axial direction, and the shaft is on the feed side. Positioned, there is axial displacement on the discharge side, and the dry gas seal is fixed on the shaft, thus causing the dry gas seal of the end face to fail. The solution is to reserve 1.5mm of the machine seal first, and when it reaches 80 °C, it just compensates for the amount of thermal expansion. After solving the effects of thermal expansion, it worked well and there has been no problem since June 2002.
4 Summary In general, dry gas seals are applied on clean media and dry gas seals are applied to centrifuges. This is the first time in our country and has been successful, providing good dry gas seals for other similar process conditions. Learn from. In June 2004, we changed the other two centrifuges into a thousand gas seals, which worked well and achieved good economic benefits.
We have not only conventional Honey but also Organic Honey, which have certified by BCS German. The main type is Organic Polyflora Honey, Organic Acacia Honey and Organic Vitex Honey, which come from the northeast of China and Northwest of China. We supply transaction issued by BCS GERMAN for each lot when export.
Organic Honey
Organic Polyflora Honey,Organic Acacia Honey,Organic Vitex Honey,Bee Honey,Vitex Honey
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