Analysis of Causes for Blockage of Outlet Valve in Flash Tank of Polypropylene Unit

Industrial Technology Synthetic Resins and Plastics, 200 〖〗 18 (Analysis of Causes for Blocking of Outlet Valves in Flash Tanks of Polypropylene Units Yang Ai-Xin (Jingmen Petrochemicals K-total R-Polypropylene from Polyene Slurry when W. Cycloquine/2GS Equipment Lil's original idle analysis r polyene '1: production I: art flash tank; 1! material valve 1: cold plug / a polypropylene device using the Italian Himont's Spheripol loop liquid phase bulk method With advanced technology, reliable technology and high degree of production automation, the company can produce 25 grades of polypropylene resin.At the beginning of this device, the flash tank discharge valve (LV301) often blocked, resulting in extremely abnormal production. The emission of propylene from the exhaust system to the torch burns caused huge economic losses.After a period of research and practice, the cause of the LV301 blockage was identified and a treatment method was proposed.

1 Introduction to the process The process of the device is: a prepared main catalyst. The co-catalyst and the electron donor are mixed and activated in a catalyst mixing tank and then passed into the pre-polymerization reactor through the refined - part of the propylene to be pre-polymerized into the loop reactor and reacted with another part directly into the loop. The propylene polymerization produces polypropylene. The slurry from the reactor enters the flash tank for flash evaporation; the vaporized propylene enters the recovery system from the top of the flash tank and the powder enters the bag filter from the LV301 for low pressure degassing. After the propylene-removed polypropylene powder is steamed and dried, it is extruded into a granulation section.

It can be seen that the role of LV301 in the entire process flow is extremely important. The ability of LV301 to work properly directly determines the continuity of production, the stability of subsequent stage operations, and the quality of products.

Causes of 2LV301 plugging 2.1 Polypropylene slurry stays in the flash tank for too long The main catalyst currently used in this device is the domestic N-type catalyst. Experiments show that the active life of N-type catalyst is greater than 6h, the highest activity up to 80kg/g. In actual production, the residence time of the catalyst in the reactor is about 1.5h. According to data reported, 1.5h can only make N-type catalyst About 1/3 of the activity is released. At the same time, according to the process requirements, the slurry from the reactor outlet valve to leave the LV301 takes about 40s. Due to a short time, the catalyst activity is not released, generally does not cause agglomeration, clogging. However, in actual production, due to some factors that will cause the reactor discharge valve, the LV301 opening degree constantly changes, so that the residence time of the slurry also changes accordingly. When the opening of the LV301 is small, the residence time of the polypropylene slurry in the flash tank is prolonged, the catalyst is activated again, and the propylene and the catalyst are polymerized in the flash tank, and a large amount of heat is released, resulting in the production of Polypropylene powder agglomerates and then plugs LV 301: 2.2 Reaction fluctuations in the loop reactor In the loop reactor, plasticized blocks are generated due to reaction fluctuations. Although the agitating action of the axial flow pump does not form a large block, the small block material will cause the discharging valve to discharge poorly. When the material discharge is smooth by increasing the opening degree of the discharge valve, small pieces of material will inevitably enter the flash tank through the flash line. If it cannot be discharged in time, it will accumulate at the bottom of the flash tank and eventually form a Large blocks, thus blocking LV301. Further analysis shows that the reasons for the reaction fluctuations in the reactor are: (1) The temperature of the catalyst mixing tank fluctuates greatly. The temperature of the catalyst mixing tank is mainly controlled by the volume of chilled water in its jacket, and the chilled water is provided by the ice machine in the device: When the device collects the date: 2000, the chemical engineering department is specialized in polymer chemicals, and is mainly engaged in the production and management of polypropylene. The post-processing research, now the Master of Materials Engineering of Tianjin University - When the demand for synthetic resin and plastic chilled water changes, the chilled water temperature will change, which will cause the temperature of the catalyst mixing tank to change, making the catalyst mix uneven, and the main catalyst cannot be uniformly activated. As a result, prepolymerization results in poor results and the polymerization reaction is not uniform. (2) The temperature and pressure of the loop reactor fluctuate. (3) Change in concentration.

2.3 The inner wall of the flashing pipeline is not smooth The polypropylene slurry from the reactor stays and accumulates at some burrs and grooves on the inner wall of the flashing pipeline and gradually forms a plasticized block. When the plasticization block becomes larger and the slurry is brought into the flash tank, the final blockage 3 measures to prevent LV301 blockage It can be seen from the above analysis that in order to prevent LV301 blockage, there are mainly the following measures: (1) In strict accordance with operating conditions (2) strictly monitor the temperature of the catalyst mixing tank; (3) increase the temperature of the catalyst mixing tank and prepolymerization reactor; (4) periodically switch the reactor discharge valve and LV301 once Fluctuates the flow of material and removes the block material.

4LV301 blockage processing method In the production, once LV301 blockage occurs, the following steps can be taken to deal with: (1) the flash tank, bag filter outlet tangential discharge system; (2) open the low pressure discharge tank jacket steam; (3 ) Close the connection valve between the flash tank and the propylene scrubber; (4) Relieve the flash tank to the flare system; (5) Reverse the top of the LV301 by the pressure of the small flash line; (6) If the flash tank material If there is no change in position, the feed system for the catalyst and hydrogen is turned off, the reaction pressure of the loop is reduced, and the flash tank is replaced by nitrogen. After passing the test, the LV301 is removed and the block is removed.

5 Conclusion The above analysis of the cause of LV301 blockage, preventive measures and treatment methods. Of course, LV301 plugging may also be caused due to malfunctions of instruments and equipment and operation errors. Therefore, in the current process conditions, improve the operating level and reduce equipment, instrument failure, is also an important guarantee for smooth LV301 discharge.

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