A cooling system for spherizone polypropylene process recycle gas

Abstract

This invention discloses a cooling system for circulating gas in a Spherizone polypropylene process. It includes two parallel coolers for cooling the circulating gas, a valve for cutting off material flow, and connecting pipelines. This invention addresses the problem of polymer blockage in the circulating gas cooler tubes. By using two coolers connected in parallel, the degree of polymer blockage at the tube inlet is determined by the pressure difference between the cooler's inlet and outlet. The inlet and outlet pipelines of the coolers are switched by controlling the valve, allowing the circulating gas to enter the cooler in the reverse direction. While being cooled, the circulating gas carries the polymer adhering to the other side back to the reactor. Once the pressure difference returns to normal, the flow is switched back to the initial state. The selected two coolers have a 100% heat exchange margin when flowing in reverse. If the blockage problem cannot be resolved by switching between forward and reverse flow for one cooler, that cooler can be shut down online, using single-unit cooling to ensure the circulating gas cooling system and the entire reaction system remain operational without interruption.

Description

Technical Field

[0001] This utility model relates to a cooling system for circulating gas in the Spherizone polypropylene process, belonging to the technical field of chemical reaction systems. Background Technology

[0002] Spherizone polypropylene is the latest generation of polypropylene production technology developed by LyondellBasell based on the Spheripol process. It is a gas-phase process whose main reactor employs a unique multi-zone circulating reactor, meaning a single reactor can be divided into two independent operating zones: a rising zone and a falling zone. Reaction temperature, hydrogen concentration, and monomer concentration can be controlled separately, achieving uniform mixing of polymer particles in an "onion-like" pattern. In addition to producing all products from the Spheripol process, it can also produce new types of products with distinct Spherizone process characteristics.

[0003] Spherizone process technology represents the latest advancement in the polyolefin manufacturing industry. This technology can significantly improve product performance, further expand product applications, and produce better products that can replace other materials. In particular, it provides a broader potential for research and development of new products.

[0004] The main flow of the Spherizone process is as follows: The catalyst enters from the bottom of the riser section and is rapidly fluidized under the condition of circulating gas delivery through the bend. After passing through the upper narrowing Ω-shaped bend, the gas carries the material tangentially into the expansion chamber at high speed. After cyclone separation, the gas is circulated through an external pipeline using a circulating gas compressor, and the heat of reaction is removed by a vertical cooler installed on the circulation line. PP particles carrying some gas fall into the PP bed in the isolation section and move in the descending section in the form of a plunger flow under gravity. Some material is discharged by the discharge valve installed at the bottom of the descending section, and the remaining material is circulated back to the riser section through the "reverse L-section". When it is necessary to produce bimodal PP products, propylene isolating liquid is injected into the isolation section, which allows the reactor's descending section to form two reaction zones with different gas phase compositions. Because the reactants continuously circulate in the two feed leg zones, the uniformity of the PP is better. Compared with the loop process, the amount of hydrogen and ethylene added to the reactor is increased, resulting in a wider variety of PP products.

[0005] Production practice has revealed that the polymer carried by the circulating gas at the outlet of the circulating gas compressor can clog the top of the tube bundle in the heat exchanger. Large-diameter polymers may even fail to pass through the tube bundle under the action of the airflow. At the same time, it blocks more small particles and fine powders in the circulating gas, which continue to react and form large-area agglomerates. This significantly reduces the heat exchange area of ​​the heat exchanger, increases the resistance of the circulating compressor, and obstructs the circulating airflow at the heat exchanger, reducing the airflow entering the rising section of the reactor. If the minimum delivery speed is not reached, the polymer in the rising section will not be able to be delivered to the falling section, the solid circulation in the reactor will terminate, and the unit may be forced to shut down. Summary of the Invention

[0006] The technical problem to be solved by this utility model is to provide a cooling system for circulating gas in Spherizone polypropylene process, which solves the problems of reduced heat exchange efficiency of circulating gas cooler and reduced circulating airflow velocity caused by polymer blockage, and avoids unplanned downtime caused by these problems, resulting in greater losses.

[0007] The present invention solves the above-mentioned technical problem through the following technical solution:

[0008] A cooling system for circulating gas in Spherizone polypropylene process includes an inlet and an outlet, two coolers connected in parallel for cooling the circulating gas, a valve for cutting off material flow, and connecting pipelines.

[0009] The inlet is externally connected to the outlet of the circulating gas compressor via pipeline. Internally, it is connected to valves 1, 11, and 6 via pipelines. Valve 1 is connected to the inlet of valve 2 and cooler 1, and valve 2 is connected to the outlet via valve 4. Valve 6 is connected to the inlet of valve 7 and cooler 2, and valve 7 is connected to the outlet via valve 9. Valve 11 is connected to valves 5 and 10. Valve 5 is connected to the outlet of cooler 1 via valve 3, and valve 10 is connected to the outlet of cooler 2 via valve 8. The outlet is connected to the reactor via pipeline. The two coolers are connected in parallel. Under normal operation, they perform counter-current heat exchange with a heat exchange margin ≥100%. They can also meet the requirements for co-current heat exchange, with a heat exchange margin ≥20% in co-current mode.

[0010] Preferably, the inlet and outlet are connected to external pipelines respectively, and the connection method can be either flange or welding, with flange connection being preferred.

[0011] Preferably, the first and second coolers are vertical shell-and-tube heat exchangers, wherein circulating gas flows through the tube side and cooling medium flows through the shell side. The first and second coolers operate normally in counter-current heat exchange with a heat exchange margin ≥100%, and can be switched to co-current operation with a heat exchange margin ≥20%. When a single cooler operates in counter-current heat exchange, it can meet the heat exchange requirements of the entire circulating gas system.

[0012] Preferably, the two coolers and connecting pipes in the cooling system are arranged symmetrically.

[0013] Preferably, all valves are shut-off valves, and the design flow rate of the shut-off valve is not less than twice the flow rate of cooler one or cooler two when operating in parallel.

[0014] Preferably, all valves are remotely controllable, and the power source is pneumatic or electric, with pneumatic being more preferred.

[0015] Preferably, both cooler one and cooler two are equipped with a differential pressure measuring device for measuring the pressure difference between the cooler inlet and outlet.

[0016] More preferably, the differential pressure measuring device adopts a remote differential pressure gauge with measurement, display, alarm and interlock functions, which can interlock control the opening and closing of the shut-off valve, and can also manually control the opening and closing of the valve through display, alarm and other functions, preferably interlock control of the opening and closing of the valve.

[0017] Preferably, the elbow in the connecting pipeline is a 90° elbow with a bending radius of not less than 3D, and more preferably a bending radius of not less than 5D.

[0018] This invention provides a cooling system for circulating gas in a Spherizone polypropylene process, addressing the problem of polymer blockage in the circulating gas cooler tubes. The system employs two coolers connected in parallel. By monitoring the pressure difference between the cooler's inlet and outlet, the degree of polymer blockage at the cooler's tube inlet is determined. The inlet and outlet lines of the cooler are then switched by controlling a shut-off valve, changing the inlet to outlet and vice versa. This adjusts the counter-current heat exchange between the circulating gas and the cooling medium in the cooler to co-current heat exchange. The circulating gas enters the cooler in the reverse direction, carrying the polymer adhering to the other side back to the reactor while being cooled. Once the pressure difference returns to normal, the original flow is switched back for cooling. Because the heat exchange margin of the two coolers in counter-current mode is not less than 100%, if the blockage problem of one cooler cannot be resolved by switching between counter-current and co-current flow, that cooler's flow can be shut off online, using a single cooler for cooling (with sufficient margin). The cooler can be put back into operation after the blockage is resolved, ensuring that the entire circulating gas cooling system operates without reduced flow or shutdown, and the entire reaction system continues to function. Attached Figure Description

[0019] Figure 1 A schematic diagram of the cooling system provided by this utility model. Detailed Implementation

[0020] To make this utility model more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0021] Example

[0022] like Figure 1 As shown, this utility model provides a cooling system for circulating gas in Spherizone polypropylene process, which includes an inlet 14 and an outlet 15, two coolers connected in parallel for cooling the circulating gas, a valve for cutting off the flow of materials, and connecting pipelines.

[0023] Inside the cooling system, inlet 14 is connected to valve 1, valve 11, and valve 6 respectively. Valve 1 is connected to valve 2 and the inlet of cooler 12 respectively. Valve 2 is connected to outlet 15 through valve 4. Valve 6 is connected to valve 7 and the inlet of cooler 2 13 respectively. Valve 7 is connected to outlet 15 through valve 9. Valve 11 is connected to valve 5 and valve 10 respectively. Valve 5 and the outlet of cooler 12 are connected to the outlet through valve 3. Valve 10 and the outlet of cooler 2 13 are connected to outlet 15 through valve 8.

[0024] External to the cooling system, inlet 14 is connected to the outlet pipeline of the circulating gas compressor, and outlet 15 is connected to the circulating gas return line (the pipeline returning to the reactor).

[0025] The cooler 12 and cooler 23 are vertical shell-and-tube heat exchangers, in which circulating gas flows through the tube side and cooling medium flows through the shell side. The two coolers and connecting pipes are arranged symmetrically.

[0026] The design flow rate of all valves shall not be less than twice the flow rate of cooler 12 or cooler 23 when operating in parallel, and the power source of all valves shall be pneumatic or electric.

[0027] Both cooler 12 and cooler 2 13 are equipped with differential pressure measuring devices for measuring the pressure difference between the cooler inlet and outlet. The differential pressure measuring devices are remote differential pressure gauges with measurement, display, alarm, and interlocking functions.

[0028] The elbows in the connecting pipeline are 90° elbows with a bending radius of not less than 3D.

[0029] The functions of each component in the above cooling system are as follows:

[0030] Cooler 1: Used to cool circulating gas. It is a shell-and-tube heat exchanger where the circulating gas flows through the tubes and the cooling medium flows through the shell. Normal operation is counter-current heat exchange with a heat exchange margin of ≥100%. It can be switched to co-current operation with a heat exchange margin of ≥20%. A single cooler can meet the heat exchange requirements of the entire circulating gas system when operating in counter-current mode. It is set up in parallel with Cooler 2.

[0031] Cooler 2: Used to cool circulating gas. It is a shell-and-tube heat exchanger where the circulating gas flows through the tubes and the cooling medium flows through the shell. Normal operation is counter-current heat exchange with a heat exchange margin of ≥100%. It can be switched to co-current operation with a heat exchange margin of ≥20%. When a single cooler is used for counter-current heat exchange, it can meet the heat exchange requirements of the entire circulating gas system. It is set up in parallel with cooler 1.

[0032] Connecting pipelines: used for connecting the system to external pipelines and connecting the internal processes of the system; the pipelines connecting the two coolers need to be arranged symmetrically. At the same time, since the circulating air contains polymers, in order to avoid affecting the accumulation of solids and the flow of materials, the pipelines in the system need to be highly polished and the surface roughness should be less than 1mm. The bending radius of the elbows should be ≥5D.

[0033] Valve: Used to cut off the flow of material, so as to switch the flow direction of circulating air or shut down the cooler; the shut-off valve is pneumatically or electrically controlled, and can be interlocked with the differential pressure gauges at the inlet and outlet of the cooler, switching on and off by changing the differential pressure. Figure 1 Valve 1 and Valve 2 are installed near point B1, Valve 3 and Valve 5 are installed near point C1, Valve 4 is installed near point F1, Valve 6 and Valve 7 are installed near point B2, Valve 8 and Valve 10 are installed near point C2, Valve 9 is installed near point F2, and Valve 11 is installed near point A.

[0034] Differential pressure measuring device PD1: a device used to measure the differential pressure at the inlet and outlet of the cooler, and also has display, alarm and interlock functions. It is preferred that PD1 be interlocked with valve 1, valve 2, valve 3, valve 4 and valve 5.

[0035] Differential pressure measuring device PD2: a device used to measure the differential pressure at the inlet and outlet of the cooler, and also has display, alarm and interlock functions. It is preferred that PD2 be interlocked with valves six, seven, eight, nine and ten.

[0036] Import: Connected to the outlet of the recirculating gas compressor;

[0037] Outlet: Connected to the recirculated gas return line (to the reactor);

[0038] This utility model provides a cooling system for circulating gas in the Spherizone polypropylene process. By switching the co-current and counter-current heat exchange mode of the cooler, the circulating gas itself carries away the blocked polymer, thus solving the blockage problem of the cooler. The switched circulating gas carries the polymer blocked at the original inlet back to the reactor while ensuring that the cooling effect is not reduced, thus ensuring the stable operation of the entire cooling system. The relevant operation process is shown in Table 1.

[0039] Table 1

[0040]

[0041] As shown in Table 1, after adopting the cooling system provided by this utility model, the blockage of the cooler can be understood immediately by using measures such as serial numbers 1-7 according to different situations. The solid material is blown away and brought back to the reactor by the backflushing of circulating air, which effectively reduces the blockage of polymer at the inlet of the cooler tube, improves the heat exchange efficiency of the cooler, and reduces the resistance at the compressor outlet, thereby greatly reducing the probability of unplanned shutdowns caused by this. Although the cooling system provided by this utility model has one more cooler and some pipelines than the traditional cooler, it is negligible compared with the economic losses caused by the shutdown. This utility model is still the preferred solution to the above problems.

Claims

1. A cooling system for the recycle gas of a Spherizone polypropylene process, characterized in that, Includes an inlet (14) and an outlet (15), two coolers connected in parallel for cooling the circulating air, a valve for cutting off the flow of materials, and connecting pipelines; The external part of the inlet (14) is connected to the outlet of the circulating gas compressor via a pipeline, and the internal part is connected to valve 1 (1), valve 11 (11), and valve 6 (6) via pipelines. Valve 1 (1) is connected to the inlet of valve 2 (2) and cooler 1 (12) respectively. Valve 2 (2) is connected to the outlet (15) via valve 4 (4). Valve 6 (6) is connected to the inlet of valve 7 (7) and cooler 2 (13) respectively. Valve 7 (7) is connected to the outlet (15) via valve 9 (9). Valve 11 (11) is connected to valve 5 (5) and valve 10 (10) respectively. The outlet of valve 5 (5) and cooler 1 (12) is connected to the outlet via valve 3 (3). The outlet of valve 10 (10) and cooler 2 (13) is connected to the outlet (15) via valve 8 (8).

2. Cooling system for the recycle gas of a Spherizone polypropylene process according to claim 1, characterized in that, The inlet (14) is connected to the outlet pipeline of the circulator compressor.

3. Cooling system for the recycle gas of a Spherizone polypropylene process according to claim 1, characterized in that, The outlet (15) is connected to the pipeline returning to the reactor.

4. The cooling system for the recycle gas of a Spherizone polypropylene process according to claim 1, characterized in that, The first cooler (12) and the second cooler (13) are vertical shell-and-tube heat exchangers, wherein the tube side is circulated with circulating gas and the shell side is circulated with cooling medium.

5. The cooling system for the recycle gas of a Spherizone polypropylene process according to claim 1, characterized in that, The two coolers and connecting pipes in the cooling system are arranged symmetrically.

6. The cooling system for the recycle gas of a Spherizone polypropylene process according to claim 1, characterized in that, The design flow rate of all valves shall not be less than twice the flow rate of cooler one (12) or cooler two (13) when operating in parallel.

7. The cooling system for the recycle gas of a Spherizone polypropylene process according to claim 1, characterized in that, All valves are powered by either pneumatic or electric power.

8. The cooling system for the recycle gas of a Spherizone polypropylene process according to claim 1, characterized in that, Both the first cooler (12) and the second cooler (13) are equipped with a differential pressure measuring device for measuring the pressure difference between the inlet and outlet of the cooler.

9. Cooling system for the recycle gas of a Spherizone polypropylene process according to claim 8, characterized in that, The differential pressure measuring device uses a remote differential pressure gauge with measurement, display, alarm, and interlocking functions.

10. Cooling system for the recycle gas of a Spherizone polypropylene process according to claim 1, characterized in that, The elbows in the connecting pipeline are 90° elbows with a bending radius of not less than 3D.

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