TDI defocussing process system and its application in TDI production process

Abstract

The application discloses a TDI decoking process system and application thereof in a TDI production process. The TDI decoking process system comprises a decoking tower, a first circulating pump, a tower kettle reboiler and a wiped film evaporator. The tower kettle liquid after decoking of the decoking tower is reprocessed through the added wiped film evaporator, so that the content of the coke in the tower kettle liquid is reduced, and therefore, the heat exchange effect of the heat exchanger caused by the coke deposit is avoided. The TDI decoking process system is applied to the TDI production process. Due to the improvement of the decoking process system, the overall operation stability is higher, and the service life is longer.

Description

Technical Field

[0001] This invention relates to the field of chemical processes, and in particular to a TDI decoking process system and its application in TDI production processes. Background Technology

[0002] Toluene diisocyanate (TDI) is a common type of isocyanate compound with high reactivity. It is widely used in the polyurethane industry and plays a key role in the production of products such as foamed plastics, coatings, adhesives and elastomers.

[0003] During TDI production, byproducts and TDI react to form tar-like substances. Excessive tar viscosity, high reaction temperatures, and prolonged retention times lead to residues remaining in the reboiler and piping. In particular, coke deposits accumulating on the heat exchangers in the reboiler reduce the heat exchange efficiency of parallel heat exchangers, limiting feed throughput, causing coking on the inner tube walls, and increasing flow rate. Furthermore, heat exchanger flow deviation worsens, tube-side scaling becomes severe, and head leaks occur; the furnace load increases, gas consumption rises, and energy consumption is high, severely impacting the long-term operation of the unit. Summary of the Invention

[0004] The purpose of this invention is to address the technical deficiencies in the existing technology by providing a TDI decoking process system. This system reprocesses the bottom liquid of the decoking tower by adding a scraped film evaporator, thereby reducing the tar content in the bottom liquid and avoiding the decrease in heat exchange efficiency of the heat exchanger caused by coke deposits.

[0005] Another objective of this invention is to provide the application of the above-mentioned TDI decoking process system in the TDI production process.

[0006] Another object of the present invention is to provide a TDI production process.

[0007] The technical solution adopted to achieve the purpose of this invention is:

[0008] A TDI decoking process system includes a decoking tower, a first circulating pump, a reboiler, and a scraped film evaporator;

[0009] The material inlet of the decoking tower is connected to the bottom outlet of the photochemical ODCB tower to remove coke from the crude TDI after ODCB removal.

[0010] The bottom liquid outlet of the decoking tower is connected to the material inlet of the scraped film evaporator via a bottom liquid outlet pipe; the high-boiling-point solid-liquid outlet at the bottom of the scraped film evaporator is connected to the LIST recovery system via a TDI / tar mixture output pipe; the TDI / tar mixture output pipe is connected to a TDI / tar mixture circulation pipe; the other end of the TDI / tar mixture circulation pipe is connected to the material inlet of the decoking tower; the bottom liquid outlet pipe, the TDI / tar mixture output pipe, and the TDI / tar mixture circulation pipe together form the decoking tower circulation pipeline; a first circulation pump and a bottom reboiler are sequentially installed on the bottom liquid outlet pipe; these provide circulation power and heat to the decoking tower circulation pipeline, respectively.

[0011] The top outlet of the decoking tower is connected to the material inlet of the refining tower, and is used to refine the decoked TDI.

[0012] The low-boiling vapor outlet of the scraped film evaporator is connected to the material inlet of the decoking tower to recover TDI and increase the TDI content in the decoking tower.

[0013] In the above technical solution, a residual liquid tank and a second circulation pump are provided on the TDI / tar mixture output pipeline;

[0014] The TDI / tar mixture circulation pipeline is connected to a residual liquid tank circulation branch; the free end of the residual liquid tank circulation branch is connected to the inlet of the residual liquid tank.

[0015] Another aspect of the present invention is the application of the above-described TDI decoking process system in the TDI production process.

[0016] Another aspect of the present invention is a TDI production process, comprising a reaction vessel, a photochemical ODCB 73# tower, the aforementioned decoking process system, a LIST recovery system, and a purification tower;

[0017] The reaction vessel is connected to the photochemical ODCB 73# tower and is used to remove phosgene from the crude TDI generated by the reaction.

[0018] The photochemical ODCB 73# tower is connected to the decoking process system and is used to decoke the crude TDI product after ODCB removal.

[0019] The decoking process system is connected to the refining tower and is used to refine the decoked TDI to obtain qualified products.

[0020] The decoking process system is connected to the LIST recovery system and is used to recover the TDI / tar mixture.

[0021] In the above technical solution, the photochemical ODCB 73# tower includes a first photochemical ODCB 73# tower and a second photochemical ODCB 73# tower.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. The TDI decoking process system provided by the present invention reprocesses the bottom liquid of the decoking tower after decoking by adding a scraped film evaporator, recovers the obtained TDI to the decoking tower, and at the same time transports the high tar content TDI / tar mixture to the LIST recovery system, thereby reducing the tar content in the decoking tower, thus avoiding coke deposits and improving the heat exchange efficiency of the reboiler heat exchanger in the bottom of the tower.

[0024] 2. The TDI decoking process system provided by the present invention greatly improves the circulation speed by adding a residual liquid tank and a second circulation pump, and the material impacts the tar, further preventing tar accumulation.

[0025] 3. The TDI production process provided by this invention has higher overall operational stability and a longer service life due to the improvement of the decoking process system. Attached Figure Description

[0026] Figure 1 The diagram shown is a schematic diagram of the TDI decoking process system in Example 1;

[0027] Figure 2 The diagram shown is a schematic diagram of the TDI decoking process system in Comparative Example 1.

[0028] Figure 3 The image shows the blockage of the heat exchange tubes in the reboiler of the tower in Comparative Example 1.

[0029] Figure 4 The diagram shown is a schematic representation of the TDI decoking process system in Example 2.

[0030] In the diagram: 1-Decoking tower, 2-First circulation pump, 3-Reboiler in the tower bottom, 4-Scraped film evaporator, 5-Photochemical ODCB tower, 6-LIST recovery system, 7-Refining tower, 8-Residual liquid tank, 9-Second circulation pump, 10-Reaction tank. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0032] Example 1

[0033] A TDI decoking process system, such as Figure 1 As shown, it includes a decoking tower 1, a first circulating pump 2, a reboiler 3, and a scraped film evaporator 4;

[0034] The material inlet of the decoking tower 1 is connected to the bottom outlet of the photochemical ODCB tower 5 to decoke the crude TDI product after ODCB removal.

[0035] The bottom liquid outlet of the decoking tower 1 is connected to the material inlet of the scraped film evaporator 4 via a bottom liquid outlet pipe L1; the high-boiling solid-liquid outlet at the bottom of the scraped film evaporator 4 is connected to the LIST recovery system 6 via a TDI / tar mixture output pipe L2; the TDI / tar mixture output pipe L2 is connected to a TDI / tar mixture circulation pipe L3; the other end of the TDI / tar mixture circulation pipe L3 is connected to the material inlet of the decoking tower 1; the bottom liquid outlet pipe L1, the TDI / tar mixture output pipe L2, and the TDI / tar mixture circulation pipe L3 together form the decoking tower circulation pipeline; a first circulation pump 2 and a reboiler 3 are sequentially installed on the bottom liquid outlet pipe L1; these provide circulation power and heat to the decoking tower circulation pipeline respectively;

[0036] The top outlet of the decoking tower 1 is connected to the material inlet of the refining tower 7, and is used to refine the decoked TDI.

[0037] The low-boiling vapor outlet of the scraped film evaporator 4 is connected to the material inlet of the decoking tower 1 to recover TDI and increase the TDI content in the decoking tower 1.

[0038] In the aforementioned TDI decoking process system, the material at the inlet of decoking tower 1 contains approximately 96% TDI and 4% tar. After decoking, the tar content in the tower bottom liquid increases to 40%, which easily leads to tar accumulation in the heat exchanger of the reboiler 3, affecting efficiency. After adding a scraped film evaporator 4, the tower bottom liquid undergoes further decoking. The tar content in the TDI / tar mixture flowing out from the high-boiling-point solid-liquid outlet at the bottom of the scraped film evaporator 4 increases to 50%. The collected TDI is returned to decoking tower 1, reducing the tar content in the tower bottom liquid, decreasing tar accumulation in the heat exchanger of the reboiler 3, and improving service life.

[0039] Comparative Example 1

[0040] A TDI decoking process system, such as Figure 2 As shown, it includes a decoking tower 1, a first circulating pump 2, and a reboiler 3.

[0041] The material inlet of the decoking tower 1 is connected to the bottom outlet of the photochemical ODCB tower 5 to decoke the crude TDI product after ODCB removal.

[0042] A circulation pipeline L5 is provided between the bottom liquid outlet and the material inlet of the decoking tower 1; a first circulation pump 2 and a tower reboiler 3 are sequentially installed on the circulation pipeline L5, providing circulation power and heat to the circulation pipeline L5 respectively; a recovery pipeline L6 is connected to the circulation pipeline L5; the other end of the recovery pipeline L6 is connected to the LIST recovery system.

[0043] In the aforementioned TDI decoking process system, the initial material at the inlet of decoking tower 1 contains approximately 96% TDI and 4% tar. After circulating decoking treatment, the tar content in the tower bottom liquid increases to 40%. This content easily leads to tar accumulation in the heat exchanger of the reboiler 3, affecting its efficiency. Figure 3 As shown.

[0044] Example 2

[0045] A TDI decoking process system includes a decoking tower 1, a first circulating pump 2, a reboiler 3, and a scraped film evaporator 4;

[0046] The material inlet of the decoking tower is connected to the outlet of the bottom of the photochemical ODCB tower 5, in order to decoke the crude TDI product after ODCB removal;

[0047] The bottom liquid outlet of the decoking tower 1 is connected to the material inlet of the scraped film evaporator 4 via a bottom liquid outlet pipe L1; the high-boiling solid-liquid outlet at the bottom of the scraped film evaporator 4 is connected to the LIST recovery system 6 via a TDI / tar mixture output pipe L2; the TDI / tar mixture output pipe L2 is connected to a TDI / tar mixture circulation pipe L3; the other end of the TDI / tar mixture circulation pipe L3 is connected to the material inlet of the decoking tower 1; the bottom liquid outlet pipe L1, the TDI / tar mixture output pipe L2, and the TDI / tar mixture circulation pipe L3 together form the decoking tower circulation pipeline; a first circulation pump 2 and a bottom reboiler 3 are sequentially installed on the bottom liquid outlet pipe L1; these provide circulation power and heat to the decoking tower circulation pipeline respectively;

[0048] The TDI / tar mixture output pipeline L2 is equipped with a residual liquid tank 8 and a second circulation pump 9.

[0049] The TDI / tar mixture circulation pipeline L3 is connected to a residual liquid tank circulation branch L4; the free end of the residual liquid tank circulation branch L4 is connected to the inlet of the residual liquid tank 8.

[0050] The top outlet of the decoking tower 1 is connected to the material inlet of the refining tower 7, and is used to refine the decoked TDI.

[0051] The low-boiling vapor outlet of the scraped film evaporator 4 is connected to the material inlet of the decoking tower 1 to recover TDI and increase the TDI content in the decoking tower.

[0052] Compared to Example 1, the TDI decoking process system described above adds a residual liquid tank 8 and a second circulation pump 9. The addition of the second circulation pump can increase the circulation speed of the decoking tower circulation pipeline, further preventing tar accumulation.

[0053] In Example 1, the normal flow rate of the bottom liquid flowing out of the coke removal tower is 327 m³ / h. 3 / h. After adding the second circulating pump 9, the discharge flow rate of the bottom liquid from the coke removal tower is approximately 8000 m³ / h. 3 / h, the LIST system feed flow rate is approximately 1600m³ / h. 3 / h, the flow rate returning to the decoking tower is approximately 6400m³ / h. 3 / h. This greatly increases the circulation speed, and the material impacts the tar, further preventing tar buildup.

[0054] Example 3

[0055] A TDI production process includes a reaction vessel 10, a photochemical ODCB tower 5, a decoking process system as described in Example 2, a LIST recovery system 6, and a purification tower 7.

[0056] The photochemical ODCB tower 5 includes a first photochemical ODCB tower 73# and a second photochemical ODCB tower 73# connected to each other; the reaction vessel 10 is connected in sequence to the first photochemical ODCB tower 73# and the second photochemical ODCB tower 73#, and is used to remove phosgene from the crude TDI generated by the reaction;

[0057] The photochemical second ODCB 73# tower is connected to the decoking tower 1 in the decoking process system, and is used to decoke the TDI crude product after ODCB removal;

[0058] The top outlet of the decoking tower 1 in the decoking process system is connected to the refining tower 7, which is used to refine the decoked TDI to obtain qualified products.

[0059] The TDI / tar mixture output pipe L2 in the decoking process system is connected to the LIST recovery system 6 for recovering the TDI / tar mixture.

[0060] In the above TDI production process, due to the improvement of the decoking process system, the overall operation stability is higher and the service life is longer.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A TDI decoking process system, characterized in that, Includes a decoking tower, a first circulating pump, a reboiler, and a scraped film evaporator; The material inlet of the decoking tower is connected to the bottom outlet of the photochemical ODCB tower to remove coke from the crude TDI after ODCB removal. The bottom liquid outlet of the decoking tower is connected to the material inlet of the scraped film evaporator via a bottom liquid outlet pipe; the high-boiling-point solid-liquid outlet at the bottom of the scraped film evaporator is connected to the LIST recovery system via a TDI / tar mixture output pipe; the TDI / tar mixture output pipe is connected to a TDI / tar mixture circulation pipe; the other end of the TDI / tar mixture circulation pipe is connected to the material inlet of the decoking tower; the bottom liquid outlet pipe, the TDI / tar mixture output pipe, and the TDI / tar mixture circulation pipe together form the decoking tower circulation pipeline; a first circulation pump and a bottom reboiler are sequentially installed on the bottom liquid outlet pipe; these provide circulation power and heat to the decoking tower circulation pipeline, respectively. The top outlet of the decoking tower is connected to the material inlet of the refining tower, and is used to refine the decoked TDI. The low-boiling vapor outlet of the scraped film evaporator is connected to the material inlet of the decoking tower to recover TDI and increase the TDI content in the decoking tower.

2. The TDI decoking process system as described in claim 1, characterized in that, The TDI / tar mixture output pipeline is equipped with a residual liquid tank and a second circulation pump. The TDI / tar mixture circulation pipeline is connected to a residual liquid tank circulation branch; the free end of the residual liquid tank circulation branch is connected to the inlet of the residual liquid tank.

3. The application of the TDI decoking process system as described in claim 1 or 2 in the TDI production process.

4. A TDI production process, characterized in that, Includes a reaction vessel, a photochemical ODCB 73# tower, the decoking process system as described in claim 1 or 2, a LIST recovery system, and a refining tower; The reaction vessel is connected to the photochemical ODCB 73# tower and is used to remove phosgene from the crude TDI generated by the reaction. The photochemical ODCB 73# tower is connected to the decoking process system and is used to decoke the crude TDI product after ODCB removal. The decoking process system is connected to the refining tower and is used to refine the decoked TDI to obtain qualified products. The decoking process system is connected to the LIST recovery system and is used to recover the TDI / tar mixture.

5. The TDI production process as described in claim 4, characterized in that, The photochemical ODCB 73# tower includes a first photochemical ODCB 73# tower and a second photochemical ODCB 73# tower.

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