CA-2950545-C - MULTI-VALVE UNI-DIRECTION BLOWDOWN SYSTEM FOR A HIGH PRESSURE TUBULAR REACTOR

CA2950545CCA 2950545 CCA2950545 CCA 2950545CCA-2950545-C

Abstract

Provided herein is a unidirectional blow down system for a high-pressure tubular reactor with a hyper that minimizes the tube wall metal temperature during a decomposition event wherein the system prevents the reactor walls from reaching a temperature capable of causing the tube metal to austenize. Also provided are methods of designing and methods of operating a unidirectional blowdown system.

Inventors

KAMAL BOTROS
ROSS MORETON
TERESA LEUNG
Benjamin Shaw

Assignees

NOVA CHEMICALS CORPORATION

Dates

Publication Date: 20260505
Application Date: 20161202
Priority Date: 20151208

Claims (5)

The embodiments of the invention in which exclusive property or privilege is claimed are defined as follow: 5 1. A unidirectional blowdown system for a high-pressure tubular reactor with a hypercompressor that minimizes a temperature of a tube wall metal during a decomposition event comprising: a front emergency blowdown valve located downstream from the hypercompressor and in a front end of the tubular reactor; and 10 at least one additional valve at an end of the tubular reactor; wherein the system prevents the tubular reactor walls from reaching a temperature that causes the tube wall metal to austenize by maintaining flow in a single direction away from the hypercompressor during a blowdown, and by maintaining specific pressure and flow velocity within the tubular reactor during blowdown so that an amount of heat transfer 15 to the tubular reactor walls is minimized.
2. The unidirectional blowdown system of claim 1 wherein an inner diameter (ID) of the front emergency blowdown valve is smaller than the at least one additional valve ID at the end of the tubular reactor.
3. The unidirectional blowdown system of claim 1 wherein the front emergency blowdown valve has an ID of from about 0.25 to about 0.5 inches.
4. The unidirectional blowdown system of claim 1 wherein the front emergency 25 blowdown valve has an ID of from about 0.3 to about 0.4 inches.
5. The unidirectional blowdown system of claim 1 wherein the front emergency blowdown valve has an ID of 0.375 inches. Date re<;ue/Date received 2023-12-13 6. The unidirectional blowdown system of claim 1 wherein the at least one additional valve ID at the end of the tubular reactor is from about 0.375 to about 2 inches. 7. The unidirectional blowdown system of claim 1 wherein the at least one additional 5 valve ID at the end of the tubular reactor is from about 1 to about 1.5 inches. 8. The unidirectional blowdown system of claim 1 wherein the at least one additional valve ID at the end of the tubular reactor is about 1 inch. 10 9. The unidirectional blowdown system of claim 1 wherein there is at least one additional valve between the front emergency blowdown valve and the at least one additional valve at the end of the tubular reactor. 10. The unidirectional blowdown system of claim 1 wherein there is one additional valve 15 with an ID of about 0.25-0.5 inches between the front emergency blowdown valve and the at least one additional valve at the end of the tubular reactor. 11. The unidirectional blowdown system of claim 1 wherein the tubular reactor comprises at least one tube made from a low alloy carbon steel. 12. The unidirectional blowdown system of claim 1 wherein the tubular reactor comprises at least one tube made from a low alloy carbon steel having a carbon content of from about 0.3 to about 0.4% carbon. 25 13. The unidirectional blowdown system of claim 1 wherein the tubular reactor comprises at least one tube that is a Grade AISI 4333 tube. 16 Date re<;ue/Date received 2023-12-13 14. The unidirectional blowdown system of claim 1 wherein the tube wall metal of the tubular reactor has an austenization temperature between about 750°C and about 850°C. 15. The unidirectional blowdown system of claim 1 wherein the tube wall metal of the 5 tubular reactor has an austenization temperature of about 785°C to about 793°C. 16. The unidirectional blowdown system of claim 1 wherein the flow velocity is less than 80 ft/s. 10 17. The unidirectional blowdown system of claim 1 wherein the flow velocity is less than 60 ft/s. 18. The unidirectional blowdown system of claim 1 wherein the flow velocity is less than 50 ft/s. 19. A method for implementing a unidirectional blowdown ofa decomposition event in a tubular reactor with a hypercompressor that minimizes a temperature of a tube wall metal during the decomposition event comprising: a. sensing the decomposition event; 20 b. delivering automated signals to initiate an opening of a front emergency blowdown valve located downstream from the hypercompressor and an opening of at least one additional valve at an end of the tubular reactor; wherein the method prevents tubular reactor walls from reaching a temperature that causes the tube wall metal to austenize by maintaining flow in a single direction away from 25 the hypercompressor during a blowdown, and by maintaining specific pressure and flow velocity within the tubular reactor during blowdown so that an amount of heat transfer to the tubular reactor walls is minimized. 17 Date re<;ue/Date received 2023-12-13 20. The method of claim 19 wherein step a further comprises delivering an automated signal to shut down the hypercompressor. 21. The method of claim 19 wherein the flow velocity is less than 80 ft/s. 22. The method of claim 19 wherein the flow velocity is less than 60 ft/s. 23. The method of claim 19 wherein the flow velocity is less than 50 ft/s. 10 24. A method for designing a blowdown system for a tubular reactor comprising: a. determining an austenization temperature for a tube metal; b. optimizing the blowdown system based on a reduction of an amount of heat being transferred to a tube wall during blowdown to eliminate austenization of the tube metal during a decomposition event instead of optimizing the blowdown system to 15 depressurize as quickly as possible. 25. The method of claim 24 wherein a method of determining the amount of heat being transferred to the tube wall during blowdown comprises: a. modeling a pressure and flow velocity inside the tubular reactor during 20 blowdown using a dynamic model; b. simulating how a decomposition wave propagates within the tubular reactor during blowdown; c. determining a heat transfer coefficient as a function of pressure, temperature and velocity at any given location within the tubular reactor; and 25 d. using temporal profiles of pressure, flow velocity, temperature, and heat transfer coefficient during blowdown to determine a tube wall temperature profile by solving a 1 D transient heat equation using a finite-difference scheme. 18 Date re<;ue/Date received 2023-12-13

Description

MULTI-VALVE UNI-DIRECTION SLOWDOWN SYSTEM FOR A HIGH PRESSURE TUBULAR REACTOR The present disclosure relates to a unidirectional blow down system for a high-pressure tubular reactor with a hyper that minimizes the tube wall metal 5 temperature during a decomposition event wherein the system prevents the reactor walls from reaching a temperature capable of causing the tube metal to austenize. Also provided are methods of designing and methods of operating a unidirectional blowdown system LDPE tubular reactors all have some arrangement of safety systems for l O relieving the reactor pressure when an ethylene decomposition event (herein after referred to as a "decamp") occurs. One example of an existing system has two blowdown valves located at the front and the back end of the reactor, respectively, which vent the contents of the reactor once a decomp is detected. In this design the hypercompressor (herein after referred to as a "hyper") continues to run while both 15 valves are open until the internal pressure reaches half of the maximum design pressure value, at which time one valve is closed. A control logic is in place to determine which of the valves to close based upon the starting location of the decamp within the reactor in order to push the flow out of the reactor most quickly. The blowdown system is designed such that the time to vent down to half pressure 20 is in the order of 1 second. Other example systems use two valves, or more, to accomplish venting in a similar time frame. The goal of these multi-valve blowdown systems is to drive the decomp out of the reactor as quickly as possible. In these systems keeping the depressurization time on the order of 1 to 2 seconds to half of the maximum design 25 pressure is claimed to be key to their success. The most adverse effect of decomp 2 I I I I is the excessively high temperatures that can damage the reactor tubes. Therefore, rapid removal of the hot gas produced by decomp is believed to be essential during emergency blowdown. It is hypothesized that high flow velocities minimize the exposure time of the tube wall metal to the decomposing ethylene. 5 The rapid depressurization within the reactor is also believed to reduce the intensity of the decamp reactions as well as the density of the ethylene and therefore the amount of heat transfer from the fluid to the tube wall. One of the disadvantages to these designs are the inevitable stagnant flow regions that occur within the reactor during blowdown as two or more valves are open simultaneously. 10 As an alternative to designs using multiple valves, some manufacturers use one valve at the back end of the reactor. The intent of such single valve systems is to maintain the flow in a single direction to avoid stagnation and/or stalling of the reacting materials in any reaction zone. A valve upstream of the hyper is closed to isolate the flow at the suction side. These one-valve systems have longer 15 depressurization time at the front end of the reactor than multi-valve systems, though they are still within acceptaple limits. In an embodiment provided herein is a unidirectional blow down system for a high-pressure tubular reactor with a hyper that minimizes the tube wall metal temperature during a decomposition event comprising a front Emergency 20 Slowdown (herein after referred to as a "EBO") valve located downstream from the hyper discharge and at the front end of the reactor; and at least one additional valve at the end of the reactor; wherein the system prevents the reactor walls from reaching a temperature capable of causing the tube metal to austenize by maintaining flow in a single direction away from the hyper during the blowdown 25 process, and by maintaining specific pressure and flow velocity within the reactor 3 during blowdown so that the amount of heat transfer to the tube reactor is minimized. In another embodiment provided herein is method for implementing a unidirection blow down of a decomp in a tube reactor with a hyper that minimizes 5 the tube wall metal temperature during a decomposition event comprising a) sensing the decamp event; and b) delivering automated signals to initiate the opening of a front EBO valve located downstream from the hyper discharge and the opening of at least one additional valve at the end of the reactor; wherein the system prevents the reactor walls from reaching a temperature capable of causing 10 the tube metal to austenize by maintaining flow in a single direction away from the hyper during the blowdown process, and by maintaining specific pressure and flow velocity within the reactor during blowdown so that the amount of heat transfer to the tube reactor is minimized. In another embodiment provided herein is a method for designing blow down 15 system for a tube reactor comprising a) determining the austenization temperature for the tube metal; b) optimizing the blow down system based on the reduction of the amount of heat being transferred to the tube w