Process and apparatus for reducing thermal shock in a hydrocarbon steam cracking furnace

Patent metadata

Field	Value
Publication number	US-10160919-B2
Application number	US-201615064901-A
Country	US
Kind code	B2
Filing date	Mar 9, 2016
Priority date	Sep 21, 2015
Publication date	Dec 25, 2018
Grant date	Dec 25, 2018

Abstract

A method and apparatus of reducing thermal shock in one or more radiant tubes of a pyrolysis furnace is provided. The apparatus is a furnace comprising a blower and blower bypass conduit providing separate fluid communication paths for flue gas from the convection section to a natural draft flue gas stack. The method comprises the steps of: redirecting at least a portion of the flue gas through the blower bypass conduit when a blower shut-off event is indicated as well as reducing the firing rate of the furnace.

First claim

What is claimed is:

1. A method of reducing thermal shock in one or more radiant tubes of a furnace, the method comprising the steps of:
(a) providing fuel to the furnace, the furnace comprising a firebox, the firebox comprising one or more burners and one or more radiant tubes having a layer of coke, a convection section in fluid communication with the firebox, a flue gas stack, a blower, and a blower bypass conduit, wherein the blower and the blower bypass conduit provide separate fluid communication paths between the convection section and the flue gas stack;
(b) combusting the fuel in the firebox burners to generate flue gas that heats the one or more radiant tubes;
(c) conducting the flue gas away from the firebox through the convection section, blower, and flue gas stack;
(d) monitoring a parameter predictive of a blower shut-off event;
(e) wherein the method further comprises the following steps (i) and (ii) as the parameter indicates the blower shut-off event:
(i) directing at least a portion of the flue gas from the convection section through the blower bypass conduit; and
(ii) reducing the heat input to the radiant tubes by reducing the amount of flue gas generated in the firebox, whereby the radiant tubes are maintained at a temperature above about 788° C. (1450° F.) to avoid the thermal shock caused by differential thermal expansion between the radiant tubes and the coke layer.

2. The method of claim 1 , wherein the parameter predictive of a blower shut-off event comprises the furnace pressure or blower speed.

3. The method of claim 1 , wherein reducing the amount of flue gas generated comprises reducing an amount of fuel provided to one or more burners configured to heat the firebox.

4. The method of claim 1 , wherein reducing flue gas generated comprises reducing an amount of fuel provided to fewer than all of the burners configured to heat the firebox.

5. The method of claim 1 , wherein reducing flue gas generated in step (f) comprises reducing the amount of fuel provided to the firebox to ≤about 50 wt % of the fuel provided in step (a).

6. The method of claim 1 , wherein the directing at least a portion of the flue gas through the blower bypass conduit in step (e) comprises closing a first damper to reduce the flow of flue gas through the blower and opening a second damper in the blower bypass conduit.

7. The method of claim 1 , further comprising providing a hydrocarbon feed in admixture with steam to the radiant tubes under steam cracking conditions.

8. The method of claim 7 , wherein the hydrocarbon feed comprises ≥50 wt. % ethane.

9. The method of claim 1 , wherein the monitoring a parameter predictive of a blower shut-off event is performed using a least one sensor and a controller in communication with the at least one sensor.

10. The method of claim 1 , wherein the directing at least a portion of the flue gas through the blower bypass conduit is performed using a first damper adapted to control flow of flue gas through the blower and a second damper adapted to control flow of flue gas through the blower bypass conduit.

11. The method of claim 1 , wherein the flue gas is conducted away via a flue gas stack from 5 to 65 m tall measured from the end of the convection section to the top of the flue gas stack.

12. The method of claim 1 , wherein the flue gas is conducted away via a flue gas stack≥30 m tall measured from the end of the convection section to the top of the flue gas stack.

13. The method of claim 1 , wherein the flue gas is redirected through a blower bypass conduit that is a portion of the flue gas stack.

Assignees

• Exxonmobil Chemical Patents Inc

Inventors

• Spicer David B
• Le Roy Philippe J
• Stephens George

Classifications

• F27B1/28

  Arrangements of monitoring devices, of indicators, of alarm devices · CPC title

• F23N5/245

  using electrical or electromechanical means · CPC title

• F23J2213/70

  Safety arrangements · CPC title

• C10G9/36

  with heated gases or vapours · CPC title

• C07C4/04

  Thermal processes {(C07C4/025 takes precedence)} · CPC title