Process and apparatus for decoking a hydocarbon steam cracking furnace

1. A hydrocarbon pyrolysis process, the process comprising:

(a) providing (i) a pyrolysis furnace, the pyrolysis furnace comprising at least one radiant coil, (ii) first and second quench stages, the first quench stage being located upstream of the second quench stage, (iii) a hydrocarbon feed, (iv) a quench oil, (v) a decoking feed, and (vi) first and second quench media, the first aqueous quench medium being primarily liquid phase and the second aqueous quench medium being primarily vapor phase;

(b) providing a flow of the hydrocarbon feed to the pyrolysis furnace and providing a flow of the quench oil to the first quench stage;

(c) pyrolysing at least a portion of the hydrocarbon feed in the radiant coil to (i) produce a radiant coil effluent and (ii) deposit coke in the radiant coil;

(d) contacting the radiant coil effluent with the quench oil in the first quench stage to produce a quenched product mixture;

(e) (i) decreasing the flow of hydrocarbon feed and providing a flow of the decoking feed to the pyrolysis furnace (ii) decreasing the flow of quench oil and providing a flow of the first aqueous quench medium to the first quench stage, and (iii) providing a flow of the second aqueous quench medium to the second quench stage;

(f) contacting the decoking feed with the deposited coke to remove at least a portion of the deposited coke from the radiant coil and produce a decoking effluent;

(g) contacting the decoking effluent with the first aqueous quench medium in the first quench stage to produce a partially quenched decoking effluent that ≧90% (vol. basis) vapor phase; and

(h) contacting the partially quenched decoking effluent with the second aqueous quench medium in the second quench stage to produce a quenched decoking effluent that is ≧90% (vol. basis) vapor phase.

2. The process of claim 1 , wherein ≧95% (vol. basis) of the decoking effluent is in the vapor phase, ≧90% (vol. basis) of the first aqueous quench medium is provided to the first quench stage in the liquid phase, ≧90% (vol. basis) of the second aqueous quench medium is provided to the second quench stage in the vapor phase, ≧95% (vol. basis) of the partially-quenched decoking effluent exits the first quench stage in the vapor phase, and ≧95% (vol. basis) of the quenched decoking effluent exits the second quench stage in the vapor phase.

3. The process of claim 1 , wherein the first aqueous quench medium is liquid water.

4. The process of claim 1 , wherein the second aqueous quench medium is steam.

5. The process of claim 1 , further comprising at least one vapor/liquid separator integrated with the pyrolysis furnace for removing from the hydrocarbon feed at least a portion of any non-volatiles, wherein the vapor/liquid separator is located upstream of the radiant coil.

6. The process of claim 1 , wherein ≧99% (vol. basis) of the first aqueous quench medium is provided to the first quench stage in the liquid phase, ≧99% (vol. basis) of the second aqueous quench medium is provided to the second quench stage in the vapor phase, ≧99% (vol. basis) of the partially-quenched decoking effluent exits the first quench stage in the vapor phase, and ≧99% (vol. basis) of the quenched decoking effluent exits the second quench stage in the vapor phase.

7. The method of claim 1 , further comprising regulating the flow of the first aqueous quench medium to maintain the partially-quenched decoking effluent within a temperature range of from 425.0° C. to 550.0° C.

8. The method of claim 1 , wherein the first aqueous quench medium is water and the second aqueous quench medium is desuperheated steam.

9. The method of claim 1 , further comprising regulating the flow of the second aqueous quench medium to maintain the quenched decoking effluent in a temperature range of from 370.0° C. to 480.0° C.

10. The process claim 1 , wherein (i) the pyrolysis furnace further comprises at least one firebox located proximate to the radiant coil for transferring heat to the radiant coil and (ii) the process further comprises conducting at least a portion of the quenched decoking effluent to the firebox.

11. A steam cracker decoking process, comprising:

(a) providing a steam cracker, the steam cracker including at least one radiant coil;

(b) providing a flow of decoking feed to the radiant coil under conditions to remove from the radiant coil at least a portion of any coke deposits, and conducting a decoking effluent away from the radiant coil;

(c) cooling the decoking effluent with a first aqueous quench medium to provide a partially-quenched decoking effluent, wherein ≧90% (vol. basis) of the first aqueous quench medium is liquid phase before the cooling and ≧90% (vol. basis) of the partially-quenched decoking effluent is vapor phase after the cooling; and

(d) further cooling the partially-quenched decoking effluent with a second aqueous quench medium to provide a quenched decoking effluent, wherein ≧90% (vol. basis) of the second aqueous quench medium is vapor phase before the further cooling and ≧90% (vol. basis) of the quenched decoking effluent is vapor phase after the further cooling.

12. The process of claim 11 , further comprising the steps of (e) discontinuing the flow of decoking feed to the radiant coil and returning the radiant coil to steam cracking service.

13. The process of claim 11 , wherein the steam cracker comprises a plurality of radiant coils.

14. The process of claim 11 , wherein (i) the steam cracker further comprises at least one convection coil in fluidic communication with the radiant coil, (ii) the decoking feed comprises air and steam, and (iii) the decoking feed is preheated in the convection coil.

15. The process of claim 11 , wherein the first aqueous quench medium comprises water and the second aqueous quench medium comprises steam.

16. The process of claim 11 , wherein the second aqueous quench medium comprises desuperheated steam.

17. The process of claim 11 , further comprising regulating the first aqueous quench medium amount in step (c) to maintain the partially-quenched decoking effluent within a temperature range of from 425.0° C. to 550.0° C.

18. The process of claim 11 , further comprising regulating the second aqueous quench medium amount in step (d) to maintain the quenched decoking effluent in a temperature range of from 370.0° C. to 480.0° C.

19. The process of claim 11 , wherein ≧90% (vol. basis) of the partially quenched decoking effluent exits the first quench stage in the vapor phase and ≧99% (vol. basis) of the quenched decoking effluent exits the second quench stage in the vapor phase.

20. The process of claim 11 , wherein substantially all of the partially quenched decoking effluent exits the first quench stage in the vapor phase and substantially all of the quenched decoking effluent exits the second quench stage in the vapor phase.