Process for recovering power in a process for producing ethylene

Patent metadata

Field	Value
Publication number	US-10309642-B2
Application number	US-201314418963-A
Country	US
Kind code	B2
Filing date	Aug 1, 2013
Priority date	Aug 3, 2012
Publication date	Jun 4, 2019
Grant date	Jun 4, 2019

Abstract

The present invention provides a process for power recovery in a process for producing ethylene, comprising steam cracking a hydrocarbon feed to produce a cracked gas product; cooling the cracked gas product by indirect heat exchange with high pressure liquid water to obtain cooled cracked gas product while evaporating the high pressure liquid water to high pressure steam; expanding the high pressure steam in a first steam expansion turbine to produce power and to obtain medium pressure steam; heating at least part of the medium pressure steam to increase the temperature of the medium pressure steam by passing the medium pressure steam through a convection zone of the cracking furnace and retrieving reheated medium pressure steam from the convection zone; expanding at least part of the reheated medium pressure steam in a second steam expansion turbine to produce power and to obtain low pressure steam.

First claim

That which is claimed is:

1. A process for power recovery in a process for producing ethylene, comprising the steps of:
a) steam cracking a hydrocarbon feed in a cracking furnace at temperatures above 1000° C. to produce a cracked gas product having a temperature in the range of from 700 to 1000° C.;
b) cooling the cracked gas product by indirect heat exchange with high pressure liquid water having an initial temperature above 270° C., an initial pressure above 65 bar (gauge) and a boiling point to obtain cooled cracked gas product while evaporating the high pressure liquid water to high pressure steam having a pressure above 65 bar (gauge) wherein the high pressure steam is at a temperature of the boiling point of the high pressure liquid water;
c) expanding at least part of the high pressure steam in a first steam expansion turbine to produce power and to obtain medium pressure steam having a reduced temperature and reduced pressure compared to the high pressure steam wherein the high pressure steam is not superheated before it is expanded in the first steam expansion turbine;
d) heating at least part of the medium pressure steam to increase the temperature of the medium pressure steam by in the range of from 40 to 100° C. by passing the medium pressure steam through a convection zone of the cracking furnace and retrieving reheated medium pressure steam from the convection zone;
e) expanding at least part of the reheated medium pressure steam in a second steam expansion turbine to produce power and to obtain low pressure steam having a reduced pressure compared to the reheated medium pressure steam.

2. The process according to claim 1 , wherein at least part of the low pressure steam obtained in step (e) is condensed to liquid water, which is pressurised and subsequently heated to form at least part of the high pressure liquid water in step (b).

3. The process according to claim 1 , wherein the high pressure water is produced by passing pressurised liquid water, having a temperature of the range of from 90 to 240° C. and a pressure in the range from 65 to 150 bar (gauge), through a section of the convection zone.

4. The process according to claim 1 , wherein the hydrocarbon feed is cracked in a radiant zone of the cracking furnace at a temperature in the range of from 1000 to 1250° C.

5. The process according to claim 1 , wherein the hydrocarbon feed comprises at least one of ethane, propane, butane (liquefied petroleum gasses or LPG), paraffinic hydrocarbons and mixtures of hydrocarbons selected from the group consisting of condensate, natural gas liquids (NGL), naphtha, gas oil, vacuum gas oil, hydrowax, synthetic hydrocarbons, Fischer-Tropsch hydrocarbons and mixtures thereof.

6. The process according to claim 1 , wherein the high pressure water in step (b) has an initial temperature of in the range of from 270 to 340° C. and an initial pressure in the range from 65 to 150 bar (gauge).

7. The process according to claim 1 , wherein the high pressure steam obtained in step (b) has a pressure in the range from 65 to 150 bar (gauge).

8. The process according to claim 1 , wherein the high pressure steam expanded in step (c) has an initial temperature above 400° C.

9. The process according to claim 1 , wherein the medium pressure steam obtained in step (c) has a pressure of in the range of from 50 to 100 bar below the pressure of the high pressure steam.

10. The process according to claim 1 , wherein the medium pressure steam obtained in step (c) has a temperature of in the range of from 50 to 200° C. below the temperature of the high pressure steam.

11. The process according to claim 1 , wherein the medium pressure steam is passed to a section of the convection zone wherein the temperature of the convection zone is in the range of from 350 and 700° C.

12. The process according to claim 1 , wherein the reheated medium pressure steam obtained in step (d) has a temperature of in the range of from 400 to 550° C.

13. The process according to claim 1 , wherein the medium pressure steam is heated in step (d) to increase the enthalpy of the medium steam by in the range of from 100 to 150 MJ per ton of reheated medium pressure steam in the convection zone.

14. The process according to claim 1 , wherein at least part of the power produced in steps (c) and (e) is used to drive one or more cracked gas compressors and/or one or more refrigeration compressors.

15. The process according to claim 14 , wherein the one or more cracked gas compressors and/or one or more refrigeration compressors are used to compress or cool at least part of the cooled cracked gas.

Assignees

• Shell Oil Co

Inventors

• Collins David Michael
• Singhal Ankit

Classifications

• F01K23/064

  in combination with an industrial process, e.g. chemical, metallurgical · CPC title

• F22B1/1838 Primary

  the hot gas being under a high pressure, e.g. in chemical installations · CPC title

• F01K7/22 Primary

  the turbines having inter-stage steam heating · CPC title

• C10G9/002 Primary

  Cooling of cracked gases · CPC title

• F01K13/006

  Auxiliaries or details not otherwise provided for · CPC title