Power Recovery Process

Abstract

Processes using multiple expansion turbines for efficient recovery of power from a plurality of very high pressure streams of superheated vapor are disclosed. Beneficially, processes of the invention use at least two classes of expansion turbines. Processes according to this invention are particularly useful for recovery of power from very high pressure streams of superheated steam in an olefins manufacturing process. Such streams are typically produced by thermal cracking of suitable petroleum derived feed stocks, and the olefins being produced and purified are typically ethylene and/or propylene.

1 . A power recovery process employing at least two classes of expansion turbines, which process comprises:
 (a) expanding a first stream of superheated vapor at first inlet conditions, including temperature and pressure, to obtain at least one first expanded stream of superheated vapor at first intermediate conditions using at least one primary class expansion turbine to thereby recover a first amount of power;   (b) combining two or more vapor streams into a single very high-pressure superheated vapor stream;   (c) cooling the resulting single very high-pressure stream from step (b) by indirect heat exchange with at least a portion of the first expanded stream from step (a) to provide all or a portion of the first stream of superheated vapor for expansion in step (a), and a resulting heated first expanded stream at second intermediate conditions;   (d) expanding at least a portion of the resulting heated stream from step (c) at second inlet conditions to obtain at least one second expanded stream of superheated vapor at third intermediate conditions using at least one secondary class expansion turbine to thereby recover a second amount of power.   
   
   
       2 . The process of  claim 1  wherein three or more vapor streams are combined in step (b) into a single very high-pressure superheated vapor stream. 
   
   
       3 . The process of  claim 1  wherein three or more of the vapor streams combined in step (b) into a single very high-pressure superheated vapor stream are derived from a petrochemical process. 
   
   
       4 . The process of  claim 1  wherein the vapor comprises a light organic component containing from about 2 to about 4 carbon atoms. 
   
   
       5 . The process of  claim 1  wherein the second intermediate temperature is no more than 100 Fahrenheit degrees below the first inlet conditions temperature. 
   
   
       6 . A power recovery process employing at least two classes of expansion turbines, which process comprises:
 (a) expanding a first stream of superheated steam at first inlet conditions of temperature and pressure to obtain at least one first expanded stream of superheated steam at first intermediate conditions using at least one primary class expansion turbine to thereby recover a first amount of power;   (b) combining three or more streams of very high pressure steam into a single very high-pressure superheated stream;   (c) cooling the resulting single very high-pressure stream from step (b) by indirect heat exchange with at least a portion of the first expanded stream from step (a) to provide all or a portion of the first stream of superheated vapor for expansion in step (a), and a resulting heated first expanded stream at second intermediate conditions including a second intermediate temperature;   (d) expanding at least a portion of the resulting heated stream from step (c) at second inlet conditions to obtain at least one second expanded stream of superheated steam at third intermediate conditions using at least one secondary class expansion turbine to thereby recover a second amount of power.   
   
   
       7 . The process of  claim 6  which further comprises treating at least a portion of one or more second expanded stream of superheated steam from step (d) to thereby provide at least a portion of the resulting single very high-pressure stream of step (b). 
   
   
       8 . The process of  claim 7  wherein three or more of the vapor streams combined in step (b) into a single very high-pressure superheated vapor stream are generated in a process for thermal cracking of suitable petroleum derived feed stocks to produce olefins. 
   
   
       9 . The process of  claim 8  wherein the olefins being produced are ethylene and/or propylene. 
   
   
       10 . The process of  claim 6  wherein three or more of the vapor streams combined in step (b) into a single very high-pressure superheated vapor stream are generated in a process for the manufacture of light olefins by the pyrolysis of hydrocarbons in a plurality of furnaces from which heat is removed in a plurality of very high pressure streams of superheated steam. 
   
   
       11 . The process of  claim 6  wherein the first inlet pressure is at least 900 psig. 
   
   
       12 . The process of  claim 6  wherein the first inlet temperature is at least 800° F. 
   
   
       13 . The process of  claim 6  which further comprises partially desuperheating the second expanded stream of superheated steam from step (d) by indirect heat exchange with a cooling medium to provide a supply of superheated low-pressure steam. 
   
   
       14 . The process of  claim 13  wherein the cooling medium is boiler feed water, and wherein at least a portion of the heated boiler feed water is used to produce at least a portion of the very high pressure steam streams of step (b). 
   
   
       15 . The process of  claim 6  wherein the second intermediate temperature is no more than 100 Fahrenheit degrees below the first inlet conditions temperature.