Process for handling variable flow rates and compositions in pressure swing adsorption systems

Abstract

The present invention generally relates to a process for responding to feed flow variations by changing the process cycle and thereby increasing the productivity and capacity of the system significantly over constant process systems. This increases the flexibility a PSA system for customers that do not require a constant or uniform product flow rate and/or for processes and applications that experience feed streams that vary in flow, temperature, and/or composition.

1 . A method for maximizing product production under variable feed conditions in a PSA system adapted for separating a pressurized feed supply gas containing at least one more readily adsorbable component from at least one less readily adsorbable product gas component to produce a stream of product gas enriched with said less readily adsorbable component and a stream of offgas that is enriched in said more readily adsorbable component, wherein said PSA system comprises a feed gas step, product gas make step, a product pressurization step, a high pressure equalization step, product make step that overlaps with feeding the bed, at least one equalization up step and one equalization down step, and a blow down step to depressurize the bed, wherein when the Required Processing Power of said PSA system is greater than 1, the PSA process cycle is modified by making at least one of the following cycle changes:
 a. Substitute at least one feed step for an equalization step provided that the cycle retains at least one equalization step pair; or   b. Substitute at least one blow down step or purge step pair for an equalization step pair provided that the cycle retains at least one equalization step pair; or   c. Substitute at least one feed step for at least one blow down step or purge step pair provided that the cycle retains at least one blow down step or purge step pair;   d. Substitute an overlap feed and product pressurization step for a product pressurization step; or   e. Substitute a purge step pair for at least one blowdown step.   
     
     
         2 . The method of  claim 1  wherein when the Required Processing Power of said PSA system is greater than 1, the PSA process cycle is modified by:
 a. Substituting at least one feed step for an equalization step provided that the cycle retains at least one equalization step pair; and 
 b. Substituting at least one blow down step or purge step pair for an equalization step pair provided that the cycle retains at least one equalization step pair. 
 
     
     
         3 . The method of  claim 1  wherein when the Required Processing Power of said PSA system is less than 1, the PSA process cycle is modified by making at least one of the following cycle changes:
 a. Substitute an equalization step pair for a feed step provided that the cycle retains at least one feed step; or 
 b. Substitute an equalization step for a blow down step or a purge step pair provided that the cycle retains at least one blow down step or purge step pair; or 
 c. Substitute at least one blow down step or purge step pair for at least one feed step provided that the cycle retains at least one feed step; or 
 d. Substitute a product pressurization step for an overlap feed and product pressurization step; or 
 e. Substitute at least one blowdown step for a purge step pair. 
 
     
     
         4 . The method of  claim 1  wherein when the Required Processing Power of said PSA system is less than 1, the PSA process cycle is modified by:
 a. Substituting an equalization step pair for a feed step provided that the cycle retains at least one feed step; and 
 b. Substituting an equalization step for a blow down step or a purge step pair provided that the cycle retains at least one blow down step or purge step pair. 
 
     
     
         5 . The method of  claim 3  wherein for Required Processing Power of less than 1, there is a deadband of up to 0.2 within no change to the process cycle is implemented. 
     
     
         6 . The method of  claim 3  wherein the Required Processing Power is less than 0.8. 
     
     
         7 . The method of  claim 1  wherein the product gas is methane and the more readily adsorbable component is N 2  and/or CO 2 . 
     
     
         8 . The method of  claim 1  wherein the product gas is helium and the more readily adsorbable component is N 2  and/or CO 2  and/or methane and/or other hydrocarbons. 
     
     
         9 . The method of  claim 1  wherein the product gas is hydrogen and the more readily adsorbable component is N 2  and/or CO 2  and/or methane and/or other hydrocarbons. 
     
     
         10 . The method of  claim 1  wherein the system has at least 4 adsorbent beds but less than 25. 
     
     
         11 . The method of  claim 1  wherein the product gas is N 2  and the more readily adsorbable component is O 2 . 
     
     
         12 . A method of  claim 1  wherein an intermediate processing cycle is created to facilitate the transition for option c. 
     
     
         13 . The method of  claim 1  wherein each adsorption bed contains zeolitic material. 
     
     
         14 . The method of  claim 1  wherein each adsorption bed contains adsorbent materials used in H 2  PSA, the product gas is H 2  and the more readily adsorbable component is selected from one or more of CO, CO 2 , CH 4 , N 2 , Ar, and hydrocarbon. 
     
     
         15 . The method of  claim 1  wherein said adsorbent is selected from at least one of activated carbon, Zeolite, 5A, CaX, LiX. 
     
     
         16 . The method of  claim 1  wherein PSA system comprises a 4131 design cycle, and wherein when the Required Processing Power for said system is greater than 1, the design cycle is modified to a 4122 cycle according to the following cycle chart:    
     
     
         17 . The method of  claim 1  wherein the PSA system comprises a 4122 design cycle, and wherein when the Required Processing Power for said system is greater than 1, the design cycle is changed to a 4221 cycle according to the following cycle chart:    
     
     
         18 . A method of  claim 3  wherein the PSA system comprises a 4221 design cycle, wherein when the Required Processing Power for said system is less than or equal to 1, the design cycle is modified to a 4122 cycle according to the following cycle chart provided that the Required Processing Power for the 4122 cycle is also less than or equal to 1:    
     
     
         19 . The method of  claim 18  wherein the cycle is not modified until the Required Processing Power for the 4122 cycle is less than about 0.95 or less than about 0.9, or less than 0.8. 
     
     
         20 . The method of  claim 3  wherein the PSA system comprises a 4122 design cycle, wherein when the Required Processing Power for said system is less than or equal to 1, the design cycle is modified to a 4131 cycle according to the following cycle chart provided that the Required Processing Power for the 4131 cycle is less than or equal to 1:    
     
     
         21 . The method of  claim 20  wherein the cycle is not modified until the Required Processing Power for the 4122 design cycle is lower than about 0.95 or lower than about 0.9, or lower than 0.8.