Process for recovering olefins from cat-cracked gas without accumulating undesirable oxides of nitrogen
First Claim
1. A process for preventing the accumulation of undesirable oxides of nitrogen during the recovery of one or more desired hydrocarbons from cat-cracked gas comprising:
- passing said gas through an alkaline solution to remove acid gases;
passing said gas through a depropanizer at a temperature between about -28.89°
C. (-20°
F.) to -40°
C. (-40°
F.) to form a first portion and a second portion;
passing said first portion through an absorber demethanizer at a temperature above about -45.56°
(-50°
F.) to form a third portion and a fourth portion;
recovering at least one desired hydrocarbon from said third portion at temperatures above about -106.67°
C. (-160°
F.).
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Accused Products
Abstract
A safe, effective, and economical method is provided for recovering olefins from cat-cracked gases without accumulating dangerous amounts of nitrogen oxides. A stream of cat-cracked gas first is scrubbed to remove acid gases, including nitrogen dioxide (NO2), and then is passed through a depropanizer fractionation tower. Hydrocarbons having four or more carbon atoms are recovered in the bottoms of the depropanizer, and the overhead from the depropanizer--which is composed of hydrocarbons having three or fewer carbon atoms--is sent to an absorber demethanizer tower. Hydrocarbons having two or more carbon atoms are recovered in the bottoms from the absorber demethanizer tower, where temperatures are no lower than about -45.56° C. (-50° F.) The overhead from the absorber demethanizer tower--which is composed of methane, hydrogen, and trace amounts of nitrogen oxide, C2, and absorbent (C3)--then is chilled to condense and recover trace amounts of C2 and heavier gases, including trace amounts of the C3 absorbent, at temperatures of about -101.11° C. (-150° F.) or higher. Thus, recovery of desired hydrocarbons from the cat-cracked gas is conducted at temperatures that are high enough to prevent the oxidation of nitric oxide (NO) to form nitrogen dioxide (NO2) and high enough to prevent the accumulation of unwanted nitrogen oxides.
6 Citations
26 Claims
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1. A process for preventing the accumulation of undesirable oxides of nitrogen during the recovery of one or more desired hydrocarbons from cat-cracked gas comprising:
-
passing said gas through an alkaline solution to remove acid gases; passing said gas through a depropanizer at a temperature between about -28.89°
C. (-20°
F.) to -40°
C. (-40°
F.) to form a first portion and a second portion;passing said first portion through an absorber demethanizer at a temperature above about -45.56°
(-50°
F.) to form a third portion and a fourth portion;recovering at least one desired hydrocarbon from said third portion at temperatures above about -106.67°
C. (-160°
F.). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification