Olefin Separation via C3/C4 Stage and Single Hydrogenation
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Solution Overview
Problem
The existing olefin plant processes require two separate catalytic hydrogenation stages and associated equipment, leading to high capital costs due to the need for sharp separation of olefins with at most three carbon atoms from those with at least four carbon atoms at full crude gas pressure, which results in undesirable polymer formation and increased costs.
Innovation Solution
Implementing a C3/C4 separation stage with a C4 absorber operating at full crude gas pressure and a depropanizer at 8-12 bar, allowing for the omission of one catalytic hydrogenation stage by compressing the crude gas to maintain pressure and separating olefins into fractions for single hydrogenation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a sharp separation into C3 and C4+ fractions is performed at full crude gas pressure, then the separation efficiency is improved, but polymer formation and deposit formation increase
Solution Approach 1:
The separation process is divided into two stages: first a C3/C4 separation at reduced pressure (8-12 bar) to obtain crude C3 fraction, then a second sharp separation at full crude gas pressure (30-39 bar) to achieve precise C3/C2 split. This segmentation allows each stage to operate under optimal pressure conditions, avoiding polymer formation while achieving the required separation sharpness.
Solution Approach 2:
The C3/C4 separation is performed as a preliminary step at reduced pressure before the final C3/C2 separation at full pressure. This preliminary action removes the bulk of C4+ components first, preventing them from interfering with the subsequent sharp separation and avoiding polymer formation during the critical separation phase.
2Reliability
If two independent catalytic hydrogenation stages are implemented, then the olefin fractions are properly treated, but the equipment scope and capital costs increase
Solution Approach 1:
The two separate catalytic hydrogenation stages are merged into a single integrated hydrogenation unit that processes the entire C3- fraction (containing both C3 and C2 olefins) from the C3/C4 separation stage. This consolidation maintains reliable olefin treatment while significantly reducing equipment scope and capital costs by eliminating redundant hydrogenation reactors and associated infrastructure.
3Object-generated harmful factors
If the crude gas pressure is reduced for C3/C4 separation, then polymer formation is reduced, but an additional compression stage is required
Solution Approach 1:
The system dynamically adjusts pressure conditions for different separation stages: operating at reduced pressure (8-12 bar) during C3/C4 separation to minimize polymer formation, then utilizing the fifth compression stage to restore full crude gas pressure (30-39 bar) for the final C3/C2 separation and downstream processing. This dynamic pressure management optimizes both polymer reduction and equipment utilization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach minimizes capital costs by eliminating the need for a separate catalytic hydrogenation stage and reduces polymer formation, enabling efficient processing of olefin fractions with reduced equipment burden.
Implementation Method 1
a C3/C4 separation stage which comprises a C4 absorber, operating at full crude gas pressure
Implementation Method 2
a separation column for separating olefins having at most three carbon atoms and olefins having at least four carbon atoms (depropanizer). The depropanizer is operated at a pressure of about 8 bar-12 bar
Implementation Method 3
The entire fraction of the olefins having at most three carbon atoms is fed to the next-highest stage of the crude gas compressor and subsequently passed on to the catalytic hydrogenation
Data Source
AI summary
To decrease capital costs of crack gas treatment of the olefin plant, a method for separation of olefins reduces the units for catalytic hydrogenation. In the method, olefins having three carbon atoms are separated from olefins having four carbon atoms. Crude gas is precompressed (1), precooled and dried (2), and passed into a C3/C4 separation stage (6) comprising a C4 absorber, operating at full crude gas pressure, and a depropanizer, operated at a pressure of 8 to 12 bar. In the C3/C4 separation stage, the olefins are separated into a fraction having at most three carbon atoms (C3−), and a fraction having at least four carbon atoms (C4+). The fraction having at most three carbon atoms is completely compressed (1) and passed to the catalytic hydrogenation (4); the fraction having at least four carbon atoms is passed out for further processing (7). The catalytic hydrogenation (4) yields a fraction having at least two carbon atoms (C2−), which is passed on to the low-temperature separation, and a fraction having three carbon atoms (C3), is passed to further processing (8).