PDH Separation With Mixed Refrigerant Cooling and Lower Power
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Solution Overview
Problem
Current Propane Dehydrogenation (PDH) separation systems face high power consumption, increased costs due to turbo-expander/generator sets, high compressor discharge pressure, and limited flexibility in adjusting separation temperatures.
Innovation Solution
A Mixed Refrigerant (MR) system with heat exchangers and drums provides refrigeration for separation and recovery of olefin products, eliminating the need for turbo-expander/generator sets and allowing for reduced compressor discharge pressure, improved maintenance, and independent refrigeration control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If turbo-expander/generator sets are used for de-pressurization and refrigeration, then refrigeration for separation is provided, but power consumption increases and maintenance requirements increase
Solution Approach 1:
The patent extracts and eliminates the turbo-expander/generator sets from the system, replacing them with a simpler valve-based de-pressurization system. This removes the complex mechanical components that consumed power and required maintenance, while still achieving the necessary refrigeration through the Joule-Thomson effect in the expansion valve.
Solution Approach 2:
The patent replaces the mechanical turbo-expander system with a non-mechanical valve-based expansion system. This substitution eliminates moving parts that require maintenance and power input, using instead a pressure-driven thermal effect to achieve refrigeration.
2Temperature
If turbo-expander/generator sets are used for de-pressurization, then refrigeration is provided, but device complexity and maintenance requirements increase
Solution Approach 1:
The patent removes the complex turbo-expander/generator sets from the system architecture, retaining only the essential function of de-pressurization and refrigeration through a simpler valve-based system. This extraction of unnecessary complexity directly reduces maintenance requirements.
Solution Approach 2:
Instead of using a complex mechanical system to actively create refrigeration, the patent inverts the approach by using a passive thermal effect (Joule-Thomson cooling) that occurs naturally during pressure reduction, eliminating the need for complex mechanical refrigeration equipment.
3Reliability
If Reactor Effluent Compressor discharge pressure is increased to high pressure, then separation and recovery is achieved, but capital costs and operating costs increase
Solution Approach 1:
The patent changes the pressure parameter from high pressure operation to a more moderate pressure range. By optimizing the compression pressure to be lower than traditional high-pressure systems, the patent reduces capital costs for pressure vessels and piping while maintaining separation efficiency through the subsequent expansion and refrigeration process.
4Reliability
If Reactor Effluent Compressor discharge pressure is increased to high pressure, then separation and recovery is achieved, but operating costs increase
Solution Approach 1:
The patent optimizes the compression pressure parameter to a lower value, reducing the work required by the compressor and thereby lowering operating costs. The separation efficiency is maintained not through high pressure alone, but through the combination of moderate pressure compression followed by expansion-induced refrigeration and condensation.
5Reliability
If fixed separation temperatures are used in prior art systems, then separation is achieved, but flexibility to adjust temperatures is limited
Solution Approach 1:
The patent introduces dynamic control capabilities to the separation system, allowing temperatures to be adjusted based on varying feed conditions and product requirements. This is achieved through controllable expansion valves and heat exchangers that can modulate their operation, transforming the system from static to dynamic temperature control.
Solution Approach 2:
The patent creates a multi-functional separation system that can handle different feed compositions and produce different product specifications by adjusting operating parameters. The system is designed to be universally applicable to various olefin separation needs, not limited to a single fixed operating point.
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
The MR system reduces power consumption, lowers capital and operating costs, enhances system reliability, and allows for more flexible and robust design, achieving efficient olefin and hydrogen separation while maintaining product recovery efficiency.
Implementation Method 1
a main heat exchanger configured to cool and partially condense an effluent stream so that a mixed phase stream is formed
Implementation Method 2
a separation system configured to separate the mixed phase stream into a vapor stream and a liquid stream
Implementation Method 3
The main heat exchanger is configured to warm the effluent stream to provide refrigeration in the main heat exchanger
Data Source
AI summary
A main heat exchanger receives and partially condenses an effluent fluid stream so that a mixed phase effluent stream is formed. A primary separation device receives and separates the mixed phase effluent stream into a primary vapor stream including hydrogen and a primary liquid stream including an olefinic hydrocarbon. The main heat exchanger receives and warms at least a portion of the primary vapor stream to provide refrigeration for partially condensing the effluent fluid stream. The main heat exchanger also receives, warms and partially vaporizes the primary liquid stream. A mixed refrigerant compression system also provides refrigeration in the main heat exchanger.