System and method used to recycle exhaust gas during olefin polymer production
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Solution Overview
Problem
Existing methods for recycling exhaust gases in olefin polymer production, such as compression condensation and pressure swing adsorption, face inefficiencies in recycling hydrocarbons and nitrogen, require high energy consumption, and rely on costly refrigeration equipment like ice machines, leading to economic and environmental challenges.
Innovation Solution
A system combining a compression cooling mechanism, hydrocarbon membrane separation, hydrogen membrane separation, and deep cooling mechanisms to efficiently recycle hydrocarbons and nitrogen, eliminating the need for refrigeration equipment like ice machines, thereby reducing energy consumption and maintenance costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If normal temperature refrigeration ice machine is used to achieve lower temperature (−10 to 35° C.), then cooling efficiency improves, but investment cost and energy consumption increase significantly
Solution Approach 1:
The system uses self-service cooling where the compressed exhaust gas itself provides the cooling medium for heat exchangers. The high-pressure compressed gas is cooled by heat exchange with lower-pressure gas streams, eliminating the need for external refrigeration cycles and ice machines. This internal heat integration achieves deep cooling without additional energy input for refrigeration.
Solution Approach 2:
The patent replaces mechanical refrigeration systems (ice machines, compressors, condensers) with a thermodynamic expansion-based cooling system. High-pressure gas expands through expansion valves or turbines, producing cold gas that directly cools subsequent gas streams. This mechanical substitution eliminates complex refrigeration machinery and reduces energy consumption.
2Productivity
If pressure swing adsorption method is used to further recycle hydrocarbons, then recycling rate improves, but procedures become complicated and operating costs increase due to extra energy consumption for pressurizing and depressurizing
Solution Approach 1:
The patent extracts and removes C1-C3 hydrocarbon components from the exhaust gas stream through deep cooling condensation before any adsorption process. By pre-concentrating the target components into liquid phase through temperature reduction, the subsequent adsorption stage only needs to handle a smaller, more concentrated stream, simplifying the overall process and reducing the number of towers needed.
Solution Approach 2:
The system performs preliminary deep cooling and condensation of C1-C3 hydrocarbons before entering the adsorption stage. This preliminary separation action removes the bulk of target components, reducing the load on subsequent adsorption towers and minimizing the frequency and intensity of pressurizing-depressurizing cycles required.
3Use of energy by stationary object
If deep cooling to lower than −40° C. is implemented without ice machine, then investment cost and energy consumption are reduced, but achieving and maintaining such low temperature is challenging
Solution Approach 1:
The system employs periodic batch cooling cycles where compressed gas is cooled in stages, with intermediate storage and reheating phases. Gas is compressed, cooled to intermediate temperature, stored, then expanded to achieve deep cooling. This periodic operation allows heat exchangers to recover cooling capacity during warm phases and apply it during cooling phases, enabling sub-40°C temperatures without continuous high-energy input.
Solution Approach 2:
The compressed gas serves multiple functions: it is the process gas being treated, the cooling medium in heat exchangers, the expansion gas for deep cooling, and the purge gas for system maintenance. This multi-functionality eliminates dedicated refrigeration equipment and achieves deep cooling through the gas's own thermodynamic properties and cycle operations.
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 system effectively recycles hydrocarbons and nitrogen, improving their purity and recycling rates, reduces equipment maintenance costs, and ensures stable operation with low energy consumption and environmental impact.
Implementation Method 1
a compression cooling mechanism; The compression cooling mechanism is used for receiving the exhaust gas, compressing pressures of respective gas components in the exhaust gas to a same level, and respectively outputting a recycled C4+ high carbon hydrocarbon stream and a remaining exhaust gas stream
Implementation Method 2
a hydrocarbon membrane separation mechanism and a hydrogen membrane separation mechanism, both connected to a first outlet of the compression cooling mechanism
Implementation Method 3
a deep cooling mechanism connected to a first outlet of the hydrogen membrane separation mechanism. The deep cooling mechanism is used for receiving the remaining tail gas stream from the hydrogen membrane separation mechanism, and respectively recycling a C2+ low carbon hydrocarbon stream and a nitrogen gas stream
Data Source
AI summary
A system used to recycle exhaust gas during olefin polymer production, comprising: a compression cooling mechanism (101); a hydrocarbon membrane separation mechanism (102) and a hydrogen membrane separation mechanism (103), both connected to a first outlet (202) of the compression cooling mechanism; and a deep cooling mechanism (104) connected to a first outlet (208) of the hydrogen membrane separation mechanism. A method used to recycle exhaust gas during olefin polymer production, comprising a compression cooling step, a hydrocarbon membrane separation step, a hydrogen membrane separation step and a deep cooling step.