Method for fractionating a stream of cracked gas to obtain an ethylene-rich cut and a stream of fuel, and related installation
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Solution Overview
Problem
Current methods for fractionating cracked gas from hydrocarbon pyrolysis installations require multiple refrigeration cycles and high energy consumption to achieve high ethylene recovery and purity, necessitating a reduction in thermal levels and energy efficiency improvements.
Innovation Solution
The method involves passing a partially expanded fuel stream through a second dynamic expander, reheating, and compressing it to form a low C2+ hydrocarbon content stream, utilizing internal heat exchanges without external refrigeration cycles, and processing liquids through heat exchangers to maintain ethylene-rich cut production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple refrigeration cycles are used to achieve high ethylene recovery and purity, then ethylene purity and recovery rate are improved, but energy consumption increases
Solution Approach 1:
The patent changes the thermodynamic parameters of the system by using a single refrigeration cycle operating at a higher temperature level (above -100°C) instead of multiple cycles at progressively lower temperatures. This parameter change allows achieving the same separation effect with reduced energy consumption by operating in a more efficient temperature range where the refrigeration cycle requires less work input.
Solution Approach 2:
The patent extracts and utilizes the cold energy from the ethylene-rich stream after separation to pre-cool the incoming cracked gas feed. This extraction of useful cold energy from what would otherwise be a cold waste stream eliminates the need for additional refrigeration stages, reducing overall energy consumption while maintaining high ethylene recovery and purity.
2Productivity
If multiple refrigeration cycles are used to achieve high ethylene recovery, then ethylene recovery rate is improved, but specific refrigeration power increases
Solution Approach 1:
The patent utilizes phase transitions (condensation and evaporation) of ethylene and other hydrocarbons at controlled temperature and pressure conditions within the single refrigeration cycle. By carefully managing these phase transitions in the heat exchangers and separators, the system achieves high ethylene recovery through selective condensation of ethylene from the cracked gas, while the single-cycle design reduces specific refrigeration power compared to multi-cycle alternatives.
3Manufacturing precision
If cooling temperature is reduced below -100°C to achieve high ethylene purity, then ethylene purity is improved, but refrigeration energy consumption increases
Solution Approach 1:
The patent performs preliminary cooling of the cracked gas feed using cold energy recovered from the ethylene-rich product stream before it enters the main refrigeration cycle. This preliminary action pre-cools the feed to a temperature where the single refrigeration cycle can more efficiently achieve the final low temperature required for high ethylene purity, thereby reducing the energy consumption of the main refrigeration system.
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 reduces energy consumption by eliminating a thermal level, achieving high ethylene recovery rates (>99.5%) while decreasing specific refrigeration power and investment costs, with improved energy efficiency and ethylene purity.
Implementation Method 1
expansion of the heated high-pressure fuel stream in at least a first dynamic expander to obtain a partially expanded fuel stream
Implementation Method 2
upstream cooling and partial condensation of a stream of raw cracked gas by at least partial heat exchange with a coolant fluid circulating in a first external refrigeration cycle
Implementation Method 3
compressing the reheated expanded fuel stream in at least one compressor coupled to at least one turbo-expander of the first dynamic expander and/or the second dynamic expander
Implementation Method 4
processing at least one liquid obtained during the upstream cooling, intermediate cooling and downstream cooling steps to form the ethylene-rich cut
Data Source
AI summary
This method includes introducing a downstream stream (140) of cracked gas from a downstream heat exchanger (58) in a downstream separator (60) and recovering, at the head of the downstream separator (60), a high-pressure fuel gas stream (144).The method includes the passage of the stream (144) of fuel through the downstream exchanger (58) and an intermediate exchanger (50, 54) to form a reheated high-pressure fuel stream (146), the expansion of the reheated high-pressure fuel stream (146) in at least a first dynamic expander (68) and the passage of the partially expanded fuel stream (148) from the intermediate exchanger (50, 54) in a second dynamic expander (70) to form an expanded fuel stream (152).The expanded fuel stream (152) from the second dynamic expander (70) is reheated in the downstream heat exchanger (58) and in the intermediate heat exchanger (50, 54).