Cracked Gas Fractionation Using Intermediate Recirculation Cooling
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Solution Overview
Problem
Current methods for fractionating cracked gas from hydrocarbon pyrolysis plants require significant investment and energy consumption for ethylene recovery, particularly challenging for small units due to the need for external ethylene-based refrigeration cycles.
Innovation Solution
The method involves forming an expanded intermediate recirculation stream from liquids obtained during cooling steps, which is circulated back through the upstream heat exchanger to cool the cracked gas without using an external refrigeration cycle, reducing the need for external cooling and minimizing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an external ethylene-based refrigeration cycle is used to cool cracked gas to below -120°C, then ethylene recovery rate is improved, but energy consumption and investment cost increase significantly
Solution Approach 1:
The fuel stream serves a dual function: it is both the product to be recovered and the refrigerant to enable cooling. By expanding the fuel stream through dynamic expansion devices, it self-cools and provides the necessary coldness for cracking gas cooling without requiring external refrigeration cycles, thereby reducing energy consumption while maintaining high ethylene recovery rates
Solution Approach 2:
The fuel stream performs multiple functions simultaneously: it acts as the refrigerant medium for cooling, as the product to be recovered, and as a heat transfer fluid in the heat exchangers. This multi-functionality eliminates the need for separate refrigeration systems and reduces overall energy consumption
2Temperature
If an external ethylene-based refrigeration cycle is installed, then cooling performance is improved, but investment cost increases significantly
Solution Approach 1:
The fuel stream serves a dual function: it is both the product to be recovered and the refrigerant to enable cooling. By expanding the fuel stream through dynamic expansion devices, it self-cools and provides the necessary coldness for cracking gas cooling without requiring external refrigeration cycles, thereby reducing energy consumption while maintaining high ethylene recovery rates
Solution Approach 2:
The fuel stream performs multiple functions simultaneously: it acts as the refrigerant medium for cooling, as the product to be recovered, and as a heat transfer fluid in the heat exchangers. This multi-functionality eliminates the need for separate refrigeration systems and reduces overall energy consumption
3Manufacturing precision
If the cracked gas is cooled to temperatures below -120°C using external refrigeration, then ethylene purity is improved, but energy consumption increases
Solution Approach 1:
The fuel stream serves a dual function: it is both the product to be recovered and the refrigerant to enable cooling. By expanding the fuel stream through dynamic expansion devices, it self-cools and provides the necessary coldness for cracking gas cooling without requiring external refrigeration cycles, thereby reducing energy consumption while maintaining high ethylene recovery rates
Solution Approach 2:
The system utilizes pressure-temperature relationship changes during fuel stream expansion to achieve the required cooling temperatures. By controlling the expansion parameters and pressure drops, the system achieves below -120°C cooling necessary for high purity ethylene recovery without external refrigeration
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 decreases the investment required for the fractionation process while maintaining high ethylene recovery rates and energy performance, making it suitable for small units with lower energy costs and reduced infrastructure needs.
Implementation Method 1
expansion of the intermediate recirculation stream in at least one dynamic expansion device to form a cold expanded intermediate recirculation stream
Implementation Method 2
circulating the expanded intermediate recirculation stream in the upstream heat exchanger to cool the upstream stream of cracked gas
Implementation Method 3
cooling of the upstream stream of cracked gas by the cold expanded intermediate recirculation stream in the upstream heat exchanger
Implementation Method 4
upstream cooling and partial condensation, in at least one upstream heat exchanger, of an upstream stream of cracked gas
Data Source
AI summary
This method comprises:forming an expanded intermediate recirculation stream (170) from a liquid (112, 128) obtained during an upstream cooling and/or intermediate cooling step, upstream from the downstream cooling step;circulating the intermediate recirculation stream (170) at least in an upstream heat exchanger (42) to cool an upstream stream of cracked gas (102);reintroducing the reheated intermediate recirculation stream (170) in a raw cracked gas (20) upstream from at least one compressor (36, 38) of a cooling and compression stage (24).The upstream, intermediate and downstream cooling steps is carried out without a heat exchanger respectively of an upstream stream of cracked gas (102), an intermediate stream of cracked gas (114) and a downstream stream of cracked gas (140) with an external refrigeration cycle.