Ethane Liquefaction With Demethanization Using Mixed Refrigerant
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Solution Overview
Problem
The challenge lies in efficiently liquefying a gaseous ethane stream from a pipeline, which contains small amounts of methane and other components, while minimizing the methane content to facilitate transportation and processing, as existing methods require cooling to liquefy ethane but also add heat to vaporize off methane.
Innovation Solution
A process utilizing a mixed refrigerant loop with heavy hydrocarbons like butane and pentane, combined with a distillation column to separate ethane from lighter components, where the feed gas is partially cooled and reduced in pressure, and heat is provided by cooling the feed gas or warm gas after the recycle compressor aftercooler, allowing for efficient liquefaction and subsequent removal of methane-rich gas for use as a fuel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the gaseous ethane stream is cooled to liquefy ethane, then ethane liquefaction is achieved, but methane content cannot be reduced effectively
Solution Approach 1:
The process is divided into two distinct operational stages: (1) cooling stage where the feed stream is cooled to a temperature range of -30°C to -100°C to partially condense ethane while keeping methane in vapor phase, and (2) heating stage where the cooled stream is heated to vaporize methane for removal. This segmentation allows independent optimization of each function without interference.
Solution Approach 2:
The process utilizes dynamic temperature parameter changes to achieve separation. By cooling the feed stream to a specific temperature range where ethane condenses but methane remains gaseous, then subsequently heating the separated liquid phase to vaporize and remove methane, the system achieves both liquefaction and demethanization through controlled parameter variation.
2Manufacturing precision
If heat is added to vaporize off methane from liquefied ethane, then methane content is reduced, but energy consumption increases
Solution Approach 1:
The system uses the feed gas stream itself as the heating medium for the reboiler. The warm feed gas (at 50-90 bar and ambient or slightly elevated temperature) provides the necessary heat for vaporizing methane from the liquefied ethane, eliminating the need for external fuel combustion or separate heating utilities.
Solution Approach 2:
The process converts the potentially wasted thermal energy in the feed gas stream into a useful resource by using it to provide reboiler duty for methane removal. What would otherwise be thermal energy requiring disposal is transformed into a beneficial heating source for the separation process.
3Manufacturing precision
If a distillation column is used to remove methane, then separation efficiency improves, but process complexity increases
Solution Approach 1:
The distillation column is designed to perform multiple functions simultaneously: (1) demethanization by removing methane and lighter components from the ethane stream, and (2) providing a reflux stream that enhances separation efficiency. The column integrates both separation and purification functions in a single unit operation.
Solution Approach 2:
The process merges the cooling and separation operations into an integrated flow path where the cooled feed stream is directly introduced to the distillation column for methane removal, and the resulting ethane-rich liquid is immediately routed to the heat exchanger for final liquefaction. This merging eliminates intermediate storage and handling steps.
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 enables efficient liquefaction of ethane while reducing methane content, optimizing refrigeration through a mixed refrigerant cycle that includes compression and cooling stages, and using the ethane feed as a reboiling fluid in the distillation column, resulting in a cost-effective and efficient ethane liquefaction process.
Implementation Method 1
cooling the ethane feed in a heat exchanger to a temperature effective for liquefying the ethane and separating the methane
Implementation Method 2
liquefying the ethane and separating the methane, wherein the heat for the reboiler is provided by cooling the feed gas
Implementation Method 3
introducing the partially cooled ethane stream into an intermediate location of a distillation column under conditions effective to cause an ethane rich liquid to accumulate near the bottom portion of the distillation column and a methane rich gas to accumulate near the top portion
Implementation Method 4
cooling the ethane feed to a first temperature to form a pre-cooled ethane feed... cooling the ethane stream from the bottom portion of the distillation column to produce liquid ethane product
Data Source
AI summary
The process for liquefying a gaseous stream received from a pipeline that is comprised predominantly of ethane and a relatively small amount of other components by using a mixed refrigerant loop incorporating heavy hydrocarbons, as well as a distillation column to remove constituents lighter than ethane.