Method for producing a flow which is rich in methane and a cut which is rich in C<sub>2</sub><sup>+ </sup>hydrocarbons from a flow of feed natural gas and an associated installation
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Solution Overview
Problem
Existing methods for producing a flow rich in methane and a cut rich in C2+ hydrocarbons from natural gas are not efficient when the feed natural gas is rich in heavy hydrocarbons like ethane, propane, and butane, requiring high cooling energy and being unsuitable for installations without external cooling cycles, such as floating plants.
Innovation Solution
A method involving the formation of a second recirculation flow from the head flow rich in methane, which is dynamically expanded and introduced into an expansion turbine to produce frigories, enhancing the recovery of C2+ hydrocarbons by reintroducing it into the separation column, thereby improving selectivity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If external cooling cycles using propane are used to cool feed natural gas, then cooling efficiency is improved, but device complexity and safety risks increase
Solution Approach 1:
The system uses its own produced refrigerant (propane from C2+ hydrocarbon separation) to cool the feed natural gas, eliminating the need for external cooling cycles. The propane is generated within the system through separation and purification units, then circulated through heat exchangers to provide cooling, making the system self-sufficient and reducing external dependencies.
Solution Approach 2:
The cooling function is merged with the hydrocarbon separation process. The same propane that is separated as a product from the natural gas feed is simultaneously used as the refrigerant for cooling the feed gas. This integration combines two functions (separation and cooling) into a unified system where the separation unit's output becomes the cooling unit's input.
2Productivity
If feed natural gas with high C2+ hydrocarbon content is processed using conventional methods, then production capacity is maintained, but energy consumption increases
Solution Approach 1:
The system changes the operating parameters by using a two-stage separation process with specific temperature and pressure conditions optimized for high C2+ content gases. The first separation occurs at higher pressure to condense heavier hydrocarbons, followed by a second separation at lower pressure. This parameter optimization allows efficient processing of high C2+ content feeds without excessive energy input.
Solution Approach 2:
The system replaces conventional mechanical compression-based cooling with a thermodynamic expansion approach. The refrigerant cycle uses expansion valves and heat exchangers to achieve cooling through phase change and heat transfer, rather than relying solely on mechanical compression and condensation systems, reducing overall energy consumption.
3Quantity of substance
If conventional separation methods are used for natural gas rich in heavy hydrocarbons, then separation is achieved, but selectivity and recovery rate decrease
Solution Approach 1:
The separation process is divided into multiple stages with different separation mechanisms. The first stage uses condensation at high pressure to separate heavier C2+ hydrocarbons from the feed gas. The second stage uses flash separation at lower pressure to further purify the methane stream. This segmentation allows each stage to target specific hydrocarbon ranges, improving overall selectivity and recovery efficiency for feeds rich in heavy hydrocarbons.
Solution Approach 2:
The system introduces an intermediary refrigerant cycle using propane as a mediator substance. This refrigerant facilitates heat transfer between the feed gas and the separation equipment, enabling precise temperature control during the separation process. The intermediary refrigerant allows the system to maintain optimal separation conditions without directly contacting the feed gas, improving separation precision.
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 method achieves high selectivity and efficiency in recovering C2+ hydrocarbons, reducing energy consumption and maintaining high recovery rates even with high content of heavy hydrocarbons, while being applicable to installations without external cooling cycles.
Implementation Method 1
forming a dynamic expansion flow from the second recirculation flow and introducing the dynamic expansion flow into an expansion turbine in order to produce frigories
Implementation Method 2
cooling the feed natural gas flow advantageously at a pressure greater than 40 bar in a first heat exchanger
Implementation Method 3
separating the cooled natural gas flow in the first separation flask and recovering a light fraction which is substantially gaseous and a heavy fraction which is substantially liquid
Data Source
AI summary
This method comprises cooling the feed natural gas in a first heat exchanger and introducing the cooled, feed natural gas into a first separation flask.It comprises the dynamic expansion of a turbine supply flow in a first expansion turbine and introducing the expanded flow into a separation column. This method comprises removing, at the head of the separation column, a head flow rich in methane and removing a first recirculation flow from the compressed head flow rich in methane.The method comprises forming at least a second recirculation flow obtained from the head flow rich in methane downstream of the separation column and forming a dynamic expansion flow from the second recirculation flow.