Offshore Fuel Gas Purification Using Turbo-Expander and Reflux Cooling
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Solution Overview
Problem
Current gas purification systems for offshore hydrocarbon production are bulky and difficult to operate in remote locations, failing to effectively remove impurities like hydrogen sulfide and carbon dioxide from raw natural gas, which can cause corrosion and reduce the BTU value of fuel gas, leading to operational issues and environmental emissions.
Innovation Solution
A method and system that involves cooling and compressing a compressed gas stream, separating liquids, dehydrating, and using a turbo-expander and reflux heat exchanger to produce a cold fuel gas stream, which is then used to cool and purify the gas, ultimately removing contaminants like CO2 and H2S, and recycling the waste stream for further processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional gas purification systems are used to remove impurities like H2S and CO2, then the fuel gas quality is improved, but the system becomes bulky and difficult to operate in remote offshore locations
Solution Approach 1:
The purification system is divided into multiple functional units including a cooling section, separation section, dehydration section, and turbo-expander section. Each unit performs a specific function (cooling, liquid separation, dehydration, expansion) that can be independently optimized and maintained, making the overall system more manageable in remote offshore locations while achieving high fuel gas quality
Solution Approach 2:
A reflux heat exchanger is introduced as an intermediary component to recover cold energy from the fuel gas stream and use it to pre-cool the incoming compressed gas. This intermediary heat exchange mechanism improves system efficiency and reduces the complexity of external cooling requirements, enhancing operability in remote locations
2Ease of operation
If raw natural gas is used as fuel without purification, then operational simplicity is maintained, but corrosion and carbon build-up occur in equipment
Solution Approach 1:
The system performs preliminary purification actions before the gas reaches the fuel combustion equipment. The cooling section condenses liquid hydrocarbons, the separation section removes them, the dehydration section eliminates water, and the turbo-expander section further cools and separates remaining contaminants. This preliminary action ensures that only purified gas reaches the fuel system, preventing corrosion and carbon build-up while maintaining operational simplicity
Solution Approach 2:
The purified fuel gas is used to power the turbo-expander and other system components, creating a self-service system where the output product drives the purification process. This reduces the need for external power sources and complex control systems, maintaining operational simplicity while ensuring reliable equipment protection through continuous purification
3Use of energy by moving object
If high levels of CO2 are present in the fuel gas, then the BTU value is reduced, but purification processes increase system complexity
Solution Approach 1:
The system utilizes phase transitions of CO2 and other contaminants by cooling the compressed gas to temperatures where these components condense from the gas phase to liquid phase. The cooling section and turbo-expander section achieve temperatures sufficient to condense CO2, which is then separated in the separation section. This phase transition approach efficiently removes CO2 to maintain high BTU value without requiring complex chemical treatment systems
Solution Approach 2:
The system changes the temperature and pressure parameters of the gas stream through the cooling section and turbo-expander section to optimize contaminant separation. By controlling the cooling temperature and expansion pressure, the system maximizes CO2 condensation while minimizing the complexity of separation equipment. The reflux heat exchanger further optimizes these parameters by recovering cold energy, reducing the overall energy input required for purification
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 the production of a high-quality fuel gas with reduced sulfur content, extending equipment lifespan, reducing operational downtime, and minimizing environmental impact by efficiently purifying gas in remote offshore settings.
Implementation Method 1
The compressed gas stream is cooled to form a cool compressed gas stream
Implementation Method 2
The dry gas stream is chilled in a first heat exchanger to produce a dry cold fluid stream
Implementation Method 3
A first part of the cold vapor stream is expanded in a turbo-expander to produce a cold two-phase fluid stream
Implementation Method 4
The cold fuel gas stream is used to cool the second part of the cold vapor stream in the reflux heat exchanger
Implementation Method 5
The compressed cold fuel gas stream and the low-temperature liquids stream are used to chill the dry gas stream in the first heat exchanger
Data Source
AI summary
Methods and systems for treating a compressed gas stream. The compressed gas stream is cooled and liquids are removed therefrom to form a dry gas stream, which is chilled in a first heat exchanger. Liquids are separated therefrom, thereby producing a cold vapor stream and a liquids stream. A first part of the cold vapor stream is expanded to produce a cold two-phase fluid stream, and a second part of the cold vapor stream is cooled to form a cooled reflux stream. Various streams are fed into a separation column to produce a cold fuel gas stream and a low temperature liquids stream. The second part of the cold vapor stream is cooled by the cold fuel gas stream, which becomes a warmed fuel gas stream that is compressed and used with the low-temperature liquids stream to chill the dry gas stream and to cool the compressed gas stream.