Lean Natural Gas Benzene Removal Using Solvent Recycle
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Solution Overview
Problem
Conventional cryogenic expander processes struggle to economically and efficiently remove benzene from lean natural gas to less than 1 ppm levels, especially when there are insufficient heavier hydrocarbons present, leading to benzene freeze-up in gas liquefaction units.
Innovation Solution
A modified process involving a rich/lean gas exchanger, demethanizer side re-boiler, expander suction drum, and solvent recycle system, utilizing a formulated hydrocarbon-based solvent to enhance benzene removal at higher pressures, even in the absence of adequate LPG components, by recycling and re-injecting the solvent back into the dehydrated gas feed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cryogenic expander processes are used to remove benzene from lean natural gas, then benzene removal is achieved when sufficient heavier hydrocarbons are present, but the process becomes economically and/or efficiently unviable when adequate LPG components are absent
Solution Approach 1:
A solvent extraction unit is introduced as an intermediary process between the dehydrator and the cryogenic expander. This solvent unit uses a hydrocarbon-based solvent to extract benzene from the lean natural gas feed before it enters the expander, enabling effective benzene removal even when the gas lacks sufficient heavier LPG components for conventional expander-based removal
Solution Approach 2:
The invention changes the operating parameters by introducing a solvent extraction step that operates at different conditions than conventional expander processes. The solvent system allows benzene removal at pressures and temperatures optimized for extraction rather than expansion, making the process viable for lean gases without adequate C3+ components
2Reliability
If cryogenic processes operate at high pressure to remove benzene, then benzene condensation is enhanced, but traces of benzene cannot be condensed and removed from lean feed gas having high methane content
Solution Approach 1:
The solvent extraction unit acts as an intermediary that preferentially extracts benzene from the high-methane lean feed gas before cryogenic processing. The solvent system enables benzene removal at levels below 1 ppm by transferring benzene from the gas phase to the solvent phase, overcoming the limitation of insufficient condensation in high-methane streams
Solution Approach 2:
The invention changes the removal mechanism from purely cryogenic condensation to solvent-based extraction followed by cryogenic processing. This parameter change allows benzene to be removed at trace levels (<1 ppm) by utilizing solvent-benzene interactions rather than relying solely on temperature and pressure-dependent condensation
3Productivity
If benzene is not removed from feed to gas liquefaction, then the process operates continuously, but benzene freezes in sub-cryogenic sections causing process disruption
Solution Approach 1:
The solvent extraction unit performs preliminary benzene removal before the gas enters the cryogenic liquefaction process. By extracting benzene in advance at the feed stage, the process prevents benzene freeze-up in downstream sub-cryogenic sections while maintaining continuous operation of the liquefaction unit
Solution Approach 2:
The invention applies preliminary anti-action by removing benzene before it can cause harmful freeze-up effects. The solvent extraction process counteracts the potential freezing problem by reducing benzene concentrations to safe levels (<1 ppm) before the gas enters the cryogenic section, preventing disruption to continuous operation
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 effectively reduces benzene levels to below 1 ppm, preventing freeze-up in liquefaction units while being economically and energy-efficient, even in lean natural gas streams lacking sufficient heavier hydrocarbons.
Implementation Method 1
providing a solvent makeup stream comprising a formulated hydrocarbon based solution... pumping the formulated hydrocarbon based solution with one or more solvent make up pumps into a liquid stream comprising the first stabilized condensate to form a combined liquid stream... feeding the combined liquid stream into one or more NGL reinjection pumps, solvent recycle pumps, or a combination thereof to form a solvent recycle stream
Implementation Method 2
splitting a dehydrated feed gas into a first input stream directed into a rich/lean gas exchanger to provide a first output stream
Implementation Method 3
condensing the gas in the demethanizer column to form a NGL (natural gas liquid) condensate
Implementation Method 4
directing a gas stream from the stabilizer into a stabilizer condenser to provide a first condensate
Data Source
AI summary
A method and apparatus for removing benzene from a lean natural gas feed is provided. The method and apparatus are capable of removing benzene from lean natural gas that is predominantly composed of methane and contains very little heavier hydrocarbon components.