High-Pressure Acid Gas Removal With Multi-Stage Solvent Flashing
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Solution Overview
Problem
Current acid gas removal methods from high-pressure gases with high CO2 and H2S content face challenges such as high capital and operating costs, energy inefficiency, and inability to produce CO2 streams with sufficient purity for Enhanced Oil Recovery (EOR) due to high hydrocarbon contamination, especially in sour gas fields.
Innovation Solution
The method involves using an ultra-lean physical solvent for acid gas removal, where C1-C3 hydrocarbons are recycled and CO2 and C4+ hydrocarbons are flashed at elevated temperatures, followed by stripping with treated feed gas to produce a CO2 stream with less than 5% C4+ components, allowing for efficient separation and recycling of hydrocarbons, reducing hydrocarbon losses and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If physical solvent is used for acid gas removal at high pressure, then acid gas loading of the solvent increases with acid gas concentration, but the CO2 stream contains more than 5 mol % hydrocarbons which fails to meet EOR purity requirements
Solution Approach 1:
The flash separation process is divided into multiple stages with different pressure levels. The first flash stage operates at intermediate pressure to separate C1-C3 hydrocarbons, while the second flash stage operates at lower pressure to separate C4+ hydrocarbons from CO2. This segmented approach allows selective removal of hydrocarbon components at different pressure stages, achieving CO2 purity suitable for EOR while maintaining high acid gas loading capacity.
2Quantity of substance
If conventional amine absorption process is used, then acid gas removal is achieved, but steam demand for solvent regeneration is relatively high at high acid gas concentration
Solution Approach 1:
The process utilizes pressure change as the driving force for solvent regeneration instead of thermal energy. By reducing pressure from high pressure (where acid gas is absorbed) to lower pressure (where acid gas is released), the system achieves solvent regeneration without steam heating. This parameter change from thermal to mechanical energy reduces steam demand significantly while maintaining effective acid gas removal.
3Use of energy by moving object
If physical solvent regeneration is accomplished by flash regeneration without external heating, then energy requirements are reduced, but the treated gas fails to meet below 4 ppmv pipeline specifications
Solution Approach 1:
The flash regeneration process is segmented into multiple stages with progressively lower pressures. The first flash stage at intermediate pressure removes C1-C3 hydrocarbons, while the second flash stage at lower pressure removes remaining acid gases and C4+ hydrocarbons. This multi-stage segmentation achieves the required treated gas purity of below 4 ppmv without requiring external heating, maintaining low energy requirements.
4Productivity
If CO2 is removed from feed gas at supercritical pressure, then removal efficiency is relatively high, but hydrocarbon losses are undesirably high
Solution Approach 1:
The process applies different pressure conditions to different components based on their properties. Light hydrocarbons (C1-C3) are removed at intermediate pressure where they have high volatility, while CO2 is removed at lower pressure. This localized approach to pressure selection minimizes hydrocarbon losses while maintaining high removal efficiency for acid gases.
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 hydrocarbon losses and energy consumption while producing a CO2 stream suitable for EOR, meeting pipeline specifications and generating a valuable C4+ hydrocarbon product, thus improving the economic viability and environmental sustainability of acid gas removal processes.
Implementation Method 1
contacting the feed gas in an absorber with an ultra-lean physical solvent to form a rich solvent and a treated feed gas
Implementation Method 2
the rich solvent is sequentially depressurized to remove C1-C3 hydrocarbons to so form a depressurized solvent
Implementation Method 3
the depressurized solvent is flashed and stripped to produce an ultra-lean solvent and a flashed gas that predominantly comprises H2S, CO2 and C4+ components
Implementation Method 4
The flashed gas is then separated in a separator to produce a CO2 stream having less than 5% C4+ components and a C4+ product
Data Source
AI summary
Physical solvent is regenerated using flashing and stripping processes to produce an ultra-lean solvent. In especially preferred aspects, flashed C1-C3 hydrocarbons are recycled to the absorber, while C4+ hydrocarbons are recovered from the CO2 that is removed from the solvent. It is further preferred that depressurization of the rich solvent provides most of the refrigeration duty.