Acid Gas Removal Flash Regeneration Using Low-Level Waste Heat
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Solution Overview
Problem
Existing methods for acid gas removal from high-pressure hydrocarbonaceous feed gases, such as those from natural and synthetic gas fields, result in high energy consumption due to the need for significant heating and recompression of CO2, which is often produced at or near atmospheric pressure, making CO2 sequestration energy-intensive.
Innovation Solution
The use of a physical solvent regeneration process involving successive flashing stages and low-level waste heat from sources like compressor discharges and feed gas heat, combined with hydraulic turbines for pressure letdown, to reduce energy demand and avoid energy-intensive devices like steam regenerators, allowing for efficient CO2 removal and production of high-pressure CO2 streams with reduced compression needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional CO2 removal methods are used, then CO2 can be removed from feed gas, but the produced CO2 requires substantial compression to high pressure for re-injection, resulting in high energy consumption
Solution Approach 1:
The patent changes the pressure parameter of the CO2 product stream by using successive flashing stages that operate at different pressure levels. Instead of producing CO2 at atmospheric pressure requiring compression to 2000 psig, the flashing process produces CO2 at elevated pressures (first flash at higher pressure, second flash at lower pressure), significantly reducing the compression energy required for re-injection.
Solution Approach 2:
The solvent regeneration process is segmented into multiple flashing stages rather than a single stage. The rich solvent is flashed in a first stage at a first pressure to produce a first CO2 stream, then the remaining solvent is flashed in a second stage at a second pressure to produce a second CO2 stream. This segmentation allows recovery of CO2 at different pressure levels, optimizing energy efficiency.
2Loss of energy
If steam heating is used for solvent regeneration, then CO2 can be effectively removed from the solvent, but the energy demand for steam generation increases overall energy consumption
Solution Approach 1:
The system uses self-service heating where the hot CO2 streams produced during the flashing process are used to heat the rich solvent for regeneration. The first CO2 stream from the first flashing stage is heated and then used to heat the rich solvent in a heat exchanger, eliminating the need for external steam generation and reducing overall energy demand.
Solution Approach 2:
The patent converts the thermal energy that would otherwise be wasted in the hot CO2 streams into a useful resource for heating the rich solvent. The heat content of the CO2 streams, which would normally be discarded, is now utilized to provide the heating requirement for solvent regeneration, transforming a waste product into a beneficial resource.
3Productivity
If sequential flashing is performed at high temperatures, then solvent regeneration is improved, but the energy demand for heating and cooling increases
Solution Approach 1:
The patent implements continuous heat recovery where the hot CO2 streams from the flashing stages continuously heat the rich solvent as it passes through the heat exchanger. This continuous exchange of thermal energy maintains the regeneration process without requiring intermittent heating and cooling cycles, improving efficiency while reducing energy demand.
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 significantly reduces energy consumption and external heating/cooling demands, enabling over 80% CO2 removal using waste heat, with the majority of CO2 produced at higher pressures that require less compression, thus lowering overall energy and capital costs, and minimizing environmental impact.
Implementation Method 1
heating the CO2-rich solvent using waste heat from flash-regenerated lean solvent and heat recovered from the feed gas and/or a compressor discharge
Implementation Method 2
the heated CO2-rich solvent is flashed to produce at least two separate CO2 streams at a pressure of between 50 psig to 500 psig
Implementation Method 3
the methods and plants according to the inventive subject matter employ pressure letdown of the rich solvent by hydraulic turbines to further recover energy
Implementation Method 4
the CO2 streams are compressed to high pressure for re-injection into the formation
Data Source
AI summary
Acid gas is removed from a feed gas using a physical solvent that is regenerated using successive flashing stages after heating of the rich solvent using low-level waste heat that is preferably produced or available within the acid gas removal plant. Especially preferred waste heat sources include compressor discharges of the refrigeration system and/or recompression system for CO2, and/or (low level) heat content from the feed gas.