Acid Gas Absorber with Intermediate Phase Recirculation
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Solution Overview
Problem
Existing methods for removing acid gases from fluid streams, such as CO2 and H2S, in the chemical industry are inefficient due to heat generation during absorption, leading to increased energy consumption and capital expenditure on additional heat exchangers, and result in a treated fluid stream that requires additional cooling and dewatering.
Innovation Solution
A method involving countercurrent flow in a contactor where a first phase (acid gases) is introduced at the lower region and a second phase (absorption medium) at the upper region, with a portion of the exhausted second phase recirculated between the regions to control temperature and reduce energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If acid gases are absorbed using aqueous base solutions in a conventional absorber, then acid gas removal efficiency is improved, but the treated fluid stream temperature increases requiring additional cooling
Solution Approach 1:
The absorber is divided into multiple stages or zones with intermediate cooling sections. The absorption process is segmented into multiple contact zones separated by cooling sections where the absorption medium is cooled by indirect heat exchange with incoming cold absorption medium, preventing excessive temperature rise in the treated fluid stream while maintaining high acid gas removal efficiency.
Solution Approach 2:
The solution introduces a spatial dimension to heat management by incorporating vertical cooling sections within the absorber column. Heat exchange occurs in a different spatial zone (cooling sections) rather than directly in the absorption contact zones, allowing simultaneous heat removal and mass transfer without interfering with each other.
2Productivity
If the treated fluid stream temperature is increased, then absorption kinetics are improved, but energy loss increases and downstream cooling is required
Solution Approach 1:
The exothermic heat of absorption, which was previously a harmful effect requiring cooling, is converted into a beneficial resource. The hot absorption medium exiting the absorber is used to preheat the incoming cold absorption medium through indirect heat exchange in cooling sections, recovering thermal energy and reducing the overall energy input required for the process.
Solution Approach 2:
The heat exchange process operates continuously throughout the absorber operation. As absorption medium flows through the column and absorbs acid gases (generating heat), it continuously exchanges heat with incoming cold medium in cooling sections, maintaining a continuous cycle of heat recovery without interrupting the absorption process.
3Temperature
If additional heat exchangers are installed to cool the absorption medium, then temperature control is improved, but capital expenditure increases
Solution Approach 1:
The heat exchangers installed in the cooling sections serve multiple functions simultaneously: they cool the outgoing hot absorption medium, preheat the incoming cold absorption medium, and provide structural support for the absorber column. This multi-functionality reduces the need for separate dedicated cooling equipment and minimizes overall capital expenditure.
Solution Approach 2:
The cooling function is merged with the absorption column structure itself. The cooling sections are integrated into the absorber column, and the heat exchangers are combined with the flow distribution system, eliminating the need for separate external cooling units and reducing overall equipment count and capital cost.
4Productivity
If the treated fluid stream temperature is increased, then mass transfer rate is improved, but water vapor content increases requiring dewatering
Solution Approach 1:
Different zones of the absorber are designed with different temperature characteristics optimized for their specific function. The upper absorption zones operate at higher temperatures to maximize mass transfer rates for acid gas removal, while the lower cooling zones maintain lower temperatures to minimize water vapor generation. This local optimization allows high productivity without excessive water vapor content.
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 the temperature of the treated fluid stream, decreases energy requirements, and allows for more efficient acid gas removal with lower residual concentrations, thereby optimizing the process by minimizing the need for downstream cooling and energy reapplication.
Implementation Method 1
When acid gases are dissolved in the absorption medium, ions form with the bases
Implementation Method 2
The reaction between the acid gases and the absorption medium is exothermic
Implementation Method 3
The absorption medium can be regenerated by expansion to a lower pressure
Data Source
AI summary
A method for bringing into contact two phases which are not completely miscible with one another, and whose contact is accompanied by heat development owing to mass transfer and/or chemical reaction, in which a first phase is introduced into the lower region of a contactor and a second phase is introduced into the upper region of the contactor and passed in countercurrent flow to the first phase in the contactor, a treated first phase and an exhausted second phase being obtained, which comprises recirculating a part of the exhausted second phase to the contactor at least one point situated between the upper region and the lower region. In the preferred embodiment, the first phase is a fluid stream comprising acid gases such as CO2, H2S, SO2, CS2, HCN, COS or mercaptans, and the second phase is an absorption medium which comprises an aqueous solution of at least one organic and/or inorganic base.