Gas-Liquid Mass Transfer Zones with Downcomer Flow Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing gas-liquid contact processes for removing hydrogen sulfide (H2S) face challenges in controlling solution circulation rates, leading to inefficiencies and byproduct formation due to uncontrolled residence time and liquid flow, resulting in either insufficient iron supply or oxygen carryover, which affects the oxidation process and increases operational costs.
Innovation Solution
A continuous process and apparatus that control liquid reagent flow between gas-liquid contact zones by varying the flow rates of gases introduced into downcomers, using density differences and gas velocities to manage solution circulation, ensuring optimal ferric iron and oxygen supply, thereby preventing byproduct formation and maintaining process efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If solution circulation rate is increased to supply sufficient iron for H2S oxidation, then hydrogen sulfide removal efficiency is improved, but oxygen is transferred from oxidizer zone to reaction zone causing unwanted sulfate byproduct formation
Solution Approach 1:
The system is divided into separate reaction zone and oxidizer zone with controlled liquid circulation pathways. The reaction zone handles H2S oxidation while the oxidizer zone regenerates ferric iron, preventing oxygen carryover to the reaction zone and eliminating sulfate byproduct formation while maintaining high H2S removal efficiency
Solution Approach 2:
The liquid circulation rate between zones is automatically controlled based on the redox state of the solution. When ferric iron concentration decreases in the reaction zone, reduced solution circulates to the oxidizer zone for regeneration, and when sufficient ferric iron is restored, circulation is modulated to prevent over-oxidation and sulfate formation
2Object-generated harmful factors
If solution circulation rate is decreased to prevent oxygen carryover, then sulfate byproduct formation is reduced, but insufficient iron is supplied to reaction zone resulting in iron sulfide precipitation
Solution Approach 1:
The circulation system monitors the redox potential and ferric/ferrous iron ratio in the solution. When ferric iron concentration falls below required levels for complete H2S oxidation, the system increases circulation to the oxidizer zone to regenerate more ferric iron, preventing iron sulfide precipitation while avoiding excessive circulation that would cause sulfate formation
Solution Approach 2:
The system uses the redox chemistry itself to control circulation rates. The reduced solution automatically circulates to the oxidizer zone where it is regenerated by oxygen, and the oxidized solution returns to the reaction zone. This self-regulating mechanism ensures optimal iron supply without mechanical pumps or external control systems
3Ease of operation
If gas injection into downcomers is increased to control liquid flow, then solution circulation control is improved, but gas liquid mixing in downcomers increases causing unintended mass transfer
Solution Approach 1:
The gas injection for flow control is extracted from the mass transfer zones and relocated to the downcomers. By injecting gas into the downcomers rather than the reaction or oxidizer zones, the system controls liquid circulation rates without creating unintended mass transfer in the contact zones, as the downcomers are not designed for gas-liquid mass transfer
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 allows for precise control of solution circulation, optimizing the removal of hydrogen sulfide while minimizing byproduct formation, ensuring sufficient iron supply and preventing over-oxidation, thus enhancing the overall efficiency and cost-effectiveness of the hydrogen sulfide removal process.
Implementation Method 1
the rate of liquid flow from one mass transfer zone to another is motivated by the difference in the aerated liquid density in a mass transfer zone and the non-aerated liquid density in a preceding liquid downcomer
Implementation Method 2
The second gas is introduced into the upstream mass transfer zone at a first flow rate where it mixes with the liquid reagent before it flows into the first downcomer
Implementation Method 3
the series of reactions involved in catalytically oxidizing sulfur contaminants, such as hydrogen sulfide, to elemental sulfur using an iron chelate catalyst
Implementation Method 4
reacting the fluid stream with a catalytic redox polyvalent metal solution for H2S gas removal
Implementation Method 5
the solution is reduced to ferrous iron and an oxidizer zone is used to oxidize the reduced ferrous iron back to the ferric iron state
Data Source
Figure 1~2
Figure 3~4
AI summary
An apparatus and method of contacting a liquid with different gases sequentially in separate mass transfer zones within a single vessel, the mass transfer zones operatively in fluid communication with each other, including intimately contacting the liquid with a process gas in co-current flow in a downstream mass transfer zone to effect mass transfer between the liquid and the process gas, and introducing the liquid into an upstream mass transfer zone with a second gas, different from the process gas, thereby effecting mass transfer between the liquid and the second gas. The rate of flow of the liquid from the upstream mass transfer zone to downstream mass transfer zone is controlled by the controlled addition of a third gas into one or more downcomers separating each mass transfer zone such that the specific density of the liquid in the downcomers provides a driving force that controls flow.