Biogas Desulfurization via Segmented Absorption and Oxidation
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Solution Overview
Problem
Existing desulfurization processes for biogas and gas mixtures containing combustible components, such as those using hydrogen peroxide (H2O2) as an oxidizing agent, pose a risk of forming explosive gas mixtures due to oxygen desorption, limiting their safety and applicability, especially when handling biogas.
Innovation Solution
A method involving selective absorption of H2S in a basic absorbent followed by phase separation and subsequent oxidation of the absorbed H2S with an oxidizing agent in a separate reactor, using a gas-tight line with siphons or non-return valves to prevent back-mixing, ensuring that combustible gas components do not come into contact with the oxidizing agent, thereby avoiding explosive risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If H2O2 is used as oxidizing agent in desulfurization process, then oxidation of H2S to elemental sulfur is achieved, but oxygen desorption forms explosive gas mixtures with combustible components
Solution Approach 1:
The process is divided into three distinct stages: absorption stage (where H2S is absorbed by basic absorbent), phase separation stage (where liquid and gas phases are separated), and oxidation stage (where H2S is oxidized to elemental sulfur). This segmentation ensures that combustible gas components are never present during oxidation, eliminating explosive risks while maintaining effective desulfurization
Solution Approach 2:
A phase separation unit acts as an intermediary between the absorption stage and oxidation stage. This intermediary device removes combustible gas components from the system before oxidation occurs, allowing H2O2 to be used safely as the oxidizing agent without forming explosive mixtures
2Productivity
If absorption and oxidation are carried out simultaneously, then process efficiency is improved, but back-mixing of phases occurs causing safety risks
Solution Approach 1:
The process is segmented into sequential stages with distinct functional zones. The absorption reactor handles H2S absorption, the phase separation unit handles phase separation, and the oxidation reactor handles oxidation. This spatial and temporal segmentation prevents back-mixing while maintaining overall process efficiency
Solution Approach 2:
Combustible gas components are extracted from the liquid phase during phase separation before the oxidation stage. This extraction ensures that only H2S-containing liquid enters the oxidation reactor, eliminating the risk of explosive mixtures while preserving process efficiency
3Stability of the object's composition
If acidic pH is used to prevent H2O2 decomposition, then oxidizing agent stability is improved, but absorption efficiency of H2S decreases
Solution Approach 1:
The process separates the functions of absorption and oxidation into different stages with different pH conditions. The absorption stage uses basic pH for high H2S absorption efficiency, while the oxidation stage uses acidic pH to stabilize H2O2. This segmentation allows each stage to operate under optimal conditions without compromising the other
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 safe and efficient desulfurization of biogas without the need for acidic pH adjustments or avoidance of metal surfaces, reducing the risk of explosive gas mixtures and optimizing the use of H2O2 as the oxidizing agent, while minimizing the amount of oxidizing agent required and enabling shorter residence times in the oxidation reactor.
Implementation Method 1
absorption of H2S in aqueous alkaline solutions (e.g. NaOH, KOH) with the formation of sulfides or hydrogen sulfides
Implementation Method 2
subsequent oxidation of the absorbed H2S with an oxidizing agent to elemental sulfur and/or higher oxidation states of sulfur
Implementation Method 3
one or more siphons, non-return valves or flaps or float-controlled or electronically level-controlled drains
Data Source
Figure 1
AI summary
The invention relates to a process for desulfurizing a gas mixture containing H2S and CO2 by means of selective absorption of the H2S into a basic absorbent and subsequent oxidation of the H2S absorbed with an oxidizing agent, which is characterized in that i) a combustible biogas containing H2 and/or CH4 is used as the gas mixture to be desulfurized; ii) after the absorption step a phase separation step is conducted to separate the liquid phase in the form of the sulfide-enriched absorbent from the gas phase containing the combustible gas components; and iii) the liquid phase thus degassed is contacted with an oxidizing agent in order to oxidize the sulfide to elemental sulfur and/or higher oxidation states of sulfur.