Two-Stage Scrubber for Off-Gas Cleaning
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Solution Overview
Problem
Existing methods for separating sulphur dioxide from flue gases are inefficient due to incomplete separation and the release of ammonia, leading to the formation of aerosols of ammonium sulphate, which incurs additional costs and environmental concerns, particularly in waste incinerators.
Innovation Solution
A two-stage scrubber process where sulphur dioxide is initially separated using ammonia, followed by oxidation with hydrogen peroxide in the second stage to form sulphuric acid, allowing for the separation of ammonia and sulphur dioxide, with pH values controlled between 4 to 6 in the first stage and 1 to 5 in the second to optimize separation and minimize ammonia release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ammonia is added to separate sulphur dioxide in a single scrubber stage, then sulphur dioxide separation is achieved, but ammonia release and formation of ammonium sulphate aerosols occur
Solution Approach 1:
The scrubbing process is divided into two distinct stages: first stage uses ammonia for sulphur dioxide separation, second stage uses hydrogen peroxide to oxidize remaining sulphur dioxide and neutralize released ammonia. This segmentation allows each stage to perform its specific function optimally without the harmful side effects of the single-stage approach.
Solution Approach 2:
Hydrogen peroxide acts as an intermediary substance in the second stage, serving dual purposes: oxidizing remaining sulphur dioxide to sulphuric acid and simultaneously neutralizing released ammonia to form ammonium sulphate. This intermediary approach resolves the contradiction by addressing both sulphur dioxide separation and ammonia control in a coordinated manner.
2Object-generated harmful factors
If low pH-values are used to prevent ammonia release, then ammonia release is minimized, but sulphur dioxide separation becomes incomplete
Solution Approach 1:
The pH value is dynamically adjusted between the two stages: first stage operates at higher pH (4-6) for optimal sulphur dioxide absorption, second stage operates at lower pH (1-5) to neutralize released ammonia. This dynamic pH adjustment allows the system to optimize for different objectives in different stages, resolving the contradiction between ammonia control and sulphur dioxide separation.
3Object-generated harmful factors
If sulphuric acid is added in a third scrubber stage to separate released ammonia, then ammonia separation is achieved, but additional costs for cleaning and disposal increase
Solution Approach 1:
Hydrogen peroxide in the second stage serves multiple functions simultaneously: it oxidizes remaining sulphur dioxide to sulphuric acid, neutralizes released ammonia to form ammonium sulphate, and eliminates the need for a separate third stage. This multi-functionality reduces system complexity and operational costs while achieving both sulphur dioxide separation and ammonia control.
Solution Approach 2:
The oxidation of sulphur dioxide and the neutralization of ammonia are merged into a single second stage operation using hydrogen peroxide. This consolidation combines what would traditionally require separate stages (sulphuric acid addition for ammonia separation) into one integrated process, reducing the number of scrubber stages from three to two.
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 method achieves high sulphur dioxide separation efficiency while minimizing ammonia release, resulting in low clean gas concentrations of both SO2 and ammonia, reducing operational and disposal costs.
Implementation Method 1
Sulphur dioxide is separated from off-gas in a first scrubber stage by means of ammonia or ammonium compounds
Implementation Method 2
in the second scrubber stage the sulphur dioxide, which has not been separated in the first scrubber stage, is oxidised by addition of hydrogen peroxide to sulphuric acid
Implementation Method 3
the ammonia released from the first scrubber stage is separated in the second scrubber stage together with the formed sulphuric acid via formation of ammonium sulphate
Data Source
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AI summary
The present invention relates to a method for cleaning off-gas comprising the following steps: 1. sulphur dioxide is separated from the off-gas by way of at least one first scrubber stage (c) by means of ammonia or ammonium compounds, 2. the off-gas is transferred into a second scrubber stage (d) and 3. in the second scrubber stage the sulphur dioxide not separated in the first scrubber stage (c), is oxidised to sulphuric acid and separated in at least one scrubber (d) and simultaneously, the ammonia released in the first scrubber stage (d) is separated by means of the formed sulphuric acid, whereby ammonium sulphate is formed, 4. the separated stream of the second scrubber stage (d) is transferred into the first scrubber stage (c).