Rotating Drum Slag Carbonation Process
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Solution Overview
Problem
Current slag treatment methods face challenges due to extreme pH, ecotoxicity, soluble salts, and high emissions of heavy metals and anions, preventing low-cost recovery and disposal of slag from incineration plants, which is classified as dangerous waste.
Innovation Solution
A process involving a continuously rotating drum with a controlled water/ash ratio and high CO2 concentration, followed by mechanical screening and chemical treatment, including deferrization, filtration, and chemico-physical purification, to achieve thorough carbonation and separation of slag components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If natural carbonation by exposure to air in heaps is used for slag treatment, then the process is simple and low-cost, but the carbonation is incomplete and takes at least six months
Solution Approach 1:
The patent uses a fluidized bed reactor where air is blown upward through the slag particles, creating fluidization that dramatically accelerates carbonation. The pneumatic flow distributes CO2 uniformly throughout the slag bed, achieving complete carbonation in hours rather than months while maintaining operational simplicity
Solution Approach 2:
The patent changes the physical state of the slag from static heap exposure to dynamic fluidized particles, and controls CO2 concentration parameters in the air stream. This parameter optimization enables rapid and complete carbonation while keeping the process relatively simple
2Quantity of substance
If water/solid ratio less than 0.5:1 is used for carbonation, then water consumption is reduced, but carbonation stops at the first layer as calcium carbonate forms blocking CO2 access
Solution Approach 1:
The patent uses a fluidized bed where particles are continuously moving and suspended by upward air flow. This dynamic state prevents calcium carbonate from forming a static blocking layer, as the constant particle motion and fluidization allow CO2 to penetrate throughout the entire slag bed even with limited water present
Solution Approach 2:
The continuous fluidization and particle circulation ensure that carbonation action continues throughout the entire slag mass without interruption. The constant movement prevents layer formation and maintains continuous CO2 access to all slag particles
3Object-affected harmful factors
If slag is treated to reduce pH and remove contaminants, then ecotoxicity and dangerous waste classification are reduced, but treatment complexity and cost increase
Solution Approach 1:
The patent combines carbonation, pH reduction, and contaminant removal into a single integrated fluidized bed process. The CO2-rich air stream simultaneously carbonates the slag (reducing pH) and the fluidization mechanism enhances contaminant removal, achieving multiple objectives in one operation rather than separate treatment steps
Solution Approach 2:
The patent converts the harmful high pH and ecotoxicity of fresh slag into beneficial effects by using CO2 carbonation to transform the chemical composition. The same fluidization process that accelerates carbonation also facilitates contaminant removal, turning a dangerous waste into a safe, reusable material
4Productivity
If mechanical screening and filtration are used to separate slag components, then recovery and reutilization are improved, but process complexity increases
Solution Approach 1:
The patent uses mechanical screening to segment the carbonated slag into different particle size fractions. This segmentation separates recoverable materials based on size, enabling efficient recovery and reutilization of valuable components while maintaining a relatively simple screening-based separation process
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 process results in a fully carbonated slag with reduced pH, removal of contaminants, and emissions within EU limits for non-dangerous waste disposal, enabling nearly total reutilization of slag materials.
Implementation Method 1
The CO2 naturally present in air reacts with the oxides and hydroxides present in the slag to give rise to carbonates and water
Implementation Method 2
the CO2, which dissolves in water, easily reaches all the basic substances, with which it reacts
Implementation Method 3
aided and accelerated in this by the grinding and mixing action performed by the vitreous inert component present in the slag
Implementation Method 4
the material, in the form of water and slag of different particle sizes, is made to pass through a mechanical screen with mesh dimensions of about 5 mm to obtain a separation
Implementation Method 5
This phase is presented as an easily sedimentable sludge separable from the water, hence the separation between the two phases can be obtained by static sedimentation
Implementation Method 6
but preferably by mechanical filtration (preferably a filter press, a belt press or a centrifuge)
Implementation Method 7
The water leaving the filter press is treated in a chemico-physical purifier
Data Source
AI summary
A process for treating heavy ash or slag in general, characterised by mixing, in the interior of a rotating body, the heavy ash and/or slag and a water quantity in a weight ratio between 0.8 and 2, while simultaneously passing into the rotating body a flow of gaseous CO2 in a concentration between 90 and 100% v/v for a period not exceeding 2 hours, on termination of the mixing stage the material being passed through at least one screen by which it is separated into ash of diameter greater than 5 mm and a mixture of water and ash with the ash of diameter less than 1 mm, said ash greater than 5 mm being subjected to deferrization treatment, to be then fed to a temporary store, the mixture of water and ash less than 1 mm being subjected to filtration treatment, the filtrate from which consists of a fine fraction of washed and carbonated slag, the water, containing salts washed from the slag and certain heavy metals, being fed to a water purification plant.