Mercury-Depleted Coal Combustion Ash via Froth Flotation
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Solution Overview
Problem
The high mercury content in bituminous coal fly ash reduces its acceptance as a cement kiln raw material due to regulatory constraints on mercury emissions, necessitating a practical and economical method for its reduction.
Innovation Solution
The method involves forming a slurry of combustion ash and water, followed by wet froth flotation with pulverization before the process to enhance mercury reduction, using collector chemicals and adjusting pH, resulting in a mercury-depleted ash suitable for both pozzolanic and cement kiln applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bituminous coal fly ash is used as cement kiln raw material, then pozzolanic properties and cementitious value are improved, but mercury content increases causing regulatory compliance issues
Solution Approach 1:
The patent applies extraction by removing mercury from combustion ash through flotation processes. The harmful mercury component is separated from the beneficial pozzolanic material, allowing the ash to meet regulatory requirements while retaining its cementitious value. This is achieved through selective flotation where mercury-containing particles are separated from the bulk ash material.
Solution Approach 2:
The patent changes physical parameters of the ash through size reduction (pulverization) and chemical parameters through flotation chemistry control. By adjusting particle size distribution and controlling flotation reagent chemistry, the process optimizes mercury removal while preserving the pozzolanic properties of the remaining ash material.
2Quantity of substance
If pulverization is performed before wet froth flotation, then mercury reduction is enhanced and particle size is reduced, but process complexity increases
Solution Approach 1:
The patent applies preliminary action by performing pulverization before flotation. This size reduction step breaks down larger particles, increasing the surface area and making subsequent mercury removal more efficient. The preliminary size reduction enables better contact between flotation reagents and mercury-containing particles, enhancing overall mercury depletion.
Solution Approach 2:
The patent segments the processing into distinct stages: pulverization followed by flotation. This segmentation allows each process to be optimized independently - size reduction for mercury accessibility and flotation for selective separation - while maintaining overall process efficiency and manageability.
3Object-affected harmful factors
If wet froth flotation is used to reduce mercury content, then mercury-depleted ash is produced, but process time and operational complexity increase
Solution Approach 1:
The patent uses wet froth flotation which relies on pneumatic (air bubbles) and hydraulic (water flow) principles to separate mercury-containing particles from the ash. Air bubbles attach to hydrophobic mercury particles while hydrophilic ash particles remain in the water phase, enabling efficient separation. This physical-chemical method achieves mercury removal without requiring lengthy thermal processing.
Solution Approach 2:
The patent employs flotation reagents as intermediaries that facilitate mercury separation. Collector chemicals modify the surface properties of mercury particles to make them hydrophobic, while frothing agents create stable air bubbles for attachment. These intermediary substances enable selective separation that would not occur through simple gravitational settling alone.
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 effectively reduces mercury content and particle size, increasing the ash's value as a pozzolanic additive and cement kiln raw material, while also minimizing ammonia levels, thereby enhancing its usability and production efficiency.
Implementation Method 1
A slurry is formed of the combustion ash and water and is subjected to froth flotation to form a mercury-enriched ash slurry and a mercury-depleted ash slurry
Data Source
AI summary
A method of producing enhanced coal combustion ash for use in pozzolanic applications or cement manufacture, in which the enhanced combustion ash has lower mercury content. A slurry is formed of the combustion ash and water and is subjected to froth flotation to form a mercury-enriched ash slurry and a mercury-depleted ash slurry. The product mercury-depleted ash slurry is isolated and may optionally be dried. The combustion ash may be pulverized prior to being used to form the slurry, reducing its mean particle size. The mercury-depleted combustion ash product has reduced levels of mercury and ammonia, and reduced particle size.