Cement Kiln Dust Mercury Removal via Volatilization and Polysulfide Treatment
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Solution Overview
Problem
Heavy metals such as mercury accumulate in the cement kiln gas stream due to the volatilization of compounds during the cement manufacturing process, leading to increased concentrations and potential atmospheric release when the raw mill is shut down or unable to absorb sufficient amounts, necessitating an effective treatment method for cement kiln dust (CKD) before recycling.
Innovation Solution
A system and method involving heating CKD to volatilize heavy metals, followed by treatment with an alkaline-earth metal polysulfide-based fluid to separate and remove mercury, utilizing a volatilization vessel and treating chamber with a nozzle for spraying the fluid to form a clean CKD stream, which can be recycled or disposed of, and incorporating a particulate collection system for further processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CKD is recycled back into the kiln process, then productivity is improved by reusing material, but heavy metal concentrations accumulate in the gas stream causing environmental harm
Solution Approach 1:
The patent extracts heavy metals from CKD through selective volatilization by heating CKD to specific temperatures where heavy metals vaporize at different rates, separating them from the CKD stream before recycling the cleaned material
Solution Approach 2:
The patent performs preliminary treatment of CKD by heating it in a volatilization zone before recycling, removing heavy metals in advance to prevent their accumulation in the kiln gas stream during subsequent recycling operations
2Object-generated harmful factors
If heating is applied to volatilize heavy metals from CKD, then heavy metal removal is improved, but energy consumption increases
Solution Approach 1:
The patent changes the temperature parameter systematically, heating CKD to specific temperature ranges (e.g., 200-400°C for mercury removal) rather than excessive temperatures, optimizing energy use while achieving effective heavy metal volatilization
Solution Approach 2:
The patent applies heating locally in a dedicated volatilization zone within the kiln system, concentrating thermal energy where needed to volatilize heavy metals from CKD without unnecessarily heating the entire kiln 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
The method effectively reduces mercury and other heavy metal concentrations in the CKD, preventing atmospheric release and enabling safe recycling or disposal, thereby reducing pollution and operational costs within the cement industry.
Implementation Method 1
heating the collected cement kiln dust to a temperature corresponding to the volatilization point of the heavy metal to be treated
Implementation Method 2
treating the heavy metal stream with an alkaline-earth metal polysulfide-based treating fluid to separate the heavy metal from the gas stream
Data Source
Figure 1
AI summary
The invention relates to a method for treating cement kiln dust comprising at least one heavy metal. The method comprises the steps of: separating the heavy metal from the cement kiln dust to create a heavy-metal-containing stream; treating the heavy metal stream with a treating fluid containing at least one of an alkaline-earth metal sulfide and an alkaline-earth metal polysulfide; and removing at least a portion of the heavy metal from the stream. Moreover, the invention relates to a method of reclaiming a desired raw material from an industrial byproduct containing mercury. The method comprises the steps of: separating the mercury from the industrial byproduct by adding sufficient kinetic energy to the industrial waste to form a stream of separated mercury and a stream containing the desired raw material; treating the stream of separated mercury with a treating fluid containing at least one of an alkaline earth metal sulfide and an alkaline earth metal polysulfide to form a particulate containing the mercury; collecting the desired raw material separately from the particulate; and collecting the particulate for subsequent handling.