Cyclodextrin Additive for Mercury Re-emission Control
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Solution Overview
Problem
Current methods for controlling mercury emissions in coal combustion flue gas face challenges in achieving low mercury emission levels due to the re-emission of elemental mercury, which has high vapor pressure and can escape through wet scrubbing systems, despite the use of oxidizing agents and sulfur-containing chemicals, which pose health and handling issues.
Innovation Solution
Incorporating cyclodextrin additives into the aqueous alkaline slurry in wet scrubbing systems to form chemically stable complexes with dissolved mercury species, preventing re-emission by adjusting the cyclodextrin dosage based on measured mercury concentrations, using α-cyclodextrin, β-cyclodextrin, or their derivatives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxidizing agents and sulfur-containing chemicals are used to remove mercury from flue gas, then mercury removal efficiency is improved, but health and handling safety deteriorates
Solution Approach 1:
The patent employs cyclodextrin, a biodegradable carbohydrate compound, as a replacement for persistent and toxic sulfur-containing chemicals. Cyclodextrin forms inclusion complexes with mercury species that are stable under scrubbing conditions but decompose harmlessly under UV irradiation or heating, eliminating long-term environmental persistence and toxicity issues associated with traditional sulfur-based reagents
Solution Approach 2:
The patent changes the chemical nature of the mercury-binding agent from sulfur-containing compounds to cyclodextrin-based compounds. This parameter change transforms the chemical mechanism from covalent bonding (sulfur-mercury) to inclusion complexation (cyclodextrin cavity-mercury), which provides sufficient stability for removal while avoiding the health and environmental hazards of sulfur compounds
2Productivity
If wet scrubbing operation is used to remove sulfur oxides, then sulfur oxide removal is improved, but mercury re-emission worsens due to high vapor pressure of elemental mercury
Solution Approach 1:
The patent introduces cyclodextrin as an intermediary substance that mediates between the wet scrubbing process and mercury control. The cyclodextrin forms inclusion complexes with dissolved mercury species in the alkaline slurry, preventing their conversion to elemental mercury and subsequent re-emission, while not interfering with the sulfur oxide removal function of the wet scrubber
Solution Approach 2:
The patent creates a composite chemical system combining alkaline slurry (for sulfur oxide removal) with cyclodextrin (for mercury complexation). This composite approach allows simultaneous achievement of sulfur oxide desulfurization and mercury emission control through a single integrated wet scrubbing 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
Effectively reduces mercury emissions and re-emissions by forming stable complexes, maintaining high removal efficiency while avoiding the health and handling concerns associated with sulfur-containing chemicals, ensuring compliance with stringent emission standards.
Implementation Method 1
including a cyclodextrin additive to the aqueous alkaline slurry to complex with the dissolved mercury species to form chemically stable complexes
Implementation Method 2
dissolving at least a portion of gaseous ionic mercury species present in the flue gas in the aqueous alkaline slurry to remove the gaseous ionic mercury species from the flue gas
Implementation Method 3
contacting the flue gas with an aqueous alkaline slurry to absorb the sulfur oxides from the flue gas
Data Source
AI summary
A method for reducing mercury emission and/or re-emission in cleaned flue gas through control of dissolved mercury species concentration within a wet flue gas desulfurization (WFGD) system is disclosed. One method for reducing mercury emission and/or re-emission through control of dissolved mercury species concentration is to measure the dissolved mercury species concentration of an aqueous alkaline slurry used in a WFGD system and/or measuring mercury concentration of cleaned flue gas from a WFGD system and comparing the same to a predetermined dissolved mercury species concentration value and/or a predetermined mercury concentration value. If the comparison reveals the measured dissolved mercury species concentration or mercury concentration is above the predetermined values therefor, the amount of cyclodextrin additive supplied to the system is increased. If the comparison reveals the measured dissolved mercury species concentration or mercury concentration is below the predetermined values, the amount of cyclodextrin additive supplied to the system is decreased.