Wet Scrubber Redox Control for Mercury Emission
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for controlling mercury discharge in flue gas during coal combustion are difficult to predict and control, especially in wet scrubbing operations, where achieving low mercury emission levels requires precise management of redox potential and reductive capacity in aqueous alkaline slurries.
Innovation Solution
Measuring and adjusting the redox potential of the aqueous alkaline slurry in wet scrubbing systems by controlling the amount of oxidation air introduced, allowing for precise regulation of mercury emissions by converting ionic mercury to elemental mercury, thereby maintaining emissions below desired limits with minimal oxidation air consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If halogen or halogen compounds are added to oxidize elemental mercury to ionic mercury and form mercury salts for removal by aqueous alkaline slurry, then mercury removal efficiency is improved, but the process becomes difficult to control and predict
Solution Approach 1:
The patent changes the chemical parameter of the slurry by controlling its redox potential within a specific range (0.2V to 0.6V). By adjusting and maintaining the redox potential parameter, the system achieves predictable mercury removal efficiency without requiring halogen additives, thus improving both removal efficiency and controllability.
Solution Approach 2:
The patent implements a feedback control mechanism where the redox potential of the slurry is continuously measured and used to adjust the oxidation air flow rate. This closed-loop feedback system ensures that the mercury removal process remains controllable and predictable, resolving the operability issue while maintaining high removal efficiency.
2Ease of operation
If redox potential of aqueous alkaline slurry is controlled to improve mercury emission control, then mercury emissions become predictable and controllable, but additional measurement and control equipment is required
Solution Approach 1:
The patent makes the slurry serve multiple functions: it simultaneously removes sulfur oxides and controls mercury emissions through redox potential control. This multi-functionality reduces the need for separate dedicated mercury removal systems, thereby offsetting the added complexity of redox measurement and control equipment.
Solution Approach 2:
The slurry system self-regulates mercury removal through controlled oxidation air injection that adjusts its own redox potential. The system uses its existing chemical composition and circulation mechanism to achieve mercury control, minimizing the need for additional complex external equipment while improving predictability.
3Object-generated harmful factors
If oxidation air is increased to convert more ionic mercury to elemental mercury for emission control, then mercury emission levels are reduced, but oxidation air consumption increases
Solution Approach 1:
The patent changes the quality parameter of oxidation by controlling the redox potential within an optimal range (0.2V to 0.6V) rather than simply increasing the quantity of oxidation air. This parameter optimization ensures efficient mercury conversion while minimizing excess air consumption, achieving low emissions without excessive substance loss.
Solution Approach 2:
The patent applies partial oxidation by injecting oxidation air in controlled amounts sufficient to achieve the desired redox potential range for mercury control, rather than using excessive oxidation air. This partial action approach achieves the necessary emission reduction while avoiding unnecessary air consumption.
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 approach enables predictable and controlled mercury emission levels, ensuring compliance with stringent emission standards while optimizing the use of oxidation air, making mercury emissions controllable and efficient.
Implementation Method 1
contacting the flue gas with an aqueous alkaline slurry to absorb the sulfur oxides from the flue gas
Implementation Method 2
at least a portion of gaseous ionic mercury species present in the flue gas are dissolved in the aqueous alkaline slurry and thereby removed from the flue gas
Implementation Method 3
converting ionic mercury to elemental mercury by controlling the amount of oxidation air introduced
Implementation Method 4
measuring a redox potential of the aqueous alkaline slurry used in the wet scrubbing operation to provide a signal indicative of the measured redox potential
Data Source
AI summary
Controlling the reductive capacity of an aqueous alkaline slurry (23) in a wet scrubber makes it possible to accurately control the mercury emission from the scrubber to a desired value. One method of controlling the reductive capacity of the slurry is to measure the reduction-oxidation potential (“redox potential”) of the aqueous alkaline slurry (23) and to add or remove substances that affect the redox potential and thus the reductive capacity of the slurry. In wet scrubbers in which limestone is used for absorption of acid gases and where a gypsum slurry is circulated, it has been found to be an attractive solution to control the amount of oxidation air blown into the scrubber in order to control the redox potential and thereby the mercury emissions.