Mercury Removal System with pH Control for Flue Gas
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Solution Overview
Problem
Existing methods for processing mercury in flue gas fail to effectively remove sulfur oxides such as dithionate and peroxo disulfate, and hexavalent selenium, which are difficult to process, due to excessive oxidation states in desulfurization devices.
Innovation Solution
A system that includes a heat exchanger, precipitator, wet desulfurization device using an alkali absorbent, and a removal assistant supply mechanism to manage oxidation reduction states, preventing hyperoxidation and using active carbon or aggregation assistants to remove impurities in the limestone and gypsum slurry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an oxidation state is maintained in the absorber to prevent reduction of mercury oxide, then mercury removal is improved, but sulfur oxides and selenium compounds are hyperoxidized to form difficult-to-process compounds
Solution Approach 1:
A pH control agent is introduced as an intermediary substance to regulate the oxidation-reduction environment in the absorber. The pH control agent adjusts and maintains the pH within a specific range (2-6), preventing both excessive oxidation and reduction while allowing effective mercury removal. This mediator resolves the contradiction by controlling the chemical environment to avoid formation of hyperoxidized harmful compounds.
Solution Approach 2:
The invention changes the key parameter of pH to control the oxidation-reduction state in the absorber. By maintaining pH in the range of 2-6, the system prevents hyperoxidation of sulfur oxides and selenium compounds while still achieving effective mercury oxide removal. This parameter control approach allows the system to operate in an optimal window that avoids harmful byproducts.
2Object-generated harmful factors
If the oxidizing air flow rate is reduced to prevent hyperoxidation, then formation of difficult-to-process compounds is reduced, but mercury oxide may be reduced to metallic mercury and discharged to the outside
Solution Approach 1:
The pH control agent serves as a mediator that allows the system to maintain appropriate oxidation conditions for mercury removal without requiring high oxidizing air flow rates. By controlling pH in the range of 2-6, the agent enables effective mercury oxide removal while preventing its reduction to metallic mercury, thus resolving the contradiction between preventing hyperoxidation and preventing mercury discharge.
Solution Approach 2:
The invention shifts from controlling oxidation through air flow rate to controlling it through pH parameter. By maintaining pH between 2-6, the system achieves stable mercury removal efficiency without needing high oxidizing air flow rates, thereby preventing both hyperoxidation and reduction of mercury oxide.
3Reliability
If absorbent slurry circulation amount is increased to improve mercury removal, then mercury capture is enhanced, but oxidation inhibition occurs and hyperoxidation state is caused
Solution Approach 1:
The pH control agent acts as a buffer that stabilizes the oxidation-reduction state in the absorber even when absorbent slurry circulation amount is increased. By maintaining pH within the optimal range of 2-6, the agent prevents oxidation inhibition and hyperoxidation that would otherwise occur with high circulation rates, allowing sustained effective mercury removal.
Solution Approach 2:
The invention uses pH as a controlling parameter to decouple mercury removal efficiency from oxidation-reduction stability. By maintaining pH in the range of 2-6 regardless of circulation rate, the system can operate at high slurry circulation for effective mercury capture without causing hyperoxidation or oxidation inhibition.
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 system effectively suppresses oxidation inhibition in desulfurization devices, preventing the production of difficult-to-process sulfur oxides and selenium compounds, ensuring efficient mercury removal and stable operation.
Implementation Method 1
a heat exchanger that performs heat exchange of the flue gas from the boiler
Implementation Method 2
a precipitator that removes soot and dust in the flue gas
Implementation Method 3
a wet desulfurization device that removes sulfur oxides and mercury oxide Hg 2+ in the flue gas by contacting the flue gas with alkaline slurry
Implementation Method 4
a reduction oxidation assistant supply means for supplying a reduction oxidation assistant to a flue gas duct in the downstream of the boiler
Data Source
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AI summary
Disclosed is an Hg removal system which removes Hg contained in flue gas (12) from a boiler (11), in which the Hg removal system includes an ammonium chloride solution supply means (a reduction oxidation assistant supply means) (16) that sprays an NH4Cl solution (14), which contains ammonium chloride as a reduction oxidation assistant, into a flue gas duct (13) that is in the downstream of the boiler (11), a reduction denitration device (a reduction denitration means) (17) that contains a denitration catalyst which reduces NOx in the flue gas (12) with an NH3 gas, while oxidizing metallic mercury (Hg0) in the coexistence of an HCl gas, a heat exchanger (18) that performs heat exchange of the denitrated flue gas (12), a precipitator (19) that removes soot and dust in the denitrated flue gas (12), a wet desulfurization device (21) that removes divalent Hg2+, which is oxidized in the reduction denitration device (17), using a limestone and gypsum slurry (an alkali absorbent) (20), and a removal assistant supply means (23) that supplies a removal assistant (22) for removing impurities into the limestone and gypsum slurry (20) that circulates through the wet desulfurization device (21).