Mercury Removal via Liquid Phase Oxidation
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Solution Overview
Problem
Existing mercury removal systems in wet gas cleaning, such as those used in IGCC, face challenges in efficiently removing minute amounts of mercury from gas streams due to its high vapor pressure and insolubility in water, leading to incomplete removal and increased maintenance costs, especially when using activated charcoal which requires extensive installation and is difficult to maintain.
Innovation Solution
A mercury removal system that immobilizes mercury in waste water by oxidizing it with an oxidizing agent or using a coagulant aid before decompression, allowing it to be precipitated as sludge, eliminating the need for activated charcoal in the gas stream and simplifying maintenance by preventing mercury from flashing into the offgas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If activated charcoal is used to adsorb mercury from offgas, then mercury removal effectiveness is improved, but device complexity and maintenance difficulty increase
Solution Approach 1:
The invention extracts the mercury removal function from the gas stream treatment to the liquid phase treatment. By adding oxidizing agents to the absorbing solution in the water washing tower, mercury is oxidized and immobilized in the liquid phase, then removed with the waste water from the flash drum, eliminating the need for multiple activated charcoal units in the gas stream.
Solution Approach 2:
The absorbing solution serves as an intermediary medium that transfers mercury from the gas phase to the liquid phase. The oxidizing agents (sodium hypochlorite, calcium hypochlorite, or hydrogen peroxide) act as mediators that convert elemental mercury to oxidized forms that can be effectively removed with the waste water stream.
2Reliability
If activated charcoal is installed in all offgas lines, then mercury removal is improved, but ease of operation deteriorates due to difficult maintenance and replacement
Solution Approach 1:
The invention extracts the mercury removal operation from difficult-to-maintain activated charcoal units to easily-maintained waste water treatment processes. The absorbing solution is continuously circulated and regenerated, and waste water is routinely discharged and replaced, making maintenance simple and operational.
Solution Approach 2:
The water washing system continuously circulates and regenerates the absorbing solution, automatically maintaining its mercury capture capability. The flash drum continuously separates and discharges waste water containing immobilized mercury, providing self-service mercury removal without manual intervention in activated charcoal units.
3Quantity of substance
If water washing is used to remove mercury, then some mercury removal is achieved, but mercury flashes into offgas during decompression
Solution Approach 1:
The invention applies preliminary anti-action by adding oxidizing agents to the absorbing solution before the flash drum decompression. This oxidizes elemental mercury to compounds that do not flash into the gas phase, preventing the harmful effect of mercury emission during pressure reduction.
Solution Approach 2:
The invention changes the chemical parameter of mercury in the absorbing solution by oxidizing it from elemental form to oxidized forms using sodium hypochlorite, calcium hypochlorite, or hydrogen peroxide. This parameter change prevents mercury from flashing into the offgas during decompression, as the oxidized forms remain dissolved in the liquid phase.
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 removes mercury from gas streams without the need for activated charcoal, reducing operational costs and maintenance complexity, while ensuring efficient mercury capture and disposal as sludge, thereby enhancing the overall efficiency and reliability of the mercury removal process.
Implementation Method 1
mercury is oxidized by adding an oxidizing agent to the waste water before being flashed
Implementation Method 2
when an absorbing solution used in the water washing process is decompressed from a high pressure to the normal pressure, Hg may be flashed out of the solution
Implementation Method 3
a waste water treatment means for discharging the mercury component contained in the separated waste water by coagulation sedimentation treatment
Implementation Method 4
a waste water treatment means for discharging the mercury component contained in the separated waste water by coagulation sedimentation treatment
Data Source
AI summary
The present invention provides a mercury removal system and method for effectively removing a mercury component, which is present in a gas stream in an extremely small amount in wet gas cleaning. The mercury removal system in wet gas cleaning includes a water washing tower for introducing therein a target gas containing a mercury component and transferring the mercury component into an absorbing solution, a flash drum (10) for flashing the absorbing solution discharged from the water washing tower to separate the absorbing solution into a gas component and waste water, an oxidation treatment means (1) for adding an oxidizing agent to the absorbing solution at the preceding stage of the flash drum, and a waste water treatment means for subjecting to coagulation sedimentation treatment the separated waste water containing the mercury component at the following stage of the flash drum to dispose of the mercury component as sludge.