Multi-functional Sorbent for High-Temperature Mercury Capture
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Solution Overview
Problem
Conventional sorbents fail to efficiently capture mercury from high-temperature flue gas streams due to reduced adsorption capacity and increased kinetic energy, which complicates mercury oxidation and sequestration, especially in coal-fired power plants where temperatures exceed 340°F.
Innovation Solution
A multi-functional composition comprising fixed carbon, minerals, and an aqueous-based solubilizing medium with specific particle size, pore volume ratios, and halogen content is injected into the flue gas stream to enhance mercury oxidation and capture, overcoming the limitations of conventional sorbents by providing a large surface area and improved reaction kinetics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sorbents are used in high temperature flue gas streams, then mercury capture is attempted, but adsorption capacity is reduced and kinetic energy of mercury increases making oxidation and sequestration difficult
Solution Approach 1:
The invention changes the chemical and physical parameters of the sorbent by incorporating halogen compounds (particularly bromine) and optimizing pore structure. The halogen content (0.1-10% by weight) and specific pore volume ratios create a sorbent that maintains effectiveness at high temperatures where conventional sorbents fail.
Solution Approach 2:
The invention uses composite materials combining carbonaceous material with halogen compounds and specific mineral compositions. This composite structure provides both the adsorption capacity of carbon and the oxidation catalysis of halogens, enabling effective mercury capture at temperatures exceeding 340°F where single-material sorbents fail.
2Productivity
If sorbent residence time in flue gas is limited to 1-2 seconds, then rapid mercury removal is required, but conventional sorbents cannot efficiently accomplish oxidation and sequestration within this timeframe
Solution Approach 1:
The sorbent is pre-treated with halogen compounds before injection into the flue gas. This preliminary action ensures that the oxidation catalysts are already in place on the sorbent surface, allowing immediate oxidation of mercury upon contact and eliminating the need for extended residence times for catalyst formation.
Solution Approach 2:
The invention incorporates halogen compounds (bromine, chlorine) as strong oxidizing agents that accelerate the oxidation of elemental mercury to oxidized mercury species. This accelerated oxidation occurs rapidly on the sorbent surface within the 1-2 second residence time window, enabling efficient mercury capture that conventional slower-acting sorbents cannot achieve.
3Reliability
If high temperature flue gas streams are treated, then mercury oxidation is attempted, but reverse reactions increase and oxidant decomposition occurs reducing capture performance
Solution Approach 1:
The invention converts the harmful effect of high temperature (which causes reverse reactions and oxidant decomposition) into a benefit by selecting halogen compounds and carbonaceous materials that are thermally stable at these temperatures. The high temperature actually enhances the kinetics of the desired oxidation reactions while the stable halogen-carbon composite prevents the adverse reverse reactions that plague conventional sorbents.
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 multi-functional composition effectively oxidizes and sequesters mercury, achieving high removal rates even at high temperatures, meeting regulatory standards with reduced sorbent usage and maintaining efficient mercury capture across varying coal types and combustion conditions.
Implementation Method 1
contact of the injected sorbent with the mercury species, which is typically present in very dilute concentrations in the flue gas (e.g., Hg0), which is relatively inert and not easily adsorbed, into an oxidized mercury species (e.g., Hg+ and/or Hg+2), which is more readily adsorbable
Implementation Method 2
Powdered activated carbon is a porous carbonaceous material having a high surface area, which exposes significant amounts of beneficial chemically functional and catalytic reaction sites and which creates high adsorptive potential for many compounds, including capturing mercury from the flue gas
Implementation Method 3
oxidized mercury species (e.g., Hg+ and/or Hg+2), which is more readily adsorbable and is significantly more soluble in an aqueous solubilizing medium such as water
Implementation Method 4
the diffusion of the oxidized mercury species into pores where it is held tightly (e.g., sequestered) without being released
Data Source
AI summary
A multi-functional composition of matter that is useful for injection into a flue gas stream to rapidly and efficiently remove mercury from the flue gas streams, particularly at above average flue stream temperatures of about 340° F. or higher. The multi-functional composition of matter may include a fixed carbon content of at least about 20 wt. %, a mineral content of from about 20 wt. % to about 50 wt. %, a sum of micropore plus mesopore volume of at least about 0.20 cc/g, a micropore volume to mesopore volume ratio of at least about 0.7, and a tapped density of not greater than about 0.575 g/ml. These compositions may be further characterized by number of particles per gram of the composition of matter such that the composition may have at least about 0.8 billion particles per gram, or even as many as 1.5 billion particles per gram. These physical and chemical properties may enhance (1) the oxidation reaction kinetics for the oxidation of mercury species, (2) frequency of contact events, and (3) capture and sequestration of mercury, to achieve efficient mercury capture by the composition even in high temperature flue gas streams.