Split Air Preheater for Mercury Chemi-Deposition
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Solution Overview
Problem
Current methods for removing elemental mercury from coal-fired power plant exhaust gases are inefficient and costly, with existing technologies failing to provide a practical, low-cost solution for industrial-scale applications, particularly due to limitations in temperature and collision frequency in conventional air preheaters.
Innovation Solution
A modified waste heat exchange device is designed with a split air preheater configuration, featuring a central reaction chamber at 500±50° F (260±30° C) to facilitate chemi-deposition of mercury, utilizing closely spaced, thin stainless steel sheets for increased collision frequency and conversion of elemental mercury into vaporizable mercury dichloride or collectable mercury oxide/sulfate compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional air preheater design is used, then heat exchange function is maintained, but mercury removal efficiency is insufficient due to inadequate temperature control and collision frequency
Solution Approach 1:
The air preheater is divided into three distinct sections: a first heat exchange section, a central reaction chamber, and a second heat exchange section. This segmentation allows the reaction chamber to be optimized for mercury conversion at controlled temperatures while the other sections maintain heat exchange functionality, thereby improving mercury removal efficiency without compromising the overall heat exchange performance of the device.
Solution Approach 2:
The central reaction chamber is designed with specific local characteristics including temperature control within the range of 200-400°F and the incorporation of collision surfaces. This local optimization creates favorable conditions for mercury chemi-deposition in the central region while the surrounding sections maintain their heat exchange functions, resolving the contradiction between mercury removal efficiency and device complexity.
2Reliability
If temperature in air preheater is increased to enhance mercury conversion, then mercury removal efficiency improves, but heat exchange performance deteriorates
Solution Approach 1:
By segmenting the air preheater into distinct thermal zones, the invention allows the central reaction chamber to maintain the elevated temperature (200-400°F) necessary for mercury conversion, while the first and second heat exchange sections operate at lower temperatures optimized for heat recovery. This spatial separation of thermal functions resolves the contradiction between mercury conversion efficiency and heat exchange performance.
Solution Approach 2:
The central reaction chamber is赋予 with specific local thermal properties (temperature control at 200-400°F) that are different from the surrounding heat exchange sections. This local quality enhancement enables efficient mercury conversion in the central region without requiring the entire device to operate at high temperatures, thus preserving overall heat exchange efficiency.
3Reliability
If activated charcoal injection is used, then mercury removal is achieved, but operational cost and complexity increase
Solution Approach 1:
The air preheater is modified to perform dual functions: heat exchange and mercury conversion. The collision surfaces within the reaction chamber enable the device to automatically promote mercury chemi-deposition through enhanced gas-surface interactions without requiring external injection of activated charcoal or other additives. This self-service capability eliminates the operational complexity and costs associated with external mercury removal systems.
Solution Approach 2:
The invention transforms the air preheater from a single-function heat exchange device into a multi-functional unit that simultaneously performs heat recovery and mercury emission control. By incorporating collision surfaces and controlling temperature in the central reaction chamber, the device achieves mercury conversion as an inherent function, eliminating the need for separate activated charcoal injection systems and reducing overall operational complexity.
4Reliability
If collision frequency is increased to enhance mercury chemi-deposition, then mercury removal efficiency improves, but device complexity increases
Solution Approach 1:
Collision surfaces are incorporated specifically within the central reaction chamber where temperature conditions favor mercury conversion. This localized addition of collision surfaces concentrates the mercury chemi-deposition activity in the region where it is most effective, without requiring complex collision surface configurations throughout the entire air preheater device, thus improving mercury removal efficiency while limiting the increase in device complexity.
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 design effectively converts elemental mercury into a molecular form that can be easily removed, achieving significant mercury removal efficiencies without increasing manufacturing costs or affecting heat exchange performance, validated through pilot-plant testing under realistic coal combustion conditions.
Implementation Method 1
cooling the exhaust gas to a first predetermined temperature range for chemi-deposition, reacting the cooled exhaust gas at the predetermined temperature range and with an adequate collision frequency of the exhaust gas with one or more collision surfaces whereon chemi-deposition of mercury occurs
Data Source
AI summary
A conventional air preheater or the conventional design of a preheater is split into two separate sections which are then communicated or connected by a thermally insulated reaction section that is maintained within a predetermined temperature range selected for optimization of heterogeneous chemi-deposition of mercury. The reaction section contains thin stainless steel sheeting which provide an enhanced area of collisional surfaces. Testing has confirmed that this design modification alters the energy heat exchanger to also enhance the oxidation of gaseous elemental mercury in combustion or high temperature source flue gases by providing the surfaces and time for the heterogeneous mechanisms to occur and so control mercury emissions in exhaust gases from coal combustion or other high temperature systems that contain traces of mercury.