Air Preheater SO3 Mitigation for Boiler Efficiency
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Solution Overview
Problem
Thermal power stations face inefficiencies in fossil fuel fired steam generators due to fouling and pollution control limitations, particularly with sulfur trioxide (SO3) condensation causing fouling in air preheaters and wet ESPs being used for SO3 removal, which limits the potential for increased heat transfer efficiency and overall system efficiency.
Innovation Solution
A method and system that mitigates SO3 in the flue gas before it enters the air preheater, using heat transfer elements with enhanced capacity to manage flue gas temperatures and incorporate SO3 mitigation upstream, allowing for improved heat recovery and particulate removal, thereby enhancing the thermal efficiency of the steam generator system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If higher efficiency heat transfer elements and greater heat transfer area are used in the air preheater, then the air preheater efficiency is improved, but fouling occurs due to SO3 condensation which limits the full realization of efficiency potential
Solution Approach 1:
The patent applies preliminary action by removing SO3 from the flue gas stream before it enters the air preheater. A dedusting section with spray nozzles injects reagent (such as ammonia water, caustic soda solution, or lime milk) to chemically react with and remove SO3 upstream of the heat transfer elements. This prevents SO3 condensation and subsequent fouling on the heat transfer surfaces, allowing the air preheater to operate at higher efficiency without the harmful fouling effect that would otherwise limit performance realization.
2Loss of energy
If flue gas temperature is reduced below the dew point of SO3 to increase heat recovery, then thermal efficiency is improved, but H2SO4 mist forms causing corrosion and fouling
Solution Approach 1:
The patent applies preliminary action by removing SO3 from the flue gas before it enters the air preheater through chemical reaction in a dedusting section. By injecting reagent spray (ammonia water, caustic soda, or lime milk) upstream, the SO3 is converted to soluble salts or other non-condensing compounds. This prevents the formation of H2SO4 mist when flue gas temperature drops below the dew point, enabling aggressive heat recovery operation without corrosion or fouling hazards.
Solution Approach 2:
The patent converts the harmful SO3 and potential H2SO4 mist into beneficial soluble salts through chemical reaction. The reagent spray transforms SO3 into ammonium sulfate, sodium sulfate, or calcium sulfate compounds that remain in the gas stream as non-condensing particles or are captured in the dedusting section. This conversion eliminates the corrosion and fouling problems while allowing maximum heat recovery, effectively turning a harmful substance into a manageable byproduct.
3Reliability
If wet ESP is used for particulate removal to handle H2SO4 mist, then particulate removal is achieved, but system complexity and water consumption increase
Solution Approach 1:
The patent applies the taking out principle by extracting and removing SO3 from the flue gas stream in a dedicated dedusting section before the gas enters the air preheater and particulate removal systems. By injecting reagent spray and creating a separate reaction zone, the harmful SO3 is removed upstream, eliminating the need for wet ESP systems designed to handle H2SO4 mist. This simplifies the overall system by removing the water consumption and complexity associated with wet ESP operation while maintaining effective particulate removal through simpler dry ESP or baghouse systems.
Solution Approach 2:
The patent introduces a reagent (ammonia water, caustic soda solution, or lime milk) as an intermediary substance that mediates between the harmful SO3 and the flue gas stream. The reagent spray acts as a chemical intermediary that reacts with SO3 to form soluble salts, which then serve as a manageable intermediate product that can be easily removed in subsequent dedusting sections. This intermediary approach eliminates the need for complex wet ESP systems while maintaining effective particulate and pollutant removal.
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 improves the thermal efficiency of steam generators by reducing fouling, enabling increased heat recovery and efficient particulate removal, while maintaining or improving boiler efficiency and reducing water discharge, thus optimizing the steam generator system's performance.
Implementation Method 1
the air supply to the steam generator vessel is heated by recovering heat from the flue gas stream in an Air Preheater (APH)
Implementation Method 2
as the flue gas temperature decreases below the dew point of SO3 at a cold-end of the APH, condensation can occur, thereby causing SO3 to form H2SO4
Implementation Method 3
Dry ESPs are more efficient and easier to maintain than wet ESPs
Data Source
AI summary
A method for improving effectiveness of a steam generator system includes providing a steam generator system including a steam generator vessel, an air supply system and an air preheater. The air supply system is in communication with the steam generator vessel through the air preheater and the steam generator vessel is in communication with the air preheater. The air supply system provides a first amount of air to the air preheater. At least a portion of the first amount of air is provided to the steam generator vessel. A flue gas mixture is discharged from the steam generator vessel. At least a portion of the flue gas mixture flows into the air preheater. SO3 in the flue gas mixture is mitigated before the flue gas mixture enters the air preheater.