Air Preheater Flow Control for Ammonium Bisulfate Decomposition
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Solution Overview
Problem
Solid fuel-fired power plants face operating challenges at low load due to ammonium bisulfate (ABS) formation in air preheaters, leading to fouling, efficiency drops, and frequent forced outages, as the formation of ABS at lower temperatures makes it difficult to clean and results in instability and capacity reduction.
Innovation Solution
An air preheater system with flow control valves and a controller that selectively adjusts air flow to create an 'air flow shadow' over the regenerative heating element, decomposing ABS to loose dry ash, which is then cleaned by flue gas, allowing for efficient operation and self-cleaning without the need for frequent shutdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If SCR is operated at high NH3/NO ratio to maintain 90% NOx reduction at partial load, then NOx reduction efficiency is improved, but ammonia slip increases leading to more ABS formation
Solution Approach 1:
The patent applies preliminary action by periodically closing air flow control valves before ABS can accumulate to problematic levels. The controller monitors differential pressure and proactively restricts air flow to create an air flow shadow that prevents ABS formation on the cold end plates, eliminating the need for reactive cleaning operations.
Solution Approach 2:
The system implements periodic action by cycling the air flow control valves between open and closed states. The controller periodically restricts air flow to create conditions that prevent ABS accumulation, then restores normal operation. This periodic modulation of air flow maintains NOx reduction efficiency while preventing harmful ABS formation.
2Adaptability or versatility
If air preheater operates at low load conditions, then power plant flexibility is improved, but ABS condenses on metal surfaces causing fouling and plugging
Solution Approach 1:
The system takes preliminary action by monitoring differential pressure across the air preheater and proactively closing air flow control valves before ABS fouling can occur. This preventive approach allows the plant to operate flexibly at low loads while the controller continuously prevents ABS condensation by creating an air flow shadow on the cold end plates.
Solution Approach 2:
The air preheater implements self-service through the automated control system that monitors its own differential pressure and autonomously adjusts air flow valves to prevent fouling. The system serves itself by detecting early signs of ABS accumulation and automatically correcting the air flow conditions to eliminate the problem without external intervention.
3Ease of repair
If sootblowing devices are installed to eliminate fouling, then cleaning effectiveness is improved, but ABS forms far away from cold end plates into hotter parts that are difficult to clean
Solution Approach 1:
The patent applies preliminary action by preventing ABS formation in the first place through proactive air flow restriction. The controller monitors differential pressure and closes air flow control valves before ABS can form on cold end plates or migrate to hotter sections, eliminating the need for difficult cleaning operations in hard-to-reach areas.
Solution Approach 2:
The system converts the potentially harmful effect of restricted air flow into a benefit by using the air flow shadow created by closed valves to prevent ABS formation. What would normally be seen as a reduction in air flow (a negative) is actually used strategically to create thermal conditions that prevent fouling, turning a limitation into a protective mechanism.
4Object-generated harmful factors
If air flow is restricted to create air flow shadow for ABS decomposition, then ABS removal is improved, but air flow rate decreases causing back pressure
Solution Approach 1:
The system applies partial action by restricting air flow to only the specific portions of the air preheater where ABS formation is detected, rather than reducing overall air flow. The controller selectively closes individual air flow control valves associated with cold end plates while maintaining normal air flow through other sections, thus decomposing ABS locally without creating significant back pressure.
Solution Approach 2:
The air preheater is segmented into multiple sections with individual air flow control valves. This segmentation allows the controller to restrict air flow to only those specific zones where ABS formation occurs (cold end plates) while maintaining normal operation in other sections. The modular valve arrangement enables localized treatment without system-wide flow reduction.
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 maintains stable operation at low loads, improves boiler efficiency, reduces air leaks, and eliminates ash fouling, enabling the use of alternative energy sources by effectively decomposing and removing ABS, thus enhancing the power plant's capacity and reliability.
Implementation Method 1
a regenerative heating element received in the housing and adapted to transfer heat from the flue gas stream to the air stream
Implementation Method 2
any ammonium bisulfate previously deposited on the selected portion is decomposed to loose dry ash
Data Source
AI summary
An air preheater for a solid fuel-fired power plant includes a housing, a regenerative heating element received in the housing and adapted to transfer heat from the flue gas stream to the air stream, a plurality of flow control valves upstream of the regenerative heating element and a controller adapted to selectively open and close each valve of the plurality of flow control valves in order to provide an air flow shadow extending downstream over a selected portion of the regenerative heating element whereby ammonium bisulfate previously deposited on the selected portion is decomposed to loose dry ash. A method of decomposing and removing ammonium bisulfate from a regenerative heating element is also presented.