Boiler Combustion Stage Transition Control for Load Fluctuations
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Solution Overview
Problem
Conventional boilers face issues with transition cancel during load fluctuations, leading to hunting and potential system stoppages due to the inability to cancel transitions between combustion stages quickly, especially with large turndown ratios, resulting in a gap between required and supplied steam amounts.
Innovation Solution
A boiler control system that includes an air supply device and fuel supply device, capable of varying combustion air and fuel, with a controller that allows transition cancel by returning to a predetermined combustion stage and prohibiting further transitions until a predetermined time period has elapsed, ensuring stable operation and preventing overshoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If transition cancel is not accepted during combustion stage transition, then hunting and system stability are prevented, but the gap between required and supplied steam amounts increases and load following capability is disabled
Solution Approach 1:
The patent implements dynamic transition control by making the acceptance of transition cancel requests dependent on the current transition state. The control unit dynamically adjusts the system's responsiveness to cancel requests based on whether a transition is actively in progress, allowing flexibility when stable and preventing instability when transitioning. This resolves the contradiction by making the system's behavior adaptive rather than fixed.
Solution Approach 2:
The control unit monitors the transition state and uses this feedback to determine whether to accept or reject transition cancel requests. By continuously checking if a transition is in progress and responding accordingly, the system maintains stability while preserving load following capability. The feedback mechanism ensures that cancel requests are only rejected when necessary to prevent hunting.
2Stability of the object's composition
If transition time is extended to ensure stable transition between combustion stages, then hunting is prevented, but the responsiveness to load fluctuations decreases and steam supply gap increases
Solution Approach 1:
The system performs preliminary checks to determine if a transition is already in progress before accepting new transition requests. This preliminary action prevents premature or conflicting transitions that would cause hunting, while allowing the system to respond quickly to legitimate load changes. By checking the transition state first, the system avoids unnecessary delays while maintaining stability.
3Adaptability or versatility
If multiple transition cancel requests are continuously accepted, then load following capability is improved, but hunting occurs and system stability deteriorates
Solution Approach 1:
The control unit takes preliminary anti-action by proactively rejecting transition cancel requests when a transition is already in progress. This prevents the harmful effect of hunting before it can occur, while still allowing the system to respond to legitimate load changes once the current transition completes. The preliminary rejection of inappropriate cancel requests prevents stability deterioration.
Data Source
AI summary
A combustion apparatus for boiler includes an air supply device that varies a supply amount of combustion air, a fuel supply device that varies a supply amount of fuel, and a control device that controls the air supply device and the fuel supply device, obtains the supply amounts in accordance with respective combustion stages, and realizes the multiple combustion stages. The the control device controls the air supply device and the fuel supply device so as to return to a predetermined combustion stage when a request for transition cancel is received during transition from the predetermined combustion stage to another combustion stage, and controls so as not to perform the transition to the other combustion stage until a predetermined time period has elapsed.