Premixing Control for Stable Excess Air Ratio in Burners
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing premixing apparatuses experience temporary poor combustion due to fluctuations in fuel gas calorific value and primary gas pressure, leading to unstable excess air ratios in the air-fuel mixture.
Innovation Solution
A premixing apparatus with a control device that adjusts the rotational speed of the fan and opening degree of the variable throttle valve based on detected excess air ratios, using threshold calculations and memorized values to quickly restore appropriate air-fuel mixture ratios, and incorporates a butterfly valve for additional control in high-capacity states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback control is used to restore excess air ratio by increasing variable throttle valve opening degree, then excess air ratio is restored to appropriate value, but temporary poor combustion occurs during the restoration process
Solution Approach 1:
The control device calculates and stores the threshold value in advance before poor combustion occurs. When fan rotational speed reaches this pre-calculated threshold, the system immediately increases the variable throttle valve opening degree, eliminating the delay inherent in traditional feedback control and preventing temporary poor combustion
2Quantity of substance
If variable throttle valve opening degree is increased to compensate for reduced primary gas pressure, then fuel gas supply amount increases, but excess air ratio becomes inappropriate temporarily
Solution Approach 1:
The system continuously monitors excess air ratio through the detecting device and uses this feedback to dynamically adjust the variable throttle valve opening degree. This closed-loop control ensures that fuel gas supply is adjusted in real-time to maintain appropriate excess air ratio, preventing both poor combustion and gas pressure fluctuations
3Productivity
If fan rotational speed is increased to meet required combustion amount, then air supply amount increases, but fuel gas supply amount becomes insufficient due to reduced primary gas pressure
Solution Approach 1:
The variable throttle valve acts as an intermediary device between the fan and the gas supply system. By adjusting the throttle valve opening degree based on fan rotational speed and excess air ratio feedback, the system mediates the relationship between air supply and fuel gas supply, ensuring proper air-fuel mixture ratios even when primary gas pressure fluctuates
Data Source
AI summary
A premixing apparatus that mixes a fuel gas with air and supplies an air-fuel mixture in a burner through a fan includes a control device that is configured to carry out a third control that: calculates and memorizes a lower limit of a rotational speed of a fan, at which an increase of an opening degree of a variable throttle valve becomes necessary, as a first threshold; and when the rotational speed of the fan increases to the first threshold or faster next time, immediately changes the opening degree of the variable throttle valve to an increased opening degree, which is larger than a predetermined standard opening degree and is obtained by multiplying a deviation of the rotational speed of the fan from the first threshold by a predetermined coefficient.