Premixing Apparatus with Flow Control Valve for Constant Excess Air Ratio
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional premixing apparatuses fail to maintain a constant excess air ratio of the air-fuel mixture when the calorific value of the fuel gas fluctuates, leading to combustion failure.
Innovation Solution
The premixing apparatus incorporates a swing valve and a bypass passage with an on-off valve to adjust the flow control valve's opening degree, ensuring a constant excess air ratio and maintaining turndown ratio, while minimizing controllability deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional premixing apparatus uses a zero governor to adjust secondary gas pressure to atmospheric pressure, then the fuel gas supply amount varies with fan rotational speed, but the excess air ratio fluctuates when calorific value of fuel gas changes
Solution Approach 1:
The patent introduces a flow control valve that receives feedback signals to adjust the fuel gas supply amount independently of fan rotational speed changes. This feedback mechanism ensures the excess air ratio remains constant even when calorific value of fuel gas fluctuates, resolving the contradiction between ease of operation and reliability.
Solution Approach 2:
The patent changes the control parameter from secondary gas pressure (atmospheric pressure) to a controlled flow rate through the flow control valve. This parameter change allows independent control of fuel gas supply, decoupling it from fan rotational speed and maintaining constant excess air ratio despite calorific value variations.
2Reliability
If the lower-limit rotational speed of the fan is set relatively high to prevent wind entry into exhaust tube, then wind resistance performance is secured, but the minimum combustion amount increases and turndown ratio becomes small
Solution Approach 1:
The patent makes the flow control valve adjustable to dynamically change the passage area of the fuel gas supply passage. This dynamic adjustment allows the system to adapt to different combustion amounts while maintaining constant excess air ratio, resolving the contradiction between wind resistance performance and turndown ratio.
Solution Approach 2:
The patent segments the control function into two independent parts: the fan controls air supply and the flow control valve controls fuel gas supply. This segmentation allows independent optimization of fan rotational speed for wind resistance and separate adjustment of fuel gas flow for turndown ratio, eliminating the trade-off between these parameters.
3Adaptability or versatility
If the range of change in opening degree of the flow control valve is enlarged to cope with different fuel gas types, then adaptability improves, but controllability deteriorates
Solution Approach 1:
The patent segments the flow control into two stages: a first flow control valve for coarse adjustment and a second flow control valve for fine adjustment. This segmentation allows the system to handle a wide range of fuel gas types while maintaining good controllability through hierarchical control, resolving the contradiction between adaptability and ease of operation.
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 solution effectively maintains a constant excess air ratio and enhances turndown ratio by adjusting the passage area and flow resistance, preventing combustion failure and improving controllability even with varying fuel gas calorific values.
Implementation Method 1
when the rotational speed of the fan is made to exceed a predetermined rotational speed, the swing valve may be swung to the bottom-up open side, into a fully-opened state against the self-weight of the swing valve due to a wind pressure from the fan
Implementation Method 2
The gas supply passage has interposed therein a zero governor for adjusting a secondary gas pressure to an atmospheric pressure
Implementation Method 3
the supply amount of the fuel gas varies with a differential pressure between the atmospheric pressure which is the secondary gas pressure and a negative pressure inside the air supply passage
Implementation Method 4
a burner having a downward combustion surface... the combustion gas generated by the combustion of the air-fuel mixture
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A premixing apparatus for mixing air with a fuel gas in order to supply a burner (1) with an air-fuel mixture through a fan (5), wherein a downstream end of a gas supply passage (7) is connected to a gas suction part (61) disposed in a portion, on an upstream side of the fan (5), of an air supply passage (6). The gas supply passage (7) has interposed therein a zero governor (73) for adjusting a secondary gas pressure to an atmospheric pressure. Even if the calorific value of the fuel gas may fluctuate, excess air ratio of the air-fuel mixture is arranged to be maintained at a constant value. The premixing apparatus is provided with: an excess air ratio detection device (9) for detecting an excess air ratio of the air-fuel mixture; and a flow control valve (74) interposed in a portion, on a downstream side of the zero governor, of the gas supply passage (7). The flow control valve (74) is controlled such that the excess air ratio detected by the excess air ratio of the air-fuel mixture detection device (9) becomes constant.