Gas Boiler Exhaust Gas Sensor for Reliable Low Power Control
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Solution Overview
Problem
Existing methods for regulating gas boiler processes are unreliable across the entire working range due to sensitivity to low power conditions and environmental influences, particularly due to the quadratic relationship between pressure and volume flow, which makes mixture control at low power points difficult.
Innovation Solution
A sensor is placed downstream of the combustion chamber in the exhaust gas stream, with condensate separation and cooling to improve measurement quality and sensor lifespan, using thermal conductivity sensors to monitor the exhaust gas composition for optimized combustion control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ionization current measurement of a flame is used to control the gas boiler process, then the system can be regulated based on flame state, but the method does not provide reliable operation across the entire operating range due to ionization current decreasing in the low power range
Solution Approach 1:
The patent introduces exhaust gas components (CO, CO2, O2) as intermediary measurement parameters between the combustion process and control system. Instead of directly measuring flame ionization current, the system measures exhaust gas composition downstream, which provides a more stable and reliable signal across the entire power range including low power conditions.
Solution Approach 2:
The patent replaces the electrical measurement method (ionization current) with a chemical/thermal measurement method (exhaust gas composition analysis using thermal conductivity sensors). This substitution eliminates the fundamental limitation of ionization current measurement at low power levels while providing continuous reliable control signals.
2Measurement precision
If a sensor is placed in the combustion chamber to measure process parameters, then direct measurement is possible, but the sensor is exposed to harsh conditions including high temperature and condensate that reduce service life and measurement quality
Solution Approach 1:
The patent inverts the measurement location from inside the combustion chamber to downstream in the exhaust gas stream. By measuring after combustion is complete and gases have cooled slightly, the sensor operates in less harsh conditions while still providing accurate combustion process information through exhaust gas composition analysis.
Solution Approach 2:
The patent implements preliminary condensate separation and cooling of the exhaust gas stream before sensor measurement. This preliminary action removes harmful condensate and reduces temperature, protecting the sensor and improving measurement quality without requiring complex in-situ sensor protection systems.
3Ease of operation
If pressure-based control is used with quadratic relationship between pressure and volume flow, then control can be implemented, but extremely low control pressures are achieved that are very sensitive to environmental influences such as wind
Solution Approach 1:
The patent implements feedback control based on exhaust gas composition measurements. The measured CO, CO2, and O2 levels are fed back to continuously adjust the air-fuel mixing ratio, providing reliable control that is independent of pressure sensitivity to environmental influences. This closed-loop feedback ensures accurate mixture control across all operating conditions.
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 enables continuous regulation of the gas boiler process over a wide modulation range, regardless of fuel gas type or ambient conditions, enhancing control precision and reliability.
Implementation Method 1
acquire the controlled variable using at least one thermal sensor, in particular a thermal conductivity sensor
Implementation Method 2
carry out condensate separation by cooling the exhaust gas stream. Reducing the temperature of the exhaust gas stream causes the exhaust gas components to transition from a gaseous to a liquid state
Data Source
Figure 1
AI summary
A method for monitoring and controlling a process of a gas boiler (10) in which a fuel gas-air mixture comprising air and a fuel gas is combusted in a combustion chamber (8), wherein a control variable of at least one sensor (1) is used to adjust a mixing ratio of air flow and fuel gas flow by suitable actuators arranged upstream of the combustion chamber (8). Here, the sensor (1) is arranged downstream of the combustion chamber (8) in an exhaust gas stream (9) and is at least partially surrounded by the exhaust gas stream (9) from the combustion chamber, and sensor data measured by the sensor (1) regarding the material composition of the exhaust gas stream (9) are recorded as the control variable.