Isokinetic Stack Gas Sampler with Dynamic Nozzle Area Control
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Solution Overview
Problem
Existing methods fail to continuously and precisely measure fine dusts (PM10 and PM2.5) in stack gases due to conflicting constraints between maintaining isokinetic suction flow rates and constant flow rates required for separation, leading to measurement errors.
Innovation Solution
A continuous isokinetic sampling device with a suction nozzle and cross-sectional area control device that automatically adjusts the nozzle's area to maintain isokinetic suction flow rates within 95-110% of the emission source's flow rate, while ensuring a constant 16.67 l/min flow rate for fine dust separation, using a thermal mass flowmeter and position control mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed nozzle caliber is used for sampling, then the device structure is simple and easy to operate, but the sampling flow rate cannot adapt to frequent changes in stack gas flow rate, causing measurement errors
Solution Approach 1:
The patent transforms the fixed nozzle caliber into a dynamic, adjustable nozzle whose cross-sectional area can be automatically changed based on real-time stack gas flow rate measurements. The control unit receives flow rate data from the stack and automatically adjusts the nozzle caliber to maintain isokinetic sampling conditions, resolving the contradiction between operational simplicity and measurement accuracy.
Solution Approach 2:
The patent changes the physical parameter of the nozzle cross-sectional area from a fixed value to a variable parameter that can be dynamically adjusted. By linking the nozzle area to the measured stack gas flow rate, the system maintains the isokinetic sampling ratio (95-110%) across varying flow conditions, thereby improving measurement precision without complicating operation.
2Measurement precision
If the nozzle caliber is manually replaced to match changing flow rates, then measurement precision is maintained, but the operation becomes complex and time-consuming
Solution Approach 1:
The patent implements a self-service system where the sampling device automatically monitors its own operating conditions (stack gas flow rate) and self-adjusts the nozzle caliber without external intervention. The control unit continuously compares the current flow rate with the required isokinetic sampling rate and automatically selects the appropriate nozzle caliber, making the system both precise and easy to operate.
Solution Approach 2:
The patent introduces a feedback control mechanism where the measured stack gas flow rate is fed back to the control unit, which then adjusts the nozzle caliber accordingly. This closed-loop control ensures that the sampling system continuously adapts to changing conditions while maintaining measurement precision, eliminating the need for manual nozzle replacement.
3Measurement precision
If the suction flow rate is adjusted using a pump to maintain isokinetic suction, then measurement precision is improved, but the flow rate passing through the cascade impactor becomes unstable
Solution Approach 1:
The patent segments the flow rate control function into two independent parts: (1) the nozzle caliber determines the sampling flow rate to maintain isokinetic suction, and (2) the pump maintains a constant flow rate through the cascade impactor. By separating these functions, the system can adjust the sampling flow rate without affecting the stability of the impactor flow rate, resolving the contradiction between measurement precision and flow stability.
Solution Approach 2:
The patent adds a new dimension of control by introducing adjustable nozzle calibers with different cross-sectional areas. Instead of controlling flow rate solely through pump speed (one-dimensional control), the system now has two independent control dimensions: nozzle area and pump speed. This allows simultaneous optimization of isokinetic sampling and impactor flow stability.
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 solution enables precise, continuous measurement of fine dust concentrations in stack gases by automatically adjusting the nozzle's cross-sectional area, minimizing measurement errors and maintaining isokinetic sampling conditions, thus linking fine dust management with data accumulation and process control.
Implementation Method 1
measuring a flow rate with a thermal mass flowmeter
Data Source
AI summary
Provided is a continuous isokinetic sampling device of a stack gas having a suction nozzle to which a cross-sectional area control device is attached, and a continuous automatic measurement system of fine dusts in the stack gas combined with the same, the device and system being configured to continuously separate and automatically measure the suspended particles into PM10 (Particulate Matter Less than 10 μm) and PM2.5 (Particulate Matter Less than 2.5 μm) by introducing a suction gas into a particle size separation device (cascade Impactor) at a constant flow rate of 16.67 l/min, simultaneously with removing an measurement error caused due to inertia force of the suspended particles by automatically adjusting the cross-sectional area of the suction nozzle to suck the sample at the same flow rate as that of the stack gas in the stationary source emissions.