Coal Pulverizer Secondary Airflow Deflector Design
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Solution Overview
Problem
Vertical spindle coal pulverizers face issues with high differential pressures, mill rumble, and coal fines accumulation due to inadequate airflow, leading to reduced performance and increased risk of mill fires, especially when dealing with coals containing high silica levels.
Innovation Solution
A secondary airflow path is introduced above the grinding surface, directed downward to enhance airflow dynamics, reduce differential pressures, and improve pulverizer efficiency by channeling a portion of the primary airflow through a bypass conduit into an annular secondary airflow chamber, which is then deflected across the grinding surface, ensuring uniform airflow and efficient classification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If larger amounts of airflow are introduced into the pulverizer to correct improper throat sizing, then airflow velocity is improved, but differential pressure increases and air-to-fuel ratio becomes too high
Solution Approach 1:
The airflow system is segmented into two separate paths: a primary airflow path through the pulverizer throat and a secondary airflow path through the bypass conduit and annular chamber. This segmentation allows independent control of each path, enabling the secondary path to provide additional airflow velocity without increasing pressure in the primary throat path, thus resolving the contradiction between maintaining airflow velocity and controlling differential pressure
2Reliability
If primary airflow is increased to prevent coal rejection, then coal transport is improved, but air-to-fuel ratio increases and pulverizer performance deteriorates
Solution Approach 1:
A secondary airflow path acts as an intermediary mechanism to provide additional airflow for coal transport. This bypass path introduces air above the grinding surface and directs it downward across the grinding zone, supplementing the primary airflow without disrupting the optimized air-to-fuel ratio in the throat, thus maintaining both reliable coal transport and pulverizer efficiency
3Stress or pressure
If secondary airflow is introduced above the grinding surface, then differential pressure is reduced, but airflow distribution must be precisely controlled
Solution Approach 1:
The secondary airflow system adds a vertical dimension to airflow introduction by entering above the grinding surface and directing downward, complementing the horizontal primary airflow through the throat. This dimensional addition provides pressure relief without requiring complex control mechanisms, as the annular chamber and deflector geometry naturally distribute the airflow
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 design maintains optimal airflow velocities, reduces mill rumble, prevents coal rejection, and minimizes the risk of mill fires by maintaining lower differential pressures and improving air-fuel ratios, thereby enhancing pulverizer performance and operational safety.
Implementation Method 1
a secondary airflow path is introduced above the grinding surface, directed downward to enhance airflow dynamics
Implementation Method 2
Airflow of approximately 7,000 fpm velocities (terminal velocity of raw coal) must be maintained in order to prevent coal from being rejected through the pulverizer throat
Implementation Method 3
maintains lower pulverizer differential pressure by introducing a secondary airflow into the mill housing above the pulverizer throat and grinding surface
Implementation Method 4
reduce low load mill rumble by clearing fine particles from the grinding zone by directing a secondary airflow entering the upper housing downward across the grinding surface
Data Source
AI summary
A coal pulverizer including a mill housing, a grinding surface disposed in said mill housing, a grinding wheel engaging said grinding surface for pulverizing coal chunks; an annular throat disposed around said grinding surface channeling a primary airflow from a lower housing portion below said grinding surface upward through an upper housing portion above said grinding surface; an annular secondary airflow chamber extending around an exterior of said upper housing portion channeling a secondary airflow circumferentially into said upper housing portion above said grinding surface; and, an annular secondary airflow deflector extending along an interior of said upper housing portion above said grinding surface directing said secondary airflow from said secondary airflow chamber downward across said grinding surface in a generally uniform uninterrupted circumferential airflow pattern.