TM 5-810-15
Table 6-2. Comparison of Pressure Dilute Phase and Dense Phase Pneumatic Ash Conveying Systems.
Dilute Phase
Dense Phase
Design Criteria
Evenly loaded single conveying line.
Typically multiple convey lines.
Loading ratio (5 to 22) lbs. of ash to lb. of air.
Loading ratio (20 to 200) lbs. of ash to lb. of air.
10 to 30 psig operating pressure.
30 to 100 psig operating pressure.
2000 to 3500 ft per mm starting velocity.
600 to 3000 ft per min starting velocity.
When
Recommended
High conveying capacity (greater than 30 TPH)
Short conveying distances (200 to 500 ft).*
Long conveying distances (greater than 1000 ft).*
Medium capacities (10 to 50 TPH).
Multiple disposal points.
Minimum collection points.
Minimum collection points.
Minimum disposal points.
Advantages
Greater capacities and distances with single line.
Smaller conveyor lines, bag filters and hoppers.
Not affected by material changes with gravity flow.
Lower conveying velocity.
Stable velocity range provides material re-entrainment.
Normally lower horsepower.
Transfer stations normally not required.
Carbon steel pipe.
Low initial cost air handling equipment
Components subjected to lower pressure.
Disadvantages
Higher airflow, larger pipe, and hoppers.
Material consistency greatly affects conveying
Often higher horsepower.
parameters and granular material remains in
Components subjected to higher velocity,
airlock with top exist.
Special pipe required-alloy pipe or ceramic lined pipe.
Positive sealing high differential discharge valve is
critical to system performance.
Transfer stations normally required.
Parallel compressed air lines required to free line plugs.
Multiple conveyor lines.
Expensive initial cost air compressors.
Components subject to higher pressure.
*An evaluation should be made for conveying distances of 500 to 1000 ft to determine whether Dilute Phase or Dense Phase pneu-
matic ash conveying systems are more feasible.
6-7
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