SESSION 104 PNEUMATIC CONVEYING SYSTEM COMPONENT …€¦ · • A rotary airlock is used as the...
56
1 Pneumatic Conveying Systems Component Selection & Troubleshooting Session 104
Transcript of SESSION 104 PNEUMATIC CONVEYING SYSTEM COMPONENT …€¦ · • A rotary airlock is used as the...
1
Pneumatic Conveying Systems Component Selection & Troubleshooting
Session 104
Line Chargers for Vacuum Conveying Systems
• No pressure differential• Air at atmospheric conditions• Venting is not an issue• Material temperature may be an issue• Material flow control is required
• Slide gates for coarse products• Rotary feeders/airlocks for powders• Air / Material mixture control is effective
2
Material Pick Up Pan for Rail Car With Discharge Gates
Air Flow
ProductFlow
3
Rail Car Unloading Attachments
Vacuum System Line Chargers
• Light weight construction for ease of handling • Controls the material to air mixture at the pick-up point• Manually adjustable • Interface with gas mover operating vacuum
4
Line Chargers for Pressure Conveying Systems
• Pressure differential • Gas is at gas mover discharge conditions• Material flow control is required• Material temperature may be an issue• Leakage to consider• Venting is very important
5
Rotary Feeder /Airlocks
Courtesy DELTA / Ducon
Courtesy Pelletron Corp
6
BearingRetainers
Bearing
Washer
End PlateHousing Rotor
Lantern RingTeflon Packing Seal
Typical Rotary Feeder Assembly
• Volumetric displacement per revolution
• Normal pressure differentials are in the range of 6-15 psig but special designs can handle 3 to 6 bar (45 to 90 PSIG) differential.
Body Options Include VentPorts & Inspection Panels
Courtesy FLSmidth
7
Specialty Rotary Feeders /Airlocks
• Blow Thru design for light density and cohesive products
• Off Set Inlets prevent clipping and wedging
Courtesy Carolina Conveying8
Rotor Options
• Different rotor configurations are available
• Open end rotors
• Closed end rotors
• Reduced capacity pockets
• Replaceable rotor tips
Courtesy Carolina Conveying
9
Rotary Airlock Leakage
• Static Leakage • Radial • Axial
• Dynamic Leakage • Pockets venting as they
return to be refilled• Function of rotor size and
speed
Don’t forget to account for the leakage gas when sizing the gas supply for the pneumatic conveying system!
10
Typical Airlock Leakage Values
Carolina Conveying Data
• Can be calculated
• Vendors provide data
11
Venting for
Coarse Products
Internal
Baffle
Rotation
12
Venting Scheme for Powders
• Fluidizable powders need different approach than coarse products
• A “flow control” device is used at the material inlet• Rotary Feeder• Screw Conveyor• Vibrating Feeder• Etc.
• A rotary airlock is used as the line charger to the pressure conveying system
• A vented transition is used between those two devices
Diagram Courtesy of Horizon Systems
13
Basic Rotary Airlock Sizing Procedure
• Start with the MASS flow rate
• Use the LOWEST Density
• Determine the VOLUMETRIC flow rate
• Divide Mass Flow Rate by Density
• Obtain Ft3 / Min = Q
• Correct for “Efficiency”
• Factors can range from 65% to 85%
• A “safe” value to use is 70%
• Q / 0.7 = Corrected Volumetric Flow Rate = Q corrected
• Vendors provide tables of Airlock Size versus Volumetric Displacement
• Select a unit size and determine airlock speed
• Qcorrected / DisplacementVolumetric = RPM
Example;
• 1000 #/min
• 25 PCF
• 1000/25 = 40 CFM
• 40/0.7 = 57 CFM
• Use 12”
• 5.7 CFM / 2.25 CFR = 25 RPMAirlock Model Displacement
(Ft3/Revolution)
6” 0.25
8” 0.60
10” 1.25
12” 2.25
14” 3.5 Be Careful About Rotor Speeds!
14
Consideration of Rotor Speed
• Curve is typical for plastic pellets.
• Finer and fluidizable material decrease capacity at a lower rotor speeds
• Normal operating speeds range between 10 and 30 rpm
• Below 10 rpm - intermittent slugs
• Above 30 rpm - reduced efficiency
15
Typical Feeder/Airlock Capacities
Courtesy Carolina Conveying
16
Pressure Tanks
• Used for high capacity or long distances
• Highly suitable for handling abrasive materials
• Numerous designs and configurations are available to meet product requirements
courtesy Nol-Tec
17
“Typical” Pressure Tank Cycle• Pressure tank fills with product
• Inlet and vent Open
• All other valves closed
• Tank contents are conveyed• Discharge and air assist valves open
• All other valves closed
• Tank is vented• Vent valve open
• All other valves closed
• Tank is refilled and cycle repeats• Design for “peak” conveying rates• High pressure ratios create high
terminal velocities unless addressed
Inlet Valve
AerationValve (Powders)
Discharge Valve
Vent Valve
PressurizationValve (Coarse)
Typical for Dilute and Two Phase Flow
Level Probe
18
Con
vey
Lin
e P
ress
ure
Time
One Cycle
Dwell Time
Discharge Time
Conveying
Typical Pressure Tank Performance(Single Tank System)
Average LinePressure
19
Dual Pressure Tank Arrangement
.
courtesy FLSmidth
20
Typical Pressure Tank Performance(Dual Tank System)
Con
vey
Lin
e P
ress
ure
Time
One Cycle
Dwell Time = 0
Average LinePressure
Tank 1 Tank 2
21
Basic Pressure Tank Sizing Procedure(Single Tank System)
• Start with the MASS flow rate • Use the lowest value of Density• Determine the VOLUMETRIC flow rate
– Divide Mass Flow Rate by Lowest Density
– Obtain Ft3 / Min = Q• Pick a tank size, Ft3 and determine Cycle
Time,– Timecycle =Tank Size / Q = minutes /
cycle• Determine Cycles / Hr
– 60 / Timecycle = cycles per hour– Recommended to be as low as possible
• Determine Conveying Time– Timeconvey = Timecycle – Timefill – Timevent
• Determine Peak Conveying Rate– Tank Size / Conveying Time = PCR
• 1000 #/min• 25 PCF• 40 CFM• 150 CF/40CFM = 3.8 MIN/CYCLE• 60 /3.8 = 16 CYCLES / HR• 3.8 – 0.3 – 0.3 = 3.2 MIN• 150/3.2 = 47 CFM = 1,175 #/MIN
Pneumatic transfer system to be designed for the Peak Conveying Rate !
22
AIR ASSISTS / BOOSTERS
• Air Assists along the conveying line “refluidize” the product
• Assist air can be continuous or “on demand”
Courtesy Nol-Tec
23
Screw Pumps
• Continuously discharges material
• Handles high capacities but energy intensive
• Works well on powders but has limitations with coarse materials
• Not suitable for materials which are temperature sensitive or friable
• Handles high pressure differentials
Courtesy FLSmidth
Courtesy IBAU24
Double Flap Valve
• Material moves in small batches
• Consumes no extra energy.
• Potential replacement for rotary airlocks with abrasive wear problems and screw pumps to reduce energy consumption
Courtesy Plattco Valves25
Summarizing Line Chargers• Rotary airlocks are used typically in low to medium
pressure conveying systems but high differential pressure and abrasion resistant designs are available
• Proper venting is paramount to performance
• Pressure tanks are more suitable for higher capacity and longer conveying distances
• Air assists / boosters along the conveying line are beneficial for materials with poor air retention
• Screw pumps are available but limited product range
• Double flap valves are a viable alternative
26
Conveying Piping and Related Components
27
Conveying LineMaterial of Construction is dependent on the product being handled and the application
• Carbon Steel• Aluminum• Stainless Steel• HDPE• PVC• Wear Resistant
• Ceramic Lined• Heat Treated• Specialty Cast Iron
• Special Internal Treatments
28
Conveying Line Considerations
• Keep lines horizontal and vertical • Conveying lines are NOT water pipes!• Bend orientation is a prime concern• Pipe alignment is important• Sloping lines can be dealt with if unavoidable• Vertical downward lines are not “forbidden”
29
Bends in a Pneumatic Conveying System
30Old School New School
Conveying Line Bend Options
31
Long Radius Sweeps With and
Without Wear Backs
Blind Tees and Vortice Ells
Short Radius Bends with Replaceable Wear BacksOne of Many Specialty Bends for the
Petrochemical Industry
Elbow Options for Air Pipe
3
2
Short Radius Welded Elbows
A Piping “Challenge”
3
3
Abrasion Resistant Bends
1. Wear back bends, pipe within a pipe, annulus filled with concrete have all been used over the years.
2. Also abrasion resistant materials with high hardness like ceramics, Ni-Hard alloys have been applied to the inside as well as outside diameters.
34
Special Considerations
• A common problem with many grades of Polymers is the formation of Streamers, Angel Hairs and Fines– Internally grooved conveying pipe provides an
irregular surface to discourage the “sliding” contact – Other techniques include shot peening and sand
blasting
Courtesy DELTA / DuconCourtesy MAC Equipment Co
LDPE Polymer
35
Pipe Coupling Options
Grooved Connection
Quick Access Design
(3) or (4) Bolt Compression Style
(3) or (4) Bolt Compression Style With Restraints
“Insta-Lok” Compression Style 36
Diverter Valves
Courtesy EVERLASTING VALVE CO.
Rotating Plug Type
Shoe Type 37
Diverter Valves• Used in conjunction with a
WYE or LATERAL
• Many types are available
• Line Blinds
• Pinch Valve
• Sliding Disc Valves
• Knife Gates
• Ball Valves
• Hose Switch Valves
38
Expansion Joints
Bellows Type Joint
Telescopic Type Joint39
Summarizing The Conveying Line Discussion
• Conveying line materials of construction are chosen based on products handled and application
• Short radius elbows are the over-all recommendation
• Specialty bends are available for special applications
• Pipe orientation is critical to over-all system performance
• Internal pipe treatment can mitigate debris formation
• Expansion joints considered for long pipe runs
40
Receiving Stations
42
Direct Discharge Into Receiver
Day Bin Storage Silo 43
Pipe Discharge Box
44
Filter Receiver
• Separates product from conveying gas
• Used in Vacuum or Pressure Service
• Different physical arrangements are available from different vendors• Top vs. Side Access• Cyclonic vs. Radial Inlet
• Filter media has many options• Geometry• Material
Product Outlet
Gas Outlet
Product &Gas Inlet
FilterMedia
SeparationZone
45
Cyclones
Used at the terminal end of a pneumatic conveying system to;
• Separate coarse product without fines • Collect a specific product cut size• Protect a downstream dust collector
46
Cyclones
Cyclone performance is based on geometry and changes in system operation and material characteristics can affect performance
47
Dust Collection / Filters
Silo Vent Filters
48
Air-to-Cloth Ratio• The ratio of dust laden air (ACFM) to be
filtered to the square feet of filter media – Velocity in feet per minute of the air passing
through the filter media– Example: 5,000 ACFM/800 square feet
=6.25:1 air-to-cloth ratio
• Remember to apply a “surge factor” for dust collector sizing
• Dilute Phase: 1.0 • Two Phase Flow: 1.5 – 2• Dense Phase: 2.5 – 3• PD Truck Unloading 2 to 3
49
Can Velocity
• Can Velocity=ACFM/AREA
• ACFM=gas volume through the bag house
• AREA=cross sectional area of the bag house
“Can
Velocity”
50
Interstitial Velocity
• The apparent velocity of a gas as it passes by a filter bag matrix
• Divide the ACFM by the NET AREA
• This number needs to be very low
InterstitialVelocity”
51
Pulse-Jet Cleaning
• Compressed air is pulsed into the top of the venturi at 80 - 100 PSIG for 0.1 seconds
• Air is induced from the clean air plenum and combines with the pulse air
• The reverse flow of air forms a bubble in the top of the filter bags which travels down the length of the bag
•As the bubble travels, dust is removed from the surface of the filter bag
52
Jet Pulse Plenum Assembly
Top Access Entry?Side Access Entry?
53
Timed cleaning is a vendor standard but the recommendation is to use a differential pressure switch for “Cleaning on Demand”
Bags, Cages, and Cartridge Filters
54
Summarizing This Lecture• Gas movers can be fans, blowers, compressors or even plant air
systems
• The selection is primarily based on the TYPE and MODE of the conveying system
• Cyclones can be used to “segregate” material by size
• Avoid tangential entries into receivers
• Radial inlets provide best protection against wear
• Can and Interstitial velocities are critical in dust collectors
• Filter media selection may require product testing
• Cleaning fabric filters “on demand” will extend media life
55
