Pneumatic Conveying Systems Theory and Principles Session 100

Transcription

1 Pneumatic Conveying Systems Theory and Principles Session 100 1

2 Controls & Instrumentation

3 P = Actual Pressure V = Actual Volume T is Typically Ignored Key Relationship PV/T Terminal Point Any Point Pick Up Point Pick Up = Any Point = Terminal Pick Up > Any Point > Terminal Pick Up < V@ Any Point < Terminal Since Q = VxA --- Velocity follows same trend as Volume

4 TYPES OF PNEUMATIC CONVEYING SYSTEMS 4

5 Vacuum System Filter Receiver Feed Air Inlet Rotary Airlock In-Line Filter Gas Mover Advantages Easy to Feed Multiple Pick-Up Points Cleaner Operation Gas Leakage is Inward Disadvantages Limited Capacity & Distance (usually 18 Hg) Potential Damage to Gas Mover High Temperature Material into Gas Mover 5

6 VACUUM CONVEYING SYSTEMS Single Destination Multiple Destination 6

7 Typical Vacuum Pick-Up Points Railcar Dust Collector Iso Container Drum or Gaylord OTHER SOURCES Central Vacuum System Directly Off a Process Stream Bag Dump Station Bulk Bags Tote Bins Silo or Day Bin 7

8 Pressure System Advantages Multiple Delivery Points Unlimited Capacity and Distance Disadvantages Potentially Dirty Operation Higher Explosion Design Pressure More Concerns for Line Chargers 8

9 PRESSURE CONVEYING SYSTEMS 9

10 Combination Vacuum / Pressure FEED FILTER RECEIVER RECEIVER ROTARY AIRLOCK VACUUM & PRESSURE BLOWERS 10

11 Combination System Advantages Easy to feed Multiple pick-up points Cleaner operation on vacuum side Leakage inward on vacuum side Multiple delivery points Unlimited capacity and distance on pressure side 11

12 Combination System Disadvantages Potential damage to air mover due to high temperature or material Potential dirty operation on pressure side Two air movers recommended Higher explosion design pressure Line charger concerns on the pressure leg Pressure leg bottleneck 12

13 Combination System Vacuum / Pressure 13

14 CLOSED LOOP CONVEYING SYSTEM FAN LINE FILTER INERT GAS SUPPLY PRESSURE RELIEF VALVE BLOWER RELIEF VALVE ROTARY AIRLOCK Water PRODUCT DISCHARGE AIR COOLER PRODUCT FEED DIRECTION OF FLOW 14

15 Vacuum vs. Pressure 1. Material doesn t know the difference in the pipe line 2. Vacuum easier to feed 3. Pressure has unlimited energy, thus higher capacities or longer distance in a given pipe diameter a) Vacuum Hg or 14.7 psig b) Pressure unlimited - usually < 60 psig 4. Pressure easier to deliver to multiple points a) Only requires diverter valves 5. Vacuum is easier to pick up from many points 15 and delivers to one common point

16 Vacuum vs. Pressure Energy Comparison Design Diameter SCFM PSIG Hg Blower ICFM Pickup velocity Adiabatic Air HP , , , , , , , , ,

17 Vacuum vs. Pressure Selection Guideline Application Normal Choice Multiple feed points Vacuum Multiple delivery points Pressure Hose pick up (unloading drums etc.) Vacuum Multiple pickup and delivery points Combination Smooth delivery to a burner Pressure (dilute phase) Hot material Pressure Limited head room at feed point Vacuum Limited head room at terminal point Pressure Quick line cleanout Pressure or Vacuum 17

18 Characteristics Vacuum vs. Pressure Other Considerations Normal Choice Smaller conveying lines pressure Smaller dust collector Pressure Smaller blower size Pressure Cleaner operation Vacuum Less complicated controls Vacuum Less initial cost Pressure 18

19 Dilute vs. Dense Phase 19

20 Dilute vs. Dense Phase 1. Is not a function of the pressure or vacuum 2. More dependent on material characteristics 3. Definition dense phase is below the saltation velocity a) Saltated layer may flow like a liquid, surge, form waves or pistons 4. Dilute phase no material settling in the horizontal 20

21 Modes of Conveying Stream Flow (Dilute Phase) Two Phase Flow Dense Phase Flow Permeable Non-Permeable 21

22 Dilute Phase Conveying Material is in complete suspension in the pipe Steady / Continuous material discharge Conveying takes place above the saltation velocity of the material Conveying pressures are typically < 15 psig High gas to material ratios: > 2.25 Ft 3 gas / # of material Low material to gas ratio: < 5.25 # material / # of gas Pick-up velocities are in the fpm range Pressure drop increases as gas velocity increases Works for all classes of materials. 22

23 Two-Phase Flow Dilute phase conveying takes place in upper section of pipe. A heavier concentration of takes place in lower section of pipe. Medium gas to material ratios: > 0.20 to 2.25 Ft 3 gas / # of material Material to gas ratios are in the 5-60 range. Conveying velocities are in the fpm range Surging / pulsing material discharge Works very well for class A materials -- long retention time 23

24 Dense Phase Conveying Pulse Piston Permeable Materials Gas Flow Slugs or plugs of material move within the pipeline. Low air to material ratio <1.0 cubic feet of gas per # of material High material to gas ratio > 30 Low velocities in range of 1500 FPM Conveying depends on the P across theplug of material Pressure drop increases as gas velocity decreases Recommended for products which are abrasive or friable Pipe forces become concerning 24

25 Dense Phase Conveying Pulse-Piston Non- Permeable Materials Material travels in intermittent, discrete controlled length plugs of material Conveying depends on P across the plug of material Usually some form of plug length control required, like boosters, air knifes, air assists, bypass pipes, etc. Pressure increases as the air flow decreases Pipe forces become more concerning 25

26 Questions? Jack D. Hilbert P.E

27 Air Activated Gravity Conveyors Pneumatic Conveying Without A Pipeline 27

28 Principle of Fluidization Angle of Repose Ø Materials have a natural Angle of Repose. For material to flow by gravity down a plate, the angle Ø must be greater than the Angle of Repose. By flowing air through a powered product, the angle to achieve gravity flow is significantly less than the Angle of Repose. 28

29 Air Activated Gravity Conveyor Permeable Membrane Product Flow Fluidization Chamber 29

30 Air Activated Gravity Conveyors Closed type units used when conveying from point to point Open type units used inside bins, hoppers, silos, railcars, etc. to aerate material to encourage flow Most effective for materials which are responsive to Fluidization - Geldart Type A materials 30

31 Air Activated Gravity Conveyors Open type units are installed in the conical portion of the bin Number of units is dependent on the bin diameter Air supply is typically a positive displacement blower at 3-5 PSIG Air flow is sequenced to open type units to promote flow Storage Bin or Silo 31

32 Air Activated Gravity Conveyors Closed type sections transfer from point to point Systems can be quite inclusive! Inlet Section Air Supply Flow Control Valves Observation Ports Curve Sections Side Discharge Connections 32

33 Media and Capacity Options 33

34 Typical Application of Air Activated Gravity Conveyor Technology Open Type on Cone Wall Rotary Flow Control Valve Open Type on Silo Floor Aerated Bin Bottom Aerated Material Trap Closed Type with Components 34

35 Air Activated Gravity Conveyors Collecting Dust Under a Fabric Filter Bag House or ESP 35

36 Air Activated Gravity Conveyors Loading Alumina into a Barge 36

37 The Fluidized Elevator Lift Pipe Inlet Receiving Vessel Often called an Air Lift. Used for primarily vertical conveying of fluidizable materials Air Supply 37

38 Questions? Jack D. Hilbert P.E