Yang Fluidization, Solids Handling, and Processing

Long Distance Pneumatic Transport and Pipe Branching 765

Figure 28. Improved dropout box splitter (Selves et al., 1995).

General Considerations. Some other important considerations that should be made when designing a flow splitting system are listed below.

•The splitter should provide a symmetrical split in all planes and preferably should be installed in the vertical plane (if possible).

•The solids-gas flow upstream of the splitter should be uniform and regular.

•Sufficient upstream pipe should be used to eliminate any flow separation effects caused by in-line components, such as bends and diverters (e.g., “roping” in dilute-phase).

•Special care should be taken when selecting the mode of solids-gas flow. For example, flow separation and roping could occur even in very dilute-phase conveying systems (e.g., m* ≤ 1 for coal-fired boilers). Fluidized dense-phase also is possible for some systems and can offer many

766 Fluidization, Solids Handling, and Processing

advantages (e.g., reduced air flow, velocity, wear, power). However, this mode of flow can be more irregular than dilutephase (e.g., increased pressure fluctuations) and hence, produce flow splitting problems, even with active splitters. The objective here should be to achieve the minimum air flow that is needed to ensure smooth and consistent flow under all operating conditions.

3.3Pressure Loss

For dust extraction systems, the concentration of solids usually is quite low. For this reason, the methods employed to calculate pressure loss are based on air-only conditions. Comprehensive information is available (ASHRAE, 1985; ACGIH, 1992) to assist the designer in estimating the pressure loss caused by pipe branches, ducts, elbows, etc.

In contrast, the amount of material being conveyed inside each pipe branch of a flow splitting application is very high and hence, design cannot be based on air-only analyses alone. For example, Low et al., 1987 have proposed the following empirical relationship to determine the head loss of a pipe branch.

where K is the branch head loss for solids-gas flow, Kf is the branch head loss for air-only conditions and can be calculated theoretically from (Low et al., 1987), C = 0.22 and a = 1.27 appear to represent satisfactorily both 90°- and 45°-branches with different branch diameters and products (Low et al., 1987). Further examples of empirically based pressure loss equations for Y-splitters of various angles and subjected to plastic pellets under different solids loadings have been presented and cited by Marcus et al., 1990.

Good flow splitting design is dependent on the accurate prediction of the pressure drop caused by the various bends, branches and straight sections of pipe. This can be achieved by employing the above branch model(s), proven for the particular material and application, coupled with the accurate “pipeline” test-design procedure described in Sec. 2.4 of this chapter.

768 Fluidization, Solids Handling, and Processing

ψParticle sphericity

Subscripts

i Initial value (at beginning of pipe)

eFinal or exit value (at end of pipe)

fFluid (gas)

mMean value (based on average air density) min Minimum value

nValue relating to pipe section n (starting from end of pipeline)

oValue relating to bend outlet

s Solids

Long Distance Pneumatic Transport and Pipe Branching 769

REFERENCES

ACGIH, Industrial Ventilation: A Manual of Recommended Practice, 21st Ed, American Conf. of Governmental Industrial Hygienists, Inc., Cincinnati, USA (1992)

Allen, T., Particle Size Measurement, Chapman and Hall Ltd, London, 2nd Ed (1975)

Anon, “Dynamics of Gas/Solids Systems,” Pneumatic Handling of Bulk Mat., Part A: Fundamentals, Bulk Solids Handling Unit, Thames Polytechnic, London (1983)

Anon, “Dust Suspended from Workplace,” PACE, Process and Control Eng., p. 56 (1995)

Arnold, P. C., Wypych, P. W., and Reed, A. R., “Advances in the Design of Pneumatic Transport Systems,” Powder Handling & Processing, 6(1):9–21 (1994)

ASHRAE, ASHRAE Fundamentals Handbook , American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc, Atlanta (1985)

Barnes, R. N., and Murnane, S. N., “The Sensing of Unbalanced Pulverised Coal Feed Rates at the Exit of Riffle Boxes in Coal-Fired Power Station Fuel Distribution Systems,” 5th Int. Conf. on Bulk Mat. Storage, Handling and Transportation, Newcastle, IEAust, Proc., 1:273-281 (1995)

Cable, P. M., Design Requirements of Ind. Dust and Fume Extraction Systems, BE Thesis, Dept. of Mech. Eng., Univ. of Wollongong (1994)

Cabrejos, F. J., and Klinzing, G. E., “Minimum Conveying Velocity in Horizontal Pneumatic Transport and the Pickup and Saltation Mechanisms of Solid Particles,” Bulk Solids Handling, 14(3):541–550 (1994)

Cürten, H. J., “Concepts and Results of Pneumatic Conveying of Support Materials in German Underground Mining,” Pneumatech 1, Int. Conf. on Pneumatic Conveying Technol., Stratford-Upon-Avon, UK (1982)

DASCG, and AIRAH, Mechanical Engineering Services Design Aids No. DA3, Air Conditioning Duct Design Manual, (F. Wickham, ed.), Dept Administrative Services Construction Group and AIRAH, Aust Govt Publishing Service, Canberra, Aust (1987)

DASCG, and AIRAH, Mech. Eng. Services Design Aids No DA4, User Guide for the Computer Program DONKEY, (F. Wickham, ed.), Dept Administrative Services Construction Group and AIRAH, Aust Govt Publishing Service, Canberra, Aust (1988)

Dixon, G., “How do Different Powders Behave?,” Bulk-Storage Movement Control, 5(5):81–88 (1979)

770 Fluidization, Solids Handling, and Processing

Dixon, G., “Pneumatic Conveying,” Plastics Pneumatic Conveying and Bulk Storage, Applied Science Publishers, London (1981)

Geldart, D., “Types of Gas Fluidization,” Powder Technol., 7:285–292 (1973)

Geldart, D., and Abrahamsen, A. R., (“Fluidization of Fine Porous Powders, Recent Advances in Fluidization and Fluid-Particle Systems,” AIChE Symp. Series, AIChE, 77(205):160–165, New York (1981)

Geldart, D., Harnby, N,, and Wong, A. C., “Fluidization of Cohesive Powders,” Powder Technol., 37:25–37 (1984)

Hilbert, J. D., “Multiple In-Line Splitting of Pneumatic Conveying Pipelines,” J. Pipelines, 3:161–172 (1982)

Jones, M. G., and Mills, D., “Low-Velocity Pneumatic Conveying: Product Characteristics,” Interbulk 89, Seminar on Pneumatic Conveying: Potentials and Capabilities, Birmingham, Organised by Glasgow College, Glasgow, Scotland and Thames Polytechnic, London, England (1989)

Kennedy, O. C., Wypych, P. W., and Arnold, P. C., “The Effect of Blow Tank Air Injection on Pneumatic Conveying Performance,” Pneumatech 3, Int. Conf. on Pneumatic Conveying Technol., Jersey, Channel Islands, UK (1987)

Lohrmann, P. C., and Marcus, R. D., “The Performance of a Bottom-Discharge Blow Vessel Pneumatically Conveying Three Group A Materials,” Bulk Solids Handling, 4(2):409–412 (1984)

Low, H. T., Winoto, S. H., and Kar, S., “Pressure Losses at the Branches of a Pneumatic Conveying System,” Bulk Solids Handling, 7(6):865–867 (1987)

Mainwaring, N. J., and Reed, A. R., “Permeability and Air Retention Characteristics of Bulk Solid Materials in relation to Modes of Dense-Phase Pneumatic Conveying,” Bulk Solids Handling, 7(3):415–425 (1987)

Marcus, R. D., Leung, L. S., Klinzing, G. E., and Rizk, F., Pneumatic Conveying of Solids, Chapman and Hall Ltd, London (1990)

Mason, J. S., Mills, D., Reed, A. R., and Woodcock, C. R., “The Use of Product Conveying Characteristics in the Design of Pneumatic Conveying Systems,” Powder Europa. 80, Seminar D, pp. 58–80 (1980)

Miletich, D., Atomisation and Pneumatic Conveying of Coarse Aluminium Powder, BE Thesis, Dept of Mech Eng, Univ. of Wollongong (1994)

Mills, D., Mason, J. S., and Stacey, R. B., “A Design Study for the Pneumatic Conveying of a Fine Particulate Material,” Solidex 82, pp. C1–C75 Harrogate, UK (1982)

Molerus, O., “Interpretation of Geldart’s Type A, B, C and D Powders by Taking into Account Interparticle Cohesion Forces,” Powder Technol., 33:81–87 (1982)

Pan, R., and Wypych, P. W., “Scale-Up Procedures for Pneumatic Conveying Design, Powder Handling & Processing, 4(2):167–172 (1992a)

Long Distance Pneumatic Transport and Pipe Branching 771

Pan, R., and Wypych, P. W., “Bend Pressure Drop in Pneumatic Conveying of Fly Ash,” Powder & Bulk Solids Conf., Reed Exhibition Companies, USA, Proc, pp. 349–360, Rosemont, Illinois, USA (1992b)

Pan, R., and Wypych, P. W., “Design of Economic Pneumatic Conveying Systems,”

MECH’94, Int. Mech. Eng. Congress & Exhibition, IEAust, Proc, 2:137– 141, Perth, WA (1994)

Selves, T. P., and Barnes, R. N., “A Review of In-Line Splitting Techniques used in Pneumatic Conveying,” 4th Int. Conf. on Bulk Materials Storage, Handling and Transportation, 2:353–358, IEAust. Proc, Wollongong (1993)

Selves, T. P., Barnes, R. N., and Reed, A. R., “The Use of Flow Diverting Air Injection to Actively Control the Split Ratio of Pneumatically Conveyed Particulate Materials,” 5th Int. Conf. on Bulk Materials Storage, Handling and Transportation, IEAust. Proc, 1:263–271, Newcastle (1995)

Timms, G., “Pneumatic Conveying - a New Application for Larox Pinch Valves,” Larox News, 14:8–11 (1992)

Wypych, P. W., Pneumatic Conveying of Manganese Oxide, ITC Bulk Materials Handling Report for BHP Engineering, North Sydney, NSW (1989b)

Wypych, P. W., Pneumatic Conveying of Bulk Solids, PhD Thesis, Department of Mechanical Engineering, Univ. of Wollongong (1989b)

Wypych, P. W., “Pressure Drop in Cement Pneumatic Conveying Systems,”Powder & Bulk Solids Conf., Reed Exhibition Companies, pp. 467–471, Rosemont, Illinois, USA (1992)

Wypych, P. W., “Optimising & Uprating Pneumatic Transport Systems,” Nat. Conf on Bulk Materials Handling, Yeppoon, Qld., IEAust. Proc., pp. 197–203 (1993)

Wypych, P. W., “Latest Developments in the Pneumatic Pipeline Transport of Bulk Solids,” 5th Int. Conf. on Bulk Materials Storage, Handling and Transportation, Newcastle, IEAust, Proc, 1:47–56 (1995a)

Wypych, P. W., “Engineering Design in the Pneumatic Pipeline Transport of Bulk Solids,” Mech. Eng. Trans., IEAust, ME20(4):293–298 (1995b)

Wypych, P. W., and Arnold, P. C., “The Use of Powder and Pipe Properties in the Prediction of Dense-Phase Pneumatic Transport Behavior,” Pneumatech 2 , Canterbury, England, Organised by the Powder Advisory Centre, London (1984)

Wypych, P. W., and Arnold, P. C., “Predicting and Improving Flow Performance in Dense-Phase Pneumatic Transportation,” Int. Symp. on the Reliable Flow of Particulate Solids, Organised by the Chr Michelsen Institute, Bergen, Norway (1985a)

Wypych, P. W., and Arnold, P. C., “A Standardised-Test Procedure for Pneumatic Conveying Design,” Bulk Solids Handling, 5(4):755–763 (1986b)

772 Fluidization, Solids Handling, and Processing

Wypych, P. W., and Arnold, P. C., “Pneumatic Transportation and Fluidization Performance of Power Station Fly Ash,” Bulk Solids Handling, 6(1):93–97 (1986a)

Wypych, P. W., and Arnold, P. C., “Feasibility and Efficiency of Dense-Phase Pneumatic Transportation,” Mech. Eng. Trans., IEAust, ME11(1):1–5 (1986b)

Wypych, P. W., and Arnold, P. C., “Minimising Wear & Particle Damage in Pneumatic Conveying Systems,” Powder Handling & Processing, 5(2):129– 134 (1993)

Wypych, P. W., and Hauser, G., “Design Considerations for Low-Velocity Conveying Systems & Pipelines,” Pneumatech 4, Int. Conf. on Pneumatic Conveying Technology, pp. 241–260, Glasgow, Scotland, Powder Advisory Centre, UK (1990)

Wypych, P. W., Kennedy, O. C., and Arnold, P. C., “The Future Potential of Pneumatically Conveying Coal through Pipelines,” Bulk Solids Handling, 10(4):421–427 (1990)

Wypych, P. W., and Pan, R., “Determination of Air-Only Pressure Drop in Pneumatic Conveying Systems,” Powder Handling & Processing, 3(4):303-309 (1991)

Wypych, P. W., and Pan, R., “Pressure Drop due to Solids-Air Flow in Straight Pipes and Bends,” Freight Pipelines, (G. F. Round, ed.), pp. 49-67, Elsevier Science Publishers BV, Amsterdam, Netherlands (1993)

Wypych, P. W., and Reed, A. R., “The Advantages of Stepping Pipelines for the Pneumatic Transport of Bulk Solids,” Powder Handling and Processing, Vol 2(3):217–221 (1990)

Yang, W. -C., “A Criterion for Fast Fluidization,” Pneumotransport 3, Paper E5, Univ. of Bath, England (1976)

Zenz, F. A., “Conveyability of Materials of Mixed Particle Size,” Ind. Eng. Chem. - Fund, 3(1):65–75 (1964)

Zenz, F. A., “Pneumatic Conveying from Grains to Powders,” Pneumatech 2 , Univ. of Kent, Canterbury, England, Organised by the Powder Advisory Centre, London (1984)

774 Fluidization, Solids Handling, and Processing

peripherals and their effects on destroying or enhancing the levels of performance predicted for the basic designs. Since several readily available references (Zenz, 1975; Zenz, 1989, Ch. 7), replete with worked examples, detail the basic dimensioning procedure, this chapter will be devoted primarily to emphasizing the precautions, essentials and peripherals within the design steps necessary to achieve a desired performance. Though discussed here in terms of a separation of solid particles from a gas, the relationships apply equally well to the separation of particles from a liquid, liquid droplets from a gas, and gas bubbles from a liquid.

2.0REQUIRED DESIGN DATA

It should be incumbent on any designer, regardless of the procedure adopted, to document all of the following input data in order to substantiate the derivation of any anticipated or verifiable subsequent performance:

(i)The viscosity, density and flow rate of the carrier gas entering the cyclone

(ii)The particle size distribution of every species of feed particles in terms of the diameter of their aerodynamically equivalent spheres

(iii)The apparent densities of the feed particles

(iv)Any non-uniformity in the particle concentration gradient in the inlet stream

(v)The rate of feed of the particles, as for example, lbs/unit volume of gas or as lbs/ unit time

(vi)The required, or desired, particle collection efficiency

(vii)The maximum available or permissible pressure drop

(viii)Any known limits on particle impact velocity, surface characteristics, or bulk flow ability which would lead to any intolerable particle attrition, or equipment erosion

(ix)Any space limitations on overall equipment height or width and the means of removal of the collected solids as for example through a dipleg pipe to a fluidized bed, through a rotary valve or ejector to a bin or conveying line, or intermittently to a sealed container