july06solids.pdf

7/22/2019 july06solids.pdf

1/7

P

rocesses incorporating bulksolids handling are ubiqui-tous in the chemical processindustries (CPI), including

the chemical, petrochemi-cal, polymer, biochemical, agriculturalchemicals, paints/pigments, energyand power, pulp and paper, and phar-maceutical industries, to name a few.

Studies conducted during the pasttwo decades have shown that: More than 50% of products are ei-

ther sold as solids or have been insolid state during production

More than 90% of solids plants ingeneral experience major perfor-mance problems

Projects processing solids are twiceas likely to fail as compared to theindustry standard.

Common culpritsA number of underlying factors are con-sidered responsible for such widespreadfailure, namely:1. Lack of sufficient and reliable

material characterization in-

formation: Unlike the situationwith liquids, where property datahas been extensively cataloged, the

properties of bulk solids must bedetermined on a case by case basisbecause of the multiple, interactingfactors usually at play. Also, there isa reluctance to expend up-front pow-der testing costs.

2. Lack of formal training or edu-

cation in the field of particletechnology: The physics of bulk sol-ids is not intuitive and is fundamen-tally dissimilar to that for liquids.Knowledge propagated by vendors(suppliers) can be biased.

3. Empiricism in design: Equipmentdesign (basis) is often empirical, andrelies heavily on experience, experi-

mentation and standard construc-tions. This poses problems when thenew set of conditions fall outsidethose of previous experience

4. Validated simulation and cal-culation tools are not commonlyavailable.

5. Scaleup of solids processes is amajor challenge: There is a dearthof research on scaleup.

6. Lack of understanding and ap-

preciation of interactions betweenvarious unit operations in a pro-

cess: The equipment for each of theseunit operations is often times multi-sourced. Lack of communication andcollaboration between various ven-dors is a common problem, and theproblem can be particularly severewhen solids are being processed.

7. Inappropriate equipment design:

The proper choice of process equip-ment and design specifications (for agiven unit operation) are critical.

8. Insufficient accommodation ofprocess upsets: Inability to antici-pate the nature of unsteady stateor transitions during operationwill lead to insufficient process ca-pability.

9. Inadequate attention paid to

equipment specification:This de-tail must be attended to at an earlystage in a project.

10. Lack of ownership of the com-

plete process: Buyer and equipmentvendor sometimes each expect theother party to be responsible for the in-tegrated plant performance problems.

Each of these issued must be ad-

Solids Processing

Solid Tips for Project SuccessMaterial characterization, equipment

specifications and contracting issues are key

Shrikant DhodapkarThe Dow Chemical Company, USA

Lyn BatesAjax Equipment Ltd.

George KlinzingUniversity of Pittsburgh

SINGLE PARTICLE PROPERTIES

FIGURE 1.Relationship between singleand bulk properties

Chemical composition Contact angle or wettability Interparticle friction Moisture Particle density

(true, skeletal, envelope) Particle hardness

Particle shape Particle size and size distribution

Physical properties of material (e.g. elas-tic modulus, melting point, glass transi-tion temperature of polymers, water ofhydration, decomposition temperature,specific heat)

Porosity Singe particle strength

Surface area Surface texture Toxicity

32 CHEMICAL ENGINEERING WWW.CHE.COM JULY 2006

Solids Processing


2/7

dressed to increase the success rateof solids processing projects. Of these

various factors, we focus on materialcharacterization, equipment specifica-tions and contracting in this article. Aprevious installment of this series fo-cused on storage, feeding and convey-ing [5]; and an upcoming one will focuson other factors and misconceptions.

GUIDELINES: TESTINGAND CHARACTERIZATIONBackgroundWith the proliferation of electronicsduring the past 30 years, the measure-

ment of single particle properties hasadvanced so that now, accurate andreproducible values of single particleproperties are easy to measure. Theease and availability of instrumenta-tion to secure these measurements re-sults in a propensity to generate suchdata. These data are rarely usablefor design purposes, however, since apredictive relationship between sin-gle particle data and bulk propertiesis difficult to establish (see Figure1). For commonly measured proper-ties, see Single Particle Properties(p. 32), Bulk Material Properties(this page, top), and Bulk Handling

Characteristics (this page, bottom).Projects that involve handling of

bulk solids frequently experience un-expected problems due to the equip-ment not being able to properly copewith the nature of the bulk materialit has to handle. This is often due tothe properties of the bulk materialfalling outside those expected. Thesesurprises usually arise from a failureto anticipate process conditions and tosecure relevant characterization datafor design purposes.

Equipment suppliers (vendors) can-not control or guarantee the homoge-

neity and consistency of the raw ma-terial. Neither can they determine therange of operating conditions that mayaffect the behavior of a bulk material.It is not reasonable to expect multiple

vendors that are competitively biddingfor a single contract to each bear thecost of independently measuring thesame flow-related values of samplesprovided by the user. Assuming thatrepresentative samples are availablefor the worst condition of the mate-rial that must be accommodated, andthat the user knows what will consti-tute the worst handling condition forthe situation in question, this initial

testing data should be collected by asingle testing vendor for use by all of

the bidding equipment vendors.In this context, there is a clear need

for a standard code of practice that out-lines basic measurements and agree-ment on key design data on which aspecification is based. The followingguidelines are good starting points.

1. Understand the process andbasic mechanismsTo shortlist relevant single-particleand bulk-material properties, the un-derlying physics for each process step

(unit operation) and that of the equip-ment must be taken into account. Letus consider a simple process shownin Figure 2. This process consists of afluid bed dryer, a pneumatic conveyingsystem and silo storage. The analysisis presented in Table 1. Sequential op-erations must consider stress historyand accumulative effects.

2. Establish the testing purposeTypical reasons for testing include thefollowing: Registration of a specific property

for identification, reference or base-line measurement

BULK MATERIAL PROPERTIES

The handling properties of bulk material can not be predicted from single particle properties. The following bulk properties are mostrelevant from a handling and characterization perspective:

Adhesion (to surfaces) Aeration / deaeration characteristics Angle of internal friction of bulk material Angle of repose (poured, drained, spatula) Angle of slide Blocking or caking tendency Bulk density (loose poured, tapped, aerated, compacted, Haus-

ner ratio) Cohesion (material flowability) Compaction (tablettng) Compressibility (relationship between bulk density and stress) Corrosiveness Drying characteristics and kinetics Dustiness Dust explosion characteristics (minimum ignition energy) Electrostatic charging and decay characteristics Floodability / Flushing characteristics

Discharge rate (conical hopper and circular outlet) Fluidization characteristics (Geldart classification, minimum flu-

idization velocity, minimum bubbling velocity, bed expansion,deaeration characteristics)

Friability Grindability (e.g. Hardgrove index, Bond Work Index) Lateral stress ratio (as measured using Odeometer)

Permeability Porosity of packed bed at various levels of compaction Shear strength / flow function (measured using shear testers) Shock sensitiveness Sintering characteristics Surface and volume resistivity Tensile strength Toxicity Wall friction (measured using Jenike tester) Wettability (liquid on particle, powder on particle)

More information on measurement of these properties can be found in Svarovsky [1], Allen [2], McGlinchey [3],Woodcock & Mason [4] and other international standards (e.g. ASTM, ISO, British, German, French, Japanese).

FIGURE 2.A simpleprocess with three unitoperations

BULK HANDLING CHARACTERISTICSThese characteristics depend on equipment and process design in addition to the bulkmaterial properties.

Abrasiveness Attrition / Friability Caking or compaction Dust generation (dustiness) Flowability (Arching and rathole dimen-

sions, mass / funnel-flow boundary,feeder load)

Pneumatic conveying characteristics o Friction factor, saltation velocity (dilute

phase) o Dense phase conveyability, slugging

characteristics, stability Segregation tendency

CHEMICAL ENGINEERING WWW.CHE.COM JULY 2006 33


3/7

Value evaluation for sale of bulkmaterial

Contractual specification for de-fining bulk material properties for

a storage or handling project or thesupply of bulk processing equipmentwith a guaranteed performance

Behavioral evaluation for assess-ment or prediction of some behav-ioral aspect in a bulk-storage, han-dling or process operation

Comparison of some propertieswith a similar or different material,or against a reference source to de-termine if a better or worse scenarioexists

Categorization so that the pro-

spective behavior in a production oruse operation may be assessed rela-tive to known products or predictedwithin acceptable bounds

Equipment manufacture for thedesign of hoppers, chutes, other han-dling equipment and process equip-ment such as pelletizing, tableting,or roll pressing

Identification of phenomena toexamine a tendencies to arch, flush,settle to differing densities, adhereto contact surfaces, and so on

Indication of the effect of prod-uct and process variations toallow sensitivity assessments andset bounds of acceptability for theproduct condition

Quality control to establish stan-dards, monitor production processes,set quality limits, form a data bank,and so on

Product research and develop-

ment to determine bulk handlingcharacteristics during shipment andcustomer handling

Equipment research and devel-opment to refine design conceptsand performance optimization

Fundamental researchon the de-velopment of powder testing devicesand procedures

Specification of a bulk materialfor purchase or sale, multisourcingof raw materials, assessing productswith natural variations, monitoringmultiple production facilities or im-parting longterm standards

Troubleshooting for the exami-nation of production problemsand process variations and failureanalysis

3. Identify the typeof tests required

Qualitative versus quantitativetests: Qualitative tests (see box, p.35) are virtually instantaneous, crude,low-cost tests to give an initial feelabout the nature of a new material,give guidance as to potential hazardsand show whether further testing isrequired. Unless these tests produceunmistakable evidence of simple be-havior, they are no substitute for prop-erly conducted quantitative tests. Forimportant considerations regardingquantitative tests, see the box, p. 36.

Single-particle versus bulk-mate-rial property versus bulk-materialhandling characteristics: Singleparticle tests are often helpful in ex-plaining differences in bulk behaviorof two samples, but the current stateof knowledge is insufficient to predictbulk behavior based on single particleproperties. To design or troubleshoot aprocess or piece of equipment, quanti-tative measurement of bulk materialproperties is essential. Bulk handlingcharacteristics are typically evaluated

as a validation of mechanism or phe-nomena expected from single particleor bulk material properties. Segrega-tion tendency is a classic example.

GUIDELINES: WRITING EQUIP-MENT SPECIFICATIONSEach process equipment specificationrequires its own level of detail. The

vendor should be allowed to proposeits designs within the constraints ofprocess and performance require-ments. Since there can be multiple

vendors involved in a given project,it is the responsibility of the process/project engineer to be aware of the ef-

fect of deviation in performance of onepiece of equipment on performance of

others. See Figure 3 for illustration ofthe appropriate roles in this context.

Consider including the followingline items in equipment specification:1. Description Equipment type

and duty. Do not specify a manu-facturer or model number if a com-petitive bid is being sought.

2. Location: Provide geographic lo-cation of installation and relevantinformation (temperature extremes,seismic zone, altitude, atmosphericdust, noise limitations).

3. Upstream and downstreamequipment, interfacing, tiepoints. Clarify space constraints re-lated to installation.

4. Material properties. Be sure toaddress the following:

Include all relevant bulk properties(see previous section)

Include nominal values and (min-max) ranges where applicable

Identify method of measurement ifcritical

Verify the units (use SI units for or-

ders outside the U.S.) Avoid abbreviations or acronyms5. Operating conditions: Define

minimum and maximum valuesof all major operational variables flowrates, temperature, pressureand so on. Identify conditions asso-ciated with various failure modes,such as loss of utilities and emer-gency process shutdown.

6. Design conditions: Design condi-tions may include additional safetyfactors over and above the operatingconditions.

7. Electrical area classification:

Class (I, II and III), division (I, II and

Solids Processing

TABLE 1.PROCESS ANALYSIS FOR IDENTIFYING APPROPRIATE PARTICLEAND BULK CHARACTERIZATION

Unitoperation

Underlyingphysics

Relevantsingle particleproperties

Relevantbulk materialproperties

Relevantbulk materialcharacteristic

Fluid beddrying

Fluidization,drying, mixing

Moisture,particle size,size distribu-tion, shape,density

Fluidizationcharacteristics,drying kinetics

Segregation,attrition

Pneumaticconvey-ing (DilutePhase)

Entrainmentin air, particle-wall impacts,particle-particleinteraction

Particle size,size distribu-tion, shape,density

Friability Conveyingcharacteristics,attrition,abrasiveness

Storage insilo

Shear flow,consolidation,cohesion,adhesion

Particle size,size distribu-tion, moisture

Shear strength, wallfriction, cohesion,compaction, bulkdensity, compress-ibility, floodability,lateral stress ratio

Flowability(archingdimension),segregation



4/7

III) and group (A G). Make sure thatappropriate references to NationalElectric Code (NEC) and NFPA (Na-tional Fire Protection Association)guidelines are made. For enclosures,

NEMA (National Electrical Manu-facturers Association) or equivalentguidelines must be followed.

8. Utilities: Identify the availableutilities in the process area alongwith limits of consumption.

9. Functional design: Include a shortparagraph on operation of the equip-ment and the duty it is supposed toperform.

10. Material of construction: Allsurfaces in contact with product,non-contact surfaces, mechanicaldetails, gasket materials

11. Construction details: Weldingstandard, support methods, critical

dimensions, surface finish, flanges(rating, orientation, location andcode), inspection ports, guards andergonomic guidelines. Make surethat relevant government and in-

dustry codes are stipulated.12. Cleanability and cross-con-

tamination: Provide information onaccess, wash-down, lockout, ease ofassembly and disassembly

13. Dust containment and sealing:Define the level of dust containmentrequired.

14. Dust explosion: Provide data ondust and vapor explosion character-istics, if applicable.

15. Noise level and abatement: De-fine the method or standard usedalong with type of noise (constant,intermittent, impulse and variable).

16. Insulation and heat tracing:

Provide specification for insulationand guidance on type of heat tracing(electric versus steam).

17. Controls: Specify preferred makeof PLC (if applicable), interface pro-

tocol, critical parameters for storage,exchange and alarms.

18. Accessories: List the positionswitches, speed indicators, ladders,handrails, platforms and grounding.

19. Power transmission: List themotor, bearings and transmission,coupler and driver type (belt, chain,gear), shaft rating, sealing method,type of seals.

20. Tests and inspections: Defineexact nature of testing and stan-dards associated at each stage

21. Performance expectation: De-fine metrics and method of evalua-tion.


TYPICAL QUALITATIVE TESTS

Some simple qualitative tests for characterization are listed hereand summarized in Table 2.Snowball test: Pickup a handful of the product and squeeze

firmly. If the resultant ball hangs together in a firm shape whenthe material is released, the material will not flow easily when sub-jected to pressure and further examination is necessary. Shouldthe material feel light and fluffy during the test and squeeze outbetween the fingers, repeat the test very slowly with material thathas been allowed to settle for some time. Similar results will indi-

cate a tendency to flush. Firm compaction shows a tendency toconsolidate over time to a poor flow condition.

Flaky, fibrous and elastic materials, such as plastic flakes, saw-dust, maize meal and ground cork will freely separate, even afterfirm compaction, but strongly resist shear in a confined, compactedcondition due to the mechanical interference of the particles. Thiseffect can be detected in a Snowball test by the feeling generatedthat the bulk product locks-together when gripped firmly. Suchmaterials can arch over large outlets in storage hoppers. Furthertesting or experienced design attention is required to avoid or deal

with overpressures acting on such products.Wall adhesion for damp of cohesive materials:Form a snow-ball of the material as above and press against a face of a mate-rial that will be used as a contact surface. If some material sticks,

be wary of wall adhesion and progressive build up of product oncorners and surfaces exposed to high contact pressure.Cliff test for fine, uniform materials:Pour the material gentlythrough a funnel onto a horizontal surface, noting the repose con-dition. Cut down the center of the pile with a dividing knife andmove one section sideways. If the remaining pile holds a cliffface at the division, poor flow conditions can be expected. If theface instead slumps to a repose angle similar to that of the originalsurface, it should present no serious flow difficulties.

Agitated bottle: Vigorously shake a sealed glass jar that is ap-proximately 75% full of the sample material. Observe if the mate-rial remains fluid after holding still a few seconds and how quicklythe surface falls to a stable level. If it settles very quickly and thesurface consistently forms a similar repose angle each time the

surface is tilted slowly back and forth, the material is non-cohesiveand should flow well in light compact conditions. If the materialtakes some time to settle and inverting the container quickly showsthe material to hold like a piston in the jar or if cracks appear inthe bulk, then expect poor flow conditions after a long period ofstanding. If the material remains soupy for long period, considerthe prospects of the material to be flushing or flooding.

Flung bottle:Agitate and settle material in a jar as above. Swingthe jar vigorously a few times to cause the contents to be acceler-ated against the bottom of the container by centrifugal action. In-

vert the jar to see if the material holds together or collapses freely.The former indicates that poor flow is likely.Poured repose: The prime value of such a test is to determine the

form of the surface profile that will be built up during the filling ofa hopper. The inclination of the surface shows the allowance thatmust be made for ullage, which represents the unfilled region ofa hopper around a material inlet point. It does not indicate howthe surface will drain as the hopper empties because the pouringcondition is essentially loose while the emptying condition is invari-ably settled and compacted by overpressures on the regions belowthe surface of the original hopper contents.

This test can be used to measure the efficiency of flow-aid addi-tives or lubricants. The material is fed through a coarse screen todrop onto the flat end of a 50-mm-dia. bar until a cone is formed.The angle of the surface to the horizontal is taken as a measureof the shear characteristics of the dilated material, hence its flow

when not strongly compacted.

Tapped density test: Observe the change in level of materialpoured in a jar after repetitively tapping for a couple of minutes.Materials that significantly alter in density at these stages are likelyto be variable in condition from behaving as a fluid when dilatedto exhibiting poor flow properties when settled under consolidatingconditions. Note that the test must be performed at the temperatureat which the material will be processed in service.

TABLE 2. TYPICAL QUALITATIVE TESTS

Tests Indication

Snowball test. Shear strength

Wall stiction Wall adhesion

Cliff formation Cohesion

Agitated bottle A tendency to flush

Flung bottle A tendency to compact

Poured repose Dilate shear strength

Tapped test Compactability

Hausner ratio Compressibility


5/7

22. Comments and feedback: Pro-vide area for vendor comments,notes and feedback.

GUIDELINES:

WRITING CONTRACTSThe contractual terms on which pur-chase orders are based have a strictlegal interpretation, so that whenproblems arise during installation orstartup, there is invariably more inter-est in examining the fine print thanthere is in addressing the problem. Atthat stage, it is too late to address theunderlying deficiencies of the contract.

Buyers, particularly those with priorexperience of such situations, are keento avoid exposure to excess costs. Theytend to tighten the contractual termsto place all performance responsibilityonto the equipment supplier (vendor).

It does not make sense to impose li-abilities far in excess of the contract

value. Such measures are usually un-realistic and often unenforceable. Onthe other hand, equipment suppliers

generally seek to limit their liabilitiesand will grasp at any variations in thebulk material condition as rationalefor not achieving target performance.

The debate is regularly exacerbatedby the lack of information contained inthe request for proposal (or quote) doc-uments, especially about the relevantflow properties. It is quite commonto see design packages that containnumerous details about the paintingspecification, inspection, welding pro-cedure and packing instruction, yet de-scribe the bulk material to be handledin one or two lines that may only in-clude a value of density and describes

the material as free flowing, or poorflowing, without describing the condi-tions of material preparation to whichthese terms apply. This is a commonmistake that must be avoided.

The following guidelines provide agood starting point for writing a fairand effective contract.1. Do not let the contract pricedominate the buying decision.Thecost of inadequate performance andteething troubles can far outweigh su-perficial initial cost savings. Prepare aCost/Liability Assessment for produc-tion delays, rectification provision andperformance shortfall.2. Do not depend on penaltyclauses or litigation for insulation

against problems. Work closely withthe vendor to get the design right inthe first place.


QUANTITATIVE TEST CONSIDERATIONS

Quantitative tests can be performed on single particles or thebulk materials. Various standards (British Standard, ASME,ISO, DIN etc.) have been developed. However, these stan-

dards are not all-inclusive. So, many measurements remain equip-ment specific.

Selection criteria Understand the purpose of the test (see main text). The data re-

quired for design must be more complete than those of qualitycontrol testing during operation Understand and emulate the underlying mechanism in a process

/ unit operation Consider the requirement for frequency of testing with complex-

ity of test Evaluate product stability, sample size requirements and hazards

associated with handling Check if a single test is sufficient or if multiple tests are required Evaluate the need for adherence to international test standards

(ISO, ASTM, German, British etc.)

SamplingHighly accurate test data on incorrect samples will result in irrel-

evant information. Ask yourself the following questions (for moredetails, refer to Allen [2]): Is the material condition during testing representative of the ma-

terial in the process? What is the scale of significance for the sample, and will specific

locations, sources, times or process variations produce differentvalues? Is the sample uniform, consistent and stable? Take mul-tiple samples (location and time) to understand variability

What is the probable (and realistic) worst-case process condi-tion?

What is the history of the sample? Document the chain of custody.Have a robust and traceable procedure for the receipt, authoriza-tion, identification, recording, storage and disposal of samples

Has the sampling procedure been defined? What is the optimal design of the sampler? What is the variability associated with sampling, and how does

that compare with variability due to analytical technique? What is the required sample size for analysis? What is the sample size obtained from the process? How will the sample size be reduced for analysis? What are the critical parameters for product quality? Sample

accordingly

Understand the safety, toxicity, hazards, disposalrequirementsMake sure that you read and understand the material safety datasheet (MSDS) before handling any new chemical. The vendor mustdiscuss specific toxicology data with the manufacturer where thereare concerns. Sample traceability and custody of possession arecritical.

Conducting tests Select the right instrument or test method (for example, particlesize analysis). Match particle size to equipment size (e.g. sheartester)

Understand the underlying mechanisms and data output of anautomated instrument: what is being measured and what ma-nipulations are being made to the data

Understand limitations of the test (accuracy, precision, repeat-ability, bias and operator dependence)

Understand and record all relevant parameters that affect the testresults (e.g. moisture, temperature, sample history)

Calibrate (and document) the measurement instrument on a pe-riodic basis

Run reference samples when possible for reality checks

Test for typical and worst-case situationsConsider equipment-specific testsSome complex process conditions cannot be replicated outside ina single test. Attrition and abrasion are classic examples. Exam-ine sensitivity of equipment performance to variability in productproperties.DocumentationHave full control over, and record, the measured values of the testconditions (e.g. relative humidity, temperature, date and time oftesting and the presence of witnesses). Use a standard data sheetthat has a prepared form to record the above details with an iden-tifying reference, as well as the test measurements.

Be prepared to invent a testNot all tests that need to be invented have been invented. Eachnew product and process poses new challenges. Do not try to fit anexisting but inappropriate test to the problem at hand. Make surethat the test replicates the basic physics underlying the unit opera-tion.


6/7

No contractor can economically meetrealistic consequential damages foralmost unlimited liability on a fullproduction facility.

The root causes of operating prob-lems are almost invariably due tobehavior characteristics of the bulkmaterial as a result of product con-ditions not accommodated becauseof inadequate up-front investiga-tion.

Disputes consume enormousamounts of unproductive and un-

recoverable time. A supplier thatstands by its equipment is invalu-able should difficulties arise. Valuethat attribute.

3. Identify and specify the mainfeatures relating to the bulk sol-

ids that are of interest. Some fac-tors are peculiar to, and known onlyto the user for example, the signifi-cance of particle attrition and segre-gation to product quality, purity, ap-pearance, solubility, and perhaps thedensity condition for packing. Draw

these features into the specificationwith an indication of their realisticimportance.4. Base the specification on mea-sured relevant values on the bulk

material that are verified, agreedand bounded by realistic limits.

These include, for example, wall fric-tion with specific material of contact,bulk density in defined conditions,shear strength in given conditions ofcompaction, range of ambient condi-tions, and maximum residence periodsto be accommodated. The definitionof the operating window along withextreme bounds of operating condi-

tions and material properties shouldbe clearly spelled out. The test meth-ods to be used for product evaluationand eventual performance evaluationmust be identified.5. Outline the tests required for

characterization of material (be-yond what was provided for bid-

ding purposes), and how theseproperties will be measured. Berealistic about the costs associatedwith conducting tests. It is commonlyassumed that it is the vendors respon-

sibility to acquire necessary data. Butkeep in mind that the vendor operateson the necessary data principle. Cut-ting corners on material characteriza-tion can result in significant problemsduring operation and headaches dur-ing litigation. Be sure to documentsampling techniques and the defini-tion of representative sample (includ-ing handling instructions).6. Secure prior agreement aboutthe options available and steps

to be taken, should the material

condition fall outside the agreedspecification. Sometimes supply,process or production changes intro-duce significant variations not in-cluded within the original design. Insome cases a representative sample,as with some pharmaceutical develop-ments, is not available at the initialcontract stage. The name of the bulkmaterial is never enough to be thebasis of a contract;neither is particlesize distribution adequate to assessmaterial behavior. A description simi-lar to material x, can only be used asa rough guide, not a contract condi-tion. Cooperation, not an arms length

FIGURE 3.Users and vendors have individual and overlapping responsibilitieswhen it comes to successfully implementing a solids handling project. Outside ofthese responsibilities, there are optional factors that can improve the success rate ifthey are adopted in the design and procurement process

Circle 25 on p. 43 or go toadlinks.che.com/6514-25


7/7

relationship, is essential between par-ties to secure best results.7. Investigate the track record of

the supplier. Specifics to consider

include technical and financial re-sources, test facilities, design experi-ence and customer list, degree of spe-cialization in the form of equipment tobe supplied.8. Ensure that emphasis is appro-priately directed.Year 2000 compli-ance and ISO 9000 documentation arenot relevant to whether flow takesplace in a hopper.9. Establish a realistic timeframe

for both the tender (bidding) stageand the contract itself. Allow due

diligence on pre-contract investiga-tions, with formal drawing approvalas needed. Make crystal clear whatauthority and responsibility is givenby approval. If they are given for in-formation only, then do not delay or

jeopardize progress by wide circula-tion for comment.10. Agree on process for futurechanges or modifications to the

design upfront in the contract. Theprocedure for incorporating changesshould take into account the fact that

design variations incur inevitabledelays for consideration, even if thechanges are not finally implemented.The cost implications of changesshould not be underestimated.11. Expectations on performance

validation and financial termsshould be spelled out upfront.

12. Establish the degree of freedomavailable to the vendor to optimizetotal cost of the project and share thereduction in cost with the purchaser.

SummaryTo improve the success rate of bulk-sol-ids handling projects, greater aware-ness regarding the unique nature of

bulk solids is required among processand project engineers. The guidelinespresented in this paper should serveto highlight those and their relevanceto project success.

Edited by Rebekkah Marshall

AuthorsShrikant V. Dhodapkar is aresearch leader in the SolidsProcessing Lab at The DowChemical Co. (B-1402, DowChemical, Freeport, TX 77541;Phone: 979-238-7940; Fax: 979-238-0969 E-mail: sdhodapkar

@dow.com). He received hisB.Tech. in Chemical Engineer-ing from I.I.T-Delhi (India)and his M.S.Ch.E. and Ph.D.from the University of Pitts-

burgh. During the past 18 years, he has publishednumerous papers in particle technology and con-tributed chapters to several handbooks. He hasextensive industrial experience in pneumatic con-

veying, silo design, gas-solid separation, mixing,coating and the design of solids processing plants.He is a member of AIChE and Vice-Chair of theParticle Technology Forum.

Lyn Bates is managing di-rector of Ajax EquipmentLtd. (Mule St., Bolton, BL22AR, U.K.; Phone: +44 1204386723, Email: lyn@ajax.

co.uk), a specialized, bulk-sol-ids-handling company. Bateshas also served on numer-ous U.K., U.S. and Europeantechnical committees, andworked alongside many ofthe pioneers in the technolo-

gies related to bulk-solids handling. Bates haspresented papers at numerous conferences andseminars, and has published articles in manytrade journals. He is the author of User Guideto Segregation (The British Materials HandlingBoard, 1997) and User Guide to the Design, Se-lection and Application of Screw Feeders (Pro-fessional Engineering Publishing Ltd., 2000),and contribued a chapter to Characterisationof Bulk Solids, edited by D. McGlinchey (Black-well, 2005). He is a member of the Institutionof Mechanical Engineers, and is a recipient ofthe I.Mech.E.s Solids Handling Award for Pro-fessional Excellence in the Technology, and the

Australian Institute of Engineers Bulk SolidsHandling Award.

George E. Klinzing is pro-fessor of chemical engineeringand vice-provost for researchat the University of Pitts-burgh (826 CL University ofPittsburgh, Pittsburgh, PA15260; Phone: 412-624-0784;Email: [email protected]). He earned his B.S. degreein chemical engineering fromthe University of Pittsburgh,

and holds a Ph.D. in chemical engineering fromCarnegie Mellon University. He has been active inthe pneumatic conveying research community, andhas published numerous papers, books and bookchapters on the subject. Presently Klinzing is ex-

ploring pressure signatures for flow analysis. Heis a Fellow of the American Institute of ChemicalEngineers, and a member of the AIChEs ParticleTechnology Forum, and serves as an accreditationreviewer for ABET.

References1. Svarovsky, L., Powder Testing Guide Meth-

ods of Measuring the Physical Properties ofBulk Powders, Elsevier Applied Science, 1987.

2. Allen, T., Powder Sampling and Particle SizeDetermination, Elsevier, 2003.

3. McGlinchey, D., editor, Characterisation ofBulk Solids, Blackwell Publishing CRCPress, 2005.

4. Woodcock, C.R. and Mason, J.S., Bulk SolidsHandling An Introduction to the Practiceand Technology, Chapman & Hall, 1987.

5. Dhodapkar, S., et. al., Guidelines for SolidsStorage, Feeding and Conveying, Chem.Eng., pp. 2633, January 2006.

AcknowledgementsThe authors would like to acknowledge WuChen, James Koch and Manjunath Konanur, ofDow Chemical, and Timothy Bell, of DuPont, fortheir suggestions. Circle 27 on p. 43 or go to

adlinks.che.com/6514-27


Solids Processing

july06solids.pdf

Documents

Transcript of july06solids.pdf