Advanced Powder Technology 22 (2011) 236–244

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Advanced Powder Technology

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Original Research Paper

Evaluation of primary and secondary fugitive dust suppression methods usingenclosed water spraying systems at bulk solids handling

J. Faschingleitner ⇑, W. HöflingerVienna University of Technology, Institute of Chemical Engineering, Getreidemarkt 9, A-1060 Vienna, Austria

a r t i c l e i n f o a b s t r a c t

Article history:Received 30 July 2010Received in revised form 30 November 2010Accepted 22 December 2010Available online 6 January 2011

Keywords:Fugitive dustBulk solidsDust suppressionWater sprayPrimary and secondary separation action

0921-8831/$ - see front matter � 2010 The Society ofdoi:10.1016/j.apt.2010.12.013

⇑ Corresponding author. Tel.: +43 1 58801 15910; fE-mail addresses: joerg.faschingleitner@tuwien

whoeflin@mail.zserv.tuwien.ac.at (W. Höflinger).

To suppress effectively fugitive dust emissions using water spraying systems at bulk solids handling anoptimal design of these devices is necessary. The dust suppression mechanism for example at conveyorbelt hand over points can be subdivided in a primary and a secondary dust minimization effect. In thiscase the moistening of the bulk solids is a primary dust minimization effect and the airborne dust captureis a secondary dust minimization effect. In this work the evaluation of both dust minimization effects iscarried out. As a first step an experimental investigation of the total and the secondary dust suppressionefficiency took place. A model of two separators which are acting in series got used to compare the mea-sured efficiencies and to calculate the primary dust suppression efficiency. The secondary dust suppres-sion effect showed low performance compared to the primary dust suppression efficiency. So it has to beclarified if the streaming situation and the dust concentration situation at the position where the nozzleoperates can get improved. Therefore enquiries at different positions in the middle and aside a concen-trated particle flow got carried out.

The results provide an informative basis how water spraying systems can get improved to suppressfugitive dust emissions at bulk solids handling.� 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder

Technology Japan. All rights reserved.

1. Introduction

1.1. Fugitive dust emission

Fugitive dust emissions are air dispersed particles which arearising from dust sources which are not as composed as conductedsources. Diffuse dust sources have often the following characteris-tics: considerable spatial extension, inhomogeneous source struc-ture, emission-relevant sectors that cannot be located ordescribed easily, low height of source, emission mass flow that var-ies with time and high ambient air concentrations in the vicinity ofthe source. Diffuse dust sources can be assigned by geometry likepoint source, line source, area source or volume source [1]. Dustsources which create fugitive dust are created for example byexposure of open faces (construction, mining or agricultural sites),roads or parking areas, stock piles or bulk solid processing to windor mechanical stress [2].

A remarkable high fraction of total emitted dust can already beassigned to fugitive dust emissions [3]. One reason for that is that

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ax: +43 1 58801 15999..ac.at (J. Faschingleitner),

emissions of non conducted sources are much harder to detect andcontrol.

1.2. Problems at primary dust suppression

The reduction of dust from diffuse dust sources is carried out byprimary actions which prevent dust generation or secondary ac-tions which suppress the generated dust. Examples for primary ac-tions are bulk solids moistening or granulation of powderymaterials or procedural provisions for example at hand over pointsat conveyor belts to reduce the drop height or using bulk solidslides or choosing operating conditions so that an optimal denseparticle flow of the dropping bulk solid is generated [4]. Thesemeasures regarding the procedural dust generation process showoften high dust suppression efficiencies. But they are often onlypartial solutions and represent no universal applicable dust sup-pression technique as the compositions of diffuse dust sourcesare alternating [5].

1.3. Problems at secondary dust suppression

The dust reduction despite primary action takes place by sec-ondary action. Examples are to enclose the diffuse source and suckoff the dust laden air and separate the dust by filtration [6,7] or to

ed by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

J. Faschingleitner, W. Höflinger / Advanced Powder Technology 22 (2011) 236–244 237

separate the dust by scrubbing [8]. These methods are effective butthe necessary ventilation has the drawback of possible dust explo-sions. At the filtration the filter cleaning is an issue and at scrub-bing the problem is waste water treatment and high waterconsumption.

1.4. Problems at combined primary and secondary dust suppressionaction

A primary as well as secondary action which is competitive anduniversal applicable to minimize dust, is the operation of spraynozzles. The spray nozzles are operated for fugitive dust suppres-sion at bulk solids handling, bulk solids crushing as well as at min-ing and storing of bulk solids. As an example the dust suppressionefficiency of snow cannons got reviewed [9]. The requirement toapply spray nozzles in general is that the bulk solid is watertolerable.

The dust suppression of fugitive dust using water sprays at bulksolids handling got improved for example by use of surfactants[10–13]. The problem is that the surfactant often has to be alignedwith material type which leads to problems at changing bulk solidscomposition [14,15]. To improve airborne dust capture the dropletsize of sprays got minimized by use of high pressure nozzles, atom-izing or fogging sprays, ultra sonic resonance nozzles, two phasenozzles or using vapor. It also was tried to improve airborne dustcapture by electrical charging of sprays [16,17]. The drawback atthis method is that the higher dust suppression efficiency perwater consumption is overcompensated by droplet evaporationwhich leads to redispersing of already captured dust and watersolved minerals [18]. Nevertheless the dust suppression action atbulk solids handling using water sprays is competitive and univer-sal applicable. Therefore the application of water sprays to sup-press fugitive dust should be studied and improved.

1.5. Problems at fugitive dust suppression action using water sprays

The dust minimizing effect at water spraying systems at bulksolids handling can be subdivided in a primary and secondary dustminimization effect. The evaluation and comparison of primaryand secondary dust minimization effects would be necessary to

Fig. 1. Primary and secondary dust reducing effects at suppression of fu

optimize the design of water spraying dust minimization devicesand to increase their efficiency. The general problems at the sec-ondary dust minimization effect using spray nozzles are the airentrainment which causes dilution, redispersion and shifting ofdust clouds [19] and secondly that at non conducted diffusive dustsources the propagation of dust emissions is likely to be irregular[20]. Therefore the dust laden airstream often doesn’t hit the sprayso that the droplets can’t perform airborne dust capture.

1.6. Approach to examine the problems

To compare the primary and secondary dust suppression effi-ciency at fugitive dust suppression using water sprays a hand overpoint at a conveyor belt was chosen as test subject. A hand overpoint at a conveyor belt was chosen to examine water spray dustsuppression because primary and secondary dust suppression ef-fects are present, specifiable and easily accessible see Fig. 1. Thedust suppression of diffuse dust emission was measured in anencasing where irregular propagation of fugitive dust takes place.The large scale encasing is compared to the nozzle spray so capa-cious that fugitive dust suppression can get examined at applicableconditions for open space (as the dust isn’t forced through thespray). Therefore are the results assignable to airborne dust cap-ture at open space. At the same time in this encasing dilution orshifting of dust clouds away from the detector can get avoided.Therefore the secondary fugitive dust suppression efficiency canget measured accurately. The dust suppression using water spraysat bulk solids handling can be seen as two separators which areacting in series. So the separation efficiency of a water sprayingsystem can be calculated as the total suppression efficiency gtot

of the efficiencies of two separators (g1 and g2), which are con-nected in series [21].

gtot ¼ g1 þ g2 � g1 � g2 ð1Þ

g1 is the primary dust suppression efficiency (�), g2 is the second-ary dust suppression efficiency (�), gtot is the total dust suppressionefficiency (�). The total dust suppression efficiency and the second-ary dust suppression efficiency of a hand over point at a conveyorbelt can get measured in different designed test rigs, respectively.Using Eq. (1) the primary dust suppression efficiency can than get

gitive dust using spray nozzles at conveyor belt hand over points.

238 J. Faschingleitner, W. Höflinger / Advanced Powder Technology 22 (2011) 236–244

calculated. Therefore all elements of fugitive dust suppression of ahand over point of a conveyor belt which was chosen as a represen-tative role model are accessible.

The general problem of secondary dust minimization effectusing spray nozzles is that the dust laden airstream has to hitthe spray so that the droplets can perform airborne dust capture.At non conducted diffusive dust sources the propagation of dustemissions is likely to be irregular. To examine the general prob-lem at secondary dust suppression efficiency a lab scale test righas to be built in a manner that such an irregular propagationof fugitive dust emissions can be simulated. In this context ithas to be clarified if the secondary dust suppression efficiencycould be increased by increasing the possibility to catch diffusespreading dust emissions by the use of numerous nozzles nextto each other in a broad range at the same total water flux as asingle nozzle.

2. Methods

2.1. Total dust suppression efficiency

In a test series the total dust suppression at bulk solid handlingwas determined on a laboratory test rig to investigate the dust aris-ing from falling bulk solids, where a spraying nozzle performs dustsuppression. By doing so, two effects are acting in series. First of allthe bulk solid gets moistened during falling which prevents dustgeneration and secondly the still generated dust gets segregatedby water droplet capturing. The scheme of the apparatus is shownin Fig. 2.

As a nozzle a two phase water/air resonance nozzle, type 1005VSR Industrietechnik GmbH [22] with water flows adjustable be-tween 0.36 and 60 L/h, pressurised air: of 1–5 bar and with a med-ian droplet size of about x50,3 = 52 lm got used.

The falling bulk material was dried construction rubble andsteel slag.

The reduction of the particle concentration was measured by acascade impactor for the two different bulk solids and at 9 differentwater volume flows and 3 different air pressures of the nozzle. Themeasurement of air humidity and temperature at the air inlet andair outlet was necessary to calculate the evaporating water volumeflow at each experiment.

Fig. 2. Scheme of the test rig to investigate t

2.2. Secondary dust suppression efficiency

In a series of experiments the fractional separation efficiencydue to water spraying for a dust, dispersed into the inlet air flowshould be measured. Therefore a lab scale test equipment (Fig. 3)was built in a manner that a concentrated particle flow matchableto bulk solid drop experiments hits the nozzle at similar position asat examinations to detect total dust suppression efficiency. Thenozzle is situated just above the outlet of the dust laden air stream(Fig. 4).

The dust material was a test dust, usually used for filter tests[23] (Pural NF, aluminium oxide) and was dispersed by a LTGNDF 100 dust generator [24]. The mass median particle size wasabout 4 microns. The dust material characteristics are matchableto steel slag and construction rubble which were used at experi-ments to detect total dust suppression efficiency [25]. The dustconcentration created by the dust generator in the concentratedparticle flow was comparable to bulk solid drop experiments(�1 g/m3).

The particle size distribution of dust dispersed into the airstream was measured at the encasing outlet using a Palas PCS2000 scattered light sensor.

The reduction of particle concentration was determined at 3 dif-ferent water volume flows.

2.3. Influence of the streaming situation and dust concentration onsecondary dust suppression efficiency

At non conducted diffusive dust sources the propagation of dustemissions is likely to be irregular. Therefore a lab scale test rig (de-scribed in chapter 2.2.) was built in a manner that such an irregularpropagation of fugitive dust emissions can be simulated. It shouldget clarified if the streaming situation and the dust concentrationsituation at the position where the nozzle operates have an impacton the secondary dust suppression efficiency.

To clarify the dependence of the secondary dust suppressionefficiency on the nozzle position, the nozzle was positioned inthe middle between the inlet and the outlet air stream openingand varied in several distances to the side (Fig. 5).

The secondary dust suppression efficiency of particles smallerthan 10 lm g2(10) was measured at 10 L/h total water volume flow

he dust arising from falling bulk solids.

Fig. 4. Position of the nozzle in the test encasing for investigation of secondary dust suppression effect (precipitation of dust by water droplets).

Fig. 5. Positions of nozzle set up in the encasing.

Fig. 6. Nozzle set up of 2 nozzles with different distances between each othershown as example for the central position (position 1).

Fig. 3. Scheme of the laboratory test equipment for determining the minimization efficiency by water droplets alone.

J. Faschingleitner, W. Höflinger / Advanced Powder Technology 22 (2011) 236–244 239

with one nozzle spraying from the top of the encasing down to thebottom at central position (position 1) and at 0.1; 0.2; 0.3 (position2,3,4) and at 0,4 m (position 5) distance from the center stream lineof the encasing.

The dust suppression tests at a lab-scale test equipment withdifferent nozzle positions shown in Fig. 6 were carried out. Thedust separation of one nozzle (water flow 10 L/h) and two nozzles,each one with a water flow of 5 L/h were compared at different dis-tances between the two nozzles as well as at different positions ofthe set of two nozzles. Therefore the middle point between thesetwo nozzles was in the same way varied to the side as for the singlenozzle tests.

The distances between two nozzles were varied from 0.02; 0.1;0.2; 0.4 and 0.8 m.

3. Results

3.1. Total dust suppression efficiency

At fugitive dust suppression like at bulk solids handling, theoperating conditions (temperature, air humidity, ventilation rateand supplying water flow) are often different. A part of the supply-ing water volume flow is evaporating. To make dust suppressionefficiencies at different operating conditions comparable the appli-cation of an effective water volume flow, which is actually avail-able to perform dust suppression, has to be worked out.Experiments were carried out at 10 different supplying water vol-

240 J. Faschingleitner, W. Höflinger / Advanced Powder Technology 22 (2011) 236–244

ume flows in the range of 0.36–10.0 L/h. By measuring the airhumidity and temperature at the air inlet and outlet at a certainventilation rate the evaporating water volume flow can get calcu-lated at each experiment. The measured data could be describedusing Eq. (2) where the effective water volume flow (Q0 � Q) canget calculated for different operating conditions (temperature, airhumidity, ventilation rate and supplying water flow). Details arein [25] where a data array of q at different operating conditionsis described.

Q 0 ¼ Q 0maxð1� e�qQ Þ ð2Þ

Q is the supplying water volume flow (L/h), Q0 is the partial watervolume flow which evaporates inside the dust encasing (L/h),Q0max is the maximum evaporating water volume flow for a certainair flow (L/h), q is the kinetic evaporation constant (empirical con-stant obtained by regression) (h/L), (Q0 � Q) is the effective watervolume flow (L/h).

The remaining dust concentration of particles smaller than10 lm for fallen bulk material dependent on the supplying watervolume flow and the water evaporation at different ventilationrates can get modelled by the following equation:

Fig. 7. Reduction of the dust particle concentration for con

Fig. 8. Reduction of the dust particle concentration fo

E ¼ Eres þ ðE0 � EresÞ � ekðQ�Q0Þ ð3Þ

E is the remaining dust concentration [mg/kg bulk solid] whenspraying on the arising dust and a falling bulk material with a watervolume flow of Q, E0 is the dust concentration without water spray-ing [mg/kg bulk solid], Eres is the residual dust concentration, whichremains, even if an infinite high water volume flow is used [mg/kgbulk solid], and k is the kinetic constant, which describes the dustminimization (empirical constant obtained by regression) [h/L].

With these equations the loss of water due to evaporation andits effect on dust minimization can be modelled.

Figs. 7 and 8 show the calculation results. For calculation of themodel curves the process specific constants (k and q) have to bedetermined by regression, details are in [25].

gtot ¼ 1� E=E0 ð4Þ

Using Eq. (4) gtot the total separation efficiency can be deter-mined and referred to an effective water volume flow. The effectivewater volume flow is the water volume flow which is available fordust suppression after evaporation at different operating condi-tions. At operating conditions at experiments (temperature, airhumidity, ventilation rate) and a supplying water flow of 10.0 L/h

struction rubble using different supplying water flows.

r steel slag using different supplying water flows.

J. Faschingleitner, W. Höflinger / Advanced Powder Technology 22 (2011) 236–244 241

an effective water volume flow of 8.8 L/h was determined using Eq.(2). So at these conditions 8.8 L/h are available to cause a total sep-aration efficiency of particles smaller than 10 lm gtot(10) of 63%for steel slag and 75% for construction rubble.

3.2. Secondary dust suppression efficiency

The mass of particles of a certain particle size encountered be-fore water spray dust suppression and after water spray dust sup-pression was determined at 3 different water volume flows asdescribed in Section 2.2. The corresponding fractional separationefficiency T(x) was calculated using following equation. (Eq. (5))

TðxÞ ¼ 1� Dmwith watersprayðxÞ=Dmwithout watersprayðxÞ ð5Þ

T(x) is the fractional separation efficiency (�), Dmwith waterspray(x) isthe mass of particles at certain particle size x encountered afterwater spray dust suppression (g), Dmwithout water spray(x) is the massof particles at a certain particle size x encountered before waterspray dust suppression (g).

Fig. 9. Dust particle size distribution on air o

Fig. 10. Fractional separation efficiency

The secondary separation efficiency of particles smaller than10 lm g2 was calculated see Eq. (6).

g2 ¼ ð1� R Dmwith watersprayðxÞ=R Dmwithout watersprayðxÞÞ � 100 ð6Þ

The particle size distribution of dust dispersed into the airstream was measured at the encasing outlet. The measurement re-sults of the dust particle size distribution without water sprayingand for different effective water volume flows are shown inFig. 9. The effective water volume flows at the operating conditionsduring experiments were calculated using Eq. (2) and the data ar-ray of q at different operating conditions [25].

The corresponding fractional efficiency T(x) is illustrated inFig. 10. The secondary separation efficiency of particles smallerthan 10 lm, show Fig. 11. As a result it can be stated that at air-borne dust capture using water sprays at bulk solids handlingthe fractional separation efficiency T(x) and the secondary separa-tion efficiency of particles smaller than 10 lm g2(10) show ratherlow values for different water volume flows.

utlet for different supplying water flows.

for different supplying water flows.

Fig. 11. PM(x) separation efficiency of secondary dust suppression effect at bulk solids handling.

242 J. Faschingleitner, W. Höflinger / Advanced Powder Technology 22 (2011) 236–244

3.3. Comparison of total, primary and secondary fugitive dustsuppression effects

The measured secondary and total dust separation efficienciescan be compared because they were determined at similar dustconcentrations and nozzle positions. The different operating condi-tions at the test assemblies which influence water evaporationwere taken into account by calculating the effective water flowwhich is actually available for dust suppression. The dust suppres-sion efficiencies are only comparable at the same effective waterflow. The measured secondary dust separation efficiency of parti-cles smaller than 10 lm (Eq. (6)) could get referred to an effectivewater flow of 8.8 L/h calculated at the environmental conditions atexperiments using Eq. (2). The corresponding total dust separationefficiency at 8.8 L/h effective water volume flow could get calcu-lated using Eqs. (2), (3) and (4)which was derived from bulk soliddrop experiments. The comparison using Eq. (1) can roughly showthe difference of the minimization efficiencies between the pri-mary and secondary dust separation mechanisms. Neverthelessare the definitions of PM10 of EPA (Environmental ProtectionAgency) and of the EU-guideline 1999/30/EG are different. But inboth cases the particulate matter is referred to an aerodynamicaldiameter. At experiments of gtot a cascade impactor got used. Itsmeasurement results are referred to an aerodynamical diameter.At experiments of g2 a PCS got used where the measurement re-sults are referred to an optical diameter. Although these experi-ments were executed with different measurement devices anddifferent dust materials (but similar particle densities and compa-rable size distributions for Pural NF, steel slag and constructionrubble), the difference in minimization efficiency found, is an infor-mative basis for optimization strategies.

gtot(10) total dust separation efficiency of particles smaller than10 lm at 8.8 L/h effective water flow (at dust suppression atbulk solids drop experiments) �70%g2(10) secondary dust suppression efficiency of particles smal-ler than 10 lm at 8.8 L/h effective water flow (due to dropletprecipitation) = 16%When using Eq. (1) to calculate g1(10) from gtot(10) and g2(10)it comes out that g1(10) is approximately 64%, this is manifoldthat of g2(10).

That means that the main minimization effect is due to bulk sol-ids moistening.

3.4. Influences of the streaming situation and dust concentration onsecondary dust suppression efficiency

The primary dust suppression efficiency is approximately 4times the secondary dust suppression efficiency. It has to be clari-fied what the reasons are that the secondary dust suppression effi-ciency is so small. The dust laden airstream often doesn’t hit thespray so that the droplets can’t perform airborne dust capture.The possibility to catch diffuse spreading dust emissions could beincreased by use of more nozzles next to each other in a broadrange. In this context it was also clarified if the streaming situationand the dust concentration situation at the position where the noz-zle operates have an impact on the secondary dust suppressionefficiency.

The secondary dust suppression efficiency (of particles smallerthan 10 lm) of nearly 80% (at an effective water flow of 10L/hfor a single nozzle at position 1) decreases down to 35% at position4 as shown in Fig. 12. So a strong dependence of g2(10) on the po-sition of the nozzle in the encasing can be followed. The sameobservation was made for a set of two nozzles with different dis-tances to each other. So it depends on the streaming regime atthe position where the nozzle operates if a single nozzle is betterthan two nozzles with the same total water flow.

At the concentrated particle flow g2 is much higher but besidesthis flow g2 decreases tremendously. That’s how the difference ofg2(10) of a single nozzle to two spray nozzles with the same totalwater flow as the single nozzle was clarified. The possibility tocatch diffuse spreading dust emissions could be increased by useof more nozzles next to each other in a broad range.

4. Discussion

At fugitive dust suppression using water spraying systems themoistening of the bulk solids (primary dust suppression) comparedto the capturing of particles by water droplets (secondary dust sup-pression) has the predominant influence on dust minimization.That’s the reason why in this regard the secondary fugitive dustsuppression should get improved. The problem is that at non con-ducted diffusive dust sources the propagation of dust emissions islikely to be irregular. Therefore a lab scale test rig (described inchapter 2.2.) was built in a manner that such an irregular propaga-tion of fugitive dust emissions can be simulated. By measuring thesecondary dust suppression efficiency in that encasing a very

Fig. 12. PM10-separation efficiency at different nozzle set ups at different positions in the encasing.

J. Faschingleitner, W. Höflinger / Advanced Powder Technology 22 (2011) 236–244 243

strong dependence on streaming situation and position of the noz-zle was discovered. In this context constant large secondary fugi-tive dust suppression efficiencies of water sprays at open placeshave to be seen critically. It should be kept in mind that these effi-ciencies could be only pretended, because the water spray is onlydiluting the dust concentration or shifting the dust cloud asidefrom dust detectors like it is demonstrated in Fig. 13. This effectis avoided in our test rig encasing. So the influence of nozzle posi-tion could be studied. If the water spray don’t get hit by a concen-trated particle flow g2 is very weak. The chances that suchconcentrated particle flows aren’t caught at diffuse spreading dustemissions are very high but the possibility to catch such concen-trated particle flows can be increased by increase the number ofnozzles which was simulated by use of a set of two nozzles com-pared to a single nozzle.

Comparing the dust suppression efficiency of a single nozzle atcentral position with the dust suppression efficiency of a set of twonozzles where one of the two nozzles is situated in central positionfollowing observation could be made. If a concentrated particleflow strikes the single nozzle spray directly the dust suppressionefficiency encountered is higher than striking one nozzle of a setof two nozzles directly. This can be explained by the fact that onlyhalf of the water flow is active in this case. If a single nozzle andsets of two nozzles is compared aside the concentrated particleflow in case of irregular propagation of fugitive dust emissionsthe opposite is the case. By changing nozzle positions at experi-ments over all a set of two nozzles achieves in average higher sec-ondary dust suppression efficiencies. This achievement could only

Fig. 13. Dilution of the dust concentration and shifting the dust cloud aside duringwater spraying.

be made if the distance between the nozzles is small enough toblock particle flows from passing between the sprays. By splittingthe total water flow by number of nozzles each single nozzle hasmuch lower suppression efficiency. Irregular and diluted dustpropagation around non conducted fugitive dust sources is verylikely at open faces. As encountered in experiments in this casethe application of numerous small nozzles next to each other isin average more efficient.

5. Conclusion

In order to design optimal water spraying devices to minimizefugitive dust emissions generated at bulk solids handling the phys-ical mechanisms responsible for their arising and their precipita-tion have to be understood. The dust suppression mechanism atbulk solids handling during water spraying can be divided into amoistening step of bulk solids, which prevents dust generation(primary dust suppression effect) - and secondly into a step bywhich the still generated dust particles will be captured by thewater droplets (secondary dust suppression effect). This primaryand secondary dust suppression effects were compared.

To do so, it was necessary, to make separation efficiencies mea-sured at different operating conditions comparable, which wasshown by an effective water flow which actually performs dustsuppression. As at fugitive dust suppression like at bulk solids han-dling, operating conditions (temperature, air humidity and windspeed) are often different the definition of an effective water flowto which the dust suppression effect has to be referred will beapplicable. The comparison method of primary and secondary dustminimization effects which appear at dust suppression using watersprays at bulk solids handling could get carried out by a formulausually used for two separators which are acting in series. Calcula-tions from the investigated total dust suppression efficiency andthe secondary dust suppression efficiency showed that the primarydust separation effect is the main separation effect. It is approxi-mately 4 times higher than the secondary dust suppression effect.

By tests to detect the secondary dust separation efficiency atdifferent dust concentrations and streaming situations it could beproven that the position of the nozzle plays an important role forthe separation efficiency and can be very low by positioning thenozzle at a wrong place. If the water spray doesn’t get hit by a con-centrated particle flow the secondary dust suppression effect isvery weak. The chances that such concentrated particle flows

244 J. Faschingleitner, W. Höflinger / Advanced Powder Technology 22 (2011) 236–244

aren’t cached at diffuse spreading dust emissions are very high. Toincrease the possibility to catch concentrated particle flows at dif-fuse spreading dust emissions numerous nozzles are necessary tocover a broad range with sprays at minimum water consumption.By experiments it could get proven that it depends on the stream-ing regime at the position where the nozzle operates if a singlenozzle is better than two nozzles with the same total water volumeflow. So the water flow, the number of nozzles as well as the dis-tance between the nozzles have to be matched with the occurringambient dust laden air flow so that a maximal range can be cov-ered with sprays and maximum dust suppression can be realizedat minimum water consumption. The evaluation and comparisonof primary and secondary dust minimization effects as well asthe clarification of the influence of the streaming situation anddust concentration pointed out possibilities how water sprayingdust minimization devices can be optimized to increase theirefficiency.

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