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ANA ELISA ACHILES PERFORMANCE OF A CYCLONE VÁDILA GIOVANA GUERRA IN REMOVAL OF FINE PARTICULATE Department of Chemical MATTER Engineering, Federal University of São Carlos, Brazil Article Highlights • Cyclone spray scrubber is an effective device for the removal of fine particles SCIENTIFIC PAPER • Great performance on fine particulate removal at low L/G flow ratio and pressure drop conditions UDC 621.928.3+641.513:66.074.2 • Inlet air velocity and water injection position influence the collection efficiency • Liquid-to-gas flow ratio strongly affects the performance of cyclone spray scrubber • Smaller droplet sizes increase the collection efficiency of fine solid particles

Abstract Cyclones are not classified as effective devices for removing fine particles, while high efficiency wet usually have high operational costs. In order to achieve better performance, the aim of this study is to evaluate, for the first time, a cyclone scrubber design based on the dimensions of a Stairmand cyclone separator with the inclusion of liquid injection nozzles located in differ- ent positions to improve the separation of fine particles. Given the lack of stu- dies considering the effect of liquid injection and other operational conditions in the removal performance of a cyclone scrubber with Stairmand dimensions, the present paper provides a complete evaluation of these effects for the separation of sugar cane bagasse ash from air. The parameters investigated were inlet gas velocity, liquid injection position, liquid-to-gas flow ratio and droplet size distribution. The cyclone scrubber performance was evaluated considering collection efficiency and pressure drop. Overall efficiency of almost 99% and low-pressure drop was achieved by employing a liquid-to-gas flow ratio of 0.43 L/m³ for the collection of ash from the combustion of sugar cane bagasse. Grade efficiencies revealed that injecting droplets into cyclones sig- nificantly improved the removal of fine particles with an aerodynamic diameter less than 2.5 µm. Keywords: cyclone scrubber, collection efficiency, fine particle separ- ation, liquid injection.

Cyclones and wet scrubbers are applied in removal of this particulate matter from gas streams many industrial processes to separate the particles can lead to negative consequences, including chronic laden in gas stream. An example of a process that respiratory problems in humans [1]. Consequently, uses such equipment is the production of sugar and the removal of particulate matter from these industrial ethanol. The bagasse is generated in the production exhaust streams is essential in order to avoid air process and this waste is used for cogeneration of [2,3]. electricity by burning it in boilers and at the end, it Dry cyclones are frequently employed in indus- produces sugar cane bagasse ash. The inadequate trial applications, due to their low operating costs, simple construction and maintenance, compactness, Correspondence: V.G. Guerra, Federal University of São Carlos. and suitability for use under harsh conditions [4]. Via Washington Luiz, km 235, 13565-905, São Carlos, SP, Brazil. However, dry cyclones are inefficient in collecting E-mail: [email protected] Paper received: 20 December, 2018 very fine particles smaller than 5 μm [5], so they are Paper revised: 11 July, 2019 mainly used for initial pretreatment, upstream of other Paper accepted: 6 August, 2019 more expensive control equipment [6]. https://doi.org/10.2298/CICEQ181220022A

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Wet scrubber techniques are applied in many erical investigation of the effects of the different col- industrial processes, due to their better capacity to lection mechanisms (Brownian diffusion, interception remove fine particles and soluble pollutants from gas and impaction) on the separation efficiency of a streams [7]. Nonetheless, major drawbacks of these gravitational wet scrubber. It was found that droplet scrubbing systems are related to the high energy cost residence time, liquid-to-gas flow ratio, and droplet associated with successful removal of submicron par- size distribution had significant effects on the wet ticles. Venturi scrubbers exhibit significant pressure scrubber efficiency. Therefore, the water droplet size drops, ranging from 2942 to 8826 Pa [8], while some is one of the most important considerations in design- types of scrubbers require the use of high liquid-to- ing a wet scrubber. gas ratios, resulting in the generation of large amounts Mohan and Meikap [11] reported on detailed of sludge [8,9]. experimental studies on the removal of dust particles In attempting to improve the collection efficiency from hot gases by using a spray-cum-bubble column of dry cyclones for smaller particles and decrease the with twin-fluid atomizers using water as the scrubbing operational cost associated with wet scrubbers, the medium. The results indicated that the spray-cum- cyclone spray scrubber combines the particle collect- -bubble column achieved almost 75-99% removal effi- ion mechanisms of these techniques, in a single dev- ciency of . In addition, a comparison of the ice. This apparatus essentially consists of a dry cyc- experimental and theoretical efficiencies was made lone adapted with nozzles that inject atomized liquid and analyzed. (usually water) into the inner chamber. The addition of Lee et al. [8] developed a novel system con- droplets within the equipment leads to improvement sisting of a cyclone and a swirl scrubber with an imp- of its performance, because in addition to the centri- act cone and plates, and evaluated the particle col- fugal force acting on the particles, other collection lection efficiency and the applications of this appar- mechanisms (impaction, interception, and Brownian atus. The parameters investigated were the plate diffusion) also operate, hence increasing the probabil- angles, nozzle size and pressure, and volumetric flow ity of removing the particles from the gas stream. In rate of the scrubbing medium. The results demon- general, the removal rate of the small particles is con- strated that particle separation efficiency improved trolled by Brownian diffusion, while impaction and with decrease of the plate angle, increased pressure interception are significant for removal of large par- of the scrubbing medium at the nozzle tip, and inc- ticles [3,10]. reased volumetric flow rate of the scrubbing medium. The performance of the cyclone spray scrubber, Ahuja [2] studied a novel type of wetted wall including its collection efficiency and pressure drop, cyclone scrubber, where wetting of the cyclone walls depends mainly on the method of liquid injection, the led to an improvement of up to 33% in the collection droplet size distribution, the droplet number, the liquid efficiency for fine particles in the size range from 1 to flow distribution and the initial liquid momentum 3 μm. Higher inlet air velocity resulted in greater [3,11]. Several previous studies have investigated the separation efficiency for all particles, under both dry influence of these parameters on the performance and wet conditions. and applications of cyclone spray scrubbers. Yang et al. [16] studied an innovative type of Krames and Büttner [12] investigated a cyclone cyclone, called a “cyclone splitter”, using numerical scrubber with dimensions based on the Barth [13] and simulation to evaluate its performance, considering Muschelknautz [14] equations. Droplets were gener- the pressure drops obtained with pure and droplet- ated by a pneumatic atomization nozzle that was laden gasses. The effect of droplets loading on the arranged at the cyclone inlet in the direction of the pressure drop was determined using droplet volume flow. A key finding of this study was an empirical rel- concentrations in the inlet gas ranging from 0.1 to ation between the residence time and the separation 1.0%. Experimental results showed that the two- result. When the cyclone was operated in dry mode, phase Euler numbers decreased with increasing the separation efficiency declined with decreasing droplets loading, and a new pressure drop model for a inlet velocity. In contrast, operation in wet mode res- gas-liquid cyclone was established by introducing a ulted in the best separation at the lowest volumetric liquid phase correction coefficient. flow rate. According to the authors, the cyclone spray The aim of the present work was to evaluate the scrubber could be classified as a high efficiency performance of a Stairmand-type cyclone adapted separator. with water injection nozzles, considering the effects of In order to improve understanding of submicron inlet air velocity, droplet size distribution, number of particle removal, Kim et al. [15] conducted a num- droplets, droplet initial velocity, liquid injection posit-

32 A.E. ACHILES, V.G. GUERRA: PERFORMANCE OF A CYCLONE SCRUBBER... Chem. Ind. Chem. Eng. Q. 26 (1) 31−40 (2020) ion, and liquid-to-gas flow ratio. To this end, several that their sprays are oriented down. Considering the experiments were performed under defined conditions nozzles located at side configuration were in the hori- in order to investigate the separation efficiency and zontal direction: 1S and 3S nozzles are facing each pressure drop behaviors of this apparatus used to other so that their sprays are oriented towards the remove sugarcane bagasse fly ash from gas streams. front and back side walls of the cylindrical body, res- pectively; the 2S nozzle was placed with its spray EXPERIMENTAL oriented toward the front side of the cylinder. In addition to the cyclone, the experimental sys- The equipment used in the experiments was a tem included a blower that delivered atmospheric air tangential inlet cyclone constructed of stainless steel. into the cyclone at three different inlet velocities (8.0, The dimensions of the cyclone scrubber were based 10.7 and 13.6 m/s), a rotary plate to inject particulate on the Stairmand-type cyclone. This geometry was matter continuously into the inlet gas, and a positive chosen because it indicates adequate values of pres- displacement pump to feed water from a storage tank sure drop and collection efficiency using correlations to the scrubber nozzles arranged on the cyclone wall. to predict the performance of cyclones. In order to During passage through the cylindrical section enhance its collection efficiency, the device was of the cyclone, the inlet gas stream contacted the adapted with nozzles placed in variable positions atomized water droplets, generating a mixture zone of along of the cylindrical cyclone body. A schematic gas and droplets. Subsequently, the flow of air and illustration of the apparatus and its main dimensions liquid droplets was transferred to the chamber walls are shown in Figure 1. by centrifugal force, with the liquid draining down to As it can be seen, there are six nozzles installed the bottom cone of the cyclone. The air stream, free on the cylindrical cyclone body: three located at the from the majority of the particulates, exited through a upper wall (U configuration) and three located at the top outlet, while the water and the solid particles were side wall (S configuration). The nozzles with U con- collected in a cylindrical discharge container con- figuration are arranged along the cross section of nected to the bottom of the cyclone. cylindrical body, as drawn in Fig. 1a. The nozzles with The overall efficiency was quantified by means S configuration are arranged along the side wall of of simultaneous isokinetic sampling in the gas inlet cylindrical at different distances from the upper wall, and outlet of the cyclone by gravimetric analysis: which are 0.13 m for the 1S and 3S nozzles and 0.24 probes connected to vacuum pumps were inserted in m for 2S nozzle, as demonstrated in Fig. 1b. Besides the inlet and upper outlet pipes, and the gas/particle the positions, another distinction among them is their mixtures were isokinetically transferred to particle col- spray orientations. The nozzles placed at upper con- lectors containing 0.8 µm pore size membranes. The figuration were installed in the vertical direction, so vacuum provided by the pumps was adjusted using

Figure 1. Dimensions of the cyclone used in the experiments and the nozzle configurations: a) upper view; b) front view.

33 A.E. ACHILES, V.G. GUERRA: PERFORMANCE OF A CYCLONE SCRUBBER... Chem. Ind. Chem. Eng. Q. 26 (1) 31−40 (2020) an air flow meter, so that the suction rate was equal to efficient and economical operation of a scrubber [16]. the air velocity within the pipes. Eq. (1) was applied to Thus, the influence of the droplet size distribution on calculate overall efficiency (ηoverall): the performance of the cyclone scrubber was evalu- ated by using two different nozzles in the experi- CC− η = in out (1) ments. Both were of the “pressure swirl” type, where overall C in the fluid pressure is converted into kinetic energy [18]. However, one of the nozzles generated a “hollow cone” where Cin and Cout are the mass concentrations of particles at the inlet and upper outlet of the cyclone, spray, while the other produced a “full cone” spray. respectively. The grade efficiency was determined by using an aerodynamic particle sizer (APS) spectrometer capable of measuring the particle size distribution - with aerodynamic diameters in terms of mass concen- tration per volume. During this procedure, isokinetic sampling conditions were also maintained and mea- surements were made separately in the inlet and outlet gas pipes of the cyclone. Grade collection η efficiency, (dp), for each particle with aerodynamic diameter (dp) was calculated using Eq. (2): − CCin()ddout() η = pp (2) ()dp C in(dp ) Figure 2. Cumulative volumetric particle size distribution. in which Cin(dp) and Cout(dp) are the mass concentration of particles at the inlet and upper outlet of the cyclone, The droplet size distributions of the sprays respectively, of particles with aerodynamic diameter generated by the nozzles were determined empirically dp. with a Spraytec® system (model RTS5134, Malvern Since the pressure drop has a significant effect Instruments) based on a laser diffraction technique. on the performance of particle removal equipment, it As shown in Figure 3, the measurements of droplet was measured for all the experimental conditions, size distribution for each nozzle were conducted out using U-shaped water manometers connected at the of the cyclone in an open environment, so that the gas inlet and outlet of the cyclone. liquid spray could be generated freely, without being The positions where the isokinetic samplings affected by the cyclone wall or the gas velocity. The (Cin and Cout) and pressure measurements (Pin and nozzle was positioned perpendicularly at the same Pout) were performed are also demonstrated in Figure level as the laser beam, and the liquid flow rate was 1. For all these locations, a Pitot tube was used to kept fixed. In order to characterize the size distri- measure the fluid velocity profile along the cross-sect- bution of the droplets generated by the spray, the ion of the pipes in order to determine the gas velocity measurements were carried out at a point next to the in the exact point where isokinetic samplings were nozzle (x). evaluated and verify the gas stream uniformity. In summary, the adjustable experimental para- Particle characterization is extremely important meters in this study were the inlet air and water flow for obtaining accurate estimates of the energy rates, the position of the water injection within the requirements of air pollution control devices [17]. The cyclone, and the type of scrubber nozzle. To account APS spectrometer (TSI Instruments) was also used to for any possible empirical errors, the tests were per- determine the particle size distribution. Figure 2 formed at least three times over a certain period of shows the particle size distribution of raw ash used in time, for each experimental condition. Table 1 shows the collection efficiency tests. The particle density the experimental conditions investigated. was 2.5 g/cm³ and its concentration in the inlet gas stream was kept below 1.0 g/m³ in all the experi- RESULTS AND DISCUSSION ments, in order to avoid the influence of this para- meter on the separation characteristics. Droplet size distribution The size of the droplets generated by atomizing Figure 4 shows the droplet size distributions for liquid in spray nozzles is a considerable parameter for the “hollow cone” and “full cone” nozzles, measured in

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Figure 3. Measurement of droplet size distribution: a) general view of the experimental equipment; b) position evaluated in the liquid spray.

Table 1. Experimental conditions investigated

-1 - Experiment Type of nozzle Number of nozzles Water injection position vi / m s (L/G) / L m ³ E-1 Hollow cone 1 1U 13.6 0.10 E-2 Hollow cone 1 1U 10.7 0.10 E-3 Hollow cone 1 1U 8.0 0.10 E-4/E-5/E-6/E-7/E-8 Hollow cone 1 2U/3U/1S/2S/3S 13.6 0.10 E-9 Hollow cone 2 1U + 1S 13.6 0.26 E-10 Hollow cone 4 1U + 1S + 3S + 2U 13.6 0.43

Figure 4. Droplet size distributions: a) “hollow cone” nozzle; b) “full cone” nozzle.

position x, with the same liquid flow rates. The initial sure; and ρL is the liquid density. The number of liquid velocity in each nozzle was obtained using Eq. droplets was obtained using the correlation of Kach- (3): hwaha et al. [19], shown in Eq. (4): 0.5 2ΔP = L 6QL UL  (3) N = (4) ρ g π 3 L D32 derived from the mechanical energy equation for where Ng is the number of the droplets generated; QL stationary incompressible fluid systems, where UL is is the liquid volumetric flow rate; and D32 is the Sauter the initial liquid velocity; ΔPL is the nozzle liquid pres- mean diameter.

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Effect of inlet air velocity on efficiency • turbulence; • Experiments E-1, E-2 and E-3 were performed residence time. to investigate the effect of the inlet air velocity on the Firstly, higher turbulence, caused by greater gas grade efficiency of the cyclone scrubber. The results flow velocities, increases the separation of larger par- obtained were compared to dry mode operation under ticles since they have difficulty following the high- the same experimental conditions, as shown in Figure 5. speed spiral motion of the gas and the vortex, so the As shown in Figure 5, the injection of water particles hit the inside walls of the container and drop within the cyclone substantially improved the grade down into a collection chamber. Nonetheless, with efficiency, for all the inlet gas velocities employed. regard to fine particles, since they have less inertia, The droplets generated inside the equipment acted as the vortex influence on them is more considerable and, additional collectors of particles and provided a resist- because of this, they are dragged with the clean gas. ance to the gas stream. Interaction of the fine par- Table 2. Grade efficiencies (%) of particles lower than 2.0 µm ticles with the droplets, by direct collision on or adher- under constant L/G ence into the droplet surfaces, acted to increase their density and, consequently, inertia. Therefore, the Air inlet velocity Overall Particle diameter, µm effect of centrifugal force on the particles became m/s efficiency, % 1.49 1.60 1.72 1.84 1.98 greater, enabling their separation. In addition, the Dry operation droplets wetted the inner wall of the equipment, 8.0 75.25 47.56 48.19 50.59 52.16 55.91 hence decreasing the energy of impact of the par- 13.6 81.00 44.83 49.74 53.09 57.64 63.58 ticles on the wall and reducing rebound of the par- Wet operation ticles into the outlet air stream. 8.0 90.18 72.52 75.59 77.52 79.71 81.25 Higher inlet air velocity increased grade effi- 13.6 95.50 61.68 67.92 72.41 77.94 83.87 ciencies under both dry and wet conditions, since it also enhanced the centrifugal force that is mainly res- Another important effect is the residence time ponsible for separating particles from the gas stream (τ), defined by Eq. (5), which is longer as the gas inlet in conventional cyclones. However, under wet oper- flow rate is lower. Therefore, it means that lower air ation, the efficiency of removal of particles smaller inlet velocities in cyclone scrubbers are able to pro- than, approximately, 2 µm improved with lower inlet vide a higher contact time between particles and air velocity. Table 2 exhibits these results with more droplets: details. As it can be observed, the experimental con- dition with lower air inlet velocity, even performing a Volume of the cyclone τ = (5) lower overall efficiency, was more efficient in collect- gas inlet flow rate ing particles smaller than 1.84 µm. This behavior associated with smaller particles Thus, the lower turbulence associated with occurs due to two main reasons: longer residence time, both occasioned by the dec-

Figure 5. Effect of inlet air velocity on grade efficiency under dry and wet operation.

36 A.E. ACHILES, V.G. GUERRA: PERFORMANCE OF A CYCLONE SCRUBBER... Chem. Ind. Chem. Eng. Q. 26 (1) 31−40 (2020) reasing of the air inlet velocity, are responsible to placed at a lower height, so the contact time between keep the smaller particles that are not dragged by the the droplets generated and the gas stream was shorter. clean gas in contact with the droplets by a longer Considering all the water injection positions, it period. Then, the collision on or adherence of these was found out the nozzles which were at positions particles into the droplet surfaces are enhanced, inc- 1U, 2U, 1S and 3S showed a quite similar effect on reasing their inertia and, consequently, their separ- the overall efficiency, with a maximum difference of ation. 2.4% between them. Higher efficiencies were achieved when the sprays had closer contact with the inlet Effect of water injection position on efficiency gas/particle stream and, consequently, provided Experiments E-1 and E-4 to E-8 were performed greater probability of collision. to examine the influence of water injection position on the overall efficiency of the cyclone scrubber, with the Effect of L/G flow ratio on efficiency other adjustable conditions being kept constant. The Since the liquid-to-gas flow ratio is crucial in the positions tested are shown in Figure 1 and the results performance of all kinds of wet scrubbers, the influ- are provided in Table 3. ence of this parameter was determined by varying it in the range from 0.10 to 0.43 L/m³ (experiments E-1, Table 3. Overall efficiency for each water injection position E-9 and E-10). This L/G range was obtained by alter-

Experiment Water injection position Overall efficiency, % ing the number of nozzles operating within the equip- ment and the results obtained were compared to E-1 1U 95.50 those for dry operation under the same conditions. E-4 2U 93.06 The nozzles liquid injection used in these tests (Table E-5 3U 92.82 1) were those that provided higher overall efficiencies, E-6 1S 95.48 as it can be observed in Table 3. The decision criteria E-7 2S 88.39 that influenced this choice was the fact that these E-8 3S 95.22 nozzles did not present a noticeable discrepancy among their overall efficiency results. Thus, this sel- The values obtained for the overall efficiency ection was a way to ensure that water injection pos- indicated that this parameter was affected by the ition would not be promote a significant effect on the position of water injection within the cyclone scrubber. results. When the nozzles were positioned in the upper wall of A higher L/G ratio increased the number of drop- the cylindrical body, the closer the water injection lets within the cyclone, so the mean distance among position was to the gas inlet, the higher the collection the droplets was reduced. Hence, the probability of efficiency was, as demonstrated by the nozzles at impaction and interception between the droplets and positions 1U and 2U. Regard to the nozzles that were the solid particles was higher, leading to important located in the side wall, the 2S configuration resulted improvements in the overall and grade efficiencies, as in the worst separation efficiency, because it was shown in Figure 6 and Table 4, respectively.

Figure 6. Effect of L/G ratio on grade efficiency.

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Table 4. Effect of liquid-to-gas flow ratio on overall efficiency E-10) was approximately 27%, which was a satis- and pressure drop factory result considering the potential harmful effects (L/G) / L m-3 Overall efficiency, % Pressure drop, Pa of these fine particles on human health. 0 81.00 657.0 Effect of droplet size distribution on efficiency 0.1 95.50 627.6 Figure 7 shows the grade efficiencies obtained 0.26 97.51 490 for each type of nozzle, as well as for dry operation 0.43 98.44 392 under the same experimental conditions. The highest collection efficiency was observed Although the increase of the L/G ratio substan- for the “hollow cone” nozzle that applied greater tially improved the separation efficiency, the improve- pressure on the liquid, as found also by Lee et al. [8]. ment was not linear (Table 4). When the L/G ratio was Higher pressure nozzles generate a larger number of doubled and quadrupled, the increments in overall smaller droplets that can achieve higher initial velo- efficiency were only 2.01 and 0.93%, respectively. cities, as shown in Figure 5, which improved the col- Therefore, this parameter should be evaluated in lection mechanism between the particles and droplets order to determine whether the increased separation since the greater kinetic energy, the higher the impact efficiency might justify the higher water consumption among them and, therefore, more particles are penet- and the operational costs associated with wastewater rated in the surface tension of the liquid scrubbing. In treatment, since an optimum value of liquid-to-gas addition, smaller droplets have a larger surface area flow ratio is that one which provides the maximum effi- and can remain in contact with the gas stream for ciency with a minimum scrubbing liquid application. longer times due to their lower inertia. On the other hand, the experimental cyclone All these characteristics increase the probability spray scrubber provided a substantial increment of of collision between the droplets and the particles, 17.44% on overall efficiency, compared to dry oper- consequently improving the separation efficiency. The ation. High fine particle collection performance of results obtained here were in agreement with the 98.44% was achieved using a low L/G ratio of 0.43 findings of Kim et al. [15], who reported that for the L/m³, which was equivalent to the performance other entire particle size range, the collection efficiency inc- high-efficiency wet scrubbers, such as Venturi scrub- reased as the droplet size decreased. bers that employ L/G ratios from 0.5 up to 5.0 L/m³ [12]. Pressure drop It is also important to point out that the injection Besides the collection efficiency, the pressure of atomized water into the cyclone mainly improved drop is another significant parameter that affects cyc- the removal of fine particles with aerodynamic dia- lone spray scrubber performance, consequently influ- meter less than 2.5 µm (PM2.5). The average increase encing the operational costs. Therefore, the pressure achieved for this particle size category (experiment drop was also evaluated in the experimental tests under dry and wet conditions.

Figure 7. Effect of liquid injection nozzles (droplet size) on grade efficiency.

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As shown in Table 4, the pressure drop of the scrubber, designed based on dimensions of a Stair- cyclone scrubber decreased from 627.6 to 392 Pa mand cyclone separator, was investigated in terms of when the L/G ratio was increased from 0.10 to 0.43 collection efficiency and pressure drop. The conclus- L/m³. ions can be summarized as follows: The decrease in the pressure drop when liquid • A higher inlet air velocity improved the collect- droplets are injected into the air streams of cyclones ion efficiency for larger particles, but decreased the can be explained by a decrease of the tangential separation of smaller particles. component of the gas velocity, resulting from the iner- • The water injection position influenced the tia of the particles/droplets contained in the air stream overall collection efficiency. and increased friction at the walls of the equipment. • The liquid-to-gas flow ratio strongly influenced According to Yang et al. [16], the main mechanism the performance of the cyclone spray scrubber, con- underlying this pressure drop reduction is enhance- sidering both separation efficiency and pressure drop. ment of the friction factor, as a result of the hydraulic • Smaller droplet sizes could increase the col- roughness of the liquid film produced on the inner wall lection efficiency of the solid particles. of the cyclone by the injection of droplets. The higher • The experimental cyclone spray scrubber friction factor is then responsible for reducing the tested here was effective in the removal of fine par- maximum tangential velocity and the swirling effect. ticles, especially those with aerodynamic diameter Table 5 shows pressure drops for the cyclone less than 2.5 µm. Separation of 98.44% of the solid spray scrubber under dry and wet operation. The particles present in the gas stream was achieved results of experiments E-1, E-2 and E3 showed that employing a low L/G ratio of 0.43 L/m³ and a low when the inlet air velocity was increased from 8.0 to pressure drop of 329 Pa. 13.6 m/s, the pressure drop under wet conditions inc- Nomenclature reased from 196.1 to 627.6 Pa. Similar behavior was observed when the cyclone was operated under dry APS Aerodynamic Particle Sizer conditions; however, the injection of water within the Cin, Cout Particle concentrations (g/m³) in the cyc- cyclone caused a slight reduction of approximately lone inlet and outlet, respectively 6.5% in the pressure drop, for all the inlet air velo- D32 Sauter mean diameter (µm) cities employed. dp Diameter of particle (µm) L/G Liquid to gas flow ratio (L/m3)

Table 5. Pressure drops (Pa) for the cyclone scrubber under Ng Number of droplets (-) dry and wet operation x Measuring position of the droplets (cm) ΔP Liquid pressure at the nozzle (Pa) Operation L Experiment PM2.5 Particulate matter with aerodynamic dia- Wet Dry meter less than 2.5 µm (-) E-1 627.6 657.0 QL Volumetric liquid flow rate (m³/s) E-2 387.0 412.0 S Side configuration of the nozzles within the E-3 196.0 215.8 cyclone (-) U Upper configuration of the nozzles within The cyclone spray scrubber investigated here the cyclone (-) showed excellent performance when compared with UL Initial liquid velocity (m/s) other high-performance wet scrubbers, such as the vi Inlet gas velocity (m/s) which usually operates at a signific- Greek letters ant pressure drop of 2942-8826 Pa and L/G range from 0,5 to 5 L/m3. The cyclone spray scrubber pro- η Collection efficiency (-) vided a highly satisfactory collection efficiency of ρL Liquid density (kg/m³) 98.44% using a reasonable L/G ratio (experiment τ Residence time (s) E-10), but at a low applied pressure drop of 392 Pa, Acknowledgements confirming its effectiveness as a device for particle control. The authors are grateful to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) CONCLUSIONS (grant number 454754/2014-0) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - In order to overcome the drawbacks of dry cyc- Brasil (CAPES) (Finance Code 001) for the financial lones and wet scrubbers, in this study a cyclone support provided for this study.

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ANA ELISA ACHILES EFIKASNOST CIKLONSKOG SKRUBERA U VÁDILA GIOVANA GUERRA UKLANJANJU SITNIH ČESTICA Department of Chemical Engineering, Federal University of São Carlos, Brazil Cikloni se ne smatraju efikasnim uređajima za uklanjanje sitnih čestica, dok jako efi- kasni vlažni skruberi obično imaju velike operativne troškove. Cilj ovog rada je da se prvi NAUČNI RAD put proceni ciklonski skruber dizajniran na osnovu dimenzija Stairmand ciklona uz uklju- čivanje mlaznica za ubrizgavanje tečnosti koje se nalaze na različitim položajima radi poboljšanja odvajanja sitnih čestica. Imajući u vidu nedostatak istraživanja koja bi uzele u obzir uticaj ubrizgavanja tečnosti i ostalih radnih uslova na performanse ciklonskog skrubera sa Stairmandovim dimenzijama, ovaj rad daje potpunu procenu ovih uticaja na odvajanje pepela otpadaka šećerne trske iz vazduha. Istraživani parametri su brzina ulaznog gasa, položaj ubrizgavanja tečnosti, odnos protoka tečnosti i gasa i raspodela veličine kapljica. Efikasnost prečišćavanja ciklonskog skrubera je procenjena uzimajući u obzir efikasnost odvajanja i pad pritiska. Ukupna efikasnost od gotovo 99 % i mali pad pritiska postignuti su korišćenjem odnosa tečnosti i gasa od 0,43 l/m³ za odvajanje pepela nastalog sagorevanjem otpadaka šećerne trske. Stepen efikasnost je pokazao da je ubrizgavanje kapljica u ciklone značajno poboljšalo uklanjanje sitnih čestica preč- nika manjim od 2,5 um.

Ključne reči: ciklonski skruber, efikasnost odvajanja, razdvajanje sitnih čestica, ubrizgavanje tečnosti.

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