Modes of Flow in Pneumatic Conveying Systems

Transcription

1 Recent Reearche in Alied Mechanic Mode o Flow in Pneumatic Conveying Sytem ALPEREN TOZLU, EMRAH ÖZAHĐ, AHMET ĐHSAN KUTLAR, MELA ÖZĐNÇ ÇARPINLIOĞLU eartment o Mechanical Engineering Univerity o Gaziante 710 Gaziante TURKEY alerentozlu@gante.edu.tr htt:// Abtract: - Pneumatic conveying ytem are ued widely to convey dierent tye o material in a variety o indutrial etting. The knowledge on low mode i articularly imortant in the deign tage o neumatic conveying line in term o energy requirement. There are ome claiication o low mode valid or both owder and bulk olid article baed on mean article ize, article and ga denity and looe oured bulk denity conidering alo air/article interaction. In thi aer, the available literature on claiication o low mode or neumatic conveying are ummarized. The material and low arameter which are deined earately with dierent ymbol are alo reented on a common bae. The reult are tabulated in term o rooed critical equation in order to rovide eae and undertanding in ractice. Key-Word: - Pneumatic conveying, Mode o low, Two-hae low, Powder, Granular article. 1 Introduction In ga-olid low tructure, the combined low nature lay an imortant role in term o eective tranort and energy conumtion, which are called a mode o low in two-hae low concet. In ractice, non-uenion or dene hae low i deirable or eective conveying in term o the ratio o conveyed material in amount to the amount o air uly wherea the uenion or dilute hae low i not. However, many roduct are/have to be conveyed in dilute hae conveying ytem. It i more convenient to determine the mode o low uing ome redictive technique intead o exerimentally conveying the material in a ieline at the tart o deign tage roviding a coniderable beneit in term o cot. In literature, there are two ditinct claiication in order to orm generalized chart in term o low mode; i) baed on hyical roertie o article conveyed [1-], and ii) baed on article/air interaction o ga-olid hae [4-7]. Moreover imrovement to the claiication baed on hyical roertie o article are carried out taking into account a looe-oured bulk denity arameter [8-10] and inter article coheion orce [11]. Air/article interaction uch a ermeability, air retention and de-aeration are alo deendent on the hyical roertie uch a: article ize, ize ditribution, denity o article, looe-oured bulk denity and hae. Looe-oured bulk denity, ρ bl, o bulk material i the weight er unit volume that i meaured when the article i in a looe, noncomacted or oured condition, exreed a ollow; ρ = ( 1 ε )( ρ ρ ) (1 ε ) ρ (1) bl where ρ i the denity o article, denity and ε i the bulk voidage. Permeability, g ρg i the luid P i a meaure o how the air low through the material under a motive orce and can be exreed a the ratio o the uericial velocity o the ga, V to the reure dro er unit ie length, a; P P / L occurred in the direction o the low = A P LQ V ( P () = Suericial ga velocity i given a; V = Q A () where Q i the volumetric ga low rate and A i the cro-ectional area o the bed/ie. Air retention i the ability o a material to retain air in the void ace o the material ater the air uly ha been terminated. e-aeration, A i a meaure ISBN:

2 Recent Reearche in Alied Mechanic o how the air naturally ecae rom the material and can be exreed a; A = t( P L) (4) where t i the time related to the reure dro decay lot rom luidization reure to atmoheric reure. Minimum luidization velocity at the onet o luidization i commonly given a; V = P ( P (5) crit Fluidization deined a the aerated tate o the material. Saltation i the roce o deoition o article along the horizontal ieline which occur when the air velocity all below the minimum conveying value. ene hae (non-uenion) i deined a a tate which occur when the ga velocity below the altation velocity o article conveyed. ilute hae (uenion) i a tate when the ga velocity equal to or above the altation velocity o article. Slug low i decribed by the reence o liquid rich lug that an the entire channel or ie diameter. Thi tye o low i roer or riable and/or granular roduct. When the air ma low rate i reduced urther, ome article conveyed accumulate at the bottom o the ieline and orm long lug. Thi tye o low i decribed a lug low. In lug low, high luctuation in reure and vibration occur due to being long lug tructure. Thi region i reerred a untable zone. Flow Mode Aroache.1 Claiication baed on hyical roertie on article conveying The behavior o ga-olid low wa claiied into our categorie by Geldart [1] in term o mean article ize and denity dierence. According to hi claiication baed on ga luidization; 1) Powder in Grou A in which material ha a mall mean ize and/or a low article denity (le than about 1.4 g/cm ) behave a dene hae exanion ater minimum luidization. When the uericial ga velocity i high enough in order to orm lugging condition, the lug are axiymmetric, while the uericial ga velocity i increaed urther, lug low tend to tranition to turbulent. Some cracking catalyt can be given a tyical examle. ) Powder in Grou B bubble at the minimum luidization velocity contrary to owder in Grou A. The material in thi grou have the mean ize and denity range o 40µ m d 500µ m and 1.4g / cm ρ 4g / cm, reectively. Sand i the tyical examle or thi grou. ) Powder in Grou C are diicult to luidize at all due to interarticle coheive orce. The owder lit a a lug in mall diameter tube, or channel (rat-hole) badly. The interarticle orce are greater than the luid orce exerted on article. Thee generally occur or the material that have very mall article ize, trong electrotatic orce and or very wet or ticky material. Pulverized owder are examled or thi grou. 4) The material in Grou have large and/or very dene article. The material in thi grou can be outed i ga i admitted only through a centrally oitioned hole. The low regime among the article may be turbulent. Geldart [1] rooed a criterion to determine the boundary between the owder in Grou A and B according to being whether the uericial ga velocity at minimum bubbling, V mb i greater than uericial ga velocity at minimum luidization, V or not. In Grou A, V 1 (6) mb V Geldart [1] ued three dierent low denity owder o iakon, reh and ent catalyt in hi exeriment. He rooed a linear equation rereenting the relationhi between mean article ize, d and minimum bubbling velocity, V, and comared it with the equation o avie and Richardon [] or the uericial ga velocity at minimum luidization, reectively a ollow; Vmb = 100d (7) V g ) = gd ( ρ ρ µ (8) where g i the gravitational acceleration and µ i the dynamic vicoity. The equation decribing the border o Grou A and B i derived by Geldart [1] inerting Eq. (7) and (8) into Eq. (6) (ee Table 1). The boundary between Grou B and i not o clear a that between Grou A and B. However, the rooed criterion by Geldart [1] i available in Table 1. There i no exact criterion decribing the boundary between Grou A-C. ixon [] claiied ga-olid low into three grou a i) axiymmetric lug, ii) weak aymmetric lug (dune) and iii) no lug at all. He conidered the relationhi between the ga lug velocity, V, terminal velocity, V t, and minimum luidization velocity, mb V uing the ollowing ISBN:

3 Recent Reearche in Alied Mechanic equation; 1 V = ( K g) (9) where i the ie diameter and axiymmetric lug; V t K =1 or K = or aymmetric lug d g ( ρ ρg ) µ ρg = (10) (1 ε) ρ (1 ε) = 150 ε µv gd (1 ε) ρgv ε gd (11) where ε i voidage which i the ratio o the ace volume among the article/owder in a bed to the total volume o bed. According to ixon [], there i no table lug ormation i V < V hence the boundary between t no lugging and aymmetric lug i denoted at V =. No ull bore lug low occur i V < V t V hence the boundary between axiymmetric lug and aymmetric lug i given a V = V.. Claiication baed on air/article interaction o ga-olid hae Mainwaring and Reed [4] develoed two diagram in term o ermeability and de-aeration actor o material with reect to teady tate luidization reure dro er unit length or dene hae conveying at minimum luidization. According to ermeability actor, two dierent area were deined with reect to the contant minimum luidization velocity o 50 mm/. The data above thi critical line eciie the conveying in a dene hae lug low in which the material have a high ermeability actor. On the other hand, the other data below the line illutrate thoe conveyed in dilute hae or luidized dene hae. In term o claiication with reect to the eciied arameter o the de-aeration actor divided by the article denity, they ound the material having the high value o the eciied arameter (above the demarcation line) can be conveyed in luidized dene hae while other material below the demarcation line can be conveyed in a dilute hae or lug low. A conventional reure veel ytem (blow tank) wa ued in their exeriment. A wide range o roduct were conveyed at low velocity in dene hae. The ine owder uch a cement, ulverized coal etc. and coare granular material uch a mutard eed, latic ellet etc. were conveyed in the range o 990 kg/m ρ 4610 kg/m, µm d 1650µm, 400 kg/m ρ bl 600 kg/m, and i.e., air ma low rate 5 g/ < mɺ air < 100 g/ or conveying o ulverized coal, g/ < mɺ air < 0 g/ or conveying o 1000 µm and. Mainwaring and Reed [4] rooed the line earating two mode o luidized dene hae and lug low by introducing a arameter denoted a X t ρ = m /kg. = Fargette et al. [5] claiied the owder conveyed in a dene hae, which are eecially ued or the manuacture o teel, according to the ermeability actor, air retention and coheion o owder. They deined the neumatic low arameter, Ω a ollow; Ω = t ρ (1) da P bl I Ω >4000, the mode o low become luidized dene hae; lug low i Ω <18 and low i dilute only i 18< Ω <4000. Chamber et al. [6] introduced a arameter imilar to that o Fargette et al. [5], N c baed on article denity intead o looe-oured bulk denity, ermeability and de-aeration time a; N = ρ P t (1) c da They claiied the conveying o material into three low mode uch a i)dene hae lugging mode, ii) lean hae mode and iii) dene hae moving bed mode. The conveyed material i aroriate or lugging dene hae tranortation i N >0.01. I N c <0.001, the material can be conveyed a a dene hae conveying in a moving bed low. At moderate rate o < N c <0.01, the material can be conveyed only in a lean hae mode. Sanchez et al. [7] took into conideration the meaurement o the ermeability and de-aeration time o the article to redict the eaibility o conveying article in dene hae mode by reviewing and comaring the available method in literature. The meaurement o the ermeability actor and the de-aeration arameter were carried out by mean o their luidization equiment. Many tye o material uch a alumina, gla bead, and, olyeter etc. were ued in the range o 91kg/m ρ 450kg/m,7.67µm d 541µm, m/ V 1.58 m/, m /bar. P 1.7 m /bar.. They claiied the material conveying in dene hae mode into two general grou; the rimary arameter which are article ize, hae, article and bulk denity, ermeability, c ISBN:

4 Recent Reearche in Alied Mechanic de-aeration, coheivene etc., and the econd arameter o adheion, moiture, electrotatic, elaticity and temerature enitivity. A a reult o their analye, it i ound that ome material do not obey the Geldart' claiication due to the econdary arameter. They alo deined a grou o dimenionle arameter a de-aeration actor, ermeability actor and Froude number baed on minimum luidization velocity a; Grt = µt d ρ + ρ / ) (14) P = P da ρ ( g gd d (15) Fr = V / gd (16). Imrovement on the claiication Moleru [8] conidered interarticle coheion orce in addition to Geldart' claiication. The limiting condition between Grou A-C; Grou A-B and Grou B- were deined uing emi-emirical criteria by analyzing the orce exerted rom the ga on the article and the coheion orce between article. There i no boundary between Grou A-C in Geldart diagram. However, Moleru [8] rooed an equation decribing the boundary between Grou A-C or hard article a; 1 max = FT = 10( ρ ρg ) d g FH = K1 1/100 (17) where 1max i maximum drag orce, F T i average tenile orce tranmitted er article, F H i adheion orce tranmitted in a article contact. Moleru [8] alo deined an equation decribing Grou A-B boundary or hard article by equation; ( ρ ρg ) πd g 6FH = K = 0.16 (18) To redict the boundary Grou B-, the ollowing equation i rooed a by Moleru [8]; ( ρ ρg ) d g= 15. (19) Pan [9] modiied Geldart' claiication uing looe-oured bulk denity intead o dierence between article and ga denitie. He claiied the low in conveying o bulk olid material into three mode: i) PC1: mooth tranition rom dilute to luidized dene-hae, ii) PC: dilute-hae, untable-zone and lug-low, and iii) PC: dilute hae only conidering reure dro and air ma low rate. i) I the air ma low rate i decreaed or a contant article ma low rate, the reure dro alo decreae and tranition to dene hae rom dilute hae occur (PC1). Many tye o ine owder a ly ah, ulverized coal etc. were ued in the range o 1415 kg/m ρ 17 kg/m, 11.5 µm bl d 46. µm, 68 kg/m ρ 957 kg/m. ii) PC i divided into three grou; dilute-hae, untable-zone, and lug low. In dilute-hae, the article are ditributed evenly over the entire cro ection o the ie. A the air ma low rate i decreaed urther, the air velocity i not adequate to tranort all article and ome article all down on the bottom o the ieline, orming long lug and thi roduce high luctuation in reure and vibration. Thi region i reerred to a the untable zone. I the air ma low rate i decreaed even urther, the article are conveyed in the orm o lug. Many tye o material uch a narain, barley, wheat etc. were ued in the range o 84kg/m ρ 1745kg/m, 5µm d 910µm, 458 kg/m ρ bl 880 kg/m. iii) Heavy granular and/or cruhed article can only be conveyed in dilute-hae, PC. Otherwie the article interlock orming a acked bed, which aect low negatively. Many tye o material in thi grou uch a high ilica lux and rimary concentrate were ued in the range o 664kg/m ρ 474kg/m, 14µm d 00µm, 1519 kg/m ρ bl 778 kg/m. William and Jone [10] analyzed to Geldart, Moleru and ixon claiication diagram and relaced the article denity arameter with looeoured bulk denity in their chart. The rooed equation in term o modiied Geldart, ixon and Moleru claiication are given in Table 1. Jone and William [11] deined two tye o redictive chart baed on baic article arameter and air-article arameter. The imrovement were carried out relacing the article denity with looeoured bulk denity in the baic arameter technique. An air-article baed technique wa imroved without the neceity o any de-aeration arameter. The equation which decribe thee boundarie between the luidized dene hae and dilute only (Eq. 0), and dilute only and lug low (Eq. 1) were introduced in Table 1 a ollow; 4 ρ bl P 00 (0) 6 P 0x10 (1) They alo modiied Chamber et al.' arameter in Eq. 1 a; ISBN:

5 Recent Reearche in Alied Mechanic N = c(mod) ρp tc () where t c i de-aeration time according to Jone or Sanchez. I N c(mod) <8x10-4, low i luidized dene-hae. It i dilute only when 8x10-4< N low i N c(mod) >0.07. c(mod) <0.07 and lug Concluion Geldart' claiication i ractical or etimation o low mode or neumatic conveying ytem. However, it i unuitable alone or rediction o low mode in dene hae. Moreover, ixon' aroach i alo convenient during deign tage, but roviional or an accurate rediction o low mode. Mainwaring and Reed' aroach i more reliable redictive method than the Geldart' and ixon' aroache due to baed on ermeability and de-aeration actor intead o only hyical roertie o article. Fargette et al. conidered the air/article interaction introducing a nondimenional arameter in term o de-aeration time, ermeability and looe-oured bulk denity. Chamber alo introduced a dimenionle arameter imilar to that rooed by Fargette et al. uing article denity intead o looe oured bulk denity. According to Sanchez, ome material do not obey Geldart' claiication due to the econdary arameter roertie o material. Moleru modiied the Geldart' claiication and alo decribed the criterion between Geldart' Grou A-C conidering coheion orce. Pan claiied the low mode a a unction o looe oured bulk denity and median article diameter howing agreement with thoe o Geldart, ixon and Mainwaring and Reed. Jone and William reviewed all available tudie in their tudy and alo rooed criteria or Geldart' Grou A-B and B- taking into account looe oured bulk denity and ermeability. Hence there are many low mode diagram and rooed criteria or determination o low mode or neumatic conveying o owder/granular article rom Geldart' aroach [1] to the tudy o Jone and William [11]. A i een, ome o the cientit conidered only hyical roertie o article/owder while other took into account both hyical roertie o article and air/article interaction. There are ome agreement and conlicting reult among the rooed aroache. In thi aer, all rooed criteria are reviewed and orted out or urther tudie. Acknowledgement The author would like to thank the Reearch Fund o the Univerity o Gaziante through the roject under grant number o RM Reerence: [1]. Geldart, Tye o Ga Fluidization, Powder Technology, Vol.7, 197, [] L. avie, J. F. Richardon, Tranaction o the Intitution o Chemical Engineer, Vol. 44, 1966, T9. [] G. ixon, The Imact o Powder Proertie on ene Phae Flow, In Proceeding o the international conerence on neumatic conveying, [4] N. J. Mainwaring, A. R. Reed, Permeability and Air Retention Characteritic o Bulk Solid Material in Relation to Mode o ene Phae Pneumatic Conveying, Bulk Solid Handling, Vol. 7(), 1987, [5] C. Fargette, M. G. Jone, G. Nubaum, Bench Scale Tet Aement o Pneumatic Conveying Behavior o Powder, Powder Handling and Proceing, Vol. 9(), 1997, [6] A. J. Chamber, S. Key, R. Pan, The Inluence o Material Proertie on Conveying Characteritic, In Proceeding o the 6 th international conerence on bulk material torage, handling and tranortation, 1998, [7] L. Sanchez, N. Vaquez, G. E. Klinzing, S. hodakar, Characterization o Bulk Solid to Ae ene Phae Pneumatic Conveying, Powder Technology, Vol. 18, 00, [8] O. Moleru, Interretation o Geldart Tye A, B, C and Powder Taking into Account Interarticle Coheion Force, Powder Technology, Vol., 198, [9] R. Pan, Material Proertie and Flow Mode in Pneumatic Conveying, Powder Technology, Vol. 104, 1999, [10] K. C. William, M. G. Jone, Claiication iagram or ene-phae Pneumatic Conveying, Powder Handling and Proceing, Vol. 15(6), 00, [11] M. G. Jone, K. C. William, Predicting the Mode o Flow in Pneumatic Conveying Sytem, Particuology, Vol. 6, 008, ISBN:

6 Recent Reearche in Alied Mechanic Geldart [1] ixon [] Table 1 Summary o Prooed Criteria in Term o Flow Mode in Pneumatic Conveying Sytem Author Mode o low Predictive diagram Limitation Boundarie and ormulation A-Fluidized dene-hae B- ilute hae Particle denity dierence - mean article diameter (kg/m ) - (m) ρ < 1.4 gr/cm A/C-B ρ >1.4 gr/cm 500 µ m > d > 40µ m C- iicult to luidize iicult to luidization B- - Plug mode o dene hae Large or dene article Axiymmetric lug- Plug tye Weak aymmetric lug- ilute hae No lugging- Fluidized dene-hae Particle denity dierence - mean article diameter (kg/m ) - (m) - V < V (m/) V t < V (m/) ( ρ ρ ) d = 5x10 g ( ρ ρ ) d = 10 g Axiymettric/aymmetric ( ρ ρ ) d g No lugging/aymmetric 1.14 d 1.64x10 ρgd = +.68 d ( ρ ρg) = 16x10 Mainwaring and Reed [4] Fargette et al. [5] Chamber et al. [6] Plug tye ilute only or luidize dene-hae Fluidized dene hae ilute only or lug low Fluidized dene hae Permeability- ( P e-aeration/denity- ( P Non-dimenional arameter ( Ω ) V >50 mm/ V <50 mm/ X>0.001m /kg X<0.001m /kg Ω >4000 ilute only 18< Ω <4000 Plug low ene-hae/moving bed Non-dimenional arameter ( N ) 18< Ω N c <0.001 Lean hae mode c 0.001< N c <0.01 Slugging dene-hae N c >0.01 P V = P = 50mm / L P A X = L ρ tda Ω = P ρbl ρp N c = tda Sanchez et al. [7] Fluidized dene hae Non-dimenional arameter: Grt, Fr Grt >0.x10 ( ) - d da ρ + ρg / P, Grt = µ t P = P ρ gd d Fr = V / gd Geldart' A-Fluidized dene-hae Geldart' B- ilute hae A-C (or hard article) 10 ( ρ ρ ) d g g = 0.01 FH Moleru [8] Geldart' C-iicult to luidized Particle denity dierence - mean article diameter (kg/m ) - (m) A-B (or hard article) ( ρ ) ρg πd / 6 g = 0.16 FH Pan [9] Geldart' - Plug low PC1- Fluidized dene-hae PC- Untable zone- lug low- dilute hae Looe oured bulk denity-mean article diameter (kg/m ) - ( µ m ) PC ilute only - B- ( ρ ρg) d g = PC1-PC/ d > 1000µ m d ρ bl = PC-PC ρ bl = 1000 Geldart' A- Geldart' B- ilute hae Geldart' C- Geldart' - Plug low A/C-B ρbl d = 11x10 B- 6 ρbl d = 59x10 ixon' Axiymmetric lug- Plug tye Aymmetric lug - axiymmetric lug William & Jone [10] ixon' Weak aymmetric lug- ilute only ixon' no lugging- Fluidized dene-hae Moleru' A- Moleru' B- Looe oured bulk denity-mean article diameter (kg/m ) - ( µ m ) d ρ bl 0.885x10 = d No lugging-aymmetric lug d ρbl = 87.4x10 A/C-B 9 ρbld = 1.7x10 Moleru' C- B- Moleru' - Plug low = ρ bl d Jone & William [11] Chamber Fluidized dene-hae Non-dimenional arameter ( N ) N c(mod) <8x10-4 Chamber ilute only c(mod) 8x10-4 < N c(mod) <0.07 Chamber Plug low Fluidized dene-hae N c(mod) >0.07 ρp N c(mod) = tc P 4 ρ bl 00 ilute only Plug low Looe oured bulk denity-ermeability (kg/m ) - (m /kg) 6 P 0x10 ISBN: