Chy N Do Cc Ht Bi

Trnh Minh Chnhngy 18 thng 03 nm 2004

PHN MTvPhn mtgii thch hin tng n.Phn hais gii thch hin tng n bng ton hc v cch phng (tnh l thot hi bng ton hc, l thot hi dng gim mnh lit hoc lm chuyn hng ca hin tng n).vHt bi(ting Anh gi l dust) y l cc ht th rn, hnh dng bt k (tt c cc loi hnh dng), t trng cng bt k (tt c cc loi t trng) c ng knh hay cnh di 500 mm (0,5 mm) (c ti liu ni di 0,2 mm).vNgn la (chy) ch c th xy ra khi p ng 3 iu kin:Vt liu c th chy v sinh ra mt sc nngC y oxygen (khng kh)C mt vt mi hu hiu (s nng hoc ngn la)Nu c hin tng n xy ra, s phi p ng thm hai iu kin na:C y cc ht bi chy cCc ht t nng v trn ln vi khng kh trong mi trng nvThng thng p sut tng ti a trong hin tng n khong 7 10 barnu bnh cha ban u c p sut khong 1 bar (p sut trong khng kh). Nu bnh cha trn 1 bar thp sut ti a c th ln n khong 5 10 ln p sut ban u.Th d bnh cha lm vic khong 3 bar th khi n c th tng n 15 30 bar. 7 bar tng ng p sut di mt nc bin khong 69 m hoc nc ngt (nc sng) khong 71,5 m.

Hnh 1:ng ta qun bi Chy n do cc ht bi1-Li m uThng thng chng ta ch s s chy n ca cht kh hay lng m coi thng s chy n ca vt rn. iu cng d hiu v cht kh v lng d bt chy hn cht rn. Nhng khi chy th vt rn s gy ra mt sc chy mnh lit v gy thit hi ng k, khng nhng ti sn m c mng sng ca con ngi. Bng 1 ch mt vi m chy, n ti Vit Nam ghi nhn c qua internet.Ngy-thng-nma imSn xutHin tng

09-03-2004Q.9, TP HCM gChy,n?

04-03-2004TP HCMMt xp cho giy dpChy,n?

26-02-2004TP HCMGia cng nm mtChy,n?

20-02-2004Hc Mn, TP HCMMy, tre, lChy,n?

16-01-2004Huyn Bnh ChnhGiyChy,n?

04-12-2003Bnh Dng giy AdidasChy,n?

11-01-2003Trng Bng, Ty NinhSy TreChy, n

19-12-2002Qung NinhM thanChy, n

05-03-2002G VpCh bin gChy, n

Bng 1:Chy n ni sn xut cc g, nha v than . (Theo tin tc t internet).N?: khng chn chn c hin tng n hay khng?Khng nhng ch c VN mi c hin tng chy n trong cc nh my sn xut m ngay c cc nc Ty Phng cng c hin tng ny (xem Bng 2)PRIVATELoi biTy c c 1965 - 1980 [%] Anh* 1979 - 1985 [%] M* 1900 - 1956 [%]

GThc nNhaThan Kim loiGiyCc loi khc 32 25 13 9 13 2 6 12 42 5 5 14 ** 22 18 51 6 6 7 1 11

Bng 2:N ti Ty c(c), Anh v M.*: n v chy;**: giy v g: 12 %.[1].Nhng hin tng chy n do cc ht bi gy ra thng mnh lit v chng ta khng c phng v coi thng s nguy him ca n. Th d nh ht kim loi nh ht nhm thng thng khng chy, nhng vi mt nng oxygen no cng vi nhit v p sut cao s chy v sinh ra mt nng lng ng k v s a n hin tng n. Nhng chng ta khng v s nguy him m chng ta ngng sn xut m chng ta phi tm hiu v phng, trnh s thit hi c vt cht ln nhn mng con ngi.Vic tm hiu, nghin cu s chy n do cc ht bi khng phi xy ra mi y m n c t lu i. Ngy xa h tm hiu s chy n ca cc ht bi xut pht t n hm m nht l m than. Cc m than thng hay c cc cht kh th d nh methane (CH4) cha cc ti nh ln ln vi than. Khi chng ta o ti cc ti kh ny cng vi mt tia la bt mi v s chy xy ra. Khi c s hin din ca cc bt than, cc bt than ny s d dng chy v sinh ra mt nng lng ng k. Nng lng sinh ra s lm nhit ca khng kh (KK) trong hm tng ln v a n th tch tng ln mt cch t ngt. Do th tch trong hm khng thay i, th tch KK s chuyn ng nhanh theo hng ca hm v hin tng n xy ra. Chi tit hin tng chy n ny s trnh by r rng hn di y.1.Th no gi l hin tng n?Gio s Eckhoff (1991)[2] nh ngha s n hay phn ng n nh sau: Hin tng n l hin tng m trong c phn ng ho hc pht nhit, hin tng ny xy ra trong mt mi trng ng tch (th tch khng thay i) v sinh ra mt s tng trng t ngt v mnh lit ca p sut. Tt c cc vt rn m c th chy nhit v p sut thng u c th pht sinh mt s tng trng t ngt v mnh lit ca p sut. S tng trng t ngt v mnh lit ca p sut ny t l thun vi din tch chung quanh ca vt (xem gii thch pha di). Ting n bang l do mt ln sng p sut tht mnh truyn i vi vn tc tht nhanh.Lemkowitz (1996) [3] phn bit chy v n nh sau:Chy l mt phn ng ho hc, xy ra tng i chm v lin tc. Chy s lm thit hi nh ca v vt liu do ngn la hoc sc nng ca n. Chy cng lm thit hi n mng sng hoc lm b thng con ngi qua ngn la, lm thiu oxygen hoc pht sinh kh c nh carbon monoxide (CO).N l hin tng chy nhanh v pht sinh bt thnh lnh mt nng lng ln, thng thng trong mt mi trng dng kh hay lng. Hin tng ny pht sinh ra mt ln sng p sut tht nhanh. p sut t hin tng n s hy hoi nh ca, vt liu v c th lm b thng hay lm cht ngi trc tip hay gin tip nh nh sp, vt , v.v. S n s gy ra m chy ln hay mt tia la di. Cng ging nh s chy, hin tng n c th git ngi bng cch lm lm thiu oxygen cng nh sa thi khi c. Thng thng n km theo s chy sau .Trong s t chy ngi ta phn bit hai loi la: 1) Cht t v oxygen (hoc khng kh) ho ln v a vo phng t bng mt ngun (premixed flame) gi l ngn la ho ln trc (Hnh 2a ); 2) Cht t v oxygen a vo phng t bng hai ngun khc nhau (diffusion flame)(Hnh 2b) gi l ngn la khuych tn.

Hnh 2:Mu hnh n gin cho hai loi ngn la. (a) ngn la ho ln trc; (b) ngn la khuych tn. Hai hnh v y ch dng gii thch. Trong thc t, ngi ta thng cho khng kh vo bng mt dng xoy ngn la d dng n nh (d dng chy lin tc, khng b tt). K thut ny hy vng s trnh by vo mt dp thun tin khc.Chy xy ra trong mi trng cht t v khng kh (hay oxygen) khng ho ln trc, nhng hin tng n xy ra mi trng cht t v khng kh trn ln trc.3.iu kin v ni c th xy raNh nu trn, tt c cc vt rn m c th chy nhit v p sut thng u c th pht sinh mt s tng trng t ngt v mnh lit ca p sut. Tuy nhin c mt ngn la pht sinh v truyn i phi p ng tt c cc iu kin di y (VDI 2263 (1992) [4]):Vt liu c th chy v sinh ra mt sc nngC y oxygen (khng kh)C mt vt mi hu hiu (sc nng hoc ngn la)Nu c hin tng n xy ra, s p ng thm hai iu kin na:C y cc ht bi chy cCc ht t nng v trn ln vi khng kh trong mi trng nGii thch cho iu kin cui cng nh sau. Ta c mt khc g hnh khi mi cnh 1 m hay 1.000 mm (Hnh 3a) v 1.000 khc g mi cnh 100 mm (Hnh 3b).

Hnh 3: 1 m3g (a) Khc g hnh khi mi cnh 1 m = 1.000 mm; (b) 1.000 khc g hnh khi mi cnh 100 mm.Gi s 1.000 khc g nh tung u trong khng kh nh hnh v (3b) c ngha l khng kh c th tip vi tt c cc b mt ca chng n v chng c th (iu kin) chy cng mt lc.Din tch chung quanh ca cc khc g tnh nh sau:Khc g ln: Achung quanh= 6 x (1 x 1) = 6 m2Cc khc kh nh: Achung quanh= 1.000 x (6 x (0,1 x 0,1) = 60 m2Nh vy ta chia khc g ln ra mt 1.000 ln n s chy nhanh hn 60 ln. l l do ti sao chng ta hay ba ci nu bp.Nu chng ta nghin nt cc khc g ra nhiu ln na thnh cc ht bi, th d mi cnh khong 1 mm hay 0,001 m. Tng din tch chung quanh c tnh nh sau: Vht bi= 0,001 x 0,001 x 0,001 = 1 x 10-9m3Tng s ht bi tng ng vi 1 m3g nht bi= V1m3/ Vht bi= 1 / (1 x 10-9) = 1 x 109ht biTng din tch chung quanh ca cc ht bi ng knh 1 mm hay 0,001 m Achung quanh= 1 x 109x (6 x 0,001 x 0,001) = 6.000 m2Nh vy cng 1 m3g, dng ht bi (mi cnh 1 mm) s chy 6.000 ln nhanh hn v s sanh ra mt nng lng khng l trong tch tc, v nhit khng kh s tng t ngt, nhit tng th tch khng kh tng, th tch bnh cha khng thay i (th d phng hay xng lm vic) v cui cng s gy ra hin tng n.Hnh 4 trnh by s khc nhau gia chy chm, chy nhanh v n cho mt khc g v m ci

Hnh 4:(a) Chy chm; (b) Chy nhanh hn; (c) Hin tng n (Hnh Eckhoff (1991)[2])4.c trng sc mnh lit ca hin tng nNgi ta c trng hin tng n bng hng s gi lKst(stl ch vit tt ca ting c staub c ngha l ht bi). Kstv tc (vn tc) tng p sut (dP/dt)maxti a dng tnh l thot ca bnh cha. Cng thc lin kt gia Kst, (dP/dt)maxv V1/3gi l cubic law dch lnh lut hnh khi(1)V l th tch bnh cha, (dP/dt)maxl vn tc ti a ca p sut, Kstl mt hng s ca ht bi. nh lut hnh khi c gi tr khi ([2], [5]):vCng mt nng gia ht bi v khng kh hay oxygenvBnh cha c hnh dng tng t nh nhauvChiu dy ca ngn la tng i nh (mng) so vi bnh cha (xem gii thch di)vHn hp (ht bi v khng kh) c cng ri lon (turbulence)nh lut hnh khi c tnh theo gi s (dP/dt)maxxy ra khi p sut t c ln nht (ti a) (Pmax) khi ngn la chm vo thnh bnh ([6], [7]). Gi s ny xy ra trong hin tng n c kh t th d hydrogen (H2) v oxygen (O2). Trong hin tng n ca cc ht bi, (dP/dt)max t c trc khi ngn la chm vo thnh bnh.Kstl hng s t th nghim ra. C rt nhiu loi bnh lm th nghim. Chng n khc nhau c v hnh dng v th tch. Ngy nay ngi ta thng dng hai loi bnh 20 lt (Hnh 5a v 5b) v 1.000 lt (1 m3). V th nghim (x dng t ht bi cho mi th nghim) cho bnh 20 lt vn r hn bnh 1.000 lt cho nn loi bnh 20 lt vn cn thng dng nhng chnh xc vn thp hn v ri lon trong bnh 20 lt thp so vi bnh 1.000 lt ([2], [10]). Th nghim cho rng Kstl mt hng s khng ty thuc vo ln ca bnh nu bnh cha ln hn 10 lt ([5]). Bnh cha lm th nghim o Kstca cc ht bi c chn theo tiu chun quc t l bnh 1.000 lt (1 m3).

Hnh5a:Bnh bom 20 lt (bom Hartmann) th nghim.Th nghim o Kst vi bt than . Bt than s a vo bnh nh (Dispersion reservoir, bn tay phi bnh). Sau bm khng kh (KK) vo trn ln vi bt than p sut vi bar. Sau m ng thng (Dispersion valve), v p sut trong bnh 20 lt (hnh cu) v bnh nh chnh lch nhau nn bt than v KK c phun vo bnh 20 lt bng b mt phn phun (Dispersion nozzle). Trong tch tc khi hn hp bt than v KK vo trong bnh 20 lt, mt tia la nhn to ngay chnh gia bnh s c to nn v hn hp s bc chy v tc p sut c ghi nhn bng my in ton.

Hnh5b:Bnh bom 20 lt (bom Hartmann) th nghim. Hnh tht s. (Hnh ly t web caKatholieke Universiteit Leuven)

Hnh 6:Tc tng ca p sut theo thi gian. Th nghim thc hin vi bt than , nng 473 g than cho 1 m3KK hay 9,46 gram cho bnh 20 lt, nng lng mi l 10 KJ v o bng bnh 20 lt. T hnh v ta c th tnh c Kst(cng thc (1)) bng cch v tip tuyn chn (dP/dt)maxv V = 20 lt.T lc bt u chy khong 70 mili giy (70 ms) (hn hp bt than v KK a vo bnh 20 lt khong 70 ms hn hp thi gian to u trong bnh) n khi bnh t p sut khong gn 6 bar khong 140 mili giy (140 ms), nh vy trong khong 70 mili giy (140 70 = 70 mili giy) bnh tng gn 6 bar. 70 mili giy c ngha l 0,07 giy, chng ta khng kp chy ra khi phng hay xng lm vic trnh p sut ny.5.Tc chy ca ngn laC rt nhiu t chuyn mn m cn gii thch cho nhng c gi khng chuyn ngnh. Chng ta nhn vo n Bunsen (Hnh 5). n Bunsen gm mt ng hnh trn di, di chng ta c mt tc ca hn hp kh t v KK khng thay i d ng di hn na (fully developed velocity profile). ng knh ca ng rt nh (khong 5 30 mm). Hn hp kh t v KK chy (thi) vo ng v c ngn la ngay pha ngoi ng. Chng ta thy mu tht sng mu xanh c hnh ch V ngc gi l ngn la (ting Anh gi l flame front), l ranh gii, mt bn pha ngoi ch V ngc l hn hp khi (kh t v KK chy xong) v pha di ch V ngc l hn hp kh t v KK cha chy. Ti mt im bt k trn ngn la s c hai loi vn tc: 1) Vn tc th nht vung gc vi ngn la c hng v pha hn hp kh t v KK cha chy (k hiu Su) gi l vn tc ca sc chy (burning velocity) v 2) Vn tc th hai c hng ra pha ngoi thnh (k hiu Ur) pha hn hp khi gi l vn tc ca hn hp kh (gas velocity). Vn tc ca sc chy rt quan trng trong s t chy v n c dng nh gi s mnh lit ca ngn la hay s mnh lit ca sc n. Hai vn tc ny cng li gi l vn tc ca ngn la (flame speed). Nu ngn la n nh (steady state) ngha l ngn la ng yn, vn tc ca ngn la bng khng.Chng ta nh ngha hai loi vn tc nh sau:a)Vn tc ca sc chy(burning velocity) l vn tc ca ngn la mc l hn hp kh t v KK. Dng t php thut ton, vn tc sc chy c th tnh c t ng biu din P-thi gian Hnh 6.b)Vn tc ca ngn lal vn tc m mc l ta c (nht) nh.Tc ca s chy ca mt loi ht rt quan trng v chng ta dng n chun on chy ca ht ( nguy him ca ht nu ht b chy n).

(a)(b)

Hnh7:M hnh v n (ngn la) Bunsen (hnh chp ly trong internet).6.S ri lon (turbulence)S ri lon rt quan trng trong s t chy hay ni mt cch khc, nu c s ri lon vn tc ca sc chy s tng ln hay sc chy hoc sc n tr nn mnh lit hn. gii thch cho iu ny, chng ta hy quan st th nghim ng-m ca ng di. Trong ng di cha hn hp cht t (dng kh hay rn) v khng kh (KK). Nng cht t trong KK trong phm vi c th xy ra phn ng n.Trng hp 1 (Hnh 8a v 8b): Mi ti u m ca ng (Hnh 8a, trng thi bt u t = 0 giy). V sc nng t ngn la (flame front), hn hp cht t xong (khi) ti ngn la s chuyn ng xuyn qua hn hp t xong v chuyn ng theo hng ra khi bnh (Hnh 8b, khi t = Dt giy). Hn hp cht t xong khng ng chm ti ngn la v ngn la c tip tc chy cho n khi khng cn hn hp cht t v KK cha chy cn li trong bnh. Ngn la c hai chiu (hnh trn) v di chuyn u. Trong trng hp ny ngn la di chuyn vi tc bng tc ca sc chy thnh lp (khng c s ri lon) (laminar burning velocity)Hnh 8:Th nghim ng-m ca ng di.Trng hp 2 (Hnh 8c v 8d): Mi ti u ng ca ng (Hnh 8c, t = 0 giy). Ngay lc bt u, ngn la vn cn dng hai chiu v bng vi vn tc ca sc chy thnh lp (khng c s ri lon). Hn hp trng thi ban u yn tnh (lng yn), khi va bt u chy th c hin tng khc xy ra, Ngn la nng ln v bt u pht ra nng lng cho hn hp kh va chy xong (khi). S gin n ca hn hp v nhit tng s y ngn la di chuyn v pha u m ca ng. Kh u ng pha sau ngn la b bt kn, bt buc hn hp kh b t quay ngc u li v chuyn ng vi vn tc ln hn vn tc ca sc chy thnh lp (khng c s ri lon) v s lm ngn la b bin dng. Hn hp kh (khi) by gi c s ri lon v lm ngn la cng tr thnh ba chiu. Din tch b mt ca ngn la tip xc vi hn hp cht t v KK (unburned gas) ln hn din tch ca ngn la dng hai chiu, nhiu nng lng pht sinh ra lm nng hn hp kh cha chy, hn hp kh cha chy nng hn, d bt mi chy hn, v s chy nhanh (nhiu) hn. Vn tc ca ngn la s bng vn tc sc chy cng vi vn tc ca hn hp kh b t (khi).Essenhigh v Woodhead (1959) [9] lm th nghim ny vi hn hp nt bn-khng kh trong mt ng bng king vi chiu di 5,2 m v ng knh bng 56 mm v 76 mm. H khm ph ra vn tc ngn la trong trng hp 2 (mi ti u ng) ln hn 20 ln so vi vn tc ngn la trong trng hp 1 (mi ti u m).Nh vy s ri lon rt quan trng trong s t chy.C rt nhiu ti liu ni v lin quan gia s ri lon v s t chy. Tc chy trong trng hp c s ri lon ln hn tc chy khng c s ri lon khong 2 4 ln cho cht t l cc ht rn (cht kh c th ln hn nhiu). C ngha l p sut tng t ngt nhanh hn 2 4 ln. p sut cng ln hn (khong 40%) trong trng hp c s ri lon [10].Khi chy n c th to ra s ri lon. S ri lon lm tng ln tc chy. Gii thch hi phc tp nn khng trnh by y.7.Nng lng ti thiu bt mi cho ngn laBao nhiu joule (1 joule = 2,77778 x 10-7kw-gi) ngn la c th bt u chy? Cu hi ny rt kh tr li v n ty thuc vo: Vt liu (bt than, ng hay g, v.v.). Bt kim loi cng c th chy th d nhm, ng. ln ca ht (ng knh bao nhiu, bao nhiu phn trm ht nh) Phn trm kh t trong ht. Th d trong than hay g c mt phn kh hydrocarbon s bay hi trc (khong 250 700oC) v nhng cht kh ny s d dng chy trc v mi phn cn li l carbon v cht bn. Nhit ca mi trng ri lon v.v.iu quan trng l chng ta phng h cc trng hp c th lm mi cho ngn la nh: La, kh (khi, khng kh, v.v.) nng Vt nng Chm in T trng (???) Hn x Tia lado hai vt rn chm vo gy ra v.v.. .Nn nh l cc htc th t chynu nhit tng ln. [2], [11] v [12] c nu rt nhiu d kin cho nhiu cc ht khc nhau. Bng 3 v 4 ch mt vi loi ht thng dng, p sut ti a (Pmax) v nhit ti thiu (Tmin) m cc ht t chyPmax(bar)Tmin(oC)

Bt m8,5

Bt go7,4490

Sa bt8,1460

C ph6,8 - 9,0470

Bt tht8,5540

Tr8,2510

Bt giy5,7 - 9,8490 - 580

G9,0500

Cao su7,5 - 8,5

Than bn (Brown coal)9,1420

Than Butiminous9,0590

Than Anthracite9,0610

B hng (trong ng khi)8,8 - 9,2760 - 840

Bng 3:Pmax: p sut ti a c th xy ra khi c hin tng n; Tmin: Nhit ti thiu m ht c th t bc chy m khng cn cc loi mi khc [2].Kim loi cng c th chy (Bng 4)Kim loiPmax(bar)Tmin(oC)

Manganese6,3330

Nhm10 - 12,5500 - 650

ng4,1390

St5,2580

Km6,0 - 7,3570 - 800

Bng 4:Pmaxv Tmincho mt vi loi kim loi tng gp [2]8.Nng ca cht t trong khng kh (hay oxygen)Cc ht c th chy khi c s hin din ca cht oxy ho nh khng kh (KK). Nhiu KK hay t KK qu cng khng th chy c. Nng ca cc ht nu xy ra hin tng chy n hon ton ty thuc vo loi ht (bt hay than hay kim loi, v.v.9. nhuyn (ng knh) ca ht biNh gii thch pha trn. Ht cng nh chy cng nhanh. iu kin chy l cc ht phi c iu kin tip xc vi khng kh.10.Cch phngCch hay nht l khng lm vic vi cht c th chy. iu ny khng th c v kim loi (ht nhm) khng chy nhng vi iu kin no s chy c v gy ra hin tng n con mnh lit hn cc ht chy c iu kin thng. Vi iu sau y nn lu : Khng cc ht bi bm trn tng, ng thng hi hay ng khi, v.v. v khi chy cc ht ny s tung ln do s ri lon v tham gia phn ng n. Nhiu loi ht (th d than ) c cha nhiu hydrocarbon nh CH4, C2H6, .v.v. cc hydrocarbon ny s thot ra khong t 150 300oC v n s d chy v s l vt mi cho cc ht. p sut ti a khong 5 10 ln p sut ban u. Nu chng ta sy vt liu p sut cao hn 1 bar (iu kin thng) th hy thit k bnh cha chu ng p sut 10 ln so vi p sut ban u. Phi thit k l thot hi (xem Hnh 9). Khi p sut trong bnh qu p sut m l thot hi c thit k, l thot hi s t ng m Nu qu trnh sn sut qu phc tp th phi c c vn thm ca ngi bit v vn ny.

Hnh 9:Bnh cha c l thot hi.Ti liu tham kho[1]Kees, van Wingerden (1995). The Safe of the Dust explosion in Process Industry. Research Programme 1996-1998, part 1, Ref.nr.:M-20-95/15, Christian Michelsen Research AS, Bergen, Norway (in Norwegian).[2]Eckhoff, R.K. (1991).Dust Explosion in the Process Industries. Butterworth-Heinemann Ltd, England.[3]Lemkowitz, S.M. (1996). Dust Explosion Behaviour and Explosion Risk. Course Dust Explosion, 30-31 May, 1996, Stockholm, Sweden.[4]VDI 2263 (1992). Dust Fire and Dust Explosions. Hazards - Assessment - Protective Measures. Verein Deutscher Ingenieure.[5]Bartknecht, W. (1981).Explosions: Course-Prevention-Protection. Springer-Verlag.[6]Hertzberg, M., Cashdollar, K.L., and Zlochower, I.A. (1986). Flammability Limit Measurements for Dust and Gases: Ignition Energy Requirements and Pressure Dependences.21st Symp. (Int.) on Combust., The Combust. Inst., PA, pp. 303-313.[7]Bradley, D., Chen, Z., and Swithenbank, J.R. (1988). Burning Rates in Turbulent Fine Dust-Air Explosions.22nd Symp. (Int.) on Combust., The Combust. Inst., PA, pp. 1767-1775.[8]Eckhoff, R.K. (1977). The Use of the Hartmann Bomb for Determining KstValues of Explosible Dust Clouds.Staub - Reinhalt. Luft,37, No.3, pp. 110-112.[9]Essenhigh, R.H., and Woodhead, D.W. (1959). Dust Explosions in Factories: Speed of Flame in Slowly Moving Clouds of Cork Dust. Safety in Mines Research Establishment, Minish of Power, Report No. 166.[10]Amyotte P.R., Chippett S., and Pegg M. J. (1988). Effects of Turbulence on Dust Explosions.Prog. Energy Combust. Sci., Vol.14, pp. 293-310.[11]Field P. (1982) Dust Explosions.Handbook of Powder Technology. Elsevier Scientific Publishing Company.[12]Institut fr Explosionsschutz und Sprengtechnik (1987).Brenn- und Explosions- Kenngrssen von Stuben. Erich Schmidt Verlag.