Ky Thuat Lo Hoi - GSTS Pham Xuan Vuong

B GIO DC V O TO TRNG I HC NNG NGHIP H NI

GS.TS. PHM XUN VNG (CH BIN) PSG.TS. NGUYN VN MUN

GIO TRNH

K THUT L HI

H NI 2007

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MC LCTrang Chng I. Khi nim v l hi 1. Nhim v, yu cu k thut, phn loi 1.1. Nhim v 1.2. Yu cu k thut 1.3. Phn loi 2. Cu to v nguyn tc lm vic 2.1. Cu to lin hp l hi 2.2. Cc b phn ca lin hp ni hi 2.3. B phn qu nhit 2.4. B phn hm nng nc 2.5. B phn hm nng khng kh 2.6. Nguyn tc lm vic ca l hi 3. Nhin liu v sn phm ca nhin liu 3.1. Thnh phn ca nhin liu 3.2. S chy ca nhin liu 3.3. Th tch khng kh l thuyt cn cho qu trnh chy 4. Phng trnh cn bng nhit v hiu sut thit b 4.1. Phng trnh cn bng nhit 4.2. Thit b nhit Chng II. Qu trnh chy v ch to l t 1. Qu trnh chy 1.1. Cc giai on ca qu trnh t chy nhin liu trong l t 1.2. Giai on sy kh v lm nng nhin liu 1.3. Giai on chy 1.4. Phn ng chy 1.5. Giai on to x 2. Phn loi v cu to l t 2.1. Yu cu k thut i vi bung la 2.2. Phn loi bung la (l t) Chng III. Qu trnh sinh hi, cc b mt truyn nhit 1 1 1 1 1 5 5 6 8 8 9 10 10 10 11 14 17 17 20 21 21 21 21 21 23 24 26 26 26 43

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1. B mt sinh hi v cch b tr 2. Tnh nhit thit b sinh hi 2.1. Phng trnh truyn nhit 2.2. Tnh nhit cc b mt truyn nhit i lu 2.3. H s truyn nhit 3. Ch nc v cht lng hi 3.1. Khi nim chung 3.2. Ch tiu cht lng nc 3.3. Cc bin php x l nc Chng IV. H thng thng gi 1. Nhim v ca h thng thng gi 2. Gii php thng gi Chng V. Vn hnh v bo dng 1. Mt s ch tiu kinh t k thut 1.1. Ch tiu kinh t 1.2. Ch tiu v ch vn hnh 2. Chn s lng ni hi v phn b ph ti gia cc l Ti liu tham kho

43 51 51 53 54 58 58 59 60 66 66 66 82 82 82 83 83 101

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Chng I : KHI NIM V L HI1 - NHIM V, YU CU K THT, PHN LOI 1.1. Nhim v: Nhim v ca l hi l chuyn ho nng lng t cc dng khc nhau khi b t chy thnh dng nng lng khc: nc nng, nc bo ho hoc hi qu nhit. Hi qu nhit l hi nhit v p sut cao. 1.2. Yu cu k thut. - Thit b sinh hi phi c nng sut hi cao (Tn/gi), hiu sut sinh hi ln. - Cht lng sn phm phi p ng yu cu sn xut: cht lng nc nng, hi bo ho hoc hi qu nhit. - Cu to ca thit b khng qu phc tp, s dng, bo dng v sa cha d dng. - Chi ph nhin liu ring thp, hiu sut l t cao. 1.3. Phn loi l hi. + L hi hin nay chia thnh hai loi chnh: loi sinh hi v loi sn xut nc nng. Tuy nhin cng c mt s l hi kim c hai chc nng ny. L hi loi sinh hi, th hin bng tn hi trong mt gi. Mt s l hi dng chuyn ho nng lng nhit thnh th nng ca hi, nn c th c trng bng cng sut (KW, MW). + Nng sut ca l hi phn thnh ba loi: loi nh ( 15 20 T/h); loi trung (160 220T/h) v loi ln (220 250T/h). Tuy nhin vic phn loi ny cng ch l qui uc, v gii hn gia cc loi cng cha tht chnh xc. p sut o bng tmtphe (atm).Trong h SI, n v o l Niutn trn mt vung (N/m2). H s chuyn i 1bar = 1.105N/m2 = 1,0196atm. + Nu phn loi theo p lc chia ra l hi p thp (< 9 atm); l hi p trung bnh (14 40 atm); l hi p cao (100 140 atm) v p sut tiu chun (255atm). Gii hn gia l hi p thp v l hi trung bnh ch l qui c. V nhit hi, biu din bng 0C (h SI) hoc 0K. Hi bo ho b t nng ti nhit 570 0C v cao hn na. L hi dng trong cng nghip, trong ngnh nng lng,... + Theo kiu l hi ngi ta c th phn ra: kiu tr ng, kiu ng nc ng c b mt bc hi c t nng v loi mn chn. Sau y gii thiu tm tt mt vi kiu l hi:

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a/ - L hi kiu tr ng: c v tr ngoi 2, thn tr bn trong 3, pha y c th lin kt qua tm m hoc gp mp tr bn trong. Pha trn c c 4, 5 dng hnh cu; lin

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vi bung khi 6 hoc h ng ng; qua kh v khi t bung la 1 vo ng khi 7. Nc a vo khong khng gian gia 2 v 3. Ti y nc bc hi di tc dng ca nhit, tp trung gia 4 v 5; thot qua ng dn hi. Trong qu trnh lm vic nc c cp lin tc vo bnh. Loi thit b ny c nng sut hi t 0,2 1 T/h; sn xut hi bo ho c p sut ti 9 atm.

a)

b)

c)

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Hnh 1.2. S cc kiu lin hp l hi. a L hi tr - ng b Loi ng nc thng ng c Kiu mn chn - L hi kiu ng nc ng (Hnh 1.2b). Gm hai trng ngang 1, 4 t pha trn nhau; lin kt vi ng nc si 2, 3 ng knh 51 60 mm. Bao ph bn ngoi h theo chiu dc, ngang dng kh khi, truyn nhit vo nc bng i lu. Nc cung cp vo phn trn trng 1 l hi. T y nc c un nng ng i xung 3 ca h thng l hi, v hng v trng di 4. Ra khi trng nc c hm nng mnh, nh ng 2 quay tr v trng trn. Di tc dng ca nhit, truyn qua thnh ng, lm nc bc hi. Lc kch thch gy ra chuyn ng ca nc theo chu k tun hon l do s sai khc v mt ca nc trn v di. Hn hp nc np y ng ln. Ti trng trn ca l hi, hi tch khi nc i ra khi trng, nc quay tr li ng xung. L hi kiu ng nc ng c nng sut hi 2,5 50 T/h, p sut hi 14 40 atm. Hi bo ho hoc hi qu nhit ti 250, 370, 425 v 440 0C. b/ L hi kiu mn chn (Hnh 1.2c). Khc nhau ch yu l b mt hm nng kiu mn chn 1, lin hp vi bung l t, v nhin liu rn chy dng bt. Loi hnh ny, khi lm vic nc c bc hi ng thi lm gim b mt trao i nhit. Loi ny dng cho cc trm in. Nng sut hi t 35 2500 T/h sn xut hi qu nhit c p sut t 40 255 atm, nhit 440 585 0C. Trong l hi c chu trnh t nhin, nc c cung cp bi bm 1, qua b hm nng nc 2 vo trng trn 3, nc c bc hi trong chu trnh 4, 5 (Hnh 1.3a). Hi to ra trng 3 i vo b qa nhit 6, v ti ni tiu th.

Tiu th

Nc cung cp

a)

b)

c)

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Hnh 1.3. S chuyn ng ca nc, hn hp hi v hi ca lin hp l hi. a - Chu trnh t nhin b - Chu trnh cng bc nhiu ln c - Kiu thng L c chu trnh cng bc nhiu ln (Hnh 1.3b), tng t loi chu trnh t nhin, nc cp vo trng 3, chuyn ng ca nc theo chu trnh khp kn 4, 5, nh bm 7. Tip theo hi t trng vo b qu nhit, sau i ti ni tiu th. Trong chu trnh thng (Hnh 1.3c), nc cung cp qua b hm nng nc, ging s trc, nhng chu trnh bc hi khp kn khng c. B mt t nng bc hi 4, 5 l b mt ko di b hm nng nc 2 v cng trc tip vo b mt t nng b qu nhit 6. Nh vy, qu trnh bc hi ca nc ch mt ln trong b mt bc hi nng. Bng 1.1. Kiu l hi Nng sut hi (T/h) 0,2; 0,4; 0,7; 1,0 2,5 4,0; 6,5; 10 E - Chu trnh t nhin vi b qu nhit, nhng hi khng qu nhit 15; 20 4,0; 6,5; 10; 15; 20 6,5; 10; 15; 20; 25; 35; 50; 75 60; 90; 120; 160; 220 160; 210; 320; 420; 480 320; 500; 640 250; 320; 500; 610 150; 1600; 2500 24 40 100 140 p sut tuyt i ca hi (atm) 9 14 Nhit hi (0C) Hi bo ho Hi bo ho Hi bo ho hoc qu nhit 250 Hi bo ho hoc qu nhit 370; 425 440 540 570 Nhit hi sau khi qua b qu nhit (0C) Nhit nc cung cp (0C) 50 80 100 100 145 215 230

EP - Chu trnh t nhin vi b qu nhit v hi c qu nhit trung gian PP - Chu trnh thng vi b qu nhit v hi c qu nhit trung gian

140 140 255

570 570 585

570 570 570

230 230 260

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2 - CU TO V NGUYN TC LM VIC. 2.1. Cu to lin hp l hi. Hin nay, lin hp l hi l loi thit b tng i phc tp, ngoi phn to hi, cn c kh nhiu b phn ph tr. a/ - L hi t th cng. y l loi l hi n gin gm cc b phn chnh: Trng (bao hi) 1 cha nc hi v cng l b mt truyn nhit; van hi chnh 2 iu chnh lng hi cung cp. Van cp nc 3 cp nc vo ni hi; ghi l 4 c nh, nhin liu chy, ng thi c khe h khng kh cp vo t chy nhin liu v thi tro, x ; ca gi 7 v ca cp nhin liu 8; ng khi 9. - L hi t phun. y l loi ni hi c th dng nhin liu lng (mazt), nhin liu kh (kh thin nhin, kh l cc,...) nhin liu rn nghin thnh bt. L hi t phun gm cc b phn: trng 1, van hi chnh 2, ng nc cp 3, vi phun 4, bung la 5, phu tro lnh 6 dng lm ngui cc ht tro x khi thi ra ngoi trng hp thi x kh, ging x 7, bm nc cp 8, ng khi 9, b sy khng kh 10, qut gi 11, b hm nc 13, dn ng nc xung 14, dn ng nc ln 15, dy phestn 17, b qu nhit 18 (Hnh 1.5.a)

Hnh 1.4. S l t th cng. b/ - L hi ghi xch (Hnh 1.5b). Thuc loi l hi cng sut nh hoc trung bnh. Cu to gm: trng 1, van hi chnh 2, ng cp nc 3, ghi l dng xch 4, bung la 5, hp tro x 6, hp gi 7 cp gi cp 1 qua ghi cho lp nhin liu trn ghi, phu than 8, ng khi 9, b sy khng kh 10, qut 11, qut khi 12, b hm nc 13, dn ng nc xung 14, ng gp di 15, dn ng nc ln 16, dy phestn 17 v b qu nhit 18. 2.2. Cc b phn ca lin hp ni hi - B mt bc hi c t nng.

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H thng b mt bc hi c t nng xc nh theo kiu lin hp l hi. H thng bc hi ca l hi c chu trnh t nhin. (Hnh 1.6 v 1.7) + B mt bc hi c hm nng ca l hi ng nc thng ng bao gm: chm ng nc si 2, trng trn 1 v trng di 3, mn chn la 6. Nc t trng qua ng i xung 7, vo ng gp 5, v h thng ng ni 4. Trng ch to bng thp ng knh 1000 1500 mm. L hi loi ny lm vic p sut 14 40 atm. ng gp c ng knh ti 219 mm.

a)

b) Hnh 1.5. S l hi. a/ Loi t than phun. b/ L hi ghi xch. + B mt bc hi hm nng ca l hi kiu mn chn gm: trng 2, h ng c mn chn 6, 7 vi ng gp mn chn 9, 10 di v 4, 5 trn; H thng ng xung 8 v h thng ng lin kt 3.

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Trng ch to bng phng php hn, y dp. ng knh trng 1200 1800 mm, chiu di gn 18 m. Chiu dy thnh trng khi p sut hi 100 atm l 90 100 mm; khi p sut hi 140 atm th chiu dy trng ln hn. Chu trnh tun hon t nhin trong ng nc si v mn chn l do tc dng ca lc trng trng; do sai khc mt nc v hn hp hi nc trong mi trng hp dn. Nu trong vng khp kn, xy ra hin tng, mt h thng ng ny nng hn h thng ng kia, hoc mt h thng ng nng, mt h thng ng khng nng, s lm cho nc chuyn ng.Nc trong ng nng dng ln, trong ng ngui h xung. Nguyn nhn do mt nc trong ng nng gim v nhit tng. Kt qu l p sut ca nc phn di vng tun hon khng nh nhau, pht sinh chuyn ng. + H thng bc hi ca l hi kiu chu trnh cng bc nhiu ln. ng knh ng khng ln, khong 42 32 mm. Chu trnh cng bc do tc dng ca ngoi lc l bm. S ln trong l hi kiu ny khong 5 10 ln. c im lm vic ca l hi loi ny l phn phi nc khng u cho cc ng song song. + L hi c chu trnh thng, chuyn ng ca nc v hn hp hi tng t loi l hi cng bc nhiu ln. Tuy nhin, y nc v hn hp hi ch i qua b phn bc hi mt ln. 2.3. B phn qu nhit B phn qu nhit thng khng c trn l hi cng nghip, v ch dng vi hi khng qu nng. B phn ny dng trong l hi nng lng, cn hi c nhit cao v p sut ln. Tng nhit hi lm tng entalpi; nng cao p sut hi li lm gim entalpi. Hin nay c hai loi b qa nhit: loi i lu v loi phi hp. Loi i lu thng c mt s hng ng t tch ring khi l. Loi phi hp cng tng t trn, nhng li c phn chu tc ng ca bc x nhit hoc na bc x t trong l. B qu nhit lm bng cc ng thp c ng knh ngoi 28 42 mm. Tc hi trong ng chn t iu kin ch nhit n nh ca n. Thng tc khi i vi b qu nhit th nht 500 1200 Kg/m2.h. Khi chn tc chuyn ng ca hi, cn lu sc cn thu lc ca b qu nhit khng c vt qu 10% p sut lm vic ca hi. 2.4. B phn hm nng nc B phn hm nng nc nhn 12 18% lng nhit chung. B phn hm nng nc c hai kiu: kiu ng gang c g v kiu ng thp nhn. Kiu ng gang c g thng b tr l hi nng sut hi khng ln v c p sut ti 24 atm. Loi ng thp c th b tr trn l hi vi bt k nng sut hi v p sut no (40 atm hoc cao hn).

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Kiu ng gang gm h thng ng gang c g v mt s hng ngang. S lng ng trong hng ngang xut pht t yu cu i hi tc chuyn ng ca sn phm chy (6 9 m/s trong ti trng tiu chun). S hng ngang xut pht t yu cu din tch b mt hm nng ca thit b. Nhit ca nc vo b phn hm nng cn vt qu nhit ng sng ca khi, nhng khng nh hn 100C, loi tr kh nng ngng t hi nc trong thnh phn ca khi v kt ta m trn ng. Nhit cui cng ca nc c hm nng trong ng gang c g, vi l cung cp nc lin tc, l c th tch nc trong trng nh, khi c b phn iu chnh t ng, cn thp hn nhit bo ho p sut cho v khng c nh hn 200C. 2.5. B phn hm nng khng kh B phn hm nng khng kh nhn c gn 7 15% nhit hu ch t l hi. B phn hm nng khng kh chia lm hai loi: loi thu hi nhit v loi hon nhit. Loi thu nhit t khi vo khng kh khng i qua thnh phn chia khi v khng kh. Loi hon nhit, nhit truyn t gch l hon nhit bng kim loi, c t nng theo chu k bi kh nng, tch t v truyn cho khng kh lnh. B phn hm nng khng kh loi thu hi nhit l mt h ng thp mng t song song hn vo tm bn. ng ng knh 25 51 mm, thnh dy 1,25 1,5 mm. ng sp t theo hnh bn c. Khong cch gia cc cnh ngoi ng k nhau 9 15 mm. Khi i trong ng. t nng khng kh bn ngoi ng theo chiu ngang ng. Tc khi 10 14 m/s. Tc khng kh nh hn hai ln tc khi.

Hnh 1.6. S nguyn l lm vic v cu to ca l bao hi.

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1-bao hi; 2-phn cha nc ca bao hi; 3-phn cha hi ca bao hi; 4-bung la; 5vi phun; 6-ng nhin liu ti; 7-cc ng dn t xung quanh bung la sinh hi; 8-ng phestn; 9-ng xung; 10-ng gp di ca dn ng; 11-cp mt ca b hm nc; 12-cp hai ca b hm nc; 13-ng dn a nc t b hm nc vo bao hi; 14-ng dn hi bo ho t bao hi ti b qu nhit; 15-cp mt ca b qu nhit; 16-b gim n iu chnh nhit hi qu nhit; 17-cp hai ca b qu nhit; 18-cp mt ca b sy khng kh; 19-cp hai ca b sy khng kh; 20-ng dn khng kh vo bung la; 21-ng dn khng kh nng ti my nghin; 22-tng bo n ca l; 23-bung qut i chiu dng khi; 24-phn ng khi t cc b mt t i lu; 25-ging thi x; 27-ht khng kh nng t nh l; 28-qut gi; 29-kh bi; 30-qut khi; 31-ng khi. 2.6. Nguyn tc lm vic ca l hi Khng kh nng cng bt than phun vo bung la qua vi phun 5 v chy, truyn nhit lng cho cc dn ng b tr xung quanh bung la. Nc trong ng c t nng, si v sinh hi. Hn hp hi nc sinh ra c a ln bao hi. Bao hi dng tch hi ra khi nc. Phn nc cha bc hi c trong bao hi c a tr li dn ng, qua cc ng xung b tr ngoi tng l, c trng lng ring ln hn hn hp hi nc trong cc dn (v khng c hp thu nhit) to nn chnh trng lng ct nc. Do mi cht chuyn ng tun hon t nhin trong mt chu trnh kn. Hi ra khi bao hi c chuyn ti b phn qu nhit to thnh hi qu nhit, c nhit cao. Khi thot khi b phn qu nhit, nhit cn cao, do b tr b phn hm nc v b phn sy khng kh tn dng nhit tha ca khi. Nhit khi thi ra khi l ch cn 120 1800C. Qut khi ht khi x ra ngoi ng khi. trnh bi cho mi trng xung quanh, khi trc khi thi ra c qua b phn tch bi. 3 - NHIN LIU V SN PHM CHY CA NHIN LIU Nhin liu s dng ph bin hin nay gm: Nhin liu rn: than , than nu, than bn, g, ... Nhin liu lng: du th, mazt, xng, ... Nhin liu kh: kh l cao, kh l cc, kh ga, kh t nhin, ... Than (than m, than gy, than ngtraxt) cht bc thay i t 2 55%. Than bn l dng ban u ca thc vt chuyn ho thnh than , m 30 90%, tro 7 15%, cht bc 70%. Nng sut to nhit 8500 12000 KJ/Kg. Than nu l dng tip theo ca than bn, m 18 60%, tro 10 50%, cht bc 30 55%, nng sut to nhit 12000 16000 KJ/Kg.

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G l nhin liu hu c tr nht, thnh phn gm ccbon chim 50%, Hyr khong 6%, xy khong 43%, Nit khong 0,5 1%, tro 0,5 2%, cht bc 85%, m thay i trong phm vi rng. Du mazt c thnh phn ccbon 80 85%, hyr t 8 10%, nhit tr khong 39000 40000 KJ/Kg. Du l nhin liu d bt la, d chy, nhit tr cao, t tro (0,1%). Kh t gm kh thin nhin v kh ga (nhn to). Kh thin nhin ch yu l kh mtan (CH4), nhit tr khong 35000 KJ/m3 tiu chun. Kh ga gm kh l cc, kh l cao, kh l ga. 3.1. Thnh phn ca nhin liu Trong nhin liu ni chung bao gm cc cht: ccbon, Hyr, lu hunh, xy, tro v m. Ccbon l thnh phn chy ch yu trong nhin liu. Nhit tr ca ccbon khong 34150 KJ/Kg. Lng ccbon trong nhin liu cng cao th nhit tr ca n cng cng cao. Hyr l thnh phn chy quan trng ca nhin liu. Nhit tr khong 144500 KJ/Kg. Lng hyr trong nhin liu rt t. Lu hunh l thnh phn chy trong nhin liu. Trong than lu hunh tn ti di ba dng: Dng lin kt hu c, khong cht v dng lin kt sunfat. Hai dng u c th tham gia qu trnh chy. Dng th ba (lu hunh sunfat) khng tham gia qu trnh chy m chuyn thnh tro ca nhin liu. Nhit tr ca lu hunh khong 1/3 nhit tr ca ccbon. Khi chy, lu hunh to thnh kh SO2 hoc SO3. Kh SO3 gp hi nc to thnh axt H2SO4. Kh SO2 thi ra ngoi l kh c, do lu hunh l thnh phn c hi ca nhin liu. Bng 1.2 l bng thnh phn ca mt s loi nhin liu. 3.2. S chy ca nhin liu Chy l phn ng ho hc gia cc thnh phn chy c c trong nhinliu vi xy cha trong khng kh. Trc khi bt u chy, nhin liu phi t ti nhit bt la: than l 400 5000C, than nu l 250 4500C, g 3000C, than bn 2250C, than cc 7000C, kh ga 700 8000C, kh l cao 700 8000C, du m 5800C, hyr khong 6000C. Khi nhin liu chy hon ton, hyr t do kt hp trc tip vi ccbon cho ta hyrccbua nh (CH2) hoc nng (C2H4). Hai kh ny d dng bt la v chy vi xy ca kh chy cho ta kh CO2 v hi nc. Khi nhin liu chy khng hon ton, kh cha chy v kh x t l hi l xtccbon (CO) v hyrccbua. Nghin cu kh x cho php nh gi cht lng ca s chy. Mun chy hon ton, cn phi cung cp mt lng khng kh ln, c ngha l xy. Hn hp gia khng kh v nhin liu rt kh hon ho, v th cn phi cp tha

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mt lng khng kh cao hn l thuyt. Ngi ta gi l tha khng kh. Mt tha khng kh qu ln, li l iu bt li, v n lm gim nhit ca l. Khi tnh nhit cn phi xc nh th tch lng khng kh l thuyt cn cho qa trnh chy, thnh phn v s lng sn phm chy. Nhng s liu ny c th xc nh nh cc phng trnh phn ng ho hc ( ng vi 1 kg nhin liu rn , lng hoc 1Nm3 nhin liu iu kin tiu chun). Phng trnh chy hon ton C: C + O2 = CO2 (1) 1mol C + 1 mol O2 = 1 mol CO2 12kg C + 32kg O2 = 44kg CO2 1 kg C + 2,67kg O2 = 3,67kg CO2 Nh th, t chy hon ton 1 kg C cn 2,67kg O2 v to thnh 3,67kg CO2.

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Bng 1.2. Thnh phn nhin liu rn. Nhin liu C H2 O2 + N2 (1) S H2O SNng sut to nhit thp Kcal/Kg (2)

A1 (2)

G1 (2)

G2 (2)

G3 = G1 + G2 (2)

Kmax

Than 79 4,5 7 1 2,5 6 7500 8,13 7,93 0,54 8,47 18,6 Westphalie Than Sarre 74 4,5 10 1 3,5 7 700 7,58 7,4 0,55 7,95 18,65 Than Anh 75 4,5 8 1 5,5 6 7100 7,73 7,54 0,57 8,11 18,5 Bnh than 8,2 4,2 3,7 1,2 1,7 7,2 7750 8,44 8,23 0,49 8,72 18,6 Westphalie Than cc 84 0,8 3,4 1 1,8 9 7000 7,72 7,7 0,11 7,81 20,35 Than nu th 23,06 1,87 12,07 1 59,28 2,72 1940 2,24 2,16 0,45 3,11 20,00 Bas-Rhin Than nu th 37,05 2,88 4,86 1 42,31 6,9 3275 3,83 3,74 0,85 4,59 18,5 Bohme Than bn nn 44 4,5 25 0,5 20 6 3800 4,38 4,3 0,75 5,05 19,7 G kh 40 4,5 37 0,5 16 1,5 3500 3,6 3,61 0,7 4,31 20,7 83,5 14 2,5 0,5 16 1,5 10000 11,17 10,41 1,57 11,98 15,00 Du = 0,87 89 7 2,8 0,2 0,2 0,1 8875 9,8 9,46 0,79 10,25 17,50 Hc n = 1,05 Ch dn: (1) Chp nhn N2 = 1%; (2) Trng hp t 00C v 1,012 bar, ngha l bng (Nm3); A1 Lng khng kh cn thit ( bng N.m3/Kg nhin liu); G1 Lng khng kh kh l thuyt ( bng N.m3/Kg nhin liu); G2 Lng hi nc ( bng N.m3/Kg nhin liu); G3 Lng kh l thuyt ( bng N.m3/Kg nhin liu); Kmax Hm lng kh CO2 l thuyt ( bng N.m3/Kg nhin liu); N - iu kin tiu chun; Khi gi u h s tha khng kh th: Lng khng kh thc l: A = u.A1 (Nm3); Lng kh thc : G = G3 + A A1 (Nm3) K K Hm lng thc ca kh CO2. H s tha khng kh u = max K

16


Bng 1.3 Nhin liu H2 CH4 C2H4 CO H2O N2 CO2 O2 Nng sut to nhit thp Kcal/N.m3

Kh ga ca than nu th - Trch t 10 2 0,5 22 57 8,3 0,2 1170 nhin - Vi thi 15 2 0,5 24 51 7,3 0,2 1355 Ca bnh than nu - Trch t 10 2,5 0,5 27 55 4,8 0,2 1360 nhin - Vi thi 15 2,5 0,6 31 47 3,7 0,2 1600 Ca than - Trch t 8 1,5 0,2 24 59 7,1 0,2 1093 nhin - Thi 12 2,0 0,2 28 53,6 4,0 0,2 1365 Kh l cao 3 27,5 5 54,5 10 8501150 Kh l cc 55 32 2,3 7 1 1,5 10 35004500 Kh t nhin 88,9 1,3 9478 Nhn xt: Thnh phn cc cht ny rt bin ng, c bit kh l cao v kh ga. Kh t nhin thnh phn chnh l mtan (CH4). Ta bit khi lng ring ca xy o2 = 1,428 kg/Nm3, ca kh ccbnic l = 1,964kg/Nm3. Thay vo phng trnh trn (1) ta c: 1kgC + 1,866Nm3O2 = 1,866Nm3CO2 Phng trnh chy ccbon khng hon ton : 1 O2 = C + CO 2 Tng t trn ta c 1kg C + 0,933 Nm3O2 = 1,866Nm3 CO Phn ng chy ca S v H2 nh sau: 1 O2 = H2O H2 + 2 1kg H2 + 5,6Nm3 O2 = 11,2Nm3H2O (2) SO2 S + O2 = 3 3 1kg S + 0,7Nm O2 = 0,7Nm SO2 i vi nhin liu kh n v o lng l Nm3. 1 O2 = H2O H2 + 2 22,4Nm3 H2 + 11,2Nm3 O2 = 22,4Nm3 H2O

17


1Nm3H2 + i vi CO ta c :

0,5Nm3O2 = CO +

1Nm3H2O

1 O2 = CO2 2 1Nm3 CO + 0,5Nm3 O2 = 1Nm3 CO2 Vi lu hunh S 1Nm S3

SO2 + O2 = 3 3 + 1Nm O2 = 1Nm SO2

Vi mtan (CH4) 2O2 = CO2 + 2H2O CH4 + 3 3 1Nm CH4 + 2Nm O2 = 1Nm CO2 + 2Nm3 H2O3

Vi ccbuahyrn n CmHn + m + O2 = mCO2 + H2O 2 4 n n 1Nm3CmHn + m + Nm3O2 = mNm3O2 + Nm3 H2O 4 2

Vi hyrsunfua H2S + 1 Nm3 H2S + 3 O2 = SO2 + H2O 2

3 Nm3 O2 = 1Nm3SO2 + 1 Nm3H2O 2 3.3 Th tch khng kh l thuyt cn cho qu trnh chy Cn c vo cc phng trnh chy trn, ta c th xc nh c lng xy cn thit cho qu trnh chy: C lv S lv H lv O lv Nm3/Kg 0,93 VO2 = + 0,7 + 5,6 100 100 100 100 1,428 Trong khng kh, xy chim 21%, Nit chim 79%. Do th tch khng kh cn thit t chy 1Kg nhin liu (rn, lng) l: 1 1 C lv S lv H lv O lv VO2 = 0, 933. + 0, 7 + 5, 6 21 0, 21 100 100 100 100 1, 428

Vkk =

Hoc

Vkk = 0,0889 C lv + 0,375 S lv + 0,265 H lv 0,0333 O lv i vi nhin liu kh:

[

(

)

]

Nm3/Kg.

18


n Vkk = 0,04760,5CO + 0,5H 2 + 2CH 4 + 1,5H 2 S + m + C m H n O2 Nm3/Kg 4 Th tch sn phm chy: Trong khi ca qu trnh chy nhin liu hu nh lun c sn phm chy hon ton v sn phm chy khng hon ton. gim bt nh hng ca chy khng hon ton, thng khng kh c cung cp vi tha nht nh. Ngi ta gi l h s khng kh tha: Nhin liu kh:

=

1 79 O ( 0,5CO + 0,5 H 2 + 2CH 4 ) 1 2 21 100 RO2 O2 H 2 CH 4t Vkk = >1 Vkk

Nhin liu rn: =

t 0, 79 Vkk = 0, 79 Vkk

1 O2 0,5CO 79 1 21 100 RO2 O2 CO

Trong : Vkkt l th tch khng kh thc t (Nm3/Kg) t chy 1Kg nhin liu. Trong chy l thuyt ( = 1) trong sn phm chy tn ti CO2, SO2, N2 v hi nc. i vi khi kh ta c: VKKh = (Vco2 + Vso2 + VN2) Nm3/Kg. Thng khi phn tch khi CO2 v SO2 thng c xc nh chung, nn k hiu chng bng RO2. VRO2 = Vco2 + Vso2 VRO2 = 1,866 C lv + 0,375 S lv 100

Nit khng tham gia qu trnh chy, v th trong khi lun tn ti. Ta cn bit rng nit trong nhin liu khi chy chuyn vo khi di dng t do, mt khc nit li c mt trong khng kh i vo l hi. Th tch nit ng vi lng khng kh l thuyt a vo bng 0,79Vkk v theo nhin liu l Kg/Nm3) Th tch l thuyt ca nit trong khi l:N lv 1 , (N2l khi lng ring ca nit = 1,251 100 N2

19


N lv 1 VN 2 = + 0, 79Vkk Nm3/kg 100 1, 251

VN2 = 0, 008 N lv + 0, 79Vkk

Hm lng nit trong nhin liu rt nh, c th b qua: v vy th tch l thuyt ca nit trong khi bng VN2 = 0, 79Vkk . Th tch khi kh l thuyt:VKKh = 0, 01866 ( C lv + 0,375S lv ) + 0, 79Vkk Lng hi nc c trong khi gm: do xy ho hyr, do m ca nhin liu, m khng kh, do hi nc dng phun du mazt khi t n . Vy th tch l thuyt ca hi nc l:VH 2O = 0,112 H lv + 0,124W lv + 0, 0161VKK + 1, 24G

(Nm3)/kg;

Trong G l lu lng nc phun mazt thnh bi (0,3 0,35 kg hi nc /kg mazt). i vi nhin liu kh, th tch l thuyt cc sn phm chy:

VRO2 = 0, 01( CO2 + CO + CH 4 + H 2 S + ( Cm H n ) ) VN 2 = 0, 79Vkk + 0, 01N 2 n VH 2 0 = 0, 01 H 2 + 2CH 4 + Cm H n +0,124d + 0,0161 Vkk 2 Trong CO2, CO, CH4, H2S, CmHn , H2, N2 tnh theo phn trm so vi th tch cc kh trong nhin liu; d m ca nhin liu kh (g/Nm3).t VH 2O = VH 2O + 0, 79 ( 1) Vkk t VH 2O = 0,112 H lv + 0, 0124W lv + 1, 24G + 0, 0161Vkk

Th tch hi nc thc t

Th tch khi thc t:

Vk t = VKKh + V t H 2O

Entalpi ca khng kh v sn phm chy . Entalpi ca khi thc t ng vi mt 1kg hoc 1Nm3 nhin liu:

20


I k t = I k + ( 1) I kk + I H 2O + I tro

(KJ/Kg hay KJ/Nm3)

y:

I kk - entalpi khng kh l thuyt Ikk = Vkk.Ckk.tI H 2O - entalpi ca phn hi m do khng kh a vo I H 2O = 0, 0161( 1) Vkk CH 2O t

Itro Entalpi ca tro: I tro y: A ab Alv = ab Ctro t 100

- tro ca nhin liu - T l tro ca nhin liu phn phi theo khi .

C tro - T nhit ca tro nhit t. (Bng 1.4)Bng 1.4. Entalpi ca Nm3 cc kh v ca 1kg tro. (C.t) co2, Nhit , (C.t) N2, (C.t) kk , 0 3 3 kJ/ m tc kJ /m3tc C kJ/m tc100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 129,95 261,24 394,89 531,20 670,90 813,36 958,86 1090,56 1256,94 1408,70 1562,55 1718,16 1874,86 2032,52 2191,50 2351,68 2512,26 2674,26 2836,32 3000,00 3163,02 3327,50 3492,32 3658,08 3823,00 170,03 357,46 558,81 771,88 994,35 1224,66 1431,07 1704,88 1952,28 2203,50 2458,39 2716,56 2976,74 3239,04 3503,10 3768,80 4035,31 4304,70 4573,98 4844,20 5115,39 5386,48 5658,46 5930,40 6202,75 129,58 259,92 392,01 526,52 683,80 804,12 947,52 1093,60 1239,84 1391,70 1543,74 1697,16 1852,76 2028,72 2166,00 2324,48 2484,04 2643,66 2804,02 2965,00 3127,32 3289,22 3452,30 3615,36 3778,50

(C.t) H20, kJ / m3tc151,02 304,46 462,72 626,16 794,85 968,88 1148,84 1334,40 1526,13 1722,90 1925,11 2132,28 2343,64 2559,20 2779,05 3001,76 3229,32 3458,34 3690,57 3925,60 4163,04 4401,98 4643,47 4887,60 5132,00

(C.t) r , kJ/ kg81,0 169,8 264 360 458 560 662,5 768 825 985 1092 1212 1360 1585 1758 1880 2065 2185 2385 2514 2640 2762

21


4 PHNG TRNH CN BNG NHIT V HIU SUT THIT B4.1. Phng trnh cn bng nhit

Quan h gia lng nhit thu vo v lng nhit chi ph gi l s cn bng nhit. Trong tnh ton nhit, s cn bng nhit s dng cc s liu nh mc xc nh chi ph gi tnh ton ca nhin liu i vi lin hp l hi thit k. Lng nhit sinh ra khi t chy nhin liu gm hai phn: Phn hu ch v phn tn tht. Phn hu ch s dng t nng nc sinh thnh hi vi cc thng s cho.Phn tn tht l phn mt i trong qu trnh lm vic ca l. ng vi 1 kg nhin liu rn, lng hoc 1Nm3 nhin liu kh chy trong l iu kin n nh, ta c phng trnh cn bng nhit tng qut: Qcc = Q1 + Q2 + Q3 + Q4 + Q5 + Q6 (kJ/kg) y: Qcc - lng nhit cung cp (kJ/kg) Q1 - lng nhit hu ch (kJ/kg) (kJ/kg) (kJ/kg) Q2 - tn tht nhit do khi thi ra ngoi

Q3 - tn tht nhit do chy khng hon ton v ho hc (kJ/kg) Q4 - tn tht nhit do chy khng hon ton v c hc Q5 - tn tht nhit ra mi trng do to nhit Q6 - tn tht nhit do x mang ra ngoi Theo phn trm ta c:Q Q Q Q1 Q Q 100 + 2 100 + 3 100 + 4 100 + 5 100 + 6 100 = 100 % Qcc Qcc Qcc Qcc Qcc Qcc

(kJ/kg)

(kJ/kg)

+ Lng nhit cung cp: Qcc = Qtlv + Qnl + Qkkn + QP (kJ/kg) , (kJ/Nm3) y: Qtlv nhit tr thp ca nhin liu Qnl - nhit vt l ca nhin liu Qnl = Cnl.tnl Cnl t nhit ca nhin liu (KJ/Kg0C)

22


Cnl = C k nl

100 W lv W lv + 4,184 100 100

(KJ/Kg0C)

Cknl t nhit ca nhin liu kh. Nhit lng do khng kh c sy nng nh ngun nhit ngoi:n ' Qkk = kk Vkk ( Ckk Tkk )n ( Ckk Tkk )l

kk - H s khng kh tha u vo b sy khng kh

( Ckk Tkk ) nv u lnh.

v (Ckk.Tkk)l nhit v t nhit ca khng kh u nng

Lng nhit do hi phun vo l hi: y

Q p = G p (i p 2500)

GP lng hi tiu hao ng vi 1 kg nhin liu iP - entalpi ca hi. 2500 entalpi ca hi trong khi.

+ Lng nhit hu ch khi khng dng hi bo ho, khng c b qu nhit trung gian Q1 = y : D B sn lng hi ca l (Kg/h) - lng nhin liu tiu hao (Kg/h) D (iqn inc ) B

iqn, iqc - entalpi ca hi qu nhit v ca nc cp . +Tn tht nhit do khi mang i:q Q2 = ( I th I kkl ) 1 4 100 y: Ith entalpi ca khi thi . Ith=Vth.Cth.trh Ikkl entalpi ca khng kh lnh a vo l . Ikkl = th.VKK.CKK.tkkl

23


q4 tn tht nhit do chy khng hon ton v c hc (%) + Tn tht nhit do chy khng hon ton v ho hc. Cng thc gn ng Q3 =3,2.CO y: - h s khng kh tha ti im xc nh CO. + Tn tht nhit do chy khng hon thon v c hc.Q4 = 32600 kx kb A lv ax + ab 100 100 k x 100 k b

y: kx, kb- t l phn trm thnh phn cht chy trong x, trong tro bay ax, ab t l tro ca nhin liu phn phi theo ng x v theo khi. + Tn tht nhit do to nhit ra mi trng xung quanh. Mt ngoi l c nhit cao hn mi trng, do lng nhit to ra bng i lu Q5. X c nh theo h s to nhit i lu v din tch mt ngoi l, chnh nhit . + Tn tht nhit do x mang ra. X thi ra thng c nhit cn kh cao do gy tn tht nhit do x mang ra. Q6 = ax vi l ghi4.2 Hiu sut thit b

Alv CX t X 100

tx 600 0CQ1 100 0 0 . Qcc

=t Ta c:q1 =

(a)

Q Q1 100 0 0 , q 2 = 2 100 0 0 L Qcc Qcc

= q1 100 (q 2 + q3 + q 4 + q5 + q6 ) 0 0

(b)

Xc nh theo phng trnh (a)gi l phng php cn bng thun. Phng php xc nh theo phng trnh (b) l phng php nghch . Xc nh l hi theo phng php thun kh khn v kh xc nh chnh xc lng nhin liu tiu hao ca l. Cc l hi ln thng dng phng php nghch

24


xc nh hiu sut l. Khi xc nh c , ta c th xc nh c lng nhin liu tiu hao: B= Q1 100 Qcc (Kg/h)

Cu hi n tp chng 1:

1. Phn bit c im cu to cc loi l hi s dng trong thc t? 2. c im cu to v nguyn tc lm vic ca l hi? 3. Trnh by cc phn ng chy ca nhin liu: Chy hon ton v chy khng hon ton? 4. Trnh by phng trnh cn bng nhit v hiu sut nhit ca thit b?

25


Chng II : QA TRNH CHY V CU TO L T1 QU TRNH CHY Chy l mt qu trnh xy ho hon ton v nhanh chng cht t, din ra nhit cao ng thi sinh nhit. c tnh chy ca nhin liu trong tng trng hp ph thuc nhiu yu t: Loi nhin liu t, phng php t, c tnh kh ng ca qu trnh, ....vv1.1. Cc giai on ca qu trnh t chy nhin liu trong l t

Qu trnh chy ca nhin liu trong bung la xy ra rt phc tp, n gin ho chng ta c th chia ra lm 4 giai on: i vi nhin liu rn : - Giai on sy kh v lm nng nhin liu - Giai on thot cht v to cc - Giai on chy cht bc v cc - Giai on to x ,tro i vi nhin liu lng khng c giai on to cc v to x. i vi nhin liu kh ch c giai on sy nng v chy. Ta nghin cu di y tng giai on ca qu trnh chy .1.2. + Giai on sy kh v lm nng nhin liu

Trong khi vn hnh, nhin liu c cung cp lin tc vo l t, xy ra qu trnh trao i nhit gia nhin liu vi ngn la; vi kh nng t sn phm chy,vi vch l nng bng i lu v bc x nhit. Nhin liu c hm nng, m gim dn, nhit tng dn ti 1000C th m thot ht khi nhin liu, nhin liu kh hon ton. Nhit tip tc tng v ti giai on thot cht bc. Thi gian sy ph thuc nhit v m ban u ca nhin liu. Cn hiu rng khng kh giai on ny ch l tc nhn sy ch khng phi l cp xy cho qu trnh chy. + Giai on thot cht bc v to cc. Mi loi nhin liu thot cht bc nhng nhit khc nhau: than ngtraxt 380 400 0C hoc cao hn, than nu 130o 170oC.o

Qu trnh t nng, ccbuahyr phn hu thnh cc nguyn t n gin C v H2. Mtan (CH4) kh nhit phn, phi trn 600oC mi phn hu, nhng li to thnh nhng ccbon th rn rt kh chy (mui than hoc m hng).1.3. + Giai on chy

Chy l qu trnh phn ng ho hc gia xy v cc cht chy c ca nhin liu, to nhit v nh sng. Tc chy ph thuc vo nhit v nng cht chy

26


c. Nng thp, tc chy chm, ko di. nh hng ca nhit ti tc chy mnh hn nhiu so vi nng . Nhit bt la ca nhin liu khc nhau th cng khc nhau. Sau khi bt la, tc chy tng mnh mc du nng chy c gim dn. Khi chy ht khong 80 90% cht chy c th tc cui gim. Sau y ta kho st chi tit hn giai on chy cc cht bc, tc cc cht kh chy c nh hyr, xt ccbon.... v giai on chy cc. Chy phn t nhin liu rn, cc cht bc lan to trn b mt phn t. xy cn cho s chy xm nhp vo b mt phn t bng khuch tn phn t qua lp kh gii hn bao quanh n. Sn phm chy thot khi b mt phn t vo mi trng xung quanh cng bng khuch tn qua lp gii hn ny.

a) b) Hnh 2.1. S chy phn t nhin liu rn v git nhin liu lng. a phn t nhin liu rn b git nhiu liu lng 1 b mt phn t nng hoc git nhin liu lng 2. lp kh gii hn bao quanh 3 - mt ngoi lp gii hn 4. vng to thnh hn hp t khi chy git nhin liu 5 vng chy ca hn hp t , O2 - dng khuch tn ca xy, CO2 - dng khuch tn ca axt ccbonc. K hiu trn mt phn t hoc git, mi trng bn ngoi. Nhit trn b mt phn t cao hn nhit mi trng, to thnh graien nhit . Kt qu truyn bng dn nhit v bc x vo mi trng. Qu trnh chy cng nhanh khi kch thc phn t cng nh v nhit mi trng, mt xy cng cao.

Thi gian chy hon ton phn t nhin liu rn, gn ng theo cng thc:

27


t= y:

02T O2

- hng s vt l, tu thuc loi nhin liu

0 - kch thc ban u ca phn tT vO2 - nhit tuyt i ca mi trng v nng xy trong mi trng. C cu chy i vi git nhin liu lng khc vi phn t nhin liu rn. Qu trnh chy khng xy ra trn b mt ca n, m xy ra trong khng gian bao quanh lp kh gii hn. Nhit trn b mt git nhin liu lng bng nhit si ca chnh phn nhin liu ny. Trong lp gii hn c graien nhit , xut hin dng nhit truyn ti b mt phn t, nh vy xy ra bc hi. Dng hi nhin liu truyn qua lp gii hn bng khuch tn phn t vo mi trng xung quanh . Hi ny trn vi xy vi t l thch hp bao quanh git nhin liu bc chy.1.4 Phn ng chy

Trong l t ca lin hp l hi xy ra phn ng chy nhiu pha ccbon v lu hunh, phn ng chy ng nht ca hir, xt ccbon , v cc hyr ccbua khc . Phn ng chy ca ccbon l phn ng ho hc tng i phc tp. Qu trnh chy ca ccbon ng thi to thnh axtccbonc v xt ccbon: xC + yO2 = mCO2 + nCO. y: x, y - l s phn t C v O2 tham gia phn ng m,n l s phn t xt to thnh Trong trng hp c lng xy cn thit, phn ng th hai gia xt ccbon vi xy to thnh axt ccbonc, din ra nhanh hn nhiu ln so vi phn ng u. Trong thc t khi cp lng xy, ta c phn ng chy hon ton: C + 1 mol + 12phn + khi lng S 1mol lng + + O2 1mol 32phn khi lng O2 1mol lng = = = = = CO2 1mol 44phn khi lng SO2 1mol 64phn khi lng (4) (3)

Phn ng chy ca S to thnh anhyrtsunfua:

32phn khi +

32phn khi =

Phn ng ca hyr, xt ccbon v hyr ccbua cng l phn ng phc tp v n l phn ng dy chuyn. Khi nhit tng cao, phn ng chy tng ln rt nhiu,

28


gp hng trm ln so vi phn ng ho thng thng. khng phi ch do nhit cao m ch yu l phn ng dy chuyn nh c trung gian gc hyrxt v alht RCHO. y gc R c th l H, CH3 , CH3CH2,, CH3CH2CH2, ... Phn ng chy dy truyn ca hyr, xt ccbon v hyrccbon dn ti hon thnh tc thi cho php s dng tnh ton thc t phng trnh ca cc phn ng ny. Phng trnh chy hyr. 2H2 2mol 4phn khi lng 2CO 2mol lng n m + O2 4 n m + mol 4 + O2 = = = = = 2H2O 2mol 36 phn khi lng 2CO2 2mol 88 phn khi lng n + H2O 2 n + mol 2 (6) (5) + 1mol +32phn khi lng + O2 + 1mol lng

56phn khi + 32 phn khi = Phng trnh chy hyrccbon CmHn 1mol + + = CO2 = m mol

(12m + n ) phn khilng

n + 32 m + phn khi = 44m phn khi + 9n phn khi 4 lng lng lng

Tc phn ng chy ph thuc vo nhit , dn ti tp trung xy trong khng kh, s dng chy, c phn ng ng nht, cng nh s tp trung kh chy trong hn hp kh chy1.5.Giai on to x

Sau qu trnh chy nhng cht rn khng chy c to thnh tro x. Tro l nhng cht rn khng chy c nhng khng b nng chy. X l tro nng chy to thnh. Trong qu trnh chy, di tc ng ca nhit, thnh phn nhin liu s c thay i tnh cht l ho. Cc tinh th ngm nc nh (CaSO4.2H2O); Al2O3.2SiO2.2H2O s bc hi nc nhit 500 0C . nhit cao, s c phn ng phn hu:

29


FeCO3 FeO + CO2 (7) CaCO3 CaO + CO2 MgCO3 MgO + CO2 Tip tc tng nhit , cc thnh phn tro nng chy. Kim loi kim v hp cht ca chng (K2O, Na2O nng chy 800 1000 0C. FeS2 nng chy 800 0C 1070 0C. Nhng trung tm hot tnh nh cc nguyn t t do hyr, xy hoc gc OH.... Trong qu trnh chy dy truyn li c th to ra nhiu trung tm hot tnh mi na. Nghin cu s chy ca hyr ch ra n c trng cho nhiu phn ng ng thi, phc tp. Phn t hyr va chm vi phn t M bt k vi tc vt qu gii hn bit, tch thnh hai nguyn t hyr theo phng trnh . H2 + M H + H + M (a) Mi phn t H phn ng vi xy (O2) theo phng trnh H + O2 OH + O (b) Kt qu l sinh ra hai gc phn t OH v hai nguyn t xy (O)

Hnh 2.2. S phn ng

dy chuyn chy ca Hyr

Phn t OH tc dng vi hyr theo phng trnh . OH + H2 H2O + H (c)

Xut hin hai sn phm cui cng: hi nc v hai nguyn t hyr, a vo phn ng (a), bt u hai chu k song song mi.Nguyn t xy phn ng vi phn t hyr theo phng trnh : O + H2 OH + H Hai phn t to thnh a vo phn ng (c), s c hai nguyn t H to thnh a vo phn ng (b), bt u bn chu k mi. (Hnh 2.2) Phn ng chy dy truyn ca xtccbon ch xy ra khi trong hn hp xtccbon vi khng kh cha mt s lng no H2 v H2O. Nguyn t hyr mi

30


trong phn ng (a) a vo phn ng (b). Kt qu l to thnh phn t OH v nguyn t xy.Cui cng c phn ng: H2O + O 2OH To thnh hai phn t hyrxt. Ba phn t hyrxt a vo phn ng: OH + CO CO2 + H To ra ba phn t cui cng CO2 v ba nguyn t hyr, cho mt dy truyn mi. Ngoi ra, nguyn t xy to nn t phn ng (4.7) c th a vo phn ng vi CO to, thnh CO2. R rng thy rng, tc chung ca phn ng chy CO tng khi hm lng hi nc trong hn hp chy tng. Phn ng dy chuyn ca hyrccbon phc tp hn so vi phn ng dy chuyn ca hyr v xtccbon. Chng dn ti vic to thnh cc sn phm. Thnh phn nng chy th lng, ho tan mt s thnh phn khc vn kh chy, to thnh cc cht c nhit chy thp. Tro c nhiu SiO2 th d nng chy. Cn c vo tnh cht v nhit nng chy ca tro, ta c th la chn phng php thi tro thch hp,thi 850 0C, thi x kh nhit cao.... 5 - PHN LOI V CU TO L T5.1. Yu cu k thut i vi bung la

Bung la l h thng thit b v khng gian tin hnh t chy nhin liu. m bo hiu sut lm vic tt, cn phi p ng cc yu cu k thut sau: - C kh nng t chy cc loi nhin liu khc nhau vi h s tha khng kh thp; tn tht nhit t nht khi ph ti thay i ln. - Kch thc nh, tit kim nhin liu. Nng cao cng chy v cng truyn nhit. Tng cng chy, phi to hn hp nhin liu v xy hp l. Mun tng kh nng truyn nhit, phi tng din tch b mt truyn nhit bc x; la chn phng php chuyn ng ca mi cht thch hp. - Cu to n gin, chc chn, tit kim. - Vn hnh v bo dng d dng.5.2. Phn loi bung la (l t)

Phn loi bung la theo dng nguyn liu c: bung la t nhin liu rn, bung la t nhin liu lng v bung la t nhin liu kh. Bung la t chy nhin liu theo lp hin nay l ph bin nht. Loi bung la ny chia lm ba loi: - Bung la c ghi c nh, lp nhin liu nm trn n c nh. - Bung la c ghi c nh, lp nhin liu nm trn n di ng.

31


- Bung la c ghi chuyn ng, lp nhin liu nm trn n chuyn ng. n gin nht l loi bung la c ghi nm ngang thao tc th cng (Hnh 2.3 a). Bung la loi ny dng cho l hi c nng sut hi rt nh (1 2Tn/h). Cu to bung la gm: ghi, bung chy v bung dn khng kh. Nhin liu da vo qua ca l 1. Ca l bnh thng ng kn hn ch tht thot nhit v ngn nga khng kh lnh vo l. Gi cung cp t gm ghi xuyn qua lp nhin liu c th iu chnh c. Trang b quan trng, nh hng ti qu trnh lm vic v hiu xut ca bung la l ghi l. Ghi ch to bng gang v nm c nh (Hnh 2.3b) thng c hai loi: ghi thanh v ghi tm. Cc thanh ghi sau khi ghp c nhiu k h cho gi i qua.+ Qu trnh chy ca nhin liu trn ghi c nh

Qu trnh chy nhin liu rn gm cc pha sau: sy kh nhin liu, tch v lm chy cc cht bc, bt la v t chy cc ca nhiin liu v pha cui l tro, x. Qu trnh chy bao gi cng gm hai phn: chy cht bc lp trn nhin liu v chy cc phn chnh ca nhin liu. i vi lp nhin liu c dy ln nm trn ghi c nh, s to nn nhiu lp v vng ngang.(Hnh 2.4) Trong lp, nhin liu chy thng tch ra: phn trn - vng nhin liu mi, c sy, kh ho v bt la. Phn gia gm ba vng chy cc. Phn di vng tro x. Nh vy, cc giai on ca qu trnh chy t sy, sinh cht bc, cht bc chy xy ra vng t trn xung. Kch thc mi vng ph thuc vo chiu cao lp nhin liu. Nhin liu cng c nhiu cht bc th nhit lng sinh ra trong bung la cng ln, nhit lng sinh ra trn ghi cng b, do cht bc sau khi thot ra s chy trong khng gian bung la . i vi than ngtraxt t cht bc, nn nhit lng sinh ra s thc hin trong lp nhin liu nm trn mt ghi. Lng xy cung cp t di ln lm cho cc trong x cha chy ht s tip tc chy. Khng kh nng s cung cp cho lp ang chy v lng xy gim dn cho ti ht. Vng xy ho l vng xy dng xy ho ccbon. Trn mt gii hn lp oxy ho, tr s CO2 t gi tr cc i, nhit cao nht, nng xy gim cn t 12%. Tip tc i ln l lp hon nguyn, thiu xy nn ccbon hon nguyn thnh CO di nhit cao. iu ny c ngha l lng CO2 gim dn, lng CO tng dn. Ta bit rng phn ng hon nguyn thu nhit, do nhit gim dn theo chiu cao. Kch thc vng xy ho v vng hon nguyn ph thuc vo c im ca nhin liu (cht bc, c ht, tro...) vo chiu dy lp than v nhit bung la. t hiu sut nhit cao, cn gim ti mc ti thiu thnh phn CO trong sn phm chy (tc gim chiu dy lp hon nguyn).

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Lp nhin liu cng dy th lp hon nguyn cng ln, tn tht nhit cng nhiu. Lp nhin liu qu mng, iu kin bc chy ca nhin liu xu i. Chiu dy ca lp nhin liu ph thuc vo chiu dy ca lp xy ho. Chiu dy ca lp xy ho ph thuc vo kch thc ht than, hm lng cht bc, tro... V th vi mi loi nhin liu c mt chiu dy thch hp.

a)

c)

b) d)

e) nhin liu khng kh x kh khi

h)

33


g) Hnh 2.3. L t nhin liu rn theo lp

a Ghi ngang th cng; b L c lp nhin liu di ng kiu ht; c L ghi xch; d L ghi xch chuyn ng ngc c c cu ht nhin liu; e L c thanh ci la; g L ghi nghing; h L t chyKh nh nhin liu ti

Chiu di lp nhin liu

Vng hon nguyn CO

Vng cc chy

Kh chy Nhin liu ti

Tro x ghi l

Chy cc Tro x ghi l Khng kh Nng Nhit 0C Khng kh

a)

b)

Hnh 2.4. S qu trnh chy nhin liu rn trong lp c nh a Qu trnh sinh kh b Qu trnh trong l Bng 2.1. Chiu dy hp l ca lp nhin liu trn ghi l Chiu dy lp nhin liu (mm) Nhin liu

Bung la ghi th cng ngtraxt c c ht 2 5 mm ngtraxt c c ht 2 3 mm ngtraxt c ht ln Than bn cc Than bn ht nhThan 60 80 100 120 200 300 900 400 200

Bung la ghi xch 200 200200 700 900 700 900 8 120

34


Lp nhin liu

G

600 1500

8 120

+ Loi l c ghi chuyn ng: Nhin liu cng chuyn ng trn n, c nhiu kiu khc nhau. Nhin liu c cp lin tc t b phn cp liu 1 vo bng ghi xch chuyn ng rt chm (thay i tc t 2 30 m/h). bo m cho ng c in khi b nh hng trc tip vng nhit cao, ngi ta b tr ng c v b gim tc pha trc bung la. Lng cung cp nhin liu thay i bng iu chnh khe h ca ra. Khng kh cung cp cho qu trnh chy c qut thi t di ln thng qua cc hc gi c th iu chnh c.

a)

b) Hnh 2.5. Bung la ghi xch. a Bung la b Cc kiu ghi xch Hai pha bn bung la do tip xc trc tip vi nhin liu chy nn rt nng. Ngi ta b tr hp lm mt ghi b tr hai tng bn bung la. Mi cht lm mt l nc. s dng nc lm mt hp th nhit, cc hp lm mt ghi c ni vi vng tun ca l. Hp lm mt ghi tr thnh nhng ng gp tng bn.

35


Chiu rng ca ghi 1,4 4,5 m. Bung la rng hn 2 m phi lm ca trang than hai bn tng l. Chiu di lm vic ca ghi t 5,5 8 m. Do din tch ln nht ca mt ghi cng ch l 36 m2,chnh v th cng sut bung la ghi xch b hn ch. + Qu trnh chy trong bung la ghi xch Trong qu trnh lm vic, lp nhin liu chuyn ng ng thi vi ghi; qu trnh xy ra theo chiu di ghi cc giai on t sy nhin liu ti to x, ngha l qu trnh xy ra ng thi v lin tc trn ghi. V tr cc giai on ny gi c nh trn ghi, khi tc ghi khng thay i.Ngn la chy

Vng chy kit

Nhin liu mi

Vng chun b Vng xy ho Vng chy

Khng kh

Hnh 2.6. S pht trin cc giai on chy nhin liu trn ghi xch. vng sy nhin liu, cht bc sinh ra v bc chy. Ngun gia nhit l bc x ca bung la, ngoi ra cn dn nhit t vng chy cc bn v gi nng thi t di ln. Qu trnh sy v chy nhin liu xy ra t trn xung. Mt khc do lp nhin liu chuyn ng t trc ra sau lm qu trnh chy xy ra theo chiu xin trn ghi.

nghing ng xin ph thuc tc ghi. Tc chuyn ng ca ghi cng ln, th cc vng chy cng ko di (gc nghing cng nh). Phn b cc vng trn ghi ch trn hnh v. (Hnh 2.6) c im ca vng chy cc l phn ng xy ra c t trn xung v t di ln; do ng ranh gii gia vng chy cc v chy x c nghing t di ln. Trong vng chy cc, cc t chy khi tip xc vi khng kh thi t di ln, t c nhit kh cao. Lng tiu th xy tng dn ln qua cc vng v cc i trong vng chy cc. Hm lng CO2 t ti cc i, hm lng xy cungcp cng ln cao cng t, gy ra hin tng thiu xy. Cc ht cc trn hon nguyn CO2 sinh ra t lp di nhit kh cao. Lng CO cng t cc i ti vng chy cc do lng CO2 sinh ra c gim i vng chy cc (ng vi vng hon nguyn ). Ti vng chy kit x, thnh phn cc kh chy gim xung bng khng; t l xy tngdn bng t l xy trong khng kh (21%) cui ghi.

36


T nhn xt trn ta thy vng u v cui ghi qu trnh chy xy ra hon ton; phn gia ghi cn chy cha hon ton. Nhit lng cung cp do nhin liu chy trn ghi chim 50 60%; s cn li do chy nt cc sn phm chy khng hon ton trong bung la. qu trnh chy nt thc hin tt cn c h thng cung cp gi cp 2 pha trn bung la. B tr s hc gi cng ln th lng khng kh a vo s gn vi lng khng kh cung cp l thuyt. Thng dng bung la c 4 hc gi. Khng kh cung cp cho l c p sut khong 600 1000 N/m2, tc khong 5 7 m/s.Bng 2.2. Cc c tnh tnh ton bung la ghi xch Than n v Cc c tnh Khng Thiu kt thiu kt Nhit th in din w/m2 1160 1000 tch trn ghi Nhit th th tch W/m3 220 280 220 280 bung la Tn tht do chy % 1 1 khng hon ton v ho hc Tn tht do chy % 6 5 khng hon ton v c hc T l cht chy % 12 20 trong x v lt T l tro trong x v % 0,8 0,8 lt T l cht chy % 30 35 trong tro bay T l tro bay % 0,2 0,2 2 N/m 800 800 p sut khng kh di ghi 0 Nhit khng kh C 25 200 25 200 + u im ca bung la ghi xch:

ngtraxt Don Cm 1160 280 330 0 7 20 0,75 50 0,25 100025 150

800 900 220 280 0 14 25 0,7 55 0,3 100025 150

- C th c gii ho ton b cc khu. - C th phn vng cp khng kh ph hp vi yu cu ca cc giai on qu trnh chy, chy tt m h s tha khng kh khng qu ln. - Lm vic n nh, kh b tt l. - Tui th l ghi cao.+ Nhc im:

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- Cng sut b hn ch (65 100T/h) do kch thc ghi, chiu dy lp nhin liu, tc ghi hn ch. - Yu cu v nhin liu cao.+ Bung la c ghi c nh, lp nhin liu dch chuyn trn ghi.

- Bung la ghi nghing.

Trong bung la ghi nghing, ghi l c b tr nghing, nh trng lng nhin liu c chuyn dn xung cui ghi trong qu trnh chy. Nhin liu t chy t phu than vo bung la. Cu to bung la ghi nghing ch trn (Hnh 2.7) gm ba b phn chnh: B phn cha nhin liu, ghi t nghing gi lp nhin liu chy, ghi t ngang chy kit s.

b)

a)

c)

Hnh 2.7. Cu to bung la ghi nghing a/ Kiu ging b/ Kiu bc thang c/ Qu trnh chy trong bung la Bung la bc thang dng t nhin liu c nhiu cht bc, c ht nh, hoc dng t than bn. Nhin liu trong qu trnh chy chy t trn xung di, nn qu trnh chy cng xy ra dn dn t trn xung. Tc di chuyn ca lp nhin liu trn ghi khong

38


(1 2 m/h); tc phn b ngn la i vi cc loi than d chy cng ch ti 0,2 m/h. Do than ngtraxt rt kh chy. Qu trnh chy xy ra theo tng vng. Vic cung cp khng kh cn iu chnh c th tho mn cc giai on chy. Vng u tha khng kh, vng cui thiu khng kh.- Bung la c tm ci la.

Bung la loi ny cng thuc bung la c lp nhin liu di chuyn. Cu to bung la c tm ci la (Hnh 2.8a). Bao gm: ghi c nh, gia c rnh rng khong 20 mm t xch vn chuyn tm ci la. Tm ci la c chiu rng bng chiu rng bung la. (Hnh 2.8b) Khi chuyn ng, tm ci la ti than t phu than ti cui ghi; kt hp ci lp nhin liu ang chy, phn b u lp nhin liu trn mt ghi. Cui ghi, tm ci gt x xung phu. Khi chuyn ng t sau ra trc, n ch c nhim v ci la. Tm ci la lm vic theo chu k vi tc 15 m/ph (chim khong 15% thi gian lm vic ca bung la). Khi ngng lm vic, tm ci la a v pha di phu than v c lm ngui. Do tm ci la lm vic theo chu k, nn vic cp nhin liu cng theo chu k v do lng nhit sinh ra trong bung la cng theo chu k. y l nhc im ca phng php ny. Loi cu trc ny dng cho cc l hi c cng sut nh (2 12 Tn/h).Mt trc l

a)Chy v sau Tin v trc

b)

39


Hnh 2.8. Bung la c tm ci la. + c tnh k thut ca bung la t nhin liu theo lp.

Yu t chnh quyt nh hiu qu lm vic ca l t nhin liu theo lp l nhit th din tch trn ghi.Q B Qtlv = R R

Trong : B Lng nhin liu t chy trong l 1 gi (Kg/h) R Din tch ghi l H n v dng i vi nhit th din tch ghi trong h c l Kcal/m2.h; trong h SI l KW/m2 (1 Kcal/m2.h = 1,163 W/m2). Gi tr ti u ca nhit th l (700 1400).103 Kcal/m2.h ph thuc kiu l v c tnh nhin liu. m bo hiu qu chy cht bc trch ra t nhin liu, cn thit phi c th tch khng gian l v chiu cao l y . ln th tch l cn thit chy cht bc c hiu qu xc nh bi nhit th th tch bung la.Q B Qtlv = Vbl v

y: Vbl Th tch khng gian bung la. Gi tr ti u ca nhit th th tch bung la ph thuc loi nhin liu, kiu l (200 300).103 Kcal/m3.h. Chiu cao khng gian l i vi l hi nng sut 4 10 T/h l 2,5 4 m. i vi l hi nng sut 20 T/h hoc cao hn, th khng nh hn 4 mBng 2.3H s khng kh tha trong l Nhit khng kh cung cp vo l 0C

Chy khng hon ton v ho hc

Kiu l

Tn nhin liu

C kh ho cung cp nhin liu

Than xu Than (V2 25%)

1,4 1,4

900 900 250

0,5 0,5

Chy khng hon ton v c hc

7 8

30 - 200 30

100 60

40


p lc kh di ghi

Nhit th din tch 103 Kcal/m3.h

Nhit th th tch 103 Kcal/m3.h

Tn tht nhit %

thnh lp c nh Ghi xch dng thng Bn c Xch bn c

ngtraxt ngtraxtThan bn cc Wp = 40 - 50% Than bn cc Wp = 40 - 50%

1,6 1,61,4 1,3

11001000 1100 1500

300250 - 300 200 - 250 200 - 250

0,50,5 2 1

1410 2 2

3030 - 150 30 - 200 30 - 250

60100 40 40

+ L t nhin liu dng bt. Bung la phun l loi bung la hon thin nht. Bung la loi ny c th t bt k loi nhin liu no (rn, lng, kh). S khc bit gia bung la phun v bung la ghi l n khng c ghi l. i vi bung la phun, than cn phi c chun b trc (nghin thnh bt, hoc ch bin thnh dng nh tng). Nhin liu hn hp vi khng kh, tin hnh cc giai on ca qu trnh chy ngay trong bung la, ri thi ra ngoi di dng tro x. Do trong bung la phun qu trnh chy xy ra theo dng ngn la, nn nhin liu kh v lng ch c th t trong bung la phun. Bung la phun dng cho l hi c cng sut t 20 T/h tr ln (nhin liu rn). i vi nhin liu lng v kh th khng c gii hn. Tro sinh ra trong bung la phi thi nhanh ra khi bung la v khng bm ln mt t bc x. Cu trc ph bin nht hin nay l kiu l t phun nhin liu bt, dng hnh hp ch nht, chiu di t thng ng. Phn trn b tr h thng ng nc si 6; kh thot khi h thng qu nhit 5. Thnh thng ng t vi phun 12. Bn trong thnh l 9, lp h thng ng 10, 11 ng knh 51 76 mm; to thnh tp hp mn chn gm vng tun hon 2 7 (8) 14 10 2 (mn trc v sau) v 2 3 13 11 4 1 2 (mn bn). Bt than c hm nng do phn nhit chy, phun qua vi phun vo l phi hp vi khng kh nng, bc chy. Khng kh nng v sn phm chy di chuyn t ca vo bung la ti khi thot khi bung la vo feston. (Hnh 2.10) Hn hp kh chy, khng kh to thnh ngn la, nhit c th t ti 1300 1500 C. Khi ra khi bung la cn 900 1100 0C. Cc mn chn ca bung la s tip nhn nng lng bc x ny v truyn cho mi cht.0

- Qu trnh chy trong bung la t than bt. Qu trnh chy ca bt than (ng knh trung bnh ht bt than 40 m, ng knh di 90 m chim khong 80 90%) theo cc giai on: sy, sinh v chy cht bc, chy cc v to x. Ht than c kch thc qu nh nn qu trnh chy din ra rt nhanh (1 2 giy). Bt than kt hp vi khng kh chy thnh ngn la. Vng trung tm chy c nhit cao nht (ngang mc t vi phun). Xa vng trung tm chy nhit gim. Ngun nhit sy nhin liu do bc x ngn la v do tip xc vi nhng ht nng hn. Gi cp 1 chim khong 11 45% c th sy nng trc ti 100 400 0C, thi bt than vo vi tc 12 26 m/s. Gi cp 2 thi vo vi tc 18 32 m/s. Nhit gi

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cp 1 nh hng ln ti qu trnh chy. Nu sy ti 900 0C, khi tip xc vi than bt chy tc khc. 100 0C phi sau 1,6 giy mi chy. Trung tm ngn la, nhit t ti 1500 1600 0C, cng gn dn ng, nhit cng gim. Kinh nghim cho thy, tc pht trin ca ngn la ph thuc vo nng bt than trong hn hp bt than khng kh. Nhit ca hn hp nhin liu nh hng ln ti qu trnh chy. Nhit cao, bt la sm, chy nhanh, chy kit. Ni chung nhit khng nn qu 400 0C. - Ming phun bt than. Cu to ming phun v b tr trong bung la phi t ba yu cu: + C kh nng lm dng hn hp bc chy nhanh. + Hiu sut qu trnh chy cao. + Bung la vn hnh n nh.

a)Mi hn

Khe nhit

Ni ng

b)

42


Hnh 2.9. Cc kiu mn chn

a Dng ngng

b Dng tm

lm cho hn hp bc chy nhanh phi to vng xoy mnh trc ming phun, hng vo tm ngn la, khuch tn dng bt than tng cng truyn nhit gia cc lp ca ngn la.Hi t trng vo b qu nhit bo ho

Kh khi v vng kh nh

khng kh th cp Hn hp bi Nc t trng l hi

x

Hnh 2.10. S l t nhin kiu dng bt

tng hiu sut qu trnh chy phi phn b ngn la ng u trong bung la chy kit v khng tn tht.

43


B phn quan trng nht ca bung la phun l vi phun. Vi phun hin nay

chia lm hai loi: vi phun trn v vi phun dt. Vi phun trn li chia lm hai loi: loi i thng v loi xoy (Hnh 2.11a, b i thng v c-xoy). Loi i thng c loi gi cp 1 i trong hoc i ngoi. Hai loi ny chy khng nhanh, nng nhin liu phn b khng u. Loi vi trn c ming loe, chnh gia c chp hnh nn (Hnh 2.11c), hn hp c nng u hn, to vng xoy chnh gia, vi phun dt (H2.11 d) tit din ch nht, gi cp 1 c th bn trong hoc ngoi; quay ln xung khong 150 so vi phng ngang.

b)

c)

a) d) Hnh 2.11. Cu to cc loi vi phun

T l gi cp 1, cp 2 tu thuc loi nhin liu. Than ngtraxt gi cp 1 chim 11% 20%, than gy 15 20%, than 20 45%. Tc gi ph thuc loi nhin liu v vi phun. Vi phun trn, tc gi cp 1 khong 12 16 m/s. S liu trn ng vi l c ph ti nh mc. Khi ph ti thay i, tc gi cp 1 khng i, tc gi cp 2 iu chnh cho ph hp. Vi phun dt gi cp 1 v cp 2 chuyn ng qua cc rnh hp+ Cch t vi phun trn bung la.

Tu thuc nhiu yu t: loi nhin liu, cng sut l hi, vi phun v bung la c th t vi phun trn tng bung la v tr khc nhau. Hin nay c 4 loi b tr

44


nh sau: t tng trc, t tng bn, t gc v t trn nh l. Mi cch vi phun cn c th b tr nhiu tng (H 2.12) t nh l, dng bt than ra khi vi ng u. Trong bung la khng c dng xoy v dng ngc. Trng nhit ng u, dng khi nh km hm chuyn ng i xung, nn c thi gian lm lnh dng ny. Hin tng ng x ln tng t. Cui dng vng thi x c nhit thp, do bung la lm vic tt khi thi x kh. Dng vi phun thch hp l vi phun dt. Nhit th th tch ca bung la (100 120).103W/m3.. Ngn la ch U, vi phun chc xung y l, sau dng chy i qut ln trn, ko di ng bt than chy, chy kit than; lm vic tt vi thi x lng. Ngn la hnh ch L, ngn la phn b u; chiu su bung phi ln ngn la ti c tng i din. Ngn la hnh ch L c nhit th tch vi nhin liu t cht bc 150.103w/m3, khi nhin liu nhiu cht bc (200- 220).103 W/m3.

a)

b)

c)

d)

g) e)

h)

i)

Hnh 2.12. S t vi phun trn tng bung la.

45


a/ t nh l; b/ t tng trc ngn la ch U; c/ t tng trc 1 tng ngn la hnh ch L. d/ t tng trc 2 tng ngn la hnh ch L, e/ t tng bn ,g/t gc phun tip tuyn, h/ gc phun cho , i/ t gc theo tng khi. Vi phun t hai pha tng l, c ngn la chon nhiu hn+ Bung la t nhin liu lng v kh

Bung la t nhin liu kh. Nhin liu kh dng cho l hi chia lm hai loi: kh thin nhin v kh nhn to( kh ga). Kh thin nhin cha t cht khong nn khng c tro, bung la n gin. Kh nhn to cha 1 t khong cht, s c tch ra khi lc bi. Nhin liu kh chy qua 3 giai on: giai on to hn hp gia nhin liu v khng kh to nn hn hp chy. Giai on t nng nhin liu v giai on chy. Loi vi phun hn hp trc th khng kh v nhin liu trn vi nhau vi h s khng kh tha nh ( = 1,05 1,1) trc khi vo vi phun.

Kh Khng khHnh 2.13. Vi phun rnh

Vi phun rnh l vi phun hn hp trc. N gm mt h cc rnh hp lt vt liu chu la. Trong qu trnh lm vic tng rnh b t nng lm nhin liu bc chy. Nhit th th tch kh cao 60.106W/m3. Loi vi phun ny gi l vi phun khng c ngn la. Qu trnh chy ch yu trong vi phun, nn khng i hi bung la c th tch ln. Vi phun loi ny ch yu dng cho cc loi kh nhn to. Vic hn hp nhin liu kh v khng kh xy ra phn cui vi phun v mt phn bung la gn vi phun. Nhng l hi ln hin nay thng phi hp gia nhin liu kh, lng(mazt) hay bt than. Vit Nam thng s dng nhin liu kh c nhit tr thp li phi hp vi bt than kh chy (ngtraxt), do nhin liu kh h tr km, nn thng s dng thm mazt.

46


+ Bung la t nhin liu lng.

Nhin liu kh qua ng vo bung. T bung qua l vo vng iu tit, cc cnh b tr nghing 450 so vi trc vi phun. Ti y kh trn vi khng kh th cp vo vi phun qua ng, to thnh chuyn ng xoy lc trong bung la. Vi phun nhin liu mazt thnh dng sng; chy qua ng lc vi phun vo bung xoy, gp dng khng kh th cp, a vo bung la v chy mnh ti y. Khng kh th cp trong vi phun cp t qut thi c p lc 100 150 KG/m2. Khng kh lm nhin liu mazt tan nh thnh bi sng cung cp bi qut c p lc gn 400 KG/m2. Vi phun c sn xut vi 4 loi kch thc, nng sut nhit t 1.106 5,5.106 KCal/h, p sut khng qu 250 300 KG/m2. + Vn khi ng bung la t bt than. khi ng bung la t bt than c th dng vi phun kh, du hay bung la ph. Cc loi thit b ny duy tr lm vic ti khi bung la duy tr s chy ca bt than. Ta thng dng bung la ph. Bung la ph thc cht l bung ghi thu nh li. Nhin liu thng l ci. Ngn la v khi t bung la ph c a vo bung la chnh t chy bt than. Bung la ph t bn cnh bung la chnh.

Hnh 2.14. Vi phun mazt thi bng hi c rnh trn. 1 V; 2 ng phun; 3 - u ni; 4 ng ni ming phun; 5 ng ngoi; 6 Loe khuch tn; 7 ng trong

47


Hnh 2.15. Cu to bung la ph khi ng bung la t bt than.

Cng sut bung la ph nh nn ch thch hp vi nhin liu d chy.Cu hi n tp chng2: Qu trnh chy v cu to bung t

1. Gii thch cc giai on trong qu trnh chy: Giai on sy kh, giai on thot cht bc v to lc, giai on chy? 2. Trnh by phn ng chy trong l t, qu trnh to x? 3. Qu trnh chy ca nhin liu trn ghi c nh? 4. c im ca bung t nhin liu dng bt?

48


Chng III : QU TRNH SINH HI, CC B MT TRUYN NHIT1.B MT SINH HI V CCH B TR C rt nhiu b mt sinh hi, thc t c th cn c v s tip xc gia mt truyn nhit vi nc v sn phm chy ta chia ra: loi ng nc (khi ngoi nc bn trong), l hi ng la (khi trong nc ngoi). Theo s chuyn ng ca nc trong mt sinh hi, c loi i lu t nhin (a), tun hon t nhin (b), tun hon cng bc (c).

Hnh 3.1. S chuyn ng ca mi cht qua cc b mt truyn nhit:

1. Balng; 2. Bm nc; 3. Hm nc; 4. Dn ng ln; 5. ng xung; 6. ng gp; 7. B qu nhit; 8. Van hi; 9. Balng hn hp

Sau y gii thiu mt s loi b mt sinh hi thng gp.+ B mt sinh hi loi ng nc thng ng (Hnh 3.2)

Gm chm ng 2, trng trn 1 v trng di 3, vch l hi 6. Nc cung cp t trng l hi qua ng xung 7 v ng ni ca b gp 5. Cc ng nc thng ng ch to bng thp tm hn li, ng knh 1000 1500 mm; chu p lc 14 40 atm. Chiu dy thnh ng khng ln lm. V d ng ng knh 1000 mm, chu p lc 14 atm c chiu dy 13 mm. Khi p lc 20 atm, cng ng knh trn nhng chiu dy l 20 mm.

49


ng gp dng ng ng knh ti 219 mm. B mt sinh hi ca lin hp l hi kiu vch, gm trng 2; h ng vch 6 v 7 vi ng di 9, 10 v ng di 4, 5 ca vch gp; h ng dn nc xung 8 v ng ni 3 (Hnh 3.3)A B C

A AA

B BB

C CC

Hnh 3.2. Mt sinh hi, l hi ng nc ng.

50


Trng ch to bng phng php hn, y bng phng php dp. ng knh trng ph thuc nng sut sinh hi ca l v p lc hi t 1200 1800 mm; di c th ti 18m. Chiu dy thnh trng 90 100 mm khi p lc hi 100 atm. bo m l hi lm vic n nh v t nng sut hi tnh ton cn phi lu ti s chuyn ng ca nc trong b mt sinh hi nng. Nc chuyn ng trong ng nc si v ng vch nhit cao, nhng kim loi lm ng li phi nhit thp, m bo an ton v bn c hc ca ng. Chu trnh t nhin ca nc trong ng si v ng vch sinh ra di tc dng ca lc hp dn, do sai khc mt hn hp hi v mt nc t trong trng hp dn. c th to nn chu trnh t nhin th cn chu trnh khp kn, bao gm hai ng ng hoc ng nghing, ni lin tip v np y nc. Khi c chnh nhit ca hai ng, nc trong ng chuyn ng. Nc ng nng hn dng ln, ng c nhit thp hn nc h xung. Nguyn nhn l thay i mt nc.

Nc vo

Hi ra

Hnh 3.3. Mt sinh hi l hi kiu vch

ng xung

51


ng ln

S chnh lch nhit trong dng mt pha do nhit to nn. Trong dng hai pha c s chnh lch mt rt ln gia pha lng v pha hi. p sut cng cao th chnh lch mt gia hai pha gim dn, ti trng thi ti hn th mt hn. Do p sut bng v trn ti hn, khng th c tun hon t nhin. S lng tun hon t nhin c trng bi phng trnh chuyn ng lin tc ca cht lng mt pha hoc hai pha. Ml = Mx (Kg/s) V phng trnh nng lngP = P (N/m2)

y: Ml, Mx P - lng cht lng chuyn ng trong ng ln v xung ca mch; - p lc chuyn ng hon ton ca chu trnh (cn gi l lc chuyn ng) do chnh mt ln v xung ca cht lng trong mch; - tn tht thu lc hon ton (tng tr lc trong ng ln v ng xung);

P

Dng hin ca phng trnh nng lng:

P = h.g x l

(

)

(N/m2)

Trong : h - Chiu cao vng chu trnh tun hon (khong cch thng ng t trc ng gp di n mc nc trung bnh trong bnh hoc n ca vo bnh ca ng ln);

x , l - Khi lng ring ca nc trong ng xung, ng ln;x x l l h.g ( x l ) = Pms + Pcb + Pms + Pcb + Pgt (N/m2)x l y: Pms , Pms - Tn tht p lc thng lc ma st trong ng;x l Pcb , Pcb - Tn tht p lc thng sc cn cc b p lc trong ng;

Pg .t

- Tn tht p lc to nn chuyn ng c gia tc ca hn hp.

Trong k thut, thng dng h n v KG/m2, nn ta c th vit phng trnh sau:h.x x l l g ( x l ) = Pms + ,Pcb + Pms + ,Pcb + Pg .t (KG/m2) 9,81 9,81 9 81 9,81 9 81 9,81

y: 9,81 - h s chuyn i n v p sut t N/m2 ra KG/m2. ln l nh hng nhiu ti ti trng nhit ca nc trong ng ln, cng nh tc tng i ca hi i vi nc trong ng ny. Gi tr ca l rt kh tnh ton chnh xc, v th trong l thuyt tun hon t nhin a vo khi nim p lc chuyn ng c ch, biu din di dng:

52


P l = h.

l g ( x l ) Pms Pg .t (KG/m2) 9,81 9,81 9,81

Rt ra phng trnh tnh ton:x x l Pms Pcb Pcb + + (KG/m2) P = 9,81 9,81 9,81 l

p lc chuyn ng hu ch l mt phn ca p lc chuyn ng hon ton P dng thng lc cn ma st trong ng xung v sc cn cc b trong ton mch. Ta bit rng, sc cn ma st v sc cn cc b hoc cc phn t khc ca h thu ng t l vi ln ca p lc ng trong phn t ny, ngha l:

Pms = ms .

u . u. (N/m2); Pcb = M (N/m2); 2 2

Trong : ms , cb - h s t l, hoc h s cn ma st v h s cn cc b; u v Cui cng ta c: - tc chuyn ng ca mi trng v khi lng ring;

l ux P = d 2 . 9 ,81l

( )

2

x

+

1

i

x cbi

(u )x i

2

2 . 9 ,81

x

+

1

j

l cbj

(u )l j

2 l K

2 . 9 ,81

Trong : l, d, x cbi ; u ix

- chiu di, ng knh v h s ma st ca ng xung. - h s cn cc b ca (phn nhnh, khp ch T, ca vo b gp,

ca ra khi b gp) phn i xung ca mch tun hon v tc chuyn ng ca cht lng trong n;l cbj ; u ljl K

- tng t nh trn nhng ng ln; - mt hn hp hi khi ra khi vng nng ca phn i ln ca

mch tun hon; Qua phng trnh ny cho thy, p lc chuyn ng hu ch i hi cn to nn s tun hon vng chc. Tc nc trong mch cng cao, cng lm p lc hi trong l cng cao. Biu thc trn l phng trnh tnh ton s tun hon t nhin trong l hi. ln p lc chuyn ng hu ch ng vi 1m chiu cao ng phn ln ca mch. iu kin khc, c th xc nh bng th. + B mt truyn nhit ph - Trong cc l hi cng sut ln v trung bnh, bn cnh b mt sinh hi chnh, thng c thm b mt truyn nhit ph nh b hm nc, b qu nhit v b sy khng kh. - B qa nhit

53


Dng sn xut hi qu nhit, lm tng hiu sut nhit. qu nhit ca hi kh cao, ln ti vi trm . C nhiu loi b qu nhit, da vo cch truyn nhit vo mt ng: b qu nhit bc x t trong bung la, trc tip nhn nhit bc x. B qu nhit i lu, t trn ng khi x. B qu nhit na bc x, t ca ra bung la. B qu nhit i lu thng t trong l hi p sut thp, trung bnh v i khi p sut cao nhng nhit hi qu nhit khng vt qu 4400 5100C. B qu nhit ch to bng thp ng; ng knh ngoi 28 42 mm. Tc hi trong ng phi bo m ch nhit n nh trong ng. Tc khi i vi hi qu nhit dn u l 500 1200 Kg/m2.h. Khi chn tc chuyn ng ca hi, coi sc cn thu lc b hi qu nhit khng vt qu 10% p lc lm vic ca hi. Phn ln thit b l hi, c b phn iu chnh nhit hi. B qu nhit i lu ca l hi DKBP (Hnh 3.4) ch to bng ng thp ko 3 ng knh 32 3 mm. u vo ng b qu nhit nng vo pha trn trng 1 ca l hi. u ra hn vo bung hi qu nhit 2, c p lc 14 v 24 atm, ng ng knh 133 5 mm. B qu nhit c thng nht ho theo pr-phin ca ni hi p lc 14 v 24 atm, v 40 atm. ng thi cng thng nht theo ng knh ng v bung. B qu nhit phi hp ni hi cao p gm i lu, bc x v na bc x (s trn hnh 3.5). Hi t trng 1 i vo phn bc x 2 t trn trn bung la; sau vo phn bn bc x 3 dng bnh phong, b tr ca ra khi l, tip theo ng 4 vo nc u b qu nhit i lu 5; qua b lm lnh hi 6, vo nc hai b qu nhit i lu 7, thot ra l hi qu nhit. - B hm nc. Nhm tn dng nhit d ca khi thi gia nhit cho nc gn n nhit si; nhm gim tn tht nhit do khi l thi ra mi trng. Nh vy tng c hiu sut nhit, trnh hin tng nc lnh phun thng vo b mt truyn nhit c nhit cao, to ng sut nhit. Da vo kim loi ch to chia ra: b hm nc bng gang v bng thp nhn. B hm nc bng gang c cnh tn nhit pha khi, ng knh 76 -120 mm, gi thnh h. Gang chu un, ko km nn khng cho php gia nhit nc n nhit si. B hm nc bng thp cho php gia nhit n nhit si v bc hi khng qu 10%. Thng b tr cho nc trong b hm i t di ln, mt mt l nc nng nh hn, thun chiu t di i ln d ko theo bt kh; ngoi ra cn l bin php t iu chnh s phn phi khng ng u v lu lng nc gia cc ng vi nhau.+ B sy khng kh

Nhm tn dng nhit khi thi sy nng khng kh trc khi cp vo bung la, gim nhit khi thi, tng hiu sut nhit. Cn c vo cch truyn nhit gia khi v khng kh c loi ngn cch v loi hi nhit.

54


Loi ngn cch gp nhiu trong thc t. Cc ng thp trn c ng knh 25 51 mm, dy 1,25 1,5 mm, hn vo mt sn phng. Cc ng t theo kiu bn c, khong cch mt ngoi hai ng k nhau 9 15 mm. Khi nng chuyn ng trong ng. Khng kh thi ngang qua ng. Tc khi 10 14 m/s, tc khng kh nh hn 2 ln tc khi.Ra hi qu nhit

Hnh 3.4. B qu nhit ca lin hp l hi kiu DKBPRa hi qu nhit

Hnh 3.5. B qu nhit i lu Bc x

55


Khi l vo

Nc ra

Nc vo

Hnh 3.6. B hm nc bng gang

Hnh 3.7. B hm nc bng thp nhn

56


+ B sy khng kh kiu hi nhit

B sy kiu ny l trng tr thng ng; trong b tr cc tm thp quay tc 2 5 vng/pht l nhng l thp dy 0,5 1,25 mm. Nhng l thp gn trn thng quay ln lt tip xc vi khi nng v khng kh lnh i hai na thng quay. Tip xc vi khi nng, l thp nhn nhit v truyn cho khng kh lnh (Hnh 3.8). B sy khng kh kiu hi nhit c u im nh, gn, tuy nhin cu to phc tp, d h hng.Khi vo Khi ra

Khng kh vo Khng kh ra

Hnh 3.8. B hm nng khng kh bng ng thp nhn, l hi cng sut nh 2.TNH NHIT THIT B SINH HI

Tnh nhit l bi ton c bn, quan trng nht khi thit k, ch to v kim tra cc thit b sinh hi. Tu theo mc ch tnh nhit c th l tnh ton thit k hoc tnh ton kim tra thit b.2.1. Phng trnh truyn nhit

Truyn nhit trong bung la l truyn nhit bc x, sau bung la l truyn nhit i lu.+ Phng trnh truyn nhit bc x

Nng lng bc x ring tng qut i vi vt en tuyt i biu din bi nh lut Stphan Boz-man. T ET = E ,T d = 4,9 100 0

4

57


Trong cng thc ny E,T l nng lng bc x ring ca vt en tuyt i, c chiu di bc sng T0K. Theo nh lut Planck th:E ,T = 2 .h .c 2

2

e

1hc KT

1

Trong : c - tc nh sng bng 2,99776.1010 cm/s K - hng s Bozman bng 1,38047.10-16; h - hng s Plank bng 6,624.10-27; Cc cng thc trn y hon ton l thuyt i vi vt en tuyt i. Thc t khng c vt en tuyt i m ch c vt xm. Ngoi ra hin tng trao i nhit trong l phc tp hn nhiu. Nhit cc vng khc nhau ca ngn la cng khc nhau. Tm l nhit 1300 15000C, cn ch ra 900 10000C. iu ny nh hng ti s phn b trao i nhit bc x theo chiu di ngn la. Ta cn lu l cng bc x t l bc 4 vi nhit . tnh ton ta dng l thuyt bn thc nghim ca A.M.Guc - bi t. ng biu din nhit khi cui l ph thuc ln b mt t nng.

T" =

4 ,9 . . H t .a t ( a + 273 )3 M 10 8 B p Vc tb

a + 273

+1

273 0 C

ln b mt t nng bi bc x, cn nhn c nhit khi cui l c dng:

Ht =Trong :

4,9.M . .aT ( + 273) ( a + 273)" T

108 B Qbx

3

3

1 a + 273 1 M 2 . 2 " M T + 273

2

T" - nhit khi l ca ra ca l (0C); a - nhit chy l thuyt (0C);M - h s, tnh ti nh hng ti qu trnh bc x tm chy (vng l c nhit cc i);

- h s tnh ti bn b mt tip nhn bc x;Ht - b mt nng tip nhn bc x (m2); - h s bo ton nhit; B - chi ph nhin liu tnh ton (Kg/h hoc m3/h) ;

58


Vctb - nhit dung tng trung bnh ca sn phm chy 1 n v khi lng nhin liu trong khong nhit (a-T) (Kcal/Kg) (Kcal/m3.) Qbx - nhit bc x trong l; aT - en bung la Trong Vc tb =" Ia IT a T"

[Kcal/Kg];

Ia, IT - entalpi chy l thuyt v entalpi sn phm chy (khi l) ra khi l; Ht = Ft.x Ft x - din tch b mt vch tng c t dn ng (m2); - h s gc ca tng c t dn ng;

2.2. Tnh nhit cc b mt truyn nhit i lu

Trong bung la, trao i nhit bc x l ch yu. B mt truyn nhit sau bung la th truyn nhit i lu l quan trng nht, nhng cn tnh ti nh hng ca bc x ca cc kh ba nguyn t, trong sn phm. Khi thit k ch to, ta bit nhit ca sn phm chy v mi cht, xc nh c nhit lng trao i. T s liu ny xc nh c din tch b mt truyn nhit. Tnh ton kim tra, thng gi thit cho nhit sn phm ra khi b mt truyn nhit, tnh Qb.xa v Ql ri so snh. Nu sai khc nhit khi ra khi b mt 100C v nhit khng kh nng 400C th coi l cho php. Lng nhit truyn bng i lu qua b mt cho trong mt n v thi gian ( ln dng nhit): Q = k.t.H Trong : k - h s truyn nhit qua b mt t nng cho. t - gi tr trung bnh chnh nhit ca b mt t nng (0C) H - din tch mt t nng (m2); Ch n v o: dng nhit tnh bng Kcal/h, h s quc t SI, s dng h n v c bn Joul/s = 1Watt = 0,860 Kcal/h.q= Q = K .t H

L lng nhit tuyn qua 1m2 b mt t nng trong 1 gi, gi l mt dng nhit. l mt ch tiu quan trng nh gi hiu qu lm vic ca b mt t nng, v cn c tn gi l ng sut nhit ca b mt t nng. K = const, do q l hm bc nht ca t.

59


Trong thc t, nhit khi l cng bin ng trong phm vi no ; nhit ca mi trng hp th nhit cng thay i. Chnh v th phng trnh tnh nhit trao i i lu phi c dng l 1 phng trnh vi phn: dQ = k( - t )dH y: v t - nhit kh khi v nhit mi trng nhn nhit v c hai pha b mt t nng dH xc nh lng nhit trao i hon ton truyn qua cc mt hm nng, ta tch phn phng trnh trn v kt qu l: Q = k.H.

t max t min =k.H. t tb t max ln . t min

y: t max , t min - hiu nhit gia hai mi cht pha c chnh nhit ln nht v b nht (0C) Trong trng hp ny khit max 1,7 ta c tnh theo cng thc t min

t max + t min ' + '' t ' + t '' t = = 2 2 22.3.H s truyn nhit

H s truyn nhit cc b mt truyn nhit u c th tnh theo cng thc chung nh sau: k=1 1 +

1 y:

t b c 1 + + + t b c 2

1 , 2 - h s trao i nhit gia khi v thnh ng, gia thnh ng v hn hp hi, nc trong ng

t , b , c - chiu dy lp tro, b hng bn bn ngoi ng v cn mt trong ng(m)

t , b , c - h s dn nhit tng ng tro, b hng v cnCc i lng trong phng trnh trn c tm quan trng khc nhau, nn khi tnh ton ta c th gin c i nhiu. V d nu trn thit b hin i, khng c b hng hoc mui than bn ngoi ng v cn bn mt trong ng th t s b b , c c s b qua trong tnh ton. Thng ln 1=20 50 Kcal/m2.h., ln 2 thay i trong gii hn ln hn nhiu 2=500 3000 Kcal/m2.h. (t thnh vo hi nc); 5000 15000

60


Kcal/m2.h. (t thnh vo nc khng si); t 10.000 100.000 Kcal/m2.h., hoc 1 1 cao hn na t thnh vo nc si. Do tr s ch chim 5 0,1% ca , nn

2

1

thng b qua. i vi ng nc si v ng nc b hm nng, ta c th dng cng thc n gin. k= 1 1

1

+

t t

=

1 1

1

+

=

1 (Kcal/m2.h.) 1 + 1

y: =

t - l h s bn ca mt ngoi ng( m2.h./Kcal) t1

i vi b qu nhit, t s b qua thnh phn 1

2

bt u nh hng ti k, nn khi tnh ton khng nn

2

v c cng thc: k =1 1 =

1 + ( + 1

1

+

t 1 + t 2

2

) 1

i vi b hm nng khng kh ta s dng cng thc: k= .

1 . 2 1 + 2

y: - h s s dng b mt t nng b hm nng khng kh 0,65 0,85 ph thuc loi nhin liu v kiu b hm nng. Trong trng hp chung, h s trao i nhit t khi l vo thnh ng xc nh theo cng thc bao gm i lu v bc x:

1 = . dl + bx ( Kcal/m2.h.) y: l, bx - h s trao i nhit i lu v bc x; - h s bao ph b mt t nng bi kh khi 0,9 0,95; ln bx tng khi nhit kh tng, nhit b mt tip nhn gim. Khi tng hm lng kh CO2 v hi nc lm tng chiu dy lp kh bc x. ln dl , ng nhn, kh truyn ngang ng (Hnh 3.9)

61


dl = 0,177C 3 . y :

k d 0.64 .( ) d k

C3 - h s tnh ti s hng ng trong chm k - h s dn nhit ca khi hoc khng kh nhit trung bnh ca dng kh (Kcal/m..h) k - h s nht ng hc ca khi (m2/s) - tc chuyn ng trung bnh ca khi trong ng (m/s) d - ng knh ng (m)

Hnh 3.9. c im chuyn ng ca kh ngang ng. a - Theo hng dc b - Kiu so le. S ( 1 1) Trng hp ng b tr kiu so le v khi d 0,7 th S ( c 1) d

k .d 0, 6 ( ) d k Cn khi ln > 0,7 th s dng cng thc dl = 0,270.C z .

dl = 0,295 .C z .

k .d 0 , 6 S 1 d 1 0 , 25 ( ) .( ) d k Sc d 1

62


Trong : S1- bc ngang ca ng (m) Sc- bc cho ca ng, xc nh theo:Sc = d 1 S1 S 2 + 4 d d 2 2

S2- bc dc ng (m) Gi tr ca k , k ph thuc vo bn cht cht mang nhit v nhit ca n. i vi kh khi, cho trong bng: Bng 3.1. Nhit (0C) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 H s dn nhit k.102 (Kcal/m.h.) 1,96 2,69 3,45 4,16 4,90 5,64 6,38 7,11 7,87 8,61 9,37 10,1 10,8 H s nht ng hc k.106 (m2/s) 12,2 21,5 32,8 45,8 60,4 76,3 93,6 112 132 152 174 197 221 (m2) Chun Prandl (Pk) 0,72 0,69 0,67 0,65 0,64 0,63 0,62 0,61 0,60 0,59 0,58 0,57 0,56

Tc trung bnh ca khi trong nhm ng. B p .Vk tb + 273 = . (m/s); 3600.Fk tb y: Bp Fk

Fk=a.(b-zd)

- chi ph nhin liu tnh ton gi cho l hi (Kg/h, m3/h) - din tch tit din ngang ng hi (m2) '+ ' ' tb - nhit trung bnh ca khi(0C) = 2 ' , '' - nhit khi vo, ra b mt hm nng.

63


a,b - kch thc dng hi theo hng ng v hng thng gc ng; d - ng knh ng. 3- CH NC V CHT LNG HI3.1. Khi nim chung

Nc t nhin thng ln tp cht th rn, th lng hoc th kh. Do nc th dng cho ni hi l khng tt v cha nhiu hn hp khong nng d ng cn v gy r. Nc tt nht l nc do ngng t hi trn cc b mt trao i nhit. Trong loi nc ny hm lng hn hp khong rt nh v trong qu trnh bc hi trong l hi, khng ko theo hn hp khong. Tuy nhin khng th c nc ngng t cung cp cho l hi; nn cn nc b xung. Nc b xung l nc th sau khi x l ho v nhit cn thn trong cc thit b chuyn dng. Ph thuc vo tnh cht ca nc, nng sut l hi v p lc hi, thit b c th n gin hay phc tp. Thng lm sch nc th v loi b hn hp keo, cc cht c th ng cn. (Hnh 3.10) l s nguyn tc chun b nc b xung c dng phn t lc catint. Nc th theo ng 1 vo b phn phn phi 2. Ti y chia lm 2 ng: mt ng vo b phn hm nng nc 3, c hi cung cp theo ng 4, vo b phn lng 6. ng kia qua b lc cn 5 v cng dn ti b lng 6. Ti b lng s tch tp cht c hc v keo, sau vo thng trung gian 7, nh bm 8 y vo phn t lc c hc 9, cui cng c lm trong. Phn t lc catint 10 lm mn nc v vo ct kh kh 11. Trong nc th cn ho tan xy, CO2, H2S ... c tc dng kch thch n mn ho hc v in ha cc b mt kim loi. Thng thng phi kh bt cc cht kh bng phng php gia nhit. Khi gia nhit nc trong b kh kh th cc cht kh b tch ra khi nc v thi ra ngoi.

Hnh 3.10. S nguyn tc thit b b xung nc c dng phn t lc catint.

64


Bng 3.2.Hm lng cc cht kh ho tan mg/kg Nhit 0C O2

CO2 3350 1690 970 580

H2S 7070 3850 2360 1480 765 0

0 20 40 60 80 1003.2. Ch tiu cht lng nc

69,5 43,4 30,8 22,8 13,8 0

Ch tiu chnh c trng cho cht lng nc l: cht kh, hm lng mui tng, cng, kim, hm lng axt Silicic, nng ion nc, hm lng kh gy r. Di y ta kho st mt s ch tiu chnh: + cng: L ch tiu ht sc quan trng, c trng hm lng mui canxi v magi trong nc. cng chia ra: cng vnh vin v cng tm thi. cng chung l tng cng tm thi v cng vnh vin; c trng bi hm lng tng ca mui canxi v mui magi trong nc: Sulft - CaSO4 v MgSO4, clorit- CaCl2 v MgCl2; Ca(NO3)2 v Mg(NO3)2; CaSiO3 v MgSiO3; Ca3(PO4)2 v Mg3(PO4)2; Ca(HCO3)2 v Mg(HCO3)2. cng tm thi c trng bi Bicacbonat v magi Ca(HCO3)2 v Mg(HCO3)2 trong nc. cng vnh cu c trng bi hm lng cao ca mui canxi v mui magi. cng chung ca nc:Ca 2+ Mg 2+ + Co = 20,04 12,16

(mg ng lng/Kg)

y: - Ca2+ v Mg2+ - cantion Canxi v Mgi trong nc (mg/Kg) - 20,04 v 12,16 - Khi lng ng lng ca chng; cng cacbnat, bng nng n v Bicacbnt Canxi v Mgi. Cc = y: - HCO3 - l nng ca aning bicacbont Canxi v Mg trong nc - 61,02 - khi lng tng ng ca nHCO3 61,02

ng lng trong nc ca

65


C0 = Cc+ Cv 10H = 10 mg CaO/lt

Cv cng vnh cu.

Ngi ta cng thng dng n v o l cng c:

i cng c ra cng mg ng lng cn nhn vi 0,35663 hoc chia cho 2,804. Da theo cng c th chia nc thnh cc loi: - Nc rt mm, c cng < 40H - Nc mm, c cng 4 80H - Nc bnh thng, c cng 8 160H - Nc cng, c cng bng 16 300H - Nc rt cng, c cng > 300H + kim: kim ca nc c trng bng hm lng cc hyrt, ccbont, bicacbont phospht v gc mui ca cc axt yu khc. kim nh hng xu ti cht lng hi v tui th cc b mt truyn nhit. + pH: Nng ion nc l mt c tnh quan trng ca nc. Trong nc lin tc xy ra qu trnh thun nghch, phn ly phn t nc thnh ion H+ v ion OHH2O H+ + OH-

Trong nc nguyn cht 220C, ta lun c (H+) = (OH-) = 10-7 (g/lt). Ta nh ngha pH = -lg(H+). i vi nc trung ho pH = -lg(10-7) = +7 i vi nc c tnh axt, pH < 7; nc c tnh kim pH > 7.3.3. Cc bin php x l nc

phng nga vic bm cu cn trong nc vo cc b mt truyn nhit, ngi ta quy nh cht lng nc cho php nh sau: i vi l hi ng l v ng la H 0 0,5 mg l/l H0 < 0,3

i vi l hi ng nc p < 16 bar,

p = 16 32 bar, H0 0,2 p = 32 100 bar, H0 0,01

66


p > 100 bar, i vi l hi trc lu

H0 0,005 H0 0,001

Lng xy trong nc < 0,03 mg/l khi p 32 bar v < 0,02 mg/l khi p > 32 bar. Cc tp cht khc cho trong bng.Bng 3.3. Hm lng cc tp cht cho php. Hm lng max cho php (mg/l) p sut trong bnh hi (bar) < 40 40 100 >100 SiO230,1 0,05 Fe2+ 70 35 20 Cu2+ 20 10 Du 3 1 0,5

- X l bng phng php ho hc: Ngi ta c th s dng vi thc hin cc phn ng: Ca(OH)2 + Ca(HCO3)2 2CaCO3 + 2H2O

2Ca(OH)2 + Mg(HCO3)2 Mg(OH)2 + 2CaCO3 + 2H2O Ca(OH)2 + MgCl2 Mg(OH)2 + CaCl2 Ca(OH)2 + MgSO4 Mg(OH)2 + CaSO4 Ca(OH)2 + CO2

CaCO3 + H2O

Vi ch kh c cng ccbnt bng cch lng lc cc kt ta. cng khng ccbnt ch thay i v tr gia Ca v Mg. tip tc kh: Khi dng xt NaOH, c cc phn ng: 2NaOH + Ca(HCO3)2 CaCO3 + Na2CO3 + 2H2O 2NaOH + Mg(HCO3)2 MgCO3 + Na2CO3 + 2H2O 2NaOH + MgCO3 Mg(OH)2 + Na2CO3 2NaOH + MgCl2 Mg(OH)2 + 2NaCl 2NaOH + CO2

Na2CO3 + H2O

Sa Na2CO3 sinh ra c th phn ng: Na2CO3 + CaCl2 CaCO3 + 2NaCl Na2CO3 + CaSO4 CaCO3 + Na2SO4 C tc dng lm mm cng canxi.- X l nc bng phng php cation

67


Phn t lc cationit (Hnh 3.11) l thp tr ng knh 1000 3000mm chiu cao 3500 6500mm. Ht cationit y 2/3 thng. Nc chy qua khe h cc ht v cui cng thot ra, ta c nc lm mm. Trong qu trnh lm mm nc, Cationit dn b tiu hao; s trao i cation gia nc v cationit s ngng. khi phc kh nng lm mm nc, cn ti sinh kh nng ca cationit. Ngi ta c th s dng c mt s nm. Dung dch mui l dung dch ti sinh. Cho nc i qua bnh ng cc cationit nh NaR, HR, NH4R... Trong R l gc ca cationit, khng ho tan trong nc, ng vai tr anion i vi cationit Na. Khi lm mm nc, din ra cc phn ng chnh nh sau: Na2R + Ca(HCO3)2 CaR + 2NaHCO3 Na2R + Mg(HCO3)2 MgR + 2NaHCO3 Na2R + CaSO4 CaR + Na2SO4 Na2R + CaCl2 CaR + 2 NaCl Na2R + MgSiO3 MgR + Na2SiO3 Na2R + MgSO4 MgR + Na2SO4 Na2R + MgCl2 MgR + 2NaCl Na2R + CaSiO3 CaR + Na2SiO3. Trong qu trnh cationit, cng thng c loi b khi nc. cng ca nc mm t ti 0,02 0,01 mgl/Kg (khi dng cationit Natri). kim v cc thnh phn anion khc khng thay i. hon nguyn cc cationit Na, thng dng dung dch mui 5 8% theo phn ng: CaR + 2NaCl Na2R + CaCl2 MgR + 2NaCl Na2R + MgCl2 Clorit CaCl2 v MgCl2 ho tan tt trong nc, s b x ra khi ra phn t lc. - i vi cationit Hyr. Dng lm mm nc c cng cacbnt ln: 2HR + Mg(HCO3)2 MgR2 + 2H2O + 2CO2. 2HR + Ca(HCO3)2 CaR2 + 2H2O + 2CO2 2HR + MgSO4 MgR2 + H2SO4. 2HR + CaSO4 CaR2 + H2SO4. 2HR + MgCl2 MgR2 + 2HCl 2HR + CaCl2 CaR2 + 2HCl 2HR + CaSiO3 CaR2 + H2SiO3.

68


2HR + MgSiO3 MgR2 + H2SiO3 2HR + Na2SO4 2NaR + H2SO4 2HR + 2NaCl 2NaR + 2HCl.

Nc mm

vt liu ion

nc tha)Phu cp liu Nc vo

Nc ra

ng ra dung dch mui

Lp thch anh Lp thch anh Lp thch anh

X

b) Hnh 3.11. Phn t lc Cationit Natri v bnh dung dch mui.

69


Axt CO2, H2SO4, HCl, H2SiO3 cn li trong nc di dng ho tan. Cc hp cht CaR2, MgR2, NaR a vo thnh phn ca vt liu cationit. cng cacbnt trong nc loi b hon ton, do lm gim hm lng mui ca nc. hon nguyn cationit hyr, ngi ta a vo 1 1,5% dung dch ho tan axit - lu hunh. Khi xy ra phn ng sau: CaR + H2SO4 2HR + CaSO4 MgR2 + H2SO4 2HR + MgSO4 2NaR + H2SO4 2HR + Na2SO4+ i vi cationit amn (NH4 - Cationt)

Qu trnh trao i theo cc phn ng: 2NH4R + CaS CaR2 + (NH4)2S 2NH4R + MgS MgR2 + (NH4)2S 2NH4R + Na2S 2NaR + (NH4)2S y: S l k hiu ca (HCO3), So4, Cl2, SiO3. Nh vy trong nc mm xut hin mui amn v n khng tr thnh axt; do khng i hi phi s dng vt liu chu axt trong ch to. y l u im ca cationit amn so vi cationit hyr. Khi trao i cation amn, cng cng gim i nhiu, nhng cc mui amn to thnh s b phn hu nhit khi a vo l theo phn ng: NH4Cl = NH3 + HCl (NH4)2SO4 = 2NH3 + H2SO4 NH4HCO3 = NH3 + CO2 + H2O. NH3 v axt ccbnc, to thnh kh a vo hi nc bo ho, H2SO4 v HCl trong nc l hi, tc dng lm r kim loi. Do thng dng phi hp cationit amn vi cationit Natri. hon nguyn cationit amn, dng cc mui amn (2 3% Sulphat amn (NH)2SO4).+ X l nc bng trao i anion.

Tng t nh phng php trao i cation. Ti y cho nc i qua cc anionit nh RaOH c phn ng: 2RaOH + H2SO4 = Ra2SO4 + H2O RaOH + HCl = RaCl + H2O

70


Phng php ny kh c axt trong nc.- Lm sch b mt truyn nhit

Trong qu trnh lm vic, cc b mt l hi thng bm cu bn, lm gim kh nng truyn nhit ca n. Thnh phn cu bn th Ca v Mg chim a s. Hin nay lm sch ta c th dng phng php c kh, ho hc hoc kt hp. Lm sch bng ho cht kh ph bin hin nay. Dung dch kim 2% c un si p sut 1 3 bar trong khong 12 24 gi, cu bn s b loi b. Ra l bng axt, tc dng nhanh hn nhng li n mn kim loi. Mi ln dng axt HCl, H2SO4 thi gian khng nn qu 5 6 gi, khi nhit dung dch 50 700C hoc khng qu 12 15 gi khi nhit di 500C. Sau khi ra bng axt, cn kim ho l trung ho axt bng NaOH 1%. Ngi ta c th s dng cht lm chm n mn nh Phocmalin (40% HCO4); hn hp 25% amnic...- Cht lng hi

+ Yu cu cht lng hi: sch ca hi phi c kim tra cht ch. Nng kh CO2 v tp cht rn c trong hi phi nm trong gii hn cho php. S d nh vy v CO2 thc y qu trnh n mn ng hi. Cc tp cht rn s ng li trong b qu nhit, trn cnh tuabin. Qu trnh ngng kt ny lm tng nhit tr, gim hiu sut trao i nhit. Nguyn nhn chnh l do hi bo ho t bnh vo b qu nhit mang theo nhng git nc c nng tp cht cao. Khi qua b qu nhit nc bay i, tp cht bm li trn b mt ng qu nhit. Ngoi ra, l hi cao p c th ho tan mui Natri Silict; loi l hi siu cao p cn ho tan NaCl, NaOH... Do vn chnh l phi tng kh ca hi ra khi bnh hi. + Cc bin php thu hi sch Bin php thng dng l phn ly hi, x cn nc l, bc hi theo cp, ra hi ... c th phn ly hi (tch ht nc khi hi), v ht nc c khi lng, nn c th dng phng php gim ng nng dng hi m, thay t ngt hng chuyn ng dng hi. X cn lin tc hc nh k l phng php n gin v hiu qu. Bc hi theo cp l chia nc trong bnh hi lm vic theo mt s vng tun hon ni tip nhau. Vng tun hon cui cng ta thu c nc bn nht, tp trung x cn ngn ny l hiu qu nht.

71


Cu hi n tp chng 3: Qu trnh sinh hi, cc b mt truyn nhit

1. 2. 3. 4. 5.

Trnh by cc c im cc dng b mt sinh hi? Trnh by c s tnh ton qu trnh tun hon t nhin tronng l hi? Cc bc tnh ton b mt truyn nhit i lu? Trnh by cc ch tiu c bn ca cht lng nc? Cc bin php x l nc?

72


Chng IV : H THNG THNG GINHIM V V CC GII PHP THNG GI 1. Nhim v ca h thng thng gi

Nhim v c bn ca h thng gi l cp khng kh cho qu trnh chy nhin liu v x kh chy lm vic ra khi thit b vo mi trng.2. Gii php thng gi

l t ca lin hp ni hi, c th thc hin s chy ca nhin liu; cn phi cung cp mt lng khng kh y . loi b khi l t cc sn phm chy v di chuyn chng qua cc mt trao i nhit ca thit b cn phi thc hin thng gi nh sc ht ca ng khi. Ta gi l thng gi t nhin. Thng gi cng bc l c s tham gia ca qut y v qut ht. (Hnh 4.1) S kh ng ca thit b l hi Nhim v bi ton thng gi l xc nh tng lc cn t khng kh vo ti khi khi thi ra ngoi vi tc cn thit. T s liu xc nh kch thc ng khi bo m thng gi t nhin hoc tnh ton, chn qut khi thng gi cng bc. S phc tp ca s l hi lm tng lc cn kh ng chung, lm gim nhit kh thot dn ti lm gim lc thng gi. ng khi c nhim v thot khi vo lp kh quyn trn cao. Phn tn chng c hiu qu vo khng kh; c bt c ngha quan trng khi trong khi c hm lng cao ca SO2 v tro nh. Khi v khng kh l nhng kh c nht, chuyn ng ca chng trong ng dn kh ca thit b ng thi vi tn tht nng lng, chi ph thng lc mast khi chy ri, c biu hin hai kha cnh: pht sinh mast khi chuyn ng ca kh vi b mt vt cng v s thay i hng chuyn ng ca n do ni lc mast trong dng. thng lc mast, cn c p sut d ca kh. - Tnh ton thng gi: Tr lc ca vng bt k ca dng kh khi thng gi bng gim p lc ton phn trong hai tit din ca dng kh. h = h1 h2 hc N/m2 p lc hon ton bng tng p sut tnh v p sut ng.

h = ht +

22

. = ht + hd

73


Hnh 4.1. S kh ng thit b kh l hi: Ch s di: h s cn mp ma st; M v tr; Mv v tr vo; MR v tr ra

Ch s trn: K hiu bung kh ca l hi

ne b qu nhit; Te Hm nng nc;

TK - t nng khng kh; Kx - ng i ca kh; zy Kh tro; - ng tht; K ng khi; q quay vng Thng gi t nhin hC = (z2 - z1).g.(kk - k) (N/m2) y: (z2- z1) - l hiu s cao trc a ca hai tit din, ngha l chiu cao dng kh.

kk k

- mt khng kh (Kg/m3) - mt kh (sn phm chy) Kg/m3

Khi tnh ton kh ng, tr lc ca vng no dng kh, c xc nh bng tng tr lc mast v cc b:

h = hms + hcb hc (N/m2)Trong iu kin b mt tri t khi t = 4oC, 1mm ct nc = 9,81 N/m2. Th nguyn ca tr lc bng mm ct nc, ta ly biu thc vi th nguyn N/m2 chia cho 9,81.

74


+ Xc nh tr lc kh ng ca l hi theo dng kh (sn phm chy).

Tr lc ca thit b l tng tr lc l t, ni hi, b qu nhit, b hm nng nc, hm nng khng kh, ca l, b iu chnh thng gi, b kh tro ng khi, vi d phng 20%.

htb = (hl + hn + hqn + hhn + hhk + hcl + htg + hkb + hok ).1,2

mm

ct nc.+ Xc nh tr lc trong iu kin ti trng hon ton ca thit b.

- Tr lc ca l t: Khi chy nhin liu to x, cn phi thng gi cng bc. Chy nhin liu lng (mazt) to s h p ca kh trong l hl = 3mm ct nc. Thng gi t nhin tr lc ca l c th tnh theo cng thc thc nghim. - Tr lc l hi: xc nh tr lc l hi cn phi bit chi ph nhin liu cho l, vi tc ca sn phm chy (m/s), v nhit trung bnh ca n gi l nhit ca dng:

k 0C = d 0CChi ph nhin liu cc i cho mt l:Bk = Qmax K .Qcc .

y:

Qmax - ti trng nhit cc i cho ca thit b (Kcal/h); K - s lng l hi; - hiu sut thit b.

Khi cn thit c th tnh c p lc ng i vi sn phm chy, tm mt ca dng kh theo cng thc:d = H

.

273 (Kg/m3) 273 + k

p sut ng

h =

22

. d (N/m2)(kg/m3)

H =VH

Mk V kH

y: Mk(Kg/Kg) - Khi lng sn phm chy ng vi 1 Kg nhin liu. - Th tch sn phm chy ng vi 1 Kg nhin liu.

75


Tr lc ca l l tng cc tr lc tt c cc dng kh v tr lc cc b. Tr lc dc chm ng l tr lc mast. Tr lc ngang chm ng, l loi tr lc c bit v n khng phi l mast v cng khng phi l tr lc cc b. Tr lc cc b l tr lc khi dng kh i hng v khi thay i tit din. - Tr lc dc chm ng: Tr lc dc chm ng vi iu kin trao i nhit xc nh theo: 2 2 l h = . . . . dt 2 Tt T 2

N/m2;

y: T v Tt - nhit tuyt i trung bnh ca vng cho ca mi trng v

2 c 0 nhit ca thnh ( K). Trong tnh ton thng thng h s hiu chnh T t T th b qua; l - chiu di dng kh; - h s tr lc do mast, ph thuc vo nhm tng i ca thnh .d dt/k v s Ry-nol Re =

2

dt k

- ng knh tng ng; - nhm ca thnh, ngha l cao cc mp m; - tc sn phm chy (m/s); - h s nht ng hc (m2/s);

c im vt l chn nhit trung bnh dng kh. Trng hp chy trong ng, ng knh tng ng bng ng knh trong ca ng. Trng hp dng kh chy theo tit din ch nht gia ng v dc theo n.

d2 4 ab z. 4 dtd = 2 ( a + b ) + z d y: a,b - cnh ca rnh (dng kh) (m) z - s ng trong dng kh

76


d - ng knh ngoi ca ng (m) Khi dng chy theo tit din bt k: y: F - tit din sng ca rnh (m2) U - chu vi t ca tit din (m) nhm tuyt i ca thnh ng ko lin, mt l hi, b hm nng khng kh kiu ng v kiu tm c K = 0,2 mm. H s cn ph thuc vo s Re, mc nhm ca thnh ng v rnh. xc nh gi tr , c nhiu dng cng thc, nhng ph bin hin nay l dng cng thc ca Blazius. d td = 4F (m) U

=

0,316 Re0, 25

i vi thnh c nhm khng ln trong gii hn ca ch s Reynol 3000 < R < 100.000. Gi tr gn ng i vi chuyn ng dng kh dc ng = 0,03. ln p lc ng theo mm ct nc ph thuc vo tc v nhit trung bnh ca dng tra theo th. - Tr lc ngang ng Tr lc ngang chm ng xc nh theo

h = .

22

. (N/m2)

y: - h s cn ph thuc vo s hng v cch b tr ng trong chm; cng nh vo s Re

- tc dng kh (m/s)- Chm ng bn: H s cn ca chm ng bn.

= 0 .Z 2 y:

- h s cn i vi mt hng ca chm

77


Z2 - s hng ng theo su ca chm.

0 - h s cn cho mt hng ng ph thuc bc ng theo chiu rng v chiu su ca chm ng S1, S2 v ng knh ngoi ca chmH s Re

kh t dng Nhit

Re = WR'.10n

d td =t = 6000

Th d: Xc nh Re khi W = 18m/s, d=120mm

d 10 n

d td =

Re = 18.12,2.102 = 22.103

120 = 1,2 mm. 10 2 Re' = 12,2

dnp - ng knh qui dnHnh 4.2. th xc nh s Re

78


Khi S1 S2:

S 0 = 1,52 1 1 d p sut ng

0 , 5

S1 d S d 2

0 , 2

.Re0, 2

hgKg/m2

p lc ng khi 760 mm pm cm

Khi S1>S2:

H s cn ca chm ng t so le, kh thi ngang:

H s cn mt hng ng si:

Trong CS h s ph thuc S1, d v

W2m/s Tc khng

Cng thc chuyn i hg2=hg1(W2/W1)2KG/m2

Hnh 4.3. th p sut ng ca khng kh 0, 2 S1 d S d 2 2

S 0 = 0,32 1 1 d = 0 (Z 2 + 1)

0,5

S1 d 0,9 S d 2

0 , 68

Re

0 = C S .Re0, 27SC = 1 2 2 S1 + S 2 4

79


Khi 0,14

S1 d S < 1,7, vi chm ng 1 < 2 SC d d S d S 2 1 C S = 3,2 + 4,6 2,7 1 S C d d

Chm ng c

S1 2 d

CS = 3,2 Khi 1,7 s1 d 5,2 SC d

S d CS = 0,44 1 + 1 S d C - Sc cn cc b

2

Sc cn cc b gy ra do i dng kh trong l t, i vo v i ra ca kh trong l. (Dng kh co hp khi i vo v dn khi i ra). Trng hp chy ngang khng tnh sc cn cc b, m ch tnh lc cn ca chm .Ton b lc cn cc b xc nh theo cng thc:

h cb = cb .

22

.

(N/m2)

H s cn cc b ph thuc vo kiu cn. quay vng trong chm: i 1800 i 900 i 450 cb = 2 cb = 1 cb = 0,5

Cng gi tr nh trn khi quay vng dng kh khng b ng chn. Tc ti v tr quay vng xc nh theo

= y:

Vk .B (273 + k ) 273 .3600 . f

Vk - th tch sn phm chy ng vi h s tha khng kh; B - chi ph nhin liu cho mt l hi; k - nhit sn phm chy ti v tr quay vng(0C); f - din tch tit din sng (m2);

Khi quay vng 900 th:

80


f =

2 1 1 + f1 f 2

(m2)

Vi: f1, f2 - din tch tit din quay vng u v cui Khi quay vng 1800 th:f =3 1 1 1 + + f1 f 2 f 2

Tng sc cn dng kh v sc cn cc b, a vo h s hiu chnh, ta c sc cn chung ca l hi. hcb = ( h + hms ).k . Trong : k - h s hiu chnh tnh sc cn; i vi l hi cng sut nh vi s quay vng kh trong mt phng ngang k =1. Cng l hi loi ny vi bung t trc chm ng th nht k = 1,5. L hi nhiu phn k = 0,9. i vi chm ng rut g: - hiu chnh mt kh, v cc th u thnh lp vi khng kh kh 1,293 iu kin tiu chun. 760 hc (mm ct nc) 1,293 hb .

H

H

760 - hiu chnh p sut barmt (Phong v biu) hbNu cao ca a hnh trn mc bin khng qu 200 mm th hb = 760 mmHg; Khi cao 1500m th hb = 630 mmHg v khi cao 3000m th mmHg; Hiu chnh bi ca sn phm chy khng a vo v ngi ta ch tnh khi chy nhin liu rn. i vi l hi nh v trung bnh thnh phn hb= 530

h

c

b qua.

Trong trng hp gn ng, ta c th tnh sc cn ca khng kh bng cng thc thc nghim

H s cn

81


i vi ng la v l hi ng nc ngang:

T s gia tit din nh v tit din ln

D hl = 0,005 H mm ct nc l

2

Hnh 4.4. H s tr lc cc b

khi tit din thay i t ngt i vi l hi ng ng kiu Xy - Khp

D hl = 0,004 H l

3 mm ct nc.

2

Trng hp lm vic vi ti trng khc so vi nh mc, sc cn tnh bng cch nhn thm vi bnh phng t s gia ti trng mi v ti trng nh mc - Sc cn ca b qu nhit. B qu nhit dng ng rut g cng tnh

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Ky Thuat Lo Hoi - GSTS Pham Xuan Vuong