NGHA KINH T - K THUT CA N K thut lnh ng vai tr rt quan trng trong nn kinh t x hi. c bit l i vi nc ta nn kinh t ch yu l nng nghip, ng nghip. Sn phm nng nghip ca chng ta di do, bn cnh l qu trnh pht trin nn kinht x hi chng ta ang dn tin ti cng nghip ha hin i ha. Sn phm bn ra ngy cng nhiu v ch bin tinh ch hn, ccngnhnngsn, chbinthysnngycng chim v th trong nn kinh t x hi.cbitvi ngnhchbinthysn, snphmsau ch bin phi c cp ng c th bo qun trong thi gian di. Do pht trin c ngnh ny th cng ngh lnh ng vai tr rt quan trng vi ngnh trng by v bn hng ti cc trung tm thng mi, siu th. V vic nghin cu v ng dng k thut lnh ng hng nc ta l rt cn thit a nn kinh t nc nh i ln.Chng 1. TNG QUAN V H THNG LNH1.1. Lch s pht trin ngnh lnhT lu con ngi bit lm lnh v s dng lnh. Cch y khong 5000 nm con ngi bit bo qun lng thc-thc phm trong cc hang ng c nhit thp do cc mch nc ngm nhit thp chy qua.Cch y khong 2500 nm trong cc tranh v trn tng cc kim t thp Ai Cp m t cnh n l qut cc bnh gm xp cho nc bay hi lm mt khng kh.Ngi n v ngi Trung quc cch y 2000 nm bit trn mui vo nc hoc nc to nhit thp hn.Tuy nhin, k thut lnh hin i ch mi bt u pht trin khi gio s Black tm ra n nhit ha hi v n nhit ngng t vo nm 1761 - 1764. Con ngi bit lm lnh bng cch cho bay hi cht lng p sut thp.Sau l s ho lng kh CO2 vo nm 1780 do Clouet v Monge tin hnh. Sang th k th 19 th Faraday ho lng c hng lot cc cht kh nh: H2S, CO2, C2H2, NH3, O2, N2, HCl.Nm 1834 Tacob Perkins (Anh) pht minh ra my lnh nn hi u tin vi y cc thit b hin i gm c my nn, dn ngng, dn bay hi, v van tit lu.Sau c hng lot cc pht minh ca k s Carres (Php) v my lnh hp th chu k v lin tc vi cc m cht khc nhau.- Mylnhhpthkhuchtnhontonkhngcchi tit chuyn ng c Gerppt (c) ng k pht minh 1899 v c Platen cngMunter (Thyin) honthinnm1922. MylnhEjector hi nc u tindo Leiblane ch tonm 1910.N cu tostn gin, nng lng tiu tn l nhit nng do c th tn dng cc ngun ph thi.- Mt s kin quan trng ca lch s pht trin k thut lnh l vic sn xut v ng dng Freon M vo nm 1930. Freon l cc kh lin carbon c thay th mt phn hay ton b cc nguyn t hidro bng cc nguyn t halogen nh: Cl, F, Br. Freon l nhng cht lnh c nhiu c tnh qu bu nh khng chy khng n, khng c hi, ph hp vi chu trnh lm vic ca my lnh nn hi. N gp phn tch cc vo vic thc y k thut lnh pht trin. Nht l k thut iu ha khng kh .Ngy nay k thut lnh hin i pht trin rt mnh m, cng vi s pht trin ca khoa hc, k thut lnh c nhng bc tin vt bc.- Phmvi nhit cakthut lnhngycngcmrng. Ngi ta ang tin dn nhit khng tuyt i .- Cng sut lnh ca my cng c m rng, t my lnh vi mW s dng trong phng th nghim n cc stoor hp c cng sut triu W cc trung tm iu tit khng kh.- H thng lnh ngy nay thay v lp rp cc chi tit, thit b li vi nhau th t hp ny ngy cng hon thin nn s dng s thun tin v ch lm vic hiu qu hn.- Hiu sut my tng ln ng k, chi ph vt t v chi ph cho mt n v lnh gim xung. Tui th v tin cy tng ln. Mc t ng ha ca cc h thng lnh v cc my lnh tng ln r rt. Nhng thit b t ng ha hon ton bng in t v vi in t thay th cho cc thit b thao tc bng tay.1.2.Tng quan v cng ngh lm ng v bo qun sn phm ng lnh1.2.1. Tc dng ca vic bo qun lnhBo qun thc phm l qu trnh bo v v hn ch nhng bin i vcht lngvhnhthccathcphmtrongkhichiais dng.Thc phm sau khi thu hoch v ch bin c bo qun nhit thp cng vi ch thng gi v m thch hp trong kho lnh, khi h nhit thp th enzyme v vi sinh vt trong nhin liu b c ch hot ng v c th b nh ch hot ng. Nh vy nguyn liu c gi ti lu khong mt thi gian na.Ni chung khi nhit nh hn 100C th vi sinh vt gy thi ra v vi khun gy bnh b kim ch phn no hot ng ca chng. Khi nhit nh hn 00C th t l pht trin ca chng rt thp, -50C -100C th hu ht chng khng hot ng. Tuy nhin c mt s loi vi khun v nm mc khi h nhit xung -150C chng vn pht trin c nh Cloromobacter, Pseudomonas Do , mun bo qun c thc phm, nht l cc mt hng thu sn trong thi gian di th nhit bo qun phi di -150C.Nh vy, qu trnh bo qun lnh c tc dng nh sau: - nhit thpccphnngsinhhotrongnguynliugim xung. Trong phm vi hot ng bnh thng c h 100C th cc phn ng sinh ho gim xung 1/2 1/3, khi h xung thp s lm c ch cc hot ng v sinh l ca vi khun cng nh nm men. - Di tc dng ca nhit thp, nc trong ng vt thu sn b ng bng lm c th ng vt b mt nc, vi khun thiu nc nn gim pht trin v c khi cn b tiu dit. Ni chung khi nhit h xung thp th ch c tc dng kim ch vi khun hn l git cht chng.1.2.2. Cc vn v cp ng thc phm1.2.2.1.Phn loi gii hn lm lnh Nhit ng bng ca thc phmNc nguyn cht ng bng 00C. Tuy nhin im ng bng ca thc phm th khc, v nng mui khong v cc cht ha tan trong dch t bo ca thc phm thay i ty theo tng loi thc phm nn chng c im ng bng khc nhau v thng nh hn 0. Cc cp lm lnh thc phmng vi khong nhit sn phm sau cp ng ngi ta phn bit cc cp lm lnh thc phm nh sau:- Lmlnh: khi nhit sn phmcui qu trnhnmtrong khong:tdb < t < 200C- Lm lnh ng (cp ng): khi nhit sn phm sau cp ng nm trong khong:-1000C < t < tdb- Lm lnh thm : khi nhit ca sn phm sau cp ng trong khong:-2730C < t < -1000C C ch ng bng trong thc phm khi cp ngNc trong thc phm do c ha tan cc cht tan nn nhit ng bng thp hn 00C.Khi hnhit xung thp cc dngnc trong thcphm ng bng dn dn ty theo mc lin kt ca chng vi t bo.Khi h nhit xung thp bng nhit cp ng, trc tin cc tinh th xut hin gian bo (khong trng gia cc t bo). Khi n im ng bng a s nc gian bo kt tinh v lm tng nng cht tan ln cao hn trong t bo. Do p sut thm thu tng ln lm cho nc trong t bo c xu hng ra ngoi qua gian bo, qua mng bn thm ca t bo. Nu tc lm lnh chm th nc trong t bo ra s lm cho cc tinh th hin din ln ln m khng to tinh th mi.Nu tc lm lnh nhanh th tinh th s to ra c bn ngoi ln bn trong t bo, tinh th s nhuyn v u.Do , nu h nhit chm t bo b mt nc, cc tinh th to ra s to v chn p lm rch mng t bo, cu to m c b bin dng, lm gim cht lng sn phm.Khi nc t do ng bng ht th n nc lin kt, bt u t nc c lin kt yu n nc c lin kt mnh.1.2.2.2. Mt s bin i ca thc phm trong qu trnh bo qun lnh nga. S bin i v nhit vt lS kt tinh ca nc Trong qu trnh cp ng nc tch ra v ng thnh cc tinh th, lm cho sn tr nn rn, tng th tch mt t. Khi nc trong thc phm kt tinh to thnh mng tinh th xen k gia cc thnh phn khc to nn cu trc vng chc, nhng khi lm tan bng, phc hi trng thi ban u th cu trc thc phm b mm yu hn, km n hi hn do cc tinh th lm rch cu trc t bo thc phm.i vi cc sn phm ng lnh trong qu trnh bo qun nu chng ta khng duy tr c nhit bo qun n nh s dn n s kt tinh li ca nc . y l hin tng gy nh hng xu cho sn phm bo qun. Do nng cht tan trong cc tinh th nc khc nhau th khc nhau, nn nhit kt tinh v nhit nng chy cng khc nhau.S bin i mu scng thi vi qu trnh trn mu sc thc phm cng bin i do hiu ng quang hc do tinh th khc x nh sng. Mu sc thc phm khi nc ng bng ph thuc tnh cht nh quang ca cc tinh th nc .Bay hi ncTrong qu trnh lm lnh ng c hin tng mt nc, gim trng lng sn phm. l s bay hi nc vo khng kh t b mt sn phm, dochnhlchmt giakhngkh st bmt vkhngkh xung quanh.m bc ln t b mt sn phm vo khng kh xung quanh, nu sn phm nhp c b mt cn t th khi cp ng chng s ng li, sau din ra qu trnh thng hoa. Nu chnh lch nhit b mt sn phm v khng kh trong bung cp ng cng ln th m bc cng mnh, gy hao ht khi lng.Khuch tn ncKhi cp ng xy ra hin tng khuch tn nc trong cu trc thc phm, nc khuch tn l do cc nguyn nhn:- S chnh lch nhit gy nn do chnh lch mt . - S ln ln ca cc tinh th nc lun thu ht nc t nhng v tr cha kt tinh dn n, lm cho nc t ni c nng cht tan thp chuyn n ni c nng cht tan cao. S di chuyn ca nc thc hin nh tnh bn thm v mao dn ca cu trc thc phm. ng lc ca qu trnh khuch tn, lm cho nc di chuyn t trong t bo ra gian bo v t trong ra ngoi, t v tr lin kt ra t do. Khi nc khuch tn cu trc t bo co rt, mt s cht tan bin hnh.Cc thng s nhit vt l thay i- Bin i nhit dung: nhit dung sn phm thay i l do nc trong thc phm ng bng.- Bin i h s dn nhit.- Bin i h s dn nhit .b. Bin i ha hcTrong qu trnh bo qun ng lnh cc bin i sinh ha, ha hc din ra chm. Cc thnh phn d b bin i l cc protein ha tan, lipid, vitamin, cht mu- Sbini protein: trongccloi proteinth proteinhatan trong nc l d b phn gii nht, s phn gii ch yu di dng tc dng ca enzyme c sn trong thc phm. S khuch tn nc do kt tinh li v thnghoacancgynnsbintnhproteinhatan. Bini protein lm gim cht lng sn phm khi s dng.- S bin i ca lipid: di tc ng ca enzyme ni tng lm cho cht bo b phn gii cng vi qu trnh thng hoa nc lm cho oxy xm nhp vo thc phm. l iu kin thun li cho qu trnh oxy ha cht bo xy ra. Qu trnh oxy ha ny sinh ra cc hp cht c mi v xu lm gim gi tr ca sn phm.- Cccht mub oxyhocnglmthayi musccasn phm.c. Bin i do vi sinhTrc khi lm lnh thc phm thng c ra sch loi b cc tp cht ni cha nhiu loi vi sinh vt.i vi sn phm ng lnh c nhit thp hn -150C v c bo qun n nh th s lng vi sinh vt gim theo thi gian. Ngc li nu sn phm lm ng khng u, v sinh khng ng tiu chun, nhit bo qun khng n nh s lm cho cc sn phm b ly nhim vi sinh vt, chng hot ng gy thi ra sn phm v gim cht lng sn phm.1.2.2.3. Cc phng php v thit b kt ng thc phmThit b cp ng c rt nhiu dng, hin nay nc ta s dng ph bin cc h thng sau:- Kho cp ng gi. - T cp ng tip xc.- T cp ng gi.- H thng cp ng dng ri, c bng chuyn IQF.+H thng cp ng c bng chuyn cp ng thng.+H thng cp ng c bng chuyn cp ng dng xon.+H thng cp ng siu tc.- H thng cp ng nhng nit lng.1.3. Mi cht lnh1.3.1. nh nghaMi cht lnh (tc nhn lnh) l cht mi gii s dng trong chu trnh nhit ng ngc chiu hp thu nhit ca mi trng cn lm lnh v thinhitramitrngcnhitcaohn. Mi chttunhonc trong h thng lnh nh qu trnh nn. Phn loi Da vo thnh phn hoa hoc: Mi cht v c: NH3 (R717), CO2(R744), Mi cht hu c: hydrocarbon, halocarbon Da vo nhit si v p sut bo ha Mi cht c p sut si cao: R744 Mi cht c p sut si trung bnh: R123, R134 Nhm mi cht c p sut si thp: R717, R507Ngoi ra cn da vo tnh c hi v tnh d chy n phn loi 1.3.2. Mi cht lnh NH3- NH3 l cht kh khng mu, c mi khai, chy trong oxy c ngn la mu vng.- L cht lnh r tin, d kim, d bo qun, c th sn xut trong nc. - Tuy NH3c hi nhng vn c coi l mi cht ca hin ti v tng lai. Tnh cht nhit ng: Hnh 1.1. Mi cht NH3- Nhit si p sut kh quyn: -33,35C- Nhit ng c: -77,7C- Nhit ngng t: 32C- p sut ngng t khong 12 15 kg/cm2- (00C) = 0,64kg/dm3 - Nng sut lnh ring khi lng q0 ln.- Nng sut lnh ring th tch qv ln (my nn v thit b gn nh).- Nhit cui tm nn cao (lm mt u xilanh v phi ht hi bo ha).- nht nh, tnh lu ng cao (tn tht p sut nh, ng ng v cc van gn nh).- H s dn nhit v trao i nhit ln (thun li cho vic thit k ch to thit b ngng t v bay hi).- Bn vng trong khong nhit v p sut cng tc, ch phn hy 2600C. (Tuy nhin nu b mt xilanh lm bng thp v c mt m lm cht xc tc th nhit 110 - 1200C b phn hy).Bng 1.1. Cc thng s trng thi 00Cn v Lng Hip sutMpa0,430,43Th tch ringdm3/kg1,57289,3Nhit dung ring - ng pkJ/(kg.K) 4,262,681,92 - ng tchkJ/(kg.K) 2,80 nht10-6 Pa.s170,099,06H s dn nhitW/(m.K)0,5590,023Sc cng b mt N/m 0,033Nhit ha hi kJ/kg 1262,2 Tnh cht ha hc NH3khng tc dng vi phi kim, kim loi en ch to my v kim loi mu (tr Cu v hp kim ca Cu). NH3 ha tan v tn trong H2O (khng b tc m van tit lu nhng phi khng ch m < 0,1%). NH3 khng ha tan du bi trn. Hn hp vi Hg s gy n. Khi c ngn la NH3 c th gy chy n nng 13% 16 % v t chy 6000C.Tnh cht sinh l c hi vi con ngi, gy kch thch nim mc mt v d dy, gy co tht cc c quan h hp, lm bng da. nng 0,007 - 0,1% th tch khng kh bt u c s hy hoi c quan h hp. T 0,2 - 0,3% c th lm m mt hoc lm cht ngt trong 30 pht. NH3 lm gim cht lng thc phm Bin php an ton Khi tip xc vi NH3 phi mang mt n phng c, khi x l s c h thng t nht phi c hai ngi. Khi b ngt phi a ra ch thong nhng phi m, xng hi m v ung cc cht kch thch: c ph, tr nng, Khi b bngphi nhanhchngrabngncschvm. Nu nng th phi a i bnh vin. 1.4. ng dng ca k thut lnh1.4.1. Bo qun thc phmLnh vc ng dng quan trng nht ca k thut lnh l dng bo qun thc phm. Theo thng k th khong 80% nng sut lnh c s dng trong cng nghip bo qun thc phm. Thc phm hu ht l cc sn phm b i thiu h hng do vi khun gy ra. bo qun thc phm ngoi phng php sy kh, phng x, bao b, x l khphng php lm lnh t ra c rt nhiu u im nh t lm gim cht lng, mu sc, mi v thc phm trong nhiu thng, thm ch nhiu nm bo qun.Bng 1.2. S ngy bo qun ph thuc vo nhit i vi c, tht b, gia cmNhit (0C) C Tht b Gia cm20 3 8 210 7 16 50 15 30 7-10 40 100 70-20 110 1000 230-30 230 2300 800Thc ra thi gian bo qun cn ph thuc vo nhiu yu t nh m, phng php bao gi, thnh phn khng kh ni bo qun, cht lng bn thnh phm,nhng nhit ng vai tr quan trong nht.Ngy nay, cng nghip thc phm xut khu ang gi mt vai tr ht sc quan trng trong nn kinh t ca nc ta v nn cng nghip ch bin thc phm ny khng th thiu nhng trang thit b hin i nht ca k thut lnh.1.4.2. Sy thng hoaSn phm sy u tin c kt ng xung - 200C sau c sy bngcchht chnkhngnncht lngsnphmhunhcgi nguyn vn. Khi s dng sn phm c ti hp th nc v gi nguyn c trng thi ban u c v cht lng, mu sc, mi vDo gi thnh sy thng hoa rt t nn t c ng dng cho thc phm m ch yu cho ngnh y, dc.1.4.3. Cng nghip ha cht ng dng quan trng nht trong cng ngh ha cht l vic ha lng v tch kh nh cng nghip sn xut kh clo, amoniac, carbonic, sulfuro, clohydryd, cc loi kh t, kh sinh hc, kh thin nhin, ha lng v tch khng kh,Ha lng v tch khng kh t khng kh ngnh cng nghip c ngha rt to ln i vi ngnh luyn kim, ch to my v cc ngnh kinh t khc k c y hc v sinh hc. Oxy v nito c s dng nhiu lnh vc khc nhau nh hn, ct kim loi, sn xut phn m, lm cht ti lnhcc loi kh tr nh heli, argon c s dng trong nghin cu vt l, trong cng nghip ha cht v sn xut bng n. K thut lnh cng h tr c lc trong cc cng ngh sn xut vi, si, t, cao su nhn to, phim nhnhit ng vai tr quan trng trong cc phn ng ha hc nn ngi ta cn s dng lnh iu khin tc phn ng ha hc. 1.4.4. iu ha ha chtiu ha khng kh cng nghip v tin nghi ngy nay l khng th thiu v thc s ang pht trin rt mnh m. Cc yu cu nghim ngt v nhit , m v thnh phn khng kh trong cc quy trnh cng ngh sn xut nh vi, si, in n, thuc l, in t, vi in t, my tnh, quang hcnht thit phi c iu ha khng kh.Cc dch v nh khch sn, du lch, vui chi gii tr, y t, th dc th thao, giao thng vn ticng khng th thiu c iu ha khng kh. Ngy nay k thut lnh thm nhp v h tr cho hng trm ngnhkinh t khc nhau.Chng 2. DY CHUYN CNG NGH V QU TRNH THIT B2.1. S t cp ng cp dch nh bm2.2. Nguyn l hot ngTrn hnhl s lnh v nguyn l hot ng ca t cp ng tip xc. H thng cp ng lm lnh nhit thp -400C v vy my nn c t s nn cao do phi s dng chu trnh nn 2 cp, 2 tit lu, lm mt bng bnh trung gian c ng xon.Hi mi cht s c ht v my nn h p v nn ln bnh trung gian, ti y mi cht s c lm mt trung gian hon ton. Sau khi c lm mt, hi mi cht c my nn cao p ht v v tip tc nn cao p. Hi sau khi nn cao p s i qua bnh tch du. Ti y, du s c tch ra khi hi mi cht trnh trng hp du s theo hi vo cc thit b trao i nhit lm gim hiu qu trao i nhit. Sau , mi cht s i vothit b ngng t. y l bnh ngng ng chm nm ngang s dng cho mi cht NH3. Bnh ngng t l thit b trao i nhit ngc dng nn mi cht c qu lnh ngay thit b ngng t. Ti bnh ngng mi cht lng s c lm mtbng nc nhmtthp giinhit. Saukhi himi chtc ngng t thnh lng s i qua bnh cha cao p, ng ng ni t bnh ngng t xung bnh cha cao p chnh l ng ng cn bng p. Bnh cha cao p dng cha lng mi cht p sut cao, gii phng b mt ca thit b ngng t duy tr s cp lng lin tc cho van tit lu. Sau mi cht lng s c tit lu t ng, lng tip tc i theo ng dn lng qua phin lc, khi qua y th cc cn bn c hc, nc, cc axit s c loi tr. Lng qua phin sy lc ri qua van in t, van in t c nhim v ng m nhm cung cp dch hoc ngng cp dch cho tit lu. Mi cht sau li i vo tit lu nhit ( y ta dng van tit lu t ng ), van tit lu t ng trong qu trnh lm vic t ng iu chnh khe h van nhm khng ch mc dch vo bnh trung gian va v duy tr, vi nhim v duy tr mc dch lun n nh nn trong bnh trung gian c gn van phao khng ch mc dch cc i trong bnh. Mi cht tip tc i qua van in t vo van tit lu tin hnh qu trnh cp dch cho h thng. Theo s ny dch lng c bm bmthng vo cc tmlc nn tc chuyn ng bn trong rt cao, hiu qu truyn nhit tng ln r rt do gim ng k thi gian cp ng. Tuy nhin, h thng phi c trang b bnh cha h p.Bnh cha h p c vai trrt quan trng, n va cnhim v cha dch cho bm hot ng, va gi vai tr tch lng: do dch chuyn ng qua cc tm lc l cng bc nn u ra cc tm lc vn cn mt lng ln lng cha bay hi, nu a trc tip v u ht my nn s rt nguyhim,gyvapthylchhngmynn. Bnhtchlngnh khng c kh nng tch ht lng lng qu ln, v th ch c bnh cha h p mi c kh nng tch ht lng lng ny. Hi mi cht sau tch lng s li c ht v li my nn h p v nh vy chu trnh mi s c lp li v tip tc.Chng 3.TNH TON S B T CP NG3.1. Cu to t cp ngT cp ng tip xc c s dng cp ng cc mt hng dng block, mi block thng c khi lng 2kg.Trn hnh 2.1 l cu to mt t ng tip xc. T c nhiu tm lc cp ng(freezerplates)bntrong, khongcchcctmcthiuchnh c bng ben thy lc, thng chuyn dch t 50-100mm. Kch thc chun ca cc tm lc l 2200L x 1250W x 22D (mm). i vi t cp ng t 2000kg/m tr ln, ngi ta s dng cc tm lc ln kch thc 2400L x 1250W x 22D (mm). Sn phm cp ng c t trong cc khay cp ng sau t trc tip len cc tm lc hoc cc mm cp ng, mi mm c 4 khay. Thng thng ngi ta t trc tip ln tm lc v hn ch c nhit tr dn nhit.Ben thy lc nng h cc tm lc t trn t cp ng. Pittng v cn dnbenthylclmbngthpkhngrmboyucuvsinh. H thng c b phn phn phi du cho truyn ng bm thy lc.Hnh 2.1. T cp ng tip xcKhi cp ng, ben thy lc p cc tm lc cho cc khay tip xc hai mt vi tm lc. Qu trnh trao i nhit l nh dn nhit. Trong cc tm lc cha ngp dch lng m su -40 -450C.Theo nguyn l cp dch, h thng lnh t ng tip xc c th chia ra lm cc dng sau:Cpdchtbnhchngtrn:vi tcpngdngny, dchlng chuyn dch dn vo cc tm lc nh chnh lch ct p thy tnh nn tc chuyn ng chm v thi gian cp ng lu 46 gi/m.Cp dch nh bm dch:mi cht chuyn ng vo cc tm lc di dng cng bc do bm to ra nn tc chuyn ng ln, thi gian cp ng gim cn 1 gi 30 2 gi 30 pht/m. Hin nay ngi ta thng s dng cp dch dng ny.Ngoi cc t cp ng s dng cc phng php nu trn vn cn c dng t cp ng bng tit lu trc tip. Trong trng hp ny, mi cht bn trong cc tm lc dng hi bo ha m, nn hiu qu truyn nhit khng cao, kh nng lm lnh km, thi gian cp ng ko di.Pha trong, bn trn t l cm ben va l gi nng cc tm lc, va l tm p khi ben p cc tm lc xung. cc tm lc khng di chuyn qua li khi chuyn ng, trn mi tm lc c gn cc tm nh hng, cc tm ny lun ta ln thanh nh hng trong qu trnh chuyn ng. Bn trong t cn c ng gp cp lng v hi ra, do cc tm lc lun di chuyn nn ng ng mi cht ni t cc ng gp vo cc tm lc l ng ni mm bng cao su chu p lc cao, bn ngoi c li inox bo v.Trn t cp ng ngi ta t bnh chng trn, h thng my nn thy lc ca ben v nhiu thit b ph khc.3.2. Kch thc s b3.2.1. Kch thc, s lng khay v tm lc cp ngCc sn phm cho vo t cp ng u c t vo trong cc khay nh v t trn cc tm trao i nhit (tm lc-freezer plates).Kch thc khay cp ng tiu chun nh sau:+ y trn: 290 x 210 mm+ y di: 280 x 200 mm+ Chiu cao: 70 mmTa chn tm lc cha 36 khay, mi khay cha 2kg sn phm Khi lng hng trn mt tm lc: 36.2 = 72kg T l chm nc t 25% - 30%, chn 28% Khi lng trn mt tm lc k c nc chm: m== 100kg/lcSlng tm lc c cha hng: N1 == = 10 tm Slng tm lc ca t: N= N1+1= 10 +1= 11 tm3.2.2.Kch thc t cp ngKch thc t cp ng c xc nh da vo kch thc v s lng cc tm lcTa b tr 36 khay trn 1 lc nh sau:T hnh v trn ta c:+ Chiu rng ca tm lc: W = 4.290 + 3.30 = 1250 mm+ Chiu di ca tm lc: L = 9.210 + 8.13 + 206 = 2200 mm Tm lc c kch thc : 2200L x 1250W x 22D (mm)3.2.2.1. Xc nh chiu di bn trong tChiudi bntrongtcpngbngchiudi tmlccngvi khong hhaiu. Khong h haiu cc tm lc va lp t cc ng gp, khnggian lp t v co gin cc ng mm v lp cc ng dn hng tm lc. Khong h l 400mm.Vy chiu di bn trong t l:L1 = 2200 + 2.400 = 3000 mm Chiu di ph b: L = L1 + 300 = 3300 mmHnh 2.2.B tr khay trn tm lc3.2.2.2.Xc nh chiu rng bn trong tChiu rng bn trong t bng chiu rng ca cc tm lc cng thm khong h 2 bn ( mi khong 125mm): W1= 1250 + 2.125= 1500mmKhi lp cc cnh ca t, mt phn 45mm cnh lt vo bn trong t v phn cn li 80mm nh ra ngoi, v vy kch thc b rng ph b l:W=W1 + 2.80=1660mm3.2.2.3. Xc nh chiu cao bn trong tKhong cch cc i gia cc tm lc: hmax=105mmChiu cao bn trong t:H1=N1.105 + h1 + h2N1 - S tm lc cha hngh1- Khong h pha di cng cc tm lc: h1 =100mmh2 - Khong h pha trn cc tm lc: h2 =400450mm3.3. Tnh cch nhit cch mCu to v t cp ng gm cc lp nh sau: lp cch nhit ch yu l polyurethan dy 150mm, c ch to theo phng php rt ngp c mt 40-42 kg/m3, c ng u v bm cao, hai mt trong v ngoi ca v t c bc bng inox dy 0,6mm bo v khi tc ng c hc, chng m v chng ng sng bn ngoi mt t.Ngoi ra bn trong v t l h thng khung chu lm bng thp c m km v cc thanh g chng to cu nhit.STT Lp vt liu dymmH s dn nhit W/m.K1 Lp Inox 0,6 222 Lp polyurethane- Vch t- Ca t1501250,0180,023 Lp Inox 0,6 22Bng 3.1. Cu trc cch nhit ca t ng tip xcChng 4. CN BNG NNG LNG CHO T CP NG4.1. Tn tht nhit do truyn nhit qua kt cu bao che (Q1) Dngnhit iquakt cubaochecnhnghaltngcc dng nhit tn tht qua tng bao, trn v nn ca t cp ng do s chnh lch nhit gia mi trng bn ngoi v bn trong t cng vi cc dng nhit tn tht do bc x mt tri qua tng bao v trn. Dotcpngct trongnhxngnnkhngchunh hng bi bc x mt tri. V vy ta ch xt tn tht nhit qua vch t, ca t cp ng. Tn tht nhit qua thn t gm vch t, ca t c tnh nh sau:Q= k.F(t1-t2)Q1=(kvFv + kcFc)(tKKN-tKKT)+ kv, kc - H s truyn nhit qua vch v qua thn t (W/m2.K)+ Fv, Fc - Din tch ca ca t v vch t (m2).+ tKKN = 250C: Nhit ca khng kh bn ngoi t.+ tKKT = -350C: Nhit khng kh trong t cui qu trnh cp ng Fv = 2.1,66.1,9 + 2.1,66.3,3 = 17,26m2 Fc = 2.3,3.1,9 = 13m2 H s truyn nhit c tnh theo cng thc sau:+ 1 - H s to nhit bn ngoi tng, 1= 23,3W/m2K.+ 2 - H s to nhit i lu t nhin trong t, 2 = 9W/m2K.+ 1 - B dy lp cch nhit cch m.+ 1 - H s dn nhit ca cc lp cch nhit, cch m.Vy:kv = =0,194 W/m2Kkc = =0,24 W/m2KQ1 = (0,194 . 17,26 + 0,24 . 13)(25 + 35) = 388W = 0,388kW4.2. Tn tht nhit do sn phm mang vo (Q2)Tn tht nhit Q2 gm:- Tn tht nhit lm ng sn phm QSP.- Tn tht nhit lm lnh khay cp ng QK.- Ngoi ra mt s sn phm khi cp ng ngi ta tin hnh chm thm nc mmtlp bng trn b mt lm cho b mt phng p, chng oxi ho thc phm, nn cng cn tnh thm tn tht nhit lm ng nc QN.4.2.1. Tn tht nhit lm ng sn phm (QSP)lmgimnhitsnphmthusnnnhityucu, h thng lnh phi ly i sn phm mt lng nhit no trong sut qu trnh lm ng.Nhit tn tht lm ng thc phm ly theo cng thc sau: QSP =G+ G - Khi lng sn phm mt m cp ng (kg).+ i1 -entanpy ca sn phm nhit ban u a vocp ng (kJ/kg), i1 = 314,4 kJ/kg (mt hng thy sn).+ i2 - entanpy ca sn phm nhit sau khi cp ng (kJ/kg), ), i1= 5 kJ/kg.+ Thi gian cp ng mt m sn phm (gi).Do sn phm c bo qun trc khi a vo lm ng nn nhit sn phm ta chn l 150C.Nhit trung bnh ca sn phm ly ra l -180C, vi cp ng cng bc bng bm dch do thi gian cp ng 2 gi. QSP=720.= 31 kW4.2.2. Tn tht nhit lm ng nc chm khun (QN)Nng sut t1000kg, khi lng sn phm thc l 720kg, vy khi lng nc chm khun l 280kg/m, h nhit nc chm khun t nhit u n nhit cui qu trnh cp ng cn qua ba giai on:QN = QN1 + QN2 + QN3+ QN1 - nhit lng lm h nc chm khun t nhit ban u n nhit im bng ca nc.+ QN2 - nhit tn tht lm ng bng nc chm khun.+ QN3 - nhit tn tht h nhit nc chm khun t nhit im bng n nhit cui ca sn phm.QN1 = MnckC (tN1 tN2)+ Mnck: khi lng nc chm khun Mnck = 280 kg/ m.+ C: nhit dung ring ca nc, C = 4,186 kJ/kg0C.+ tN1: nhit ca nc chm khun 50C.+ tN2: nhit im bng ca nc 00C.QN1 = 280.4,186.(5 - 0) = 5860,4 kJ/mThi gian lm vic mi m l 2 gi: QN1= = 0,81 kWQN2 = MnckL+ L - Nhit lng ng bng ca nc L = 335 kJ/kg.QN2 = 280.335 = 93800 kJ/m = 13 kWQN3 = CN3 Mnck(tN2 tN3)+ C3 - Nhit dung ring ca nc C3 = 2,18 kJ/kg.+ tN3 - Nhit ca nc cui qu trnh cp ng tN3 = -180C.QN3 = 280.2,18.(0+18)= 16027,2 kJ/m =1,52 kWVy nhit tn tht lm ng nc chm khun:QN = 0,81 + 13 + 1,52 = 15,33 kW4.2.3. Tn tht nhit lm lnh khay cp ng (QK) QK = CKMK + MK - Tng khi lng khay cp ng (kg).+ CK - Nhit dung ring ca vt liu lm khay, vi vt liu lm khay bng km theo ti liu, CK = 0,094kcal/kg = 0,39 kJ/kg0C.+ t1K - nhit khay trc khi a vo cp ng ly t1K = 250C.+ t2K - nhit ca khay sau qu trnh cp ng ly t2K = -350C. + - thi gian ca mt m cp ng (gi).Ta c 11 tm lc, 10 tm ng sn phm, mi tm c 36 khay, mi khay nng 2kg Vy ta c tng khi lng khay cp ng l : 10 . 36 = 360 khay.Khi lng mi khay l 2kg vy: MK = 2 . 360 = 720 kg/m QK = 0,39.720 . = 2,34 kW Vy tn tht nhit do sn phm mang voQ2= QSP + QN + QK = 31 + 15,33 + 2,24 = 48,67 kW4.3. Tn tht nhit t cc ngun khc nhau (Q3)Ngoi nhng tn tht nhit ni trn cn phi k n:- Tn tht nhit lm lnh cc tm lc QTL- Tn tht nhit lm lnh khng kh trong t QKK- Tn tht nhit khi m ca QC4.3.1. Tn tht nhit lm lnh tm lc (QTL)T ng tip xc lm vic tng m sau khi lm ng xong s dng my v ra hng, khi lng v din tch ca tm lc rt ln do nhit lm lnh cc tm lc l rt ln v vy ta phi tnh lng nhit ny. QTL =(t1-t2) + MTL - khi lng cc tm lc (kg).+ CTL - nhit dung ring ca cc tm lc, tm lc ch to bng nhm nn c CTL = 0,92 kJ/kg0C.+ - Thi gian cp ng.+ t1, t2 - Nhit trc v sau khi cp ng, t1 = 250C, t2 = -350C.Vt liu tm lc lm bng nhm c = 2670 kg/m3.Th tch tm lc: V = 2,2 . 1,25 . 0,022 = 0,06 m3Khi lng mt tm lc:M = 0,06 . 2670 = 161 kgT 1000 kg trn m gm 11 tm lc:MTL = 11 . 161 = 1771 kg QTL= (25+35)=13,57 kW4.3.2. Tn tht nhit lm lnh khng kh trong t (QKK)Nhit tn tht do khng kh trong t c tnh nh sau:Qkk = CkkGkk(td tc)+ td - nhit khng kh lc bt u chy my 250C+ tc - nhit khng kh cui qu trnh cp ng -350C+ Ckk - nhit dung ring ca khng kh trong t Ckk=0,242 Kcal/kg0C = 1,013kJ/kg 0C.+ Gkk - khi lng ca khng kh c trong t, c xc nh:Gkk = Vkk .kkKch thc trong ca t:L = 3000 mmW = 1500 mmH = 1600 mm+ Vkk: th tch ca khng kh c trong tVkk =Vt =. 3.1,5 . 1,6 = 4,8 m3+ kk- khi lng ring trung bnh ca khng kh trong t -300C, kk =1,453kg/m3Gkk = 4,8 . 1,453 = 6,97 7kg/m Qkk = 1,013 . 7 = 0.06kW4.3.3. Tn tht nhit do m ca (QC)Tn tht nhit do m ca c tnh theo cng thcQC = B . F(W)+ F - Din tch ca t cp ng (m2)Theo nh tnh ton ta c :Chiu di t l : L = 3,3 mChiu rng t l : W = 1,66 m Do d F = 3,3 . 1,66 = 5.478 m2+ B - Dng nhit khi m ca, W/m2. Chn B = 20 W/m2.[1-87]Vy QC = 20 . 5,478 = 110W = 0,11 kWVy tn tht nhit t cc ngun khc nhau l:Q3= QTL + QKK + QC = 15,37 + 0.06 + 0,11 = 13,74Tng tn tht nhit l:Q01= Q1 + Q2 + Q3= 0,388 + 48,67 + 13,74 = 68,2 kW t hot ng an ton mi iu kin nn cn phi nhn thm h s an ton l 1,1.Q01 = 1,1 . 62,8 = 69,1 kWVy nng sut lnh ca my nn theo yu cu ca t cp ng tip xc l:Q0 = 69,1 kWChng 5.TNH CHN MY NN5.1. Chn mi cht cho t cp ngMichtlnhthngdngtronghthnglnlNH3, NH3tuyc nhc im c hi nhng c u im v mt kinh t cng nh tnh cht nhit ng, tn tht p sut trn ng ng v cc ca van nh v vy ta chn mi cht NH3 cho t cp ng.5.2.Ccthngscachlmvicvchnchu trnh lnh ca h thng5.2.1. Nhit si ca mi cht lnh (t0)Nhit si ca mi cht lnh ng vi t ng tip xc l -400C.5.2.2. Nhit ngng t ca mi cht (tk)Ta s dng thit b ngng t lm mt bng nc kiu bay hi.tk = tw2+tk+ tw2 Nhit nc ra khi dn ngng.+ tk Hiu nhit ngng t yu cu, tk= 350C.tw2 = tw1+(260C)+ tw1 nhit nc vo dn ngng.Do nh my s dng nc thnh ph nn nhit s ly cao hn nhit trung bnh nm 30C.Nh my xy dng ti Vng Tu, theo bng ta c ttb = 240C.tw1 = 24 + 3 = 270Ctw2 = 27 + 2 = 290Ctk = 29 + 4 = 330CT nhit tk = 330C tra bng hi bo ho NH3 , pk = 1,27 Mpa.5.2.3. Nhit qu lnh, qu nhit v chu trnh lnh Nhit qu lnhL nhit mi cht lnh trc khi i vo van tit lu. Nhit qu lnh cng thp nng sut lnh cng ln do ngi ta h c nhit qu lnh xung cng thp cng tt. Tuy nhin i vi my lnh khng hi nhit NH3 th nhit qu lnh khi i qua thit b trao i nhit ngc chiu vn cao hn nhit nc l 350C.tql = tw1 + (350C) = 27+ 4 = 310C Nhit qu nhitNhit qu nhit l nhit ca hi nc trc khi vo my nn. Nhit qu nhit lun ln hn nhit si ca mi cht. Hi phi l hi qu nhit khng ht phi lng. i vi tc nhn l NH3.tqn = - 40 + 10 = -300C Chu trnh lnhi vi h thng cp ng hai cp chu trnh lnh l h thng c chn hai cpbnh trung giancng xon.Micht lnhlng qu lnh trong ng xon nhit khng h n nhit trung gian v tn ti hiu nhit trao i nhit khng thun nghch trongng xon nhit qu lnh ln hn nhit trung gian khong 50C.Hnh 5.1. Chu trnh hai cp nn bnh trung gian c ng xonHisau khi ra khi thitbbay hic my nn h pnnon nhit n p sut trung gian (im 2) ri c sc vo bnh trung gian v c lm mt hon ton thnh hi bo ho kh, hn hp hi bo ho kh to thnh bnh trung gian c my nn cao p ht v v nn on nhit - BH : Bnh bay hi- NHA :My nn h p- NCA : My nn cao p- NT : Bnh ngng t- TL1, TL2: Vantit lu1 v 2.- BTG Bnh trung gian n p sut ngng t PK(im 4). Sau i vo thit b ngng t v nh nhit trong mi trng lm mt ngng t thnh lng cao p (im 5). Ti y n chia ra lm 2 dng, mt dngnhthiqua vantitlu 1 gim p sutnp sut trung gian Ptg (im 7) ri i vo bnh trung gian. Ti y lng hi to thnh do van tit lu 1 cng vi lng hi to thnh do lm mt hon ton hi nn trung p v lng hi to thnh do lm qu lnh lng cao p trong ng xon c ht v my nn cao p . Mt dng lng cao p cn li i vo trong ng xon ca bnh trung gian v c qu lnh ng p n im 6 sau i qua van tit lu 2 gim p sut n p sut bay hi (im 10). Sau i vo thit b bay hi nhn nhit ca sn phm cn lm lnh ho hi ng p ng nhit thnh hi (1) v chu trnh c th tip tc .Hnh 5.2. chu trnh biu din trn th T - s1 1: Qu nhit hi ht h thng bay hi -400C.1 2: Nn on nhit cp h p -400C.2 - 3: Lm mt hi qu nhit n hi bo ha.3 - 4: Nn on nhit cp cao p.4 5: Lm mt bng ngng t.5 5: Qu lnh trong bnh ngng.5 7: Tit lu t bnh trung gian h p sut t pk xung ptg.5 6: Qu lnh lng ti bnh trung gian.6 -10: Tit lu h t pk xung p0.10 1: Trao i nhit ng p thit b bay hi.5.3. Tnh chu trnh lnh v chn my nn5.3.1. Tnh chu trnh lnhTa c: Ptg =+ ptg p sut trung gian.Hnh 5.3. S chu trnh lnh310C+ p0 p sut thit b bay hi -400C, p0 = 0,072 MPa.+ pk p sut ngng t h thng, pk = 1,27 MPa. Ptg == 0,302 MPa.Tra bng hi bo ha ca NH3 ta c ttg = -90C.[2-342]Chn nhit qu lnh trong ng xon l -40C.+ T s nn:01, 2717, 6 90, 072kpp >Chn chu trnh lnh nn 2 cp bnh trung gian c ng xon.T cc thng s trn tra bng hi bo ha v th lgP h ca mi cht NH3 ta c cc thng s bng di y:Bng 5.1. Cc thng s im nt ca chu trnhNhit p sut Entanpy Th tchim nt t , 0C P, Mpa h, kJ/kg v, m3/kg1 -40 0,072 1720 1,751 -30 0,072 1735 1,82 60 0,302 1920 0,533=8 -9 0,302 1750 0,44 90 1,27 1950 0,135 31 1,27 6456 -4 1,27 4907 -9 0,302 6457 -9 0,302 4909 -9 0,302 45510 -40 0,072 490 Nng sut lnh ringNng sut lnh ring l nng sut ca 1 kg cht lng p sut cao v nhit cao to ra trong qu trnh tit lu v bay hi ht trong thit b bay hi thnh hi bo ha kh nhit bay hi v p sut bay hi.q0= h1 - h10= 1720 490 = 1230 kJ/kg Nng sut lnh ring th tch3 01230683, 3 /1, 8vqq kJ mv Cng nn ringCn bng enthalpy bnh trung gian ta c:1 5 3 1 7 1 2 3 3 1 6. ( ). . . . m h m m h m h m h m h + + +3 2 5 7 61 3 7m h h h hm h h+ Cng nn ring 31 21.ml l lm+2 61 23 71920 4901920 1735 (1950 1750) 444 /1750 645h hl l l kJ kgh h + + Nng sut ring34 51( )kmq h hm 1920 490(1950 645) 1689 /1750 645kq kJ kg Tnh h p Lu lng thc t qua my nn h p01069,10, 056 /1230Qm kg sq Th tch ht thc t ca my nn h p31 1. 0, 056.1, 8 0,1 /ttHAV m v m s H s cp nn h p. . . .c tl k w r c: h s tnh n th tch chit.tl: h s tnh n tn tht do van tit lu.w: h s tnh n tn tht do hi ht vo xilanh b t nng,w = 0,95.r: h s tnh n tn tht do r r mi cht qua piston xilanh. Chn r = 0,97.C th rt gn thnh = i.ww = 0,97.0,95 = 0,9210 0 010 0 0. .mtg tgoc tl kp pp p p pcp p p 1+ _ 1 1 , 1 ]Vi my nn amoniac m = 0,95 1,1. Chn m = 1.c: t s th tch chit, c = 0,03 0,05. Chn c = 0,04.0 0 0 00 0 0.0, 92tg tgHAp pp p p pcp p p 1 1 + _ 1 1 1 , ] ]Thng ly p0 = 5.103 Pa,ptg = 10.103 Pa.72 5 302 10 72 50, 04 .0, 92 0, 7572 72 72HA 1 1 _ 11 , ] ] Th tch ht l thuyt cp h p30,10,135 /0, 75ttHAttHAHAVV m s Cng nn on nhitNsHA = m1.l1 = m1.(h2 - h1) = 0,056.(1920 1735) =10,36 kW Hiu sut ch th00 0233. 0, 001. 0, 001.( 40) 0, 84264i wtgTb t tT + + + Cng sut ch th10,3612,330,84sHAiHAiNkW Cng sut ma st.ms ttHA msN V p pms: l p sut ring ma st, pms = 49 69 Pa, chn pms = 59 Pa.0,1.59 5, 9msN kW Cng sut hu ch12, 33 5, 9 18, 23eHA i msN N N kW + + Cng sut tip in cp h p.eelHAtd elNNN td: hiu sut truyn ng ca khp, ai td = 0,95.el: hiu sut ng c, el = 0,85.18, 2322, 580, 95.0, 85elHAN kW Tnh cp cao p Lu lng hi thc t qua my nn cao p2 63 13 71920 4900, 056. 0, 0725 /1750 645h hm m kg sh h Th tch ht thc t cao p33 3. 0, 0725.0, 4 0, 029 /ttCAV m v m s H s cp ca cp cao p. .0, 93tg tg tg tgk ki wtg tg tgp p p pp pcp p p 1 _ + 1 1 , ]302 5 1270 10 302 50, 04 .0, 93 0, 793302 302 302 + 1 _ 1 , ] Th tch ht l thuyt cao p30, 0290, 037 /0, 793ttCAltCAVV m s Cng nn on nhit cp cao p3 2. 0, 0725.(1950 1750) 14, 5sCAN m l kW Hiu sut ch th cp cao p2640, 001.( 9) 0, 85306tgi w tg tgkTbt btT + + + Cng sut ch th cp cao p14, 5170,85sCAiCAiNN kW Cng sut ma st cao p. 0, 029.59 1, 71msCA ttCA msN V p kW Cng sut hu ch17 1, 71 18, 71eCA i msN N N kW + + Cng sut tip in cp cao p18, 7123,17. 0, 95.0, 85eelCAtd elNN kW Cng sut tip in cp h p v cao p22, 58 23,17 45, 75elN kW + Cng sut ng c lp t cho my nn hot ng an ton, cng sut ng c lp t phi ln hn cng sut tip din, do ta nhn thm h s an ton k (k = 1,1 2,1).1, 6.45, 75 73, 2DCN kW 5.3.2. Chn my nnChn my nn pittng MYCOM hai cp nn mi cht NH3. [2-55]Tk, 0C K hiu Pittng xS, mmS xilanhTc Th tch qut, m3 /hQo, 1000 Kcal/hNe, kW-40 -4040 N62A 95 x 76S6+2 10001200258,6310,325,330,419,323,1Chng 6.TNH TON THIT B TRAO I NHIT6.1. Tnh chn thit b ngng t6.1.1. Vai tr ca thit b ngng tThit b ngng t c nhim v: khi my nn nn mi cht t trng hi bo ha thnh hi qu nhit v c thit b ngng t lm mi cht chuyn sang trng thi lng. Thit b ngng t c nh hng n p sut v nhit ca chu trnh lnh do nh hng n hiu qu v an ton ca h thng. Khi thit b ngng t lm vic km hiu qu th cc thng s ca h thng s b thay i theo chiu hng xu nh:- Nng sut lnh h thng gim, tn tht tit lu tng.- Nhit cui qu trnh nn tng.- Cng nn tng, ng c c th qu ti.- an ton gim do p sut pha cao tng, rle HP c th tc ng dng my nn- Nhit cao nh hng n nht ca du, dn ti chy du6.1.2. Cu to v nguyn l lm vic ca thit b ngng tTrn hnh 6.1. trnh by cu to bnh ngng ng chm nm ngang s dng trong cc h thng lnh NH3. Bnh ngng c thn hnh tr nm ngang lm t vt liu thp CT3, bn trong l cc ng trao i nhit bng thp p lc C20. Cc ng trao i nhit c hn kn hoc nc ln hai mt sng hai u. c th hn hoc nc cc ng trao i nhit vo mt sng, n phi c dy kh ln t 20 30mm. Hai u thn bnh l cc np bnh. Cc np bnh to thnh vch phn dng nc nc tun hon nhiu ln trong bnh ngng. Mc ch tun hon nhiu ln l tng thi gian tip xc ca nc v mi cht; tng tc chuyn ng ca nc trong cc ng trao i nhit nhm nng cao h s to nhit . C mt ln nc chuyn ng t u ny n u kia ca bnh th gi l mt pass. V d bnh ngng 4 pass, l bnh c nc chuyn ng qua li 4 ln. Mt trong nhng vn cn quan tm khi ch to bnh ngng l b tr s lng ng ca cc pass phi u nhau, nu khng u th tc nc trong cc pass s khc nhau, to nn tn tht p lc khng cn thit.Hnh 6.1. Cu to bnh ngng ng chm nm ngang1- Np bnh;2- ng x kh khng ngng; 3- ng cn bng; 4- ng trao inhit; 5- ng gas vo;6- ng lp van an ton; 7-ng lp p k ; 8- ng xhi ca nc; 9- ng nc ra; 10- ng nc vo; 11- ng x cn; 12- nglng v bnh chaCc trang thit b i km theo bnh ngng gm: van an ton, ng h p sut vi khong lm vic t 0 30 kG/cm2l hp l nht, ng ng gas vo, ng cn bng, ng x kh khng ngng, ng lng v bnh cha cao p, ng ng nc vo v ra, cc van x kh v cn ng nc. gas phn b u trong bnh trong qu trnh lm vic ng ng gas vo phn thnh hai nhnh b tr hai u bnh v ng ng lng v bnh cha nm tm bnh. Nguyn l lm vic ca bnh nh sau: gas t my nn c a vo bnh t hai nhnh hai u v bao ph ln khng gian gia cc ng trao i nhit v thn bnh. Bn trong bnh gas qu nhit trao i nhit vi nc lnh chuyn ng bn trong cc ng trao i nhit v ngng t li thnh lng. Lng ngng t bao nhiu lp tc chy ngay v bnh cha t bn di bnh ngng. Mt s h thng khng c bnh cha cao p m s dng mt phn bnh ngng lm bnh cha. Trong trng hp ny ngi ta khng b tr cc ng trao i nhit phn di ca bnh. lng ngng t chy thun li phi c ng cn bng ni phn hi bnh ngng vi bnh cha cao p.6.1.3. Tnh thit b ngng tNhit lng thit b ngng t l nhit lng m nc v gi lm mt ly i mi cht ngng t, tnh nhit thit b ngng t tnh cng sut ca thit b ngng t.Qk = m3 (h4 - h5) = 0,0725.( 1950-645) = 94,61 kWTrong :Mt khc: Qk = K.F.ttb ttb=== = 5,150C+ K = 700 W/m2.K [3-194]294, 61.100013, 52. 700.10BHtbQF mK t Chn bnh ngng ng v NH3 nm ngang do Nga ch to.[2-161]Kiu B mt F, m2Kch thc S ng nS li zChiu di ng l, mmDung tch khng gian, m3Khi lng, kgng knh D1Di Rng BCao HNgoi ngTrong ngThit bCng tcKT-2525 500 3430810 910 144 8 3000 0,39 0,17 1140 15606.2. Thit b bay hi6.2.1. Vai tr ca thit b bay hiThit b bay hi c nhim v ho hi gas bo ho m sau tit lu ng thi lm lnh mi trng cn lm lnh. Nh vy cng vi thit b ngng t, my nn v thit b tit lu, thit b bay hi l mt trong nhng thit b quan trng nht khng th thiu c trong cc h thng lnh. Qu trnh lm vic ca thit b bay hi nh hng n thi gian v hiu qu lm lnh. l mc ch chnh ca h thng lnh. V vy, d ton b trang thit b h thng tt n u nhng thit b bay hi lm vic km hiu qu th tt c tr nn v ch.Khi qu trnh trao i nhit thit b bay hi km th thi gian lm lnh tng, nhit phng khng m bo yu cu, trong mt s trng hp do khng bay hi ht lng trong dn lnh dn ti my nn c th ht m v gy ngp lng.Ngc li, khi thit b bay hi c din tch qu ln so vi yu cu, th chi ph u t cao v ng thi cn lm cho qu nhit hi ra thit b ln. Khi qu nhit ln th nhit cui qu trnh nn cao, tng cng sut nn.La chn thit b bay hi da trn nhiu yu t nh hiu qu lm vic, c im v tnh cht sn phm cn lm lnh.6.2.2. Tnh chn thit b bay hi QBH = m1 (h1 - h10) = 0,056.(1720 - 490)= 68,88 kWMt khc:QBH = k.F.ttbChn thit b bay hi ng v kiu ngp+ F - Din tch trao i nhit ca thit b bay hi.+ K - H s truyn nhit ca thit b bay hi, xc nh theo kinh nghim.+ ttb - Hiu nhit gia mi cht si trong ng v khng kh trong kho, ttb = 100C.+ H s truyn nhit K= 460580W/m2K. Chn K= 520W/m2K. [3-201]268,88.100013, 25. 520.10BHtbQF mK t Chn dn lnh NH3 Alfa Laval. [2-186]TypAVQ0KWVm3/hPbarFm2D1mmD2mmLmmL1mmBmmHmmVdm3mkg35,20 98,6 16,9 0,12 13,25 355,6 114,3 355,62000 2290 570 834+D2100 410Chng 7.TNH TON THIT B PH7.1. Bnh tch duTrong my nn c du bi trn bi trn cc chi tit chuyn ng v lm mt my nn. Khi my nn lm vic du thng cun theo mi cht lnh, vic du b cun theo mi cht lnh c th gy ra cc hin tng:- My nn thiu du lm ch bi chn khng tt- Du sau khi theo mi cht lnh s ng bm cc thit b trao i nhit nh thit b ngng t, thit b bay hi, lm gim hiu qu trao i nhit, nh hng chung n ch lm vic ca ton h thng Nguyn l lm vicGim tc tngt dnggast tccao(khong18 25m/s) xung tc thp 0,5 1 m/s. Khi gim tc t ngt cc git du mt ng nng v ri xung, do nhtca gas nh hn ca du nn ng nng nh v dng hi nn vn chuyn ng bnh thng.Du c tch nh 3 nguyn nhn:- Gim vn tc ca dng khi i t ng nh ra ng to lm lc qun tnh gim v di tc dng ca trng lc cc ht du nng ri xung. - Do lc ly tm khi ngot dng cc ht du nng b vng ra va p vo thnh bnh ri xung. - Do s mt vn tc t ngt khi va p vo cc tm chn. Cc ht du nng c gi li v ri xung y bnh. Cu to bnh tch duHnh 7.1. Cu to bnh tch du1.Hi vo t u y my nn; 2. Van an ton; 3. ng ra hi cao p; 4,5. Nn chn; 6. Phao; 7. ng x du Tnh chn bnh tch dud4dmV : tc mi cht ng ni vo bnh tch du. Chn = 18 (m/s).[2-222] Vd: th tch ring thc t ca mi cht ra khi my nn.m: lu lng hi (kg/s).Vd = VCA=0,4(m3/kg)m = mCA = 0,0725 (kg/s) 4 4.0, 0725.0, 40, 0453,14.18dmVd m 7.2. Bnh cha duBnh thu hi du nhm mc ch thu gom du t cc thit b nh bnh cha thp p bnh trung gian, bnh cha cao p gim tn tht v gim nguy him khi x du cc thit b c p sut cao Cu to bnh cha duHnh 7.2. Cu to bnh tp trung du1.Gas v ng ht h p my nn; 2.p k ; 3,4,5.Du vo bnh tp trung t cc thit b; 6. Knh xem mc; 7. ng du ra.7.3. Bnh cha cao pBnh cha cao p phi tho mn cc yu cu sau:+ Khi h thng ang vn hnh th lng lng cn li trong bnh t nht l 20% dung tch bnh.+Khi sacha, bodngth bnhchaphi ckhnngcha c ton b mi cht ca h thng v ch chim khong 80% dung tch bnh. Cu to bnh cha cao p Sc cha ca bnh cha cao p c tnh nh sau:VCA = = 0,7VdHnh 7.3. Nguyn l cu to bnh cha cao p1. Knh xem mc; 2. Van chn; 3. ng lp van an ton; 4. nglp p k x; 5. ng lng vo; 6. ng cn bng p; 7. ng cp dch; 8. ng hi lng; 9. Thn bnh; 10. X du; 11. X cn; 12. Chn bnh121 25116341198713+ VCA - Th tch cha ca bnh cha cao p.+ Vd - Th tch cha ca dn bay hi. Th tch cha mi cht ca t ng tip xc.Kch thc ca tm lc l 2200 x 1250 x 22mmVy kch thc cha mi cht 2194 x 1244 x 16mm = 21,94 x 12,44 x 0,16 dmVbh = Vd = 11 . 21,94 . 12,44 . 0,16 = 480 ltVy th tch ca bnh cha cao p.VCA = 0,7 .480 = 336 lt7.4. Bnh cha trung gianCng dng chnh ca bnh trung gian l lm mt mi cht trung gian gia cc cp ca my nn. Ngoi ra n cn c nhim v tch lng mi cht m bo cho hi ht tm cao ca my nn cao p l hi bo ho kh. Trong h thng lnh s dng bnh trung gian c ng xon. Cu to bnh trung gian12345678Hnh 7.4. Cu to bnh trung gian1.ng vo ca hi nn trung p; 2. ng lng cao p tit lu vo bnh;3. ng ra ca hi trung p; 4. Cc nn chn; 5. ng thu ti v van phao;6. Phin lc; 7. ng xon TN; 8. ng x du; 9. ng tho lng ra khi bnh; 10. ng ra lng cao p; 11. Van an ton; 12. p k; 13. L cn bngTnh din tch b mt ng xon da vo b mt truyn nhit chn bnh trung gian cho thch hp. F= K: h s dn nhit thp, K = 54.ttb: khong chnh lch nhit , ttb= 31 - (-4) = 350CQ0x Ph ti nhit ca ng xon.Q0x= m3 (h5-h6)= 0,029 (645-490) =4,495 kWSuy ra:24, 495.10002, 3854.35F m 7.5. Thp gii nhit Cu toThp gii nhit l mt thit b trao i nhitHnh 7.5. Cu to thp gii nhit1. Qut ht; 2. B phn tch nc; 3. Dn ti nc; 4. B phn lm ti nc; 5. V bo v; 6. Mng cha nc; 7. Phao cp nc b sung; 8. ng dn nc Tnh lu lng v din tch cn thitLu lng:VM= +C - Nhit dung ring ca nc, C= 4,186kJ/kg0C.+- Khi lng ring ca nc, = 998 kg/m3.+ttb - chnh lch nhit ca nc vo v ra,ttb = 29-26,5 = 2,50C.VM == 9 l/sDin tch:F = = = 2,1 m2+ qf- Ti nhit ring, qf =45kW/m2.Vy chn thp gii nhit c thng gi vi lu lng nc l 9 l/s.7.6. H thng ng ngTt c ng knh trong ca cc ng ng c tnh theo cng thc sau: di=+ di - ng knh trong ca ng dn.+ - tc dng chy trong ng+ m - Lu lng thc t ca mi cht i qua my.+ Vd - Th tch ring ca mi cht lnh.Ta chn vn tc ca mi cht trn ng nn = 20m/s, trn ng ng ht = 17m/s, trn ng ng dn lng = 0,5 m/s.on ng m(kg/s) v(m3/kg) (m/s) d(mm) Chn da/ di (mm)Ht h p my nn cp ng0,064 1,8 17 93 108/100Ht cao p my nn cp ng0,083 0,4 17 50 76/69Nn h p my nn cp ng0,064 0,53 20 46,5 76/69Nn cao p my nn cp ng0,083 0,13 20 40,9 57/50ng dn lng t ngng t v BCCA , v BTG v v BCHA0,303 0,0016 0,7 29,7 38/33,5ng dn lng t bm dch n t cp ng0,1995 0,0016 0,7 10 18/14ng gp nn mi cht t cp nn h p n trunggian0,235 0.53 20 88,8 108/100ng gp nn mi cht tcp nn cao p n ngng t0,303 0,13 20 51 76/79ng gp ht mi0,303 0,4 17 95,3 108/100cht t trung gian v my nn cao png gp ht mi cht tBCHA v cpmy h p0,2335 0,7 17 172 219/209KT LUNDa vo cc kt qu tnh ton trong bi ta c th la chn nhng thit b chnh ph hp vi h thng a vo hot ng. Trong qu trnh hot ng m bo tnh an ton v n nh trong vn hnh, ta cn phi tnh n phn kim tra an ton h thng v tnh t ng ha cho h thng. C nhvy th h thng mi hot ng an ton, hiu qu v ng yu cu t ra ca ngi thit k. Tuy vy, trong khun kh ni dung ca ti, nhm em khng th trnh by ton b ni dung ca phn ny m ch ch trng vo phn tnh ton v thit k h thng theo yu cu ca ti c giao.Kt qu tnh ton:- Kch thc t cp ng: 3300 x 1660 x 1900 (D x R x C).- S tm lc: 11 tm.- Cng sut my nn lp t: 73,2 kW.- Thit b ngng t: + Cng sut thit b ngng t: 93,96 kW.+ Din tch b mt: 26,06 m2.- Thit b bay hi: din tch trao i nhit: 540m2Trong qu trnh tnh ton thit k, tuy tnh n cc tn tht c bn ca h thng lnh nhng vn cha cp n nhng tn tht lnh c th c v c b qua qu trnh tnh ton c nhanh chng v n gin hn. V vy kt qu xc nh c tuy khng phi l chnh xc tuyt i nhng cng p ng c cc yu cu c bn ca h thng.Mc d c gng rt nhiu nhng do kh nng c hn nn chc chn khng th trnh khi sai st. Rt mong Qu Thy C v cc bn ng gp kin qu bu gip ti hon thin hn.TI LIU THAM KHO[1]. Nguyn c Li Hng dn thit k h thng lnh NXB Khoa hck thut, H Ni 1999. [2]. Nguyn c Li Phm Vn Ty K thut lnh c s - NXB Gio dc 2007 (ti bn ln th 7).[3]. Nguyn c Li Phm Vn Ty- My v thit b lnh NXB Gio dc 2005 (ti bn ln th 4).[4]. Nguyn c Li Phm Vn Ty Bi tp k thut lnh NXB Gio dc 2004.