Giả lỏng các hạt rắn để ứng dụng trong sấy muối tinh bằng lớp hạt sôi liên tục

NGHIEN cuu - TRAO DOI GIA LONG CAC HAT RAN DE UfNG DUNG TRONG SAY WIUOI TINH BANG LdP HAT SOI LIEN TUG THE FLUIDIZATION OF SOLID PARTICLES FOR APPLICATIONS TO REFINED SALT IN THE CONTINOUS FLUIDIZED BED TS Bui Trung Thanh Khoa Cong nghe Nhiet lanh, Traong Dai hoc Cong nghiep TP H6 Chi Minh TOM TAT Ky thuat lam gia long cac hat vat lieu roi duffc img dung nhieu thuc tien nhu: Say tdng s tao hat lop soi hoc vien nang bang lap soi nganh Duoc pham va dot nhien lieu l lap hat soi Trong bai bao, tac gia trinh bay cac dac tinh cua phuang phap "gia long " va ihtg dijng de xay mo hinh say mudi tinh lop hat soi Tic mo hinh toan tac gia da tien den thuc hien thiet ke, ch va thuc nghiem say mudi tinh tdng soi vai ndng sudt sdy 3.000 kg/gia san xuat thuc tien Tir Khoa: Gid long; Trao doi nhiet; Dong hat; Tdng soi; Mdy sdy mudi tinh ABSTRACT Fluidization of solid particles ts the operation by which solidparticles are transformed intofluid state This method of contacting has some unusual characteries and in practice, it's engineering p them to good use In this paper, an expansion for fluidization of solid particles for drying on thefluidized is give Method, modeling, comparison, expriment in Lab and industral Techonologyfor drying with its ca is 3.000kg refined salts by an hour Keywords: Fluidization; Fluid-solid; Heat transfer: Fluidized bed drying, refined Salt dryer TAP CHi CO KHi VIET NAlVt, S6 nam 2014 www.cokhivietnam.vn NGHIEN CUU - TRAO DOI BAT VAN DE De lam khd mudi tinh sau cdng doan nghiln, nia, ly tam ngudi ta phai thuc hien s4y khd chung bang each: Say rang (ung dung nguyen ly truyin nhiet d§n nhiet kk hop vdi s4y ddi lim) cdn goi la say tiep xiie bang, may say thung quay cd cac canh dao tron cd gan gan bi de go chdng dinh bam, hoac say tren may say rung (ung dung nguyen ly truyen nhiet ddi luru) Trong thuc te cdn cd th6 sSy chung bSng phucmg phap say tang soi, phuang phap sSy tang soi khdng can khuay, khong can dao trdn, khdng can rung De say dugc Idp mudi tinh bang phuang phap say nay, ngudi ta phai thuc hien lam gia Idng cac hat ran, nham tao su ddng nhat ve nguyen vat lidu Khi say hat d trang thai sdi gia Idng, cac hat dugc nhan nhiet bang truyen nhiet ddi luu - hat, truyen nhiet dan nhiet va bue xa hat-hat va truyen nhiet dan nhiet hat vdi be mat ndng [10] Cac each truyen nhiet lam cho am nhanh chdng dugc tach khdi be mat hat de hat nhanh chdng dugc lam khd, trd san pham cd kha nang luu trii dai cho qua trinh sur dung Thdng thudng de say cac hat rin bang Idp hat sdi, ngudi ta che tao cac may say dang hinh tru, cd chidu cao thudc theo kich thudc va loai san phim cin s^y Trong [3], tac gia dd xuat phuang phap sdy ting sdi say khdi hat mudi tinh cd tiet dien dang "hinh nam" Tiet dien mat ck ngang cd dang dudng cong thoai thoai, hep dan tu tren xudng va da thu dugc ket qua: Chat lugng hat say dat tieu chuin ky thuat, hieu suat say cao va chi phi cho san phim cd gia thip Trong bai bao nay, tac gia xay dung md hinh md phdng quy hinh gia Idng cac hat ran de say hat mudi tinh Idp hat sdi vdi 03 dac tinh co ban: (a) Trao ddi nhiet; (b) Chuyen ddng ddng hat; (c) Tdn ap cua ddng klii qua Idp hat sdi DC LIEU VA PHlTONG PHAP NGHIEN ClTU 2.1 Phuimg phap gia long cac hat ran Mot quy luat cua tir nhien la cac chat Idng va chat ludn tuan thu nguyen ly ddng hgc: Cd su ddng nhat ve cau true cac phan tu; tao khudn de dang vdi thiet bi dung dd dung; Cd ddng chay Cdn ddi vdi chat ran thi cd cau true khdng ddng nhat, nhin thay bang mat thudng dudi dang hat Ngoai ra, cac hat san pham can say khd bao gid ciing cd am cao, cd dp ket dinh cao Phuang phap gia long cac hat ran dua tren cac khai niem [10] Dinh nghia 2.1: Dudng kinh cac hat ran dugc xac dinh la dai Idn nhat cua cac hat nguyen lieu dua vao may say, dugc ky hieu bang d > (diameter of particle) Djnh nghia 2.2: Do rdng gitta cac hat la tinh tach biet giiia cac phan tu', dugc xac dinh la khoang each giiia cac hat, dugc ky hieu bang s > (fraction of the bed volume) Djnh nghia 2.3: Tang roi cac ddng hat la tang ma d dd sau hat nhan nang lugng se tang ndi nang va chuyen ddng khdng theo quy luat, dugc ky hieu bang h^^ > (higher of tubulent level) Djnh nghia 2.4: Tang chuyen tiep cac ddng hat la tang ma d sau thoat khdi ting rdi, cac hat bat dau chuyen ddng theo hudng len, dugc ky hieu bang h^^ > (higher of transitional level) Tang cung cd ten ggi la tang ban sdi ' CHI CO KHi VIET NAM, S6 nam 2014 www.cokhivietnam.vn NGHIEN cuu-TRAO001 Q,.=-P(|^)UP-'^ an Mat khac, gia sii nhiet dp toan phan ciia Idli, hat may s^y la t = i(-x^,x^,^,), nhiet ciia tac nhan th6i vao bu6ng say kho la tg > 0, Nhiet ciia hat la t , sir chenh lech vfi nhiet co thS xkp xi lien tuc la d t = t , - t^va moi trucmg hat CO he s6 truyen nhiet doi lira la a, ta co sir bijn d6i nhiet ciia truyin nhiet d6i lira Q^^ se la: Hinh 1: Lap hat mudi tinh dang soi dong ; (2.2) dt Khi nghiem cua phuong trinh (2.2) la; tdc nhan nong mo hinh thi nghiem duac tdc gid thiet lap dimg thi nghiem Q „ = « ( t = - t p ) (2-V Dinh nghia 2.5: Ting sdi la tang ma d dd cac hat rin cd dac tinh nhu chat Idng (gia long) dugc Can bang cac phuang trinh (2.1)- (2.3) ta co he s6 trao doi nhiet doi luu: dun va sdi, dugc ky hieu bang hfb > (higher of fluidized bed level) Djnh nghia 2.6: Say Idp hat sdi la tach i m tir cac hat ran bang each truyen nhiet ddi luu - hat dudi trang thai Idp hat sdi bdng benh He sd trao ddi nhiet ddi luu thuc te thudng dugc bang thuc nghiem, vi du theo Bolter! [5] dugc tinh theo cdng thuc c: ddng ndng, am tit hat ran thoat va di a =a theo ddng thai ngoai hudng say = 35,8.p'".?L"'.d-°''' (2.5) mnx ' '^P P P ' ' 2.2 S^' truyen nhiet lap hat ran cua Idp Trong dd: soi p ^ - Khdi lugng rieng cua hat ran, kg/m^ X I' - Dd dan nhiet cua hat ran,W/m dp Truyen nhiet lap hat ran thudng xay qua ba hinh thuc: Truyen nhiet dan nhiet, truyen nhiet ddi luu va truyen nhiet biic xa Thuc te Bang md hinh nay, tac gia da ap dung tinh cho say hat mudi tinh nhiet dp say tac nhan say thap, ta chi can quan tam - Nhiet lugng trao ddi dugc tinh theo cong hai dang dudi day thuc (2.3) vdi he sd cua (2.5): 2.2.1 Phuang trinh truyen nhiet doi luu Q^^ - a(t^ - t^,)= [35.8.p;'.^p".d;""']x (160 - 31,2) (2.6^ Sat be mat cac hat chat ran thudng cd mot Idp mdng chat khdng chuyen ddng, ngudi ta ap dung dinh luat Fourier doi vdi Idp ay nhu sau: TAP C H i CO KHI VIET NAM, S6 nam 2014 www.cokhivietnam.vn Trong dd: Nhiet dp t - 160 °c Nhiet dp hat siy liy t - 31,2 °c NGHIEN cuu-TRAODOI 2.2.2 Phuang trinh viphan nang luang Gia sir chat (hat) gia Idng la ddng nhat, khdng bi nen, ngudn nhiet la nhiet lugng cua cac hat bien ddi sau khoang thdi gian dx The tich cua hop chua chat Idng klidng gian ba chieu dugc dv = dx^.dx^-dx^ Khi dd, theo tung phuang, ta lap phuang trinh vi phan nang lugng cd dang: Chii y: Trong hoat ddng say tren tang sdi, tac nhan say d nhiet dp 600"C thi phan truyen nhiet biic xa mdi bat dau trd nen dang ke [8], ma trudng hgp say mudi tinh, nhiet dp gidi han nhd ban 200^^ C, nen ta khong cin xet he sd trao ddi nhiet buc xa [4] 2.3 Chuyen dong ciia dong hat thu nhiet vao: dQ^ = q^dx, dx, dx^, 2.3.1 Thong so ky thuat cac hat say j = 1.2,3 (2.7) Tda ra: dQj^,i,^ = q^^,^ dXj.dx^.dx^^, j = 1,2,3 ^2 S) Nhiet lugng tich tu lai cac hat theo phuang trinh (2.8) Nhiet lupng tich lai cac hat theo phuang x , j - 1,2,3 dugc xac dinh bdi (Pt 2.9) dQ -dQ, , - Nhiet cua san pham khdi budng say la 9, = 70OC; ^dv.dT ] = l,2.5 (2.9) J Bing md hinh nay, tac gia [2] da ap dung de tinh toan siy va thu dupe ket qua thuc nghiem nhu sau: - Nhiet cua khdng trudc vao budng ddt la t^ -30 °c; - Nhiet ciia dugc gia nhiet tac nhan say cap vao budng say t^- 160°c; - Nhiet cua tren dudng dng thai am la t,^ 850c; + Kich thudc hat say (xem dinh nghia 2.1), can phai chu y den kich thudc cua hat ran can say, vi du, ddi tugng cd the la hat dudng cat, hat me, hat mudi tinh (trong say tang sdi thudng ung dung de say cac hat cd kich thudc be thi cd hieu qua cao) + Do rdng giua cac hat (xem dinh nghia 2.2): Do dac tinh ran, nen giira cac phan tu bao gid ciing cd khoang each Idn han (E > 0) Do rdng cang Idn thi thdi gian qua trinh gia Idng cac hat ran cang keo dai va tieu tdn nang lugng nhieu hon + Phan tang hat ran (xem cac dinh nghia 2.32.5): Khi dua vao budng say cung vdi nhiet va van tdc cd the tao 03 tang hat ran: Tang rdi, tang chuyen tiep va tang sdi Ddi tugng ciia nghien cuu la hat mudi tinh cd cac thdng sd ky thuat trinh bay [2] - Do xop cita hat trang thai tir nhien £ = 0,5= 0,52; - Nhiet cua hat ran trudc vao budng say - Khdi lugng rieng cua hat: p - 2018-2014kg/ la e„-32,l°C; - Nhiet ciia hat ran budng say la 9| =120 - Khdi lugng the tich cua hat udt p^^ -982 kg/ °C; TAP CHI CO KHI VIET NAM, So nam 2014 www.cokhivietnam.vn NGHIEN CirU-TRAO DOI - Dp ciu cua hat d 30 °c (p = 0,67^0,74, lay trung binh 0,71; nh4t, khdng bi nen, dd su bidn thien nhiSt dp cua budng say la: - Chi§u cao Idp hat nguyen lieu: 45mm; dt - Chi^u cao Idp hat hda sdi tdi thieu: 49.5cm; Trd-.'ld^-i^