NGHIEN COTU

NGHIEN COTU - TRAO D(!)l

NGHIEN CLfU QUA TRJNH HINH THANH KHJ T H A I NOX TRONG BU6NG D6T Sir DUNG 6NG PILOT PHUN NHIEN UEU BANG MO HiNH MO P H 6 N G K ^ T HOP CFD VA CRN 8 T H A N H P H A N

A STUDY OF CRN-CFD EIGHT-ELEMENT MODEL TO PREDICT THE CARBON OXIDE EMISSIONS IN INDUSTRIAL COMBUSTOR

USING PILOT FUEL INJECTION

Nguyen Thanh Hao Trudng Dai hpc Ndng Lam TP. Hd Chi Minh

Bdi bdo trinh bdy kit qud nghien cuu qud trinh hinh thdnh khi thdi dpc hgi NOx trong buong dot su dung ong pilot phun nhien lieu bdng phuang phdp kit hap hai mo hinh mo phong img dung ca hpc luu chdt tinh todn (CFD) vd mo hinh mo phdng ung dung mgng phdn img hda hpc 8 thdnh phdn (CRN). Trong nghien ciru ndy mo hinh so CRN 8 thdnh phdn duac thiit lap diing de xdc dinh thdnh phdn NOx trong buong dot su dting ong pilot phun nhien lieu dugc xdy dimg dua tren kit qud tic mo hinh so CFD. Cdc dieu kien biin vd diiu kien ddu vdo cua mo hinh CRN 8 thdnh phdn dugc Idy tir thuc nghiim. Ket qud nghien ciru mo phong dugc kiem chung vai thuc nghiem de khdng dinh dp tin cay vd hu&ng phdt trien trong viec du dodn thdnh phdn gdy 6 nhiem moi tru&ng.

Tfr kho^: CRN (mgngphdn img hod hoc): CFD (dpng luc hpc luu chdt tinh todn): PSR (todn tu phdn ung PSR); PFR (todn tu- phdn img PFR): Buong dot nhien lieu hod tron trudc, NOx.

ABSTRACT

The development of chemical reactor models to predict NOx emission is very important for the modern combustion system design. In this study, chemical reactor networks eight-element

(CRN) models are constructed base on the computational fluid dynamics (CFD). The boundary and operating conditions used for these CRN model reflect the typical operating conditions of the lean premixedgas turbine combustor. The global mechanism has been developed by GRI 3.0 in the UW chemical reactor code. For reliability of the predictive model, the model was analyzed and compared to the experimental test combustor

Keywords: CRN, CFD, PSR, PFR, Lean Premixed Combustor, NOx. ^

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NGHIEN CIJfU-TRAOD6l

1. DAT VAN DE

Kiem soat khi thai gay d nhiem mdi trudng bang md hmh CFD-CRN 6 thanh phan [1] da dugc nhdm tac gia nghien ciru va xay dyng thanh cdng eho budng ddt cdng nghiep.

Tuy nhien, ddi vdi nhihig budng ddt su dung dng pilot de phun nhien lieu thi md hinh nay khdng ling dung dugc do tinh chat ciia ngpn lua trong md hinh md phdng bing CFD cho thiy cd nhirng khac biet rit Idn. Sy hinh thanh NOx trong ngpn lira ciia qua trinh chay phu thugc vao rat nhieu yeu td, nhung thay doi ve thiet bi ong phun pilop d dieu kien dau vao ciing se dan den sy phat thai khac di ve chat 6 nhiem nhu NOx.

Nhilu nghien cmi md phdng iing dung ca hpc luu chat tinh toan ve qua trinh chay cua ddng phun rdi trong budng ddt cong nghiep da cho ket qua cd the iing dung dugc. Tuy nhien, chua cd nhieu nghien cihi ket hgp dong thai hai md hinh CFD va CRN dung d l md phdng qua trinh chay nhien lieu trong budng ddt cdng nghiep. Day la hudrng nghien ciiu cd nhieu im diem, trong dd dinh lupng dugc thanh phin NOx va CO ciia ngpn lua trong qua trinh chay la mdt trong nhung van de dugc quan tam hien nay. Khai niem md phdng qua trinh chay img dung ea che mang phan img hda hpc su dung toan tu PSR va PFR dugc gidi thieu bdi Bragg S. L., sau dd Swithenbank phat triln bing each chia viing ngpn lira trong md hinh thdng qua cac thdng sd tucmg quan va thyc nghiem [2]. Trong cac viing md phdng ngpn lira, t h i tich khdng gian chay dugc bieu diln bang cac phin tu phan iing dac dimg nhu PSR, PFR va MIX. Rubins & Pratt da iing dung eae nghien cuu nay de dieu khien lugng khi thai phat sinh trong budng ddt turbine khi [3]. Phuang phap ket hgp hai md hinh md phong CFD-CRN iing dung trong turbine khi dugc d l xuit bdi Sturgess

& Shouse, Roby, Novosselov [4], Park, J. K. [5].

Cac ket qua nghien ciru sau phan ung ciia CFD dugc ung dung de xay dyng mo hinh CRN.

Mo hinh CRN dugc xay dyng dya tren CO sd ly thuyet cua cac ngjiien eiiu da trinh bay d phan tren, trong do dieu kien dau vao cua mo hinh lay tii md hmh thyc nghi$m nhu hinh 1 va md hinh CFD trong hinh 2 , 3 va 4. Ket qua dinh lugng thanh phan NOx bang md hmh CRN 8 thanh phan dugc thyc hien cho nhieu trudng hgp tai khac nhau va he sd xoay khac nhau nhSm muc dich xac dinh dugc thdng sd tdi uu cho qua trinh chay nhien lieu trong budng dot cdng nghiep.

Md hinh CRN dugc xay dyng dya tren CO sd ly thuyet cua cac nghien eiiu da trinh bay d phan hen, trong dd dieu k i | n diu vao ciia md hinh lay tir md hinh thyc nghiem nhu hmh 1 va mo hinh CFD trong hirdi 2 , 3 va 4. Kit qua dinh lugng thanh phin NOx bing md hinh CRN 8 thanh phan dugc thyc h i ^ cho nhieu trudng hgp tai khac nhau va he sd xoay khac nhau nham muc dich xac dinh dugc thdng sd tdi uu cho qu^ trmh chay nhien lieu trong budng dot cdng nghiep.

Khong khi chay KhddgkhiliiDiiul Nh»aU(u /

(a) Sado nguyen ly

Kliongkhicbay !Ui6ngkhilimm«t 6n5piloi ( Ong ca

(b) Md hinh thiec nghiem Hinh 1. Mo hinh budng dot cdng nghiep

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NGHIEN cufu - TRAO D O I

2. XAY DUlVG MO HINH CFD-CRN 2.1. Mo hinh thu-c nghiem

2.2. M8 hinh CFD

(~^ ChiimiialasCT ri T y u kinh hinh irv

(f-50mm) I Thau kmh l6i I (f^SOOmin)

IC CD Camera (512*512) May pbat dinh ^ a

(a) Sa do nguyen ly he thong phdn tich Testo 3600

(b) He thong thiit biphdn tich Testo 360 Hinh 2. Mo hinh thiet bi do thuc nghiem

So dd nguyen ly va mo hinh thyc nghiem budng ddt cdng nghiep dugc trinh bay trong hinh 1. Mo hinh bao gdm budng ddt, cac dau ddt chinh va pilot dang khuech tan. Md hinh nay sir dung thiet bi phan tich Testo 360 de xac dinh thanh phan NOx va thiet bi cap nhi?t do kieu R de xac dinh nhiet dp (hinh 2).

Vi tri do thuc hien tir tam ra den bien tai dudi cua budng ddt, khong khi cap vao budng ddt dugc gia nhiet so bp den 650K, ap suat latm, ty 1? duang lugng giiia nhien lieu va khong khi dugc thay ddi tir 0,5 den 0,8, he sd xoay thay ddi tuang iing vai gde tao xoay lan lugt la 30°, 45° va 60°.

Hinh 3. Md hinh budng dot trong khong gian 3D

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Hinh 4. Phdn bo nhiet dp ngpn lua khi thay ddi ty le duang lupng nhien lieu cda pilot Md hinh CFD dugc xay dyng bang phin mem STAR-CD phien ban 4.06, md hinh rdi k-e, md hinh ngpn lira EBU va nhien lieu ddt CH^. Ket qua tir md hinh nay cung cap nhung hinh anh ve thong sd ca ban ben trong ngpn lira (hinh 4 va 5), day la nhirng thdng sd dugc sii dung de xay dung md hinh CRN. Md hinh md phdng trong khdng gian 3 chieu dugc trinh bay trong hinh 3.

Hinh 4 cho thay khi thay ddi gdc tao xoay thi phan bd nhiet dp cua ngpn lua cung thay ddi ro ret, vung nhiet do cue dai dat din 2522K. Cac viing cua ngpn lira dugc phan chia*^^

I S S N 0 8 6 6 - 7 0 5 6

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NGHIEN cufu-TRAO Ddi

thanh: virng nggn lira ehinh, vimg hoi luu tai tam ciia ngpn liia, vimg hdi luu tai bien thanh ran va viing san pham ehay phia sau ngpn lira.

2.3. M6 hinh CRN 8 thanh phin Md hinh CRN 8 thanh phan dugc xay dyng bang phan mem CHEMKIN va ca che dugc lyc hgc cac phan iing hda hgc GRI 3.0.

Budng ddt dugc phan chia thanh cac vimg khac nhau dya theo nhiet dp, van tdc va ndng dp cac ehat hmh thanh sau phan iing da dugc xac dinh tir md hinh CFD. Hinh 5a bieu dien cac vimg dugc phan chia tren ket qua tim duge tir md binh CFD trong trudfng hgp budng ddt su dung dau phun pilot.

Hinh 5b trinh bay md hinh md phdng ling dung mang phan img hda hgc bao gdm 8 phan tir dua trSn ket qua tit hinh 5a. Mo hinh bao gdm; 6 phSn tu PSR, 1 phan tir PFR va 1 phan tir MIX. Phin tir PSR (Perfectly Stirred Reactor) bieu dien cho vimg cd phan img chay vdi gia thiet qua trinh hda trdn giira nhien lieu va khdng khi xay ra ddng thdi vdi qua trinh phan irng, qua trinh chay dugc xem la ddng nhat. Phan tii PFR (Plug Flow Reactor) bieu dien cho viing phan iing dugc xem nhu d trang thai ly tuang, mdt chieu va vol gia thiet khdng ton tai qua trinh hda trdn giiia nhien lieu va khdng khi. MIX (Mixture) bieu dien eho vimg hda trdn giira nhien lieu va khdng khi ma khdng xay ra qua trinh phan iing. Phan tir diu tien trong md hinh CRN la MIX bieu diln cho vimg hoa tron giiia nhien lieu va khdng khi dau vao chua phan iing. 5 phan tir ke tiep la cac PSR lin lugt bieu dien cho viing nggn lua chinh, vimg hdi luu tai tam ciia ngpn lua va vimg hdi luu tai bien thanh ran. PSR thii 6 bieu diln cho vimg phia sau nggn lira nhung van tdn tai phan iing chay nhimg phan nhien lieu chua chay hit hoan toan. Cudi cimg la PFR bieu dien cho viing san

pham ehay phia sau nggn lira nhung khdng tdn tai phan iing chay. San pham chay sau khi ra khdi vimg ngpn lira chinh dugc chia thanh 2 phin, 1 phin di vao vimg phia sau ngpn lira chmh, 1 phin di vao viing hdi luu tai bien thanh

Sau khi xay dyng xong md hinh CRN 8 thanh phan, viec xac dinh gia tri the tich cac vimg trong md hinh CFD la mpt trong nhiing thdng sd quan trgng dimg lam thdng sd dau vao cho md hinh CRN. Ngoai ra, cac thdng sd cdn lai nhu Iim lugng, ap suat... dugc lay md hinh thyc thyc nghiem.

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(a) Chia vimg ngpn lua, gdc xoay 45", ty te duang lugng ^=0,6

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(b) Mo hinh CRN 8 phdn tu Hinh 5 Mo hinh CRN trong tru&ng hgp ditng pilot 3. QUA T R I N H HINH T H A N H K H I THAI NOx

Qua trinh hinh thanh NOx khi thay ddi ty le duang lugng giira nhien lieu va khdng khi ciia dng pilot lan lugt la 2%, 6% va 10% dugc xac dinh theo md hinh CRN 8 phin tir (hinh 6).

So sanh vdi thye nghiem cho thay kit qua tir md hinh ket hgp CFD-CRN la hoan toan phii hgp. Ket qua tim duge cho thay lugng khi thai

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NGHIEN CUTU-TRAO Ddi

NOx tang khi ty le duang lugng giiia nhien lieu va khdng khi tang. Anh hudng cua gdc tao xoay la khdng Idn, tuy nhien, ket qua cung cho thay lugng khi thai NOx giam khi gdc tao xoay la 45°, cac trudng hgp khac thi lugng khi thai NOx deu tang.

Lugng khi thai NOx tai mdi vung trong budng dot vdi gde tao xoay bing khdng, ty le duang lugng giua nhien lieu va khdng khi ciia

pilot lan lugt la 2%, 6% va 10% duge xac dinh trong hinh 7. Lugng khi thai NOx tang khi ty le duang lugng giiia nhien lieu va khong khi eua pilot tang. Dieu nay la vi khi ty le duang lugng tang thi nhiet dp tang nhu minh hoa trong hinh 8, do do lupng khi thai NOx ciing tang theo.

Nhiet dp tai vimg hdi luu ngoai bien thanh ran la nhd nhat, cho nen lugng khi thai NOx cung tuong ddi nhd ban so vdi cae vimg khac.

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Hinh 6. Thdnh phdn NOx ra khdi buong dot trong tmo hinh CRN

Hinh 7. Thdnh phdn NOx tgi cdc viing ngpn lua khi thay dot ty le duang lugng ^ trong mo hinh

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Hinh 8. Nhiet do tgi cdc vimg ngon lua khi thay doi ty le duang luang (j>

trong mo hinh CRN cd gdc tgo xody 45"

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NGHIEN CUTU - TRAO D 6 |

4. KET LUAN

Nghien ciiu cho thiy viec kit hgp giiia md hinh CFD va md hinh CRN cd kha nang dy doan chinh xac ham lugng khi thai NOx trong cac budng dot cdng nghiep sir dung dng pilot phun nhien lieu.

Ham lugng khi thai NOx tang theo ty le duang lupng giua nhien lieu va khdng khi cua pilot tang. Nguyen nhan la do khi ty le duang lugng tang thi nhiet dp cua ngpn lira tang. Md hinh md phdng kit hgp CFD-CRN 8 thanh phin cd t h i xem nhu mgt cdng cu huu hieu trong viec phan tich va xac dinh ham lugng cac thanh phin khi thai trong budng dot cdng nghiep sii dung dng pilot.

Trong nghien ciiu nay chi trinh bay phuang phap xac dinh thanh phan khi thai NOx la mpt trong nhiing khi thai ddc hai cho mdi trudng. •

Ngay nhan bai: 07/01/2015 Ngay phan bien: 03/02/2015

Tki li@u tham khao:

[1]. Nguyin Thanh Hao, Park, J. K, Nghien ciru qud trinh hinh thdnh khi thdi NOx trong buong dot cong nghiep bang md hinh mo phong kit hgp CFD vd CRN 6 thdnh phdn. Tap chi Nang lugng Nhi?t, so 98*3/201 l,p.l 1-14

[2]. Bragg, S. L.(1953). AppHcation reaction rate theory to combustion chamber analysis, aeronautical research council pub. ARC 16170, Ministry of Defense, London, England, 1629-1633.

[3]. Ruta, T, Malte, R C , and Kiamlich, J C. (2000). Investigation of NOx and CO formation in lean premixed, methane-air, high-intensity, confined flames at elevated pressures, Proc. Combust. Inst., 28, 2435-2441.

[4]. Novosselov, I. V. (2006). Chemical reactor network modeling of combustion systems. Ph.D. Dissertation, University of Washington, Settle, WA.

[5]. Park, J. K (2006). Modelling study of the effect of chemical additives on soot precursors reaction, InternationalJournal of Automotive Technology, 1, 4, 501-508.

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