Dab tsi tseem ceeb ib feem ntawm cov pa oxygen hauv combustion Gases ntawm 600℃Sheath kub tiv thaiv kom ceev Oxidation ntawm 316 Stainless Steel Heater Tubes

Kev txwv ntawm Oxidising Potential rau Kev Tiv Thaiv Scale Tsim

Rau 316 stainless hlau sheathed hluav taws xob cua sov tub nyob rau hauv combustion gas ib puag ncig xws li duct heaters, furnace atmospheres los yog pa pa recirculation systems, ib feem ntawm cov pa oxygen (pO2) nyob rau hauv ib puag ncig cov pa yuav txiav txim seb lub sheath tsim ib tug tiv thaiv chromium oxide scale los yog kev paub ceev oxidation (breakaway oxidation). Raws li kev ua haujlwm ntawm dej vapor thiab lwm hom reactive, qhov tseem ceeb pO2 rau qhov ruaj khov Cr2O3 nplai ntawm qhov kub thiab txias (600 deg C, tus neeg sawv cev ntawm cov ntawv thov cua sov tab sis ntawm qhov siab kawg rau 316) yog nyob ntawm qhov kev txiav txim ntawm 10-10 txog 10-15 atm. Yog tias cov pa oxygen poob qis dua qhov pib no, cov chromium oxide poob qis thiab cov hlau oxides tsim ib qho kev loj hlob sai uas tsis yog{18}} tiv thaiv nplai. Saum toj no qhov chaw pib (cov pa oxygen nplua nuj ib puag ncig zoo li huab cua ntawm 0.21 atm pO2), ib txheej nyias nyias Cr2O3 tsim, muab kev tiv thaiv mus ntev. Tab sis nrog ntau cov pa oxygen ib nrab siab, cov dej vapor tuaj yeem tsim nyob rau hauv chromium oxyhydroxides uas tsis muaj zog, uas txo cov thickness ntawm cov nplai. Nyob rau hauv txoj kev tshawb no, kev nyab xeeb pO2 qhov rais rau 316 sheaths ntawm 600℃yog kom muaj nuj nqis thiab combustion ib puag ncig cov txheej txheem rau lub rhaub lub neej txuas ntxiv.

Mechanism ntawm stability thiab volatility ntawm chromium oxide

Kev tiv thaiv nplai ntawm 316 stainless hlau ntawm qhov kub thiab txias yog feem ntau Cr 2 O 3, uas yog tsim los ntawm kev xaiv oxidation ntawm chromium. Rau kev ruaj ntseg ntawm Cr2O3, lub ambient oxygen ib feem siab yuav tsum siab tshaj qhov dissociation siab ntawm chromium oxide ntawm qhov kev txhawj xeeb kub. Lub dissociation siab ntawm Cr₂O₃ (pO₂ uas Cr₂O₃ decomposes rau hlau Cr thiab O₂) yog ~ 10⁻²⁶ atm ntawm 600 degree, zoo hauv qab cov pa oxygen theem ntawm ib txwm combustion gases. Txawm li cas los xij, nyob rau hauv lub xub ntiag ntawm dej vapor, Cr2O3 hloov mus rau ib tug volatile daim ntawv ntawm chromium oxyhydroxide: Cr2O3(s) + 2}H2O(g) + 3/2O2(g) → 2CrO2(OH)2(g). Cov tshuaj tiv thaiv no tshem tawm qhov ntsuas tiv thaiv ntawm qhov nrawm raws li pO2 thiab pH2O. Qhov siab tshaj plaws tshwm sim ntawm pO2 hauv qhov kwv yees li ntawm 10-10-10-12 atm, es tsis yog pO2 siab heev lossis qis heev. Qhov no qhia tau hais tias me ntsis lean (oxygen-deficient) combustion atmospheres yog, qhov tseeb, ntau corrosive rau 316 dua li oxidising tag nrho (cua) los yog txo cov cua kub.

Quantified pO₂ Windows rau Kev Tiv Thaiv Scale Tsim ntawm 600 degree

Tus nqi oxidation ntawm 316 stainless hlau raws li kev ua haujlwm ntawm cov pa ib feem ntawm lub siab tau txiav txim siab los ntawm kev ntsuas thermogravimetric ntawm 600℃hauv kev sib xyaw roj sib txawv ntawm pO₂ thiab pH₂O.

Oxygen Partial Pressure (atm) Dej Vapor Ib Feem Siab (atm) Scale Formed Oxidation Rate (mg/cm2-hr) tom qab 500 teev Scale Adherence Pom zoo rau 600℃Kev Pabcuam 0.21 (cua)<0.01 Cr2O3 (thin, protective) <0.02 Excellent Yes 0.21 (air) 0.10-0.30 Cr2O3 + slight volatilisation 0.02-0.05Good Yes (under supervision)
0.21 (air) >0.30 Enhanced volatilisation, thinning 0.05-0.10 Nruab nrab Marginal
10-5 txog 10-8 (lean combustion) 0.05-0.15 Mixed Cr2O3/Fe2O3 0.10-0.30 Poor Tsis pom zoo 10-9 txog 10-12 (stoichiometric combustion) 0.10-0.20 Very FeCr2O4 spinel + volatilization 10.
10-12 txog 10-15 (nplua nuj combustion) 0.10-0.20 Fe 3 O 4 (magnetite) 1.00-3.00 Cov neeg pluag heev (spalls) Tsis tau txais<10-15 (strongly reducing) <0.01 FeO (wustite) >5.00 Tsis yog- tiv thaiv Tsis tau
Kev cuam tshuam ntawm roj Sulfur thiab lwm yam khoom ntawm combustion

Ntxiv nrog rau cov pa oxygen thiab dej vapour, cov combustion gases muab tau los ntawm fossil fuels muaj sulfur dioxide (SO2) thiab kab hlau uas catalyze oxidation 316. Cr₂O₃ cuam tshuam nrog SO₂ los tsim chromium sulphides, uas ua rau cov txheej txheem tiv thaiv oxidation thiab ua rau tawg. Rau 316 ntawm 600 degree, oxidation tus nqi yog ob npaug ntawm cov sulfur concentration nyob rau hauv cov roj ntau tshaj 50 ppm (suav txog li 100 ppm SO 2 hauv cov roj flue). Rau cov roj uas muaj sulfur siab tshaj 500 ppm (xws li siab- cov roj sulfur lossis thee) 316 tsis pom zoo rau qhov kub siab tshaj 500oC. Cov tshuaj chlorine uas muaj cov roj combustion (los ntawm hlawv cov chlorinated plastics lossis qee qhov pov tseg) yog qhov hnyav dua, ua rau cov hlau tsis muaj zog ntawm cov nqi ntawm 10-100 npaug ntawm oxide raws li corrosion. Kev txheeb xyuas roj muaj pes tsawg leeg yuav tsum tau siv rau txhua daim ntawv thov uas 316 sheaths raug rau combustion gas impingement.

Tswv yim Specification rau kev siv cov combustion rhaub

Cov nram qab no tsis yog rau 316 sheathed heaters nyob rau hauv combustion gas ib puag ncig ntawm 600℃sheath kub los xyuas kom meej zus tau tej cov kev tiv thaiv scale thiab txaus oxide loj hlob tus nqi. Lub combustion yuav tsum tau ua nrog huab cua ntau dhau (xws li oxidising, pO2> 0.01 atm) kom khaws cov Cr2O3 nplai - tawm tsam qhov kev ntseeg ib txwm hais tias txo cov cua sov tsawg dua. Lub siab ib nrab ntawm cov dej vapor yuav tsum tau khaws cia hauv qab 0.15 atm (15% ya raws los ntawm ntim). Qhov no tuaj yeem ua tiav los ntawm kev ua ntej- ziab cov cua combustion los yog siv cov roj tsawg hauv cov ntsiab lus hydrogen. Cov roj yuav tsum muaj sulfur concentration qis dua 0.05% (500 ppm) thiab, qhov zoo tshaj, qis dua 0.01% (100 ppm). Yog tias ib qho ntawm cov kev txwv no tsis tuaj yeem ncav cuag, cov ntaub qhwv yuav tsum tau hloov kho mus rau 310 stainless hlau (25Cr-20Ni) lossis Inconel 600, ob qho tib si muaj kev ua siab ntev dua los txo qis pO2 thiab dej vapor ntau dua.

Kev ntsuam xyuas teb ntawm oxidation tsis ua hauj lwm tshwm sim los ntawm pO2

Qhov ntsuas morphology rau 316 sheaths tsis ua haujlwm hauv kev pabcuam roj combustion distinguishes ntawm ua rau txuas rau oxygen ib nrab siab. Nyob rau hauv oxidising tej yam kev mob (dhau cua), lub nplai yog nyias (<10 µm), greenish-gray (Cr2O3) and homogeneous. The scale is thick (>50 µm), dub, txheej thiab feem ntau qhia tau hais tias spalled cheeb tsam nyob rau hauv stoichiometric los yog me ntsis txo cov xwm txheej. Cov nplai yog tsaus grey, ntxeem tau, tsis muaj kev sib txuas thiab muaj cov wustite (FeO) raws li tau txiav txim los ntawm x-ray diffraction nyob rau hauv cov xwm txheej hnyav heev. Qhov kev tawm tsam tsim los ntawm leej faj ua rau lub microstructure txawv ntawm cov nplai uas hu ua "sulfide stringer". Yog tias lub tshuab cua sov muaj qhov hnyav thiab qhov hnyav, qhov chaw combustion yuav tsum tau hloov pauv kom muaj cua ntxiv los yog lub rhaub yuav tsum tau tsiv tawm ntawm qhov siab tshaj oxygen - thaj tsam tshaib plab.

Cov ntsiab lus: Tuav Oxidising Conditions rau 316 Combustion Heater Longevity

Qhov tseem ceeb pO 2 rau kev tsim cov kev tiv thaiv Cr 2 O 3 nplai ntawm 316 stainless hlau encased heaters ntawm 600℃hauv combustion gas atmospheres yog siab dua li ntawm 10-2 atm (2 % oxygen los ntawm ntim). Lub stoichiometric los yog roj me ntsis - nplua nuj combustion (pO2=10-9 rau 10-12 atm) ua rau sai thiab tsis muaj kev tiv thaiv oxide txoj kev loj hlob thiab scale volatility, thiab txo lub cua sov lub neej ntawm 20,000 teev mus rau 500-2,000 teev. Cov kws tsim qauv qhia txog 316 lub tsho rau cov cua sov uas raug rho tawm haujlwm lossis cov ntawv tso pa tawm yuav tsum tau ua kom cov combustion khiav hauv huab cua (tsawg kawg 3-5% O₂ hauv cov pa roj) thiab cov roj sulfur cov ntsiab lus raug tswj. Lub moj khaum no txuas lub siab ib nrab ntawm cov pa oxygen nrog ntsuas tus nqi ntawm oxidation. Nws tso cai rau cov neeg yuav khoom xaiv cov kab mob sib kis uas khaws cov kev tiv thaiv chromium oxide nplai ntawm 316 lub tshuab cua sov thiab tsis txhob tawg oxidation thiab ua tsis tiav ntxov.