Yuav Ua Li Cas Lub Cuam Tshuam ntawm Dissolved Silica ntawm 100 Degree Bulk Dej Kub Tswjhwm Tsim Cov Txheej Txheem ntawm Insulating Silicate Scale ntawm 316 Stainless Steel Heater Sheaths

Lub mechanism ntawm deposition ntawm amorphous silica thiab nws thermal kuj

Kev tsim ntawm amorphous silicate scale sawv cev rau ib qho teeb meem tshwj xeeb rau 316 stainless hlau sheathed hluav taws xob cua sov raj ua haujlwm hauv cov dej kub uas muaj cov silica yaj (SiO₂) uas muaj nyob hauv dej hauv dej, boiler feedwater thiab qee cov txheej txheem kev lag luam, thiab txawv ntawm calcium carbonate scaling. Silicate scale tshwm sim los ntawm polymerization ntawm silicic acid (Si (OH) 4) ntawm rhuab hlau nto, whereas carbonate scale tshwm sim los ntawm nag lossis daus ntawm crystalline ntsev. Ntawm cov dej kub ntawm 100℃(kub boiling), cov concentration ntawm yaj silica ntau tshaj li ntawm 50-80 ppm (raws li SiO2) polymerise sai sai rau ntawm qhov chaw sov. Qhov tshwm sim amorphous silica nplai ntawm qhov chaw muaj qhov thermal conductivity tsawg heev (kwv yees li 0.5-1.5 W / m·K piv rau 15-20 W / m·K rau 316 stainless hlau), thiab li no tsim ib txheej rwb thaiv tsev uas ua rau siab kub los ntawm 20-50℃hauv lub lis piam. Qhov kub no nce ntxiv ua rau cov silica deposition thiab tuaj yeem ua rau overheating tsis ua hauj lwm. Tsab ntawv xov xwm no suav txog qhov sib txuas ntawm cov concentration ntawm cov silica yaj, tus nqi ntawm kev loj hlob thiab poob ntawm thermal kev ua tau zoo ntawm 100 degree.

Mechanism ntawm silicate polymerization ntawm rhuab chaw

Cov silica yaj hauv dej feem ntau yog nyob rau hauv daim ntawv ntawm monomeric silicic acid Si (OH) 4. Amorphous silica muaj ib tug solubility ntawm ~ 300 - 400 ppm ntawm 100 degree, nyob ntawm pH. Tshaj li qhov txwv tsis pub solubility, silica polymerises thiab colloidal hais yog tsim uas thaum kawg precipitate li amorphous opaline nplai. Hauv qab qhov kev txwv tsis pub solubility, txawm li cas los xij, cov hlau kub kub tuaj yeem ua rau cov khoom siv polymerization, txij li qhov kub ntawm qhov chaw siab nce qhov tshwm sim (Arrhenius tus cwj pwm). Lub zog ua kom muaj zog rau silica polymerization rau 316 stainless hlau yog nyob rau ntawm qhov kev txiav txim ntawm 40-60 kJ / mol, kom cov deposition npaum li cas ob npaug rau txhua 10-15℃nce hauv sheath kub. Ib txheej silica nyias yog tsim thiab nws cov kev ua haujlwm insulating ntxiv ua rau qhov kub thiab txias hauv lub voj voog nws tus kheej.

Quantified kev sib raug zoo ntawm silica concentration thiab scale tsim ntawm 100C

Cov nram qab no cov nqi tsim thiab lub tsev ntawm thermal kuj ntau tshaj 1,000 teev tau txiav txim los ntawm kev tswj fouling kev tshawb fawb ntawm 316 stainless hlau sheaths (kub flux 5 W / cm2) nyob rau hauv dej ntawm 1000C tej kub nrog ntau npaum li cas ntawm yaj silica (pH 7.5).

Dissolved Silica Concentration (ppm as SiO2) Scale Thickness tom qab 1,000 teev (µm) Silica Scale Thermal Conductivity (W/m. K) Ntxiv Thermal Resistance (m2. K/W) Sheath Temperature Rise Above Bulk (degree , at 5 W/cm2) Lub Sijhawm Rau Ruaj Khov 100℃Kev pabcuam<20 <5 1.0-1.5 <0.0005 <2.5 >5,000 Yes 20-40 5-15 1.0-1.5 0.0005-0.0015 2.5-7.5 2,000-5,000 Yes 40-60 15-30 0.8-1.2 0.0015-0.0030 7.5-15 1,000-2,000 Acceptable with monitoring 60-80 30-50 0.7-1.0 0.0030-0.0050 15-25 500-1,000 Marginal 80-100 50-80 0.6-0.9 0.0050-0.0080 25-40 200-500 Not recommended 100-150 80-120 0.5-0.7 0.0080-0.0120 40-60 100-200 Unacceptable >150 >120 <0.6 >0.0120 >60 <100 Unacceptable
Cov nyhuv ntawm pH ntawm tus nqi ntawm Silica Deposition

Polymerisation ntawm silica yog pH heev - nyob ntawm, nrog rau qhov qis tshaj solubility thiab deposition tus nqi ntawm pH 7.5-8.0. Thaum qis pH (acidic) silicic acid yog uncharged thiab polymerises qeeb dua. Nyob rau hauv alkaline tov (high pH) silica muaj nyob rau hauv silicate (SiO3 2-) ions uas sai polymerise thiab kuj ua ke nrog calcium thiab magnesium los tsim complex silicates. Kev cuam tshuam ntawm pH ntawm qhov tso nyiaj ntawm 100 ppm SiO2 yog muab rau hauv cov lus hauv qab no.

pH ntawm 100℃Silica Speciation Relative Deposition Rate (pH 7.5=1.0) Scale Morphology Pom zoo pH Range<6.0 Si(OH)4 (monomeric) 0.3-0.5 Thin, glassyAcceptable but corrosive 
6.0-7.0 Si(OH)₄ dominates 0.6-0.8Moderate rau tuab Tau txais
7.0-7.5 Mixed 0.9-1.1 Nruab Nrab Optimal
7.5-8.0 Mixed nrog qee SiO3 2- 1.0-1.5 Nruab nrab mus rau hnyav Marginal
8.0-9.0 SiO3 2- dominant 1.5-3.0 Heavy, occasionally crystallineNot advisable >9.0 SiO₃²⁻ + hlau silicates 3.0-5.0 hnyav heev, adherent Tsis zoo
Dej Chemistry Specifications - Silica Control Tswv yim

Cov kev txwv silica hauv qab no yog npaj rau 316 sheathed heaters nrog cov dej kub ntawm 100℃rau lub neej kev pab cuam.

Maximum Dissolved Silica (ppm as SiO2) Desired Service Life (hours)Max. Heat Flux (W/cm²)>Pom zoo kho dej 10,000<30 <5 None required 10,000 30-50 <4 Monitor silica 5,000-10,000 50-70 <3 Silica removal (reverse osmosis) or periodic cleaning
3,000-5,000 70-90 <2 Removal of silica necessary <3,000 >90Txhua yam 316 tsis qhia; tshawb xyuas alloy kho kom zoo dua lossis cov cua sov sab nraud
Field Identification ntawm Silicate Scale Failures

Cov cim qhia ntawm 316 lub rhaub dej kub hauv siab -silica dej yog ib qho nyuaj, iav, translucent rau cov nplai dawb uas nyuaj heev rau kev tshem tawm cov tshuab (xav tau tshuaj ntxuav nrog hydrofluoric acid lossis kub caustic). Cov nplai feem ntau yog du thiab tej zaum yuav muaj 'crazed' saib rau nws. Qee qhov kev xeb tuaj yeem pom ntawm cov hlau nto tom qab qhov ntsuas - tsis ua haujlwm feem ntau yog thermal (overheating) es tsis yog corrosive. Lub tshuab cua sov tuaj yeem ua tsis tiav los ntawm kev kub nyhiab (melted resistance wire), tsis yog sheath perforation. Nyob rau hauv xws li tsis ua hauj lwm, X-ray diffraction (XRD) kev tshawb fawb ntawm lub teev qhia amorphous silica (wide hump qauv) los yog, nyob rau hauv lub kub kub, crystalline cristobalite. Zog dispersive X-ray spectroscopy (EDS) qhia silicon thiab oxygen nrog me ntsis hlau thiab chromium. Kev daws yog txo cov silica cov ntsiab lus los ntawm thim rov qab osmosis los yog ion pauv los yog dilution los yog ua hauj lwm ntawm ib tug tsawg tshav kub flux kom txo lub sheath kub.

Txoj hauv kev kom txo qis siab -Silica Waters

Peb qhov kev xaiv rau kev txo qis tuaj yeem ua kom lub neej ntev ntawm lub tshuab cua sov thaum cov qib silica tsis tuaj yeem txo qis kev lag luam. Thawj yog kom txo cov cua sov kom tsawg. Rau ib tug muab wattage, ntau sheath nto cheeb tsam (ntev los yog loj txoj kab uas hla sheaths) txhais tau hais tias ib tug qis sheath kub, uas exponentially slows silica polymerization. Piv txwv li, txo cov cua sov ntawm 5 W / cm² mus rau 3 W / cm² txo cov silica deposition npaum li cas los ntawm 50-70%. Cov txheej txheem thib ob yog ua haujlwm ntawm qhov kub thiab txias: txo nws los ntawm 100oC txog 90oC txo tus nqi ntawm silica polymerization li ntawm 40-50%. Qhov thib peb kev xaiv yog los qhia scale inhibitors. Qee cov phosphonates thiab polymers tuaj yeem ua rau qeeb ntawm cov polymerization ntawm silica, txawm hais tias lawv tsis zoo dua li cov carbonate scale. Tib txoj kev txhim khu kev qha rau cov silica fouling hnyav yog hloov mus rau qhov cua sov tsis ncaj (xws li cov cua kub hloov pauv) lossis siv lub tshuab cua sov nrog lub plhaub tshem tau.

NYEEM NTXIV: 316 TUB ROG RELIBAILITY nrog 100℃DISSOLVED SILICA CONTROL

Kev tsim sai sai ntawm cov txheej txheem insulating amorphous silicate ntawm 316 stainless hlau sheathed heaters yog pom nyob rau hauv 100℃tej dej ntawm yaj silica concentrations tshaj 60-80 ppm. Qhov tsim ntawm qhov ntsuas no ua rau nce ntawm 15-25℃hauv sheath kub li ntawm 500-1,000 teev thiab ua rau overheating tsis ua hauj lwm. Qhov tseem ceeb txwv rau 10,000 teev kev pabcuam yog 30 ppm SiO2 ntawm 5 W / cm2 tshav kub flux. engineers xaiv 316 sheaths rau geothermal, boiler pub los yog lwm yam siab silica kwj yuav tsum tau soj ntsuam yaj silica concentration los txwv nws (los ntawm thim rov qab osmosis los yog dilution) los yog txo tshav kub flux los them. Tshaj 80 ppm silica qib, 316 sheaths tsis pom zoo rau cov cua kub ntws. Lub moj khaum tsim los ntawm no muab kev sib raug zoo ntawm cov concentration ntawm yaj silica thiab ntsuas tus nqi ntawm kev loj hlob scale thiab thermal tiv thaiv tsub zuj zuj, tso cai rau tus neeg yuav khoom thov kev kho dej los yog lub rhaub tsim kev hloov pauv uas zam lub stealth tsis ua hauj lwm hom ntawm silicate induced overheating.