1. A.J. Faber & H. van Limpt TNO Glass Group Evaporation of volatile components from glass melts

2. ICF, October 20052 Contents Introduction Sources and mechanisms of volatilization from glass melts Methods to study volatilization – exemplary results General guidelines for volatilization control

3. ICF, October 20053 Introduction Consequences of evaporation from glass melts Emissions of dust, HF, HCl, Se, metals (Pb, Sb, Na, K, Se,..) Deposition in regenerator/recuperator Attack of superstructure refractory (by Na-, K- and Pb-vapors) Depletion at glass melt surface of volatile compounds Glass defects (e.g. cord) due to ‘surface glass’ Loss of raw material (B, Pb)

4. ICF, October 20054 Sources of emissions from glass furnaces Gaseous emissions by Combustion process => CO 2, NO x,.. Dissociation of batch/glass components => CO 2, SO 2, NO x,.. Direct or reactive evaporation from glass melt => NaOH, Pb-, Se- components, B-components, Sb(OH) 3, fluorides, chlorides,.. Dust emissions by Carry-over of raw materials: sand, dolomite, limestone,.. Evaporation of melt components, followed by condensation reactions in flue gases: NaOH reacting with SO 2, or borates, condensating at lower T

5. ICF, October 20055 Evaporation mechanisms, sources and emissions Volatile component Source/raw material Mechanism Emitted components NaOH Soda, salt, Feldspar Reactive evaporation: Na 2 O + H 2 O  2 NaOH Na 2 SO 4 dust KOH Potash Feldspar Reactive evaporation: K 2 O + H 2 O  2 KOH K 2 SO 4 dust K 2 CO3 dust NaClSoda, culletDirect NaCl-evaporation from batch/meltHCl(g), Na 2 SO 4 dust Pb, PbORed lead, cullet Direct evaporation of PbO; Reactive: PbO + CO  Pb(g) + CO 2 PbO and PbSO 4 dust HF Minerals, CaF 2, cullet Reactive evaporation: 2F - + H 2 O  2HF + O 2- HF(g) Sb 2 O 3, Sb(OH) 3 Sb-fining agent Direct evaporation of Sb 2 O 3 Reactive: Sb 2 O 3 + 3 H 2 O  2Sb(OH) 3 Sb-containing dust SO 2 Na 2 SO 4 SO 2 fining reactionNa 2 SO 4 dust, SO 2, SO 3 SeO 2 Na 2 SeO 3, ZnSeO 3, Se Probably SeO 2 evaporationSeO 2 HBO 2 Na/KBO 2 Colemanite, borax, H 3 BO 3 B 2 O 3 + H 2 O  2HBO 2 (Na/K) 2 B 4 O 7  2 Na/KBO 2 + B 2 O 3 Borates (dust), boric acid

6. ICF, October 20056 Scheme of reactive evaporation of Na-compounds in fuel fired glass furnace

7. ICF, October 20057 Methods to study volatilization –1- Experimental laboratory set-up Thermodynamic effects: glass chemistry, temperatures, combustion Kinetic effects: gas velocities, diffusion coefficients

8. ICF, October 20058 Recycled cullet in container glass – Lead evaporation Pb = -4.84 * log(pO2) – 3.69 Pb input: 150 till 400 mg/kg

9. ICF, October 20059 Evaporation of lead from soda lime glass melt: effect of temperature and combustion atmosphere

10. ICF, October 200510 Evaporation of Na and K from TV-glass melt

11. ICF, October 200511 Release of Sb from TV-glass melt

12. ICF, October 200512 Methods to study volatilization –2- Prediction of evaporation rates of volatile species by Thermochemical calculations Partial pressures of volatile components in equilibrium with the glass melt Provides insight in effects of Glass chemistry Temperature of the glass melt surface Combustion atmosphere (water vapour content, oxidation state, CO level) Mass transfer modelling Convection and diffusion processes in gas phase Diffusion in the melt

13. ICF, October 200513 Modelling of PbO evaporation from glass melts

14. ICF, October 200514 Calculated Na 2 O evaporation as a function of the glass melt temperature and the pO 2 v g = 10 m/s 18 vol.% water vapor

15. ICF, October 200515 Methods to study volatilization –3- Industrial evaporation measurements: use of sampling probe

16. ICF, October 200516 Na-volatilisation from soda lime container glass furnace prediction vs. industrial measurements oxy-gas furnaceair-gas furnace average glass melt temperature ( o C) 1450 water vapour pressure (bar) 0.550.20 average gas velocity (m/s) 0.4 2 net surface area for evaporation (m 2 ) 7574 predictedNa emissions (g/h) 5441173 measuredNa emissions (g/h) 6141000 measuredNaOH concentration (mg/m n 3 ) 45040

17. ICF, October 200517 General guidelines for volatilization control Measures related to batch components, like Replacement of Se by less volatile Se compounds Replacement of B by alternative fluxing agent Measures related to process conditions Limit maximum melt surface temperatures Use of low velocity burners/electrical boosting electrodes Prevent reducing combustion conditions/flames near the melt surface Measures related to (hot top) furnace design Adequate distance between melt surface and burners Height of the crown

18. ICF, October 200518 Evaporation of Se in different forms