Dutch goals for glass recycling

A review with 3 refs. [on SciFinder (R)

Thermal behaviour of glass batch on batch heating

The heating process of a Ba-Sr glass batch was studied in a 40 L pot furnace, using a multiple thermocouple assembly. The effect of several batch parameters on the heating process was measured, including layer thickness, cullet fraction, water content, and pellets. The results were evaluated using a heat penetration batch model. In the model 2 heating stages, below and above a certain batch transition temp., ns, typically 800 to 900 Deg, are distinguished. Values for the temp.-dependent thermal diffusivity of the batch were derived from exptl. temp. distributions in the batch during heating. Below ns, the thermal diffusivity has an almost const. value of 0.4 * 10-6 m2/s for a std. (powder) batch blanket; for n > ns, the net thermal diffusivity strongly increases with temp., due to the formation of primary melt phases. For ns <n <1100 Deg, the av. value is about 1.4 * 10-6 m2/s. A 100% cullet layer has a 50% higher thermal diffusivity for n <ns; pelletizing the batch has little influence on the virtual thermal diffusivity and (extra) wetting has a retarding effect on batch heating due to extra heat absorption. As for the furnace temp., it appears that increasing the temp. of the glass melt is more effective for improving the batch heating rate than increasing the temp. of the combustion chamber. Practical recommendations are given for batch prepn., charging, and heating in industrial glass tanks. [on SciFinder (R)

Theory for incongruent crystallization: application to a ZBLAN glass

Equations which describe incongruent nucleation and subsequent crystal growth are derived. A ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) glass was used to test the validity of these equations. Nucleation rate measurements were fitted to theory and some growth rate measurements were in reasonable agreement with theor. predictions. Both nucleation theory and crystal growth theory were used for computer simulations of the crystn. behavior during heat treatments. Some heat treatments were performed in a DSC app. to verify the theories. The exptl. results were in good agreement with the numerical data. Using these theor. results it is possible to est. fiber scattering losses due to crystn. Depending on drawing temp., estd. losses can vary from 0.014 (310 Deg) to >=25 decibel/km (320 Deg). [on SciFinder (R)

De emissiereductie in de keramische industrie door middel van procesgeïntegreerde maatregelen (deel 2)

As a continuation of the previous article all circumstances affecting fluoride emission during firing of ceramics are discussed. Besides firing time and temp., kiln atm., microstructure of the ceramics, the presence of glazes and engobes, type of kiln, and the compn. of the ceramics det. the total fluoride emission. The possibilities of process-related measures and end-of-pipe solns. for reducing fluoride emissions are discussed. [on SciFinder (R)

Potentials and obstacles of the implementation of efficient energy technologies

Increasing the energy efficiency of continuous tableware glass melting furnaces fired with fossil fuel is discussed in a review with 22 refs. Topics are (1) general factors detg. energy consumption and relations with emissions and glass quality, (2) energy balances in glass furnaces and (3) increasing the energy efficiency of glass melting. [on SciFinder (R)

Influence of glass furnace operational conditions on the evaporation from soda-lime and borosilicate glass melts.

The evaporation of sodium and boron species from the melts in industrial glass furnaces leads to emissions of particulates (dust) and to furnace atmospheres containing reactive evaporation products. These reactive species, especially alkali vapors, can react with the superstructure refractories causing attack on or corrosion of these materials. The vapors form condensation products during the cooling process in the flue gas channels, recuperators or in regenerators, causing deposition of salt. In some cases, this deposition leads to reduced heat transfer in these heat exchangers or blockage of the flue gas channels. The evaporation processes at the glass melt surface include: - direct evaporation of glass components; - evaporation of compounds formed by a reaction of different glass components in the melt; - evaporation of compounds formed by a reaction of a glass component with gases in the furnace atmosphere. In the last case, the composition of the furnace atmosphere will influence the vapor pressures of the volatilized compounds. Diffusion of gases from the melt into bubbles or evaporation into gas bubbles may take place, especially during the primary fining process. This hardly contributes to the total evaporation losses of boron and alkali species, but it is essential for the SO2 release from the melt during fining. Under industrial conditions, gas flows above the melt may be high. Experimental investigations show that evaporation kinetics are enhanced by higher gas flows especially for evaporating components having high concentration levels in the melt. For minor but volatile components in the melt, diffusion from the bulk of the melt to the surface may limit the evaporation rates, depending on diffusion coefficient and convection flows. Evaporation is drastically enhanced by high glass melt surface temperatures, high gas velocities and high activity coefficient values of components in the melt. The presence of both boron and alkali in melt gives high activity coefficient values for alkali borates in the melt, which leads to high vapor pressures of these compounds. Increasing water vapor pressures will enhance evaporation of HBO2 and NaOH or KOH but will hardly have an impact on KBO2 or NaBO2 evaporation. This means that high water vapor pressures in the furnace atmosphere, as encountered with oxygen firing, will increase NaOH, KOH or HBO2 vapor pressures, however for sodium borosilicate glasses, NaBO2 is the major evaporating species. NaBO2 evaporation is not directly influenced by water vapor. In oxygen-fired furnaces combustion gas volume flows are much less than in air-fired furnaces, the lower gas velocities will suppress the evaporation process. Initially, a high evaporation rate may lead to depletion of volatile components at the surface of the melt. This depletion will slow down the evaporation process from stagnant melts as time proceeds. Thus there may be compensating effects for NaOH, KOH and HBO2 evaporation, but for NaBO2 or KBO2 volatilization, oxygen firing will lead to lower specific (per unit quantity of molten glass) evaporation losses of these components

Metingen van rookgasemissies bij de fabricage van keramiek en glas

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