EA040747B1 - GLASS COMPOSITION CONTAINING NICKEL TO REDUCE ENERGY CONSUMPTION DURING COMPOSITION MELTING STAGE - Google Patents

Description

The field of technology to which the invention belongs

The present invention relates to a nickel-containing glass composition for reducing energy consumption in the melting step of the glass composition.

Description of the Prior Art

Reducing energy consumption in industrial glass melting furnaces is a major challenge from both an economic and an environmental point of view. Improvements in industrial process steps, such as additional furnace insulation, combustion optimization, etc., have already been developed. Additional process step improvements, however, will require significantly higher capital investment. Another way to reduce energy consumption would be to work on the glass compositions themselves by lowering the melting point of the glass composition. The melting point is defined as the temperature at which the viscosity of the glass is 10 Pa-s. The melting point thus decreases as the viscosity of the glass composition decreases at high temperature. In this case, the energy that must be supplied to the furnace can be reduced.

Recently, ultra-white or ultra-clear glasses have become increasingly preferred in the solar energy or construction industry due to their high light and/or energy transmission. These glasses contain a low amount of iron and are therefore also often referred to as low iron glasses. In the case of commercial soda-lime glasses, low-iron glasses have a total iron content, expressed as total Fe2O3, of less than about 0.1% by weight, typically less than 600 ppm. However, these low iron glass compositions have a high radiant thermal conductivity and thus are difficult to be heated by radiation in the wavelength ranges emitted inside the glass melting furnace. In the case of these low iron glass compositions, the enhancement of radiation absorption by the molten glass at high temperature will be very beneficial in terms of energy consumption.

Lowering the melting point of glass compositions has been considered in the art. US 5,071,796 discloses a window glass formulation where SiO2 has been partly replaced by Na2O and Al2O3 to provide high temperature viscosity reduction. WO 2014/128714 proposes to replace approximately half of the silica component and part or all of the calcium oxide component with a boron component. However, it is difficult to maintain glass properties such as clearing temperature, glass transition temperature, glass chemical stability or optical properties in such highly modified formulations. In addition, some of the alternative components can be quite expensive and thus limit their industrial applications.

Glass compositions containing nickel are known in the art. Reference is made, for example, to documents US 2013/0316162, US 2014/0017500, US 3881905 describing glass or tempered glass for displays; and to US 5,888,917, which discloses varieties of clear, non-dull colored glass.

Thus, it is an object of the present invention to cost-effectively provide a low iron glass composition with low radiant thermal conductivity at high temperature in order to reduce energy consumption in the manufacturing process without compromising the properties of the glass composition.

The essence of the invention

The present invention relates to a glass composition containing the following components in weight percent, based on the total weight of the glass composition:

_SiO2 50-85% A1 ₂ 0z 0-30% At ₂ 0z 0-20% _Na2O 0-25% Cao 0-25% MgO 0-15% K ₂ O 0-20% VAO 0-20% Re ₂ 0z total 0.002-0.1%

- 1 040747 moreover, the specified glass composition also contains nickel, presented in the form of NiO, at a level of

0.0001 to 0.0020% by weight.

The present invention further relates to a glass article made from said glass composition, in particular in the form of a glass sheet, hollow glass article or glass fiber.

The present invention also relates to the use of nickel to reduce energy consumption during the melting step of the glass composition of the present invention.

Brief description of graphic materials

In FIG. 1A shows the absorption coefficient (κ _λ ) of the glass composition of the prior art (XCL) and the composition of the present invention (XCL-Ni) as a function of wavelength at room temperature. In FIG. 1B shows the absorption coefficient (κ _λ ) of the same glass composition of the prior art (XCL) and the composition of the present invention (XCL-Ni) as a function of wavelength at 1200°C. In FIG. 1B further shows the emissivity gradient (dE _λ /dT) of a blackbody versus the same wavelength at 1200°C.

In FIG. 2 graphically shows the effect of adding a nickel component to low iron formulations to reduce the relative radiant thermal conductivity, Rk _r . The glass composition used for normalization (Rk _r = 1) contains 1000 ppm Fe ₂ O3 (total iron content) and 0 ppm NiO.

In FIG. 3 shows the increase in specific energy consumption in % obtained in the case of glass compositions enriched in iron or nickel, starting with a glass base with 670 ppm Fe ₂ O ₃ . The black dots represent industrial data recording incremental specific energy consumption with incremental Fe ₂ O ₃ starting at 670 ppm Fe ₂ O ₃ . The dashed curves above the black dots represent the calculated gain in specific energy for glasses containing a nickel component at levels of 5, 10, and 15 ppm NiO for glass compositions with a total iron content ranging from 670 to 870 ppm.

Detailed description of the invention

The aim of the present invention is to provide a glass composition with low iron content and low radiant thermal conductivity to reduce energy consumption during the manufacturing process. Surprisingly, it has been found that the addition of a small amount of nickel to a low iron glass composition provides a significant reduction in radiant thermal conductivity while maintaining the mechanical properties, toughness and chemical resistance of the glass composition in a cost-effective manner.

In this text, when specifying a range, its extreme values are included. In addition, all integer and fractional values in the numeric range are included unconditionally, as if they were explicitly specified. Also in this text, content values are given as a percentage by weight, in other words, expressed relative to the total weight of the glass, unless explicitly stated otherwise (eg, in ppm). In the present text, the iron content is total and is expressed as Fe ₂ O ₃ unless explicitly stated otherwise.

The glass composition of the present invention contains nickel, represented as NiO, at a level of 0.0001 to 0.0020% by weight.

In a preferred embodiment, the glass composition of the present invention contains nickel, present as NiO, at a level of <0.0018%, preferably <0.0015%, more preferably <0.0010%, most preferably <0.0008% by weight.

In another preferred embodiment, the glass composition of the present invention contains nickel, present as NiO, at a level of >0.0002%, more preferably >0.0003% or even >0.0005% by weight.

The glass composition of the present invention has a total iron content (expressed as Fe ₂ O ₃ ) of 0.002 to 0.1% by weight. In a preferred embodiment, the glass composition has a total iron content, expressed as Fe2O3, of 0.002 to 0.06%, preferably 0.002 to 0.04%, more preferably 0.002 to 0.02% by weight.

The present invention solves the technical problem of formulating a glass composition with low radiant thermal conductivity at high temperature by reducing the coefficient of radiant thermal conductivity (k _r ) and therefore by increasing the absorption coefficient (κ _λ ) of the glass composition in the wavelength range corresponding to the energy radiated in the melting furnace at the temperature reached in said furnace. Surprisingly, it has been found that the addition of a small amount of nickel to a glass composition with a relatively low total iron content provides such a low radiative thermal conductivity. In addition, this technical solution thus only slightly modifies the composition, which ensures the preservation of the mechanical and chemical properties of the glass composition.

Radiant energy transfer in a molten glass composition can be estimated using the Rosseland approximation based on the assumption that photon propagation can be simulated by the diffusion law, i.e. that the energy flux F is proportional to the temperature gradient ET/Sz, where z is

- 2 040747 glass height, and the proportionality factor kr is the coefficient of radiant thermal conductivity, according to equation I.

dT/dz = F/k _r . (Equation I)

The radiative thermal conductivity kr can be calculated by adding, at all wavelengths, the emissivity gradient, δE _λ /δT, (which is the rate of change of emissivity with respect to temperature) with the inverted absorption coefficient κ _λ according to Equation II below. For the purpose of the present invention, the emissivity Εχ emitted in the furnace is equated to a black body.

1 δΕ _λ ^to '~z1

It has been found that in order to improve heat exchange with the molten glass in a low iron glass formulation, the temperature gradient dT/dz should be increased in Equation I. This can be achieved by lowering the radiative thermal conductivity k _r of the glass composition and thus by increasing its absorption coefficient κ _λ . In addition, it has been found that the absorption curve of the glass composition should match as far as possible the emissivity gradient resulting from the energy radiated in the furnace in order to have a significant effect on the radiant thermal conductivity.

Absorption coefficients, κ _λ compositions of the prior art and according to the present invention according to table. 1 below was measured at room temperature and at high temperature. The high temperature corresponds to the temperature normally reached in a glass melting furnace.

Table 1

The absorption coefficient was measured in the laboratory according to the following method. A special spectrometer has been developed to measure transmission in the range from 250 to 2800 nm at high temperature. The temperature of 1200°C was chosen as an exemplary temperature reached in the furnace. The radiation sources were xenon and halogen lamps (from 250 to 2000 nm) and a ceramic element for wavelengths above 2000 nm. The radiation was modulated and divided into two beams to enter the laboratory furnace. The optical path of one of the beams is designed to measure the transmission of the glass sample, the other beam did not pass through the sample and was used as a blank sample. Transmission detectors are a photomultiplier tube or semiconductors. The glass sample holder is an alumina ring with two sapphire waveguide windows. The measurements were carried out at two different thicknesses of 1 and 2 mm. The absorption coefficient was thus calculated from the two recorded transmission spectra.

The absorption coefficient (κ _λ ) of the above two low iron glass compositions, XCL without nickel (composition of the prior art) and XCL-Ni with low nickel (composition of the present invention) was measured at wavelengths from 250 to 2800 nm. The absorption coefficient was measured according to the method described above depending on the wavelength at room temperature (Fig. 1A) and at 1200°C (Fig. 1B). In FIG. 1B additionally shows the emissivity gradient (dE _λ /dT) of a blackbody versus the same wavelengths at the same temperature of 1200°C. Only the shape of this last curve is important for the purpose of illustration, and the values in FIG. 1B are normalized with respect to the maximum of the function dE _λ /dT.

In FIG. 1A, it can be seen that the XCL composition of the prior art is characterized by a band of strong

- 3 040747 absorption with a peak at about 1000 nm due to Fe ²⁺ , while the absorption coefficients of the glass compositions were measured at room temperature at various wavelengths. The XCL-Ni composition of the present invention is characterized by several strong absorption bands in the visible range, as well as several peaks in the infrared spectrum at about 1000 and 2000 nm. These peaks account for the somewhat higher IR absorption of the nickel-containing glass composition at room temperature compared to the prior art composition.

In FIG. 1B shows an unexpected benefit of the composition of the present invention. Compared with the reference (XCL, state of the art composition), the absorption in the visible range of the composition of the present invention (XCL-Ni) decreases at high temperature, but increases strongly in the infrared region (above 1700 nm), which is very preferable for improving absorption radiation emitted in the oven.

As shown below in FIG. 1A and 1B, it was surprisingly found that the composition of the present invention preferentially absorbs the radiation emitted by the flame and re-radiated by the refractory materials in the furnace. Indeed, the composition of the present invention, containing a small amount of nickel, at high temperature is characterized by absorption bands at wavelengths in the infrared region, which correspond to the energy emissivity gradient of the furnace, equated in this case with a black body (Fig. 1B)

Using Equation II and the absorption coefficient values, κ _λ , obtained from FIG. 1B, the radiative thermal conductivity, k _r , was calculated for low iron glass compositions having different levels of iron and different levels of nickel.

The relative radiant thermal conductivity, Rk _r , was calculated using Equation II (above). The absorption coefficients, κ _λ , for iron and nickel were derived from an optical model calibrated to the measured absorption curves at room temperature and 1200° C. from FIG. 1A and 1B. The k _r values are normalized to glass containing 1000 ppm Fe ₂ O3 without nickel to give the relative radiant thermal conductivity, Rkr.

In FIG. 2 shows the benefit of adding nickel to low iron compositions to reduce the relative radiant thermal conductivity, Rkr. In FIG. 2 shows that the effect of nickel addition to the glass composition on radiative conductivity is stronger for compositions with lower iron content. It further demonstrates that the first few ppm of nickel are the most effective in reducing the radiative thermal conductivity. Increasing the nickel level to more than 0.002% by weight of the total glass composition does not provide a significant incremental benefit.

Fluid simulation models of glass melting furnaces typically use the radiant thermal conductivity approximation calculated in this document. The data from FIG. 2 can therefore be used by the glass industry to estimate the energy gain as a function of the amount of nickel added to the melt relative to a given amount of iron. In FIG. 3 shows an alternative estimate based on industrial data reporting the change in specific consumption (in percent) per amount of iron.

Industry data has been collected regarding the energy gain of silicate glass formulations at various iron levels: reference is made to the points depicted in FIG. 3. These industry data report a gain in specific energy consumption (ie energy reduction) with increasing Fe ₂ O ₃ total starting from a formulation with an initial 670 ppm Fe ₂ O ₃ total. From these industrial data obtained with different amounts of iron, the thermal conductivity coefficient k _r can be calculated and hence a function f relating the decrease in k _r to the increase in specific consumption can be obtained. In addition, based on the measured κ _λ from FIG. 2, one can calculate k _r for glass compositions containing both nickel and iron and apply the same f function to convert k _r of these glass compositions into specific energy gains, as shown in FIG. 3. Indeed, in FIG. 3 shows the energy gain obtained with glass compositions containing nickel at various addition levels (5, 10 and 15 ppm NiO) calculated for glass compositions with a total iron content ranging from 670 to 870 ppm. In a glass composition containing 670 ppm Fe ₂ O ₃ sum, 5 ppm NiO will provide a reduction in specific energy consumption of approximately 1%, which is really significant in the current field of glass melting. Adding 10 to 15 ppm NiO to the same glass composition will provide gains in specific energy consumption of 1.7 and 2.2%, respectively. For glass compositions with higher iron content, the gain per ppm NiO is smaller, but still significant. In glass compositions containing 870 ppm Fe ₂ O ₃ sum., the addition of 5 to 15 ppm NiO will provide a gain in specific energy consumption of 0.7 to 1.5%, respectively.

In a preferred embodiment, the glass composition of the present invention further comprises cobalt, preferably at levels of 0.00005 to 0.0020%, represented as CoO, more preferably 0.00005 to 0.0015% by weight. Indeed, it has been found that the addition of nickel, even at the low levels required by the present invention, can slightly affect the optical properties, such as color, of the final product. Depending on the intended application/use, this may or may not be a problem. If necessary, the yellow color imparted by nickel can be easily neutralized by the addition of cobalt.

In another embodiment, the glass composition of the present invention also contains chromium, preferably at a level of 0.0001 to 0.0025%, represented as Cr ₂ O3, more preferably 0.0001 to 0.002% by weight. Indeed, it has been found that the addition of chromium to the glass composition of the present invention can provide similar benefits as the addition of nickel in that it reduces the radiant thermal conductivity of the respective glass composition, but is less effective than nickel.

In a preferred embodiment, the glass composition of the present invention does not contain selenium. Without selenium is herein understood to mean a glass composition with a selenium content, represented as Se, < 3 ppm, preferably < 2 ppm. In a more preferred embodiment, the glass composition of the present invention does not contain selenium and cobalt in combination.

The composition of the glass according to the present invention is made of glass, which can belong to different categories. The glass may be, for example, soda-lime silicate, aluminosilicate or borosilicate type glass and the like.

In addition to iron and nickel, the glass composition of the present invention contains the following components in weight percent, based on the total weight of the glass composition:

_SiO2 50-85% A1 ₂ 0z 0-30% At ₂ 0z 0-20% _Na2O 0-25% CaO 0-25% MgO 0-15% K ₂ O 0-20% VAO 0-20%

In a preferred embodiment, the glass composition of the present invention contains the following components in weight percent, based on the total weight of the glass composition:

Preferred compositions of the present invention, particularly suitable for producing glass sheets and hollow glassware, are of the soda-calcium silicate type. Preferably, according to this preferred embodiment, the composition contains the following components in weight percent, based on the total weight of the glass composition:

- 5 040747

Other preferred glass compositions of the present invention, particularly suitable for use as glass fibers, contain the following components in weight percent, based on the total weight of the glass composition:

_SiO2 50-75% A1 ₂ 0z 10-30% B ₂ O ₃ 0-20% _Na2O 0-5% CaO 0-25% MgO 0-15% K ₂ O 0-5%

Illustrations of glass compositions according to the present invention, which are known to be applicable to the production of glass fibers, are shown in the following table:

The glass compositions of the present invention are of particular interest when used for the manufacture of glass products, in particular hollow glass products, glass sheets and/or glass fibers. Hollow glass products may be glass bottles, glass flasks, glass vessels, and the like. Fiberglass is glass in a fibrous form used to make various products (such as glass wool for insulation) and is usually made up of entangled fine glass fibers.

In a preferred embodiment, the present invention relates to a hollow glass product made from the composition of the present invention.

In an alternative preferred embodiment, the present invention relates to glass fibers made from the glass composition of the present invention.

Typically, a glass manufacturing process includes the steps of (i) melting a batch of starting material that contains a mixture of glass starting material and/or cullet in a glass melting furnace/glass melting pool; and then molding the molten glass into the desired shape. The melting step includes the supply of heat to the raw materials or cullet through the transfer of radiant energy to provide melting/melting. Typically, heat is generated by burners that use fossil fuels (i.e. natural gas) with preheated

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Claims (13)

ty air. For example, molten glass can be continuously drawn from a spinneret to form fibers. To form hollow glass such as bottles, molten glass is placed in a mold, and the glass is then molded into a glass bottle by blowing technology. The glass sheet may be produced by a float process, a drawing process, a rolling process, or any other known process for making a glass sheet, starting from a molten glass composition. In an embodiment according to the present invention, the glass sheet is a float glass sheet. The term float glass sheet is understood to mean a sheet of glass formed by a float glass manufacturing process which consists in pouring molten glass onto a bath of molten tin under reducing conditions. The present invention also relates to the use of nickel to reduce energy consumption during the melting step of the glass composition of the present invention. Embodiments of the present invention will be further described by way of examples. The following examples are presented for illustrative purposes and are not intended to limit the scope of the present invention. Examples To obtain glass compositions in accordance with the examples, the following was performed. Powdered starting materials were mixed together and placed in melting crucibles according to each composition defined below. The mixture of starting materials was then heated in an electric furnace to a temperature to ensure complete melting of the starting material. The following glass compositions were prepared according to the present invention. These glass compositions are particularly suitable for use as glass sheets or hollow glass products. 1 2 3 4 5 6 7 8 SiO ₂ (%) 72.2 72.2 72.3 72.2 72.2 72.2 72.2 72.3 A1 ₂ O ₃ (%) 0.62 0.63 0.61 0.62 0.62 0.61 0.62 0.61 Fe ₂ O ₃ (%) 0.075 0.077 0.074 0.074 0.074 0.074 0.074 0.073 CaO (%) 8.89 8.91 8.85 8.87 8.84 8.87 8.86 8.67 MgO (%) 4.28 4.26 4.29 4.30 4.30 4.29 4.30 4.21 Na ₂ O (%) 13.50 13.53 13.46 13.48 13.50 13.50 13.52 13.44 K ₂ O (%) 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 Ni (ppm) 4 5 9 13 h 6 6 8 Co (ppm) - - - - 0.75 1.5 2.5 3.5 CLAIM 1. Glass composition containing the following components in weight percent, expressed in terms of the total weight of the glass composition: SiO ₂ 50-85% o< ai ₂ o ₃ < 30% 0< B ₂ Oz<20% 0<Na ₂ O<25% 0<CaO<25%0<MgO<15%0< K ₂ O<20 % 0<BaO<20% Pe ₂ 0z total 0.002-0.1% _SiO2 50-85% 0< A1 ₂ 03 < 30% 0< V ₂ oz<20% 0<Na ₂ O<25% 0<CaO<25% 0<MgO<15% 0< _K2O <20% 0<BaO<20% Re ₂ 0z total 0.002-0.1% _SiO2 50-85% 0< A1 ₂ 03 < 30% 0< V ₂ oz<20% 0<Na ₂ O<25% 0<CaO<25% 0<MgO<15% 0< _K2O <20% 0<BaO<20% Pe ₂ 0z total 0.002-0.1%, characterized in that the glass composition additionally contains nickel, presented as NiO, at a level from 0.0001 to 0.0018% by weight and cobalt, presented as CoO, at a level from 0 .00005 to 0.0020% by weight. 2. Glass composition according to claim 1, characterized in that it contains nickel, present as NiO, at a level of >0.0005% by weight. 3. Glass composition according to any one of the preceding claims, characterized in that it contains Fe ₂ O ₃ in total at a level of from 0.002 to 0.06% by weight, preferably from 0.002 to 0.04%, more preferably from 0.002 to 0.02 % by weight. - 7 040747 4. Glass composition according to any of the preceding claims, characterized in that it contains the following components in weight percent, expressed in terms of the total weight of the glass composition: 5. The glass composition according to the previous paragraph, characterized in that it contains the following components in weight percent, expressed in terms of the total weight of the glass composition: 6. A glass composition according to any one of the preceding claims, wherein the cobalt, present as CoO, is at a level of 0.00005 to 0.0015% by weight. 7. Glass composition according to any of the preceding paragraphs, characterized in that it additionally contains chromium. 8. A glass composition according to the preceding claim, characterized in that it contains chromium, represented as Cr2O3, at a level of 0.0001 to 0.0025%, more preferably 0.0001 to 0.002% by weight. 9. A glass article made from a glass composition according to any one of the preceding claims. 10. A glass article according to claim 9, which is in the form of a hollow glass article. 11. A glass article according to claim 9, which is in the form of a sheet of glass. 12. The glass product according to claim 9, which is in the form of fiberglass. 13. The use of nickel to reduce energy consumption during the melting process of a glass composition containing the following components in weight percent: _SiO2 50-85% 0< A1 ₂ O ₃ < 30% 0< B ₂ O ₃ <20% 0<Na ₂ O<25% 0<CaO<25% 0<MgO<15% 0< K ₂ O<20% 0< ВаО<20% Ge ₂ 0z total 0.002-0.1% -