Glass manufacturing method and glass processing furnace

Abstract

An improved method for making glass is provided. [Solution] The method for producing glass includes preparing a mixture of glass raw materials for a glass processing furnace. Water, sand, and sodium carbonate are mixed in mass proportions of 0-5%, 40-65%, and more than 0% but not more than 25%, respectively, and calcium oxide is added in a mass proportion of 1-20% of the total amount, preferably simultaneously, within a time period of less than 10 minutes. The particle size of the calcium oxide is such that more than 97% by weight does not pass through a 0.125 mm sieve, more than 96% by weight does not pass through a 0.5 mm sieve, and preferably more than 95% by weight does not pass through a 1 mm sieve.

Description

[Technical field]

[0001] The present invention relates to the field of glass industry. To melt the materials that form glass, it is necessary to provide a large amount of energy. The temperature of the glass bath is around 1300-1500 ° C. Depending on its composition, glass is intended for direct domestic use, e.g. drinking glasses, for indirect use, e.g. glazes, e.g. glass-ceramic plates, or for industrial use. [Background technology]

[0002] The furnaces are subjected to very high thermal and mechanical stresses. They are constructed with high quality refractory linings. These refractory linings are expensive and sensitive to certain constituents of the glass which can cause chemical reactions. As the refractory linings have poor thermal conductivity, the glass bath is heated from above.

[0003] Liquid or gas fuel flame burners are placed between the glass bath and the top of the furnace, called the crown. The glass bath is heated primarily by radiation. The gas outlet temperature is between 1300 and 1600 °C, depending on the type of glass.

[0004] In addition, the production of glass releases large amounts of gas. To avoid the formation of bubbles in the glass, the glass bath is degassed for several hours. To facilitate degassing, refining additives such as sulfates may be used. The furnace is run for each batch of glass of the selected composition.

[0005] The exhaust gases resulting from the deaeration and the exhaust gases resulting from the combustion are exhausted through a chimney.

[0006] The Applicant has pursued the objective of significantly reducing the consumption of energy compared to the mass of glass produced.

[0007] In lime-soda glass, the main starting materials are limestone, soda in the form of sodium carbonate, e.g. Na2CO3, and silica in the form of quartz sand. The limestone and sodium carbonate release CO2 during the refining of the glass.

[0008] US Pat. No. 5,399,433 describes the use of slag for the production of glass. However, many technical obstacles remain unaddressed. To the applicant's knowledge, such a technique has not been implemented industrially.

[0009] US Patent No. 5,399,633 describes a glassworks furnace charge produced from wet-mixed dolomite and kaolin. A slurry of dolomite and kaolin is calcined and then mixed with soda ash, sand, and quicklime.

[0010] US Pat. No. 5,399,433 describes pre-reacting a premix of Na2CO3 and SiO2 in parallel with a premix of CaCO3 and SiO2, then mixing the two premixes, adding SiO2, and then introducing them into a glass processing furnace.

[0011] US Patent No. 5,399,633 relates to a method for making glass comprising firing CaCO3 to form CaO, forming liquid phase Na2SiO3 glass, and mixing CaO and Na2SiO3 in the liquid phase to form lime-soda glass.

[0012] Furthermore, the applicant is aware of the seminar "Glass Trends Seminar" held in Eindhoven on 18th and 19th October 2012, where he met Hande Sesigur, Melek Orhon and Banu Arslan of SISECAM, who presented the paper "Glass Trends Seminar" (2012), which reports on the attempt to introduce calcined limestone into glass processing furnaces. This slightly reduces the energy consumption, facilitates melting and increases the specific power of the furnace, but it also leads to a higher cost price per metric ton of glass produced, more volages above the glass bath, increased corrosion of the furnace walls and problems with adhesion between particles.

[0013] The applicant has carried out tests. The replacement of limestone in glass-making materials with quicklime creates problems, especially related to the reactivity of lime with moisture in the air. The economy of lime is less favorable than that of limestone, despite the reduced tonnage of transport and handling. Furthermore, larger particle size lime melts slower in the glass bath and may leave unmelted particles. Smaller particle size lime creates carryover that is entrained by the combustion gases. Some of the lime is lost and fouls the downstream flue of the furnace.

[0014] Despite these obstacles, the applicant has pursued and developed a glass raw material mixture. Certain difficulties have been encountered during the preparation of the mixture. In the absence of water, the powdered mixture lacks strength and produces a large amount of carryover. However, when water and lime are combined, they react exothermically. The temperatures reached make the mixture difficult to handle.

[0015] The applicant has developed a method for preparing a precursor mixture that provides a mixture with low heating and low carry-over generation (see patent document 5). The particle size of the components added to the mixture is substantially maintained, except that a grinding effect that reduces the particle size slightly may occur due to mechanical transfer operations. The mixture introduced into the glass processing furnace results in a reduction of CO2 emissions and energy required for glass production of the order of 3-6%. Furthermore, the melting time of the mixture is shorter than that observed during the use of calcium carbonate. This results in an increase in furnace productivity and an additional reduction in energy consumption of about 4-6%.

[0016] The applicant carried out a study with the aim of understanding the phenomenon of carryover. To obtain a high melting motion, fine lime was used according to availability from the lime supplier. However, in the workshop where the mixture was prepared, the drawback appeared that the circuit conveying the prepared composition emitted dust into the surrounding air. A dust removal circuit was installed. However, the dust removal circuit became clogged with sticky fine lime and became unstable over time. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Publication No. 55-100236 [Patent Document 2] U.S. Patent No. 2,084,328 [Patent Document 3] US Patent Application Publication No. 2005 / 0022557 [Patent Document 4] US Patent Application Publication No. 2012 / 0216574 [Patent Document 5] International Publication No. 2019 / 002802 [Non-patent literature]

[0018] [Non-Patent Document 1] Alternative Raw Materials for Improving the Melting Properties in Glass Production Summary of the Invention [Problem to be solved by the invention]

[0019] The present invention improves this situation. [Means for solving the problem]

[0020] The present invention proposes a method for producing glass, which comprises preparing a mixture of glass raw materials for a glass processing furnace, in which water, sand and sodium carbonate are mixed in mass proportions of 0-5%, 40-65% and more than 0% but not more than 25%, respectively, and adding, within a time period of less than 10 minutes and preferably simultaneously, calcium oxide and optionally calcium carbonate in mass proportions of 1-20% relative to the total amount, said calcium oxide having a particle size such that more than 97% by weight does not pass through a 0.125 mm sieve, more than 96% by weight does not pass through a 0.5 mm sieve and preferably more than 95% by weight does not pass through a 1 mm sieve.

[0021] In one embodiment, the secondary glass forming raw materials include at least one of Al2O3, MgO, K2O, BaO, CeO2, Er2O3, TiO2, B2O3, ZnO, SrO, and SnO2.

[0022] In one embodiment, the preparation of the mixture is carried out without the application of heat.

[0023] In one embodiment, the ingredient is in powder form.

[0024] In one embodiment, the particle size is measured using a square mesh sieve.

[0025] In one embodiment, the calcium oxide has a particle size of d10 of 0.5 to 2 mm and d90 of 3 to 4.5 mm.

[0026] In one embodiment, the calcium oxide is formed of grains having a thickness of 20 to 60% of the length and width. The grain size of the long grains may be measured by screening.

[0027] In one embodiment, the calcium oxide is formed from grains less than 10 mm wide.

[0028] In one embodiment, the calcium oxide is formed from grains less than 3 mm thick.

[0029] In one embodiment, the calcium oxide is formed from grains in which 90% of the grains are less than 15 mm in length.

[0030] In one embodiment, the mixture of water, sand, calcium oxide, and sodium carbonate has a moisture content of 5% or less.

[0031] In one embodiment, the sodium carbonate has a particle size such that less than 5% passes through a 0.075 mm sieve, less than 15% passes through a 0.150 mm sieve, and less than 5% does not pass through a 0.600 mm sieve.

[0032] In one embodiment, the mixture of water, sand, and sodium carbonate has a moisture content of 3% or less, and the particle size of the sodium carbonate is predominantly greater than 0.500 mm and less than 1.000 mm.

[0033] In one embodiment, the mixture of water, sand, and sodium carbonate has a moisture content of 2% or less, and the particle size of the sodium carbonate is predominantly less than 0.250 mm.

[0034] In one embodiment, the calcium oxide contains less than 1000 ppm, preferably less than 900 ppm, more preferably less than 850 ppm Fe2O3 by mass.

[0035] In one embodiment, the initial temperature of the feedstock is at least 30° C. This increases the rate of hydration of the sodium carbonate.

[0036] In one embodiment, the calcium oxide has a particle size such that more than 98% by weight does not pass through a 0.08 mm sieve.

[0037] In one embodiment, the calcium oxide has a particle size such that more than 97.5% by weight does not pass through a 0.2 mm sieve.

[0038] In one embodiment, the calcium oxide has a particle size such that more than 97.5% by weight does not pass through a 0.5 mm sieve.

[0039] In one embodiment, the calcium oxide has a particle size such that more than 98% by weight does not pass through a 0.125 mm sieve.

[0040] In one embodiment, the calcium oxide has a particle size such that more than 97% by weight does not pass through a 1 mm sieve.

[0041] In one embodiment, the calcium oxide has a d50 particle size of 1-4 mm, preferably 1.5-4 mm, more preferably 2-3.25 mm.

[0042] In one embodiment, the sand is dry. The amount of water added is well controlled. In another embodiment, no water is added, preferably with medium or large grain size, energy consumption is reduced. The sand is considered dry with a moisture content of less than 0.1%. The sand may be dried by heating at 15-20°C above ambient temperature.

[0043] In one embodiment, the water is preferably present in the sand at 3-6% by weight. At least 3% avoids drying of the sand. 4.8% or less is preferred to slow down heating. 6% or less is preferred to reduce dust emissions. The cost of intentionally adding water is avoided.

[0044] In one embodiment, the calcium oxide is free of any intentional addition of aluminum oxide, which may be added during mixing.

[0045] In one embodiment, cullet is added to the mixture of raw materials, either before or after the addition of calcium oxide, in a mass proportion of 5-40% of the total. The cullet may be obtained from a downgraded batch of glass. Since the batch is of known composition, the amounts of the other raw materials are adjusted to the required quality of glass.

[0046] In one embodiment, the mixture of ingredients is prepared in a solid state, the evaporation of water in the case of a slurry is avoided, and the energy consumption for pre-melting the ingredients is avoided.

[0047] In one embodiment, the mixture of ingredients is prepared at a temperature ranging from ambient temperature to ambient temperature plus 20°C.

[0048] In one embodiment, the mixture of ingredients is prepared at a temperature in the range of +0 to +35° C. relative to the pre-temperature of the water, the sand, the sodium carbonate, and the calcium oxide. A weighted average may be used as the pre-temperature.

[0049] In one embodiment, the raw material mixture is prepared without the addition of thermal energy. Drying of the mixture, which would generate fines and therefore carryover, is avoided.

[0050] In one embodiment, the mixture is placed into an electric furnace.

[0051] In one embodiment, a mixture of water, sand, soda, calcium oxide and optionally calcium carbonate is provided in a glass processing furnace. The mass percentage of said calcium oxide is 1-20% with respect to the total amount of said mixture. The mixture is melted by at least one flame burner directed at said mixture. The burner provides a good efficiency and effect of burning carryover towards the surface of the melting or already molten glass bath.

[0052] In one embodiment, the oxidant supplied to the burner is oxygen, which increases the effectiveness of burning off carryover.

[0053] In one embodiment, the water, sand, sodium carbonate and calcium oxide and optionally calcium carbonate are present in mass proportions of 0-5%, 40-65%, 1-25%, and 1-20% relative to the 25% cullet added, respectively, and the proportion of cullet can be varied by adjusting the above proportions.

[0054] In one embodiment, the decarbonation of Na2CO3 is carried out in the liquid phase in a glass processing furnace.

[0055] Generally, the mixture of raw materials refers to glass-forming raw materials.

[0056] Other features and advantages of the present invention will become apparent from consideration of the following detailed description and accompanying drawings. [Brief description of the drawings]

[0057] [Figure 1] 1 is a graph of ambient air measurements in a furnace dog house using a test batch of quicklime. [Diagram 2] 1 is a graph of ambient air measurements in the vibrating passage below the hopper of a furnace using a test batch of quicklime. [Diagram 3] 1 is a graph showing the temperature variation of the vitrifiable mixture depending on the moisture content of the quicklime and sand used. [Figure 4] 1 is a graph showing the variation in the amount of carryover recovered during laboratory testing depending on the moisture content of the quicklime and sand used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] The accompanying figures not only supplement the invention but also, where applicable, can contribute to the definition of the invention.

[0059] In addition to the tests reported in US Pat. No. 5,399,533, other tests were also performed.

[0060] In most of the glass processing activity subsectors, wet mixes are used to limit the carryover of raw materials, especially sodium carbonate and sand (crystalline silica). The target moisture content varies from facility to facility. In the presence of moisture, quicklime reacts, which results in the release of heat and increased dust generation due to the effect of exothermic hydration reactions. Hydrated lime is much more susceptible to this phenomenon than quicklime or anhydrous lime. This dust is released in the conveying circuit upstream of the furnace when the raw material mix is ​​prepared, when the mix is ​​introduced into the furnace, and also in the furnace itself. In the long term, this causes failure of the regenerator by depositing on the refractory packing downstream of the furnace.

[0061] Furthermore, commercially available quicklime is rarely used in glass production and is therefore not suitable for the specific requirements of clear glass.

[0062] Chemical properties: Very few limes have an iron content that matches our requirements. Iron is a contaminant in glass, which leads to discoloration and poor transparency of the glass produced.

[0063] · To meet the requirements of existing applications, for example in metallurgy, chemistry, or agriculture, the particle size of quicklime is often very fine (d50 in the range 0.15-0.5 mm).

[0064] The applicant, through its research program, has successfully used this type of quicklime in its own glass processing furnaces.

[0065] It was found that lime particles smaller than 0.100 mm were problematic. It was then found that reducing the proportion of small particles, where applicable, by fixing a limit value above 0.100 mm would be advantageous in order to obtain substantial, stable and reproducible results for dust emissions. Several batches of quicklime were then tested.

[0066] The two batches differed greatly in particle size: batch no. 1 had particle sizes of d10 < 0.08 mm, d50 0.17 mm, d90 3.18 mm, batch 2 had particle sizes of d10 < 0.08 mm, d50 > 2.5 mm, and d90 3.76 mm. The particles had a shape that was approximately equal in all three dimensions. Batch 2 seemed particularly affected by the presence of very coarse particles that did not pass the 8 mm sieve and therefore melted extremely slowly.

[0067] [Table 1]

[0068] [Table 2]

[0069] After removing the coarsest particles by sieving in the laboratory, the particle size spectrum of sieved batch 2 was similar to that of batch 1, with particle sizes of d10 less than 0.08 mm, d50 0.19 mm, and d90 1.9 mm.

[0070] [Table 3]

[0071] Batch no. 3 of quicklime granules with a particle size of less than 3.6 mm. The particles had a shape with approximately equal dimensions. The proportion of fines is similar to that of batch no. 4.

[0072] Batch no. 4 of quicklime granules having a flattened shape. In other words the thickness is about 20-60% of the length and width. The width is less than 10 mm. The thickness is less than 3 mm. The length is generally less than 15 mm.

[0073] Industrial Testing To confirm the effect of these particle sizes in a production setting, tests were conducted in a production furnace using batches 1 to 4 shown above.

[0074] The quicklime was introduced according to US Pat. No. 5,399,633. The effect on dust emissions into the working environment was measured.

[0075] [Table 4]

[0076] For batches 1 and 2 no significant improvement in dust emissions can be guaranteed. When the balance is favorable for the material input to the furnace, the emission levels in the feed passages remain unchanged or worsen as shown above. It was found that the proportion of fine particles present is the cause of this concern.

[0077] Batch 3 shows an interesting dust emission, especially near the vibrating aisle: a reduction of 85-95% for inhalable dust and 80-90% for alveolar dust defined according to Technical aid memoir ED 984 of the INRS, 4th edition, October 2016, ISBN 978-2-7389-2240-3.

[0078] Batch 4 shows very interesting dust emissions, regardless of the measurement location: a reduction of more than 80% for inhalable dust and a reduction of more than 80% for alveolar dust defined as above.

[0079] In light of these results, batch 4 was selected.

[0080] Longer tests were carried out with the batch 4 particle size, both to obtain a more complete picture of the behavior of this material in the furnace and to estimate the impact of this new particle size on the performance of the tonnage produced and the energy consumption observed in the milled fines.

[0081] Phase 1: Implemented according to US Patent No. 5,933,663.

[0082] [Table 5]

[0083] Measurements 1 and 2 were made by sampling two portions of the same batch of lime that was then mixed and fed into the kiln. The percentage of fines less than 0.20 mm is less than 2.5%. The percentage of fines less than 0.125 mm is less than 2.0%.

[0084] The main teachings of this study were:

[0085] Tonnage per day achieved: Increased for the same glass obtained from limestone without quicklime. Tonnage per day performance is maintained compared to fine lime despite the increase in particle size.

[0086] Energy consumption per metric ton of molten glass: There is no increase in furnace consumption for increasing raw material particle size, or even a slight decrease of 3.46% for batch 4 quicklime.

[0087] The table below compares four different periods using quicklime from the reference batch, batch 3 and batch 4. All these production periods are with the same percentage of cullet (25%) and the same other raw materials: sand, sodium carbonate, etc. During these four periods, the daily production was kept constant according to the industrial requirements without any specific performance. The normal production of the furnace was 110 metric tons / day with the conventional feed with limestone and no quicklime.

[0088] The reference batch is quicklime with particle sizes d10<0.1 mm; d50<0.1 mm; d90<0.92 mm.

[0089] [Table 6]

[0090] Production with benchmark lime had an average output of 128.9 metric tons per day over 8 days, normalized to 100% energy consumption in methane gas equivalents corrected for temperature and pressure, giving the following comparison: The daily values ​​are not very representative due to the residence time and high inertia of the material in the furnace, but the average over 5 days shows something interesting.

[0091] [Table 7]

[0092] The production with batch 3 lime resulted in an output of 131.2 metric tons per day over 5 days, with an energy consumption per metric ton of molten glass of 100.6% of the reference lime. This difference in consumption is not significant, except that consumption was expected to be very slightly below 100%. This is because, for the same raw material, a higher production volume results in a faster melting motion without the furnace heat losses increasing at the same rate, and therefore a lower energy consumption per metric ton of molten glass. Going deeper, it will be understood that maintaining the furnace at the temperature when production is zero consumes energy, and the more production, the smaller this maintenance energy value becomes by more metric tons, resulting in a lower total energy consumption per metric ton of molten glass.

[0093] [Table 8]

[0094] During days 1-6, production with batch 4 lime resulted in an output of 124.3 metric tons per day, with an energy consumption per metric ton of molten glass of 100.6%. Compared to the reference lime, the energy consumption per metric ton is very close, with an output of 3.57% less. On the other hand, the energy consumption per metric ton was expected to increase by a few points. Compared to batch 3, the energy consumption per metric ton was the same, with an output of 5.53% less. For such a decrease in output, a significant increase in the energy consumption per metric ton was expected.

[0095] [Table 9]

[0096] Production with batch 4 lime during days 7-18 resulted in an output of 131.3 metric tons per day with 97.2% energy consumption per metric ton of molten glass. Compared to the reference lime, the energy consumption per metric ton decreased by 2.8% and the output increased by 1.86%.

[0097] Compared to Batch 3, the power output is virtually identical and the energy consumption per metric ton is down 3.40 percentage points. Such a drop in energy consumption per metric ton is unexpected.

[0098] From another perspective, assuming that the energy consumption per metric ton varies linearly with the power output, the power output of 128.9 metric tonnes corresponds to an energy consumption per metric ton of 98.4%, i.e., a drop of 1.60 percentage points. However, it is generally believed that in glass production, coarse raw materials take longer to melt than fine raw materials, and therefore require more energy per metric ton of molten glass. This unexpected behavior is shown by batch 3, which increases the energy consumption per metric ton by 0.6% for a power increase of 1.78%. The same behavior was predicted for batch 4. However, the energy consumption per metric ton of batch 4 is reduced by 3.40 percentage points compared to batch 3. This difference is considerable and difficult to explain. One hypothesis could be that the heat is better transferred within the raw materials related to the flat shape of the limestone grains.

[0099] The temperature of the composition in the composition day hopper is not higher in batch 4 than in the reference batch. The temperature is around 37 / 38°C. The dust emission in the ambient air is clearly reduced. The dust emission in the furnace is evaluated by measurements over 24 hours with a cooled paddle installed at the top of the regenerator.

[0100] On average, 84 mg of dust per metric ton of molten glass was collected on the puddle during this test with Batch 4 quicklime, compared to an average of 100 mg of quicklime per metric ton of molten glass for the reference batches. Furthermore, chemical analysis of the collected dust showed a 50% reduction in its CaO content, proving that this carryover difference indeed results from a change in the behavior of the quicklime in the furnace.

[0101] Then, industrial test A was prepared. An identical mixture was prepared with quicklime from batch no. 4. This time, the quicklime was introduced directly into the mixer without following the introduction delay specified in patent application WO 2005 / 023311 and sent to the same furnace. The temperature of the composition was measured at 22°C in the mixer, 25°C in the delivery lorry at the start of the processing site and 27°C in the furnace hopper receiving the lorry. When the lorry was emptied into the hopper, there was no obvious release of dust. These mixtures were introduced into the furnace and the composition temperature was measured at 37°C, without any concerns in the furnace. This test corresponds to approximately 2 hours of operation of the furnace.

[0102] During test B, the feed to the furnace was carried out continuously for about 30 hours, with an equivalent composition. The mixture was prepared with quicklime from batch no. 4, without waiting periods for the quicklime to come into contact with the rest of the wet raw materials. This long-term test made it possible to confirm that the conditions of handling the mixture, both in the composition processing area and in the production sector, were good (no dust emissions along conveyors, elevators, vibrating paths, furnace dog houses, etc.), and that no temperature rise was observed either in the composition processing area or in the furnace, whether the measurements were made in the hopper receiving the charge with a measurement temperature in the range of 25-31 °C or in the day hopper with a measurement temperature in the range of 30-45 °C. This observation is valid whatever the moisture level required for the composition: 1.4% at the start of the test and 2.5% for the last three charges.

[0103] A continuous recording of the temperature of the composition in the hopper immediately upstream of the furnace shows in parallel an improved stability of this parameter compared to the run with the reference batch of quicklime.

[0104] No abnormalities in the operation of the furnace were observed during this test.

[0105] To complement these industrial tests, laboratory experiments were carried out to confirm the behaviour of this quicklime of batch no.

[0106] These studies were carried out by preparing a vitrifiable mixture of lime-soda glass in a test mixer (concrete mixer) according to the following operating method.

[0107] Moisten the dry sand by adding water to the required moisture level and mix for 180 seconds.

[0108] · Sodium carbonate, alumina, dolomite and quicklime are added simultaneously to the moistened sand and mixed in a concrete mixer with the lid on for 120 seconds.

[0109] All ingredients were weighed out to replicate Applicant's standard lime-soda mix on a reduced scale.

[0110] Two separate but complementary approaches were carried out.

[0111] · Study of the reaction of quicklime with moist raw materials: The temperature of the vitrifiable mixture after preparation was recorded by inserting a thermocouple into the core of the material. The onset temperature is the same for all tests. With a low moisture level of 1.3% in the sand and lime of batch no. 4, no reaction was observed (thin dashed curve in Figure 3, indicating "Test 15"), which confirms the industrial tests. This result is compared with the curve of the reference lime with a sand moisture of 1.6% (thin continuous curve indicating "Test 14"), which reaches 40 °C in about 5-6 minutes. By targeting a higher moisture level of 4.8% in the lime and sand of batch no. 4, an exothermic reaction occurs in Figure 3 (long dashed curve indicating "Test 17"), which reaches 40 °C in about 10 minutes. This rise is obviously slower than in the case of the reference batch quicklime with a sand moisture level of 4% (mixed dashed curve indicating "Test 16") and 6% (thick dashed curve indicating "Test 3"). These two tests with the reference lime with a sand moisture of 4% and 6% show a strong and rapid rise in temperature within a few seconds. The test with the reference lime with a sand moisture of 3% (short-dashed curve indicating "test 3b") has an intermediate behavior, but the temperature is higher than test 17 between 10 and 60 minutes after mixing. In other words, temperatures of 40, 50 and 60 °C are reached faster in test 3 than in test 17. Tests with lime of batch no. 4 with moisture levels up to at least 4.8% are compatible with industrial tools.

[0112] Measurement of fly ash - / - dust emission: The mixtures were prepared by the same operating method. The dust emission from the concrete mixer was measured by periodically (every 15 minutes) rotating the concrete mixer in order to simulate the operation of the composition (conveying, passing through a vibrating passage, etc.). The measurements were carried out by a dust measuring device over a total period of about 3.5 hours, a period that allows taking into account the temporary storage of the composition in a storage element before feeding it to the furnace.

[0113] Comparing the readings of the reference batch quicklime with those of batch 4 quicklime, it can be seen that there is a very significant improvement by using quicklime of batch 4: the dust emission is reduced by at least 50% and even 90% whether the water percentage in the sand is a value of 3% or 6% (the graphs in Figure 4 are on the same scale; the reduction in the amplitude of the peaks indicates a lower dust emission). Thus, the water percentage in the sand can be from 2% to at least 7%.

[0114] Thus, quicklime with a low level of fines is advantageous for the preparation and handling of vitrifiable mixtures by significantly reducing the emission of dust into the ambient air. Its high particle size allows the smaller exposed surface area to suppress the exothermic hydration reaction. Unexpectedly, the layer of hydrated lime formed on the surface of the quicklime grains by contact with the water present in other materials, especially sand, does not seem to contribute to the fly ash in the feed and storage elements upstream of the furnace. This allows such raw materials to be used without waiting for the quicklime to come into contact with the remaining raw materials.

Claims

1. A method for manufacturing glass, comprising: preparing a mixture of glass raw materials for a glass processing furnace, wherein water, sand, and sodium carbonate are mixed at mass ratios of 0 to 5%, 40 to 65%, and more than 0% and 25% or less, respectively, calcium oxide is added at a mass ratio of 1 to 20% with respect to the total amount to the secondary glass-forming raw materials within a time of less than 10 minutes, the particle size of the calcium oxide is such that more than 97% by mass does not pass through a 0.125 mm sieve and more than 96% by mass does not pass through a 0.5 mm sieve.

2. In the method according to claim 1, the calcium oxide is formed from particles having a thickness of 20 to 60% of the length and width.

3. In the method according to claim 1, the mixture of the water, the sand, the calcium oxide, and the sodium carbonate has a moisture level of 5% or less.

4. In the method according to any one of claims 1 to 3, the particle size of the sodium carbonate is such that less than 5% passes through a 0.075 mm sieve, less than 15% passes through a 0.150 mm sieve, and less than 5% does not pass through a 0.600 mm sieve.

5. The method according to any one of claims 1 to 3, wherein the calcium oxide contains Fe in an amount of less than 1000 ppm by mass ２ O ３ and the method.

6. In the method according to any one of claims 1 to 3, the initial temperature of the raw materials is at least 30°C.

7. In the method according to any one of claims 1 to 3, the particle size of the calcium oxide is such that more than 98% by mass does not pass through a 0.08 mm sieve.

8. In the method according to any one of claims 1 to 3, the particle size of the calcium oxide is such that more than 98% by mass does not pass through a 0.125 mm sieve.

9. In the method according to any one of claims 1 to 3, the d50 particle size of the calcium oxide is 1 to 4 mm.

10. In the method according to any one of claims 1 to 3, the sand is dry.

11. In the method according to any one of claims 1 to 3, the water is present in the sand at 3 to 6% by mass.

12. In the method according to any one of claims 1 to 3, no intentional addition of aluminum oxide is made to the calcium oxide, and cullet is added to the mixture of the glass raw materials at a mass ratio of 5 to 40% with respect to the total amount.

13. The method according to any one of claims 1 to 3, wherein the mixture of glass raw materials is prepared in a solid state.

14. The method according to any one of claims 1 to 3, wherein the mixture of glass raw materials is prepared at a temperature in the range from ambient temperature to ambient temperature plus 20 °C, and the mixture of glass raw materials is prepared without applying thermal energy.

15. The method according to any one of claims 1 to 3, wherein the mixture is charged into an electric furnace.

16. The method according to any one of claims 1 to 3, wherein the oxidant supplied to the burner is oxygen.

17. The method according to claim 15, wherein the water, the sand, the sodium carbonate, and the calcium oxide are present in mass ratios of 0 to 5%, 40 to 65%, 1 to 25%, and 20%, respectively.

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