JP7554150B2 - Glass manufacturing method using biological Ca source - Google Patents

Description

The present invention relates to a method for producing glass using eggshells, which are a biological Ca source .

According to the Ministry of Agriculture, Forestry and Fisheries' egg distribution statistics (2019), the total egg production in Japan is 2.64 million tons. As the weight of eggshells is approximately 11% of this, 290,000 tons of eggshells are discarded. It is said that more than 200,000 tons of eggshells are discarded from the egg processing and manufacturing process. From the perspective of environmental protection, some are reused as resources, but only about 20% of them are reused, and the remaining 80% are landfilled or incinerated at disposal costs. In addition, a large amount of shells are generated by scallop and oyster farming. As shown in Patent Document 1, some of them are used as soil conditioners to supply Ca to the soil, but most are discarded by waste disposal companies, incurring a lot of disposal costs. In addition, pearl farming companies also discard waste pearls that cannot be sold on the market, incurring disposal costs.

The above-mentioned eggshells, shells, waste pearls, etc. are mainly composed of Ca derived from living organisms, but most of them are disposed of as waste and are not effectively utilized. One of the reasons for this is that eggshells have an organic membrane called eggshell membrane attached to them, and shells have parts of the adductor muscle, decaying shellfish matter, algae, and other living organisms attached to them, making them difficult to handle as industrial raw materials. If these eggshells, shells, etc. are discarded without being effectively utilized, in addition to the problem of processing costs, there is also the problem of large amounts of _CO2 being emitted during the disposal process.

Meanwhile, glass factories use a large amount of limestone as a Ca source in addition to silica sand as a Si source as glass raw materials. Limestone is excavated from mining sites called limestone mines using heavy machinery, refined, and then loaded onto freight vehicles and transported to glass factories. This causes a large amount of _CO2 to be emitted from the heavy machinery at the mines and the refinement process. In addition, since limestone mines are often located far from glass factories, a large amount of _CO2 is also emitted from freight vehicles that travel long distances loaded with heavy limestone. Thus, when limestone is used as a glass raw material, there is a problem that a large amount of _CO2 is emitted in the process from mining to refinement and transportation.

In addition, in glass melting furnaces that use fossil raw materials such as petroleum and natural gas, a large amount of _CO2 is emitted during combustion. In addition, a large amount of _CO2 is emitted during glass manufacturing when carbonate raw materials such as limestone are vitrified. Most of the limestone currently mined and used in Japan is thought to have been added to the Japanese archipelago due to crustal movement, from calcareous material that was deposited on the seabed as biological reefs such as coral more than 200 million years ago. Coral and other materials have the function of fixing _CO2 in the atmosphere, but since it takes hundreds of millions of years for them to become limestone again, it is considered that almost no of the _CO2 emissions released from limestone during vitrification are absorbed and fixed by limestone again, and they cannot be considered carbon-neutral raw materials. These problems are factors that hinder the achievement of Japan's carbon-neutral goal. Figure 5 shows the cycle described above.

While examining the reduction of _CO2 emissions from glass factories from various angles, the inventor came up with the idea that by replacing part or all of the discarded eggshells with limestone, a raw material for glass, egg companies and aquaculture producers would be able to reduce the amount of industrial waste generated and the disposal costs, glass companies would be able to reduce raw material costs, and _CO2 emissions overall would be reduced, contributing to a recycling-oriented society through the recycling of waste. Conventionally, glass companies have endeavored to improve the melting property of glass and reduce burner fuel by reusing glass collected from the market as cullet, but the use of a biological Ca source as a Ca source for glass has not been known until now.

JP 2020-164770 A

In view of the above-mentioned current situation, an object of the present invention is to provide a method for producing glass which can reduce _CO2 emissions from a glass factory compared to conventional methods, contribute to achieving the carbon neutral target, and also enable cost reduction.

The present invention, made to solve the above problems, is characterized by the fact that when practical glass is produced from silica sand, limestone, and cullet as the main raw materials, a portion of the limestone is replaced with eggshells, which are a biological source of Ca, thereby reducing the amount of CO2 generated _during glass production .

In the present invention, eggshells can be used as a glass raw material after being fired to remove organic matter . When the biological Ca source is eggshell, this pretreatment preferably includes a separation step of the eggshell membrane . In addition, in the present invention, the biological Ca source can be used as a glass raw material while still containing organic matter, and the S content in the organic matter can be used as a colorant. The S content in the organic matter can be used as a fining agent (defoaming agent) in addition to being used as a colorant. Sodium sulfate, which contains sulfur, is generally used as a fining agent in glass.

According to the present invention, since a biological Ca source is used as a glass raw material, the amount of limestone excavated from limestone mines can be reduced, and the amount of _CO2 generated from the excavation, refining, and transportation of limestone can be reduced. Furthermore, since _CO2 in the atmosphere is fixed by plants, chickens that eat plants essentially play a role in reducing _CO2 in the atmosphere. Therefore, according to the present invention, it is possible to reduce _CO2 emissions from glass factories compared to conventional methods, and contribute to achieving the carbon neutral goal.

Furthermore, by using eggshells, which were previously disposed of as waste, as a glass raw material, egg processing companies and egg farmers can eliminate waste disposal costs, and glass companies can reduce the amount of limestone they purchase, thereby reducing raw material costs. In addition, this also has the effect of reducing the _CO2 emissions generated during the waste disposal process.

Furthermore, when organic matter such as eggshell membrane attached to the biological Ca source is not required, the organic matter can be removed by pretreatment and the source can be used as a pure Ca source. When it is desired to utilize the S and C in the organic matter in glass production, the source can be used without pretreatment.

FIG. 1 is a conceptual diagram illustrating an embodiment of the present invention. FIG. 1 is a conceptual diagram illustrating a reference embodiment of the present invention. FIG. 13 is a conceptual diagram illustrating another embodiment of the present invention. FIG. 1 is a diagram showing a cycle of the present invention. FIG. 1 illustrates a conventional cycle. FIG. 1 is a conceptual diagram illustrating a conventional technique.

Before describing the embodiments of the present invention, the prior art shown in FIGS. 5 and 6 will be described.
As shown in Fig. 6, a glass factory is equipped with a glass melting furnace 10, and the inside of the furnace is heated to a high temperature of about 1200 to 1700°C by a burner (not shown). Glass raw materials are mixed according to the purpose and fed into the furnace from a raw material hopper 11. The glass molten in the furnace is fed to a forming machine (not shown) and formed into a glass product 12. The burner combustion gas containing _CO2 passes through a heat regenerator 13 and is released into the atmosphere from a chimney 14.

The main components of practical glass used for plate glass and glass containers are SiO ₂ , CaO, Na ₂ O, Al ₂ O _3, etc., and silica sand is usually used as the Si source and limestone is usually used as the Ca source. In addition, to improve melting property, cullet made by crushing glass waste collected from the market is added to the glass raw material. Limestone is excavated from a remote limestone mine 15 using heavy machinery 16, and after a refining process, it is transported long distances to the glass factory by freight vehicles 17. Since these heavy machinery 16 and freight vehicles 17 use fossil fuels as their energy source, they release a large amount of CO ₂ into the atmosphere before the limestone reaches the glass factory. In this way, glass factories release CO ₂ into the atmosphere when calcium carbonate is vitrified both at the raw material procurement stage and at the melting stage (CaCO ₃ →CaO+CO ₂ ), which, as mentioned above, is a factor that hinders the achievement of Japan's carbon neutral goal.

In contrast, in the present invention, instead of limestone, a biological Ca source is used. A typical biological Ca source is eggshell, which can be purchased inexpensively from food companies that process eggs. Since eggshells contain eggshell membranes containing organic matter and a few percent of moisture, the eggshells are pretreated to remove the organic matter in the first embodiment shown in FIG. 1. Specifically, the eggshells are fired in a firing furnace 18 to remove the organic matter and moisture, and then classified to obtain a Ca raw material with few impurities. The firing can be performed at 550°C x 1 hour, for example. The classification can be performed to the extent that the eggshells pass through a sieve with a mesh size of 5 mm. However, these values can be changed as appropriate. In addition to firing, methods for removing the eggshell membranes can also be used, such as alkaline water, centrifugation, and methods using specific gravity differences.

Composition analysis of the fired eggshells revealed that they were CaO: 98.66%, MgO: 0.9%, _SiO2 : 0.4%, _Fe2O3 : 0.004%, and confirmed that they could be used as a CaO _source with the same low impurities as limestone. As is well known, _Fe2O3 is a harmful component that colors glass, and _limestone contains about 0.016% _Fe2O3 , but eggshells contain only 1/4 of that _amount , making them suitable as a glass raw material with few impurities. MgO and _SiO2 are _also glass components, so they do not pose _any problems.

In this way, the fired eggshell can be used as a nearly pure Ca source and can be used to replace part or all of the limestone in the glass raw materials that have been used in the past. However, eggshells from which the organic matter has not been removed, as described below, contain impurities that affect the operation of the glass melting furnace 10, and replacing all of the limestone with eggshells may result in a decrease in the appearance quality, such as coloring and bubbles. Therefore, if the eggshell replacement rate is to approach 100%, it is preferable to remove the organic matter by pretreatment.

The eggshells used as a biological Ca source in the present invention are produced by chickens that feed on plants, and plants have the function of fixing _CO2 in the atmosphere. On the other hand, in the case of limestone, _CO2 is released from the limestone during vitrification as described above, and the released _CO2 is not reabsorbed forever. If we compare the speed at which _CO2 released into the atmosphere is absorbed and fixed, the carbon cycle fixed in limestone mines is significantly slower than the carbon cycle absorbed by plants through photosynthesis. Therefore, by using eggshells produced through the food chain as a substitute for limestone, we can contribute to reducing the generation of _CO2 in the glass product raw material procurement to manufacturing process cycle. The cycle of the present invention is shown in Figure 4.

In addition to eggshells, shells such as scallops and oysters can also be used as a biological Ca source, as shown in the reference form in Figure 2. Shells have adductor muscles and other organic matter attached to them, so pretreatment is desirable . When the composition of oyster shells was analyzed after firing, the results were CaO: 96.10%, MgO: 1.01%, SiO ₂ : 2.21%, Fe ₂ O ₃ : 0.61%, and the Fe ₂ O ₃ content tended to be higher than that of eggshells. For this reason, oyster shells are not suitable as a raw material for transparent glass, but they can be used as a raw material for colored glass. In contrast, the Fe ₂ O ₃ content of scallop shells is equal to or lower than that of eggshells, so they can also be used for transparent glass. In addition, waste pearls can also be crushed and used. Pearls use shells as the nucleus, and the nacreous membrane, which is an organic substance, is very thin, so they can be treated essentially the same as shells. Shellfish also feed on marine phytoplankton, which, like terrestrial plants, fix and reduce _CO2 , so by using shells and waste pearls that are produced through the food chain as a substitute for limestone, just like eggshells, it is possible to contribute to the reduction of _CO2 emissions from the raw material procurement to manufacturing process of glass products. It also reduces the _CO2 emitted from waste disposal.

Next, the second embodiment shown in Fig. 3 will be described. In this embodiment, eggshells are used as they are as a glass raw material without being fired. Eggshells contain sulfur-containing amino acids, cystine and methionine, and if they are used as a glass raw material as they are, S components will be introduced into the glass.

Amber glass, which is used for beer bottles, tumblers, etc., contains iron sulfide as a colorant, and is made by adding S and Fe to the glass raw materials and melting them. If eggshells are used as a Ca source, S will be brought into the glass. This makes it possible to reduce the amount of S added by the amount of S brought in from the eggshells. When manufacturing colored glass that contains S in this way, it is possible to use a biological Ca source as a glass raw material while still containing organic matter, and use the S in the organic matter as a colorant.

In addition, when eggshells containing eggshell membranes are added as a raw material, the combustion of the eggshell membranes can generate additional heat to assist in melting. In addition, as fuel for melting burners has been increasingly converted from heavy oil to gas in recent years, it has become difficult to generate a luminous flame due to the nature of the fuel, and heat transfer by radiation is inevitably reduced. When eggshell membranes are added using a direct injection nozzle or powder spray and burned with a burner flame, a luminous flame can be generated, and it is expected that the radiant heat will contribute to improving the melting efficiency. In any embodiment, if the particle size of the biological Ca source is too fine, it will cause problems with conveyor transport, etc., so it is preferable to provide a classification process using a sieve, etc.

Using the raw material mix for tableware glass shown in Table 1 as a base, a melting test was conducted in which limestone was replaced with eggshell (without pretreatment). The amount of replacement was set to six levels: 1%, 5%, 10%, 30%, 50%, and 100%. A clay crucible was used, and the melting conditions were 1350°C for 1.5 hours. After melting, the material was granulated in water and dried in an electric furnace, 30 g of which were placed in a platinum bead dish, melted at 1350°C for 4 hours, and cooled slowly in an electric furnace. The material was then polished and subjected to composition analysis using fluorescent X-rays. The results are shown in Table 2. Note that the values for each component in Tables 2 and 3 are in weight percent.

As shown in Table 2, there was no significant difference in glass composition regardless of the substitution rate from 0 to 100%. There was also no difference in the occurrence of bubbles compared to when there was no substitution, and there was no change in meltability.

When limestone was 100% replaced with eggshells that had not been pretreated and no cullet was mixed into the raw material, amber coloring was observed.

(Reference example)
A melting experiment was conducted by replacing the egg shell of Example 1 with a scallop shell or an oyster shell. The replacement rate was 100% in both cases. The results are shown in Table 3.

As shown in Table 3, when limestone was replaced with scallop shells, no significant difference in glass composition was observed, and transparent glass was obtained. On the other hand, when limestone was replaced with oyster shells, the _glass contained about 12.4 times as much _Fe2O3 as when no replacement was used, and blue coloring was observed.

As described above, according to the present invention, the following effects can be obtained by using a Ca source of biological origin, which has been discarded until now, as a glass raw material.
(1) It can reduce the amount of _CO2 emissions and contribute to achieving the carbon neutral goal.
(2) Waste materials can be used to produce glass of the same quality as conventional glass.
(3) It reduces waste generation and disposal costs, and for glass companies, it reduces raw material costs.

10 Glass melting furnace 11 Raw material hopper 12 Glass product 13 Regenerator 14 Chimney 15 Limestone mine 16 Heavy machinery 17 Freight vehicle 18 Sintering furnace 19 Crusher

Claims (3)

A method for producing practical glass using silica sand, limestone, and cullet as the main raw materials, in which part of the limestone is replaced with eggshells, which are a biological calcium source, thereby reducing the amount of CO2 generated _during glass production. The method for producing glass using a Ca source of biological origin according to claim 1, characterized in that the eggshells are fired to remove organic matter and then used as a glass raw material . 2. A method for producing glass using a biologically derived Ca source according to claim 1, characterized in that eggshells containing organic matter are used as a glass raw material, and the S content in the organic matter is used as a colorant .

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