JP7489296B2 - Glass heat treatment furnace, how to use glass heat treatment furnace, waste glass heat treatment furnace - Google Patents

Description

The present invention relates to a heat treatment furnace for glass, which is used to obtain porous glass by firing a material to be treated, a method for using the heat treatment furnace for glass, and a heat treatment furnace for waste glass.

Porous glass is considered useful for various applications such as water purification material, humidity control material, volatile organic compound adsorbent, etc., taking advantage of the water permeability and filtering property derived from the porosity. Porous glass is manufactured by firing a material to be treated including silicon dioxide (SiO ₂ ), sodium oxide (Na ₂ O), calcium oxide (CaO), calcium carbonate (CaCO ₃ ), etc. As a method for manufacturing a porous gas, for example, Patent Documents 1 and 2 have been proposed.
To perform a calcination treatment on a material to be treated, high heat of about 900° C. is required because the reaction temperature of calcium carbonate (CaCO ₃ ) is high. For this reason, heat-resistant treated members are used for the calcination treatment.
Heat-resistant members usually contain chromium as a chromium oxide coating, as described in, for example, Patent Document 3. In the firing process for producing glasses such as porous glass, the chromium contained in the heat-resistant members may generate hexavalent chromium (Cr ⁶⁺ ), which has extremely high toxicity. In order to suppress the generation of hexavalent chromium, for example, Patent Document 4 proposes providing a boride-based cermet spray coating at the contact portion with the glass (material to be treated), and Patent Document 5 proposes using a powder composition for tin oxide-based monolithic refractories.

JP 2009-298644 A WO2014/132877 JP 2002-222807 A JP 2014-181347 A JP 2015-9992 A

It is believed that hexavalent chromium (Cr ⁶⁺ ) is easily produced due to the influence of three factors: the presence of oxygen, the reaction temperature and reaction time, and the presence of calcium compounds.
The firing process for producing glass requires high heat of around 900°C, and air (oxygen) is required to burn the fuel gas to obtain this heat. Furthermore, since the material to be treated contains calcium compounds such as calcium oxide (CaO) and calcium carbonate ( _CaCO3 ), this process is highly susceptible to the production of hexavalent chromium (Cr6 ⁺ ).
Furthermore, chromium element is not limited to heat-resistant treated members, but may also be contained as elemental chromium (Cr) or trivalent chromium (Cr ³⁺ ) used in paints and plating in treated materials made from shredder dust as a starting material, as in Patent Document 1. In this case, hexavalent chromium (Cr ⁶⁺ ) is generated from the chromium element in the treated material during the firing treatment.
In other words, since the firing treatment of glass is highly susceptible to the production of hexavalent chromium (Cr ⁶⁺ ), it is required to suppress the production of hexavalent chromium (Cr ⁶⁺ ) in all aspects, such as the materials of the components used in the treatment, the configuration of the equipment, and the method of use.

The present invention seeks to solve the problems associated with the conventional technology, and aims to provide a heat treatment furnace for glass, a method for using a heat treatment furnace for glass, and a heat treatment furnace for waste glass that can suppress the generation of hexavalent chromium.

In order to solve the above problems, the present invention provides a heat treatment furnace for glass, which produces porous glass by contacting a material to be treated containing at least calcium oxide and calcium carbonate with a gas filling the furnace body, the furnace body being kept at a predetermined furnace temperature, the heat treatment furnace comprising:
The furnace body;
a conveying device disposed in the furnace for conveying the material to be treated;
a gas supply system connected to the furnace body for filling the furnace with the gas;
A temperature adjusting means is provided in the furnace body to adjust the temperature inside the furnace,
The gas is a reducing gas, and the atmosphere inside the furnace body is deoxidized.
The invention described in claim 2 is the invention described in claim 1, wherein the gas supply system includes at least an air supply system that supplies the air, a fuel gas supply system that supplies the fuel gas, a gas generator to which the air supply system and the fuel gas supply system are connected, and a dew point adjustment device connected to the gas generator,
The temperature adjusting means includes a heat exchange type heater device disposed in the furnace.
The invention described in claim 3 is the invention described in claim 1, wherein the gas supply system includes at least an air supply system that supplies the air and a fuel gas supply system that supplies the fuel gas,
The temperature control means is connected to the air supply system and the fuel gas supply system, and includes a combustion-type burner device attached to the furnace body so as to send the reducing gas, which is a combustion gas of the air and the fuel gas, into the furnace, and a cooling device attached to the furnace body for cooling the inside of the furnace.
The invention described in claim 4 is the invention described in claim 3, wherein the cooling device includes a heat exchange type cooling tube disposed in the furnace.
The invention described in claim 5 is the invention described in claim 3, wherein the cooling device includes a circulation system connected to the furnace body for circulating the gas between the inside and outside of the furnace, and a cooler device connected to the circulation system.
The invention described in claim 6 is characterized in that, in the invention described in any one of claims 3 to 5, the temperature adjustment means further includes a heat exchange type heater device arranged in the furnace.
The invention described in claim 7 is the invention described in any one of claims 1 to 6, wherein the conveying device includes a belt conveyor and an interposition member interposed between the belt conveyor and the material to be treated,
The belt conveyor is made of a heat-resistant material containing chromium,
The present invention relates to a method for manufacturing a steel sheet comprising the steps of: forming a steel sheet using a non-ferrous material that does not contain chromium;
The invention described in claim 8 is characterized in that in the invention described in claim 7, the intermediate member is a heat-resistant sheet made of a silica-based material.
The invention described in claim 9 is characterized in that, in the invention described in claim 7, the intervening member is a heat-resistant container having at least one side open to the outside and inside which the material to be treated is housed.
The invention as set forth in claim 10 is characterized in that in the invention as set forth in claim 7, the intermediate member is a heat-resistant plate having a plate shape and on a surface of which the material to be treated is placed.
The invention described in claim 11 is the invention described in any one of claims 1 to 10, wherein the treated material is a waste glass material in which a foaming agent containing calcium carbonate is added to a powder of waste glass containing calcium oxide.

The invention described in claim 12 is a method for using a heat treatment furnace for glass, in which a gas filling the furnace body is brought into contact with a material to be treated containing at least calcium oxide and calcium carbonate in a furnace body having a predetermined furnace temperature, to obtain porous glass, comprising:
The glass heat treatment furnace comprises:
The furnace body;
a conveying device disposed in the furnace for conveying the material to be treated; a gas supply system connected to the furnace body for filling the furnace with the gas;
A temperature adjusting means is provided in the furnace body to adjust the temperature inside the furnace,
The holding time for which the workpiece is held in the furnace by the conveying device is 5 minutes to 30 minutes;
The temperature inside the furnace is set to 800° C. or more and 950° C. or less by a temperature control means,
The gas is a reducing gas obtained by burning air and a fuel gas at an air-fuel ratio of less than 1;
The furnace body has an atmosphere devoid of oxygen.
The invention described in claim 13 is the invention described in claim 12, wherein the gas supply system includes at least an air supply system that supplies the air, a fuel gas supply system that supplies the fuel gas, a gas generator to which the air supply system and the fuel gas supply system are connected, and a dew point adjustment device connected to the gas generator,
the temperature adjustment means includes a heat exchange type heater device disposed in the furnace,
the gas generator combusts the air supplied from the air supply system and the fuel gas supplied from the fuel gas supply system at an air-fuel ratio of less than 1 to generate the reducing gas;
The dew point of the reducing gas is adjusted to 10° C. to 60° C. by the dew point adjustment device,
The reducing gas is heated in the furnace by the heater device, and the temperature in the furnace is set to 800°C to 950°C.
The invention described in claim 14 is the invention described in claim 12, wherein the gas supply system includes at least an air supply system that supplies the air and a fuel gas supply system that supplies the fuel gas,
The temperature adjustment means is connected to the air supply system and the fuel gas supply system, and is provided with a combustion burner device attached to the furnace body so as to combust the air and the fuel gas and send the resulting combustion gas, that is, the reducing gas, into the furnace, and a cooling device attached to the furnace body for cooling the inside of the furnace;
The combustion of the air and the fuel gas in the burner device is constantly maintained, so that the reducing gas is constantly fed into the furnace,
The gist of the present invention is that the temperature inside the furnace is set to 800°C to 950°C by heating the inside of the furnace with the burner device having an adjusted amount of fuel gas supplied thereto, or by heating the inside of the furnace with the burner device having an adjusted amount of fuel gas supplied thereto and cooling the inside of the furnace with the cooling device.
The invention described in claim 15 is the invention described in any one of claims 12 to 14, wherein the furnace body is divided into a plurality of regions in the transport direction of the material to be treated,
Among the plurality of regions, a region on the most upstream side in the transport direction is a pre-heating region, and a region on the downstream side of the pre-heating region in the transport direction is a heating region,
The temperature inside the furnace in the heating region is set to 800° C. or more and 950° C. or less,
The furnace temperature in the pre-heating region is set to a temperature that is 50° C. to 150° C. lower than the furnace temperature in the heating region.
The invention described in claim 16 is the invention described in claim 14 or 15, wherein the furnace body is divided into a plurality of regions in the transport direction of the material to be treated, and further includes a heat exchange type heater device disposed in the furnace as the temperature adjustment means,
The heat treatment in which the material to be treated is brought into contact with the gas is carried out in two stages,
In the first stage of the two stages, the heater device is used as the temperature adjustment means,
The latter stage of the two stages is characterized in that the burner device and the cooling device are used as the temperature adjustment means.
The invention described in claim 17 is characterized in that, in the invention described in any one of claims 12 to 16, the treated material is a waste glass material in which a foaming agent containing calcium carbonate has been added to a powder of waste glass containing calcium oxide.

The invention described in claim 18 is a method for using a heat treatment furnace for glass, in which a gas filling the furnace body is brought into contact with a material to be treated containing at least calcium oxide and calcium carbonate in a furnace body having a predetermined furnace temperature, to obtain porous glass, comprising:
The glass heat treatment furnace comprises:
The furnace body;
a conveying device disposed in the furnace for conveying the material to be treated; and a gas supply system connected to the furnace body for supplying the gas into the furnace.
A temperature adjusting means is provided in the furnace body to adjust the temperature inside the furnace,
The holding time for which the workpiece is held in the furnace by the conveying device is 5 minutes to 30 minutes;
The temperature inside the furnace is set to 800° C. or more and 950° C. or less by a temperature control means,
The gas is an oxidizing gas obtained by burning air and a fuel gas at an air-fuel ratio of 1 or more,
The conveying device includes a heat-resistant plate made of a non-ferrous material not containing chromium, and a conveying roll made of a ceramic material,
The heat-resistant plate is transported through the furnace by the transport rolls with the material to be treated placed on the surface of the heat-resistant plate.
The invention according to claim 19 is the invention according to claim 18, wherein the gas supply system includes at least an air supply system that supplies the air and a fuel gas supply system that supplies the fuel gas,
the temperature adjustment means is connected to the air supply system and the fuel gas supply system, and includes a combustion burner device attached to the furnace body so as to combust the air and the fuel gas and send the resulting combustion gas, that is, the oxidizing gas, into the furnace, and a heat exchange cooling tube disposed in the furnace;
The combustion of the air and the fuel gas in the burner device is constantly maintained, so that the oxidizing gas is constantly fed into the furnace,
The gist of the present invention is that the temperature inside the furnace is set to 800°C to 950°C by heating the inside of the furnace with the burner device having an adjusted amount of fuel gas supplied, or by heating the inside of the furnace with the burner device having an adjusted amount of fuel gas supplied and cooling the inside of the furnace with the cooling tube.
The invention described in claim 20 is the invention described in claim 18, wherein the gas supply system includes at least an air supply system that supplies the air and a fuel gas supply system that supplies the fuel gas,
The temperature adjustment means is equipped with a combustion burner device attached to the furnace body, connected to the air supply system and the fuel gas supply system, and configured to combust the air and the fuel gas and send the resulting combustion gas, that is, the oxidizing gas, into the furnace, a circulation system connected to the furnace body and circulating the oxidizing gas between the inside and outside of the furnace, and a cooler device connected to the circulation system;
The combustion of the air and the fuel gas in the burner device is constantly maintained, so that the oxidizing gas is constantly fed into the furnace,
The gist of the present invention is that the temperature inside the furnace is set to 800°C to 950°C by heating the inside of the furnace using the burner device with the supply amount of the fuel gas adjusted, or by heating the inside of the furnace using the burner device with the supply amount of the fuel gas adjusted and cooling the oxidizing gas using the cooler device in the circulation system.
The invention described in claim 21 is characterized in that, in the invention described in any one of claims 18 to 20, the treated material is a waste glass material in which a foaming agent containing calcium carbonate has been added to a powder of waste glass containing calcium oxide.

According to the invention of claim 22, there is provided a heat treatment furnace for waste glass, which produces porous glass by contacting a gas filling the furnace with a waste glass material in a furnace body having a predetermined furnace temperature, comprising:
The furnace body;
a conveying device disposed in the furnace for conveying the waste glass material; a gas supply system connected to the furnace body for filling the furnace with the gas;
A temperature adjusting means is provided in the furnace body to adjust the temperature inside the furnace,
The waste glass material is a powder of waste glass containing calcium oxide to which a foaming agent containing calcium carbonate is added,
the gas is a reducing gas,
The furnace body has an atmosphere deoxidized.

The present invention provides a heat treatment furnace for glass that can suppress the generation of hexavalent chromium, a method for using the heat treatment furnace for glass, and a heat treatment furnace for waste glass.

FIG. 1 is a schematic explanatory diagram showing a heat treatment furnace for glass according to an embodiment. FIG. 1 is a schematic explanatory diagram showing a glass heat treatment furnace according to a first embodiment. FIG. 5 is a schematic explanatory diagram showing a glass heat treatment furnace according to a second embodiment. FIG. 11 is a schematic explanatory diagram showing a glass heat treatment furnace according to a third embodiment.

The matters set forth herein are illustrative and are intended to provide an illustrative description of the embodiments of the present invention, with the objective of providing what is believed to be the most effective and easily understood explanation of the principles and conceptual features of the present invention. In this regard, it is not intended to provide structural details of the present invention beyond the extent necessary for a fundamental understanding of the present invention, and the description, taken together with the drawings, will make clear to those skilled in the art how some forms of the present invention may be embodied in practice.

[1] Glass heat treatment furnace The glass heat treatment furnace 10 of the present invention is a glass heat treatment furnace in which a gas filling the furnace body 11, which is kept at a predetermined furnace temperature, is brought into contact with a material to be treated 20 containing at least calcium oxide and calcium carbonate, to obtain porous glass 30 (see FIG. 1 ).
The glass heat treatment furnace 10 comprises a furnace body 11, a transport device 12 arranged within the furnace for transporting the material to be treated 20, a gas supply system 13 connected to the furnace body 11 for filling the furnace with gas, and a temperature adjustment means 14 provided in the furnace body 11 for adjusting the temperature within the furnace.
In the glass heat treatment furnace 10, the gas filling the furnace is a reducing gas, and the atmosphere inside the furnace body 11 is kept in a deoxidized state.

(1) Furnace Body The furnace body 11 has a space provided inside (hereinafter, simply referred to as "inside the furnace"), and is used for carrying out a firing process in which a material to be treated 20 is fired in the furnace to obtain porous glass 30 (see FIG. 1).
The furnace body 11 is not particularly limited in configuration, such as size and furnace volume, as long as the material to be treated 20 can be fired within the furnace.
In order to withstand the temperature inside the furnace during the firing process, a heat-resistant material can be used for the wall material of the furnace body 11. There is no particular restriction on whether the heat-resistant material contains chromium.

The chromium element is contained in various forms, such as simple chromium, chromium alloys, chromium oxides, chromium compounds, etc., in the compositions and components of heat-resistant treatment materials, heat-resistant materials, non-ferrous materials, ceramic materials, etc.
In the present application, it does not matter whether the chromium element is contained in the composition or component in any form, such as simple chromium, a chromium alloy, a chromium oxide, or a chromium compound.
In other words, in the present application, anything that contains chromium (Cr) as an element in a composition or component is considered to include chromium, regardless of whether it is in the form of simple chromium, a chromium alloy, a chromium oxide, a chromium compound, or the like.
In the present application, "not containing chromium element" means that chromium element (Cr) is not present as an element in the composition or components, regardless of whether it is in the form of simple chromium, a chromium alloy, a chromium oxide, a chromium compound, or the like.

The furnace body 11 is not particularly limited as to whether it is a batch type for treating a small lot of the material 20 to be treated, or a continuous type for treating a large amount of the material 20 to be treated. By using the furnace body 11 as a continuous type, the production amount of the porous glass 30 can be improved.
The furnace body 11 has an inlet 111 for charging the material 20 to be treated into the furnace, and an outlet 112 for extracting the material 20 from the furnace. The furnace body 11 can also be provided with doors (not shown) for closing or opening the inlet 111 and the outlet 112.
As long as the furnace atmosphere can be kept deoxidized, the inlet 111 and the outlet 112 of the furnace body 11 may be closed or open during the firing process. Usually, the inlet 111 and the outlet 112 of the furnace body 11 are closed until the furnace atmosphere is stabilized, and are kept open after the furnace atmosphere is stabilized. In particular, when the furnace body 11 is of a continuous type, the inlet 111 and the outlet 112 are kept open, so that the number of materials 20 to be treated per unit time can be improved.

The furnace body 11 may be configured such that the interior of the furnace is divided into a plurality of regions in the transport direction of the material 20. This division of the interior of the furnace may be realized by providing a partition wall 113 within the furnace body 11.
When the inside of the furnace is divided into a plurality of regions, the furnace body 11 may, for example, set the most upstream region in the conveying direction as a pre-heating region 115, and set the downstream region in the conveying direction from the pre-heating region 115 as a heating region 116. Furthermore, the furnace body 11 may set the downstream region of the heating region 116 as a region for slow cooling or cooling.
That is, the furnace body 11 has an interior divided into a plurality of regions, so that the heating or cooling of the workpiece 20 during the firing process can be carried out efficiently in a stepwise manner.

Partition walls 113 that divide the interior of the furnace body 11 are provided with communication ports 114 that connect the multiple regions. The material 20 to be treated is transported between the regions through the communication ports 114.
There is no particular limitation on whether the communication opening 114 of the partition wall 113 is closed or opened by a door or the like, but it is preferable to leave it open from the viewpoint of maintaining a constant atmosphere inside the furnace throughout the entire furnace body 11.
That is, by leaving the communication opening 114 of the partition wall 113 open, the gas spreads uniformly throughout the furnace, so that the atmosphere inside the furnace can be kept constant.

(2) Conveying Device The conveying device 12 is disposed within the furnace body 11 and conveys the material 20 to be treated.
The transport device 12 is not particularly limited in terms of its configuration, etc., as long as it is capable of transporting the workpiece 20 .
Specific examples of the conveying device 12 include a belt conveyor and a roller conveyor.

In the transport device 12, the belt conveyor 121 transports the material to be treated 20 placed on the surface of a driven transport belt (see Figs. 2, 3 and 4).
From the viewpoint of heat resistance, a mesh belt made of a heat-resistant material is usually used as the conveyor belt. This heat-resistant material may or may not contain chromium.
The material to be treated 20 can be placed directly on the surface of the conveyor belt, but an interposing member 122 can be interposed between the material to be treated 20 and the conveyor belt.
Since the material to be treated 20 is a powder, it is preferable to use an intermediate member 122 to prevent the material to be treated 20 from spilling off the conveying belt, particularly when a mesh belt is used as the conveying belt.

That is, the conveying device 12 includes a belt conveyor 121 and an intervening member 122 interposed between the belt conveyor 121 and the workpiece 20, and the belt conveyor 121 can be configured to use a heat-resistant material containing chromium elements.
In this configuration, it is preferable that a non-ferrous material that does not contain chromium is used for the intervening member 122 that comes into direct contact with the workpiece 20. In other words, it is preferable that the non-ferrous material used for the intervening member 122 does not contain elemental chromium, chromium alloys, chromium oxides, chromium compounds, etc. By using a non-ferrous material that does not contain chromium for the intervening member 122, it is possible to prevent the generation of hexavalent chromium due to contact with the workpiece 20.
Examples of the interposing member 122 using a non-ferrous material include a heat-resistant sheet made of a silica-based material, and a heat-resistant container or plate made of a ceramic material.
The heat-resistant container has a shape such as a dish or box, at least one side of which is open to the outside, and is configured so that the material to be treated 20 is contained therein.
The heat-resistant plate is in the form of a plate, and is configured so that the material to be treated 20 can be placed on its surface.

In the transport device 12, the roller conveyor transports the material 20 placed on a plurality of rotating transport rolls 123 (see FIG. 1).
From the viewpoint of heat resistance, a heat-resistant material is usually used for the transport roll 123. When the inside of the furnace body 11 is filled with a reducing gas and the inside atmosphere is kept in a deoxidized state, the heat-resistant material may or may not contain chromium, but it is preferable to use a ceramic material that does not contain chromium.

When the conveying device 12 is a roller conveyor, the material to be treated 20 is a powder and therefore falls out between the conveying rolls 123. For this reason, in the case of a roller conveyor, a plate-shaped heat-resistant plate, which is the intermediate member 122, is disposed on the conveying rolls 123, and the material to be treated 20 is placed on this heat-resistant plate and conveyed.
As described above, the heat-resistant plate that is the intermediate member 122 is made of a non-ferrous material that does not contain chromium, is formed into a plate shape, and is configured so that the material to be treated 20 can be placed on its surface.
The non-ferrous material is a metallic material other than iron and an alloy mainly composed of iron. Specific examples of non-ferrous materials that do not contain chromium include mullite, which is a compound of aluminum oxide and silicon dioxide, and silicon carbide ceramics containing metal oxides such as ScSiC.
That is, the conveying device 12 can be configured to include a plate-shaped heat-resistant plate (intervening member 122) made of a non-ferrous material that does not contain chromium, and a conveying roll 123 made of a ceramic material.

(3) Gas Supply System The gas supply system 13 is connected to the furnace body 11 and fills the interior of the furnace body 11 with gas.
The gas supply system 13 is not particularly limited in terms of its configuration, etc., as long as it can supply gas into the furnace body 11 .
The gas supply system 13 can be configured to generate the gas to fill the interior of the furnace body 11 outside the furnace body 11 (hereinafter, abbreviated as "outside the furnace"), or can be configured to generate the gas inside the furnace body 11.

The gas supply system 13 includes at least an air supply system 131 that supplies air, and a fuel gas supply system 132 that supplies fuel gas (see FIGS. 2, 3, and 4).
The gas supply system 13, which is configured to generate gas outside the furnace, can be configured to include at least an air supply system 131, a fuel gas supply system 132, a gas generator 133 to which the air supply system 131 and the fuel gas supply system 132 are connected, and a dew point adjustment device 134 connected to the gas generator 133 (see Figure 2).
The gas generator 133 reacts air supplied from the air supply system 131 with fuel gas supplied from the fuel gas supply system 132 to generate gas to be supplied into the furnace body 11 .
The dew point adjusting device 134 adjusts the humidity (dryness) of the gas generated by the gas generator 133 by adjusting the dew point temperature (the temperature at which dew, i.e., condensation occurs).

A gas supply line 135 is connected between the dew point adjusting device 134 and the furnace body 11 (see FIG. 2). The gas whose dew point temperature has been adjusted by the dew point adjusting device 134 is supplied to the inside of the furnace body 11 through the gas supply line 135.
In addition, the air supply system 131, the fuel gas supply system 132, and the gas supply path 135 can be connected, as necessary, to valves for adjusting the supply amount, ducts or fans for taking in gases such as air, and tanks for temporarily storing gases.

That is, the gas supply system 13, which is configured to generate gas outside the furnace, is configured to supply gas generated by a gas generator 133 and whose dew point temperature has been adjusted by a dew point adjustment device 134 into the furnace body 11.
The gas supply system 13 having this configuration can supply an appropriate amount of gas generated outside the furnace to the inside of the furnace body 11 as needed, and can keep the amount of gas inside the furnace constant.

The gas supply system 13, which is configured to generate gas in the furnace, can be configured to include at least an air supply system 131, a fuel gas supply system 132, and a combustion-type burner device 142 to which the air supply system 131 and the fuel gas supply system 132 are connected (see Figure 3).
The burner device 142 burns the air supplied from the air supply system 131 and the fuel gas supplied from the fuel gas supply system 132. The burner device 142 also constitutes the temperature adjustment means 14.
In addition, the air supply system 131 and the fuel gas supply system 132 can be connected to valves for adjusting the supply amount, ducts and fans for taking in gas such as air, tanks for temporarily storing gas, etc., as necessary.

That is, the gas supply system 13, which is configured to generate gas within the furnace, burns air and fuel gas using the burner device 142, and sends the combustion gas generated during combustion into the furnace body 11, thereby filling the furnace with gas (combustion gas).
The gas supply system 13 having this configuration can simplify the configuration of the gas supply system 13 and reduce the costs associated with equipment and maintenance.

In the gas supply system 13, the gas that is supplied to the inside of the furnace body 11 and fills the inside of the furnace contains carbon monoxide (CO) and hydrogen gas (H ₂ ), and has the property of reacting with free oxygen (O ₂ ) to remove the oxygen (O ₂ ).
In this application, a gas that has the property of combining, adding, bonding, etc., with oxygen ( _O2 ) is referred to as an "oxidizing gas." In contrast to this oxidizing gas, a gas that has the property of reacting with oxygen ( _O2 ) and removing the oxygen ( _O2 ) is referred to as a "reducing gas."
The inside of the furnace body 11 is filled with a reducing gas, and oxygen (O ₂ ) is taken away by this reducing gas, making the inside of the furnace deoxidized.

The reducing gas can be obtained by combusting a fuel gas with air at an air-fuel ratio of less than 1.
The fuel gas is not particularly limited as long as it can generate a reducing gas, and typically, a hydrocarbon gas such as propane gas is used as the fuel gas.
In other words, the reducing gas of the present application is a gas that contains carbon monoxide (CO) and hydrogen gas ( _H2 ) and has the property of reacting with oxygen ( _O2 ) to remove the oxygen ( _O2 ), and is a gas obtained by burning air and fuel gas at an air-fuel ratio of less than 1.

In addition, the gas supplied to the furnace body 11 in the gas supply system 13 and filling the inside of the furnace may be an oxidizing gas.
The oxidizing gas can be obtained by burning a fuel gas (hydrocarbon gas) with air at an air-fuel ratio of 1 or more.
When an oxidizing gas is used, the conveying device 12 is preferably configured to include a plate-shaped heat-resistant plate (insertion member 122) made of a non-ferrous material that does not contain chromium, and a conveying roll 123 made of a ceramic material that does not contain chromium, in order to suppress the generation of hexavalent chromium.

(4) Temperature Adjustment Means The temperature adjustment means 14 is provided in the furnace body 11 and adjusts the temperature inside the furnace.
The temperature adjustment means 14 is not particularly limited in terms of its configuration, etc., so long as it can obtain the high temperature required for the firing process and can adjust the temperature inside the furnace, particularly, lower the temperature when the temperature inside the furnace rises excessively.
The temperature adjustment means 14 may be, for example, a heat exchange type heater device 141, or a combustion type burner device 142 and a cooling device 143.

The heater device 141 heats the gas filling the inside of the furnace body 11 by heat exchange, thereby adjusting the temperature inside the furnace (see FIG. 2).
Specific examples of the heater device 141 include a radiant tube burner and an electric heater.

The heater device 141 can adjust the temperature inside the furnace by turning it on and off using a controller.
In other words, the heater device 141 can heat the gas by turning it ON to increase the temperature inside the furnace, and when the temperature inside the furnace becomes excessive, the heater device 141 can stop heating the gas by turning it OFF, thereby allowing the temperature inside the furnace to be lowered without the need for a cooling device or the like.
Furthermore, the heat exchange type heater device 141 can heat the material to be treated 20, which is a powder, without scattering it.

The burner device 142 burns the fuel gas and air supplied thereto, and ejects high-temperature combustion gas into the furnace body 11 (see FIGS. 3 and 4).
That is, the burner device 142 ejects high-temperature combustion gas into the furnace body 11, thereby increasing the temperature inside the furnace.
In addition, the burner device 142 can form a gas supply system 13 since it can fill the inside of the furnace with the combustion gas ejected into the furnace.

The burner device 142 can lower the temperature inside the furnace by stopping the combustion of the fuel gas and air when the temperature inside the furnace becomes excessively high. However, when a gas supply system 13 is configured, stopping the combustion also stops the supply of gas.
For this reason, when the burner device 142 is used, it is preferable to use the cooling device 143 in combination to lower the temperature inside the furnace when the temperature inside the furnace becomes excessively high.
Specific examples of the cooling device 143 include a heat exchange type cooling tube 144 (see FIG. 3), a circulation system 145, and a cooler device 146 (see FIG. 4).

The cooling tube 144 is disposed inside the furnace body 11 and serves to cool the gas filling the furnace by heat exchange within the furnace, thereby lowering the temperature within the furnace (see FIG. 3).
That is, the cooling tube 144 is configured to cool the gas inside the furnace.
The cooling tube 144 can reduce the size of the furnace and simplify the structure, and can cool the material 20 to be treated, which is a powder, without scattering it.

The circulation system 145 is connected to the outside of the furnace body 11 and circulates the gas between the inside and outside of the furnace. The cooler device 146 is connected to the circulation system 145 and cools the gas circulating through the circulation system 145 (see FIG. 4).
That is, the circulation system 145 and the cooler device 146 are configured to temporarily take out the gas from inside the furnace to outside the furnace and to cool the taken out gas outside the furnace.
The circulation system 145 and the cooler device 146 can cool a large amount of gas at once, thereby improving the cooling capacity.

Furthermore, since the burner device 142 ejects combustion gas into the furnace, there is a risk that the material 20 to be treated, which is a powder, will be scattered if used in the early stages of heating in the firing process.
For this reason, when the burner device 142 is used, it is preferable that the temperature adjustment means 14 further includes a heat exchange type heater device 141 disposed in the furnace.
That is, in the initial stage of heating in the firing process, it is preferable to heat the material to be treated 20 by the heater device 141 to melt the surface of the material to be treated 20 to an extent that scattering can be suppressed, and then heat the material to be treated 20 by the burner device 142 to melt the entire material to be treated 20.

The temperature adjustment means 14 can have a configuration corresponding to the configuration of the gas supply system 13 .
That is, the temperature adjustment means 14 can be configured in a manner appropriate for the case where the gas supply system 13 is configured to generate gas outside the furnace (see FIG. 2) or the case where the gas supply system 13 is configured to generate gas inside the furnace (see FIGS. 3 and 4).

When the gas supply system 13 is configured to generate gas outside the furnace, the temperature adjustment means 14 is preferably configured to include a heat exchange type heater device 141 disposed inside the furnace (see FIG. 2).
In other words, when the gas supply system 13 is configured to generate gas outside the furnace, the gas supplied from outside the furnace body 11 to the inside of the furnace may not satisfy the furnace temperature required for the firing process, so a heat exchange type heater device 141 is disposed in the furnace to raise the furnace temperature to a temperature sufficient for the firing process.

When the gas supply system 13 is configured to generate gas within the furnace, it is preferable that the temperature adjustment means 14 is configured to include a burner device 142 and a cooling device 143 attached to the furnace body 11 (see Figures 3 and 4).
In other words, when the gas supply system 13 is configured to generate gas within the furnace, gas can be supplied into the furnace body 11 by using the burner device 142 to eject combustion gas into the furnace.
Furthermore, when the temperature inside the furnace becomes excessively high, a cooling device 143 is used to lower the temperature inside the furnace without stopping the supply of gas by the burner device 142 .

(5) Material to be Treated and Porous Glass The material to be treated 20 is intended to be fired at high temperatures to obtain the porous glass 30.
The material to be treated 20 is usually used in a powder state. There are no particular limitations on the particle size or shape of the powder.
The porous glass 30 is obtained by firing the material to be treated 20, and is porous with many fine pores. Taking advantage of the water permeability and filtering properties derived from the porosity, the porous glass 30 can be used for various purposes such as a water purification material, a humidity control material, and an adsorbent for volatile organic compounds.

The composition of the material to be treated 20 is not particularly limited as long as it contains at least calcium oxide (CaO) and calcium carbonate (CaCO ₃ ).
Calcium carbonate (CaCO ₃ ) mainly functions as a foaming agent. Calcium carbonate (CaCO ₃ ) is thermally decomposed to generate calcium oxide (CaO) and carbon dioxide (CO ₂ ). By using this carbon dioxide (CO ₂ ) as a foaming gas, the porous glass 30 is made finely porous.
Calcium oxide (CaO) improves the water resistance and durability of the porous glass 30. The origin of this calcium oxide (CaO) is not particularly limited, and it may be calcium oxide produced by thermal decomposition of calcium carbonate (CaCO ₃ ), or calcium oxide that has been added in advance to the material to be treated 20 as lime, calcia, or the like.

The material to be treated 20 contains silicon dioxide (SiO ₂ ) as a main component in order to create the main structure (mesh structure) of the porous glass 30. Since silicon dioxide (SiO ₂ ) has a high melting point, the material to be treated 20 may contain sodium carbonate (Na ₂ CO ₃ ), sodium oxide (Na ₂ O), potassium oxide (K ₂ O), or the like in order to lower the melting point and make it easier to perform the firing treatment.

The reaction formulas of calcium carbonate (CaCO ₃ ) in the material to be treated 20 during the firing treatment are (1) to (3) below.
(1) _CaCO3 → CaO + _CO2
(2) _CaCO3 + _H2O → Ca(OH) ₂ + _CO2
(3) Ca(OH) ₂ → CaO + _H2O
The above formulas (1) to (3) are equilibrium reactions, and depending on the reaction conditions (furnace atmosphere), a reverse reaction may occur.

As shown in the above formula (1), calcium carbonate (CaCO ₃ ) generates calcium oxide (CaO) and carbon dioxide (CO ₂ ) by thermal decomposition.
Furthermore, as shown in the above formula (2), calcium carbonate (CaCO ₃ ) reacts with moisture (H ₂ O) to produce calcium hydroxide (Ca(OH) ₂ ).
As shown in the above formula (3), calcium hydroxide (Ca(OH) ₂ ) generates calcium oxide (CaO) and water (H ₂ O) by thermal decomposition.
That is, if the atmosphere inside the furnace contains a lot of moisture (H ₂ O), the reaction of calcium carbonate (CaCO ₃ ) proceeds, and calcium oxide (CaO) and carbon dioxide (CO ₂ ) are more likely to be produced.

In the firing treatment of the workpiece 20, if trivalent chromium (Cr3 ⁺ ) is taken as an example of a chromium element, calcium oxide (CaO) undergoes, for example, the reaction shown in (4) below in the presence of oxygen, converting the trivalent chromium (Cr3 ⁺ ) to hexavalent chromium (Cr6 ⁺ ).
(4) _{2Cr2O3 +} 4CaO + _3O2 → _4CaCrO4
In the above formula (4), Cr ₂ O ₃ is an oxide of trivalent chromium (Cr ³⁺ ), and CaCrO ₄ is an oxide of hexavalent chromium (Cr ⁶⁺ ).
Moreover, the reaction of formula (4) above proceeds more easily as the reaction temperature (temperature inside the furnace) increases or as the reaction time (the retention time of the material to be treated in the furnace) increases.

That is, hexavalent chromium (Cr ⁶⁺ ) is produced from chromium element due to the influence of the following three factors: <1> to <3>.
<1> The presence of oxygen ( _O2 ).
<2> The presence of calcium compounds.
<3> Reaction temperature (temperature inside the furnace) and reaction time (retention time of the material 20 to be treated inside the furnace).

In the glass heat treatment furnace 10, the gas filling the interior of the furnace body 11 is a reducing gas, so that the atmosphere within the furnace body 11 is deoxidized.
That is, the reducing gas removes oxygen (O ₂ ) from the inside of the furnace body 11 to make the inside of the furnace deoxidized. In this deoxidized state, the above formula (4) does not progress.
Therefore, in the glass heat treatment furnace 10, even if calcium oxide (CaO) in the material to be treated 20 comes into contact with the chromium element (e.g., trivalent chromium (Cr3 ⁺ )) in the heat-resistant treatment material, hexavalent chromium (Cr6 ⁺ ) is not generated, and the generation of hexavalent chromium can be prevented.

Furthermore, carbon monoxide (CO) and hydrogen gas (H ₂ ) in the reducing gas react with oxygen (O ₂ ) to produce carbon dioxide (CO ₂ ) and water (H ₂ O).
Carbon dioxide (CO ₂ ) and water (H ₂ O) promote the above-mentioned reactions (1) to (3) relating to calcium carbonate (CaCO ₃ ).
Therefore, the glass heat treatment furnace 10 can suitably sinter the material 20 to produce the porous glass 30 while preventing the generation of hexavalent chromium (Cr ⁶⁺ ).

[2] Method of using a glass heat treatment furnace (1)
The method of using the heat treatment furnace for glass 10 of the present invention is a method of using the heat treatment furnace for glass 10 in which a gas filling the furnace body 11, which has been set to a predetermined furnace temperature, is brought into contact with a material to be treated 20 containing at least calcium oxide and calcium carbonate, to obtain porous glass 30.
The glass heat treatment furnace 10 comprises a furnace body 11, a transport device 12 arranged within the furnace for transporting the material to be treated 20, a gas supply system 13 connected to the furnace body 11 for filling the furnace with gas, and a temperature adjustment means 14 provided in the furnace body 11 for adjusting the temperature within the furnace.
In a method of using the glass heat treatment furnace 10, the material to be treated 20 is held in the furnace by the conveying device 12 for a retention time of 5 to 30 minutes, and the temperature inside the furnace is set to 800° C. or more and 950° C. or less by the temperature adjustment means 14.
The gas filling the interior of the furnace body 11 is a reducing gas obtained by burning air and fuel gas at an air-fuel ratio of less than 1, and the atmosphere inside the furnace body 11 is deoxidized.

A glass heat treatment furnace 10 used in this method includes a furnace body 11, a transport device 12, a gas supply system 13, and a temperature adjustment means 14.
The configuration of the glass heat treatment furnace 10, that is, the furnace body 11, the conveying device 12, the gas supply system 13, and the temperature adjustment means 14, can be shared with the description of “[1] Glass heat treatment furnace” above.
Therefore, in the following description, unless otherwise specified, repeated explanations, such as the configuration of the glass heat treatment furnace 10, will be omitted.

(1) Holding Time The holding time is the time during which the material 20 is held in the furnace body 11 by the transport device 12.
Furthermore, the material 20 to be treated is brought into contact with the gas filling the furnace inside the furnace body 11, which is kept at a predetermined furnace temperature, and while being melted, the chemical reaction of calcium carbonate (CaCO ₃ ) and the like described above proceeds.
Therefore, the holding time can also be said to be the heating time or reaction time of the material 20 to be treated.

The porous glass 30 is formed when carbon dioxide ( _CO2 ) generated from calcium carbonate (CaCO3) in the material ₂₀ to be treated, which is melted at high temperature, becomes a foaming gas and forms bubbles, which then turn into numerous fine holes, making the glass porous.
If the retention time, i.e., the reaction time, is excessively short, a sufficient amount of carbon dioxide (CO ₂ ) is not generated, which may cause variations in foaming and result in non-uniform pores in the porous glass 30 .
If the holding time, i.e., the heating time, is excessively long, the molten material 20 to be treated will become excessively soft and will undergo excessive foaming, producing an excessive amount of carbon dioxide ( _CO2 ). As a result, the foaming gas, carbon dioxide ( _CO2 ), will not remain in the material 20 to be treated but will escape, causing the porous glass 30 to shrink.
Therefore, the retention time is set to be short enough to prevent uneven foaming, and long enough to prevent excessive foaming.

In addition, hexavalent chromium (Cr ⁶⁺ ) is produced from chromium element due to the influence of the three factors <1> to <3> mentioned above, but the holding time of the workpiece 20 in the furnace is related to factor <3> of the three factors.
That is, hexavalent chromium (Cr ⁶⁺ ) is more likely to be produced from chromium element depending on the reaction time. This reaction time is the time required for the firing treatment, that is, the retention time of the workpiece 20 in the furnace.
Therefore, the holding time is set to be short enough to prevent hexavalent chromium (Cr ⁶⁺ ) from being produced from elemental chromium, and long enough to allow the material 20 to be sufficiently fired.

The holding time of the material 20 to be treated in the furnace can be set by the conveying time (conveying speed) by the conveying device 12. More specifically, the holding time is the time required from when the material 20 to be treated passes through the entrance 111 of the furnace body 11 until the same material 20 to be treated passes through the exit 112 of the furnace body 11.
Specifically, the retention time is 5 to 30 minutes, preferably 7 to 28 minutes, and more preferably 9 to 26 minutes.

(2) Furnace Temperature The furnace temperature is the temperature inside the furnace body 11.
Further, the inside of the furnace body 11 is filled with gas, and the temperature inside the furnace is the temperature of the gas filling the furnace, that is, it can also be said to be the atmospheric temperature.
Furthermore, since the material to be treated 20 is heated by coming into contact with the gas filling the furnace body 11, which has a predetermined furnace temperature, the furnace temperature can also be said to be the heating temperature of the material to be treated 20.

In the porous glass 30, calcium carbonate (CaCO ₃ ) undergoes the reactions of the above formulas (1) to (3) in the material to be treated 20 heated to a predetermined temperature, and the generated carbon dioxide (CO ₂ ) forms bubbles as a foaming gas, and the bubbles become numerous fine holes, making the glass porous.
If the temperature inside the furnace, that is, the heating temperature, is excessively low, a sufficient amount of carbon dioxide (CO ₂ ) is not generated, which may result in poor foaming and failure to form porous materials.
If the holding time, i.e., the heating temperature, is excessively high, the molten material 20 to be treated will become excessively soft and will become excessively foamed, which may cause the foaming gas, carbon dioxide (CO ₂ ), to escape rather than remain in the material 20 to be treated, causing the porous glass 30 to shrink.
For this reason, the temperature inside the furnace is set to a temperature low enough to avoid insufficient foaming and high enough to avoid excessive foaming.

In addition, hexavalent chromium (Cr ⁶⁺ ) is produced from chromium element under the influence of the three factors described above, <1> to <3>. Of the three factors, the furnace temperature is related to factor <3>.
That is, hexavalent chromium (Cr ⁶⁺ ) is easily produced from chromium element depending on the reaction temperature, which is the atmospheric temperature during the firing treatment, that is, the temperature inside the furnace.
For this reason, the temperature inside the furnace is set to a temperature low enough to prevent the production of hexavalent chromium (Cr ⁶⁺ ) from elemental chromium, but high enough to sufficiently sinter the material 20 to be treated.

The temperature inside the furnace can be measured, for example, by a sensor, a thermocouple, or the like attached inside the furnace body 11, and can be adjusted based on the measurement results by the above-mentioned temperature adjustment means 14. More specifically, the temperature inside the furnace is adjusted so as to be kept between a lower limit value and an upper limit value according to the lower limit value and the upper limit value of the set temperature of the temperature adjustment means 14 inputted to a controller or the like.
Specifically, the temperature inside the furnace is set to 800° C. to 950° C. In addition, the temperature inside the furnace is preferably set to 820° C. to 930° C.

When the temperature adjusting means 14 is a heat exchange type heater device 141, the temperature inside the furnace can be adjusted by turning the heater device 141 on and off using a controller or the like.
That is, the heater device 141 is turned on to heat the inside of the furnace when the temperature inside the furnace drops below the lower limit (800°C) or when the temperature inside the furnace is at an appropriate temperature between the lower limit (800°C) and the upper limit (950°C).
Moreover, when the temperature inside the furnace rises above the upper limit (950° C.), the heater device 141 is turned off to stop heating inside the furnace.

When the temperature adjustment means 14 is a combustion-type burner device 142 and a cooling device 143, the temperature inside the furnace can be adjusted mainly by adjusting the combustion range of the burner device 142 using a controller, etc. The combustion range of this burner device 142 is adjusted by the amount of fuel gas supplied to the burner device 142 by the fuel gas supply system 132.
The amount of fuel gas supplied is adjusted so that 0% is the case where the supply of fuel gas to the burner device 142 is stopped, and 100% is the case where the maximum amount of fuel gas is supplied to the burner device 142 .
However, the burner device 142 is also intended to constantly maintain the combustion of the fuel gas, thereby constantly feeding gas (reducing gas) into the furnace body 11. In other words, the lower limit of the amount of fuel gas supplied is set to a value at which the combustion of the fuel gas can be maintained, and the upper limit of the amount of fuel gas supplied is usually set to 100%.
Specifically, the amount of fuel gas supplied is preferably 20% to 100%, more preferably 25% to 100%, and even more preferably 30% to 100%.

In other words, when the temperature inside the furnace drops below the lower limit (800°C), the burner device 142 supplies 100% fuel gas, and when the temperature inside the furnace is at an appropriate temperature between the lower limit (800°C) and the upper limit (950°C), the burner device 142 adjusts the supply of fuel gas to an appropriate value and combusts the fuel gas to heat the inside of the furnace.
When the temperature inside the furnace rises above the upper limit, the burner device 142 adjusts the amount of fuel gas supplied to the lower limit (20%) to maintain the supply of gas (reducing gas) into the furnace. However, as long as the supply of fuel gas continues, the burner device 142 continues to heat the inside of the furnace. Therefore, when the temperature inside the furnace rises above the upper limit, the cooling device 143 is used to cool the inside of the furnace and keep the temperature inside the furnace below the upper limit (950°C).

(3) Air-Fuel Ratio The air-fuel ratio is the ratio (A/F) of the mass of air (A) to the mass of fuel gas (F) when fuel gas is combusted with air.
Hexavalent chromium (Cr ⁶⁺ ) is produced from chromium element under the influence of the three factors described above, <1> to <3>. Of the three factors, this air-fuel ratio is related to factor <1>.
That is, chromium element is likely to produce hexavalent chromium (Cr ⁶⁺ ) due to the influence of oxygen (O ₂ ) present in the furnace.
The air-fuel ratio is adjusted so that the gas produced by burning the fuel gas with air becomes a reducing gas and oxygen (O ₂ ) is eliminated from within the furnace, that is, the furnace is deoxidized.

Specifically, the air-fuel ratio can be adjusted by adjusting the amount of fuel gas supplied and the amount of air supplied in accordance with a set value input to a controller or the like.
As the fuel gas, typically, a hydrocarbon gas such as methane gas, butane gas, or propane gas is used.

The fuel gas is burned together with air at a predetermined air-fuel ratio to generate reducing gas. This reducing gas contains carbon monoxide (CO) and hydrogen gas (H ₂ ). The carbon monoxide (CO) and hydrogen gas (H ₂ ) contained in the reducing gas react chemically with oxygen (O ₂ ) present in the furnace or introduced from outside the furnace to generate carbon dioxide (CO ₂ ) and water (H ₂ O), thereby deoxidizing the inside of the furnace.
A specific air-fuel ratio when generating reducing gas by burning fuel gas is less than 1. The lower limit of the air-fuel ratio is usually 0.6 or more from the viewpoint of preventing abnormal combustion. The air-fuel ratio is preferably 0.7 to 0.99, more preferably 0.8 to 0.97, and even more preferably 0.85 to 0.95.

(4) Dew Point When the temperature adjustment means 14 is a heat exchange type heater device 141, the dew point of the gas can be adjusted by the dew point adjustment device 134.
In this case, by adjusting the dew point, the concentrations of moisture (H ₂ O) and carbon dioxide (CO ₂ ) can be kept constant in the above-mentioned reaction formulas (1) to (3) of calcium carbonate (CaCO ₃ ), and the foaming state of the treated material 20 during the firing process can be stabilized.
Specifically, the dew point is preferably from 10°C to 60°C, more preferably from 12°C to 58°C, and even more preferably from 15°C to 55°C.
When the temperature adjustment means 14 is a combustion type burner device 142, the dew point of the gas is maintained at about 60°C.

(5) Heating method As described above, when the furnace body 11 is divided into multiple regions in the transport direction of the material 20 to be treated, the region furthest upstream in the transport direction among the multiple regions may be designated as a pre-heating region 115, and the region downstream of the pre-heating region 115 in the transport direction may be designated as a heating region 116 (see Figure 1).
The pre-heating area 115 is an area for pre-heating the material 20 to be treated in the initial stage of the firing treatment.

That is, during the firing process, foaming of the material 20 begins from the surface portion which is easily heated. However, when foaming progresses in the inner portion, which is delayed from the surface portion, if the surface portion where foaming has progressed hardens first, the foaming gas, carbon dioxide ( _CO2 ), is not able to escape properly, resulting in an uneven foaming state.
In other words, the material 20 to be treated during the firing process has a non-uniform heat distribution throughout the material, which results in a non-uniform foaming state. Therefore, the material 20 to be treated is preheated in the pre-heating region 115, heat is spread throughout the material 20 to approximately uniformize the heat distribution throughout the material 20, and the foaming state can be made uniform.

The temperature inside the furnace in the pre-heating region 115 is preferably set to a temperature lower than the temperature inside the furnace in the heating region 116, from the viewpoint of pre-heating the material 20 to be treated without promoting foaming.
Specifically, the furnace temperature in the pre-heating region 115 is preferably 50°C to 150°C lower than the furnace temperature in the heating region 116, more preferably 50°C to 120°C lower, and even more preferably 50°C to 100°C lower.
Specifically, the temperature inside the furnace in the pre-heating region 115 is preferably 650°C to 800°C, more preferably 680°C to 800°C, and further preferably 700°C to 800°C.

As described above, when the temperature adjustment means 14 is configured to further include a heat exchange type heater device 141 in addition to the combustion type burner device 142 and the cooling device 143, the heat treatment (firing treatment) in which the workpiece 20 is brought into contact with gas in a furnace can be carried out in two stages (see Figure 1).
That is, the glass heat treatment furnace 10 equipped with both the burner device 142 and the heater device 141 can employ a heating method for heating the material 20 that is divided into two stages.

When a heating method divided into two stages is adopted, it is preferable that a heater device 141 is used as the temperature adjustment means 14 in the first stage 116A of the two stages, and a burner device 142 and a cooling device 143 are used as the temperature adjustment means 14 in the second stage 116B of the two stages.
In other words, when heating the powdered material to be treated 20, the combustion burner device 142 sprays combustion gas into the furnace, and there is a possibility that the force of the sprayed combustion gas may cause the material to be treated 20 to fly apart.
Therefore, in the first stage 116A of the two stages, a heater device 141 is used to melt the material 20 to suppress scattering.
Furthermore, since the burner device 142 has lower installation costs, maintenance costs, etc. than the heater device 141, the burner device 142 is used in the latter stage 116B of the two stages in which scattering of the material 20 to be treated is suppressed.

When adopting a heating method divided into two stages, as described above, the interior of the furnace body 11 can be divided into a plurality of regions, and heating in the first stage 116A can be performed in the upstream region of the plurality of regions, and heating in the second stage 116B can be performed in the downstream region of the plurality of regions.
For example, the pre-heating region 115 may be referred to as a front-stage heating 116A, and the heating region 116 may be referred to as a back-stage heating 116B.
Alternatively, the heating region 116 may be further divided into a plurality of regions, with the upstream heating region being designated as a front-stage heating region 116A and the downstream heating region being designated as a rear-stage heating region 116B.
When the inside of the furnace is divided into a plurality of regions and heating is performed in two stages, it is useful to use a continuous type furnace body 11.

In addition, when a two-stage heating method is adopted, heating can be performed in two stages without dividing the interior of the furnace body 11 into multiple regions, or within one of the multiple divided regions.
When heating is performed in two stages in one furnace or one region as described above, a batch type furnace body 11 is useful.

[3] Method of using a glass heat treatment furnace (2)
The method of using the heat treatment furnace for glass 10 of the present invention is a method of using the heat treatment furnace for glass 10 in which a gas filling the furnace body 11, which has been set to a predetermined furnace temperature, is brought into contact with a material to be treated 20 containing at least calcium oxide and calcium carbonate, to obtain porous glass 30.
The glass heat treatment furnace 10 comprises a furnace body 11, a transport device 12 arranged in the furnace for transporting the material to be treated 20, a gas supply system 13 connected to the furnace body 11 for supplying gas into the furnace, and a temperature control means 14 provided in the furnace body 11 for adjusting the temperature inside the furnace.
In a method of using the glass heat treatment furnace 10, the material to be treated 20 is held in the furnace by the conveying device 12 for a retention time of 5 to 30 minutes, and the temperature inside the furnace is set to 800° C. or more and 950° C. or less by the temperature adjustment means 14.
The gas filling the interior of the furnace body 11 is an oxidizing gas obtained by burning air and a fuel gas at an air-fuel ratio of 1 or more.
The conveying device 12 is equipped with a plate-shaped heat-resistant plate (intervening member 122) made of a non-ferrous material that does not contain chromium elements, and a conveying roll 123 made of a ceramic material. With the workpiece 20 placed on the surface of the heat-resistant plate (intervening member 122), the heat-resistant plate (intervening member 122) is conveyed inside the furnace by the conveying roll 123.

A glass heat treatment furnace 10 used in this method includes a furnace body 11, a transport device 12, a gas supply system 13, and a temperature adjustment means 14.
The configuration of the glass heat treatment furnace 10, that is, the furnace body 11, the conveying device 12, the gas supply system 13, and the temperature adjustment means 14, can be shared with the description of “[1] Glass heat treatment furnace” above.
In the method (2) for using the heat treatment furnace for glass 10, the holding time and the temperature inside the furnace can be the same as those explained in the above-mentioned “(1) Holding Time” and “(2) Temperature Inside the Furnace” in “[2] Method (1) for Using the Heat Treatment Furnace for Glass.” In addition, the contents explained in the above-mentioned “(4) Dew Point” and “(5) Heating Method” in “[2] Method (1) for Using the Heat Treatment Furnace for Glass” can be applied to the method (2) for using the heat treatment furnace for glass 10.
Therefore, in the following description, unless otherwise specified, repeated explanations, such as the configuration of the glass heat treatment furnace 10, will be omitted.

(1) Air-Fuel Ratio The air-fuel ratio is the ratio (A/F) of the mass of air (A) to the mass of fuel gas (F) when fuel gas is combusted with air.
Specifically, the air-fuel ratio can be adjusted by adjusting the amount of fuel gas supplied and the amount of air supplied in accordance with a set value input to a controller or the like.
As the fuel gas, typically, a hydrocarbon gas such as methane gas, butane gas, or propane gas is used.

The fuel gas is combusted with air at a predetermined air-fuel ratio to generate an oxidizing gas, which contains oxygen (O ₂ ), water vapor (H ₂ O), and carbon dioxide (CO ₂ ).
The oxidizing gas can maintain constant concentrations of water vapor (H ₂ O) and carbon dioxide (CO ₂ ) in the above-mentioned reaction formulas (1) to (3) of calcium carbonate (CaCO ₃ ), and can stabilize the foaming state of the treated material 20 during the firing process.
A specific air-fuel ratio when generating an oxidizing gas by burning a fuel gas is equal to or greater than 1. Moreover, the upper limit of the air-fuel ratio is usually equal to or less than 10 from the viewpoint of preventing abnormal combustion. The air-fuel ratio is preferably 1.05 to 9.5, and more preferably 1.1 to 8.5.

(2) Transportation method Hexavalent chromium (Cr ⁶⁺ ) is generated from chromium element due to the influence of the three factors <1> to <3> described above. However, when an oxidizing gas is used as the gas filling the interior of the furnace body 11, among the three factors, factor <1> cannot be avoided.
For this reason, the conveying device 12 is provided with a plate-shaped heat-resistant plate (intervening member 122) made of a non-ferrous material that does not contain chromium, and a conveying roll 123 made of a ceramic material that does not contain chromium (see FIG. 1).
The transport method used involves transporting the heat-resistant plate (intervening member 122) through the furnace by transport rolls 123 with the material 20 placed on the surface of the heat-resistant plate (intervening member 122).
This transportation method is related to factor 2 out of the three factors.

That is, the presence of calcium compounds such as calcium oxide (CaO) contained in the material 20 to be treated affects the chromium element (for example, trivalent chromium (Cr ³⁺ )), generating hexavalent chromium (Cr ⁶⁺ ).
In the above-mentioned conveying method, a non-ferrous material not containing chromium is used for the heat-resistant plate (intervening member 122) on which the workpiece 20 is placed. Also, a ceramic material not containing chromium is used for the conveying roll 123 that conveys the heat-resistant plate (intervening member 122).
In other words, in the above-mentioned conveying method, materials that do not contain chromium are used for the heat-resistant plate (intervening member 122) with which the workpiece 20 comes into contact and the conveying roll 123 with which the workpiece 20 may come into contact.
Therefore, even if the treated material 20 containing a calcium compound is calcined in an atmosphere containing oxygen ( _O2 ), the production of hexavalent chromium (Cr6 ⁺ ) from chromium element can be suppressed by preventing contact between the treated material 20 and chromium element.
In addition, when the material to be treated 20 contains chromium element, by setting the holding time to 5 to 30 minutes and the furnace temperature to 800°C to 950°C, it is possible to suppress the generation of hexavalent chromium (Cr ⁶⁺ ) from the chromium element, as described above.

[4] Heat Treatment Furnace for Waste Glass The heat treatment furnace for waste glass of the present invention is a heat treatment furnace for waste glass in which a gas filling the furnace body 11 is brought into contact with waste glass material within the furnace body 11, the furnace body being kept at a predetermined furnace temperature, to obtain porous glass 30.
The waste glass heat treatment furnace comprises a furnace body 11, a transport device 12 arranged inside the furnace for transporting the waste glass material, a gas supply system 13 connected to the furnace body 11 for filling the furnace with gas, and a temperature adjustment means 14 provided in the furnace body 11 for adjusting the temperature inside the furnace.
The waste glass material is made by adding a foaming agent containing calcium carbonate to waste glass powder containing calcium oxide.
In the waste glass heat treatment furnace, the gas filling the furnace is a reducing gas, and the atmosphere inside the furnace body 11 is kept in a deoxidized state.

The waste glass heat treatment furnace comprises a furnace body 11, a conveying device 12, a gas supply system 13, and a temperature adjustment means 14.
The furnace body 11, the transport device 12, the gas supply system 13, and the temperature adjustment means 14 can be the same as those described above in “[1] Glass heat treatment furnace.”
Moreover, the contents explained in the above "(2) Method of using a heat treatment furnace for glass (1)" can also be applied to a heat treatment furnace for waste glass.
Therefore, in the following text, unless otherwise specified, repeated explanations will be omitted.

In the above-mentioned glass heat treatment furnace 10, the material to be treated 20 may be waste glass material in which a foaming agent containing calcium carbonate (CaCO ₃ ) is added to waste glass powder containing calcium oxide (CaO).
That is, when waste glass material is used as the material to be treated 20, the above-mentioned glass heat treatment furnace 10 can be used as a waste glass heat treatment furnace.

Waste glass is usually crushed into powder and melted by heat treatment for reuse. For example, the composition of green-colored glass contains chromium as a colorant, specifically, trivalent chromium (Cr ³⁺ ) oxide.
In addition, most of the machines used to crush waste glass are provided with a plating film containing chromium for the purpose of rust prevention and corrosion resistance. Therefore, most of the waste glass contains chromium due to the plating film peeled off from the machine.
Therefore, when the material 20 to be treated containing waste glass is heat-treated, hexavalent chromium (Cr ⁶⁺ ) is likely to be produced from the chromium element.

In the glass heat treatment furnace 10 used as a waste glass heat treatment furnace, the gas filling the interior of the furnace body 11 is made a reducing gas, so that the atmosphere within the furnace body 11 is made deoxidized.
For this reason, even if the material 20 to be treated contains calcium oxide (CaO) and chromium elements (e.g., trivalent chromium (Cr3 ⁺ )), the glass heat treatment furnace 10 is in a deoxidized state and there is no oxygen available for reaction, so hexavalent chromium (Cr6 ⁺ ) is not produced from the chromium elements (see formula (4) above), thereby preventing the production of hexavalent chromium.

In the above-mentioned glass heat treatment furnace 10, when waste glass material including waste glass is subjected to heat treatment, even if the waste glass material contains chromium element (e.g., trivalent chromium (Cr3 ⁺ )), the atmosphere inside the furnace is deoxidized and heat treatment is performed, so that hexavalent chromium can be prevented from being produced from the chromium element. Therefore, the above-mentioned glass heat treatment furnace 10 is useful as a waste glass heat treatment furnace.
In addition, waste glass does not usually contain a sufficient amount of calcium carbonate (CaCO ₃ ) as a foaming agent to obtain porous glass, so it is preferable to appropriately add a foaming agent containing calcium carbonate (CaCO ₃ ) to the waste glass.

Hereinafter, a more specific embodiment of the glass heat treatment furnace of the present invention will be described with reference to the drawings.
In each of the embodiments shown below, the furnace body 11 is shown in a simplified form in each drawing.

[First Example]
As shown in FIG. 2, the glass heat treatment furnace 10 includes a furnace body 11, a conveying device 12, a gas supply system 13, and a temperature adjusting means 14.
The furnace body 11 has a space therein for firing the material to be treated 20. The furnace body 11 is provided with an inlet 111 for introducing the material to be treated 20 into the furnace, and an outlet 112 for removing the porous glass 30 obtained by firing the material to be treated 20 from the furnace.

The transport device 12 transports the material to be treated 20 and the porous glass 30 within the furnace body 11 .
The transport device 12 includes a belt conveyor 121 disposed at the bottom of the furnace, and an interposing member 122 disposed on the surface of the belt conveyor 121. The interposing member 122 is a heat-resistant sheet made of a silica-based material.
The material to be treated 20 is placed on the intermediate members 122 and transported by the belt conveyor 121 within the furnace body 11 from the entrance 111 side to the exit 112 side.

The gas supply system 13 is connected to the furnace body 11 to fill the inside of the furnace with gas.
The gas supply system 13 includes an air supply system 131, a fuel gas supply system 1322, a gas generator 133 to which the air supply system 131 and the fuel gas supply system 1322 are connected, and a dew point adjusting device 134 connected to the gas generator 133. The dew point adjusting device 134 is connected to the furnace body 11 via a gas supply path 135.

The air supply system 131 supplies air to the gas generator 133 , and the fuel gas supply system 132 supplies fuel gas to the gas generator 133 .
The gas generator 133 generates gas by causing a combustion reaction between the supplied air and fuel gas, and sends the gas to the dew point adjustment device 134 .
The dew point adjusting device 134 adjusts the dew point temperature of the gas sent from the gas generator 133 , and then supplies the gas through a gas supply path 135 into the furnace body 11 .

The temperature adjusting means 14 adjusts the temperature inside the furnace body 11 .
The temperature adjustment means 14 includes a heat exchange type heater device 141 disposed in the furnace.
Specifically, the heater device 141 is a radiant tube burner, and high-temperature combustion gas supplied from a combustion gas supply unit 141A passes through the interior of a substantially U-shaped tube heater, thereby heating the surroundings.

The combustion gas supplier 141A is electrically connected to the controller 141B.
A thermocouple 141C attached to the furnace body 11 is electrically connected to this controller 141B.
The thermocouple 141C measures the temperature inside the furnace body 11 and sends the information to the controller 141B.
The controller 141B controls the heating of the furnace by the heater device 141 so as to achieve the set furnace temperature by adjusting the amount of combustion gas supplied from the combustion gas supply device 141A to the heater device 141 based on information from the thermocouple 141C.

In the glass heat treatment furnace 10, the material 20 is held in the furnace body 11 by the conveying device 12 for 5 to 30 minutes. This holding time can be adjusted by adjusting the conveying speed of the belt conveyor 121.
The temperature inside the furnace is set to 800° C. or more and 950° C. or less by the temperature adjusting means 14. This temperature inside the furnace can be adjusted by the controller 141B controlling the heating inside the furnace by the heater device 141.

The gas that is supplied to the inside of the furnace body 11 by the gas supply system 13 and fills the inside of the furnace is a reducing gas obtained by burning air and a fuel gas at an air-fuel ratio of less than 1.
The air-fuel ratio can be adjusted by adjusting the amounts of air and fuel gas supplied to the gas generator 133 by the air supply system 131 and the fuel gas supply system 1322 .

The interior of the furnace body 11 is filled with reducing gas supplied from a gas supply system 13 .
This reducing gas contains carbon monoxide (CO) and hydrogen (H ₂ ). Oxygen (O ₂ ) remaining in the furnace or entering from outside the furnace reacts with carbon monoxide (CO) and hydrogen (H ₂ ) contained in the reducing gas to become carbon dioxide (CO ₂ ) and water vapor (H ₂ O).
That is, oxygen (O ₂ ) is used to react with the reducing gas, so that the inside of the furnace body 11 is made into an oxygen-free state.

The material to be treated 20 contains silicon dioxide (SiO ₂ ) as a main component, and also contains at least calcium oxide (CaO) and calcium carbonate (CaCO ₃ ).
In the furnace body 11, whose furnace temperature is set to 800° C. or higher and 950° C. or lower, the material 20 to be treated is brought into contact with the reducing gas filling the furnace, and is melted, and silicon dioxide (SiO ₂ ) forms the glass skeleton of the porous glass 30.
Calcium carbonate (CaCO ₃ ) in the material 20 to be treated generates carbon dioxide (CO ₂ ) as a foaming gas, and this carbon dioxide (CO ₂ ) forms a large number of fine holes in the molten material 20 to be treated, thereby obtaining porous glass 30 from the material 20 to be treated.

In addition, calcium oxide (CaO) contained in the material to be treated 20, which is generated from calcium carbonate (CaCO ₃ ), acts on the glass skeleton made of silicon dioxide (SiO ₂ ), thereby improving the durability of the porous glass 30.
When calcium oxide (CaO) comes into contact with chromium element (for example, trivalent chromium (Cr ³⁺ )) in the presence of oxygen (O ₂ ), it undergoes a chemical reaction to produce hexavalent chromium (Cr ⁶⁺ ).

In the glass heat treatment furnace 10, a reducing gas is used as the gas filling the interior of the furnace body 11, and the interior of the furnace body 11 is kept in an oxygen-depleted state.
Therefore, even if chromium elements (e.g., trivalent chromium (Cr3 ⁺ )) are present in the furnace, since oxygen ( _O2 ) is not present, a chemical reaction between calcium oxide (CaO) and, for example, trivalent chromium (Cr3 ⁺ ) does not occur, and hexavalent chromium (Cr6 ⁺ ) is not produced.
As a result, in the firing treatment of the material 20 using the above-mentioned glass heat treatment furnace 10, generation of hexavalent chromium (Cr ⁶⁺ ) is prevented.

[Second Example]
The glass heat treatment furnace 10 of the second embodiment will be described below, focusing on the differences from the first embodiment described above.
As shown in FIG. 3, the glass heat treatment furnace 10 includes a furnace body 11, a conveying device 12, a gas supply system 13, and a temperature adjusting means 14.
The furnace body 11 and the transport device 12 are similar to those in the first embodiment described above, and therefore a description thereof will be omitted.

The gas supply system 13 includes an air supply system 131, a fuel gas supply system 1322, and a combustion-type burner device 142 to which the air supply system 131 and the fuel gas supply system 1322 are connected.
The air supply system 131 supplies air to the burner device 142 , and the fuel gas supply system 1322 supplies fuel gas to the burner device 142 .
The burner device 142 combusts the supplied air and fuel gas, and sends the resulting combustion gas into the furnace body 11, thereby filling the inside of the furnace with combustion gas.

In addition, an air supply valve 131A is connected to the air supply system 131, and a fuel gas supply valve 132A is connected to the fuel gas supply system 1322.
The air supply valve 131A adjusts the amount of air supplied to the burner device 142 , and the fuel gas supply valve 132A adjusts the amount of fuel gas supplied to the burner device 142 .
Furthermore, the air supply valve 131A and the fuel gas supply valve 132A are each electrically connected to a controller 141B, and the controller 141B can control the amounts of air and fuel gas supplied.

The combustion gas that fills the furnace interior is supplied to the interior of the furnace body 11 by the burner device 142 that constitutes the gas supply system 13, and is a reducing gas obtained by burning air and fuel gas at an air-fuel ratio of less than 1.
The air-fuel ratio can be adjusted by controlling the amounts of air and fuel gas supplied to the burner device 142 by the controller 141B.
In the glass heat treatment furnace 10, the interior of the furnace body 11 is filled with a reducing gas, thereby making the interior of the furnace deoxidized, and the generation of hexavalent chromium (Cr ⁶⁺ ) is prevented during the firing process to obtain porous glass 30 from the treated material 20.

The temperature adjustment means 14 includes the above-mentioned combustion-type burner device 142 and a cooling device 143 .
The above-mentioned combustion type burner device 142 constitutes the gas supply system 13 and also constitutes the temperature adjustment means 14. The burner device 142 heats the inside of the furnace by ejecting high-temperature combustion gas into the furnace body 11.
Specifically, the cooling device 143 is a heat exchange type cooling tube 144. The cooling tube 144 cools the surroundings by passing a refrigerant sent from a cooling fan 144A through the inside of a substantially U-shaped tube heater.
Moreover, the cooling fan 144A is electrically connected to the controller 141B, and the amount of refrigerant supplied and the operation of the fan 144A can be controlled by the controller 141B.

The temperature inside the furnace is set to 800° C. or more and 950° C. or less by the temperature adjustment means 14. This temperature inside the furnace can be adjusted by the controller 141B controlling the heating inside the furnace by the burner device 142 and the cooling inside the furnace by the cooling tube 144.
That is, based on information from the thermocouple 141C, the controller 141B adjusts the amount of fuel gas supplied to the burner device 142, thereby adjusting the heat of the burner device 142 so that the set furnace temperature is achieved, thereby controlling the heating inside the furnace.

When the temperature inside the furnace rises above 950°C, the above-mentioned burner device 142 also serves as the gas supply system 13, so if the combustion is stopped, reducing gas is not supplied to the furnace, and the furnace is no longer kept in an oxygen-free state.
Therefore, when the temperature rises excessively, the inside of the furnace is cooled by the cooling tube 144 while maintaining combustion in the burner device 142 .

That is, when the controller 141B detects an excessive rise in the temperature inside the furnace as measured by the thermocouple 141C, it activates the cooling fan 144A. The cooling fan 144A sends a refrigerant to the cooling tube 144, and the cooling tube 144 cools the inside of the furnace.
In addition, the controller 141B continues to cool the inside of the furnace by the cooling tube 144 until the excessive temperature inside the furnace is eliminated by, for example, adjusting the rotation speed of the cooling fan 144A while measuring the temperature inside the furnace by the thermocouple 141C.
Then, when the condition of the excessive furnace temperature is resolved, the controller 141B stops the operation of the cooling fan 144A, stops the cooling of the furnace interior by the cooling tube 144, and adjusts the heat of the burner device 142 so that the set furnace temperature is reached, thereby controlling the heating inside the furnace.

[Third Example]
The glass heat treatment furnace 10 of the third embodiment will be described below, focusing on the differences from the first and second embodiments described above.
As shown in FIG. 4, the glass heat treatment furnace 10 includes a furnace body 11, a conveying device 12, a gas supply system 13, and a temperature adjusting means 14.
The furnace body 11 and the transport device 12 are similar to those in the first embodiment described above, and therefore a description thereof will be omitted.
The gas supply system 13 is similar to that in the second embodiment described above, and a description thereof will be omitted.

The temperature adjustment means 14 includes a combustion type burner device 142 and a cooling device 143. The combustion type burner device 142 is the same as that in the second embodiment described above, and a description thereof will be omitted.
Specifically, the cooling device 143 includes a circulation system 145 connected to the furnace body 11, and a cooler device 146 connected to the circulation system 145. Furthermore, a circulation fan 145A and a circulation valve 145B are connected to the circulation system 145.
The circulation system 145 circulates the reducing gas between the inside and outside of the furnace body 11 by the operation of a circulation fan 145A.
The cooler device 146 cools the reducing gas flowing through the circulation system 145 .
The circulation valve 145B adjusts the amount of reducing gas circulated by the circulation system 145. The circulation valve 145B is electrically connected to the controller 141B, and the amount of reducing gas circulated can be controlled by the controller 141B.

The temperature inside the furnace is set to 800° C. or more and 950° C. or less by the temperature adjustment means 14. This temperature inside the furnace can be adjusted by the controller 141B controlling the heating inside the furnace by the burner device 142 and the cooling inside the furnace by the circulation system 145 and the cooler device 146.
That is, based on information from the thermocouple 141C, the controller 141B adjusts the amount of fuel gas supplied to the burner device 142, thereby adjusting the heat of the burner device 142 so that the set furnace temperature is achieved, thereby controlling the heating inside the furnace.

When the temperature inside the furnace rises above 950°C, the above-mentioned burner device 142 also serves as the gas supply system 13, so if the combustion is stopped, reducing gas is not supplied to the furnace, and the furnace is no longer kept in an oxygen-free state.
Therefore, when the temperature rises excessively, the inside of the furnace is cooled by the circulation system 145 and the cooler device 146 while maintaining the combustion of the burner device 142 .

That is, when the controller 141B detects that the temperature inside the furnace has risen excessively as measured by the thermocouple 141C, the controller 141B opens the circulation valve 145B to circulate the reducing gas, which has become hot inside the furnace, through the circulation system 145.
The high-temperature reducing gas circulating through the circulation system 145 is cooled by a cooler device 146 connected to the circulation system 145 to become a low-temperature reducing gas. Then, the low-temperature reducing gas circulated through the circulation system 145 and returned to the furnace cools the inside of the furnace.
The controller 141B continues circulating the reducing gas while adjusting the circulation amount by the circulation valve 145B, while measuring the temperature inside the furnace by the thermocouple 141C, until the excessive temperature inside the furnace is eliminated.
Then, when the condition of excessive furnace temperature is resolved, the controller 141B closes the circulation valve 145B, stops the circulation of reducing gas through the circulation system 145, and adjusts the heat of the burner device 142 so that the set furnace temperature is reached, thereby controlling the heating inside the furnace.

10: Glass heat treatment furnace,
11; furnace body, 111; inlet, 112; outlet, 113; partition, 114; communication port, 115; pre-heating zone, 116; heating zone, 116A; front stage, 116B; rear stage,
12; conveying device; 121; belt conveyor; 122; intermediate member; 123; conveying roll;
13; gas supply system, 131; air supply system, 131A; air supply valve, 132; fuel gas supply system, 132A; fuel gas supply valve, 133; gas generator, 134; dew point adjustment device, 135; gas supply line,
14; temperature control means, 141; heater device, 141A; combustion gas supply device, 141B; controller, 141C; thermocouple, 142; burner device, 143; cooling device, 144; cooling tube, 144A; cooling fan, 145; circulation system, 145A; circulation fan, 145B; circulation valve, 146; cooler device,
20: material to be treated, 30: porous glass.

Claims (18)

1. A heat treatment furnace for glass, which produces porous glass by contacting a material to be treated, the material including at least calcium oxide and calcium carbonate, with a gas filling the furnace body, the temperature of which is set to a predetermined value,
The furnace body;
a conveying device disposed in the furnace for conveying the material to be treated;
a gas supply system connected to the furnace body for filling the furnace with the gas;
A temperature adjusting means is provided in the furnace body to adjust the temperature inside the furnace,
2. A heat treatment furnace for glass, comprising: a furnace body having a furnace atmosphere deoxidized; and a furnace gas having a reducing gas and a furnace body having a furnace atmosphere deoxidized. the gas supply system includes at least an air supply system that supplies air , a fuel gas supply system that supplies fuel gas, a gas generator to which the air supply system and the fuel gas supply system are connected, and a dew point adjustment device that is connected to the gas generator;
2. The glass heat treatment furnace according to claim 1, wherein said temperature adjusting means comprises a heat exchange type heater device disposed within said furnace. the gas supply system includes at least an air supply system that supplies air and a fuel gas supply system that supplies fuel gas;
The glass heat treatment furnace according to claim 1, wherein the temperature control means is connected to the air supply system and the fuel gas supply system, and comprises a combustion burner device attached to the furnace body so as to send the reducing gas, which is a combustion gas of the air and the fuel gas, into the furnace, and a cooling device attached to the furnace body for cooling the inside of the furnace. The glass heat treatment furnace according to claim 3, wherein the cooling device is provided with a heat exchange type cooling tube disposed within the furnace. The glass heat treatment furnace according to claim 3, wherein the cooling device comprises a circulation system connected to the furnace body for circulating the gas between the inside and outside of the furnace, and a cooler device connected to the circulation system. The glass heat treatment furnace according to any one of claims 3 to 5, further comprising a heat exchange type heater device disposed within the furnace as the temperature adjustment means. The conveying device includes a belt conveyor and an interposition member interposed between the belt conveyor and the material to be treated,
The belt conveyor is made of a heat-resistant material containing chromium,
7. The glass baking furnace according to claim 1, wherein the intermediate member is made of a non-ferrous material that does not contain chromium. The glass firing furnace according to claim 7, wherein the intermediate member is a heat-resistant sheet made of a silica-based material. The glass firing furnace according to claim 7, wherein the intermediate member is a heat-resistant container having at least one surface open to the outside and containing the material to be treated. The glass firing furnace according to claim 7, wherein the intermediate member is a heat-resistant plate having a plate shape and on whose surface the material to be treated is placed. The glass heat treatment furnace according to any one of claims 1 to 10, wherein the material to be treated is waste glass material in which a foaming agent containing calcium carbonate is added to waste glass powder containing calcium oxide. A method for using a heat treatment furnace for glass, in which a gas filling the furnace body is brought into contact with a material to be treated containing at least calcium oxide and calcium carbonate in a furnace body having a predetermined furnace temperature, to obtain porous glass, comprising the steps of:
The glass heat treatment furnace comprises:
The furnace body;
a conveying device disposed in the furnace for conveying the material to be treated;
a gas supply system connected to the furnace body for filling the furnace with the gas;
A temperature adjusting means is provided in the furnace body to adjust the temperature inside the furnace,
The holding time for which the workpiece is held in the furnace by the conveying device is 5 minutes to 30 minutes;
The temperature inside the furnace is set to 800° C. or more and 950° C. or less by a temperature control means,
The gas is a reducing gas obtained by burning air and a fuel gas at an air-fuel ratio of less than 1;
2. A method for using a glass heat treatment furnace, comprising the steps of: making the atmosphere inside the furnace body deoxidized. the gas supply system includes at least an air supply system that supplies the air, a fuel gas supply system that supplies the fuel gas, a gas generator to which the air supply system and the fuel gas supply system are connected, and a dew point adjustment device that is connected to the gas generator;
the temperature adjustment means includes a heat exchange type heater device disposed in the furnace,
the gas generator combusts the air supplied from the air supply system and the fuel gas supplied from the fuel gas supply system at an air-fuel ratio of less than 1 to generate the reducing gas;
The dew point of the reducing gas is adjusted to 10° C. to 60° C. by the dew point adjustment device,
13. The method for using a heat treatment furnace for glass according to claim 12, wherein the reducing gas is heated in the furnace by the heater device to set the temperature in the furnace to 800° C. to 950° C. the gas supply system includes at least an air supply system that supplies the air and a fuel gas supply system that supplies the fuel gas,
The temperature adjustment means is connected to the air supply system and the fuel gas supply system, and is provided with a combustion burner device attached to the furnace body so as to combust the air and the fuel gas and send the resulting combustion gas, that is, the reducing gas, into the furnace, and a cooling device attached to the furnace body for cooling the inside of the furnace;
The combustion of the air and the fuel gas in the burner device is constantly maintained, so that the reducing gas is constantly fed into the furnace,
The method for using the glass heat treatment furnace according to claim 12, wherein the temperature inside the furnace is set to 800°C to 950°C by heating the inside of the furnace with the burner device whose supply amount of the fuel gas is adjusted, or by heating the inside of the furnace with the burner device whose supply amount of the fuel gas is adjusted and cooling the inside of the furnace with the cooling device. The furnace body is divided into a plurality of regions in the transport direction of the material to be treated,
Among the plurality of regions, a region on the most upstream side in the transport direction is a pre-heating region, and a region on the downstream side of the pre-heating region in the transport direction is a heating region,
The temperature inside the furnace in the heating region is set to 800° C. or more and 950° C. or less,
The method for using the glass heat treatment furnace according to any one of claims 12 to 14, wherein the furnace temperature in the pre-heating region is 50°C to 150°C lower than the furnace temperature in the heating region. The temperature adjusting means further includes a heat exchange type heater device disposed in the furnace,
The heat treatment in which the material to be treated is brought into contact with the gas is carried out in two stages,
In the first stage of the two stages, the heater device is used as the temperature adjustment means,
16. The method for using a glass heat treatment furnace according to claim 14 or 15, wherein in the latter stage of the two stages, the burner device and the cooling device are used as the temperature adjusting means. The method for using a glass heat treatment furnace according to any one of claims 12 to 16, wherein the material to be treated is waste glass material in which a foaming agent containing calcium carbonate has been added to waste glass powder containing calcium oxide. 1. A heat treatment furnace for waste glass, which produces porous glass by contacting a gas filling the inside of a furnace body, the furnace body being kept at a predetermined furnace temperature, with a waste glass material,
The furnace body;
A conveying device disposed in the furnace for conveying the waste glass material;
a gas supply system connected to the furnace body for filling the furnace with the gas;
and a temperature adjusting means provided in the furnace body for adjusting the temperature inside the furnace.
The waste glass material is a powder of waste glass containing calcium oxide to which a foaming agent containing calcium carbonate is added,
the gas is a reducing gas,
2. A heat treatment furnace for waste glass, wherein the atmosphere inside the furnace body is deoxidized.

Images