Ceramics firing method

Abstract

This invention provides a method for firing ceramics that can suppress the generation of exhaust gases. [Solution] The ceramic firing method utilizes a firing furnace 10 capable of performing both gas firing, which is carried out by burning gas G in a burner 12, and electric firing, which is carried out by applying electricity to a heater 13. In the ceramic firing method, gas firing and electric firing are carried out simultaneously when the temperature inside the firing furnace 10 is 1100°C (heater heating dominant temperature) or higher.

Description

Technical Field

[0001] This disclosure relates to a method for firing ceramics.

Background Art

[0002] Patent Document 1 discloses a batch-type heat treatment furnace used for conditioning aluminum or the like. The one in Patent Document 1 can perform precise conditioning by raising the temperature in the furnace to an approximate temperature with a burner and then precisely controlling the temperature in the furnace with an electric heating element.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The firing temperature of ceramics is often higher than the temperature when conditioning metal (hereinafter, also simply referred to as the conditioning temperature). Therefore, when raising the temperature in the furnace to a temperature at which firing of ceramics is possible using a burner, more gas will be burned compared to when raising the temperature in the furnace to the conditioning temperature, and there is a concern that more exhaust gas will be generated. Therefore, from the perspective of suppressing CO2 (carbon dioxide) emissions, a method for firing ceramics that can suppress the generation of exhaust gas is desired. Here, ceramics include tiles, sanitary ceramics, ceramic filters, insulators, tableware, etc.

[0005] This disclosure has been made in view of the above conventional situation, and an object to be solved is to provide a method for firing ceramics that can suppress the generation of CO2.

Means for Solving the Problems

[0006] The ceramic firing method of the present disclosure is a method for firing ceramics using a firing furnace capable of performing gas firing by burning gas with a burner and electric firing by applying electricity to a heater, wherein the gas firing and the electric firing are performed simultaneously when the temperature inside the firing furnace is above a heater heating dominant temperature at which heating by the heater is dominant over heating by the burner. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram showing the configuration of the firing furnace in Embodiment 1. [Figure 2] This is a time chart showing an example of control in the control unit. [Figure 3] This graph shows the changes in temperature and total energy content inside the firing furnace over time. [Modes for carrying out the invention]

[0008] <Embodiment 1> Hereinafter, Embodiment 1, which embodies a firing furnace 10 for carrying out the ceramic firing method of this disclosure, will be described with reference to Figures 1 to 3.

[0009] [Configuration of the firing furnace] The firing furnace 10 is used when firing ceramics (tiles, sanitary ware, ceramic filters, insulators, tableware, etc.). As shown in Figure 1, the firing furnace 10 comprises a furnace body 11, a burner 12, a heater 13, and a control unit 30. The furnace body 11 has an insulating material 11A and an outer wall portion 11B provided to cover the insulating material 11A. For the insulating material 11A, for example, a known refractory insulating material is used. The insulating material 11A is formed in the shape of a box with a containment space C formed inside. For the outer wall portion 11B, for example, a metal material such as carbon steel or stainless steel is used. The outer wall portion 11B is arranged to cover the insulating material 11A. An opening 11C is formed on the side of the furnace body 11 (the side facing the viewer in Figure 1). The opening 11C can be opened and closed by a lid portion (not shown).

[0010] An exhaust passage E is formed in the furnace body 11. For example, the exhaust passage E communicates with the lower end of the containment space C and extends laterally below the containment space C. For example, a flow meter (not shown) is provided in the exhaust passage E. A known type of flow meter is used. The flow meter can measure the amount of exhaust gas Ge that has passed through the exhaust passage E. A stand 11D is placed in the containment space C. For example, the stand 11D is supported by a plurality of legs 11E and is positioned above the exhaust passage E that communicates with the containment space C. For example, a ceramic product Ce is placed on the stand 11D. A temperature sensor 11F for detecting the temperature of the product Ce (inside the firing furnace 10) is provided near the product Ce placed on the stand 11D. For example, a known thermocouple is used for the temperature sensor 11F. The temperature sensor 11F is configured to output a voltage signal V indicating the temperature of the product Ce to the outside.

[0011] Multiple burners 12 are provided on the side of the firing furnace 10. In Figure 1, only one burner 12 is shown. Fuel, gas G, is supplied to the burner 12 from an external source. For example, city gas, LNG (liquefied natural gas), propane gas, hydrogen, methane gas, etc., can be used as gas G. The amount of gas G supplied to the burner 12 per unit time can be changed, for example, by adjusting the opening degree of a throttle valve Sv provided in the gas G flow path. The gas G supplied to the burner 12 is ignited by an ignition device (not shown) provided in the burner 12. The temperature inside the firing furnace 10 rises as the gas G burns. When gas G burns, it changes into exhaust gas Ge, which is exhausted to the outside through the exhaust passage E.

[0012] Multiple heaters 13 are provided on the side of the firing furnace 10. For example, heaters made of molybdenum disilicide are used for the heaters 13. Heaters made of molybdenum disilicide can generate heat up to about 1800°C without melting themselves.

[0013] Heating by heater 13 is due to heat transfer by radiation from the high-temperature surface of heater 13. On the other hand, heating by burner 12 is a combination of heat transfer by convection from the high-temperature gas flow associated with the combustion of gas in burner 12, and heat transfer by radiation from the high-temperature gas and burner flame (flame). Furthermore, in the case of heating by burner 12, it is necessary to discharge exhaust gas Ge from the containment space C, so heat is released to the outside along with the exhaust gas Ge. For this reason, when raising the temperature of containment space C, the degree of combustion of gas G increases in proportion to the temperature, and along with this, the amount of exhaust gas Ge (i.e., the amount of heat released to the outside) also increases in proportion, so it is necessary to consider the release of heat to the outside (exhaust loss). It is also known that in the high-temperature range of several hundred degrees Celsius or more used in ceramic firing, radiant heat transfer is greater than convective heat transfer.

[0014] Here, if we consider the ratio of the amount of heat actually contributing to the heating of the product to the amount of heat input as the heating efficiency, then the change in the heating efficiency of the heater 13 in the firing process is only related to the change in the efficiency of radiant heat transfer. In contrast, the change in the heating efficiency of the burner 12 in the firing process requires considering the change in the total sum obtained by subtracting exhaust loss (heat release to the outside) from the sum of convective heat transfer and radiant heat transfer. As a result, the temperature of 1100°C, which will be described later in this embodiment, can be considered a heater heating dominant temperature where the heating efficiency of the heater 13 is greater than (dominant of) the heating efficiency of the burner 12, given the firing furnace 10, product conditions, and heating conditions. That is, in the temperature range below 1100°C (heater heating dominant temperature), the heating efficiency of burner heating is superior, so using burner heating can suppress CO2 generation. In contrast, in the temperature range above 1100°C (heater heating dominant temperature), the heating efficiency of heater heating is superior, so using heater heating can suppress CO2 generation.

[0015] The control unit 30 is configured, for example, by mounting a CPU and memory on a circuit board. For example, the control unit 30 receives a voltage signal V from the temperature sensor 11F. Based on the voltage signal V from the temperature sensor 11F, the control unit 30 grasps the temperature of the base 11D and has the function of changing the opening degree of the throttle valve Sv to control the amount of gas G flowing into the burner 12 per unit time, and to control the amount of current I supplied to the heater 13 per unit time. For example, the control unit 30 controls a power supply device 50 that supplies current I from the commercial power supply Ps to each heater 13, and controls the supply of current I from the commercial power supply Ps to each heater 13 via the power supply device 50. The firing furnace 10 configured in this way can perform gas firing by burning gas G in the burner 12, and electric firing by energizing the heater 13.

[0016] [An example of a ceramic firing method in a firing furnace] Next, an example of a method for firing ceramics in the firing furnace 10 will be described. First, the ceramic product Ce is placed on the stand 11D and the opening 11C is closed with a lid. Then, as shown in Figure 2, at time T0, the control unit 30 starts supplying gas G to the burner 12. The flow rate of gas G at time T0 is 0 (m³). 3 The flow rate is F1(m / h), and from time T0 onwards, the flow rate is gradually increased, and at time T1, F1(m 3 The rate is increased to ( / h). At time T0, for example, the control unit 30 opens the throttle valve Sv provided in the gas G flow path to start supplying gas G to the burner 12, and ignites the gas G with the ignition device provided in the burner 12. After time T0, the control unit 30 controls the opening of the throttle valve Sv to gradually increase. Once combustion of gas G in the burner 12 begins, the temperature inside the firing furnace 10, which was at room temperature (approximately 25°C) at time T0, continues to rise at a constant rate. At this time, only gas firing, which is performed by burning gas G, is carried out. The temperature sensor 11F continues to output a voltage signal V to the control unit 30 indicating the temperature near the product Ce (see Figure 1). As a result, the control unit 30 can keep track of the temperature near the product Ce (inside the firing furnace 10).

[0017] Then, at time T1, when the voltage signal V from the temperature sensor 11F reaches a value indicating 1100 °C (the dominant temperature for heater heating), the control unit 30 starts energizing the heater 13. The control unit 30 outputs a power supply start signal Ss, which is a control signal, to the power supply device 50, and starts supplying the current I from the commercial power supply Ps to each heater 13 via the power supply device 50 (see FIG. 1). That is, the heater 13 is a high-temperature heater used in a temperature range of 1100 °C or higher.

[0018] Furthermore, at time T1, the control unit 30 reduces the supply amount of the gas G to the burner 12 from F1 (m 3 / h) by a predetermined amount to change it to F2 (m 3 / h). Specifically, at time T1, the control unit 30 decreases the opening degree of the throttle valve Sv provided in the gas G flow path by a predetermined degree. As a result, the energy amount per unit time of the gas G after time T1 (hereinafter also simply referred to as the energy amount) is reduced compared to before time T1. That is, the energy amount of the gas G when the temperature in the firing furnace 10 is 1100 °C (the dominant temperature for heater heating) or higher is less than the energy amount of the gas G when the temperature in the firing furnace 10 is less than 1100 °C (the dominant temperature for heater heating). Thus, after time T1 (when the temperature in the firing furnace 10 is 1100 °C (the dominant temperature for heater heating) or higher), gas firing by burning the gas G and electric firing by energizing the heater 13 are performed in parallel and simultaneously. Thereby, even if the supply amount of the gas G to the burner 12 is reduced from F1 (m 3 / h) to F2 (m 3 / h) at time T1, the temperature in the firing furnace 10 can continue to rise due to the electric firing being performed. In contrast, before time T1 (when the temperature in the firing furnace 10 is less than 1100 °C (the dominant temperature for heater heating)), only gas firing is executed.

[0019] [An example of the execution result of performing gas firing and electric firing in a firing furnace] The graph shown in Fig. 3 shows an example of the change over time in the temperature inside the firing furnace 10 and the amount of energy input into the furnace by the combustion gas G and the electric heater 13 when gas firing and electric firing are actually performed in the firing furnace 10. The dotted graph D is a curve showing the temperature change required when firing a certain sanitary ware (product Ce). The solid graph S that changes along the dotted graph D is a graph showing the actual temperature change of the accommodation space C when gas firing and electric firing are performed so that the temperature of the accommodation space C follows the dotted graph D. During the initial period (from 0 h to approximately 1.5 h) and the final period (from approximately 9 h to 12 h) during the execution of gas firing, the solid graph S deviates from the dotted graph D, but it can be adjusted so as not to deviate by adjusting the parameters.

[0020] The graph P shown as a collection of thin gray dots is a graph showing the total amount of energy obtained by adding the amount of gas combustion and the amount of electric heating (hereinafter simply referred to as the total energy amount) when gas firing and electric firing are performed so that the temperature of the accommodation space C follows the dotted graph D. The graph Comp is a graph showing the total energy amount when only gas firing is performed so that the temperature of the accommodation space C follows the dotted graph D, and it is a comparative example.

[0021] At time T0, the combustion of the gas G in the burner 12 was started. After time T0, the temperature inside the firing furnace 10 (solid graph S) continued to rise while changing the degree of increase.

[0022] When plotting the graph P, the energization of the heater 13 was started at time T01. Thereafter, the magnitude of the current I supplied to the heater 13 was increased step by step. The magnitude of the current I supplied to the heater 13 at time T02 was set to the maximum magnitude that is allowed to flow through the heater 13.

[0023] For example, if the temperature inside the firing furnace 10 is increased gradually and then rapidly, the amount of energy per unit time of gas G will increase. Referring to graph P, the total amount of energy increases after time T02 compared to before time T02. This is because, after time T02, the temperature inside the combustion furnace 20 is increased rapidly, which increases the amount of energy of gas G after time T02 compared to before time T02.

[0024] In contrast, when the temperature inside the firing furnace 10 is rapidly increased and then gradually increased, the amount of energy per unit time of gas G will decrease compared to the amount of energy when the temperature was rapidly increased. For example, referring to graph P, the total amount of energy decreases after time T1 compared to time T1. This is because, after time T1, the temperature inside the combustion furnace 20 is increased gradually, which reduces the amount of energy of gas G after time T1 compared to time T1.

[0025] At time T1, the temperature inside the firing furnace 10 reached approximately 1100°C. Compared to before time T1, the temperature inside the firing furnace 10 was increased more gradually from time T1 onward. As a result, the amount of energy in gas G was reduced from time T1 onward compared to time T1. Consequently, the total energy amount decreased in proportion to the amount of energy in gas G (see graph P).

[0026] Furthermore, the temperature inside the firing furnace 10 continued to rise after time T1. Then, at time T2, the supply of gas G to the burner 12 and the supply of current I to the heater 13 were stopped. As a result, the temperature inside the firing furnace 10 dropped sharply after time T2.

[0027] [Comparison of Graph P and Graph Comp] Between time T0 and time T01, there was no significant difference between graph P and graph Comp; they were almost the same. Between time T01 and time T1, a slight difference occurred between graph P and graph Comp, but it was small enough to be considered roughly the same. In other words, between time T0 and time T1, the total energy amounts for graph P and graph Comp were roughly the same. Let's consider the reason for this. Although power was supplied to the heater 13 at time T01, the temperature inside the firing furnace 10 was less than 1100°C until time T1, so the heating efficiency of the product Ce in the heater 13 had not increased (burner heating efficiency and heater heating efficiency were roughly the same). Therefore, between time T01 and time T1, heating by the burner 12 and heater 13 proceeded with roughly the same heating efficiency. As a result, it is thought that the total energy amount at the time of plotting graph P was roughly the same as the total energy amount at the time of plotting graph Comp.

[0028] During the period from time T1 to time T2, graph P was clearly smaller than graph Comp. In other words, when the temperature inside the firing furnace 10 was 1100°C or higher (heater heating dominant temperature), the total energy used when gas firing and electric firing were performed simultaneously was less than the total energy used when only gas firing was performed (i.e., the amount of electric heating was 0). The reason for this is thought to be that, at the time graph P was plotted, after time T1 the temperature inside the firing furnace 10 rose above 1100°C, which relatively increased the heating efficiency of the product Ce in the heater 13. As a result, the heater 13 began to contribute to the temperature rise inside the firing furnace 10, and the temperature rise inside the firing furnace 10 could be achieved as planned even with reduced combustion of gas G compared to when graph Comp was plotted.

[0029] In contrast, when plotting graph Comp, the total amount of energy is considered to be greater than in graph P because the temperature inside the firing furnace 10 is raised solely by gas firing, since electric firing is not performed (i.e., the heater 13 is not energized). In other words, it was found that the total amount of energy generated from the firing furnace 10 when firing the product Ce can be suppressed by starting to energize the heater 13 when the temperature inside the firing furnace 10 is 1100°C or higher.

[0030] According to the embodiment configured as described above, the following effects are achieved.

[0031] The ceramic firing method utilizes a firing furnace 10 capable of performing both gas firing, which is carried out by burning gas G in a burner 12, and electric firing, which is carried out by applying electricity to a heater 13. In the ceramic firing method, gas firing and electric firing are carried out simultaneously when the temperature inside the firing furnace 10 is 1100°C or higher (heater heating dominant temperature, where heating by the heater 13 is more dominant than heating by the burner 12). With this configuration, it is possible to replace a portion of the combustion of gas G when the temperature inside the firing furnace 10 is 1100°C (heater heating dominant temperature) or higher with the application of electricity to the heater 13, thereby suppressing the total amount of energy used when the temperature is 1100°C (heater heating dominant temperature) or higher.

[0032] The ceramic firing method involves performing gas firing only when the temperature inside the firing furnace 10 is below 1100°C (heater heating dominant temperature). With this configuration, for example, if the heating efficiency of product Ce in the heater 13 is high above 1100°C and low below 1100°C, the temperature inside the firing furnace can be raised while saving power by stopping the power supply to the heater 13 in the temperature range below 1100°C where the heating efficiency of product Ce is low.

[0033] Heater 13 is a high-temperature heater. A high-temperature heater is a heater that can be used in a temperature range of 1100°C or higher.

[0034] Molybdenum disilicide is used for the heater 13. With this configuration, the temperature inside the firing furnace 10 can be easily maintained at 1100°C (heater heating dominant temperature) or higher.

[0035] In a ceramic firing method, the amount of energy per unit time of gas G when the temperature inside the firing furnace 10 is 1100°C (heater heating dominant temperature) or higher is less than the amount of energy per unit time of gas G when the temperature inside the firing furnace 10 is below 1100°C. With this configuration, it is possible to suppress the generation of exhaust gas Ge at temperatures above 1100°C compared to when the temperature inside the firing furnace 10 is raised to 1100°C or higher by gas firing alone.

[0036] When the temperature inside the firing furnace 10 is 1100°C (heater heating dominant temperature) or higher, the total energy per unit time when gas firing and electric firing are performed simultaneously is less than the total energy per unit time when only gas firing is performed. With this configuration, CO2 emissions from the firing furnace 10 can be reduced compared to when only gas firing is performed, thereby reducing the burden on the environment.

[0037] This disclosure is not limited to Embodiment 1 described above in the description and drawings, but also includes, for example, the following embodiments within the technical scope of the ceramic firing method of this disclosure.

[0038] (1) Unlike Embodiment 1, a heater other than molybdenum disilicide may be used, as long as it has the characteristic that the heating efficiency of the product at 1100°C (heater heating dominant temperature) or above is higher than the heating efficiency at temperatures below 1100°C. (2) In Figure 3, the heater is energized when the temperature inside the firing furnace is lower than 1100°C (heater heating dominant temperature). However, it is considered that energizing the heater when the temperature inside the firing furnace is lower than 1100°C does not contribute to raising the temperature inside the furnace. Therefore, it is preferable to start energizing the heater when the temperature inside the firing furnace is 1100°C or higher. (3) The mounting position of the temperature sensor is not limited to the mounting position of Embodiment 1 (near the product). (4) Unlike Embodiment 1, the operator may control the amount of gas flowing into the burner or the amount of current supplied to the heater based on a voltage signal from a temperature sensor, without relying on a control unit. (5) Electric firing may be started when the temperature inside the firing furnace is higher than 1100°C (heater heating dominant temperature) (for example, 1150°C or 1200°C, etc.) and performed at the same time as gas firing. (6) The heater-dominant temperature is not limited to 1100°C, but varies depending on the specifications of the firing furnace, the form of the product, and the combustion schedule (curve).

[0039] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is not limited to the embodiments disclosed herein. [Explanation of Symbols]

[0040] 10...Firing furnace, 12...Burner, 13...Heater, Ce...Ceramics, G...Gas, Ge...Exhaust gas

Claims

1. A method for firing ceramics using a firing furnace capable of performing gas firing by burning gas in a burner and electric firing by applying electricity to a heater, A method for firing ceramics, wherein the gas firing and the electric firing are performed simultaneously when the temperature inside the firing furnace is above a heater heating dominant temperature, where heating by the heater is more dominant than heating by the burner.

2. The method for firing ceramics according to claim 1, wherein the gas firing is performed only when the temperature inside the firing furnace is below the heater heating dominant temperature.

3. The method for firing ceramics according to either claim 1 or claim 2, wherein the heater is a high-temperature heater.

4. The method for firing ceramics according to claim 3, wherein molybdenum disilicide is used in the heater.

5. The method for firing ceramics according to claim 2, wherein the amount of energy per unit time of the gas when the temperature inside the firing furnace is above the heater heating dominant temperature is less than the amount of energy per unit time of the gas when the temperature inside the firing furnace is below the heater heating dominant temperature.

6. The method for firing ceramics according to claim 2, wherein, when the temperature inside the firing furnace is above the heater heating dominant temperature, the total amount of energy per unit time when the gas firing and the electric firing are performed simultaneously is less than the total amount of energy per unit time when only the gas firing is performed.

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