The present specification generally relates to firing and kilns such as to produce ceramic articles. More specifically, the present specification relates to imposed differential temperature gradients in a kiln's ware space, such as a periodic kiln, for example to control reaction rates while firing ware made of ceramic and/or ceramic-forming material.
In conventional firing cycles burners in a ware space are fired to keep the temperature of the ware space uniform, and intentional temperature gradients within the ware space are avoided. A problem associated with firing ware with conventional firing cycles is that uncontrolled temperature differentials within the kiln may form. For example, ware containing organic compounds that are removed by partial decomposition and/or oxidation during the firing cycle tend to produce large amounts of exothermic heat. Exothermic heat can produce an uncontrolled temperature differential within the kiln that can cause non-uniform firing of the ware. In addition, oxygen present in the atmosphere tends to react with the organic compounds thereby accelerating release and increasing the exothermic reaction. Large, uncontrolled temperature differentials within kiln can make it difficult to control the temperature of the ware within the kiln, and can cause the ware to fire non-uniformly and/or crack.
According to one embodiment, a method for firing ware in a periodic kiln is provided. The method comprises positioning at least one stack of ware in a ware space of the periodic kiln. The ware space comprises a plurality of temperature control zones that are oriented in a first direction, and a plurality of temperature control zones that are oriented in a second direction. The method further comprises heating the ware space in a first heating stage from an ambient temperature to a first temperature that is greater than the ambient temperature, heating the ware space in a second heating stage from the first temperature to a second temperature that is greater than the first temperature, and heating the ware space in a third heating stage from the second temperature to a top soak temperature that is greater than the second temperature. In the method at least one of the following conditions is satisfied: (i) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the first direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the first direction; and (ii) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the second direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the second direction.
In another embodiment, a method for firing ware in a down-draft periodic kiln is provided. The method comprises positioning at least one stack of ware in a ware space of the down-draft periodic kiln. In some embodiments, the ware space is defined by: a crown; a hearth opposite the crown; a first sidewall spanning between the crown and the hearth; a second sidewall opposite the first sidewall and spanning between the crown and the hearth, a front wall bounded by the first sidewall, the second sidewall, the hearth, and the crown; a back wall opposite the front wall and bounded by the first sidewall, the second sidewall, the hearth, and the crown. The ware space can comprise: a plurality of temperature control zones that are oriented in a vertical direction, and a plurality of temperature control zones that are oriented in a horizontal direction. The method further comprises heating the ware space in a first heating stage from an ambient temperature to a first temperature that is greater than the ambient temperature, heating the ware space in a second heating stage from the first temperature to a second temperature that is greater than the first temperature, and heating the ware space in a third heating stage from the second temperature to a top soak temperature that is greater than the second temperature. In the method at least one of the following conditions is satisfied: (i) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the vertical direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the vertical direction; and (ii) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the horizontal direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the horizontal direction.
Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.
Reference will now be made in detail to embodiments of systems for and methods of applying or imposing differential temperature gradients within the ware space of a periodic kiln, embodiments of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. In one embodiment, a method for firing ware in a periodic kiln is provided. The method comprises positioning at least one stack of ware in a ware space of the periodic kiln. The ware space comprises a plurality of temperature control zones that are oriented in a first direction, and a plurality of temperature control zones that are oriented in a second direction. The method further comprises heating the ware space in a first heating stage from an ambient temperature to a first temperature that is greater than the ambient temperature, heating the ware space in a second heating stage from the first temperature to a second temperature that is greater than the first temperature, and heating the ware space in a third heating stage from the second temperature to a top soak temperature that is greater than the second temperature. In the method at least one of the following conditions is satisfied: (i) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the first direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the first direction; and (ii) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the second direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the second direction. Various systems for and methods of applying or imposing differential temperature gradients within the ware space of a periodic kiln will be described herein with specific reference to the appended figures. Although the figures depict a kiln that burns fuel, an electric kiln could be used in embodiments to create the temperature gradients disclosed and described herein.
A periodic kiln according to embodiments that is configured to provide desired differential temperature gradients to be applied to or imposed within the ware space of a periodic kiln is described below in reference to
In the embodiment depicted in
In the embodiment shown in
In addition to the exhaust gas exiting the periodic kiln through the flue openings 103, other gases, such as air, nitrogen, CO2, etc. may enter the periodic kiln through ducts (not shown). The ducts may be located in any surface of the periodic kiln 100 that does not comprise the flue openings. For instance, in the embodiment shown in
In embodiments, the ware space 110 is heated by burners 120. In the embodiment depicted in
The embodiments shown in
In embodiments, control thermocouples (not shown) are positioned on the second sidewall opposite each burner 120. For example, in embodiments where there is a column of three burners 120, the thermocouples measure the temperature of the corresponding heat source 121 that extends through a fire lane 125 from the burner 120 in the first sidewall 100b to the second sidewall 100d. The amount of air and fuel and the ratio thereof that is fed to the burner 120 may be adjusted to increase or decrease the temperature of the corresponding heat source 121. Thereby, the temperature outputs of the burners 120 may be modified. In some embodiments the temperature setpoint for each burner 120 may be separately and individually controlled. For example, the temperature setpoint of burner 120a may be the same as or different from the temperature setpoint of burner 120b, and the temperature setpoint of burner 120c may be the same as or different from the temperature setpoints of burners 120a and 120b. In other embodiments, the temperature setpoints of groups of burners 120 may be controlled together. For example, the temperature setpoint of all burners 120a positioned near the top of the ware space 110 may be set to a first temperature, the temperature setpoint of all burners 120b positioned near the vertical middle of the ware space 110 may be set to a second temperature that is the same as or different from the first temperature, and the setpoint of all burners 120c nearest the hearth 100a may be set to a third temperature that is the same as or different from the first and second temperature setpoints. In embodiments, the burners are grouped in any configuration that will provide the desired control of the temperature within the ware space 110.
In some embodiments, there are no thermocouples positioned opposite the burners 120 to measure the temperature of the corresponding heat source 121. In such embodiments, the temperature of a heat source 121 may be calculated by the amount of combustion gas fed to the corresponding burner 120 or by the combustion gas to oxygen ratio fed to the corresponding burner 120. In some embodiments, the source of oxygen is air. In other embodiments, industrial grade 02 is used as the oxygen source. As such, if the temperature of a heat source is to be reduced or increased, the amount of fuel or the fuel to oxygen ratio for the corresponding burner 120 may be increased or decreased accordingly to affect the desired temperature increase or decrease of the heat source 121 corresponding to that burner. In embodiments, the fuel or oxygen to fuel ratio fed to each burner may be separately and individually controlled so that the temperature of each heat source 121 may be individually controlled. Or, in other embodiments, the amount of fuel or oxygen to fuel ratio may be controlled by groups of burners, such as the groups of burners described above, so that the temperature of heat sources generated by a group of burners is about the same.
According to embodiments, one way to regulate VOC release is to control the temperature in various temperature control zones of the ware space 110. For instance, as the firing cycle continues, the buoyancy of the heat causes the top of the ware space to have a higher temperature. This allows the VOCs to be released at the top of the ware space sooner than a target time, the VOCs are released at the middle of the ware space at the target time; the VOCs are formed at the bottom of the ware space later than a target time. By controlling the formation of the VOCs in this manner, the total formation of VOCs is the same as if all temperature control zones were at the same setpoint, but peak concentrations are reduced. Reducing peak concentrations of the VOCs reduces the need for additional volumes of dilution gas, and allows for faster heating rates.
Embodiments for regulating the temperature in temperature control zones of the ware space will be described now with reference to the embodiment depicted in
In embodiments, each temperature control zone within the ware space 110 is controlled by a row of burners that corresponds to the temperature control zone. Referring to
In embodiments, and with reference now to
In embodiments, each temperature control zone 310, 320 within the ware space 110 is controlled by columns of burners that corresponds to the temperature control zone. Referring to
In embodiments, the firing cycle for ware can be divided into two or more stages. In some embodiments, the firing cycle for ware is divided into three or more stages. In the first stage, the ware is heated from ambient temperature to a first temperature. In the second stage, the ware is heated from the first temperature to a second temperature. In the third stage, the ware is heated from the second temperature to a top soak temperature.
In embodiments, the ware is heated in first stage from ambient temperature to a first temperature that is from about 250° C. to about 700° C., such as from about 400° C. to about 650° C. In other embodiments, the first temperature is from about 575° C. to about 625° C., such as about 600° C. In the first stage, the firing cycle progresses through a temperature range in which organic material degrades and releases VOCs from the ware under the applied heat. Accordingly, in this first stage, temperature gradients may be created within the kiln space to control the release of VOCs.
Within the first stage, the ware space may be heated from ambient temperature to the first temperature in various sub-stages. For instance, in the first stage, the ware space may be heated from ambient temperature to a first sub-stage temperature that is less than the first temperature. The ware space may be held at the first sub-stage temperature for a duration of time. Subsequently, the ware space may be heated from the first sub-stage temperature to a second sub-stage temperature that is higher than the first sub-stage temperature and lower than the first temperature. The temperature of ware space may be held at the second sub-stage temperature for a duration of time. In embodiments, the first stage may comprise any number of sub-stages with or without holds and with or without change in heating rates between sub-stages.
In embodiments, the ware is heated in a second stage from the first temperature to a second temperature that is from about 600° C. to about 1000° C., such as from about 650° C. to about 950° C. In other embodiments, the second temperature is from 700° C. to about 900° C., such as from about 750° C. to about 850° C., or about 800° C. In the second stage intermediate reactions occur, such as dehydroxylation, pore former decomposition, etc.
As was the case in the first stage, in the second stage, the ware space may be heated from the first temperature to the second temperature in various sub-stages. For instance, in the second stage, the ware space may be heated from the first temperature to a first sub-stage temperature that is less than the second temperature. The ware space may be held at the first sub-stage temperature for a duration of time. Subsequently, the ware space may be heated from the first sub-stage temperature to a second sub-stage temperature that is higher than the first sub-stage temperature and lower than the second temperature. The temperature of ware space may be held at the second sub-stage temperature for a duration of time. In embodiments, the second stage may comprise any number of sub-stages. In embodiments, the ware is heated in a third stage from the second temperature to a top soak temperature that is from about 1200° C. to about 1550° C., such as from about 1250° C. to about 1400° C. In other embodiments, the top soak temperature is from about 1300° C. to about 1450° C. In the third stage, the properties of the green body are refined and the top soak temperature is tailored to the constituent raw materials and variability therein of those materials used to fabricate the ware. Properties affected may comprise ceramic phase, porosity, shrinkage and ware dimensions, or other properties.
As was the case in the first stage and second stage, in the third stage, the ware space may be heated from the second temperature to the top soak temperature in various sub-stages. For instance, in the third stage, the ware space may be heated from the second temperature to a first sub-stage temperature that is less than the top soak temperature. The ware space may be held at the first sub-stage temperature for a duration of time. Subsequently, the ware space may be heated from the first sub-stage temperature to a second sub-stage temperature that is higher than the first sub-stage temperature and lower than the top soak temperature. The temperature of ware space may be held at the second sub-stage temperature for a duration of time. In embodiments the third stage may comprise any number of sub-stages. In addition, the ware space may be held at the top soak temperature for a duration of time sufficient to impart the desired properties to the ware.
Methods for heating ware according to embodiments using the above described periodic kiln will now be described. In embodiments, the ware space is heated from an ambient temperature to a first temperature that is greater than the ambient temperature. During the heating of the ware space from the ambient temperature to the first temperature, a plurality of temperature control zones 201, 202, 203 oriented in a first direction have different setpoint temperatures, and a plurality of temperature control zones oriented in a second direction (not shown) have approximately the same setpoint temperature. In this example, the setpoint temperature anywhere within the first temperature control zone 201 will be the same and the setpoint temperature anywhere in the second temperature control zone 203 will be the same. However, the setpoint temperature in the first temperature control zone 201 may be the same or may not be the same as the temperature in the second temperature control zone 203. In embodiments, the third temperature control zone 202 may have a setpoint temperature that is the same as or different from the setpoint temperature of either the first temperature control zone 201 or the second temperature control zone 203.
In embodiments, the plurality of temperature control zones oriented in a first direction comprises three temperature control zones extending from a first wall 100b of the periodic kiln to a second wall of the periodic kiln 100d, such that a first temperature control zone is positioned next to a first wall of the periodic kiln, a second temperature control zone is positioned next to a second wall of the periodic kiln, and a third temperature control zone is positioned in the middle of the periodic kiln between the first temperature control zone and the second temperature control zone. For example, in embodiments during the heating of the ware space from ambient temperature to the first temperature, temperature control zones 201, 202, 203 oriented in a vertical direction, as shown in
In embodiments that comprise three temperature control zones when the ware space is heated from ambient temperature to a first temperature, and the third temperature control zone is positioned between the first temperature control zone and the second temperature control zone, each of the temperature control zones may have a different setpoint temperature. The setpoint temperature of the first temperature control zone may be from about 10° C. to about 50° C. greater than the setpoint temperature of the third temperature control zone, such as from about 15° C. to about 30° C. greater than the setpoint temperature of the third temperature control zone. In other embodiments, the setpoint temperature of the first temperature control zone may be from about 15° C. to about 25° C. greater than the setpoint temperature of the third temperature control zone, such as from about 17° C. to about 25° C. greater than the setpoint temperature of the third temperature control zone. In such embodiments, the setpoint temperature of the second temperature control zone may be from about 10° C. to about 50° C. less than the setpoint temperature of the third temperature control zone, such as from about 15° C. to about 30° C. less than the setpoint temperature of the third temperature control zone. In other embodiments, the setpoint temperature of the second temperature control zone may be from about 15° C. to about 25° C. less than the setpoint temperature of the third temperature control zone, such as from about 17° C. to about 20° C. less than the setpoint temperature of the third temperature control zone.
The ware space is subsequently heated from the first temperature to a second temperature that is greater than the first temperature. In some embodiments, during the heating of the ware space from the first temperature to the second temperature, the plurality of temperature control zones oriented in the first direction have different setpoint temperatures, and the plurality of temperature control zones oriented in the second direction have the same setpoint temperature. In embodiments in which the plurality of temperature control zones oriented in a first direction comprises three temperature control zones extending from one wall of the periodic kiln to a second wall of the periodic kiln, each of the three temperature control zones may have a different setpoint temperature. For example, in embodiments and with reference to
In embodiments that comprise three temperature control zones during heating the ware space from the first temperature to the second temperature, where the third temperature control zone is positioned between the first and second temperature control zones, each of the temperature control zones may have a different setpoint temperature. In such embodiments, the setpoint temperature of the first temperature control zone may be from about 10° C. to about 50° C. greater than the setpoint temperature of the third temperature control zone, such as from about 15° C. to about 30° C. greater than the setpoint temperature of the third temperature control zone. In other embodiments, the setpoint temperature of the first temperature control zone may be from about 15° C. to about 25° C. greater than the setpoint temperature of the third temperature control zone, such as from about 17° C. to about 25° C. greater than the setpoint temperature of the third temperature control zone. In such embodiments, the setpoint temperature of the second temperature control zone may be from about 10° C. to about 50° C. less than the setpoint temperature of the third temperature control zone, such as from about 15° C. to about 30° C. less than the setpoint temperature of the third temperature control zone. In other embodiments, the setpoint temperature of the second temperature control zone may be from about 15° C. to about 25° C. less than the setpoint temperature of the third temperature control zone, such as from about 17° C. to about 20° C. less than the setpoint temperature of the third temperature control zone.
In yet other embodiments, during the heating of the ware space from the first temperature to the second temperature, the plurality of temperature control zones oriented in the first direction have the same setpoint temperature and the plurality of temperature control zones oriented in the second direction also have the same setpoint temperature. For example, in embodiments and with reference to
The ware space is subsequently heated from the second temperature to a top soak temperature that is greater than the second temperature. In some embodiments, during the heating of the ware space from the second temperature to the top soak temperature, the plurality of temperature control zones oriented in the first direction have different setpoint temperatures, and the plurality of temperature control zones oriented in the second direction have approximately the same setpoint temperature. In embodiments in which the plurality of temperature control zones oriented in a first direction comprises three temperature control zones extending from one wall of the periodic kiln to a second wall of the periodic kiln, each of the three temperature control zones may have a different setpoint temperature. For example, in embodiments, during the heating of the ware space from the second temperature to the top soak temperature, temperature control zones 201, 202, 203 oriented in a vertical direction as shown in
In embodiments that comprise three temperature control zones during heating the ware space from the second temperature to the top soak temperature, where the third temperature control zone is positioned between the first and second temperature control zones, each of the temperature control zones may have a different temperature. In such embodiments, the setpoint temperature of the first temperature control zone may be from about 10° C. to about 50° C. greater than the setpoint temperature of the third temperature control zone, such as from about 15° C. to about 30° C. greater than the setpoint temperature of the third temperature control zone. In other embodiments, the setpoint temperature of the first temperature control zone may be from about 15° C. to about 25° C. greater than the setpoint temperature of the third temperature control zone, such as from about 17° C. to about 25° C. greater than the setpoint temperature of the third temperature control zone. In such embodiments, the setpoint temperature of the second temperature control zone may be from about 10° C. to about 50° C. less than the setpoint temperature of the third temperature control zone, such as from about 15° C. to about 30° C. less than the setpoint temperature of the third temperature control zone. In other embodiments, the setpoint temperature of the second temperature control zone may be from about 15° C. to about 25° C. less than the setpoint temperature of the third temperature control zone, such as from about 17° C. to about 20° C. less than the setpoint temperature of the third temperature control zone.
In still other embodiments, during the heating of the ware space from the second temperature to the top soak temperature, the plurality of temperature control zones oriented in the first direction have the same setpoint temperature and the plurality of temperature control zones oriented in the second direction have different setpoint temperatures. For example, in embodiments and with reference to
In such embodiments, the setpoint temperature of the second temperature control zone may be from about 3° C. to about 20° C. greater than the setpoint temperature of the first temperature control zone, such as from about 3° C. to about 15° C. greater than the setpoint temperature of the first temperature control zone. In other embodiments, the setpoint temperature of the second temperature control zone may be from about 3° C. to about 10° C. greater than the setpoint temperature of the first temperature control zone, such as from about 7° C. to about 10° C. greater than the setpoint temperature of the first temperature control zone.
In embodiments, the periodic kiln may be configured to supply dilution gas to each temperature control zone oriented in a first direction. In embodiments, the dilution gas may be air, nitrogen, or any other non-flammable gas. The flow rate of the dilution gas supplied to each temperature control zone may be individually varied. For example, and with reference to
In some embodiments, the VOC level is measured in some or many temperature control zones oriented in the first direction during the heating of the ware space from ambient temperature to the first temperature. For example, and with reference to
Aspects of the disclosure will now be disclosed.
According to a first aspect, a method for firing ware in a periodic kiln comprises: positioning at least one stack of ware in a ware space of the periodic kiln, wherein the ware space comprises a plurality of temperature control zones that are oriented in a first direction, and a plurality of temperature control zones that are oriented in a second direction; heating the ware space in a first heating stage from an ambient temperature to a first temperature that is greater than the ambient temperature; heating the ware space in a second heating stage from the first temperature to a second temperature that is greater than the first temperature; and heating the ware space in a third heating stage from the second temperature to a top soak temperature that is greater than the second temperature, wherein at least one of the following conditions is satisfied: (i) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the first direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the first direction; and (ii) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the second direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the second direction.
A second aspect comprises the method of the first aspect, wherein the first direction is a vertical direction and the second direction is a horizontal direction.
A third aspect comprises a method of any of the first and second aspects, wherein the plurality of temperature control zones that are oriented in the first direction comprises a first temperature control zone adjacent to a hearth of the ware space, a second temperature control zone adjacent to a crown of the ware space, and a third temperature control zone between the first temperature control zone and the second temperature control zone.
A fourth aspect comprises a method of the third aspect, wherein during the first heating stage: a setpoint temperature of the first temperature control zone is from about 10° C. to about 50° C. less than the setpoint temperature of the third temperature control zone; and a setpoint temperature of the second temperature control zone is from about 10° C. to about 50° C. greater than the setpoint temperature of the third temperature control zone.
A fifth aspect comprises a method of the third aspect, wherein during the first heating stage: a setpoint temperature of the first temperature control zone is from about 15° C. to about 30° C. less than the setpoint temperature of the third temperature control zone; and a setpoint temperature of the second temperature control zone is from about 15° C. to about 30° C. greater than the setpoint temperature of the third temperature control zone.
A sixth aspect comprises a method of any of the first to fifth aspects, wherein the plurality of temperature control zones that are oriented in a second direction comprises a first temperature control zone adjacent to a front wall of the ware space and a second temperature control zone adjacent to a back wall of the ware space.
A seventh aspect comprises a method of the sixth aspect, wherein during the third heating stage, a setpoint temperature of the second temperature control zone is from about 3° C. to about 20° C. greater than the setpoint temperature of the first temperature control zone.
An eighth aspect comprises a method of the sixth aspect, wherein during the third heating stage, a setpoint temperature of the second temperature control zone is from about 3° C. to about 15° C. greater than the setpoint temperature of the first temperature control zone.
A ninth aspect comprises a method of any of the first to eighth aspects, wherein during the second heating stage: each temperature control zone of the plurality of temperature control zones that are oriented in the first direction has a same setpoint temperature, and each temperature control zone of the plurality of temperature control zones oriented in the second direction has a same setpoint temperature.
A tenth aspect comprises a method of any of the first to ninth aspects, wherein during the second heating stage: each temperature control zone of the plurality of temperature control zones that are oriented in the first direction has a different setpoint temperature, and each temperature control zone of the plurality of temperature control zones oriented in the second direction has a same setpoint temperature.
A eleventh aspect comprises a method of any of the first to tenth aspects, wherein the first temperature is from about 250° C. to about 700° C., the second temperature is from about 600° C. to about 1000° C., and the top soak temperature is from about 1200° C. to about 1550° C.
A twelfth aspect comprises a method of any of the first to eleventh aspects, further comprising supplying a dilution gas to each of the plurality of temperature control zones that are oriented in the first direction during the first heating stage, wherein the dilution gas has a different volumetric gas flow rate at each of the plurality of temperature control zones that are oriented in the first direction.
A thirteenth aspect comprises a method of any of the twelfth aspect further comprising: measuring or calculating a VOC level in each of the plurality of temperature control zones that are oriented in the first direction during the first heating stage; supplying a largest volumetric dilution gas flow rate of the dilution gas to a temperature control zone oriented in the first direction having a highest measured or calculated VOC level; and supplying a least volumetric dilution gas flow rate to a temperature control zone oriented in the first direction having a lowest measured or calculated VOC level.
A fourteenth aspect provides a method for firing ware in a down-draft periodic kiln, the method comprising: positioning at least one stack of ware in a ware space of the down-draft periodic kiln, wherein the ware space is defined by: a crown; a hearth opposite the crown; a first sidewall spanning between the crown and the hearth; a second sidewall opposite the first sidewall and spanning between the crown and the hearth; a front wall bounded by the first sidewall, the second sidewall, the hearth, and the crown; a back wall opposite the front wall and bounded by the first sidewall, the second sidewall, the hearth, and the crown; wherein the ware space comprises a plurality of temperature control zones that are oriented in a vertical direction; and a plurality of temperature control zones that are oriented in a horizontal direction; heating the ware space in a first heating stage from an ambient temperature to a first temperature that is greater than the ambient temperature, heating the ware space in a second heating stage from the first temperature to a second temperature that is greater than the first temperature; and heating the ware space in a third heating stage from the second temperature to a top soak temperature that is greater than the second temperature, wherein at least one of the following conditions is satisfied: (i) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the vertical direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the vertical direction; and (ii) during at least one of the first heating stage, the second heating stage, and the third heating stage, one temperature control zone of the plurality of temperature control zones that are oriented in the horizontal direction has a setpoint temperature that is different from a setpoint temperature of at least one other temperature control zone of the plurality of temperature control zones that are oriented in the horizontal direction.
A fifteenth aspect comprises a method of the fourteenth aspect, wherein the first temperature is from about 250° C. to about 700° C., the second temperature is from about 600° C. to about 1000° C., and the top soak temperature is from about 1200° C. to about 1550° C.
A sixteenth aspect comprises a method of any of the fourteenth and fifteenth aspects, wherein the plurality of temperature control zones that are oriented in the vertical direction comprises a first temperature control zone adjacent to the hearth, a second temperature control zone adjacent to the crown, and a third temperature control zone between the first temperature control zone and the second temperature control zone, wherein during the first heating stage: a setpoint temperature of the first temperature control zone is from about 10° C. to about 50° C. less than the setpoint temperature of the third temperature control zone; and a setpoint temperature of the second temperature control zone is from about 10° C. to about 50° C. greater than the setpoint temperature of the third temperature control zone.
A seventeenth aspect comprises a method of any of the fourteenth to sixteenth aspects, wherein the plurality of temperature control zones that are oriented in the horizontal direction comprises a first temperature control zone adjacent to the front wall and a second temperature control zone adjacent to the back wall, wherein during the third heating stage a setpoint temperature of the second temperature control zone is from about 3° C. to about 15° C. greater than the setpoint temperature of the first temperature control zone.
An eighteenth aspect comprises a method of any of the fourteenth to sixteenth aspects, wherein during the second heating stage: each temperature control zone of the plurality of temperature control zones that are oriented in the vertical direction has a same setpoint temperature, and each temperature control zone of the plurality of temperature control zones oriented in the horizontal direction has a same setpoint temperature.
A nineteenth aspect comprises a method of any of the fourteenth to eighteenth aspects, wherein during the second heating stage: each temperature control zone of the plurality of temperature control zones that are oriented in the vertical direction has a different setpoint temperature, and each temperature control zone of the plurality of temperature control zones oriented in the horizontal direction has a same setpoint temperature.
A twentieth aspect comprises a method of any of the fourteenth to nineteenth aspects, further comprising: supplying a dilution gas flow to each of the plurality of temperature control zones that are oriented in the vertical direction during the first heating stage; and measuring or calculating a VOC level in each of the plurality of temperature control zones that are oriented in the vertical direction during the first heating stage, wherein a largest volumetric dilution gas flow rate is supplied to a temperature control zone oriented in the vertical direction having a highest measured or calculated VOC level; and a least volumetric dilution gas flow rate is supplied to a temperature control zone oriented in the vertical direction having a lowest measured or calculated VOC level.
Thus, embodiments disclosed herein may minimize or eliminate uncontrolled temperature differential and cracking within the ware. Additionally, variability in naturally occurring raw materials used for manufacturing the articles may be accommodated by using differing top soak temperatures in different areas of the kiln to ensure uniform physical properties within the fired bodies in a kiln load, if there are groups of ware or articles within the kiln space that were manufactured with different lots of raw materials or raw materials having degrees of variability, for example as may occur with naturally sourced raw materials.
It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.
This application is a Continuation of U.S. application Ser. No. 16/069749 filed on Jan. 13, 2017, which claims the benefit of International Application No. PCT/US2017/013411 filed on Jan. 13, 2017, claims the benefit of priority of U.S. Provisional Application Ser. No. 62/279,386 filed on Jan. 15, 2016, the content of which is relied upon and incorporated herein by reference in its entirety.
Number | Date | Country | |
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62279386 | Jan 2016 | US |
Number | Date | Country | |
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Parent | 16069749 | Jul 2018 | US |
Child | 17499385 | US |