Clay calcination color control method

Abstract

The present disclosure provides a clay calcination color control method. First a first fuel inlet is used to introduce a natural gas fuel for combustion, to provide all the heat for ignition of the kiln; then a second fuel inlet and a third fuel inlet are used to introduce a traditional fossil fuel and an RDF fuel for combustion, respectively to provide calcination heat to a rotary kiln; a high-temperature flue gas at the kiln tail generated during calcination is cooled to become a low-temperature mixed gas with a temperature of 70-80 degrees Celsius, and the low-temperature mixed gas circulates into a cooler; when high-temperature kiln material enters the cooler, it exchanges heat with the low-temperature mixed gas circulating into the cooler, and is simultaneously sprayed with water by a water spray apparatus; carbonaceous dust, the low-temperature mixed gas and the sprayed water undergo a Boudouard reaction and a water-gas reaction to produce more reducing gas, and go to the kiln head, a combustion chamber and a main burner of the rotary kiln, respectively, to ensure that the calcination atmosphere in the rotary kiln is a reducing atmosphere. According to the method provided in the present disclosure, it can be ensured that the color of a material after calcination is gray.

Description

Method for controlling color of calcined clay

[0001] Related applications

[0002] This disclosure claims priority to a Chinese patent application filed with the Patent Office of China on July 28, 2023, with application number CN202310941753.1 and invention name “Clay Calcination Color Control Method,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the technical field of clay calcination, and in particular to a method for controlling the color of clay calcination. Background Art

[0004] Statistics show that the cement industry accounts for approximately 7% of global carbon emissions, and my country's cement industry accounts for approximately 13% of total societal carbon emissions. A large portion of my country's cement production is Portland cement. Currently, aluminosilicate minerals are becoming mainstream as a replacement for traditional Portland cement clinker to achieve lower carbon emissions. Since aluminosilicate minerals are the primary component of clay, calcining clay has become a viable method for obtaining aluminosilicate minerals. The rotary kiln is currently the most commonly used calcining device in industry.

[0005] In the process of implementing the present disclosure, the inventors discovered that the prior art has at least the following problems:

[0006] During the calcined clay production process, if the iron oxide content exceeds 5% by weight, the resulting calcined clay product will appear brownish-red, which, when mixed with cement clinker, will affect the color of LC3 cement. Furthermore, in the art, calcined flue gas or exhaust gas is currently treated with simple methods such as filtration and adsorption before being released into the atmosphere. While this reduces pollution levels, it also results in a certain degree of resource waste.

[0007] Therefore, a method for controlling the color of calcined clay is needed to at least partially solve the above technical problems.

[0008] Summary of the Invention

[0009] The embodiments of the present disclosure provide a method for controlling the color of clay calcined, which can ensure that the color of the material after calcination is gray.

[0010] The present disclosure provides a method for controlling the color of clay calcined, comprising a clay calcining system, the system comprising a rotary kiln, a flue gas treatment device, a cooler, and a water spray device; the kiln tail of the rotary kiln is provided with a raw material inlet and a first flue gas outlet, the raw material inlet is used to introduce raw materials to be calcined, and the first flue gas outlet is used to discharge high-temperature flue gas generated during calcination;

[0011] The kiln head of the rotary kiln is connected to the combustion chamber, which is equipped with a main burner. The main burner has a first fuel inlet for introducing natural gas fuel and a first air inlet for introducing air. The combustion chamber also has a second fuel inlet for introducing traditional fossil fuels, a third fuel inlet for introducing RDF fuel, and a second air inlet for introducing air. Refuse-derived fuel (RDF) is a fuel made by crushing, sorting, drying, adding reagents, and compression molding combustible waste. RDF fuel has the characteristics of high calorific value and stable combustion.

[0012] The flue gas treatment device is used to cool the high-temperature flue gas discharged through the first flue gas outlet, and the low-temperature flue gas formed after the treatment is connected to the cooler through a circulation pipeline; and

[0013] The inlet end of the cooler has a kiln material inlet and a second flue gas outlet; the kiln material inlet is connected to the unloading point of the kiln head of the rotary kiln through a connecting pipe, and is used to introduce high-temperature kiln materials and unburned or burned carbonaceous dust of RDF fuel after calcination in the rotary kiln; the second flue gas outlet is connected to the kiln head of the rotary kiln, the first air inlet and the second air inlet through pipes, respectively, and is used to discharge the reducing gas generated when the carbonaceous dust contacts the low-temperature flue gas, and the low-temperature flue gas after heat exchange;

[0014] A water spraying device provided in the cooler is used to spray water to cool the high-temperature kiln material;

[0015] The method comprises the following steps:

[0016] First, natural gas fuel is introduced through the first fuel inlet for combustion to provide all the heat for ignition and kiln start-up. After the kiln starts, the introduction of natural gas is stopped. Then, traditional fossil fuel and RDF fuel are introduced through the second and third fuel inlets respectively for combustion to provide calcination heat to the rotary kiln, of which RDF fuel provides 50%-90% of the heat.

[0017] When the raw materials to be calcined are dehydrated and decomposed in the rotary kiln, the high-temperature flue gas at the kiln tail is cooled and turned into a low-temperature mixed gas with a temperature of 70-80 degrees Celsius. The low-temperature mixed gas circulates into the cooler;

[0018] When the high-temperature discharge material from the rotary kiln enters the cooler after calcination, it undergoes heat exchange with the low-temperature mixed gas circulating in the cooler. Simultaneously, it is sprayed with water by the water spray device in the cooler, rapidly cooling it to below 300 degrees Celsius to ensure that the high-temperature discharge material remains gray and avoids discoloration. During this process, unburned or burned carbonaceous dust from the RDF fuel enters the cooler along with the high-temperature discharge material through the discharge point at the kiln head. There, it undergoes Boudall reaction and water-gas reaction with the low-temperature mixed gas and the sprayed water, producing a large amount of reducing gas.

[0019] Part of the low-temperature mixed gas after heat exchange and the generated reducing gas enters the kiln head of the rotary kiln, and the other part goes to the combustion chamber and main burner connected to the kiln head of the rotary kiln to ensure that the calcining atmosphere in the rotary kiln is a reducing atmosphere.

[0020] According to the method disclosed in the present invention, the high-temperature flue gas (with very low oxygen content, mainly CO and CO2) generated during calcination in the rotary kiln is treated by the flue gas treatment device and becomes low-temperature flue gas (or waste gas) with a low temperature (generally at 70-80 degrees Celsius). The low-temperature flue gas inherits the characteristics of the high-temperature flue gas with very low oxygen content and a certain amount of CO and CO2. After entering the cooler, on the one hand, it acts as cooling air to exchange heat with the high-temperature kiln material (about 600 degrees Celsius) to reduce the temperature of the high-temperature kiln material for use in subsequent processes. On the other hand, the low-temperature flue gas The CO2 in the gas reacts with the unreacted carbon in the unburned or burned carbonaceous dust of the RDF fuel mixed with the high-temperature kiln material in a high-temperature state to produce more reducing gas CO; after the above heat exchange, the low-temperature flue gas has a larger amount of reducing gas CO, and the temperature of the low-temperature flue gas increases (about 200 degrees Celsius). The low-temperature flue gas after heat exchange is divided into two parts, one part enters the rotary kiln, and the other part goes to the combustion chamber and the main burner, ensuring that the calcination atmosphere in the rotary kiln is a reducing atmosphere, thereby ensuring that the color of the calcined material is gray. At the same time, the system disclosed in the present invention allows the high-temperature flue gas generated during calcination in the rotary kiln to be recycled, reducing carbon emissions. In addition, since the low-temperature flue gas is higher than the normal temperature air temperature (about 200 degrees Celsius), fuel consumption can be reduced.

[0021] At the same time, when the rotary kiln is ignited, natural gas fuel is first introduced through the first fuel inlet for combustion to provide all the heat for ignition and kiln start-up. After the kiln is started, the introduction of natural gas is stopped. Then, traditional fossil fuels and RDF fuels are introduced through the second and third fuel inlets respectively for combustion to provide calcination heat to the rotary kiln, of which RDF fuel provides 50%-90% of the heat (a large proportion). The advantages of this design are: 1. RDF fuel is cheaper than natural gas, which greatly reduces costs; 2. After ignition and kiln start-up, RDF fuel is mainly used, which effectively reduces the use of traditional fossil fuels and further achieves the effect of energy conservation and emission reduction; 3. After the rotary kiln is ignited, RDF fuel is used as the main heat source. The ash (i.e., carbonaceous dust) after the combustion of RDF fuel enters the kiln discharge point and mixes with the high-temperature kiln discharge material after calcination, which can also provide a carbon source for the Boudor reaction occurring in the cooler.

[0022] Optionally, the flue gas treatment device includes at least one of the following:

[0023] A cyclone separator, used to separate the high-temperature flue gas into materials and waste gas;

[0024] a desulfurization tower, used for desulfurizing the high-temperature flue gas;

[0025] A dust collector, used for removing dust from the high-temperature flue gas;

[0026] The RTO device is used to eliminate volatile organic compounds in the high-temperature flue gas.

[0027] Optionally, the flue gas treatment device includes the cyclone separator, the desulfurization tower, the dust collector and the RTO device (i.e., a regenerative thermal incinerator) connected in sequence:

[0028] The material separated by the cyclone separator also enters the rotary kiln again through the raw material inlet, and / or the material obtained after dust removal by the dust collector also enters the rotary kiln again through the raw material inlet.

[0029] Optionally, the water spraying device includes:

[0030] A first water spraying device located at the inlet end of the cooler is used to quickly cool the high-temperature kiln material;

[0031] The second water spraying device located at the outlet end of the cooler is used for linkage control with the first water spraying device to control the temperature of the high-temperature kiln material passing through the outlet end of the cooler to be below a preset threshold.

[0032] In the present embodiment, the water spray device (comprising the first and second water spray devices) cools the high-temperature kiln discharge material by the water spray mode, further enhancing the high-temperature kiln discharge material cooling effect.Except being able to cool the high-temperature kiln discharge material, part of the water becomes water vapor when contacting with the high-temperature kiln discharge material, and the water vapor and the unburned or burned carbonaceous dust containing unreacted carbon in the RDF fuel of the high-temperature kiln discharge material mixed in the high-temperature state produce water gas reaction, generating reducing gases CO and H2, this part of the reducing gases CO and H2 generated enters the rotary kiln together with the low-temperature flue gas after heat exchange, goes to the combustion chamber and the main burner, further ensuring that the calcining atmosphere in the rotary kiln is a reducing atmosphere, and more ensuring that the color of the material after calcination is gray.The first water spray device at the inlet end of the cooler is used to quickly cool the high-temperature kiln discharge material entering the cooler (from about 600 degrees Celsius to below 300 degrees Celsius), which can avoid the discoloration of the material (high-temperature kiln discharge material) after calcination. The second water spray device at the outlet of the cooler is used to control in conjunction with the first water spray device to control the temperature of the high-temperature kiln material passing through the outlet of the cooler to be below a preset threshold (e.g., 80-150 degrees Celsius) to meet the needs of subsequent processes. The first water spray device or the second water spray device itself can have a control device or an externally coupled control device, as well as a temperature sensor that can monitor the temperature of the high-temperature kiln material passing through the outlet of the cooler in real time. The control device adjusts the water spray flow rate of the first water spray device or the second water spray device based on the comparison result of the temperature value monitored by the temperature sensor and the preset threshold. When the temperature value monitored by the temperature sensor is greater than the preset threshold, the water spray flow rate of the first water spray device or the second water spray device is increased; when the temperature value monitored by the temperature sensor is less than the preset threshold, the water spray flow rate of the second water spray device is reduced. The above-mentioned control process is a common existing control technology and does not involve changes to the internal program. It is based on the functions set by the control device itself.

[0033] Optionally, the flue gas treated by the flue gas treatment device is also connected to the chimney through an exhaust pipe.

[0034] Optionally, an auxiliary burner is further provided at the kiln head of the rotary kiln near the material discharge point to further consume the oxygen entering the rotary kiln.

[0035] By utilizing the technical solution according to the embodiments of the present disclosure, the beneficial effects that can be obtained are at least:

[0036] 1. The high-temperature flue gas generated during calcination in the rotary kiln is treated by the flue gas treatment device and then used again to cool the high-temperature materials discharged from the kiln. On the one hand, it acts as cooling air to reduce the temperature of the high-temperature materials discharged from the kiln. On the other hand, the treated low-temperature flue gas reacts with the unburned RDF fuel or the unreacted carbon in the burned carbonaceous dust mixed with the high-temperature materials discharged from the kiln in a high-temperature state to generate more reducing gas CO, which enters the rotary kiln, combustion chamber and main burner to ensure that the calcination atmosphere in the rotary kiln is a reducing atmosphere, thereby ensuring that the color of the calcined material is gray. In addition, since the low-temperature flue gas is higher than the normal temperature air temperature (about 200 degrees Celsius), it can reduce fuel consumption.

[0037] 2. The inner cavity of the cooler is connected to a water spray device for spraying water to cool the high-temperature materials discharged from the kiln, further enhancing the cooling effect of the high-temperature materials discharged from the kiln. In addition, part of the water in the cooler turns into water vapor when it comes into contact with the high-temperature materials discharged from the kiln. The water vapor reacts with the unburned RDF fuel or the unreacted carbon in the burned carbonaceous dust mixed with the high-temperature materials discharged from the kiln in a high-temperature state to produce water gas, generating reducing gases CO and H2, which then enter the rotary kiln, combustion chamber and main burner, further ensuring that the calcining atmosphere in the rotary kiln is a reducing atmosphere and that the color of the calcined materials is gray.

[0038] Additional advantages, objects, and features of the present disclosure will be described in part in the following description and will become apparent to those skilled in the art upon study of the following or may be learned from practice of the present disclosure. The objects and other advantages of the present disclosure may be achieved and obtained by the structures specifically pointed out in the description and drawings.

[0039] Those skilled in the art will understand that the purposes and advantages that can be achieved by the present disclosure are not limited to the above specific descriptions, and the above and other purposes that can be achieved by the present disclosure will be more clearly understood from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described herein are intended to provide a further understanding of the present disclosure, constitute a part of the present disclosure, and do not constitute a limitation of the present disclosure. The components in the drawings are not drawn to scale, but are only for the purpose of illustrating the principles of the present disclosure. To facilitate the illustration and description of some parts of the present disclosure, the corresponding parts in the drawings may be enlarged, that is, they may be larger than other parts in the exemplary devices actually manufactured according to the present disclosure. In the drawings:

[0041] FIG1 is a flow chart of a method for controlling the color of clay calcined according to an embodiment of the present disclosure; and

[0042] FIG2 is a schematic diagram of a clay calcining system in a method for controlling color of clay calcined according to an embodiment of the present disclosure.

[0043] Explanation of Reference Numerals: 100: system; 110: rotary kiln; 111: raw material inlet; 112: first flue gas outlet; 113: combustion chamber; 114: main burner; 115: first fuel inlet; 116a: first air inlet;

[0044] 116b: second air inlet;

[0045] 117: unloading point;

[0046] 118: auxiliary burner;

[0047] 119a: Second fuel inlet;

[0048] 119b: third fuel inlet;

[0049] 121: Cyclone separator;

[0050] 122: Desulfurization tower;

[0051] 123: dust collector;

[0052] 124: RTO device;

[0053] 130: cooler;

[0054] 131: kiln material entrance;

[0055] 132: Second smoke outlet;

[0056] 141: Circulation pipeline;

[0057] 142: Connecting pipes;

[0058] 143: Exhaust pipe;

[0059] 144: Chimney;

[0060] 151: first water spray device;

[0061] 152: The second water spray device. DETAILED DESCRIPTION

[0062] The purposes and functions of the present disclosure, as well as methods for achieving these purposes and functions, will be clarified by reference to exemplary embodiments. However, the present disclosure is not limited to the exemplary embodiments disclosed below; it can be implemented in various forms. The essence of the description is merely to help those skilled in the relevant art to comprehensively understand the specific details of the present disclosure.

[0063] It should be noted that the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0064] Ordinal numbers such as “first” and “second” cited in the present disclosure are merely identifiers and do not have any other meanings, such as a specific order, etc. Moreover, for example, the term “first component” itself does not imply the existence of a “second component”, and the term “second component” itself does not imply the existence of a “first component”.

[0065] It should be noted that the terms "upper", "lower", "front", "back", "left", "right", "inside", "outside" and similar expressions used in this document are for illustrative purposes only and are not limiting.

[0066] The present disclosure provides a method for controlling the color of clay calcined. The method can be applied, for example, to the field of clay calcination technology, such as calcining clay so that the color of the calcined material is gray. First, a rotary kiln refers to a rotary calcining kiln (commonly known as a rotary kiln), which is similar in appearance to a rotary bed and is also called a rotary bed kiln. It belongs to the category of building materials equipment. Rotary kilns can be divided into cement kilns, metallurgical chemical kilns, and lime kilns according to the materials they process. Cement kilns are mainly used to calcine cement clinker and are divided into two categories: dry process cement kilns and wet process cement kilns. Metallurgical chemical kilns are mainly used in the metallurgical industry for magnetization roasting of lean iron ore in steel mills; oxidation roasting of chromium and nickel iron ore; roasting of high-aluminum bauxite in refractory plants and roasting of clinker and aluminum hydroxide in aluminum plants; and roasting of chromium ore sand and chromium ore powder in chemical plants. Lime kilns (i.e., active lime kilns) are used to roast active lime and light-burned dolomite for steel mills and ferroalloy plants. The rotary kiln 110 in this embodiment generally refers to a cement kiln.

[0067] Referring to FIG1 , the method includes the following specific steps:

[0068] First, natural gas fuel is introduced through the first fuel inlet for combustion to provide all the heat for ignition and kiln start-up. After the kiln is started, the introduction of natural gas is stopped. Then, traditional fossil fuel and RDF fuel are introduced through the second and third fuel inlets respectively for combustion to provide calcination heat to the rotary kiln, among which RDF fuel provides 50%-90% of the heat.

[0069] When the raw materials to be calcined are dehydrated and decomposed in the rotary kiln, the high-temperature flue gas at the kiln tail is cooled and turned into a low-temperature mixed gas with a temperature of 70-80 degrees Celsius. The low-temperature mixed gas circulates into the cooler.

[0070] When the high-temperature material discharged from the rotary kiln after calcination enters the cooler, it undergoes heat exchange with the low-temperature mixed gas circulating into the cooler, and is simultaneously sprayed with water by the water spray device in the cooler, rapidly cooling the temperature to below 300 degrees Celsius to ensure that the high-temperature material discharged from the kiln remains gray and avoids discoloration. During this process, unburned or burned carbonaceous dust from the RDF fuel enters the cooler along with the high-temperature material discharged from the kiln through the discharge point at the kiln head, and undergoes Boudol reaction and water-gas reaction with the low-temperature mixed gas and sprayed water, producing a larger amount of reducing gas.

[0071] Part of the low-temperature mixed gas after heat exchange and the generated reducing gas enters the kiln head of the rotary kiln, and the other part goes to the combustion chamber and main burner connected to the kiln head of the rotary kiln to ensure that the calcining atmosphere in the rotary kiln is a reducing atmosphere.

[0072] Among them, the clay calcination color control method provided by the present disclosure includes a clay calcination system 100. In a preferred embodiment, as shown in Figure 2, the clay calcination system 100 includes a rotary kiln 110, a flue gas treatment device and a cooler 130. The rotary kiln 110 is mainly used to calcine cement clinker (clay). The flue gas treatment device is used to treat the high-temperature flue gas generated by clay calcination to cool it down, and also includes but is not limited to material recovery, desulfurization and / or dust removal. The cooler 130 is used to cool the high-temperature kiln discharge material generated by calcination and provide reducing gas to the rotary kiln 110.

[0073] Specifically, referring to Figure 2 , in the illustrated embodiment, the rotary kiln 110 has a raw material inlet 111 and a first flue gas outlet 112 at the kiln tail. The raw material inlet 111 is used to introduce raw materials to be calcined. For example, the raw materials can be delivered into the rotary kiln 110 through a pipeline or conveyor. The first flue gas outlet 112 is used to discharge the high-temperature flue gas generated during calcination. For example, the high-temperature flue gas can be discharged through a pipeline. The kiln head of the rotary kiln 110 is connected to a combustion chamber 113. The combustion chamber 113 is equipped with a main burner 114, which preheats the gas entering the rotary kiln 110 through combustion, provides the heat required for calcined clay production, and provides reducing gas. The main burner 114 has a first fuel inlet 115 for natural gas fuel and a first air inlet 116a for air. The combustion chamber 113 has a second air inlet 116b for air, a second fuel inlet 119a for traditional fossil fuels, and a third fuel inlet 119b for RDF fuel. External air is supplied to the main burner 114 and the combustion chamber 113 through the first air inlet 116a and the second air inlet 116b respectively to provide oxygen to assist combustion.

[0074] Among them, the present invention is provided with a first fuel inlet 115, a second fuel inlet 119a and a third fuel inlet 119b, etc. When the rotary kiln is ignited, the first fuel inlet is used to introduce natural gas fuel for combustion to provide all the heat for ignition and kiln. After the kiln is started, the introduction of natural gas is stopped, and then the second fuel inlet and the third fuel inlet are used to introduce traditional fossil fuels and RDF fuel for combustion to provide calcination heat to the rotary kiln, wherein RDF fuel provides 50%-90% of the heat (accounting for a large proportion). The advantages of this design are: 1. RDF fuel is cheaper than natural gas, which greatly reduces the cost; 2. After the kiln is ignited, RDF fuel is used as the main fuel, which effectively reduces the use of traditional fossil fuels and further achieves the effect of energy conservation and emission reduction; 3. After the rotary kiln is ignited, RDF fuel is used as the main heat source. The ash after the combustion of RDF fuel (i.e., dust containing carbon) enters the kiln discharge point and mixes with the high-temperature kiln material after calcination, which can also provide a carbon source for the Boudor reaction occurring in the cooler. In addition, if one of the fuel inlets fails or the fuel cannot be used, other fuel inlets can be used to continue combustion, achieving the purpose of multiple protection.

[0075] The flue gas treatment device is used to treat the high-temperature flue gas discharged through the first flue gas outlet 112. The high-temperature flue gas discharged from the first flue gas outlet 112 has a very low oxygen content and contains a certain amount of CO and CO2. It may also contain undecomposed raw materials and calcined materials. The flue gas treatment device can be used to treat the high-temperature flue gas generated by clay calcination, cooling it to a lower temperature, low-temperature flue gas, or to convert it into low-temperature waste gas. For example, the high-temperature flue gas can undergo treatment including but not limited to material recovery and dust removal. After treatment, it no longer contains solid impurities and is a nearly pure gas. The specific structure of the flue gas treatment device will be elaborated below.

[0076] For ease of explanation, this embodiment uses the illustrated embodiment as an example, in which the high-temperature flue gas generated by clay calcination passes through a flue gas treatment device and is converted into low-temperature exhaust gas (generally around 70-80 degrees Celsius). This is not intended to be limiting. The treated low-temperature exhaust gas is then connected to cooler 130 via circulation pipe 141. At this point, the low-temperature exhaust gas inherits the high-temperature flue gas's low oxygen content and contains a certain amount of CO and CO₂.

[0077] The cooler 130 is a long cylindrical structure with an inner cavity. The inlet end of the cooler 130 may have an inlet 131 for kiln materials and a second flue gas outlet 132 (i.e., an exhaust gas outlet). The inlet 131 for kiln materials is connected to the unloading point 117 at the kiln head of the rotary kiln 110 through a connecting pipe 142, and is used to introduce high-temperature kiln materials (about 600 degrees Celsius) calcined by the rotary kiln 110 and unburned or burned carbonaceous dust of the RDF fuel. Among them, the CO2 in the low-temperature exhaust gas reacts with the unreacted carbon in the unburned or burned carbonaceous dust of the RDF fuel of the high-temperature kiln materials in a high-temperature state to generate more reducing gas CO. Second flue gas outlet 132 is connected via pipes to the kiln head and air inlets 116a and 116b of rotary kiln 110, respectively. It is used to discharge low-temperature exhaust gas and the resulting reducing gas after heat exchange with the high-temperature exiting kiln material. This low-temperature exhaust gas, which contains a higher amount of reducing gas CO, is then fed into rotary kiln 110, combustion chamber 113, and main burner 114, respectively, ensuring a reducing atmosphere within rotary kiln 110. Preferably, to further reduce the oxygen content entering rotary kiln 110, a secondary burner 118 may be installed at the kiln head near the discharge point 117 of rotary kiln 110. According to the method disclosed herein, the high-temperature flue gas generated during calcination in the rotary kiln 110 is treated by a flue gas treatment device and becomes a low-temperature waste gas. After the low-temperature waste gas enters the cooler 130, on the one hand, it acts as cooling air to exchange heat with the high-temperature material discharged from the kiln, thereby reducing the temperature of the high-temperature material discharged from the kiln for use in subsequent processes. On the other hand, the CO2 in the low-temperature waste gas undergoes a Boudouard reaction with the unreacted carbon in the unburned or burned carbonaceous dust of the RDF fuel in a high-temperature state, generating more reducing gas CO. The low-temperature waste gas after heat exchange has a larger amount of reducing gas CO, and the temperature of the low-temperature waste gas increases (about 200 degrees Celsius). The low-temperature waste gas after heat exchange is divided into two parts, one part enters the rotary kiln 110, and the other part goes to the combustion chamber 113 and the main burner 114, ensuring that the calcination atmosphere in the rotary kiln 110 is a reducing atmosphere, thereby ensuring that the color of the calcined material is gray.

[0078] To provide a flue gas treatment device with high performance, referring to Figure 1 , the flue gas treatment device may include a cyclone separator 121, a desulfurization tower 122, a dust collector 123, and an RTO unit 124 (i.e., a regenerative thermal incinerator) connected in sequence. The cyclone separator 121 is used to separate materials from waste gases in the high-temperature flue gas. This separation separates any unburned fuel, undecomposed raw materials, and calcined materials that may be present from the flue gas. The desulfurization tower 122 is used to desulfurize the high-temperature flue gas to remove harmful components. The dust collector 123 is used to remove dust from the high-temperature flue gas. In other words, the dust collector 123 further absorbs any materials that have not been completely separated. The RTO unit 124 is used to eliminate volatile organic compounds (VOCs) from the high-temperature flue gas. Volatile organic compounds (VOCs) are any carbon compounds that participate in atmospheric photochemical reactions, excluding CO, CO2, H2CO3, metal carbides, metal carbonates, and ammonium carbonate. The main components of VOCs are hydrocarbons, halogenated hydrocarbons, oxygenated hydrocarbons, and nitrogenated hydrocarbons, including benzene series, organic chlorides, Freon series, organic ketones, amines, alcohols, ethers, esters, acids, and petroleum hydrocarbon compounds. After being treated by the above-mentioned flue gas treatment device, the high-temperature flue gas becomes a low-temperature exhaust gas that is almost pure gas.

[0079] Furthermore, in order to fully utilize the separated or absorbed materials, the materials separated by the cyclone separator 121 can be re-entered into the rotary kiln 110 for calcination through the relevant pipelines via the raw material inlet 111. Similarly, the materials obtained after dust removal by the dust collector 123 can also be re-entered into the rotary kiln 110 for calcination through the pipelines via the raw material inlet 111.

[0080] It is understood that although FIG1 shows a specific flue gas treatment device, it is not intended to be limiting. The flue gas treatment device, when achieving flue gas cooling, may include one or more of a cyclone separator 121, a desulfurization tower 122, a dust collector 123, and an RTO device 124, or other equipment that achieves the same function.

[0081] Continuing from the above, the inner cavity of the cooler 130 can also be connected to a water spray device that can spray water to cool the high-temperature kiln material. Specifically, the water spray device may include a first water spray device 151 and a second water spray device 152. The first water spray device 151 and the second water spray device 152 can be spray devices connected to a water source through a water pipe. Among them, the first water spray device 151 is located at the inlet end of the cooler 130, and is used to quickly cool the high-temperature kiln material entering the cooler 130, so as to avoid discoloration of the calcined material (high-temperature kiln material). For example, the high-temperature kiln material is reduced from about 600 degrees Celsius to below 300 degrees Celsius within a predetermined time. The second water spray device 152 is located at the outlet end of the cooler 130, and is used to control the temperature of the high-temperature kiln material passing through the outlet end of the cooler 130 to be below a preset threshold.

[0082] Specifically, first, the water spray device cools the high-temperature kiln material by spraying water, which can further enhance the cooling effect of the high-temperature kiln material, allowing it to cool down faster and below a preset threshold. More importantly, in addition to being able to cool the high-temperature kiln material, some of the water in it will turn into water vapor when it comes into contact with the high-temperature kiln material. The water vapor reacts with the unreacted carbon in the high-temperature kiln material at high temperature to produce water gas, generating reducing gases CO and H2. This portion of reducing gases CO and H2, together with the low-temperature exhaust gas after heat exchange, enter the rotary kiln 110, combustion chamber 113, and main burner 114, respectively, further ensuring that the calcination atmosphere in the rotary kiln 110 is a reducing atmosphere, and can also ensure that the color of the calcined material is gray.

[0083] In this embodiment, a second water spray device 152 at the outlet of the cooler 130 controls the temperature of the high-temperature material exiting the kiln at the outlet of the cooler 130 to be below a preset threshold to meet the requirements of subsequent processes. The preset threshold can be between 80 and 150 degrees Celsius, for example, 80 degrees Celsius, 100 degrees Celsius, or 120 degrees Celsius. To achieve temperature control, the first water spray device 151 or the second water spray device 152 can have its own control device or be coupled to an external control device, as well as a temperature sensor that can monitor the temperature of the high-temperature material exiting the kiln at the outlet of the cooler 130 in real time. The control device adjusts the water flow rate of the first water spray device 151 or the second water spray device 152 based on the result of comparing the temperature value monitored by the temperature sensor with the preset threshold. When the temperature value monitored by the temperature sensor is greater than the preset threshold, the water flow rate of the first water spray device 151 or the second water spray device 152 is increased. When the temperature value monitored by the temperature sensor is less than the preset threshold, the water flow rate of the second water spray device 152 is reduced. The above-described control process is a common existing control technology and does not involve any changes to the internal program. It is based on the functions set by the control device itself. In the present disclosure, the control device detects the monitoring value of the sensor at a certain sampling frequency (e.g., 2s, 5s, or 10s) to timely adjust the operating state of the first water spray device 151 or the second water spray device 152.

[0084] Referring to Figure 1 , waste gas treated by the flue gas treatment device can be discharged through exhaust duct 143 to chimney 144. To facilitate emission control and safe discharge, valves and gas concentration monitoring sensors can be installed on exhaust duct 143, circulation duct 141, and intermediate ducts of the flue gas treatment device. When the final waste gas meets the requirements for safe discharge, the valves are opened and discharged into the atmosphere through chimney 144.

[0085] In summary, according to the method disclosed herein, the high-temperature flue gas generated during calcination in the rotary kiln 110 is treated and then used again to cool the high-temperature material discharged from the kiln. Furthermore, more reducing gas CO is generated in the cooler 130 based on the Boudor reaction, and then enters the rotary kiln 110, the combustion chamber 113, and the main burner 114, ensuring that the calcination atmosphere in the rotary kiln 110 is a reducing atmosphere, thereby ensuring that the color of the calcined material is gray. Furthermore, the water spraying device for spraying water to cool the high-temperature material discharged from the kiln further enhances the cooling effect of the high-temperature material discharged from the kiln, while also generating reducing gases CO and H2 based on the water-gas reaction, and then entering the rotary kiln 110, the combustion chamber 113, and the main burner 114, further ensuring that the calcination atmosphere in the rotary kiln 110 is a reducing atmosphere. At the same time, since the low-temperature exhaust gas is at a higher temperature than normal temperature air, the fuel consumption in the combustion chamber 113 can be reduced.

[0086] In addition, the present disclosure treats the flue gas generated by the calcination of clay in the rotary kiln 110. In addition to being used to cool the high-temperature materials discharged from the kiln and provide a large amount of CO to the rotary kiln 110 and the combustion chamber 113, the flue gas also utilizes the characteristics of the exhaust gas having a very low oxygen content (or almost no oxygen) and a certain amount of CO and CO2. In the cooler 130, the flue gas reacts with the carbon in the high-temperature materials discharged from the kiln to generate more reducing gas CO, forming a protective gas to better cool the high-temperature materials discharged from the kiln without oxygen. Compared with the existing simple treatment such as filtration and adsorption before discharging into the atmosphere, or simple heat utilization and recovery methods, the exhaust gas is recycled and reused in multiple aspects.

[0087] Other embodiments of the present disclosure will be readily apparent to those skilled in the art from the description and practice of the present disclosure disclosed herein. The description and embodiments are intended to be exemplary only, with the true scope and spirit of the present disclosure being defined by the claims.

Claims

1. A method for controlling the color of calcined clay, characterized in that: The method comprises the following steps: First, natural gas fuel is introduced through the first fuel inlet for combustion to provide all the heat for ignition and kiln start-up. After the kiln starts up, the introduction of natural gas is stopped. Then, traditional fossil fuel and RDF fuel are introduced through the second fuel inlet and the third fuel inlet respectively for combustion to provide calcination heat for the rotary kiln, wherein RDF fuel provides 50%-90% of the heat. When the raw materials to be calcined are dehydrated and decomposed in the rotary kiln, the high-temperature flue gas at the end of the kiln is cooled and turned into a low-temperature mixed gas with a temperature of 70-80 degrees Celsius. The low-temperature mixed gas circulates into the cooler; When the high-temperature materials discharged from the rotary kiln after calcination enter the cooler, the high-temperature materials exchange heat with the low-temperature mixed gas circulating into the cooler, and are sprayed with water by the water spray device in the cooler, and the temperature is quickly reduced to below 300 degrees Celsius to ensure that the high-temperature materials discharged from the kiln are still gray and avoid discoloration; in this process, the unburned or burned carbonaceous dust of the RDF fuel enters the cooler with the high-temperature materials discharged from the kiln through the unloading point at the kiln head, and undergoes Boudol reaction and water-gas reaction with the low-temperature mixed gas and sprayed water to produce more reducing gas; Part of the low-temperature mixed gas after heat exchange and the generated reducing gas enters the kiln head of the rotary kiln, and the other part goes to the combustion chamber and main burner connected to the kiln head of the rotary kiln to ensure that the calcining atmosphere in the rotary kiln is a reducing atmosphere.

2. The method according to claim 1, characterized in that A clay calcining system is provided, wherein the system comprises a rotary kiln, a flue gas treatment device, a cooler and a water spray device; The kiln tail of the rotary kiln is provided with a raw material inlet and a first flue gas outlet, wherein the raw material inlet is used to introduce the raw material to be calcined, and the first flue gas outlet is used to discharge the high-temperature flue gas generated during calcination; The kiln head of the rotary kiln is connected to a combustion chamber, the combustion chamber is provided with a main burner, the main burner has a first fuel inlet for introducing natural gas fuel and a first air inlet for introducing air; the combustion chamber has a second fuel inlet for introducing traditional fossil fuel, a third fuel inlet for introducing RDF fuel and a second air inlet for introducing air; The flue gas treatment device is used to cool the high-temperature flue gas discharged through the first flue gas outlet, and the low-temperature flue gas formed after the treatment is connected to the cooler through a circulation pipeline; as well as The inlet end of the cooler has a kiln material inlet and a second smoke outlet; the kiln material inlet is connected to the unloading point of the kiln head of the rotary kiln through a connecting pipe, and is used to introduce high-temperature kiln materials calcined by the rotary kiln. The second flue gas outlet is connected to the kiln head of the rotary kiln, the first air inlet and the second air inlet through pipelines, respectively, to guide out the reducing gas generated when the carbonaceous dust contacts the low-temperature flue gas, and the low-temperature flue gas after heat exchange; The water spraying device arranged in the cooler is used for spraying water to cool the high-temperature kiln material.

3. The method according to claim 2, characterized in that The flue gas treatment device comprises at least one of the following ： A cyclone separator, used to separate materials and waste gas from the high-temperature flue gas; A desulfurization tower, used for desulfurizing the high-temperature flue gas; A dust collector, used for removing dust from the high-temperature flue gas; The RTO device is used to eliminate volatile organic compounds in the high-temperature flue gas.

4. The method according to claim 3, characterized in that The flue gas treatment device comprises the cyclone separator, the desulfurization tower, the dust collector and the RTO device which are sequentially connected through pipelines: The material separated by the cyclone separator also enters the rotary kiln again through a pipeline connected to the raw material inlet; and / or The material obtained after the dust collector performs dust removal also enters the rotary kiln again through the pipeline connected to the raw material inlet.

5. The method according to claim 4, characterized in that The water spray device comprises: A first water spray device located at the inlet end of the cooler is used to quickly cool down the high-temperature kiln material; The second water spray device located at the outlet end of the cooler is used for linkage control with the first water spray device to control the temperature of the high-temperature kiln material passing through the outlet end of the cooler to be below a preset threshold.

6. The method according to claim 1, characterized in that The flue gas treated by the flue gas treatment device is also connected to the chimney through the exhaust pipe.

7. The method according to claim 1, characterized in that A secondary burner is also arranged at the kiln head of the rotary kiln near the material discharge point to further consume the oxygen entering the rotary kiln.

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