Clay calcination color control method

Abstract

The present disclosure provides a clay calcination colour control method, firstly, natural gas fuel is introduced via a first fuel inlet for combustion to provide all the heat for ignition and start of a rotary kiln; and then conventional fossil fuel and RDF are introduced respectively via a second fuel inlet and a third fuel inlet for combustion to provide calcination heat to the rotary kiln; a high-temperature flue gas generated during the calcination at a kiln tail is cooled, becomes a low-temperature mixed gas with a temperature of 70-80 degrees Celsius, and circulates into a cooler; when a high-temperature material exiting from the kiln calcined in the rotary kiln enters the cooler, it exchanges heat with the low-temperature mixed gas circulating into the cooler, and is sprayed with water by a water spraying device in the cooler; a carbonaceous dust has a Boudouard reaction and a water-gas reaction with the low-temperature mixed gas and sprayed water, to produce larger amount of reducing gases partly, and separately going into the kiln head of the rotary kiln, a combustion chamber and a main burner, so as to ensure that calcination atmosphere in the rotary kiln is a reducing atmosphere. According to the method provided in this disclosure, it can be ensured that the colour of the calcined material is gray.

Description

CROSS-REFERENCE TO RELATED DISCLOSURES

[0001] The present disclosure claims priority to the Chinese Patent Disclosure CN202310941753.1, filed with the China National Intellectual Property Administration on July 28, 2023 and entitled "Caly Calcination Colour Control Method", the entire content of which is incorporated herein by reference .TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of clay calcination, and specifically relates to a clay calcination colour control method.BACKGROUND

[0003] According to statistics, carbon emissions from the cement industry account for about 7% of global carbon emissions, while in China carbon emissions from the cement industry account for about 13% of the whole carbon emissions of the society. Among the cement produced in China, a large part of it is silicate cement. At present, aluminosilicate minerals have gradually become the mainstream alternative to traditional silicate cement clinker to achieve low-carbon emissions, and aluminosilicate minerals is the main component of clay, and thus calcining clay is a feasible way of obtaining aluminosilicate minerals. Currently, rotary kilns are the most commonly used calcining equipment in industry.

[0004] In the course of realizing the present disclosure, the inventor found at least the following problems in the prior art: During the production process of calcined clay, if the iron oxide contained in the components exceeds 5%wt, the produced calcined clay product will appear brownish-red in colour, which will affect the colour of LC3 cement when mixed with cement clinker. In addition, in this technical field, for the flue gas or waste gas generated from calcination, they are currently discharged into the atmosphere after simple treatment such as filtration and adsorption, although this reduces the degree of pollution, there is also a waste of resources to a certain extent .

[0005] Therefore, there is a need for a clay calcination colour control method to at least partially solve the above technical problems.SUMMARY

[0006] Embodiments of the present disclosure provide a clay calcination colour control method, which could ensure that the colour of the calcined material is gray.

[0007] The present disclosure provides a clay calcination colour control method, a clay calcination system is included, said clay calcination system comprises a rotary kiln, a flue gas treatment device, a cooler and a water spraying device; said kiln tail of the rotary kiln has a raw material inlet and a first flue gas outlet, said raw material inlet is configured to introduce a raw materials to be calcined, and said first flue gas outlet is configured to discharge a high-temperature flue gases generated during calcination; said kiln head of the rotary kiln is in communication with a combustion chamber, said combustion chamber is provided with a main burner, said main burner has a first fuel inlet for introducing natural gas fuel and a first air inlet for introducing air; said combustion chamber has a second fuel inlet for introducing traditional fossil fuel, a third fuel inlet for introducing RDF, and a second air inlet for introducing air; wherein the Refuse Derived Fuel (RDF for short) is a fuel made by crushing, sorting, drying, adding agents, compression moulding and other treatments of combustible waste. The RDF has the characteristics of high calorific value and stable combustion; said flue gas treatment device is configured to perform a cooling treatment on said high-temperature flue gas discharged from the first flue gas outlet, and a low-temperature flue gas is obtained after the colling treatment and is channeled to said cooler through a recycling pipeline; and said inlet end of the cooler has a inlet for material exiting from the kiln and a second flue gas outlet; said inlet for material exiting from the kiln is in communication with an unloading point at the kiln head of said rotary kiln through a connecting pipeline, so as to introduce the high-temperature material exiting from the kiln and the unburnt or burnt carbonaceous dust of the RDF which are calcined by said rotary kiln; said second flue gas outlet is respectively in communication with said kiln head of the rotary kiln, said first air inlet and said second air inlet through pipelines, so as to discharge the reducing gases generated when said carbonaceous dust comes into contact with the low-temperature flue gases, and the low-temperature flue gases after heat exchange; the water spraying device provided in said cooler is configured to spray water to cool said high-temperature material exiting from the kiln; wherein the method comprises the following steps: firstly, natural gas fuel is introduced by means of a first fuel inlet for combustion to provide all the heat for ignition and start of a rotary kiln; after the rotary kiln is started, the introduction of natural gas is stopped, and then conventional fossil fuel and RDF are introduced respectively by means of a second fuel inlet and a third fuel inlet for combustion to provide calcination heat to the rotary kiln, where the RDF provides 50%-90% of the heat; when a raw materials to be calcined are dehydrated and decomposed in the rotary kiln, a high-temperature flue gas at a kiln tail becomes a low-temperature mixed gas with a temperature of 70-80 degrees Celsius after being treated by a cooling process, and the low-temperature mixed gas circulates into a cooler; when a high-temperature material exiting from the kiln calcined in the rotary kiln enters the cooler, the high-temperature material exiting from the kiln exchanges heat with the low-temperature mixed gas circulating into the cooler, and is sprayed with water by a water spraying device in the cooler, rapidly cooled to below 300 degrees Celsius, to ensure that the high-temperature material exiting from the kiln is still gray and avoid colour change; in this process, a carbonaceous dust that is not burnt out or burnt out of the RDF enters the cooler through a unloading point of a kiln head along with the high-temperature material exiting from the kiln, and has a Boudouard reaction and a water-gas reaction with the low-temperature mixed gas and sprayed water, to produce larger amount of reducing gases; the low-temperature mixed gas after heat exchange and the generated reducing gas together partly go into the kiln head of the rotary kiln, and the other part of them goes to a combustion chamber and a main burner, both of which being in communication with the kiln head of the rotary kiln, so as to ensure that calcination atmosphere in the rotary kiln is a reducing atmosphere.

[0008] According to the method of the present disclosure, the high-temperature flue gas (the oxygen content is very low, mainly CO and CO 2 ) generated during the calcination in the rotary kiln is treated by the flue gas treatment device and become a low-temperature flue gas (or exhaust gas) with a low temperature (typically 70-80 degrees Celsius), wherein the low-temperature flue gas inherits the characteristics of the high-temperature flue gas with a very low oxygen content and a certain amount of CO and CO 2 , after entering the cooler 130, the low-temperature exhaust gas serves as cooling air on the one hand and exchanges heat with the high-temperature material exiting from the kiln to reduce the temperature of the high-temperature material exiting from the kiln for subsequent use in the process, and on the other hand, the CO 2 in the low-temperature flue gas has Boudouard reaction with unreacted carbon in the high-temperature unburnt or burnt carbonaceous dust of RDF to generate more reducing gas CO; and after the heat exchange, the low-temperature exhaust gas has a larger amount of reducing gas, and the temperature of the low-temperature exhaust gas increases (about 200 degrees Celsius); the low-temperature exhaust gas after heat exchange is divided into two parts, one part enters the rotary kiln, and the other part advances to the combustion chamber and the main burner, thereby ensuring that the calcination atmosphere in the rotary kiln is a reducing atmosphere and that the color of the calcined material is gray. At the same time, the system of the present disclosure enables the high-temperature flue gas generated during calcination in the rotary kiln to be recycled, reducing carbon emissions. In addition, due to the higher temperature of the low temperature flue gas compared to ambient air (about 200 degrees Celsius), fuel consumption can be reduced.

[0009] At the same time, when a rotary kiln is ignited and started, firstly, natural gas fuel is introduced by means of a first fuel inlet for combustion to provide all the heat for ignition and start of a rotary kiln; after the rotary kiln is started, the introduction of natural gas is stopped, and then conventional fossil fuel and RDF are introduced respectively by means of a second fuel inlet and a third fuel inlet for combustion to provide calcination heat to the rotary kiln, where the RDF provides 50%-90% (a large proportion) of the heat. The advantages of this design are as follows: 1. The RDF is cheaper than natural gas, which greatly reduces the cost; 2. after ignition, RDF is used as the main fuel, which effectively reduces the use of conventional fossil fuel and further achieves the effect of energy conservation and emission reduction; 3. after the rotary kiln is ignited and started, RDF is used as the main heat source, and ash (i.e., the carbonaceous dust) generated after the combustion of RDF enters the unloading point of the kiln and is mixed with the calcined high-temperature material exiting from the kiln to further provide a carbon source for the Boudouard reaction in the cooler.

[0010] Optionally, the flue gas treatment device comprises at least one of the following: a cyclone separator for separating materials and exhaust gases in said high-temperature flue gas; a desulphurization column for desulfurizing said high-temperature flue gas; a dust collector for removing dust from said high-temperature flue gas; an RTO device for eliminating volatile organic compounds from said high-temperature flue gas.

[0011] Optionally, the flue gas treatment device comprises the cyclone separator, the desulphurization column, the dust collector and the RTO device (i.e., regenerative thermal incinerator) which are sequentially connected in sequence: the material separated by the cyclone separator also re-enters the rotary kiln via the raw material inlet, and / or the material obtained after dust removal by the dust collector also re-enters the rotary kiln via the raw material inlet.

[0012] Optionally, the water spraying device comprises: a first water spray device located at the inlet end of the cooler for rapid cooling of the high-temperature material exiting from the kiln; a second water spray device located at the outlet end of the cooler is used for linkage control with the first water spray device, so as to control the temperature of the high-temperature material exiting from the kiln passing through the outlet end of said cooler below a preset threshold value.

[0013] In this embodiment, the water spraying devices (include the first and second water spraying device) cools the high-temperature material exiting from the kiln by spraying water, further enhancing the cooling effect of the high-temperature material exiting from the kiln. In addition to cooling the high-temperature material exiting from the kiln, some of the water becomes water vapor when in contact with the high-temperature material exiting from the kiln, and the water vapor reacts with the non-reacted carbon of the unburnt or burnt out carbonaceous dust of the RDF mixed in the high-temperature material exiting from the kiln in the high-temperature state, and generate the reducing gases CO and H 2 , and the generated part of the reducing gases CO and H 2 and the heat-exchanged low-temperature flue gas together respectively enter the rotary kiln, go to the combustion chamber and the main combustor, further ensure that the calcination atmosphere in the rotary kiln is a reducing atmosphere, and further ensure that the colour of the calcined material is gray. By means of the first water spraying device at the inlet end of the cooler, the high-temperature material exiting from the kiln entering the cooler is rapidly cooled (reduced from about 600 degrees Celsius to below 300 degrees Celsius), and colour change of the calcined material (high-temperature material exiting from the kiln) can be avoided. The second water spraying device at the outlet end of the cooler is configured to perform linkage control with the first water spraying device, and control the temperature of the high-temperature material exiting from the kiln passing through the outlet end of the cooler to be below a preset threshold (for example, 80-150 degrees Celsius) to meet the needs of subsequent process. The first water spraying device or the second water spraying device itself could have a control device or an externally coupled control device, and could also have a temperature sensor which could monitor the temperature of the high-temperature material exiting from the kiln passing through the outlet end of the cooler in real time. The control device adjusts the water flow of the first water spraying device or the second water spraying device according to a comparison result between a temperature value monitored by the temperature sensor and a preset threshold. When the temperature value monitored by the temperature sensor is greater than the preset threshold, the water flow of the first water spraying device or the second water spraying device is increased; when the temperature value monitored by the temperature sensor is less than the preset threshold, the water flow of the second water spraying device is reduced. The described adjustment process is a common existing adjustment technology and is completely based on the function set by the control device itself without involving changes in the internal program.

[0014] Optionally, the flue gas treated by the flue gas treatment device is further channeled to a chimney through an exhaust pipeline.

[0015] Optionally, an auxiliary burner is also provided in the kiln head of said rotary kiln at a position close to the unloading point,, and is configured to further consume oxygen entering the rotary kiln.

[0016] By utilizing the technical solution according to the embodiments of present disclosure, the advantages that can be obtained are at least as follows: 1. After the high-temperature flue gas generated during calcination of the rotary kiln is treated by the flue gas treatment device and then reused to cool the high-temperature material exiting from the kiln. On the one hand, the treated low-temperature flue gas serves as cooling air to reduce the temperature of the high-temperature material exiting from the kiln. On the other hand, the treated low-temperature flue gas has Boudouard reaction with unreacted carbon in the unburned or burned carbonaceous dust of RDF, mixed in the high-temperature material exiting from the kiln in a high-temperature state, to generate more reducing gas CO which then enters the rotary kiln, the combustion chamber and the main burner, thereby ensuring the calcination atmosphere in the rotary kiln is a reducing atmosphere, and ensuring that the color of the calcined material is gray. In addition, since the temperature (about 200 °C) of the low-temperature flue gas is higher than that of normal-temperature air, fuel consumption can be reduced. 2. The inner cavity of the cooler is in communication with the water spraying device for spraying water to cool the high-temperature material exiting from the kiln, thereby further enhancing the cooling effect for the high-temperature material exiting from the kiln. In addition, part of the water turns into water vapor when it contacts the high-temperature material exiting from the kiln, and the water vapor has water-gas reaction with the unreacted carbon in the unburned or burned carbonaceous dust of RDF mixed in the high-temperature material exiting from the kiln in a high-temperature state to generate reducing gases CO and H 2 which then enter the rotary kiln, the combustion chamber and the main burner, thereby further ensuring that the calcination atmosphere in the rotary kiln is a reducing atmosphere and that the color of the calcined material is gray.

[0017] Additional advantages, objectives, and features of the present disclosure will be partially described in the following description, and will become partially apparent to those of ordinary skill in the art after studying the following, or may be learned from the practice of the present disclosure. The objectives and other advantages of the present disclosure can be achieved and obtained by the structures specifically indicated in the specification and the drawings.

[0018] It will be understood by those skilled in the art that the objects and advantages that can be realized with the present disclosure are not limited to the above detailed description, and that the above and other objects that can be realized by the present disclosure will be more clearly understood from the following detailed description.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings described herein are used to provide a further understanding of the present disclosure, constitute a part of the present disclosure, and do not constitute a limitation on the present disclosure. The components in the drawings are not drawn to scale, but merely to illustrate the principles of the present disclosure. To facilitate the illustration and description of some portions of the present disclosure, the corresponding portions in the figures may be exaggerated, that is, they may become larger relative to other components in an exemplary device actually manufactured in accordance with the present disclosure. In the drawings: FIG. 1 is a flowchart of a clay calcination colour control method according to an embodiment of the present disclosure; and FIG. 2 is a schematic diagram of a clay calcination system in a clay calcination colour control method according to an embodiment of the present disclosure.

[0020] Description of the reference numbers in the Figures: 100: clay calcination 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; 116b: second air inlet; 117: unloading point; 118: auxiliary burner; 119a: second fuel inlet; 119b: third fuel inlet; 121: cyclone separator; 122: desulphurization column; 123: dust collector; 124: RTO device; 130: cooler; 131: inlet for material exiting from the kiln; 132: second flue gas outlet; 141: recycling pipeline; 142: connecting pipeline; 143: exhaust pipeline; 144: chimney; 151: first water spraying device; 152: second water spraying device. DESCRIPTION OF EMBODIMENTS

[0021] Referring to the exemplary embodiments, the objectives and functions of the present disclosure and the methods for realizing them will be clarified. However, the present disclosure is not limited to the exemplary embodiments disclosed hereinafter; it could be implemented in different forms. The essence of the specification is merely to help those skilled in the art to comprehensively understand the specific details of the present disclosure.

[0022] It should be noted that the terms used herein are only intended to describe specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, the singular form is also intended to include the condition of plural form unless the context clearly indicates otherwise. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, wholes, steps, operations, elements and / or components, but do not exclude the presence of, or the addition of, one or more other features, wholes, steps, operations, elements, components, assemblies and / or combinations thereof.

[0023] Ordinal words such as "first" and "second" used in this disclosure are merely identifiers and do not have any other meaning, such as not implying a particular order. Moreover, for example, the term "first component" does not by itself imply the existence of a "second component", and the term "second component" does not by itself imply the existence of a "first component".

[0024] It should be noted that, the expressions "left", "right", "inside", "outside" and similar expressions are used herein for illustrative purposes only and are not for any limitation.

[0025] The present disclosure provides a clay calcination colour control method. The method herein for example can be applied to the technical field of clay calcination, and for example to clay calcination such that the colour of the calcined material is gray. First of all, a rotary kiln refers to a rotary calcination kiln (commonly known as revolving kiln), which is similar to the shape of rotary bed, also called a rotary bed kiln, and belongs to the category of building material device. Rotary kilns can be classified as cement kilns, metallurgical and chemical kilns, and lime kilns according to the materials they treat. The cement kilns are mainly used for calcining cement clinker and are divided into two categories: dry cement kilns and wet cement kilns. The metallurgical and chemical kilns are mainly used for: magnetization roasting of lean iron ores in steel plants in the metallurgical industry; oxidation roasting of chromium and nickel iron ores; roasting of high-aluminum vanadium ores in refractory materials plants and roasting of clinker and aluminum hydroxide in aluminum plants; and roasting of chromium ore sand and chromium ore powder and other minerals in chemical plants. The lime kilns (i.e., active lime kilns) are used for roasting active lime and light-burnt dolomite for steel plants and ferroalloy plants. The rotary kiln 110 in this embodiment generally refers to a cement kiln.

[0026] Reference to Fig. 1, the mentioned method specifically comprises the following steps: Firstly, natural gas fuel is introduced by means of a first fuel inlet for combustion to provide all the heat for ignition and start of a rotary kiln. After the rotary kiln is started, the introduction of natural gas is stopped, and then conventional fossil fuel and RDF are introduced respectively by means of a second fuel inlet and a third fuel inlet for combustion to provide calcination heat to the rotary kiln, where the RDF provides 50%-90% of the heat.

[0027] When a raw materials to be calcined are dehydrated and decomposed in the rotary kiln, high-temperature flue gas at a kiln tail becomes a low-temperature mixed gas with a temperature of 70-80 degrees Celsius after being treated by a cooling process, and the low-temperature mixed gas circulates into a cooler.

[0028] When a high-temperature material exiting from the kiln calcined in the rotary kiln enters the cooler, the high-temperature material exiting from the kiln exchanges heat with the low-temperature mixed gas circulating into the cooler, and is sprayed with water by a water spraying device in the cooler, rapidly cooled to below 300 degrees Celsius, to ensure that the high-temperature material exiting from the kiln is still gray and avoid colour change; in this process, a carbonaceous dust that is not burnt out or burnt out of the RDF enters the cooler through a unloading point of a kiln head along with the high-temperature material exiting from the kiln, and has a Boudouard reaction and a water-gas reaction with the low-temperature mixed gas and sprayed water, to produce larger amount of reducing gas.

[0029] The low-temperature mixed gas after heat exchange and the generated reducing gas together partly go into a kiln head of the rotary kiln, and the other part of them goes to a combustion chamber and a main burner, both of which being in communication with the kiln head of the rotary kiln, so as to ensure that calcination atmosphere in the rotary kiln is a reducing atmosphere.

[0030] In the clay calcination colour control method provided in the present disclosure, a clay calcination system 100 is included. In a preferred embodiment, as shown in FIG. 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 configured to calcine cement clinker (clay). The flue gas treatment device is configured to treat the high-temperature flue gas generated by the calcination of the clay, to cool the high-temperature flue gas, including but not limited to material recovery, desulfurization, and / or dust removal. The cooler 130 is configured to cool the high-temperature material exiting from the kiln generated by calcination and provide a reducing gas to the rotary kiln 110.

[0031] Specifically, reference to Fig. 2, in the illustrated embodiment, the kiln tail of the rotary kiln 110 has a raw material inlet 111 and a first flue gas outlet 112. Wherein the raw material inlet 111 is configured to introduce raw material to be calcined, for example, raw materials can be fed into the rotary kiln 110 through the raw material inlet 111 by means of a pipeline, a conveying device, or the like. The first flue gas outlet 112 is configured to discharge high-temperature flue gas generated during calcination. For example, the high-temperature flue gas is sent by means of a pipeline. The kiln head of the rotary kiln 110 is in communication with a combustion chamber 113. The combustion chamber 113 is provided with a main burner 114, which can preheat the gas entering the rotary kiln 110 by combustion and provide the heat required for the production of calcined clay, and also provide a reducing gas. The main burner 114 has a first fuel inlet 115 for introducing natural gas fuel and a first air inlet 116a for introducing air. The combustion chamber 113 has a second air inlet 116b for introducing air, a second fuel inlet 119a for introducing a conventional fossil fuel, and a third fuel inlet 119b for introducing RDF. External air is provided to the main burner 114 and the combustion chamber 113 via the first air inlet 116a, the second air inlet 116b to provide oxygen to assist combustion.

[0032] The present disclosure provides a first fuel inlet 115, a second fuel inlet 119a, a third fuel inlet 119b and the like; and to ignite and start the rotary kiln, firstly, natural gas fuel is introduced by means of the first fuel inlet for combustion to provide all the heat for ignition and start of the rotary kiln. After the kiln is started, the introduction of natural gas is stopped, and then conventional fossil fuel and RDF are introduced respectively by means of the second fuel inlet and the third fuel inlet for combustion to provide calcination heat to the rotary kiln, where the RDF provides 50%-90% (a large proportion) of the heat. The advantages of this design are as follows: 1. The RDF is cheaper than natural gas, which greatly reduces the cost; 2. after ignition, RDF is used as the main fuel, which effectively reduces the use of conventional fossil fuel and further achieves the effect of energy conservation and emission reduction; 3. after the rotary kiln is ignited and started, RDF is used as the main heat source, and ash (i.e., the carbonaceous dust) generated after the combustion of RDF enters the unloading point of the kiln and is mixed with the calcined high-temperature material exiting from the kiln to further provide a carbon source for the Boudouard reaction in the cooler. In addition, if one of the fuel inlets fails or the fuel cannot be used, other fuel inlets may be used for further combustion, thereby achieving the purpose of multiple protection effects.

[0033] The flue gas treatment device is used to treat the high-temperature flue gas discharged from 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 CO 2 , and may also be mixed with the undecomposed raw material and the calcined material. The flue gas treatment device may be configured to treat the high-temperature flue gas generated during the calcination of clay, so that the high-temperature flue gas is cooled and becomes low-temperature flue gas with a low temperature, or becomes low-temperature waste gas. For example, the high-temperature flue gas may undergo treatments, including but not limited to, material recovery and dust removal, etc., and here the treated gas no longer contains solid impurities and is almost pure gas. The specific structure of the flue gas treatment device will be specifically explained below.

[0034] For ease of explanation, this embodiment is described by taking the illustrated embodiment as an example, that is, the high-temperature flue gas generated by the calcination of clay becomes low-temperature waste gas (generally around 70- 80 degrees Celsius) after passing through the flue gas treatment device, but it should not be construed as a limitation. The treated low-temperature waste gas is channeled to the cooler 130 by a recycling pipe 141. At this moment, the low-temperature waste gas inherits the characteristics of the high-temperature flue gas with a very low oxygen content and a certain amount of CO and CO 2 .

[0035] The cooler 130 is configured as a long cylindrical structure with an inner cavity. The inlet end of the cooler 130 could have an inlet for material exiting from the kiln 131 and a second flue gas outlet 132 (i.e., an exhaust gas outlet). The inlet for material exiting from the kiln 131 is in communication with an unloading point 117 at the kiln head of the rotary kiln 110 through a connecting pipeline 142, so as to introduce the high-temperature material exiting from the kiln (about 600 degrees Celsius) and the unburnt or burnt carbonaceous dust of the RDF which are calcined by the rotary kiln 110. The CO 2 in the low-temperature exhaust gas has Boudouard reaction with the unreacted carbon in the unburnt or burnt carbonaceous dust of RDF mixed in the high-temperature material exiting from the kiln in a high-temperature state to generate more reducing gas CO. The second flue gas outlet 132 is respectively in communication with the kiln head of the rotary kiln 110 and the air inlets 116a and 116b through pipelines, so as to discharge the low-temperature exhaust gas after heat exchange with the high-temperature material exiting from the kiln and the generated reducing gas, and the low-temperature flue gas with a larger amount of reducing gas CO after heat exchange is respectively sent to the rotary kiln 110, the combustion chamber 113 and the main burner 114, thereby ensuring that the calcination atmosphere in the rotary kiln 110 is a reducing atmosphere. Preferably, in order to further reduce the oxygen content entering the rotary kiln 110, the rotary kiln 110 could also be provided with an auxiliary burner 118 at a position close to the unloading point 117 of the kiln head.

[0036] According to the method of the present disclosure, the high-temperature flue gas generated during the calcination in the rotary kiln is treated by the flue gas treatment device and become low-temperature exhaust gas with a low temperature. After entering the cooler 130, the low-temperature exhaust gas serves as cooling air on the one hand and exchanges heat with the high-temperature material exiting from the kiln to reduce the temperature of the high-temperature material exiting from the kiln for subsequent use in the process. On the other hand, CO 2 in the low-temperature exhaust gas has Boudouard reaction with unreacted carbon in the high-temperature unburnt or burnt carbonaceous dust of RDF to generate more reducing gas CO. After the heat exchange, the low-temperature exhaust gas has a larger amount of reducing gas, and the temperature of the low-temperature exhaust gas increases (about 200 degrees Celsius). The low-temperature exhaust gas after heat exchange is divided into two parts, one part enters the rotary kiln 110, and the other part advances to the combustion chamber 113 and the main burner 114, thereby ensuring that the calcination atmosphere in the rotary kiln 110 is a reducing atmosphere and that the color of the calcined material is gray.

[0037] Referring to FIG. 1, in order to provide a flue gas treatment device with a good use effect, the flue gas treatment device could include a cyclone separator 121, a desulphurization column 122, a dust collector 123 and an RTO device 124 (i.e., a regenerative thermal incinerator) which are sequentially connected in sequence. Among them, the cyclone separator 121 is configured to separate materials and exhaust gas in the high-temperature flue gas, that is, to separate the unburnt fuel, undecomposed raw materials, and calcined materials, which could be mixed therein, from the gas. The desulphurization column 122 is configured to desulfurize the high-temperature flue gas to remove harmful components. The dust collector 123 is configured to remove dust from the high-temperature flue gas. That is, the dust collector 123 once again to absorb the unthoroughly separated materials. The RTO device 124 is configured to eliminate volatile organic compounds in the high-temperature flue gas. The volatile organic compound (VOC) are any carbon compounds that participate in atmospheric photochemical reaction except CO, CO 2 , H 2 CO 3 , metal carbides, metal carbonates and ammonium carbonate. The main components of VOC include hydrocarbons, halogenated hydrocarbons, oxygenated hydrocarbons and nitrogen hydrocarbons, and VOC includes benzene series, organic chlorides, freon series, organic ketones, amines, alcohols, ethers, esters, acids and petroleum hydrocarbon compounds, and the like. 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.

[0038] Furthermore, in order to make full use of separated or absorbed materials, the materials separated from the cyclone separator 121 could enter the rotary kiln 110 again by relevant pipelines via the raw material inlet 111 for calcination. Similarly, the material obtained after dust removal by the dust collector 123 could also enter the rotary kiln 110 again by pipelines via the raw material inlet 111 for calcination.

[0039] It can be understood that although a specific flue gas treatment device is shown in FIG. 1, it should not be construed as a limitation. For achieving the flue gas cooling function, the flue gas treatment device could include one or more of the cyclone separator 121, the desulphurization column 122, the dust collector 123, and the RTO device 124, or other devices that achieves the same function.

[0040] Continuing from the above, the inner cavity of the cooler 130 could also be in communication with a water spraying device which could spray water to the high-temperature material exiting from the kiln. Specifically, the water spraying device could include a first water spraying device 151 and a second water spraying device 152. The first water spraying device 151 and the second water spraying device 152 could be spraying devices connected to a water source through water pipes. The first water spraying device 151 is located at an inlet end of the cooler 130, and is configured to rapidly cool the high-temperature material exiting from the kiln entering the cooler 130, so as to avoid discoloration of the calcined material (high-temperature material exiting from the kiln). For example, the high-temperature material exiting from the kiln is cooled from about 600 degrees Celsius to below 300 degrees Celsius within a predetermined time period. The second water spraying device 152 is located at an outlet end of the cooler 130, and is configured to control the temperature of the high-temperature material exiting from the kiln passing through the outlet end of the cooler 130 to be a preset threshold or below.

[0041] Specifically, firstly, the water spraying device cools the high-temperature material exiting from the kiln through water spraying, which can further enhance the cooling effect for the high-temperature material exiting from the kiln, and the high-temperature material exiting from the kiln can be cooled more quickly and cooled to a preset threshold or below. More importantly, in addition to being able to cool the high-temperature material exiting from the kiln, some of the water turns into water vapor when it contacts with the high-temperature discharging kiln material. The water vapor has water-gas reaction with the unreacted carbon in the high-temperature discharging kiln material in a high-temperature state, and generate reducing gases CO and H 2 . The generated reducing gases CO and H 2 , together with the heat-exchanged low-temperature exhaust gas, respectively enter the rotary kiln 110, the combustion chamber 113 and the main burner 114, so as to further ensure that the calcining atmosphere in the rotary kiln 110 is a reducing atmosphere, and to further ensure that the colour of the calcined material is gray.

[0042] In this embodiment, by means of the second water spraying device 152 at the outlet end of the cooler 130, the temperature of the high-temperature material exiting from the kiln passing through the outlet end of the cooler 130 is controlled to be the preset threshold or below to meet the needs of subsequent processes. The preset threshold could be between 80 and 150 degrees Celsius, for example, 80 degrees Celsius, 100 degrees Celsius, or 120 degrees Celsius. To achieve temperature regulation, the first water spraying device 151 or the second water spraying device 152 itself could have a control device or an externally coupled control device, and could also have a temperature sensor which could monitor the temperature of the high-temperature material exiting from the kiln passing through the outlet end of the cooler 130 in real time. The control device adjusts the water flow of the first water spraying device 151 or the second water spraying device 152 according to a comparison result between a 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 flow of the first water spraying device 151 or the second water spraying device 152 is increased. When the temperature value monitored by the temperature sensor is less than the preset threshold, the water flow of the second water spraying device 152 is reduced. The described adjustment process is a common existing adjustment technology and is completely based on the function set by the control device itself without involving changes in the internal program. In the present disclosure, the control device detects the monitoring value of the sensor at a certain sampling frequency (such as 2s, 5s or 10s) to timely adjust the working state of the first water spraying device 151 or the second water spraying device 152.

[0043] Referring to FIG. 1, the exhaust gas treated by the flue gas treatment device could be channeled to a chimney 144 through a exhaust pipe 143 to be discharged. In order to facilitate discharge control and safety discharge, the exhaust pipe 143, the recycling pipeline 141, and the intermediate pipe of the flue gas treatment device could be provided with valves and gas concentration monitoring sensors, when the exhaust gases finally meet the requirements for safe discharge, the valve is opened and the exhaust gases are discharged into the atmosphere through the chimney 144.

[0044] In summary, according to the method of the present disclosure, the high-temperature flue gas generated during the calcination in the rotary kiln 110 is treated and then reused to cool the high-temperature material exiting from the kiln. Moreover, more reducing gas CO is generated in the cooler 130 based on the Boudouard reaction, and then enters the rotary kiln 110, the combustion chamber 113 and the main burner 114 to ensure that the calcination atmosphere in the rotary kiln 110 is a reducing atmosphere, thereby ensuring that the colour of the calcined material is gray. In addition, the water spraying device for spraying water to cool the high-temperature material exiting from the kiln further enhances the cooling effect for the high-temperature material exiting from the kiln, and while reducing gases CO and H 2 can also be generated based on the water-gas reaction, and then enters the rotary kiln 110, the combustion chamber 113 and the main combustor 114, so as to further ensure that the calcination atmosphere in the rotary kiln 110 is a reducing atmosphere. Meanwhile, since the temperature of the low-temperature exhaust gas is higher than that of normal-temperature air, fuel consumption in the combustion chamber 113 can be reduced.

[0045] In addition, in the present disclosure, after waste gas treatment, the flue gas generated by the calcination of clay in the rotary kiln 110 is used for cooling the high-temperature material exiting from the kiln and providing a large amount of reducing gas CO to the rotary kiln 110 and the combustion chamber 113. With the characteristics of exhaust gas having a low oxygen content (or almost no oxygen) and a certain amount of CO and CO 2 , the flue gas reacts in the cooler 130 with carbon in the high-temperature material exiting from the kiln to generate more reducing gas CO and form a protective gas so that the high-temperature material exiting from the kiln is better cooled without oxygen. Compared with the existing simple treatment such as filtration and adsorption before discharge into the atmosphere, or simple heat utilization and recovery methods, the present disclosure achieves resource recycling of waste gas in multiple aspects.

[0046] Other embodiments of the present disclosure are readily conceivable and understood by a person skilled in the art in conjunction with the description and practice of the disclosure disclosed herein. It is intended that the description and examples be considered as exemplary only, with the true scope and spirit of the present disclosure being defined by the claims.

Claims

1. A clay calcination colour control method, <b>characterized in that, the method comprises the following steps: firstly, natural gas fuel is introduced by means of a first fuel inlet for combustion to provide all the heat for ignition and start of a rotary kiln; after the rotary kiln is started, the introduction of natural gas is stopped, and then conventional fossil fuel and RDF are introduced respectively by means of a second fuel inlet and a third fuel inlet for combustion to provide calcination heat to the rotary kiln, where the RDF provides 50%-90% of the heat; when a raw materials to be calcined are dehydrated and decomposed in the rotary kiln, a high-temperature flue gas at a kiln tail becomes a low-temperature mixed gas with a temperature of 70-80 degrees Celsius after being treated by a cooling process, and the low-temperature mixed gas circulates into a cooler; when a high-temperature material exiting from the kiln calcined in the rotary kiln enters the cooler, the high-temperature material exiting from the kiln exchanges heat with the low-temperature mixed gas circulating into the cooler, and is sprayed with water by a water spraying device in the cooler, rapidly cooled to below 300 degrees Celsius, to ensure that the high-temperature material exiting from the kiln is still gray and avoid colour change; in this process, a carbonaceous dust that is not burnt out or burnt out of the RDF enters the cooler through a unloading point of a kiln head along with the high-temperature material exiting from the kiln, and has a Boudouard reaction and a water-gas reaction with the low-temperature mixed gas and sprayed water, to produce larger amount of reducing gases; the low-temperature mixed gas after heat exchange and the generated reducing gas together partly go into the kiln head of the rotary kiln, and the other part of them goes to a combustion chamber and a main burner, both of which being in communication with the kiln head of the rotary kiln, so as to ensure that calcination atmosphere in the rotary kiln is a reducing atmosphere.

2. The method according to claim 1, characterized in that, a clay calcination system is included, said clay calcination system comprises a rotary kiln, a flue gas treatment device, a cooler and a water spraying device; said kiln tail of the rotary kiln has a raw material inlet and a first flue gas outlet, said raw material inlet is configured to introduce a raw materials to be calcined, and said first flue gas outlet is configured to discharge a high-temperature flue gases generated during calcination; said kiln head of the rotary kiln is in communication with a combustion chamber, said combustion chamber is provided with a main burner, said main burner has a first fuel inlet for introducing natural gas fuel and a first air inlet for introducing air; said combustion chamber has a second fuel inlet for introducing traditional fossil fuel, a third fuel inlet for introducing RDF, and a second air inlet for introducing air; said flue gas treatment device is configured to perform a cooling treatment on said high-temperature flue gas discharged from the first flue gas outlet, and a low-temperature flue gas is obtained after the colling treatment and is channeled to said cooler through a recycling pipeline; and said inlet end of the cooler has a inlet for material exiting from the kiln and a second flue gas outlet; said inlet for material exiting from the kiln is in communication with an unloading point at the kiln head of said rotary kiln through a connecting pipeline, so as to introduce the high-temperature material exiting from the kiln and the unburnt or burnt carbonaceous dust of the RDF which are calcined by said rotary kiln; said second flue gas outlet is respectively in communication with said kiln head of the rotary kiln, said first air inlet and said second air inlet through pipelines, so as to discharge the reducing gases generated when said carbonaceous dust comes into contact with the low-temperature flue gases, and the low-temperature flue gases after heat exchange; the water spraying device provided in said cooler is configured to spray water to cool said high-temperature material exiting from the kiln.

3. The method according to claim 2, <b>characterized in that, said flue gas treatment device comprises at least one of the following: a cyclone separator for separating materials and exhaust gases in said high-temperature flue gas; a desulphurization column for desulfurizing said high-temperature flue gas; a dust collector for removing dust from said high-temperature flue gas; an RTO device for eliminating volatile organic compounds from said high-temperature flue gas.

4. The method according to claim 3, <b>characterized in that, said flue gas treatment device includes said cyclone separator, said desulphurization column, said dust collector and said RTO device which are sequentially connected in sequence through pipelines: the material separated by said cyclone separator also re-enters said rotary kiln by pipeline being in communication with said raw material inlet; and / or the material after dust removal by said dust collector also re-enters said rotary kiln by pipeline being in communication with said raw material inlet.

5. The method according to claim 4, characterized in that, said water spraying device comprising: a first water spray device located at an inlet end of said cooler for rapid cooling said high-temperature material exiting from the kiln; a second water spray device located at an outlet end of said cooler is used for linkage control with the first water spray device, so as to control the temperature of the high-temperature material exiting from the kiln passing through the outlet end of said cooler below a preset threshold value.

6. The method according to claim 1, characterized in that, the flue gas treated by said flue gas treatment device is further channeled to a chimney through an exhaust pipeline.

7. The method according to claim 1, characterized in that, an auxiliary burner is also provided in the kiln head of said rotary kiln at a position close to the unloading point, so as to further consume oxygen entering said rotary kiln.

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