Rotary kiln treatment system and method for low-moisture and high-moisture clay minerals

Abstract

The present disclosure provides a rotary kiln treatment system and method for low-moisture and high-moisture clay minerals. The treatment system comprises a rotary kiln, a feeding subsystem, a flue gas treatment subsystem, a cooling subsystem and a post-treatment subsystem, wherein the rotary kiln comprises a kiln tail, a drying section, a transition section, a calcining section and a kiln head, which are connected in sequence, the kiln tail being provided with a raw material inlet and a first flue gas outlet; a main burner is provided with a first fuel inlet for introducing natural gas fuel and a first air inlet; a combustion chamber is provided with a second fuel inlet for introducing conventional fossil fuel and a second air inlet, and the combustion chamber is in communication with a gasifier having a third fuel inlet for introducing RDF; the cooling subsystem comprises a cooler, an out-of-kiln material inlet and a second flue gas outlet being provided at an inlet end of the cooler; and a water-spraying device capable of spraying water to cool high-temperature out-of-kiln materials is provided in an inner cavity of the cooler. The treatment system provided in the present disclosure can ensure the clay calcination quality, reduce the cost and reduce carbon emissions.

Description

Rotary kiln processing system and method for low- and high-moisture clay minerals

[0001] Related applications

[0002] This disclosure claims priority to Chinese patent application number CN202310941752.7 filed with the Patent Office of China on July 28, 2023, entitled “Rotary Kiln Processing System and Method for Low and High Moisture Clay Minerals,” 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 rotary kiln processing system and method for low- and high-moisture clay minerals. Background Art

[0004] Cement manufacturing is central to global infrastructure development and, like every energy-intensive industry, it also generates significant pollutant emissions. Approximately 6% of the world's carbon dioxide emissions come from cement production.

[0005] As society develops, countries are adopting stricter greenhouse gas emission reduction policies. One potential solution widely considered by the cement industry is to partially replace clinker with supplementary cementitious materials (SCMs) to create so-called "green cement." Calcined clay has become an increasingly popular alternative due to its widespread availability and low cost. This form of synthetic SCM has proven to be a sustainable alternative, offering environmental and economic benefits for production and helping to enhance the durability and plasticity of concrete. Clay deposits are often highly heterogeneous, but clays suitable for use as pozzolans typically range from 50-65% SiO2 and 17-38% Al2O3. The content of sand and other impurities varies widely, typically ranging from 5-50%. Several types of clay can be used, with kaolinite, illite, and montmorillonite being the most common. The fineness of the dried clay can range from a few microns to several millimeters. The primary purpose of industrial processing of pozzolans is to remove hydroxyl groups from the clay structure (as opposed to removing carbon dioxide from the limestone structure in clinker production), resulting in activated aluminum oxide and silicon dioxide.

[0006] In the process of implementing the present disclosure, the inventors discovered that the prior art has at least the following problems:

[0007] During calcination, temperatures that are too low will not fully activate the clay, while temperatures that are too high will cause recrystallization of the clay structure. Both of these situations significantly reduce the clay's reactivity. Furthermore, clay calcination can currently be achieved through various methods. Industrial solutions generally use rotary kilns or flash / suspension calciners, but each of these methods presents significant cost increases, significant reductions in calcination quality, or unsatisfactory emissions reductions. There is growing interest in how industry can reduce carbon emissions without significantly increasing costs or compromising quality.

[0008] Therefore, a rotary kiln processing system and method for low- and high-moisture clay minerals are needed to at least partially solve the above technical problems.

[0009] Summary of the Invention

[0010] The embodiments of the present disclosure provide a rotary kiln processing system and method for low- and high-moisture clay minerals, which can ensure the quality of clay calcination, reduce costs, and reduce carbon emissions.

[0011] In a first aspect, the present disclosure provides a rotary kiln processing system for low- and high-moisture clay minerals, the processing system comprising a rotary kiln, a feeding subsystem, a flue gas treatment subsystem, a cooling subsystem, and a post-processing subsystem;

[0012] The rotary kiln includes a kiln tail, a drying section, a transition section, a calcining section, and a kiln head, which are sequentially connected from left to right. The kiln tail of the rotary kiln has a raw material inlet and a first flue gas outlet. The raw material inlet is used to introduce clay raw materials to be calcined, and the first flue gas outlet is used to discharge high-temperature flue gas generated during calcination.

[0013] The kiln head of the rotary kiln is connected to the combustion chamber, which 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 and a second air inlet for introducing air. The combustion chamber is also connected to a gasifier, which has a third fuel inlet for introducing RDF fuel. 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.

[0014] The feeding subsystem includes a metering bin for providing clay raw materials that do not require grinding or water removal and have a particle size of no more than 30 mm to the rotary kiln;

[0015] The flue gas treatment subsystem 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 cooling treatment enters the cooling subsystem through the circulation pipeline;

[0016] The cooling subsystem includes a cooler, wherein the inlet end of the cooler has an inlet for kiln materials and a second flue gas outlet; the inlet for kiln materials is connected to a discharge point at the kiln head of the rotary kiln through a connecting pipe, and is used to introduce high-temperature kiln materials calcined in the rotary kiln and unburned or burned carbonaceous dust from the RDF fuel introduced into the gasifier; the inner cavity of the cooler is provided with a water spray device capable of spraying water to cool the high-temperature kiln materials; the second flue gas outlet is connected to the kiln head, the first air inlet, and the second air inlet respectively through an air supply pipe, and is used to discharge reducing gas generated when the carbonaceous dust contacts the low-temperature flue gas and the water spray, as well as the low-temperature flue gas after heat exchange; and

[0017] The post-processing subsystem is used to further crush the high-temperature kiln materials after cooling so as to be used as cement clinker.

[0018] The processing system disclosed herein provides a feeding subsystem for clay raw materials that do not require grinding or dehydration to the rotary kiln, significantly reducing equipment investment. The high-temperature flue gas (with a very low oxygen content, primarily CO and CO₂) generated during calcination in the rotary kiln is treated by a flue gas treatment device and converted into low-temperature flue gas (or waste gas) with a low temperature (generally 140-150 degrees Celsius). The low-temperature flue gas inherits the low oxygen content of the high-temperature flue gas and contains a certain amount of CO and CO₂. After entering the cooler, it serves as cooling air, exchanging heat with the high-temperature kiln discharge material (around 600 degrees Celsius), thereby lowering the temperature of the high-temperature kiln discharge material for use in subsequent processes. Furthermore, the CO₂ in the low-temperature flue gas reacts with unburned RDF fuel or unreacted carbon in burnt carbonaceous dust mixed with the high-temperature kiln discharge material in a Boudall reaction, generating more reducing gas CO. The water spray device cools the high-temperature kiln discharge material by spraying water, further enhancing the cooling effect of the high-temperature kiln discharge material. In addition to cooling the high-temperature materials discharged from the kiln, part of the water in the kiln 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 mixed with the high-temperature materials discharged from the kiln in a high-temperature state or the unreacted carbon in the burned carbonaceous dust to produce water gas, generating reducing gases CO and H2. This part of the reducing gases CO and H2 enter the rotary kiln together with the low-temperature flue gas after heat exchange, and go to the combustion chamber and the main burner respectively, further ensuring that the calcination atmosphere in the rotary kiln is a reducing atmosphere, and can also ensure that the color of the calcined material is gray. After the above-mentioned heat exchange, the low-temperature flue gas has a larger amount of reducing gas, 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 enables the high-temperature flue gas generated during calcination in the rotary kiln to be recycled, reducing carbon emissions; in addition, since the temperature of the low-temperature flue gas is higher than that of normal temperature air (about 200 degrees Celsius), fuel consumption can be reduced.

[0019] 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.

[0020] Optionally, the flue gas treatment subsystem includes at least one of the following:

[0021] A cyclone, used to separate the high-temperature flue gas into materials and waste gas;

[0022] a desulfurization and denitrification tower, used for desulfurizing and denitrifying the high-temperature flue gas;

[0023] A dust collector is used to remove dust from the high-temperature flue gas.

[0024] Optionally, the flue gas treatment subsystem includes the cyclone, the desulfurization and denitrification tower, and the dust collector connected in sequence:

[0025] The material separated from the cyclone also enters the rotary kiln again through the raw material inlet. And / or

[0026] The material obtained after the dust collector performs dust removal also enters the rotary kiln again through the raw material inlet.

[0027] Optionally, the water spraying device includes:

[0028] A first water spraying device located at the inlet end of the cooler is used to quickly cool the high-temperature kiln material;

[0029] 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.

[0030] In this embodiment, the first water spray device at the inlet end of the cooler is used to quickly cool down the high-temperature kiln material entering the cooler (from the original 600 degrees Celsius to below 300 degrees Celsius), which can avoid discoloration of the calcined material (high-temperature kiln material). The second water spray device at the outlet end 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 end of the cooler to be below a preset threshold value (e.g., 80-150 degrees Celsius) to meet the needs of subsequent processes. Among them, the first water spray device or the second water spray device itself can have a control device or an externally coupled control device, and a temperature sensor that can monitor the temperature of the high-temperature kiln material passing through the outlet end 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 value. When the temperature value monitored by the temperature sensor is greater than a 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 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, and is based on the functions set by the control device itself.

[0031] Optionally, the flue gas treated by the flue gas treatment subsystem is also connected to the chimney through an exhaust duct.

[0032] 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.

[0033] In a second aspect, the present disclosure further provides a rotary kiln treatment method for low- and high-moisture clay minerals. The treatment system based on the above technical solution comprises the following steps:

[0034] First, natural gas fuel is introduced into 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, under normal conditions, traditional fossil fuel and RDF fuel are introduced into the second fuel inlet and the gasifier respectively for combustion to provide calcination heat for the rotary kiln. The RDF fuel in the gasifier provides 50%-90% of the heat.

[0035] The clay raw material to be calcined is crushed to meet the particle size of no more than 30mm, and then directly fed into the rotary kiln without grinding or removing moisture, and sequentially undergoes moisture drying in the drying section, the beginning of the dehydroxylation reaction stage in the transition section, and the completion of the dehydroxylation reaction stage in the calcination section;

[0036] When the clay 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 140-150 degrees Celsius. The low-temperature mixed gas circulates into the cooler;

[0037] 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 in the cooler. Simultaneously, it is sprayed with water by the first water spray device at the cooler inlet, rapidly cooling it to below 300 degrees Celsius to ensure that the high-temperature material remains gray and avoids discoloration. During this process, unburned or burned carbonaceous dust from the gasifier's RDF fuel enters the cooler along with the high-temperature material through the discharge point at the kiln head. There, it undergoes Boudreau reaction and water-gas reaction with the low-temperature mixed gas and the sprayed water, producing a large amount of reducing gas.

[0038] 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.

[0039] Optionally, the method further comprises the following steps:

[0040] The low-temperature mixed gas after heat exchange and the generated reducing gas enter the kiln head of the rotary kiln and are burned by the auxiliary burner to further consume the oxygen entering the rotary kiln; and / or

[0041] When the rotary kiln is ignited and calcining clay, if an emergency occurs: if the fuel introduced from the second fuel inlet or the gasifier cannot be used, the remaining fuel will be used to provide all the heat to achieve multiple protection effects.

[0042] By utilizing the technical solution according to the embodiments of the present disclosure, the beneficial effects that can be obtained are at least:

[0043] 1. The high-temperature flue gas generated during calcination in the rotary kiln is treated by the flue gas treatment subsystem 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 (about 200 degrees Celsius), it can reduce fuel consumption.

[0044] 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.

[0045] 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.

[0046] 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

[0047] 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:

[0048] FIG1 is a schematic diagram of a rotary kiln processing system for low- and high-moisture clay minerals according to an embodiment of the present disclosure;

[0049] FIG2 is a schematic diagram of a rotary kiln processing system for low- and high-moisture clay minerals according to another embodiment of the present disclosure;

[0050] FIG3 is a schematic diagram showing the connection between the kiln head, the combustion chamber and the main burner in the rotary kiln processing system for low- and high-moisture clay minerals shown in FIG2 ; and

[0051] FIG4 is a flow chart of a rotary kiln treatment method for low- and high-moisture clay minerals according to an embodiment of the present disclosure.

[0052] Explanation of Reference Numerals: 100: Processing System; 110: Rotary Kiln; 111: Raw Material Inlet; 112: First Flue Gas Outlet; 113: Kiln Rear; 114: Drying Section; 115: Transition Section; 116: Calcination Section; 117: Kiln Head; 118: Material Discharging Point;

[0053] 119: auxiliary burner;

[0054] 120: combustion chamber;

[0055] 121: main burner;

[0056] 122: first fuel inlet;

[0057] 123: first air inlet;

[0058] 124: Second air inlet;

[0059] 125: Second fuel inlet;

[0060] 126: gasifier;

[0061] 127: Third fuel inlet;

[0062] 131: Cyclone;

[0063] 132: Desulfurization and denitrification tower;

[0064] 133: dust collector;

[0065] 140: cooler;

[0066] 141: kiln material entrance;

[0067] 142: Second smoke outlet;

[0068] 151: Circulation pipeline;

[0069] 152: Connecting pipes;

[0070] 153: Exhaust duct;

[0071] 154: air supply pipeline;

[0072] 155: chimney;

[0073] 161: first water spray device;

[0074] 162: Second water spray device;

[0075] 171: Silo;

[0076] 172: Crusher;

[0077] 173: Measuring bin;

[0078] 181: Crusher;

[0079] 182: Clay Library;

[0080] 183: Cement mill. DETAILED DESCRIPTION

[0081] 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.

[0082] 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.

[0083] 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”.

[0084] 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.

[0085] In a first aspect, the present disclosure provides a rotary kiln processing system 100 for low- and high-moisture clay minerals. The processing system 100 can be applied to the field of clay calcination technology, such as calcining clay to ensure clay calcination quality while reducing costs and carbon emissions.

[0086] First of all, a rotary kiln refers to a rotary calcining kiln (commonly known as a rotary kiln), which is similar in appearance to a rotary bed, also called a rotary bed kiln, and 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 for magnetic roasting of lean iron ore in steel plants in the metallurgical industry; oxidation roasting of chromium and nickel iron ore; roasting of high-aluminum bauxite 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. Lime kilns (i.e., active lime kilns) are used to roast active lime and light-burned dolomite for steel plants and ferroalloy plants. The rotary kiln 110 in this embodiment generally refers to a cement kiln.

[0087] The present disclosure provides a rotary kiln processing system 100 for low- and high-moisture clay minerals. In a preferred embodiment, as shown in Figures 1 and 2, the processing system 100 includes a rotary kiln 110, a flue gas treatment subsystem, a feeding subsystem, a cooling subsystem, and a post-processing subsystem. The rotary kiln 110 is used to calcine cement clinker (clay). The flue gas treatment subsystem is used to treat the high-temperature flue gas generated by the calcination of clay to cool it down, and also includes but is not limited to material recovery, desulfurization and / or dust removal. The feeding subsystem is used to feed clay raw materials into the rotary kiln. The cooling subsystem is used to cool the high-temperature kiln discharge material generated by calcination and provide reducing gas to the rotary kiln 110. The post-processing subsystem is used to process the cooled kiln discharge material to form cement clinker.

[0088] Specifically, referring to Figures 1 to 3, in the illustrated embodiment, the rotary kiln 110 may include, sequentially from left to right, a kiln tail section 113, a drying section 114, a transition section 115, a calcining section 116, and a kiln head section 117. The kiln tail section of the rotary kiln 110 has a raw material inlet 111 and a first flue gas outlet 112. The raw material inlet 111 is used to introduce raw materials to be calcined. For example, the raw materials can be fed into the rotary kiln 110 through a pipeline or conveyor. In this embodiment, clay raw materials are fed into the rotary kiln 110 via a feeding subsystem. The first flue gas outlet 112 is used to discharge high-temperature flue gases generated during calcination, for example, by conveying the high-temperature flue gases through a pipeline. The kiln head section of the rotary kiln 110 is connected to a combustion chamber 120. The combustion chamber 120 is equipped with a main burner 121, which preheats the gases entering the rotary kiln 110 through combustion, provides the heat required for calcined clay production, and provides reducing gas. The main burner 121 has a first fuel inlet 122 for introducing natural gas fuel and a first air inlet 123 for introducing air. The main burner 121 in the combustion chamber 120 has a second air inlet 124 for introducing air and a second fuel inlet 125 for introducing traditional fossil fuels. External air is supplied to the main burner 121 and combustion chamber 120 through the first and second air inlets, respectively, to provide oxygen to aid combustion. Because this rotary kiln performs drying and calcining in the same facility, it eliminates the need for raw material grinding (the raw material size entering the kiln can reach 30 mm) and eliminates the need for raw material moisture treatment, thus streamlining the process.

[0089] Furthermore, the combustion chamber 120 is also connected to the gasifier 126. The gasifier has a third fuel inlet 127 for introducing RDF fuel. The gasifier can be used for RDF fuels of different particle sizes (within 50 mm), which effectively reduces the use of traditional fossil fuels and achieves the effect of energy conservation and emission reduction. The unburned dust (including carbonaceous dust) of the RDF fuel is processed by entering the cooler along with the high-temperature kiln materials to avoid unburned or burned materials from entering the kiln and affecting the quality of the clay; the gasifier can provide 50-90% of the heat, and the rest of the heat is provided by the combustion chamber, which mainly controls the temperature and color of the calcined materials through the heat of the combustion chamber; the material flow and air flow are produced in opposite directions throughout the production.

[0090] Among them, the present invention is provided with a first fuel inlet 122, a second fuel inlet 125 and a third fuel inlet 127. 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. 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 (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.

[0091] The feeding subsystem includes a metering bin 173, which is used to provide the rotary kiln 110 with clay raw materials that do not require grinding or dehydration and have a particle size of no more than 30 mm. In addition, the feeding subsystem may also include a silo 171 and a crusher 172. The clay raw materials are crushed by the crusher and then transported to the metering bin. After the stored clay is crushed, it is directly fed into the rotary kiln through the metering bin to dry and calcine the clay, so that the clay completes the raw material drying, preheating and dehydroxylation processes in a stacked state; there is no need to grind the raw materials or remove moisture, which is easy to control. In view of the viscosity of the material, the design of the silo cannot be too large. The flue gas treatment subsystem is used to treat the high-temperature flue gas discharged through the first flue gas outlet 112. Among them, 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 can also be mixed with undecomposed raw materials and calcined materials. The flue gas treatment subsystem is used to treat the high-temperature flue gas generated by clay calcination, cooling it to low-temperature flue gas or low-temperature waste gas. For example, the high-temperature flue gas can undergo treatments including, but not limited to, material recovery and dust removal, leaving it free of solid impurities and virtually pure gas. The detailed structure of the flue gas treatment subsystem is detailed below.

[0092] 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 the flue gas treatment subsystem and is converted into low-temperature exhaust gas (generally around 140-150 degrees Celsius). However, this is not intended to be limiting. The treated low-temperature exhaust gas is then connected to cooler 140 via circulation pipe 151. 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.

[0093] The cooler 140 is a long cylindrical structure with an inner cavity. The cooler is a rotary cooler, which contacts the low-temperature flue gas during the forward movement of the high-temperature kiln material and fully exchanges heat. The inlet end of the cooler 140 may have a kiln material inlet 141 and a second flue gas outlet 142. The kiln material inlet 141 is connected to the unloading point 118 at the kiln head of the rotary kiln 110 through a connecting pipe 152, and is used to introduce the high-temperature kiln material (about 600 degrees Celsius) calcined by the rotary kiln 110 and the 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 mixed in the high-temperature kiln material in a high-temperature state to generate more reducing gas CO.

[0094] In addition, the inner cavity of the cooler 140 is provided with a water spraying device capable of spraying water to cool the high-temperature kiln materials. The water spraying device cools the high-temperature kiln materials by spraying water, further enhancing the cooling effect of the high-temperature kiln materials. In addition to being able to cool the high-temperature kiln materials, part of the water turns into water vapor when it comes into contact with the high-temperature kiln materials, and the water vapor reacts with the unburned RDF fuel of the high-temperature kiln materials mixed in the high-temperature state or the unreacted carbon in the burnt carbonaceous dust to generate water gas, 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, and goes to the combustion chamber and the main burner, further ensuring that the calcination atmosphere in the rotary kiln is a reducing atmosphere, and can also ensure that the color of the calcined material is gray.

[0095] Next, the second flue gas outlet 142 is connected to the kiln head, first air inlet 123, and second air inlet 124 of the rotary kiln 110 via an air supply pipe 154 (consisting of multiple pipes). This outlet is used to discharge the low-temperature flue gas and the reducing gas generated after heat exchange with the high-temperature material leaving the kiln. The low-temperature flue gas, which contains a larger amount of reducing gas after heat exchange, is then fed into the rotary kiln 110, the combustion chamber 120, and the main burner 121, respectively, to ensure that the calcining atmosphere in the rotary kiln 110 is a reducing atmosphere. Preferably, to further reduce the oxygen content entering the rotary kiln 110, an auxiliary burner 119 can be installed at the kiln head of the rotary kiln 110 near the material discharge point 118.

[0096] According to the treatment system 100 disclosed herein, the high-temperature flue gas generated during calcination in the rotary kiln 110 is treated by the flue gas treatment subsystem and converted into low-temperature exhaust gas. After entering the cooler 140, the low-temperature exhaust gas serves as cooling air, exchanging heat with the high-temperature material leaving the kiln, thereby lowering the temperature of the material for use in subsequent processes. Furthermore, the CO2 in the low-temperature exhaust gas undergoes a Boudall reaction with unreacted carbon in the unburned or burned carbonaceous dust of the high-temperature RDF fuel, generating more reducing gas CO. Water sprayed by the water spray device contacts the high-temperature material leaving the kiln to generate water vapor, which in turn undergoes a water-gas reaction with the unburned or burned carbonaceous dust of the RDF fuel to produce reducing gases CO and H2. The low-temperature exhaust gas after heat exchange 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 goes to the combustion chamber 120 and the main burner 121, 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.

[0097] The processing system provided by the present disclosure can calcine clay at a temperature of about 800 degrees Celsius, which is much lower than the calcination temperature of traditional clinker of 1400 degrees Celsius, and can save a lot of fuel and electricity. The raw materials do not produce carbon emissions during the production process, and the calcined clay can partially replace traditional cement clinker. At the same time, the performance of the cement product is guaranteed to remain unchanged, which can significantly reduce carbon emissions. The entire system has low pressure loss, which fully reduces the heat consumption of the product. The rotary kiln calcination solution can process various types of clay with low and high moisture content, effectively broadening the scope of use of clay, eliminating the need for a clay grinding system, and saving investment.

[0098] In order to provide a flue gas treatment subsystem with good use effect, referring to Figure 1, the flue gas treatment subsystem may include a cyclone 131, a desulfurization and denitrification tower 132 and a dust collector 133 connected in sequence. Among them, the cyclone 131 is used to separate the materials and exhaust gas from the high-temperature flue gas. That is, the undecomposed raw materials and calcined materials that may be mixed are separated from the gas. The desulfurization and denitrification tower 132 is used to desulfurize and denitrify the high-temperature flue gas to remove harmful components. Desulfurization and denitrification can be carried out in the form of limestone injection and SNCR (selective non-catalytic reduction) to control the emission of NOx in the system. The dust collector 133 is used to remove dust from the high-temperature flue gas. That is, the dust collector 133 once again absorbs the materials that are not completely separated. 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.

[0099] Furthermore, in order to fully utilize the separated or absorbed materials, the materials separated by the cyclone 131 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 133 can also be re-entered into the rotary kiln 110 for calcination through the pipelines via the raw material inlet 111.

[0100] It is understood that although FIG1 illustrates a specific flue gas treatment subsystem, this is not intended to be limiting. The flue gas treatment subsystem, while achieving flue gas cooling, may include one or more of a cyclone 131, a desulfurization and denitrification tower 132, and a dust collector 133, or other equipment that achieves the same function.

[0101] Continuing from the above, the water spray device may include a first water spray device 161 and a second water spray device 162. The first water spray device 161 and the second water spray device 162 may be spray devices connected to a water source through a water pipe. Among them, the first water spray device 161 is located at the inlet end of the cooler 140, and is used to quickly cool down the high-temperature kiln material entering the cooler 140, 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 162 is located at the outlet end of the cooler 140, and is used to control the temperature of the high-temperature kiln material passing through the outlet end of the cooler 140 to be below a preset threshold.

[0102] In this embodiment, the main burner 121 of the combustion chamber 120 controls the temperature of the high-temperature material exiting the kiln through the cooler 140 through the first and second water spray devices 161, 162, to be below a preset threshold to meet the requirements of subsequent processes. The preset threshold can be 80-150 degrees Celsius, for example, 80 degrees Celsius, 100 degrees Celsius, or 120 degrees Celsius. To achieve temperature control, the first and second water spray devices 161, 162 can have their 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 through the cooler 140 in real time. The control device adjusts the water flow rate of the first and second water spray devices 161, 162 based on the result of comparing the temperature value monitored by the temperature sensor with the preset threshold. Specifically, when the temperature value monitored by the temperature sensor is greater than the preset threshold, the water flow rate of the first and second water spray devices 161, 162 is increased. When the temperature value monitored by the temperature sensor is less than a preset threshold, the water spraying of the second water spraying device 162 is reduced. The above-described 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. In the present disclosure, the control device detects the sensor monitoring value at a certain sampling frequency (for example, 2s, 5s, or 10s) to timely adjust the operating state of the first water spraying device 161 or the second water spraying device 162.

[0103] Referring to Figure 2 , exhaust gas treated by the flue gas treatment subsystem can be discharged through exhaust duct 153 to chimney 155. To facilitate emission control and safe discharge, valves and gas concentration monitoring sensors can be installed on exhaust duct 153, circulation duct 151, and intermediate ducts in the flue gas treatment subsystem. When the final exhaust gas meets safe discharge requirements, the valves are opened and discharged into the atmosphere through chimney 155.

[0104] In summary, according to the treatment system 100 disclosed in the present invention, 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 based on the Boudouard reaction in the cooler 140, and then enters the rotary kiln 110, the combustion chamber 120, and the main burner 121, 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. In addition, 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, and can also generate reducing gases CO and H2 based on the water-gas reaction, and then enter the rotary kiln 110, the combustion chamber 120, and the main burner 121, 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 higher than the normal temperature air temperature, the fuel consumption in the combustion chamber 120 can be reduced.

[0105] In addition, the present disclosure treats the high-temperature 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 reducing gas to the rotary kiln 110 and the combustion chamber 120, the high-temperature flue gas is treated. The low oxygen content (or almost no oxygen) and certain amounts of CO and CO2 of the exhaust gas are utilized to react with the carbon in the unburned or burned carbonaceous dust of the RDF fuel in the cooler 140 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.

[0106] Referring to FIG4 , in a second aspect, the present disclosure further provides a rotary kiln treatment method for low- and high-moisture clay minerals. The treatment system based on the above technical solution comprises the following steps:

[0107] 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, under normal conditions, traditional fossil fuel and RDF fuel are introduced through the second fuel inlet and the gasifier respectively for combustion to provide calcination heat to the rotary kiln, among which the RDF fuel of the gasifier provides 90% of the heat.

[0108] The clay raw material to be calcined is crushed to meet the particle size of no more than 30mm, and then directly fed into the rotary kiln without grinding or removing moisture, and sequentially undergoes moisture drying in the drying section, the initial dehydroxylation reaction stage in the transition section, and the completion stage of the dehydroxylation reaction in the calcination section.

[0109] When the clay 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 140-150 degrees Celsius. The low-temperature mixed gas circulates into the cooler.

[0110] 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 first water spray device at the inlet end of 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, the unburned or burned carbonaceous dust of the RDF fuel of the gasifier 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.

[0111] 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.

[0112] 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 rotary kiln processing system for low- and high-moisture clay minerals, characterized in that: The processing system includes a rotary kiln, a feeding subsystem, a flue gas treatment subsystem, a cooling subsystem and a post-processing subsystem; The rotary kiln comprises a kiln tail, a drying section, a transition section, a calcining section and a kiln head connected in sequence from left to right, the kiln tail of the rotary kiln has a raw material inlet and a first flue gas outlet, the raw material inlet is used to introduce clay raw materials to be calcined, and the first flue gas outlet is used to discharge high-temperature flue gas generated during calcination; The kiln head of the rotary kiln is connected to a combustion chamber, and a main burner is arranged in the combustion chamber, and 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 and a second air inlet for introducing air, and the combustion chamber is also connected to a gasifier, and the gasifier has a third fuel inlet for introducing RDF fuel; The feeding subsystem includes a metering bin for providing clay raw materials that do not require grinding and dehydration and have a particle size of no more than 30 mm to the rotary kiln; The flue gas treatment subsystem is used to cool down the high-temperature flue gas discharged through the first flue gas outlet, and the low-temperature flue gas formed after the cooling treatment enters the cooling subsystem through the circulation pipeline; The cooling subsystem includes a cooler, and the inlet end of the cooler has an inlet for kiln materials and a second flue gas outlet; the inlet for kiln materials 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 and unburned or burned carbonaceous dust of RDF fuel introduced by the gasifier; the inner cavity of the cooler is provided with a water spraying device capable of spraying water to cool the high-temperature kiln materials, and the second flue gas outlet is respectively connected to the kiln head, the first air inlet and the second air inlet through an air supply pipe, and is used to lead out the reducing gas generated when the carbonaceous dust contacts the low-temperature flue gas and the water spray, and the low-temperature flue gas after heat exchange; as well as The post-processing subsystem is used to further crush the high-temperature kiln materials after the temperature is reduced so as to be used as cement clinker.

2. The processing system according to claim 1, 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 the high-temperature kiln material to below 300 degrees Celsius; 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.

3. The processing system according to claim 2, characterized in that The flue gas treatment subsystem includes at least one of the following: A cyclone, used to separate materials and waste gas from the high-temperature flue gas; A desulfurization and denitrification tower, used for desulfurizing and denitrifying the high-temperature flue gas; A dust collector is used to remove dust from the high-temperature flue gas.

4. The processing system according to claim 3, characterized in that The flue gas treatment subsystem includes the cyclone, the desulfurization and denitrification tower and the dust collector which are sequentially connected through pipelines: The material separated by the cyclone also enters the rotary kiln again through the 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 processing system according to claim 4, characterized in that The feeding subsystem also includes a silo and a crusher. The raw materials are crushed by the crusher and then transported to the metering silo.

6. The processing system according to claim 1, characterized in that The flue gas treated by the flue gas treatment subsystem is also connected to the chimney through the exhaust pipe for discharge.

7. The processing system according to claim 1, characterized in that The post-processing subsystem includes a crusher, a clay storage and a cement mill connected to the outlet end of the cooler. The crusher further crushes the high-temperature kiln material after cooling to a predetermined particle size, and then transports it to the cement mill for grinding after storage to reduce the amount of clinker added.

8. The processing system according to any one of claims 1 to 7, characterized in that An auxiliary 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.

9. A rotary kiln treatment method for low- and high-moisture clay minerals, based on the treatment system according to any one of claims 1 to 8, characterized in that: The processing 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, under normal conditions, traditional fossil fuel and RDF fuel are introduced through the second fuel inlet and the gasifier respectively for combustion to provide calcination heat for the rotary kiln, wherein the RDF fuel of the gasifier provides 50%-90% of the heat; The clay raw material to be calcined is crushed to a particle size of no more than 30 mm, and then directly fed into the rotary kiln without grinding or removing moisture, and sequentially undergoes moisture drying in the drying section, the beginning of the dehydroxylation reaction stage in the transition section, and the completion of the dehydroxylation reaction stage in the calcination section; When the clay 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 becomes A low-temperature mixed gas with a temperature of 140-150 degrees Celsius is circulated into the cooler; When the high-temperature kiln material discharged from the rotary kiln after calcination enters the cooler, the high-temperature kiln material exchanges heat with the low-temperature mixed gas circulating into the cooler, and is sprayed with water by the first water spray device at the inlet end of the cooler, and is quickly cooled to below 300 degrees Celsius to ensure that the high-temperature kiln material remains gray and avoids discoloration; in this process, the unburned or burned carbonaceous dust of the RDF fuel of the gasifier enters the cooler with the high-temperature kiln material through the unloading point at the kiln head, and undergoes Boudol reaction and water-gas reaction with the low-temperature mixed gas and the sprayed water, producing 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.

10. The processing method according to claim 9, characterized in that: The following steps are also included: The low-temperature mixed gas after heat exchange and the generated reducing gas enter the kiln head of the rotary kiln and are burned by the auxiliary burner to further consume the oxygen entering the rotary kiln; and / or When the rotary kiln is ignited and clay is calcined, if an emergency occurs: the fuel introduced from the second fuel inlet or the gasifier cannot be used, the remaining fuel will be used to provide all the heat to achieve multiple protection effects.

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