Method and system for preparing cement clinker by full-system oxy-fuel combustion using alternative fuel

Abstract

Disclosed in the present invention are a method and system for preparing a cement clinker by full-system oxy-fuel combustion using an alternative fuel. The alternative fuel in a decomposition furnace is combusted and thus releases heat for endothermic decomposition of a raw material in the decomposition furnace; heat in a rotary kiln is supplied by coal and the alternative fuel which are mixed, the alternative proportion of the alternative fuel being ≥80%; and cooling is performed in a cooler to obtain a cement clinker. A gas outlet of a cyclone at the top end of a preheater discharges CO2 circulating flue gas, which serves as a cooling medium to be mixed with a bypass kiln gas and to directly enter a middle cooling zone of the cooler. The high-temperature bypass kiln gas extracted from a kiln inlet chamber is subjected to contact cooling to 150-250°C with the CO2 circulating flue gas cooling medium; then the flue gas and high-concentration oxygen simultaneously enter a head cooling zone of the cooler; the flue gas entering the head cooling zone has a temperature range of 100-200°C and an acidic gas concentration of ≤500mg / Nm3; and the flue gas entering the middle cooling zone has a temperature range of 60-100°C and an acidic gas concentration of ≤50mg / Nm3.

Description

A method and system for preparing cement clinker using an all-oxygen combustion system with alternative fuels. Technical Field

[0001] This invention relates to the field of flue gas carbon capture technology, and in particular to a method and system for preparing cement clinker using an all-oxygen combustion system with alternative fuels. Background Technology

[0002] Oxygen-based combustion, based on existing industrial kiln systems, replaces combustion air with high-purity oxygen. Simultaneously, flue gas recirculation regulates the flow rate and heat transfer characteristics of the entire kiln system, enriching all CO2 from fuel combustion and raw material decomposition. This achieves CO2 concentrations exceeding 80% by volume in the flue gas, enabling permanent CO2 sequestration or resource utilization at a relatively low cost, thus achieving large-scale industrial CO2 enrichment and emission reduction. Existing analyses indicate that compared to other carbon capture methods, oxygen-based combustion technology offers advantages in investment cost, operating cost, CO2 emission reduction cost, scalability, and compatibility with existing technologies.

[0003] The stability of the thermal regime in cement kilns is crucial for ensuring clinker quality and yield. The use of alternative fuels can impact clinker calcination. When large quantities of alternative fuels are directly introduced into the cement kiln system, their large particle size, low calorific value, and high moisture content lead to incomplete combustion, low burnout rate, and the generation of large amounts of CO in the preheating furnace. Common solutions include increasing the high-temperature fan speed, increasing the excess air coefficient, and increasing the preheating furnace volume. However, this results in excessively high airflow in the preheating and pre-decomposition system, reaching 1.7-1.8 Nm³. 3 The preheater system has a high outlet temperature and a large air volume, resulting in a heat consumption that is 80-100 kcal / kg·cl higher than that of cement production using normal fossil fuel combustion.

[0004] More importantly, in the all-oxygen combustion process system, the use of alternative fuels in the cement clinker calcination process causes harmful components such as alkali, sulfur, and chlorine to decompose at high temperatures and condense at low temperatures in the kiln gas. This leads to repeated accumulation and circulation of these components in the rotary kiln flue gas, resulting in various negative conditions such as crusting, blocked ventilation, and decreased product quality. To address these issues, Chinese Patent Publication No. CN115164608A proposes an all-oxygen combustion system with bypass venting and its process principle. This process utilizes the cooled exhaust gas from the preheater system outlet to control the temperature of the flue gas in the bypass venting system. Oxygen from the oxygen production system is mixed with the low-temperature flue gas from the bypass venting system and blown into the front chamber of the grate cooler. However, this patent does not clearly address the issue that when the flue gas is recycled, the bypass venting flue gas contains large amounts of acidic gases such as SOx, HCl, and HF. During recycling, the temperature drop easily reaches the acid dew point, forming liquid acid, which can corrode pipes and core equipment over long-term use.

[0005] Furthermore, based on the adiabatic flame temperature under different oxygen concentrations, it is known that the flame temperature increases significantly with increasing oxygen concentration. Under a 50% O2 concentration, the theoretical combustion temperature is approximately 400°C higher than that of conventional air. Since the formation of thermal NOx is mainly affected by combustion temperature, the high combustion temperature in the rotary kiln of the all-oxygen combustion system leads to a significant increase in thermal NOx. Relying solely on waste gas treatment and environmental protection equipment will significantly increase the overall investment and operating costs of the system. Therefore, it is necessary to develop a targeted solution for NOx control using an all-oxygen combustion system. Summary of the Invention

[0006] This invention addresses the problems arising from the use of alternative fuels in cement clinker calcination under oxy-fuel combustion conditions. It proposes a method and system for preparing cement clinker using oxy-fuel combustion across the entire system. While ensuring stable clinker production quality, this system optimizes the distribution of heat, airflow, and combustion products within the process system based on the combustion characteristics of the combustion medium and alternative fuels in oxy-fuel combustion. It precisely addresses key issues arising from the switch from traditional air combustion to oxy-fuel combustion with alternative fuels, such as increased raw material decomposition temperature, enrichment of harmful components, decreased thermal efficiency of the calcination system, and acid exposure in bypass vents. The system achieves a heat substitution rate of over 90%, with a dry basis CO2 concentration of ≥85% in the flue gas entering the CO2 capture and purification system. Simultaneously, it comprehensively considers the enthalpy of the bypass vents and the cooling air from the oxy-fuel combustion cooler, and improves the system's CO2 recovery rate by rationally designing the cooler's air supply method. This avoids acid condensation and significantly reduces system heat consumption and CO2 capture and purification costs, achieving optimal energy consumption and efficient operation of the technical system.

[0007] This invention is implemented as follows: a method for preparing cement clinker using an all-oxygen combustion system with alternative fuels, comprising the following steps:

[0008] Raw meal is fed into a preheater and preheated to the decomposition temperature. The preheated raw meal is then fed into a decomposition furnace. In the oxygen-rich combustion environment of the decomposition furnace, the alternative fuel burns and releases heat to supply the raw meal for endothermic decomposition, resulting in calcined raw meal. The calcined raw meal enters a rotary kiln, where heat is supplied by a mixture of coal and alternative fuel, with the alternative fuel substitution ratio being ≥80%, generating hot clinker. The hot clinker is then cooled in a cooler to obtain cement clinker.

[0009] CO2 circulating flue gas is discharged from the cyclone outlet at the top of the preheater and used as a cooling medium to mix with the bypass vented kiln gas and directly enter the cooling zone in the middle of the cooler.

[0010] In this process, the high-temperature bypass vent gas from the kiln tail flue is cooled to 150–250°C by contact with the CO2 circulating flue gas cooling medium. Then, the flue gas and high-concentration oxygen simultaneously enter the cooling zone at the head of the cooler. The temperature of the flue gas entering the head cooling zone ranges from 100–200°C, and the concentration of acidic gases is ≤500 mg / Nm³. 3 The flue gas temperature entering the central cooling zone ranges from 60 to 100°C, and the concentration of acidic gases is ≤50 mg / Nm³. 3 .

[0011] In the above technical solution, preferably, the CO2 circulating flue gas discharged from the cyclone outlet at the top of the preheater, after desulfurization, dust collection, and condensation, has an SO2 content of less than 50 mg / Nm³. 3 The flue gas temperature is ≤50℃ and the H2O content is 2-10%; then the flue gas temperature is raised to ≥60℃; then it is used as a cooling medium to mix with the bypass vent gas and directly enter the cooling zone in the middle of the cooler.

[0012] In the above technical solution, preferably, the venting ratio of bypass venting kiln gas is controlled at 10-20%.

[0013] In the above technical solution, preferably, the high-temperature bypass vent gas from the kiln tail flue comes into contact with the CO2 circulating flue gas cooling medium and is first rapidly cooled to 350-450°C, then separated by a cyclone separator. The coarse particles are returned to the decomposition furnace, while the fine particles containing dust are cooled to 150-250°C by contacting the CO2 circulating flue gas cooling medium again.

[0014] In the above technical solution, a further preferred embodiment involves the flue gas, after being cooled twice, first undergoing a sulfur-fixing reaction with an active desulfurizing agent at 150–250°C, thereby controlling the SO2 emission in the flue gas after the two cooling processes to 500 mg / Nm³. 3 Next, the sulfur-fixing waste residue is discharged from the system after dust collection.

[0015] In the above technical solution, preferably, the cooler is divided into three sections. The high-temperature gas exiting the cooling zone at the head of the cooler is used as secondary and tertiary air, respectively, and is introduced into the rotary kiln and the decomposition furnace. The circulating flue gas exiting the cooling zone in the middle of the cooler is used as lifting air and is introduced into the bottom of the decomposition furnace. The tertiary air inlet of the decomposition furnace is located above the lifting air inlet, forming a reduction zone between the lifting air inlet and the tertiary air inlet, controlling the excess oxygen coefficient to ≤0.5, thereby achieving the reduction of NO in the flue gas exiting the kiln. X It removes and lifts the material below the tertiary air inlet; it forms a combustion zone above the tertiary air inlet, achieving complete combustion of the alternative fuel.

[0016] In the above technical solution, it is further preferred that the O2 concentration in the secondary and tertiary air is 30% to 70%; the CO2 dry basis concentration in the lifting air is ≥85%, the O2 concentration is ≤5%, and the temperature range is 500 to 900℃.

[0017] In the above technical solution, a further preferred embodiment is that the lifting air swirls into the decomposition furnace, and along the lifting air flow direction, the lifting air first contacts the raw material and then contacts the fuel.

[0018] In the above technical solution, it is further preferred that the wind speed at the bottom of the decomposition furnace is maintained between 30 and 50 m / s.

[0019] In the above technical solution, a further preferred embodiment is that the gas residence time in the decomposition furnace is controlled to be 10-20s, the CO concentration at the decomposition furnace outlet is controlled to be 0.1%-1%, and the decomposition furnace outlet temperature is controlled to be 850-950℃ to ensure that the decomposition rate of raw materials entering the rotary kiln is ≥90%.

[0020] In the above technical solution, preferably, the CO2 dry basis concentration in the CO2 circulating flue gas discharged from the cyclone outlet at the top of the preheater is ≥85%, and the temperature is 250~400℃.

[0021] In the above technical solution, preferably, high-concentration oxygen is preheated and mixed with the flue gas after bypass venting, referred to as O2 / CO2 mixture, and then enters the cooling zone of the cooler head together; or, high-concentration oxygen is directly introduced into the air chamber under the feed slope of the cooling zone of the cooler head at room temperature, and the flue gas after bypass venting is introduced into the remaining air chambers of the cooling zone of the cooler head.

[0022] In the above technical solution, preferably, the CO2 circulating flue gas also enters the carbon capture and purification system.

[0023] In the above technical solution, preferably, there is no cross-flow between the cooling zone at the head of the cooler, the cooling zone in the middle of the cooler, and the cooling zone at the tail of the cooler.

[0024] In the above technical solution, preferably, the CO2 circulating flue gas exiting the cooling zone in the middle of the cooler is also used as enthalpy recovery air and enters the decomposition furnace outlet, with a temperature range of 500-900℃.

[0025] In the above technical solution, preferably, air is introduced into the cooling zone at the tail of the cooler; the air exiting the cooling zone at the tail of the cooler is low enthalpy air with a temperature range of 200-300℃, which is used as a heat source for drying raw materials.

[0026] A system for preparing cement clinker using alternative fuels through full oxygen combustion includes a preheater, a decomposer, a kiln tail flue, a rotary kiln, and a cooler connected in sequence.

[0027] It also includes a bypass ventilation system, the intake point for the bypass ventilation kiln gas is located in the rising flue of the kiln tail smoke chamber, the bypass ventilation system includes a cooling system, the cooling system is connected to the kiln tail smoke chamber through a pipeline, the outlet of the cooling system is connected to the air inlet of the cooling zone at the head of the cooler, and the cooling zone at the head of the cooler is also provided with a high-concentration oxygen inlet; the outlet of the cyclone at the top of the preheater is connected to the cooling system and the air inlet of the cooling zone in the middle of the cooler respectively.

[0028] In the above technical solution, preferably, the cooling system includes a quenching chamber and a cyclone separator. The quenching chamber is connected to the kiln tail smoke chamber through a pipeline. The air outlet of the quenching chamber is connected to the air inlet of the cyclone separator. The feed pipe of the cyclone separator is connected to the decomposition furnace. The air outlet of the cyclone separator is connected to the air inlet of the cooling zone at the head of the cooler.

[0029] In the above technical solution, a further preferred embodiment is that the bypass ventilation system also includes a bypass ventilation dust collector, the air inlet of which is connected to the air outlet of the cyclone separator, and the air outlet of which is connected to the air inlet of the cooling zone at the head of the cooler.

[0030] In a further preferred embodiment of the above technical solution, a desulfurizing agent storage tank is also provided on the connecting pipeline between the cyclone separator and the bypass exhaust dust collector. The desulfurizing agent storage tank is used to deliver the active desulfurizing agent into the connecting pipeline, allowing the active desulfurizing agent to react with the volatile sulfur in the flue gas after two cooling cycles at 150–250°C to achieve a sulfur-fixing reaction, thereby controlling the SO2 emission in the flue gas after two cooling cycles to 500 mg / Nm³. 3 The sulfur-fixing waste residue is then discharged from the system via a bypass venting dust collector.

[0031] In the above technical solution, preferably, the air outlet of the cyclone at the top of the preheater is connected in sequence to the wet desulfurization system, the bag dust collector, the flue gas condenser, and the flue gas preheater, and the air outlet of the flue gas preheater is connected to the cooling system and the air inlet of the cooling zone in the middle of the cooler.

[0032] In the above technical solution, preferably, a first resistance baffle is provided between the cooling zone at the head of the cooler and the cooling zone in the middle of the cooler to reduce the leakage of O2 / CO2 mixture from the cooling zone at the head of the cooler into the cooling zone in the middle of the cooler; a second resistance baffle and a central roller crusher are provided between the cooling zone in the middle of the cooler and the cooling zone at the tail of the cooler, and steam generated from indirect drying fuel / alternative fuel is introduced into the air chamber below the central roller crusher as a cooling medium to form an air curtain to further block leakage; the height of the bottom of the first resistance baffle and the second resistance baffle and the gap between the corresponding cooler bed are ≤300mm, and the first resistance baffle and the second resistance baffle are rotating and movable baffles.

[0033] In the above technical solution, preferably, the decomposition furnace is provided with a tertiary air inlet, a lifting air inlet, a raw material feeding point, and a fuel feeding point, with the lifting air inlet located below the tertiary air inlet; the top outlet of the decomposition furnace is connected to a pipe for flue gas to first rise and then fall, with a recovery enthalpy air inlet on the falling pipe; the secondary air intake and tertiary air intake of the cooler are located in the cooling zone at the head of the cooler, and the lifting air intake is located in the cooling zone in the middle of the cooler; the secondary air intake is connected to the rotary kiln, and the tertiary air intake is connected to the tertiary air inlet of the decomposition furnace through a pipe; the lifting air intake... The air intake is connected to the lifting air inlet and the recovery heat enthalpy air inlet of the decomposition furnace through pipelines; at least two raw material feeding points are set, of which at least one raw material feeding point is located between the lifting air inlet and the tertiary air inlet, and at least one raw material feeding point is located above the tertiary air inlet; the height of the lifting air inlet is below the raw material feeding point below the tertiary air inlet; the fuel feeding point is located between the lifting air inlet and the tertiary air inlet, and above the tertiary air inlet; a reduction zone is formed inside the decomposition furnace between the lifting air inlet and the tertiary air inlet, and a combustion zone is formed above the tertiary air inlet.

[0034] In the above technical solution, preferably, the decomposition furnace has a first narrowing at the tertiary air inlet and a second narrowing at the lifting air inlet.

[0035] The advantages and positive effects of this invention are:

[0036] (1) This invention fully considers the problem that harmful elements such as potassium, sodium, chlorine and sulfur in alternative fuels accumulate in the kiln system, causing serious scaling and blockage in parts such as the kiln tail flue and rotary kiln feed slope, which affects the operating conditions and clinker quality. It innovatively uses CO2 circulating flue gas as a cooling medium to enter the bypass venting system to reduce the harmful components in the cement kiln system. On the one hand, it ensures that no external gas is introduced to affect the CO2 enrichment concentration in the calcination system. On the other hand, it circulates all the bypass venting flue gas with enthalpy back to the cooler as clinker cooling air, which will not significantly increase the heat consumption of the all-oxygen combustion system.

[0037] (2) This invention takes special consideration into account the problem of cross-flow between cooling sections caused by the air pressure difference in the air chamber of the cooler in the all-oxygen combustion system. By reasonably setting a resistance baffle one near the zero pressure point of the cooling zone at the head of the cooler and the cooling zone in the middle of the cooler, the O2 / CO2 mixture containing O2 in the cooling zone at the head of the cooler is prevented from escaping to the cooling zone in the middle of the cooler, resulting in some O2 not being effectively utilized and entering the preheater, which in turn causes the energy consumption and cost of CO2 purification to increase when entering the CO2 capture and purification system. By reasonably setting a resistance baffle two near the zero pressure point of the cooling zone in the middle of the cooler and the cooling zone in the tail of the cooler, not only is the cross-flow of CO2 circulating flue gas from the cooling zone in the middle of the cooler to the air in the cooling zone in the tail of the cooler, which causes CO2 to escape and affect the CO2 recovery rate, but also the cross-flow of air from the cooling zone in the tail of the cooler into the CO2 circulating flue gas in the cooling zone in the middle of the cooler, which dilutes the CO2 enrichment concentration and causes the energy consumption of the CO2 capture and purification system to increase.

[0038] (3) This invention fully considers the problem of decreased thermal efficiency of the oxy-fuel combustion cooler, and fully recovers heat to the calcination system, thereby improving the thermal efficiency of the cooler, saving fuel consumption, and reducing energy consumption in cement production. Compared with the conventional air system, the total air volume of the secondary and tertiary air in the oxy-fuel combustion system is significantly reduced, which leads to the inability to fully utilize the recovered waste heat in the second stage of the cooler, resulting in a decrease in the heat recovery efficiency of the cooler. This invention introduces high-temperature waste heat-generating lift air into a suitable location within the decomposition furnace. Firstly, it serves as the kinetic energy medium for the necessary wind speed required for the raw material suspension decomposition process. Secondly, it utilizes the low oxygen concentration characteristic of the CO2 circulating flue gas as a combustion control medium to regulate the combustion environment in the reduction zone of the decomposition furnace, enabling the fuel at the bottom of the furnace to generate a reducing atmosphere in an oxygen-deficient combustion environment, thus achieving the purpose of self-denitrification in the decomposition furnace. Thirdly, it serves as a means of controlling the raw material decomposition temperature under high CO2 partial pressure within the decomposition furnace. If the lift air, composed entirely of CO2 circulating flue gas, is introduced into the furnace entirely from the bottom, it will lead to an increase in the CO2 partial pressure in the flue gas, causing the raw material decomposition temperature to rise to 950℃ or even above 1000℃. Fourthly, it serves as a means of controlling the decomposition furnace outlet temperature, avoiding the problem of scale buildup and blockage inside the final stage cyclone separator of the preheater due to the increased raw material decomposition temperature and the delayed combustion of alternative fuels. Attached Figure Description

[0039] Figure 1 is a schematic diagram of a cement clinker preparation system using an all-oxygen combustion system with applicable alternative fuels provided in Embodiment 1 of the present invention.

[0040] Figure 2 is a schematic diagram of a cement clinker preparation system using an all-oxygen combustion system with applicable alternative fuels provided in Embodiment 2 of the present invention.

[0041] Figure 3 is a top view of the lifting air intake of the furnace provided by embodiments 1 and 2 of the present invention;

[0042] Figure 4 is a top view of the lifting air intake of the furnace provided in Embodiment 3 of the present invention.

[0043] In the diagram: A - O2 / CO2 mixture; B - CO2 circulating flue gas; C - Air; D - Carbon capture and purification system; g2 - Secondary air; g3 - Tertiary air; g4 - Flue gas exiting the middle cooling zone of the cooler; g41 - Lifting air; g42 - Recovered enthalpy air; g5 - Air exiting the tail cooling zone of the cooler; F1 - Fuel entering the rotary kiln; F2 - Fuel entering the decomposition furnace; R - Raw meal; K - Cement clinker; 1 - Cooler; 101 - Cooler head cooling zone; 102 - Cooler middle cooling zone; 103 - Cooler tail cooling zone; 104 - Central roller crusher; 1041 - First resistance baffle; 1042 - Second resistance baffle; 1a - Cooler head cooling zone material bed; 1b - Cooler middle cooling zone material bed; 1c - Cooler tail cooling zone material bed; 2-Rotary kiln; 3-Decomposition furnace; 301-Reduction zone; 302-Combustion zone; 303-Burner; 304-Feeding box; 305-Lifting air inlet; 4-Kiln tail flue; 5-Preheater; 6-High temperature fan; 7-Bag dust collector; 8-Wet desulfurization system; 9-Tail exhaust fan; 10-Flue gas condenser; 11-Flue gas preheater; 1201-Circulating fan; 1202-Secondary cooling fan; 1203-Bypass fan; 13-Quick cooling chamber; 14-Cyclone separator; 15-Desulfurizing agent storage bin; 16-Bypass venting dust collector; 1701-Circulating air volume regulating valve; 1702-Bypass venting regulating valve; 1703-Reduction zone air volume regulating valve; 1704-Combustion zone air volume regulating valve; Dashed arrows indicate airflow direction. Solid arrows indicate material flow direction. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0046] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0047] Example 1

[0048] Please refer to Figure 1. An embodiment of the present invention provides a cement clinker preparation system using oxy-fuel combustion with alternative fuels, comprising a preheater 5, a decomposition furnace 3, a kiln tail flue 4, a rotary kiln 2, a cooler 1, and a bypass venting system connected in sequence.

[0049] Preheater 5 is a two- to five-stage or two- to six-stage preheater; this embodiment uses a five-stage preheater as an example. The air inlet of the fifth-stage cyclone separator of the preheater is connected to the air outlet pipe of the decomposition furnace. The air outlet of the first-stage cyclone separator of the preheater discharges low-temperature flue gas containing CO2. A raw material inlet is provided on the connecting duct between the first-stage and second-stage cyclone separators of the preheater. The discharge outlet of the fifth-stage cyclone separator of the preheater is connected to the kiln tail flue chamber 4.

[0050] Cement raw meal R is fed into the preheater from the top raw meal inlet. The raw meal R is heated and preheated in the preheater 5 from top to bottom until it enters the fourth-stage cyclone and then enters the decomposition furnace 3 through the discharge chute. After decomposition in the decomposition furnace, it passes through the fifth-stage cyclone for gas-solid separation. The hot raw meal enters the rotary kiln 2 through the kiln tail smoke chamber 4 for calcination to obtain hot clinker. Then it enters the cooler 1 for cooling to obtain cement clinker K. The cement clinker K exiting the cooler is the product of cement production corresponding to this invention.

[0051] The heat required for cement clinker production comes from fuel F1 fed into the rotary kiln and fuel F2 fed into the precalciner. Fuel F1 fed into the rotary kiln is supplied by both coal and alternative fuels, with the alternative fuels accounting for ≥80% of the total fuel consumption. Fuel F2 fed into the precalciner is entirely supplied by alternative fuels, with a 100% replacement rate. Alternative fuels include treated waste textiles, leather scraps, waste plastics, municipal solid waste, light slag from paper mills, and sludge. In this embodiment, the alternative fuels are treated waste textiles, municipal solid waste, and sludge, etc.

[0052] When alternative fuels are used extensively in a system, harmful elements (potassium, sodium, chlorine, sulfur, etc.) can cause the chlorine to accumulate in the system, leading to scaling and blockage in the cement kiln, thus affecting the normal operation of the system and the quality of clinker, and impacting the normal operation of the cement kiln. Bypass venting in conventional air combustion systems is an effective measure to address the accumulation of harmful components. It extracts and releases some gas from the accumulation points of harmful elements in the cement kiln, thereby disrupting the chlorine cycle in the system, reducing the risk of scaling, and effectively improving the kiln system's operating rate. However, the bypass venting gas still contains approximately 100–200°C of enthalpy that is not fully utilized, and direct discharge results in a loss of enthalpy in the system.

[0053] The oxygen-fired cement clinker calcination system of the present invention is equipped with a bypass ventilation system to reduce the accumulation and circulation of harmful components such as chlorine, alkali, and sulfur in the calcination system.

[0054] The intake point for the bypass venting kiln gas is located in the rising flue of the kiln tail smoke chamber 4. The bypass venting system includes a cooling system, which is connected to the kiln tail smoke chamber 4 via a pipeline. The outlet of the cooling system is connected to the inlet of the cooling zone 101 at the head of the cooler. The cooling zone 101 at the head of the cooler is also provided with a high-concentration oxygen inlet. The outlet of the cyclone at the top of the preheater 5 is connected to the cooling system and the inlet of the cooling zone 102 in the middle of the cooler, respectively.

[0055] The CO2 circulating flue gas B discharged from the cyclone outlet at the top of preheater 5 is introduced as a cooling medium into the bypass venting system and the middle cooling zone 102 of the cooler. The temperature of the flue gas entering the head cooling zone is controlled within the range of 100-200℃, and the concentration of acidic gases is ≤500mg / Nm³. 3 The flue gas temperature entering the central cooling zone ranges from 60 to 100°C, and the concentration of acidic gases is ≤50 mg / Nm³. 3 This achieves simultaneous temperature and sulfur control, preventing acid condensation.

[0056] In a preferred embodiment, the cooling system includes a quenching chamber 13 and a cyclone separator 14. The quenching chamber 13 is connected to the kiln tail smoke chamber 4 via a pipeline. The air outlet of the quenching chamber 13 is connected to the air inlet of the cyclone separator 14. The feed pipe of the cyclone separator 14 is connected to the decomposition furnace 3. The air outlet of the cyclone separator 14 is connected to the air inlet of the cooling zone 101 at the head of the cooler.

[0057] The bypass ventilation system also includes a bypass ventilation dust collector 16, the air inlet of which is connected to the air outlet of the cyclone separator 14, and the air outlet of the bypass ventilation dust collector 16 is connected to the air inlet of the cooling zone 101 at the head of the cooler.

[0058] Specifically, the bypass venting system includes a quenching chamber 13, a cyclone separator 14, and a bypass venting dust collector 16. The intake point for the bypass venting kiln gas is located in the rising flue of the kiln tail smoke chamber 4. Part of the rotary kiln exhaust gas enters the bypass venting system, and the venting ratio of the bypass venting kiln gas is controlled at 10-20%. The quenching chamber 13 is connected to the kiln tail smoke chamber 4 via a pipeline. The outlet of the quenching chamber 13 is connected to the inlet of the cyclone separator 14. The feed pipe of the cyclone separator 14 is connected to the decomposition furnace. The outlet of the cyclone separator 14 is connected to the bypass venting dust collector 16. The outlet of the bypass venting dust collector 16 is connected to the inlet of the cooling zone 101 at the head of the cooler. The cooling zone 101 at the head of the cooler is also equipped with a high-concentration oxygen inlet. The top of the preheater 5 is cyclone... The air outlet of the duct is connected in sequence to the wet desulfurization system 8, the bag dust collector 7, the flue gas condenser 10, and the flue gas preheater 11. The air outlet of the flue gas preheater 11 is connected to the connecting pipeline between the quench chamber 13 of the bypass venting system, the cyclone separator 14, and the bypass venting dust collector 16, so that the flue gas discharged from the top of the preheater is treated and used as a cooling medium to enter the bypass venting system. The air outlet of the flue gas preheater 11 is also connected to the air inlet of the cooling zone 102 in the middle of the cooler.

[0059] The flue gas from the decomposition furnace 3 and the raw materials complete the heat exchange process in the preheater 5. The flue gas discharged from the cyclone outlet at the top of the preheater 5 is CO2 circulating flue gas B, with a CO2 dry basis concentration ≥85% and a temperature of 250~400℃.

[0060] In this embodiment, the CO2 circulating flue gas B is introduced into the wet desulfurization system 8 by the high-temperature fan 6 to control the SO2 content of the CO2 circulating flue gas to ≤50mg / Nm³. 3 Then it enters the bag filter 7 to reduce the particulate matter content to 100mg / Nm³. 3 The CO2 circulating flue gas from the baghouse dust collector 7 is then introduced into the flue gas condenser 10 via the tail exhaust fan 9 to cool to ≤40℃, causing saturated water vapor in the flue gas to condense and controlling the flue gas moisture content to 2%–10%. To prevent water and acid condensation from corroding the pipelines under these moisture conditions, the CO2 circulating flue gas at ≤40℃ is heated to ≥60℃ via the flue gas preheater 11, making the flue gas unsaturated. Simultaneously, the pipelines are constructed of corrosion-resistant stainless steel and insulated on the outside to maximize the flue gas temperature. The preheated CO2 circulating flue gas to ≥60℃ is then introduced into the bypass venting system, the central cooling zone 102 of the cooler, and the carbon capture and purification system D via the circulating fan 1201 and the secondary cooling fan 1202.

[0061] In this embodiment, a flue gas circulation volume regulating valve 1701 is installed on the outlet pipe of the circulating fan 1201 to control the amount of flue gas entering the carbon capture and purification system D.

[0062] The cooling medium of the bypass venting system is CO2 circulating flue gas. The high-temperature bypass venting gas entering the bypass venting system undergoes two cooling cycles with the CO2 circulating flue gas to reduce the enrichment and circulation of harmful components such as sulfur and chlorine in the high-temperature bypass venting gas. The first cooling process uses a quenching chamber to ensure that the high-temperature bypass venting gas containing harmful components in the kiln tail flue chamber 4 comes into full contact and mixes with the CO2 circulating flue gas, cooling the high-temperature bypass venting gas containing harmful components from 950-1200℃ to 350-450℃. Volatile chlorine-containing harmful components condense and adhere to the surface of the dust carried out with the high-temperature bypass venting gas. Since harmful components are more likely to concentrate on the surface of fine particles, the medium-temperature kiln gas after the first quenching enters the cyclone separator 14 to separate coarse and fine particles. The coarse particles are returned to the decomposition furnace through the cyclone separator 14, reducing the amount of dust collected by the bypass venting system. The medium-temperature kiln gas, coated with fine particles containing harmful components, exits the cyclone separator 14 and is then cooled to 150–250°C through secondary contact with CO2 circulating flue gas. The dust-laden low-temperature exhaust gas then enters the bypass venting dust collector 16, which discharges fine particles containing harmful components such as Cl and S from the system. The low-temperature exhaust gas is then mixed with high-concentration O2 (O2 concentration ≥ 95%) and enters the cooling zone of the cooler head as O2 / CO2 mixture A to recover enthalpy. In this embodiment, the high-concentration oxygen generated by the oxygen production system is preheated to 100–150°C before being mixed with the low-temperature exhaust gas after bypass venting dust collection. This prevents water and acid condensation from corroding the cooler equipment, grate connectors, and other metal materials during flue gas cooling.

[0063] The combustion-supporting gas used in the system is replaced by the O2 / N2 of the conventional air combustion system with the O2 / CO2 mixture of the all-oxygen combustion system, and is fed into the rotary kiln 2 and the decomposition furnace 3 by the cooler 1 respectively. In this embodiment, the oxygen production system using the existing cryogenic distillation technology produces high-concentration oxygen, which can generally achieve an oxygen concentration of ≥96%, an argon concentration of ≤3%, and an N2 concentration of ≤1%.

[0064] In a preferred embodiment, the cooler 1 is divided into three sections from the clinker inlet to the outlet (the process of cooling clinker): the head cooling zone 101, the middle cooling zone 102, and the tail cooling zone 103. The secondary air intake and tertiary air intake of the cooler are located in the head cooling zone 101, and the lifting air intake is located in the middle cooling zone 102.

[0065] As a preferred embodiment, to further reduce the problem of air leakage caused by the difference in induced draft pressure between different sections of the cooler 1, a first resistance baffle 1041 is installed between the head cooling zone 101 and the middle cooling zone 102 of the cooler to reduce the leakage of O2 / CO2 mixture A from the head cooling zone 101 into the middle cooling zone 102. The first resistance baffle is located at the rear of the air chamber of the head cooling zone 101 to prevent the O2 / CO2 mixture from leaking and mixing with the CO2 circulating flue gas, thus preventing O2 from being introduced into the decomposition furnace outlet by the recovered heat enthalpy air due to incomplete combustion in the cement kiln, which would increase the load on the oxygen production system and the power consumption of the carbon capture and purification system. A second resistance baffle 1042 and a central roller crusher 104 are installed between the middle cooling zone 102 and the tail cooling zone 103 of the cooler. The second resistance baffle can prevent air C from entering the cooling zone through the gap of the central roller crusher. The cooling zone 102 in the middle of the machine affects the CO2 enrichment concentration. Steam generated from indirect drying of fuel / alternative fuel is introduced into the air chamber at the bottom of the central roller crusher 104 as a cooling medium to form an air curtain, further blocking cross-flow. Since there are gaps between the rollers of the central roller crusher, to avoid cross-flow of the cooling medium during continuous cooling, steam generated from indirect drying of fuel / alternative fuel is introduced between the cooling zone 102 in the middle of the machine and the cooling zone 103 at the tail of the machine as a cooling medium. This further blocks direct cross-flow between the CO2 circulating flue gas cooling medium in the middle cooling zone and the air cooling medium in the cooling zone 103 at the tail of the machine. This reduces the impact of air entering the middle cooling zone through the gaps in the central roller crusher 104 on the CO2 enrichment concentration and reduces CO2 escape caused by CO2 circulating flue gas entering the cooling zone 103 at the tail of the machine, thus affecting the CO2 recovery rate.

[0066] In this embodiment, the cooling air in the tail cooling zone 103 of the cooler is divided into two streams. The first stream is located at the front section of the tail cooling zone 103 (the air chamber under the central roller crusher), and steam generated for drying moisture in fuel / alternative fuel is introduced into the cooling air chamber under the central roller crusher. The second stream is located at the rear section of the tail cooling zone 103 and is supplied with air C. This further controls air leakage in the middle cooling zone 102 and the tail cooling zone of the cooler, and minimizes the impact on the clinker cooling effect, ensuring clinker quality. The air exiting the tail cooling zone 103 of the cooler is low enthalpy air with a temperature range of 200–300°C, and is used as a heat source for drying raw materials.

[0067] The height of the bottom of the first resistance baffle 1041 and the second resistance baffle 1042 is ≤300mm from the corresponding cooler material bed. The first resistance baffle 1041 and the second resistance baffle 1042 are rotating and movable baffles. When large lumps or balls of clinker enter the cooler and the material layer comes into contact with the resistance baffle, hindering the reciprocating movement of the grate, they can rotate flexibly.

[0068] In a preferred embodiment, the decomposition furnace 3 is provided with a tertiary air inlet, a lifting air inlet 305, a raw material feeding point, and a fuel feeding point. The lifting air inlet 305 is located below the tertiary air inlet. The secondary air intake of the cooling zone 101 at the head of the cooler is connected to the rotary kiln 2. The tertiary air intake is connected to the tertiary air inlet of the decomposition furnace through a pipe. The lifting air intake of the middle cooling zone is connected to the lifting air inlet 305 of the decomposition furnace through a pipe. Raw material feeding points and fuel feeding points are provided above the tertiary air inlet and between the lifting air inlet 305 and the tertiary air inlet. At least one raw material feeding point is located between the lifting air inlet 305 and the tertiary air inlet, and at least one raw material feeding point is located above the tertiary air inlet. The height of the lifting air inlet 305 of the decomposition furnace is below the raw material feeding point below the tertiary air inlet, thereby lifting the material below the tertiary air inlet and preventing material collapse. A reduction zone 301 is formed between the lifting air inlet 305 and the tertiary air inlet in the decomposition furnace, and a combustion zone 302 is formed above the tertiary air inlet.

[0069] Compared to conventional air combustion systems, oxy-fuel combustion systems produce significantly less flue gas without the introduction of N2. To prevent material collapse in the decomposition furnace, the air velocity at the bottom constriction must be maintained between 30 and 50 m / s. However, simply reducing the furnace diameter will increase system resistance. Therefore, introducing CO2 circulating flue gas as a lifting airflow into the bottom of the decomposition furnace can ensure the effective flotation of raw materials within the furnace. Simultaneously, based on the adiabatic flame temperature under different oxygen concentrations, it is known that the flame temperature increases significantly with increasing oxygen concentration. Under a 50% O2 concentration, the theoretical combustion temperature is approximately 400°C higher than that of conventional air. Since the formation of thermal NOx is primarily influenced by combustion temperature, as shown by the expression for the thermal NOx formation rate:

[0070] In the formula, T is the absolute temperature, t is the time, R is the universal gas constant, and [N2], [O2], and [NO] are the concentrations of N2, O2, and NO, respectively.

[0071] The high combustion temperature inside the rotary kiln in an oxy-fuel combustion system leads to a significant increase in thermal NOx. Therefore, it is necessary to create a reduction zone in the decomposition furnace to control NOx production in the rotary kiln. By providing an oxygen-deficient combustion environment at the bottom of the decomposition furnace and controlling the excess oxygen coefficient in the reduction zone to ≤0.5, the CO and NO produced by incomplete fuel combustion can be reduced. X A reduction reaction occurs, which can remove NO from the rotary kiln flue gas. X Effective removal ensures NOx emissions at the decomposition furnace outlet are ≤600 mg / Nm³. 3(@10% O2). Above the tertiary air inlet is the fuel combustion zone 302. The excess oxygen coefficient at the decomposition furnace outlet is controlled the same as in a conventional air combustion system, with an excess oxygen coefficient between 1.05 and 1.2, ensuring complete combustion of the alternative fuel and combustion products within the decomposition furnace to release heat. To guarantee complete combustion of the alternative fuel, a combustion zone 302 is formed above the tertiary air inlet, controlling the gas residence time within the decomposition furnace to 10–20 seconds. The combustion state within the furnace is judged by the CO concentration at the decomposition furnace outlet; CO should be controlled within the range of 0.1%–1%. Simultaneously, the decomposition furnace outlet temperature is controlled at 850–950℃ to ensure a raw material decomposition rate ≥90% entering the rotary kiln.

[0072] In a preferred embodiment, the top outlet of the decomposition furnace is connected to a pipe that allows flue gas to flow upwards and then downwards, with a recovery enthalpy air inlet on the downward-flowing pipe; the lifting air intake of the cooling zone 102 in the middle of the cooler is also connected to the recovery enthalpy air inlet via a pipe. Considering that the total cooling air volume required for cooling a unit of clinker in a conventional air-fired calcination system cooler is 1.8–2.0 Nm³, the cooling capacity is estimated to be 1.8–2.0 Nm³. 3 / kg.cl, the air volume for secondary and tertiary air is 0.8~0.9Nm. 3 / kg.cl, while the all-oxygen combustion system, due to the reduction in N2 introduction, significantly reduces the secondary and tertiary air consumption to 0.4–0.6 Nm³. 3 / kg.cl, if the waste heat from cooling clinker is discharged from the system, it will result in a waste of enthalpy.

[0073] More importantly, while utilizing the lift air to provide an oxygen-deficient combustion environment at the bottom of the decomposition furnace and achieve the raw material flotation effect, the remaining lift air is introduced into the decomposition furnace outlet as recovered heat enthalpy air g42 to further improve the heat recovery efficiency of the cooler. Simultaneously, this achieves: 1. Lowering the raw material decomposition temperature under high CO2 partial pressure within the decomposition furnace. If all the lift air, composed of CO2 circulating flue gas, is introduced into the furnace from the bottom, it will lead to an increase in the CO2 partial pressure in the flue gas, causing the raw material decomposition temperature to rise to 950℃ or even above 1000℃; 2. Adjustable decomposition furnace outlet temperature, avoiding the risk of scale buildup and blockage in the final stage cyclone of preheater 5 due to increased raw material decomposition temperature and delayed combustion of alternative fuels.

[0074] The O2 / CO2 mixture from the cooling zone 101 at the head of the cooler enters the firing system as secondary air g2 and tertiary air g3. Both secondary air g2 and tertiary air g3 are O2 / CO2 mixtures after heat exchange, which enter the rotary kiln 2 and the decomposition furnace respectively to provide a combustion environment. The O2 concentration in the O2 / CO2 mixture A ranges from 30% to 70%, the temperature of secondary air g2 ranges from 900 to 1200℃, and the temperature of tertiary air g3 ranges from 800 to 1100℃. In the cooling zone 102 in the middle of the cooler, the CO2 circulating flue gas, after heat exchange with the clinker, has a flue gas temperature range of 500 to 900℃, a CO2 dry basis concentration ≥85%, and an O2 concentration less than 5%.

[0075] In summary, the O2 / CO2 mixture exiting the cooling zone 101 at the head of the cooler enters the firing system as secondary air g2 and tertiary air g3, respectively, and enters the rotary kiln 2 and the decomposition furnace to provide a combustion environment; the CO2 circulating flue gas exiting the cooling zone 102 in the middle of the cooler is mainly divided into two paths, one path as lifting air g41 enters the bottom inlet of the decomposition furnace, and the other path as enthalpy recovery air enters the outlet of the decomposition furnace.

[0076] As a preferred embodiment, as shown in Figure 3, in this embodiment, the lifting air g41 enters the furnace in a dual-inlet configuration. The decomposition furnace is equipped with two lifting air inlets 305, two material distribution boxes 304, and two burners 303. The two lifting air inlets are centrally symmetrically arranged, the two burners are axially symmetrically arranged, and the two material distribution boxes are axially symmetrically arranged. As seen in Figure 3, the two lifting air streams g41 enter the decomposition furnace in swirling motions. Looking along the lifting air flow direction, each stream first contacts its adjacent downstream raw material, and then its adjacent downstream fuel. On the one hand, the lifting air is relatively close to the raw material, which is beneficial for lifting it; on the other hand, the lifting air temperature is 500–900℃, which is lower than the temperature of the kiln exhaust gas (1000–1200℃). The lifting air is relatively far from the fuel, so it will not reduce the temperature of the fuel feeding area or the fuel gasification rate.

[0077] As a preferred embodiment, the decomposition furnace has a first constriction at the tertiary air inlet and a second constriction at the lifting air inlet 305, which enhances gas-solid mixing and turbulence effects, prevents material settling and accumulation, and further ensures system stability.

[0078] In a preferred embodiment, a combustion zone airflow regulating valve 1704 is installed on the pipe between the tertiary air inlet of the decomposition furnace and the tertiary air outlet of the cooler, and a reduction zone airflow regulating valve 1703 is installed on the pipe between the lifting air inlet 305 of the decomposition furnace and the lifting air outlet of the cooler. The airflow to the lower reduction zone 301 and the upper combustion zone of the decomposition furnace is distributed according to the actual temperature along the decomposition furnace and the flue gas composition, so as to realize the airflow regulation.

[0079] In a preferred embodiment, a desulfurizing agent storage tank 15 is also provided on the connecting pipeline between the cyclone separator 14 and the bypass venting dust collector 16. The desulfurizing agent storage tank is used to feed active desulfurizing agents such as CaO, Ca(OH)2, NaCO3, and NaHCO3 into the connecting pipeline between the cyclone separator 14 and the bypass venting dust collector 16, so that the active desulfurizing agents react with the volatile sulfur in the flue gas after two cooling cycles at 150–250°C to fix sulfur, thereby controlling the SO2 emission in the flue gas after two cooling cycles to 500 mg / Nm³. 3 The desulfurization waste is then discharged from the system through a bypass venting dust collector to reduce the accumulation and recycling of harmful components.

[0080] In this embodiment, a bypass ventilation regulating valve 1702 and a bypass fan 1203 are sequentially installed on the pipeline connecting the air outlet of the bypass ventilation dust collector 16 and the air inlet of the cooling zone 101 at the head of the cooler.

[0081] Example 2

[0082] As shown in Figure 2, unlike Example 1, in this example, the high-concentration oxygen at room temperature generated by the oxygen production system is directly introduced into the air chamber under the feed slope of the cooling zone 101 at the head of the cooler. The remaining air chambers of the cooling zone 101 at the head of the cooler are still supplied with CO2 circulating flue gas after bypass venting and dust collection. When the chloride ion content brought into the kiln system by raw materials, pulverized coal, and alternative fuels is ≥1000ppm / kg clinker, in order to maintain the temperature of the CO2 circulating flue gas above the acid dew point and avoid further corrosion of the metal equipment and connecting parts of the cooler, this example only changes the air supply method of the high-concentration oxygen in the cooling zone at the head of the cooler. It does not mix with the CO2 circulating flue gas and directly enters the air chamber under the feed slope of the cooling zone at the head of the cooler, but the air supply volume remains unchanged, so it will not affect the cooling effect and quality of the clinker.

[0083] Example 3

[0084] As shown in Figure 4, unlike Example 1, the lifting air in this example is a single-inlet type. The decomposition furnace is equipped with a lifting air inlet 305, a feeding box 304, and two burners 303, with the two burners arranged axially symmetrically. As shown in Figure 4, the raw material feeding box in the reduction zone is located between the lifting air inlet and the burner. The lifting air enters the decomposition furnace in a swirling motion. Looking along the lifting air flow direction, the lifting air first contacts the raw material and then the fuel. On the one hand, the lifting air is relatively close to the raw material, which is beneficial for lifting the raw material; on the other hand, the temperature of the lifting air is 500-900℃, which is lower than the temperature of the flue gas in the exhaust chamber (1000-1200℃). The lifting air is relatively far from the fuel, so it will not reduce the temperature of the fuel feeding area or the fuel gasification rate.

[0085] Example 4

[0086] A method for preparing cement clinker using an all-oxygen combustion system with alternative fuels includes the following steps:

[0087] Raw materials are fed into preheater 5, where they exchange heat with flue gas and undergo gas-solid separation, preheating the raw materials to the decomposition temperature.

[0088] The preheated raw meal is fed into the decomposition furnace through a raw meal feeding point located between the lifting air inlet and the tertiary air inlet, and a raw meal feeding point above the tertiary air inlet. In the oxygen-rich combustion environment of the decomposition furnace, the alternative fuel combustion releases heat to supply the raw meal in the decomposition furnace for endothermic decomposition, resulting in calcined raw meal. The calcined raw meal enters the rotary kiln 2, where mineral phases are synthesized in a temperature range of 1100–1450℃. The heat in the rotary kiln 2 is supplied by a mixture of coal and alternative fuel, with the alternative fuel substitution ratio ≥80%, generating hot clinker. The clinker is cooled in a cooler to obtain cement clinker.

[0089] The cooler is divided into three sections, with no cross-flow between the first, second, and third sections. The cooling media in the first, second, and third sections of the cooler make full contact with the clinker in the corresponding cooling zone bed 1a at the head of the cooler, the cooling zone bed 1b in the middle of the cooler, and the cooling zone bed 1c at the tail of the cooler for sufficient heat exchange.

[0090] The high-temperature gas exiting the cooling zone at the head of the cooler is used as secondary air g2 and tertiary air g3, respectively. Secondary air g2 is introduced into the rotary kiln 2, and tertiary air g3 is introduced into the decomposition furnace 3. The circulating flue gas exiting the cooling zone 102 in the middle of the cooler is used as lifting air and introduced into the bottom of the decomposition furnace. The tertiary air inlet of the decomposition furnace is located above the lifting air inlet. Fuel and raw materials are introduced between the lifting air inlet and the tertiary air inlet, with an oxygen coefficient of less than 0.5, forming a reduction zone 301, which realizes the reduction of NO in the flue gas exiting the kiln. X The system automatically removes and lifts materials below the tertiary air inlet; fuel and raw materials are introduced above the tertiary air inlet to form a combustion zone, achieving complete combustion of the alternative fuel.

[0091] The O2 concentration in the secondary air g2 and the tertiary air g3 is 30% to 70%; the CO2 dry basis concentration in the lifting air is ≥85%, the O2 concentration is ≤5%, and the temperature range is 500 to 900℃.

[0092] The lifting air enters the decomposition furnace in a swirling stream. Along the direction of the lifting air flow, it first contacts the raw materials and then the fuel. On the one hand, the lifting air is relatively close to the raw materials, which is beneficial for lifting them; on the other hand, the temperature of the lifting air is 500-900℃, which is lower than the temperature of the flue gas exiting the kiln (1000-1200℃). The lifting air is relatively far from the fuel, so it will not reduce the temperature of the fuel feeding area or the fuel gasification rate.

[0093] The flue gas generated within the system flows in the opposite direction to the material flow. The CO2 circulating flue gas produced by fuel combustion and raw material decomposition serves as the main cooling medium within the cooler. The O2 required for combustion is mixed with the CO2 circulating flue gas in the cooling zone at the head of the cooler. The O2 / CO2 mixture, the cooling medium in the cooling zone at the head of the cooler, is introduced into the rotary kiln 2 and the decomposition furnace 3. The raw material undergoes a decomposition reaction within a temperature range of 850–950℃. The O2 / CO2 mixture in the cooling zone at the head of the cooler serves as the secondary and tertiary air, respectively, providing a combustion-supporting environment for fuel combustion in the rotary kiln and the decomposition furnace. The main purposes of introducing the CO2 circulating flue gas from the cooling zone 102 in the middle of the cooler into the bottom of the decomposition furnace are twofold: firstly, the amount of flue gas in the all-oxygen combustion rotary kiln is significantly reduced compared to conventional air combustion, and the exhaust gas from the kiln tail flue alone cannot provide the necessary wind speed to suspend the raw material in the decomposition furnace. It needs to serve as a lifting wind to ensure that the wind speed at the bottom of the decomposition furnace is 30–50 m / s, preventing the raw material from agglomerating and collapsing at high temperatures. Secondly, the O2 concentration in the O2 / CO2 mixture A entering the rotary kiln is significantly higher than that in air. This increased combustion temperature leads to a large amount of NOx. To effectively control NOx, the CO2 circulating flue gas provides an oxygen-deficient combustion environment for the decomposition furnace, promoting NOx reduction. The flue gas from the decomposition furnace ultimately enters preheater 5, where it exchanges heat with the fed ambient-temperature raw materials and undergoes separation. The flue gas is then discharged through the outlet of the cyclone separator at the top of the preheater.

[0094] To ensure complete combustion of the alternative fuel, the gas residence time in the decomposition furnace is controlled at 10–20 seconds, which is more than 40% longer than that in conventional calcination systems. The combustion state in the furnace is judged by the CO concentration at the decomposition furnace outlet, and the CO is controlled within the range of 0.1%–1%. At the same time, the decomposition furnace outlet temperature is controlled at 850–950℃ to ensure that the decomposition rate of raw materials entering the rotary kiln is ≥90%.

[0095] The low-temperature flue gas discharged from the top cyclone outlet of preheater 5, after desulfurization, dust collection, and condensation, has an SO2 content of 50 mg / Nm³. 3 The flue gas temperature is ≤40℃ and the H2O content is 2-10%. The flue gas is then heated to ≥60℃ and used as a cooling medium to enter the bypass venting system, the cooling zone 102 in the middle of the cooler, and the carbon capture and purification system D. The high-temperature bypass venting gas from the kiln tail flue enters the bypass venting system and comes into contact with the cooling medium, which rapidly cools the high-temperature bypass venting gas to 350-450℃. After cyclone separation, the coarse particles are returned to the decomposition furnace, and the fine particles and dust-laden flue gas are cooled again by contacting the cooling medium to 150-250℃. After dust collection, it is mixed with preheated high-concentration oxygen and enters the cooling zone at the head of the cooler. The temperature of the mixed gas is 100-200℃.

[0096] Specifically, the low-temperature flue gas (CO2 circulating flue gas) discharged from the cyclone outlet at the top of the preheater has a CO2 dry basis concentration ≥85% and a temperature of 250–400℃. The CO2 circulating flue gas sequentially passes through a wet desulfurization system 8, a bag filter 7, and a flue gas condenser 10 to control the SO2 content at 50 mg / Nm³. 3 Below, the dust concentration is reduced to 100 mg / Nm³. 3 Below, the CO2 circulating flue gas temperature is ≤40℃, and the H2O content is reduced from 15%–20% to 2%–10%. To avoid condensation problems caused by the presence of water, sulfur, and chlorine, the CO2 circulating flue gas is heated to unsaturated flue gas through the flue gas preheater 11. The heated CO2 circulating flue gas is divided into three paths: one path enters the carbon capture and purification system D to provide a carbon source for downstream carbon utilization; the second path enters the central cooling zone 102 of the cooler as a clinker cooling medium; and the third path serves as the cooling medium for the bypass venting system.

[0097] In the bypass venting system, the proportion of bypass venting kiln gas is controlled at 10-20%. The high-temperature bypass venting kiln gas directly contacts the CO2 circulating flue gas to achieve a cooling process. The CO2 circulating flue gas first enters the quenching chamber to fully contact and mix with the high-temperature bypass venting kiln gas containing harmful components, cooling the high-temperature bypass venting kiln gas containing harmful components from 950-1200℃ to 350-450℃. Volatile harmful components containing Cl condense and adhere to the surface of the dust carried out with the high-temperature bypass venting kiln gas. Then, the coarse and fine particles are separated by a cyclone separator 14. The coarse particles are returned to the decomposition furnace via the cyclone separator 14, reducing the amount of fly ash discharged. The dust-laden flue gas with attached harmful components undergoes a second contact with the CO2 circulating flue gas to cool it to 150-250℃, and then the fine particles containing harmful components such as Cl and S are discharged from the system via the bypass venting dust collector 16. The CO2 circulating flue gas can be mixed with preheated high-concentration O2 (O2 concentration ≥ 95%) to form O2 / CO2 mixture A, which enters the cooling zone at the head of the cooler to recover enthalpy. Simultaneously, the temperature of O2 / CO2 mixture A is maintained within the range of 100–150℃ to prevent water and acid condensation from corroding the metal materials of the cooler fan, grate connectors, etc., due to flue gas cooling. The temperature and airflow of the O2 / CO2 mixture remain constant.

[0098] In a preferred embodiment, the flue gas in the bypass venting system, after being cooled twice, first undergoes a sulfur-fixing reaction with an active desulfurizing agent at 150–250°C, thereby controlling the SO2 emission in the flue gas after the two cooling processes to 500 mg / Nm³. 3 Next, the sulfur-fixing waste residue is discharged from the system after dust collection.

[0099] As a preferred embodiment, under normal firing conditions, the total cooling air volume required for the cooler to cool a unit of clinker is currently 1.8–2.0 Nm³. 3 / kg.cl, the air volume for secondary and tertiary air is 0.8~0.9Nm. 3 / kg.cl, while under oxy-fuel combustion conditions, due to the reduction in N2 introduction, the air volume required for secondary and tertiary air decreases significantly to 0.4–0.6 Nm³. 3 / kg.cl, the waste heat from cooling the clinker would be wasted if discharged from the system. Therefore, the CO2 circulating flue gas exiting the cooling zone 102 in the middle of the cooler is also used as enthalpy recovery air and enters the preheater, with a temperature range of 500-900℃. This avoids the problem of the lifting air composed of CO2 circulating flue gas being introduced into the furnace from the bottom of the decomposition furnace, which would increase the partial pressure of CO2 in the flue gas in the decomposition furnace and cause the raw material decomposition temperature to rise to 950℃ or even above 1000℃; it also avoids the problem of scale buildup and blockage in the last stage cyclone of the preheater due to the increased raw material decomposition temperature and the delayed combustion of alternative fuels.

[0100] In one preferred embodiment, air C is introduced into the cooling zone 103 at the tail end of the cooler; the air g5 exiting the cooling zone at the tail end of the cooler is low enthalpy air with a temperature range of 200-300°C, and is used as a heat source for drying raw materials.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing cement clinker using an all-oxygen combustion system with alternative fuels, characterized in that: Includes the following steps: Raw meal is fed into a preheater and preheated to the decomposition temperature. The preheated raw meal is then fed into a decomposition furnace. In the oxygen-rich combustion environment of the decomposition furnace, the alternative fuel burns and releases heat to supply the raw meal for endothermic decomposition, resulting in calcined raw meal. The calcined raw meal enters a rotary kiln, where heat is supplied by a mixture of coal and alternative fuel, with the alternative fuel substitution ratio being ≥80%, generating hot clinker. The hot clinker is then cooled in a cooler to obtain cement clinker. CO2 circulating flue gas is discharged from the cyclone outlet at the top of the preheater and used as a cooling medium to mix with the bypass vented kiln gas and directly enter the cooling zone in the middle of the cooler. In this process, the high-temperature bypass vent gas from the kiln tail flue is cooled to 150–250°C by contact with the CO2 circulating flue gas cooling medium. Then, the flue gas and high-concentration oxygen simultaneously enter the cooling zone at the head of the cooler. The temperature of the flue gas entering the head cooling zone ranges from 100–200°C, and the concentration of acidic gases is ≤500 mg / Nm³. 3 The flue gas temperature entering the central cooling zone ranges from 60 to 100°C, and the concentration of acidic gases is ≤50 mg / Nm³. 3 .

2. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 1, characterized in that: The CO2 circulating flue gas discharged from the cyclone outlet at the top of the preheater, after undergoing desulfurization, dust collection, and condensation, has an SO2 content of 50 mg / Nm³. 3 The flue gas temperature is ≤50℃ and the H2O content is 2-10%; then the flue gas temperature is raised to ≥60℃; then it is used as a cooling medium to mix with the bypass vent gas and directly enter the cooling zone in the middle of the cooler.

3. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 1, characterized in that: The bypass ventilation ratio of kiln gas should be controlled at 10-20%.

4. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 1, characterized in that: The high-temperature bypass vent gas from the kiln tail flue comes into contact with the CO2 circulating flue gas cooling medium and is first rapidly cooled to 350-450°C. Then, it is separated by a cyclone separator. The coarse particles are returned to the decomposition furnace, while the fine particles and dust-laden flue gas are cooled to 150-250°C by contacting the CO2 circulating flue gas cooling medium again.

5. The method for preparing cement clinker using a fully oxy-fuel combustion system with applicable alternative fuels according to claim 4, characterized in that: The flue gas, after being cooled twice, first undergoes a sulfur-fixing reaction with an active desulfurizing agent at 150–250°C, thereby controlling the SO2 emission in the flue gas to 500 mg / Nm³. 3 Next, the sulfur-fixing waste residue is discharged from the system after dust collection.

6. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 1, characterized in that: The cooler is divided into three sections. The high-temperature gas exiting the head cooling zone of the cooler is used as secondary and tertiary air, respectively, and is introduced into the rotary kiln and the decomposition furnace. The circulating flue gas exiting the middle cooling zone of the cooler is used as lifting air and is introduced into the bottom of the decomposition furnace. The tertiary air inlet of the decomposition furnace is located above the lifting air inlet, forming a reduction zone between the lifting air inlet and the tertiary air inlet. The excess oxygen coefficient is controlled to be ≤0.5, thereby achieving the reduction of NO in the kiln flue gas. X It removes and lifts the material below the tertiary air inlet; it forms a combustion zone above the tertiary air inlet, achieving complete combustion of the alternative fuel.

7. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 6, characterized in that: The O2 concentration in the secondary and tertiary air is 30%–70%; the CO2 dry basis concentration in the lifting air is ≥85%, the O2 concentration is ≤5%, and the temperature range is 500–900℃.

8. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 6, characterized in that: The lifting air swirls into the decomposition furnace, and along the lifting air flow direction, the lifting air first contacts the raw material and then contacts the fuel.

9. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 6, characterized in that: The wind speed at the bottom of the decomposition furnace is maintained between 30 and 50 m / s.

10. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 6, characterized in that: The residence time of gas in the decomposition furnace is controlled at 10-20 seconds, and the CO concentration at the decomposition furnace outlet is controlled at 0.1%-1%. The outlet temperature of the decomposition furnace is controlled at 850-950℃ to ensure that the decomposition rate of raw materials entering the rotary kiln is ≥90%.

11. The method for preparing cement clinker using a fully oxy-fuel combustion system with applicable alternative fuels according to claim 1, characterized in that: The CO2 dry basis concentration of the CO2 circulating flue gas discharged from the cyclone outlet at the top of the preheater is ≥85%, and the temperature is 250~400℃.

12. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 1, characterized in that: High-concentration oxygen is preheated and mixed with the flue gas after bypass venting, referred to as O2 / CO2 mixture, and then enters the cooling zone of the cooler head together; or, high-concentration oxygen enters the air chamber under the feed ramp of the cooling zone of the cooler head at room temperature, and the flue gas after bypass venting is passed into the remaining air chambers of the cooling zone of the cooler head.

13. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 1, characterized in that: The CO2 circulating flue gas also enters the carbon capture and purification system.

14. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 1, characterized in that: There is no cross-flow between the cooling zones at the head, middle, and tail of the cooler.

15. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 1, characterized in that: The CO2 circulating flue gas exiting the cooling zone in the middle of the cooler is also used as enthalpy recovery air and enters the decomposition furnace outlet, with a temperature range of 500-900℃.

16. The method for preparing cement clinker using a fully oxy-fuel combustion system with alternative fuels according to claim 1, characterized in that: Air is introduced into the cooling zone at the tail end of the cooler; the air exiting the cooling zone at the tail end of the cooler is low enthalpy air with a temperature range of 200-300℃, which is used as a heat source for drying raw materials.

17. A system for preparing cement clinker using an all-oxygen combustion system with alternative fuels, for implementing the method for preparing cement clinker using an all-oxygen combustion system with alternative fuels as described in any one of claims 1-16, comprising a preheater, a decomposer, a kiln tail flue, a rotary kiln, and a cooler connected in sequence; characterized in that: It also includes a bypass ventilation system, the intake point for the bypass ventilation kiln gas is located in the rising flue of the kiln tail smoke chamber, the bypass ventilation system includes a cooling system, the cooling system is connected to the kiln tail smoke chamber through a pipeline, the air outlet of the cooling system is connected to the air inlet of the cooling zone at the head of the cooler, and the cooling zone at the head of the cooler is also provided with a high-concentration oxygen inlet; the air outlet of the cyclone at the top of the preheater is connected to the cooling system and the air inlet of the cooling zone in the middle of the cooler respectively.

18. The system for preparing cement clinker using oxy-fuel combustion as described in claim 17, characterized in that: The cooling system includes a quenching chamber and a cyclone separator. The quenching chamber is connected to the kiln tail flue chamber via a pipeline. The air outlet of the quenching chamber is connected to the air inlet of the cyclone separator. The feed pipe of the cyclone separator is connected to the decomposition furnace. The air outlet of the cyclone separator is connected to the air inlet of the cooling zone at the head of the cooler.

19. The system for preparing cement clinker using a fully oxy-fuel combustion system according to claim 18, characterized in that: The bypass ventilation system also includes a bypass ventilation dust collector, the air inlet of which is connected to the air outlet of the cyclone separator, and the air outlet of which is connected to the air inlet of the cooling zone at the head of the cooler.

20. The system for preparing cement clinker using a fully oxy-fuel combustion system according to claim 19, characterized in that: A desulfurizing agent storage tank is also installed on the connecting pipeline between the cyclone separator and the bypass exhaust dust collector. The desulfurizing agent storage tank is used to deliver active desulfurizing agent into the connecting pipeline, allowing the active desulfurizing agent to react with the volatile sulfur in the twice-cooled flue gas at 150–250°C to solidify sulfur, thereby controlling the SO2 emission in the twice-cooled flue gas to 500 mg / Nm³. 3 The sulfur-fixing waste residue is then discharged from the system via a bypass venting dust collector.

21. The system for preparing cement clinker using a fully oxy-fuel combustion system according to claim 17, characterized in that: The air outlet of the cyclone at the top of the preheater is connected in sequence to the wet desulfurization system, the bag dust collector, the flue gas condenser, and the flue gas preheater. The air outlet of the flue gas preheater is connected to the cooling system and the air inlet of the cooling zone in the middle of the cooler.

22. The system for preparing cement clinker using a fully oxy-fuel combustion system according to claim 17, characterized in that: A first resistance baffle is installed between the cooling head zone and the middle cooling zone of the cooler to reduce the leakage of O2 / CO2 mixture from the cooling head zone into the middle cooling zone. A second resistance baffle and a central roller crusher are installed between the middle cooling zone and the tail cooling zone of the cooler. Steam generated from indirect drying fuel / alternative fuel is introduced into the air chamber below the central roller crusher as a cooling medium to form an air curtain to further block leakage. The height of the bottom of the first and second resistance baffles and the gap between them and the corresponding cooler bed are ≤300mm. The first and second resistance baffles are rotating and movable baffles.

23. The system for preparing cement clinker using a fully oxy-fuel combustion system according to claim 17, characterized in that: The decomposition furnace is equipped with a tertiary air inlet, a lifting air inlet, a raw material feeding point, and a fuel feeding point. The lifting air inlet is located below the tertiary air inlet. The top outlet of the decomposition furnace is connected to a pipe that allows flue gas to flow upwards and then downwards. A recovered heat enthalpy air inlet is provided on the downward pipe. The secondary air intake and tertiary air intake of the cooler are located in the cooling zone at the head of the cooler, while the lifting air intake is located in the cooling zone in the middle of the cooler. The secondary air intake is connected to the rotary kiln, and the tertiary air intake is connected to the tertiary air inlet of the decomposition furnace through a pipe. The lifting air intake is connected to... The pipeline connects to the lifting air inlet and the recovery heat enthalpy air inlet of the decomposition furnace; at least two raw material feeding points are set, of which at least one raw material feeding point is located between the lifting air inlet and the tertiary air inlet, and at least one raw material feeding point is located above the tertiary air inlet; the height of the lifting air inlet is below the raw material feeding point below the tertiary air inlet; the fuel feeding point is located between the lifting air inlet and the tertiary air inlet, and above the tertiary air inlet; a reduction zone is formed inside the decomposition furnace between the lifting air inlet and the tertiary air inlet, and a combustion zone is formed above the tertiary air inlet.

24. The system for preparing cement clinker using a fully oxy-fuel combustion system according to claim 23, characterized in that: The decomposition furnace has a first narrowing at the tertiary air inlet and a second narrowing at the lifting air inlet.

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