A cement kiln system for oxycombustion carbon capture and a method of producing cement clinker

Abstract

This invention discloses a cement kiln system with carbon capture through all-oxygen combustion and a method for preparing cement clinker. The system includes a first raw meal preheating and pre-decomposition system, a second raw meal preheating and pre-decomposition system, and a flue gas capture and purification system. The outlet of a second cyclone preheater is connected to both the circulating flue gas inlet of the pre-combustion furnace and the flue gas inlet of the flue gas capture and purification system. A portion of the flue gas from the flue gas capture and purification system is connected to the outlet pipe of the second decomposition furnace via a branch pipe. The high-purity oxygen has a purity of 75-85%, the CO2 dry basis concentration in the flue gas discharged from the second raw meal preheating and pre-decomposition system is 75-85%, and the CO2 dry basis concentration in the flue gas entering the outlet pipe of the second decomposition furnace from the flue gas capture and purification system is 95-99%. This invention reduces the purity of the high-purity oxygen and the outlet flue gas temperature of the second decomposition furnace, further increasing the CO2 dry basis concentration in the flue gas from the second raw meal preheating and pre-decomposition system. This improves the raw meal heat exchange efficiency and the CO2 concentration in the subsequent captured and purified flue gas, achieving energy saving and consumption reduction.

Description

Technical Field

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

[0002] Currently, the cement industry widely adopts the new dry process production technology, which mainly consists of a cooler, burner, rotary kiln, precalciner, and cyclone preheater. Raw materials are preheated in the cyclone preheater and decomposed in the precalciner, where most of the fuel is burned to provide the heat required for raw material decomposition. The decomposed material is then calcined in the rotary kiln to produce cement clinker, which is subsequently cooled to a suitable temperature by the cooler. The CO2 generated during cement clinker production mainly comes from three sources: direct CO2 emissions from the process itself, direct CO2 emissions from fuel combustion, and indirect CO2 emissions from purchased electricity consumption. Of these, process-related CO2 emissions account for over 60%, primarily from the thermal decomposition of limestone raw materials during clinker calcination; fuel combustion emissions are the second largest, at approximately 35%; and emissions from purchased electricity consumption are the smallest, at approximately 5%.

[0003] The main carbon emission reduction technologies available for the cement industry include pre-combustion capture, post-combustion capture, and self-enrichment technologies during combustion. Pre-combustion capture refers to pre-treating fuel before combustion to separate carbon from it. However, due to the characteristics of cement clinker production processes, a significant drawback of pre-combustion CO2 capture is that it only separates CO2 produced by fuel combustion, while CO2 produced by raw material calcination is emitted with the flue gas without any treatment. Furthermore, compared to other CO2 capture technologies, pre-combustion capture requires extremely stringent conditions for hydrogen combustion during clinker calcination, necessitating special designs for rotary kiln burners. Therefore, this technology has low feasibility in the cement industry and can be excluded. Post-combustion capture technologies mainly refer to capturing or separating CO2 from the flue gas after combustion. The main technologies include chemical absorption methods such as hot potassium hydroxide, benzil, and ethanolamine, as well as physical absorption methods such as propylene carbonate, polyethylene glycol dimethyl ether, and methanol. Currently, air is the combustion medium introduced into cement kiln systems, and the dry basis CO2 concentration in the flue gas at the preheater outlet is generally 25-35%. Due to the low CO2 concentration in the flue gas, directly adopting post-combustion capture technology would result in high investment and operating costs for the capture and purification system. Combustion process self-enrichment technology refers to using technical means to significantly increase the CO2 concentration in the flue gas at the kiln tail preheater outlet, thereby greatly reducing the investment and operating costs of the subsequent flue gas CO2 capture and purification system. Typical combustion process self-enrichment technologies mainly include oxy-fuel combustion and indirect heat exchange technology, among which oxy-fuel combustion technology is more closely related to cement production. From a technical perspective, oxy-fuel combustion uses high-purity oxygen and circulating flue gas without the introduction of N2, which can significantly increase the CO2 concentration in the flue gas at the preheater outlet (under conventional air-assisted combustion conditions, the dry basis CO2 concentration in the flue gas at the preheater outlet is generally 25-35%; while under oxy-fuel combustion conditions, the dry basis CO2 concentration in the flue gas at the preheater outlet is generally 70-80%), while reducing the amount of flue gas that needs to be treated, effectively reducing the energy consumption and operating costs of the carbon capture and purification system.

[0004] Based on the characteristics of cement clinker production processes, oxy-fuel combustion technology in cement kiln systems can be divided into two main categories: First, the entire cement kiln system employs oxy-fuel combustion technology. This technology requires focused design of the preheater, decomposer, main burner, and cooler, enabling complete capture of direct CO2 emissions during cement clinker production. Second, the cement kiln system employs partial oxy-fuel combustion technology, also known as decomposer oxy-fuel combustion technology. This involves adding a CO2 self-enrichment system outside the main cement kiln system, with oxy-fuel combustion taking place within this system. This technology only requires focused design of the decomposer and preheater, achieving complete capture of direct CO2 emissions within the CO2 self-enrichment system. Because decomposer oxy-fuel combustion technology only requires focused design of the decomposer and preheater, and the CO2 self-enrichment system can be flexibly designed according to downstream carbon market demands, it offers numerous advantages over the entire system oxy-fuel combustion technology.

[0005] The decomposition furnace oxy-fuel combustion technology significantly increases the CO2 concentration in flue gas by using high-purity oxygen (generally 80-95% purity) instead of air for combustion. This significant increase in CO2 concentration can effectively reduce the investment and operating costs of subsequent carbon capture and purification systems. However, relying solely on high-purity oxygen for oxy-fuel combustion will significantly increase the consumption of high-purity oxygen.

[0006] Furthermore, the main processes occurring in the decomposer are pulverized coal combustion and raw meal decomposition. However, the raw meal decomposition reaction is reversible, and a significant increase in flue gas CO2 concentration will inhibit it. Without appropriate measures, this will lead to a significant decrease in the raw meal decomposition rate (the percentage of carbonates decomposed into oxides before entering the kiln after passing through the decomposer and subsequent preheater) under oxy-fuel combustion conditions. This decrease not only prevents the decomposer from fully utilizing its capabilities but also increases the load on the rotary kiln, negatively impacting both production increases and energy conservation in the calcination system. Simultaneously, to ensure the optimal raw meal decomposition rate, the calcination temperature of the decomposer needs to be significantly increased, but this will cause scaling and blockage in the subsequent suspension preheating system. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a cement kiln system for carbon capture through all-oxygen combustion and a method for preparing cement clinker. This system solves the technical problems of excessively high oxygen purity required under all-oxygen combustion conditions, which leads to a significant increase in the overall energy consumption and cost of CO2 preparation per unit, as well as the inhibition of raw material decomposition reaction affecting the quality of the calcination system and causing excessively high temperatures in the decomposition furnace, resulting in crusting and blockage in the subsequent suspension preheating system.

[0008] This invention is implemented as follows: a cement kiln system for carbon capture using oxy-fuel combustion includes a smoke chamber, a rotary kiln, a cooler, a first raw material preheating and predecomposition system, and a second raw material preheating and predecomposition system. A first burner is installed on the rotary kiln. The first raw material preheating and predecomposition system is a conventional system and is connected to the smoke chamber. The second raw material preheating and predecomposition system is a carbon dioxide self-enrichment system using oxy-fuel combustion.

[0009] The second raw material preheating and pre-decomposition system includes a pre-combustion furnace, a second decomposition furnace, and a second row of cyclone preheaters. The pre-combustion furnace has an inlet for combustion medium and an inlet for circulating flue gas. A third burner is installed at the top of the pre-combustion furnace. The bottom of the pre-combustion furnace is connected to the conical section of the second decomposition furnace via a connecting pipe. A fourth burner is installed on the second decomposition furnace, and a second row of raw material inlets is provided on the second decomposition furnace. The air inlet of the bottom cyclone separator of the second row of cyclone preheaters is connected to the air outlet pipe of the second decomposition furnace, and the air outlet of the top cyclone separator of the second row of cyclone preheaters discharges low-temperature flue gas. A second feed inlet is provided at the inlet of the top cyclone separator of the second row of cyclone preheaters, and the discharge outlet of the bottom cyclone separator of the second row of cyclone preheaters is connected to the smoke chamber.

[0010] The cement kiln system also includes a flue gas capture and purification system. The outlet of the top cyclone separator of the second cyclone preheater is connected to the circulating flue gas inlet of the pre-combustion furnace and the flue gas inlet of the flue gas capture and purification system via a circulating fan. A portion of the low-temperature flue gas from the flue gas capture and purification system is connected to the outlet pipe of the second decomposition furnace via a branch pipe. A high-purity oxygen inlet is provided on the pipeline between the circulating fan and the circulating flue gas inlet of the pre-combustion furnace.

[0011] The purity of the high-purity oxygen is 75-85%, the dry basis concentration of CO2 in the low-temperature flue gas discharged from the second raw material preheating and pre-decomposition system is 75-85%, the dry basis concentration of CO2 in the low-temperature flue gas entering the outlet pipe of the second decomposition furnace after being captured and purified by the flue gas capture and purification system is 95-99%, and the dry basis concentration of CO2 in the second decomposition furnace is 70-80%.

[0012] Furthermore, the first raw material preheating and pre-decomposition system includes a first decomposition furnace and a first row of cyclone preheaters; a second burner is installed on the first decomposition furnace, and a first row of raw material inlets is opened on the first decomposition furnace; the air inlet of the bottom cyclone separator of the first row of cyclone preheaters is connected to the air outlet pipe of the first decomposition furnace, and the air outlet of the top cyclone separator of the first row of cyclone preheaters discharges low-temperature flue gas, in which the CO2 dry basis concentration is 25-35%; a first feed inlet is provided at the inlet of the top cyclone separator of the first row of cyclone preheaters, and the discharge outlet of the bottom cyclone separator of the first row of cyclone preheaters is connected to the smoke chamber.

[0013] Furthermore, the first cyclone preheater has 4 to 7 stages.

[0014] Furthermore, the second cyclone preheater has 4 to 7 stages.

[0015] The present invention preferably delivers a portion of the high-purity CO2 gas product with a concentration of 95-99% prepared by the flue gas capture and purification system to the decomposition furnace outlet pipe. Alternatively, it may be considered to deliver a portion of the CO2 product with a concentration of 99.9% or higher prepared by the flue gas capture and purification system, or to directly purchase a small amount of high-purity CO2 product, to the decomposition furnace outlet pipe.

[0016] The method for preparing cement clinker using the above-mentioned cement kiln system for oxy-fuel combustion carbon capture includes the following steps:

[0017] Raw materials are fed into the first and second cyclone preheaters respectively, and the raw materials exchange heat with the flue gas and undergo gas-solid separation in the corresponding cyclone preheaters.

[0018] Raw materials preheated by the first cyclone preheater enter the first decomposition furnace, and raw materials preheated by the second cyclone preheater enter the second decomposition furnace;

[0019] The CO2 dry basis concentration in the low-temperature flue gas discharged from the outlet of the top cyclone separator of the second cyclone preheater is 75-85%. The low-temperature flue gas discharged from the outlet of the top cyclone separator of the second cyclone preheater enters the circulating fan and is then divided into two paths. One path enters the pre-combustion furnace, and the other path enters the flue gas capture and purification system.

[0020] The low-temperature flue gas entering the flue gas capture and purification system has a CO2 dry basis concentration of 95-99% after capture and purification. Part of this low-temperature flue gas enters the exhaust pipe of the second decomposition furnace through the branch pipe, forming a local mixing zone at the outlet of the second decomposition furnace. The other part enters the low-temperature distillation and purification system to obtain food-grade or industrial-grade liquid CO2 products or solid dry ice or other forms of CO2 products with a purity of 99.9% or higher.

[0021] High-purity oxygen (75-85%) is mixed with low-temperature flue gas (75-85% dry basis concentration of CO2) discharged from the top of the second cyclone preheater and then enters the pre-combustion furnace through the circulating flue gas inlet. This mixture powers the combustion of fuel entering the pre-combustion furnace from the top. The combustion products then enter the second decomposition furnace from the bottom of the pre-combustion furnace via connecting pipes. In the second decomposition furnace, combustion occurs entirely in oxygen. The calcination temperature in the second decomposition furnace is 880-920℃. The large amount of heat released from fuel combustion powers the raw materials in the second decomposition furnace. The process involves endothermic decomposition to obtain hot raw materials and generate a large amount of flue gas. The CO2 dry basis concentration in the flue gas in the second decomposition furnace is 70-80%. The high-temperature flue gas generated in the second decomposition furnace is discharged through the exhaust port of the second decomposition furnace and mixed with the low-temperature flue gas with a CO2 dry basis concentration of 95-99% discharged from the flue gas capture and purification system, so that the temperature of the flue gas exiting the second decomposition furnace is 840-880℃. Then, it enters the second cyclone preheater to exchange heat with the raw materials. After heat exchange, the flue gas is discharged through the exhaust port of the cyclone separator at the top of the second cyclone preheater.

[0022] The hot raw materials generated in the first and second decomposition furnaces enter the rotary kiln through the smoke chamber, where they are calcined to form cement clinker. The cement clinker then enters the cooler from the rotary kiln, where it exchanges heat with air to obtain cooled cement clinker. Fuel combustion in the rotary kiln generates kiln gas, which passes through the smoke chamber and the first decomposition furnace in sequence and enters the first cyclone preheater. The gas is then discharged through the outlet of the cyclone separator at the top of the first cyclone preheater.

[0023] Furthermore, the raw material in the first decomposition furnace absorbs heat and decomposes to obtain hot raw material, and generates a large amount of flue gas. The flue gas in the first decomposition furnace enters the first cyclone preheater and exchanges heat with the raw material to become low-temperature flue gas. The CO2 dry basis concentration in the low-temperature flue gas discharged through the outlet of the cyclone separator at the top of the first cyclone preheater is 25-35%.

[0024] The second decomposition furnace uses oxy-fuel combustion. The raw materials in the second decomposition furnace undergo endothermic decomposition to obtain hot raw materials and generate a large amount of flue gas. The combustion medium in the second decomposition furnace is a mixture of circulating flue gas and high-purity oxygen. Due to the significantly reduced N2 content in the combustion medium, the CO2 content in the flue gas generated from raw material decomposition and pulverized coal combustion in the second decomposition furnace is significantly increased (from 25-35% in conventional air-assisted combustion to approximately 75-85% in oxy-fuel combustion). This is because the raw material decomposition reaction (i.e....) The reaction is reversible. The significant increase in CO2 concentration in the flue gas greatly increases the local partial pressure of CO2, causing the raw meal decomposition reaction to proceed in the direction of the raw meal synthesis reaction (i.e., CaO + CO2 → CaCO3). At this point, the raw meal decomposition rate will decrease significantly. Considering that the raw meal decomposition reaction is a strongly endothermic reaction, to ensure the normal progress of the raw meal decomposition reaction under oxy-fuel combustion, a possible measure is to increase the calcination temperature in the decomposition furnace to a certain extent.

[0025] Through extensive experimental research, the inventors discovered that increasing the calcination temperature in the second decomposition furnace by 60–80°C can achieve a raw material decomposition rate comparable to conventional air combustion under all-oxygen combustion. In other words, by increasing the calcination temperature in the decomposition furnace by 60–80°C, the raw material can be fully decomposed within the furnace, while the CO2 concentration in the flue gas is significantly higher than in conventional air combustion. However, increasing the calcination temperature in the decomposition furnace by 60–80°C will correspondingly increase the temperature of the flue gas and materials exiting the furnace (theoretical calculations show that this increase will raise the furnace outlet temperature to 900–960°C, while the outlet temperature of a conventional air-assisted combustion decomposition furnace is approximately 840–880°C). This significant increase in the temperature of the flue gas and materials exiting the furnace will adversely affect the stable operation of the subsequent self-enrichment preheater system (for example, exacerbating the tendency for high-temperature scaling and blockage in the final stage cyclone separator of the preheater system connected to the decomposition furnace). Based on the above analysis, the inventors considered first increasing the calcination temperature in the second decomposition furnace by 40-60℃ (the CO2 concentration in the decomposition furnace is 5-10% lower than that of conventional all-oxygen combustion technology). Secondly, by further capturing and purifying the low-temperature flue gas discharged from the outlet of the top cyclone separator of the second cyclone preheater, the inventors connected it to the outlet pipe of the second decomposition furnace. This would create a mixing and cooling zone at the outlet of the second decomposition furnace. By rationally designing the amount of flue gas entering the outlet of the second decomposition furnace, the temperature of the flue gas and material at the outlet of the second decomposition furnace could be cooled to a reasonable temperature range (considering an outlet temperature of 840-880℃ for conventional air-assisted combustion).

[0026] The advantages and positive effects of this invention are:

[0027] 1. This invention fully considers the technical characteristics of conventional cement kiln production, which uses air-assisted combustion, resulting in low CO2 concentration in the flue gas at the preheater outlet. This leads to high energy consumption, complex capture and purification processes, and high operating costs in the CO2 capture and recovery system. The invention adjusts the cement kiln production process from conventional air-assisted combustion to all-oxygen combustion. This can significantly increase the dry basis CO2 concentration in the flue gas at the cyclone preheater outlet from 25-35% to 75-85%, thereby significantly reducing the operating cost of the flue gas capture and purification system and the overall energy consumption per unit of CO2 product.

[0028] Furthermore, while fully utilizing the beneficial effect of oxy-fuel combustion technology in significantly increasing flue gas CO2 concentration, this invention also fully considers avoiding or significantly mitigating the negative impact of oxy-fuel combustion technology on existing combustion systems. Specifically, due to the raw material decomposition reaction (i.e.... The reaction is reversible. The significant increase in CO2 concentration in the flue gas greatly increases the local partial pressure of CO2, causing the raw meal decomposition reaction to proceed in the direction of the raw meal synthesis reaction (i.e., CaO + CO2 → CaCO3). At this time, the raw meal decomposition rate will decrease significantly. Considering that the raw meal decomposition reaction is a strongly endothermic reaction, in order to ensure the normal progress of the raw meal decomposition reaction under oxy-fuel combustion (i.e., to ensure that the raw meal decomposition rate under oxy-fuel combustion is comparable to that under conventional air-assisted combustion, so as not to affect the production and quality of cement clinker), conventional oxy-fuel combustion technology often requires a significant increase in the calcination temperature in the decomposition furnace (generally considered to be increased by 50-80℃ or even close to 100℃). The increase in the calcination temperature in the decomposition furnace will significantly increase the risk of high-temperature scaling and blockage in the final stage cyclone separator of the preheater system connected to the decomposition furnace. Furthermore, to achieve a CO2 dry basis concentration of ≥80% in the preheater outlet flue gas under oxy-fuel combustion, conventional oxy-fuel combustion technology requires the use of high-purity oxygen products with an oxygen purity of 85-95%. This significant increase in oxygen concentration not only complicates the control of the oxy-fuel combustion flame and temperature within the decomposition furnace but also increases the energy consumption of the oxygen production system. This invention delivers a portion of the 95-99% high-purity CO2 product prepared by the capture and purification system to the decomposition furnace outlet duct. This creates a localized mixing and cooling zone within the decomposition furnace outlet duct, thereby avoiding or significantly mitigating the risk of high-temperature scaling and blockage in the final-stage cyclone separator of the preheater system connected to the decomposition furnace. Furthermore, because the CO2 concentration from the flue gas capture and purification system is relatively high, even when the CO2 dry basis concentration of the flue gas after oxy-fuel combustion in the decomposition furnace can be controlled at a relatively low value of 70-80%, the CO2 dry basis concentration at the preheater system outlet can still maintain a relatively high value. The above design has three main advantages: 1) The purity of the high-purity oxygen product can be reduced to 75-85% (conventional oxy-fuel combustion technology generally requires 85-95%). This reduction in oxygen purity effectively lowers the energy consumption of the oxygen production system and reduces the difficulty of controlling the flame and temperature of oxy-fuel combustion in the decomposition furnace; 2) The CO2 concentration in the decomposition furnace can be controlled at a relatively low value of 70-80%, allowing for a temperature increase of 40-60℃ (conventional oxy-fuel combustion technology requires an increase of 60-80℃ or even higher). This reduces the risk of high-temperature scaling and blockage in the final stage cyclone separator of the preheater system connected to the decomposition furnace; 3) Even if there is air leakage in the preheater system, the dry basis CO2 concentration of the flue gas at the preheater outlet can still be maintained at a relatively high value of 75-85% (conventional oxy-fuel combustion technology generally requires 70-80%). This increase in CO2 concentration reduces the energy consumption of the flue gas capture and purification system and improves its adaptability.

[0029] 2. While adopting the all-oxygen combustion technology, this invention focuses on the cement kiln system. The cement kiln system provided by this invention does not require redesign of key firing equipment such as rotary kiln, cooler and kiln head burner, which greatly simplifies the process and reduces the transformation cost. Specifically, the raw meal enters the second cyclone preheater, and after multiple heat exchanges and gas-solid separations, it enters the second decomposition furnace. The combustion medium, including high-purity oxygen purchased from an external source or produced by an oxygen production system, mixes with the circulating flue gas and enters the pre-combustion furnace from the circulating flue gas inlet. This mixture fuel entering the pre-combustion furnace from the top is used for combustion. The combustion products enter the second decomposition furnace from the bottom of the pre-combustion furnace, where they undergo full oxygen combustion. The combustion releases a large amount of heat, which is used to decompose the raw meal in the second decomposition furnace, resulting in hot raw meal and a large amount of flue gas. The flue gas carries the hot raw meal out of the second decomposition furnace and enters the bottom cyclone separator of the second cyclone preheater. Subsequently, the hot raw meal and flue gas undergo gas-solid separation. The flue gas moves upward through the second cyclone preheater and continues to exchange heat with the raw meal fed into the second cyclone preheater multiple times, eventually becoming low-temperature flue gas with a CO2 dry basis concentration of 75-85%. The hot raw meal enters the rotary kiln through the flue gas chamber and is calcined in the rotary kiln to form cement clinker. In addition, the amount of raw material fed into the second cyclone preheater can be flexibly adjusted according to the market demand for CO2 products, thereby achieving the goal of carbon emission reduction in the cement industry. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some specific embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a flow chart of a cement kiln system for carbon capture by all-oxygen combustion provided in an embodiment of the present invention.

[0032] The system comprises: 1. Smoke chamber; 2. Rotary kiln; 201. First burner; 3. Cooler; 4. First raw material preheating and pre-decomposition system; 401. First decomposition furnace; 402. Second burner; 403. Bottom cyclone separator of the first row of cyclone preheaters; 404. Top cyclone separator of the first row of cyclone preheaters; 5. Second raw material preheating and pre-decomposition system; 501. Pre-combustion furnace; 502. Second decomposition furnace; 503. Third burner; 504. Fourth burner; 505. Bottom cyclone separator of the second row of cyclone preheaters; 506. Top cyclone separator of the second row of cyclone preheaters; 6. First circulating fan; 7. Flue gas capture and purification system. Detailed Implementation

[0033] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0034] 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.

[0035] Example 1

[0036] Please see Figure 1 This invention provides a system for low-energy carbon purification coupled with full oxygen combustion in a cement kiln, comprising a smoke chamber 1, a rotary kiln 2, a cooler 3, a first raw material preheating and predecomposition system 4, a second raw material preheating and predecomposition system 5, and a flue gas capture and purification system 7. The smoke chamber 1, the rotary kiln 2, and the cooler 3 are connected in sequence, and a first burner 201 is provided on the rotary kiln 2.

[0037] The first raw material preheating and predecomposition system 4 is a conventional raw material preheating and predecomposition system.

[0038] The first raw material preheating and pre-decomposition system 4 includes a first decomposition furnace 401 and a first row of cyclone preheaters; a second burner 402 is provided on the first decomposition furnace 401, and a first row of raw material inlets is opened on the side wall of the first decomposition furnace 401; the air inlet of the bottom cyclone separator 403 of the first row of cyclone preheaters is connected to the air outlet pipe of the first decomposition furnace 401, and the air outlet pipe of the first decomposition furnace 401 can be set at the top or side of the first decomposition furnace; the air outlet of the top cyclone separator 404 of the first row of cyclone preheaters discharges low-temperature flue gas; a first feed port is provided at the inlet of the top cyclone separator 404 of the first row of cyclone preheaters for feeding raw materials, and the discharge port of the bottom cyclone separator 403 of the first row of cyclone preheaters is connected to the smoke chamber 1.

[0039] The CO2 dry basis concentration in the low-temperature flue gas discharged from the first raw material preheating and predecomposition system 4 is 25-35%, and the temperature range is 240-450℃ (depending on the number of stages of the first cyclone preheater).

[0040] In order to regulate the temperature field distribution inside the first decomposition furnace 401, the first raw material inlet can be set to multiple, which can be set by those skilled in the art according to actual needs.

[0041] The second raw material preheating and predecomposition system 5 is a carbon dioxide self-enrichment system that uses full oxygen combustion.

[0042] The second raw material preheating and pre-decomposition system 5 includes a pre-combustion furnace 501, a second decomposition furnace 502, and a second cyclone preheater. The pre-combustion furnace 501 has an inlet for combustion medium and an inlet for circulating flue gas. The combustion medium is high-purity oxygen, which can be purchased externally or produced using an air separation device. It should be noted that the purity range of the high-purity oxygen is preferably 75-85%. A third burner 503 is installed at the top of the pre-combustion furnace 501. The bottom of the pre-combustion furnace 501 is connected to the conical part of the second decomposition furnace 502 through a connecting pipe. The third burner 503 at the top of the pre-combustion furnace 501 is a multi-channel burner with an oil gun channel. When the second raw material preheating and pre-decomposition system 5 is first put into operation, oil gun ignition is used. After the temperature inside the pre-combustion furnace 501 stabilizes at 600-700℃, it switches to fuel combustion. The fuel can be solid fuel, liquid fuel, or gaseous fuel. A fourth burner 504 is provided on the second decomposition furnace 502, and a second row of raw material inlets is opened on the second decomposition furnace 502; the air inlet of the bottom cyclone separator 505 of the second row of cyclone preheaters is connected to the air outlet pipe of the second decomposition furnace 502, and the air outlet of the top cyclone separator 506 of the second row of cyclone preheaters discharges low-temperature flue gas; a second feed inlet is provided at the inlet of the top cyclone separator 506 of the second row of cyclone preheaters for feeding raw materials, the discharge outlet of the penultimate cyclone separator of the second row of cyclone preheaters is connected to the second row of raw material inlets of the second decomposition furnace, and the discharge outlet of the bottom cyclone separator 505 of the second row of cyclone preheaters is connected to the smoke chamber 1.

[0043] The CO2 dry basis concentration in the low-temperature flue gas discharged from the second raw material preheating and predecomposition system 5 is 75-85%, and the temperature range is 200-350℃ (depending on the number of stages of the second cyclone preheater).

[0044] It should be noted that the number of the first raw material preheating and predecomposition system 4 and the second raw material preheating and predecomposition system 5 is only illustrative. Those skilled in the art can set them according to actual needs. The cooler 3 can be a grate cooler, a single-cylinder cooler, or a multi-cylinder cooler. In this embodiment, the number of stages of the first row of cyclone preheaters is preferably 4 to 7; the number of stages of the second row of cyclone preheaters is preferably 4 to 7.

[0045] The outlet of the top cyclone separator 506 of the second cyclone preheater is connected to the circulating flue gas inlet of the pre-combustion furnace 501 and the flue gas inlet of the flue gas capture and purification system 7 via a circulating fan 6. A portion of the low-temperature flue gas from the flue gas capture and purification system is connected to the outlet pipe of the second decomposition furnace via a branch pipe. The CO2 dry basis concentration in the low-temperature flue gas entering the outlet pipe of the second decomposition furnace after capture and purification by the flue gas capture and purification system is 95-99%.

[0046] Specifically, the low-temperature flue gas discharged from the second cyclone preheater is divided into two paths. The first path of flue gas is connected to the circulating flue gas inlet of the pre-combustion furnace. High-purity oxygen mixes with the circulating flue gas and enters the pre-combustion furnace from the circulating flue gas inlet to fuel entering from the top of the pre-combustion furnace for combustion. The combustion products enter the second decomposition furnace from the bottom of the pre-combustion furnace through a connecting pipe. The second decomposition furnace is a fully oxygen-based combustion furnace. The large amount of heat released by the fuel combustion is used for the endothermic decomposition of the raw material in the second decomposition furnace to obtain hot raw material and generate a large amount of flue gas. The flue gas generated in the second decomposition furnace enters the second cyclone preheater and exchanges heat with the raw material to become low-temperature flue gas. The low-temperature flue gas is discharged through the outlet of the cyclone separator at the top of the second cyclone preheater. The dry basis CO2 concentration in the low-temperature flue gas is 75-85%.

[0047] The second stream of flue gas enters the flue gas capture and purification system. Due to the complex composition of the kiln tail flue gas, impurities must first be removed to further improve the efficiency of the CO2 capture and purification system. The low-temperature flue gas entering the flue gas capture and purification system 7 first undergoes pre-cooling and dust removal via a flue gas cooler (not shown in the flow chart) and a dust collector (not shown in the flow chart). Then, pressure swing adsorption (PSA) concentration increases the CO2 concentration from 75-85% to 95-99%. After PSA concentration, a portion of the high-purity CO2 gas enters the outlet duct of the second decomposition furnace, while the remainder undergoes low-temperature distillation to obtain liquid carbon dioxide that meets national industrial and food-grade carbon dioxide product standards. This liquid is then stored in a product storage tank and transported for use. The flue gas entering the outlet duct of the second decomposition furnace mixes with the high-temperature flue gas exiting from the outlet of the second decomposition furnace, creating a localized mixing and cooling zone at the outlet of the second decomposition furnace. By rationally designing the amount of flue gas entering the outlet of the second decomposition furnace, the temperature of the flue gas and materials at the decomposition furnace outlet can be cooled to a reasonable temperature range.

[0048] The method for preparing cement clinker using the above-mentioned cement kiln system for oxy-fuel combustion carbon capture includes the following steps:

[0049] Raw materials are fed into the first and second cyclone preheaters through their respective feed inlets. The raw materials exchange heat with the flue gas and undergo gas-solid separation in the corresponding cyclone preheaters. The raw materials preheated by the first cyclone preheater enter the first decomposition furnace 401, and the raw materials preheated by the second cyclone preheater enter the second decomposition furnace 502.

[0050] The raw material in the first decomposition furnace 401 absorbs heat and decomposes to obtain hot raw material and generates a large amount of flue gas. The flue gas in the first decomposition furnace 401 enters the first cyclone preheater and exchanges heat with the raw material to become low-temperature flue gas. The CO2 dry basis concentration in the low-temperature flue gas discharged through the air outlet of the top cyclone separator 404 of the first cyclone preheater is 25-35%.

[0051] The low-temperature flue gas discharged from the outlet of the cyclone separator 506 at the top of the second cyclone preheater enters the first circulating fan 6, and is then divided into two paths. One path enters the pre-combustion furnace 501, and the other path enters the flue gas capture and purification system 7. High-purity oxygen with a purity of 75-85% mixes with low-temperature flue gas with a dry basis concentration of 75-85% CO2 discharged from the top of the second cyclone preheater and enters the pre-combustion furnace 501 through the circulating flue gas inlet to fuel entering the pre-combustion furnace 501 from the top. The combustion products enter the second decomposition furnace 502 from the bottom of the pre-combustion furnace 501 through a connecting pipe, where full oxygen combustion takes place. The calcination temperature in the second decomposition furnace is 880-920℃. The large amount of heat released by fuel combustion is used for the endothermic decomposition of raw materials in the second decomposition furnace 502. The process yields hot raw materials and generates a large amount of flue gas. The CO2 dry basis concentration in the flue gas in the second decomposition furnace is 70-80%. The high-temperature flue gas generated in the second decomposition furnace 502 is discharged through the outlet of the second decomposition furnace and mixes with the low-temperature flue gas with a CO2 dry basis concentration of 95-99% discharged from the flue gas capture and purification system 7, so that the temperature of the flue gas leaving the second decomposition furnace is 840-880℃. Then, it enters the second cyclone preheater and exchanges heat with the raw materials to become low-temperature flue gas. The low-temperature flue gas is discharged through the outlet of the cyclone separator 506 at the top of the second cyclone preheater. The CO2 dry basis concentration in this low-temperature flue gas is 75-85%.

[0052] The hot raw materials generated in the first decomposition furnace 401 and the second decomposition furnace 502 enter the rotary kiln 2 through the smoke chamber 1. They are calcined in the rotary kiln 2 to form cement clinker. The cement clinker enters the cooler 3 from the rotary kiln 2 and exchanges heat with the air to obtain cooled cement clinker. The fuel in the rotary kiln 2 is burned to generate kiln gas. The kiln gas enters the first cyclone preheater through the smoke chamber 1 and the first decomposition furnace 401 in sequence, and is discharged through the air outlet of the cyclone separator 404 at the top of the first cyclone preheater.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not 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; and these 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 cement kiln system for carbon capture using oxy-fuel combustion, comprising a flue, a rotary kiln, a cooler, a first raw material preheating and predecomposition system, and a second raw material preheating and predecomposition system, wherein a first burner is installed on the rotary kiln, the first raw material preheating and predecomposition system is a conventional raw material preheating and predecomposition system, and the first raw material preheating and predecomposition system is connected to the flue; the second raw material preheating and predecomposition system is a carbon dioxide self-enrichment system using oxy-fuel combustion. The second raw material preheating and pre-decomposition system includes a pre-combustion furnace, a second decomposition furnace, and a second row of cyclone preheaters. The pre-combustion furnace has an inlet for combustion medium and an inlet for circulating flue gas. A third burner is installed at the top of the pre-combustion furnace. The bottom of the pre-combustion furnace is connected to the conical section of the second decomposition furnace via a connecting pipe. A fourth burner is installed on the second decomposition furnace, and a second row of raw material inlets is provided on the second decomposition furnace. The air inlet of the bottom cyclone separator of the second row of cyclone preheaters is connected to the air outlet pipe of the second decomposition furnace, and the air outlet of the top cyclone separator of the second row of cyclone preheaters discharges low-temperature flue gas. A second feed inlet is provided at the inlet of the top cyclone separator of the second row of cyclone preheaters, and the discharge outlet of the bottom cyclone separator of the second row of cyclone preheaters is connected to the smoke chamber. Its characteristic is that: The cement kiln system also includes a flue gas capture and purification system. The outlet of the top cyclone separator of the second cyclone preheater is connected to the circulating flue gas inlet of the pre-combustion furnace and the flue gas inlet of the flue gas capture and purification system via a circulating fan. Part of the flue gas from the flue gas capture and purification system is connected to the outlet pipe of the second decomposition furnace via a branch pipe, forming a local mixing and cooling zone in the outlet pipe of the decomposition furnace. A high-purity oxygen inlet is provided on the pipeline between the circulating fan and the circulating flue gas inlet of the pre-combustion furnace. The purity of the high-purity oxygen is 75-85%, the dry basis concentration of CO2 in the low-temperature flue gas discharged from the second raw material preheating and pre-decomposition system is 75-85%, the dry basis concentration of CO2 in the low-temperature flue gas entering the outlet pipe of the second decomposition furnace after being captured and purified by the flue gas capture and purification system is 95-99%, and the dry basis concentration of CO2 in the second decomposition furnace is 70-80%.

2. The cement kiln system for carbon capture by all-oxygen combustion according to claim 1, characterized in that, The first raw material preheating and pre-decomposition system includes a first decomposition furnace and a first row of cyclone preheaters; a second burner is installed on the first decomposition furnace, and a first row of raw material inlets is opened on the first decomposition furnace; the air inlet of the bottom cyclone separator of the first row of cyclone preheaters is connected to the air outlet pipe of the first decomposition furnace, and the air outlet of the top cyclone separator of the first row of cyclone preheaters discharges low-temperature flue gas, the CO2 dry basis concentration in this low-temperature flue gas is 25-35%; a first feed inlet is provided at the inlet of the top cyclone separator of the first row of cyclone preheaters, and the discharge outlet of the bottom cyclone separator of the first row of cyclone preheaters is connected to the smoke chamber.

3. The cement kiln system for carbon capture by all-oxygen combustion according to claim 2, characterized in that, The first cyclone preheater has 4 to 7 stages.

4. The cement kiln system for carbon capture by all-oxygen combustion according to claim 1, characterized in that, The second cyclone preheater has 4 to 7 stages.

5. A method for preparing cement clinker using an oxy-fuel combustion carbon capture system according to any one of claims 1 to 4, comprising the following steps: characterized in that, Raw materials are fed into the first and second cyclone preheaters respectively, and the raw materials exchange heat with the flue gas and undergo gas-solid separation in the corresponding cyclone preheaters. Raw materials preheated by the first cyclone preheater enter the first decomposition furnace, and raw materials preheated by the second cyclone preheater enter the second decomposition furnace; The CO2 dry basis concentration in the low-temperature flue gas discharged from the outlet of the top cyclone separator of the second cyclone preheater is 75-85%. The low-temperature flue gas discharged from the outlet of the top cyclone separator of the second cyclone preheater enters the circulating fan and is then divided into two paths. One path enters the pre-combustion furnace, and the other path enters the flue gas capture and purification system. The low-temperature flue gas entering the flue gas capture and purification system has a CO2 dry basis concentration of 95-99% after capture and purification. Part of this low-temperature flue gas enters the exhaust pipe of the second decomposition furnace through the branch pipe, forming a local mixing zone at the outlet of the second decomposition furnace. The other part enters the low-temperature distillation and purification system to obtain food-grade or industrial-grade liquid CO2 products or solid dry ice or other forms of CO2 products with a purity of 99.9% or higher. High-purity oxygen with a purity of 75-85% is mixed with low-temperature flue gas with a CO2 dry basis concentration of 75-85% discharged from the top of the second cyclone preheater and enters the pre-combustion furnace through the circulating flue gas inlet of the pre-combustion furnace to fuel entering the pre-combustion furnace from the top. The combustion products enter the second decomposition furnace from the bottom of the pre-combustion furnace through the connecting pipe. In the second decomposition furnace, full oxygen combustion takes place. The calcination temperature in the second decomposition furnace is 880-920℃. The large amount of heat released by fuel combustion is used for the endothermic decomposition of raw materials in the second decomposition furnace to obtain hot raw materials and generate a large amount of flue gas. The CO2 dry basis concentration in the flue gas in the second decomposition furnace is 70-80%. The high-temperature flue gas generated in the second decomposition furnace is discharged through the outlet of the second decomposition furnace and mixed with the low-temperature flue gas with a CO2 dry basis concentration of 95-99% discharged from the flue gas capture and purification system, so that the temperature of the flue gas exiting the second decomposition furnace is reduced to 840-880℃. Then it enters the second cyclone preheater to exchange heat with the raw material. After heat exchange, the flue gas is discharged through the outlet of the cyclone separator at the top of the second cyclone preheater. The hot raw materials generated in the first and second decomposition furnaces enter the rotary kiln through the smoke chamber, where they are calcined to form cement clinker. The cement clinker then enters the cooler from the rotary kiln, where it exchanges heat with air to obtain cooled cement clinker. Fuel combustion in the rotary kiln generates kiln gas, which passes through the smoke chamber and the first decomposition furnace in sequence and enters the first cyclone preheater. The gas is then discharged through the outlet of the cyclone separator at the top of the first cyclone preheater.

6. The method for preparing cement clinker by carbon capture through oxy-fuel combustion according to claim 5, characterized in that, The raw material in the first decomposition furnace absorbs heat and decomposes to obtain hot raw material, and generates a large amount of flue gas. The flue gas in the first decomposition furnace enters the first cyclone preheater and exchanges heat with the raw material to become low-temperature flue gas. The CO2 dry basis concentration in the low-temperature flue gas discharged through the cyclone separator at the top of the first cyclone preheater is 25-35%.

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