Process for co-combusting low calorific value coal with cement clinker

Abstract

The application discloses a kind of low calorific value coal synergic calcining cement clinker process method, it is related to cement production technical field, including S1, raw material performance detection: to low calorific value coal carries out industrial analysis and element analysis, the calorific value of low calorific value coal, ash melting point, ignition characteristic and burnout characteristic are determined, the chemical composition detection of calcium, siliceous, aluminium, iron raw material of cement raw material is carried out, determines raw material basic batching parameter;The application is through to low calorific value coal carries out systematic performance detection and combustion characteristic analysis, clear its compatible calcining control path, through the way of quality coordination and head and tail coal respectively grinding, give consideration to the large-scale accommodation of low calorific value coal and burning zone temperature stability, through fuel fine preparation, raw material easy burning optimization, effectively improve the ignition and burnout performance of low calorific value coal, through the synergic optimization of calcining equipment and combustion parameter, strengthen the mixing efficiency of pulverized coal and air, stabilize the thermal regime in kiln.

Description

Technical Field

[0001] This invention relates to the field of cement production technology, specifically to a process for co-calcining cement clinker with low-calorific-value coal. Background Technology

[0002] Low-calorific-value coal refers to inferior coal resources characterized by low calorific value, high ash content, and high moisture content. It mainly includes middlings coal, coal gangue, low-quality bituminous coal, and lignite. my country has vast reserves of this resource, but for a long time, due to difficulties in ignition, poor combustion stability, and low burnout rate, it has not been utilized on a large scale and with high efficiency in industry. The long-term accumulation of large quantities of low-calorific-value coal not only occupies valuable land resources but also easily causes a series of environmental problems such as dust and leaching pollution. Cement clinker calcination is a core step in cement production. It refers to the process of feeding proportionally proportioned cement raw materials into a rotary kiln system, where they undergo a series of physicochemical reactions at high temperatures, including dehydration, decomposition, solid-phase reaction, sintering, and cooling, ultimately forming silicate minerals with hydraulic activity. The quality of the fuel, its combustion stability, and its thermal efficiency directly determine the product quality of cement clinker, production energy consumption, and the continuous operation stability of the production line. Applying low-calorific-value coal to the cement clinker calcination process can turn inferior coal resources into valuable resources, significantly broaden the fuel sources for cement production, reduce enterprise fuel procurement costs, and at the same time reduce the consumption of high-quality coal resources, thus contributing to the green and low-carbon transformation of the cement industry and yielding significant resource, environmental, and economic benefits.

[0003] However, the current calcination process for cement clinker, especially specialty clinker, is highly dependent on high-calorific-value, high-quality coal. Existing calcination application technologies for low-calorific-value coal are still immature. Conventional calcination equipment and processes for low-calorific-value coal generally suffer from problems such as difficulty in ignition, unstable combustion, low burnout rate, and poor thermal efficiency. This can easily lead to significant fluctuations in the thermal regime of the rotary kiln system, preheater scaling and blockage, kiln ring formation, and raw material runoff, among other production failures. At the same time, it results in large fluctuations in the 28-day compressive strength of clinker, low free calcium oxide qualification rate, and high standard coal consumption per ton of clinker, which seriously limits the stable application of low-calorific-value coal in the large-scale production of cement clinker. Therefore, developing a process method for co-calcining cement clinker with low-calorific-value coal is of great significance. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a process for co-calcining cement clinker with low-calorific-value coal. This process can solve the problems of poor combustion stability, low burnout rate, easy kiln condition fluctuations, unstable clinker quality, and high energy consumption of low-calorific-value coal in cement clinker calcination. It enables the large-scale and stable application of low-calorific-value coal in cement clinker production, while reducing production energy consumption and fuel costs, and ensuring the product quality of cement clinker.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a process for co-calcining cement clinker with low-calorific-value coal, the method comprising the following steps:

[0006] S1. Raw material performance testing: Industrial and elemental analysis of low-calorific-value coal is conducted to determine its calorific value, ash melting point, ignition characteristics and burnout characteristics. Chemical composition testing of calcareous, siliceous, aluminous and ferrous raw materials of cement raw materials is conducted to determine the basic raw material batching parameters.

[0007] S2. Differentiated Coal Blending: The coal used in the decomposition furnace is low-calorific-value coal with a calorific value of <21000kJ / kg and an ash content of ≤10%, accounting for 60% of the total coal mass. The coal used in the kiln head is high-calorific-value coal with a calorific value of ≥22000kJ / kg and a volatile matter content of ≥35%, accounting for 40% of the total coal mass.

[0008] S3. Fuel preparation: Low-calorific-value coal for the decomposition furnace and high-calorific-value coal for the kiln head are prepared by separate grinding. The fineness of the coal powder is controlled to be ≤6% residue on a 0.08mm square hole sieve and ≤1.0% moisture content.

[0009] S4. Raw material optimization: Adjust the three raw material ratios to set the lime saturation coefficient to 0.88-0.92, silicon content to 2.6-2.8, and aluminum content to 1.5-1.7, thereby controlling the particle size of raw materials entering the mill and the homogenization effect of raw materials, and stabilizing the raw material feed rate.

[0010] S5. Calcination system optimization: Adjust the air ratio inside the rotary kiln burner to 30%-35%, optimize the angle of the feed box in the decomposition furnace, control the decomposition rate of raw materials entering the kiln to ≥92%, optimize the operating parameters of the grate cooler, adopt thick material layer cooling technology, and control the secondary air temperature to ≥1000℃.

[0011] S6. Operation control: The operation mode of adding or subtracting coal in small increments is adopted, and the raw material feed rate and rotary kiln speed are simultaneously and proactively adjusted.

[0012] S7. Calcination Completion and Discharge: After the cement raw meal is calcined at high temperature in the rotary kiln to form clinker, the clinker is cooled to below 100°C by a grate cooler. The cooled clinker is discharged from the rotary kiln head discharge device, completing the entire process of low-calorific-value coal co-calcining of cement clinker.

[0013] Further, in step S1, the combustion characteristics of low-calorific-value coal are determined by a tubular furnace combustion test. The temperature range of the combustion test is set to room temperature - 1200℃, and the heating rate is set to 10-20℃ / min. Under atmospheric conditions with oxygen concentrations of 18%, 21%, 23%, and 25%, the ignition temperature, the temperature corresponding to the maximum combustion rate, and the burnout temperature of the low-calorific-value coal are measured. The thermogravimetric change curve and differential thermal change curve of the combustion process are recorded to clarify the combustion reaction process of low-calorific-value coal under different calcination atmospheres.

[0014] Furthermore, in step S2, the low-calorific-value coal for the decomposition furnace is prepared by mixing two or more low-calorific-value coals from different sources in a fixed proportion. The low-calorific-value coal for mixing includes two or more of washed middlings coal, low-quality bituminous coal, and lignite. Each component of low-calorific-value coal is metered by a belt scale according to a preset proportion and then sent to the coal mixing silo. The mixing process adopts continuous stirring and mixing, and the coefficient of variation of the mixing uniformity is ≤0.5%. The mixed low-calorific-value coal is sent to a special coal grinding equipment for the decomposition furnace.

[0015] Furthermore, in step S3, the low-calorific-value coal for the decomposition furnace and the high-calorific-value coal for the kiln head are respectively fed into two independent vertical coal mills for grinding. During the grinding process, hot air is simultaneously introduced to dry the coal powder, and the hot air temperature is controlled at 250-300℃. The ground coal powder is classified by the air classifier and then sent to the corresponding coal powder silo. The coal powder silo is equipped with an online sampling device, and the fineness and moisture content of the coal powder are sampled and tested every 2 hours. The operating parameters of the coal mill and the speed of the air classifier are adjusted according to the test results.

[0016] Furthermore, in step S4, the raw material is crushed in two stages by a jaw crusher and an impact crusher before entering the mill. The maximum particle size of the crushed raw material is ≤25mm. After being metered and batched, the crushed raw material is sent to a raw material mill for grinding. The ground raw material is then sent to a continuous homogenization silo for homogenization. The coefficient of variation of the chemical composition of the homogenized raw material is ≤0.3%. The raw material feeding process uses a loss-in-weight weigher for metering, and the fluctuation range of the feeding amount is controlled within ±2% of the rated feeding amount.

[0017] Furthermore, in step S5, the rotary kiln burner adopts a four-channel burner, the internal air adopts swirl air with a swirl angle set to 25°-30°, the external air adopts direct current air, the central air volume accounts for 5%-8% of the total primary air volume, the decomposition furnace feeding box is set at the upper part of the constriction of the decomposition furnace, the feeding plate angle of the feeding box is adjusted to 30°-40°, and the feeding air pressure set for the feeding box is controlled at 0.05-0.15MPa. After being dispersed by the feeding box, the raw material enters the downward flue of the decomposition furnace.

[0018] Furthermore, in step S5, the material layer thickness corresponding to the thick material layer cooling technology of the grate cooler is set to 600-700mm. The grate cooler is divided into three cooling zones: a high-temperature zone, a medium-temperature zone, and a low-temperature zone. The ventilation volume of the grate bed corresponding to the high-temperature zone accounts for 60%-65% of the total ventilation volume. The grate gap width in the high-temperature zone is set to 2-3mm, and the grate gap width in the medium-temperature zone and the low-temperature zone is set to 3-4mm. All the high-temperature hot air from the grate cooler is sent to the rotary kiln as secondary air, and the medium-temperature hot air is sent to the decomposition furnace as tertiary air.

[0019] Furthermore, in step S5, oxygen-enriched combustion technology is used to oxygenate the primary air. The oxygen-enriched gas is prepared by cryogenic air separation with a purity of ≥99.5%. After being metered by a flow regulating valve, the oxygen is sent into the primary air duct to mix with the ambient air. The oxygen content of the mixed primary air is controlled at 23%-25%. The delivery pressure of the oxygen-enriched gas is set to 0.03-0.8MPa. An online oxygen content detection device is installed in the primary air duct to detect the oxygen content of the primary air in real time and adjust the oxygen flow rate accordingly.

[0020] Furthermore, in step S6, the single adjustment range of adding or subtracting coal is set to 1%-2% of the total coal feed, the time interval between two adjacent coal addition or subtraction operations is ≥5 minutes, the single adjustment range of raw material feed is set to 1%-3% of the rated feed, and the single adjustment range of rotary kiln speed is set to 0.1-0.2 rpm. The adjustment of raw material feed, rotary kiln speed and coal feed is synchronized and linked, and the kiln filling rate is kept stable during the adjustment process.

[0021] Furthermore, the cement clinker prepared by this method is a special type of cement clinker. The calcination temperature in the rotary kiln is controlled at 1350-1500℃, the total residence time of the material in the rotary kiln is set to 30-40 min, the residence time of the material in the calcination zone of the rotary kiln is set to 15-25 min, the inclination of the rotary kiln is set to 3.5%-4%, the operating speed of the rotary kiln is set to 3.0-3.5 rpm, and the oxygen content of the exhaust gas at the kiln tail during the calcination process is controlled to 1.5%-2.5%.

[0022] Compared with existing technologies, this process for co-calcining cement clinker with low-calorific-value coal has the following advantages:

[0023] This invention systematically tests the performance and analyzes the combustion characteristics of low-calorific-value coal to identify suitable calcination control paths. By employing differentiated coal blending and separate grinding of head and tail coal, it balances the large-scale consumption of low-calorific-value coal with stable calcination zone temperature. Through refined fuel preparation and optimization of raw material combustibility, it effectively improves the ignition and burnout performance of low-calorific-value coal. By synergistically optimizing calcination equipment and combustion parameters, it enhances the mixing efficiency of pulverized coal and air, stabilizing the kiln thermal regime. Through refined and proactive operation control, it avoids operational fluctuations caused by the lag in combustion of low-calorific-value coal. Ultimately, it achieves the stable application of low-calorific-value coal in cement clinker calcination, reduces clinker strength fluctuations, lowers standard coal consumption for clinker, improves clinker quality qualification rate, and simultaneously reduces fuel production costs, realizing the efficient and environmentally friendly utilization of low-quality coal resources.

[0024] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0026] Figure 1 A flowchart of a process for co-calcining cement clinker with low-calorific-value coal;

[0027] Figure 2 This is a flowchart illustrating the steps of a process for co-calcining cement clinker with low-calorific-value coal. Detailed Implementation

[0028] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0029] This invention belongs to the field of cement production technology. It addresses the problems of difficult ignition, unstable combustion, low burnout rate, fluctuation of thermal regime in the kiln, poor clinker quality and high energy consumption when low-calorific-value coal is used for cement clinker calcination. It proposes a complete co-calcination process scheme to realize the large-scale and efficient utilization of low-quality coal, while ensuring stable cement clinker production and quality compliance.

[0030] This process forms a comprehensive collaborative control system, consisting of seven core steps. First, raw material performance testing is carried out. Low-calorific-value coal undergoes industrial and elemental analysis to determine its calorific value, ash melting point, ignition, and burnout characteristics. Combustion tests in a tubular furnace are conducted to clarify the combustion reaction process under different calcination atmospheres. Simultaneously, the chemical composition of cement raw materials, including calcium, silica, alumina, and ferrous elements, is tested to determine the basic raw material batching parameters.

[0031] Secondly, differentiated coal blending is implemented. Low-calorific-value coal with a calorific value of no more than 21,000 kJ / kg and an ash content of no more than 10% is selected for the decomposition furnace, accounting for 60% of the total coal consumption. Washed middlings, low-quality bituminous coal, lignite, etc. can be mixed in proportion. High-calorific-value coal with a calorific value of no less than 22,000 kJ / kg and a volatile matter content of no less than 35% is selected for the kiln head, accounting for 40% of the total coal consumption, taking into account both the consumption of low-calorific-value coal and the temperature stability of the burning zone.

[0032] Subsequently, the fuel is refined. The low-calorific-value coal in the decomposition furnace and the high-calorific-value coal in the kiln head are ground separately by two independent vertical coal mills and dried with hot air at 250-300℃. The fineness of the coal powder is controlled so that the residue on a 0.08mm square hole sieve is no more than 6% and the moisture content is no more than 1.0%. Sampling and testing are carried out regularly and the grinding parameters are adjusted accordingly.

[0033] At the same time, the combustibility of raw materials is optimized, and the three ratios of raw materials are adjusted to a lime saturation coefficient of 0.88-0.92, a silicon ratio of 2.6-2.8, and an aluminum ratio of 1.5-1.7. The raw materials are crushed in two stages to a maximum particle size of no more than 25mm. The coefficient of variation of chemical composition after raw material homogenization is no more than 0.3%, and the fluctuation of feed rate is controlled within ±2% of the rated value.

[0034] In the calcination system optimization process, the air ratio inside the four-channel burner is adjusted to 30%-35%, and the angle of the feed box in the decomposition furnace is optimized to ensure that the decomposition rate of raw materials entering the kiln is not less than 92%. The grate cooler adopts a 600-700mm thick material layer cooling technology, the secondary air temperature is not less than 1000℃, and the oxygen-enriched combustion technology is used to control the oxygen content of the primary air at 23%-25%.

[0035] The operation control adopts a small-amplitude coal addition / reduction mode, with a single adjustment range of 1%-2% of the total coal feed. The interval between adjacent operations is no less than 5 minutes, and the raw material feed rate and rotary kiln speed are synchronously controlled to stabilize the kiln filling rate. Finally, the cement raw meal is calcined into clinker at a high temperature of 1350-1500℃, cooled to below 100℃, and then discharged to complete the entire production process.

[0036] This invention achieves stable and efficient application of low-calorific-value coal in cement clinker production through the synergistic effects of raw material testing, coal blending based on quality, fine preparation, system optimization, and precise operation.

[0037] Example 1

[0038] This embodiment adopts a patented core standard technical solution, which achieves large-scale and stable calcination of special cement clinker from low-calorific-value coal through full-performance testing and combustion characteristic experiments of low-calorific-value coal, graded blended coal, independent grinding of head and tail coal, precise optimization of raw material burnability, coordinated control of calcination equipment and combustion parameters, and refined synchronous operation. This effectively solves the problems of difficult ignition, poor burnout, and thermal fluctuations in kiln caused by low-calorific-value coal, ensuring that clinker quality meets standards, reducing production energy consumption, and realizing the efficient resource utilization of inferior coal.

[0039] See Figure 1 and Figure 2 The specific implementation process of this embodiment is as follows:

[0040] S1. Raw Material Performance Testing: Low-calorific-value coal, a blend of washed middlings coal and low-quality bituminous coal, was selected for industrial and elemental analysis to determine calorific value, ash fusion point, ignition, and burnout characteristics. Combustion characteristics were determined through tubular furnace combustion tests, with a test temperature range from room temperature to 1200℃ and a heating rate of 15℃ / min. Ignition temperature, maximum combustion rate temperature, and burnout temperature were measured at oxygen concentrations of 18%, 21%, 23%, and 25%, respectively. Thermogravimetric and differential thermal curves were recorded to clarify the combustion reaction process. Simultaneously, the chemical composition of calcareous, siliceous, aluminous, and ferrous raw materials in cement raw materials was tested to determine the basic raw material batching parameters.

[0041] S2. Differentiated coal blending: Low-calorific-value coal with a calorific value of 20,500 kJ / kg and 9% ash content is used in the decomposition furnace, accounting for 60% of the total coal consumption. Washed middlings and low-quality bituminous coal are weighed by belt scales and sent to the mixing silo for continuous stirring and mixing, with a mixing uniformity variation coefficient of 0.4%. High-calorific-value coal with a calorific value of 22,500 kJ / kg and 36% volatile matter is used at the kiln head, accounting for 40% of the total coal consumption, to ensure stable temperature in the burning zone.

[0042] S3. Fuel preparation: Low-calorific-value coal from the decomposition furnace and high-calorific-value coal from the kiln head are fed into two independent vertical coal mills for grinding. Hot air at 280℃ is introduced for drying. The fineness of the coal powder is controlled to be 5% residue on a 0.08mm square hole sieve and 0.8% moisture content. An online sampling device is installed in the coal powder silo to test the fineness and moisture content every 2 hours and adjust the parameters of the coal mill and classifier in real time.

[0043] S4. Raw material optimization: The three raw material ratios are set as follows: lime saturation coefficient 0.90, silicon content 2.7, and aluminum content 1.6. The raw materials are crushed to a maximum particle size of 22mm by a jaw crusher and an impact crusher. After metering and batching, they are fed into a raw material mill for grinding. After grinding, they are sent to a continuous homogenization silo for homogenization. The chemical composition variation coefficient is 0.25%. The raw materials are fed by a loss-in-weight weigher, and the feed rate fluctuation is controlled within ±1.5%.

[0044] S5. Calcination System Optimization: A four-channel burner is adopted, with an internal air ratio of 32%, a swirl air angle of 28°, and the central air volume accounting for 6% of the total primary air; the decomposition furnace feeding box is located at the upper part of the constriction at an angle of 35°, with a supply air pressure of 0.5MPa, and the decomposition rate of raw materials entering the kiln is 94%; the grate cooler adopts a 650mm thick material layer, divided into high-temperature, medium-temperature, and low-temperature zones, with the high-temperature zone ventilation volume accounting for 63%, and the grate gap width of 2.5mm. High-temperature hot air is used as secondary air, and medium-temperature hot air is used as tertiary air, with a secondary air temperature of 1050℃; 99.5% pure oxygen is prepared by cryogenic air separation, with a delivery pressure of 0.9MPa, and the primary air oxygen content is controlled at 24%.

[0045] S6. Operation control: The single adjustment range for adding or subtracting coal is 1.5%, with an interval of 6 minutes between adjacent operations; the single adjustment of raw material feed rate is 2%, and the single adjustment of rotary kiln speed is 0.15 rpm. The three parameters are synchronized to stabilize the kiln filling rate.

[0046] S7. Calcination discharge: Rotary kiln inclination 3.8%, kiln speed 3.2 rpm, calcination temperature 1420℃, total material residence time 35 min, calcination zone residence time 20 min, oxygen content of kiln tail exhaust gas 2%; clinker is cooled to below 90℃ by grate cooler and discharged by kiln head discharge device.

[0047] In summary, this embodiment operated continuously and stably for 30 days. The clinker performance and energy consumption indicators were determined by conventional laboratory testing methods: free calcium oxide was tested batch by batch using the glycerol-ethanol titration method, and the pass rate was 99% based on daily valid test data; the standard coal consumption per ton of clinker was calculated to be 105 kg using the industry-standard heat consumption calculation method; the 28-day compressive strength was measured to be 58 MPa using the conventional cement mortar strength testing method; there were no kiln ring formations, preheater scaling and blockages, or raw material leakage during the production process; the proportion of low-calorific-value coal consumed reached 60%; the process operation was stable; and the overall effect was excellent.

[0048] Example 2

[0049] Based on the patented standard scheme, this embodiment optimizes the oxygen-enriched combustion concentration, the thick material layer parameters of the grate cooler, and the burner air ratio to further improve the low-calorific-value coal burnout rate and waste heat recovery efficiency, enhance combustion stability and thermal regime controllability, further reduce energy consumption and improve clinker performance on the standard scheme, and adapt to the production of high-quality special cement clinker.

[0050] See Figure 1 and Figure 2 The specific implementation process of this embodiment is as follows:

[0051] S1. Raw material performance testing: The testing process is the same as in Example 1, with the addition of a tubular furnace combustion test at a 25% oxygen concentration to accurately determine the optimal oxygen-enriched combustion conditions and clarify the burnout characteristics of low-calorific-value coal in a high-oxygen atmosphere.

[0052] S2. Coal blending by quality: The low-calorific-value coal used in the decomposition furnace is a blend of lignite and low-quality bituminous coal, with a calorific value of 20,800 kJ / kg, ash content of 8.5%, and a coefficient of variation of uniformity of continuous stirring and mixing of 0.3%, accounting for 60% of the total coal consumption; the parameters of the high-calorific-value coal at the kiln head are the same as in Example 1, and the amount used accounts for 40%.

[0053] S3. Fuel preparation: Two independent vertical coal mills are used for grinding. The hot air temperature is 280℃. The fineness of the coal powder is controlled to be 4.5% residue on a 0.08mm square hole sieve and 0.7% moisture. Online sampling and testing are conducted every 2 hours, and grinding parameters are dynamically adjusted.

[0054] S4. Raw material optimization: The raw material three-rate values ​​and crushing and homogenization process are the same as in Example 1, and the feed rate fluctuation is controlled within ±1%, further improving the stability of raw material feeding.

[0055] S5. Calcination system optimization: The proportion of internal air in the four-channel burner is 35%, the swirl air angle is 30°, and the central air volume accounts for 8% of the total primary air; the angle of the feed box in the decomposition furnace is 40°, the air supply pressure is 0.6MPa, and the decomposition rate of raw materials entering the kiln is 95%; the material layer thickness of the grate cooler is 700mm, the ventilation volume in the high-temperature zone accounts for 65%, the grate gap width is 2mm, and the secondary air temperature is 1100℃; the oxygen enrichment concentration is increased to 25%, and the oxygen delivery pressure is 1.0MPa to ensure complete combustion of pulverized coal.

[0056] S6. Operation control: The coal addition / reduction adjustment range is 1% at a time, with an interval of 5 minutes; the kiln speed is adjusted by 0.2 rpm at a time; the raw material feed rate, kiln speed, and coal feed rate are synchronized and linked to strictly control the kiln filling rate.

[0057] S7. Calcination discharge: Rotary kiln inclination 4%, kiln speed 3.3 rpm, calcination temperature 1450℃, total material residence time 38 min, oxygen content of kiln tail exhaust gas 1.5%; clinker is discharged after cooling to 85℃.

[0058] In summary, this embodiment operated continuously and stably for 45 days, and all indicators were measured using conventional laboratory testing methods: the free calcium oxide qualification rate was 99.5% according to the glycerol-ethanol method; the standard coal consumption per ton of clinker was 102 kg calculated using the industry-standard heat consumption method; the 28-day compressive strength was 60 MPa measured using conventional cement mortar strength testing methods; the coal powder combustion rate was increased to 98%, the waste heat recovery efficiency was increased by 8%, and there were no production failures. The clinker quality and energy consumption indicators were superior to those of Embodiment 1, demonstrating excellent process performance.

[0059] Example 3

[0060] This embodiment optimizes the three ratios of raw materials, rotary kiln operating parameters, and low-calorific-value coal blending scheme to adapt to the higher demand for low-calorific-value coal consumption. Under the premise of ensuring the quality of clinker, it increases the scale of low-calorific-value coal utilization, enhances the adaptability of the process to low-calorific-value coal from different sources, and takes into account both production stability and cost control.

[0061] See Figure 1 and Figure 2 The specific implementation process of this embodiment is as follows:

[0062] S1. Raw material performance testing: Low-calorific-value coal, a blend of lignite and washed middlings coal, was selected. The heating rate of the tubular furnace combustion test was 20℃ / min. The calorific value, ash melting point, and ignition and burnout characteristics under different oxygen concentrations were comprehensively measured to determine the appropriate control parameters.

[0063] S2. Differentiated coal blending: Low-calorific-value coal with a calorific value of 20200kJ / kg and an ash content of 9.5% is used in the decomposition furnace, accounting for 60% of the total coal consumption; high-calorific-value coal at the kiln head has unchanged parameters and accounts for 40% of the consumption, ensuring basic thermal stability.

[0064] S3. Fuel preparation: The coal powder is ground using an independent vertical coal mill and dried with 300℃ hot air. The fineness of the coal powder is 5.5% sieve residue and 0.9% moisture. Samples are taken every 2 hours for testing and the parameters of the coal mill are adjusted accordingly.

[0065] S4. Raw material optimization: The three raw material ratios are set as follows: lime saturation coefficient 0.92, silicon ratio 2.8, and aluminum ratio 1.7. The raw materials are crushed in two stages to a maximum particle size of 25mm. After homogenization, the coefficient of variation of chemical composition is 0.3%, and the feed rate fluctuation is controlled within ±2%.

[0066] S5. Calcination system optimization: The proportion of internal air in the four-channel burner is 30%, the swirl air angle is 25°, and the central air volume accounts for 5% of the total primary air; the angle of the feed box in the decomposition furnace is 30°, the air supply pressure is 0.4MPa, and the decomposition rate of raw materials entering the kiln is 93%; the material layer thickness of the grate cooler is 600mm, the ventilation volume in the high-temperature zone accounts for 60%, the grate gap width is 3mm, and the secondary air temperature is 1020℃; the oxygen concentration of the primary air is 23%, and the oxygen delivery pressure is 0.8MPa.

[0067] S6. Operation control: The coal addition / reduction adjustment range is 2% per cycle, with an interval of 7 minutes; the kiln speed is set to 3.5 rpm, with a single adjustment of 0.1 rpm, synchronously controlling the feed rate to maintain a stable kiln filling rate.

[0068] S7. Calcination discharge: Rotary kiln inclination 3.5%, calcination temperature 1400℃, total material residence time 40min, calcination zone residence time 25min, oxygen content of kiln tail exhaust gas 2.5%; clinker is discharged after cooling to 95℃.

[0069] In summary, this embodiment operated continuously and stably for 60 days, and all indicators were measured using conventional laboratory testing methods: the free calcium oxide qualification rate was 98.5% according to the glycerol-ethanol method; the standard coal consumption per ton of clinker was 106 kg calculated using the industry-standard heat consumption method; the 28-day compressive strength was 57 MPa measured using the conventional cement mortar strength testing method; the low-calorific-value coal consumption was increased by 5% compared to the traditional process; the production process was trouble-free, the kiln condition was stable, and the process effect was good.

[0070] Comparative Example

[0071] This comparative example uses the traditional clinker calcination process in the cement industry. It does not employ measures such as differentiated coal blending, separate grinding of head and tail coal, oxygen-enriched combustion, thick material layer cooling, or system parameter optimization. Instead, it directly uses mixed low-calorific-value coal for calcination and does not conduct combustion characteristic tests on low-calorific-value coal or optimize the burnability of raw materials. It is used to verify the technical superiority of this patented process.

[0072] The specific implementation process of this comparative example is as follows:

[0073] S1. Only a simple industrial analysis was conducted on low-calorific-value coal, without carrying out combustion characteristic tests in tubular furnaces, and the ignition and burnout parameters were not clearly defined; the raw materials were not optimized in terms of batching and combustibility, and conventional chemical composition was directly used for batching.

[0074] S2. Coal blending was not implemented based on coal quality. Low-calorific-value coal was mixed with high-calorific-value coal at will, without fixed proportions or control over the uniformity of mixing. All coal materials were used uniformly.

[0075] S3. A single coal mill is used for unified grinding, without separate grinding processes. The fineness of the coal powder is 10% residue on a 0.08mm square hole sieve, and the moisture content is 1.5%. There is no online detection or parameter adjustment.

[0076] S4. The raw material adopts the conventional three-rate values ​​and has not been optimized for easy burning; the raw material is only crushed in one stage, the particle size exceeds the standard, there is no efficient homogenization treatment, and the feed rate fluctuates greatly.

[0077] S5. The burner uses conventional parameters and the internal air ratio and swirl angle are not adjusted, resulting in no oxygen-enriched combustion; the angle of the feed box in the decomposition furnace is not optimized, and the decomposition rate of raw materials entering the kiln is 85%; the grate cooler operates without a thick material layer, the secondary air temperature is only 850℃, and the waste heat recovery efficiency is low.

[0078] S6. It adopts large-scale coal addition and reduction operations, with a single adjustment range exceeding 5%, without synchronous control logic, and the kiln speed and feed rate are not linked, resulting in frequent fluctuations in the kiln's thermal regime.

[0079] S7. The clinker was calcined at a conventional temperature and discharged after cooling to 120°C, without precise control of the cooling temperature.

[0080] In summary, after 30 days of continuous operation, the following indicators were measured using conventional laboratory testing methods: the free calcium oxide pass rate was only 75%, the standard coal consumption per ton of clinker was 130 kg, and the 28-day compressive strength was 45 MPa. Frequent problems occurred during the production process, including preheater scaling and blockage, kiln ring formation, and raw material leakage. Low-calorific-value coal could not be used stably, resulting in poor process performance.

[0081]

[0082] The comparison results in the table above show that the three embodiments of this patent, relying on the core processes of differentiated coal blending, separate grinding, system optimization, and refined operation, completely solve the technical pain points of traditional processes, such as difficulty in igniting low-calorific-value coal, poor burnout, kiln thermal fluctuations, unstable clinker quality, and high energy consumption. Embodiment 2, through optimization of oxygen concentration and thick material layer, achieves optimal overall performance and is suitable for high-quality clinker production; Embodiment 1 is a standard stable solution, suitable for large-scale industrial production; Embodiment 3 focuses on increasing the utilization of low-calorific-value coal, balancing cost and practicality. The comparative embodiment, lacking the patented core technology, suffers from problems such as low clinker strength, poor free calcium oxide qualification rate, high coal consumption, and frequent equipment failures, making stable utilization of low-calorific-value coal impossible. In summary, this patented process enables large-scale, efficient, and stable application of low-calorific-value coal, while improving clinker quality, reducing production energy consumption, and promoting the green and low-carbon transformation of the cement industry.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A process for co-calcining cement clinker with low-calorific-value coal, characterized in that, The method includes the following steps: S1. Raw material performance testing: Industrial and elemental analysis of low-calorific-value coal is conducted to determine its calorific value, ash melting point, ignition characteristics and burnout characteristics. Chemical composition testing of calcareous, siliceous, aluminous and ferrous raw materials of cement raw materials is conducted to determine the basic raw material batching parameters. S2. Differentiated Coal Blending: The coal used in the decomposition furnace is low-calorific-value coal with a calorific value of <21000kJ / kg and an ash content of ≤10%, accounting for 60% of the total coal mass. The coal used in the kiln head is high-calorific-value coal with a calorific value of ≥22000kJ / kg and a volatile matter content of ≥35%, accounting for 40% of the total coal mass. S3. Fuel preparation: Low-calorific-value coal for the decomposition furnace and high-calorific-value coal for the kiln head are prepared by separate grinding. The fineness of the coal powder is controlled to be ≤6% residue on a 0.08mm square hole sieve and ≤1.0% moisture content. S4. Raw material optimization: Adjust the three raw material ratios to set the lime saturation coefficient to 0.88-0.92, silicon content to 2.6-2.8, and aluminum content to 1.5-1.7, thereby controlling the particle size of raw materials entering the mill and the homogenization effect of raw materials, and stabilizing the raw material feed rate. S5. Calcination system optimization: Adjust the air ratio inside the rotary kiln burner to 30%-35%, optimize the angle of the feed box in the decomposition furnace, control the decomposition rate of raw materials entering the kiln to ≥92%, optimize the operating parameters of the grate cooler, adopt thick material layer cooling technology, and control the secondary air temperature to ≥1000℃. S6. Operation control: The operation mode of adding or subtracting coal in small increments is adopted, and the raw material feed rate and rotary kiln speed are simultaneously and proactively adjusted. S7. Calcination Completion and Discharge: After the cement raw meal is calcined at high temperature in the rotary kiln to form clinker, the clinker is cooled to below 100°C by a grate cooler. The cooled clinker is discharged from the rotary kiln head discharge device, completing the entire process of low-calorific-value coal co-calcining of cement clinker.

2. The process method for co-calcining cement clinker with low-calorific-value coal according to claim 1, characterized in that, In step S1, the combustion characteristics of low-calorific-value coal are determined by a tubular furnace combustion test. The temperature range of the combustion test is set to room temperature - 1200℃, and the heating rate is set to 10-20℃ / min. Under atmospheric conditions with oxygen concentrations of 18%, 21%, 23%, and 25%, the ignition temperature, the temperature corresponding to the maximum combustion rate, and the burnout temperature of the low-calorific-value coal are measured. The thermogravimetric change curve and differential thermal change curve of the combustion process are recorded to clarify the combustion reaction process of low-calorific-value coal under different calcination atmospheres.

3. The process method for co-calcining cement clinker with low-calorific-value coal according to claim 1, characterized in that, In step S2, the low-calorific-value coal for the decomposition furnace is prepared by mixing two or more low-calorific-value coals from different sources in a fixed proportion. The low-calorific-value coal for mixing includes two or more of washed middlings coal, low-quality bituminous coal, and lignite. The low-calorific-value coals of each component are metered by a belt scale according to a preset proportion and then sent to the coal mixing silo.

4. The process method for co-calcining cement clinker with low-calorific-value coal according to claim 1, characterized in that, In step S3, the low-calorific-value coal for the decomposition furnace and the high-calorific-value coal for the kiln head are ground separately. During the grinding process, hot air is simultaneously introduced to dry the coal powder. The hot air temperature is controlled at 250-300℃. After the ground coal powder is classified by the classifier, it is sent to the corresponding coal powder silo.

5. The process method for co-calcining cement clinker with low-calorific-value coal according to claim 1, characterized in that, In step S4, the raw material is crushed in two stages before entering the mill. The maximum particle size of the crushed raw material is ≤25mm. After being metered and batched, the crushed raw material is sent to the raw material mill for grinding. The ground raw material is then homogenized. The coefficient of variation of the chemical composition of the homogenized raw material is ≤0.3%. The fluctuation range of the raw material feed rate is controlled within ±2% of the rated feed rate.

6. The process method for co-calcining cement clinker with low-calorific-value coal according to claim 1, characterized in that, In step S5, the rotary kiln burner adopts a four-channel burner, the internal air adopts swirl air with a swirl angle set to 25°-30°, the external air adopts direct current air, and the central air volume accounts for 5%-8% of the total primary air volume. The decomposition furnace feeding box is located at the upper part of the constriction of the decomposition furnace, the feeding plate angle of the feeding box is adjusted to 30°-40°, and the feeding air pressure corresponding to the feeding box is controlled at 0.05-0.15MPa. After being dispersed by the feeding box, the raw material enters the downward flue of the decomposition furnace.

7. The process method for co-calcining cement clinker with low-calorific-value coal according to claim 1, characterized in that, In step S5, the material layer thickness corresponding to the thick material layer cooling technology of the grate cooler is set to 600-700mm. The grate cooler is divided into three cooling zones: high temperature zone, medium temperature zone, and low temperature zone. The ventilation volume of the grate bed corresponding to the high temperature zone accounts for 60%-65% of the total ventilation volume. The grate gap width in the high temperature zone is set to 2-3mm, and the grate gap width in the medium temperature zone and the low temperature zone is set to 3-4mm. All the high temperature hot air from the grate cooler is sent to the rotary kiln as secondary air, and the medium temperature hot air is sent to the decomposition furnace as tertiary air.

8. The process method for co-calcining cement clinker with low-calorific-value coal according to claim 1, characterized in that, In step S5, oxygen-enriched combustion technology is used to oxygenate the primary air. The oxygen-enriched gas is prepared by cryogenic air separation with a purity of ≥99.5%. After being metered by a flow regulating valve, the oxygen is sent into the primary air duct to mix with the ambient air. The oxygen content of the primary air after mixing is controlled at 23%-25%, and the delivery pressure of the oxygen-enriched gas is set to 0.03-0.8MPa.

9. The process for co-calcining cement clinker with low-calorific-value coal according to claim 1, characterized in that, In step S6, the single adjustment range of adding or subtracting coal is set to 1%-2% of the total coal feed, the time interval between two adjacent coal addition or subtraction operations is ≥5min, the single adjustment range of raw material feed is set to 1%-3% of the rated feed, and the single adjustment range of rotary kiln speed is set to 0.1-0.2rpm.

10. The process method for co-calcining cement clinker with low-calorific-value coal according to claim 1, characterized in that, In step S7, the calcination temperature in the rotary kiln is controlled at 1350-1500℃, the total residence time of the material in the rotary kiln is set to 30-40 min, the residence time of the material in the firing zone of the rotary kiln is set to 15-25 min, the inclination of the rotary kiln is set to 3.5%-4%, the operating speed of the rotary kiln is set to 3.0-3.5 rpm, and the oxygen content of the exhaust gas at the kiln tail during the calcination process is controlled to 1.5%-2.5%.

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