A method for alternative fuel staged dechlorination pretreatment and blending for cement kilns

Abstract

The present application relates to cement production solid waste resource utilization technical field, specifically to a kind of cement kiln's alternative fuel grading dechlorination pretreatment and blending method.The present application is first to alternative fuel according to chloride ion content grading, to high chloride fuel using winnowing, washing, pre-drying combined process to remove chlorides, then through quantification proportion blending three kinds of fuel, and real-time monitoring total chlorine load into kiln dynamic adjustment of dosage.The present application reduces chloride ion from source, without increasing bypass air volume, can the cement kiln alternative fuel rate by 20%~30% to 60%~80%, effectively solve the problem of high proportion of alternative fuel burning caused by chloride ion enrichment, preheater skin, heat consumption rises and so on, system stable operation, adaptation cement kiln large-scale collaborative disposal solid waste scene.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology in cement production, specifically to a graded dechlorination pretreatment and blending method for alternative fuels adapted to cement kilns. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the advancement of policies promoting the co-processing of solid waste in the cement industry, the proportion of alternative fuels used in cement kilns is gradually increasing. In existing technologies, alternative fuels are not graded according to chloride ion content, and high-chlorine components are directly fed into the kiln, leading to a continuous accumulation of chloride ions in the kiln system. This causes problems such as preheater scaling, flue gas blockage, and equipment corrosion. Conventional methods, relying solely on increasing bypass ventilation to balance chloride ions, result in a significant increase in heat consumption and production costs.

[0004] Meanwhile, existing alternative fuels only undergo simple crushing and do not undergo pretreatment to remove soluble chloride salts, resulting in large fluctuations in fuel chlorine content, which cannot stably support an increase in the alternative fuel rate to 60%~80%; moreover, there is a lack of quantitative blending rules, leading to drastic fluctuations in system chlorine load and poor stability of kiln system operating conditions. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a graded dechlorination pretreatment and blending method for alternative fuels adapted to cement kilns. The purpose is to reduce the total amount of chloride ions entering the kiln from the source without increasing the bypass venting volume or significantly increasing heat consumption, thereby achieving a stable increase in the alternative fuel rate of cement kilns from 20%~30% to 60%~80%, and maintaining the chloride ion balance and long-term stable operation of the kiln system.

[0006] To achieve the above effects, the present invention provides the following technical solution: Firstly, a method for graded dechlorination pretreatment of alternative fuels adapted to cement kilns is provided. The method is used to pretreat the alternative fuels before they enter the kiln, and includes the following steps: 1) Chloride ion detection and fuel classification: The chloride ion content in alternative fuels is determined, and alternative fuels are classified into three categories according to the mass fraction of chlorine: low-chlorine fuels: Cl < 0.2%, medium-chlorine fuels: 0.2% ≤ Cl ≤ 0.5%, and high-chlorine fuels: Cl > 0.5%; 2) Graded pretreatment: The low-chlorine fuel is crushed to 20~30mm; the medium-chlorine fuel and high-chlorine fuel are sequentially subjected to air classification to remove impurities, water washing to remove chlorine and low-temperature pre-drying, wherein the pre-drying temperature is 200~300℃; 3) Homogeneous mixing: The low-chlorine fuel, medium-chlorine fuel and high-chlorine fuel after the pretreatment in step 2) are homogeneously mixed according to the following mass ratio: low-chlorine fuel accounts for ≥75% of the total substitute fuel, medium-chlorine fuel accounts for ≤20% and is greater than 0% of the total substitute fuel, and high-chlorine fuel accounts for ≤5% of the total substitute fuel.

[0007] To achieve a long-term, stable high proportion of alternative fuel blending, this invention effectively reduces the chlorine content in the alternative fuel through low-temperature drying pretreatment, reduces pretreatment costs through alternative fuel grading, and provides a reasonable blending ratio of graded fuels. Based on the above solutions provided by this invention, the amount of alternative fuel blended in cement kilns can be increased to more than 60% of the total fuel proportion, significantly increasing the solid waste treatment capacity and effectively reducing the wear and tear on cement kilns, thus achieving long-term, stable operation.

[0008] In some embodiments of the present invention where the effects are better, the first aspect described above also has the following preferred solutions: In step 1) above, the method for determining the chloride ion content includes, but is not limited to, high-temperature combustion hydrolysis method and oxygen bomb combustion-ion chromatography method.

[0009] The determination steps of the high-temperature combustion hydrolysis method are as follows: The sample to be tested is put into a mixed gas flow of oxygen and water vapor at 1000-1100℃, so that the sample is completely burned and all forms of chlorine are converted into HCl gas. After being absorbed by water, the chloride ion content is determined by titration.

[0010] The determination steps of the oxygen bomb combustion-ion chromatography method are as follows: Weigh 0.2-0.5g of the sample to be tested and place it in the oxygen bomb, add 20-30mL of alkaline absorption solution, tighten the oxygen bomb cap, fill it with 3.0MPa pure oxygen, ignite it, and let it stand for absorption under sealed conditions; open the oxygen bomb, rinse all parts inside the oxygen bomb repeatedly with deionized water, and after diluting all the washing solution to a certain volume, detect it by ion chromatography.

[0011] In step 2) above, the low-chlorine fuel is crushed in two stages, and the specific steps are as follows: (1) Primary crushing The above-mentioned low-chlorine fuel is crushed to a particle size of approximately 80-150 mm to obtain primary crushed material; (2) Secondary crushing The primary crushed material is further crushed to 20-30mm. This particle size range ensures that the material flows smoothly and burns completely in the conveying and combustion systems.

[0012] The medium-chlorine fuel and high-chlorine fuel are sequentially subjected to mechanical air separation for impurity removal, water washing for dechlorination, and low-temperature pre-drying. The specific steps are as follows: (1) Mechanical air separation for impurity removal Select a suction-type gravity destoner, spread the above-mentioned medium-chlorine fuel and high-chlorine fuel evenly on the entire screen surface, keep the screen surface inclination angle between 10° and 13°, adjust the damper until the material on the screen surface reaches a "semi-suspended" state - it looks like it is "boiling" or "floating" and moving, but it will not be blown away directly, thus obtaining the impurity-removed material.

[0013] (2) Dechlorination by rinsing with clean water The process involves using a countercurrent washing method. The material to be cleaned is fed into the feed inlet and slowly pushed upwards. The washing water is heated to 25-60°C with a liquid-to-solid ratio of 3-6:1 and sprayed downwards onto the surface of the material to achieve countercurrent washing. The washing cycle is 1-3 times.

[0014] The wastewater generated by the aforementioned countercurrent washing contains impurities such as heavy metals and calcium and magnesium ions. Direct evaporation will cause severe scaling, affecting equipment operation and product quality. Commonly used purification methods in this field include heavy metal capture: adding chemical agents and adjusting the pH value to cause heavy metal ions to form precipitates for separation; softening treatment; and chemical precipitation methods (such as adding sodium carbonate or calcium hydroxide) to remove calcium and magnesium ions from the water and prevent scaling in the evaporator.

[0015] The purified washing liquid can be reused for countercurrent washing. Once the residual soluble salt content increases significantly, industrial salt by-products can be obtained through evaporation and crystallization. The condensate is then returned to the countercurrent washing section, achieving resource utilization.

[0016] (3) Low-temperature pre-drying The washed material is heated at 200-300℃ for 20-30 minutes. This drying temperature is primarily used to remove moisture while simultaneously removing over 90% of the chlorine. In chlorinated organic compounds, the C-Cl chemical bond energy is relatively low. When the temperature is uniformly raised to approximately 200-300℃, these C-Cl bonds preferentially break, releasing chlorine, mainly as hydrogen chloride (HCl) gas. The pyrolysis gas of the released HCl is passed into a scrubbing tower and absorbed by spraying with water or an alkaline solution, generating hydrochloric acid or salt byproducts for recovery. Within this temperature window, the more stable carbon-carbon (CC) and carbon-hydrogen (CH) bonds in the fuel remain largely intact. This means that while removing harmful chlorine, the main structure and most of the calorific value of the fuel are effectively preserved, preparing it for subsequent utilization.

[0017] In step (3) above, the pretreated low-chlorine fuel, medium-chlorine fuel and high-chlorine fuel are mixed according to the following mass ratio: low-chlorine fuel accounts for ≥75% of the total substitute fuel, medium-chlorine fuel accounts for ≤20% of the total substitute fuel and is greater than 0, and high-chlorine fuel accounts for ≤5% of the total substitute fuel. After mixing, they are thoroughly homogenized by high-speed stirring.

[0018] In a second aspect, a method for blending alternative fuels adapted to cement kilns is provided, the method comprising blending in alternative fuels pretreated by the method described in the first aspect.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention constructs a graded, quantitatively blended, and dynamically controlled end-to-end chloride ion management system, providing a standardized, quantifiable, and industrially applicable management system for industrial solid waste treatment. The management model shifts from end-of-pipe treatment to source control. Using a high proportion of low-chlorine fuel as the base, a system chloride load buffer is formed, effectively diluting the localized high chloride ion concentrations generated by the combustion of medium- and high-chlorine fuels. This avoids instantaneous high-chlorine corrosion in critical parts of the kiln, stabilizing the system chloride load from the source without significantly increasing bypass ventilation, thus reducing energy consumption and operation and maintenance costs.

[0020] 2. Pure low-chlorine alternative fuels are expensive and resource-constrained, making it impossible to meet the demand for large-scale blending. High-chlorine solid waste is inexpensive, but causes significant damage to cement kilns. This invention addresses this by setting tiered blending limits, enabling the compliant use of low-cost medium- and high-chlorine solid waste fuels within a controllable range. It also relaxes the extreme precision requirements of front-end dechlorination pretreatment, eliminating the need for deep dechlorination of the fuel and effectively reducing pretreatment energy consumption and raw material screening costs. Furthermore, quality control shifts from precise numerical regulation to proportional limit control, simplifying production line testing and maintenance processes and enhancing process tolerance.

[0021] 3. Homogeneous and Stable Feeding and Blending. After precise blending and forced homogenization of different types of fuels, the particle size, composition, and moisture content of the materials are uniform, allowing for stable and continuous feeding to the cement kiln combustion system for blending and ensuring stable thermal operation of the kiln system. Traditional processes can only limit the proportion of alternative fuels to 20%~30% due to chlorine enrichment. This solution stabilizes the chlorine balance of the system from the source, avoids preheater scaling and corrosion, and ensures continuous stability of thermal operation. Tests have shown that, under the same production capacity, the method of this invention can stably increase the proportion of alternative fuels to 60%~80%. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 This is a flowchart of the graded dechlorination pretreatment method for alternative fuels adapted to cement kilns described in this invention. Detailed Implementation

[0024] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] In the context of this specification, the word "comprising" is considered to mean "especially including". It should not be interpreted as "consisting of only".

[0027] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0028] Example 1 This embodiment provides a graded dechlorination pretreatment method for alternative fuels adapted to cement kilns. The alternative fuels collected in this embodiment include the following: Agricultural and forestry waste: 500 kg of corn stalk pellets (8-10 mm in diameter) with a moisture content ≤15% and a chlorine content ≤0.10%.

[0029] Industrial solid waste: 200kg of waste textiles (composed of natural cotton and linen fibers, cut to a particle size of ≤20mm) with a moisture content of ≤5% and a chlorine content of ≤0.15%.

[0030] Waste-derived fuel (RDF): 200kg, commercial RDF pellets with a moisture content ≤10% and a chlorine content between 0.30% and 0.80%, mainly composed of waste plastics, waste paper, textiles, etc., with a particle size ≤25mm.

[0031] Industrial solid waste: 50kg, specifically waste plastic film with a moisture content ≤2% and a chlorine content between 1.50% and 2.50%, mainly made of PE / PP material, which has been compressed and packaged.

[0032] 1) Chloride ion detection and fuel grading The chlorine content of the above-mentioned alternative fuels was determined by oxygen bomb combustion-ion chromatography (referencing EN 15408:2011 standard). The specific determination method is as follows: Accurately weigh 0.2-0.5 g of the sample to be tested and place it in the sample dish of the oxygen bomb. Add 20-30 mL of alkaline absorption solution (0.1 mol / L NaOH or Na2CO3 / NaHCO3 solution) to the oxygen bomb to absorb the acidic gases (such as HCl, Cl2) produced by combustion. Tighten the oxygen bomb cap and fill it with pure oxygen at 3.0 MPa. Place the oxygen bomb in the ignition device, turn on the power to ignite, and allow it to stand for absorption for 30 minutes under sealed conditions. Open the oxygen bomb and repeatedly rinse the inner wall of the oxygen bomb, electrodes, sample dish, and all other parts with deionized water. Transfer all the washing solution to a 100 mL volumetric flask and dilute to the mark.

[0033] After the solution was brought to a final volume, it was filtered through a 0.22 μm filter membrane and then injected into an ion chromatograph.

[0034] Example of chromatographic conditions: Chromatographic column: Metrosep A Supp 5-250 / 4.0 anion analyzer column; Eluent: A mixed solution of 3.2 mmol / L Na₂CO₃ and 1.0 mmol / L NaHCO₃; Flow rate: 0.7 mL / min; Detector: Conductivity detector.

[0035] Calculate the chloride ion concentration in the sample solution, and then calculate the dry basis mass fraction of chloride in the sample using the following formula. w (Cl), in percentage (%): w (Cl) = Where C is the chloride ion concentration (mg / L) determined by ion chromatography, V is the volume of the sample solution (mL), m is the mass of the sample (g), and X is the air-dried moisture content of the sample (%).

[0036] The chloride ion content of various alternative fuels is calculated based on the above formula, and they are classified as follows: Low-chlorine fuels: Cl < 0.2%; Medium-chlorinated fuels: 0.2% ≤ Cl ≤ 0.5%; High-chlorine fuels: Cl > 0.5%.

[0037] The results of the chloride ion content determination and grading are as follows: Table 1 Classification of various alternative fuels After the alternative fuels have been tested, they are categorized and stored for further processing.

[0038] 2) Graded pretreatment The low-chlorine fuel undergoes crushing and homogenization treatment using a two-stage crushing process, with the specific steps as follows: (1) Primary crushing The low-chlorine fuel in Table 1 was used to crush the above-mentioned agricultural and forestry waste and waste textiles to a particle size of about 80-150mm using a twin-shaft shear crusher to obtain primary crushed material.

[0039] (2) Secondary crushing The above-mentioned primary crushed material is transferred to a single-shaft fine crusher or a ring hammer crusher to further crush the material to a particle size of 20-50mm.

[0040] The above-mentioned medium-chlorine fuels and high-chlorine fuels are subjected to mechanical air separation for impurity removal, water washing for dechlorination, and low-temperature pre-drying in sequence. The specific steps are as follows: (1) Mechanical air separation for impurity removal Select a suction-type gravity destoner, spread the above-mentioned medium-chlorine fuel or high-chlorine fuel evenly on the entire screen surface, keep the screen surface inclination angle between 10° and 13°, and adjust the damper until the material on the screen surface reaches a "semi-suspended" state.

[0041] (2) Dechlorination by rinsing with clean water The countercurrent washing method is adopted. The above-mentioned impurity-removing material is fed in through the feed inlet and slowly pushed upward. The washing water is heated to 25~60℃, the liquid-solid ratio is 3-6:1, and it is sprayed downward from a height onto the surface of the material to achieve countercurrent washing. The washing is performed twice.

[0042] (3) Low-temperature pre-drying The washed material is transferred into a mesh belt conveyor dryer, and the temperature is set to 250℃ to start drying. The drying time is 30 minutes. The gas overflowing during the drying process is recovered through an alkaline spray absorption tower.

[0043] Using the above pretreatment method, 820 kg of low-chlorine fuel, 140 kg of medium-chlorine fuel, and 40 kg of high-chlorine fuel were obtained after treatment.

[0044] 3) Homogeneous mixing The pretreated low-chlorine fuel, medium-chlorine fuel, and high-chlorine fuel are mixed according to the following mass ratio: low-chlorine fuel accounts for 78% of the total substitute fuel, medium-chlorine fuel accounts for 20% of the total substitute fuel, and high-chlorine fuel accounts for 2% of the total substitute fuel. The pretreated low-chlorine fuel, medium-chlorine fuel, and high-chlorine fuel are weighed according to the ratio and transported to a twin-shaft forced mixer for high-speed mixing for 5 minutes to achieve uniform mixing at both the macroscopic and microscopic levels.

[0045] Example 2 In this embodiment, another alternative fuel staged dechlorination pretreatment method adapted for cement kilns is provided, which differs from Embodiment 1 in that: In step 1), the chloride ion detection is performed using a high-temperature hydrolysis combustion method. The specific steps are as follows: the sample is completely combusted in a mixed gas stream of oxygen and water vapor at 1000-1100℃. All forms of chlorine are converted into HCl gas, which is absorbed by water and then the chloride ion content is determined by potentiometric titration.

[0046] Example 3 In this embodiment, a method for blending alternative fuels suitable for cement kilns is provided. The low-chlorine fuel, medium-chlorine fuel, and high-chlorine fuel pretreated in Example 1 are used as alternative fuels, and the mass ratio of alternative fuels in the total fuel is 80%. Among the alternative fuels, the mass ratio of pretreated low-chlorine fuel, medium-chlorine fuel, and high-chlorine fuel is 82:14:4.

[0047] The specific steps of the blending method are as follows: the homogenized alternative fuel is blended into the ordinary fuel to obtain a mixed fuel.

[0048] Performance testing The blended and homogenized alternative fuel from Example 3 was subjected to a 30-day industrial trial on a cement kiln co-processing line with a daily clinker production of 5,000 tons. The results showed: Total chlorine control in the kiln: The chloride ion content in the hot raw materials is kept stable between 0.012% and 0.018%, which is lower than the bypass venting start threshold of 0.03%.

[0049] Fuel utilization rate: The average heat substitution rate (TSR) reached 58%, indicating that the fuel was fully burned in the decomposition furnace and the energy utilization rate was high.

[0050] Equipment status: After the trial firing, the kiln was shut down for inspection. There was no obvious scaling in the inner cylinders of the C5 and C6 stages of the preheater and the smoke chamber. No significant thinning of the wall thickness due to chlorine corrosion was found in key parts. The system was operating stably.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for staged dechlorination pretreatment of alternative fuels adapted to cement kilns, characterized in that, The method is used for pretreatment of alternative fuels before they are fed into the kiln, and includes the following steps: 1) Chloride ion detection and fuel classification: The chloride ion content in alternative fuels is determined, and alternative fuels are classified into three categories according to the mass fraction of chlorine: low-chlorine fuels: Cl < 0.2%, medium-chlorine fuels: 0.2% ≤ Cl ≤ 0.5%, and high-chlorine fuels: Cl > 0.5%; 2) Graded pretreatment: The low-chlorine fuel is crushed to 20~50mm; the medium-chlorine fuel and high-chlorine fuel are sequentially subjected to air classification to remove impurities, water washing to remove chlorine and low-temperature pre-drying, wherein the pre-drying temperature is 20~300℃; 3) Homogeneous mixing: The low-chlorine fuel, medium-chlorine fuel and high-chlorine fuel after the pretreatment in step 2) are homogeneously mixed according to the following mass ratio: low-chlorine fuel accounts for ≥75% of the total substitute fuel, medium-chlorine fuel accounts for ≤20% of the total substitute fuel but not 0, and high-chlorine fuel accounts for ≤5% of the total substitute fuel.

2. The graded dechlorination pretreatment method for alternative fuels adapted to cement kilns as described in claim 1, characterized in that, In step 1), the method for determining the chloride ion content includes, but is not limited to, high-temperature combustion hydrolysis method and oxygen bomb combustion-ion chromatography method.

3. The graded dechlorination pretreatment method for alternative fuels adapted to cement kilns as described in claim 2, characterized in that, The determination steps of the high-temperature combustion hydrolysis method are as follows: In a mixed gas flow of oxygen and water vapor at 1000-1100℃, the sample is completely combusted, and all forms of chlorine are converted into HCl gas, which is absorbed by water and then the chloride ion content is determined by potentiometric titration. The determination steps of the oxygen bomb combustion-ion chromatography method are as follows: Weigh 0.2-0.5g of the sample to be tested into the oxygen bomb, add 20-30mL of alkaline absorption solution, tighten the oxygen bomb cap, fill with 3.0MPa pure oxygen, ignite by power, and allow to stand for absorption under sealed conditions; open the oxygen bomb, rinse all parts inside the oxygen bomb repeatedly with deionized water, and after diluting all the washing solution to a fixed volume, detect by ion chromatography.

4. The graded dechlorination pretreatment method for alternative fuels adapted to cement kilns as described in claim 1, characterized in that, In step 2), the low-chlorine fuel is crushed in two stages, and the specific steps are as follows: (1) Primary crushing The low-chlorine fuel is crushed to a particle size of approximately 80-150 mm to obtain primary crushed material; (2) Secondary crushing The primary crushed material is further crushed to 20-50mm. This particle size range ensures that the material flows smoothly and burns completely in the conveying and combustion system.

5. The graded dechlorination pretreatment method for alternative fuels adapted to cement kilns as described in claim 1, characterized in that, The medium-chlorine fuel and high-chlorine fuel are sequentially subjected to mechanical air separation for impurity removal, water washing for dechlorination, and low-temperature pre-drying. The specific steps are as follows: (1) Mechanical air separation for impurity removal Select a suction-type gravity destoner, spread the above-mentioned medium-chlorine fuel and high-chlorine fuel evenly on the entire screen surface, keep the screen surface inclination angle between 10° and 13°, and adjust the damper until the material on the screen surface reaches a semi-suspended state. (2) Dechlorination by rinsing with clean water The above-mentioned impurity-removing material is fed into the feed inlet and slowly pushed upwards. The washing water is heated to 25~60℃ with a liquid-solid ratio of 3-6:1 and sprayed downwards onto the surface of the material to achieve countercurrent washing. The number of washing cycles is 1-3. (3) Low-temperature pre-drying The washed material is heated at 200-300℃ for 20-30 minutes.

6. The graded dechlorination pretreatment method for alternative fuels adapted to cement kilns as described in claim 1, characterized in that, In step 3), the pretreated low-chlorine fuel, medium-chlorine fuel, and high-chlorine fuel are mixed in the following mass ratios: low-chlorine fuel accounts for ≥75% of the total substitute fuel, medium-chlorine fuel accounts for ≤20% of the total substitute fuel but not 0%, and high-chlorine fuel accounts for ≤5% of the total substitute fuel. After mixing, the mixture is thoroughly mixed by high-speed stirring.

7. A method for blending alternative fuels suitable for cement kilns, characterized in that, The method includes blending in 60-80% by total mass of the alternative fuel pretreated by the method of any one of claims 1-6.

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