Combined upgrading method of flue gas modified wheat straw and lignite mixed fuel

Abstract

The present invention discloses a combined quality improvement method for a flue gas modified wheat straw and lignite mixed fuel, comprising the following steps: uniformly mixing wheat straw powder and lignite powder to obtain a mixture, drying the mixture at 200-270°C for 25-30 minutes in a flue gas atmosphere, and cooling to room temperature to obtain a flue gas modified wheat straw and lignite mixed fuel. The fuel quality and physical properties of the flue gas modified wheat straw and lignite mixed fuel are improved. The combined quality improvement method can compensate for the loss of combustible components during the drying process, enhance the hydrophobicity of the flue gas modified wheat straw and lignite mixed fuel while improving the quality of the combined quality improved fuel, effectively improve the combined utilization value of lignite and wheat straw, significantly reduce the emission of NOx from the combustion product, and reduce pollution, effectively improve the utilization value of wheat straw and lignite, and achieve efficient energy saving and carbon reduction at the production capacity end.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel quality improvement, and in particular relates to a combined fuel quality improvement method of flue gas modified wheat straw and lignite mixed fuel. Background Art

[0002] Currently, global lignite reserves amount to approximately 320.47 billion tons, accounting for approximately 24.4% of the world's total coal reserves. China's lignite reserves are approximately 211.8 billion tons, representing approximately 13% of China's total coal reserves. Lignite reserves are vast, shallow, and have thick mineable seams, making it mostly suitable for open-pit mining and low-cost extraction. However, lignite suffers from high water content (25-65 wt%), low energy density (5500-6500 kcal / kg), and a strong tendency to spontaneous combustion, which severely restrict its efficient utilization and safe storage and transportation.

[0003] Water in lignite is primarily divided into three types: free water, capillary water, and molecular water. Free water is primarily found in the coal's macropores or on the coal surface and is relatively easy to remove. Capillary water exists in the coal's capillaries as water clusters. Molecular water exists as monolayer adsorbed water and multilayer adsorbed water. Monolayer adsorbed water binds to hydrophilic oxygen-containing groups in the coal through strong hydrogen bonds, while multilayer adsorbed water adheres to the coal surface and to the monolayer adsorbed water through weaker hydrogen bonds. This type of molecular water requires a high level of energy to remove.

[0004] While traditional drying pretreatment technologies can remove significant amounts of moisture from lignite, efficient removal requires intense drying conditions (drying temperatures of 200-500°C), which often require additional heat input and result in significant energy consumption. Traditional boiler exhaust (flue gas) carries significant amounts of heat energy in its waste heat form, which has attracted considerable attention. However, due to its low temperature (70-140°C), it cannot be effectively utilized.

[0005] Although dehydration pretreatment technology is effective, deep dehydration will lead to the growth of pore structure on the surface of lignite, enhance the water holding capacity of the dried lignite, and make the dried lignite easy to reabsorb water, thus affecting the quality improvement effect. In recent years, the use of additives, such as petroleum coke and asphalt, has been explored to improve the surface structure of dried lignite and reduce its ability to re-adsorb water. Although this method has been successful to a certain extent, the cost of petroleum coke and asphalt is high, and the effective stripping of hydrophilic groups usually requires a higher drying temperature, that is, mixing at a higher temperature is required, which will undoubtedly increase the overall cost of lignite quality improvement. It is urgent to solve the problem of lignite dehydration pretreatment while enhancing its hydrophobicity and ensuring the integrity of its active structure, and reducing the heat load required for the quality improvement process to achieve energy-saving quality improvement and modification. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method for jointly upgrading the quality of flue gas modified wheat straw and lignite mixed fuel. The present invention utilizes the low-temperature waste heat of flue gas to jointly upgrade wheat straw and lignite, so that the wheat straw releases volatile organic compounds to block the pore structure on the surface of lignite particles and passivate the hydrophilic groups on the surface of lignite particles. The flue gas can compensate for the loss of combustible components during the drying process, thereby improving the quality of the flue gas modified wheat straw and lignite mixed fuel while enhancing its hydrophobicity.

[0007] The purpose of the present invention is achieved through the following technical solutions.

[0008] A combined quality improvement method for flue gas modified wheat straw and lignite mixed fuel comprises the following steps:

[0009] Wheat straw powder and lignite powder are uniformly mixed to obtain a mixture, and the mixture is dried at 200-270° C. for 25-30 minutes in a flue gas atmosphere (combined quality improvement), and cooled to room temperature to obtain a flue gas modified wheat straw and lignite mixed fuel, wherein the ratio of wheat straw powder to lignite powder is (1-3):(1-3) by mass.

[0010] In the above technical solution, the ratio of wheat straw powder to lignite powder is preferably (2-3):1 by mass.

[0011] In the above technical solution, the flue gas includes: carbon dioxide (CO2), water vapor (H2O), oxygen (O2) and argon (Ar), wherein, by volume, the ratio of carbon dioxide, water vapor, oxygen and argon is (9-11): (9-11): (5.5-6.5): (73-75).

[0012] In the above technical solution, the method for obtaining wheat straw powder includes: crushing and screening the wheat straw in sequence to obtain the wheat straw powder.

[0013] In the above technical solution, the method for obtaining lignite powder includes: crushing and screening the lignite in sequence to obtain the lignite powder.

[0014] In the above technical solution, the particle size of the wheat straw powder is 90 to 125 meshes.

[0015] In the above technical solution, the particle size of the lignite powder is 90 to 125 meshes.

[0016] In the above technical solution, flue gas is introduced at a flow rate of 1.5 to 3 L / min to form a flue gas atmosphere.

[0017] In the above technical solution, the drying temperature rising rate is 10 to 20°C / min.

[0018] The flue gas modified wheat straw and lignite mixed fuel obtained by the above-mentioned combined upgrading method.

[0019] The use of the flue gas modified wheat straw and lignite mixed fuel in improving calorific value.

[0020] The use of the flue gas modified wheat straw and lignite mixed fuel in reducing the burnout temperature, NO conversion rate and / or water re-adsorption amount.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The calorific value of the flue gas modified wheat straw and lignite mixed fuel obtained by the combined upgrading method of the present invention can reach 17.49 MJ·kg -1 The combustion temperature is 634.85℃, the NO conversion rate can reach 6.36%, the moisture re-adsorption amount can reach 0.821%, the energy saving rate of preheating unit volume of atmosphere is 24.68%, and the preheating unit volume of flue gas atmosphere can reduce carbon emissions by 12.98g. Its fuel quality and physical properties are improved.

[0023] (2) The combined upgrading method of the present invention can compensate for the loss of combustible components during the drying process, enhance the hydrophobicity of the flue gas modified wheat straw and lignite mixed fuel while improving the quality of the combined upgraded fuel, effectively improve the combined utilization value of lignite and wheat straw, significantly reduce the emission of NOx by the combustion product, and reduce pollution, effectively improving the utilization value of wheat straw and lignite, and achieving efficient energy saving and carbon reduction at the production capacity end. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Graphs showing the moisture resorption of the flue gas-modified wheat straw and lignite mixed fuel obtained in Examples 1 to 9, the air-modified wheat straw and lignite mixed fuel obtained in Examples 10 to 18, the lignite fuel obtained in Comparative Examples 1 to 6, the wheat straw fuel obtained in Comparative Examples 7 to 12, the lignite, and the wheat straw;

[0025] Figure 2 These are scanning electron micrographs of lignite, wheat straw, and the flue gas-modified wheat straw and lignite mixed fuel obtained in Examples 5-6. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0027] In the following examples, the purity and purchase manufacturers of the raw materials involved are shown in Table 1.

[0028] Table 1

[0029]

[0030] The models and manufacturers of the instruments involved in the following examples are shown in Table 2.

[0031] Table 2

[0032]

[0033] In the following embodiments, the method for obtaining wheat straw powder includes: crushing and sieving the wheat straw in sequence using a wall breaking machine to obtain the wheat straw powder.

[0034] In the following embodiments, the method for obtaining lignite powder includes: crushing and screening lignite in sequence using a wall breaker to obtain lignite powder.

[0035] Flue gas is a mixed gas produced by the combustion of fuel during combustion or industrial production processes. Its oxygen content is significantly lower than that of normal air, reducing the risk of fire and explosion. In laboratories, a mixture of inert gases, oxygen, water vapor, and carbon dioxide is often used to represent the main components of actual flue gas. Therefore, this invention uses a mixture of Ar, O₂, H₂O, and CO₂ to simulate flue gas.

[0036] Examples 1 to 9

[0037] A combined quality improvement method for flue gas modified wheat straw and lignite mixed fuel comprises the following steps:

[0038] Wheat straw powder with a particle size of 90 to 125 meshes and lignite powder with a particle size of 90 to 125 meshes are uniformly mixed to obtain a mixture, and the horizontal tube furnace is heated to T°C at a heating rate of 10°C / min through an atmosphere preheating wire. After the temperature stabilizes, flue gas is introduced into the horizontal tube furnace at a flow rate of 2 L / min to form a flue gas atmosphere. In the flue gas atmosphere, the mixture is placed in a horizontal tube furnace and dried at T°C for 30 minutes (combined quality improvement), and cooled to room temperature to obtain a flue gas-modified wheat straw and lignite mixed fuel, wherein the ratio of wheat straw powder to lignite powder is W by mass, and the flue gas is a mixed gas of carbon dioxide (CO2), water vapor (H2O), oxygen (O2) and argon (Ar), and the ratio of carbon dioxide, water vapor, oxygen and argon is 10:10:6:74 by volume.

[0039] The T and W of the flue gas modified wheat straw and lignite mixed fuel obtained in Examples 1 to 9 are shown in Table 3.

[0040] Table 3

[0041]

[0042]

[0043] Examples 10 to 18

[0044] A combined quality improvement method for air-modified wheat straw and lignite mixed fuel comprises the following steps:

[0045] Wheat straw powder with a particle size of 90 to 125 mesh and lignite powder with a particle size of 90 to 125 mesh are uniformly mixed to obtain a mixture, and the horizontal tube furnace is heated to T°C at a heating rate of 10°C / min by an atmosphere preheating wire. After the temperature stabilizes, air is introduced into the horizontal tube furnace at a flow rate of 2 L / min to form an air atmosphere. In the air atmosphere, the mixture is placed in a horizontal tube furnace and dried at T°C for 30 minutes (combined quality improvement), and cooled to room temperature to obtain an air-modified wheat straw and lignite mixed fuel, wherein the ratio of wheat straw powder to lignite powder is W by mass.

[0046] The T and W of the air-modified wheat straw and lignite mixed fuel obtained in Examples 10 to 18 are shown in Table 4.

[0047] Table 4

[0048]

[0049] Comparative Examples 1 to 6

[0050] A method for upgrading lignite fuel comprises the following steps:

[0051] The horizontal tube furnace is heated to T℃ at a heating rate of 10℃ / min by an atmosphere preheating wire. After the temperature stabilizes, G is introduced into the horizontal tube furnace at a flow rate of 2L / min to form a G atmosphere. Under the G atmosphere, lignite powder with a particle size of 90-125 mesh is placed in a horizontal tube furnace and dried at T℃ for 30 minutes. It is then cooled to room temperature to obtain lignite fuel. G is flue gas or air, and the flue gas is a mixed gas of carbon dioxide (CO2), water vapor (H2O), oxygen (O2) and argon (Ar). The ratio of carbon dioxide, water vapor, oxygen and argon is 10:10:6:74 by volume.

[0052] The T and G of the lignite fuels obtained in Comparative Examples 1 to 6 are shown in Table 5.

[0053] Table 5

[0054]

[0055] Comparative Examples 7 to 12

[0056] A method for upgrading straw fuel is basically the same as the upgrading method of Comparative Example 1, except that the lignite powder with a particle size of 90-125 mesh is replaced with wheat straw powder with a particle size of 90-125 mesh. The upgrading methods of Comparative Examples 7-12 yield wheat straw fuel. The T and G of the wheat straw fuel obtained in Comparative Examples 7-12 are shown in Table 6.

[0057] The T and G of the straw fuels obtained in Comparative Examples 7 to 12 are shown in Table 6.

[0058] Table 6

[0059]

[0060] Example 19

[0061] The flue gas modified straw and lignite mixed fuel obtained in Examples 1 to 9, the air modified straw and lignite mixed fuel obtained in Examples 10 to 18, the lignite fuel obtained in Comparative Examples 1 to 6, the straw fuel obtained in Comparative Examples 7 to 12, the lignite and straw were subjected to elemental analysis and calorific value determination using an elemental analyzer and an oxygen bomb calorimeter to determine the content and calorific value of each C, H, O and N element. The test results are shown in Table 7. It can be seen from Table 7 that, when the drying temperature and mass ratio (wheat straw powder: lignite powder) are the same, the C content in the flue gas modified straw and lignite mixed fuel obtained in Examples 1 to 9 is increased compared with the air modified straw and lignite mixed fuel obtained in Examples 10 to 18, and the calorific value is increased. Moreover, as the lignite content increases, the C content also increases, corresponding to the calorific value.

[0062] Example 20

[0063] In an air environment at a flow rate of 100 mL / min, 5 mg of fuel was placed in an alumina crucible, heated to 800°C at a rate of 10°C / min, and thermogravimetric analysis was performed using a thermogravimetric analyzer to explore the pyrolysis characteristics, and a thermogravimetric (TG) curve and a differential thermogravimetric (DTG) curve were obtained, wherein the fuel was the flue gas-modified wheat straw and lignite mixed fuel obtained in Examples 1 to 9, the air-modified wheat straw and lignite mixed fuel obtained in Examples 10 to 18, the lignite fuel obtained in Comparative Examples 1 to 6, the straw fuel obtained in Comparative Examples 7 to 12, lignite, and one of wheat straw. Further according to the national standard GB / T33304-2016, the burnout temperature was determined by analyzing the DTG curve and TG curve by the tangent method. The burnout temperature is shown in Table 7. It can be seen from Table 7 that, at the same drying temperature and mass ratio (wheat straw powder: lignite powder), compared with the air-modified wheat straw and lignite mixed fuel obtained in Examples 10 to 18, the burnout temperature of the flue gas-modified wheat straw and lignite mixed fuel obtained in Examples 1 to 9 is lower, and the burnout temperature of the flue gas-modified wheat straw and lignite mixed fuel gradually decreases with the decrease of lignite content.

[0064] Example 21

[0065] The gases (such as NH3 and NO) produced during the combustion of the above-mentioned fuels were measured using a flue gas analyzer to obtain the volume fraction of NO, and the NO conversion rate was obtained according to the NO conversion rate formula in the literature (Experimental investigation on the evolution characteristics of anthracite-N and semi-coke reactivity under various O2 / H2O pre-oxidation atmospheres, Fuel Processing Technology, 216(2021)106725). The calculation results are shown in Table 7. It can be seen from Table 7 that the NO conversion rate of the flue gas-modified straw and lignite mixed fuel obtained in Example 6 was significantly reduced to 6.36%. This is because NH3 and NO can be produced during the combustion of the flue gas-modified straw and lignite mixed fuel, and the alkali metal ions rich in straw can catalyze the reduction of NO by NH3, which significantly reduces the conversion of N element to NO in the flue gas-modified straw and lignite mixed fuel.

[0066] Example 22

[0067] Moisture reabsorption test: The mass m0(m 0＝ The fuel (1.5g) was placed in a constant temperature and humidity cabinet (temperature: 20℃, humidity: 50% H2O) to absorb water for 120 hours. The mass of the fuel was weighed every hour for the first 10 hours (the mass of the fuel corresponding to each weighing was m1). The mass of the fuel was weighed every 10 hours for the next 110 hours (the mass of the fuel corresponding to each weighing was m1). The water re-adsorption amount at each water adsorption time was calculated using the water re-adsorption amount formula. The results are as follows: Figure 1 As shown in Table 7 (the change of the measured mass at the 120th hour compared with the measured mass at the 110th hour is less than 0.1%, and the water re-adsorption amount at the 0th hour is 0%), the water re-adsorption amount ε after the adsorption of water for 120 hours is shown in Table 7, wherein the fuel is the flue gas modified wheat straw and lignite mixed fuel obtained in Examples 1 to 9, the air modified wheat straw and lignite mixed fuel obtained in Examples 10 to 18, the lignite fuel obtained in Comparative Examples 1 to 6, the straw fuel obtained in Comparative Examples 7 to 12, lignite and straw.

[0068] The formula for moisture re-adsorption is:

[0069] Table 7

[0070]

[0071]

[0072] Figure 1The water resorption amount diagram of the flue gas modified wheat straw and lignite mixed fuel obtained in Examples 1 to 9, the air modified wheat straw and lignite mixed fuel obtained in Examples 10 to 18, the lignite fuel obtained in Comparative Examples 1 to 6, the wheat straw fuel obtained in Comparative Examples 7 to 12, the lignite and wheat straw is shown in FIG. Figure 1 As shown in (b), the moisture re-adsorption of the flue gas modified wheat straw and lignite mixed fuel obtained in Examples 4 to 6, the lignite fuel obtained in Comparative Example 2, the wheat straw fuel obtained in Comparative Example 8, the lignite, and the wheat straw increased rapidly in the first 10 hours, then gradually reached a certain level of equilibrium. After 120 hours of moisture adsorption, the fuels all reached moisture saturation, with lignite having the highest moisture re-adsorption (4.611%) and straw having 3.702%. The moisture re-adsorption of the flue gas modified wheat straw and lignite mixed fuel obtained in Example 6 was the lowest at 0.821%, which was a significant decrease of 3.79% compared to lignite and 2.881% compared to straw. Compared with the lignite fuel obtained in Comparative Example 2, the water re-adsorption amount of the flue gas modified wheat straw and lignite mixed fuel obtained in Example 6 decreased by 0.353%. Compared with the wheat straw fuel obtained in Comparative Example 8, the water re-adsorption amount of the flue gas modified wheat straw and lignite mixed fuel obtained in Example 6 decreased by 0.357%. It is difficult to reduce the water re-adsorption amount since both lignite fuel and straw fuel have been dried and dehydrated. However, the flue gas modified wheat straw and lignite mixed fuel further reduces the water re-adsorption capacity, causing its water re-adsorption amount to decrease. This is because during the combined upgrading process, the low-temperature pyrolysis of biomass (wheat straw) releases tar and tar cracking products (light carbon-containing organic matter) to block the surface pore structure of the lignite particles and passivate the surface hydrophilic groups of the lignite particles, thereby inhibiting the interaction between water molecules and the wheat straw and lignite combined upgraded fuel obtained in Example 6. On the other hand, irreversible shrinkage changes will occur after thermal upgrading (drying), which will destroy the diffusion path of water and inhibit the diffusion of water into the interior of the lignite particles.

[0073] Figure 2 The scanning electron micrographs of the flue gas modified wheat straw and lignite mixed fuel, lignite and wheat straw obtained in Examples 5 and 6 are shown in FIG. Figure 2 It can be seen that straw effectively releases volatile organic compounds (tar and tar cracking products) during the heating and drying process, which can diffuse and adsorb to the surface of lignite particles, resulting in a large amount of filling of the pore structure to form a coating. As the straw blending content increases, the surface morphology of the flue gas-modified wheat straw and lignite mixed fuel obtained in Example 6 becomes smoother, and the contact between moisture and the surface active structure can be weakened at room temperature.

[0074] According to the definition of specific heat capacity in Engineering Thermodynamics (Fifth Edition), the energy saving rate per unit volume of preheating atmosphere of the flue gas modified wheat straw and lignite mixed fuel obtained in Example 6 is 24.68%, and preheating per unit volume of flue gas atmosphere can reduce carbon emissions by 12.98g.

[0075] In summary, the combined upgrading method of the present invention can increase the C content, significantly improve the calorific value, enhance the burnout characteristics, inhibit NO conversion, and enhance the hydrophobicity, effectively improving the energy quality of the flue gas-modified wheat straw and lignite mixed fuel and reducing the release of pollutants, with significant energy-saving and carbon-reduction effects.

[0076] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A flue gas modified wheat straw and lignite mixed fuel for reducing burnout temperature, NO conversion rate and / or water re-adsorption, characterized in that: The combustion temperature of the flue gas modified wheat straw and lignite mixed fuel is 634.85℃, the NO conversion rate can reach 6.36%, the water re-adsorption capacity can reach 0.821%, the energy saving rate per unit volume of preheating atmosphere is 24.68%, and the carbon emissions per unit volume of preheating flue gas atmosphere can be reduced by 12.98g. The combined upgrading method of flue gas modified wheat straw and lignite mixed fuel comprises the following steps: uniformly mixing wheat straw powder and lignite powder to obtain a mixture; drying the mixture at 220°C for 25-30 minutes in a flue gas atmosphere; and cooling the mixture to room temperature to obtain a flue gas modified wheat straw and lignite mixed fuel, wherein the ratio of wheat straw powder to lignite powder is 3:1 by mass; and the flue gas comprises carbon dioxide, water vapor, oxygen and argon, wherein the ratio of carbon dioxide, water vapor, oxygen and argon by volume is (9-11):(9-11):(5.5-6.5):(73-75).

2. The use according to claim 1, characterized in that The method for obtaining wheat straw powder comprises: crushing and screening the wheat straw in sequence to obtain the wheat straw powder.

3. The use according to claim 1, characterized in that The method for obtaining lignite powder comprises: crushing and screening lignite in sequence to obtain lignite powder.

4. The use according to claim 1, characterized in that The particle size of wheat straw powder is 90~125 mesh.

5. The use according to claim 1, characterized in that The particle size of lignite powder is 90~125 mesh.

6. The use according to claim 1, characterized in that Flue gas was introduced at a flow rate of 1.5~3 L / min to form a flue gas atmosphere.

7. The use according to claim 1, characterized in that The drying heating rate is 10~20℃ / min.

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