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

Abstract

The invention discloses a combined upgrading method of flue gas modified wheat straw and lignite mixed fuel, which comprises the following steps: uniformly mixing wheat straw powder and lignite powder to obtain a mixture, drying the mixture at 200-270 DEG C for 25-30 minutes in a flue gas atmosphere, and cooling to room temperature to obtain the 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. According to the combined upgrading method, loss of combustible components in the drying process can be compensated, the hydrophobicity of the flue gas modified wheat straw and lignite mixed fuel is enhanced while the quality of the combined upgrading fuel is improved, the combined utilization value of the lignite and the wheat straw is effectively improved, the emission load of a combustion product NO is greatly reduced, pollution is small, and the method is suitable for industrial production. The utilization value of the wheat straw and the lignite is effectively improved, and efficient energy conservation and carbon reduction at the energy production end are realized.

Description

Technical Field

[0001] The 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] At present, the global lignite reserves are about 320.47 billion tons, accounting for about 24.4% of the world's total coal reserves. China's lignite reserves are about 211.8 billion tons, accounting for about 13% of China's total coal reserves. Lignite reserves are huge, and the burial depth is shallow, the mineable coal seam is thick, most of them are suitable for open-pit mining, and the mining cost is low. However, it has problems such as high water content (water content: 25-65wt%), low energy density (5500-6500Kcal / kg) and strong spontaneous combustion tendency, which seriously restricts the efficient utilization and safe storage and transportation of lignite.

[0003] The water content in lignite can be divided into three types: free water, capillary water and molecular water. Free water is mainly found in the large pores of coal or on the surface of coal and is easy to remove; capillary water exists in the capillary pores of coal in the form of water clusters; molecular water exists in the form of monolayer adsorbed water and multilayer adsorbed water. Monolayer adsorbed water combines with hydrophilic oxygen-containing groups in coal with strong hydrogen bonds, while multilayer adsorbed water is adsorbed on the surface of coal and monolayer adsorbed water with weaker hydrogen bonds. This type of molecular water requires higher energy to be removed.

[0004] Although traditional drying pretreatment technology can remove a large amount of moisture from lignite, the efficient removal of moisture from lignite requires drastic drying conditions (drying temperature is 200-500℃), and this process often requires additional heat input, resulting in a large amount of energy consumption. Traditional boiler tail gas (flue gas) carries a large amount of heat energy under waste heat and has attracted widespread attention, but due to its low temperature state (temperature is 70-140℃), it cannot be reasonably 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 lignite after drying, and make it easy for lignite after drying to reabsorb water, thus affecting the quality improvement effect. In recent years, the use of additives, such as petroleum coke and asphalt, has begun to be explored to improve the surface structure of lignite after drying 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, blending at a higher temperature is required, which will undoubtedly increase the overall cost of lignite quality improvement. It is now 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 deficiencies in the prior art, the object of the present invention is to provide a method for jointly upgrading a 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 matter 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] The wheat straw powder and the lignite powder are uniformly mixed to obtain a mixture, and the mixture is dried at 200-270° C. for 25-30 min (combined upgrading) in a flue gas atmosphere, and cooled to room temperature to obtain a flue gas modified wheat straw and lignite mixed fuel, wherein the ratio of the wheat straw powder to the 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 (CO 2 ), water vapor (H 2 O), oxygen (O 2 ) 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 sieving 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 90-125 meshes.

[0015] In the above technical solution, the particle size of the lignite powder is 90-125 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 rise 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 above 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 burnout 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 preheating unit volume of flue gas atmosphere can reduce carbon emissions by 12.98g, and its fuel quality and physical properties are improved.

[0023] (2) The combined quality improvement 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 quality improvement 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The graphs are the moisture re-adsorption amount 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;

[0025] Figure 2 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 in conjunction with 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 comprises: 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 comprises: crushing and screening the lignite in sequence using a wall breaking machine to obtain the lignite powder.

[0035] Flue gas is a mixed gas produced after fuel is burned during combustion or industrial production. Its oxygen content is much lower than that in normal air, which reduces the risk of fire and explosion. In the laboratory, a mixed gas of inert gas, oxygen, water vapor and carbon dioxide is often used to represent the main components of actual flue gas. Therefore, the present invention uses Ar, O 2 , H 2 O and CO 2 A mixed gas is used to simulate smoke.

[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 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℃ by an atmosphere preheating wire at a heating rate of 10℃ / min. When the temperature is stable, flue gas is introduced into the horizontal tube furnace at a flow rate of 2L / 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℃ for 30min (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 carbon dioxide (CO 2 ), water vapor (H 2 O), oxygen (O 2 ) and argon (Ar) gas mixture, 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] Embodiments 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 90-125 mesh and lignite powder with a particle size of 90-125 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 through an atmosphere preheating wire. After the temperature is stable, air is introduced into the horizontal tube furnace at a flow rate of 2L / 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 30min (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 improving the quality of lignite fuel comprises the following steps:

[0051] The horizontal tube furnace is heated to T℃ by the atmosphere preheating wire at a heating rate of 10℃ / min. When the temperature is stable, G is introduced into the horizontal tube furnace at a flow rate of 2L / min to form a G atmosphere. In the G atmosphere, lignite powder with a particle size of 90-125 mesh is placed in the horizontal tube furnace and dried at T℃ for 30min, and then cooled to room temperature to obtain lignite fuel. G is flue gas or air, and the flue gas is carbon dioxide (CO 2 ), water vapor (H 2 O), oxygen (O 2 ) and argon (Ar) gas mixture, 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 wheat 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 to 125 mesh is replaced with wheat straw powder with a particle size of 90 to 125 mesh. The upgrading methods of comparative examples 7 to 12 obtain wheat straw fuel. The T and G of the wheat straw fuel obtained in comparative examples 7 to 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] Embodiment 19

[0061] Elemental analysis and calorific value determination were performed on 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 using an elemental analyzer and an oxygen bomb calorimeter to determine the contents and calorific values ​​of the respective C, H, O and N elements. The test results are 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 straw and lignite mixed fuel obtained in Examples 10 to 18, the flue gas modified straw and lignite mixed fuel obtained in Examples 1 to 9 has an increased C element content and an increased calorific value, and as the lignite content increases, the C element content also increases, corresponding to the calorific value.

[0062] Embodiment 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, one of lignite and wheat straw. Further according to the national standard GB / T33304-2016, the burnout temperature was determined by analyzing the DTG curve and the 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 temperatures of the flue gas-modified wheat straw and lignite mixed fuel obtained in Examples 1 to 9 are lower, and the burnout temperature of the flue gas-modified wheat straw and lignite mixed fuel gradually decreases with the decrease of the lignite content.

[0064] Embodiment 21

[0065] The flue gas analyzer is used to measure the gases (such as NH 3 and NO), and the volume fraction of NO was obtained. According to the literature (Experimental investigation on the evolution characteristics of anthracycline-N and semi-coke reactivity under various O 2 / H 2 The NO conversion rate was obtained by using the NO conversion rate formula in (10.36%), and the calculation results are shown in Table 7. From Table 7, it can be seen 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 the combustion of flue gas modified straw and lignite mixed fuel can produce NH 3 and NO, while the alkali metal ions rich in wheat straw can catalyze the 3 The reduction of NO significantly reduced the conversion of N to NO in the flue gas modified wheat straw and lignite mixed fuel.

[0066] Embodiment 22

[0067] Moisture reabsorption test: Place a mass of m 0 (m 0＝ The fuel was placed in a constant temperature and humidity cabinet (temperature: 20°C, humidity: 50% H 2 O) absorbs moisture for 120 hours, and weighs the mass of the fuel every hour for the first 10 hours (the mass of the fuel corresponding to each weighing is m 1 ), and weigh the fuel mass every 10 hours for the next 110 hours (the corresponding fuel mass for each weighing is m 1 ), the water re-adsorption amount at each water adsorption time is calculated by the water re-adsorption amount formula, and 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 the 120th hour is as 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 one of wheat straw.

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

[0069] Table 7

[0070]

[0071]

[0072] Figure 1 The water re-adsorption graphs of 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 are shown in FIG. Figure 1 (b) shows that the moisture re-adsorption of the flue gas modified straw and lignite mixed fuel obtained in Examples 4 to 6, the lignite fuel obtained in Comparative Example 2, the straw fuel obtained in Comparative Example 8, the lignite and straw increased rapidly in the first 10 hours, and then gradually reached a certain level of balance. After 120 hours of moisture adsorption, the fuels all reached moisture saturation, with the lignite having the highest moisture re-adsorption (4.611%) and the straw having 3.702%. The moisture re-adsorption of the flue gas modified straw and lignite mixed fuel obtained in Example 6 was the lowest at 0.821%, which was significantly reduced by 3.79% compared with lignite and 2.881% compared with 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 wheat 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, which reduces its water re-adsorption amount. 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 lignite particles and passivate the surface hydrophilic groups of lignite particles, thereby inhibiting the interaction between water molecules and the wheat straw and lignite combined upgrading 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 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 5-6 are shown in FIG. Figure 2 It can be seen that the straw effectively releases volatile organic matter (tar and tar cracking products) during the heating and drying process, which can diffuse and adsorb to the surface of the 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 of preheating unit volume atmosphere of the flue gas modified straw and lignite mixed fuel obtained in Example 6 is 24.68%, and preheating 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 improve the energy quality of the flue gas modified wheat straw and lignite mixed fuel and reduce the release of pollutants, with significant energy-saving and carbon-reducing effects.

[0076] The present invention is described above by way of example. 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 those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. A combined quality improvement method for flue gas modified wheat straw and lignite mixed fuel, characterized in that: The following steps are involved: The wheat straw powder and the 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, and cooled to room temperature to obtain a flue gas modified wheat straw and lignite mixed fuel, wherein the ratio of the wheat straw powder to the lignite powder is (1-3):(1-3) by weight.

2. The combined upgrading method according to claim 1, characterized in that: In terms of mass fraction, the ratio of wheat straw powder to lignite powder is preferably (2-3):

1.

3. The combined upgrading method according to claim 1, characterized in that: Flue gases include: Carbon dioxide, water vapor, oxygen and argon, wherein the ratio of carbon dioxide, water vapor, oxygen and argon is (9-11): (9-11): (5.5-6.5): (73-75) by volume.

4. The combined upgrading method according to claim 1, characterized in that: The method for obtaining wheat straw powder comprises: crushing and sieving the wheat straw in sequence to obtain the wheat straw powder.

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

6. The combined upgrading method according to claim 1, characterized in that: The particle size of wheat straw powder is 90-125 mesh; the particle size of lignite powder is 90-125 mesh.

7. The combined quality improvement method according to claim 1, wherein flue gas is introduced at a flow rate of 1.5 to 3 L / min to form a flue gas atmosphere; The drying heating rate is 10-20°C / min.

8. A flue gas modified wheat straw and lignite mixed fuel obtained by the combined upgrading method according to any one of claims 1 to 7.

9. Use of the flue gas modified wheat straw and lignite mixed fuel according to claim 8 in improving calorific value.

10. Use of the flue gas modified wheat straw and lignite mixed fuel according to claim 8 in reducing the burnout temperature, NO conversion rate and / or water re-adsorption amount.

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