Lignite upgrading and modifying method and lignite fuel prepared by lignite upgrading and modifying method

Abstract

The invention provides a lignite upgrading and modifying method and lignite fuel prepared by the lignite upgrading and modifying method, and relates to the field of lignite clean utilization. Comprising the following steps: S1, pretreatment: crushing and screening lignite until the particle size is less than or equal to 5mm; spraying a sodium methyl silicate solution on the surface of the lignite, and standing and permeating for 2-4 hours; s2, chemical modification: spraying a calcium chloride solution on the surface of the lignite, uniformly mixing, and aging for 12-24 hours to obtain modified lignite; s3, high-pressure dehydration: putting the modified lignite into a pressure container, heating to 50-150 DEG C, pressurizing to 5-10 MPa, and maintaining the pressure for 30-90 minutes; and S4, post-treatment: after pressure relief, drying until the moisture content is less than or equal to 10% to obtain the lignite fuel. Through synergistic modification of methyl sodium silicate and calcium chloride and combination of a 50-150 DEG C and 5-10 MPa high-pressure dehydration process, the moisture of lignite is reduced to be less than or equal to 10%, the heat value is increased to be 5500 kcal / kg or above, and efficient curing of fluorine / phosphorus pollutants is achieved. The obtained fuel can be directly used for supercritical power generation, and the environmental protection property and economical efficiency are obviously superior to those of a traditional process.

Description

Technical Field

[0001] The present invention relates to the field of clean utilization of lignite. Specifically, it relates to a method for upgrading and modifying lignite and a lignite fuel prepared thereby. Background Art

[0002] Lignite is a mineral coal with the lowest degree of coalification, between peat and bituminous coal, brownish-black or blackish-brown, without luster, and with a loose texture (earthy lignite) or a dense texture (dark lignite). The density is about 1.1 - 1.2 g / cm 3 , with low hardness and easy to break. It has a high water content (15% - 60%), a volatile matter content exceeding 40%, and is prone to smoking when burning. The gross calorific value at constant humidity and ash-free basis is about 23.0 - 27.2 MJ / kg (5500 - 6500 kcal / kg), lower than that of bituminous coal and anthracite. It has a low ignition point (about 270°C) and is prone to spontaneous combustion when stored in the air for more than two months, requiring special storage conditions.

[0003] Due to the low calorific value and poor combustion efficiency of lignite, with an average calorific value lower than 3000 kcal / kg, a large amount of lignite needs to be burned to meet industrial demands, resulting in low energy utilization efficiency. The emissions of sulfur and nitrogen oxides need to be additionally treated. The high water content leads to an increase in transportation costs, and it is prone to weathering and spontaneous combustion, with a storage period of no more than two months.

[0004] To reduce the water content of lignite, drying and forming processes (such as coal briquettes) can be used to reduce moisture, increase calorific value, and extend the storage period. Patent 201410329878.X discloses a lignite additive and a lignite dehydration treatment method. The additive is a substance prepared by mixing at least three types of compounds selected from anionic surfactants, non-ionic surfactants, organic acids, water glass, carbonates, and chlorides in proportion with water. This additive significantly increases the hydrophobicity and permeability of the "internal water" and "bound water" in lignite, significantly improves the strength after cold pressing of lignite, and significantly reduces the dusting property after drying of lignite. Patent 202210058967.X discloses a lignite modification dehydration method, its production process, and the application of modified dehydrated lignite. The lignite is mixed with a "hydrophobic modification additive" in a mass ratio greater than 2, and the mixture is stirred and heated, so that the outer surface layer of the lignite changes from hydrophilic to hydrophobic, obtaining hydrophobic lignite, and then a drying and dehydration process, such as drying in the sun or ventilation, is used to remove the total water.

[0005] By adding hydrophobic and water-repellent additives to lignite to improve the dehydration efficiency of lignite, but the current additives have complex compositions and low dehydration efficiency. Therefore, there is an urgent need to provide a method for upgrading and modifying with good dehydration effect. Summary of the Invention

[0006] The object of the present invention is to provide a method for upgrading and modifying lignite. Through the synergistic modification of sodium methyl silicate and calcium chloride, combined with a high-pressure dehydration process at 50 - 150°C and 5 - 10 MPa, the moisture content of lignite is reduced to ≤10%, the calorific value is increased to more than 5500 kcal / kg, and efficient solidification of fluorine / phosphorus pollutants is achieved.

[0007] Another object of the present invention is to provide a lignite fuel with its moisture content reduced to ≤10% and calorific value increased to more than 5500 kcal / kg.

[0008] The present invention solves its technical problems by adopting the following technical solutions.

[0009] On the one hand, an embodiment of the present invention provides a method for upgrading and modifying lignite, including the following steps:

[0010] S1 Pretreatment: Crush and screen the lignite to a particle size of ≤5 mm; spray a sodium methyl silicate solution on the surface of the lignite and let it stand and penetrate for 2 - 4 h;

[0011] S2 Chemical modification: Subsequently, spray a calcium chloride solution on the surface of the lignite, mix evenly, and age for 12 - 24 h to obtain modified lignite;

[0012] S3 High-pressure dehydration: Place the modified lignite in a pressure vessel, heat it to 50 - 150°C, pressurize it to 5 - 10 MPa, and keep the pressure for 30 - 90 min;

[0013] S4 Post-treatment: After depressurization, dry it to a moisture content of ≤10% to obtain a lignite fuel.

[0014] In some embodiments of the present invention, in the step S1, the mass fraction of the sodium methyl silicate solution is 5% - 10%.

[0015] In some embodiments of the present invention, in the step S2, the mass fraction of the calcium chloride solution is 10% - 15%.

[0016] In some embodiments of the present invention, the mass of the calcium chloride solution is 1 - 3% of the dry matrix of the lignite.

[0017] In some embodiments of the present invention, in the step S3, the temperature of the high-pressure dehydration is 100 - 130°C and the pressure is 6 - 8 MPa.

[0018] On the other hand, an embodiment of the present invention provides a lignite fuel prepared by the above method.

[0019] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0020] The lignite upgrading and modification method provided by the present invention synergistically modifies with sodium methyl silicate and calcium chloride, combines a high-pressure dehydration process at 50 - 150 °C and 5 - 10 MPa, reduces the moisture content of lignite to ≤10%, increases the calorific value to above 5500 kcal / kg, and achieves efficient solidification of fluorine / phosphorus pollutants. The resulting fuel can be directly used for supercritical power generation, and its environmental protection and economy are significantly superior to traditional processes. Detailed implementation manners

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can all be obtained as conventional products through commercial purchase.

[0022] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0023] The embodiment of the present invention provides a lignite upgrading and modification method, including the following steps:

[0024] S1 Pretreatment: Crush and screen the lignite to a particle size of ≤5 mm; spray a sodium methyl silicate solution on the surface of the lignite, and let it stand and penetrate for 2 - 4 h; the mass fraction of the sodium methyl silicate solution is 5% - 10%. By reducing the particle size of the lignite and increasing its specific surface area, a larger contact area is provided for subsequent penetration of substances such as calcium chloride, and at the same time, the high-pressure dehydration efficiency is improved. Spraying sodium methyl silicate on the surface of the lignite can improve the hydrophobicity of the lignite, that is, form a hydrophobic film on the surface of the lignite, reduce water absorption, and prevent moisture reabsorption during storage.

[0025] S2 Chemical modification: Subsequently, spray a calcium chloride solution on the surface of the lignite, mix evenly, and age for 12 - 24 h to obtain modified lignite; the mass fraction of the calcium chloride solution is 10% - 15%. The mass of the calcium chloride solution is 1% - 3% of the dry matrix of the lignite. Calcium chloride reacts with active groups in the lignite such as carboxyl and hydroxyl groups, forms a network structure through chelation, and improves the strength of the lignite. Reduce the volatile content and reduce the spontaneous combustion tendency. Calcium ions can also break the hydrogen bond network and assist in dehydration.

[0026] S3 High-pressure dehydration: Place the modified lignite in a pressure vessel, heat it to 50 - 150 °C, pressurize it to 5 - 10 MPa, and keep the pressure for 30 - 90 min; Preferably, the temperature for high-pressure dehydration is 100 - 130 °C, and the pressure is 6 - 8 MPa. At high temperatures, the fluidity of liquid water is enhanced, making it easier to discharge from the pores of lignite. At the same time, high temperatures and pressures promote the decomposition of oxygen-containing functional groups such as hydroxyl and carboxyl groups in lignite, destroying the hydrophilic structure, and the energy consumption is significantly lower than that of traditional evaporation drying. Under high pressure, the pressure forces the water to be extruded from the coal particles, especially the bound water. Moreover, under high pressure, the lignite coal body shrinks, and the capillary pores collapse, reducing the channels for water reabsorption.

[0027] S4 Post-treatment: After depressurization, dry it to a moisture content of ≤ 10%, and obtain lignite fuel. When depressurizing, it is necessary to depressurize slowly to avoid coal body rupture, and at the same time recover volatile gases (such as CO2, methane). Drying to a moisture content of ≤ 10% can further increase the calorific value, and a low moisture content can inhibit microbial activity, reducing the risk of spontaneous combustion and transportation costs.

[0028] The features and properties of the present invention will be further described in detail below in conjunction with the embodiments.

[0029] Example 1

[0030] Prepare the lignite fuel of this example according to the following method:

[0031] S1 Pretreatment: Crush and screen the lignite to a particle size of ≤ 5 mm; Spray a sodium methyl silicate solution on the surface of the lignite, mix evenly, and then let it stand for infiltration for 4 h; Among them, the mass fraction of the sodium methyl silicate solution is 10%. The mass of the sodium methyl silicate solution is 5% of the dry matrix of the lignite.

[0032] S2 Chemical modification: Subsequently, spray a calcium chloride solution on the surface of the lignite, mix evenly, and age for 24 h to obtain modified lignite; The mass fraction of the calcium chloride solution is 10%. The mass of the calcium chloride solution is 3% of the dry matrix of the lignite.

[0033] S3 High-pressure dehydration: Place the modified lignite in a pressure vessel, heat it to 130 °C, pressurize it to 8 MPa, and keep the pressure for 90 min;

[0034] S4 Post-treatment: After depressurization, dry it to a moisture content of ≤ 10% to obtain lignite fuel.

[0035] Example 2

[0036] Prepare the lignite fuel of this example according to the following method:

[0037] S1 Pretreatment: Crush and screen the lignite to a particle size of ≤ 5 mm; Spray a sodium methyl silicate solution on the surface of the lignite, let it stand for infiltration for 4 h; The mass fraction of the sodium methyl silicate solution is 5%. The mass of the sodium methyl silicate solution is 5% of the dry matrix of the lignite.

[0038] S2 Chemical modification: Subsequently, a calcium chloride solution was sprayed on the surface of the lignite. After mixing evenly, it was aged for 12 h to obtain modified lignite. The mass fraction of the calcium chloride solution was 15%. The mass of the calcium chloride solution was 3% of the dry matrix of the lignite.

[0039] S3 High-pressure dehydration: The modified lignite was placed in a pressure vessel, heated to 150 °C, pressurized to 10 MPa, and the pressure was maintained for 60 min.

[0040] S4 Post-treatment: After depressurization, it was dried to a moisture content ≤ 10% to obtain lignite fuel.

[0041] Example 3

[0042] The lignite fuel of this example was prepared by the following method:

[0043] S1 Pretreatment: The lignite was crushed and screened to a particle size ≤ 5 mm; a sodium methyl silicate solution was sprayed on the surface of the lignite and allowed to stand for infiltration for 4 h. The mass fraction of the sodium methyl silicate solution was 8%. The mass of the sodium methyl silicate solution was 5% of the dry matrix of the lignite.

[0044] S2 Chemical modification: Subsequently, a calcium chloride solution was sprayed on the surface of the lignite. After mixing evenly, it was aged for 24 h to obtain modified lignite. The mass fraction of the calcium chloride solution was 13%. The mass of the calcium chloride solution was 1% of the dry matrix of the lignite.

[0045] S3 High-pressure dehydration: The modified lignite was placed in a pressure vessel, heated to 100 °C, pressurized to 5 MPa, and the pressure was maintained for 90 min.

[0046] S4 Post-treatment: After depressurization, it was dried to a moisture content ≤ 10% to obtain lignite fuel.

[0047] Example 4

[0048] The lignite fuel of this example was prepared by the following method:

[0049] S1 Pretreatment: The lignite was crushed and screened to a particle size ≤ 5 mm; a sodium methyl silicate solution was sprayed on the surface of the lignite and allowed to stand for infiltration for 2 - 4 h. The mass fraction of the sodium methyl silicate solution was 10%. The mass of the sodium methyl silicate solution was 5% of the dry matrix of the lignite.

[0050] S2 Chemical modification: Subsequently, a calcium chloride solution was sprayed on the surface of the lignite. After mixing evenly, it was aged for 24 h to obtain modified lignite. The mass fraction of the calcium chloride solution was 10%, and the mass of the calcium chloride solution was 3% of the dry matrix of the lignite.

[0051] S3 High-pressure dehydration: The modified lignite was placed in a pressure vessel, heated to 150 °C, pressurized to 10 MPa, and the pressure was maintained for 30 min.

[0052] Post-treatment of S4: After pressure relief, it is dried until the moisture content ≤ 10% to obtain lignite fuel.

[0053] Comparative Example 1

[0054] The difference from Example 1 is that sodium methyl silicate solution and calcium chloride solution are not sprayed on the surface of lignite, and the remaining steps are the same as those in Example 1.

[0055] Experimental Example

[0056] Taking the lignite fuels of Examples 1-4 and Comparative Example 1 as objects, their calorific values, fluoride ion leaching amounts, phosphorus oxide emissions, and combustion efficiencies were tested, and the results are shown in Table 1.

[0057] Table 1

[0058]

[0059]

[0060] It can be concluded from Table 1 that the lignite fuel treated by the upgrading and modification method provided in Example 1 has a high calorific value, low fluorine and phosphorus contents, produces less harmful substances when used as a fuel, and has a high combustion efficiency.

[0061] In summary, the lignite upgrading and modification method and lignite fuel provided by the embodiments of the present invention, through the synergistic modification of sodium methyl silicate and calcium chloride, combined with the high-pressure dehydration process at 50-150°C and 5-10 MPa, reduce the moisture content of lignite to ≤ 10% and increase the calorific value to more than 5500 kcal / kg, and achieve efficient solidification of fluorine / phosphorus pollutants. The obtained fuel can be directly used for supercritical power generation, and its environmental protection and economy are significantly better than traditional processes.

[0062] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

Claims

1. A method for upgrading and modifying lignite, characterized in that, It includes the following steps: S1 Pretreatment: Crush and screen lignite to a particle size ≤ 5 mm; Spray a sodium methyl silicate solution on the surface of lignite and let it stand for infiltration for 2 - 4 h; S2 Chemical modification: Subsequently, spray a calcium chloride solution on the surface of lignite, mix evenly, and age for 12 - 24 h to obtain modified lignite; S3 High-pressure dehydration: Place the modified lignite in a pressure vessel, heat it to 50 - 150 °C, pressurize it to 5 - 10 MPa, and keep the pressure for 30 - 90 min; S4 Post-treatment: After depressurization, dry it to a moisture content ≤ 10% to obtain lignite fuel.

2. The lignite upgrading and modification method according to claim 1, wherein In the step S1, the mass fraction of the sodium methyl silicate solution is 5% - 10%.

3. The lignite upgrading and modification method according to claim 1, characterized in that, In the step S2, the mass fraction of the calcium chloride solution is 10% - 15%.

4. The lignite upgrading and modification method according to claim 3, characterized in that, The mass of the calcium chloride solution is 1 - 3% of the dry matrix of lignite.

5. The lignite upgrading and modification method according to claim 1, characterized in that In the step S3, the temperature of high-pressure dehydration is 100 - 130 °C, and the pressure is 6 - 8 MPa.

6. A lignite fuel prepared by the lignite upgrading and modification method according to any one of claims 1 - 5.

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