Clean coal and preparation method thereof

Abstract

The present invention provides a clean coal and a preparation method thereof, belonging to the technical field of coal products. The method comprises the following steps: (1) dispersing starch in water, stirring evenly, and then fully gelatinizing the mixture; (2) adding a sulfur-fixing agent to the gelatinized liquid, and centrifuging to obtain a starch gelatinized liquid containing the sulfur-fixing agent; (3) crushing the coal to obtain coal particles; (4) transporting the coal particles to a fluidized bed, spraying the starch gelatinized liquid containing the sulfur-fixing agent on the particles while the particles are suspended, and drying to obtain coal particles adsorbed with the sulfur-fixing agent and gelatinized starch. The method dissolves a soluble sulfur-fixing agent in the starch gelatinized liquid, and then in situ adsorbs the starch liquid onto the coal particles, so that the soluble sulfur-fixing agent is uniformly adsorbed into the coal. The sulfur in the coal reacts efficiently in situ with the adsorbed soluble sulfur-fixing agent, effectively improving the combustion efficiency and sulfur-fixing effect of the coal, while not causing any negative effects on the boiler.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal products, and in particular relates to clean coal and a preparation method thereof. Background Art

[0002] Coal is the main energy source in my country. The SO2 produced by its combustion can cause serious air pollution. Therefore, how to use coal resources cleanly and efficiently has always been an important technical issue.

[0003] Coal desulfurization can be divided into desulfurization before combustion, desulfurization during combustion and desulfurization after combustion.

[0004] Pre-combustion desulfurization removes sulfur from coal before combustion, preventing or reducing the release of SO2 during combustion, thereby alleviating flue gas corrosion and environmental pollution. For example, physical coal washing is a pre-combustion desulfurization technology that is simple to operate and low-cost, but typically only removes a majority of inorganic sulfur.

[0005] Desulfurization (sulfur fixation) during coal combustion typically involves adding a sulfur fixation agent or sulfur fixation aid to the furnace during the coal combustion process at 800-850°C. This allows the SO2 produced by the coal combustion to react chemically with the sulfur fixation agent again, generating a difficult-to-decompose sulfur fixation product that is then discharged as solid ash. Commonly used sulfur fixations include CaCO3, CaO, and MgO. Current challenges with this technology include slagging, wear, and clogging, high costs, and reduced boiler efficiency. Because sulfur fixation is not effective at high temperatures, it is essential to select the appropriate sulfur fixation agent for the specific coal type.

[0006] Post-combustion desulfurization of coal refers to the desulfurization of flue gas produced after combustion, also known as flue gas desulfurization. This method can be categorized as either a disposal method or a recovery method, depending on whether the product is recovered. While this method offers high desulfurization rates, it is complex and the overall processing cost is significantly higher than other technologies.

[0007] The sulfur fixation mechanism of using sulfur fixers in coal combustion is as follows: coal burns at high temperature to generate SO2 or SO3, and the sulfur fixer decomposes under high temperature conditions to obtain metal oxides. When using calcium-based, magnesium-based, barium-based and other sulfur fixers, the sulfur fixation reaction occurs between SO2 or SO3 and the metal oxides, and finally generates sulfates or sulfites.

[0008] Chinese patent CN1699526A discloses a composite sulfur-fixing additive for coal combustion. The additive contains, by mass percentage, 36-74% CaO and 26-64% BaCO₃. Furthermore, the additive may contain one or more of Al₂O₃, KMnO₄, and MnO₂. The invention exhibits good high-temperature sulfur-fixing efficiency, exceeding 70% within the temperature range of 900-1100°C and reaching 40%-70% at temperatures of 1200-1300°C. However, the sulfur-fixing agent contains insoluble components, which can lead to uneven mixing, resulting in poor sulfur-fixing effectiveness and significant coking, which reduces the thermal efficiency of the boiler.

[0009] Chinese patent CN108251174A discloses an environmentally friendly, sulfur-fixing coal briquette and its preparation method. The briquette comprises the following materials by weight: 50-60 parts coal powder, 15-20 parts coal slime, 10-20 parts sulfur-fixing additive, and 5-10 parts binder. The sulfur-fixing additive includes 45-50 parts carbide slag powder, 1-10 parts potassium permanganate, 5-15 parts iron ore powder, 10-20 parts magnesium oxide, and 1-3 parts sodium chloride. The binder includes 50-60 parts lignin, 20-40 parts bentonite, and 5-10 parts starch. The sulfur-fixing additive, primarily made from carbide slag and supplemented with a certain amount of iron ore powder, magnesium oxide, and sodium chloride, enhances the carbide slag's high-temperature sulfur-fixing stability and improves its sulfur-fixing efficiency, effectively reducing sulfur emissions from coal combustion. First, the invention claims protection for briquette, a type of coal product mechanically pressed into a variety of shapes and sizes with a defined strength. However, briquette is unsuitable for large-scale coal consumption, such as in power plant boilers, and suffers from low combustion efficiency. Furthermore, the sulfur-fixing agent used in the invention contains insoluble components, making it difficult to disperse well in the pulverized coal. Furthermore, starch is used as a binder to compress the pulverized coal into various shapes.

[0010] However, most of the existing sulfur-fixing agents are insoluble components, and there will be uneven problems when mixed with coal powder, resulting in poor sulfur-fixing effect. In addition, the addition of insoluble sulfur-fixing agents will cause coking, which will have a negative effect on the boiler. It will also lead to reduced combustion efficiency. Therefore, it is necessary to develop a clean coal with good sulfur-fixing effect, high combustion efficiency and no negative impact on the boiler, and its preparation method. Summary of the Invention

[0011] Based on the deficiencies in the prior art, the present invention aims to provide a clean coal and a preparation method thereof. Specifically, a soluble sulfur-fixing agent is dissolved in starch gelatinized liquid, so that the soluble sulfur-fixing agent is uniformly adsorbed in the coal. The sulfur in the coal and the adsorbed soluble sulfur-fixing agent react efficiently in situ, which can effectively improve the sulfur-fixing effect. In addition, the starch liquid in the present invention is adsorbed in situ in the coal particles to play a combustion-supporting role, thereby effectively improving the combustion efficiency of the coal. The clean coal of the present invention does not have a negative effect on the boiler.

[0012] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0013] In one aspect, the present application provides a method for preparing clean coal, comprising the following steps:

[0014] (1) dispersing starch in water and stirring uniformly to obtain starch milk; heating the starch milk to 70-100° C. and gelatinizing for 10-60 minutes to obtain starch gelatinized liquid;

[0015] (2) controlling the temperature of the starch gelatinized liquid to be 30-60° C., adding a sulfur-fixing agent thereto, and removing insoluble matter by centrifugation to obtain a starch gelatinized liquid containing the sulfur-fixing agent;

[0016] (3) crushing the coal and screening it to obtain coal particles;

[0017] (4) The coal particles are transported to a fluidized bed, and starch gelatinized liquid containing a sulfur-fixing agent is sprayed on them in a suspended state, and after drying, coal particles adsorbed with the sulfur-fixing agent and gelatinized starch are obtained.

[0018] in,

[0019] The concentration of the starch milk described in step (1) is 5-20 g / L; preferably 10-15 g / L.

[0020] The sulfur-fixing agent described in step (2) is a soluble sulfur-fixing agent; the soluble sulfur-fixing agent is one or more of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2;

[0021] Preferably, the soluble sulfur-fixing agent is a mixture of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2.

[0022] More preferably, the mass ratio of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2 is 1:2-5:1-3;

[0023] Further preferably, the mass ratio of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2 is 1:3-4:2-3;

[0024] Still further preferably, the mass ratio of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2 is 1:4:2.

[0025] The present invention uses a mixture of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2 in different proportions as a sulfur-fixing agent. The three components are all water-soluble components. When dissolved in a gelatinized starch solution, a uniformly dissolved solution can be formed. Spraying the coal particles with the solution can allow the curing agent components to penetrate into the pores of the coal, thereby increasing the contact area between the curing agent and the coal, thereby improving the sulfur-fixing effect. In addition, the present invention uses a mixed sulfur-fixing agent and controls the mass ratio of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2 to be 1:2-5:1-3, so that the coal can solidify the generated SO2 or SO3 at different stages of combustion, thereby achieving a better sulfur-fixing effect.

[0026] The mass volume ratio of the soluble sulfur-fixing agent and the starch gelatinization liquid described in step (2) is 5-15:1 (g / L);

[0027] Preferably, the mass volume ratio of the soluble sulfur-fixing agent to the starch gelatinization liquid is 8-12:1 (g / L);

[0028] More preferably, the mass-to-volume ratio of the soluble sulfur-fixing agent to the starch gelatinization liquid is 10:1 (g / L).

[0029] The coal particles after crushing in step (3) have a particle size of 5-200 μm.

[0030] In step (4), the starch gelatinized liquid containing the sulfur-fixing agent is evenly sprayed on the coal at a ratio of 3‰-5‰ at room temperature;

[0031] Preferably, the starch gelatinized liquid containing the sulfur-fixing agent is evenly sprayed on the burning coal at a ratio of 4‰ at room temperature.

[0032] The drying temperature in step (4) is above 80°C.

[0033] As some preferred embodiments, amylase is further added in step (2), and the amount of amylase added is 3-6% of the mass of starch, preferably 5%.

[0034] The amylase is selected from one or more of α-amylase, β-amylase, saccharifying enzyme and isoamylase;

[0035] Preferably, the amylase is β-amylase and / or isoamylase;

[0036] More preferably, the amylase is β-amylase and / or isoamylase in a mass ratio of 1:1.

[0037] The enzymatic activity of the beta-amylase is 50-100 U / g starch; the enzymatic activity of the isoamylase is 50-100 U / g starch.

[0038] The present invention also adds amylase to the starch gelatinized liquid. The addition of amylase can, on the one hand, disperse the sulfur-fixing agent in the gelatinized starch liquid, and on the other hand, increase the flow rate of the starch gelatinized liquid, thereby allowing the starch gelatinized liquid containing the sulfur-fixing agent to quickly enter the gaps between the coal particles. Using a mixture of β-amylase and isoamylase, and controlling the mass ratio of the two to be 1:1, can better disperse the various components of the sulfur-fixing agent in the starch gelatinized liquid. Secondly, during the spraying process, the interaction between the β-amylase and isoamylase and the gelatinized starch can ensure the fluidity and stability of the starch gelatinized liquid, allowing the various components of the sulfur-fixing agent to better penetrate into the interior of the coal, thereby improving the sulfur-fixing effect of the sulfur-fixing agent.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention uses a mixture of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2 in different proportions as a sulfur-fixing agent. The three components are all water-soluble components. When dissolved in a gelatinized starch solution, a uniformly dissolved solution can be formed. Spraying the coal particles with the solution can effectively adsorb the curing agent components into the pores of the coal, thereby increasing the contact area between the curing agent and the coal, thereby improving the sulfur-fixing effect. In addition, the present invention uses a mixed sulfur-fixing agent and controls the mass ratio of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2 to 1:2-5:1-3, so that the coal can solidify the generated SO2 or SO3 at different stages of combustion, thereby achieving a better sulfur-fixing effect.

[0041] (2) The present invention uses starch gelatinized liquid to dissolve the soluble sulfur-fixing agent, and then adsorbs the starch liquid into the coal particles in situ, so that the soluble sulfur-fixing agent is evenly adsorbed into the coal. The sulfur in the coal reacts efficiently with the adsorbed soluble sulfur-fixing agent in situ, effectively improving the combustion efficiency and sulfur-fixing effect of the coal, while not having a negative impact on the boiler.

[0042] (3) The present invention also adds amylase to the starch gelatinization liquid. The addition of amylase can regulate the viscosity and molecular weight of the starch gelatinization liquid on the one hand, and on the other hand, it can increase the flow rate of the starch gelatinization liquid, so that the starch gelatinization liquid containing the sulfur-fixing agent can quickly enter the gaps of the coal particles. A mixture of β-amylase and isoamylase is used, and the mass ratio of the two is controlled to be 1:1, which can make the various components of the sulfur-fixing agent better dispersed in the starch gelatinization liquid. Secondly, during the spraying process, the interaction between β-amylase and isoamylase and gelatinized starch can ensure the fluidity and stability of the starch gelatinization liquid, so that the various components of the sulfur-fixing agent can better penetrate into the interior of the coal, thereby improving the sulfur-fixing effect of the sulfur-fixing agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a SEM scanning electron microscope image of coal particles adsorbed with sulfur-fixing agent and gelatinized starch prepared in Example 1. DETAILED DESCRIPTION

[0044] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to specific examples. In the examples, the experimental methods used are conventional methods unless otherwise specified, and the materials and reagents used are all commercially available unless otherwise specified.

[0045] Example 1 A method for preparing clean coal

[0046] The steps include:

[0047] (1) dispersing starch in water and stirring uniformly to obtain starch milk, wherein the concentration of the starch milk is 5 g / L; fully gelatinizing the starch milk at 70° C. to obtain starch gelatinized liquid;

[0048] (2) controlling the temperature of the starch gelatinization liquid to be 30-60° C., adding a sulfur-fixing agent thereto, wherein the mass volume ratio of the sulfur-fixing agent to the starch gelatinization liquid is 5:1 (g / L), and removing insoluble matter by centrifugation to obtain a starch gelatinization liquid containing the sulfur-fixing agent; the sulfur-fixing agent is a mixture of Ba(OH)2, Ca(HCO3)2, and Mg(HCO3)2, wherein the mass ratio is 1:2:1;

[0049] (3) crushing the coal and screening it to obtain coal particles with an average particle size of 5 μm;

[0050] (4) The coal particles are transported to a fluidized bed, and the starch gelatinized liquid containing the sulfur-fixing agent is evenly sprayed on the coal at a ratio of 5‰ under a suspended state at room temperature. After drying at 80°C, the coal particles adsorbed with the sulfur-fixing agent and gelatinized starch are obtained.

[0051] Example 2 A method for preparing clean coal

[0052] The steps include:

[0053] (1) dispersing starch in water and stirring uniformly to obtain starch milk, wherein the concentration of the starch milk is 20 g / L; fully gelatinizing the starch milk at 100° C. to obtain starch gelatinized liquid;

[0054] (2) controlling the temperature of the starch gelatinization liquid to be 30-60° C., adding a sulfur-fixing agent thereto, wherein the mass volume ratio of the sulfur-fixing agent to the starch gelatinization liquid is 15:1 (g / L), and removing insoluble matter by centrifugation to obtain a starch gelatinization liquid containing the sulfur-fixing agent; the sulfur-fixing agent is a mixture of Ba(OH)2, Ca(HCO3)2, and Mg(HCO3)2, wherein the mass ratio is 1:5:3;

[0055] (3) crushing the coal and screening it to obtain coal particles with an average particle size of 50 μm;

[0056] (4) The coal particles are transported to a fluidized bed, and the starch gelatinized liquid containing the sulfur-fixing agent is evenly sprayed on the coal at a ratio of 3‰ under a suspended state at room temperature. After drying at 100°C, the coal particles adsorbed with the sulfur-fixing agent and gelatinized starch are obtained.

[0057] Example 3 A method for preparing clean coal

[0058] The steps include:

[0059] (1) dissolving starch in water and stirring uniformly to obtain starch milk, wherein the concentration of the starch milk is 10 g / L; fully gelatinizing the starch milk at 90° C. to obtain starch gelatinized liquid;

[0060] (2) controlling the temperature of the starch gelatinization liquid to be 30-60° C., adding a sulfur-fixing agent thereto, wherein the mass volume ratio of the sulfur-fixing agent to the starch gelatinization liquid is 10:1 (g / L), and removing insoluble matter by centrifugation to obtain a starch gelatinization liquid containing the sulfur-fixing agent; the sulfur-fixing agent is a mixture of Ba(OH)2, Ca(HCO3)2, and Mg(HCO3)2, wherein the mass ratio is 1:4:2;

[0061] (3) crushing the coal and screening it to obtain coal particles with an average particle size of 200 μm;

[0062] (4) The coal particles are transported to a fluidized bed, and the starch gelatinized liquid containing the sulfur-fixing agent is evenly sprayed on the coal at a ratio of 4‰ under room temperature in a suspended state. After drying at 100°C, coal particles adsorbed with the sulfur-fixing agent and gelatinized starch are obtained.

[0063] Example 4

[0064] The only difference from Example 3 is that amylase is also added in step (2), the amount of amylase added is 5% of the mass of starch, and the amylase is β-amylase and isoamylase in a mass ratio of 1:1. The other steps and operations are the same as in Example 3.

[0065] Example 5

[0066] The only difference from Example 4 is that the amount of amylase added in step (2) is 3% of the mass of starch, and the other steps and operations are the same as Example 4.

[0067] Example 6

[0068] The only difference from Example 4 is that the amount of amylase added in step (2) is 6% of the mass of starch, and the other steps and operations are the same as Example 4.

[0069] Comparative Example 1

[0070] The difference from Example 3 is that the sulfur-fixing agent is a mixture of Ca(HCO3)2 and Mg(HCO3)2 in a mass ratio of 4:2, the total amount of the sulfur-fixing agent added is the same as that in Example 3, and the other steps and operations are the same as those in Example 3.

[0071] Comparative Example 2

[0072] The difference from Example 3 is that the sulfur-fixing agent is a mixture of Ba(OH)2 and Ca(HCO3)2 with a mass ratio of 1:4, the total amount of sulfur-fixing agent added is the same as the total amount added in Example 3, and the other steps and operations are the same as in Example 3.

[0073] Comparative Example 3

[0074] The difference from Example 3 is that the sulfur-fixing agent is a mixture of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2, with a mass ratio of 8:1:1, the total amount of sulfur-fixing agent added is the same as the total amount added in Example 3, and the other steps and operations are the same as in Example 3.

[0075] Comparative Example 4

[0076] The difference from Example 3 is that the sulfur-fixing agent is Ca(OH)2, the total amount of the sulfur-fixing agent added is the same as the total amount added in Example 3, and the other steps and operations are the same as in Example 3.

[0077] Comparative Example 5

[0078] The difference from Example 4 is that the mass ratio of β-amylase to isoamylase is 3:1, the addition amount is the same as that in Example 4, and the other steps and operations are the same as those in Example 4.

[0079] Comparative Example 6

[0080] The difference from Example 4 is that the mass ratio of β-amylase to isoamylase is 1:3, the addition amount is the same as that in Example 4, and the other steps and operations are the same as those in Example 4.

[0081] Comparative Example 7

[0082] The difference from Example 4 is that only β-amylase is used, and the amount of β-amylase added is the same as that in Example 4. Other steps and operations are the same as those in Example 4.

[0083] Comparative Example 8

[0084] The difference from Example 4 is that the particle size of the coal particles in step (3) is different, specifically: (3) the coal is crushed and sieved to obtain coal particles with an average particle size of 4 mm; the other steps and operations are the same as Example 4.

[0085] Effect detection:

[0086] Detection of combustible matter content and sulfur content in ash obtained after full combustion of coal

[0087] Blank sample (raw coal): The coal was crushed to a particle size range of 5-200 μm and no adsorption treatment was performed.

[0088] Test method: The combustible content is determined according to the DNL567.6-2016 drying oven + muffle furnace method, and the sulfur content is determined according to the DL / T567.7-2007 coulometric titration method. The test results are shown in Table 1 below.

[0089] Table 1

[0090]

[0091]

[0092] After coal combustion, in addition to gaseous combustion products, it generally also includes small particles of fly ash and large particles of slag. The higher the combustible content of the fly ash and slag, the less complete the coal combustion; the higher the sulfur content of the fly ash and slag, the better the sulfur capture effect.

[0093] According to the test data in Table 1 above, in Examples 1-3 of the present invention, a mixture of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2 was used as a sulfur-fixing agent, the sulfur-fixing agent was dissolved in starch gelatinized liquid, and the starch liquid was in situ adsorbed on the coal particles, so that the soluble sulfur-fixing agent was uniformly adsorbed on the coal, thereby significantly improving the combustion efficiency and sulfur-fixing effect of the coal; in Examples 4-6, β-amylase and isoamylase were added to the starch gelatinized liquid in a mass ratio of 1:1, which enabled the components of the sulfur-fixing agent to be better dispersed in the starch gelatinized liquid and increased the fluidity of the starch gelatinized liquid. , thereby improving the combustion efficiency and sulfur fixation effect of coal; in comparative examples 1-3, changing the ratio or type of sulfur fixer has little effect on the combustion efficiency of coal, but will significantly affect the sulfur fixation effect; in comparative example 4, replacing the sulfur fixer with Ca(OH)2 will significantly affect the sulfur fixation effect of coal; in comparative examples 5-7, changing the ratio or type of β-amylase and isoamylase will affect the fluidity of starch gelatinization liquid, and will have a significant effect on the combustion efficiency and sulfur fixation effect of coal; in comparative example 8, changing the particle size of coal particles will significantly affect the adsorption efficiency of coal on the sulfur fixer and the combustion efficiency, thereby weakening the sulfur fixation effect.

[0094] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art may still modify or make equivalent substitutions for the specific implementation schemes of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing clean coal, characterized in that: The steps include: (1) dispersing starch in water and stirring uniformly to obtain starch milk, wherein the concentration of the starch milk is 5-20 g / L; heating the starch milk to 70-100° C. and gelatinizing for 10-60 minutes to obtain starch gelatinized liquid; (2) controlling the temperature of the starch gelatinized liquid to be 30-60° C., adding a sulfur-fixing agent thereto, and removing insoluble matter by centrifugation to obtain a starch gelatinized liquid containing the sulfur-fixing agent; (3) crushing the coal and screening it to obtain coal particles; (4) transporting the coal particles to a fluidized bed, spraying them with starch gelatinization liquid containing a sulfur-fixing agent in a suspended state, and drying them to obtain coal particles adsorbed with the sulfur-fixing agent and gelatinized starch; The sulfur-fixing agent in step (2) is a soluble sulfur-fixing agent; the soluble sulfur-fixing agent is one or more of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2; In step (2), amylase is also added, and the amount of the amylase added is 3-6% of the mass of the starch.

2. The preparation method according to claim 1, wherein: The soluble sulfur-fixing agent is a mixture of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2.

3. The preparation method according to claim 2, wherein: The mass ratio of Ba(OH)2, Ca(HCO3)2 and Mg(HCO3)2 is 1:2-5:1-3.

4. The preparation method according to claim 1, wherein: The mass volume ratio of the soluble sulfur-fixing agent and the starch gelatinization liquid described in step (2) is 5-15:1 (g / L).

5. The preparation method according to claim 1, wherein: The average particle size of the coal particles after the crushing treatment in step (3) is 5-200 μm.

6. The preparation method according to claim 1, wherein: In step (4), the starch gelatinized liquid containing the sulfur-fixing agent is evenly sprayed on the burning coal at a ratio of 3‰-5‰ under room temperature.

7. The preparation method according to claim 1, wherein: The drying temperature in step (4) is above 80°C.

8. The preparation method according to claim 1, wherein: The amylase is selected from one or more of α-amylase, β-amylase, saccharifying enzyme and isoamylase.

9. The preparation method according to claim 8, characterized in that: The amylase is beta-amylase and isoamylase in a mass ratio of 1:

1.

10. Clean coal prepared by the preparation method according to any one of claims 1 to 9.

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