Fire coal composite sulfur-fixing agent as well as preparation method and application thereof

Abstract

The invention discloses a fire coal composite sulfur-fixing agent as well as a preparation method and application thereof, and belongs to the technical field of fire coal catalysts. The composite sulfur-fixing agent comprises the following components in parts by mass: 90-98 parts of a basic sulfur-fixing agent, 0.5-5 parts of a rare earth element compound and 1-5 parts of a metal compound. By utilizing the synergistic effect of the nano sulfur-fixing agent, the metal oxide and the rare earth, the sulfur-fixing efficiency is improved by 25% compared with that of sulfur fixation by purely adding calcium oxide, the blending combustion ratio of high-sulfur coal is improved, the use amount of the sulfur-fixing agent under the same sulfur content is reduced, and the emission of sulfur dioxide is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of coal-fired catalysts and relates to a coal-fired composite sulfur-fixing agent and a preparation method and application thereof. Background Art

[0002] In the power generation process of coal-fired power plants, fuel cost control and the current energy strategic layout have a profound impact on the fuel selection of power plants. Given that high-sulfur coal is relatively low in cost and relatively abundant in reserves, power plants often need to burn high-sulfur coal with a higher sulfur content to balance power generation costs and energy supply. However, with the increasing global attention to environmental protection, environmental protection standards are also continuously being upgraded. In the flue gas emissions of coal-fired power generation, sulfur dioxide is a major pollutant, and its emission limits are subject to extremely strict requirements. How to effectively reduce sulfur emissions in flue gas while ensuring the normal combustion of high-sulfur coal has become a key technical problem that coal-fired power plants urgently need to solve.

[0003] At present, some power plants adopt the method of blending high-sulfur coal and low-sulfur coal, and control the sulfur content of the coal entering the furnace so that the sulfur content of the flue gas does not exceed the load of the back-end sulfur treatment system to meet the demand for high-sulfur coal blending. For example, CN202410893848 discloses a method, device, equipment and storage medium for calculating the sulfur content of the coal entering the furnace for blending coal. It can calculate the sulfur content entering the furnace and improve the blending efficiency, but this method can only blend a low proportion of high-sulfur coal. If solid sulfur substances are added simultaneously during the blending process, and the flue gas sulfur treatment system is coordinated, it is expected to take into account the safe operation of the unit, environmental protection requirements and combustion cost control.

[0004] From the perspective of the occurrence form of sulfur in coal, sulfur in coal mainly exists in the form of inorganic sulfur (including elemental sulfur, sulfides, sulfates) and organic sulfur (such as mercaptans, sulfides, heterocyclic sulfur, and thioquinones). Except for a very small amount of sulfate, the rest is combustible sulfur, which will participate in chemical reactions to form sulfur oxides during the combustion process, thereby increasing the content of pollutants such as sulfur dioxide in the flue gas. In terms of sulfur fixation technology, although traditional sulfur fixers such as calcium oxide and calcium carbonate can achieve sulfur fixation effects to a certain extent, they have the significant disadvantage of low sulfur fixation efficiency. When high-sulfur coal is mixed with coal at a high proportion, traditional sulfur fixers are difficult to meet strict environmental emission requirements. In addition, when using traditional sulfur fixers, in order to achieve a good sulfur fixation effect, a high calcium-sulfur ratio is often required, which will lead to a significant increase in the amount of ash. The increase in ash not only increases the maintenance cost of the boiler, but also affects the operating efficiency and economy of the boiler, further increasing the operating pressure of the power plant.

[0005] In summary, existing coal blending methods and sulfur reduction technologies cannot meet the multiple requirements of coal-fired power plants for environmental emissions, safe unit operation, and cost control during the high-sulfur coal blending process. Therefore, there is an urgent need for a new sulfur reduction additive that is highly effective for high-sulfur coal blending and a more scientific and efficient blending method to reduce the content of sulfur dioxide and sulfur trioxide in flue gas, lower the pressure of the flue gas sulfur treatment system, increase the proportion of high-sulfur coal in the blended coal, meet environmental emission requirements, reduce unit operating costs, and achieve optimal economic benefits. Summary of the Invention

[0006] The purpose of the present invention is to provide a coal-fired composite sulfur-fixing agent and its preparation method and application, so as to solve the technical problem that the sulfur-fixing agent in the prior art has low sulfur-fixing efficiency, is difficult to meet the demand of high-proportion blending of high-sulfur coal, and leads to a large load on the back-end sulfur treatment system.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a composite coal-fired sulfur-fixing agent, which comprises, by mass, 90 to 98 parts of a basic sulfur-fixing agent, 0.5 to 5 parts of a rare earth element compound, and 1 to 5 parts of a metal compound.

[0009] Furthermore, the basic sulfur-fixing agent is a mixture of one or more of calcium oxide, barium oxide, magnesium oxide, hydroxide and carbonate.

[0010] Furthermore, the rare earth element compound is a mixture of one or more lanthanide oxides or salts.

[0011] Furthermore, the metal compound is a mixture of one or more of iron oxide, manganese oxide, nickel oxide, titanium oxide and aluminum oxide.

[0012] Furthermore, the basic sulfur-fixing agent is a nano sulfur-fixing agent.

[0013] In a second aspect, the present invention provides a method for preparing the coal-fired composite sulfur-fixing agent, which is characterized by comprising the following steps:

[0014] Weigh the basic sulfur-fixing agent, rare earth element compound and metal compound;

[0015] Divide the weighed basic sulfur-fixing agent into two parts;

[0016] A basic sulfur-fixing agent is mixed with a rare earth element compound to prepare a mixture A;

[0017] Another portion of the basic sulfur-fixing agent is mixed with the metal compound to prepare mixture B;

[0018] The mixture A and the mixture B are mixed and stirred to prepare a composite sulfur-fixing agent.

[0019] Furthermore, in the step of dividing the weighed basic sulfur-fixing agent into two parts, the two parts of basic sulfur-fixing agent have the same mass, each accounting for one half of the mass of the weighed basic sulfur-fixing agent.

[0020] In a third aspect, the present invention provides an application of the coal-fired composite sulfur-fixing agent in the combustion of high-sulfur coal, characterized in that high-sulfur coal and low-sulfur coal are mixed to form mixed coal, and the composite sulfur-fixing agent is added to the mixed coal for combustion.

[0021] Furthermore, the added amount of the composite desulfurizing agent accounts for 0.9%-8% of the mass of the entire mixed coal.

[0022] Furthermore, the mass ratio of the high-sulfur coal to the low-sulfur coal is 3:(1-3).

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention discloses a coal-fired composite desulfurizer, its preparation method and application. When the sulfur in the coal participates in the combustion reaction during the combustion process to generate sulfur dioxide SO2, SO2 continues to react with oxygen under the action of an oxidant to generate sulfur trioxide SO3. The generated SO3 reacts with the desulfurizer in the additive to generate stable sulfate, which is precipitated in the slag instead of being discharged into the flue gas. In addition, the rare earth element compound in the desulfurizer of the present invention has an oxygen storage and release effect. Under high-temperature combustion conditions, it can quickly release and store oxygen, can be used as a catalyst or catalyst carrier, can reduce the reaction activation energy, and enhance the activity of the calcium-based desulfurizer in coal combustion. The metal compound can be used as an oxidant to accelerate the oxidation of SO2 to generate SO3, and can also form a composite system with the desulfurizer to increase the surface area and improve the reaction efficiency. In addition, the use of nano desulfurizers in the present invention can increase the specific surface area and improve the reaction rate. The present invention utilizes the synergistic effect of nano-sulfur fixers, metal oxides and rare earths to increase the sulfur fixation efficiency by 25% compared with sulfur fixation by adding pure calcium oxide, thereby increasing the blending ratio of high-sulfur coal, reducing the amount of sulfur fixer used at the same sulfur content, and reducing sulfur dioxide emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 Flowchart of a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0028] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0029] Herein, all features such as values, amounts, amounts, and concentrations defined in numerical ranges or percentage ranges are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to include and specifically disclose all possible subranges and individual values ​​within the range (including integers and fractions).

[0030] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0031] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0032] The present invention is described in further detail below with reference to the accompanying drawings:

[0033] See also Figure 1 The present invention discloses a composite coal-fired sulfur-fixing agent, comprising, by weight, 90-98 parts of a base sulfur-fixing agent, 0.5-5 parts of a rare earth element compound, and 1-5 parts of a metal compound. This invention utilizes the synergistic effect of the base sulfur-fixing agent, metal oxides, and rare earth elements to construct a multi-component synergistic sulfur-fixing system. This increases the in-furnace sulfur-fixing efficiency from 40%-60% to 60%-85%, reduces the calcium-sulfur ratio, and reduces the sulfur dioxide and sulfur trioxide content in the flue gas.

[0034] In one feasible embodiment of the present invention, the base sulfur-fixing agent is a mixture of one or more of calcium oxide, barium oxide, magnesium oxide, hydroxide, and carbonate. The rare earth element compound is a mixture of one or more of lanthanide oxides or salts. The metal compound is a mixture of one or more of iron oxide, manganese oxide, nickel oxide, titanium oxide, and aluminum oxide. Furthermore, the base sulfur-fixing agent is a nano-sulfur-fixing agent. The use of nanomaterials can increase the specific surface area and improve the reaction rate.

[0035] The present invention discloses a method for preparing a composite sulfur-fixing agent for coal combustion, comprising the following steps:

[0036] S1, weighing the basic sulfur-fixing agent, rare earth element compound and metal compound;

[0037] S2, divide the weighed basic sulfur-fixing agent into two parts; the two parts of basic sulfur-fixing agent have the same mass, each accounting for half of the mass of the weighed basic sulfur-fixing agent.

[0038] S3, mixing a basic sulfur-fixing agent with a rare earth element compound to prepare a mixture A;

[0039] S4, another portion of the basic sulfur-fixing agent is mixed with the metal compound to prepare a mixture B;

[0040] S5, mixing the mixture A and the mixture B to prepare a composite sulfur-fixing agent.

[0041] The principles of the present invention are as follows:

[0042] (1) Sulfur fixation principle: The sulfur in the coal participates in the combustion reaction during the combustion process to generate sulfur dioxide SO2. Under the action of the oxidant, SO2 continues to react with oxygen to generate sulfur trioxide SO3. The generated SO3 reacts with the sulfur fixation agent in the additive to generate stable sulfate, which is precipitated in the slag instead of being discharged into the flue gas.

[0043] (2) Oxygen storage and release effect of rare earth element compounds: Cerium oxide CeO2 has a strong oxygen storage capacity. Under high temperature combustion conditions, CeO2 can quickly release and store oxygen through the following reactions: It can be used as a catalyst or catalyst carrier, can reduce the reaction activation energy, enhance the activity of calcium-based desulfurizers in coal combustion, and is a good sulfur-fixing catalyst; the chemical properties of gadolinium oxide Gd2O3 are similar to those of cerium oxide CeO2, and it also has a high oxygen storage capacity; yttrium oxide Y2O3 can be used in combination with cerium oxide CeO2 to form a composite oxide to improve the synergistic efficiency of oxygen storage and sulfur fixation; lanthanum oxide has strong alkalinity and high temperature resistance, and can also be used as a catalyst.

[0044] (3) Catalytic effect of metal compounds: Fe2O3, MnO2, CuO, etc. can act as oxidants to accelerate the oxidation of SO2 to SO3, and can also form a composite system with sulfur-fixing agents such as CaO-Al2O3-Fe2O3 to increase the surface area and improve the reaction efficiency.

[0045] (4) Increase the surface area of ​​the sulfur-fixing agent: The use of nanomaterials can increase the specific surface area and improve the reaction rate.

[0046] (5) Multi-component synergistic catalysis: There is a synergistic effect between various catalysts and sulfur-fixing agents. The present invention utilizes the synergistic effect between nano-sulfur-fixing agents, metal oxides, and rare earths to increase the sulfur-fixing efficiency by 25% compared with the sulfur-fixing by adding pure calcium oxide, thereby increasing the blending ratio of high-sulfur coal, reducing the amount of sulfur-fixing agent used at the same sulfur content, and reducing sulfur dioxide emissions.

[0047] The embodiment of the present invention discloses the application of a coal-fired composite sulfur-fixing agent in mixed coal, wherein high-sulfur coal and low-sulfur coal are mixed to form mixed coal, and the composite sulfur-fixing agent is added to the mixed coal for combustion. The mass ratio of the high-sulfur coal to the low-sulfur coal is 3:(1-3). The amount of the composite sulfur-fixing agent added accounts for 0.9%-8% of the mass of the entire mixed coal. The blending method is: according to the load data of the flue gas sulfur treatment system, the sulfur-fixing efficiency, the actual demand for coal blending, and the ratio of sulfur element to sulfur-fixing element, the blending amount of the composite sulfur-fixing agent is accurately calculated and adjusted. The specific calculation formula is:

[0048]

[0049] Wherein, m1 is the mass of the composite sulfur-fixing agent, m2 is the mass of the mixed coal, M is the average relative molecular mass of each sulfur-fixing element in the composite sulfur-fixing agent, a is the maximum sulfur treatment capacity of the flue gas sulfur treatment system, b is the number of basic sulfur-fixing agents in every 100 parts of the composite sulfur-fixing agent, and η is the sulfur-fixing efficiency when the ratio of sulfur element to sulfur-fixing element is 1:1.

[0050] For example: the maximum processing capacity a of the flue gas treatment system is 1.5% sulfur content, the sulfur fixation efficiency η after adding the new sulfur fixation agent is 60%-85%, the minimum sulfur fixation efficiency η is 60%, and the sulfur fixation agent is all calcium oxide. When M is 56 and b is 95 parts, then

[0051] This invention optimizes the high-sulfur coal blending process. It achieves deep synergy between solid sulfur additives, coal blending, and flue gas treatment systems. By accurately calculating the addition ratio of solid sulfur additives, the blending ratio of high-sulfur coal with a sulfur content of more than 4% is increased from 40% in traditional processes to 50% or more, breaking through the existing technology's restrictions on the blending ratio of high-sulfur coal.

[0052] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0053] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0054] Example 1:

[0055] The embodiment of the present invention discloses a composite sulfur-fixing agent for high-sulfur coal co-combustion in thermal power plants and a co-combustion method, which is prepared by the following raw materials and methods:

[0056] (1) Weigh the following raw materials: 96 parts of nano-sulfur fixative, 2 parts of rare earth element compound, and 2 parts of metal compound.

[0057] (2) In the nano-sulfur fixer, 100 parts of CaO.

[0058] (3) Among the rare earth oxides, 27 parts of CeO2, 26 parts of La2O3, 29 parts of Gd2O3, and 18 parts of Y2O3.

[0059] (4) Among the metal oxides, there are 39 parts of Al2O3 and 61 parts of Fe2O3.

[0060] (5) Mixing half of the nano-sulfur fixative with rare earth oxide to prepare mixture A.

[0061] (6) Mixing half of the nano-sulfur fixative with the metal oxide to prepare a mixture B.

[0062] (7) Mix the mixture A and the dispersion B and stir them thoroughly for 30 minutes to prepare a composite sulfur-fixing agent.

[0063] (8) Calculate the sulfur content in the coal blending furnace and add a composite sulfur fixer appropriately. For example, a 1:1 blend of high-sulfur coal with a sulfur content of 5% and medium-sulfur coal with a sulfur content of 1.4% produces a mixed coal with a sulfur content of 3.2%. Adding 58 kg of composite sulfur fixer to each ton of coal with a sulfur content of 3.2% can reduce sulfur dioxide in the flue gas by 60%-85%, equivalent to coal with a sulfur content of 0.48%-1.28%. The blending ratio of high-sulfur coal with a sulfur content of 5% reaches 50%.

[0064] Example 2:

[0065] The embodiment of the present invention discloses a composite sulfur-fixing agent for high-sulfur coal co-combustion in thermal power plants and a co-combustion method, which is prepared by the following raw materials and methods:

[0066] (1) Weigh the following raw materials: 90 parts of nano-sulfur fixative, 5 parts of rare earth element compound, and 5 parts of metal compound.

[0067] (2) In the nano-sulfur fixer, there are 28 parts of CaO, 51 parts of CaCO3, and 21 parts of MgO.

[0068] (3) Among the rare earth oxides, 64 parts of CeO2 and 36 parts of Y2O3.

[0069] (4) Among the metal oxides, there are 39 parts of Al2O3 and 61 parts of Fe2O3.

[0070] (5) Mixing half of the nano-sulfur fixative with rare earth oxide to prepare mixture A.

[0071] (6) Mixing half of the nano-sulfur fixative with the metal oxide to prepare a mixture B.

[0072] (7) Mix the mixture A and the dispersion B and stir them thoroughly for 30 minutes to prepare a composite sulfur-fixing agent.

[0073] (8) Calculate the sulfur content in the coal blending furnace and add a composite sulfur fixer appropriately. For example, a 3:2 ratio blend of high-sulfur coal with a sulfur content of 5% and low-sulfur coal with a sulfur content of 0.5% is used to obtain a mixed coal with a sulfur content of 3.2%. Adding 74 kg of composite sulfur fixer to each ton of mixed coal with a sulfur content of 3.2% can reduce the sulfur dioxide in the flue gas by 60%-85%, which is equivalent to using coal with a sulfur content of 0.48%-1.28%. The blending ratio of high-sulfur coal with a sulfur content of 5% reaches 60%.

[0074] Example 3:

[0075] The embodiment of the present invention discloses a composite sulfur-fixing agent for high-sulfur coal co-combustion in thermal power plants and a co-combustion method, which is prepared by the following raw materials and methods:

[0076] (1) Weigh the following raw materials: 95 parts of nano-sulfur fixative, 3 parts of rare earth element compound, and 2 parts of metal compound.

[0077] (2) In the nano-sulfur fixer, there are 56 parts of CaCO3 and 44 parts of MgO.

[0078] (3) Among the rare earth oxides, 40 parts of Gd2O3, 42 parts of La2O3, and 18 parts of Y2O3.

[0079] (4) Among the metal oxides, 61 parts of Fe2O3 and 39 parts of MnO2

[0080] (5) Mixing half of the nano-sulfur fixative with rare earth oxide to prepare mixture A.

[0081] (6) Mixing half of the nano-sulfur fixative with the metal oxide to prepare a mixture B.

[0082] (7) Mix the mixture A and the dispersion B and stir them thoroughly for 30 minutes to prepare a composite sulfur-fixing agent.

[0083] (8) Calculate the sulfur content in the coal blending furnace and add composite sulfur fixers appropriately. For example, a 3:1 blend of high-sulfur coal with a sulfur content of 4% and low-sulfur coal with a sulfur content of 0.8% produces a mixed coal with a sulfur content of 3.2%. Adding 50 kg of composite sulfur fixers to each ton of coal with a sulfur content of 3.2% can reduce sulfur dioxide in the flue gas by 60%-85%, equivalent to coal with a sulfur content of 0.48%-1.28%. The blending ratio of high-sulfur coal with a sulfur content of 4% reaches 75%.

[0084] Example 4:

[0085] The embodiment of the present invention discloses a composite sulfur-fixing agent for high-sulfur coal co-combustion in thermal power plants and a co-combustion method, which is prepared by the following raw materials and methods:

[0086] (9) Weigh the following raw materials: 94 parts of nano-sulfur fixative, 1 part of rare earth element compound, and 1 part of metal compound.

[0087] (10) In the nano-sulfur fixer, there are 55 parts of BaCO3 and 45 parts of MgO.

[0088] (11) Among the rare earth oxides, 40 parts of Gd2O3, 42 parts of La2O3, and 18 parts of Y2O3.

[0089] (12) Among the metal oxides, 60 parts of Fe2O3 and 40 parts of MnO2

[0090] (13) Mix one-half of the nano-sulfur fixative and rare earth oxide to prepare mixture A.

[0091] (14) Mix one-half of the nano-sulfur fixative and the metal oxide to prepare mixture B.

[0092] (15) Mix the mixture A and the dispersion B and stir them thoroughly for 30 minutes to prepare a composite sulfur-fixing agent.

[0093] (16) Calculate the sulfur content in the coal blending furnace and add a composite sulfur fixer appropriately. For example, a 3:1 blend of high-sulfur coal with a sulfur content of 4% and low-sulfur coal with a sulfur content of 1% produces a mixed coal with a sulfur content of 3.2%. Adding 15 kg of composite sulfur fixer to each ton of coal with a sulfur content of 3.2% can reduce sulfur dioxide in the flue gas by 60%-85%, equivalent to coal with a sulfur content of 0.48%-1.28%. The blending ratio of high-sulfur coal with a sulfur content of 4% reaches 65%.

[0094] The present invention utilizes the synergistic effect of nano-sulfur fixers, metal compounds, and rare earth element compounds to increase sulfur fixation efficiency by 25% compared to pure calcium oxide addition. This increases the blending ratio of high-sulfur coal, reduces the amount of sulfur fixer used at the same sulfur content, and reduces sulfur dioxide emissions. The blending ratio of high-sulfur coal with a sulfur content of 4% or more can be increased to over 50%.

[0095] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A composite sulfur-fixing agent for coal combustion, characterized in that: Calculated by mass, the components include: 90 to 98 parts of a basic sulfur-fixing agent, 0.5 to 5 parts of a rare earth element compound, and 1 to 5 parts of a metal compound.

2. A coal-fired composite sulfur-fixing agent according to claim 1, characterized in that: The basic sulfur-fixing agent is a mixture of one or more of calcium oxide, barium oxide, magnesium oxide, hydroxide and carbonate.

3. A coal-fired composite sulfur-fixing agent according to claim 1, characterized in that: The rare earth element compound is one or more mixtures of lanthanide oxides or salts.

4. A coal-fired composite sulfur-fixing agent according to claim 1, characterized in that: The metal compound is a mixture of one or more of iron oxide, manganese oxide, nickel oxide, titanium oxide and aluminum oxide.

5. A coal-fired composite sulfur-fixing agent according to claim 1, characterized in that: The basic sulfur-fixing agent is a nano sulfur-fixing agent.

6. A method for preparing the composite coal-fired sulfur-fixing agent according to any one of claims 1 to 5, characterized in that: The following steps are involved: Weigh the basic sulfur-fixing agent, rare earth element compound and metal compound; Divide the weighed basic sulfur-fixing agent into two parts; A basic sulfur-fixing agent is mixed with a rare earth element compound to prepare a mixture A; Another portion of the basic sulfur-fixing agent is mixed with the metal compound to prepare mixture B; The mixture A and the mixture B are mixed and stirred to prepare a composite sulfur-fixing agent.

7. The method for preparing a composite sulfur-fixing agent for coal combustion according to claim 6, characterized in that: In the step of dividing the weighed basic sulfur-fixing agent into two parts, the two parts of the basic sulfur-fixing agent have the same mass, each accounting for half of the mass of the weighed basic sulfur-fixing agent.

8. Use of the coal-fired composite sulfur-fixing agent according to any one of claims 1 to 5 in the combustion of high-sulfur coal, characterized in that: High-sulfur coal and low-sulfur coal are mixed to make mixed coal, and a composite sulfur-fixing agent is added to the mixed coal for combustion.

9. The use of the coal-fired composite sulfur-fixing agent in mixed coal according to claim 8, characterized in that: The added amount of the composite desulfurizing agent accounts for 0.9%-8% of the mass of the entire mixed coal.

10. The use of the coal-fired composite sulfur-fixing agent in mixed coal according to claim 8, characterized in that: The mass ratio of the high-sulfur coal to the low-sulfur coal is 3:(1-3).

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