Coal flame retardant based on calcium salt substances

Abstract

The invention discloses a coal flame retardant based on calcium salt substances, which consists of the following components in percentage by weight: 50-90% of a main flame retardant which is one or more calcium salt substances; 5%-30% of a catalytic synergist which is a metal oxide or hydroxide; the surfactant is used for improving the wettability and adhesiveness of the flame retardant on the surface of coal; and the balance of a filler. According to the coal flame retardant based on the calcium salt substances, the characteristic that calcium salt (such as calcium carbonate and calcium hydroxide) is decomposed and releases carbon dioxide and water when heated is utilized, the oxygen concentration on the surface of coal can be effectively reduced, a large amount of heat is absorbed, and therefore the oxidation process of coal is efficiently inhibited from the two aspects of the gaseous state and the heat source.

Description

Technical Field

[0001] This invention relates to the field of flame retardant technology, and more specifically to coal flame retardants based on calcium salts. Background Technology

[0002] During storage and transportation, coal is prone to oxidation and exothermic reactions when it comes into contact with air, which can lead to increased temperature and spontaneous combustion, resulting in huge waste of resources and safety hazards.

[0003] Currently, commonly used coal flame retardants mainly include halogenated, phosphorus-based, and nitrogen-based compounds. However, halogenated flame retardants may release toxic gases at high temperatures, posing environmental and health risks; phosphorus-based and nitrogen-based flame retardants may have problems such as high cost, limited flame retardant efficiency, or impact on coal quality. Therefore, developing a highly efficient, environmentally friendly, low-cost flame retardant with minimal impact on subsequent coal utilization has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] Therefore, this invention provides a coal flame retardant based on calcium salts to address the problems of existing halogen-based flame retardants potentially releasing toxic gases at high temperatures, posing environmental and health risks; and phosphorus-based and nitrogen-based flame retardants potentially having high costs, limited flame retardant efficiency, or impacting coal quality.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] Coal flame retardants based on calcium salts consist of the following components by weight percentage:

[0007] The main flame retardant is 50%-90%, which is one or more calcium salt substances;

[0008] Catalytic synergists, 5%-30%, are metal oxides or hydroxides;

[0009] Surfactants of 1%-10% are used to improve the wettability and adhesion of flame retardants on the coal surface;

[0010] And the remaining filler.

[0011] Preferably, the calcium salt in the main flame retardant is selected from at least one of calcium carbonate, calcium hydroxide, calcium chloride, and calcium nitrate, and its particle size distribution is 200 mesh to 800 mesh; the catalytic synergist is selected from at least one of zinc oxide, magnesium hydroxide, and ferric oxide; the surfactant is at least one of sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether; and the filler is inert diatomaceous earth or bentonite.

[0012] Preferably, the main flame retardant is a compound mixture of nano-sized calcium carbonate and micron-sized calcium hydroxide, wherein the weight of nano-sized calcium carbonate accounts for 10%-40% of the total weight of the main flame retardant, and the weight of micron-sized calcium hydroxide accounts for 60%-90%; the catalytic synergist is a mixture of nano-sized zinc oxide and micron-sized magnesium hydroxide, wherein the weight of nano-sized zinc oxide accounts for 20%-50% of the total weight of the catalytic synergist.

[0013] Preferably, the method for preparing the flame retardant includes the following steps:

[0014] The first step is to premix the nano-sized calcium carbonate and micron-sized calcium hydroxide in the main flame retardant at room temperature for 15-30 minutes in a high-speed mixer to make them initially dispersed evenly and form a basic powder.

[0015] The second step involves activating the nano-zinc oxide and micron-sized magnesium hydroxide in the catalytic synergist by dry grinding in another container for 20-40 minutes.

[0016] The third step is to slowly add the activated catalytic synergist powder into the base powder in the high-speed mixer and continue mixing at a speed of 300-500 rpm for 40-60 minutes to ensure that the catalytic synergist is evenly coated or embedded on the surface of the main flame retardant particles to form a composite flame retardant base material.

[0017] The fourth step is to dissolve the surfactant in an appropriate amount of deionized water to prepare an aqueous solution with a concentration of 5%-15%. The aqueous solution is then slowly sprayed into the composite flame retardant base material under stirring using a spraying device to uniformly wet the powder surface.

[0018] Fifth step: Add the filler and transfer the entire system into a vacuum drying oven. Dry at 60℃-80℃ for 2-4 hours to remove excess moisture. Then, pulverize the powdered coal flame retardant product through a pulverizer until it passes through a 400-mesh sieve.

[0019] Preferably, it further comprises 0.5%-5% of an antioxidant by weight of the total flame retardant, wherein the antioxidant is hindered phenolic antioxidant 1010 or phosphite antioxidant 168.

[0020] Preferably, the flame retardant can be prepared into a suspension with water at a weight ratio of 1:5 to 1:20 and applied to the coal surface by spraying, soaking or brushing.

[0021] The present invention has the following advantages: The coal flame retardant based on calcium salts provided by the present invention utilizes the property that calcium salts (such as calcium carbonate, calcium hydroxide, etc.) decompose and release carbon dioxide and water when heated, which can effectively dilute the oxygen concentration on the surface of coal and absorb a large amount of heat, thereby efficiently inhibiting the oxidation process of coal from both gaseous and heat source aspects.

[0022] Meanwhile, the calcium oxide generated after decomposition can firmly cover the surface of coal particles, forming a dense physical barrier layer that prevents oxygen from further contacting the coal matrix.

[0023] Compared with traditional flame retardants, the flame retardant of the present invention has a wide range of raw material sources, low price, environmental friendliness and no toxic side effects, and its decomposition products do not have a significant negative impact on the calorific value of coal and subsequent processing (such as coking and gasification), showing excellent comprehensive application prospects. Detailed Implementation

[0024] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. It should be understood that these embodiments are merely for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Technical engineers in the field can make some non-essential improvements and adjustments to the present invention based on the above-described content. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The coal flame retardant based on calcium salts comprises the following components by weight percentage: 50%-90% main flame retardant, which is one or more calcium salts; 5%-30% catalytic synergist, which is a metal oxide or hydroxide that can promote the thermal decomposition of calcium salts or produce a synergistic flame retardant effect with calcium salts; 1%-10% surfactant, used to improve the wettability and adhesion of the flame retardant on the coal surface; and the balance being a filler; wherein the calcium salt in the main flame retardant is selected from at least one of calcium carbonate, calcium hydroxide, calcium chloride, and calcium nitrate, and its particle size distribution is 200 mesh to 800 mesh to ensure good dispersibility and coverage among coal powder particles; the catalytic synergist... The synergist is selected from at least one of zinc oxide, magnesium hydroxide, and ferric oxide. It interacts with the main flame retardant under heating conditions, reducing the decomposition temperature of the main flame retardant and generating a more stable composite metal oxide coating layer, thereby enhancing the durability of the flame retardant effect. The surfactant is an anionic or nonionic surfactant, specifically selected from at least one of sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether, used to reduce the surface tension of the flame retardant aqueous solution, enabling it to quickly penetrate and spread on the hydrophobic coal surface. The filler is inert diatomaceous earth or bentonite, used to adjust the overall viscosity of the flame retardant and prevent the components from clumping during storage.

[0026] When flame retardants are applied to the surface of coal, their main flame retardant (calcium salt) forms the first line of defense. Micron-sized particles can extensively cover the surface of coal particles, forming an initial physical barrier that effectively isolates the coal from oxygen, thereby delaying the initiation of the oxidation reaction.

[0027] Subsequently, when the ambient temperature rises or the coal begins to oxidize and release heat, the flame retardant enters the active chemical flame retardant stage. Thermally unstable calcium salts (such as calcium hydroxide) decompose first, absorbing a large amount of ambient heat, effectively "physically cooling" the coal and directly weakening the energy source required for the oxidation reaction. Next, salts such as calcium carbonate decompose at even higher temperatures, releasing non-flammable carbon dioxide gas. This gas rapidly dilutes and disperses the oxygen concentration in the coal's pores and surface, effectively eliminating the necessary conditions for combustion in the gaseous environment. This combined heat absorption and gas release process constitutes the second layer of highly efficient flame retardancy.

[0028] Finally, catalytic synergists play a crucial "synergist" role in this process. They not only promote the decomposition of the main flame retardant at lower temperatures, activating the flame-retardant mechanism earlier, but also react further with the decomposition products of calcium salts to generate a denser and more stable composite metal oxide coating. This coating can be firmly sintered onto the surface of coal particles, significantly enhancing the durability and high-temperature resistance of the flame-retardant layer, thus achieving a sustained flame-retardant effect. Simultaneously, surfactants improve the wetting and penetration properties of the agent, ensuring that all the aforementioned active ingredients can adhere uniformly and firmly to the hydrophobic coal surface; while fillers guarantee the overall stability and application performance of the agent. This multi-component, multi-mechanism synergistic design collectively endows the flame retardant with efficient, durable, and environmentally friendly performance.

[0029] The main flame retardant is a compound mixture of nano-sized calcium carbonate and micron-sized calcium hydroxide, wherein the weight of nano-sized calcium carbonate accounts for 10%-40% of the total weight of the main flame retardant, and the weight of micron-sized calcium hydroxide accounts for 60%-90%; the catalytic synergist is a mixture of nano-sized zinc oxide and micron-sized magnesium hydroxide, wherein the weight of nano-sized zinc oxide accounts for 20%-50% of the total weight of the catalytic synergist.

[0030] In some embodiments, 30% by weight of nano-calcium carbonate (particle size approximately 50 nm) and 70% by weight of micron-sized calcium hydroxide (particle size approximately 800 mesh) are mixed. In the catalytic synergist, 40% by weight of nano-zinc oxide (particle size 30-50 nm) and 60% by weight of micron-sized magnesium hydroxide (particle size approximately 1250 mesh) are combined. When this optimized flame retardant is applied to high-volatile bituminous coal, its flame retardant efficiency is significantly improved compared to flame retardants using a single-particle-size calcium salt.

[0031] The method for preparing the flame retardant includes the following steps: First, premixing nano-sized calcium carbonate and micron-sized calcium hydroxide in the main flame retardant at room temperature for 15-30 minutes in a high-speed mixer to achieve initial uniform dispersion and form a basic powder; Second, activating nano-sized zinc oxide and micron-sized magnesium hydroxide in the catalytic synergist by dry grinding in another container for 20-40 minutes; Third, slowly adding the activated catalytic synergist powder to the basic powder in the high-speed mixer and continuously mixing at a speed of 300-500 rpm for 40-60 minutes. The process involves several steps: First, ensuring that the catalytic synergist is uniformly coated or embedded on the surface of the main flame retardant particles to form a composite flame retardant base material. Second, dissolving the surfactant in an appropriate amount of deionized water to prepare a 5%-15% aqueous solution, and then slowly spraying this aqueous solution into the composite flame retardant base material while stirring, so that the powder surface is uniformly wetted. Third, adding the filler and transferring the entire system into a vacuum drying oven, drying at 60℃-80℃ for 2-4 hours to remove excess moisture, and then pulverizing it through a pulverizer until it passes through a 400-mesh sieve to obtain the final powdered coal flame retardant product.

[0032] It also contains 0.5%-5% antioxidant by weight of the total flame retardant, wherein the antioxidant is hindered phenolic antioxidant 1010 or phosphite antioxidant 168, which is used to further delay the initial oxidation rate of coal under the flame retardant coating.

[0033] The spontaneous combustion of coal begins with the reaction of its internal active groups with oxygen, generating peroxide free radicals—an autocatalytic process. Although the main flame retardant can physically isolate oxygen, the oxidation reaction may still slowly initiate in microscopic areas where the flame retardant coverage is incomplete or defective. In this case, added hindered phenolic (e.g., 1010) or phosphite (e.g., 168) antioxidants play a crucial role. They act as hydrogen donors, effectively capturing and eliminating these initial free radicals, interrupting the chain reaction, essentially setting up a "chemical barrier" on the chemical pathway of coal oxidation and spontaneous combustion. This complements the physical isolation, heat absorption, and gas-phase dilution mechanisms of the main flame retardant, creating a comprehensive flame retardant system that works on both physical and chemical levels. This system is particularly suitable for coal varieties that are extremely sensitive to oxidation or require long-term storage.

[0034] When used, the flame retardant can be mixed with water at a weight ratio of 1:5 to 1:20 to form a suspension, which is then applied to the coal surface by spraying, soaking, or brushing. Preparing the powdered flame retardant into a suspension first solves the dust pollution problem that may arise from dry powder spraying, thus improving the working environment. More importantly, water, as a carrier, can significantly enhance the spreading, wetting, and penetration ability of the flame retardant on the hydrophobic coal surface with the help of surfactants.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. Coal flame retardant based on calcium salt substances, characterized in that, consists of the following components by weight percentage: 50%-90% of a main flame retardant, which is one or more calcium salt substances; 5%-30% of a catalytic synergist, which is a metal oxide or hydroxide; 1%-10% of a surfactant for improving the wettability and adhesion of the flame retardant on the surface of coal; and the balance of a filler.

2. The calcium salt-based coal flame retardant according to claim 1, characterized by, The calcium salt substance in the main flame retardant is selected from at least one of calcium carbonate, calcium hydroxide, calcium chloride, and calcium nitrate, and has a particle size distribution of 200-800 mesh; the catalytic synergist is selected from at least one of zinc oxide, magnesium hydroxide, and diiron trioxide; the surfactant is at least one of sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether; and the filler is inert diatomite or bentonite.

3. The calcium salt-based coal flame retardant according to claim 2, characterized by, The main flame retardant is a compounded mixture of nano calcium carbonate and micron calcium hydroxide, wherein the weight percentage of nano calcium carbonate in the total weight of the main flame retardant is 10%-40%, and the weight percentage of micron calcium hydroxide is 60%-90%; and the catalytic synergist is a mixture of nano zinc oxide and micron magnesium hydroxide, wherein the weight percentage of nano zinc oxide in the total weight of the catalytic synergist is 20%-50%.

4. The calcium salt-based coal flame retardant according to claim 3, characterized by Preparation method of the flame retardant comprising the following steps: In a first step, nano calcium carbonate and micron calcium hydroxide in the main flame retardant are premixed in a high-speed mixer at room temperature for 15-30 minutes to preliminarily disperse uniformly and form a base powder; In a second step, nano zinc oxide and micron magnesium hydroxide in the catalytic synergist are activated by dry grinding in another container for 20-40 minutes; In a third step, the activated catalytic synergist powder is slowly added to the base powder in the high-speed mixer, and the mixture is continuously mixed at a speed of 300-500 rpm for 40-60 minutes to ensure that the catalytic synergist is uniformly coated or embedded on the surface of the main flame retardant particles, forming a composite flame retardant base; In a fourth step, the surfactant is dissolved in a proper amount of deionized water to prepare an aqueous solution with a concentration of 5%-15%, and the aqueous solution is slowly sprayed into the composite flame retardant base under stirring to uniformly wet the surface of the powder; In a fifth step, the filler is added, and the whole system is transferred into a vacuum drying oven, dried at 60-80°C for 2-4 hours to remove excess water, and then crushed by a crusher to pass through a 400-mesh sieve to obtain the final powdered coal flame retardant product.

5. The calcium salt-based coal flame retardant according to claim 3, characterized by, The flame retardant further comprises 0.5%-5% of an antioxidant based on the total weight of the flame retardant, and the antioxidant is hindered phenolic antioxidant 1010 or phosphite antioxidant 168.

6. The calcium salt-based coal flame retardant according to claim 2, characterized by, The flame retardant can be prepared into a suspension in a ratio of 1:5-1:20 by weight when used, and applied to the surface of coal by spraying, soaking, or brushing.