Microbial gel foam for preventing spontaneous combustion of coal

Abstract

The invention belongs to the technical field of coal mine fire prevention and extinguishing, and particularly relates to microbial gel foam for preventing coal spontaneous combustion. The microbial gel foam is prepared from the following components in percentage by mass: 0.3 to 0.5 percent of composite foaming agent, 0.03 to 0.12 percent of foam stabilizer, 0.2 to 0.6 percent of gelling agent, 0.1 to 0.3 percent of cross-linking agent, 5 to 25 percent of nutrient substance, 5 to 20 percent of activated oxygen-consuming microbial solution and the balance of water. The composite foaming agent is formed by mixing AES and APG, the foam stabilizer is XG, the gelling agent is SA, and the cross-linking agent is CL; the nutrient substance consists of glucose, peptone and yeast extract powder, and the activated oxygen-consuming microorganism solution contains enterobacter and saccharomycetes. According to the microbial gel foam, the concentration of environmental oxygen can be reduced to 5%, the concentration of produced carbon dioxide is as high as 60%, and coal oxygen reaction can be effectively hindered after the gel foam collapses.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mine fire prevention and extinguishing, and particularly relates to a microbial gel foam for preventing and controlling coal spontaneous combustion. Background Art

[0002] As the largest fossil energy source in terms of reserves, coal has always played a vital role in global development. In China, a country rich in coal but poor in oil, coal consumption still accounts for the majority of energy consumption. The rapid development of coal production technology necessitates supporting safety technologies. Mine fires, one of the five major hazards in coal mines, cause significant losses to coal mine production each year. The harmful gases produced by combustion not only endanger worker health but also cause serious environmental pollution. Therefore, the development of effective fire prevention and extinguishing technologies has always been a research priority for scholars both domestically and internationally.

[0003] To address the mechanism of coal spontaneous combustion, technologies such as pressure equalization, leak plugging, grouting, and inert gas injection have been developed. Among these, fire-fighting foams prepared using a foaming agent and an inert gas have gained widespread recognition due to their high volume expansion ratio and simple preparation process. While traditional water-based foams offer the advantage of large volume and easy accumulation, their barrier lifespan is often short. Foam is thermodynamically unstable and therefore cannot survive for long periods of time. Once the foam ruptures, it loses its fire-fighting capabilities. To increase the stability of the foam, some researchers have added thickening macromolecules to the foaming solution, effectively extending the foam's half-life. However, the increased viscosity of the solution leads to a decrease in the foamed volume. Furthermore, the viscous foams with added macromolecules still have poor water retention. To address these shortcomings of water-based foams, researchers have proposed the concept of gel foam. Gel foams are achieved by adding a crosslinking agent to crosslink long-chain macromolecules, gelling the foam. This allows the system to firmly lock in moisture and significantly prolong the foam's stability. Zhang et al. (Zhang L, WuW, Wei J, Bian Y, Luo H. Preparation of foamed gel for preventing spontaneous combustion of coal. Fuel 2021;300:121024. https: / / doi.org / 10.1016 / j.fuel.2021.121024.) prepared a composite foaming system by mixing two foaming agents in a ratio of 1:2. The foam gel prepared had the best effect when the mass fractions of the foaming system and polymer X were 6 g / L and 3 g / L, respectively. Experiments have shown that the inhibitory effect of the gel foam is better than that of traditional halide inhibitors. Shi et al. (Shi Q, Qin B. Experimental research on gel-stabilized foam designed to prevent and control spontaneous combustion of coal. Fuel 2019;254:115558. https: / / doi.org / 10.1016 / j.fuel.2019.05.141.) successfully foamed a foam using a homemade composite foaming agent, thickener, and cross-linker, forming a gel structure in the foam film. Measurements showed that the formation of the gel structure increased the viscosity of the foaming liquid, reduced the foaming properties, but significantly improved the foam stability. Ultimately, the optimal addition range of the thickener was determined to be 3.4-5.5 g / L, and the optimal addition range of the cross-linker was 2.1-4.0 g / L.

[0004] Each type of gel foam currently available can be broadly divided into two components. The first is the foaming component, which provides foaming power and increases solution volume. This component is typically composed of a foaming agent and a foam stabilizer. The foaming agent reduces the surface tension of the solution, allowing it to foam, while the foam stabilizer improves foam stability and prolongs its half-life, ensuring that the foam maintains a large volume during gelation. The other component is the gel component, composed of polymers and crosslinkers. Its primary function is to enhance foam stability. The crosslinker crosslinks the macromolecular polymers to form a three-dimensional network, locking in water and reducing the foam's drainage rate, thereby inhibiting foam decay. Traditional gel foams have successfully addressed the issues of poor foam stability and low water retention. However, the volume of the gel foam produced by this method is primarily dependent on the properties of the foaming agent. The crosslinking of the gel increases the solution viscosity, thereby weakening the foaming power. Furthermore, the gel foam collapses as it loses water. Upon collapse, oxygen re-enters the coal surface, triggering a coal-oxygen reaction and potentially enabling spontaneous combustion. Summary of the Invention

[0005] To address the problems of the prior art, the present invention proposes a novel gel foam preparation method. This method combines aerobic microorganisms with gel foam technology, using the gel foam as a microbial carrier and providing the nutrients necessary for microbial growth and proliferation. By leveraging the oxygen-consuming properties of aerobic microorganisms to produce carbon dioxide, the gel foam is endowed with the ability to control oxygen concentrations in the mine area. This allows the gel foam to retain a certain oxygen-isolating ability even after collapse, hindering coal-oxygen reactions and, consequently, preventing coal spontaneous combustion. This innovative gel foam technology offers a novel approach to future gel foam technology for preventing coal spontaneous combustion.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: A microbial gel foam for preventing and controlling coal spontaneous combustion comprises the following components in mass fractions: 0.3-0.5% composite foaming agent, 0.03-0.12% foam stabilizer, 0.2-0.6% gelling agent, 0.1-0.3% cross-linking agent, 5-25% nutrient substance, 5-20% activated oxygen-consuming microbial solution, and the balance being water.

[0007] Preferably, the composite foaming agent is a mixture of fatty alcohol polyoxyethylene ether sulfate (AES) and alkyl polyglycoside (APG), the foam stabilizer is xanthan gum (XG), the gelling agent is sodium alginate (SA), and the cross-linking agent is calcium lactate (CL).

[0008] Preferably, the nutrients consist of glucose, peptone and yeast extract powder.

[0009] Further preferably, the specific composition of the nutrients includes, by mass fraction: 2-10% glucose, 2-10% peptone and 1-5% yeast extract powder.

[0010] Preferably, the activated aerobic microbial solution contains enterobacteria and yeast.

[0011] Further preferably, the method for preparing the activated aerobic microbial solution comprises the following steps: In step (1), 9 g of activated sludge from a sewage treatment plant was taken and centrifuged at a speed of 12,000 r / min for 10 minutes using a TG18 centrifuge.

[0012] Step (2): After centrifugation, the supernatant was removed and the bottom sediment was inoculated into YPD liquid culture medium at an inoculation rate of 2%. The main components of YPD culture medium were: 20 g / L glucose, 20 g / L peptone, and 10 g / L yeast extract powder.

[0013] Step (3) is to place the inoculated YPD culture medium in a HZQ-X300 constant temperature oscillator and culture at 25°C and 150 rpm for 48 hours to obtain the desired aerobic microbial solution.

[0014] Preferably, the microbial gel foam material is composed of the following components in mass fractions: 0.3-0.5% composite foaming agent, 0.06% foam stabilizer, 0.4-0.45% gelling agent, 0.1% cross-linking agent, 5-25% nutrients, 5-20% activated aerobic microbial solution, and the balance is water.

[0015] Further preferably, the mass ratio of AES to APG in the composite foaming agent is 4:1.

[0016] More preferably, the mass fractions of the following components in the gel foam are: composite foaming agent 0.3%, foam stabilizer 0.06%, gelling agent 0.4%, cross-linking agent 0.1%, activated microbial solution 10%, nutrients 10%, and water 79.14%.

[0017] The method for preparing the microbial gel foam for preventing and controlling coal spontaneous combustion comprises the following steps: Step (1), adding the nutrient substance to deionized water, stirring to fully dissolve it, and dividing the resulting solution into three parts, namely solution 1 with a proportion of 33.3%, solution 2 with a proportion of 44.4%, and solution 3 with a proportion of 22.3%; Step (2), inoculating a portion of the activated aerobic microbial solution into solution 1, and dissolving the composite foaming agent therein to obtain solution A; Step (3), adjusting the stirring rate of the stirrer to fully foam the solution A; Step (4): When the foam is stirred to a dense and uniform size, a foam stabilizer is added to the foam and stirring is continued until a climbing phenomenon occurs; Step (5), dissolving the gelling agent in solution 2 to obtain solution B; Step (6), dissolving the cross-linking agent in solution 3 to obtain solution C; Step (7), adding solution B and solution C successively to the foam described in step (4); Step (8), spraying another portion of the activated aerobic microbial solution on the surface of the foam obtained in step (7).

[0018] Preferably, in step (2), the composite foaming agent is dissolved in solution 1, and the dissolution process is carried out under continuous stirring conditions of 600-700 r / min.

[0019] Preferably, in step (3), the stirring speed is 1300-1500 r / min, and the foaming time is 3-5 min.

[0020] Preferably, after adding the foam stabilizer in step (4), stirring is continued at 1300-1500 r / min for 2-3 min.

[0021] Preferably, in step (5), the gelling agent is dissolved in solution 2, and the dissolution process is carried out under continuous stirring conditions of 600-700 r / min; More preferably, in step (7), solution B is added and stirred for 2 to 3 minutes, and then solution C is added and stirred for 0.5 to 1 minute.

[0022] Further preferably, in step (7), when adding solution B and solution C, stirring is maintained at a speed of 1300-1500 r / min to fully mix the components.

[0023] More preferably, the mass ratio of the activated aerobic microbial solution in step (2) to that in step (8) is 1:1.

[0024] Compared with the prior art, the present invention has the following beneficial effects: Based on the oxygen-consuming characteristics of microorganisms, the present invention loads them into the mine fire prevention and extinguishing material - gel foam, giving the gel foam the ability to consume oxygen and produce carbon dioxide, proposing an innovative microbial gel foam and using it for preventing and controlling coal spontaneous combustion in mine goafs. Nutrients required by microorganisms are added to the gel foam composition to ensure that the microorganisms have the nutritional conditions for survival and proliferation. The combination of alkyl glycosides and fatty alcohol polyoxyethylene ether sulfates gives the microbial gel foam a higher foaming multiple. The cross-linking time of sodium alginate and calcium lactate is controllable, which is more conducive to actual field application. The combination of direct addition and surface spraying of oxygen-consuming microbial solutions ensures that the microorganisms can fully play their role. The microbial gel foam can reduce the ambient oxygen concentration to 5%, and the output carbon dioxide concentration is as high as 60%, which can effectively hinder the coal-oxygen reaction after the gel foam collapses. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a graph showing the changes in oxygen and carbon dioxide in the microbial gel foam gas production experiment of Comparative Example 1; Figure 2 Graph showing oxygen change results in the gas production experiments of the microbial gel foams of Examples 1-4; Figure 3 This is a graph showing the carbon dioxide change results in the gas production experiment of the microbial gel foam of Examples 1-4; Figure 4 Graph showing oxygen change results in the gas production experiments of the microbial gel foams of Examples 1 and 5-7; Figure 5 This is a graph showing the carbon dioxide change results in the gas production experiments of the microbial gel foams of Examples 1 and 5-7. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with specific embodiments. The advantages and features of the present invention will be more clearly reflected in the description. However, the embodiments are merely exemplary and do not limit the scope of the present invention in any way. It should be understood by those skilled in the art that the details and forms of the technical solutions may be modified or replaced without departing from the spirit and scope of the present invention, and such modifications and replacements all fall within the scope of protection of the present invention.

[0027] Example 1 A microbial gel foam material, with excellent water retention, can evenly retain moisture and nutrients, creating conditions for the survival of aerobic microorganisms. It is prepared by combining a foaming agent, a foam stabilizer, a gelling agent, a crosslinking agent, water, and nutrients through physical stirring and foaming, followed by a chemical crosslinking reaction. During the preparation process, an activated aerobic microbial solution is inoculated. The foaming agent consists of fatty alcohol polyoxyethylene ether sulfate and alkyl glycosides, the foam stabilizer is xanthan gum, the gelling agent is sodium alginate, and the crosslinking agent is calcium lactate. The nutrients include glucose, peptone, and yeast extract powder.

[0028] In this example, the masses of the fatty alcohol polyoxyethylene ether sulfate, alkyl glycoside, xanthan gum, sodium alginate, calcium lactate, glucose, peptone, yeast extract powder, activated microbial solution and deionized water used in the preparation of the microbial gel foam material are 0.12 g, 0.03 g, 0.03 g, 0.2 g, 0.05 g, 1 g, 1 g, 0.5 g, 5 g and 42.07 g, respectively, with a total mass of 50 g.

[0029] The preparation method of the microbial gel foam material comprises the following steps: In the first step, 1 g of glucose, 1 g of peptone, and 0.5 g of yeast extract powder were added to 42.07 g of deionized water, stirred thoroughly with a glass rod to dissolve, and then divided into three parts: solution 1 (14.82 g), solution 2 (19.8 g), and solution 3 (9.95 g).

[0030] In the second step, 2.5 g of activated microbial solution was added to solution 1, and then a composite foaming agent composed of fatty alcohol polyoxyethylene ether sulfate and alkyl glycoside was added, and the stirrer speed was adjusted to 650 r / min to stir the solution and dissolve it fully.

[0031] The third step is to adjust the mixer speed to 1500r / min and stir for 3 minutes to make it fully foamed.

[0032] Step 4: After sufficient foaming, add xanthan gum and continue stirring at 1500 r / min for 2 minutes to obtain foam solution A.

[0033] Step 5: Add 0.2 g of sodium alginate to Solution 2, and keep stirring at a stirring rate of 650 r / min during the addition process to completely dissolve the sodium alginate in Solution 2, thereby obtaining a gel solution B.

[0034] Step 6: Add calcium lactate to solution 3 and stir thoroughly with a glass rod to dissolve to obtain cross-linking solution C.

[0035] In step 7, gelling solution B was added to foaming solution A and stirred at 1500 rpm for 2 minutes to thoroughly mix the foaming solution and gelling solution. Crosslinking solution C was then added and stirred at 1500 rpm for 0.5 minutes to obtain a foamed and crosslinked gel foam.

[0036] In the eighth step, 2.5 g of the activated aerobic microbial solution is sprayed on the surface of the gel foam prepared in the seventh step to obtain the final microbial gel foam material.

[0037] The prepared microbial gel foam material is sealed to detect its oxygen consumption and carbon dioxide gas production.

[0038] The microbial gel foam materials of other specifications were prepared using the formula in Table 1 to obtain Examples 2-7. The preparation methods of the microbial gel foam materials of other specifications were all the same as those in Example 1. In addition, the present invention provides the technical solutions of the gel foam materials described in the comparative examples: Comparative Example 1 A primary microbial gel foam for preventing and controlling coal spontaneous combustion comprises the following components, expressed in mass fractions: 2% foaming agent, 2% gelling agent, 2% cross-linking agent, 5% nutrients, and 10% activated microbial solution. The balance is water, for a total mass of 100g.

[0039] The foaming agent is sodium lauryl sulfate, the gelling agent is sodium alginate, and the cross-linking agent is anhydrous calcium chloride.

[0040] Preferably, the nutrients are 2% glucose, 2% peptone and 1% yeast extract powder.

[0041] The method for preparing the primary microbial gel foam for preventing and controlling coal spontaneous combustion comprises the following steps: In the first step, 2 g of glucose, 2 g of peptone, and 1 g of yeast extract powder were added to 79 g of deionized water, stirred thoroughly with a glass rod to dissolve, and then divided into three parts: solution 1 (35 g), solution 2 (35 g), and solution 3 (14 g).

[0042] In the second step, 5 g of activated microbial solution was added to solution 1, followed by 2 g of sodium lauryl sulfate. The stirrer speed was adjusted to 650 r / min, and the solution was stirred to allow it to fully dissolve.

[0043] In the third step, the stirrer speed was adjusted to 1500 r / min and stirred for 3 minutes to fully foam the mixture to obtain solution A.

[0044] Step 4: Add 2 g of sodium alginate to Solution 2, and keep stirring at a stirring rate of 650 r / min during the addition process to completely dissolve the sodium alginate in Solution 2, thereby obtaining a gel solution B.

[0045] Step 5: Add anhydrous calcium chloride to solution 3 and stir thoroughly with a glass rod to dissolve to obtain cross-linking solution C.

[0046] Step 6: Add gelling solution B to foaming solution A and stir at 1500 rpm for 2 minutes to thoroughly mix the foaming solution and gelling solution. Then, add crosslinking solution C and stir at 1500 rpm for 0.5 minutes to obtain a foamed and crosslinked gel foam.

[0047] In the seventh step, 5 g of the activated aerobic microbial solution is sprayed on the surface of the gel foam prepared in the seventh step to obtain a microbial gel foam material.

[0048] The prepared microbial gel foam material was sealed, and the same sealed container was used in Comparative Example 1 and Examples 1 to 7 to detect the oxygen consumption and carbon dioxide gas production.

[0049] Table 1. Mass of each component of microbial gel foam in the examples

[0050] The gas production experiment of microbial gel foam was carried out on the embodiment and the comparative example. The main instrument used was a GC-6900 gas chromatograph. The experimental data results are as follows: Figure 1-5 The gas production test results of Comparative Example 1 using sodium lauryl sulfate as foaming agent, sodium alginate as gelling agent and anhydrous calcium chloride as cross-linking agent are shown as follows. Figure 1 . After the third day of inoculation of microorganisms, the gas content showed significant changes, that is, the microorganisms began to play a role on the third day, and the carbon dioxide percentage reached a maximum around the seventh day and then declined. Figure 2-5Experimental results show that in Examples 1-7, the microorganisms of the present invention can function as early as the first day after inoculation, consuming oxygen and producing carbon dioxide. This effect is significant, effectively advancing the gas production lag phase by 66.7%. The total mass of the materials prepared in Example 1 was 50% of that of the materials in Comparative Example 1, but the carbon dioxide percentage exceeded 40% on the third day and continued to rise, reaching a maximum on the ninth day. Compared to the comparative example, this method can maintain high carbon dioxide concentrations for a longer period using less raw material. When the microbial inoculum size was used as a variable, the overall trend was that the oxygen concentration rapidly decreased and then remained stable, while the carbon dioxide concentration rapidly increased and then remained stable. The microbial inoculum size had little effect on the final gas concentration. When the content of glucose, peptone, and yeast extract was adjusted, the oxygen concentration initially decreased rapidly and then gradually stabilized, while the carbon dioxide concentration rapidly increased and then gradually increased slowly. With 8% as the oxygen concentration cutoff, when the glucose, peptone, and yeast extract content were 2%, 2%, and 1%, respectively, the oxygen concentration ultimately ranged from 8 to 10%. In Examples 5, 6, and 7, the oxygen concentrations were all between 5 and 7, indicating a significant increase in oxygen consumption. In addition, the carbon dioxide output gradually increased with the addition of nutrients, and the carbon dioxide concentration in Example 7 reached a maximum concentration of 64.12% on the ninth day of the experiment.

Claims

1. A microbial gel foam for preventing and controlling coal spontaneous combustion, characterized in that: The composition includes the following components by mass fraction: composite foaming agent 0.3-0.5%, foam stabilizer 0.03-0.12%, gelling agent 0.2-0.6%, cross-linking agent 0.1-0.3%, nutrients 5-25%, activated aerobic microbial solution 5-20%, and the balance is water.

2. The microbial gel foam for preventing and controlling coal spontaneous combustion according to claim 1, characterized in that: The composite foaming agent is composed of a mixture of fatty alcohol polyoxyethylene ether sulfate and alkyl glycoside, the foam stabilizer is xanthan gum, the gelling agent is sodium alginate, and the cross-linking agent is calcium lactate.

3. The microbial gel foam for preventing and controlling coal spontaneous combustion according to claim 1, characterized in that: The nutrients are composed of glucose, peptone and yeast extract powder; preferably, the specific composition of the nutrients includes, by mass fraction: 2-10% glucose, 2-10% peptone and 1-5% yeast extract powder.

4. The microbial gel foam for preventing and controlling coal spontaneous combustion according to claim 1, characterized in that: The activated aerobic microbial solution contains enterobacteria and yeast; Preferably, the method for preparing the activated aerobic microbial solution comprises the following steps: Step (1), take 9 g of activated sludge from a sewage treatment plant and centrifuge it at a speed of 12000 r / min for 10 minutes; Step (2), after centrifugation, the supernatant was removed and the bottom sediment was inoculated into a liquid culture medium at an inoculation rate of 2%. The main components of the culture medium were: 20 g / L glucose, 20 g / L peptone, and 10 g / L yeast extract powder; Step (3), culturing the inoculated culture medium at 25°C and 150 rpm for 48 hours to obtain an activated aerobic microbial solution.

5. The microbial gel foam for preventing and controlling coal spontaneous combustion according to claim 2, characterized in that: The microbial gel foam material is composed of the following components by mass fraction: 0.3-0.5% composite foaming agent, 0.06% foam stabilizer, 0.4-0.45% gelling agent, 0.1% cross-linking agent, 5-25% nutrients, 5-20% activated aerobic microbial solution, and the balance is water; Preferably, the mass ratio of AES to APG in the composite foaming agent is 4:1; Further preferably, the mass fractions of the following components in the gel foam are: composite foaming agent 0.3%, foam stabilizer 0.06%, gelling agent 0.4%, cross-linking agent 0.1%, activated microbial solution 10%, nutrients 10%, and water 79.14%.

6. The method for preparing the microbial gel foam for preventing and controlling coal spontaneous combustion according to claims 1-5, characterized in that: The following steps are involved: Step (1), adding the nutrient substance to deionized water, stirring to fully dissolve it, and dividing the resulting solution into three parts, namely solution 1 with a proportion of 33.3%, solution 2 with a proportion of 44.4%, and solution 3 with a proportion of 22.3%; Step (2), inoculating a portion of the activated aerobic microbial solution into solution 1, and dissolving the composite foaming agent therein to obtain solution A; Step (3), adjusting the stirring rate of the stirrer to fully foam the solution A; Step (4): When the foam is stirred to a dense and uniform size, a foam stabilizer is added to the foam and stirring is continued until a climbing phenomenon occurs; Step (5), dissolving the gelling agent in solution 2 to obtain solution B; Step (6), dissolving the cross-linking agent in solution 3 to obtain solution C; Step (7), adding solution B and solution C successively to the foam described in step (4); Step (8), spraying another portion of the activated aerobic microbial solution on the surface of the foam obtained in step (7).

7. The method for preparing the microbial gel foam for preventing and controlling coal spontaneous combustion according to claim 6, characterized in that: In step (2), the composite foaming agent is dissolved in solution 1, and the dissolution process is carried out under continuous stirring conditions of 600-700 r / min; Preferably, in step (3), the stirring speed is 1300-1500 r / min, and the foaming time is 3-5 min.

8. The method for preparing the microbial gel foam for preventing and controlling coal spontaneous combustion according to claim 6, characterized in that: After adding the foam stabilizer in step (4), continue stirring at 1300-1500 r / min for 2-3 minutes; Preferably, in step (5), the gelling agent is dissolved in solution 2, and the dissolution process is carried out under continuous stirring conditions of 600-700 r / min.

9. The method for preparing the microbial gel foam for preventing and controlling coal spontaneous combustion according to claim 8, characterized in that: In step (7), solution B was added and stirred for 2 to 3 minutes, and then solution C was added and stirred for 0.5 to 1 minute.

10. The method for preparing the microbial gel foam for preventing and controlling coal spontaneous combustion according to claim 8, characterized in that: In step (7), when adding solution B and solution C, stirring is maintained at a speed of 1300-1500 r / min to ensure that the components are fully mixed; Preferably, the mass ratio of the activated aerobic microbial solution in step (2) to that in step (8) is 1:1.

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