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• The effect of CMC addition on bubble size of dust suppression foam was investigated. • Influence of CMC on bubble size distribution and uniformity were quantitatively analyzed. • Mechanism of CMC affecting the morphology of dust-suppression foams was explored. • Reasonable addition concentration of CMC for improving foam performance was suggested. Foam dust suppression is an efficient method to control dust hazards, in which the foam morphology is closely related to its dust-suppression performance. As a commonly used foaming agent auxiliary, water-soluble polymer (e.g. carboxymethyl cellulose) is believed to be able to change foam morphology. To explore the effect of carboxymethyl cellulose (CMC) on the foam morphological characteristics, CMC was added in alpha-olefin sulfonate (AOS) solution at different concentrations and tested for the influence on bubble size, distribution and uniformity of AOS foams. The results showed that both during the foam formation and decay, the average bubble size decreased, and the foam uniformity simultaneously increased with an increase of AOS concentration, and furthermore, the size and uniformity gradually stabilized when the AOS concentration was higher than 0.1 %. After CMC addition, there is an optimal turning point (0.1 % AOS) where the effect of 800 mg/L CMC addition on foam morphology is most pronounced, the average radius of bubbles could reach a minimum of 0.13 mm, and the uniformity reaches the highest. Adding CMC of 800 mg/L in 0.1 % AOS solution is an effective way to optimize the morphology of dust-suppression foam. This study provides important reference for using water-soluble polymer to improve the performance of dust-suppression foam in engineering. [ABSTRACT FROM AUTHOR]

• XG can still significantly improve the performance of dust suppression foam in the solutions with high concentration of inorganic salts. • The appropriate concentration of polymers should be greater than 0.5‰ to enhance the stability of the dust suppression foam. • The principle of improving foam stability with XG in different concentrations of inorganic salt solutions is revealed. Mine dust is a prevalent pollutant generated during the mining process, often leading to explosion accidents and causing pneumoconiosis. Foam dust suppression technology has emerged as a promising method for efficient dust control due to its high-efficiency dust collection and ease of use. However, the application of foam in the field has revealed higher concentrations of inorganic salts in the mine dust suppressants, resulting in suboptimal foaming performance. As a result, additional foaming agent and increased concentration are often required to achieve the desired effect, which escalates the cost of mine dust control. To address this issue, this study proposes optimizing the performance of mine dust suppression foam through the incorporation of polymers with excellent salt resistance. In this investigation, foam liquids comprising xanthan gum (XG) and sodium carboxymethyl cellulose (CMC) were tested using FoamScan to evaluate their foaming performance and foam stabilization at various concentrations of inorganic salt. Additionally, the rheological properties of the foam liquids were analyzed by measuring the viscoelastic modulus using an interfacial rheometer. Experimental results demonstrated that the addition of XG and CMC did not compromise the foaming ability of sodium fatty alcohol polyoxyethylene ether sulfate (AES). Moreover, the liquid-carrying capacity of bubbles, in terms of foam stability, was enhanced. Specifically, the foam stabilization remained relatively stable when the XG concentration exceeded 0.5‰, even under different salt concentrations. Interfacial rheological tests revealed that the addition of XG substantially increased the viscoelastic modulus of the foam liquid. Furthermore, the phase angle remained below 45°, indicating the dominant role of the elastic modulus in the foam liquid, resulting in improved bubble resistance to interference and deformation. This experimental study successfully resolved the issue of poor stability in mine dust suppression foam caused by high salt content during the foam preparation process. The findings can significantly contribute to the widespread adoption and application of dust suppression foam technology in mining operations. [ABSTRACT FROM AUTHOR]

Foam is an effective material for controlling industrial dust. To optimize and upgrade the performance of dust-suppression foam, this paper proposes a method of exposing the foaming agent solution to a magnetic field of specific intensity prior to foaming. The effects of magnetization on foaming capacity, foam stability and foam size were investigated. Two types of foaming agent, anionic and non-ionic, were selected to test the foam expansion (FE) and foaming time (FT), both reflecting the foaming capacity, and foam stability (FS) at different concentrations before and after magnetization. The size of the bubbles, which directly affects the dust suppression performance, was also examined. The experimental results indicated that the foaming capacity and foam stability of the foaming agent solution after magnetization were higher than that of the original solution, and the size distribution of the bubbles has a trend to concentrate towards smaller size ranges. It proves that magnetization can enhance the performance of dust-suppression foam and reduce the quantity of foaming agent. Then we explored the mechanism of the observed experimental phenomena. This study is of significant importance in promoting foam as a more efficient material in dust control. [ABSTRACT FROM AUTHOR]

Mine dust is one of the most serious environmental hazards in the coal mining process. This paper introduces a numerical simulation of a novel foam generator used for dust control in coal mines. The amount of foam generated by this device significantly depends on the amount of air entrainment. Therefore, a computational fluid dynamics (CFD) method was used to study three influencing factors, namely, throat-nozzle distance, mixing throat length, and the contraction angle of the suction chamber. The predicted values by the CFD simulation proved to be in good agreement with the experimental data. The results revealed that the air entrainment reached its maximum when the ratio of throat-nozzle distance to mixing throat length was 2/3. The optimum values of the throat ratio (its length to diameter) and the contraction angle of the suction chamber were obtained at 20 and 5°, respectively. This research provides essential guidance in the geometric parameter design of the self-suction type foam generator, which has the advantage of negating the need for compressed-air pipelines and having high reliability, compared to traditional foam generators. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Foam dust suppression is an important way to control dust hazards. Polymers are believed to be able to change foam properties. To investigate the effect of polymers addition to foaming agent solution on the key dust-suppression performance of the foam, tests were conducted by measuring and comparing the contact angle, viscous modulus and foam-drainage rate of several different surfactant/polymer solutions, which can characterize the wettability, surface viscosity and stability of foam. The results show that the polymer (HEC, HPAM, PVA) addition increased the contact angle between the liquid and coal dust by increasing the surface tension of the surfactant solution. The variation is more obvious with an increase in polymer concentration (especially over 0.3 wt.‰); simultaneously, the polymer increases the surface viscosity of the foaming agent solution significantly, and slows down the foam-drainage rate, which is advantageous for increasing the foam stability. Because of the variation, the low concentration of polymer (0.1–0.3 wt.‰) has a weak influence on the wetting ability of the foaming agent while improves the surface viscosity and stability of foam significantly, which is an improvement in terms of the dust-suppressing ability of foams. [ABSTRACT FROM AUTHOR]

• The interfacial viscoelastic properties of four foaming agents were revealed. • The effect of interfacial viscoelasticity on foaming capacity was investigated. • The relationship between interfacial viscoelasticity and foam stability was obtained. • Specific requirements for properties of dust-suppressing foam were concluded. Foam dust suppression is an effective technique for controlling dust at its source. Dilatational interfacial rheology is an important property of aqueous foam. It characterizes the strength and toughness of liquid film and acts on the foaming process and drainage, affecting foaming capacity (FC) and foam stability (FS). The interfacial viscoelastic properties of anionic and nonionic surfactants commonly used were studied by testing the viscoelastic properties with different foaming agent concentrations (FAC) and their effects on foam performance were investigated. The results show that increasing FAC from 0.1 wt. ‰ to 1.0 wt. ‰ generally decreased the viscoelastic modulus, which was negatively correlated with FC: 6501 had a highly linear relationship between FC and viscoelastic modulus. The viscoelastic modulus of K12 and AES were positively correlated with FC in the low-modulus range, then negatively correlated at higher viscoelastic modulus values; the turning point was defined as the optimal viscoelastic modulus. The viscoelastic modulus had a significant positive effect on FS. The surface viscoelasticity contributed greatly to improving FS before the critical micelle concentration (CMC) was reached. After reaching CMC, micelle properties of bulk phase mainly affected the foam life. [ABSTRACT FROM AUTHOR]

Foamability, liquid holdup, and foam appearance are key factors that determine dust control efficiencies. As the foam production method of the FoamScan instrument is similar to foaming device used for dust control, and its measurement means can satisfy the requirements of precise measuring, the FoamScan technology is adopted to explore the influence of xanthan gum (XG) and partial hydrolytic polyacrylamide (HPAM) on dust-related foam properties of sodium dodecyl benzene sulfonate (SDBS). It was found that with the increase of the polymer mass fraction, the liquid volume in the foam gradually increased. Additionally, the foaming timet200of the foaming agent decreased at first, then remained almost constant for both polymers, which indicated that the foamability and liquid holdup were enhanced by the addition of polymers into SDBS. In addition, the efficiencies of XG are higher than that of HPAM. The image analysis using the CSA software revealed that the mean radius formed by XG was smaller than that by HPAM and the number of bubbles was larger with XG than with HPAM. Thus, the XG foam has more area to contact with dust and could control dust better. The highly branched molecular structure and hydrogen bonds formed by XG played important roles in dust-related foam properties. [ABSTRACT FROM PUBLISHER]

Foamability, foam initial liquid volume, and bubble size of fatty alcohol sodium polyoxyethylene ether sulfate (AES) surfactant solution were studied with and without the addition of sodium carboxymethylcellulose (CMC) at different gas flow rates, using a sparging method. The generation time decreased with increasing gas flow rate. At low gas flow rates, the added CMC greatly enhanced the foamability by preventing bubble collapse. The initial liquid volume of the foam first increased rapidly, and then gradually decreased. Increasing the CMC concentration increased the initial liquid volume of the foam. The mean bubble diameter first clearly decreased, then increased slowly with increasing gas flow rate. CMC showed different effects on bubble size at high and low gas flow rates. Adsorption of CMC on AES molecules forms a network structure and improves bubble film stability, which can explain the above results. These findings provide guidelines for generating foam with excellent properties suitable for coal mine dust control by adjusting the gas flow rate and the concentration of the added water-soluble polymer. [ABSTRACT FROM AUTHOR]

Highlights: [•] An innovative design of foam generator used for dust control was introduced. [•] The main performances of this new foam generator have been investigated. [•] The new foam generator has a strong air self-suction ability of 20–40m3/h. [•] The water flow that this new foam generator requires is as low as 0.4–0.6m3/h. [•] The new foam generator is of convenient operation and low running cost and can control dust effectively. [ABSTRACT FROM AUTHOR]

The cutting dust created by the shearer drum is the main source of dust on a fully mechanized coal face. However, overexposure to respirable dust may cause pneumoconiosis in coal workers, while coal dust may lead to serious explosions. The fully mechanized face known as II1051 Face, found at the Zhuxianzhuang Coal Mine located in east China, generates dust by way of the drum on a high-power shear. The coal seam involves hard rock parting so there is a high concentration of cutting dust when the shearer is working. Thus, we developed a new foam dust suppression method with an air self-suction system based on an analysis of the dust generation characteristics that suppressed the shearer cutting dust level. The new foam system was evaluated in a field test where the dust concentration was measured at two points. The results showed that the foam reduced the cutting dust concentration significantly. The respirable dust exposure levels were reduced from 378.4 mg/m3to 53.5 mg/m3and the visibility was enhanced dramatically. Thus, we conclude that our new foam system is highly efficient at capturing cutting dust, and it has a much lower water consumption. [Supplementary materials are available for this article. Go to the publisher's online edition ofJournal of Occupational and Environmental Hygienefor the following free supplemental resource: Contact angle of cutting dust sample, migration trajectory of cutting dust, technological process for suppressing shearer cutting dust using foam, the layout of the foam dust suppression system on coal face, real object of the air self-suction type foam generator, the special foam nozzle used for shearers, relevant experimental results of the air self-suction foam system.] [ABSTRACT FROM AUTHOR]

Abstract: The greatest source of rock dust on rock roadway heading face is the roadheader. Overexposure to respirable rock dust can be a serious health hazard to roadheader operators and other workers. One of the rock roadways, named North Belt Main Entry (NBME), belonging to the underground coal mine Zhuxianzhuang, located in east China, is being driven by the EBZ318H roadheader. The cross-section of the roadway is 15.84m2, and the heading face has a high concentration of respirable rock dust. This paper presents a study of rock roadheader dust control by foam, taking into account the dust generation characteristics. A new foam preparation system and application method has been proposed and the dust suppression effect of foam has been assessed by dust concentration measurements taken at two points next to the roadheader operator in the previously mentioned underground coal mine. The results have shown that the foam dramatically reduced the rock dust concentrations. The roadheader operator’s respirable dust exposures were lowed from 540.2mg/m3 to 84.3mg/m3, and the dust suppression efficiency reached 84.4% on the NBME heading face. In addition, the visibility and environment of the heading face was significantly improved. It is concluded that the foam showed a significant improvement on the rock dust capture efficiency, and avoided the main deficiencies of conventional water sprays. [Copyright &y& Elsevier]

• The cavitating jet pump is simultaneously used as a mixing device and flow meter. • 3D printed foam nozzle and vertical foam generator are designed and tested. • The proposed system reduced the required water inlet pressure to 0.87 MPa. • Dust is successfully suppressed in tunneling face with high ventilation volume. Due to large energy loss, current foam technology for dust suppression requires high inlet water pressure, but performance is poor where ventilation volume is high. This paper proposes modifying key foam device components, including the agent mixing device, foam generator, and nozzle, to address these problems. A cavitating jet pump was simultaneously employed for accurate agent mixing and flow meter, guaranteeing accurate agent flow and low energy loss. A vertical foam generator was designed to increase foam volume and ensure even foam distribution among the foam nozzles. The two-layered foam nozzles were designed and fabricated using 3D printing to ensure even and thick foam impact area on the dust source, effectively blocking dust escape passages. Experiments were performed in the laboratory and on a real heading face. Ventilation volume was 560–570 m3/min for the field experiment with initial total dust concentration 589–679 mg/m3. The proposed system reduced required inlet water pressure to 0.87 MPa, while achieving 86.8% average total dust suppression efficiency and reducing long-term time average respirable dust concentration to 3.9–5.7 mg/m3. This study will help improve performance and expand application fields for foam dust suppression technology. [ABSTRACT FROM AUTHOR]

Foam technology utilizes the good coverage of foam to form a closed space around dust sources. The foam then wets the dust particles, causing them to adhere before they spread into the air, resulting in better dust control than with water sprays. In the process of foam dust control at a heading face, the foam spray trajectory is highly influenced by the wind, making it difficult to focus foam on the dust sources, which wastes the foam and reduces dust control efficiency. To resolve this problem, the idea of transporting foam to the cutting head through the roadheader’s inner pipeline is proposed. To adapt to the high resistance of foam delivery in the roadheader’s inner pipeline, according to the water and air supply of the heading face, a table water-jet suction device and porous spiral coupling foaming device were designed, and the working conditions were tested using a self-designed experiment system in the laboratory. The results showed that the foaming agent could be automatically added into the device at a working water flow rate of 1–1.6 m 3 /h at a ratio of 1%. The optimum air flow was 45–50 m 3 /h, in which range the foam expansion ratio reached the maximum and the outlet pressure demand was satisfied. Field application showed that the new foam method had a better dust control efficiencies than traditional foam methods. [ABSTRACT FROM AUTHOR]

[Display omitted] • Both WL and CBM increase the surface tension slightly at high AOS concentrations. • Foamability is improved after adding WL and CBM at low AOS concentrations. • WL and CBM can enlarge the bubble size of AOS foam. • The addition of WL and CBM prolongs the wetting time of coal dust. • The optimized foaming agent is obtained at 0.2 wt% AOS and 0.1 wt% polymer. Using foam to reduce coal dust is one of the effective means to control coal dust pollution. In this work, the solution and foam properties of foaming agents consisting of sodium alpha-olefin sulfonate (AOS), welan gum (WL) and carbomer (CBM) were investigated, the wetting ability of the composite system on coal dust was compared, and the adsorption mechanism among AOS, WL and CBM was analyzed. The results show that with the increase of AOS concentration, the viscosity of AOS/WL solutions decreases gradually and then becomes stable, while the viscosity of AOS/CBM solutions displays an opposite trend. The addition of WL and CBM promotes foam production at low AOS concentrations but inhibits it at high concentrations. Both WL and CBM can improve the liquid volume and half-life time of foam drainage of AOS solutions. The WL molecules spontaneously form a zipper network structure, making the foam liquid film significantly thicker and slightly enlarging the bubble size. The addition of CBM can form a viscoelastic surface layer on the Plateau borders, making foam less permeable and delaying the bubble Ostwald ripening. The wetting time of coal dust is extended after adding WL and CBM. These results can provide theoretical guidance for the formula study of foaming agents for coal dust suppression. [ABSTRACT FROM AUTHOR]

The influence of vertical channel with various structure factors (α) on downward flame spread over extruded polystyrene (XPS) foam is investigated. The flame shape, flame height (H f), temperature in the channel (T v) and on the curtain wall surface (T c), flame spread rate (V f), and induced air flow (Q) are obtained. H f first drops and then increases as α rises, attributing to similar changing trends of induced airflow rate and Froude number. Concerning the temperature history, T c > T v at the initial stage while T c < T v at the middle stage. Both T c ‾ (average value) and T v ‾ drop as α rises, and T v ‾ > T c ‾ under most conditions. A model is established to predict the total, convective and radiative heat fluxes transferred to preheating zone. The convective heat flux is more dominant than the radiative heat feedback from the curtain wall. V f first rises and then drops as α increases. For α < 1.0, the oxygen supply determines the changing trend of V f , while the total heat transfer is dominant for 1.0< α < 2.0. Predicted results using the model built in this work indicate that Q increases as α rises, which corresponds to experimental results. • Flame height first drops and then increases as structure factor (α) rises. • Channel temperature and curtain wall surface temperature drop as α rises. • A model is built to predict heat fluxes transferred to preheating zone. • Downward flame spread rate first rises and then drops as α rises. • A model is built to predict induced air flow, which increases as α rises. [ABSTRACT FROM AUTHOR]