Inhibition of diammonium phosphate on the wheat dust explosion
Graphical abstract
Introduction
The main component of wheat, corn and potato is starch which is applied in many industrial fields such as medicine, food, papermaking and textile [1]. During starch processing, the dust particles in the air are usually removed by dust-cleaning apparatus. Once the dust concentration in the apparatus exceeds the lower limit of explosion, serious explosion accidents will occur [[2], [3], [4]], which poses great threats to industrial safety [[5], [6], [7], [8],49].
Dust explosion intensity was affected by multiple factors, such as particle parameter (size distribution, heat transfer, and material feature), external loads and initial conditions [[9], [10], [11], [12], [13], [14], [15]]. Based on these characteristics, many methods were brought out to inhibit the dust explosion. It is found that water mist, inert powder and gas were widely studied due to the efficient inhibiting effect. The main mechanisms for inert material addition are the significant reduction of oxygen concentration and obvious heat loss. Some solid powders can also form a protective barrier on the particle surface to increase the destruction of free radicals during dust combustion so that they are popular with many scholars. Anne et al. [16] found that the addition of fine MgO powder completely inhibited the explosion of AlMg mixed dust (50:50) with 70–75%. Bu et al. [17] selected four kinds of Al2O3 powder in the experiments of aluminum dust explosion and found that the nano-Al2O3 powder shown the best inhibition effect due to the agglomerating phenomenon in the surface of aluminum dust. Jiang et al. [[18], [19], [20], [21], [22]] investigated the effects of ammonium dihydrogen phosphate, sodium bicarbonate, ABC powder, melamine cyanurate and melamine polyphosphate addition on the aluminum dust explosion. The results showed that the explosive power of aluminum dust was effectively weakened so that the flame temperature and velocity were significantly reduced. Meanwhile, Chen et al. [23] found that NaHCO3 powder also contributes to the inhibition of aluminum dust explosion with a certain amount.
Besides the explosion of metal dust, the organic dust also attracted widespread attention. Scholars have carried on many experiments towards the inherent reactions due to the complexity of organic dust explosion. Huang et al. [24][48] compared the effect of micron and nanometer Mg(OH)2 on wood dust explosion. They found the inhibition of nanometer powder showed better than that of micron powder. Yu et al. [25] experimentally studied the acrylates copolymer dust explosion with the addition of ammonium polyphosphate which showed a significant inhibition effect. Coal dust, as a typical organic material, mainly comes from the coal mining and processing, which often results in explosion accidents. Yu et al. [26] found the fly ash after coal combustion showed a inhibition effect on the coal dust explosion. In addition, the inhibition effect can be greatly increased by the chemical modification [27].
Wheat dust as a typical component dust can also result in serious explosion accidents during its processing. With the rapid development of starch industry, the safety technologies of starch processing become more and more important. Diammonium phosphate ((NH4)2HPO4) is a white powder with transparent monoclinic crystal, which is usually used to many feed or food industry as an additive. However, (NH4)2HPO4 also shows a good performance of fire extinguishing so that it was adopted to inhibit the explosion of starch dust in this paper. A experimental vertical pipeline was built to study the wheat dust with different particle sizes. And the flame propagation velocity, temperature and explosion residues were analyzed to show the inhibiting mechanism of (NH4)2HPO4 which is important to the practical application.
Section snippets
Experimental apparatus
Fig. 1 shows the experimental apparatus of dust explosion. The main space of flame propagation is a rectangular tube with the cross section of 80 × 80 mm and height of 1500 mm. Two opposite sides of the tube are quartz glass to observe the images of flame propagation, and the other sides are stainless steel plates with high pressure resistance. Meanwhile, the ion probes and micro-thermocouples were arranged in the sides of steel plates. In order to improve the measuring accuracy, the R-type
Flame propagation behavior
Fig. 6 shows the flame propagation images of 200 mesh wheat dust with the addition of (NH4)2HPO4. It can be found that the dust flame front becomes irregular and non-uniform with dim brightness due to the inhibition effect of (NH4)2HPO4. And as the mass fraction increases, the inhibition to the dust flame was enhanced. Besides the flame with (NH4)2HPO4, the fault phenomenon appeared in some dust flames without (NH4)2HPO4, which are mainly caused by the gravity effect of particles with large
Conclusions
A vertical pipeline was built to study the wheat dust explosion in this paper. The (NH4)2HPO4 with different mass fractions were added to investigate the inhibition on wheat dust flame propagation. The main conclusions are as follows.
- 1)
(NH4)2HPO4 causes some phenomena in wheat dust flame propagation behavior, such as the irregular flame front, the obvious flame fault, and the delayed ignition time. In the dust combustion zone, the releasing and consumption of intermediate ions were greatly
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors wish to acknowledge the support to this work by the National Key Research and Development Program of China (No. 2018YFC0808500), the National Natural Science Foundation of China (No. 51804237 and No. 51774221), the Natural Science Foundation of Hubei Province of China (No. 2018CFB207), and the Fundamental Research Funds for the Central Universities (WUT: 2019IVB035).
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