Flame Propagation Behavior And Inerting Suppression Characteristics Of Starch Dust Deflagration In Pipeline

Dust explosion disasters are always the key issue that restricts the safety of industrial production processes.Effective prevention and control techniques have important practical significance for reducing the probability of accidents and reducing the effects of dust explosions.Inerting technology is a safety protection method that conforms to the principle of mitigation in the principle of intrinsic safety.It prevents the occurrence of dust explosion accidents by introducing inert gas or adding inert powders to the production equipment or system.However,due to the complexity of the dust explosion mechanism,the study of inerting suppression for the disaster process is affected by many factors,especially the microscopic evolution process of dust explosion flame and its propagation control mechanism under inertization mode needs further research.Based on this,starch dust is used as the research object of industrial organic dust.Two kinds of inert media,nitrogen and ultrafine Mg（OH）₂ powders,are used as dust explosion-proof inerting agent to study starch dust in gas phase/solid phase inertization mode.The kinetics of pyrolysis combustion and the dynamic process of deflagration flame propagation in confined space are studied.A physical model of flame propagation is established to introduce characteristic parameters to characterize the process of inerting suppression,and explore the inerting suppression mechanism of dust explosion flame propagation.Based on the theory of thermal analysis kinetics,a comprehensive thermal analysis experimental platform was used to systematically study the pyrolysis combustion behavior of starch dust under two inerting modes of nitrogen and ultrafine Mg（OH）₂ powders.It is found that the decrease of oxygen concentration causes the rate of dust thermal weight loss to decrease and the pyrolysis process to slow down.At the same time,the combustion exothermic process overcomes the increase of resistance and the difficulty of pyrolysis increases.Ultrafine Mg（OH）₂ powders accelerates the thermal decomposition process of starch dust,but it has an inerting inhibition effect on the overall pyrolysis combustion reaction process.The combustion reaction kinetic parameters and the most probable mechanism function under inerting conditions were obtained by using the Malek-Achar method.In addition,the release law of the main pyrolysis gas phase products of dust under two inertization modes was studied by combining the thermogravimetry-mass spectrometry technique.It was found that during the inerting of nitrogen,the escape amount of CO and H₂ increased with the increase of the inerting ratio and H₂O,CO₂ and CH₄ emissions are reduced.The combustion reaction process of dust pyrolysis gas phase products is inhibited by lack of oxygen.Ultrafine Mg（OH）₂ particles thermally interpret the crystallization water,increase the amount of H₂O in the pyrolysis gas phase product of the starch,and dilute and cool the combustion process of the starch flammable gas phase product,resulting in dust combustion and heat release.The chemical reaction process is blocked.Building the dust cloud explosion flame propagation experimental platform,the high-speed photography technology and thermal disaster diagnosis technology are combined to study the process of explosion flame propagation in the pipeline under inerting.The suppression behaviors of flame propagation behavior,flame microstructure,flame propagation velocity,flame temperature and detonation wave pressure were obtained.The results show that the nitrogen inerting environment increases the fuel-oxygen equivalent ratio in the combustion system,which leads to the suppression of the accelerated flame propagation process under the inerting of nitrogen.The flame propagation velocity decreases continuously with the decrease of the inerting oxygen concentration.The flame front structure is affected by diffusion-heat instability and exhibits chaotic irregular patterns in the early stages of propagation.The flame temperature is greatly attenuated by the combination of inerting oxygen concentration and dust cloud concentration.The detonation effect of the flame deflagration wave is weakened,and the oxygen concentration is lower than 15%,which can effectively suppress the starch deflagration flame by inerting nitrogen.Under the inerting of ultrafine Mg（OH）₂,the agglomeration effect of the dust cloud is aggravated,and the ignition and ignition process of the dust cloud is blocked.A small amount of Mg（OH）₂ powders will increase the disturbance of the flame front,causing the wrinkle deformation of the flame structure,causing local intense combustion and enhancing the damage effect.The flame propagation velocity is affected by the ultrafine Mg（OH）₂pyrolysis process,showing obvious pulsation propagation phenomenon,and the pulsation degree becomes larger with the increase of Mg（OH）₂ content.The dust cloud concentration increases,and the maximum flame temperature first increases and then decreases and moves toward the low dust cloud concentration.The inerting ratio is greater than 10%by weight,the flame propagation process is limited,and the inerting suppression effect appears.A physical model of detonation flame propagation under two gas phase/solid phase inertization modes based on flame temperature characteristics and ion current characteristics was established.The flame front propagation structure is subdivided into an unburned zone,a preheating zone,a combustion reaction zone,and a rear flame zone.Both inerting modes cause a reduction in the thickness of the preheating zone compared to the non-inertized propagation process.For the combustion reaction zone,the gas phase inertization process leads to thickening of the flame combustion reaction zone,and the structure of the flame combustion reaction zone in the solid phase inertization mode is complicated,and is composed of a plurality of agglomerated dust flame small reaction zone structures.Based on the comprehensive experimental analysis,the theoretical analysis of the inerting inhibition behavior of the starch deflagration flame propagation process was carried out.The control mechanism of the deflagration flame propagation in the gas phase inertization process is analyzed by introducing the dimensionless number of features Bi,Da and Pc.It is found that under the action of gas phase inertization,the heat extraction process and the volatile heat analysis process of dust particles are mainly controlled by the external heat transfer of dust（Bi<1 and Da>1）.The flame propagation process is controlled by the volatile heat of the dust particles（Pc>1）,and the oxygen concentration is reduced,which causes the heat transfer of the external heat source to enhance the control of the dust pyrolysis process.The dust volatile heat analysis process is limited,thus achieving the suppression of the flame propagation process by the gas phase inerting mode.Characterization of inerting process of solid phase powders by dust flame burning rate S_u.The heat dissipation effect of inert solid phase particles destroys the heat balance process of combustion,and the flame burning rate Su is attenuated.The inerting ratio of ultrafine Mg（OH）2 increases,the attenuation of Su increases,and the flame propagation process shifts to flameout.