Experimental Study On Spontaneous Combustion Characteristics Of Typical Biomass Materials And Its Suppression By Chemical Inhibitors

Biomass materials are an important renewable energy source that humans rely on in the process of development.In view of this,this paper studies the spontaneous combustion characteristics of typical biomass pine,and proposes a new method for evaluating the tendency of biomass to spontaneous combustion.In order to prevent biomass spontaneous combustion efficiently,chemical reagents were used to inhibit spontaneous combustion of biomass to study its flame retardancy at low temperature and high temperature,and compares and analyzes the inhibition effect based on characteristic temperature points,thermal weight loss,exothermic characteristics and activation energy.Based on the change law of active groups,the flame-retardant mechanism of various chemical reagents was explored.A simulation test was carried out to verify the feasibility and effect of material gas in the neighborhood of biomass fuel fire extinguishing.The results of temperature-programmed oxidation experiments show that the CO generation law is related to the temperature of the sample.Between 40-90°C,the CO concentration curve of each sample basically does not change,indicating that the biomass samples produce little CO gas at this temperature section.Between 90-200℃,the CO concentration increases with temperature,and all show exponential function growth.According to the oxidation kinetics reaction equation,with the easy spontaneously combustible material hemp silk as the judgment index,and the low-temperature oxidation apparent activation energy of biomass as the spontaneous combustion tendency index:E<70 is easy spontaneous combustion;70≤E≤80 is spontaneous combustion;E>80 is not easy to ignite spontaneously.The results of adiabatic oxidation experiments show that changes in particle size（0.18-4.00mm）,water content（1%-30%）and ventilation rate（80-160 ml/min）all affect the biomass oxidation heating process.Among them,biomass with smaller particle size and lower water content oxidizes faster,which means that the possibility of spontaneous combustion is higher.In addition,the lower ventilation rate only promotes the spontaneous combustion of biomass in the low temperature stage（<70°C）.The analysis of oxidation characteristics shows that the 12 selected chemical reagents all have an inhibitory effect on the spontaneous combustion process of biomass.However,in different oxidation reaction stages,the inhibitory effect of each reagent is different,which is mainly reflected in the deviation of the characteristic temperature point and the decrease of weight loss.Meanwhile,chemical reagents inhibit the exothermic heat during the spontaneous combustion of biomass,causing some samples to maintain resistance at high temperatures,which is not conducive to the subsequent combustion process,such as C₆H₁₈O₂₄P₆,C₁₈H₂₂N₂,Na H₂PO₂and Na H₂PO₄.Based on the calculation results of oxidation kinetics,chemical reagents increase the energy required for the internal oxidation reaction of biomass,especially in the slow oxidation reaction stage at 40-200°C.Comprehensive evaluation,chemical reagents such as Ca Cl₂,Mg Cl₂,C₆H₈O₇and Na₃PO₄ are more suitable for field application as inhibitors.The results of Fourier transform infrared spectroscopy showed that the use of chemical inhibitors significantly reduced the content of key active groups such as C-O,C=O,C-H,and-OH,thereby inhibiting the biomass and oxygen reaction process.Based on the variation of functional groups,it can be inferred that the chemical flame-retardant mechanism of biomass mainly includes:changing the reaction pathway to reduce the production of volatile substances;forming precipitation with active metal ions to weaken the oxidation of metal ions.The results of physical simulation fire extinguishing experiments show that the fire extinguishing efficiency of nitrogen/liquid nitrogen,carbon dioxide and heptafluoropropane is better than self-extinguishing fire extinguishing.When the biomass is smoldering,heptafluoropropane can reduce the temperature（>300°C）to 46.9°C within 5.5 minutes,and the fire extinguishing performance is the best.However,the self-extinguishing fire only cooled to around 238°C within 7.5 minutes.When the fuel itself is in incomplete combustion or unburned state,carbon dioxide can reduce the temperature to 68.4-82.4°C within 7 minutes,and the fire extinguishing performance is significantly better than other fire extinguishing methods.