Fire-Extinguishing Performance and Mechanism Study on Water Mist with Potassium Additives

Author:Zhang Tian Wei

Supervisor:du zhi ming


Degree Year:2017





Water Mist Fire Suppression System(WMFSS)was widely studied and also applied in various situations for its advantage of little pollution,high efficiency,low water consumption,less cost and hazardous effect.However,the ordinary WMFSS could only be used for physical fire extinguishing and had limitations in special and protected situations.The development of WMFSS with additives had become a hot research topic in fire safety science.Because of the WMFSS with additives had a complicated fire suppression mechanism and various influence on fire extinguishing effect,neither uniform principle nor universal standard was built except the fire extinguishing tests,which will undoubtedly lead to different evaluation standards and conclusion,which is harmful for future promotion.The key point to the previous problems was to clarify the efficiency influencing factors and working mechanism of the WMFSS with additives.Based on available literature and research condition,the content and findings of this dissertation were as follows:(1)After comparing and analyzing different small gaseous flame experiment system,Cup-burner fire extinguishing experiment system was independently developed and characterized by mist flux and CH4 diffusion flame interaction.The flame character of Cup-burner reacted with pure water mist was experimented and numerically modeled,which provided experimental data and theoretical direction for studying the fire extinguishing efficiency of water mist with potassium additives.(2)Cup-burner was used to test the minimum fire extinguishing concentration of water mist containing K2C2O4,CH3COOK,KNO3,KCl,K2CO3 and KH2PO4.By comparing experiment data with pure water mist,the fire extinguishing efficiency was:K2C2O4≈CH3COOK≈K2CO3≈KNO3>KCl>KH2PO4>pure water.The results showed that water mist with potassium additives had chemical fire extinguishing effect,and the model which to quantize the chemical efficiency of water mist with different additives according to energy equilibrium on CH4 flame was built.(3)The key component of fire extinguishing efficiency by potassium additives was KOH according to the chemical thermodynamics.K2CO3,KNO3 and KCl could be activated by water vapor in high temperature environment,which generating vaporous KOH after hydrolysis reaction.The most quantity of KOH was given by K2CO3 in the equilibrium states,followed by KNO3 and KCl.The influence factor could be classified as decisive,competitive and applied factors by analyzing the factors on the chemical fire extinguishing efficiency of water mist with potassium additives.(4)The influence of vapor KOH on burning process was mainly done by controlling the key elementary reaction,specifically with OH element by PSR model in CHEMKIN.The higher the vapor KOH concentration in CH4 flame,the stronger the inhibitory effect was.The inhibition path of CH4 flame doped with vapor KOH could be obtained by analyzing intermediate product using PSR model,and the reaction mechanism would not be changed with the KOH concentration.The minimum extinguishing concentration(MEC)of vapor KOH could be affected by environmental temperature,humidity and atmospheric pressure.The MEC of vapor KOH would be rised with the increase of temperature and atmospheric pressure but showed a different trend which calculated by PSR model.Humidity had a larger influence on the MEC of vapor KOH comparing with temperature.(5)The feasibility experiment which applied self-developed full-size water mist fire extinguishing system on class B and class F fire by water mist with potassium additives was conducted.The effectiveness on class B fire was KNO3≈K2CO3>KCl>KH2PO4>pure water,and on class F fire was K2C2O4>KNO3>CH3COOK>KCl>KH2PO4>NH4H2PO4>pure water.Water evaporation could be lowered by additives in the study of oil cooling experiment through increasing the resultant force of hydrated ions and the droplet size,which was against oil cooling.The development of boiling-overflowing layer was restricted by water mist containing additives through decreasing the water mass in oil.The additives which had features of high efficiency,reliable cooling performance and effective inhibition of oil splash for class F fire should be the potential water mist additives.