Effect of initial pressure on the burning behavior of ethanol pool fire in the closed pressure vessel
Introduction
In the industrial processes, there are much pressure vessels and piping frequently involved in the storage and transportation. Fire Hazards associated with pressure vessel seriously threaten the process safety in chemical industries, including pool fires, spill fires, boiling liquid expanding vapor explosion (Jujuly et al., 2015; Khan and Abbasi, 1999; Naderpour and Khakzad, 2018; Shang et al., 2021; Yin et al., 2013). The pressure vessel exposed to pool fire could be considered as one of the primary cause of the domino incidents (Bradley et al., 2021), and has been extensively studied for long time. In order to understand of critical safety conditions, lots of full-scale tests and laboratory experiments were conducted for the pressure vessel in the fire impingement, where the relevant phenomena including thermal stratification and liquid expansion were identified (Dancer and Sallet, 1990; Gong et al., 2004). The related models were developed to predict the main phenomena occurring inside and outside a pressure vessel. Recently, some scholars (Iannaccone et al., 2021; Scarponi et al., 2018) conducted numerous studies for the pressure vessels in pool fire scenario using CFD (Computational Fluid Dynamics). The results provide more detailed analysis on the evolution of pressure and temperature during fire exposure. There is no doubt that these available models and analysis are useful for the prediction of domino effect and accident process (Bradley et al., 2021; Khan et al., 2015).
The effect of initial pressure on flammability and accidental combustion phenomena in a closed pressure chamber is significant and attracts increasing attention. Benedetto et al. (2018) proposed the empirical formula for predicting the flash point at different pressure, which was validated for both pure substances and their binary mixtures. Cammarota et al. (2019) studied the explosion behavior of n-dodecane in a closed cylindrical vessel by varying different initial pressure and temperature. The result show that the flammability range would increase with initial temperature or pressure. However, the fire behavior occurring inside the pressure vessel seems to lack the investigation. The fires in the pressure vessel often cause disastrous consequences due to rapid growth of heat release rate and the difficulty of fire control. Besides, a significant pressure rise generated by the fire in the closed vessel might be greater than the withstanding limit of pressure vessel, and could result in the occurrence of secondary or tertiary accident along with severe impact on economy and society (Chow and Zou, 2009; Pretrel et al., 2012). For example, a fire accident occurred in Ringhals nuclear power plant during the pressurized test, which caused social panic and huge economic losses (Zhao et al., 2020). When a pool fire occurs in the pressure vessel, the pool fire characteristics would determine the evolution of disasters and the possibility of secondary accident, including evolution of mass burning flux, self-extinction time and the variation of pressure in the vessel. Therefore, available description and prediction models quantifying pool fire in the pressure vessel are important for fire risk management and safety design for pressure vessel involved with the industrial processes.
During the past decades, studies on the burning characteristics of pool fire under various pressure have mainly focused on open space or cabin fires during in-flight (Fang et al., 2011; Hu et al., 2013; Yao et al., 2015). Li et al. (2009) measured the burning rate of n-heptane pool fire at different altitudes, and found the burning rate was proportional to the environmental pressure. Hu et al. (2011) indicated that this relationship scale would be related to the burner diameter. To obtain a global relationship for mass burning flux, a considerable number of experiments were performed in Hefei (100.8 kPa) and Lhasa (64.4 kPa) (Fang et al., 2011). The results showed that the dependence of burning rate on pressure (i.e.) varies with dominated heat transfer and n is between 0.6–1.3 for convection- and radiation-dominated pool fire, whereas n is approximately 0 for the conduction-dominated pool fire. Given the large expenditure in field testing, researchers (Hu et al., 2013; Ma et al., 2018, 2017; Yao et al., 2015; Zhu et al., 2019) subsequently created some closed pressure chambers to simulate the different environmental pressures, wherein fresh air is supplied to avoid the effect of chamber closure. Some small-scale pool fires performed in a laboratory low-pressure chamber and some rectangular pool fires under reduced pressure have also shown a similar tendency, when the scale of pool fire is smaller enough (Hu et al., 2013). In order to develop the hazard assessment for cabin fires during in-flight, Li et al. (2017) conducted pool fire under various dynamic pressure, and found that the shows a power function growth with the pressure. Li et al. (2018) conducted n-heptane pool fires at different depressurization rates. They found that the ventilation would influence the burning behavior of pool fire, and introduced a dimensionless factor to characterize the influence of ventilation.
These studies increase our understanding for the dependence of pool fire behavior on pressure and improve the fire risk assessment for plateau region and aviation industry. However, limited studies have been conducted on pool fire in a completely closed pressure vessel. There are several studies about fire in closed vessel, but the majority of previous studies were conducted in normal pressure. Zhang et al. (2013) measured the self-extinction time for n-heptane by using two chambers and found the burning time increases with the vessel volume and decreases with the area of pool fire. Zhang et al. (2012) studied the effect of the height of fire source on pool fire in a closed vessel. Their results showed that the development of fire mainly depends on the heat transfer from the hot gases toward the fuel surface, and the restriction of oxygen in the chamber. Bailey et al. (1993) performed some fire tests in a large pressure vessel, and concluded that fire will be extinguished when the value of oxygen concentration reaches 12 %. In addition, Pretrel et al. (2012) conducted pool fire under in a confined and force-ventilated enclosure and found that the pressure change in the vessel would be determined by the heat release rate, the ventilation conditions and the chamber characteristics. Recently, Li and Zhang (2021) investigated the influence of initial temperature and relative humidity on the burning behavior of pool fire in the closed chamber, and found that the fire development would be inhibited as the decrease of initial temperature or the increase of relative humidity in the chamber.
Notably, these studies have primarily considered only a single influencing factors, the environmental pressure or enclosed condition of the vessel. Fire accidents, especially those related with pressure, are common in closed vessels in the industrial processes, such as sealed enclosures and nuclear containment shells. Furthermore, fire behavior in these closed pressure vessel would be more complicated, where the effect of pressure and enclosed condition of the vessel are incorporated. For these fire behavior in the closed pressure vessel, whether the obtained prediction of self-extinction time remains applicable, or whether the pressure change would exceed the withstanding limit of pressure vessel is still unknown. The combined effect of pressure and enclosed vessel on burning behaviors of pool fire requires clarification. Our previous research (Chen et al., 2020a,b) focused on the theoretical analysis for oscillating behavior of pool fire in the closed chamber. In present study, the fuel mass, flame video, and oxygen concentration are measured, furthermore the change in flame appearance, evolution of mass burning flux, self-extinction time and the variation of pressure in the vessel are analyzed. Moreover, the empirical relationships for predicting the self-extinction time of pool fire, the over pressure peak in the closed pressure vessel are developed and verified by the experimental data. This study provides important insights into the burning parameters of ethanol pool fire in a closed pressure vessel. The obtained prediction model in the present study can also contribute a theoretical basis for fire risk management and safety design of pressure vessel involved with the industrial processes.
Section snippets
Experimental platform and measurements
The experimental platform was shown in Fig. 1. The pool fires were carried out in a pressure vessel with internal dimensions of 0.4 m (diameter) ×0.6 m (height), and the range of design work pressure is 60 kPa to 300 kPa. The burner used to hold the liquid fuel was placed 20 cm above the vessel bottom and at the center of the vessel. For each condition, the vacuum pump or pressure pump was activated to reduce or increase the pressure in the vessel until the designed value was reached, and all
Flame appearance
Fig. 2 presents the images of 4-cm-diameter ethanol pool fires at a typical time under different vessel pressures, wherein the time was normalized by the total burning duration, from the time of ignition to the time of fuel-burnout. As the vessel pressure increased, the curvature of the flame shape increases and additional wrinkles appear on the flame surface, indicating that the flame structure changes from laminar to turbulent. For some given pressures, it is also observed that flame becomes
Conclusions
In order to know the evolution of fire phenomenon under closed pressure vessel, the effect of initial pressure on the burning behaviors of ethanol pool fire in the closed pressure vessel is experimentally investigated. Flame appearance, mass burning flux and variation of pressure in the vessel are measured and analyzed. The results are summarized as follows:
- (1)
As the increase of the pressure or the decrease of the gas temperature, the flame structure changes from laminar to turbulent and the flame
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
The authors would like to acknowledge financial support sponsored by National Natural Science Foundation of China (No. 52076203; No. 51874344), Fundamental Research Funds for the Central Universities (No. 20CX06068A, No. 19CX07006A), Qingdao Postdoctoral Science Foundation Funded Project (No. qdyy20200095).
References (37)
- et al.
An overview of test standards and regulations relevant to the fire testing of pressure vessels
Process Saf. Environ. Prot.
(2021) - et al.
Influence of initial temperature and pressure on the explosion behavior of n-dodecane/air mixtures
J. Loss Prev. Process Ind.
(2019) - et al.
Effect of pressure on the heat transfer and flame characteristics of small-scale ethanol pool fires
Fire Saf. J.
(2018) - et al.
Oxygen concentration effects on the burning behavior of small scale pool fires
Fuel
(2019) - et al.
Experimental study of the effect of ambient pressure on oscillating behavior of pool fires
Energy.
(2020) - et al.
Numerical simulation of pressure changes in closed chamber fires
Build. Environ.
(2009) - et al.
Pressure and temperature response of liquefied gases in containers and pressure vessels which are subjected to accidental heat input
J. Hazard. Mater.
(1990) - et al.
Influence of low air pressure on combustion characteristics and flame pulsation frequency of pool fires
Fuel
(2011) - et al.
Momentum- and buoyancy-driven laminar methane diffusion flame shapes and radiation characteristics at sub-atmospheric pressures
Fuel
(2016) - et al.
A simplified model to predict the thermal response of PLG and its influence on BLEVE
J. Hazard. Mater.
(2004)
Combustion characteristics of n-heptane at high altitudes
Proc. Combust. Inst.
Burning characteristics of conduction-controlled rectangular hydrocarbon pool fires in a reduced pressure atmosphere at high altitude in Tibet
Fuel
Numerical simulation of LNG tanks exposed to fire
Process Saf. Environ. Prot.
Major accidents in process industries and an analysis of causes and consequences
J. Loss Prev. Process Ind.
Methods and models in process safety and risk management: past, present and future
Process Saf. Environ. Prot.
Combustion characteristics of n-heptane and wood crib fires at different altitudes
Proc. Combust. Inst.
Influence of depressurized environment on the fire behaviour in a dynamic pressure cabin
Appl. Therm. Eng.
Factors affecting the burning rate of pool fire in a depressurization aircraft cargo compartment
Appl. Therm. Eng.
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