Due to their high reactivity, alkali metals pose a fire hazard as spontaneous ignition in air is possible in several high temperature applications. In the present study, the ignition and burning rates of a hot, shallow potassium pool of 0.06 and 0.10 m diameter have been studied experimentally. Thermodynamic equilibrium calculations of K–air system show that vapour phase combustion of potassium is possible. This has been verified experimentally. Over much of the duration of fire, the pool temperature is found to be in the 900–1000 K range; therefore, the oxides formed as a result of combustion would be molten and solid residues are formed only at the end of the fire, unlike in the case of sodium and lithium. Burning rate of potassium has been found to be in the range of 30–60 kg/m2s for various conditions and is typically lower than that of sodium and lithium under similar conditions. Auto-ignition temperatures lie in the range of 500–650 K, the higher temperatures occurring in smaller pools and low oxygen concentrations. Using different mass transfer scenarios, it is shown experimentally that the burning rate of potassium pool is limited by mass of transfer of oxidant. © 2016 The Combustion Institute

Sreenivas Jayanti

Department Of Chemical Engineering

Sampath Bharadwaj Kota

A. Subramani

combustion

Fires

High temperature applications

High temperature operations

Ignition

Lakes

MASS TRANSFER

potassium

Sodium

Temperature

AUTO IGNITION TEMPERATURES

Burning rate

Heterogeneous combustion

High reactivity

MASS TRANSFER CONTROL

Pool fires

SPONTANEOUS IGNITION

THERMODYNAMIC EQUILIBRIUM CALCULATION

SPONTANEOUS COMBUSTION

lithium

oxide

Airflow

article

Comprehension

enthalpy

FLAME

priority journal

Thermodynamics

vapor

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IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Combustion and Flame

Pool combustion experiments have been conducted for three alkali metals, namely, lithium (Li), sodium (Na) and potassium (K). Lithium and sodium are found to show a two-stage combustion behaviour which has been reported for a number of other metals. Here, the combustion is characterized by a sporadic rise in the flame temperature accompanied by a bright glow. Potassium is found to burn in vapour phase combustion in all cases without sporadic temperature excursions. In the present study, this different burning behaviour is attributed to the formation of thick oxide agglomerates in the case of Li and Na through the pores of which oxygen/metal vapour has to diffuse for combustion to occur. In such cases, a second stage of vapour phase combustion occurs when the oxide agglomerate is heated sufficiently so that the vapour of the liquid metal trapped in the pores breaks through to the surface. In the case of potassium, a self-cleaning mechanism, attributable to the high solubility of the metal oxides in liquid potassium and the relatively low melting point of the potassium oxides, enables a clear liquid surface to be exposed throughout for vapour phase combustion to prevail always. Recorded temperature profiles, SEM analysis of the oxide agglomerates as well as calculations of the metal-oxygen equilibrium thermo-chemistry for the three metals confirm this scenario. © 2011 The Combustion Institute.

On the occurrence of two-stage combustion in alkali metals

A hypothetical leak of liquid sodium in a fast breeder type of reactor could result in potential fire hazards. It can be shown that for typical leak rates of 10,000-50,000 kg/h, a stable, shallow pool will be formed in a very short time compared to the duration of the fire (Subramani et al., 2009). As a follow-up, in the present work, the experimental study of the burning characteristics of sodium pools of shallow depth (of 12 and 16 mm) under controlled environmental conditions is reported. It is found that the combustion of liquid sodium in a shallow pool can be very different when compared to the combustion in a deep pool. Estimated burning rates revealed that the average burning rate for a shallow pool is higher by a factor of two than the steady burning rate value of 40 kg/h m2 commonly used in most of the sodium fire safety computer codes. If the prevailing wind conditions are such that the aerosols produced at the flame sheet are prevented from depositing on the pool, then even higher rates of burning can be expected. © 2010 Elsevier B.V. All rights reserved.

Nuclear Engineering and Design

Experimental studies on burning behaviour of liquid sodium in a shallow pool

The spreading of burning liquid sodium has been investigated using a depth-averaged shallow water equation for isothermal and non-isothermal (burning) conditions. In the latter case, the spreading is one-way coupled with the flame through a separate energy equation for the pool, with appropriate source terms for radiative and conductive heat transfer from the flame, and a sink term (for the continuity equation) to account for loss due to burning. Pool fires on soil and concrete surface have been considered with appropriate friction and heat transfer terms in the momentum and energy equations, respectively. Using this model, numerical simulations have been carried out for a wide range of leak rates, and for a range of burning rates of liquid sodium. Results obtained from the non-isothermal model show that the non-isothermal effects of liquid sodium spreading can safely be neglected for the case or spreading of burning liquid sodium on a typical ground surface such as concrete or soil. Based on these conclusions, dimensionless correlations are proposed for the prediction of spreading parameters such as, equilibrium pool radius, pool formation time, and for mass inventory under pool fire conditions for liquid sodium. These parameters which are obtained from the spreading code can be specified, as input parameters for the existing sodium fire safety codes. © 2009 Elsevier B.V. All rights reserved.

Dynamics of liquid sodium pool spreading under sodium fire conditions

Combustion of liquid sodium is of interest in the safety assessment of liquid metal cooled fast breeder reactor systems. In the present study, a detailed thermodynamic analysis of sodium-air system has been carried out for equivalence ratios in the range of 0.1-1.9 and for flame temperatures ranging from 1100 to 1950 K. In addition to this, decomposition calculations presented for product aerosols such as sodium oxide (Na2O), sodium dioxide (Na2O2) and sodium hydroxide (NaOH) in normal oxygen and oxygen-deficient conditions (which are some form of phase diagrams of these aerosols) are used rigorously to find out the predominant aerosol that should be present in and outside the burn pan for a pool fire of liquid sodium. The conditions of occurrence of various sodium oxides under two different fire conditions namely pool and jet fires have been worked out. It is established that heterogeneous reactions involving sodium oxide are responsible for the formation of sodium dioxide and sodium hydroxide. It is necessary to take account of the rates of these heterogeneous reactions as well as the equivalence ratio-dependent decomposition calculations to correctly estimate the aerosol product mix in practical situations. © 2008 Elsevier B.V. All rights reserved.

Equilibrium considerations in aerosol formation during sodium combustion

Fire Safety Journal

Suppression of sodium fires with liquid nitrogen

Auto-ignition temperature and burning rate of potassium pool fire in a confined enclosure

Journal	Data powered by TypesetCombustion and Flame
Publisher	Data powered by TypesetElsevier Inc.
ISSN	00102180
Open Access	No