Modelling propagation of gas contaminants in tunnels during

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Budownictwo Podziemne i Bezpieczeństwo w Komunikacji Drogowej i Infrastrukturze Miejskiej
Modelling propagation of gas contaminants in tunnels during
normal operation and fires with mine ventilation software
VENTGRAPH
Jerzy Krawczyk
Strata Mechanics Research Institute of Polish Academy of Sciences
Wacław Dziurzyński
Strata Mechanics Research Institute of Polish Academy of Sciences
ABSTRACT: Paper outlines the properties of fire simulators developed for underground
mine ventilation networks based on one dimensional flow model. Similarity of ventilation
systems of complex tunnels and mines justifies exchange of experiences between those
domains. An example of a simulation of a fire in a large tunnel, with a hybrid semi transverse
and transverse ventilation system was presented. Interactive graphical interface allows for
immediate monitoring of effects of several actions like opening of exhaust ports or reversal
of ventilation. Series of “what if” simulations may be performed in a short time. Due to their
simplicity, they are capable to provide a life animation of flow transients, including transport
of contaminants and development of a fire in complex networks. Such property may be useful
for training and education, if users are also aware of the limitations resulting from
a simplified model.
KEYWORDS: fire simulator, one dimensional flow model, ventilation network, training and
education, case study
1. INTRODUCTION
Ventilation systems of underground mines and tunnels have many similarities.
Investigations on recent accidents resulted in numerous studies on ventilation and fire safety
in tunnels. Problems of fire hazard, detection, suppression and evacuation form zones
endangered by toxic or explosive gazes have been crucial for underground mine ventilation.
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Results of progress in solutions for tunnelling have been applicable for mining. For example
the FDS Smokeview software [4],[9] has been applied for analysis of local migration of
explosive gases for the longwall coal excavation systems. On the other hand a long term
experience in hazard prevention and suppression may be useful for design and operation of
tunnels.
The extent of underground mine ventilation systems, totalling in a length exceeding 100
km is by one order of magnitude longer than tunnels. Such size of computational domain
justifies application of one dimensional flow models [2], [3], which for tunnels have been
considered obsolete and replaced by three dimensional CFD simulations. Present paper shows
results of a preliminary study on adaptation of the fire and contaminant propagation
simulator incorporated in the VENTGRAPH software to tunnel ventilation.
2. MINE VENTILATION NETWORK FLOW SIMULATOR
2.1. General description
The main application of VENTGRAPH software is ventilation network flow simulation,
both in normal and emergency conditions. Geometry of a network and ventilation survey
provide a database to calculate the steady flow in the network. The steady model is a base for
series of case studies and “what-if” simulations. Results are displayed on an isometric
scheme of a network, which makes easier their interpretation. This feature is quite popular
among several simulators of this kind, developed in the USA, Australia and South Africa.
A unique feature is the fire and contaminant simulator. The core of model is based on
a lumped constants model of fire and a unique approach combining steady flow modeling and
unsteady transport simulation, which provides sufficient representation at minimized
computational effort. Effect of buoyancy, leading to unintentional flow reversals, throttling
effect, point gas sources are considered. During the simulation a several fire suppression
actions may be simulated, like closing or opening of ventilation door, changes in operation
point of fans, reversals of ventilation or application of inert gases.
The only comparable program MFIRE, developed by the US [12], has much smaller
capabilities, especially in terms of a user-friendly, interactive graphical interface.
VENTGRAPH software is used for preplanning of miners evacuation and fire games for
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Budownictwo Podziemne i Bezpieczeństwo
ństwo w Komunikacji Drogowej i Infrastrukturze Miejskiej
ventilation students and engineers or rescuers. On the other hand, the old fortran code of the
SES software developed for tunneling is hardly available [4]
Rys. 1. Symulacja pożaru
żaru w kopalnianej sieci wentylacyjnej
Figure 1. Simulation of a fire in a mine ventilation network.
2.2. Mathematical model of the fire propagation module
The flow of the air and gas mixture in the mine heading is described by a system of
equations
uations of momentum, continuity and state. This system combines equations of steady flow
of air and admixed gases with unsteady equations of fire development, gas transport and
energy in the way described below. For flow distribution in the network, the re
response time to
changes of boundary conditions, like quantity of methane inflow, or parameters like
resistance and natural ventilation, is on the order of a minute. The process of admixed gas
propagation lasts for hours, justifying the treatment of the phen
phenomena as quasi-static with
respect to flows. Detailed description of assumptions, mathematical model and some
information about numerical methods may be found in papers [2] and [3].
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Budownictwo Podziemne i Bezpieczeństwo
ństwo w Komunikacji Drogowej i Infrastrukturze Miejskiej
2.2. Graphical interface for animated simulation of transients
Transients generated by fires lead to a complex distribution of parameters in a ventilation
network, which vary both in time and space. The presentation of such phenomena requires
additional resources. As regards
egards spatial distribution, branches of the network are divided into
segments. Values of i.e. carbon dioxide concentration or temperature of air in a section are
displayed as a particular color.
r. Thus the network scheme is transformed into a map of i.e.
temperature
mperature distribution. During the simulation this distributions may vary with time,
transforming a scheme into an animated colored
red map. This solution allows the observation of
transients during simulation. In contrast to steady states computations, in
information about
individual colors
rs for presentation is displayed (e.g. distribution of oxygen concentration
levels in fire gases). Another advantage is the possibility of obtaining time diagrams of
observed parameters in selected network points (by placing virt
virtual sensors). The application
of a solution with a legible colorr screen makes the interpretation of phenomena occurring in
the network much easier and helps the user to take correct decisions during simulated rescue
actions
Rys. 2. Schemat tunelu z poprzecznąą i półpoprzecznąą wentylacją
Figure 2. Scheme of a tunnel with combined transverse and semi
semi-transverse ventilation system.
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3. REMARKS ON THE SCOPE OF APPLICATION
Models of transverse ventilation systems for several kilometers long tunnels have been developed.
Simulations include non moving carbon dioxide sources (for example cars in a traffic jam),
development of a fire, smoke evacuation through oversized flow ports and ventilation reversal [10],
[13]. Results are presented in a form of color maps of smoke, oxygen and temperature distributions
and graphs of a evolution of several flow parameters like flow quantity or CO/oxygen concentration.
Paper of A Wala [16] shows how by running simulations for simple networks one may gain some
insight into some features of underground fires, like throttling effect, chimney effect and reversal of
flow resulting from diagonal connections in a structure of the ventilation network. Limitations of one
dimensional approximation do not allow for showing such phenomena like smoke backlayering,
plug-holing of exhaust ports or consider effects of jet fans.
Anyway it is possible to build and efficiently run fire simulations in a model of an extent
ventilation network with several fans shafts and transverse or semi-transverse ventilation systems, as
shown in a Figure 2. Prior to the simulation a steady state model has been developed on assumed
physical characteristics of the tunnels: cross-section, slope, the number of roadways, the type of
ventilation, the resistances of the airways, the number of ducts, the sizes of the air intake and exhaust
ports, the number and the characteristics of the fans.
Actual simulation starts with selection of the place of the fire its intensity and time constant of
development. For applied model, the output of the fire depends also on the quantity and composition
of gases feeding it. Due to several feedback loops in the model, development of the fire depends on
interactions of the ventilation network and the fire. User has several means to influence the
simulation:
•
By changing the resistance of branches one may mimic the effect of opening oversized exhaust
ports for easier evacuation of smoke.
•
Actions aimed at restricting the supply of oxygen to the fire may be reproduced by increasing
resistances of selected ducts.
•
Specific gas sources, representing inertizing devices may mimic effect of inertization on
development of fire.
•
User may also control the pressure of fans which enables the simulation of switching them on or
off.
•
Combining changes of resistance of bypass and regular fan ducts with modification of fan
pressure the whole sequence of ventilation reversal may be performed.
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The delays resulting from convective transport of heat or contaminants are represented quite well.
Estimating the time scale of phenomena User must be aware that the quasi static model does not
represent effects neither inertia of air and admixed gases nor such phenomena like pressure and
velocity waves resulting from rapid changes. The real response of systems will be delayed by seconds
or even minutes for large tunnels.
4. CONCLUSSION
Despite a progress in application of three-dimensional CFD software, still there might be
some benefit from adaptation of one dimensional mine ventilation simulators to selected
problems of tunnel ventilation [8]. Due to their simplicity, they are capable to provide a life
animation of flow transients, including transport of contaminants and development of a fire
in complex networks. Such property may be useful for training and education [16], if users
are also aware of the limitations resulting from a simplified model [6], [14], [15].
Application of a hybrid, multi-scale modeling approach [1] might be a way to use potential of
simple 1D approach and overcome limitations of 3D representation for advanced studies on
phenomena in complex tunnel ventilation systems
REFERENCES
[1]
Colella F., Rein G., Borchiellini R., Carvel R., Torero J.L., and Verda V.: Calculation and design
of tunnel ventilation systems using a two-scale modeling approach, Building and Environment 44
2357–2367, 2009.
[2]
Dziurzyński W., Krawczyk J., Pałka T.: The computer simulation of air and methane flow
following an outburst in transport gallery D-6, bed 409/4, Journal of the South African Institute
of Mining and Metallurgy , Vol 108, pp 139-145, 2008.
[3]
Dziurzyński W., Krach A., Krawczyk J., Pałka T.: The flow of humid air in the ventilation
network of a mine with an underground fire, Arch. Min. Sci., Monogr. No 4. p.p. 112, 2008.
[4]
Elpidorou D. P., Kennedy W. D., The SES: From the 1970s into the Future Spring 1996 • Issue
No. 34 • Volume X • Number 1, retrieved from www.pbworld.com
[5]
http://www.fire.nist.gov/fds/ - Fire Dynamics Simulator and Smokeview (FDS-SMV) - Official
Website, Hosted at the National Institute of Standards and Technology (NIST), 2009.
[6]
Krawczyk J.: On Transients in Mine Ventilation Systems Caused by Fans, Archives of Mining
Sciences Monograph No 7, 2009.
92
[7]
Krawczyk J., Dziurzyński W., Pałka T., Skotniczny P., Rossotto R.: Adaptation of mine
ventilation software VENTGRAPH to simulation of propagation of gas contaminants in tunnels
during normal operation and fires Proc. of the Fourth Int. Symp. on Tunnel Safety and Security,
Frankfurt am Main, Germany, March 17-19, pp 549-552, 2010.
[8]
Nawrat S., Napieraj S.: “Fire hazard in road and railway tunnels” (in Polish), Budownictwo
Górnicze i Tunelowe Quarterly, issue 2, pp. 31-40, 2005.
[9]
Nawrat S., Kuczera Z., Napieraj S.: Possibilities of CFD computer software utilization in
underground mines ventilation (in Polish) Wiadomości Górnicze Vol. 57, issue 9, pp. 449-457,
2006.
[10] Napieraj S.: Zasady przewietrzana, klimatyzacji i bezpiecznej eksploatacji podziemnych tuneli
komunikacyjnych Praca Dyplomowa na Wydziale Górnictwa i Geoinżynierii, 2002 - nie
publikowana
[11] Laage1 L. W., Greuer R. E, Pomroy W. H., “MFIRE Users Manual Version 2.20” August 1995
http://www.cdc.gov/niosh/mining/pubs/pdfs/mumvt.pdf, 1995.
[12] NIOSH: MFIRE 2.20 Feasibility Study,
www.cdc.gov/niosh/mining/productss/software/MFIRE%20Files/MFIREContract1.zip, 2008.
[13] Rossotto R.,: Adaptation of mine ventilation software VENTGRAPH to simulation of propagation
of gas contaminants in tunnels during normal operation and fires, including ventilation reversal,
Industrial Placement Rapport at IMG-PAN Cracow Poland, 2004.
[14] Sahlin P., Eriksson L., Grozman P., Johnsson H., and Aalenius L.: 1D models for thermal and air
quality prediction in underground traffic systems, Proc. of the 12th International Symposium on
Aerodynamics and Ventilation of Vehicle Tunnels, Portoroz, Slovenia: 11 – 13 July 2006
[15] Vardy A.E. “Thermotun/5.2”, User Manual; Dundee Tunnel Research, August 2001
[16] Wala A. M.,: Teaching Mine Fire Principles with Intelligent Computer Assisted Instruction,
Proceedings of the Fifth International Mine Ventilation Congress, Marshalltown, South Africa,
1992.
MODELOWANIE PROPAGACJI GAZÓW POŻAROWYCH W TUNELACH PODCZAS
POZARÓW
I
NORMALNEJ
EKSPLOATACJI
Z
WYKORZYSTANIEM
PRZEZNACZONEGO DO SYMULACJI KOPALNIANYCH SIECI WENTYLACYJNYCH
OPROGAMOWANIA VENTGRAPH
STRESZCZENIE ARTYKUŁU: Przedstawiono właściwości symulatora pożarów w tunelach
będącego adaptacją programu Ventgraph, przeznaczonego do modelowania przepływów
93
w sieciach wentylacyjnych kopalń głębinowych, opartego na modelu jednowymiarowego
przepływu. Podobieństwa złożonych struktur systemów wentylacyjnych niektórych tuneli
i układów wyrobisk kopalnianych uzasadniają ideę wykorzystania doświadczeń aerologii
górniczej dla oceny zagrożeń pożarowych w tunelach i opracowania metod ich zwalczania.
Moduł pożarowy programu może być wykorzystany do animowanych symulacji stanów
przejściowych przepływu w sieci podczas pożaru lub propagacji zanieczyszczeń gazowych
w systemach wentylacyjnych tuneli. Interaktywny interfejs graficzny umożliwia obserwację
skutków działań zaradczych, takich jak otwieranie klap oddymiających lub rewersji
wentylacji. Dzięki prostemu modelowi matematycznemu w krótkim czasie można
przeprowadzić serie wielowariantowych symulacji nawet dla złożonych sieci. Ten sposób
modelowania
może
być
wykorzystany
do
celów
edukacyjnych
i
szkoleniowych
i prognozowania, pod warunkiem uwzględnienia ograniczeń w stosowalności programu,
wynikających z przyjętych w nim upraszczających założeń
SŁOWA KLUCZOWE: symulator pożarów, jednowymiarowy model przepływu, sieć
wentylacyjna, edukacja i szkolenia, studium przypadków
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Modelling propagation of gas contaminants in tunnels during

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