The Ventilation Challange Hardcastle Kocsis CIM2004

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The ventilation challenge
Article · May 2004
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TECHNICAL PAPER
Mining at Depth
CIM Bulletin
May 2004
▲ The ventilation challenge
S.G. Hardcastle and C.K. Kocsis, Natural Resources Canada, CANMET—MMSL,
Sudbury, Ontario
KEYWORDS: Deep mining, Ventilation, Mechanization, Health, Environment.
Paper reviewed and approved for publication
by the Metal Mining Division of CIM.
ABSTRACT
Worldwide, metal mines are going
deeper. For example, in Canada there are six
such mechanized mines planning production at
3000 m (10 000 ft). Working at such depths
challenges all aspects of mining including the
provision of ventilation to supply an equitable
working climate for personnel and machinery.
This paper explores the overall challenges
of supplying ventilation in Canada’s deepest
mines and how the volumes required could be
minimized. This is essential because it must be
remembered that ventilation and refrigeration
are not only costly items to supply, but the
magnitude of their cost is also very sensitive to
the volume supplied. For the primary ventilation system this is obvious because of the cubic
relationship between volume and cost.
In deep mines, the main function of ventilation is the removal of heat transferred from
the strata and generated by the mining
machinery, and the air volumes supplied are
designed accordingly. The second consideration is the removal of other pollutants that
could be harmful to humans such as diesel and
explosive fumes. However, the need for ventilation at its present design levels could be
reduced. This paper discusses the implications
of such technologies as: tele-remote mining
and alternatives to diesel equipment on the
magnitude of the volume supplied; ventilationon-demand which recognizes ventilation as a
costly and limited resource; plus other aspects,
such as the benefits of controlled recirculation,
local cooling, and possibly heat rejection back
to the strata to gain further advantage from
new developments.
Furthermore, this paper advances the
need to be able to design ventilation systems
more cost effectively and how such new
advances as process simulators can be used in
conjunction with ventilation simulators to
explore the diverse options that could affect
the air volumes required and provide more
realistic economic data upon which to base
design decisions.
Introduction
Canada has six metal mines or projects
that are planning production 3000 m below
surface. Some of these are extensions of current mining operations and others are new
mines. Consequently, as with the worldwide
industry, the ability to mine at depth is becoming an increasing concern to maintain the viability of the Canadian industry. At depth, the
provision of ventilation due to its associated
capital and operating costs is always a concern
and one of the potential limiting factors. Hence
the considerable time and effort put into the
design and commissioning is evident for the
documented upgrades of both Inco’s Creighton
mine (O’Connor et al., 2002) and Falconbridge’s Kidd Creek mine (Hortin and Sedlacek,
2002; Howes and Sedlacek, 2001). This paper,
by way of discussion, will show how the impact
of depth could be mitigated by means of technological change and by questioning current
ventilation practices.
Looking at the underground metal mining
industry, three trends can be observed: mines
are getting deeper; production is becoming
increasingly mechanized and/or automated;
and health standards for the miners plus environmental concerns are becoming more stringent. To varying degrees, these trends
challenge the provision of ventilation in a mine,
and to ensure the feasibility of the industry, it is
essential to understand why ventilation is
required.
In metal mines, ventilation serves three
primary functions: it is needed to supply oxygen
for humans, and for the combustion process in
diesel engine-powered vehicles; it is required to
remove and/or dilute pollutants generated from
the strata or the mining process; and lastly, it
must supply a suitable thermal environment for
man and machinery.
Now let us look at the three industry
trends and how they relate to the primary functions of ventilation.
The Depth Challenge
Depth can affect the economics of ventilation in three ways. Firstly, as the distance that
ventilation must be supplied lengthens the
associated cost can increase linearly. This can
be demonstrated through a basic airflow relationship:
Pressure Loss = Airway Resistance x Air Quantity2,
or simply P = RQ2
Stephen Hardcastle
joined CANMET, Mining and Mineral
Science Laboratories (MMSL) in 1983,
and has progressively been promoted
to his current senior research
scientist/mine ventilation specialist
status. In 1983, he started working at
the Elliot Lake Laboratory primarily
focussing on dust/particulate research.
In the late 1980s and continuing
through to today, his research interests
and engineering support to the mining
industry have been orientated toward
mine ventilation. In 1993, he was
transferred to MMSL’s Sudbury Laboratory. Within mine ventilation, his
primary emphasis is in optimization and facilitating this through improved
surveys, modelling, design and controls, and then introducing demandbased systems through automation. Dr. Hardcastle holds a Bachelor’s degree
in mining engineering, and a Doctor of Philosophy degree in mine
environmental engineering; both were obtained from the University of
Nottingham, United Kingdom.
May 2004
Charles Kocsis
joined CANMET, Mining and Mineral
Sciences Laboratories (MMSL) in 1999
where he is now a senior research
engineer involved in both engineering
and research projects dealing with
ventilation modelling, the design and
optimization of underground
ventilation systems and in mine
ventilation automation. Prior to that, in
Canada, he was with Golder Associates
Inc. and H.A. Simons Ltd. providing
engineering services in production
planning, mine design, underground
and surface blasting, and mine ventilation. Mr. Kocsis is a licensed
Professional Engineer in the province of Ontario and has a mining
engineering degree from the University of Petrosani, Romania and a Masters
degree in mineral resources engineering from Laurentian University. He is
currently a Doctor of Philosophy candidate, researching new ventilation
design methods with the University of British Columbia.
In this equation the pressure loss through
the ventilation system is what the fans must
overcome to generate the desired airflow. And
generally, all other things being equal, it is the
length of the system that will dictate the pressure loss because resistance is defined by:
Friction Factor (k) x Circumference (C)
x Length (L)
Resistance = ––––––––––––––––––––––––––
,
Area (A)3
kCl
or R = –––––––
A3
51
S.G. HARDCASTLE and C.K. KOCSIS
CIM Bulletin
Furthermore, the power required by the
fans, which is generally proportional to the
operating cost, is defined as:
Air Power (AP) = Pressure Loss (P) x Air Quantity (Q),
or AP = PQ
Upon substitution this becomes:
AP (which approximates to operating cost) = RQ3
So this equation not only shows cost is
linearly proportional to resistance and hence
distance, or depth for a vertical mine, but more
importantly cost is a function of the cubic of the
quantity. The importance of this cost/quantity
cubic relationship cannot be overstated.
Secondly, depth can affect the ventilation
economics because it can result in increased
leakage within the system, however this would
also be the case for lateral deposits with distance from surface connections. In a large ventilation system, if a mine has to supply 10%
additional airflow to combat leakage as compared to a smaller mine, the resultant
power/cost will be 33% greater. This starts to
show the need to optimize the amount of air
sent underground.
Thirdly, and most importantly for deep
mines, is that with increasing depth air temperatures in a mine would tend to increase. This
would be the result of, firstly, autocompression
of the air, whereby the air becomes more
dense, and secondly, due to the additional heat
transfer from the strata as it gets closer to the
earth’s molten core. This is unavoidable unless
ameliorative measures are taken. To combat
this heat gain, plus provide the same capacity
for the removal of machine heat, the airflow in
deep mines has to increase with depth. For
example, in a Canadian mine already operating
at over 2000 m below surface, an additional
300 m depth increases the air volume required
by 20% and according to the cubic relationship, these deeper areas would be 73% more
costly to ventilate. How much will it increase for
the next 300 m, another 20% to 30%? So it
can be easily seen that when heat management starts to become a concern, the ventilation costs start to increase dramatically.
The Impact of Mechanization
Mining like any other industry has gone
from primarily hand-tool mining through the
introduction of manned electrical- and dieselpowered equipment, namely mechanization,
and is now heading toward remote-controlled
and semi-autonomous machines, which is
automation. This change has also challenged
ventilation. When diesel equipment started to
52
May 2004
be introduced into mines in the 1960s, the
equipment was comparatively small with
engines of less than 75 kW (<150 hp) and their
number few. Since that time, the number
and/or total installed power of such units has
dramatically increased. Initially it was in the primary production fleet such as LHDs (or Scooptrams), drills and trucks, but a more recent
trend in Canada is that for mobility, the majority of underground personnel now have access
to a vehicle.
Within the production fleet, the size of
vehicles and their diesel engines have
increased. In Canada there are now 9.2 m3
(12 cu. yd) bucket capacity LHDs with 260 kW
(350 hp) engines being used at depth. However, these are not the largest vehicles underground; one metal mine employs at depth a
490 kW (650 hp) diesel haulage truck, and in
shallow non-metal mines, even larger equipment of >550 kW (735 hp) is not uncommon.
However, there has been a trend in bulk mining, whereby the actual numbers of production
vehicles decreases with increased capacity.
For personnel carrier and service vehicles,
in Canada, the situation is very different. There
has not only been an increase in numbers to
the extent that such vehicles can now represent
50% of a mine’s vehicle population, but also
the size of the vehicles’ engines have dramatically increased. Initially small engine vehicles
were the norm such as 55 kW (73 hp) Toyota
Landcruisers; however mines have been gradually replacing them with larger units and today
a 100 kW (134 hp) Landcruiser is more typical.
Some mines have also started to use commercial highway vehicles; this has led to 160 kW
(215 hp) personnel carriers and utility vehicles.
In ventilation design, the air volume supplied in mechanized mines is often based upon
the need to dilute diesel exhaust contaminants
and such criteria as 0.063 m3/s air /kW
diesel (100 cfm/bhp) is routinely employed
(Gangal and Grenier, 2002). So, similar to
greater depths, it can be seen that increased
mechanization and workforce mobility has
required mines to supply more and more air
underground. Again, this increased air volume
dramatically increases the required power and
resultant cost due to the cubic relationship.
Health and Environmental
Considerations
Ventilation is required for the dilution and
removal of contaminants, which provides a safe
atmosphere for personnel to breathe. The most
common contaminants are:
• strata gases — these include methane,
which is flammable, and radioactive radon
and thoron;
• process gases — these routinely include
the by-products of combustion from diesel
engines and fumes from explosives;
• mineral dust — created from blasting and
attrition of the rock, liberated during the
blast and throughout the mineral handling
chain; and
• non-mineral dusts such as soot — another
by-product of combustion from diesel
engines.
For the majority of Canadian mines, flammable and radioactive gases are not a significant issue, and dust, for the most part, can be
controlled at source through wetting practices
or mechanical removal. The bulk of the blast
fumes are generated when the mine, or area
therein, is not occupied, and should have been
easily flushed from the workplace by the ventilation system prior to re-entry. Consequently,
blast fumes are not a major concern. So, the
primary concern for Canadian metal mines is
the control of by-products of diesel combustion, and due to the volumes of air currently
supplied to dilute these by-products, for the
most part, all other contaminants are also controlled.
What are these ventilation requirements
in dieselized mines? Firstly, there is a dilution
requirement of the raw exhaust, and secondly,
the regulations pertaining to personnel exposure stating threshold limit values (or TLVs). In
Canada, the dilution requirements vary widely
according to the provincial jurisdiction (Gangal
and Grenier, 2002). Where specifically stated,
at the least, it could be 0.045 m3/s/kW (71
cfm/bhp) where multiple diesel vehicles are in
use, and then it ranges through various values
to a maximum of 0.092 m3/s/kW (145
cfm/bhp) for vehicles with non-certified
engines. In addition, the regulations could be
either a common fixed value for all vehicles
regardless of engine type and fuel used (e.g.
0.063 m3/s/kW,100 cfm/bhp), or a specific volume for a particular engine with a certain quality fuel (sulphur content) as a result of engine
certification according to CAN/CSA (1990) or
MSHA (1996) criteria.
Where certain Canadian provinces have
adopted the certified engine approach to determine ventilation rates, this has allowed mines
to take advantage of clean engine technology,
such as electronically controlled engines and
low-sulphur fuels to alleviate the air volumes
required underground. For such engines and
fuels, CAN/CSA flow requirements of 0.032 to
0.044 m3/s/kW (50-70 cfm/bhp) are not
uncommon (Natural Resources Canada, 2002).
At Barrick Gold’s Bousquet II mine, this change
meant that it would not have to increase its
ventilation as it went deeper to combat
increasing leakage and resistance, and hence
reduced airflows. Similarly, the mine no longer
CIM Bulletin ■ Vol. 97, N° 1080
May 2004
needed to proceed with ventilation automation
and directing flow only to those areas requiring
it, despite it offering attractive cost savings
(Hardcastle et al., 1999) Therefore, with mechanization and increasing equipment size, the
regulations dictating diesel exhaust dilution
requirements can play a significant role in the
economics of ventilation and mine viability.
With respect to personnel exposure limits,
some of these are met through the dilution
requirements of such encompassing relationships as the EQI/AQI that is used in the
CAN/CSA standard (CAN/CSA, 1990). However, over the last 10 to 15 years, the solid fraction of the exhaust, diesel particulate matter,
due to the suspected carcinogenic nature of
some of its components has become a concern.
The Canadian ad hoc Diesel Committee suggested a DPM limit of 1.5 mg/m3 in 1990 that
was subsequently adopted by several provincial
jurisdictions. This was the first diesel soot regulation in North America. However, of possibly
more concern is the pending legislation in the
United States that is currently under review
(MSHA, 2001), that other countries could follow. MSHA originally proposed an interim
0.40 mg/m3 limit for total carbon (TC), which
constitutes about 80% of DPM, to be followed
by a final limit of 0.16 mg/m3 TC. Although this
could mean that a much cleaner environment
has to be supplied, it cannot be addressed by
ventilation alone and other control measures at
source will be required.
The next area of concern is the global
environment. Here, like all industries, mining is
responsible either directly or indirectly for the
production of greenhouse gases (GHGs). In
mines, direct sources include diesel engines,
explosives, air heating fuels and strata gas;
indirect sources are through the use of electricity that has been generated from carbon-based
fuels. According to “Canada’s Energy Outlook
1996-2020” (Natural Resources Canada,
1998), the mining industry’s energy requirements have increased since 1996 and will continue to increase through to 2020 at a greater
rate than the rest of the industrial sector. As an
increasing energy user, the mining industry will
also be an increasing producer of GHGs. In
1997, the Canadian government’s position at
the Third Conference of Parties on Climate
Change, Kyoto, Japan, was to reduce GHG
emission to 3% below 1990 levels by 2010
and then by a further 5% by 2015. The Canadian government’s current position on GHGs is
to reduce emissions to 6% below 1990 levels
by 2010, consequently, energy usage and alternate energy forms will have to be addressed
industry wide.
With respect to energy usage within a
mine, in Canada, ventilation accounts for
approximately 40% primarily through the use
May 2004
CIM Bulletin
of electricity for fans and through fossil fuels
for heating. Within fans, auxiliary ventilation
systems can account for up to 50% of the electricity consumption. The other main electricity
user is compressed air systems that typically
account for another 40%. The proportion of
energy usage would increase further where
mines also had to refrigerate their air. Therefore, if mines cannot eliminate the use of compressed air, energy reductions would have to be
achieved in their ventilation systems.
So, summarizing the drivers of ventilation,
increased need to remove heat, larger diesel
equipment and more stringent exposure regulations, historically have meant more air and
increased power, cost, and GHG emissions. In
opposition to this, remaining cost effective and
reducing GHG emissions through less power
usage would tend to indicate less air should be
supplied. The only way both these goals can be
achieved is through innovation and better
management and or utilization of the air sent
underground.
Ventilation Design—Current Practice
In order to find potential savings in ventilation, one must look at how ventilation systems are designed and operated, and how they
have developed through a mine’s life. Historically, mine ventilation systems are designed
upon peak demand based upon diesel or heat
criteria, and are operated at this maximum
level regardless of the true demand. A common
scenario is to continuously ventilate every
potential working level/area with air from surface and distributed through auxiliary systems.
For example, when Barrick Gold’s Bousquet II mine was considering increasing its ventilation (Hardcastle et al., 1999), it initially
supplied air to 12 potential working levels
despite only having the equipment to operate
at 10 locations. Upon expansion and increasing
the size of the engines of its LHDs, the potential number of working levels could increase to
18 and the volume required at each location
increased by 30%. In combination, these
changes would dictate a 58% increase in the
total flow entering the mine if all the potential
locations were ventilated according to the
diesel requirements. Without new surface connections (ventilation raises), the higher ventilation demand combined with increased depth
and leakage would result in a 375% increase
in power and hence cost. This was unacceptable and the mine started to pursue ventilation
automation whereby air would only be supplied to the active levels and the mine could
operate with the same volume of air entering
the mine. Despite the benefits of ventilation
automation, changes in diesel regulations rec-
S.G. HARDCASTLE and C.K. KOCSIS
ognizing clean engine technology and production demands resulted in automation being
uneconomical considering the remaining life of
the mine.
At another mine (Hardcastle et al., 1998),
one crew was responsible for drilling, blasting,
and mucking at each production location. Consequently, they only required the high volumes
prescribed for LHD diesel activities for half of
their eight-hour shift, twice a day, and ten
times a week. For the rest of the shift they
would be operating electric-hydraulic drills.
Therefore, it could be shown that a ventilation
system working constantly at peak demand
would be overventilating the mine 77% of the
time. Furthermore, on defining the flow needed
for the drilling period of the production shift,
plus the requirements of the maintenance night
shift and the flow for weekends and holidays, it
could be shown that the power required for a
ventilation system modulated to meet demand
would only be 8% of a fixed flow system. In
addition, the average flow through the mine
would also be reduced by 38%, which would
be directly reflected in reduced heating
demands.
Even in mines that operate 24/7, there
can still be times when less air is required and
locations that do not need air that would otherwise be ventilated with a fixed flow peak
demand system.
Another trend is that as mines have gone
beyond their original design, they have kept the
same ventilation practice without checking its
applicability under the new conditions. This was
the case at Falconbridge’s Kidd Creek mine
(Hortin and Sedlacek, 2002). Initially, it was
designed as a shallow 850 m mine with a simple push-pull ventilation system. This mine is
now mining down to 2100 m and planning to
go to 3100 m. As the mine deepened, the same
push-pull method of ventilation was maintained to the point that it had 200 “main” fans
that were consuming 12 000 kW despite models showing it only needed 7000 kW. Further
modelling showed that for the planned deepening, the operating cost of this inefficient primary ventilation system would increase from
CDN$4.32 M per year to CDN$11.4 M per
year. Consequently, the mine re-evaluated its
ventilation design and decided to switch to an
exhaust system with 70% reduction in
annual operating costs, which more than justified the CDN$11.9 M conversion cost.
When one really starts to look at where
and when ventilation savings can be achieved,
one must ask the following questions:
• Do all areas need to be ventilated, i.e., are
they truly active?
• Do these areas require a constant volume;
does drilling require the same volume as
mucking?
53
S.G. HARDCASTLE and C.K. KOCSIS
CIM Bulletin
• In an active area with multiple headings,
are all auxiliary systems required at the
same time?
• For how long should the ventilation be supplied at any location?
• For what period of the shift is the mine
active?
• Have the original system design criteria
been exceeded?
When the answers to these questions are
considered with the ventilation/power cubic
relationship, even small airflow reductions can
become significant power savings.
Conversely it must be asked, is ventilation
required during the non-active periods? In
some instances it is required continuously, such
as to control radiation or flammable gas levels,
but is this as demanding as for diesel usage? It
can also be needed for dust control and blast
fume clearance, but again, is it required at the
same magnitude and for how long? In deep
mines, ventilation is required to remove heat,
but considering the strata is an infinite source,
what would be the result if the airflow were
stopped for a few hours or a day? Obviously
the area could heat up, but how long would it
take for the area to return to suitable conditions once the airflow was resumed. In some
mines, where large auxiliary ventilation fan systems are used, they can actually increase the
temperature of the air downstream.
Therefore, although ventilation systems
have to be designed to meet a peak demand,
they need not necessarily always operate at
this level. For the most part, the industry has
recognized this, and mines have made various
efforts to control their ventilation. However, the
full benefit has never been achieved. The primary cause for this has been a lack of the necessary control and information-gathering
infrastructure.
For optimal efficiency a mine requires a
“ventilation-on-demand” based system (Hardcastle et al., 1998, 1999). Such systems are
comprised of four main building blocks:
1. Decision Logic — In order to be able to
direct the air accordingly, it is essential to know
where the primary demand is at any time. In
highly mechanized mines, this means knowing
where vehicles are and their identity. This
requires a reliable and cost-effective vehicle
tracking and identification system, and it is the
lack of such a technology that has been one of
the hurdles to the implementation of the
demand concept. Depending upon the degree
of control to be achieved, i.e., mine-wide as
opposed to local, the actions prompted by such
a system may also have to be evaluated
through ventilation simulators to ensure their
validity and safety.
2. Control Devices — In a ventilation system,
there are two types of control, active (fans) and
54
May 2004
passive (doors and regulators). Today, both can
be controlled easily and cost effectively. Fans
can be fitted with remote soft starters and their
delivery controlled through either variable pitch
or speed. Most commercial ventilation doors
can be adapted for remote operation to turn
the airflow on or off in specific areas. Some
doors can also act as regulators when partially
open; alternatively, specific regulators with a
finer control of volume may be required.
3. Compliance Monitors — To ensure the system is working effectively, two types of monitoring may be required. First, the airflow
designed to go to an area must be guaranteed.
For this non-intrusive ultrasonic airflow, sensors
are best suited to active mine airways however
other technologies may also be considered in
ducts. Second, the quality of the air must be
ensured. For this, there are a variety of single
and multiple gas monitors available to measure
the by-products of diesel activity. However, the
placement of gas sensors and flow monitors
cannot always guarantee that an equipment
operator is in “clean” air, so such systems may
have to be supplemented with on-board gas
monitors.
4. Communication/Management Infrastructure
— This is the backbone and brains of the system by which information is gathered, commands sent, and the outcome determined. The
availability of reliable and cost-effective communications and programmable control has
historically been another hurdle to the implementation of the demand concept. However,
with the advancements of the information age,
this demand concept has become more achievable as it can often be piggy-backed on other
control systems being implemented within
mines.
CANMET-MMSL has been a long-standing
proponent of “ventilation-on-demand,” and
consequently, considerable resources have
been put toward developing the supporting
technologies needed for its implementation. In
1998, the concept was proven in conjunction
industry through a pilot trial at Barrick’s Bousquet mine (Hardcastle et al., 1999). More
recently, a new in-house designed vehicle
tracking system is being tested at the Val d’Or
Experimental mine as part of a demonstration
ventilation control system. Currently, CANMET
is also performing a feasibility study for such a
demand system in a deep Canadian mine.
Maximum Airflow Requirements
Through ventilation automation and the
demand concept, the number of places to
which air is supplied and its duration can both
be reduced. Consequently, the average and
even total flow through the system can be
reduced and significant cost savings achieved
due to the cubic relationship. However, the
maximum flows supplied have yet to be
addressed.
Again, the starting point is the requirement to control heat or dilute diesel fumes but
depending on how this is addressed, the peak
demand can differ greatly.
First, looking at diesel exhaust control, the
differing provincial regulations (Gangal et Grenier, 2002) have already been discussed in
respect to the volumes required. Across
Canada, there can be as much as a 2:1 difference between the required flow for a piece of
equipment at a given engine size. This can
depend either on whether old potentially
“dirty” or new “clean” engines are used, or on
whether the CAN/CSA certification air quality
approach as opposed to a fixed requirement
are employed. Initially, it might be thought that
heat issues would override the benefit of using
clean engine technologies in deep mines. At
depth this is true, but there is the possibility to
minimize peak demand elsewhere in multidepth operations that is important as it can
reduce the overall demand on the ventilation
system.
Another aspect that may be considered is
the operational layout of the mine and an
equipment operator’s relationship to any generated contaminant (Hardcastle et al., 1998).
For example, in some mines, an LHD operator
when loading may effectively always be in fresh
air and any contaminants generated are
rejected to a return air system; in other mines,
an LHD operator could be in a captive area and
exposure is unavoidable. Do both of these scenarios require the same volume of air? In “captive” areas, the prescribed ventilation may not
be sufficient. In a study of an auxiliary ventilated room and pillar operation it was shown
that a complete flush of the working room took
20 minutes, but the LHD cycle time was only 8
minutes, so the operator was always returning
to a contaminated environment. Another consideration is what influence contamination may
have if it comes into the general mine atmosphere as opposed to being rejected from the
system. In the same room and pillar study, the
LHD operator travelled to an ore dump downwind of the mucking site; this route accounted
for >50% of his diesel/dust exposure.
When it comes to heat management,
should ventilation be designed upon the worstcase scenario for heat generation or some
other situation? For heat, similar considerations
to diesel exposure could apply. If LHDs are
being operated remotely, if the operators are in
air-conditioned cabs or if the heat from the
machinery is being rejected elsewhere, what
are the ventilation requirements? If the operator is no longer a concern at the muck pile, the
CIM Bulletin ■ Vol. 97, N° 1080
May 2004
ventilation can be designed for the machine’s
requirements which can be less demanding.
Depending on operational layout, it may be
possible within the general body of the mine to
determine ventilation based upon the
machine’s heat generation while in transit.
These requirements would be significantly less
than required at a fixed location where the LHD
is working much harder.
For heat control, the number and location of fans within the system can also be significant. At the Kidd Creek mine (Hortin and
Sedlacek, 2002), it was estimated that continuing with the push-pull system of ventilation
would ultimately require 25 250 kW of fan
power increasing the heat load and raising
wet-bulb temperatures by 2°C to 3°C and
dry-bulb temperatures by 8°C to 12°C. On
converting to an exhaust system, it was estimated that ultimately only 8700 kW of fan
power would be required. In addition, this
lower heat load would be downwind of mining operations. Consequently, depending on
the proximity of the fan heat source, less air
could be required to maintain the same working environment.
So once again the assumed maximum
demand might not be the true demand due to
the variability of operations, ventilation layouts
(including the placement of fans), and how
these relate to personnel exposure. Each mine
has to be evaluated independently and it is
through an understanding of what is truly
needed that there is potential to reduce the
overall volumes of air sent underground.
The Benefits of Future Technology
To reduce the ventilation challenge with
depth one must reduce the need for air supplied at its current volumes. So far, the need for
ventilation has been discussed in terms of
diesel requirements and heat control, but can
technology change these requirements?
Returning to diesel equipment, such units
are popular because of their mobility, and most
mining operations are reluctant to replace
them with tethered electrical equipment
despite the obvious removal of diesel contaminants and significantly lower heat generation
(35% of an equivalent diesel). However, a
diesel-electric vehicle as being currently evaluated by CANMET-MMSL could be beneficial. In
this unit, a constant load diesel generator feeds
batteries, which in turn power electrical motors
that drive the equipment. To understand the
benefit of what is still a diesel unit, one needs
to understand the engine certification criteria.
Typically, the required airflow to dilute an
engine’s exhaust is either based upon the worst
operating condition or an average of multiple
May 2004
CIM Bulletin
operating conditions. In a hybrid diesel/electric
unit, the constant load diesel generator can be
optimized for minimal emissions and hence
lower dilution air requirements.
This technology, similar to diesel regulations based upon air quality, will not have a
direct impact upon ventilation needs in deep
mines once heat becomes the controlling criteria. This is because it will still produce the same
order of heat as a conventional diesel unit.
However, similar to the air quality approach, it
could significantly reduce the quantities at the
higher elevations of multi-level mines, so making more air available at depth.
Another area CANMET-MMSL is currently
investigating is the viability of hydrogen fuel
cell-powered vehicles for use in underground
metal mines. Wide-scale application of this
technology to the primary production fleet
could dramatically reduce the volumes of air
needed underground where the dilution of
diesel fumes is the primary concern. So similar
to the hybrid vehicle, the use of this technology
in areas where heat is not the concern will free
up ventilation capacity for heat critical areas.
Fuel cell-powered vehicles, however, could
have an additional advantage in deep mines. In
terms of heat generation, they are comparable
to electric units, which only use 35% of the
power of an equivalent diesel, which ends up
as a heat load in the environment. For fuel cellpowered vehicles, the reduced power and subsequent heat generation advantage could be
even greater because a certain portion of the
machine’s heat could be required to release the
hydrogen fuel from the hydride bed where it is
stored. Consequently, where the additional
heat from the machinery, above that from other
sources, would dictate higher volumes, the use
of fuel cells as opposed to diesels would reduce
that additional demand.
The most advanced technology that could
be applied to mining is Telemining™ (Baiden,
1999) with remotely controlled equipment
operated from surface. This concept was investigated and shown to be achievable under the
Mining Automation Program (MAP) between
1996 and 2001. This was an international collaboration between: Inco, a Canadian nickel
mine operator; Sandvik-Tamrock, a mining
equipment supplier; Dyno Nobel, an explosives
manufacturer; and the Canadian government’s
Natural Resources Canada’s mining research
sector (CANMET-MMSL).
With respect to ventilation (Hardcastle
and Kocsis, 2001), such automation has the following benefits:
• In the absence of humans in the production
areas, the dilution of diesel pollutants is no
longer a concern and the design criteria
shifts to heat which can be much less
demanding.
S.G. HARDCASTLE and C.K. KOCSIS
• In an automated mine when the design criteria shifts from diesel fume dilution to
heat, it can also shift from the mobile diesel
equipment to the stationary electric drilling
equipment.
• At depth, when heat typically starts to
become a concern in conventional mines,
designing ventilation requirements for
machine heat limits at 40°C dry bulb for
their hydraulic systems, as opposed to
<30°C wet bulb for humans would be less
demanding.
• Due to greater machine utilization, less production machinery would be required for
the same mineral output; hence the overall
volumes required would decrease.
• As there would be fewer personnel in the
mine, significantly fewer diesel personnel
carriers would be needed and the overall
ventilation demand would again be less.
In combination, these reduced ventilation
demands and hence power and cost savings
would be significant. Despite this, in deep
mines the volumes required for a single piece
of machinery would still be of the same order.
For example, an LHD in an automated mine
could still require two to three times more air at
3000 m than would be required for diesel
exhaust dilution based upon 0.063 m3/s/kW.
However, in an automated mine, the
machines are only affected by the thermal environment, the actual quality of the atmosphere
is secondary as long as there is sufficient oxygen for diesel vehicles to operate. As part of the
MAP program, it was shown that diesel performance would start to drop off at 17% oxygen. To maintain this level, a fresh air supply
rate of 0.00084 m3/s/kW would be required
(Sarin et al., 1997). This is 1.3% of the dilution
requirement. Consequently, the air supplied to
keep equipment cool does not have to be fresh
air delivered from surface, it could be recirculated.
Using controlled recirculation of air would
greatly benefit deep mines as it reduces the
volume that has to be brought underground
through shafts and raises which can be the
most expensive aspect of ventilation. To some
degree, this could increase the volumes
required because the recirculated component
would be hotter than that coming from surface.
However, depending on the size of the recirculation circuit, the heat generated from the
equipment above local strata conditions could
be lost before it is recirculated. Furthermore,
the use of local refrigeration as opposed to surface cooling, in combination with recirculation
as proposed for ultra-deep manned mines in
South Africa (Ramsden et al., 2001) could also
be beneficial in limiting the volume of air
required to be brought underground and also
the cooling requirements.
55
S.G. HARDCASTLE and C.K. KOCSIS
CIM Bulletin
Ventilation Design — Future Practice
The preceding sections have only discussed in general terms how the volumes that
are supplied underground can be minimized
and used effectively. Initially, this can be
achieved through “ventilation-on-demand”
and only supplying the appropriate amount of
air. Secondly, considering design, equipment
power sources, and level of automation could
reduce the actual quantities that make up this
demand. To find the optimum solution, considering all the variables, the industry needs better
economic-based models.
In addition, one area that has not been
looked at is the physical elements of the distribution network and for ventilation systems to
be their most cost effective, we must again
return to current ventilation design practice to
see how one comes up with a specific design.
A typical design practice is to define what
volume of air is required at some point in the
future (say five or ten years from now), and
then size the infrastructure accordingly. For
example, primary airways are often designed
upon their final requirements, which could be
oversized for a significant portion of the mine’s
life. These airways can also be designed in isolation without considering their interrelationship with the rest of the ventilation system. This
could lead to potentially oversized airways,
developed at unnecessary extra expense, or
proposed costs that could negate the viability
of the mine. So again, better economic-based
models are required.
Today, mining process simulators that can
display the development of a mine from start to
finish are being used to test varying mining
scenarios and the economics thereof. For example, such simulators were used by Inco to show
how Telemining™ would improve the economics of a low-grade deposit on considering the
accelerated extraction and increased equipment utilization that the automated process
could provide.
The authors believe and are currently
exploring how such process simulators, which
show the whole mine life, could be adapted to
forecast the need for materials or a specific
resource, and one of these would be the ventilation. The results from these would then be
used in standard ventilation simulators to
determine the ventilation costs. Using such
simulators, it should be possible to:
• Compare the long-term life cycle requirements
for the ventilation system under various mining methods, with different mobile equipment,
and at various levels of automation.
• Evaluate the short-term life cycle requirements as would be supplied in a “ventilation-on-demand” system.
56
May 2004
• Obtain the minimum through to maximum
ventilation requirements, the duration of
each, and what processes are contributing
to the peak demand.
• Explore options to reduce peak ventilation
demand similar to electrical power management practice.
• Integrate in parallel the development of the
ventilation system with mining, so heading
toward “pay-as-you-go” as opposed to
developing for final requirements with high
upfront costs.
• Size the infrastructure according to life cycle
demands as opposed to final or peak
demands. For example, it may be more cost
effective to have a slightly smaller fan or
raise and pay the penalty for the duration
the higher demand is required.
Discussion Summary
Ventilation will continue to be a requirement in underground mining. For the most
part, it is either necessary to dilute and remove
diesel contaminants or heat to provide an
acceptable working environment for personnel
and/or machinery. What will change is the volume of air required.
Ventilation can be expensive, not only due
to the power used by fans, but also the need to
climatize the air with heating or refrigeration.
Increasing depth and mechanization and more
stringent health regulations would generally
dictate that more air is supplied. However, any
increase in ventilation can produce a disproportionate increase in power usage and hence
cost due to a cubic relationship.
Consequently, to avoid prohibitive ventilation costs, the industry must try and minimize
the volumes being sent underground to what is
needed for their current mining method, and
explore the potential for further reductions
through the application of new technology. This
paper has shown that there are significant benefits to “ventilation-on-demand” whereby supply is modulated to match needs of production.
Furthermore, the physical needs of a production
process can be dependent on mining layout, the
power source of the primary production equipment, and the degree of automation.
In regard to the challenges imposed of the
ventilation system with depth in Canada:
1. In multi-depth mines, where ventilation is dictated by either heat or diesel requirements
depending upon depth, a wide array of strategies can be used to mitigate ventilation demand:
• Cleaner diesel engine technology, hybrid
engines and fuel cells can be used in shallower regions to reduce their ventilation
demands and free-up capacity for the
deeper areas.
• “Ventilation-on-demand” should be used
throughout.
• At depth, automation should be considered,
due to its higher heat tolerance, and insensitivity to other contaminants that would
accommodate the controlled recirculation
of air.
Such strategies can be essential for Canadian
mines if they are to avoid or limit the use of
refrigeration. Currently, Inco’s Creighton and
Falconbridge’s Kidd Creek, employ natural
cooling of their air, however these systems have
limited cooling power so it is essential they are
used effectively.
2. In deep mines where heat is the overriding
factor, “ventilation-on-demand” and isolating
humans from the heat effects should be the
strategies to pursue. Automation can obviously
remove the human as far away as the surface,
but mine layouts can also be modified to reject
heat away from personnel and machinery operator cabs can also generate their own micro-climates.
Conclusions
Ventilation is an expensive prerequisite
for underground mining. Current mining
trends, including greater depth, would generally require that increasingly more air is
required and consequently more power consumed. At depth, heat becomes the overriding
ventilation issue and refrigeration is always an
option but this can greatly increase power consumption. Power usage is not only a cost issue
but is increasingly becoming an environmental
issue when, worldwide, industry is trying to
reduce greenhouse gas emissions.
For Canadian mines, it is believed that on
reviewing the way we design our ventilation
systems and exploring technologies that reduce
the demands upon which we base our designs,
considerable savings can be achieved.
Quantifying these benefits is extremely
difficult, yet it must be done to prove the viability of deep deposits and what might otherwise appear as marginal orebodies.
Consequently, although designing and supplying ventilation in deep mines will remain challenging, the same basic methods and options
we have been using for years will still apply. The
major challenge is to keep ventilation from
being cost prohibitive, and for that we need
improved economic model capabilities.
References
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hard rock metal mining at Inco Limited. Website:
http://www.telemining.net/publicationsandresearch/.
CIM Bulletin ■ Vol. 97, N° 1080
May 2004
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CIM Bulletin
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CALL FOR PAPERS
Lead & Zinc ‘05
Kyoto, Japan — October 2005
The Lead & Zinc ‘05 Symposium, co-organized by The Metallurgical
Society of CIM, will provide an international forum for the world’s lead
and zinc industries to exchange information on current processing
technologies for primary and seconday lead and zinc, as well as emerging technologies for both metals.
Authors are encouraged to submit 150-word abstracts by
September 1, 2004, in electronic format, to the MMIJ Conference
Management System at http://www.mmij.or.jp/lead-zinc2005/ or to
J.E. Dutrizac, CANMET-MMSL, 555 Booth Street, Ottawa, ON, Canada
K1A 0G1; Tel.: (613) 995-4823; Email: [email protected].
May 2004
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