The analysis of ventilation and cooling requirements for mines

and coo lingThe analysis of ventilatiorequirements for mines

by J. VAN DER WALT*, Pr. En ., Ph.D. (Eng.), F.S.A.I.M.M., E. M. DE KOCK*Pr. Eng., B.Sc. (Eng.), and L. K. MITH*, Pr. Eng., C. Eng., B. Tech.

SYNOPSISA systematic approach to the analysis ofalternat ve methods of ventilating and cooling large hot mines is presented.

The important factors that have a bearing on ve tilation and cooling requirements and practices, such as air flowthrough the mine, geographical distribution of eat loads, and micro-ventilation considerations, are dealt with.The analysis of these factors leads to definitive entilation and cooling strategies, air and water process design,specifications of details, and designs of the associ ed plant and equipment.

SAMEVATTING'n Sistematiese benadering om alternatiewe m todes vir myn ventilasie en verkoeling te evalueer word beskryf.

Belangrike faktore soos massa lug vloei, geografi se verspreiding van hitte bronne, mikro omgewings, ens., wordbehandel. Die evaluering van hierdie faktore lei ot finale en bepalende ventilasie en verkoelingsstrategiee, lug enwater vloei proses ontwerp, detail spesifikasies en ntwerp van die sisteem en toerusting.

Introduction

The method presented here for the analysis of ventila-tion and cooling requirements in large, hot undergroundmines is that general1y fol1owed by the authors. Themethod has been developed over several years, and isbased on expelience gained on a number of mines inSouth Africa and overseas. This development would nothave been possible without the research and develop-ment work conducted by the Chamber of Mines of SouthAfrica 1-5. The authors' exposure to mines in other partsof the world enabled them to modify the ventilation andcooling principles that had been established for the SouthAfrican gold-mining industry to suit the total1y differentrequirements of mines using a variety of mining methodsunder varying climatic conditions.

There are essential1y three types of ventilation andcooling projects.(1) In those associated with existing mines, the object

is to audit the ventilation and cooling practices sothat their inefficiencies can be determined andanalysed, and ways can be found of improving theunderground environment without having toincrease the ventilation and cooling infrastructuresignificantly6. As the layout of the mine and theflowrates of air are essential1y fixed, improvementof the underground environment depends primarilyon the success with which the utilization of air andexisting cooling plant and equipment can beimproved. These are referred to here as type Aprojects.

(2) In those associated with existing mines where theobject is to extend mining operations into newground and often to greater depth, the aim is tomake the best possible use of the existing facilitiesand to define the additional infrastructure required.An essential part of this type of project is to deter-mine the influence of worked-out areas and extendedairways on the underground environment for futuremining operations, and to revise the mining prac-

-""--* EMS Minerals (Pty) Ltd, P.O. Box 585, Bedfordview 2008,

Transvaal.@ 1983.

tices and long-term production planning to bestsuit them 7. These are referred to as type B projects.

(') In those for new mines, the aim is to create thenecessary infrastructure and to analyse the proposedmining methods and layouts to establish whetherthey are conducive to the creation of an acceptableenvironments. These are referred to as type Cprojects.

The achievement of an acceptable undergrounde vironment often poses problems that are not onlyc stly to rectify but can result in serious losses, particu-I rly when these are associated with Iow productivity.T e reasons for these problems are multiple and can bes mmarized as fol1ows.( ) Often historical management and organizational

developments have not taken sufficient cognizanceof environmental control. The need for a well-established ventilation or environmental depart-ment has not been recognized by many mines,particularly the older ones and those which startedby mining the outcrops of an ore body. The long-term mine layout and production planning wereconducted without the necessary expertise on ven-tilation and cooling, and consequently the associatedinfrastructure (shafts, airways, major exhaust fans,cooling plant, and associated facilities) becameinadequate.

( ) Ventilation and cooling problems often escalate asmining operations extend into new ground. Theeffect of extending airways and keeping worked-outareas open usual1y results in

- an increase in the flow of pol1utants such as heatand radon from the constantly increasingsurface area of exposed rock, and

- an escalation of the problems associated with thedistribution and control of air and cooling waterto the working places4.

() The thermodynamic and thermal behaviour of minesis complex and difficult to quantify. The significanceof phenomena such as autocompression, the geo-thermal gradient ofthe earth's crust, thermal inertiaof the side wal1s of excavations, etc. is often not

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND ETALLURGY FEBRUARY 1983 25

----.---..-

DEFINf: PRODUCTION. VU,lILATION MID C{)lJlltiG 14()UU~;{IN CUIUUliUllJN WITH Ill" t~II't I

ANALYSE AIR FLOW lHROU~H MINE!

IPRlPARE HEAT LOAD DATA PROFORMA FOR EACH GEOGRAPHICALI

. .PfWDUCTIDN AREA

(DISTINGUISH BETWEEN TEMPERATURE DEPENDENT AND INDEPENDENT HEAT LOADS

COMPUTE DETAIL HEAT LOAD CALCULATIONS([)ISTII,GlIISH BETWEEN AIR AND SERVICE WATER

COOLING)

EVALUATE MICRO VENTILATION SCENE

I DEFINE VENTILATION AND COOLING STRATEGYPARAMETERS)

PREPARE VENTILATION ANDCOOLING STRATEGIES

{AIR FLOWRATES FIXED}

PREPARE VENTILATION ANDCOOLING STRATEGIES

lAIR FLOW RATES TO BE DETERMINED)

COMPLETE WATER SIDE OF VENTILATIONAND COOLING STRATEGIES

PREPARE DEFINITIVE VENTILATION AND COOLlN[i STRATEGIES

CONTINUE WITH DEFINITIVE AND DETAIL DESIGN

Fig. I-Project sequence in the analysis of ventilation and cooling requirements for mines

26 FEBRUARY 1983 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

fully understood, resulting in the provision of facili-ties that are inadequate.

(d) The thermodynamic and process design require-ments associated with ventilation and cooling areoften in conflict with practical operational con-straints.

(e) Ventilation and cooling engineering on mines ismulti-disciplinary and involves the co-ordinatingand planning of mining, process, mechanical, electri-cal, and instrumentation engineering. In otherwords, it is project-engineering orientated, which isoften not recognized.

Analysis of Requirements

The most important aspect in the auditing andengineering of ventilation and cooling systems forunderground mines is the preparation of definitiveventilation and cooling strategies. These strategies aresimilar to those for the dilution of other pollutants suchas radon, methane, and diesel exhaust fumes, exceptthat they are more complex and involve considerablymore calculation. These strategies have the followingobjectives.(i) They serve to define the policy to be followed by the

mine, as well as the operational responsibilitiesassociated with ventilation and cooling that are tobe borne by the various departments on the mine,viz mining and production engineering, engineeringservices, environmental (ventilation) engineering,etc. It is therefore essential that the senior personnelof each department, who have extensive experienceof the mine, should provide the input for the pre-paration of the strategies. Furthermore, it is essen-tial that the strategies devised should be acceptableand clearly understood by all who will be concernedwith their implementation. To ensure that themeasures and decisions finally agreed upon arecarried out, it is preferable that a senior manager,or even the Mine Manager, should assume theresponsibility for co-ordinating their preparation.

(ii) The associated major capital and operating expenses(such as those for shafts, airways, major fans,refrigeration machines, cooling towers, bulk spraycoolers, stope air coolers, pumping, and piping)are all determined.

(iii) The strategies serve as the basis for the processdesign of the ventilation-air and cooling-watersystems, and the refrigeration installation,as well as for the process analysis of the entireventilation and cooling system. Here processanalysis means the evaluation of the performanceand utilization of equipment under the variousconditions that exist on the mine.

A diagram showing the sequence of activities in thepreparation of definitive strategies is given in Fig. 1 forthe three types of projects referred to previously. Thediagram depicts the various steps and the iterative natureof the preparation.

Production, Ventilation, and Cooling ModelsMines are usually too complex, and the future produc-

tion planning too undefined, to permit the preparation of

etailed strategies. Care must therefore be taken not toc eate too much work in their preparation for one soonr aches a point of diminishing returns.

The exercise should start with simplified ventilationd cooling models that accurately represent the currentd expected future production scenes on the mine.

hese models define the production areas geographically,s well as the principal routes for ventilating the variouseas. A model should be prepared for each future

roduction phase, starting with a situation, say, 3 to 5ears in the future and further models for, say, 7 to 9,

12 to 15, 18 to 22, and 25 to 30 years in the future. Inefining the models, it is essential that all concerned, andarticularly the production engineering staff, should be

i volved. Mistakes or erroneous interpretation ofproduc.t on requirements at this early stage will inevitably resulti a considerable amount of abortive work, and will leadt incorrect assumptions and decisions.

Each geographical production area is defined by. the production for both ore and waste,. the centre (depth) of production, as well as the

geographical boundaries, i.e. the shallowest anddeepest production levels,

. the virgin-rock temperature at the centre ofproduction,

. the total length of haulages, airways, and accesses,as well as their average cross-sectional dimen-sions, and

. the number of stoping areas and the average dimen-sions of stopes and working excavations, eachstoping (mining) method being treated separate-ly.

A geographical production area is defined in such aanner that a ventilation and cooling strategy can be

evised on the assumption that all production is on oneI vel, i.e. at the centre of production, and the extremities0 the area do not have to be treated differently from thea erages. Fig. 2 depicts the principle of a simplified

odel, and Fig. 3 indicates the model for a typical mine.

SURFACE--rT7T

>-...«IV1

>-"-<tIV1

~z30

.0

MINING AREA:UPPER LE VE L :LOWER LEVEL:PRODUCTION:MEAN ROCK BREAKING DEPTH:VIRGIN ROCK T~MPERATURE:NUMBER OF STOPES:LENGTH OF AIRWAYS:

>-V1<tuCl.:::J

F g.1- The principles of a simplified production, ventilation,a d cooling model defining a geographical production!area

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND ETALLU~GY FEBRUARY 1983 27

.....::.rv>

.....

~:rv>

'"Z

.....::.:r111m

Z .....~::r:v>

'"Z

z>-::.:rV>->Z

.:u

B4[ .§i':::::"'

~;:":'Ofl1:~

'

b' '~

\;~;i f::'-'?

,-. 5 0", I'~

~~"cD

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~3000m

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AREA "A": "MAIN" ORE BOOY; BOOm TO 1700111,PRODUCTION 10200 TPM; M,R.B.D. .1500m: 36°C VR.T.; B STOPES;

74000m AIRWAYS.

AREA "B": "VERTICAL" ORE BODY; 2200m TO 2600..,PRODUCTION 57100 TPM; M.R.B.D.2500m; 5BoC VR.T. 22 STOPES;

76000m AIRWAYS. .

AREA "C": "INCLINED" ORE BODY; 2500m TO 300018;PRODUCTION 69000 TPM. MRBD.2BOOm. 65°[ VR.T. 26 S1QPES;

50000m AIRWAYS.

AREA "0": "HORIZONTAL" ORE BODY; 2000m TO Z509lo;PRODUCTION 10000 TPM; MR.B.O.ZZOQm; 5ZoC V.R.T. 9 STOPES;

63000m AIRWAYS.

N

Z3000",

Fig.3-A typical production, ventilation, and cooling model

Analysis of Air Flow through a Mine

Before the preparation and collection of data for thedetermination of the heat loads of the various productionareas of a model, it is necessary for the airflows, particu-larly the associated air velocities'aond pressure losses, tobe analysed briefly to ensure that the model represents apractical proposition. The following are guidelines foruse in the assessment of the practicality of models.(1) Flowrates should typically be between 3 and 5 m3/s

per kiloton per month at standard density. How-ever, values outside this range are not necessarilyincorrect or unacceptable.

(2) Pressure losses should typically be between 1000and 1500 Pa for each of the downcast and upcastshafts, and between 2000 and 4000 Pa through theworkings. The total pressure losses at this stage ofthe investigation should not exceed 7000 Pa. Thesevalues may be too high for shallow mines.

(3) Velocities should preferably be less than 7 m/s inintake airways that are in constant use. In the returnairways, where there is little activity, they shouldpreferably be less than 10 m/so Experience has shownthat mine layouts that have been based on higherair velocities often result in unacceptable pressurelosses.

When existing mines (type A projects) are audited, itis usually possible for the relationship between air flow-rates and pressure losses to be determined fairly accurate-ly. This also applies to type B projects provided theextensions depend largely on the existing shafts andairways. On type C projects (new mines), the sizes of


airways and shafts are usually dictated by the air flowrequirements and the above guidelines.

Heat Load Data and Data Proforma

Once the models have been prepared, i.e. the mine hasbeen divided into geographical production areas for eachof the future production phases, data sheets can beprepared for the collation of the necessary information.The data sheets have to comply with the requirementsof the model, and must present the results of the heat-load calculations in such a way that they can be trans-ferred onto the flow diagrams depicting the ventilationand cooling strategy. For this reason, the heat-load datasheet consists of two parts.

TABLE I

HEAT-LOAD DATA FOR THE SIDE WALLS OF SHAFTS

Exposed surface areaThermal diameterThermal ageHeat from side walls

m"mmthkW

In the first part, the tables distinguish firstly betweenheat loads that depend on air temperature and those thatare independent of temperature, and secondly betweenheat generated in downcast shafts, main interconnectingairways, airways in the geographical production area,and stopes (Tables I to IV.)

In the second part, the values are re-arranged anddistinguish between the geographical distribution of heat

loads for each of the various areas, i.e. shafts and/orinterconnecting airways, airways in the production area,and stopes. For each of these, the tables then distinguishbetween temperature-dependent and temperature-independent heat loads with the added complication ofdefining what portion of each of these should becountered by the ventilation air and/or by the use ofchilled service water (Tables V to VII.)

TABLE II

HEAT-LOAD DATA FOR THE WALLS AND BROKEN ROCK IN AIRWAYS

Development production (rock breaking)Heat from broken rock

t/mthkW

Airways and drifts:Total lengthAverage widthAverage heightAge of production areaHeat from side, hangingwall, and footwall

Number of development headingsFace advance for all headingsFace advance per headingDevelopment cycleHeat from side, hangingwall, and footwall

mmmmthkW

m/mthm/mthmthkW

TABLE III

HEAT-LOAD DATA FOR THE WALLS AND BROKEN ROCK IN STOPES

Stope production (rock breaking)Heat from broken rockNumber of stopesAverage length of stopesAverage width of stopesAverage height of stopesAverage time between blastsExposed rock surface areaHeat from side, hangingwall, and footwall

mthkW

mmmmthm2kW

TABLE IV

HEAT-LOAD DATA FOR ALL ELECTRICALLY- AND DIESEL-POWEREDEQUIPMENT

Utiliza-tion

%Rating

kWHeat

% kWShaft and shaft stations:

FansPumpsHoistsOther

Total

Airways:LocomotivesPumpsTransformers (kVA*)Other

Total

Stopes:FansScrapersLHD vehiclesOther

Total

*

TABLE V

H AT-LOAD DATA FOR HEAT GENERATED IN THE DOWNCAST SHAFT

Cold airkW

Cold servicewater, kW

T mperature dependent:Exposed rockGround water

Total

T mperature independent:FansPumpsHoistsOther

Total

TABLE VI

HEAT-LOAD DATA FOR HEAT GENERATED IN THE AIRWAYS

Cold airkW


T/3mperature-dependent:Exposed rockBroken rockGround water

Total

~ emperature-independent:LocomotivesPumpsTransformersOther

Total

TABLE VII

HEAT-LOAD DATA FOR HEAT GENERATED IN THE STOPES

Cold airkW


emperature-dependent:Exposed rockBroken rockGround water

Total

~ emperature-independent:FansScrapersLHD vehiclesOther

Total

Although it is possible to standardize on the formatf Jr the calculation and presentation of heat-load data,(are must be taken to ensure that a systematic and logicalEet of data sheets is prepared for each model, and that a(lear definition of the geographical boundaries and equip-I ent for each of these is given.

Calculations of Heat Load

The various sources of heat in the mine can be placedip. one of two categories: temperature-dependent or1emperature-independent loads. Temperature-dependent

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY FEBRUARY 1983 29

heat loads are those of which the magnitude depends onthe temperature of the ventilation air. There are essen-tially three sources of heat in this category: from the sidewalls of excavations and the broken rock, from wateron the footwall, and from fluids in pipes, e.g. groundwater that is pumped out of the mine in an uninsulatedpipe. Temperature-independent heat loads are those ofwhich the magnitude is independent of the temperatureof the air, e.g. all heat generated by electrically drivenequipment such as pumps, hoists, scrapers, and fans, aswell as heat from diesel-driven equipment such as loco'sand LHD vehicles.

Experience on a number of mines has shown thattypically 70 to 80 per cent of all the heat generated comesfrom two or three sources. On the gold mines in SouthAfrica, heat from the exposed rock surfaces dominatesthe scene to such an extent that other sources of heatare often ignored. On many coal or base-mineral mines,heat from mechanical equipment, particularly fromdiesel-driven LHD vehicles, is the major source of heat.On other mines, it may be the ground water or, whereblind-hole mining takes place, it could be the fans forventilating the blind-hole working ends, etc.

Much has been written on the subject of sources of heatin mines2,3,9-12. Reference is therefore made only to thesources of heat that often dominate the heat-load scene.

Heat from the Rock

Heat from the exposed rock surface, i.e. from the sidewalls, hanging walls, and footwalls of airways and stopesis often the major source of heat. Although the Starfieldmethod9 is the theoretically correct one for the calcula-tion of the heat load in airways, it is often difficult toapply because it depends on air velocities. These are notalways known with an accuracy that justifies the use ofthis method over others such as the Goch-PattersonmethodlO, which assumes that the temperature of therock face is the same as that of the air. Also, the accuracywith which lengths and average cross-sectional dimen-sions of airways can be obtained or anticipated is usuallyfar less than the improved accuracy obtainable withthe Starfield method. When the Goch-Patterson methodis used, the heat load for airways is likely to be over-estimated by about 10 to 20 per cent, and for this reasonit is advisable not to allow for a contingency in the heatload. Furthermore, care should be taken in the use ofthe Goch- Patterson tables that the correct value is chosensince two values are given for each time interval. Thefirst relates to the instantaneous heat load after a periodof time has elapsed and should be used only for shaftsand connecting airways that are old, i.e. 5 or more yearsafter the excavations have been completed. The othervalue is the time-average heat load, being a measure ofthe amount of energy stored in the rock walls, and shouldbe used in all cases where excavation and developmentwork is a continuous activity.

The calculation of heat from the side walls in stopesis usually difficult, and requires a fair amount of investi-gation before a reliable and satisfactory method can bedeveloped. This is because of the great variety of miningmethods, and the odd shapes and sizes of stopes associa-ted with them. For narrow-reef mining as found in the

gold mines of South Africa, and for some room-and-pillar mining, the method proposed by Van del' WaIt andWhillier2 gives satisfactory results. For other miningmethods, it is best to relate stopes to cylindrical equiva-lent shapes and to apply the Goch-Patterson methodl0.

The heat from broken rock is usually small comparedwith that from the side walls of excavations. The othertemperature-dependent heat loads, i.e. heat from groundwater and water on the footwall, can be neglected andoften are. As these can be detrimental to the environ-ment, they should be countered by containing the waterin a pipe that is preferably insulated. Seldom can thecost associated with an increase in air flowrate andrefrigeration requirements be justified to counter theeffect of heat from this source, although instances doexist8.

An essential part of the calculations associated withthe preparation of a flow diagram depicting ventilationand cooling strategy is the calculation of marginal heatloads. These are the portion of the temperature-depen-dent heat loads because the actual temperature of the airis above or below the 'reference' temperature (often takenas 30 °C).

Heat from Underground Ventilation Fans

Underground fans can be major contributors totemperature-independent heat loads since all the energyrequired for the fans is converted to heat. A phenomenonthat could easily be overlooked in respect of fans and theassociated rise in the wet-bulb temperature of the air asit passes through a fan is the amount of cooling that isrequired to re-cool the air to its original wet-bulbtemperature. Large underground booster fans mayrequire up to twice as much cooling energy as the energyabsorbed by the fan to offset its effect on the wet-bulbtemperature. Auxiliary fans require somewhat less,depending on the type of installation and the length ofdischarge ducts. In a number of instances where auxiliaryfans were used to force air through coolers and intostopes, the effect of the fan on the wet-bulb temperaturewas greater than the cooling effect of the cooler, resultingin a net increase in the temperature of the air passingthrough the system. In such cases, preference should begiven to other methods of ventilation and mine layoutthat would eliminate as many of the underground fansas possible.

Heat from Mechanical Mining Equipment

All the energy that is required to power mining equip-ment is converted to heat, and results in an increase inthe wet-bulb temperature of the ventilation air. The heatgenerated from the equipment depends on. the rated capacity,. the percentage of time it is utilized, which can vary

from as little as 5 per cent for poorly utilizedscrapers to as much as 80 per cent for continuousmining equipment, and. the extent to which the rated capacity is employed,which once again can be low for tramming equip-ment and high for continuous mining equipment. whether it is driven by internal combustion enginesor electrically.


It should be noted that the heat load associated withinternal combustion engines can be much higher than therated capar;ty of the equivalent electrical piece of equip-ment. In a number of instances where serious problemswith the thermal environment were experienced, a changefrom equipment driven by internal combustion enginesto electrically driven equipment alleviated the problemto such an extent that no further action was necessary.

Pumps and hoists located underground are also con-tributors to temperature-independent heat, even thoughthey a:re not necessarily major contributors. In thisregard, it should be borne in mind that most of the energyrequired to raise matter such as sludge, water, and rockgoes into increasing its potential energy. When matter islowered or transported horizontally, all the potentialenergy or the energy required to move it horizontally isconverted to heat. It should be noted that these heatloads are not based on the rated capacity of the equip-ment but on the actual mass and height that is raised orlowered during a given period of time.

Micro-ventilation and Cooling Strategy Parameters

Before strategies are prepared, the micro-ventilationscene, i.e. in stopes, drawpoints, etc., should be evaluated,which involves. the analysis and definition of layouts and design

principles in regard to the ventilating and coolingof the underground environment, cognizance beingtaken of all related matters;

. the definition of airflow requirements; and. the definition ofthe desired wet-bulb temperatures ofthe air entering and leaving in view of the expectedtemperature distribution in these areas.

When the heat dissipated by the exposed rock surfacesin working places is analysed, it should be borne in mindthat this heat is time-dependent and that it is often notpossible for cooling to be provided to offset the heatdissipated during the first few days after a blast. Thereason for this is that a large surface area at a tempera-ture close to the virgin-rock temperature is exposed, and itusually requires several hours or days for the skin of therock to cool to the 'reference' temperature.

For the determination of air flowrates in workingplaces, and of the required wet-bulb temperatures for theair entering and leaving them, the calculation of heatload is based on the average heat dissipated inthe first 15 to 20 per cent of the period between consecu-tive blasts. This implies that the temperatures willgenerally exceed the desired wet-bulb temperature forthat period. In the case of continuous mining, 01' whenblasting of the working face takes place once a day oronce every two days, this problem does not exist and thecalculation of heat load is fairly straight-forward.

One of the most important aspects in the evaluationof working-place layouts and design practices is thepreference for through-flow ventilation, which is thepassing of the majority of the air on a particular levelthrough each of the working places with a minimum ofair bypassing them and without auxiliary fans. Thisgenerally has the following advantages over the alter-native of forcing air to the working places with fans.(a) The temperature distribution is generally between

the temperature of the air entering and the tempera-ture of the air leaving. In the case of blind-holemining where it is not possible to employ through-flow ventilation, the temperature distribution in thestopes is largely unpredictable.

( ) The need for underground auxiliary fans is sig-nificantly reduced.

() The wet-bulb temperature of the air entering theworking place can often be significantly higherwithout jeopardizing the thermal environment.

( ) Less air is required to pass through the mine.() Less refrigerated cooling is required.

The main disadvantage of through-flow ventilation ist e requirement for ventilation doors and additionala ays and for their control, which could be costly.

reparation of Ventilation and Cooling Strategies

The model, together with the results of the associatedeat-load calculations and strategy parameters, can beresented in flow diagrams like those given in Figs. 4 and. Fig. 4 demonstrates the principles employed in the

s rategies, while Fig. 5 is a typical strategy flow diagram.Fig. 4, the basic flow path for the ventilation air is

s own along with the various cooling elements and theeat loads in the shaft, airways, and stopes. The effect ofdiabatic compression (autocompression) on the tem-erature of the descending air is taken into account in

t e leg depicting the downcast shaft. The flow diagramfers to the macro-ventilation and cooling scene, which

i applicable to the entire mine, as opposed to the micro-s ene, which is applicable only to the various working

laces.Although there are several types of strategies with

arying degrees of complexity and sophistication, theyn generally be placed into one of two categories.

(1) Those where the air flowrates are determined byfactors that are not related to the thermal environ-ment such as- the availability and sizes of existing shafts and

airways, and the ventilation and cooling infra-structure,

- the dilution of pollutants other than heat, i.e.dust, radon, noxious vapours, gases, etc.

This category is largely limited to type A projectsand to type B projects where the extension ofmining operations depends heavily on the utiliza-tion of the existing infrastructure. Experience hasshown that too little air is likely to be available fromthe point of view of the thermal environment.

2) Those where the air flowrates are to be determinedwith the aid of the strategies, Le. where heat is themajor pollutant. The amount of air passing throughthe mine in this instance is determined by factorssuch as- the micro-ventilation requirements in respect of

the wet-bulb temperature of the air entering andleaving stopes and working places,

- the preference for bulk cooling of the ventilationair, rather than cooling of the air at entrances tostopes and in stopes for practical considerations.

This category of strategies is applicable to type C


projects (new mines), as well as to type B projectswhere the extension of mining operations requiresa major new surface and underground infrastructure.

Cooling of Service Water

Service water is an integral part of the mine operation,and provides effective cooling in remote working placeswhere men are using the water and where the wet-bulbtemperatures are often high as a result of problems withventilation. Cooling with service water is essentially adirect form of cooling, i.e. the water is not used to coolthe ventilation air but to remove heat directly fromcertain sources, thus preventing them from raising thetemperature of the air. Because this form of cooling is soeffective in practice, it is essential that consideration isgiven to artificially increasing the quantity of waterused.

Bulk Cooling of Air on Surface

This type of cooling should be considered in all caseswhere the average daily wet-bulb temperature for thehottest month in the year is above about 16 DC. Thefactors that should be evaluated are the magnitude of thetemperature-dependent heat loads in the shaft and intakeairways, air leakages, and the year-round utilization ofequipment associated with the cooling of the air onsurface. In the evaluation of a strategy employing thisform of cooling, the marginal heat load is calculated andshown on the flow diagram in the same block that givesthe details of the temperature-dependent andtemperature-independent heat loads. The amount ofcooling that has to be wasted when the air is cooled onsurface can thus be assessed. Experience has shown that,when the air flowrates are low, or when shafts are wetowing to a continuous inflow of ground water, it is mostunlikely that cooling of the ventilation air on surface canbe justified.

The main advantage of cooling the air on surface isthat it reduces the amount of cooling to be done under-ground, and hence the flowrate of the cooling water,which is often a major problem on large installations.The operating and capital cost per unit of cooling is lowwhen compared with other alternatives. The successwith which surface bulk air coolers can be operated andmaintained generally offsets many of the inefficienciesassociated with them.

Bulk Cooling of Air Underground

Where underground cooling of the air is required, it isessential that consideration should be given to coolingthe air in bulk near to the shaft. This is particularly thecase where the effect of auto compression and shaft heatloads on the temperature of the air is appreciable. Thefactors that should be evaluated are the effect of the coldair leaving the bulk coolers on the temperature-depen-dent heat loads in the airways to the stopes, and theamount of air that leaks through worked-out areas andis therefore not used beneficially.

When air flow through a mine is limited to what canpass through the shaft and airways, the thermal capacityof the air after it leaves the bulk coolers is ofteninadequate, resulting in a rapid rise in the temperature


of the air due to the increase in temperature-dependentheat loads. In such cases, there is little merit in coolingthe air in bulk as it leaves the shaft unless the air flow-rate can be increased. In type B or C projects where theextension to mining operations requires additional infra-structure and shafts, the flowrate through the mine isusually determined by the requirement to cool the airin bulk without any subsequent cooling.

The relative ease, reliability, and success with whichbulk coolers can be operated generally justifies the in-efficiencies associated with air leakages and the increasein the temperature-dependent heat loads in airways.They remain an essentially fixed installation over thelife ofthe mine, and hence are more accessible and requireless manpower for maintenance, reduce the amount ofwater to be handled in stopes and airways, and have alower capital and operating cost per unit of cooling overthe life of the mine than those of the remaining alter-natives4.

Cooling of A ir at Entrances to Stopes and Working Places

Although this is not desirable for many practicalreasons4, it is often unavoidable for type A projects andcertain type B projects, viz when the air flow throughthe mine is inadequate and recirculation of the air isnecessary to introduce the required cooling. For practicaland economic reasons, cooling of air at the entrances ispreferred to cooling in the working places. Most strategiesinvolving coolers at the entrances to stopes require lessrefrigeration capacity than a bulk air-cooling installationfor the same end result. The reason for this is the loss ofcooling associated with air leakages and the increase intemperature-dependent heat loads in the airways whenbulk air coolers are employed. However, care should betaken that this does not become a decisive factor in thechoice of strategy since there are many practical con-siderations that are much more important than thisapparent saving.

The disadvantage of this method is that it is a move-able form of cooling installation that, if not fullyintegrated with the mining operation and properly main-tained, can be very ineffective. Experience has shownthat these installations are expensive, and difficult tomaintain and advance timeously as new stopes are beingdeveloped and brought into production. In very fewcases in practice can it be stated that their use hasachieved the design objective. In successful applications,it was noted that very little cooling was required toachieve acceptable thermal environmental conditionsand that the refrigeration requirement was of the orderof 50 kW (R) per kiloton per month. Furthermore, thelife of all these stopes was several years and the instal-lations were in fixed positions during this period.

Cooling of Air in Stopes

If possible, this should be avoided since it usuallycreates serious problems in stopes and is seldom worththe trouble and expenditure13. It can often be overcomeonly by an increase in the air flowrate or by recirculationof some of the air that passes into the stopes. Both thisand the previous method can seldom be afforded if thewet-bulb temperature of the inlet air during the summer

months at stopes and working places is below about24 °C since air at this temperature is often acceptable.

The regulation of water to the various cooling instal-lations is usually the main problem. This is because thepressure losses through the cooling-water pipes are usual-ly much higher than those across the cooling units(particularly cooling coils) and, with a multiple of paral-lel paths and continuous changes to the system, itbecomes totally impossible to balance4.

Water Side in Ventilation and Cooling Strategies

Once the air side of the strategy has been defined, thewater side can be completed and a first estimate of therefrigeration plant requirements and pipe sizes made.

Fig. 4 depicts cooling water being supplied to thevarious users from a common source with the returnthrough a common pipe system. The latter is notnecessarily correct: the strategy serves only as a basisfor the process design of the air and cooling-waterdistribution system. What is important, however, is thatthe water requirements and temperatures of the waterentering and leaving the various cooling elements (users)should be defined.

An important rule with regard to the temperature atwhich water is supplied to the various elements is thatit must at all times be as low as is practically possible.The reason for this is that water flowrates should be keptto an absolute minimum, thus permitting the maximumamount of cooling to be distributed for a given quantityof water.

The principle of the supply of chilled water to bulk aircoolers on surface is different from that of the supply ofcold water to other users because there are no restric-tions to water flowrates. In the former, the temperatureof the supply water depends on the wet-bulb temperatureof the ambient air, and it is therefore desirable for therefrigeration plant to be separate from the other plantssupplying water to the underground users. The engineer-ing of refrigeration plant forms the subject of otherpublications14,15.

Ventilation and Cooling-water DistributionSystems

After definitive strategies have been prepared, theprocess design and analysis of the ventilation and cooling-water distribution system, as well as the process analysisof the various cooling elements and the refrigerationplant, can be undertaken.

Process Design for A ir Side

This involves the preparation of flowsheets and theanalysis of the shaft and airways with respect to. air flowrates (mass and volume) for each leg,. pressure losses through each leg,. air velocities in each airway,. dimensions of each airway,. air control facilities.

During the process design, consideration should begiven to the elimination of areas where the pressurelosses are relatively high by the provision of additionalairways. The natural distribution of the air through themine should be carefully evaluated, and may require the

e of computer programs as these calculations are often0 an iterative nature that cannot be done manually.

he air distribution underground should be controlled,referably by the use of air-control doors and regulators

r ther than fans, unless the latter are close to the exhaust£ cilities. Fans introduce heat into the mine, are less

exible, and can fail, resulting in a maldistribution of air.Once flowsheets have been prepared for each of the

s rategies over the life of the mine, the exhaust fans andssociated equipment can be specified to meet the long-

t rm requirements of the mine.

rocess Design for Water Side

This involves the preparation of quantitative ande gineering flowsheets for

the overall water distribution and reticulationsystem,

the bulk air coolers including the air side,the stope air coolers including the air side,the refrigeration plant14,15,the water-settling and treatment plant.

Quantitative flowsheets essentially depict the designergy and mass balances, i.e. mass flowrates of air and

ater, pressure losses, temperatures, and heat-transferr tes across heat exchangers such as air coolers, evapo-

tors, condensers, and cooling towers. Engineeringowsheets depict pipe and valve sizes, control gear and

i strumentation, electrical equipment, etc. For the air.de, only quantitative flowsheets incorporating the

ngineering flowsheets are required. Once the processesign for each cooling strategy over the life of a mineas been completed, the specifications for the variousieces of equipment can be prepared.

rocess A nalysis of the Ventilation and Cooling System

With the aid of the various flowsheets, the processharacteristic of each of the cooling elements andajor pieces of equipment can be determined with

espect to daily fluctuations, seasonal variations, andl'fetime changes to water and air flowrates andemperatures, as well as the utilization of equipment.

It should be borne in mind that shafts, airways, andipes serve a mine throughout its life, and failure toeet this requirement can be costly and may force theine to interrupt production. Major capital equipment

uch as fans, refrigeration plant, and bulk air coolershould be selected accordingly, and their installationhould be scheduled to cope with the various productionhases throughout tb~ life of the mine and yet offer aeatly engineered installation that at all times fulfils theequirements of simplicity and ease of operation and

aintenance.

Conclusion

The method described in this paper offers a systematicpproach to the analysis and definition of the ventilationnd cooling requirements for hot underground mines.he importance of definitive ventilation and cooling

trategies prepared in conjunction with senior personneln a mine prior to any process or detail design works stressed.


Acknowledgement

The authors are indebted to Engineering ManagementServices Limited and their clients who enabled them todevelop this approach, and trust that all who endeavourto create a better underground working environmentwill benefit from this paper. In acknowledgement of thecontribution made by the United States mining frater-nity to the development of this technology, a version ofthis paper was presented at the First National Ven-tilation Symposium at the University of Alabama inMarch 1982. Much ofthe detailed practical design criteriaand considerations, with which mining engineers inSouth Africa are familiar, were omitted from the papergiven here.

1.References

VAN DER W ALT, J. Cooling of gold mines in the Republicof South Africa. Prof. Eng., vol. 7, no. 1. Jan. 1978. pp. 5-11.VAN DER WALT, J., and WHILLIER, A. Heat pick-up fromthe rock in gold mines: the water-rock thermal balance andthe thermal efficiency of production. J. Mine Vent. Soc. S.Afr., vol. 32, no. 7. Jul. 1979. pp. 125 - 144.VAN DER WALT, J., and WHlLLIER, A. Prediction of therefrigeration requirements for cooling the service water andthe ventilation air in South African gold mines. Chamber ofMines of South Africa, Research Report 28/77, Jul. 1977.VAN DER WALT, J., and WHILLIER, A. Considerations inthe design of integrated systems for distributing refrigera-tion in deep mines.J. Mine Vent.Soc.S. Afr., vol. 31, no. 12.1978. pp. 217 - 243.VAN DER WALT, J., and WHILLIER, A. The cooling experi-ment at the Hartebeestfontein Gold Mine. J. Mine Vent.

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6.Soc. S. Afr., vo!. 31, no. 8. Aug. 1978. pp. 141 - 147.SMITH, L. K., and VAN DER WALT, J. Cooling strategy andcooling requirements for the No. 6 and No. 6 North Shaftsof the Hartebeestfontein Gold Mine - Stilfontein. Engineer-ing Management Services, Contract 4257, Jun. 1981.VAN DER WALT, J., et al. Report on the infrastructurerequired to maintain and extend mining operations at theHomestake Gold Mine - South Dakota. EngineeringManagement Services, Contract 4284, Jun. 1981.VAN DER WALT, J., and SMITH, L. K. Cooling strategy andcooling requirements for Section 31 of the Nose Rock Mine-New Mexico. Engineering Management Services, Contract4263, Dec. 1980.STARFIELD, A. M. Tables for the flow of heat into a rocktunnel with different surface heat transfer coefficients.J. S. Afr. Inst. Min. Metall., vol. 66, no. 12. Jul. 1966.pp. 692 - 694.GOCH, D. C., and PATTERSON,H. S. The heat flow intotunnels. J. Chem. Metal/. Min. Soc. S. Afr., vol. 41, no. 3.Sep. 1940. pp. 117 - 128.WHILLlER, A., and RAMSDEN, R. Sources of heat in deepmines and the use of mine service water for cooling. Proceed-ings, First International Mine Ventilation Congress.Johannesburg, The Mine Ventilation Society of SouthAfrica, 1976. pp. 339 - 346.FENTON, J. L. Survey of underground mine heat sources.Montana College of Mineral Science and Technology(U.S.A.), M.Sc. Thesis, 1972.VAN DER WALT, J., and DE KOCK, E. M. Contribution to'In-line water spray cooler for hot mines', First- NationalMine Ventilation Congress, University of Alabama, Tusca-loesa, Alabama, March 1982.VAN DER W ALT, J. Engineering of refrigeration installa-tions for cooling mines. J. S. Afr. Inst. Mech. Engrs, vol. 29,no. 10. Oct. 1979. pp. 360 - 372.VAN DER WALT, J., DE KOCK, E. M., and SMITH, L. K.Recent developments in the engineering of refrigorationinstallation for cooling mines. J. S. Afr. Inst. Mech. Engrs,vel. 33, nos. ]-3, Jan.-Mar. 1983.

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Asian Mining '84Asian Mining '84 will take place from 6th to 10th

November, 1984, in Manila, The Philippines, and will besponsored by the Philippines Chamber of Mines. It willbe the first event outside Singapore organized by ITFPTE Limited, the Singapore-based subsidiary of Indus-trial and Trade Fairs International Limited of the U.K.and an associate company of the Times Organization ofSingapore.

An international conference organized by theInstitution of Mining and Metallurgy, U.K., and sup-ported by many international bodies, will be held inconjunction with the exhibition and will take place from5th to 8th November, 1984, in Manila.

The conference held alongside Asian Mining '81 wasa great success, attended by 350 delegates from aroundthe world. Asian Mining '81 featured exhibitors from 23countries and attracted visitors from 25 countries, themajority of them from ASEAN, Hong Kong, Japan,Australia, Taiwan, China, and the U.K.

The venue for the 1984 event has been moved toManila in recognition of the importance of the mining


industry there. Indeed, all the ASEAN countries -Philippines, Thailand, Malaysia, Indonesia, and Singa-pore - plus countries further afield such as India, Korea,and Australia, provide a vast, expanding market formining equipment and know-how, and a most favourableclimate exists throughout the region for foreign exportersof mining equipment. The Philippines is a central pointof an area that has enormously rich coal and mineralreserves, and that has an urgent need for modern, easilymaintained equipment and technical and managerialexpertise.

Asian Mining '84 will take into account all aspects ofland and sea mining, prospecting, and surveying, andallied areas such as communications, clothing, andsafety. It will provide a shop window for such areas asdrilling, dredging, blasting, and extraction equipment,cranes, conveyor systems, and handling equipment.

Further information is available from Mr Peter Lim,Sales Manager, ITF PTE LTD, 1 Maritime Square,Singapore 0409. Telephone: 2711013, Telex: RS 26085.

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The analysis of ventilation and cooling requirements for mines