Copyright © M-Tech Industrial, 2011 Energy audit of mine refrigeration water systems by means of...

Copyright © M-Tech Industrial, 2011

Energy audit of mine refrigeration water

systems by means of simulation

16 August 2012Dr. Herman van Antwerpen

Pr.EngM-Tech Industrial


Introduction

Purpose of this paper:

• Demonstrate the benefits of integrated system simulation,

• Its use in energy assessment of a mine refrigeration system.

Type of simulation:

Conservation of mass, energy and momentum at system level,

i.e. flow rates, temperatures and pressures


Mine cooling water network


Motivations for simulating a system

On a new design:

• Do component sizing

• Verify component selection, control philosophies, etc.

On an existing plant:

• Compile the data set that describes system operation

• Develop good understanding of system operation

• Check instrumentation consistency / high-level fault finding

• Assess changes at a system-level

• Identify savings opportunities: survival of deep mines


Classification of loads and savings

Time of day

Co

ns

um

pti

on

Energy efficiency

“DSM valves”Baseload

Peak load


Basic refrigeration loop

Refrigeration plant (pumps,

dams, etc.)

Dewatering pumps

Working levels

Clean makeup water Bleed water

Surface

-1800m

-2400m

1800m

600m

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 3 6 9 12Month

Ave

rage

pow

er c

onsu

mpt

ion

[kW

]

Pumping Refrigeration Total


Water distribution system

Fridge plants

Pipe column in shaft

PRVs on levels

Pipes in haulages

Cooling cars

Level of instrumentation and control

Ease of maintenance

Influence on total flow requirement

Refrigeration plant (pumps, dams, etc.)

Drilling, stoping

Pip

e co

lum

n in

sha

ft

PRV

PRV

Pipes in haulages

Drilling, stoping

Drilling, stoping

Manos Engineering, Welkom


Network for level

Network for level

Network for level

Network for level


Required phenomena

• Elevation differences• Cooling car characteristics• Heat pickup along pipes in haulages

Refrigeration plant (pumps, dams, etc.)

Drilling, stoping

Pip

e c

olum

n in

sha

ft

PRV

PRV

Pipes in haulages

Drilling, stoping

Drilling, stoping


Cooling car characteristics


Chilled water heating along haulages

Journal of the SA Institute of Mining and Metallurgy:Rawlins, C.A. (2007) “Mine cooling and insulation of chilled water transport pipes”Jones, M.Q.W. (2003) “Thermal properties of stratified rocks from Witwatersrand

gold mining areas”

Virgin Rock Temperature

Haulage wall

Ventilation air

Chilled water

Distance from shaft, along haulage

Tem

pera

ture

Shaft Cooling car

Low flow rate

High flow rate

Conduction

Convection

Convection


TT

PID

25ºC

0

65

130

195

260

0 2 4 6 8 10 12 14 16

T_chilled water [C]

Wat

er d

eman

d t

o le

vels

[l/s

]

Reference data

With thermostatic control

Cooling car control


Power consumption

0

500

1000

1500

2000

2500

3000

3500

4000

5 6 7 8 9 10 11 12 13 14 15

Chilled water temperature [C]

Ave

rage

d po

wer

req

uire

men

t

0

200

400

600

800

1000

1200

1400

1600

Pre

ssur

e at

coo

ling

car

inle

t [k

Pa]

kW_Pump kW_Refrig_elec kW_Total Pressure


Conclusions

Regarding mine refrigeration

• Opportunity: “Mine-proof” cooling car flow control.

• For some mine layouts:

• Minimum refrigeration cost: highest possible chilled water

temperature.

• Constraint: cooling car inlet pressure.

Regarding simulation

• Industrial Energy Efficiency projects or system-level optimisation

requires integrated simulation: flow rate, temperature and pressure.


Questions?

Acknowledgements

Copyright © M-Tech Industrial, 2011 Energy audit of mine refrigeration water systems by means of...

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