IMPROVING COOLING SYSTEM EFFICIENCY WITH PRE-COOLING

AJ Schutte

15 August 2012

Introduction National power network under strain

Electricity price increases

Mining is electricity intensive

Cost effective mining

Inefficient mine cooling and ventilation system

South African mining Reduce operational cost

SA mining depth requires cooling

Surface refrigeration system

System components

Dams and transfer pumps

Heat exchange towers

Refrigeration machines

Surface refrigeration system layout

Mine cooling Surface refrigeration

Cooling load Mine production water

Bulk air coolers (BAC)

Cooling components Pre-cooling towers

Refrigeration machines

BAC thermal load contribution

Production thermal load contribution

Pre-cool tower thermal energy

Resultant refrigeration machine thermal energy

Mine water quality Production cause water temperature increase

Salts dissolve

Evaporation increases solution concentration

Water treatment

Solid particles suspension

Settlers

Mine production surpass settlers and treatment

Pre-cool towers Layout

Fan

Mist eliminators

Spray nozzles

Fill

Production water cools

Crystals + solid particles

Electric motor

Mist eliminator

Fill

Ambient air

Water to pre-cool

dam

Water from chill dam

Spray nozzles

Gear box

Case study: Replace pre-cool towers

Mine production exceeding infrastructure

Summer refrigeration operate at 100%

Winter period maintenance

High efficiency film fill used

Tower fan maintenance

Replaced pre-cool towers Original design

exceed requirement

New fill specified

Direct drive fans

New fill vibrates

Results - Temperatures Inlet temperature of 30oC

Flow 340l/s

Old tower outlet temperature 23oC

New tower outlet temperature 19oC

Improvement of 4oCPre-cool tower electrical energy

Electrical energy saving

Refrigeration machine electrical energy

Pre-cool tower thermal energy

Pre-cool towers thermal energy gained

Resultant refrigeration machine thermal energy

Results - Electricity

1 MW saving through out the day

010002000300040005000600070008000

00:0

001

:00

02:0

003

:00

04:0

005

:00

06:0

007

:00

08:0

009

:00

10:0

011

:00

12:0

013

:00

14:0

015

:00

16:0

017

:00

18:0

019

:00

20:0

021

:00

22:0

023

:00

kW

Hour

Mine refrigeration system power profile

Baseline Actual profile

Conclusion Replacing mine pre-cool towers resulted in a

4oC colder outlet temperature

This resulted in 24hour average electricity

saving of 1MW

Fans utilisation increased

Winter period pre-cooling now possible

The End

Questions?

Thank you