Eskom and Water - eWISA

ESKOM AND WATER
Vasanie Pather
Eskom: Primary Energy (Water), PO Box 1091, Johannesburg, 2000.
ABSTRACT
Eskom, the South African wholly state-owned electricity utility, is among the top ten utilities in the
world in terms of size and sales. With its 24 power stations and nominal capacity of 40 585
megawatts, it is also one of the lowest cost producers of electricity in the world. Eskom’s power
stations supply in excess of 95% of South Africa’s electrical energy, and more than half of the
electricity used on the African continent.
The main component of operational costs for a coal-fired power station is fuel, i.e. coal. The power
stations are constructed close to the coalfields to eliminate the high cost of coal transportation.
These coal fields are located in the dry regions of the country where water availability is low hence
it is necessary to transfer water from neighboring regions, to the locality of the power station. The
generation of electricity is entirely demand driven since storage is very limited. Since water is a
vital input to the process, a high level of assurance is required by Eskom, emphasising the priority
that water is given as a resource.
Over the years Eskom has initiated various new technologies and management protocols in order
to control and reduces its water use. These include construction of dry cooled power stations,
desalination of mine water for re-use, minimising effluent discharge, introduction of water as an
indicator in the performance management system etc.
As a direct result of Eskom’s use of innovative technologies, management practices and other
strategies regarding water use since the late 1980’s, a significant reduction in water use has been
achieved at its thermal power plants. The quantity of energy produced over the period 1989 to
2003 increased by 62% (119 tigawatt hours per annum to 193 tigawatt hours per annum) but the
corresponding increase in water consumption was only 22% (224 million cubic meters per annum
to 273 million cubic meters per annum). This improved water use efficiency equates to a saving of
1020 million cubic meters since 1989, which equates to nearly 4 times Eskom’s average water use
per annum
INTRODUCTION
Eskom, the South African wholly state-owned electricity utility, is among the top ten utilities in the
world in terms of size and sales. With its 24 power stations and nominal capacity of 40 585
megawatts, it is also one of the lowest cost producers of electricity in the world. Eskom’s power
stations supply in excess of 95% of South Africa’s electrical energy, and more than half of the
electricity used on the African continent.
In pursuing its function of supplying the electricity on which modern society depends, Eskom
operates a wide portfolio of generation technologies which includes coal-fired power stations, gas
turbine, hydroelectric – both conventional and pumped storage, nuclear and wind turbine.
Eskom uses three major sources of energy for electricity generation, i.e. coal, nuclear and water.
Coal-fired power stations account for the largest proportion of the production (89% of its operating
generation capacity) making Eskom one of the single biggest consumers of water in South Africa,
accounting for approximately 1.5% of the country’s total water consumption. Approximately 97% of
Eskom’s total power generation water usage is for cooling purposes at the coal-fired stations.
Therefore it is in this area that Eskom has concentrated their effort in water conservation, and as
Proceedings of the 2004 Water Institute of Southern Africa (WISA) Biennial Conference 2 –6 May 2004
ISBN: 1-920-01728-3 Cape Town, South Africa
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such this is the focus of this paper.
The company has taken a pro-active stance in its efforts to conserve water, in some cases even
pre-empting new legislation in implementing efficient and effective water use practices. It has
constantly striven to improve on its water use targets, continually researching and implementing
new technologies to reduce or limit water use, and working closely with the Department of Water
Affairs and Forestry (DWAF) to contribute towards long-term water resource planning and
management. This commitment is documented in Eskom’s Water Management Policy.
INNOVATIVE USE OF WATER TECHNOLOGIES
Over the last two decades, Eskom has introduced a number of innovative technologies to save
water. These include dry cooling - both direct and indirect, desalination of polluted mine water for
use at power stations, use of limited pumped storage and hydropower potential and technical
improvements in treatment regimes to maximise the beneficial use of water.
Dry Cooling
In the 1960’s and1970’s, Eskom realised the limitations in South Africa’s water resources and
investigated and tested the use of dry cooling technology for its new coal-fired power stations.
Today, the total dry cooled installed capacity is 10 477 megawatts.
Dry-cooling technology does not rely on evaporative cooling for the functioning of the main cooling
systems. As a result dry cooled power stations use approximately 15 times less water than
conventional wet cooled power stations. Eskom’s leading role in this field is attested to by the fact
that it operates the largest indirect dry cooled power station (Kendal – 4 116 megawatts) and the
largest direct dry cooled power station (Matimba – 3 990 megawatts) in the world (figures 1 and 2).
Figure 1. Kendal Power Station. Figure 2. Finned tube condensers above forced
draught fans at Matimba Power Station.
The investment in dry-cooling results in an estimated combined saving of over 200 Ml/day
megaliters of water per day, or in excess of 90 million cubic metres per annum (figure 3).
Despite the limitations of dry cooling technology, such as a loss of operational efficiency with a
concomitant loss in revenue, and higher capital and operating costs, this investment is imperative
on a national perspective.

Figure 3. Water savings due to Dry Cooled Technology from 2000 to 2003 (based on average wet cooled
coal fired power station water use).
Desalination
The National Water Act (Act No. 36 of 1998) prohibits the discharge of wastewater into water
resources without proper authorisation. Wastewater has to be treated to acceptable standards
before it may be discharged. The mines that supply coal to Eskom’s power stations produce
significant volumes of wastewater. Eskom accepts this water from the mines associated with two
power stations. They treat the water then use it in their cooling process.
Figure 4. Process Flow Diagram showing reverse osmosis and microfiltraion units in Lethabo Power
Station’s water treatment plant.
The two power stations, namely Tutuka and Lethabo (figure 4), operate desalination plants to treat
the contaminated mine water. These plants were initially commissioned in 1985 and both were
later refurbished. Desalination processes are relatively expensive. The total capital cost for both
the treatment plants was about US$ 7 million. The operational cost is also very high, which

negatively impacts the financial feasibility of installing this technology. Both desalination plants use
spiral wound reverse osmosis membranes in their process, and delivers permeate water recovery
rates of 87% and 80% respectively. The benefit to Eskom is a reduced water intake for the two
stations, with a combined potential saving of about 14.6 Ml/day (5.16 million cubic meters per
annum).
Lime Treatment
When water supply is unlimited, operating a thermal power station with a once-through cooling
process is ideal. For Eskom, however, the location of power stations is dependent on coal sources,
usually where the water supply happens to be scarce, hence water is recycled in the cooling
process. The cooling water systems have to be supplemented as a result of evaporation, windage
and drift. Evaporation causes a concentration of salts in the cooling water recycle process, which in
turn limits the recycle volumes. To overcome this, Eskom practices alkalinity control of the cooling
water, using acid neutralisation (at two plants) or cold lime softening by precipitation (at six plants).
This is largely dependent on the chemical drivers of the ash dump as compared to the abstracted
raw water. By controlling and optimising these processes cooling water effluent volumes are
minimised.
Eskom is probably the world leader in operating large cooling water systems at high cycles of
concentration without the use of corrosion and scaling inhibitors. Operation at elevated cycles of
concentration is one of the key strategies contributing to water conservation.
Hydropower and Pumped Storage
Eskom operates hydropower stations with a total capacity of 661 megawatts, and pumped storage
stations with total a capacity of 1400 megawatts. These stations are mainly operated during
periods of peak electricity demand.
South Africa has limited potential for large-scale hydroelectric power due to limited water
resources. River flows in South Africa are not constant, but vary from high floods to low flows. In
order to provide energy at a very high assurance level, run of river schemes are generally not a
feasible option. Hence large and expensive storage dams have been constructed to facilitate
hydropower production. Apart from a small quantity of water lost to evaporation, pumped storage
schemes do not consume water.
Figure 5. Gariep Hydro Power Station on the Orange River.
The utilisation of hydro power and pump storage stations results in a water saving of about 2.7
million cubic meters per annum.
INNOVATIVE WATER AND WASTEWATER MANAGEMENT PRACTICES
Limiting water consumption and eliminating the contamination of water resources are Eskom’s
main goals with water management. This has been successfully achieved in a number of ways.

Re-Use of Water Through Cascading
Eskom adopted the ZLED (Zero Liquid Effluent Discharge) policy during 1987, in terms of which all
reasonable measures are taken to prevent pollution of water resources through the establishment
of a hierarchy of water uses based on quality. Cascading the water from higher quality to lower
quality uses enables extensive re-use. Where possible, water is lost only through evaporation,
retaining the accompanying dissolved and suspended solids. The net result is that there is no
deliberate discharge of pollutants to a water resource under normal operating conditions and
average climatic conditions.
Ash Disposal
The coal-fired power generation process produces large quantities of ash, which is disposed of in
ash dumps and dams. Eskom uses coal of a low grade (16 megajoules per kilogram to 22
megajoules per kilogram) which produces a larger mass of ash during combustion. The
higher-grade predominantly serves the export market. Eskom uses either wet or dry ashing. Both
utilise effluent water or wastewater, which is the end product of the cascading water re-use
process. Wet ash disposal entails the hydraulic conveyance of ash, while dry ash disposal entails
the conveyance of partially moistened ash on conveyer belts. The dry ash disposal method
requires less water.
The volume of wastewater that can be accommodated in the ash is referred to as the effluent sink.
Good water management and accurate water balances ensure optimisation of the effluent sink.
The water saving is realised in that clean water is not used to suppress the blow off from the dry
ash. Contamination of water resources is furthermore minimised as the output of the cascading
water re-use process is not discharged into a water resource but assimilated into the ash.
INNOVATIVE WATER MANAGEMENT STRATEGY
A direct relationship, expressed as liters per kilowatt-hour (l/kWh), exists between energy produced
and water consumed, and is calculated by dividing water consumption by energy sent out. This
relationship is commonly referred to as 'specific water consumption' and is the key indicator for the
organisation’s water management drive. This measure is used to assess the performance of both
individual power stations and the company as a whole.
Sustainability Index (SI)
The SI was introduced in 1996 to ensure the long-term sustainability of Eskom’s business in the
areas of technical, financial, social and environmental issues. The SI forms part of the performance
contract of each employee from executive level to the operational level, With the targets for the
various elements allocated according to the responsibility and accountability exercised within that
area. The specific water use indicator (l/kWh) forms part of the SI. Using this index Eskom is able
to monitor its water use, allowing water practitioners to identify individual power stations with
specific water management problems in order to implement targeted corrective strategies. The
historical data shows a decrease in the specific water consumption (for all Eskom generation
technologies) from 2.85 l/kWh in 1980 to 1.29 l/kWh in 2003.
COMMITMENT TO CO-OPERATIVE GOVERNANCE
Eskom has fostered an excellent relationship with DWAF over the last four decades. As a major
stakeholder in the water industry, Eskom assists and supports DWAF in its infrastructure planning,
water management initiatives and formulation of policies. The company has been a corporate
sponsor of the South Africa’s National Water Week Campaign for over 5 years and takes an active
role in promoting this event on a regional level as well as Eskom’s power stations. The
organization has recently been selected as patron member of the Water Institute of South Africa
(WISA) in 2003.

CONCLUSION
As a direct result of Eskom’s use of innovative technologies, management practices and other
strategies regarding water use since the late 1980’s, a significant reduction in water use has been
achieved at its thermal power plants. The quantity of energy produced (for coal fired power stations
only) over the period 1989 to 2003 increased by 62% (119 tigawatt hours per annum to 193
tigawatt hours per annum) but the corresponding increase in water consumption was only 22%
(224 million cubic meters per annum to 273 million cubic meters per annum). This improved water
use efficiency equates to a saving of 1020 million cubic meters since 1989, which equates to
nearly 4 times Eskom’s average water use per annum. This is an achievement of which the
organisation is rightfully proud, and it will continue to strive to improve in its performance to assist
in conserving and preserving the nation’s scarce and precious water resource.
REFERENCES
Figure 6. Liters per kilowatt energy sent out for coal fired power stations.
1. Technical Information, Matimba - Power for Tomorrow, Communications Department - Eskom,
(1995).
2. Technical Information, Kendal – breaking through new technology, Communications Department,
Eskom, (1985).
3. Water Book for Chemists, Training Manual, D. J Hanekom, (2000).
4. Chemistry Standard for Cooling Water, D. J Hanekom, GGS 1153, (2003).
5. Eskom Annual Report, (2002).
6. Personal Communication, D Hanekom, Chief Consultant, Eskom – Primary Energy (Water).