Water Quality Impacts on Eskom

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Water Quality Impacts on Eskom

• Parliamentary Portfolio Committee on
• Water Affairs and Forestry
• June 2008

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Overview

• Water to Eskom is supplied at 99,5 assurance
  level
• All power generation water supply and storage is
  considered as strategic i.e. given priority use
  and approved at DWAF Ministerial level
• Eskoms power stations are concentrated mainly in
  three water management areas
• Upper Olifants River Water Management Area
• Upper Vaal River Water Management Area and
• Limpopo Water Management Area
• Eskom uses approximately 325 million cubic metres
  per annum
• Water is sourced from a number of dams in and
  around these water management areas and supplied
  to the power stations through a network of
  pipelines and pumping systems
• The sourcing of water is based on the quantity
  needed and the quality
• Raw water quality in the power generation process
  needs to be better than that sourced for potable
  production required for domestic use
• Of this approximately 97 of this water is used
  at wet cooled power stations which are more
  susceptible to water quality impacts
• Water quality impacts eventually translate into
  using a larger quantity of water.

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Schematic of Water SupplyVRESS
Komati Water Scheme
Hendrina
Dams Nooitgedacht and Vygeboom
Arnot
Duvha
Witbank
Komati
KWSAP
Usutu Water Scheme
Bravo
Camden
Dams Jericho, Morgenstond and Westoe
Kriel
Kendal
UCG CCGT
Majuba
Dams Zaaihoek
Usutu - Vaal Water Scheme
Matla
Grootdraai
Vaal
Dams Heyshope
Sasol II III
VRESAP
Lethabo
Grootvlei
Natural river Pumping main
Gravity main Proposed new pipeline
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Water Quality Impacts Komati System

• Water quality impacts are complex and issues such
  as permanent hardness and other chemical species
  need to be understood as well. For example in
  Witbank Dam permanent hardness causes Mg and Ca
  to be limiting parameters.

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Schematic of Water SupplyMogol
Mokolo Water Scheme
Lephalale
Matimba
Dam Mokolo
Grootgeluk
Medupi
Petro-chemicals and mining
Crocodile West-Marico Water Management Area
Vaal
Natural river Pumping main
Gravity main Proposed new pipeline
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Water Quality Impacts on Power Stations

• Typical water quality impacts are
• Problematic pollutants such as sulphates (SO4)
  and mobile salts such as sodium (Na),
• Organic pollutants requiring introduction of
  mobile salts to mitigate impacts
• Permanent hardness as a result of acid mine
  drainage impacts
• Trace metals emanating from mine water.
• Typical Eskom Threshold Water Quality Values for
  the cooling water system
• Table 1 Typical Threshold Water Quality
  Values for the cooling water system
• Dependant on quality of concrete

Parameter Concentration Units
Sodium 500 mg/kg as Na
Chloride 400 mg/kg as Cl
Sulphate 750-1500 mg/kg as SO4
M Alkalinity 120-160 mg/kg as CaCO3
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Schematic of Power Station Impacts
Cooling Tower Lower cycles of concentration
Increased effluent generation and
increased water use
Ash system Increased chemicals in ash disposal
system due to raw water
quality and increased
chemical reagents used in water treatment,
long term liability
impacted negatively.
Condensor De-zincification
Plugging condensor tubes impacts efficiency
Replace condensors R60 M/ condensor plus outage
time
Water Treatment Plant
Organics impact water treatment plants
effectiveness Introduction of mobile salts to
restore effectiveness
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Potential Water Quality Impacts

• Potential Impacts on a Power Station are
• Poorer water quality leads to lower cycles of
  concentration in the cooling towers
• For example, a poorer water quality leads to
  lower cycles of concentration increasing the
• amount of effluent generated. This implies that
  more water is required for the same energy
• output.
• Table 1 Impacts of Different Water Qualities on
  Water Use at a typical Power Station

Parameters Source One (Usutu) Source Two (Usutu-Vaal)
Water Quality (mg/l SO4) 4,3 32,4
Cooling tower evaporation (ML/d) 94,18 94,18
Cycles of Concentration 30 8,5
Treatment requirement (ML/d) 13,04 78,2
Effluent generated (ML/d) 3,2 12,6
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Water Quality ImpactsMedupi Power Station

• From the above, based on moving water abstraction
  from the ideal quality (Mogol water) to impacted
  water quality (Crocodile West) requires
  additional treatment costs.

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Potential Water Quality Impacts

• Other Potential Impacts on a Power Station are
• Possible de-zincification of condensor tubes
• The condensor is an integral part of the power
  generation unit and when chemical
• excursions occur, de-zincification (pitting) of
  the consdensor occurs. This needs
• either to be repaired/plugged or the condensor
  needs to be replaced. Replacement
• costs is in the order of R60 M per condensor and
  about 2 months of outage time-
• possibly making the energy shortage currently
  experienced worse.
• Increased chemical use and encapsulation of
  chemical species- chemicals that come
• with the raw water and that what is used for
  treatment- in the ash that has the potential to
• impact groundwater in the long term if the field
  capacity of the ash system occurs
• Potential impacts on water transfers
• The use of natural conduits to transfer water is
  restricted due to the adverse impacts of water
  quality
• For example, the Komati Water Scheme requires
  augmentation and the use of the natural conduit
  is possible as the necessary infrastructure can
  be restored at a very low cost. Due to the
  negative impact of water quality in the
  Steenskoolspruit and Upper Olifants, a new
  pipeline at a cost of approximately R850 M needs
  to be implemented to mitigate the impact of water
  quality
• Creation of water stress as more water is
  required to compensate for water quality impacts.
  

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Conclusions

• Actions by Eskom
• Co-operative action to mitigate the impact of
  water quality on its business.
• Eskom will be entering into a joint initiative
  agreement with the major coal mines to explore
  the use of excess mine water at the power
  stations and the treatment thereof
• Continuously look at improvements on power
  station operational water efficiencies and water
  treatment regimes
• Robust operational water management systems to
  deal with varying water quality
• Ensure compliance by power stations with Water
  Use Licence conditions and reporting thereof
• Being mindful of potential impact its facilities
  could have on water quality and Eskom has
  undertaken the following
• Continues to pursue a philosophy of zero liquid
  effluent discharge i.e. not to discharge any
  water from the site, under normal climatic
  conditions, by cascading water from one use to
  the next until final use in the effluent water
  systems of the power station.
• Ongoing research to understand the impact of
  stack emissions on water quality and to implement
  appropriate mitigation.
• Advocates the speedy implementation of the Waste
  Discharge Charge System.

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Thank You
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