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Water Quality Impacts on Eskom

Water Quality Impacts on Eskom

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Water Quality Impacts on Eskom

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  1. Water Quality Impacts on Eskom Parliamentary Portfolio Committee on Water Affairs and Forestry June 2008 1

  2. 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; • Eskom’s 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.

  3. Schematic of Water Supply:VRESS 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 3

  4. 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. 4

  5. Schematic of Water Supply:Mogol 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 5

  6. 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 **Based on crystal modification program implemented 6

  7. 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 7

  8. 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 8

  9. Water Quality Impacts:Medupi 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. 9

  10. 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. 10

  11. 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. 11

  12. Thank You 12