Water Quality Impacts on Eskom

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; 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.

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Schematic of Water Supply:VRESS

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Dams: Nooitgedacht and VygeboomArnotHendrinaDuvha

KomatiWitbank

KrielKendalDams: Jericho, Morgenstond and Westoe

Usutu Water Scheme

Grootdraai

VaalSasol II & III

MatlaUsutu - Vaal Water Scheme

Natural riverPumping main

Gravity mainProposed new pipeline

Bravo

VRESAP

Majuba

Komati Water Scheme

UCG & CCGT

Camden

Dams: Heyshope

Dams: Zaaihoek

LethaboGrootvlei

KWSAP

Water Quality Impacts: Komati System

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Komati Water Scheme Water Quality (Jan 2004 to Feb 2008)

0

25

50

75

100

125

150

175

200

225

250

275

Month of Period

Con

cen

trati

on

(m

g/k

g)

SO

4

Ideal Acceptable Nooitgedacht Vygeboom Witbank

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.

Schematic of Water Supply:Mogol

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Mokolo Water Scheme

Natural riverPumping main

Gravity mainProposed new pipeline

GrootgelukDam: Mokolo

Crocodile West-Marico Water Management Area

Vaal

Medupi

Matimba

Petro-chemicals and mining

Lephalale

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

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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

Schematic of Power Station Impacts

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Condensor: De-zincification Plugging condensor tubes impacts efficiency

Replace condensors: R60 M/ condensor plus outage time

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.

Water Treatment Plant: Organics impact water treatment plants effectiveness

Introduction of mobile salts to restore effectiveness

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

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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

Water Quality Impacts:Medupi Power Station

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Medupi WTP Life-Cycle Cost Comparisons

R 521,462

R 504,243

R 580,248

R 940,985

R 626,946

R 1,686,724

0

250000

500000

750000

1000000

1250000

1500000

1750000

2000000

2010

2015

2020

2025

2030

2035

2040

2045

Year

Ran

ds

x 10

00

RO-Mok IX-Mok RO-Mix IX-Mix Ro-Croc IX-Croc

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

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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ConclusionsActions 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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