The Victorian coal-fired electricity industry and water

The Victorian coal-fired electricity industry is a major user of the State's water resources and is currently heavily reliant on old water intensive coal-fired power stations.

Background
A conventional wet-cooled coal-fired power station uses water for:
 * the boiler for steam raising;
 * the cooling system;
 * managing and disposing of ash; and
 * services and potable water supply.

High quality water is required for boilers and on-site potable water supply, while lower quality water can be used for cooling. Typically, more than 90 percent of total water use is consumed in the cooling system.

There are several different cooling technologies employed in existing Australian power stations. Wet cooling uses high volumes of water to remove the thermal load from the source, while dry cooling transfers the thermal load to the air. Wet cooling uses water to cool steam that is discharged from a turbine. Not all water extracted for cooling is ‘consumed’, as water not otherwise evaporated in the course of cooling or disposed of to reduce build-up of salts in cooling water, is returned to the environment.

Based on data used in a report for the National Water Commission, the approximate water consumption of different cooling technologies for coal-fired power stations are:

There are two types of wet cooling systems in operation in the Latrobe Valley:
 * Hazelwood Power Station uses a ‘once-through’ cooling system;
 * Loy Yang A Power Station, Loy Yang B Power Station and Yallourn W power station all use closed cycle or recirculated cooling systems.

Once-through cooling
In a once-through cooling system, water is drawn from a natural source such as a lake, sea or river, passed through the power station’s steam condenser and then returned to the water source at an elevated temperature. A relatively small proportion of the total water extracted for cooling is ‘consumed’ by evaporation, with typically around 90 percent of extracted water being returned to the environment. For example, a 1000 MW base load plant extracting 1300 GL of water per year would consume approximately 13 GL per year from evaporation.i

Hazelwood Power Station’s cooling system is supplied by Hazelwood Cooling Pond, which is in turned supplied by Moondarra Reservoir and groundwater from mine de-watering to replace water lost through evaporation (see the table below.)

Closed cycle or recirculated cooling
In a closed system, energy rejected by the turbine is transferred to the cooling water system through a condenser. The heat in the cooling water is then discharged to the atmosphere using a cooling tower. In the cooling tower, heat is removed from the falling water and transferred to the rising air by the evaporative cooling process. The moisture-laden air is often visible in the plume of water vapour above the cooling towers in times of high humidity. The evaporation rate of a typical 350 MW cooling system is typically 1.8 ML of water per GWh of power generated. For a base loaded 1000 MW plant generating 7400 GWh per year, this equates to around 13 GL of water used in evaporation per year.

There are two typical cooling tower designs that enhance the evaporation process – natural draft cooling and forced draft cooling. Forced draft cooling towers employ fans to create airflow, while natural draft cooling towers do not require fans and consequently have lower operating costs.

Loy Yang A and B, and Yallourn power stations all utilize natural draft, closed cycle cooling systems.

The Latrobe Valley power generation industry typically extracts around 95,000 ML of surface water a year from the region’s rivers. In addition, the Yallourn, Morwell and Loy Yang A power generation companies hold licences to pump a combined total of approximately 45,000 ML per year of groundwater, although in recent years the actual amount extracted has been up to about 30,000 ML of groundwater per year.

While not all of this water is ‘consumed’ and some proportion is returned to the environment. However, the key issue for river health is the impact of total volumes extracted rather than net volume consumed.

Electricity demand varies throughout the year but market operating rules impose standards for maintaining a secure supply of electricity at all times. As a result, electricity plants that are reliant on water for generation require a high proportion of their water supply to be high security to meet supply reliability criteria.

Power station water use efficiency measures
One of the key ways of improving water use efficiency in a coal-fired power station is to more closely monitor cooling tower blowdown which is used for managing the increased concentrations of salts in the recirculating water cooling towers. The increased ‘cycling up’ of the cooling towers (increasing the number of times water is cycled through the towers) can help reduce water consumption.

Loy Yang A power station claims to have reduced water consumption per unit of output from 3.6 ML/GWh in 1991 to the current level of 2.2 ML/GWh. Loy Yang A also claims to have reduced ‘domestic’ (presumably potable) water consumption by 50 percent, to around 1 GL. However, this represents a minute proportion of the power station’s total water yearly surface water use (26 GL).

Furthermore, it is not clear whether water efficiency measures which have resulted in discharge to the Traralgon Creek now being the “lowest on record” are having any detrimental impact on flow regimes within the creek. The Loy Yang A Sustainability Report makes no mention of any relevant investigations having been carried out.

According to the most recently available published reports, Loy Yang B Power Station has improved the efficiency of its use of low quality water from a baseline of figure of 2.30 kL/MWh to 1.96 kL/MWh in 2006, representing an efficiency improvement of nearly 15 percent. With respect to Hazelwood, the total volume of water used over the last ten years and extracted relative to the power generated by the business since 1999 has fallen by 24 percent, from 2.9 to 2.2 ML/GWh in 2006.

However, the key issue with claims of water use efficiency is whether efficiencies have been achieved by reducing the water-intensity of the product (ie. using the same amount of water to produce more power) or by actually reducing water consumption.

Recent data from the Victorian Water Accounts summarized in the table below suggest that it may be the former, as in 2006-07 Power generators were alone amongst all consumptive users in Victoria in increasing their use from the previous year.


 * Table 3. Urban metered water consumption in Victoria 2006/07

This pattern of static if not increasing water use is confirmed by figures dating back to 2003-04 (the earliest year for which statewide water accounts have been published by the Victorian Government) which shows that water diverted under bulk water entitlements held by Loy Yang A & B and Yallourn power stations has risen from a total of 69,532 ML in 2003-04 to 74,174 ML in 2006-07. Furthermore, Loy Yang A power station acknowledges in its most recent Sustainability Report that total water consumption in 2006 was higher than 2005 due to increased electricity production.

Dry cooling
In a direct dry cooling system, turbine exhaust steam is piped directly to an air-cooled, finned tube condenser. A dry cooled thermal power plant’s water requirements are around 10 percent of wet cooled plants. Dry cooling eliminates water consumption for cooling, although dry-cooled power stations still require water for boiler water replacement, ash disposal, fire-fighting and other services. A 1000 MW dry cooled coal-fired power station would typically require around 2.5 GL of water per year.

While dry cooling reduces water consumption to around 2 GL/year (from around 17 GL/year), it also reduces sent-out efficiency, which leads to higher fuel requirements and higher emissions of carbon dioxide and other greenhouse gases.

The cost of installing dry cooling in a new power station is estimated to be up to 5 percent higher than for an equivalent wet cooled plant. A key issue relevant to the retrofitting of dry cooling to an existing plant, is that dry cooling typically requires an amount of space which is not necessarily available in all power stations. One estimate of the cost of retrofitting a 1000 MW coal station with air cooled condensers or a hybrid dry cooling system could be around $400 million. ACIL Tasman estimated that this would result in the cost of water saved exceeding $3000/ML, although other estimates put this at $1500/ML.

Another disadvantage of dry cooling systems along with lower sent-out efficiency (leading to higher fuel consumption) is higher auxiliary power consumption. The power required to operate the fans of this system can be several times that required for natural draft wet cooling towers, and is typically 4-5 MW for a 420 MW unit.

None of Victoria’s power stations utilize dry cooling technology. Two plants with dry cooling systems have recently been built in Queensland – Kogan Creek and Millmerran Power Stations.

Combined-cycle gas turbine (CCGT)
One low greenhouse gas intensive technology that is commercially able to provide base load power is gas combined cycle gas turbine (CCGT). As well as having lower carbon emissions, CCGT power plants also typically use a little over one-third of the water used in a comparable wet-cooled coal-fired power station.

Victoria presently has only one combined cycle gas-fired power plant at Newport. Other Australian plants include Pelican Point and Osborne power stations in South Australia, and Swanbank East and Townsville in Queensland. Renewable forms of electricity generation that can provide baseload power include hydro power and biomass, while geothermal and large-scale solar are developing quickly and are likely to be commercially viable ahead of carbon capture and storage.

Link between coal, greenhouse emissions and reduction in water availability
The Gippsland Region SWS Discussion Paper acknowledges that climate change poses the biggest risk to the region’s water supplies for the future. Over the last 12 years, rainfall across almost all of Victoria has been well below average. Importantly for the state’s rivers, a decrease in rainfall is typically amplified three-fold in terms of reduced run-off to storages and waterways. As soils dry out, more rain is needed to saturate the soil before any run-off can begin to occur, while observed seasonal changes (ie. less rain than usual falling in autumn and winter) are further reducing run-off rates.

Since 1997, there has been a 41 percent reduction in average annual inflows into south Gippsland river systems (from 611 GL to 359 GL), with record low inflows in 2006-07 (106 GL). Across the Gippsland region over the last 12 years, streamflows have reduced by between 23 and 50 percent of the long-term average. Importantly, there have been no years of above average inflows, raising the possibility that the current drought is in fact a sign of a permanent reduction in rainfall due to climate change.

Key areas of climate change risk identified for Victoria include buildings in coastal settlements, natural ecosystem-based tourism, irrigated agriculture, water scarcity, health issues and deaths caused by more frequent heat waves, and greater risk of extreme fire danger with consequent risks for life and property. As well as the biophysical impact, it is clear that climate change also has economic implications. For example, the 2006-07 drought is estimated to have reduced the rate of economic growth in Australia by around 0.75 percentage points of what would have been otherwise achieved.

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