Air quality

The generation of electricity at Eskom’s coal- and gas- (liquid fuel) fired power stations results, inter alia, in the release of combustion gases and particulate matter, which can affect local and regional air quality. The legislation governing air quality and atmospheric emissions is the National Environmental Management: Air Quality Act (39 of 2004) and the implementation plans detailed in the 2007 National Framework for Air Quality Management (11 September 2007).

Our approach to air quality considers the emission of particulates, sulphur dioxide (SO₂), oxides of nitrogen (NOx), heavy metals, fugitive emissions, volatile organic compounds (VOCs) and greenhouse gases.

In the past, our focus was on reducing our particulate emissions significantly, with continual improvement over two decades. The current focus is on gaseous emissions. The bigger issues relate to climate change and ambient air quality and we recognise the need to control the emissions to the atmosphere emanating from our power stations.

To this end, we take a pro-active stance in discussions of possible environmental impacts with DEAT, and comply with requirements as included in environmental authorisations issued by DEAT as an outcome of the EIAs for our future power stations.

Particulate emissions

The emission of particulates from power station stacks has been a focal point since the early 1980s. Significant reductions in the quantity of particulates emitted have been achieved through the use of technologies that enhance the efficiency of electrostatic precipitators, such as sulphur trioxide flue gas conditioning, skew flow technology and modern control systems, and through the retrofitting of pulse jet fabric filters.

The actual particulate emissions based on a 12-month moving index (12mmi) were 0,21kg/MWh sent out (2007: 0,20kg/MWh) against a target of ≤0,21kg/MWh sent out. Although the target set was achieved, there was no improvement when compared to the previous year as a result of an overall deterioration in power station plant performance, poorer coal quality and the running of the power stations to their limits in attempts to avoid load shedding. Poor coal quality has led to electrostatic precipitator problems at Duvha; ash plant technical problems at Kendal and failure of the SO₃ plant at Matla.

In the 1980s, the reduction of particulate emissions from the coal-fired power stations was the most significant environmental challenge that we faced.  Initial reductions resulted from the mothballing and closure of many of the older plants.  In the late 1990s, a stringent five-year target was developed to cut particulate emissions from an average of 0,37kg/MWh to 0,28kg/MWh sent out.  Between 1990 and 2003, the total annual particulate emissions were reduced from 271 000 tonnes to 57 000 tonnes, while the energy sent out increased by 64 000GWh.  This was achieved while still ensuring that the optimisation of life-cycle costing was factored into all decisions made at every power station.

The technologies employed to manage and reduce particulate emissions include electrostatic precipitators, bag filters and flue gas conditioning.

Gaseous emissions

South African standards for emissions of SO₂ and NO_x are being formulated and will be incorporated into DEAT’s 2008 national framework for air quality management. Numerous removal technologies are available to reduce the quantities of these gases prior to their release, ranging from low NO_x boilers and clean coal technologies to flue gas desulphurisation (FGD) and flue gas denitrification. FGD and denitrification systems have not been installed at any of the current power stations. However, FGD will be installed for the proposed Project Bravo coal-fired power station in Mpumalanga.

¹ Calculated annual figures based on coal characteristics and power station design parameters, excluding Camden and Grootvlei and gas-turbine power stations.

We calculate and record on a monthly basis the annual amounts of oxides of nitrogen (NO_x), sulphur dioxide (SO₂) and carbon dioxide (CO₂) emitted from power stations, based on the coal characteristics and power station design parameters. All coal-fired power stations are installing a continuous emissions monitoring system on one unit per power station.

Research into SO₂ reduction

A study is underway to identify alternative ways to reduce SO₂ emissions at coal-fired power stations. These include:

• identification of coal beneficiation/processing options to reduce sulphur in the product for use in an Eskom plant on a site-specific basis
• improved calorific value impacts on emissions
• quantification of the reduction of contaminants associated with identified technology options
• peripheral or lifecycle impact on the environment due to the beneficiation options, for example, increased discard production
• amounts of water that may be required for these processes

Eskom has operated an ambient air quality monitoring network since the 1980s to provide national and regional information on long-term trends in air quality.  The network includes monitoring sites in the immediate vicinity of certain power stations and research sites.  Additional monitoring stations have been installed near proposed new power stations and relocated to more appropriate locations.

The network measures not only Eskom emissions, but all emissions from surrounding sources.  Monitoring equipment is calibrated against National Meteorological Laboratory standards in a laboratory accredited by the South African National Accreditation System.  All sites, except two, are equipped to monitor SO₂, NOx, ozone (O3), fine particulate matter (FPM), wind speed, wind direction and ambient temperature.  The other two sites monitor SO₂, FPM and meteorological parameters.

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