DATA AND METHODS

The data used in this research report has been drawn from a variety of published literature and Eskom internal documentation. All data used in the calculation of water demand curves as well as ambient air quality databases was obtained from Eskom databases pertaining to the planning and construction of the Medupi Power Station.

The following chapter outlines the source of all air quality data and water data utilised in this research report. Modelling methodologies are also briefly discussed.

2.1. Data Requirements 2.1.1. Emissions data

Emissions from Matimba power station are assumed to be the same as those in the 2005/06 financial year (April 2005 to March 2006). Emissions from Medupi power station were calculated using a flow rate of 675.5 Sm3/s and a 90% load factor (and 100% availability). SO2 emissions from Medupi were calculated using the specifications of the expected coal (sulphur content of 1.2%, ash content of 35%, and calorific value of 20.5 MJ/kg) and assuming that the FGD system has an SO2 removal efficiency of 90%. An average diurnal emission profile is assumed. NOx emissions from Medupi will be reduced by low NOx burners and over-firing. The expected NOx emission rate of 500 mg/Nm3 is considered. It is assumed that 98% of the NOx is emitted in the form of NO, and the remainder as NO2. The NO to NO2 conversion is calculated by the CALPUFF modelling system.

FGD reduces the exit temperature, and thus the buoyancy, of the flue gas. It is assumed that no gas-to-gas reheater is installed.

Table 2-1 Emissions data utilised to input into the CALPUFF Model Matimba Medupi/Coal3/ Coal4 without FGD Medupi with FGD on 3 units Medupi/Coal3/ Coal4 with FGD SO2 315 971 439 474 241 711 43 947* NOx (as NO2)** 67 599 57 514 57 514 57 514 NO 43 206 36 759 36 759 36 759 NO2 1 352 1 150 1 150 1 150

*219 737 tons/annum are emitted from the three units at Medupi without FGD, and 21 974 tons/annum from the three units with FGD.

Figure 2-1 Map of modelling domain (Map not to Scale)

Stack parameters

No reheating was considered

Table 2-2 Emissions data utilised to input into the CALPUFF Model Matimba Medupi/Coal3/ Coal4 without FGD Medupi/Coal3/ Coal4 with FGD Exit temperature (°C) 132 130 49 Exit velocity (m/s) 24.84 26.0 18.0

Effective stack diameter (m)

12.82 12.75 13.70

Stack height (m) 250 220 220

Flow rate from Hitachi data sheet for Medupi: 1106.6 m3/s

(Calculated flow at 49°C is 884.18 m3/s)

2.1.2. Ambient air quality data

Ambient air quality data was obtained from previous monitoring campaigns undertaken by Eskom’s Sustainability and Innovation Department. Since 1984, Eskom has undertaken several monitoring campaigns within the Lephalale region, many of which have focused on the continuous monitoring of ambient SO2 in the vicinity of the Matimba Power Station. Monitoring was conducted at Zwartwater for

station was relocated to Grootstryd. In 2005 the monitoring station was subsequently relocated to the Marapong Township, as part of the conditions of the Medupi Environmental authorisation. At this time the station was also expanded to include a NOx analyser. Typically the monitoring stations measured both SOx and PM however for the purposes of these discussions only the SO2 data will be considered

Additional historical SO2 monitoring campaigns, relevant to this study included: • Sampling at five sites (M1-M5) during the August 1991 to January 1992; • Sampling at Waterberg station during the 1984 to 1989 period;

All data was obtained from the Eskom EDWEIS air quality data management system. EDWEIS is an Eskom developed ambient air quality database and analysis tool. The software allows the user to review and perform basic analysis, such as pollution roses and pollution trends for all of Eskom’s, current and historical ambient air quality data. Eskom’s ambient air quality monitoring network is SANAS accredited.

Figure 2-2 Location of all monitoring campaigns in the Lephalale region

2.1.3. Water Data

Water data for the Medupi Power Station was based on the existing Matimba power station which uses approximately 0.16 l/kW sent out which equates to approximately 5Mm3/a. Water used in the FGD process was obtained from literature surveys and various discussions with external engineers and Eskom engineers. The figure utilised of 0.21 l/kW sent out or 7.2Mm3/a is the same figure that Eskom is currently using for all planning purposes with respect to the power station. All supporting water data for the Grootstryd mine and Lephalale town was obtained from Exarro and the local municipality. Data pertaining to the possible development of an additional coal to liquid plant in the Waterberg area were obtained through Eskom Sasol research partnerships.

2.2. Methods

All water calculations were undertaken by means of an excel model.

Dispersion modelling was undertaken for 5 scenarios including a base case of Matimba without any FGD. Alternatives modelled included the no FGD on either Matimba or Medupi, the inclusion of FGD on 3 units as well as six units of Medupi. With respect to future scenarios and Eskom’s current investigations to construct 2 additional coal fired power stations in the Lephalale region two additional scenarios were run including no FGD on any of the coal fired power stations and FGD on the proposed additional two coal fired power stations (coal 3 and 4)

2.2.1. Dispersion modelling and meteorological data

The CALMET/CALPUFF suite of models was used due to the size of the baseline region to be included in the study. The dispersion modelling was conducted for a 100 by 100 km domain at a resolution of 2 km. CALMET simulates a three dimensional meteorological profile for the study area using more than one surface weather station and upper air data. The model requires hourly average meteorological data including wind speed, wind direction and temperature. Given the sparse surface meteorological data available for the region, upper air meteorological data was obtained from the Conformal Cubic Atmospheric Model (C-CAM) run at the University of Pretoria. Hourly surface meteorological data was obtained from monitoring stations in the vicinity of the power stations.

Calpuff is a regional model suitable for application in modelling domains of 50 km to 200 km. Due to its puff-based formulation the CALPUFF model is able to account for various effects, including spatial variability of meteorological conditions, dry deposition and dispersion over a variety of spatially varying land surfaces. The simulation of plume fumigation and low wind speed dispersion are also facilitated. CALPUFF allows for first order chemical transformation modelling to determine gas phase reactions for SOx and NOx. Chemical transformation rates were computed internally by the model.