| Summary and Recommendation | WNP Processing Plant Air Discharge Assessment | 4397169-66885702-113 | 16/06/2022 | 2 Sensitivity: General Sensitivity of Model Predictions Overview The modelled discharge parameter for the carbon regeneration stack have been based on information provided by the OGNZL. The additional modelling has been undertaken to assess the sensitivity of the ambient air mercury prediction to the assumed discharge parameters. For this assessment, annual average cumulative mercury concentration have been predicted for Scenario 1 and Scenario 2 assuming a substantially lower discharge velocity temperature for the carbon regeneration stack but the same mercury emission rate (refer to Sensitivity Model – Scenario 1 and Sensitivity Model – Scenario 2). These predictions have been compared to annual mercury concentrations predicted for Reference Model using the carbon regeneration stack discharge information provided by OGNZL (refer Section 6.1) A summary of the assumed carbon regeneration stack emission parameter assumed in the Sensitivity Model emission scenarios is show in Table D1. The modelled discharges assumed a discharge velocity of 15.2m/s and a discharge temperature of 20°C. the Sensitivity Models will predicted lower plume rise heights for the carbon regeneration stack and therefore higher ground level mercury concentrations compared to the Reference Model It should be noted that Sensitivity Model discharge parameters are not intended to be representative of likely emission conditions. Discharges from the electrowinning and oven/furnace stack are assumed to be unchanged from the Reference Model. Table D1. Summary of the discharge parameter for the carbon regeneration stack assumed in the dispersion model assessment and sensitivity model Discharge parameter Model Discharge Parameter Sensitivity Model Discharge Parameters Stack height (m) (horizontal discharge) 12.5 12.5 Stack Diameter (m) 0.15 0.15 Discharge velocity (m/s) 30.4 15.2 Discharge temperature (°C) 60 20 Mercury Emission – Scenario 1 (g/s) 0.0039 0.0039 Mercury Emission – Scenario 2 (g/s) 0.0039 0.0039 Model Predictions A summary of the annual average mercury concentrations predicted at nearby sensitive receptors for the two Sensitivity Model emission scenarios are summarised in Table D2. The maximum predicted concentration for Sensitivity Model -Scenario 1 is 0.0229 µg/m3, or 76% of the of the OEHHA REL of 0.03 µg/m3. A similar maximum concentration of 0.021 µg/m3 is predicted for the Scenario 1 for the expected modelled discharges conditions (refer Table 6-1). The maximum predicted concentration for Sensitivity Model -Scenario 1 is 0.0092 µg/m3, or 31% of the of the OEHHA REL of 0.03 µg/m3. A similar maximum concentration of 0.0074 µg/m3 is predicted for the Scenario 2 for the expected modelled discharges conditions (refer Table 6-1). The results of the modelling indicate that predicted annual average mercury concentration are comparatively insensitive to the carbon regeneration stack emission parameters.
RkJQdWJsaXNoZXIy MjE2NDg3