AIR QUALITY IMPACT ASSESSMENT METAL MAN GALVANIZING OPERATIONS PORT ELIZABETH FINAL REPORT JUNE 2012

Transcription

1 AIR QUALITY IMPACT ASSESSMENT Prepared for METAL MAN GALVANIZING OPERATIONS PORT ELIZABETH FINAL REPORT JUNE 2012 Lethabo Air Quality Specialists cc PO Box Lynnwood Ridge 0040 Page 1 of 24

2 AIR QUALITY IMPACT ASSESSMENT 1 INTRODUCTION Messrs Metal Man's Galvanising Techniques (MM-GT) operates a hot-dip galvanizing plant in the Deal Party industrial area of the Nelson Mandela Bay Municipality (NMBM) in the Eastern Cape. The process employed by MM-GT is listed as a controlled emitter in terms of Section 21 of the Air Quality Act and an atmospheric emissions license (AEL) is required by MM-GT to operate the process. MM-GT wishes to apply for such a license and subsequently requested assistance from Lethabo Air Quality Specialists CC (LAQS) in this regard. LAQS modelled the dispersion of hydrochloric acid (HCl) fumes emitted from MM- GT s operations to estimate ground-level concentrations and assessed the risk that HCl vapours may pose to health in general by comparison of estimated ground-level concentrations against data published in literature. This report discusses the dispersion modelling work and risk assessment outcome in detail. 2 PROCESS DESCRIPTION MM-GT currently galvanises approximately 480 tons steel per month, but has the capacity to treat 750 tons steel per month. A typical hot-dip galvanising process of degreasing, pickling, rinsing, drying and galvanising is followed by MM-GT in a U- shaped process flow. Untreated metal enters the process through the western entrance to the plant where degreasing, pickling and rinsing occurs. Prepared metal is transported to the eastern Page 2 of 24

3 side of the plant inside the building along the southern wall of the plant where drying is achieved. Dipping of the metal into the zinc bath occurs in the eastern part of the plant. Metals components destined for galvanization are delivered to MM-GT s premises by clients. These components are galvanized in a process that consists of the following six steps: STEP 1: Degreasing bath: Prior to galvanising, the metal is dipped in a degreasing baths where a caustic solution is used to remove all grease, oils and other matter that can prevent proper bonding between the zinc and steel. STEP 2: HCl Pickling baths (4 baths): HCl Concentration 15% with an added inhibitor is used to reduce reaction with mild steel and limit fuming. Metal to be galvanized is cleaned in the pickling bath prior to galvanizing. STEP 3: Rinse bath: Excess acid is rinsed in water which is subsequently used to dilute HCl to 15% when replacing the pickling bath contents. ST'EP 4: Flux bath: Metal to be galvanised is dipped in a ZnCl / NH 4 Cl solution which acts as flux for the galvanizing step. STEP 5: Galvanising kettle: The main component is molten Zn maintained at a temperature of about 450 C. Metal to be galvanized is dipped in this solution where the zinc metal bonds with the steel surface. STEP 6: Passivation: Galvanized components are dipped into a pacifier solution to halt zinc bonding reaction. MM-GT is capable of the following maximum production rates: Daily: 30 tons steel Page 3 of 24

4 Monthly: 750 tons steel 3 WASTE STREAMS Two liquid / solid waste streams are generated in Steps 1 and 4 above and are dealt with as follows: Depleted acid and sludge from the pickling baths are removed by a qualified / registered waste management company and disposed of in an appropriately certified landfill site. Zinc slag material is returned to the metal supplier where the ZnO is recycled to pure Zn for further galvanizing operations. Two gaseous waste streams are generated in Steps 1 and 4 above and are dealt with as follows: Hydrochloric acid (HCl) fumes are released from the pickling baths due to the evaporation of acid in the four picking tanks. No extraction hoods exist, but fresh air is blown over the baths to protect workers from exposure to excessive HCl fumes. The fumes are emitted directly to atmosphere through side vents and the opening to the building. No gas cleaning equipment is installed. Particulate matter in the form of ZnO is generated by the galvanizing kettle. No extraction hoods are installed and the particulates are emitted to atmosphere mainly through the opening to the building. 4 DISPERSION MODELLING STUDY The dispersion modelling study was carried out with EnviMan, a GIS-based emissions management software suite produced by Opsis AB in Sweden. The dispersion modelling component of the suite consists of the following four modules: Page 4 of 24

5 Mapper: A map manipulation tool Emissioner: An extensive, relational emissions data base Envimet: A meteorological data management program Planner: The actual dispersion model MAPPER Mapper is a digital map compiler. It is used to define GIS data sets and map sets to be used by all EnviMan GIS modules. It can import a variety of digital maps and structure the data in suitable forms, e.g. sheets, objects, etc. It is the basis of the EnviMan GIS suite as it defines all co-ordinates for subsequent use by the various EnviMan modules. EMISSIONER Emissioner is a comprehensive, relational emissions data base that locates emission sources at fixed co-ordinates on the map compiled with Mapper. Sources are placed on the map by the user and the co-ordinates are automatically generated by Mapper. Emissioner can handle particulate and gaseous emissions from the following sources: -- Point sources, e.g. industrial stacks -- Area sources, e.g. landfill sites -- Grid sources, e.g. complete informal settlement areas -- Line sources, e.g. motor vehicle emissions Of these, area sources are of interest in this study (please see Section below). When multiple sources are investigated, it is possible to add keywords to each source to uniquely identify it and to investigate plume dispersion from a single, or group of sources. Page 5 of 24

6 ENVIMET Envimet uses meteorological data collected at ground level to calculate boundary scaling data sets used in dispersion modelling studies. Of primary importance are those parameters that define scaling of the boundary air layer. These are: -- Wind speed -- Wind direction -- Standard deviation of wind direction -- Temperature -- Solar radiation These parameters are used by Envimet to calculate all of the parameters, e.g. stability of the air boundary layer, mixing heights, climate sets, etc., which are required by Planner in calculating the dispersion of pollutants from a source. PLANNER Planner is the dispersion module of the EnviMan suite and links with Mapper, Emissioner and Envimet to carry out dispersion modelling activities. It is designed to run simulations of air quality based on emission data created in Emissioner for the following scenarios: -- Hypothetical weather definitions, i.e. user-supplied information about temperature, wind speed, wind direction, cloud cover, etc. -- True weather period, i.e. using recorded data from a weather monitoring station to simulate plume dispersion hour-by-hour over a defined period. Page 6 of 24

7 -- Statistical weather period, i.e. using a pre-calculated sample of various weather conditions that typically occur during a year. This allows the creation of annual air quality maps for comparison against national guidelines and limit values. Of these scenarios, the statistical period is applicable to the study of plume dispersion from MM-GT's plant. Planner makes use of three different dispersion models, two of which are aimed at motor vehicle emissions. Use is made of the Aermod dispersion model for the purposes of calculating the dispersion of plumes from point, area and grid sources. Aermod is an USEPA-approved Gaussian plume dispersion model and is capable of simulating dispersion of pollutants over a distance up to approximately 50 km from the source. 5 INPUT DATA 5.1 MAPPER A 256-colour bitmap of the area around MM-GT's plant was obtained from Google Earth and imported into Mapper. The map is shown in Figure 1 below. The emissions data base (Emissioner) links with the map and places emission sources on specific locations, as defined by the user. Page 7 of 24

8 Figure 1: Map covering 2 km x 1.2 km 5.2 EMISSIONER Due to the size of MM-GT's building and the absence of extraction hoods and stacks, MM-GT's operations were modelled as an area source with approximate dimensions of 30 metres by 30 metres. A pollutant release height of 5 metres was assumed. EMISSION DETAILS: In estimating emissions from MM-GT's operations LAQS followed a conservative approach as such an approach would yield an over-estimation of emissions rather than an underestimation. The rationale behind this approach is the fact that the actual impact of emissions would be lower than the estimated impact. Emissions of HCl and particulates were calculated using the method defined by the Air Permits Division of the Texas Commission on Environmental Quality, USA, in their Hot Dip Galvanising Calculations Guidance Package. This source was chosen as the Page 8 of 24

9 USEPA s AP-42 Emission Factors contains very little useful emission factors applicable to hot-dip galvanizing operations. The Calculations Guidance Package provides emission factors for both HCl fumes from pickling baths and particulate emissions from galvanising kettles based on the various factors described below. Throughout the calculation phase a conservative approach was followed to ensure a higher than normal emission rate and, therefore, a worst case scenario. Thus it was assumed that the plant operates at maximum capacity, i.e. 24 hours per day for 300 days per year instead of the day-shift, five days per week operation currently applicable to MM-GT s operation. HCl fumes: The following parameters are used in calculating emissions from the acid pickling baths: Bath surface area Acid strength Acid temperature Vapour pressure of HCl acid given the acid strength and temperature The use and efficiency of evaporation inhibitors The use and efficiency of glue gas cleaning equipment. Vapour pressure is the driving force behind all forms of evaporation. The higher the vapour pressure, the greater the rate of evaporation and, hence, the concentration in the air extracted over the baths. MM-GT provided details of the pickling bath dimensions and gave acid strength as an average of 11% and its temperature as 25 C. For the purposes of estimating the emissions and acid it was assumed that no inhibitor was added to the pickling baths, thus following a conservative emissions estimation approach. Page 9 of 24

10 Given the conservative approach followed, the total mass emission rate of HCl fumes from the four pickling baths was calculated to be 434 kg/annum. ZnO Particulates: The Calculations Guidance Package uses a fixed emission factor of 0.52 lb/ton (0.24 kg/ton) per annum of metal galvanized for galvanizing kettle emissions. It further makes use of the following criteria to calculate emissions of particulates: Mass of material galvanized Efficiency of extraction hood Efficiency of air pollution control equipment In MM-GT's case no extraction system and particulate collection devices are used. Given the conservative approach followed the total mass emission rate of particulates from the two pickling baths was calculated to be 2.1 tons per annum. Output units: Given an input of tons per annum, the output of Planner is in units of micrograms per cubic meter (µg/m 3 ). 5.3 ENVIMET Extensive meteorological data collected at the Coega Industrial Development Zone was obtained by LAQS. The dataset is complete and of high quality, containing the five parameters essential for reliable dispersion modelling, i.e. wind speed, wind direction, standard deviation of wind direction, temperature and solar radiation. Page 10 of 24

11 5.4 PLANNER Planner does not require any user input as it extracts data from Mapper, Emissioner and Envimet. 6 RESULTS The approach to the project was to determine both the annual average ground-level concentrations and 95-percentile concentrations (the concentrations that may occur for 5% of the time) of the two pollutants in the immediate vicinity of the plant, i.e. where the concentrations are expected to be the highest. All simulations were carried out for a receptor height of 2 metres above ground level and a plume dispersion period of 120 minutes. This simulation period ensured that very low winds, e.g. below 1 m/s, would carry pollutants some distance from the plant. 6.1 HYDROCHLORIC ACID FUMES The dispersion of HCl fumes from the operations at MM-GT's property is shown graphically in Figures 2 and 3 below. Figure 2 represents annual average estimations while Figure 3 represents 95-percentile estimations. A closer view of the 95-percentile isopleths is given in Figure 4. The maximum annual average concentration and maximum 95-percentile concentration anywhere along MM-GT's fence-line were found to be less than 5 μg/m 3 and 24.3 µg/m 3 (both to the south) respectively. The annual average concentration at the nearest residential area (west of north-west of the plant) was estimated to be less than 0.05 μg/m 3 while the maximum 95-percentile value was estimated to be 0.13 μg/m 3. Page 11 of 24

12 6.2 TOTAL PARTICULATE MATTER The dispersion of particulates is shown graphically in Figures 5 and 6 below. Figure 5 represents annual average estimations while Figure 6 represents 95-percentile 24-hour estimations. A closer view of the 95-percentile isopleths is given in Figure 7. The maximum annual average concentration and maximum 95-percentile 24-hour concentration anywhere along MM-GT's fence-line were found to be 29.3 μg/m 3 and 105 µg/m 3 (both to the south) respectively. The annual average concentration at the nearest residential area (west of north-west of the plant) was estimated to be 0.11 μg/m 3 while the maximum daily 95-percentile value was estimated to be 0.63 μg/m 3. Page 12 of 24

13 Figure 2: Annual Average HCl Concentrations Page 13 of 24

14 Figure 3: 95-percentile HCl Concentrations Page 14 of 24

15 Figure 4: Closer View of 95-Percentile HCL Concentrations Page 15 of 24

16 Figure 5: Annual Average TPM Concentrations Page 16 of 24

17 Figure 6: 95-percentile 24-hour TPM Concentrations Page 17 of 24

18 Figure 7: Closer View of 95-percentile 24-hour TPM Concentrations Page 18 of 24

19 7 DISCUSSION 7.1 MODEL RELIABILITY The results of any computer model are only as reliable as the quality of the input data Emissioner: The concentrations of both HCL and total particulate matter emissions were obtained from estimated data and have not been verified. The data must, therefore, be regarded as preliminary data only. The conservative approach followed implies that the predicted results are an over-estimation of expected actual conditions, but the degree of overestimation cannot be determined Envimet: The meteorological data obtained from the Coega monitoring stations is comprehensive and no gaps exist in the final data set. It is, therefore, complete and a reliable meteorological data set could be compiled. The distribution of winds in the area is shown graphically in Figure 8 below. Page 19 of 24

20 Figure 8: Frequency of Wind Direction Planner: As was stated previously, the user provides no direct data input to Planner. It uses Aermod, the latest USEPA approved Gaussian plume dispersion model, and there is no reason to doubt the reliability of the dispersion calculations. 8 IMPACT ON OVERALL AIR QUALITY 8.1 AMBIENT AIR QUALITY Air quality standards for some pollutants are defined by the Standards South Africa (SSA) in their publication SANS 1929:2005, South African National Standard, Ambient Air Quality Limits for Common Pollutants, but this list does not include HCl. Page 20 of 24

21 8.1.1 HCl The time-weighted average threshold limit value (TLV-TWA) used in occupational health applications is 1.5 mg/m 3. The TLV-TWA value is the concentration to which a normal person can be exposed to for 8 hours per day, day after day, without any adverse affects. The maximum estimated 95-percentile fence-line concentration of HCL to the south of the plant is 24.3 µg/m 3. This concentration is approximately 61 times lower than the TLV-TWA value Particulate Matter Two air quality standards for PM10 particulates are defined for South Africa, i.e. a 24- hour level concentration of 75 µg/m 3 and an annual average concentration of 40 µg/m 3, both aimed at the protection of human health. The maximum estimated 95-percentile 24-hour particulate concentration along MM- GT's fence-line to the south of the plant is 129 µg/m 3. This concentration is in excess of the official air quality standard. The estimated average annual concentration of particulates is 29.3 µg/m 3 which is below the official air quality standard. It must be noted that air quality standards for PM10 particulate matter only is given, and not total particulate matter (TPM). The definition of a PM10 particle is "the diameter of a particle that behaves aerodynamically the same as a spherical particle with a diameter of 10 micron and unit specific gravity". Aerodynamic behaviour is a function of, inter alia, particle shape and particle density. A more detailed study is required to determine the percentage of particulate emissions from MM-GT's operations that will qualify as PM10 particles. Page 21 of 24

22 8.2 HEALTH ISSUES Inspection of a HCL material safety data sheet (MSDS) will render the following risk information: Inhalation of the spray mist may produce severe irritation of respiratory tract, characterized by coughing, choking, or shortness of breath. Inhaling spray mist implies direct exposure to high concentrations of HCl, i.e. close to a strong source, and not the ambient air quality levels predicted by the dispersion model. As is stated in Section 7.1 above TLV-TWA is 1 ppm, or 1.5 mg/m 3, a level approximately 61 times higher than the predicted ground-level concentration at MM- GT's fence line. A more reliable interpretation of the potential long-term risk posed by gaseous HCL has been defined by the Integrated Risk Information System (IRIS) of the USEPA. IRIS defines the following concentration for chronic inhalation exposure (RfC): The inhalation Reference Concentration (RfC) is analogous to the oral RfD and is likewise based on the assumption that thresholds exist for certain toxic effects such as cellular necrosis. The inhalation RfC considers toxic effects for both the respiratory system (portal-of-entry) and for effects peripheral to the respiratory system (extrarespiratory effects). It is expressed in units of mg/cu.m. In general, the RfC is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily inhalation exposure of the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. Inhalation RfCs were derived according to the Interim Methods for Development of Inhalation Reference Doses (EPA/600/8-88/066F August 1989) and subsequently, according to Methods for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry (EPA/600/8-90/066F October The Defined RfC for HCl is 20 µg/m 3, i.e. marginally less than the highest predicted ground-level concentration along the fence line. Page 22 of 24

23 9 CONCLUSIONS As described in Section 4 above a conservative approach was followed in estimating emissions from MM-GT s plant in Port Elizabeth. The rationale behind this approach is that the outcome will be an overestimation of the impact air quality. Should this impact prove negligible the real impact would be even less. The estimated ground-level concentrations of HCl at the nearest residential area are very low and the concentrations within the industrial zone are well below occupational health limits. LAQS is, therefore, of the opinion that the emissions do not pose a health risk to the community in general. However, the emissions could pose a long-term corrosion problem to neighbours. The estimated ground-level concentrations of particulates at the nearest residential area are very low and, in LAQS's opinion, do not pose a health risk to that community. However, significantly higher concentrations will prevail in and around MM-GT's site. It must be borne in mind that the emissions of HCl are constant whereas the emissions of particulates occur mainly when uncoated metal is dipped into the galvanising kettle. It is, therefore, feasible that instantaneous concentrations, i.e. those that occur when metal is dipped into the kettle, could be higher. Already the concentrations are of the order of magnitude of the ambient air quality standards and LAQS is of the opinion that these emissions may pose a health and/or nuisance risk to MM-GT's neighbours in the long run. 10 RECOMMENDATIONS 10.1 EMISSIONS REDUCTION PLAN Because of the potential impact on air quality close to the plant LAQS is of the opinion that a dedicated emissions reduction program must be defined. The building in which the galvanising activity takes place was constructed to facilitate the flow of work through the galvanising process and boasts huge openings so that large items could Page 23 of 24

24 enter and leave the process with ease. These large openings, however, are not conducive to efficient fume extraction operations. Nevertheless, LAQS is of the opinion that steps can be taken to reduce the emissions of both HCL fumes and particulate matter from the process. The following steps are suggested: -- Reduce the product entrance and exit openings as much as possible. -- Upgrade the extraction fans in the western wall of the building to extract air from the pickling ranks and collect the fumes in a wet scrubber. -- Install extraction fans in the roof over the galvanising kettle to extract all particulate matter emitted from the kettle. -- Install a bag filter to remove collected particulate matter from the air extracted EMISSIONS VERIFICATION The estimated emissions data and corresponding results must be regarded as preliminary values only, subject to confirmation after installation of appropriate air pollution control equipment. Emissions cannot currently be verified reliably as they occur into a large open space from where it is dispersed into the atmosphere. However, should the steps suggested above be taken, it will result in reduced emissions from two separate stacks. MM-GT should then appoint a suitably qualified and experienced contractor to verify emissions on an annual basis. Continuous emissions monitoring equipment is not recommended at this stage. Page 24 of 24