For the Localization of a MSW Incinerator Results of Atmospheric
Total Page：16
File Type：pdf, Size：1020Kb
Results of atmospheric dispersion model for the localization of a MSW incinerator E. Brizio1, G. Genon2 & M. Poggio2 1Cuneo Province Administration, Italy 2Turin Polytechnic, Italy Abstract The present study reports the attempt to localize a MSW incinerator, starting from three proposed sites, on the basis of the atmospheric transport and dispersion modelling. The considered area, around Turin, in North-Western Italy, is characterized by a high percentage of hours of calm wind, so the choice of the atmospheric model is very important in order to have reliable and convincing results. In the present study we used the AERMOD model by the U.S. EPA, that is a hybrid atmospheric dispersion model which can treat the calm hours within a more restrained computational time with respect to Eulerian or Lagrangian models. The investigated issue is generally a very delicate and thorny argument because of the natural opposition of the people against this kind of plant. The first thing to do to treat the localization of a MSW incinerator is to calculate the concentrations at the ground level due to the emitted pollutants and to compare them to the air quality regulations; secondly, one can think about the possibility of building a district heating system or distributing technological vapour service to industrial users, avoiding the respective emission of pollutants. In practice, the concentrations at the ground level when the incinerator is placed in the three proposed sites are very comparable and, for each site, much smaller than the air quality regulations and the measured levels of the area. The best localization is then determined by the possibility of realising a large district heating system. Keywords: incinerator, AERMOD, concentration, district heating, calm hours, MSW, avoided emissions. 1 Introduction In the present paper we simulated the atmospheric transport and dispersion of pollutants generated by the incineration of the solid waste deriving from the Development and Application of Computer Techniques to Environmental Studies X G. Latini, G. Passerini & C. A. Brebbia (Eds) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-718-3 148 Development and Application of Computer Techniques to Environmental Studies X mechanical selection of the MSW produced by the metropolitan area of Turin, in North-Western Italy. There are three possible localizations for the plant: Volpiano, 20 km far from Turin, Strada del Francese and Gerbido, respectively in the North-Western and South-Western part of Turin; each of these three sites has different possibilities of realising or increasing the district heating systems. 2 Data at disposal 2.1 Technical features and possible localization As concerns the plant, we know that the MSW incinerator would be fed by 245.000 t/y of selected MSW (approximately 34 t/h, composed by 38,6% C, 5,1% H, 22,4% O, 1,0% N, 0,1% S, 0,8% Cl, 15,0% ashes and 17,1% H2O, enthalpy of combustion = 3.595 kcal/kg). The thermal power of the plant is 142,2 MW. The emitted flow is approximately 258.138 Nm3/h, with a humidity volume of 15% and a oxigen content near 9,4% (vol/vol for dry smoke). The flue gas temperature has been assumed 140 °C, the stack height is 80 m and the stack diameter is 3 m. The emission limits for the incineration can be referred to the EC regulations, in particular 76/2000/CE; on the other hand, the emission levels, taken from measurements on existing plants, can be often much smaller than the limits, as reported in Table 1. Table 1: Emission limits and levels for a MSW incinerator. EMISSION LIMITS EMISSION LEVELS YEARLY MASS POLLUTANT 3 3 (mg/Nm , dry gas, O2 @ 11%) (mg/Nm , dry gas, O2 @ 11%) FLUX (t/y) TSP 10 1 2,2 NO2 200 60 134,4 SO2 50 10 22,4 CO 50 25 55,9 Σ Heavy metals 0,5 0,1 0,2 PAH 0,01 0,002 4 E-3 3 PCDD/DF (ng/m ) 0,1 0,05 1 E-7 Cd+Tl 0,05 0,02 4 E-2 T.O.C. 10 10 22,4 HCl 10 10 22,4 HF 1 1 2,2 Hg 0,05 0,05 0,1 Zn 5 5 11,2 Table 2 reports the different features relating to the electric energy generated by the incinerator, the distributed thermal energy and the avoided emissions from the displaced heating plants for the three sites. It is important to observe that the assumed scenarios would overlap the existing district heating systems which, at present, are supplied by cogeneration plants: as a consequence, the net displaced heating plants are fewer than those corresponding to the total distributed thermal energy whereas the electric energy generated by the cogeneration plants can be Development and Application of Computer Techniques to Environmental Studies X G. Latini, G. Passerini & C. A. Brebbia (Eds) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-718-3 Development and Application of Computer Techniques to Environmental Studies X 149 larger. We assume that the existing heating plants burn natural gas (77%), gas oil (20,6%) and oil (2,4%). The avoided emissions should be modelled over 6 months per year, 14 h/d; we supposed that the eliminated sources have a flue gas temperature of 180°C, a stack exit gas velocity of 2,5 m/s, a stack height of 20 m and a thermal power of approximately 2 MW each. On the other hand, the incinerator has been assumed to emit continuously over the entire year. Table 2: Three possible sites for the incinerator. STRADA DEL VOLPIANO GERBIDO FRANCESE Electric power (GWh/y) 232,6 213,5 205,7 Thermal energy (GWh/y) 103,5 364,7 475,5 Net displaced heating plants (GWh/y) 6,8 127 145,5 NO2: 1,5 NO2: 27,6 NO2: 31,7 SO : 0,7 SO : 10,4 SO : 10,4 Avoided emission (t/y) referable to the 2 2 2 TSP: 0,1 TSP: 1,2 TSP: 1,2 increased district heating system CO: 0,9 CO: 17,8 CO: 20,4 CO2: 1.400 CO2: 25.900 CO2: 29.600 Increment of electric energy generated by existing cogeneration plant 18,8 49,2 75,8 (GWh/y) 2.2 Meteorological data We have at disposal a meteorological database for 1 year, from June 1st, 1999 to May 31st, 2000, calculated for the entire Province of Turin (Finardi [1]) by means of the diagnostic model MINERVE, which can define the 3-dimensional wind field, and the meteorological pre-processor SURFPRO, which assesses the atmospheric turbulence parameters (the sensible heat flux, the friction velocity, the convective velocity scale, the Monin-Obukhov lenght, the mixing height and the stability classes) on the basis of the land cover and the solar radiation. The models employ surface wind observations from the regional meteorological network as well as from Milano Linate airport radio-soundings and ECMWF (European Centre for medium range Weather Forecast) data. In particular, MINERVE is a mass-consistent model which interpolates the available observations considering the orography of the domain and the surface roughness, giving back, as results, the wind and temperature hourly vertical profiles with an horizontal resolution of 1 km. Figure 1 points out the wind roses for the three sites (Volpiano, Strada del Francese and Gerbido) and for the centre of Turin. 3 The AERMOD model In order to calculate the concentrations of the pollutants at the ground level referable to the incinerator or to the emissions of the displaced heating plants, we applied the AERMOD model by U.S. EPA [2], which was born to replace the Industrial Source Complex Model (3rd version), up to now used for the environmental planning, the risk assessment and the emission permits in the U.S.A.. The AERMOD model has been designed for the short-range simulations Development and Application of Computer Techniques to Environmental Studies X G. Latini, G. Passerini & C. A. Brebbia (Eds) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-718-3 150 Development and Application of Computer Techniques to Environmental Studies X (distances from sources generally smaller than 50 km), both for simple and complex orography. AERMOD is a steady state plume model; when the boundary layer is stable (SBL), it assumes the concentration distribution to be Gaussian in both the vertical and the horizontal. On the other hand, in the convective boundary layer (CBL) the horizontal distribution is also assumed to be Gaussian but the vertical distribution is described with a bi-Gaussian probability density function (pdf). Moreover, in the CBL, AERMOD treats “plume lofting”, whereby a portion of plume mass, released from a buoyant source, rises to and remains near the top of the boundary layer before becoming mixed into the CBL. Figure 1: Wind roses: clock-wise, Volpiano (80 m), Strada del Francese (80 m), Gerbido (80 m) and the centre of Turin (30 m). Development and Application of Computer Techniques to Environmental Studies X G. Latini, G. Passerini & C. A. Brebbia (Eds) © 2004 WIT Press, www.witpress.com, ISBN 1-85312-718-3 Development and Application of Computer Techniques to Environmental Studies X 151 AERMOD also tracks any plume mass that penetrates into the elevated stable layer and then allows it to re-enter the boundary layer when and if appropriate. For sources in both the CBL and the SBL AERMOD treats the enhancement of lateral dispersion resulting from plume meander. As concerns the treatment of the orography, AERMOD is strongly different from the previous regulatory models (e.g. ISC3) that distinguish among simple, intermediate and complex terrain. Actually, AERMOD has been designed to be more physically realistic: where appropriate, the plume is modelled as either impacting and/or following the terrain by applying the dividing streamline concept; the streamline height depends on the parameter “height scale” which represents the terrain height that dominates the flow in the vicinity of the receptor.