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HOMEWORK I (DUE ON Feb 08) 1. H2S is vented from a stack which has an effective height of 50 m. The wind speed is 2.5 m/s on an overcast night. For an emission rate of 0.06 g/s, determine the maximum ground-level concentration on the plume center line downwind from the stack. If the odor threshold for H2S is 0.00047 ppm, plot the region which an average person could detect H2S by smell. (10%) 2. A ground-level source (H = 0) is emitting pollutants at an unknown rate. At 1 km directly downwind of the source, the measured ground-level concentration of the pollutant is 10 g/m3. The stability category is A. Estimate the emission rate of this source. (5%) 3. A power plant is emitting its stack gas from a 50-m high stack. For its conditions, the plume rise is given by 200 m 2 / s h u where us is the wind speed in m/s. The stability category is C. At what speed will the maximum calculated ground-level concentration occur? Hint: This requires a trial-and-error solution. (10%) 4. An industrial source is in a rural location. It has a 30 m stack with a top inside diameter of 2.6 m. Under its normal operating capacity, it emits 50 g/s of PM10 at an exit velocity of 20 m/s and with an exit temperature of 325 K. On June 18th at 1100 with clear skies, the wind speed at 10 meters above ground is 3 m/s, and the wind at 30 meters above ground is 3.5 m/s. The surface pressure is 997 mb and the ambient air temperature is 20 oC, and the mixing height is 500 m. (a) What is the plume rise, the effective stack height , the distance to maximum concentration and the maximum concentration? (b) At a distance twice the distance to the maximum concentration, what is the concentration directly downwind and what fraction of the maximum concentration is this? (c) What is the crosswind distance to the 10 g/m3 at these two downwind distances, 0.465 and 0.93 km? (d) If the wind direction is 5o different than was thought, what is the concentration at the position 0.93 km downwind that we previously thought was directly downwind? (e) Assuming this source is operating at 70% capacity which causes the emissions to be 35 g/s and the exit velocity is 14 m/s. The exit temperature is 318 K. What is the result plume rise, effective stack height, distance to maximum concentration and maximum ground level concentration? (25%) 5. A proposed pulp processing plant is expected to emit 0.5 ton per day of H2S from a single stack. The company property extends a minimum of 1500 m from the proposed location. The nearest receptor is a small town of 500 inhabitants, 1700 m NE of the plant. Plant managers have decided that it is desirable to maintain concentrations below 20 ppbv or approximately 2.910-5 g/m3, for any period greater than 30 min. Wind direction frequencies indicate that winds blow from the proposed location toward this town between 10 and 15 percent of the time. What height should the stack be erected? It is assumed that a design wind speed of 2 m/s will be sufficient, since the effective stack rise will be quite great with winds less than 2 m/s. Other than the stipulation, assume that the physical stack height and effective height are the same, to incorporate safety factor. (10%) 6. A smelter is located near an airport. The smelter stack is 300 m high and has a plume rise of 100 m. It is emitting 5 kg/s of SO2. Assume that the stability class is always C, and that the wind speed is always 3 m/s. The flight path for the airport is perpendicular to the plume and 5 km downwind of the smelter. The airport safety office has determined that it is unsafe for planes to go through any portion of the plume that has an average SO2 concentration higher than 500 g/m3. They have decided that flying under the plume is unsafe, so the places must always fly over it. What is the minimum altitude at which they can fly under these circumstances and not be exposed to SO2 concentrations 500 g/m3. (10%)

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posted: | 6/4/2013 |

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