Question 1 It is reported that the emission of CO 2 from a coal-fired power plan

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Question 1

It is reported that the emission of CO2 from a coal-fired power plant is 1650 g/s (E) and the pollutant’s downwind concentration at ground level is 1.6×10-3 g/m3 at 1 km downwind on an overcast summer afternoon. The following are the information on stack, atmospheric and wind conditions,

            Stack Parameters:                             Diameter, d = 1.20 m

                                                                    Exit velocity, vs = 10.0 m/s

                                                                    Temperature, T = 315ºC

            Atmospheric conditions:                     Pressure, P = 100 kPa

                                                                    Temperature, Ta = 25.0ºC

            Wind condition:                                  Wind speed, u = 4.50 m/s

a. Determine the physical stack height, h (in m), of the coal-fired power plant if the stability of that condition is to fall in “D” class. (Note: “centerline” implies y = 0)

This problem can be solved by using Gaussian Dispersion Model as follows.

Where,

X(x,y,0,H)         = downwind concentration at ground level, g/m³

E                     = emission rate of pollutant, g/s

Sy                   = plume standard deviation in y direction = ax0.894 (Refer to Table 1)

Sz                   = plume standard deviation in z direction = cxd + f (Refer to Table 1)

u                      = wind speed, m/s

H                      = h + H (or physical stack height + plume rise), m

To determine plume rise, one can use the equation as expressed

Where,

vs                     = stack velocity, m/s

d                      = stack diameter, m

u                      = wind speed, m/s

P                      = pressure, kPa

Ts                     = stack temperature, K

Ta                     = air temperature, K

b. During the early morning it was observed that a fanning plum is formed in the area. Based on the shape of the plume can you deduce the atmospheric stability of the place in the early morning?                                                                                                                         

c. Gobal warming is one of a major environmental problem facing the world today. Describe this phenomena and discuss in detail it’s the causes.

d. Describe how a wet scrubber works and what is its advantage over a simple cyclone.  

Explanation / Answer

c. Global warming is phenomenon which is responsible for the rapid rise in the earth's temperature. Because of global warming, the earth's temperature is gradually increasing. Because of this rise in the temperature of the earth, many species of earth are in danger of extinction.

Causes for global warming are mainly anthropogenic ie. man-made. Greenhouse houses like carbon dioxide, sulfur dioxide etc. are mainly responsible for the greenhouse effect. These gases, after being emitted from industries, cars etc. rise up in thre atmosphere and form a layer over the earth's surface. These gases prevent the escape of heat from the earth's surface and lead to an increase in the temperature of the earth.

Rapid deforestation and loss of forest cover is also one of the reasons for global warming.

(d) A wet scrubber operates by introducing the dirty gas stream with a scrubbing liquid - mostly water. In this way, the scrubbing liquid absorbs the dirt from the gas and exits. The gas is now clean and is taken out.

In a simple cyclone, we don't use a scrubbing liquid to separate the dust and dirt. Instead we use centrifugal force to separate the solid impurities from the gas.

(b) If a fanning plume is formed, then there is little turbulence in the atmosphere. There is inversion only at a considerable distance from the stack. Hence, the atmosphere is extremely stable.

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