Enviromental Engineering review problems

1. Consider a 400-MW, 32 percent efficient coal-fired power plant that uses cooling water withdrawn from a nearby river (with an upstream flow of 10-m3/s and temperature 20 °C) to take care of waste heat. The heat content of the coal is 8,000 Btu/lb, the carbon content is 60% by mass, and the sulfur content is 2% by mass.

i. How much electricity (in kWh/yr) would the plant produce each year?

ii. How many pounds per hour of coal would need to be burned at the plant?

iii. Estimate the annual carbon emissions from the plant (in metric tons C/year).

iv. Convert the carbon emissions to g C/kJ of energy produced. Compare your answer to that in Problem 2.7 of Homework 3 for petroleum combustion, and Example 2-3 for methane combustion. Comment on why coal is considered the “dirtiest” fossil fuel!

v. If the cooling water is only allowed to rise in temperature by 10 °C, what flow rate (in m3/s) from the stream would be required? Is this sustainable? What would you recommend?

vi. What would be the river temperature if all the waste heat was transferred to the river water assuming no heat losses during transfer? Would that be a problem? Why or why not.

vii. Estimate the hourly SO2 emissions (in kg/h) from the plant assuming that all the sulfur is oxidized to SO2 during combustion.

viii. What would be the problem in releasing SO2 to the atmosphere? Is sulfur dioxide a regulated priority pollutant? If yes, report the NAAQS?

ix. How would you propose to remove sulfur dioxide at the power plant?

x. Report on the required efficiency (in removal %) of the SO2 scrubber, if the plant is only allowed to emit the legal limit of 0.6 lb SO2 per million Btu of heat input.

xi. How much particulate matter could be released (in kg/year particulates) if the plant met New Source Performance Standards (NSPS) that limit particulate emissions to 0.03 lb per 106 Btu heat?

xii. Comment on the sources of particulates in the plant emissions? We have seen a dramatic decrease in particulate emissions since the 1970 Clean Air Act. How are particulate emissions controlled at stationary sources?

2. Consider an area-source box model for air pollution above a peninsula of land. The length of the box is 50 km, its width is 20 km, and a radiation inversion restricts mixing to 20 m. Wind is blowing clean air into the long dimension of the box at 0.4 m/s. Between 8 and 10 a.m. there are 300,000 vehicles on the road, each being driven 50 km, and each emitting 4 g CO/km. CO gets oxidized to carbon dioxide in the atmosphere. The half-life for CO in the atmosphere is 3 hours. Assume air temperature is 20⁰C.

i. Estimate the steady state CO concentration in the air shed (in mg/m3)

ii. Convert to ppmv and determine whether it exceeds the NAAQS.

iii. If there was no CO at 8 a.m., determine the CO concentration(in mg/m3) at 10 o’clock.

iv. How would air quality change if the wind speed picked up to 20 mph (miles per hour)? Here you need to recalculate the steady state CO concentration (in mg/m3).