Chemical Engineers in Action: Innovation at Work

Pollution-control systems developed by chemical engineers generate clean stack gas containing steam instead of the smoky flue gases produced by power plant stacks, as shown in this artist’s rendering. Courtesy Constellation Energy.

Chemical engineers have helped provide new technologies to enable electric power plants and industrial facilities to significantly reduce such harmful airborne emissions as

Sulfur dioxide (SO₂),
Nitrogen oxides (collectively called NO_x),
Mercury, and
Unburned hydrocarbons.

Reducing industrial air pollution

SO₂ and NO_x react with water to create acid gases, which in turn lead to acid rain. Acid rain damages cars and buildings, kills trees, destroys lakes and streams, and leads to respiratory and other health problems.

Chemical engineers developed flue gas desulfurization (FGD), now a widely used method of reducing acid gases in smokestacks. FGD works by using a wet scrubber spray tower in the flue or smokestack. During operation, acid gases are converted to neutral salts and other solid by-products, which are then removed.

Solutions to NO_x emissions include selective catalytic reduction (SCR) systems that convert NO_x emissions to harmless nitrogen gas and water.

Through the inventiveness of chemical engineers, wet scrubbers, SCR systems, and other pollution-control technologies have significantly reduced the amount of SO₂, NO_x, and other harmful emissions being released into the atmosphere. Specifically, the U.S. electric power industry has

Reduced SO₂ emissions in the United States by more than 5.5 million tons per year since 1990,
Reduced NO_x emissions by about 3 million tons per year since 1990, and
Reduced acid rain deposition in the United States and Canada.

Cleaner coal use

Coal remains the cheapest and most plentiful of all the fossil fuels. However, it is also the most polluting. Chemical engineers have worked to perfect coal gasification, a method to generate electricity and produce fuels from coal with significantly less environmental impact. Now utilities can burn clean synthetic gas made from coal and have considerably fewer emissions than with traditional pulverized coal combustion.