Flue Gas Desulfurization Processes

What Are the Effluent Limitation Guidelines (ELG)?

The combustion of fossil fuels to power manufacturing and refining facilities occurs across a wide range of industrial sectors. Fossil fuel plants power chemical and oil refineries, as well as those facilities that produce cement, paper, glass, steel, iron, copper, and other metals. The SO₂ gases emitted as a result of that process are a primary contributor to acid rain and has long been regulated by every industrialized nation in the world due to their harmful effects on human health and the environment. In the U.S., ELG rules regulate wastewater discharges from coal-fired power plants and IGCC power plant wastewaters utilized in flue gas air pollution control systems or solid waste handling systems. Flue-gas desulfurization was an important development to meet environmental challenges.

 

 

Flue Gas Desulfurization Processes

The process of FGD is designed to absorb the sulfur dioxide in the flue gas before it is released. This is accomplished through either a wet or a dry process.

Dry FGD

In the process of dry scrubbing injection systems, lime is used as a reagent to react and remove gaseous pollutants. There are two common dry methods, the dry injection system and spray drying systems. Each process injects lime into flue gas to remove SO₂. A dry injection process injects dry hydrated lime directly into the flue gas duct, whereas the spray dry system injects atomized lime slurry into a separate vessel. Both methods yield a dry final product, collected in particulate control devices for further treatment.

Wet FGD

The process of wet scrubbing typically utilizes an alkaline-based slurry of lime to scrub gases. A shower of lime slurry is then sprayed into a flue gas scrubber, where the SO₂ is absorbed into the spray and becomes a wet calcium sulfite. One by-product of that sulfite is it can be converted to salable gypsum. Wet scrubbing provides high-efficiency sulfur dioxide removal capacity, in addition to reducing any scaling potential.