Flue Gas Desulfurization — A Low Cost Emissions Solution

Flue-gas desulfurization plant

Flue gas desulfurization is the process by which sulfur dioxide is removed from flue gases. Many different industrial processes such as burning fossil fuels, refining gasoline, or manufacturing steel, glass, and cement all produce sulfur dioxide as a byproduct.

Sulfur dioxide has been linked with human health and environmental hazards. The highest concentration of this gas generally occurs near large industrial facilities. When inhaled, sulfur dioxide can cause multiple ailments, especially among the very young, the elderly, and those with respiratory conditions. These symptoms worsen if sulfur dioxide combines with other airborne pollutants to form sulfate as these particles cause additional respiratory damage such as tearing lung tissue and affecting the cardiovascular system.

In the environment, sulfur dioxide can combine with nitrous oxide to form acid rain, particulate air pollution, and regional haze. These conditions are hazardous to both plant and animal life, stunting growth and other adverse health impacts. The combination of the two gases also causes corrosion in metal, concrete, and other building materials, weakening the structures and decreasing their lifespan.

The EPA regulates sulfur dioxide, and sets limits on its emissions. Those limits can be achieved  by using wet, semi dry and dry scrubbers. Scrubbers use an alkaline reagent, which  reacts with the gas producing a solid compound. They can reduce the emissions anywhere from 50 percent to 98 percent, depending on the type of scrubber.

Source: wikipedia.org

A wet scrubbing system employs jets to spray emissions with a limestone slurry. The slurry is then injected with forced air to form gypsum, which can be sold commercially. This process is approximately 90 percent efficient at removing sulfur dioxide.

A semi dry scrubbing system uses the same basic principle as the wet system, but it is applied through an atomizer that creates a finer droplet. This system is more difficult to use, but less expensive as it does not require a separate component for handling wet waste. It is also less efficient than wet scrubbers, removing only 80 to 90 percent of the sulfur dioxide.

A dry scrubbing system injects the reagent directly into the furnace. The byproduct is then eliminated through particulate control equipment. Water can be injected further downstream in the emission flow to increase efficiency. Dry scrubbers are less expensive to install, require less space, and have simpler byproduct disposal. However, they also have the lowest efficiency at only 50 to 60 percent for calcium injections, and up to 80 percent for sodium injections.

Rubber lining significantly lowers the cost to operate flue gas desulfurization systems. The water required to run each system, and the quantity of wastewater produced, can be the single largest expense. Rubber lining reduces that expense by reducing the amount of water required to achieve maximum efficiency.