Pollution turned into ag byproduct

Soil additive | U.S. coal plant captures sulphur emissions and turns it into gypsum

INDIANAPOLIS, Indiana — It was a chemical marriage between pollution from coal-fired power plants and limestone that created a useful product for agriculture.

It took a chemists’ mind to know that adding water and limestone to the sulphur collected from a coal-fired electrical generating station could create gypsum, a valuable soil additive.

The Indianapolis Power and Light Company produces a little less than 200,000 tonnes of gypsum each year from its Harding Street Station in Indianapolis. It’s just one of a handful of coal-fired power plants that are turning a government directive to clean up the pollution spewing from their stacks into a useful byproduct.

About 60 percent of the gypsum from the Harding Street plant is used in agriculture as a limestone and sulphur additive in crops. The rest is used for making wallboard and concrete.

In 1991, the U.S. Clean Air Act was enacted to require all coal-fired power plants to clean the sulphur and other emissions from flue gas.

Some plants ignore the directive and pay a fine. Others turn the emissions into ash and haul it to a landfill or store the gypsum byproduct as a slurry in a settling pond.

At the Indianapolis plant, ash and metals are filtered from the gas. Powdered limestone is then mixed with water and sprayed into the cleaned flue gas. The chemical reaction creates a slurry of calcium sulphate, or gypsum. It is dried on belt dryers and stockpiled, ready to be used in fields or industry.

The gypsum produced in the plant is considered a clean form of the mineral for agriculture use.

In 2000, agrologist Ron Chamberlain saw the benefits of gypsum on farmland as a way to improve soil tilth, water filtration and pod and kernel development.

Chamberlain then started his company, Gypsoil. In 2009, Chicago-based Beneficial Reuse Management, designed to reuse products, bought Chamberlain’s company.

The company now has contracts with 25 power plants across the United States to buy the gypsum byproduct.

Cory Schurman, national sales manager for Gypsoil, said he expects to sell a million tons of gypsum product this year for agriculture.

“I think it’s big. I think it’s going to get a lot bigger in North America,” said Schurman.

Farmers who live close to a source of natural gypsum have applied the “land plaster” to their soils for years. Peanut farmers have historically used it as a source of soluble calcium in a top dressing.

An Ohio State University study is looking at ways to use gypsum to reduce phosphorus loading into watersheds.