The equipment upgrades are expected to include selective catalytic reductions systems to reduce nitrogen oxide emissions and scrubbers to reduce sulphur dioxide emission and are planned for installation by the end of 2017.

The TVA said it spent more than US$5 billion on emission controls at its fossil-fuel plants in 2011 and was taking steps to upgrade its Gallatin station as part of its mission to be the nation’s leading clean energy provider by 2020.

The retrofitted improvements are expected to reduce sulphur dioxide production in the Tennessee Valley region by 90-95% – but the renovation plan is experiencing resistance from environmentalists, who say the large investment may be better spent elsewhere.

Louise Gorenflo is a volunteer with the Tennessee chapter of the Sierra Club and spoke to the TVA board about the emission control strategy last week.

“For what you will pay for the pollution controls on a doomed coal plant you can replace Gallatin and be well on the way to joining other modern utilities in generating energy savings,” she was quoted as saying by Associated Press.

A workhorse the likes of Gallatin, however, may not be so easy to replace.

The giant station burns 12,350 tonnes of coal a day in four coal-fired units, typically generating 7 billion kilowatt-hours of electricity per year, enough to supply 480,000 Nashville-area homes.

According to a report prepared by Congressional Research Services, capital and financing costs for new power plants can be prohibitive, with coal-fired stations costing US$1200 per kilowatt or more.

Using this estimate, construction of a 976-megawatt power station comparable to Gallatin would cost more than US$2 billion in initial expenses alone.

The TVA expects to spend up to US$5 billion on pollution control measures at its coal-fired plants and retire 18 stations across Tennessee and Alabama.