The Idaho Department of Environmental Quality has extended until Tuesday, June 10, the period for public comment about the J.R. Simplot Co.’s draft modified air quality permit that would remove production limits at a sulfuric acid plant at Simplot’s industrial phosphate fertilizer complex west of Pocatello. IDEQ also has scheduled a public informational meeting and a public hearing to discuss Simplot’s proposed permit modification for Wednesday night, May 21, at Pocatello City Hall.
Although it’s anticipated that sulfur dioxide, nitrous oxide, sulfuric acid mist, and particulate emissions would increase, the IDEQ has proposed to issue the permit after determining the modifications will not result in violations of air quality standards or have an unreasonable impact on humans, animals, or vegetation. Actual emissions of PM10 are now estimated at 8.17 pounds per hour. Simplot estimates if output limits are removed, emissions would not exceed 11.25 pounds per hour – or 49 tons per year of PM10, up from 36 TPY. Simplot says the nitrous oxide emission rate would be reduced from an estimated 64 tons per year to 58 tons per year.
Simplot’s Don Plant operates two sulfuric acid plants – the No. 300 and No. 400 plants, which have been subject to a standard of sulfur dioxide emissions at four pounds per ton of 100 percent sulfuric acid produced, with excess emissions defined on a three-hour rolling average basis. In June 2006, Simplot submitted a permit to construct modification application requesting removal of a 1,750-tons-per-day production limit for the No. 300 sulfuric acid plant. It estimates it would produce 2,000 tons per day without the restriction.
Simplot received a draft permit to construct in October 2006, but objected to requirements pertaining to continuous emissions monitoring, which it says produce biased results 7 to 10 percent higher and represent a significant departure from current monitoring requirements, which rely upon periodic source testing and production rate monitoring. Simplot said it was not aware of any other sulfuric acid plants required to monitor mass emissions using a continuous emission rate monitoring approach. It contracted with RTP Environmental Associates to assist in a further review of the draft permit to construct.
The Don Plant manufactures two concentrations of sulfuric acid – 93 percent during the winter and 98 percent during the summer. Increased production of sulfuric acid would be used in other processes at the Don Plant. In 1998, Simplot bought about 42,185 tons of sulfuric acid off site to compensate for shortfalls. It purchased 50,489 tons in 1999 and 2,643 tons in 2004 for use in other plant processes. Increasing the No. 300 plant’s production will reduce the amount of sulfuric acid Simplot acquires from other sources, but will not affect production rates of other processes at the plant, IDEQ said.