Potash (primarily potassium chloride, pronounced “Pot-ash”) is an essential nutrient for plants and a nutritional need for humans and animals. As a key component of agricultural fertilizer, potash is said to have the potential to be Michigan’s next billion-dollar industry, comparable to that of oil and gas. With U.S.’s declining domestic potash supply and significant reliance on imports, Michigan is equipped with a unique opportunity to fill a high-demand market in major agricultural Midwestern states, with a product manufactured from pristine Michigan potash deposits.
Working alongside an exceptional team of professionals at Michigan Potash Company, LLC (MPC), NTH’s Air Quality group helped to secure an air permit to install (PTI) on March 8, 2016 for manufacturing of potash in Hersey, Michigan. MPC had come to learn about NTH based on our success in air permitting for combined heat and power (CHP) facilities, such as the Holland Energy Park and Lansing’s REO Town, and MPC contacted NTH directly for our assistance. The potash manufacturing process consists of solution extraction to recover potash from the subsurface by pumping a heated brine solution via subsurface wells, dissolving the product into the brine, and then pumping the solution back out. Depending on hydrogen sulfide (H2S) concentrations in subsurface formations, the brine feed may contain H2S at concentrations constituting “sour” brine. This brine feed is treated for removal of H2S utilizing an air stripper followed by an oxidizer and caustic scrubber. The resulting “sweet” potash-enriched brine is then transferred to the manufacturing facility where potash is dried, cooled, compacted, and sized into a saleable product. The facility uses boilers to provide process steam for drying and evaporation; in the future, MPC is considering a CHP option where they would produce steam for use in the manufacturing process and also create their own electricity to reduce reliance on the electrical grid.
Several air permitting challenges were overcome through the collective effort of NTH’s dynamic Air Quality team. Nearly concurrent with project initiation in March 2015, the MDEQ Air Quality Division finalized a new policy on dispersion modeling, a tool used to quantify the off-site maximum pollutant concentrations for comparison to national air quality standards. With the ink barely dry, we worked through several policy interpretations with MDEQ, ultimately requiring additional dispersion modeling analyses and demonstrations.
In addition to dispersion modeling challenges, the manufacturing project was still very preliminary when we started the air permit application (air permits must be obtained prior to starting construction), engineering was not yet finished, and equipment vendors were not yet selected. With very limited information, NTH worked closely with MPC to manage worst-case expectations of process equipment emissions and control technology performance for utilization in the permit analysis.
A successful air permit lays the groundwork for productive operation and puts the facility in the best position to achieve environmental compliance. A final and crucial step of an air permitting project is negotiation of air permit conditions. NTH was able to negotiate multiple options to demonstrate compliance, flexible timing on malfunction plan development, and facility restrictions to “opt-out” of additional reporting requirements with minimal added record-keeping burden on the facility. With the air permit now in place, we look forward to watching the potash industry grow in Michigan!