As some oil companies slash capital spending, Flint Hills Resources said Thursday it plans to invest $750 million in its Pine Bend refinery in Rosemount to replace or upgrade major equipment and add advanced emission controls.

It will be the largest construction project at the refinery in at least a decade, and at its peak it will employ 2,500 workers, the company said. The planned work, which will need state permits, is expected to start in 2017 and take three years, executives said.

"Our philosophy has been to invest and never stay status quo," said Geoff Glasrud, vice president and manufacturing manager. "It is our company philosophy, and it's in the spirit of all the people we have here."

The planned upgrades are designed to more efficiently process hydrocarbons that have gone through initial refining steps, turning them into ultralow-sulfur motor fuels, he said. The largest investment is the replacement of two 1960s-era coking units and integrated heaters that are a key step in converting asphalt, or "bottoms," into higher-value fuels. The refinery will remain a major asphalt producer, however.

Federal rules already require refineries to produce diesel with less sulfur, a major contributor to diesel particulate emissions. Rules for reducing sulfur in gasoline are being phased in over several years.

During the refinery project, state-of-the-art air-pollution controls also will be installed as the coking and heating units are replaced. Other new, innovative technology will recover waste heat from some processes and use it for other refining steps, reducing cost and emissions while producing cleaner fuel, Glasrud said. The goal is to cut more than 500 tons of nitrogen oxides and other refinery emissions annually.

"Most of this is aimed at efficiency," Glasrud said of the capital projects. "What we are doing to improve efficiency is to recover heat in our own processes. What that does is avoid us having to fire heaters downstream."

'A couple Viking stadiums'

The refinery, built in 1955, has expanded over the decades, and now is the nation's 13th largest, with the capacity to process 339,000 barrels of oil per day. It supplies about half of Minnesota's motor fuel and 40 percent of Wisconsin's. Over the past five years, federal data show, Pine Bend has operated at 80 percent to 87 percent of capacity.

The $750 million in capital projects will mean years of paydays for construction workers. The upgrades will require craftsmen from at least 10 trades ranging from pipe fitters to electricians to ironworkers and carpenters, said Don Mullin, executive secretary of the St. Paul Building & Construction Trades Council, an umbrella group for the unions.

"It is probably a couple Viking stadiums we are building out there," said Mullin, who expects workers to be drawn from the Twin Cities and southern Minnesota.

With back-to-back capital projects estimated at more than $2 billion since 2006, "there are guys in this industry who can have a career at the refinery," Mullin said.

Flint Hills is wrapping up $400 million in other capital investments that required up to 2,500 workers in 2015, and the upcoming work overlaps with other projects. The contract construction workforce is on top of the 1,300 employees who operate the refinery.

The new investment comes at a challenging time for the oil industry, which has been hammered by crude oil prices hovering around $30 per barrel, less than one-third of the mid-2014 price. Oilfield investment is down sharply, and some exploration companies have filed for bankruptcy. In North Dakota, 44 drilling rigs are operating, less than one-quarter of the number two years ago.

Big, integrated oil companies also are hurting. Chevron, the nation's second-largest oil company, slashed capital outlays $6 billion last year, announced 7,000 job cuts in October and reported its first quarterly loss since 2002 last week. Exxon Mobil, BP and Royal Dutch Shell also have announced weak earnings and job cuts.

Refining also has been affected, but generally not as much. Flint Hills Resources focuses on oil and ethanol refining and owns two more oil refineries in Texas. It is part of Wichita, Kan.-based Koch Industries, which is privately held and does not publicly report financial results.

Oil refineries owned by public companies like Phillips 66 and Valero had good margins in 2015, said Justin Jenkins, an analyst for Raymond James who tracks those companies. As a result, capital investment in the refining sector hasn't suffered, he said.

"When we think of refining margins, for the most part they're relatively immune from the absolute price of oil and more a function of refined product demand than anything else," he said. "When oil prices came down as much as they did, they really spurred a consumer demand response and … surprised a lot of people."

But refiners are affected by commodity markets, which at times squeeze operating margins.

"Competitive position is important," Glasrud said. "Where we want to be is the best."

David Shaffer • 612-673-7090 Twitter: @ShafferStrib