CHEYENNE - The only sign that significant changes are happening at the Frontier Oil Corp. refinery in south Cheyenne is the enormous blue crane boom that stands like a beacon at the east end of the property.

The crane, among the largest in the world, is being put into service to add equipment needed for the refinery to make ultra-low sulfur diesel.

By June, all U.S. refineries must be able to produce diesel fuel that has at most 15 parts per million of sulfur for use by vehicles like buses and trucks that use the nation's highways. The goal is to cut the amount of sulfur dioxide coming out of tailpipes.

The current cap is 500 parts per million, which was set about two decades ago.

Making that happen was no simple thing.

"We started planning in 2004 for this," Lloyd Nordhausen, vice president and refinery manager for Frontier Refining, said recently. "We knew it was coming."

The change means that emission control devices in diesel engines can work more efficiently. That will address clean-air concerns in places like Denver, where air pollution - including diesel truck exhaust - is a problem.

The change also means that Frontier, which enjoyed one of its most successful years in 2005, is investing about $14 million in its Cheyenne facility.

Extracting the extra measure of sulfur during diesel production requires some additional steps.

In company parlance, the distillate hydrotreater unit will be revamped; that includes modifying an existing reactor, and adding a new reactor and furnace.

"To get the sulfur out, you have to add steam and natural gas," he said.

With the lower standard, Nordhausen estimates that the refinery will produce an extra 300 tons of sulfur a year, or about a ton a day more. The refinery already produces between 75 and 80 tons of sulfur daily; it's sold to fertilizer makers.

The reactor, now being fabricated in Casper, will be 10 feet wide and more than 80 feet long, Nordhausen said.

When the vessel arrives in Cheyenne later this month, the crane, which sits on a foundation of layers of timbers, will be able to lift it into place. It will stand vertically.

It's not something that many people are likely to see. Nordhausen said. Fifth Street is likely to be shut down so that traffic won't be exposed to any risk.

And even after it's in place, the public won't see much difference in the refinery because of the high-dollar project.

"Other than the tall heating stack, nothing will be visible from the road," he said.

To prepare the site at the 125-acre refinery, workers laid the timber foundation in the fall. The crane arrived in December, shipped in on more than 40 trucks.

After it's in place, he said, the diesel treatment plant will be shut down on April 10 for about 18 days.

In the meantime, diesel will be stockpiled to carry over customers - most of them in Colorado - until the plant is up and running again.

"We made sure we have a plan to supply fuel," he said.

Changes at the refinery won't be apparent locally, and probably neither will the impact of the cleaner-burning fuel.

Nordhausen said his refinery sells into a market that determines the price, so the fuel will cost what the market dictates.

The U.S. Environmental Protection Agency estimates that the fuel will cost a few cents more per gallon.

"It's been a coming thing for a several years," Mick Branigan, manager at the Pine Bluffs Service Center, said. "I don't see it should be a cause for a big increase in fuel prices," but prices might spike a little before the changeover.

Pine Bluffs, on Interstate 80 at Wyoming's eastern border, has carved out a niche for itself in fuel sales and truck service. As a result, it has a front-row seat for the coming changes, which include expanding the use of ultra-low sulfur diesel to off-road diesel engines such as those used in construction equipment.

The new fuel is driving some changes in existing diesel engines. While all new engines are designed to run on the lower sulfur fuel, Branigan said older engines have to be modified; sulfur provides a measure of lubrication, he said.

The June deadline is not the end of the line. By Sept. 1, the fuel has to be available at terminals, Nordhausen said. And by Oct. 15, it has to be available at gas stations.

Branigan is philosophical about the change. "It's mainly an environmental issue. And it has to be done to meet federal standards," he said.