The largest supplier of industrial gases in America is building a $25-million air-separation plant at Geneva Steel to supply the mill with gases used to make steel.

The Linde Division of Union Carbide Industrial Gases Inc. will produce 550 tons of oxygen, nitrogen and argon gases daily at the new facility. The gases will be used in Geneva's new basic oxygen-process furnaces, currently being installed at the plant. The two furnaces, called Q-BOPs, will replace Geneva's open-hearth furnaces in the steel-making process.Plans for the plant were announced Tuesday at a press conference at Geneva.

The Q-BOPs use pure oxygen rather than combustion air, which contains 80 percent nitrogen; nitrogen is converted into nitrogen oxide, a precursor of fine particulate matter less than 10 microns in diameter (PM10), in the open-hearth furnaces. Switching to the Q-BOP process will eliminate approximately 92 percent of the PM10 emissions now occurring at the open hearth, Geneva officials said.

Bill Jehle, Linde project manager, said the gases are produced by cooling regular air to minus 300 degrees Fahrenheit and then distilling it, which causes the air to liquefy and separate into nitrogen, oxygen and argon.

Linde will hire seven people to operate the air-separation facility, which is scheduled to begin operating in September 1991.

Linde operates a similar facility in Garfield which supplies Kennecott with gaseous oxygen. The plant also provides liquid nitrogen, oxygen and argon to electronics, and steel- and food-processing companies near Salt Lake City.

"We are pleased with this contract with Geneva Steel, especially since Linde has a longtime commitment in the Salt Lake area," said E. G.

Hotard, president of Union Carbide Industrial Gases. "This plant will be safe, and it will also be environmentally benign."

To commemorate construction of the new facility, Union Carbide will plant a 15-foot elm tree - "representing the original oxygen plant" - at Geneva Steel.

Linde, which has headquarters in Danbury, Conn., has a 15-year contract to provide industrial gases to Geneva.

Geneva Steel President Joseph A. Cannon, noting that one year ago to the day Geneva announced its environmental modernization program, said the company has made substantial progress in meeting its modernization goals.

Geneva is spending $80 million on environmental modernization projects. This fall, Geneva finished construction of a biological wastewater treatment facility which will begin operating in the spring.Construction of the Q-BOPS will be completed by next fall. Other projects scheduled include installation of a coke oven gas sulfur removal system and of a gas blanketing system to reduce benzene emissions.

By the time Utah County has an adopted state implementation plan to control PM10 emissions, Geneva will "already have done a large amount of what needs to be done in meeting our commitment," Cannon said.

In addition to contributing to cleaner air, Geneva's new Q-BOPs will be capable of finishing one-third more steel than the plant produces at the present, Cannon said.