By Peter Henderson

(Reuters) -California climate technology company Heirloom on Thursday unveiled what it says is the first U.S. commercial direct air capture (DAC) plant to suck planet-warming carbon dioxide from the air, a milestone in the effort to scale up nascent carbon removal technologies and hit global climate goals.

Scientists expect the world will need to remove billions of tons of carbon-dioxide from the air annually. Direct air capture such as that used by Heirloom can secure the CO2, but it is not yet clear whether it can do so at a price that makes the technology practical.

The new facility, which uses crushed limestone to capture 1,000 metric tons a year, is part of a ramp up that Heirloom says will cut costs. Current industry prices for carbon removal by direct air capture are around $600-$1,000 a ton, one person familiar with the situation said.

Some of Heirloom's first sales for capture and storage, in 2021, were more than $2,000 per ton. The U.S. government is aiming in about a decade for $100 a ton.

"We've got to scale. Scale is the only way we're going to be able to move that quickly," U.S. Secretary of Energy Jennifer Granholm said in an interview on Thursday after visiting the site.

The new plant, about an hour and a half from San Francisco Bay in Tracy, California, has tall stacks of trays holding limestone open to the air. The rock naturally absorbs CO2 and Heirloom has treated it to do so in a few days. Rock that has captured CO2 is heated with renewable energy to release the gas, and then reused. Heirloom works with startup CarbonCure to store the gas from the new plant in concrete.

The Department of Energy is spending billions in grants to build direct air capture demonstration hubs. Heirloom is one of the winners of the largest tier grant.

Occidental Petroleum, another hub grant winner, aims to marry acquired DAC technology with its own expertise managing resources underground, where most of the carbon dioxide is expected to be stored.

BlackRock Inc, the world's biggest money manager, on Tuesday said it will invest $550 million in Occidental's West Texas plant.

(Reporting By Peter Henderson; Editing by Marguerita Choy and Tom Hogue)