SOMERSET — The girders have been poking above the tree line for weeks. You can see the change in the skyline near the Brayton Point Power Station as you travel west across the Braga Bridge.

And officials of GreatPoint Energy, who are erecting the structure to test a new method of converting coal and other materials into natural gas, say their $25-million research and test facility should be in full operation by April.

“There has never been a facility of this size anywhere that has demonstrated this process on this scale,” Avi Goldberg, chief operating officer of the company, said during a recent tour.

Somerset is becoming a hot spot for coal-to-gas conversion processes.

Further up the Taunton River, NRG Energy Inc. plans to convert its Somerset Generating Station on Riverside Avenue into a facility that uses plasma to convert coal it now burns into a synthetic gas, which burns cleaner.

GreatPoint uses a heavy metal catalyst, a substance that turbocharges a chemical reaction, to make the conversion, producing a form of natural gas that could be pumped directly into any existing pipeline.

The facility, going up just south of Route 195, would not generate power, said Goldberg. It will do a monitored, controlled conversion in a 6-inch-wide, 140-foot-long burn chamber known as a gasifier. Workers will keep tinkering with the process to make it as efficient as possible.

“We’re taking the most abundant fossil fuel we have in this country and converting it into the cleanest — pipeline-grade natural gas,” Goldberg said.

The researchers will also try to make the process practical for biomass fuels such as switchgrass, cornstalks and wood chips.

The most prominent structure at the facility is the test tower, which is 20 stories high. It will house the gasifier.

North of the tower will be a bunker that holds coal for the test.

“We take the raw coal from the enclosed bunker, moving it through the building, grind it to a certain size, load the catalyst and then we load it up in a bin in this tower,” said Thomas F. Robinson, the company’s vice president for products. The material will fall into the gasifier and the material will be cleaned to remove pollutants.

“We’re not trying to produce gas for any other reason but to find out its makeup, its constituents,” he said.

If the process proves economical, full-scale plants would be built outside New England, where coal or other fuel sources would be plentiful and the resulting natural gas could be pumped through conventional natural gas pipelines.

The 20-story tower being built in Somerset will eventually be dwarfed when Dominion Resources, which owns the Brayton Point Power Station, erects two massive cooling towers — both about 500 feet high — for its coal-fired facility. The towers will be as tall as the plant’s highest smokestack.

Construction on that project is scheduled to begin in 2010.

gemery@projo.com