Original smokestacks come down as NGS demolition continues

Navajo Generating Station Nov. 20, 2019 Photo by Bob Hembree

LECHEE, Ariz. – The sound of the original 220-foot smokestacks crashing down traveled through the air late last month as demolition crews watched from afar.

The implosion was exactly as planned and it was perfect, according to the demolition crews from Dykon Blasting Corp. and Adams Contracting and Excavating that detonated the original smokestacks at the Navajo Generating Station on Oct. 29.

“They were detonated with 5 second intervals,” said George Hardeen, spokesperson for the Navajo Generating Station, “and two fell to the south and then one fell to the north. And they did it that way because they didn’t want to knock down an overhead conveyor that was there.”

Demolition crews planned it this way so that the 220-foot stacks, which were made out of concrete and rebar, wouldn’t become entangled.

“No other structures were hit, and the concrete broke up exactly as they hoped it would,” Hardeen explained, “and so did the rebar.”

The 220-foot stacks were once 775-foot tall generating units constructed by Bechtel Corporation in the 1970s. Generating units 1, 2, and 3 were completed in 1974, 1975, and 1976 respectively at a total cost of about $650 million.

However, the generating units were deconstructed to 220 feet in the late 1990s after they were replaced by large diameter stacks of the same height, resulting in the plant having up to six stacks for a time.

The large diameter stacks were installed in the 1990s because so much water vapor was created through the original stack’s sulfur dioxide pollution controls that it needed bigger stacks. The generating units weren’t designed for that.

The 220-foot stacks weren’t noticeable, said Hardeen.

“There’s been a lot that has been dismantled, all around the stacks,” he explained. “And that has to happen before the (large diameter) stacks come down. We have no date for that yet.”

Plant operator Salt River Project is currently waiting for a project blasting plan to implode the large diameter stacks, which are among the tallest structures in Arizona.

With the original generating units gone, it isn’t too unusual at the NGS site, said Hardeen.

“Except for what it used to look like,” he said. “There were overhead structures and a road that vehicles could go underneath. The (original) stacks were the very first pollution controls that took the fly ash out of the emissions, so it didn’t go up into the atmosphere.”

While equipment and pipes once surrounded the large diameter stacks, the 220-foot stacks were used as storage areas that were perfectly round. There was no operating equipment inside.

“Now, all of that is gone,” Hardeen added. “It’s just open air through that area. They removed a lot of those buildings. There used to be these big cylinder-like structures that were called absorber vessels, (which) were part of the sulfur dioxide pollution controls. They had to be gone. So, now the three big stacks that you see, the land is clear all the way around them.”


Plant demolition

When the coronavirus pandemic hit the U.S., SRP in late March notified the Navajo Nation and the NGS Decommissioning Project contractors that the utility would suspend major on-site decommissioning activities at the plant site. 

Contractors at that time were asked to leave the plant site free of any hazards as they suspend activities and exit the property. Security personnel though remained on site to ensure the safety of equipment left behind. And a select few worked activities during the four-month suspension.

The decommissioning project resumed in mid-July with the demolition of the Unit 3 absorber pumphouse and the 10-story-high limestone prep conveyor.

The first structure the contractor – Independence, Ohio-Independence Excavating – brought down was the plant’s limestone handling building on the south side of the plant site. Independence later demolished the absorber maintenance holding tanks. These structures were part of the sulfur dioxide scrubber equipment, said Hardeen. The limestone was crushed and mixed with water. The limestone slurry was then sprayed through the flue gas to remove more than 95 percent of sulfur dioxide from emissions.

“We had the limestone handling building (and) the limestone conveyor, which conveyed crushed limestone from the handling building to the limestone prep building,” Hardeen explained. “And those were the very first things to be demolished. “But the power block still stands. Anything that can be recycled is being recycled––the metal.”

Hardeen added that the concrete from the 220-foot stacks will be used as backfill to contour the land.

“For months, they’ve been taking things like diesel fuel and anything that may be hazardous material, all of that has to be moved off site,” he added. “So, everything has to be drained from the plant before you can demolish it. And lots of stuff has been sold through what’s called ‘investment recovery,’ which is a department within SRP.”

A diesel train also runs on the 78-mile Black Mesa and Lake Powell Railroad that operated three roundtrips per day transporting coal from the Kayenta Mine to the plant. The line was electrified by overhead catenary.

Hardeen said the diesel train runs only to complete the catenary removal.

“They’re removing everything,” he added. “They’re all the way out to the (coal) silos (near Kayenta Mine) now.”


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