Power No More
January 23, 2024
Beginning operations in 1970, the coal-powered Asbury Power Plant was a landmark in Jasper County, Missouri, delivering 200 megawatts of electricity to 157,000 customers in Missouri, Kansas, Oklahoma and Arkansas for over 50 years. Over time, the plant became less competitive with other power generation options and, like all power companies, efforts were made to reduce its carbon footprint. Owned by Empire District Electric Company (now Liberty Utilities), the plant officially went offline in March 2020 and its capacity has been replaced, in part, by North Fork Wind Farm, a $1.5 billion wind power project.
After a competitive bid process, the environmental remediation and demolition contract to clear the site was awarded to GSD Companies (GSD) in September 2022. GSD’s proposal gave its team 17 months to complete environmental and demolition operations per contract schedule.
The demolition scope included a 400-foot-tall, reinforced concrete chimney with brick liner; a 465-foot-tall reinforced concrete flue-gas desulfurization (FGD) chimney with top-hung steel liner; a 200-megawatt, 175-foot-tall hung boiler with integral silo bay; a selective catalytic reduction (SCR) unit; and an absorber/ baghouse facility.
The design of the SCR unit being on an elevated truss system and hung boiler conditions created safety considerations for a conventional demolition approach to both structures. Given that explosives demolition was the likely choice to fell the two chimneys, GSD turned to NDA member Controlled Demolition Inc. (CDI) to design and price an explosives demolition approach for the steel structures as well.
GSD mobilized in October of 2022 to begin performing environmental remediation over a six-month period. Once completed, CDI mobilized a two-man crew to the site in March 2023 to lay out 179 cut points for pre-burning in anticipation of linear-shaped charge placement on the steel structures. The CDI team also designed an implosion sequence for the hung boiler, silo bay and the truss-supported SCR to bring the differential natural failure modes of the structures into line with one another.
CDI then mobilized a two-man drill crew in May 2023 to lay out structural modifications on the two reinforced concrete chimneys.
“Using pneumatic feed-leg drills, the crew drilled a total of 225 holes in the brick liner and concrete shell of the 31.8-feet-in-diameter, 400-foot-tall chimney and an additional 279 holes in the 40.3-feet-in-diameter FGD chimney,” says Mark Loizeaux, president and owner of CDI.
In June 2023, after two months of preparation with the GSD crew, it was “all hands-on deck” for a nine-man CDI crew to load explosives and install the complex initiation sequence. “The CDI crew loaded the steel structures with 448 pieces of linear-shaped charges with a net explosives weight of 314 pounds and a total of 319 pounds of dynamite into the chimneys,” Loizeaux says. “Over 6,700 lineal feet of detonating cord, 556 detonators and 43 micro delays were used in the initiation system for the sequential felling of all five structures in a single, carefully choreographed implosion sequence.”
To mitigate fly of debris, linear-shaped charges placed in the steel structures were contained with plywood boxes and multiple layers of rubber conveyor belting. Explosive charges placed in the chimneys were covered with layers of chain link fence and geotextile fabric to keep debris within the blast area.
To document vibration and air overpressure generated by CDI’s implosion operations, six, three-component, Instantel MiniMate Plus seismographs were placed around the blasting area in consideration of third party improvements to remain and the adjacent switchyard to the west of the structures being felled.
The baghouse/absorber facility, hung boiler, SCR unit and two chimneys were independently delayed in CDI’s sequential felling of all five structures at the site in a single implosion sequence the morning of June 29, 2023. CDI designed the implosion plan so that the baghouse/absorber facility, hung boiler and SCR unit would “roll” over to a height that would match the reach and capacity of the equipment GSD had on-site.
All five structures were felled on schedule and exactly per CDI’s plan. Vibration and air overpressure levels monitored during implosion operations were well below regulatory limits, and there was no interruption of service in the switchyard.
“Preparation and execution for explosive felling of the structures went exceptionally well,” says Mike Huber, GSD project manager. “The client has been completely satisfied with both CDI’s and GSD’s performance on the project.”
GSD continues to conduct site clearance and debris processing/removal of over 8,000 metric tons of steel at the Asbury Power Plant site and is expected to finish their operations by March 2024.