Kuck Mechanical was awarded the contract to furnish and install the custom duct for the Odor Control System, the stainless steel ductwork, carbon steel exhaust stacks, and accessories. We chose this project for our Excellence in Construction application because of the complexity of fabrication and installation of the materials and equipment. The material handling alone was an intricate process. Our team worked through the challenges with successful solutions which exemplifies our commitment to quality, safety, and providing our customer with a finished project on time and within budget.
Metro Wastewater District, the governing wastewater treatment authority for the Denver Metro area, broke ground on the Northern Treatment Plant (NTP) in August 2011. This is the first satellite facility for the district and one of the largest design-build wastewater treatment projects in the United States which was budgeted at $475 million. The plant benefits the region by consolidating several wastewater treatment facilities and protecting the water quality of the South Platte River. It will treat and clean 24 million gallons of wastewater per day.
Ductwork in the treatment process
The wastewater enters the treatment plant and flows into tanks that filter solid material to the bottom, then moves through pipes to another series of tanks where micro-organisms start their cleaning process. Remaining contaminants are filtered out. The water is then disinfected and reintroduced to the South Platte River.
During this process, the wastewater emits nuisance odors to the surrounding geographical areas resulting from anaerobic or septic conditions. Bacteria that cause the odors utilize the sulfate ion that is naturally abundant in most waters as an oxygen source for respiration. The byproduct of this activity is hydrogen sulfide, which has a low solubility in water and a strong, offensive rotten-egg odor. In addition, hydrogen sulfide can cause severe corrosion problems.
This foul air is controlled using custom duct made from fiberglass reinforced plastic (FRP) in the treatment plant's Odor Control Systems. FRP duct was selected because it is not affected by hydrogen and has other non-corrosive properties. The FRP duct moves the foul air through the plant and makes its way to the Bioscrubbers and Biofilters that treat the air. This treated air then enters the carbon steel stacks where it is exhausted.
Stainless steel was used for the treatment plant’s internal air systems which included duct, isolation dampers, and accessories. Stainless steel has the attributes of being able to handle a wide range of aggressive corrosive substances. It’s corrosion resistance combined wtih its durability and minimal maintenance requirements ensures long and economic life cycles.
Complex fabrication and installation.
The lamination material had to be made onsite due to its quick curing time. The curing time was dramatically affected by application temperature, which required extra care. During colder months, tents were used to contain heat around lamination points which could not be completely enclosed due to ventilation requirements. High outdoor temperatures also complicated joining procedures by advancing the gelatin and cure of the resins; therefore, the operator needed to closely monitor the weather conditions and make adjustments accordingly.
All FRP connections had to be laminated with four layers on the inside and seven layers on the outside to seal the connecting points. The interior laminations had to be done in sequence so installation could be achieved with safe access to interior connections, which required physical entrance into the FRP duct. Extreme safety measures and confined space protocol had to be followed with flammable chemicals inside of the duct. All employees had additional confined space training and were fit tested for using face masks. Safety fans were used to supply fresh air into the duct.
Installation of the FRP duct at the Headworks facility had to be strategically planned. The support stands and building connection locations were coordinated months beforehand due to structural steel requirements and coordination with other trades. Risers and offsets also had to be carefully measured and laminated together before each section could be hoisted by crane onto the rooftop location, which was 40’ high. Workers were tied onto safety lines working up to forty feet from the entrance point to the duct.
Each of the four foul odor exhaust stacks measured 35’ in height, 48” in diameter and weighed 7,500 pounds. The stacks were constructed and assembled in Kuck Mechanical’s “State of the Art” fabrication shop in Loveland, Colorado. A single stack took approximately three weeks to build which involved coordination between our project teams to ensure delivery of a high quality product . The stacks were made out of ¼” thick cold-rolled carbon steel and welded on the interior as well as the exterior in accordance with specifications, AWS (American Welding Society) Code and ASTM (American Society for Testing and Materials) Standards. Individual stacks were delivered from our facility to the jobsite, then sand blasted and painted with special epoxy paint then moved from the painting area to their installation locations on the project site. The stacks were set by a crane on to stainless steel embedded studs which were preset by using a template designed and manufactured by Kuck Mechanical.
Kuck Mechanical also installed 316 stainless steel duct on the inside of the buildings. 78" welded round duct was manufactured for inside of the fan room buildings. One 90-degree elbow took about one week to weld together before being able to ship to the site. Once the material was received on site it was lifted using a forklift into the building and then had to be raised to the installation location by chain fall. Each piece required careful measurements for fabrication to align structural supports, equipment connections, and structural openings. Custom flanges for connection to equipment and underground pipe was also manufactured by our shop. The connection to the underground pipe in the fan room required 64 2" stainless steel bolts, each bolt, washer, and nut set weighed about pounds.
Extensive pre-planning and consulting with the General Contractor occurred prior to selecting and configuring duct. Because the job involved installing very large material close to the roof edge, preparation and safe procedures were necessary. Safety controls such as guardrails, 100% tie off, safety netting and signage were used to protect workers on the job. The Fiberglass Reinforced Plastic duct that was selected for the project need to be connected and sealed on both interior and exterior surfaces. Due to the size of the duct, interior sealing was performed while inside the duct itself, creating a confined space. and potential for exposure to dangerous chemicals in addition to the fiberglass. During the lamination process, air quality testing for combustible gases, O2, CO and H2S occurred daily. Additionally, workers wore respirators, and underwent extensive training for rescue procedures in the case of chemical exposure.