NTH Consultants, Ltd.
William R. Neal
Total Project Budget:
NTH’s Value Added: NTH’s unique contributions to the project were the full scale field sedimentation basin demonstration and the recognition of the potential benefits that could be realized from utilization of the existing bottom ash impoundment to site the proposed dewatering facility.
DTE Monroe Power Plant
Bottom Ash Dewatering Facility Conversion
Consistent with its corporate environmental stewardship policy, DTE Energy Company elected to investigate alternative methodologies for bottom ash dewatering at their 3,000 MW coal-fired power plant located in Monroe, Michigan. DTE retained the services of NTH beginning in January 2015 to assist with the identification and evaluation of alternate dewatering methods for the sluicing of bottom ash to a 250-acre surface impoundment. In recognition of a looming regulatory deadline, advance planning and engineering were critical to schedule compliance.
NTH worked cooperatively with DTE’s contractor and their Capital Projects Group to integrate the design and construction schedules for the new 11.5 million gallon per day dewatering system. Prior to the establishment of a firm end date, NTH investigated the siting of the facility on the existing ash impoundment, where historically sluiced ash resulted in less than desirable subsurface conditions. A full-scale earthen sedimentation basin was constructed to assess the feasibility of the proposed settling tanks. Additionally, the presence of the historical ash required the design details for a landfill final cover elements beneath the new facility to address future closure requirements.
After consideration of several alternatives, DTE selected a series of elevated concrete dewatering tanks for primary and secondary settlement of the bottom ash. NTH developed a pre-load plan to pre-consolidate the historical bottom ash fill deposits and overcome the geotechnical challenges of the site.
Since bottom ash is reclaimed from the settling tanks for beneficial re-use in the construction and concrete industry, NTH worked throughout the design with our mechanical subconsultant to design a dewatering scheme for the settling tanks to meet the project goal of allowing uninterrupted operation of the four boiler units while recovering ash from the settling tanks while meeting the regulatory discharge limits of the treated water.
As the work progressed, NTH and the contractor developed a systematic approach to field or design changes. This systematic approach to detailed sequencing and staging of work, coupled with overcoming the unique geology of the site, resulted in the completion of the project within the regulatory time frame.
This project demonstrates what can be accomplished with the cooperation of multiple stakeholders and innovative professionals. Assessing risk and addressing complex
and differing concerns, the team’s efforts to thoroughly understand site conditions and incorporate effective and innovative engineering helped to successfully solve each problem, while safeguarding existing infrastructure and maintaining plant processes.