Generating Station NPDES Compliance

Background

The National Pollution Discharge Elimination System (NPDES) permit for the Platte Generating Station requires either elimination of the pollutants in the bottom ash transport water, or elimination of the discharge of bottom ash transport water to the settling pond, or any impoundment by December 31, 2023.  We are providing engineering services to the City of Grand Island, Nebraska to identify, evaluate and implement options to meet this permit condition and to eliminate the discharge of bottom ash transport water to settling ponds that discharge to the Platte River.

Approach

The City determined that converting the bottom ash handling system from the current wet ash transport system to a dry ash handling system is not economically viable. Foth is focusing on alternatives to reduce and allow reuse of the bottom ash transport water, which would require water quality similar to the groundwater. The City wishes to have the system improvements completed and operating by December 2022.

Our tasks are to:

• Perform a regulatory assessment and compliance planning
• Monitor and characterize data
• Sample and analyze the bottom ash hopper inlet water, ash transport sluicing water and discharge from the surge tank
• Create a conceptual design basis – process flow diagram, thermal calculations, ELG criteria for normal and upset conditions, potential areas for reuse and water quality requirements
• Identify and screen potential cooling and treatment technologies for recycling and reuse of bottom ash transport water utilizing the conceptual design basis. The separate technologies are combined into one of three general options: a closed loop system for bottom ash transport water; reuse of the ash transport water in other processes, if possible; and modifications to the bottom ash handling system to reduce water consumption.
• Screen out unsuitable technologies using the Best Available Technology (BAT) principle and identify up to three alternatives to eliminate the need for discharging bottom ash transport water. We will prepare block process flow diagrams for each alternative, prepare a matrix table presenting the advantages and disadvantages of each alternative, and develop order-of-magnitude opinions of probable construction cost.

Results

Our team will advance the conceptual design basis based on the alternative selected. The updated conceptual design will include a process flow diagram, heat and mass balances, preliminary equipment schedules and sizing criteria, preliminary equipment layout drawings, budgetary estimates, opinion of probable construction cost, and a preliminary schedule for implementing the proposed improvements.