Water/Wastewater Management Evaluation


Prairie State Generating Company, LLC


Marissa, IL

CEC Services

  • Wastewater Engineering
  • Process Design
  • Water Balance Evaluation
  • CCR Management
  • FGD Operation Assistance
  • CCR Beneficial Reuse
Process water used for reuse within the plant.

Owner Objective

Prairie State Generating Company, LLC (PSGC) owns and operates a 1,600-MW coal-fired generating plant and adjacent Illinois Basin coal mine in Marissa, Illinois. The Facility was designed with a water balance that included zero discharge of process water outside of cooling water blowdown. Process water was designed to be reused for CCR conditioning using pug mills. However, the balance was off, creating excessive water build-up in on-site ponds. PSGC staff attributed excessive water to the unexpected mix of fly ash and gypsum, which exhibits less absorptive capacity. Further, PSGC constructed an on-site landfill, which was not considered in the original overall water balance. The excess water represents a significant cost liability and prevents the sale of fly ash that could bring significant income to the facility.

CEC Approach

Water management at the PSGC plant is a complicated process that involves multiple systems and system owners. The purpose of CEC’s evaluation was to identify the source of excess water and associated issues, particularly chloride cycling in the FGD absorbers. This required working with nearly every department within the organization to identify the root cause of the excessive water and recommended sustainable solutions for immediate implementation. The first step in the evaluation was to collect water quality and quantity data from plant records, which included daily logs and the plant distributed control system (DCS). Data was also collected during a field visit, which included taking water samples and installing temporary flow meters. The data was compared to design data and also used to develop flow and mass balances of a number of components.

CEC identified the root cause of excess water which was high chloride loading to the absorbers resulting in above design FGD blowdown and excess rainfall that created more leachate than the on-site landfill was designed to handle. CEC recommended operational improvements to reduce this effect and management tools to process the excess leachate. CEC also showed that more than 500,000 tons of fly ash could be used for beneficial reuse. Finally, CEC evaluated disposal options if full reuse was desired. The disposal options included surface water, deep well injection, natural based systems, zero liquid discharge, and CCR disposal with volume reduction.