Single-Stage Dewatering of FGD Waste

The Escalante Unit No. 1 flue gas desulfurization (FGD) waste slurry dewatering system represents the first domestic utility to deviate from the typical industry two-stage dewatering system design. Evaluations conducted during the design phase compared three dewatering options: 1) thickener in series with vacuum filters, 2) thickener in series with centrifuges, and 3) centrifuges with no thickener. The evaluation showed that centrifuges with no thickener (one stage) could significantly reduce capital costs. Coupled with capital costs, this option also decreases operation and maintenance costs, reduces the complexity of the system, saves a considerable amount of space, and centralizes the FGD and dewatering systems within one building. This paper describes the evaluation that took place during the design phase of the project comparing the three dewatering options. Operational data for the first year of operation are presented, and operating and maintenance costs are discussed and compared with conventional two-stage dewatering systems.