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PRODUCING STEADY-STATE FEED CONDITIONS FOR THERMAL PROCESSES

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Abstract:

Solids generated in wastewater treatment typically involves separation of a portion of the water from the treated liquid solids mixture, followed by treatment, or disposal, of the resulting cake. These options include Landfill, Drying and Pelletizing, or Incineration. Each of these have costs associated with the quality and quantity of the material being processed. In addition, Drying and Incineration systems achieve better efficiency when processing a consistent, steady-state feed. A thermal process optimization system should generate feedback signals allow for optimization of fuel consumption, solids throughput, and emissions standards.

Automated control and optimization of the unit processes upstream of a thermal system is a valuable tool for making unit processes more efficient, thus reducing O&M costs.

Mass flow unit processes, including thickening and dewatering, have proven difficult to effectively control due to the non-linear nature of the process variables. This meant, when using control systems based on PID control, operators had to frequently re-enter FIXED set points, in order to maintain process control or continually make manual adjustments to accommodate for changing conditions. Fortunately, in recent years, algorithms have been developed which create DYNAMIC set points. The use of dynamic set points allows the optimization process to be automated which in turn allows greater control in producing a consistent feed product to a downstream thermal process.

This paper will focus on the Automation of process control and optimization of the thickening and dewatering process in order to produce the optimum product to the downstream thermal process. The optimization and control includes parameters such as dryness of cake and/or feed rate.

The author has been providing comprehensive control systems for numerous wastewater thermal processes since 1988. He provided a SCADA mass flow control system for a new furnace and centrifuge at the Hatfield WWTP in 1991. In the mid 1990s he furnished a control system upgrade for the Fitchburg WWTP. Equipment included a wet ESP, and a multiple venturi scrubber. In 1998 he was chosen as a controls consultant for the WERF 98-REM-3 project on dewatering automation. Two of the four test sites had Fluid Bed and Multiple Hearth furnaces.

The effective results for the recommended thermal control process include reduced fuel cost, consistent throughput, better emissions and reduced Operator attendance.

Document Type: Research Article

DOI: https://doi.org/10.2175/193864703784292647

Publication date: 2003-01-01

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