UTILIZATION OF HYDRO-TURBINES IN WASTEWATER TREATMENT PLANTS (WWTPS) Mohammad Qandil

Outline Introduction: Industrial Assessment Center Objectives Methodology Results Conclusions

Industrial Assessment Center (IAC) Funded by Department of Energy Support small and medium-sized manufacturing companies The professional support is NO Cost to participating companies IAC focus Improve energy efficiency Reduce wastes and prevent pollution Improve manufacturing productivity UWM-IAC the only center in Wisconsin Sustainable Manufacturing

Introducing a hydro turbine in wastewater treatment plant in Wisconsin Objectives Introducing a hydro turbine in wastewater treatment plant in Wisconsin Evaluating the power output from the plant Determining the energy savings from the total plant energy consumption

Methodology flow chart Selection of the hydro-turbine type System sizing by using HOMER software Rim Drive Hydro-Turbine (RTD) design with In-house code Performance of Hydro Turbine by Computational Fluid Dynamics (CFD)

Selection of the hydro-turbine type The head in the investigated WWTP is 3 meters. Average yearly effluent flow rate is 7,750 L/s per day. Kaplan hydro-turbine type is selected for this case with a low head and high flow rate.

System sizing by using HOMER Through the system simulation using HOMER, the nominal capacity of the system (in kW) can be determined as well as the energy generated (in kWh) around the year based on the effluent flow rate available.

Hydro Turbine Design with In-house Code Parameter Value Number of blades for the rotor 5 Number of meridional sections (rotor) 3 Number of blades for the stator 9 Number of meridional sections (stator) Turbine diameter (meter) 2.0 Rotational speed (rpm) 100 - 200 Specific speed (nq) 138.7 - 277.5 Swirl angle (degrees) 90 Rim (shroud) length (m) 0.7 Rim (shroud) thickness (m) 0.02 RDT Front view RDT Isometric view Stator Front view Stator Isometric view

Performance of Hydro Turbine by (CFD) Enabled Models Gravity Gradients, Three dimensional Turbulent, Segregated Flow Implicit Unsteady, Transient Large Eddy Simulation (LES), WALE Subgrid Scale Multiphase Interaction, Volume of Fluid (VOF) Parameter Value Outlet pressure (kPa) 101.325 Timestep (s) 10-3 Number of iterations (per time step) 5

Results System sizing by HOMER: HOMER inputs of 3 meters of water head and an average daily flow rate of 7,750 L/s led to 1,564 MWh/year of electricity generation, which can be considered as an annual energy savings for the WWTP. Taking into account the average electricity cost of $56.8/MWh, hence the annual cost savings is $88,835/year. Parameter Value Nominal capacity (kW) 270.8 Minimum output (kW) 149.7 Maximum output (kW) 207.3 Annual total production (MWh) 1,564 Annual hours of operation (hour) 8,760

Results CFD Simulation Results: As a result, simulations matrix of 15 different cases for the proposed turbine were performed, by varying the flow rate between 5,000 L/s and 10,000 L/s as well as the rotational speed in the range of 100 – 200 RPM. It can be noticed that the system performs better for the 200 RPM curve, with a maximum efficiency of 94.9% at the design reference flow rate of 10,000 L/s.

Conclusions The average daily effluent flow rate for the selected WWTP ranges between 6,500 L/s to 9,000 L/s with an average flow rate of 7,750 L/s. Such flow rate accommodates a hydro turbine of 270 kW nominal capacity. The simulation performed through HOMER indicated that the 270-kW hydro turbine can produce a total electric energy of 1,564 MWh/year. This amount can be considered as an annual energy savings for the plant with an annual cost savings of $88,835/year leading to 16% of energy savings the designated WWTP. The significance of employing the in-house code concluded in optimizing the CAD design for the hubless RDT and the hubless stator. Two meters diameter turbine with 5 blades for the rotor and 9 blades for the stator was selected. A performance curve for the proposed hubless RDT design was generated by 15 different CFD simulations. Such proposed design contributes in increasing the efficiency of Kaplan hydro turbine up to 94.9%.

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