Estimating Water Consumption from Open-Loop Power Plant Cooling

Transcription

1 Estimating Water Consumption from Open-Loop Power Plant Cooling Ashlynn S. Stillwell and Clark W. Bullard Illinois Water 2014 Urbana, IL October 14-15, 2014

2 Energy and water are interrelated. We use water for energy Cooling during power generation Liquid fuels production We use energy for water Treatment and disinfection Distribution Heating slide 2

3 Thermoelectric power plants require cooling. Electricity Boiler Turbine Generator Water Consumption Cooling Return Flow Water Withdrawal slide 3

4 Open-loop cooling is used at many power plants. Control volume withdrawal Thermoelectric Power Plant Typical reported data (coal power plant) Withdrawal: 40,000 gal/mwh Consumption: 0 gal/mwh [U.S. DOE EIA] consumption forced + natural evaporation slide 4

5 Rivers and lakes/reservoirs are common cooling water sources. Thermoelectric Power Plant Thermoelectric Power Plant River Lake/Reservoir slide 5

6 Rivers: calculating consumption uses the Navier- Stokes + U j Reynolds-Averaged Navier-Stokes j = CORMIX model RMA-10 finite elements model Numerical-simulation based FVM i + U @x j u 0 i u0 j i =1, 2, 3 slide 6

7 Lakes: calculating consumption employs many methods. Harbeck method [Harbeck, 1964] HR = Heat input of fuel Net power output air temperature H = HR HRpower HR flue water temperature H heat to dissipate e i fraction of heat input lost as evaporation forced evaporation FE = H e i 100L L latent heat of vaporization density slide 7

8 Lakes: calculating consumption employs many methods. Empirical methods H(T )=E(T )+C(T )+R(T ) evaporation heat loss from water surface heat loss from evaporation conduction radiation E(T )= Lf(W )[e(t ) e a ] [USGS, 2013] L latent heat of vaporization density f(w ) wind function slide 8

9 Different calculations require different data inputs. Open-loop cooling: River Data Inputs Waterway Flow speed Dispersion/decay coefficients Water density Jet/plume behavior Climate Air, water temperatures; sun, clouds Wind speed function Relative humidity Open-loop cooling: Lake/reservoir Waterway Water surface area Water density Mixing depth Climate Air, water temperatures; sun, clouds Wind speed function Relative humidity slide 9

10 Selecting the most applicable method depends on site-specific circumstances. Different factors complicate labeling of open-loop versus closedloop, river versus lake cooling, etc. Assumptions and space/ time boundaries change the estimated consumption Dresden Generating Station slide 10

11 Acknowledgements. Anurag Chandak, M.S. student in Civil and Environmental Engineering slide 11

12 QUESTIONS? slide 12

13 Contact information Ashlynn S. Stillwell Assistant Professor Department of Civil and Environmental Engineering University of Illinois at Urbana-Champaign stillwell.cee.illinois.edu Stillwell Research water energy policy slide 13

14 Abstract. Thermoelectric power plants require condenser cooling, historically using open-loop (or once-through) cooling systems. These open-loop cooling systems withdraw large volumes of water from a river or other water source, use it once in a heat exchanger, and return the water to the source, albeit at a higher temperature. The elevated temperature return flow contributes to a certain amount of induced evaporation, termed water consumption. Unlike the case of wet cooling towers where the evaporation occurs on-site, the induced evaporation from once-through cooling occurs downstream and is typically unmeasured; thus, most power generation facilities do not account for water consumption associated with open-loop cooling. Despite these limitations, various approaches exist to estimate water consumption from open-loop cooling. These estimations use an energy balance approach to account for evaporation, conduction, convection, and radiation in the overall system heat transfer. This analysis presents a critical review of different water consumption estimation methods, illustrating both strengths and weaknesses in applying these methods in the context of different power plants. Results suggest that tailored methods and locationspecific assumptions might better estimate water consumption from open-loop cooled power plants. slide 14