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  • Indian Journal of Marine Sciences Vol. 43(7), July 2014, pp.

    Thermal pollution modelling of cooling water discharge into a closed creek system

    S. Buvaneshwari1*, Vijaya Ravichandran2 & B. V. Mudgal3

    1Indian Institute of Science, Department of Civil Engineering, Bangalore, India.

    2Coastal and Environmental Engineering Division, National Institute of Ocean Technology, Chennai, India.

    3Centre for water resources, Anna University, Chennai, India.


    Received 26 august 2013; revised 16 October 2013

    This paper is focused on the behaviour of the heated effluent discharged at an elevated temperature into the Ennore creek by North Chennai Thermal Power Station (NCTPS).Functioning of thermal power plants near tidal creeks and estuaries, due to the feasibility of intake and discharge of water for cooling poses serious environmental concern from heated water discharge due to the flow characteristics of the creek. Discharge of the heated effluent and its dispersion is a function of ebb and flood flow into the Ennore creek as the creek mouth remains closed for most part of the year. This study aims to investigate the dispersion characteristics of the heated effluent in the near-field and far-field under various discharge and dynamic conditions of the creek using calibrated hydrodynamic models and comparisonwith the field data measured during varying tidal conditions. [Keywords:Thermal Pollution; Hydrodynamics; CORMIX; MIKE21] Introduction

    Urban sprawl, industrialization and development, fuel the insatiable demand for energy. Thermal power contributes to the major portion of the power demand. It uses the fossil fuel to generate power. The heat that is generated by the power plants needs to be taken out of the system and is generally done through cooling waters. If the cooling water is recycled, then cooling towers are adopted, else in a once through cooling systems the heated water is safely discharged back into the water bodies adhering to the norms. Here heated water becomes the pollutant.

    Tamil Nadu Electricity board operates a thermal power station of 600 MW capacity at Ennore, North Chennai Thermal Power Station (NCTPS).The power plant uses sea water to meet its cooling water requirement and the condenser reject heated water which is about 8C higher than the intake waters is let into the Ennore creek. The heated water discharge is about 27.5 m3/s. Ennore creek is a dynamic and ecologically sensitive water body receiving waste water from numerous sources including industrial and municipal effluents.

    In open coastal waters effluent discharged from outfalls undergoes rapid initial dilution, typically within a few hundred meters of the outfall, before reaching either a level of neutral buoyancy or the ocean surface. It undergoes a number of physical,

    chemical and biological processes in the water column before being transported out of the region or settling down into the sediments or being accumulated by biota. Mixing and dilution of the effluent occur due to turbulence that causes entrainment and diffusion.The source of this turbulence changes with distance from the discharge point. Near the diffuser, the primary source of turbulence is shear, induced by the discharge momentum and buoyancy. Local currents and local boundaries may modify this self induced turbulence. This region is often called near field or initial mixing region. Farther from the diffuser, this self-induced turbulence decays, and mixing is primarily due to turbulence naturally present in the ocean. This region is called far field1,2.

    A prerequisite for estimating the changes to the water environment is the understanding of the movement of the water mass as defined by the waves and tides, otherwise called wave and tidal hydrodynamics and current circulation patterns. Behaviour of plumes from ocean outfalls can be predicted using numerical models and assessment needs to be made of the three different stages, viz., initial dilution (near field modeling), transport (advection and dispersion modeling) and decay (fate) of pollutants (water quality modeling).

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    Materials anStudy area Ennore Creek

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    Fig. 1.Enno

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    , VOL. 43, NO.

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    7, JULY 2014

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    water entersgham canal iniyarriver andEnnore The

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    2.5 km, after water channel

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    s are generallmouth conditof the creek of April and

    treated and li Industrial Bemical indus

    ek is given ogical produce northern ser backwater w with North the satellite the creen the north and Amullavoyermal Powe

    water fromter into sea

    hermal Powercooling waterith Ennore Chaving width

    r flowing thrfor about 2kmf 4.5 km to ixing with thean arrangemellution. sure of the Ecient tidal aters for thPS has opted

    into the crin an attemp

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    wer plant witoperations, from creek

    taken inside E

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    dy the n the 72 m


    Field Investigation The temperature observation of NCTPS plant

    effluent is divided into two parts as shown in the Fig. 2.

    In Fig. 2 I indicates the observations inside the NCTPS plant of about 2km stretch cha


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