thermal pollution modelling of cooling water discharge ... ?· thermal pollution modelling of...

Download Thermal pollution modelling of cooling water discharge ... ?· Thermal pollution modelling of cooling…

Post on 31-Aug-2018

213 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • 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.

    *[Email: buvanasriramulu@gmail.com]

    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).

  • hccbttCroyid MSE

    imElCI

    bpmu

    oCn

    aafcao

    The mixinhighly depenconditions3,4.coast and clobar formationthe creek. Thtransport of Creek in the results are vaobserved in year and diinfluence of adispersion ch

    Materials anStudy area Ennore Creek

    The southstretch of coainto the Bay marine faunEnnore creeklocated in tChennai cityIndia as show

    Most of tbeach dunes,part. Ennoremarshes andunder water dsea opening iof the creek Creek channenorth and to t

    Ennore crand fauna. It a predominanfishermen cocreek once fian excellent out by the

    ng and transpndent on the tShoreline chosure of the n results in lohis study aim

    thermal discnear field a

    alidated againthe field durfferent timesambient temp

    haracteristics o

    nd Methods

    k heast coast oastline, whereof Bengal an

    a than the k (1313'54.4the northeasty, Thiruvalluwn in Fig. 1.

    Fig. 1.Enno

    the area cons, tidal flats e comprises d backwatersduring high tiin to the Bay is 4 km2 an

    els connect tthe Kortalaiyareek was oncwas not only

    nt source for ommunity seilled with richgreen belt wuntreated se

    INDIAN

    ort process intidal ebbing

    hanges along creek mouth ow circulatio

    ms at modelingcharges into

    and far field. st real time mring various s of the daperature on thof the creek.

    of India is ae many majornd they are awestern coa8" N, 8019' t coast of

    ur district, T

    ore Creek-Enviro

    sists of alluviand creek in

    of lagoonss, which arede and form aof Bengal. T

    nd is nearly 4o the Pulicatarriver in the ce a place wiy the naturessupporting th

    ettled in this h biodiversity

    which is now ewage from

    N J. MAR. SCI.,

    n the creek isand flooding

    the Ennoredue to sand

    on of flow ing the fate and

    the Ennore The model

    measurementsseasons of ay given thehe advection-

    an importantr rivers drainalso richer inast of India.

    26.60" E) ismetropolitan

    Tamil Nadu,

    ons

    ial tracts andn the easterns, with salte submergedan arm of the

    The total area400 m wide.t Lake in thesouth. ith rich floras gift but alsohe traditional

    Creek. They contributedtotally takenRoyapuram

    N

    , VOL. 43, NO.

    s g e d n d e l s a e -

    t n n

    s n

    d n t d e a

    e

    a o l e d n

    m

    sewage effluenthuge nuwealth channelhas comis the Kto the PPower WastewBuckingKortalaisouth. withdrawdisposesoutfall.

    Nortunit disccanal wpre cooabout 2warm wtravels creek anobjectivdown th

    The resultedreducedplants. warm wBuckingwater quthat the intake resultingwater withdrawwater fo Ennore

    The by the Currentfrom Mfrom Nois a scharacte

    The current currentson the mwidth omonth owide.

    7, JULY 2014

    outfall, untts from Manaumber of cheof the cree and the biolo

    me down. TheKosasthalaiyarPulicat Lake,Plant and t

    water entersgham canal iniyarriver andEnnore The

    ws cooling s warm wat

    th Chennai Thcharges the c

    which joins wiling channel

    2.5 km, after water channel

    a distance ofnd thereby mive of such ahe thermal pol

    frequent clod in insufficd cooling wHence NCTPwater back gham Canal, uantity in thewarm water wstructure wig in the powfor their wing water or cooling is t

    Creek Mouthcurrents in thseasonal circs move along

    March to Octoovember to Fesignificant ceristics in the dynamic Ennand tide p

    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

    e creek. Howwould flow dith minimum

    wer plant witoperations, from creek

    taken inside E

    h he coastal watculation in thg the coast tober and moebruary. The

    component oEnnore creek

    nore creek mopattern insidely tidally infltion. As a par

    mouth was it was found

    treated induBelt, which hostries. The na

    place to sectivity of the ection of the which is conn

    Chennai Theport of En

    ek through nd south of cyal canal iner Station Em the creek a through m

    r Station (NCr into Bucking

    Creek. It has ah up to 130 mrough the exim, the warm wreach the En

    e creek waterent was to

    Ennore mouthinflow and e thermal p

    d to dischargreek throughpt to maintaiever, it was f

    directly back tm retention thdrawing wa

    it has stoand now i

    Ennore port.

    ters are influehe Bay of Betowards the Nove towards flood and ebb

    of the dischk outh influencee the creekluenced depenrt of the stud

    measured ind that it was

    ustrial ouses atural

    ewage coast creek

    nected ermal

    nnore. the

    creek, n the ETPS

    and marine

    CTPS) gham aopen m for isting water nnore r. The bring

    h has thus

    power ge the h the in the found to the time,

    armer opped ntake

    enced engal. North south b tide harge

    es the , the nding

    dy the n the 72 m

  • BUVANESHWARI et al.: THERMAL POLLUTION MODELLING OF COOLING WATER DISCHARGE

    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

Recommended

View more >