Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
Evaluation of Warm Water (thermal) dispersion using a numerical model at the Binceta Coast (North Sulawesi) in PLTU Development
By Mahatma Lanuru1
1 Department of Marine Science, Faculty of Marine Science and Fishery, Hasanuddin University, Makassar, Indonesia, e-mail: [email protected]
Abstract
A numerical study was conducted to model warm water (thermal) dispersion from Steam-Electric Power Plant (PLTU) at Binceta Coast (North Sulawesi). The main objective of the this study was to determine the possibility of warm water discharged from power plant outfall re-entering the power plant intake. Modelling is done with one intake and one outfall on the west and east monsoon. Each monsoon is modeled with two scenarios, i.e. Scenario 1: temperature of the water coming out of outfall is 5 ° C higher than the ambient temperature of the sea water and Scenario 2: The temperature of the water coming out of the outfall is 8 ° C higher than the ambient temperature of the sea water. Result of the simulations of Scenario 1 and Scenario 2 show that warm water plume discharged from power plant outfall will not re-entering the power plant intake both on the west and east monsoon.
Introduction
A Steam-Electric Power Plant (PLTU) to be built on the Village Binceta
(North Sulawesi) to improve the reliability of the electrical system of North-
Sulawesi Gorontalo by taking sea water as cooling power plants, and throw it
back into the sea. To determine the possibility of warm water discharged from
power plant outfall re-entering the power plant intake, it is necessary to study
the thermal dispersion within the framework of those plans. The purpose of this
study is to estimate thermal plume dispersion once the Power Plant run using a
numerical modeling of SMS/RMA2 and RMA4 models.
The Surface Water Modeling System (SMS), which is developed and
enhanced at the Environmental Modeling Research Laboratory(EMRL) at
Brigham Young University, is a comprehensive environment for one-, two-, and
three-dimensional hydrodynamic modeling. It comprise: TABS-MS (GFGEN,
RMA2, RMA4, RMA10, SED2D-WES), ADCIRC, CGWAVE, STWAVE, BOUSS2D
and PTM etc. Each numerical model is designed to address a specific class of
problems. Some of them calculate hydrodynamic data such as water surface
elevations and flow velocities. Others can compute wave mechanics such as
wave height and direction. Still others track contaminant migration or suspended
sediment concentrations (Yin et al., 2010). In this paper, the RMA2 and RMA4
models are adopted.
SMS (Surfacewater Modeling System) has been used elsewhere, e.g., to
model tidal current in in Zhanjiang Harbor, China (Yin et al., 2010), water
elevation distribution, velocity distribution, and BOD (Biological Oxygen
demand) concentration along the Brantas River Stream, Indonesia (Sholichin and
Othman, 2006), water circulation and the distribution of contaminant
concentrations (oil spill) on The northeastern coast of the Sea of Marmara, Turkey
(Kazeziyilmaz et al., 1998), and thermal distribution at The Muria Peninsula
Coast in NPP’s development, Indonesia (Susiati, et al., 2010).
Methodology
Model area includes the coastal waters of power plant construction plans
SULUT-1 Binceta Village, Bolangitang East District, North Bolaan Mongondow
Rengecy, North Sulawesi (0O 53’ 27,98’’ N - 0O 53’ 57,53’’ N, 123O 27’ 58,62’’ E -
123O 28’ 36,74’’ E) with an area of approximately 1,0 km x 0.67 km (Figure 1).
Figure 1. The coverage area of model (red lines)
Current circulation and warm water (thermal) dispersion from the Steam-
Electric Power Plant was performed using SMS 8.1. Two numerical models of
SMS are used to simulate the current circulation and the thermal dispersion. The
first of these models, RMA-2, is a two-dimensional, depth averaged, free surface
finite element model, which can simulate the current circulation. After a finite
element mesh has been constructed and boundary conditions and material
properties have been defined, the water surface elevation and flow velocity at
each grid point can be computed.
Based on the hydrodynamic solution obtained by RMA-2, a second
numerical model, RMA-4 is used to simulate the thermal effluent transport. The
thermal effluent transport model requires as input the initial thermal (warm
water) conditions as a set of point loads in addition to the physical parameters
used in the hydrodynamic model.
For the simulation of current circulation, a model grid is developed, i.e. a
mesh for the Binceta Coastal Water. The inputs are the bathymetry of the region,
the coastline, the water level/tide data, warm water discharged from power
plant outfall data, the wind data, turbulent exchange coefficients, friction
coefficient and the boundary conditions. The governing equations for shallow
water circulation model are given as follows (Donnel et al., 2006):
Fluid mass conservation equation:
(Eq.1)
Momentum conservation equation: in the x-direction:
(Eq. 2)
(Eq.3)
where h is water depth; u and v are velocities in the Cartesian directions; x, y and t
are Cartesian coordinates and time; ρ is density of fluid; E is eddy viscosity
coefficient; g is acceleration due to gravity; a is elevation of bottom; n is
Manning’s roughness n-value; ζ is empirical wind shear coefficient; Va is wind
speed; ψ is wind direction; ω is rate of earth’s angular rotation; Φ is local latitude
The warm water (thermal) dispersion modelling is conducted with RMA-4,
a numerical model to simulate the migration and dissipation of the constituent for
a given number of time steps by solving an advection-diffusion type differential
equation. The model uses the following as input; the velocity distribution
computed by the current circulation model (RMA-2), initial mass or concentration
of the pollutant (in this case initial temperature of warm water discharged from
power plant outfall), the decay rate and the dispersion coefficient of the
pollutant.
The governing equations for shallow transport and thermal dispersion
model are given as follows (Letter et al., 2011):
(Eq. 4)
Where h = water depth c = concentration of pollutant for a given constituent, t
=time, u,v = velocities in x direction and y direction, Dx, Dy = turbulent mixing
(dispersion) coefficient , k = first order decay of pollutant, σ = source/sink of
constituent, and R = rainfall/evaporation rate.
Modelling of thermal dispersion is done with one intake and one outfall on
the west and east monsoon. Each monsoon is modeled with two scenarios, i.e.
Scenario 1: temperature of the water coming out of outfallt is 5 ° C higher than the
ambient seawater temperature and Scenario 2: The temperature of the water
coming out of the outfall is 8 ° C higher than the ambient seawater temperature.
All scenarios are simulated using the following data:
• discharge of the water coming out of outfallt is 2,7 m3 /second for
Power Plant with total watt of 2 x 25 MW.
• temperature of the water coming out of outfallt is 35 ° C for normal
condition (Scenario 1) and 38 O C for extreem condition (Scenario 2).
• ambient temperature of the seawater in the study site was 30 O C
that is taken from author observation on 12-13 December 2011.
• Model is simulated for 15 days (360 h) with time step of 1 h.
• Model is simulated in the west monsson (wind speed 5,6 m/second,
wind direction 270 O) and east monsoon (wind speed 5,6 m/second,
wind direction 90 O)
Results
Thermal dispersion model of Scenario 1
In this simulation, hydrodynamic circulation is driven by amplitude and
phase of tide at all open boundry points in the initial condition (t = 0) and
westerly wind with velocity of 5,6 m/second (wind direction of 270 O ) during
west monsson and easterly wind with velocity of 5,6 m/second (wind direction of
90O ) during east monsson. Temperature of the water coming out of outfallt is 5O
C higher than the ambient temperature of the sea water.
In the initial condition (t = 1 hour), thermal plume dispersion is still
limited around the power plant outfall both in the west monsoon and east
monsoon. Temperature at the outfall ranged from 33 to to 35 O C. The temperature
decrease with increasing time distance from the outfall. The further from the
source (outfall) then the temperature is reduced.
At the end of simulation (t = 15 days model), as shown in Figure 2, thermal
plume dispersed further to the east direction approaching power plant intake in
the west monsoon condition. Thermal dispersion raise seawater temperature up
to 31 ºC to a radius of 83 m eastward approaching the intake. It can be seen from
here that aftaer 15 days model simulation the maximum increase in temperature
over the ambient seawater, is close to 4 °C at the outfall, though this decreases to
a maximum of 1 °C at the location 83 m eastward from the outfall. It shows also
from the simulation that seawater temperature in the intake remain the same with
ambient seawater temperature at the end of simulation indicating that intake is
not affected by thermal discharge from outfall.
Gambar 2. Thernal plume dispersion after 15 model days (360 hours) during west moonson condition. Colors indicating temperature between 30 ºC and 35 ºC.
A different thermal dispersion pattern was obtained for east monsoon
condition at the end of simulation (after 15 days model) where thermal plume
dispersion moved westward away from the intake. As shown at Figure 3, after 15
days run seawater temperatur incresed up to 1ºC above ambient seawater
temperature to a radius of 117 m from the outfall. Simulation results of scenario
1 show that warm water plume discharged from power plant outfall will not re-
entering the power plant intake both on the west and east monsoon.
Figure 3. Thernal plume dispersion after 15 model days (360 hours) during
east moonson condition. Colors indicating temperature between 30 ºC and 35 ºC.
Thermal dispersion model of Scenario 2
In Scenario 2 simulation, temperature of the water coming out of outfallt is
8O C higher than the ambient seawater. Other input parameters, i.e. tide and
wind velocity and direction remain unchanged. Simulation results showed that
thermal plume dispersion at the initial condition (t = 1 hour) is still limited
around the power plant outfall both in the west monsoon and east monsoon as
shown at Scenario 1. Temperature at the outfall ranged from 35 to to 38 O C. The
temperature decrease with increasing time distance from the outfall.
As in Scenario 1, at the end of simulation (after 15 days model), thermal
plume dispersed further to the east direction approaching power plant intake in
the west monsoon condition. Thermal dispersion raised seawater temperature up
to 31,6 ºC to a radius of 84 m eastward approaching the intake (Figure 4). In
contrast, thermal plume dispersion moved westward away from the intake
during east monsoon condition. After 15 days model, seawater temperatur
incresed up to 1.6 ºC above ambient seawater temperature to a radius of 117 m
from the outfall (Figure 5). Simulation results of scenario 2 also confirm that
warm water (thermal) plume discharged from outfall will not re-entering the
power plant intake both on the west and east monsoon.
Figure 4. Thernal plume dispersion after 15 model days (360 hours) during
west moonson condition in Scenario 2. Colors indicating temperature between 30 ºC and 38 ºC.
Figure 5. Thernal plume dispersion after 15 model days (360 hours) during
east moonson condition in Scenario 2. Colors indicating temperature between 30 ºC and 38 ºC.
Discussion
Binceta (North Sulawesi) Power Plant (PLTU) will utilizes intake sea water
at ambient conditions from a depth of 6 m and discharges the thermal effluent at
a depth of 1.5 m. Thermal dispersion model using RMA-2 and RMA-4 of SMS
were performet to asses the possibility of warm water discharged from power
plant outfall re-entering the power plant intake.
The results of the thermal dispersion simulation show that maximum
increase in temperature over the ambient seawater, is close to 4 °C at the outfall
for Scenario 1 and 6,4 °C for Scenario 2. However, the temperature decrease with
increasing time distance from the outfall. The further from the source (outfall)
then the temperature is reduced.
The extent of the thermal plume movement is slightly higher during the
east monsoon than that during west monsson. However, the extent of the
temperature increase over the ambient seawaters is remain the same duing east
and west monsoons indicating that wind play an importang role in affecting the
extent plume movement but no the extent of the temperature increase.
At the end of simulation (after 15 days model), seawater temperature in
the intake remain the same with ambient seawater temperature indicating that
intake location is not affected by thermal discharge from outfall during the west
and east monsoon both in Scenario 1 and Scenario 2. The simulations resuts
confirm that warm water (thermal) plume discharged from outfall will not re-
entering the power plant intake. This study shows that numerical models play an
important role in determining the extent of thermal plume movement and
temperature increase over the ambient seawater. The model is an useful tool to
select a correct location of intake structure with respect to discharge point but it
needs calibration to make more meaningful.
References
Donnell, B.P., Letter, J.V., McAnally, W.H., and others. 2006. Users Guide for RMA2 Version 4.5. (http://chl.wes.army.mil/software/tabs/docs.htp).
Kazezyilmaz, M.C. Gulac, S.B. and E.N. Otay. 1998. A Case Study Of Contaminant Transport Modelling: Tuzla Oil Spill. Proceedings of the International Conference on Oil Spills in the Mediterranean and Black Sea Regions. p.K01.1-9.
Letter, J.V., Donnell, B.P., and others. 2011. Users Guide for RMA4 Version 4.5.
(http://chl.erdc.usace.army.mil/tabs). Sholichin, M., and Othman, F. 2006. Application of Surface-water Modeling
System (SMS) on River Stream: A Case Study in Brantas River. 4th National Technical Postgraduate Symposium (TECHPOS"O6), p 24 – 28.
Susiati, H., Pandoe, W., and S.B.S. Yarianto. 2010. Evaluation of thermal
distribution at the muria peninsula coast in NPP’s development. Prosiding
Seminar Nasional ke-16 Teknologi dan Keselamatan PLTN Serta Fasilitas
Nuklir, p 376 – 386 (in Bahasa Indonesia)
Yin. Y, Qi. Y.Q., Mao. Q.W., et al., 2010. Numerical simulation of tidal current in
Zhanjiang harbor using SMS/RMA2 model. Proceedings of the International
Offshore and Polar Engineering Conference, v 1, p 228-232.