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The main purpose of this research effort was to investigate and reduce the volume of thermal polluted cooling water from returning to the Kafr-Al-Batek power station. Traditional cooling systems, such as cooling towers or ponds can be very challenging with regards to implementation in developing countries; mainly due to the lack of financial capacity. This research focused on low-cost simulation solutions that could improve thermal outcomes. Comparisons were performed between three different scenarios to decrease the elevated temperature of the discharged water (43 °C) released by the Kafr-Al-Batek power station on the Damietta branch. The different scenarios were simulated by using Star CCM+ software. The base scenario examined the discharge angle of an existing outlet. The second scenario examined a new outlet downstream from the existing outlet. The third scenario increased the width of the existing outlet in order to reduce flow velocity. A comparative analysis is provided between the aforementioned solutions to identify the most suitable and cost-effective alternative. Simulation results show that changing the discharge angle from 90° to 135° is the most effective solution. Applying this solution has the potential to decrease the water temperature at the inlet by 7 degrees Celsius (from 32 °C to 25 °C).

Thermal pollution is the act of changing the surface water’s temperature which may cause a degradation of water quality [

One of the facilities that face this problem is the Kafr-Al-Batek power station located along the Damietta branch in Egypt. This station has a net design capacity of 1200 MW, making it one of the largest power stations in Egypt. Daily, the facility discharges nearly 3.20 × 10^{6} m^{3} of cooling water to the adjacent water body. Elevated temperature can reach 43˚C (~18˚C higher than the normal river temperature). In violation of Egyptian law, outcomes of the thermal pollution can include fish kills along the Damietta branch [

Short-circuiting is the process of returning the thermally charged cooling water to the power station. This problem mainly occurs when the river velocity is relatively low when compared to the withdrawing velocity at the inlet of the power station [

The research was carried out in the Damietta branch of the Nile River which measure approximately 245 km (152.2 miles). The Damietta branch receives thermally polluted cooling water from Kafr-Al-Batek power station. The study area included about 1712 m (1.064 miles) of the Damietta branch, as shown in

Sample collection began in December 2012 and ended in October 2013 and involved taking water samples from 20 sites every 30 days along the Damietta branch; three sites downstream the outlet of the station, three sites at the outlet of the station, six sites upstream the outlet of the station, three sites at the inlet of the station, three sites upstream the inlet of the station, and two sites inside the inlet and the outlet of the station. Approximately 220 samples were collected and analyzed according to the standard methods for wastewater analysis [

Star CCM+ was used to model and simulate the scenarios in this research effort. Star CCM+ provides complete mesh flexibility [

The model geometry and boundary conditions are shown in

Geometries in this research are meshed using a prism layer. A prism layer is a layer of cells extending from the surface of geometry (see

Star CCM+ was used to model and simulate the different proposed scenarios in this study. Star CCM+ provides complete mesh flexibility [

For the fluid element, the rate of increase of mass in fluid element equals the net rate of flow of mass into element. The mass balance can be expressed by the following equation [

or written in vector notation:

Equation (4.2) is the unsteady, three-dimensional mass conservation or continuity equation at a point in a compressible fluid. The first term on the left side called “the convective term”, and describes the net flow of mass leaving the elements across its boundaries [

or in longhand notation:

For the momentum equation, Newton’s second law states that the rate of change of momentum of a fluid particle equals the sum of the forces on the particle. The rates of increase of x, y and z momentum per unit volume of a fluid particle are given by:

Equation (4.8) represents a transport equation that can be used to describe how a scalar, ϕ, changes in a closed physical system as a consequence of diffusion and convection [

where ϕ = the transported scalar, e.g. temperature, energy or mass.

V = the cell volume (m^{3}).

A = the cell surface-area (m^{2}).

ρ = the density (m^{3}/kg).

x = the porosity (dimensionless).

A = the cell area (m^{2}).

Γ = the diffusion coefficient (dimensionless).

a = the face area vector (m^{2}).

v = the velocity (m/s).

v_{g} = the grid-velocity (m/s).

S_{ϕ} = a source term for the scalar (N).

The energy equation can be obtained from Equation (4.8) to describe the transport of energy (E) in a solid:

where C_{P} = the material’s specific heat capacity (J/kg×K).

v_{s} = solid convective velocity which can be used to model rotation of a pure body (m/s).

The energy equation for a fluid is represented by Equation (4.10). The commercial software STAR-CCM+ used in this project employs finite volume methods (FVM) to solve Equations (4.8) and (4.10) in order to determine the behavior of the physical system.

where E = the total energy

H = the total enthalpy

T = the viscous stress tensor which consists of a laminar and a turbulent part (N/m^{2}).

f = the body force vector (N).

Ν = the velocity vector (m/s).

This research aims to reduce the effect of the thermal pollution by preventing the cooling water from being short circuited by the Kafr Al-Batek power station. The different scenarios, simulated by using Star CCM+ software, are: 1) a scenario developed to optimize the width of the existing outlet, 2) a scenario developed to close the existing water outlet and construct/optimize a new outlet downstream, and 3) a scenario developed to optimize the discharge angle of the existing outlet. Finally, a comparison was conducted between the aforementioned scenarios to find the most suitable and cost effective solution to be implemented.

The accuracy of the Star CCM+ modeling was verified by comparing between the actual data and those achieved by using the model (

The correlation coefficient, r, between the actual and predicted values was found to be 0.998, as well as the coefficient of determination, R^{2}, was found to be 0.9979, as shown in

First, the Computational fluid dynamics (CFD) analysis was performed using Star CCM+ to simulate the current situation to allow for the baseline assessment of the real-life problem. In the current situation, the outlet is located 412 m downstream the inlet of the station and the discharge angle is perpendicular to the river flow.

Location | Predicted, temperature, (˚C) | Actual, temperature, (˚C) | ΔT(˚C) |
---|---|---|---|

200 m downstream the outlet of the station (LB) | 37.22 | 37.0 | +0.22 |

200 m downstream the outlet of the station (M) | 34.75 | 35.0 | −0.25 |

200 m downstream the outlet of the station (RB) | 36.72 | 37.0 | −0.28 |

At the outlet of the station (LB) | 41.71 | 42.0 | −0.29 |

At the outlet of the station (M) | 41.12 | 41.0 | +0.12 |

At the outlet of the station (RB) | 39.34 | 39.50 | −0.16 |

100 m upstream the outlet of the station (LB) | 37.27 | 37.50 | −0.23 |

100 m upstream the outlet of the station (M) | 36.14 | 36.0 | +0.14 |

100 m upstream the outlet of the station (RB) | 38.12 | 38.50 | −0.38 |

112 m downstream the inlet of the station (LB) | 36.71 | 37.0 | −0.29 |

112m downstream the inlet of the station (M) | 35.28 | 35.50 | −0.22 |

112 m downstream the inlet of the station (RB) | 37.65 | 37.50 | +0.15 |

At the inlet of the station (LB) | 35.43 | 35.50 | −0.07 |

At the inlet of the station (M) | 34.53 | 35.0 | −0.47 |

At the inlet of the station (RB) | 31.14 | 31.50 | −0.36 |

50 m upstream the inlet of the station (LB) | 28.35 | 28.50 | −0.15 |

50 m upstream the inlet of the station (M) | 26.73 | 27.0 | −0.27 |

50 m upstream the inlet of the station (RB) | 24.33 | 24.50 | −0.17 |

Inside the inlet of the station | 32.20 | 32.0 | +0.2 |

LB: left bank, RB: right bank, M: middle of the river.

river normal temperature (25˚C) and this due to the hydraulic short-circuiting, where the thermally charged cooling water flows upstream and toward the inlet of the station. This occurs because the discharging and withdrawing water velocities are much higher than the river water velocity.

The CFD analysis was performed to simulate the first proposed scenario in which the outlet width was increased from 9.0 m to 27.0 m. The other parameters were kept the same as the existing case, the distance between the inlet and the outlet is 412 m and the discharge angle is perpendicular to the river flow.

The second proposed scenario was to construct a new outlet in order to increase the distance between the inlet and the outlet.

The third proposed scenario was to construct a new outlet at distance 612 m downstream the inlet with dimensions 27-m width and 3-m depth, while the discharge angle is perpendicular to the river flow.

well as at a reasonable distance from the inlet will significantly reduce the chances of returning the cooling water to the power station.

The forth proposed scenario was to change the discharge angle of the existing outlet.

Thermal pollution can create a variety of adverse impacts on the environment and may generate tremendous stress within the aquatic ecosystem. Therefore, this effort targeted ways to reduce the effect of the thermal pollution by preventing the cooling water from being short-circuited. The case study was conducted on Kafr-Al-Ba- tek power station. At present, the intake of the station exhibits a temperature of 32˚C resulting from the short spatial distance between the inlet and the outlet. Furthermore, because the water velocity at the outlet (2.0 m/sec) is much higher than the water velocity upstream of the outlet (0.37 m/sec), the discharged water can flow nearly perpendicularly to the river where it is obstructed by an erosion protection wall. Coupled with the intake velocity (3.0 m/s), the thermal flux is dissipated upstream and can adversely influence the cooling system [

Regression analysis for the actual and predicted values was performed using Microsoft Excel, and the correlation coefficients were obtained to help identify the nature of correlations between the actual and predicted values. A significant correlation coefficient value (r ~ 0.998) was obtained between both data sets. The CFD results also showed that the solution of changing the discharge angle was more effective than the other proposed solutions, especially after increasing the discharge angle to 135˚ because it would effectively prevent the cooling water from returning to the inlet of the station. Therefore, it is recommended to physically change the discharge angle from 90˚ to 135˚ in order to keep the water temperature at the inlet of the station the same as the ambient temperature of the river. Applying this solution should decrease the discharge water temperature at the outlet by up to 7 degrees (from 43˚C to 36˚C) which may significantly reduce the effect of the thermal pollution along the Damietta branch of the Nile River in Egypt. This solution is also more cost-effective than the other proposed solutions.

Saadeldin K.Mostafa,Mohamed K.Mostafa,Jason T.Kirby, (2015) The Choice of Appropriate Scenario in Order to Reduce the Effect of Thermal Pollution at the Damietta Branch Caused by Cooling Water Discharged from Kafr-Al-Batek Power Station. Journal of Environmental Protection,06,857-866. doi: 10.4236/jep.2015.68078