Hydraulic Model Study of Haripur 360 MW Combined Cycle Power Plant

Location

Type of Project

Period of Study

Client

Hyundai

Description

A 360 MW Combined Cycle Power Plant (CCPP) is planned to be constructed on the Lakhya River near Haripur where the flow is very low during dry period subject to weak tidal influence. The CCPP would draw cool water from the river and discharge the hot water into the river. Inappropriate location of intake and outlet of water can create condition that would cause tremendous loss of efficiency particularly in the dry season and also endanger the aquatic life.The guidelines of the World Bank require that: " the effluent should result in a temperature increase of no more than 3 degrees Celsius at the edge of the Zone where initial mixing and dilution takes place. Where the zone is not defined, use 100 metres from the point of discharge when there are no sensitive aquatic ecosystems within this distance."

The hydraulic model study, which has been carried out by DHI/SWMC, aims at river hydraulics, advection-dispersion of heated water and sediment transport, and scouring along the proposed location of the plant using advanced mathematical tools, eg. MIKE 11, MIKE 21 and MIKE 3, developed by Danish Hydraulic Institute (DHI). Three probable positions of intake and outlet were investigated for the critical condition that may occur with respect to re-circulation and absolute temperature of intake with the help of a suite of one or more of the above models.

It has been found that April will be the critical time of the year, though the precise time for a critical situation to occur will vary from year to year. It has also been found that excess temperatures at the intake (and also near the outlet) of the Haripur CCPP are mainly caused by other power plants on the Lakhya in the vicinity. With all 4 power plant units in operation, the Haripur CCPP will be responsible for less than one third of the excess temperatures. The advective transport in the dry period causes re-circulation of cooling water. Re-circulation takes place when outlet water heated to a certain excess temperature affects the temperature at the intake. Especially in the period from December to April, when the net flow would typically be close to zero, the cooling water may re-circulate several times. The outlet cooling water flows towards the intake, enters the power plant cooling system and flows back to the power plant intake.

At the outlet, the cooling water will rise as a plume to the surface due to the density difference between the river water and the discharge. The cooling water will initially stay at the surface while being transported with the main river flow. Due to the flow of the main river (0.2 m/s in average) the depth of the top layer of cooling water will be small (0.2-0.5 m). the cooling water will gradually mix vertically and horizontally. The stratification will be weak will be weak because the density difference between the diluted cooling water and the river water will be small (approximately 0.1 percent of the water density). Therefore, a high vertical mixing can be expected in the sense that the heated top layer and the cooler river water below will mix into one homogenous layer with respect to temperature.