Reference no: EM132951884
Question: It is known that in a thermal power plant the efficiency is roughly 33%. The remainder is dissipated nearly equally between the chimney and the cooling tower. Flue gases in the chimney are at about 200?. Take a typical 1000 MW thermal power plant. This is the net power supplied to grid. It implies that 1000 MW each is dissipated through the chimney and the cooling tower.
In the cooling tower, the water used for condensing the steam is cooled back by allowing some water to evaporate.
Estimate the rate of water evaporation in the cooling tower assuming that evaporation occurs at about 40?.
Water evaporated in the cooling tower needs to be replenished with fresh water from a local source. This water has to be of condenser grade which has to be purer than what we drink. Collect the cost of water from your local water supplier and estimate the annual cost of this water.
Typical temperature raise of cooling water in the condenser is 5 ?. Water cannot be cooled below the wet bulb temperature of the location. A typical approach of cooling tower is 2 ?. Collect data on annual maximum wet bulb temperature in your place and then calculate the water inlet and outlet temperatures at the condenser.
Calculate flow rate of water through the condenser and calculate what fraction of this water is lost in the cooling tower.
A typical condenser length does not exceed 25 m. So, allow for maximum tube length of no more than 24 m. Water velocity in the tubes is typically 1 m/s. Calculate the inner diameter of tubes to be used which will depend on number of passes. Note that water flow must be in the turbulent region. Also note that the diameter has to be reasonable from engineering point of view. You can get standard steel pipe dimensions from web sites. Choose a wall thickness not less than 2 mm such that the pipe is able withstand water pressure on the inside and vacuum on the outside.
Calculate the number of tubes required if single pass is used.
Calculate the Reynolds number and the heat transfer coefficient on the water side.
As a first approximation, neglect the thermal resistance of the tube wall and effects of scaling. Assume that a minimum temperature difference of 5 ? is required between steam and water. Further, assume that the steam side heat transfer coefficients will be so large that the governing factor is only the water side one. Calculate the condenser tube surface area required to remove 1000 MW.
Calculate the length of each tube carrying water. Check if this length satisfies the maximum permissible length of 24 m. Also calculate the pressure drop of water for this case assuming that the tubes are smooth.
In a more detailed calculation, calculate the length of each condenser tube, if the tube wall resistance is accounted for. Assume that the tubes are made of carbon steel.
Write a final report including your design calculations as mentioned above and provide your conclusions. Include any method you can suggest to recover the water evaporated in the cooling tower. Remember that a heat source is available in chimney gases for any method you may think of.