Question

A steam condenser typical of a large coal-fired plant is to cool 2.6E6 kg/hr of steam that has quality of 95% and pressure of 20 kPa. The steam is to leave the condenser at the same pressure, but as a saturated liquid. River water will be used to sink the heat out of the steam, and the river water can be assumed to be at about 25C. Due to environmental considerations, the river water's temperature is not to be increased more than 10C as a consequence of passing it through the condensor. Find the mass flow rate of river water necessary to cool the steam.

Answer 1

steam flow rate 2.6E+6 kg/hr

quality = 95%

quantity of steam = 2.6E+6 kg/hr * 0.95 = 2.47E+6 kg/hr

latent heat of steam = 2.25E+6 J/kg

This much heat has to be removed from the steam so that it turns saturated liquid.

Total heat to be removed form the steam = 2.47E+6 * 2.25E+6 J/hr

= 5.558 E+12 J/hr.

temperature of the river water = 25 ⁰C

10 C raise in temp is allowed

max. temp. of the outflow water = 35 ^oC

specific heat of water = 4186 J/kg-K

We have m kg/hr of water flow

heat removed by the water = m*10 *4186 J/hr , this must be equal to the heat removed from the steam flow.

m*10 *4186 = 5.558E+12 J /hr

m = 1.328E+8 kg/hr , mass flow rate of water required.