It is a chemical engineering problem. The flow rate of a boiler (see figure) is

Question

It is a chemical engineering problem.

The flow rate of a boiler (see figure) is 10 kg/s, with water entering at a temperature of 100 degree C and a pressure of 1 atm. The steam leaves the turbine at a pressure of 1 atm and 500 degree C. How much heat is needed to operate this boiler? Neglect kinetic and potential energies. To examine the accuracy of neglecting Delta KE, consider the following: if the inlet flow speed is 2 m/s and the outlet flow speed is 200 m/s, what would the rate of change in KE be (in W)? To examine the accuracy of neglecting Delta PE, consider the following: if there is a 10-m difference between the inlet and outlet locations, what would the rate of change in PE be (in W)?

Explanation / Answer

(a)

From steam table

At 100 0C h1 = 2256.99 kJ/kg

At 500 0C h2 = 3485.38 kJ/kg

We neglect PE and KE

So

energy needed=h2-h1=1228.39 kJ/kg

Power =m*enegy=10 kg/s *1228.39 kJ/kg =12283.9 kW

(b)

KE =1/2 mV2 =1/2 *10*(2002-22) =199980 W=199.980 kW

(c)

g= gravity accerlation=9.8 m/s2

PE =mgZ =10*9.8*10=980 W

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