ChE 201 Washington State University Chemical Process Principles and Calculations Voiland School of Chemical Engineering and Bioengineering Fall, 2009 Richard L. Zollars Problem 7.26, Felder and Rousseau Liquid water is fed to a boiler at 24°C and 10 bar and is converted at constant pressure to

saturated steam. Use the steam tables to calculate H (kJ/kg) for this process, and then calculate the heat input required to produce 15,000 m3/h of steam at the exiting conditions. Assume that the kinetic energy of the entering liquid is negligible and that the steam is discharged through a 15-cm ID pipe. SOLUTION From Table B.5 for water at 24°C the specific enthalpy is 100.6 kJ/kg and that for saturated steam is 2776.2 kJ/kg (and the temperature is 179.9°C) from Table B.6. Thus the enthalpy change is

kg

kJH 6.26756.1002.2776ˆ

Also from Table B.6 we see that the specific volume of the saturated steam is 0.1943 m3/kg. So the mass flow rate of the steam is

h

kg

kg

mh

m

m 200,77

1943.0

15000

3

3

The linear velocity of the steam at the exit is

s

m

h

m

mh

m

Rh

m

uout 8.2351049.8075.0

15000150006

2

3

2

3

So the energy balance becomes

kWs

kJ

h

kJ

kg

kJ

h

kgQ

kg

kJJ

kJ

kg

kg

s

m

kg

kJ

h

kgQ

kg

kJs

m

kg

kJ

h

kgQ

QHmu

Hm inout

out

48

2

2

2

1080.55800010087.24.2703200,77

6.1002

1000

1

1

18.235

2.2776200,77

6.1002

8.235

2.2776200,77

ˆ2

ˆ