Page 150 - Chemical engineering design

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CHEMICAL ENGINEERING
T d
Interval temperature
T int Datum temperature for enthalpy calculations q q
T n Temperature in nth interval q
T p Phase-transition temperature q
T r Reduced temperature
T s Source temperature q
T t Target temperature q
T min Minimum temperature difference in heat exchanger q
T n Internal temperature difference q
t Temperature, relative scale q
t Time T
t r Reference temperature, mean specific heat q
t f Inlet-stream temperatures, heat-exchanger networks q
t o Outlet-stream temperatures, heat-exchanger networks q
2 2
U Internal energy per unit mass L T
u Velocity LT 1
V 1 Initial volume L 3
V 2 Final volume L 3
L
v Volume per unit mass M 1 3
X Compressibility function defined by equation 3.33
x Distance L
x a Mol fraction component a in a mixture
x b Mol fraction component b in a mixture
x c Mol fraction component c in a mixture
Y Compressibility function defined by equation 3.34
2 2
W Work per unit mass L T
2 3 1
W i Heat capacity of streams in a heat-exchanger network ML T q
Z Compressibility factor
z Height above datum L
Z min Minimum number of heat exchangers in network
3.20. PROBLEMS
3.1. A liquid stream leaves a reactor at a pressure of 100 bar. If the pressure is reduced
to 3 bar in a turbine, estimate the maximum theoretical power that could be
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obtained from a flow-rate of 1000 kg/h. The density of the liquid is 850 kg/m .
3.2. Calculate the specific enthalpy of water at a pressure of 1 bar and temperature of
Ž
200 C. Check your value using steam tables. The specific heat capacity of water
can be calculated from the equation:
Ž
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C p D 4.2 2 ð 10 t;where t is in Cand C p in kJ/kg.
Take the other data required from Appendix C.
3.3. A gas produced as a by-product from the carbonisation of coal has the following
composition, mol per cent: carbon dioxide 4, carbon monoxide 15, hydrogen 50,
methane 12, ethane 2, ethylene 4, benzene 2, balance nitrogen. Using the data
given in Appendix C, calculate the gross and net calorific values of the gas. Give
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your answer in MJ/m , at standard temperature and pressure.
Ž
3.4. In the manufacture of aniline, liquid nitrobenzene at 20 C is fed to a vaporiser
Ž
where it is vaporised in a stream of hydrogen. The hydrogen stream is at 30 C,
and the vaporiser operates at 20 bar. For feed-rates of 2500 kg/h nitrobenzene and
366 kg/h hydrogen, estimate the heat input required. The nitrobenzene vapour is
not superheated.