Page 151 - Chemical engineering design

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FUNDAMENTALS OF ENERGY BALANCES
3.5. Aniline is produced by the hydrogenation of nitrobenzene. The reaction takes
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place in a fluidised bed reactor operating at 270 C and 20 bar. The excess heat of
reaction is removed by a heat transfer fluid passing through tubes in the fluidised
bed. Nitrobenzene vapour and hydrogen enter the reactor at a temperature of
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260 C. A typical reactor off-gas composition, mol per cent, is: aniline 10.73,
cyclo-hexylamine 0.11, water 21.68, nitrobenzene 0.45, hydrogen 63.67, inerts
(take as nitrogen) 3.66. Estimate the heat removed by the heat transfer fluid, for
a feed-rate of nitrobenzene to the reactor of 2500 kg/h.
The specific heat capacity of nitrobenzene can be estimate using the methods given
in Chapter 8. Take the other data required from Appendix C.
3.6. Hydrogen chloride is produced by burning chlorine with an excess of hydrogen.
The reaction is highly exothermic and reaches equilibrium very rapidly. The
equilibrium mixture contains approximately 4 per cent free chlorine but this is
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rapidly combined with the excess hydrogen as the mixture is cooled. Below 200 C
the conversion of chlorine is essentially complete.
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The burner is fitted with a cooling jacket, which cools the exit gases to 200 C.
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The gases are further cooled, to 50 C, in an external heat exchanger.
For a production rate of 10,000 tonnes per year of hydrogen chloride, calculate
the heat removed by the burner jacket and the heat removed in the external cooler.
Take the excess hydrogen as 1 per cent over stoichiometric. The hydrogen supply
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contains 5 per cent inerts (take as nitrogen) and is fed to the burner at 25 C. The
chlorine is essentially pure and is fed to the burner as a saturated vapour. The
burner operates at 1.5 bar.

3.7. A supply of nitrogen is required as an inert gas for blanketing and purging vessels.
After generation, the nitrogen is compressed and stored in a bank of cylinders,
at a pressure of 5 barg. The inlet pressure to the compressor is 0.5 barg, and
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3
temperature 20 C. Calculate the maximum power required to compress 100 m /h.
A single-stage reciprocating compressor will be used.
3.8. Hydrogen chloride gas, produced by burning chlorine with hydrogen, is required
2
at a supply pressure of 600 kN/m , gauge. The pressure can be achieved by either
operating the burner under pressure or by compressing the hydrogen chloride
gas. For a production rate of hydrogen chloride of 10,000 kg/h, compare the
power requirement of compressing the hydrogen supply to the burner, with that
to compress the product hydrogen chloride. The chlorine feed will be supplied at
the required pressure from a vaporiser. Both the hydrogen and chlorine feeds are
essentially pure. Hydrogen will be supplied to the burner one percent excess of
over the stoichiometric requirement.
A two-stage centrifugal compressor will be used for both duties. Take the polytro-
pic efficiency for both compressors as 70 per cent. The hydrogen supply pressure
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2
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is 120 kN/m and the temperature 25 C. The hydrogen chloride is cooled to 50 C
after leaving the burner. Assume that the compressor intercooler cools the gas to
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50 C, for both duties.
Which process would you select and why?