Page 129 - Plant design and economics for chemical engineers

GENERAL DESIGN CONSIDERATIONS 105

12. When a flammable material is burned, there will be an increase in either the volume
of the gas produced (provided the pressure is constant) or the pressure in the
container (provided the volume is constant). Calculate the volume of gas formed
during the adiabatic combustion of 100 lb moles of gaseous propane at a constant
pressure of 1 atm. Assume that the 200 percent theoretical air and the propane
involved in the combustion are at 25°C and that the combustion goes to completion.
13. A mixture of ethylene and air with a C,/C, ratio of 1.25 is to be compressed from
an initial temperature and pressure of 70°F and 14.7 psia, respectively, to 1000 psia.
If the compression is performed essentially isentropically, what is the final tempera-
ture? If the autoignition temperature (the temperature at which a fuel-air mixture
will ignite without the need for an ignition source) is 913”F, will an explosion occur if
the mixture being compressed is flammable?
14. Many commercial chemical reactions are exothermic. If the heat that is generated is
not appropriately removed, the reaction rate can get out of control and the reactor
will be damaged if it is not adequately vented or protected. Consider a reaction in a
continuously stirred reactor that has an activation energy of 28,000 Cal/g mole. The
water-cooled jacket surrounding the reactor utilizes cooling water with an inlet
temperature of 15°C. What is the maximum temperature at which the reaction can
operate without having the reaction run away? What actions might be taken to
maintain safe operation of the reactor?
15. Materials like acetylene may decompose under the appropriate conditions with a
fairly large liberation of energy. Determine the temperature and pressure attained in
a closed spherical container when acetylene, initially at 25°C and 10 atm, rapidly
decomposes to carbon and hydrogen after accidentally being subjected to an electri-
cal spark. What thickness of carbon steel would have been required to contain the
decomposition reaction if no relief valve had been available to relieve the pressure
buildup? (Assume that a safety factor of 4 has been used in the thickness calculation.)
16. One pound of TNT explosive releases about 2000 Btu of energy when it detonates.
Estimate the equivalent energy release rate in pounds of TNT when a 150-ft3-high
pressure cylinder filled with gaseous nitrogen fails at 2200 psia.
17. A 70-gal hot water tank in a worker change room has a working pressure of 75 psia
and a burst pressure of 300 psia. During installation the relief valve becomes
inoperable. After filling the tank, the fill and exit valves are shut and the heater
energized. The pressure in the tank increases until the tank ruptures at 300 psia.
Estimate the blast energy in terms of the TNT equivalent (2000 Btu/lb explosive).
To simplify the calculation, assume that the explosion is adiabatic with the saturated
water flashing isentropically to steam and water at 14.7 psia pressure. Since the
explosion is rapid, very little air mixes with the steam.
18. Liquid chlorine may be transferred from a chlorine storage container by pressurizing
with dry chlorine gas. Develop two systems
(al using recompressed chlorine vapor
(b) using vaporized chlorine
and provide the appropriate control and alarm system for each system.
19. A distillation unit has been designed to handle a very hazardous material. The unit
utilizes a reflux drum and buffer storage. List several ways in which the inventory of
the hazardous material can be reduced or eliminated. Sketch and instrument the
system that is recommended.