PROCESS BALANCES SAP 19CGA007 SAP 2020 Loughborough University
Q1. Gas containing 20% methane, 60% propane and 20%carbon dioxide is fed to a boiler where it is burnt with 100% excess air. Gas is supplied to the boiler at 25ºC and the combustion air enters at a temperature of 225ºC. The boiler stack temperature is 425ºC. The state of all reactants and products is gaseous.
Relevant data are provided overleaf.
Air consists of 21% O2 and 79% N2 on a volume basis
Cp(O2) = 30 J mol-1 K-1 Cp(N2) = 30 J mol-1 K-1
Cp(H2O) = 35 J mol-1 K-1 Cp(CO2) = 39 J mol-1 K-1
Cp(CH4) = 35.7 J mol-1 K-1 Cp(C3H8) = 73.6 J mol-1 K-1
Latent heat of vaporisation of water at 100ºC = 2257 kJ kg-1
Energies of formations refer to each mole formed at a datum temperature of 25ºC.
▵Hof(CH4) = -74.5 kJ mol-1 ▵Hof(C3H8) = -103.8 kJ mol-1
▵Hof(CO2) = -393.5 kJ mol-1 ▵Hof (H2O) = -241.8 kJ mol-1
Q2 A chemical laboratory with a volume of 500 m3 is equipped with a ventilation system. The volumetric flow rate of the ventilation air is 0.6 m3 s-1. A polymerisation reactor is housed within the laboratory. In the event of a reactor seal failure, the reactor would release a maximum of 1 mol of vinyl chloride monomer (C2H3Cl), which is a gas at ambient conditions, occupying a volume of 22.4 L at 1 atm and 0oC. The molecular weight of vinyl chloride is 62.498 g mol-1. The ideal gas constant is 0.082 L atm K-1 mol-1. A mole fraction of C2H3Cl (1 mol) in the room air greater than 10-6 constitutes a health hazard.
Suppose that the reactor seal ruptures at a time t = 0 and the maximum amount of C2H3Cl is emitted and spreads uniformly throughout the room almost instantaneously.
A number of stages are involved in the manufacture of bars of white chocolate.
The production of 1 kg of chocolate requires 0.3 kWh of electricity (at 9 p kWh-1), 0.5 kWh of gas (at 5 p kWh-1) and 0.2 m3 of water (at 25 p m-3). White chocolate contains: 50% cocoa butter, 15% milk solids, 5% milk fat and the remainder is sugar.
Calculate the variable cost per 100 g bar of chocolate based on the following costs:
sugar £0.30 per kg, milk solids £1.50 per kg, milk fats £0.50 per kg, wrapper £0.02 per chocolate bar, cocoa beans £2200 per tonne and 2.25 kg of beans are converted to 1 kg of cocoa butter. [5 marks]
Q4 Methanol is produced by the reaction of carbon dioxide and hydrogen as follows:
CO2 + 3 H2 → CH3OH + H2O
The fresh feed to the process contains hydrogen, carbon dioxide and 0.5 mol% of inerts (I). The reactor effluent passes to a condenser that removes essentially all of the methanol and water formed. The unconsumed reactants and the inerts (I) are recycled and mixed with the fresh feed before entering the reactor. To avoid buildup of the inerts in the system, a purge stream is withdrawn from the recycle. The feed to the reactor (not the fresh feed to the process) contains 28 mol% CO2, 70 mol% H2, and 2 mol% inerts. The single-pass conversion of hydrogen is 66%. Use a basis of 100 kmolh-1 for the feed to the reactor.
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