Process Conditions and Assumptions

The chemistry is the exothermic, irreversible, gas-phase reaction A + B — C, which is conducted in the presence of a solid catalyst in a tubular reactor. The production rate of C is fixed at 0.12kmol/s for all designs. This means that the two gas-phase fresh feedstreams are both 0.12 kmol/s. Their temperature is 313 K. 

A maximum reactor temperature of 500 K is used in this study. This maximum temperature occurs at the exit of the adiabatic reactor under steady-state conditions. Plug flow is assumed with no radial gradients in concentrations or temperatures and no axial diffusion or conduction. 

The energy requirement of the furnace is zero for this adiabatic reactor case since the reactor exit stream at maximum temperature can provide enough heat. The design of the FEHE and the amount of bypassing are determined by the reactor inlet temperature T-m. A temperature difference of 25 K is assumed for the hot end of the FEHE. The hot reactor effluent enters the hot side of the FEHE at the high-temperature limit of 500 K, so the cold-side exit stream is 475 K. If the specified reactor inlet temperature is less than 475 K, bypassing is used. A fairly low overall heat transfer coefficient of 

One important physical property assumption is made about heat capacities. The mass heat capacities of all components are assumed to be the same (2kJkg-1 K-1). This means that the product of the mass flowrate and the mass heat capacity is constant for any stream and equal to the sum of the product of the component molar flowrates times the corresponding molar heat capacities. Thus, despite the fact that molar flowrates of individual components vary down the length of the reactor, the term F Ylf=A yjcpj is constant, where F is the total molar flowrate, y - is the mole fraction of component j, and cpj is the molar heat capacity of component j. This relationship is used in the design procedures discussed below to calculate the inlet flowrate from an energy balance around the reactor. 

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