• Author / Uploaded
• Emmanuel Cervantes Velázquez

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• Combustión
• Modularidad
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• Gas natural
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5606ch31.qxd_lb 9/25/03 10:25 AM Page 954

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Solving Material and Energy Balances Using Process Simulators

Chap. 31

Fixed parameters Reactor volume  VR  13.3 ft3 Heat transfer area  A  29.9 ft2 Heat transfer coefficient  U  74.5 Btu/(hr)(ft2)(F) Variable input Reactant feed rate Reactant feed temperature Water feed rate Water feed temperature

 Fi (see table above)  T1  80F  F3  247.7 lb mol/hr water  T3  75F

Physical and thermodynamic data Reaction rate constant  k0  34 ft3/(lb mol)/(hr) Activation energy/gas constant  E/R  1000R

Figure P31.2

Heat of reaction  H  5000 btu/lb mol A Heat capacity of water  Cpw  18 Btu/(lb mol)(F) Product component density  r  55 lb/ft3

31.3

31.4

The densities of each of the product components are essentially the same. Assume that the reactor contents are perfectly mixed as well as the water in the jacket, and that the respective exit stream temperatures are the same as the reactor contents or jacket contents. The stream flows for a plant are shown in Figure P31.3. Write the material and energy balances for the system and calculate the unknown quantities in the diagram (A to F). There are two main levels of steam flow: 600 psig and 50 psig. Use the steam tables for the enthalpies. Figure P31.4 shows a calciner and the process data. The fuel is natural gas. How can the energy efficiency of this process be improved by process modification? Suggest at least two ways based on the assumption that the supply conditions of the air and fuel remain fixed (but these streams can be possibly passed through heat exchangers). Show all calculations.

5606ch31.qxd_lb 9/25/03 10:25 AM Page 955

Chap. 31

Problems

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Figure P31.3

Figure P31.4

31.5

Limestone (CaCO3) is converted into CaO in a continuous vertical kiln (see Figure P31.5). Heat is supplied by combustion of natural gas (CH4) in direct contact with the limestone using 50% excess air. Determine the kilograms of CaCO3 that can be processed per kilogram of natural gas. Assume that the following average heat capacities apply: Cp of CaCO3  234 J/(g mol)(C) Cp of CaO  111 J/(g mol)(C)