A front feed evaporation system has 2 effects and a condenser. The evaporator (2 effects) is used to concentrate an aqueous solution of solids with a flow rate of 8000 kg/s and a mass composition of solids of 10%. Consider cp of the evaporating solution = (1-0.48x) kcal/kg oC, where x is the mass fraction of solute. The solution has negligible heat of dilution. The system must produce concentrate with 50% solids. The boiler steam used only in the first effect is at 3.0 kgf/cm2. The vapor space of the 1st effect operates at 110º C and 1.1 kgf/cm2, while in the 2nd effect the pressure is 0.15 kgf/cm2. The temperature difference in the 2nd effect is 40ºC. In the 1st effect, 4000 kg/s of steam are produced, but part of this current is diverted (bleeded) for use in a plate heat exchanger. The purpose of the exchanger is to take advantage of part of the steam generated by the evaporation system to bring a process stream closer to boiling, as it will be used in another operation in the industrial unit. Thus, the bleed steam heats the stream in question, which has a flow rate of 20000 kg/s, a specific heat of 0.8 kcal/kg ºC and would boil at a temperature of 105ºC. Calculate what is ordered in the items that follow. a) The process stream that is heated in the exchanger can be brought to what temperature? Would it boil in the changing table? b) Assuming that the solution is fed into the 2-effect evaporator at a temperature of 70ºC, what will be the savings of the evaporator? c) If the system before the evaporator suffers operational problems and thus changes the feed temperature to 40ºC (without changing flow and composition), what will be the savings of the evaporator?
A front feed evaporation system has 2 effects and a condenser. The evaporator (2 effects) is used to concentrate an aqueous solution of solids with a flow rate of 8000 kg/s and a mass composition of solids of 10%. Consider cp of the evaporating solution = (1-0.48x) kcal/kg oC, where x is the mass fraction of solute. The solution has negligible heat of dilution. The system must produce concentrate with 50% solids. The boiler steam used only in the first effect is at 3.0 kgf/cm2. The vapor space of the 1st effect operates at 110º C and 1.1 kgf/cm2, while in the 2nd effect the pressure is 0.15 kgf/cm2. The temperature difference in the 2nd effect is 40ºC. In the 1st effect, 4000 kg/s of steam are produced, but part of this current is diverted (bleeded) for use in a plate heat exchanger. The purpose of the exchanger is to take advantage of part of the steam generated by the evaporation system to bring a process stream closer to boiling, as it will be used in another operation in the industrial unit. Thus, the bleed steam heats the stream in question, which has a flow rate of 20000 kg/s, a specific heat of 0.8 kcal/kg ºC and would boil at a temperature of 105ºC. Calculate what is ordered in the items that follow.
a) The process stream that is heated in the exchanger can be brought to what temperature? Would it boil in the changing table?
b) Assuming that the solution is fed into the 2-effect evaporator at a temperature of 70ºC, what will be the savings of the evaporator?
c) If the system before the evaporator suffers operational problems and thus changes the feed temperature to 40ºC (without changing flow and composition), what will be the savings of the evaporator?
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