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Unformatted text preview: Improving what? Minimize the number of heat exchangers needed and the utility requirements in a plant. History: Use of thermal energy contained in product streams in oil refineries to preheat the crude prior to distillation. Very important beginning in the 1970s due to the increase in cost of fuel and energy. Linhoff, B., and J.R. Flower, Synthesis of Heat Exchange Networks: 1. Systematic Generation of Energy Optimal Networks, AIChE J., 24 , 633 (1978) Umeda, T., Itoh, J., and K. Shiroko, Heat Exchanger System Synthesis, Chem. Eng. Prog., 74 (7), 70 (1978) HEAT INTEGRATION ChE 4253  Design I MUMNE algorithm (5 steps) 1. Choose a minimum approach temperature. This is a parametric optimization, since for every minimum approach temperature a different solution can be found. 2. Construct a temperature interval diagram. 3. Construct a cascade diagram and determine the minimum utility requirements and the pinch temperatures. 4. Calculate the minimum number of heat exchangers above and below the pinch. 5. Construct the heat exchanger network. Minimum Utility, Minimum Number of Exchangers ChE 4253  Design I Six process streams for heating or cooling. A stream is HOT if it requires cooling. A stream in COLD if it requires heating. Design the MUMNE for the following system: Stream Condition Flowrate C p mC p T in T out Q available # (kg/s) (kJ/kg o C) (kW/ o C) ( o C) ( o C) (kW) 1 Hot 10. 0.8 8. 300 150 1200 2 Hot 2.5 0.8 2. 150 50 200 3 Hot 3. 1. 3. 200 50 450 4 Cold 6.25 0.8 5. 190 290 500 5 Cold 10. 0.8 8. 90 190 800 6 Cold 4. 1. 4. 40 190 600 Example for MUMNE ChE 4253  Design I Total 50 Question: What is the minimum possible utility that we need for this system? Example for MUMNE ChE 4253  Design I Need to make sure that both the 1 st and the 2 nd laws of Thermodynamics can be satisfied MUMNE algorithm (5 steps) 1. Choose a minimum approach temperature. This is a parametric optimization, since for every minimum approach temperature a different solution can be found. 2. Construct a temperature interval diagram. 3. Construct a cascade diagram and determine the minimum utility requirements and the pinch temperatures. 4. Calculate the minimum number of heat exchangers above and below the pinch. 5. Construct the heat exchanger network. Minimum Utility, Minimum Number of Exchangers ChE 4253  Design I It is a rather arbitrary value (between 10 o C to 20 o C). Represents the smallest temperature difference that two streams leaving or entering a heat exchanger can have. Lets choose 10 o C for this example. Note that a positive value will yield a viable heat exchanger network. Step 1: Choose a Minimum Approach Temperature ChE 4253  Design I MUMNE algorithm (5 steps) 1. Choose a minimum approach temperature....
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 Spring '09
 Lobban

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