Hi all,

Let's consider the flowsheet below.

**Flowsheet_HEN.png** **130.91KB**
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Stream S1 is heated to 180°C and is entering reactor 1. The product leaving the reactor at 250°C is split into two streams. Stream S3 is cooled to 40°C, whereas stream S4 is cooled down to 200°C and then enters reactor 2 together with stream S5, which in turn heated from 100°C to 200°C. Finally, the outlet stream of the isothermal reactor 2 at 200°C is cooled to 80°C. No phase changes take place in the described streams so we can assume constant FC_{p}.

I need to compute and plot the hot and cold composite curves for the problem and determine the amount of cold and hot utilities. Here are data I will need:

**Screen Shot 2018-11-06 at 23.15.44.png** **54.13KB**
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So, to build my composite curve, I firstly took an approach temperature of 10°C (DeltaT_min). I'll put every temperature in the cold reference (ie. subtracting the hot streams temperatures by 10°C). Afterwards, I divided the problem into intervals (7 in my case) following this YouTube video . By doing so, I end up with Q_{1} = 12 MW (1 stands for interval 1 which is between 240-200°C). Everything is fine for all intervals except interval 2 (ie. between 200 and 190°C) where I find Q_{2} = 0 MW. Does it mean it is the pinch point?

Finally, I don't see how to built my composite curve from this data... Can I say if Q > 0 -> Cold composite and if Q < 0 -> Hot composite ?

Thank you for your help!

NB: Below are full results of Q's for each temperature interval:

Interval 1: 240-200°C , Q1 = 12 MW

Interval 2: 200-190°C , Q2 = 0 MW

Interval 3: 190-180°C , Q3 = 1 MW

Interval 4: 180-100°C , Q4 = -8 MW

Interval 5: 100-70°C , Q5 = 6 MW

Interval 6: 70-30°C , Q6 = -2 MW

Interval 7: 30-20°C , Q5 = -2 MW