Practical Considerations. Richard Beaman, PE. Senior Chemical Process Engineer. Business Leader

Transcription

1 Energy Optimization Using Pinch Analysis Practical Considerations Richard Beaman, PE Senior Chemical Process Engineer Cliff Reese, PE Business Leader

2 Pinch Analysis Systemized method to utilize as much energy contained in the process streams as is economically possible. Reduces utility requirements. Documents minimum utility requirements.

3 Introduction to Pinch Analysis AIChE Webinar Introduction to Pinch Analysis by Alan Rossiter, Ph.D. President of Rossiter & Associates Red Vector Online Course Chemical Engineering: Pinch Technology Pinch Analysis and Process Integration by Ian C. Kemp Chemical Engineering Progress: Improve Energy Efficiency via Heat Integration by Alan Rossiter, Ph.D. President of Rossiter & Associates

4 Pinch Analysis Definitions Hot Stream Any stream that needs to be cooled. Cold Stream Any stream that needs to be heated. Pinch Temperature The minimum temperature difference (approach) between the hot streams and the cold streams. Composite Curve The sum of the flowing heat capacity of all of the hot or cold streams, over the temperature re range of the streams.

5 Hot Composite Curve Flowing Heat Capacity Definition CP = m C P T 1 DUTY C (T 1 -T 2 )*(CP C ) T 2 A B (T 2 -T 3 )*(CP A +CP B +CP C ) T 3 (T 3 -T 4 )*(CP A +CP B ) T 4 (T 4 -T 5 )*(CP A ) T 5 Duty

6 Hot Composite Curve T 1 T 2 T 3 T 4 T 5 Duty

7 3 Process Only Unshifted Composite Curve Hot Utility Duty = 42 MBTU/hr 25 2 F) Temperature ( 15 1 Pinch = 2 F Cold Utility Duty = 114 MBTU/hr Heat Duty (MBTU/hr)

8 Pinch Temperature How do you choose the Pinch Temperature? Basis of the pinch uses the heat transfer equation: Q = Uo A LMTD Smaller Process Pinch Temperature = Larger Process Duty Recovered (Q). To increase the Duty, with a smaller LMTD, means increasing the Surface Area (A). If we know the process on either side of the pinch point or have TEMA data sheets for the heat exchangers, we can get the Uo.

9 Pinch Temperature If Uo is small, then getting extra duty will take a lot of surface area per BTU, increasing the capital cost a lot. So we should use a larger Pinch Temperature. If Uo is large, then getting extra duty will take only a little extra surface area per BTU, increasing the capital cost less than the small U o case. So we can use a much smaller Pinch Temperature. In addition, we need to look at the magnitude of the duty that can be saved. Larger duty savings can pay for a lot of extra heat transfer surface area.

10 3 Process Only Unshifted Composite Curve 25 2 ( F) Temperature ( 15 1 Pinch = 2 F Heat Duty (MBTU/hr)

11 3 Process Only Shifted Composite Curve Hot Utility Duty = 42 MBTU/hr 25 Shifted Tempera ature ( F) Cold Utility Duty = 114 MBTU/hr Heat Duty (MBTU/hr)

12 3 Unoptimized Utilites Unshifted Composite Curve Hot Utility Duty = 42 MBTU/hr 25 2 Temperature e ( F) Cold Utility Duty = 114 MBTU/hr Heat Duty (MBTU/hr)

13 3 Process Only Shifted Composite Curve 25 Shifted Tempera ature ( F) Heat Duty (MBTU/hr)

14 3 Process Only Grand Composite Curve 25 Shifted Tempera ature ( F) Pinch Point Hot Utility Duty = 42 MBTU/hr Cold Utility Duty= 114 MBTU/hr Heat Duty (MBTU/hr)

15 3 Shifted Optimized Utilities Curve Shifted Tempera ature ( F) Process Pinch Points Hot Utility at 159 F Utility Pinch Points 5 Cold Utility at 65 F Heat Duty (MBTU/hr)

16 3 Optimized Utilities Grand Composite Curve 25 Shifted Tempera ature ( F) Pinch Points 5 Hot Utility at 159 F Cold Utility at 65 F Heat Duty (MBTU/hr)

17 3 Process Only Unshifted Composite Curve 25 2 ( F) Temperature ( Heat Duty (MBTU/hr)

18 3 Process Only Unshifted Composite Curve No Hot Utility ( F) Temperature Pinch = 1 F Cold Utility= 72 MBTU/hr Heat Duty (MBTU/hr)

19 3 Unoptimized Utilities Shifted Composite Curve No Hot Utility Shifted Temperatu ure ( F) Process Pinch Point Cold Utility= 72 MBTU/hr Heat Duty (MBTU/hr)

20 3 Unoptimized Utilities Grand Composite Curve No Hot Utility 2 re( F) Shifted Temperatu Shifted Temperature = 85 o F Actual Temperature = 8 o F Cold Utility=72 MBTU/hr Heat Duty (MBTU/hr)

21 Cost Analysis l Cost ($/yr) Annua Total Cost Energy Cost Capital Cost T (Pinch Point)

22 Cost Analysis l Cost ($/yr) Total Cost Potential Savings of Tighter Pinch Approach Temperature Energy Cost Annual Capital Cost T (Pinch Point)

23 Real Process Example

24 Temperature e ( F) Process Only Composite Curve 23 F Pinch 5, 1, 15, 2, 25, 3, 35, 4, 45, Heat Duty (btu/hr)

25 Shifted Temperatu ure ( F) Process Only Shifted Composite Curve 23 F Pinch 5, 1, 15, 2, 25, 3, 35, 4, 45, Heat Duty (BTU/hr)

26 1 Grand Composite Curve Process Only Process Pinch Point = 23 o F 4 Sh hifted Temperature e ( o F) , 2, 3, 4, 5, 6, 7, 8, 9, 1, 11, Heat Duty (BTU/hr)

27 F) Temperature ( Composite Curve with Cold Utility Pinch = 8 F 5, 1, 15, 2, 25, 3, 35, 4, 45, Heat Duty (BTU/hr)

28 Shifted Temperatu ure ( F) Utility Pinch Shifted Composite Curve with Cold Utility Process Pinch = 23 o F 5, 1, 15, 2, 25, 3, 35, 4, 45, Heat Duty (BTU/hr)

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30 1 9 8 Grand Composite Curve Pinch = 15 F Ignore Changes in this Section Sh hifted Temperature e ( F) Duty transferrable to -28 o F Refrigerant o F Refrigerant Shifted by 1/2 of 15 o F - Approach -8 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 11, Heat Duty (BTU/hr)

31 12 Shifted Composite Curve Process Only F Pinch 6 ( F) fted Temperature Shif F Pinch Duty (BTU/hr)

32 12 Process Only Grand Composite Curve Sh hifted Temperature e ( F) F Refrigeration Duty = 542 BTU/hr -28 F Refrigeration Duty = 453 BTU/hr Duty (BTU/hr)

33 Optimized Composite Curve F) Temperature ( Heat Duty (BTU/hr)

34 New Process Diagram Optimized Process Flow Diagram

35 Summary Perform a full Pinch Analysis and develop your Heat Exchanger Network on your process streams. Then perform a localized Pinch Analysis on each stream that requires utilities in order to achieve the desired outlet temperatures. Know your process, so that you have an idea of what the heat transfer coefficients (U o ) are and the order of magnitude of the possible duty reductions, in order to pick a proper Pinch Temperature(s). Know what your utilities are: Temperatures and available Loads.

36 Summary (cont.) Plot and perform the Pinch Analysis on the Composite Curves, Shifted Composite Curves, and the Grand Composite Curves for the Process Streams only, to maximize process stream energy utilization. Look for Opportunities to eliminate utilities, by adjusting the Pinch Temperature. Look for Opportunities to use lower energy utilities (cooler hot utilities and warmer cold utilities).

37 Thank You!