MANE 6980: Third Progress Report November 21, 2013 Stephanie Barnes

1. Using Pinch Analysis to Optimize the Heat Exchanger Network of a Regenerative Rankine Cycle for an Existing Modern Nuclear Power Plant MANE 6980: Third Progress Report November 21, 2013 Stephanie Barnes

2. Background • Millstone Unit III Power Plant • Regenerative Rankine Cycle • Consists of a steam generator, high pressure turbine, three low pressure turbines, condensers, six feedwater heaters, feed pumps • Condensate is reheated using the heat exchanger network (feedwater heaters) to improve plant efficiency

3. Pinch Analysis • Optimize a power plant by using the heat energy from the streams, instead of using external heating and cooling methods (heat exchanger, furnace, cooler, etc.), to increase the thermal efficiency of the plant and minimize energy costs

4. Problem Statement • Analyze a Regenerative Rankine Cycle, based on the Millstone Unit III heat balance, using pinch analysis techniques. • Determine the pinch point and minimum hot and cold utilities. • Evaluate retrofit methods and recommend improvements to the heat exchanger network to improve plant efficiency.

5. Methodology • Data Extraction: Performed a simplified analysis using 7 streams (1 cold from the condenser to the steam generator and 6 hot streams (1 for each feedwater heater in the current design)). • Obtain the Heat Capacities, Problem Table, Composite Curves, and Heat Cascade

6. Results • Determined the pinch point and hot and cold utility requirements for the Millstone Unit III heat exchanger network (HEN), using the problem table and heat cascade (shown). • The minimum hot and cold utility requirements are 1,641 MBtu/hr and 370,852 MBtu/hr, respectively, as determined by the software and 1,642 MBtu/hr and 371,225 MBtu/hr as determined by hand calculations.

7. Results - Cont. • Shifted Hot and Cold Composite Curves • Curves touch at the pinch point • External Utilities determined by the gaps between hot and cold curves at the endpoints

8. Results - Cont. • Grand Composite Curve • Combined Hot and Cold Composite Curves • Can determine the minimum external utilities (x-axis) and the associated temperatures at the endpoints of the curve. • Pinch temperature is the point where net heat flow is equal to zero.

9. Results - Cont. • Determined the optimal minimum temperature difference between the hot and cold streams is 50 F based on external utility requirements.

10. Results - Cont. • Evaluated 10 additional cases to determine the effect of the number of heat exchangers and the supply and target temperatures on the external utilities. • Case11 provided the most significant decrease in the cold utility requirement. • Deleting the 5th and 6th point heaters decreased the cold utility requirement from 370,852 MBtu/hr to 37,228 MBtu/hr, as determined by the software, while keeping the hot utility at 1,641 MBtu/hr. • To provide adequate cost savings, it is recommended that the 5th and 6th point heaters be deleted and the exhaust from the turbines that enters the 5th and 6th point heaters be directed elsewhere, such as the main condenser.

11. Project Schedule • Continue to work on the report and analysis based on advisor’s comments.