1. Optimization of the Cooling System Operation for CCGTs
Marco Dieleman M&N Power Solutions Ltd., Thailand
Milton Venetos, Wyatt Enterprises LLC, USA
Peter Pechtl, VTU Energy, Austria
Josef Petek, VTU Energy, Austria

2. Summary of Analysis Study
Study and compare designs of cooling systems for CCGT plants
Various commercially available configurations implemented for a SGT800 based plant at a site location in Thailand
For the each cooling system, a studies were run to quantify the average heat rate over the course of the year, for the assumed load dispatch and weather conditions. Once with all pumps and fans in operation, once with the number of fans/pumps optimized.
The study was performed using the EBSILON Professional heat and mass balance software

3. Cooling System Configurations Considered for the Study
A year’s worth of hourly runs (8760 runs) were performed for each of the configurations.
Mechanical Draft Cooling Tower + Water Cooled Condenser
Air Cooled Condenser
Air Cooled Condenser with Inlet Water Spray
Heller System Dry Tower
Heller System Dry Tower with Flue gas integration
Heller System with Air Cooler

4. Cooling System Configurations Considered for the Study (continued)
g. Heller System with Air Cooler + Standard water cooled condenser
Hybrid Cooling Tower with 10, 30 and 50% of the steam going to the dry air cooled side
Plume Abatement Tower with 15, 30 and 45% of the air going through the air cooler
Natural Draft Cooling Tower
Natural Draft Cooling Tower with Flue gas integration
Cooling Pond
The Ebsilon models use a base model that was derived from design information of a real plant, and for the analysis the operating conditions were modified for the cases that were studied

5. Performance runs used to evaluate Plant Performance
The following runs were performed per configuration:
determine capacity at reference site conditions. This case was used to design/size the power plant.
determine fuel consumption, for an assumed yearly dispatch load profile, operating all pumps and fans.
to determine fuel consumption, for the same yearly dispatch load profile, but now with reduced number of pumps or fans, whenever this is more efficient.
Using VTU Energy’s distributed calculations these 8760 runs can be processed in about 15 minutes (on 91 processors). A total of nearly 300 sets of 8760 runs were performed.

6. Load dispatch and weather forecasts used to evaluate Plant Performance
The forecasted load profile for Thailand was based upon a typical daily load profile, super-imposed on a monthly profile, both based upon historical data.
An hourly weather profile was based upon historical data.
For the Thailand profile: The power plant is assumed to have 90M of firm capacity, and 23 MW of non-firm power sales. The 90MW firm capacity was assumed to follow the dispatch profile equal to the variation in electricity sales to the grid. And the 23 MW non-firm power sales and the steam export were both assumed to follow the profile equal to the variation of EGAT’s direct sales figures. A minimum dispatch of 65% was assumed for the firm capacity. The end result was an average dispatch of 81% of the firm capacity plus 70% of the non-firm “capacity”.

7. Assumptions for the cooling systems
For this study, we assumed the following:
3C approach (either to condenser saturation temperature, wet bulb temperature, dry bulb temperature)
2x50% pumps were used at reference site conditions, either 1 or 2 pumps were in operation throughout the year.
3 mechanical draft fans were used at reference site conditions, either 1, 2 or 3 fans were in operation throughout the year.
Cycles of Concentration: 4
Note some configurations have no water, and thus no pumps. Some configurations do not have mechanical draft air flow, and thus no pumps

8. Overall plant simulation model
The overall plant model has 2 SGT800 gas turbines, without chillers or evaporative coolers, 2 2-pressure-level HRSGs and one ST with an extraction for process steam. Note: This is a cooling tower, the block on the right would be replaced depending on the cooling system chosen

9. Overall plant simulation model
2 x 2 x 1 combined cycle plant
SGT800 gas turbine
No inlet air conditioning
2 Pressure Level Unfired Cycle
Horizontal HRSG configuration
Process Steam Export, assumed at a maximum of 40 tonm/hour
Different Cooling Systems

10. Heat balance model of the Cooling System (Mechanical Draft Cooling Tower)
Note: Red lines are steam, blue lines are water, pink line are electrical, green lines are shafts and yellow lines are air
2 Pumps, 3 Fans

11. Heat balance model of the Cooling System (Air Cooled Condenser)
3 Fans

12. Heat balance model of the Cooling System (Air Cooled Condenser with Spray)
3 Fans, Spray On/Off

13. Heat balance model of the Cooling System (Heller System – Dry Tower)
2 Cooling Water pumps. This configuration can also have a single condensate pump, after which a valve regulates the flow to the dry tower vs. the HRSG. In that case some of the energy is recovered in a water turbine. Or you can have a condensate pump, followed by booster condensate pumps.

14. Heat balance model of the Cooling System (Heller System – Dry Tower with Flue Gas )
2 Pumps

15. Heat balance model of the Cooling System (Heller System - Air Cooler)
2 Pumps, 3 Fans

16. Heat balance model of the Cooling System (Heller System – Regular Condenser + Air Cooler)
2 Pumps, 3 Fans

17. Heat balance model of the Cooling System (Hybrid Cooling Tower – ACC + Cond/Mech. Draft CTW)
3 Fans in ACC, 3 Fans in Cooling Tower, 2 Cooling Water Pumps

18. Heat balance model of the Cooling System (Natural Draft Cooling Tower)
2 Pump

19. Heat balance model of the Cooling System (Natural Draft Cooling Tower – With Flue Gas)
2 Pumps

20. Heat balance model of the Cooling System (Cooling Pond)
2 Pumps

21. Heat balance model of the Zero Liquid Discharge – Brine Concentrator + Crystallizer
Alternative options, such as Reverse Osmosis and an Evaporation Pond were not considered.

22. Key design parameters of the base model
Variable Design parameters for the different cooling systems:
Vary design condenser pressure between 80, 100 and 120 mbar
Vary Air to Water ratio between 0.6, 0.8 and 1.0

23. Comparison of overall plant performance for the various cases at RSC
(optimized for design condenser pressure and design air to water ratio)
Note: all cases have the same fuel consumption at Reference Site Conditions (RSC), 33C, 80% RH, (8.5343e8 kJ/hr), so lowest heat rate = highest power
RSC = 33C, 80% relative humidity

24. Comparison of overall plant performance for the various cases, averaged over the year
(optimized for design condenser pressure and design air to water ratio)

25. Comparison of overall plant performance for the various cases, averaged over the year
(optimized for design condenser pressure and design air to water ratio)

26. Impact of adding ZLD on overall plant performance for various cases
(optimized for design condenser pressure and design air to water ratio)

27. Water Consumption and Drain
(optimized for design condenser pressure and design air to water ratio)
Note for Zero Liquid Discharge systems, you would still have makeup water, but no drain

28. Mech. Draft Cooling Tower Mech. Draft Cooling Tower with ZLD
Impact of design condenser pressure and air to water ratio on Heat Rate
Air Cooled Condenser
Mech. Draft Cooling Tower
Mech. Draft Cooling Tower with ZLD

29. Impact of design condenser pressure and air to water ratio on Water Makeup and Drain
Mech. Draft Cooling Tower - Drain
Mech. Draft Cooling Tower - Makeup
Air Cooled Condenser
Mech. Draft Cooling Tower + ZLD - Makeup

30. Impact of design condenser pressure on Heat Rate
Air Cooled Condenser with Spray
ACC with Spray and with ZLD
Heller Dry Tower

31. Impact of design condenser pressure on Water Makeup and Drain
Air Cooled Condenser with Spray
- Drain
Air Cooled Condenser with Spray
- Makeup
Air Cooled Condenser with Spray + ZLD
- Makeup

32. Impact of design condenser pressure on Heat Rate
Heller System with Air Cooler
Hybrid Cooling Tower-30% ACC
Hybrid Cooling Tower-30% ACC with ZLD

33. Impact of design condenser pressure on Water Makeup and Drain
Heller System with Air Cooler
Hybrid Cooling Tower-30% ACC
- Drain
Hybrid Cooling Tower-30% ACC
- Makeup
Hybrid Cooling Tower-30% ACC
- Makeup

34. Impact of design condenser pressure on Heat Rate
Plume Abatement CTW-15% AC
with ZLD
Heller System with Air Cooler and Standard Cond.
Plume Abatement CTW-15% AC

35. Impact of design condenser pressure on Water Makeup and Drain
Heller System with Air Cooler and Standard Cond
Plume Abatement CTW-15% AC
- Drain
Plume Abatement CTW-15% AC
- Makeup
Plume Abatement CTW-15% AC+ ZLD
- Makeup

36. Impact of design condenser pressure on Heat Rate
Plume Abatement CTW-45% AC
with ZLD
Plume Abatement CTW-45% AC
Pond

37. Impact of design condenser pressure on Water Makeup and Drain
Plume Abatement CTW-45% AC
- Drain
Plume Abatement CTW-45% AC
- Makeup
Plume Abatement CTW-45% AC + ZLD
- Makeup

38. Impact of design condenser pressure on Heat Rate
Natural Draft Cooling Tower
with ZLD
Natural Draft Cooling Tower

39. Impact of design condenser pressure on Water Makeup and Drain
Natural Draft Cooling Tower
Natural Draft Cooling Tower
Natural Draft Cooling Tower
with ZLD

40. Heat Rate vs Drain Flow (all units on)

41. Heat Rate vs Makeup Flow (all units on)

42. Heat Rate vs Drain Flow (units optimized)

43. Heat Rate vs Makeup Flow (units optimized)

44. Mechanical Draft Cooling Tower (3 Fans, 2 Pumps)
Selection of Optimal Off-design configuration per hour for various design conditions
Mechanical Draft Cooling Tower (3 Fans, 2 Pumps)
Note that for any size condenser, cooling tower (Higher condenser pressure (smaller condenser size) and lower AWR (smaller cooling tower), in part load, it is beneficial to not run all fans/pumps. So for example for a relatively large condenser and small cooling tower (80mbar, 0.6 AWR), most of the time, you would reduce air flow to about 2/3rd and water to half of the design flow.
This is in part because the plant runs during the course of the year in part load, and in part because the extraction steam is 0 in the design case, but higher during the course of the year, and finally because the reference ambient conditions are somewhat above the average temperature and humidity encountered during the year.
The lower achievable condenser pressure (by running all fans and pumps) is not beneficial for most hours. The benefit of the increased ST power does not balance out the power savings achieved by reducing auxiliary equipment such as fans/pumps.

45. Air Cooled Condenser (3 Fans)
Selection of Optimal Off-design configuration per hour for various design conditions
Air Cooled Condenser (3 Fans)

46. Air Cooled Condenser with Inlet Air Spray (3 Fans, Spray on/off)
Selection of Optimal Off-design configuration per hour for various design conditions
Air Cooled Condenser with Inlet Air Spray (3 Fans, Spray on/off)

47. Dry Heller Tower (2 Pumps)
Selection of Optimal Off-design configuration per hour for various design conditions
Dry Heller Tower (2 Pumps)

48. Heller with Air Cooler (3 Fans)
Selection of Optimal Off-design configuration per hour for various design conditions
Heller with Air Cooler (3 Fans)

49. Heller with Standard Condenser and Air Cooler (3 Fans)
Selection of Optimal Off-design configuration per hour for various design conditions
Heller with Standard Condenser and Air Cooler (3 Fans)

50. Selection of Optimal Off-design configuration per hour for various design conditions
Hybrid with Standard Condenser/CTW (3 Fans/2Pumps) and Air Cooled Condenser (3 Fans)

51. Selection of Optimal Off-design configuration per hour for various design conditions
Hybrid with Standard Condenser/CTW (3 Fans/2Pumps) and Air Cooled Condenser (3 Fans)

52. Selection of Optimal Off-design configuration per hour for various design conditions
Plume Abatement with Standard Condenser/CTW (3 Fans/2Pumps) - 15% Air to Air Cooler

53. Selection of Optimal Off-design configuration per hour for various design conditions
Plume Abatement with Standard Condenser/CTW (3 Fans/2Pumps) – 45% Air to Air Cooler

54. Natural Draft Cooling Tower (2 Pumps)
Selection of Optimal Off-design configuration per hour for various design conditions
Natural Draft Cooling Tower (2 Pumps)

55. Conclusions Highest capacity at RSC: Natural draft CT.
Best yearly average heat rate (all pumps/fans in operation): Natural Draft Cooling Tower.
Best configuration using optimal number of pumps/fans: Natural Draft CT.
Best dry/ZLD configuration, at RSC: Heller Dry tower
Best dry/ZLD configuration using all fans/pumps: Heller Dry tower
Best dry/ZLD confguration using optimal number of pumps/fans: Natural Draft CT with ZLD & Heller Dry Tower
Best possible improvement of heat rate when optimizing pumps/fans operation: % for the Air cooled Condenser with Inlet Air Spray option

56. Conclusions (continued)
Minimum improvement of heat rate when optimizing pumps: 0.21% for the natural draft cooling tower
The optimal design pressure is a clear function of the configuration
The optimal heat rate over the year and the optimal capacity are not necessarily at the same design pressure
If simply turning fans/pumps equipment on/off, then a variable speed drive for the fans or variable speed pumps would be able to provide even more benefits

57. Conclusions (continued)
Further optimization parameters are: AWR ratio (this was only tested at several intervals), pinch point (currently 3C), design pressure, (this was only tested at several intervals)
Given the large variation in loads and temperatures, an entire year's worth of part load points is required to provide narrow down the accurate design options, as was done in this study.
Regardless of the configuration or design pressure or air to water ratio, part load optimization of either pump of fan operation will almost always be beneficial for heat rate.

58. Conclusions (continued)
Flue gas added to Heller or Natural draft tower, does not add much to the performance, but it reduces the tower design height for the same performance.
Accurate weather projections and dispatch profiles will have to be known, to estimate the fuel savings which can be achieved.

59. Questions?
In case of questions, don’t hesitate to contact the author at: