Page 355 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 6 .2 Gas Turbine Best Practices

1. Scope
The purpose of this specification is to estimate the site shaft horsepower and heat rate for a given set of site conditions.
2. Applicable documents
Figures 6.2.9D–6.2.9F
3. Requirements
3.1 The following site condition must be known:
A. Elevation (ft.)
B. Inlet temperature (°F)
C. Inlet duct pressure loss (inches of water)
D. Exhaust duct pressure loss (inches of water)
4. Procedure
4.1 Read the shaft horsepower (SHP) and heat rate (HR) for the site inlet temperature (from Figure 6.2.9D).
4.2 Read the elevation correction factor (d) for the site elevation (from Figure 6.2.9E).
4.3 Site shaft horsepower:
A. Read the inlet correction factor (Ki) for the site inlet duct pressure loss (from Figure 6.2.9F).
B. Read the exhaust correction factor (Ke) for the site exhaust duct pressure loss (from Figure 6.2.9F).
C. Calculate the site shaft horsepower:
Site SHP = SHP (from Figure 6.2.9D) × × Ki × Ke
4.4 Site heat rate:
A. No elevation correction factor ( ) is used for the heat rate.
B. Read the heat rate correction factor (Kh) from Figure 6.2.9F for the duct pressure loss (sum of site inlet and exhaust duct pressure
losses).
C. Calculate the site heat rate:
Site HR = HR (from Figure 6.2.9E) × Kh
5. Sample calculation
5.1 Assume the following site conditions:
A. Elevation (ft.) 1000 ft
B. Inlet temperature (°F) 59°F
C. Inlet duct pressure loss (inches of water) 3.5 inches of water
D. Exhaust duct pressure loss (inches of water) 4.5 inches of water
5.2 Read the shaft horsepower (SHP) and heat rate (HR) with no inlet or exhaust duct pressure losses for the site inlet temperature (from
Figure 6.2.9D).
59°F site inlet temperature
Shaft horsepower (SHP) 29,200
Heat rate (HR) 7,035 BTU/HP-HR
5.3 Read the elevation correction factor ( ) for the site elevation (from Figure 6.2.9E).
1000 ft. site elevation:
Elevation correction factor ( ) 0.964
5.4 Site shaft horsepower:
A. Read the inlet correction factor (Ki) for the site inlet duct pressure loss (from Figure 6.2.9F).
3.5 inches of water site inlet duct pressure loss:
Inlet correct factor (Ki) 0.9845
B. Read the exhaust correct factor (Ke) for the site exhaust duct pressure loss (from Figure 6.2.9F).
4.5 inches of water site exhaust duct pressure loss: 0.991
Exhaust correction factor (Ke)
C. Calculate the site shaft horsepower:
Site SHP = SHP (from Figure 6.2.9D) × × Ki × Ke
= 20.200 × 0.964 × 0.9845 × 0.991
Site SHP = 27,463
5.5 Site heat rate:
A. Read the heat rate correction factor (Kh) from Figure 6.2.9F for the duct pressure loss (sum of site inlet and exhaust duct pressure
losses).
Duct pressure loss is the sum of 3.5 inches of water site inlet duct pressure loss and 4.5 inches of water site exhaust duct
pressure loss, equaling 8.0 inches of water duct pressure loss:
Heat rate correction factor (Kh) 1.016

B. Calculate the site heat rate:
Site HR = HR (from Figure 6.2.9D) × Kh
= 7,035 × 1.016
Site HR = 7,148 BTU/HP-HR

Fig 6.2.9A-C Typical gas turbine site rating exercise

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