Boiler Classification on the basis of temperature and pressure and Cost/kWh (Fuel Cost) for a Coal Fired Power Plant

1. 1. BOILER CLASSIFICATION
2. COST /kWh

2. Get Idea about
Different Temperature
and Pressure Ratings
and their effects on
Power Plants
Economics
Calculation of Fuel
Cost per Unit of
Electricity Produced

3. BOILER CLASSIFICATIONS
 Mentioning Two circulating Fluidized Bed Boilers of
same capacity having different temperatures and
Pressures ratings
 Boiler-1: High Temperature and Pressure CFBC
Steam Generating Capacity : 130 Tons/ Hour
Rated Evaporation Pressure : 8.43 Mpa (84.3
Bar)
Rated Evaporation Temperature : 515 C

4.  Boiler-2: Medium Temperature and Pressure
CFBC
Steam Generating Capacity: 2 x 65 Tons / Hour
Rated Evaporation Pressure: 3.82 Mpa ( 38.4
Bar)
Rated Evaporation Temperature: 450 C

5.  At what temperature and Pressure limits boilers are
classified whether they are
i. Low temperature and Low Pressure
ii. Medium temperature and Medium Pressure
iii. High temperature and High Pressure
 Advantages and Disadvantage associated with both
sort of configuration for a 25 MW Power Plant

6. CLASSIFICATION ON THE BASIS OF PRESSURE
As per ASME code, Boilers are classified into two basic
classes
 Low Pressure Boiler: Pressure is below 15 Psi
 High Pressure Boiler: Pressure is above 15 Psi.
High Pressure Boilers are further classified in to Sub
Critical, Supercritical and Ultra Super Critical
 Sub-Critical (Operated around 19 Mpa):
Example: 170 bar, 540 C, Efficiency: 38 %
 Super-Critical (Operated above 22.1 Mpa):
Example: 250 bar, 600/615 C, Efficiency: 42 %
 Ultra Super-Critical:
Example: 300 bar, 615/630 C, Efficiency: 44 %

7. POWER PLANT USING BOTH CONFIGURATIONS
25 MW Power Plants Using Boiler - 1
 Steam in Kg / kWh around 3.9 to 4.0 at 6000 kcal / kg of
Coal with 1 % Sulphur
 Net Thermal Efficiency of around 24 %
 Have high Cost of Boiler and Turbine due to high pressure
 Have long pay back opportunities
25 MW Power Plants Using Boiler – 2
 Steam in Kg / kWh around 4.5 to 5.0 at 6000 kcal / kg of
Coal with 1 % Sulphur
 Net Thermal Efficiency around 22.5 to 22.8 %
 Have low Cost of Boiler and Turbine due to low pressure
 Better control over low electrical load equipments
 Low initial Cost

8. COST / kWh ?
Plant Capacity : 25 MW
Auxiliary Consumption: 9 % of the rated
Efficiency:
Boiler : 88 %
Turbine : 35 %
Other : 78.5 %
i. GCV of Coal : 6500 kcal / kg (Foreign Coal)
ii. GCV of Coal : 4600 kcal / kg (Local Coal)

9. FOR FOREIGN COAL
 Calorific Value of Coal:
3600 kJ = 1 kWh = 856 kcal
6500 kcal / kg = 27336 kJ / kg
 Net Thermal Efficiency:
Efficiency = 0.88 x 0.35 x 0.78
= 24 %
 Heat Rate:
Heat Rate = 3600 / Efficiency
Heat Rate = 3600/ 0.24 = 15000 kJ/ kWh

10.  Power Input:
Pin = Pout / Efficiency
Pin = 25, 000, 000 / 0.24
Pin = 104166 kW
 Coal Consumption:
= Pin/ GCV
= 104166/ 27336
= 3.81 kg / Sec
Consumption = 13. 71 metric Tons /Hour

11.  Cost/ kWh: (For Foreign Coal)
1.0 Ton = Rs 17,000. 00
13.71 Tons = Rs 233, 070.00
Energy Produced = 25, 000 kWh
Auxiliary Power = 9 % of 25, 000 kWh
Net Available Power = 22,750.00 kWh
Cost / kWh = Net Units available / Cost of
Coal
= 22, 750.00/233, 070.00
Cost / kWh = Rs 10. 244

12. FOR LOCAL COAL
 Calorific Value of Coal:
3600 kJ = 1 kWh = 856 kcal
4600 kcal / kg = 19345.8 kJ / kg
 Net Thermal Efficiency:
Efficiency = 0.88 x 0.35 x 0.78
= 24 %
 Heat Rate:
Heat Rate = 3600 / Efficiency
Heat Rate = 3600/ 0.24 = 15000 kJ/ kWh

13.  Power Input:
Pin = Pout / Efficiency
Pin = 25, 000, 000 / 0.24
Pin = 104166 kW
 Coal Consumption:
= Pin/ GCV
= 104166/ 19345.8
= 5.3844 kg / Sec
Consumption = 19.4 Tons /Hour

14.  Cost/ kWh: (For Local Coal)
1.0 Ton = Rs 10,000. 00
19.4 Tons = Rs 194, 000.00
Energy Produced = 25, 000 kWh
Auxiliary Power = 9 % of 25, 000 kWh
Net Available Power = 22,750.00 kWh
Cost / kWh = Net Units available / Cost of
Coal
= 22, 750.00/ 194, 000.00
Cost / kWh = Rs 8.53

15. LOCAL Vs FOREIGN COAL
 Cost / kWh for Foreign Coal: Rs 10.244
 Cost / kWh for Local Coal: Rs 8.53
 Difference = 10 . 244 – 8.53
= Rs 2.714 / kWh
If Local Coal is used then money saved in
Hour = 2.714 x 22750 = Rs 61,743.50
Day = 61,743.50 x 24
= 1.481844 million Rupees
Year = 270 x 1.481844 = 400.1 million Rupees