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Energy Balance for Power, Heat, Cooling

September 27th, 2011 Posted in Trigeneration and Cogeneration

Energy Balance for Power, Heat, Cooling

Addressing climate change and global warming needs effective counter measures such as reducing GHG emission from carbon dioxide emitted by fossil-fired power plants.

Using tri-generation systems is one effective measure that could be used to reduce fuel consumption  as it increases energy utilization efficiency from the traditional 33% for Rankin steam cycles (oil, gas, coal thermal) to 54% for combined cycle gas turbine (CCGT) to tri-generation (power, heat, cooling) that could utilize as much as 85% of the fossil energy.

When the simultaneous provision of power, process heat and space cooling or refrigeration is required in an industry and commercial building such as hotels, hospitals, office buildings and computer data centers, then tri-generation sytems is a good investment as it offers cost and energy saving to the building owner and the country.

Your energy technology expert has prepared an easy-to-use Excel model for preparing an energy balance for power, heat, chilled water (tri-generation) and co-generation (power, heat) system

The equations are as follows:

1 Btu = 3600 / 1.05506 = 3412.12822 kWh

1) Main Fuel = xxx.xx MMBtu/hr = (fuel quantity, kg/hr) x (gross heating value, Btu/kg) x (MMBtu/10^6 Btu)

2) Auxiliary Fuel = xxx.xx MMBtu/hr

3) Imported Power = xxx.xx kWh/hr = yyy.yy MMBtu/hr

4) Total Energy Input = Main Fuel + Auxiliary Fuel + Imported Power

5) Power Output of Generator 1 = (30% efficiency) x Main Fuel

6) Generator 1 Losses (gear box, clutch, windage) = (Power Output of Generator 1) x 2% / (100% – 2%)

7) Total Heat Energy Supply = (100% – 30%) x Main Fuel + Auxiliary Fuel

8) Duct Losses before HRSG 1 = 2% x (Total Heat Energy Supply)

9) Energy Input to HRSG 1 = (100% – 2%)  x (Total Heat Energy Supply)

10) Steam Output of HRSG 1 (80% boiler efficiency) = 80% x (Energy Input to HRSG 1)

11) Energy Loss from HRSG 1 = (100% – 20%) x (Energy Input to HRSG 1)

12) Shaft Power to Generator 2 (42% steam turbine efficiency) = 42% x Steam Output of HRSG 1

13) Steam Turbine Loss = (100% – 42%) x Steam Output of HRSG 1

14) Generator 2 Losses  (gear box, clutch, windage) = 2% x (Shaft Power to Generator 2)

15)  Power Output of Generator 2 = (100% – 2%) x (Shaft Power to Generator 2)

16) Power Input to Electric Centrifugal Chiller = (0.9 kWh/TRh) x (Chilled Water Demand 1, TRh/hr)

17) Parasitic Load of System = xxx.xx kWh/hr

18) Total Electrical Load (kWh/hr) = Power Input to Electric Centrifugal Chiller + Parasitic Load of System

19) Energy Input to Absorption Chiller = (0.4 kWh/RTh) x (Chilled Water Demand 2, TRh/hr)

20) Imported Power + Power Output of Generator 1 +  Power Output of Generator 2 =Total Electrical Load

21) Total Energy Losses =  Duct Losses before HRSG 1 + Energy Loss from HRSG 1 + Steam Turbine Loss + Generator 1 Losses + Generator 2 Losses

22) Total Heat Energy Supply = Energy Input to Absorption Chiller + Total Energy Losses

After making the above calculations, the energy balance is presented as follows:

 

Total Energy Input:

Fuel energy input to the Gas Turbine
Imported power from grid
Fuel energy to auxiliary boiler

 

Total Energy Output:

Surplus power to grid (export sales)
Power losses (gear box, clutch, Generator 1 windage)
Power losses (gear box, clutch, Generator 2 windage)
Duct Losses before HRSG 1
HRSG 1 losses to atmosphere (stack)
Power  consumption of Centrifugal Chiller
Parasitic Load
Energy Input to Absorption Chiller
Steam Turbine losses

 

Cheers,

The energy technology expert.

 

 

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