How to calculate the specific fuel consumption of Power plant??

Specific Fuel Consumption (SFC) in Power Plants refers to the amount of fuel required to generate a unit of energy output. It is a key performance metric used to assess the efficiency of different power generation systems.

Specific fuel consumption (SFC)= Fuel consumption in kg/hr / Power generation in Kwh

Specific fuel consumption (SFC)= Specific steam consumption (SSC) / Steam to fuel ratio (SFR)

Factors affecting the Specific fuel consumption:

1-Steam consumption of the Turbine: Higher steam consumption of steam Turbine leads to more Specific fuel consumption (SFC).

2-Main steam parameters like pressure & temperature: Should be always on higher side but within design limit.

3-Boiler efficiency: High efficiency boilers consumer lesser fuel and hence Specific fuel consumption (SFC) will be on lower side.

4-Turbine efficiency: High efficiency Turbines will have higher out put on lesser input, hence Specific fuel consumption (SFC) of such Turbines is LESS

5-Fuel type & quality: High GCV fuel firing power plants will have lesser Specific fuel consumption (SFC).

6-Boiler operator competency: Efficient Operation of the Boiler, Turbine and other power plant equipment depends on the skill & competency of the operators.

7-Plant load factor: Operation of the Power plant units on higher loads or optimised loads leads to lower Specific fuel consumption (SFC) & Vice Versa, that is operation of plant on partial loads results into more fuel consumption and hence leads in more Specific fuel consumption (SFC).

8-Atmospheric conditions: Atmospheric conditions like temperature, pressure & humidity play a very vital role on achieving best efficiency of power plant equipment.

Specific fuel consumption (SFC) is also termed in terms of heat rate.

Heat rate = Energy consumed in kcal/ Power generation

It is measured in terms of kcal/kwh

Specific fuel consumption (SFC) is different for different fuels, fuels having higher heating value or calorific value will have lesser Specific fuel consumption (SFC) & fuels having lower calorific value will have higher specific fuel consumption.

It’s always recommended that Specific fuel consumption (SFC) should LESS.

Power plants having lesser Specific fuel consumption (SFC) are in more profit.

How to calculate the specific fuel consumption???

Specific steam consumption (SSC) is the amount of steam consumed by Turbine is always lesser to achieve lesser Specific fuel consumption (SFC). It’s measured in kg/kwh or MT/MW.

Similarly, Stam to fuel ratio (SFR) is the amount of steam generated on burning 1 MT or 1 Kg of fuel. It’s measured in kg/kg or MT/MT.

Examples:

1-Calculate the specific steam consumption of a 50 MW thermal power plant, which consumes around 960 MT of coal to generate 1200 MW power.

Given data,

Power generation = 1200 MW

Fuel consumed = 960 MT

Specific fuel consumption (SFC)= Fuel consumption in kg/hr / Power generation in Kwh

Specific fuel consumption (SFC)= 960/1200 =0.8 kg/kwh or 0.8 MT/MW

2-A 225 MW Thermal power plant’s steam turbines Specific steam consumption (SSC) is 3.5 MT/MW and it’s Boiler’s Steam to fuel ratio (SFR) is 4.5. Calculate the specific steam consumption of that plant

Given data,

Specific steam consumption (SSC) = 3.5

Stam to fuel ratio (SFR) = 4.5

Specific fuel consumption (SFC)= Specific steam consumption (SSC) / Steam to fuel ratio (SFR)

Specific fuel consumption (SFC)= 3.5/4.5 =0.78 Kg/kwh or 0.78 MT/MW

3-A Boiler consumes 25 MT of bio mass to generate 55 MT of steam per hour at pressure 67 kg/cm2 and temperature 490 deg C, which is used to run the 12 MW condensing Turbine. What would be the specific fuel consumption of this plant?

Given data,

Fuel consumption = 25 MT

Steam generated = 50 TPH

Power generation = 12 MW

Steam to fuel ratio (SFR) = Steam generated per hour / Fuel consumed per hour

Steam to fuel ratio (SFR) = 55 / 25 =2.2

Specific steam consumption (SSC) = Steam consumption by Turbine TPH / Power generated in MW

Specific steam consumption (SSC) = 50 / 12

Specific steam consumption (SSC) = 4.16 MT/MW

Specific fuel consumption (SFC)= Specific steam consumption (SSC) / Steam to fuel ratio (SFR)

Specific fuel consumption (SFC)= 4.16 / 2.2 =1.89 MT/MW

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How to convert gas flow from M3/hr to Nm3/hr and Sm3/hr???

 

How to convert M3/hr to NM3/hr and Sm3/hr

How to convert Nm3/hr to SM3/hr and M3/hr

 

In order to understand the above, need to understand the basics of STP & NTP

STP - Standard Temperature and Pressure

STP is commonly used to define standard conditions for temperature and pressure of air or gases.

As per IUPAC STP is  air at 0 ^oC (273.15 K, 32 ^o F) and 10 ⁵ pascals (1.03 kg/cm2).

 As per  Imperial and USA system of units STP is air at 60 ^o F (520 ^o R, 15.6 ^oC ) and 14.696 psia (1 atm,  1.01325 bara)

Note! The earlier IUAPC definition of STP to 273.15 K and 1 atm (1.03kg/cm2) is discontinued. 

NTP - Normal Temperature and Pressure

NTP is commonly used  as a standard condition  for testing and documentation of fan capacities:

NTP - Normal Temperature and Pressure - is defined as air at 20 oC (293.15 K, 68 o F) and 1 atm ( 101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 29.92 in Hg, 407 in H2O, 760 torr). Density 1.204 kg/m 3 (0.075 pounds per cubic foot)

 

In order to convert M3/Hr to NM3/hr, we use below formula

PaVa/Ta = PnVn/Tn

Vn = PaVaTn / TaPn

Where, Pa, Va & Ta are air parameters at actual condition

Pn,Vn & Tn are air parameters at Normal condition

In order to convert M3/Hr to SM3/hr, we use below formula

PaVa/Ta = PsVs/Ts

Vs = PaVaTs / TaPs

Where, Pa, Va & Ta are air parameters at actual condition

Ps,Vs & Ts are air parameters at Normal condition

In order to convert NM3/Hr to SM3/hr, we use below formula

PnVn/Tn = PsVs/Ts

Vs = PnVnTs / TnPs

Pn,Vn & Tn are air parameters at Normal condition

Ps,Vs & Ts are air parameters at Normal condition

Solved examples:

1-A 25 m3/sec capacity forced draft fan  discharges air at 250 mmwc static pressure and 30 deg C temperature, calculate the air flow at Nm3/hr and Sm3/hr

Pa = 250mmwc = 250/10000 = 0.025 kg/cm2

Va = 25 m3/sec

Convert it into M3/hr = 25 X 3600 = 90000 m3/hr

Ta = 30 + 273.15 = 303.15 K

Tn = 20 + 273.15 = 293.15 K

Ts = 15.6 + 273.15 =288.75 K

We have the formula

PaVa/Ta = PnVn/Tn

Vn = PaVaTn / TaPn

Vn = ((0.0025+1.033) X 90000 X 293.15) / (303.15 X 1.033)

Vn =89137.445 NM3/hr

Similarly

PaVa/Ta = PsVs/Ts

Vs = PaVaTs / TaPs

Vs =(0.025+1.033) X 90000 X 288.75) / (303.15 X 1.033)

Vs = 87,799.54 Sm3/hr

Now convert Nm3/hr to SM3/hr to cross check the flow

PnVn/Tn = PsVs/Ts

Vs = PnVnTs/TnPs

Vs =1.033 X 89137.445 X 288.75 / (293.15 X 1.033)

Vs = 87,799.54 Sm3/hr

2-A boiler of 100 TPH produces flue gas 27 MT/hr of flue gases at pressure 350 mmwc (ID fan inlet) and 145 deg C temperature, calculate the flue gas flow in Nm3/hr  and Sm3/hr

Given data,

Flue gas flow = 27MT/hr = 27 X 1000 = 27000 kg/hr

Convert to M3/hr

Density of flue gas at 145 deg C temperature = 1.293 X 273.15 / (273.15 + 145) = 0.84 kg/m3

Flue gas flow in M3/hr = 27000 kg/hr / 0.84 kg/m3 = 32142.85 M3/hr

Pa = 350 mmwc = 350 / 10000 =(1.033+ 0.035=1.068 kg/cm2)

Ta = 273.15 + 145 = 418.15 K

We have,

PaVa/Ta = PnVn/Tn

Vn = 1.068 X 32142.85 X (20 + 273.15) / (418.15 X 1.033)

Vn = 23,297.70 Nm3/hr

Similarly,

PaVa/Ta = PsVs/Ts

Vs =1.068 X 32142.85 X (15.6 + 273.15) / (418.15 X 1.033)

Vs = 22,948.01 Sm3/hr

Now convert Nm3/hr to SM3/hr to cross check the flow

PnVn/Tn = PsVs/Ts

Vs = PnVnTs/TnPs

Vs =1.033 X 23297.70 X 288.75 / (293.15 X 1.033)

Vs = 22,948.015 Sm3/hr

 

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How to calculate the quantity of lime stone required to reduce SO2 emission ??

We know that, Lime stone is nothing but Calcium carbonate (CacO3)

 

Lime stone (CaCo3) on heating gets converted into slaked lime and carbon dioxide

 

i.e,

CaCo3 + Heat = Cao + Co2

Shall calculate, quantity of CacO3 required for converting into Cao.

Molecular weight of Ca = 40 g/mol

Molecular weight of Oxygen = 16 g/mol

Molecular weight of Carbon = 12 g/mol

Molecular weight of Sulphur = 32 g/mol

Sulphur on heating gets converted into Sulphur di-oxide (SO2)

Therefore we have,

CaCo3 + Heat = Cao + CO2

(40+12+3X16) + Heat = (40+16) + (12+2X16)

100 + Heat           = 56 + 44

1 + Heat = 0.56 + 0.44-----------I

This implies, 1 kg of calcium carbonate (CaCO3) on heating gets converted into 0.56 kg of slaked lime & 0.44 kg of CO2

Further,Sulphur present in coal, on combustion gets converted into sulphur dioxide (SO2)

Shall calculate, quantity of SO2 generated on combustion of 1 kg of sulphur

 

S + O2 = SO2

32 + 2X16 = 32+2X16

32 + 32 = 64

1 + 1 = 2-----II

This means, 2 kg of SO2 will produce on combustion of 1 kg of sulphur.

Further,Slaked lime (Cao) reacts with Sulphur dioxide (SO2) & converts into Calcium sulphate (CaSO4)

i.e

Cao + SO2 + O2 = CaSO4

(40+16) + (32 + 2X16) + 16 = (40+32+4X16)

56 +(32 + 2X16) + 16 = 136

56 + 64 + 16 = 136

0.875 + 1 + 0.25 = 2.12------III

This means, 1 kg of So2 needs 0.875 kg of Cao to produce  2.42 kg of Calcium sulphate

i.e, On burning 1 kg of sulphur there produces 2 kg of SO2 (refer equation-II), hence Cao required to reduce sulphur from 1 kg So2 = 2 X 0.875 = 1.75 kg

Similarly referring equation-I, 1 kg of calcium carbonate (CaCO3) on heating gets converted into 0.56 kg of slaked lime(Cao)

Therefore  lime stone required for 1 kg sulphur to convert it into CaSO4 is;

 

1.75/0.56 = 3.125 kg

Considering 95% efficiency for above combustion, total lime stone required for 1 kg sulphur to get converted it into CaSo4 is;

3.125 X 105% = 3.28 kgs-------IV

 

Demonstration with example.

A 50 MW coal based power plant has specific fuel consumption 0.75 kg/kwh.The sulphur content in the coal is 0.75%, the maximum permissible limit of sulphur in the coal is 0.5%.Calculate the amount of lime stone required to reduce SO2 emission.

 

Assuming SO2 emission at 0.5% sulphur in coal is normal.

Extra % of sulphur in coal is = 0.75-0.5 = 0.25%

Coal consumption per day

Specific fuel consumption = 0.75 kg/kwh

Total power generation in a day = 50 X 1000 X 24 = 1200000 kw

Total coal consumption = 1200000 X 0.75 / 1000 = 900 MT/day

Extra Sulphur burned  = 900 X 0.25% = 2.25 MT or 2250 kg/day

Lime stone required to reduce SO2 emission is 2250 X 3.28 = 7380 kg (refer equation-IV)

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What is the significance of Drain cooler approach (DCA)??

 

In the context of feed water heaters, "DCA" could stand for "Drain Cooler Approach." The drain cooler approach in feed water heaters is a parameter that represents the temperature difference between the temperature of the extracted steam and the temperature of the drain (condensate) leaving the feed water heater.

 

Feed water heaters are devices used in power plants to preheat the water before it enters the boiler. The heat for this preheating process comes from extracting steam from various stages of the turbine. The drain cooler approach is a key parameter to monitor and control because it affects the overall efficiency of the power plant.

 

A lower drain cooler approach means that more heat is transferred from the extracted steam to the feed water, increasing the overall efficiency of the power plant. It's an important factor in designing and operating feed water heaters to optimize the thermal performance of the power generation system.

 

DCA is the temperature difference between the drains (steam condensate) leaving the heater and the temperature of feed water entering the heater. For more cycle efficiency TTD value should be small.

 

 Significance of DCA. 

1-It gives the feed back on performance of heat exchanger

2-Higher TTD is nothing but thee is more difference between saturation temperature of steam and feed water leaving the heater.This indicates the poor performance of heater.Similarly lower TTD is nothing but thee is small difference between saturation temperature of steam and feed water leaving the heater.This indicates the good heat transfer between steam and feed water & hence there is better performance of heater

3-The concept of "temperature approach" is closely related to ΔT. The temperature approach is the difference between the temperature of the hot fluid and the temperature of the cold fluid at the end of the heat exchanger. A smaller temperature approach is often desired to maximize heat transfer efficiency, but it is limited by practical considerations.

4-the terminal temperature difference is a key parameter in the analysis, design, and optimization of heat exchange systems. It plays a vital role in determining heat transfer rates, efficiency, and the size of heat exchangers, ultimately impacting the performance and cost of thermal systems in various engineering applications

5-Station heat rate will improve

6-Cycle efficiency will increase

7-Less steam consumption for feed water heating

Click here to know about Terminal temperature difference in feed water heaters

Calculation of DCA

1-A HP heater is used to heat the feed water from 170 °C to 190 °C by using turbine bleed steam at 17 kg/cm2 and 340 °C. The condensate returning from heater is at 180 °C, calculate the DCA of heater.

We have,

DCA = Temperature of condensate leaving the heater – Temperature of feed water entering the heater

DCA = 180 - 170 = 10 °C

Note: For best performance, heaters are designed to get DCA 3 to 5 °C at full operation capacity.

 

2-A LP heater is used to heat the feed water from 55 °C to 70 °C by using turbine extraction steam at 1.1 kg/cm2 and 125 °C. The condensate returning from heater is at 75 °C, calculate the DCA of heater.

We have,

DCA = Temperature of condensate leaving the heater – Temperature of feed water entering the heater

DCA = 75 - 55 = 20 °C

Note: For best performance, heaters are designed to get DCA 3 to 5 °C at full operation capacity.

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