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Performance Evaluation of A Steam Generator
P M V SubbaraoProfessor
Mechanical Engineering Department
A Measure of Efficient Combustion …..
First Law Analysis of Furnace at Site
• CXHYSZOK + 4.673 (X+Y/2+Z-K/2) AIR + Moisture in Air + Ash Moisture in fuel→ P CO2 +Q H2O +R SO2 + T N2 + U O2 + V CO + W C + Ash
• Mass of air: *4.673* (X+Y/2+Z-K/2) *28.89 kg.
• Mass of Coal: 100 kg.
• Excess Air: -1)4.673* (X+Y/2+Z-K/2) *28.89 kg.
Fuel of Mass
Air of Mass RatioFuelAir
CXHYSZOK + 4.673 (X+Y/2+Z-K/2) AIR + Moisture in Air + Ash + Moisture in fuel→ P CO2 +Q H2O +R SO2 + T N2 + U O2 + V CO + W C + Ash
First Law Analysis of Furnace:SSSF
Conservation of Mass:
m fuel
m air
m fluegas
Q
Q
Wfans0
ashfluegasfuelair mmmmm ash
CV
ashfluegas
fuelair
CV
WgzV
hmgzV
hm
gzV
hmgzV
hmQ
22
22
22
22
First Laws for furnace in SSSF Mode:
Flue Gas Analyzer
Ps CO2 +Qs H2O +Rs SO2 + Ts N2 + U sO2 + Vs CO
Measurements of Gas Analyser
• Dry Exhaust gases: Ps CO2 +Rs SO2 + Ts N2 + Us O2 + Vs CO kmols.
• Volume of gases is directly proportional to number of moles.
• Volume fraction = mole fraction.
• Volume fraction of CO2 : x1 = Ps * 100 /(Ps +Rs + Ts + Us + Vs)
• Volume fraction of CO : x2= V s* 100 /(Ps +Rs + Ts + Us + Vs)
• Volume fraction of SO2 : x3= Rs* 100 /(Ps +Rs + Ts + Us + Vs)
• Volume fraction of O2 : x4= U s* 100 /(Ps +Rs + Ts + Us + Vs)
• Volume fraction of N2 : x5= T s* 100 /(Ps +Rs + Ts + Us + Vs)
• These are dry gas volume fractions.
• Emission measurement devices indicate only Dry gas volume fractions.
Analysis of Ash & Measurement of UC
100
AshUC
UC
mm
mR
• Measurements:
• Volume flow rate of air.
• Volume flow rate of exhaust.
• Dry exhaust gas analysis.
• x1 +x2 +x3 + x4 + x5 = 100 or 1
• Ultimate analysis of coal.
• Combustible solid refuse.
nCXHYSZOK +n 4.673 (X+Y/4+Z-K/2) AIR + Moisture in Air + Ash & Moisture in fuel
→ x1 CO2 +x6 H2O +x3 SO2 + x5 N2 + x4 O2 + x2 CO + x7 C + Ash
Moisture due to Combustion air
OHsat
OHact
p
pRH
2
2
,
, atmOHair
OHOHact p
nn
np
2
2
2,
OHair
OHOHsat nn
npRH
2
2
2,
atmOHOHairOHsat pnnnpRH 222,
OHsatatm
airOHsatOH pRHp
npRHn
2
2
2
,
,
OHsatatm
OHsat
airOH pRHp
kz
yxnpRH
n2
2
2
,
,
,
24673.4
Moisture due to fuel
18,2
Mnn fuelOH
nCXHYSZOK +n 4.76 (X+Y/4+Z-K/2) AIR + Moisture in Air + Ash & Moisture in fuel → x1 CO2 +x6 H2O +x3 SO2 + x5 N2 + x4 O2 + x2 CO + x7 C + Ash
•x1, x2,x3, x4 &x5 : These are dry volume fractions or percentages.
•Conservation species:
•Conservation of Carbon: nX = x1+x2+x7
•Conservation of Hydrogen: nY = 2 x6
•Conservation of Oxygen : nK + 2 n (X+Y/4+Z-K/2) = 2x1 +x2 +2x3 +2x4+x6
•Conservation of Nitrogen: n 3.76 (X+Y/4+Z-K/2) = x5
•Conservation of Sulfur: nZ = x3
nCXHYSZOK +n 4.76 (X+Y/4+Z-K/2) AIR + Moisture in Air + Ash & Moisture in fuel → x1 CO2 +x6 H2O +x3 SO2 + x5
N2 + x4 O2 + x2 CO + x7 C + Ash
• Re arranging the terms (Divide throughout by n):
CXHYSZOK + 4.76 (X+Y/4+Z-K/2) AIR + Moisture in Air + Ash & Moisture in fuel → (x1 /n)CO2 +(x6/n) H2O +(x3/n)
SO2 + (x5/n) N2 + (x4/n) O2 + (x2/n) CO + (x7/n) C + Ash
CXHYSZOK + 4.76 (X+Y/4+Z-K/2) AIR + Moisture in Air + Ash Moisture in fuel
→ P CO2 +Q H2O +R SO2 + T N2 + U O2 + V CO + W C + Ash
Specific Flue Gas Analysis
• For each kilogram of fuel:• Air : 4.76 (X+Y/2+Z-K/2) * 29.9 /100kg.
• CO2 : P * 44/100 kg.
• CO : V * 28/100 kg.
• Oxygen in exhaust : 32 * U/100 kg.
• Unburned carbon: 12*12/100 kg.
Various Energy Losses in A SG
• Heat loss from furnace surface.• Unburned carbon losses.• Incomplete combustion losses.• Loss due to hot ash.• Loss due to moisture in air.• Loss due to moisture in fuel.• Loss due to combustion generated moisture.• Dry Exhaust Gas Losses.
•Heat loss from furnace surface.
•Unburned carbon losses.
•Incomplete combustion losses.
•Loss due to hot ash.
•Loss due to moisture in air.
•Loss due to moisture in fuel.
•Loss due to combustion generated moisture.
•Dry Exhaust Gas Losses
•~ 4.5%
Heat gained by superheater & reheater
40%
Heat gained by economizer & air preheater
12%
Fuel Energy100%
Heat gained by boiling water40%
Hot gas
Flue gas
Energy Credits
• Chemical Energy in the fuel.
• Energy credit supplied by sensible heat in entering air (recycling of energy).
• Energy credit supplied by sensible heat in the fuel(Recycling of energy).
• Energy credit supplied by auxiliary drives.
Furnace Energy Balance
• First Laws for Furnace in SSSF Mode (in molar form):
Q +n air hair + n fuel hfuel = n fluegas hfluegas + W
n fuel
n air
n fluegas
Q
Q
Wfans