Modelling of Combustion & Heat Transfer Effects in A Rankine Cycle
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Transcript of Modelling of Combustion & Heat Transfer Effects in A Rankine Cycle
Modelling of Combustion & Heat Transfer Effects in A Rankine Cycle
Modelling of Interactions between Source of Power & Steam Power ……
P M V SubbaraoProfessor
Mechanical Engineering Department
I I T Delhi
Fuel Model
Analysis of Fuel
• Proximate Analysis & Ultimate Analysis.• Proximate analysis - to determine the moisture, ash,
volatiles matter and fixed carbon• Ultimate or elementary analysis - to determine the
elemental composition of the coal• The Energy content -- CFRI Formulae --• Low Moisture Coal(M < 2% ) -- CV (Kcal/kg) = 71.7 FC + 75.6
(VM-0.1 A) - 60 M• High Moisture Coal(M > 2%) -- CV(kcal.kg) = 85.6 {100 -
(1.1A+M)} - 60 M
• Where, M, A, FC and VM denote moister, ash , fixed carbon and Volatile mater (all in percent), respectively.
Fuel Model
• Ultimate Analysis of fuel: Gravimetric : • Percentage of carbon : x --- Number of k moles, X = x/12• Percentage of combustible hydrogen : y --- Number of
atomic kmoles
Percentage of sulfur: z – Number of atomic kmoles, Z = z/32Equivalent chemical formula : CXHYSZOK
Equivalent Molecular weight : 100 kgs.Also called as Representative Chemical Formula (RCF).A mathematical model for useful part of 100kg of fuel.
19M
yY
Percentage of available oxygen for combustion : k --- Number of atomic kmoles, K = k/16
169
8Mk
K
Fuel Model
• Ultimate Analysis of fuel: Gravimetric : • Percentage of carbon : x --- Number of k moles, X = x/12• Percentage of combustible hydrogen : y --- Number of
atomic kmoles
Percentage of sulfur: z – Number of atomic kmoles, Z = z/32Equivalent chemical formula : CXHYSZOK
Equivalent Molecular weight : 100 kgs.Also called as Representative Chemical Formula (RCF).A mathematical model for useful part of 100kg of fuel.
19M
yY
Percentage of available oxygen for combustion : k --- Number of atomic kmoles, K = k/16
169
8Mk
K
Model Testing for Determination of important species
Air Flow Rate
Fuel Flow Rate
Water Flow Rate
Flue gas Analysis
Selection of Excess air
Optimization of Furnace Parameters.
Average value of CO at different O2 %
y = 226.73x4 - 1900.5x3 + 5809.9x2 - 7698.6x + 3757.9
R2 = 0.9665
0
100
200
300
400
500
0 1 2 3 4
O2 % in Flue gas
CO
( in
pp
m)
U/C % at Different O2 % (in Flue Gas)
y = 3.0149x5 - 28.108x4 + 97.822x3 - 153.3x2 + 98.668x - 13.094
R2 = 0.9953
0123456789
10
0 1 2 3 4
% O2 in FG
U/C
(in
%)
Results of Model Testing.
• For a given fuel and required steam conditions.• Optimum air flow rate.• Optimum fuel flow rate.• Optimum steam flow rate.• Optimum combustion configuration!!!
Realization of MATt Theory
• Mixing: Fuel preparation systems.
• Air: Draught systems.
• T : Preheating of fuel.
• t : Dimensions of combustion chamber. : Turbulence generation systems.
Stoichiometry of Actual Combustion
• CXHYSZOK + 4.773 (X+Y/4+Z-K/2) AIR → P CO2 +Q H2O +R SO2 + T N2 + U O2 + V CO
• Conservation species:
• Conservation of Carbon: X = P+V• Conservation of Hydrogen: Y = 2 Q• Conservation of Oxygen : K + 2 (X+Y/2+Z-K/2) =
2P +Q +2R +2U+V• Conservation of Nitrogen: 2 3.76 (X+Y/2+Z-K/2) = T• Conservation of Sulfur: Z = R
Stoichiometric Analysis of Furnace at Site
• CXHYSZOK + 4.76 (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: *4.76* (X+Y/2+Z-K/2) *28.89 kg.• Mass of Coal: 100 kg.• Excess Air: -1)4.76* (X+Y/2+Z-K/2) *28.89 kg.
Fuel of Mass
Air of Mass RatioFuelAir
Composition of Gas in A Furnace
• For every 100 kg of Coal (A Representative Molecular Weight).
• 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
• Dry Exhaust gases: P CO2 +R SO2 + T N2 + U O2 + V CO kmols.
• Volume of gases is directly proportional to number of moles.
• Volume fraction = mole fraction.
• Volume fraction of CO2 : x1 = P * 100 /(P +R + T + U + V)
• Volume fraction of CO : x2= VCO * 100 /(P +R + T + U + V)
• Volume fraction of SO2 : x3= R * 100 /(P +R + T + U + V)
• Volume fraction of O2 : x4= U * 100 /(P +R + T + U + V)
• Volume fraction of N2 : x5= T * 100 /(P +R + T + U + V)
• These are dry gas volume fractions.
• Emission measurement devices indicate only Dry gas volume fractions.
• 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 4.76 (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
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.
Excess
air
%
Moles of NiAFT (K) VCPi
(KJ/Kg K)CO2 H20 O2 N2
0 3.279 1.165 0 13.79 2220 1.4137
103.279 1.165
0.366 15.174 2085 1.3919
203.279 1.165
0.7323 16.55 1966 1.3723
303.279 1.165
1.098 17.93 1864 1.3553
403.279 1.165
1.465 19.3 1776 1.3398
503.279 1.165
1.83 20.68 1696 1.3242
First Law Analysis of Furnace at Site
• CXHYSZOK + 4.76 (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
Qlosses + n air hair + n fuel hfuel = n fluegas hfluegas + W
• Unburned carbon losses.• Incomplete combustion losses.• Loss due to ash.
• Radiation and Convection Losses from Furnace Surface
Capacity of Flue Gas
Total Thermal Power available with flue gas:
chimneyflamegaspgas TTcm ,
Rate of steam production:
steam
chimneyflamegaspgassteam h
TTcmm
,
s
1
2
3
4
5
6
2f
2s
4523 hhmhhm mreheatsteafmainsteam
Paths of Steam and Gas
Water walls
Drum
Economizer
Sequence of Energy Exchange from Flue Gas to Steam
FLUE GAS
PLATEN SH
PENDENT SH
COVECTIVE SH
ECONOMIZER
RHEVAPORATOR
Fuel Power
Furnace absorption
Platen SH
Final SHLTSH
Reheater
Economizer APH
Combustion Losses C & R losses Hot Exhaust Gaslosses
Sequence of Energy Exchange from Flue Gas to Steam
FLUE GAS
PLATEN SH
PENDENT SH
COVECTIVE SH
ECONOMIZER
RHEVAPORATOR
FEGT
1225
1200
1175
1150
1125
1100
0C
FEGT of An Healthy Furnace
It is very essential to know the mass flow rates of Fuel, Air and various flue gases for further Design and Analysis!
Heat available for Radiation
• Incomplete combustion loss
• Unburned Carbon loss
• Loss due to slag
• Energy brought in by preheated air & fuel.
44wafleffflaislagCCOcfu TTAQQQQLHVmQ
COQ
slagQ
CQ
aiQ
Simplified Approach
• Emitted Radiation heat flux of flames:24 / mkwTJ flflfl
flabs Jq
kWTAQ flflabs 4
444flflwafleffradabs TAkWTTAQQ
• Emitted Radiation = Available Heat
Heat flux absorbed by walls :
Thermal efficiency factor, .
The rate of heat absorption
flame
fufl A
QJ