Fuels & combustion part2

1. 1. Fuels and Combustion
Dr.M.Vivekanandan M.E.,PhD
Adjunct Faculty, Kongunadu College of Engineering
and Technology,
CEO, TryCAE Industrial Engineering Pvt Ltd.,

2. Stoker Firing

3. Pulverised
Fuel Firing

4. PF burner

5. Tangential Firing

6. Fluidised Bed Combustion

7. Example:
Technical Presentation

8. Cynthia Schmidt
Mechanical Engineering Department
University of Texas
Methods to Reduce
Sulfur Dioxide Emissions
From Coal-Fueled Utilities

9. • 90% removal capability
• low capital cost—able to
use in existing equipment
• high operating cost
• ability to use different
grades of coal
separator
air
inlet
cleaned
exhaust
grid
Choose a format that's professional
The most effective combustion method
is an atmospheric fluidized bed

10. Percentage Reduction of SO2
coal cleaning
coal switching
fluidized bed
absorption
adsorption
25 50 75
40%
40%
80%
90%
95%
80%
By using these methods, coal utilities
can greatly reduce SO2 emissions

11. Coal Combustion

12. Contents
• What is coal? Formation, sources, applications.
• Coal combustion description.
• Coal power plants and air pollution:
Mechanisms and control technologies.
• Coal and air pollution in Israel.
Eshkol power station
Haifa

13. Coal – what is it?
65-95%
C
2-7%
H
<25%
O
<10%
S
1-2%
N
20-70%
Char
5-15%
Ash
2-20%
H2O
20-45%
VM
• Inhomogeneous organic fuel
formed mainly from
decomposed plant matter.
• Over 1200 coals have been
classified.
Time, Temperature
Coal Rank
• Coalification forms different
coal types:
(Peat)
Lignite
Bituminous coal
Anthracite
(Graphite)
Proximate
Analysis
Elemental
Composition

14. Coal

15. Coal Sources
• Coal is the world’s most plentiful fossil fuel.
• Recoverable world coal reserves are estimated at about
1X1012 tons.
32%
29%
12%
8%
7%
7%
5%
United States
Russia
China
Australia
Germany
South Africa
Poland
World Coal Reserves (1989)

16. Coal Applications
• Homes – heat and cooking
• Transportation – steam
engines
• Industry – metal works
• Electricity – power plants

17. Main Processes in Coal
Combustion
coal particle
p-coal, d=30-70m
devolatilization
volatiles
char
homogeneous
combustion
heterogeneous
combustion
CO2, H2O, …
CO2, H2O, …
tchar=1-2sec
tvolatiles=50-100ms
tdevolatile=1-5ms
t

18. The physical processes influencing
pulverized coal combustion
• Turbulent/swirling flow of air and coal.
• Turbulent/convective/molecular diffusion of
gaseous reactants and products.
• Convective heat transfer through the gas and
between the gas and coal particles.
• Radiative heat transfer between the gas and
coal particles and between the coal/air
mixture and the furnace walls.

19. From Fumifugium by John Evelyn (1661)
- on London’s air pollution -
“…but so universally mixed with the otherwise wholesome and excellent Aer,
that her Inhabitants breathe nothing but an impure and thick Mist,
accompanied by a fuliginous and filthy vapour, which renders them
obnoxious to a thousand inconveniences, corrupting the Lungs, and
disordering the entire habit of their Bodies; so that Catharrs, Phthisicks,
Coughs and Consumptions, rage more in this one City, than the whole Earth
besides. For when in all other places the Aer is most Serene and Pure, it is
here Ecclipsed with such a Cloud of Sulphure, as the Sun itself, which gives
day to all the World besides, is hardly able to penetrate and impart it here; and
the weary Traveller, at many Miles distance, sooner smells, than sees the City
to which he repairs. This is that pernicious Smoake which sullyes all her
Glory, superinducing a sooty Crust or Fur upon all that it lights, spoyling the
moveables, tarnishing the Plate, Gildings and Furniture, and corroding the
very Iron-bars and hardest Stones with those piercing and acrimonious Spirits
which accompany its Sulphure; and executing more in one year, than exposed
to the pure Aer of the Country it could effect in some hundreds.”

20. Coal Combustion Air Pollutants
• CO2
• CO
• NOx
• SOx
• Particulate matter
• Trace metals
• Organic compounds

21. Carbon Dioxide, CO2
C + O2 CO2
Almost 99% of C in coal is converted to CO2.
In order to lower CO2 emission levels, coal power
plants will have to leave steam-based systems (37%
efficiency) and go towards coal gasification technology
(60% efficiency).
Meanwhile, CO2 sequestration is being tested.

22. Carbon monoxide, CO
C + ½O2 CO
CO is minimized by control of the
combustion process (air/fuel ratio,
residence time, temperature or turbulence).

23. Particulate Matter
PM composition and emission levels are a
complex function of:
1. Coal properties,
2. Boiler firing configuration,
3. Boiler operation,
4. Pollution control equipment.
Bottom Ash Fly Ash
In PC power plants, since combustion is almost complete, the emitted PM is
primarily composed of inorganic ash residues.

24. PM controls (AP-42, EPA)
Mainly post combustion methods:
Electrostatic precipitator
(ESP)
99% (for 0.1>d(m)>10)
<99% (for 0.1<d (m)<10)
Fabric filter (or baghouse) As high as 99.9%
Wet scrubber 95-99%
Cyclone 90-95% (d(m)>10)

25. Trace metals
Class 1
Elements that are
approximately equally
concentrated in the fly
ash and bottom ash
(Mn, Be, Co, Cr)
Class 2
Elements that are
enriched in fly ash
relative to bottom ash
(Ar, Cd, Pb, An)
Class 3
Elements which are
emitted in the gas
phase (mainly Hg).
Control of total
particulate matter
emissions
Collection of fine
particles.
Sorbents ???
CONTROL
FORMATION
Concentration of metal in coal, physical and chemical properties of the
metal, combustion conditions.

26. Organic Compounds
Include volatile, semivolatile and condensable organic
compounds either present in the coal or formed as
a product of incomplete combustion.
Characterized by hydrocarbon class: alkanes,
alkenes, aldehydes, alcohols and substituted
benzenes.
The main groups of environmental concern are:
1) tetrachloro- through octachloro- dioxins and
furnans.
2) Polycyclic organic matter (POM).
Emissions dependent on combustion behavior in the
boiler (air/fuel ratio, residence time, temperature or turbulence).

27. Sulfur Oxides, SOx

28. Sulfur in coal (<10%)
Organic sulfur (40%)
Chemically bonded to the hydrocarbon matrix
in the forms of thiophene, thiopyrone, sulfides
and thiol.
Inorganic sulfur (60%)
Imbedded in the coal, as loose pyrite - FeS2
or marcasite, and calcium/iron/barium
sulfates.
Sources of sulfur in coal: Seawater sulfates,
Limestone

29. Coal-S SH)
S,
,
2
S
CS,
(
char
2
CS
COS, S
2
H
SO 2
SO 3
SO
M
,
2
O
4
SO
-
molecule
2
SO
radicals
SOx Formation

30. SOx reduction
• Pre combustion removal:
– Physical cleaning (30-50% removal inorganic sulfur)
– Chemical and biological cleaning (90% removal organic
sulfur)
• Combustion configuration:
– No benign sulfur species!
– gasification combined-cycle systems (IGCC systems)
• Post-combustion removal:
– Wet Flue Gas Desulfurization (FGD) (80-98%)
• In situ sulfur capture:
– Dry Sorbent Injection (DSI) (50%)

31. Nitrogen Oxides, NOx

32. Nitrogen in Coal (1-2%)
Name Structure ~ Relative
amount
Stability
Pyridine1 15-40% More stable
Pyrrole1 60% Less stable
Aromatic
amines
6-10% Stable
N
N
H
NH2
··
··
1Including structures made up of 2-5 fused aromatic rings.

33. Main NO Mechanisms
1. Thermal NO
2. Prompt NO
3. Fuel NO: volatiles-NO and char-NO

34. Thermal NO
(Zeldovich mechanism)
N2 + O  NO + N
N + O2  NO + O
Strong temperature-dependence: >1300-1500°C
Not a major source of NO in coal utility boilers.

35. Prompt NO
N2 + CHx  HCN + N + …
N + OH  NO + H
Prevalent only in fuel-rich systems.
Not a major source of NO in coal utility boilers.

36. Fuel NO (-N in volatiles)
Fuel-N HCN/NH3
volatiles
(formation)
(destruction)
HCN/NH3 + O2
N2
NO
NO + HCN/NH3
The major source of NO in coal utility boilers (>80%).

37. Char NO (-N in the char)
Char-N + ½O2  NO
Char-C + NO  ½N2 + Char(O)
(formation)
(destruction)
[char-NO = ~25%] < [volatiles-NO = ~75%]

38. NO Reduction
Combustion controls:
1. Modification of combustion configuration:
• Reburning
• Staged Combustion (air/fuel)
Post combustion controls:
1. Injection of reduction agents in flue gas.
2. Post-combustion denitrification processes.

39. Reburning
devolatilization
volatiles
char
homogeneous
combustion
heterogeneous
combustion
CO2, H2O, NO…
Excess air
CO2, H2O, NO…
CO2, H2O, N2…
CHi·
CHi· + NO  HCN
HCN + NO  N2 + …

40. Staged Combustion
devolatilization
volatiles
char
homogeneous
combustion
heterogeneous
combustion
CO, CO2, H2O, N2…
Fuel Rich
CO, CO2, H2O, N2…
CO2, H2O, N2…
O2

41. NOx control options
(from AP-42, EPA)
Control Technique NO Reduction Potential(%)
Overfire air (OFA) 20-30
Low Nox Burners (LNB) 35-55
LNB + OFA 40-60
Reburn 50-60
SNCR 30-60
SCR 75-85
LNB with SCR 50-80
LNB with OFA and SCR 85-95
(Selective Non Catalytic Reduction)
(Selective Catalytic Reduction)

42. Fuel Oil and Coal Consumption for Electricity
in Israel (1980-2001) (1000 Tons)
Source: Israeli CBS, 2001
0
2000
4000
6000
8000
10000
12000
1980 1990 1999 2000 2001
Fuel Oil Coal

43. Fuel Combustion Emissions in Israel
by Fuel, 2002 (1000 Tons)
Source: Israeli Central Bureau Statistics (CBS), 2002
0
100
200
300
400
500
LPG Gasoline Diesel Oil Coal Heavy Fuel
Oil
CO SOx NOx SPM

44. Fuel Combustion Emissions in Israel
by Sector, 2002 (1000 Tons)
Source: Israeli CBS, 2002
0
100
200
300
400
500
Motor Vehicles Industry Electricity
Production
CO SOx NOx SPM
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
45,000
Motor Vehicles Industry Electricity
Production
CO2

45. 1) Coal combustion in Israel has tripled since
1990. Almost all of coal use is for
electricity production.
2) Coal combustion emissions in Israel:
• 71% of total SO2 emissions.
• 62% of total CO2 emissions.
• 39% of total NOx emissions.
• 38% of total SPM emissions.
• 1% of total CO emissions.

46. Gas Burner
 Low pressure burners
 Operate over range of 25-100 mm Water Column Gas Supply Pressure
 High pressure burners operate over range of 120 – 1750 mm WC

47. Draft
Draft : The function of draft is to exhaust the products of combustion into the
atmosphere.
Natural Draft : It is the draft produced by a chimney alone. It is caused by the
difference in weight between the column of hot gas inside the chimney and column
of outside air of the same height and cross section.
Mechanical Draft: It is draft artificially produced by fans. (Three basic types)
Balanced Draft: Forced-draft fan pushes air into the furnace and an induced-draft
fan draws gases into the chimney thereby providing draft to remove the gases from
the boiler. (0.05 to 0.10 in. of water gauge below atmospheric pressure)
Induced Draft: Fan provides enough draft for flow into the furnace, causing the
products of combustion to discharge to atmosphere. Furnace is kept at a slight
negative pressure below the atmospheric pressure
Forced Draft: The Forced draft system uses a fan to deliver the air to the furnace,
forcing combustion products to flow through the unit and up the stack.

48. Knowing how a Combustion
Engine works
Showing us through
an animation design,
Luke explained to us
how a combustion
engine operates.

49. Fuels
We tested both Methanol
and Acetone, we found
that Methanol provided
more power than Acetone.
As we increased the load on
the engine, the RPMs
decreased while the torque
increased.

50. Power = RPMs x Torque
Methanol Power vs. RPM
0
50
100
150
200
250
0 1 2 3 4 5 6 7 8
RPM
Power

51. Acetone Power vs. RPM
0
50
100
150
200
250
300
350
0 2 4 6 8 10
RPM
Power
Power = RPMs x Torque

52. Alternator
• Our engine was hooked up
to a generator/alternator
and we were able to turn
on a 50 Watt light bulb.
• Also, we used to
multimeter to measure the
voltage and current output

53. Piston-Cylinder models
• We made piston-cylinders with the
connecting rods
• Unfortunately we have to finish them at
home
• Our models convert linear motion (from the
piston-cylinder) to rotational motion (for the
wheels)

54. Combustion appliances