1. Pulverized Coal Combustion Systems
P M V Subbarao
Professor
Mechanical Engineering Department
Efficient & Eco-friendly Methods for Destruction of Entropy Vehicles…..

3. How to develop eco-friendly & large Capacity Coal Combustion Systems ?
In the early 1900s, a 50MW plant (considered large at that time) housed five 10 MW steam turbines and typically required 50–60 boilers to power the turbines .
The Big Challenge:
How to develop eco-friendly & large Capacity Coal Combustion Systems ?

4. 1920 : A Need for Break Through for Coal Combustion
A practical engineering limit seems to be reached when the length and width of the grate are about 9 m with grate area 80 m2.
At 2 MW/m2, the steam capacity at 85% efficiency would be 150 MW or 270 tons per hour.
The limitation is partly grate area and partly firing density.
The limitation on firing density exist due to:
The rate of movement of the reaction plane could not match the opposed rate of fuel flow leading to blow-off.
The experience with grate combustion led to development of many requirements for further development.

5. An Audit of Grate/Stoker Systems in 1920s
Combustion Factor
Pre 1920 Status
A volumetric combustion intensity, Iv (kW/m3)
250 – 750
Area Combustion Intensity, IA (kW/m2)
300 – 1800
Coal Firing Density Jf,V ( kg/m3.hr)
30 – 100
Area Firing Density, Jf,A (kg/m2.hr)
40 – 250
Air Velocity (m/sec)
Up to 0.5
Exhaust Gas Velocity (m/sec)
Up to 3
Combustion time (sec)
Up to 5000
Fuel Particle Heating Rate (0C/sec)
<1
Heat Transfer Coefficients (W/m2 K)
~10
Heat Fluxes to Heat exchange (kW/m2)
~ 10

6. Duties of A Furnace Dixon’s Theory:
Generate an environment of excited fuel and oxygen molecules.
All the fuel molecules should be surrounded by oxygen molecules.
Facilitate frequent collisions among excited fuel molecules and excited fuel molecules.
A successful collision can lead to combustion.
Development of suitable technologies is the need for efficient combustion of fuels (coals).

7. Five Requisites for Good Combustion
MATtr Theory:
M : Proper mixing of the reactants.
A: Sufficient air.
T: Conducive temperature
t: Sufficient time
r: Satisfactory local density of reactant.

8. Realization of MATtr Theory
Mixing: Fuel preparation systems.
Air: Draught systems.
T : Preheating of fuel.
t : Dimensions of combustion chamber.
: Turbulence generation systems.

9. Current Three Ts & One S Options for Coal Combustion
Size the Coal and Add the Air !!!
Technology
Time
Temperature
Turbulence
Size
Stoker
large
Medium
Low
Big
Pulverized
Short
High
Tiny
Circulating Fluidized Bed
Łagisza power plant (460-MW ) began commercial operation in late June 2009, it marked the beginning of a new era in the evolution of circulating fluidized bed (CFB) technology.

10. Eco-friendly Air Distribution System for PC Combustion
Pulveriser C
Furnace
~350C
Rotary Air Preheater
~140C
~250C
Coal+
Primary air
Tair,amb
FD Fan

11. Combustion Gas Flow Path
Burners

12. 210 MW Draught System

13. FD Fan
Duct
SCAPH
APH
Duct
Wind
Box
Duct
Boiler
ID Fan
APH
ESP

14. Effect of Fan Power on Furnace vacuum

15. Operational Data of 210 MW plant

16. Realization of MATtr Theory
Mixing: Fuel preparation systems.
Air: Draught systems.
T : Preheating of fuel.
t : Dimensions of combustion chamber.
: Turbulence generation systems.

17. Stockholm 1920 The Ljungström Air Preheater
The first installation in a commercial boiler saved as much as 25% of the fuel consumption.

18. Historical Significance of Landmark
In a modern Steam generator the Ljungström Air Preheater provides up to 20% of the total heat transfer in the boiler process.
The Ljungström Air Preheater only represents 2% of the investment.
The Ljungström Air Preheater is a remarkable invention in many ways.
It saves the fuel so much that the cost of the preheater is generally recovered after only a few months.
It has been estimated that the total world-wide fuel savings resulting from all Ljungström Air Preheaters which have been in service is equivalent to 4,500,000,000 tons of oil.
An estimate shows that the Ljungström Air Preheaters in operation annually saves about $30 Billion US.

19. The Idea: One Shot Two Birds
Data for the hand fired boiler before and after the installation of Ljungström Air Preheater is as follows:

20. The Modern Air preheater