TO STUDY AND INVESTIGATION ON AFBC · PDF fileTO STUDY AND INVESTIGATION ON AFBC BOILER. Poulik Kathiria. 1, Patel Drumil. 2 ... Hydrodynamics of 150MW circulating fluidized bed boiler

TO STUDY AND INVESTIGATION ON AFBC BOILER

Poulik Kathiria1, Patel Drumil

2, Gujjar Kaushik

3, Malvi Sanjay

4

Student, Mechanical department, Laxmi institute of Technology, Sarigam-Valsad. Gujarat

Corresponding Author Detail:

Poulik Kathiria

Student, Mechanical department,

Laxmi institute of Technology,

Sarigam-Valsad, Gujarat.

Internal Guide Detail:

Mr. Jignesh Chaudhary

Assistant Professor, Mechanical department,

Laxmi institute of Technology,

Sarigam-Valsad. Gujarat.

ABSTRACT

Boiler is a most useful device for any developing industries to process & production. It is

necessary to optimized good boiler efficiency. Boiler efficiency can be measured by two method,

direct method and indirect method. Both methods give a different result. Direct method did not

include any losses for calculating boiler efficiency, while indirect method includes all the heat

losses from a system to find boiler efficiency. This paper gives simulating with the various value

of the fuel. GCV of fuel indicate the heating value of fuel. As the heating value is high,

efficiency is also increased with increased with the higher GCV coal. Compare with the different

GCV of coal to find out the proper fuel selection of fuel. There are different parameters

regarding to the boiler system which helps to improved boiler efficiency.

KEYWORDS: Increase efficiency, Identify different losses, comparison

INTRODUCTION

ON December 16, 1921 a new chapter opened in the history of the energy and power industries.

Fritz Winkler of Germany introduced gaseous products of combustion into the bottom of a

crucible containing coke particles, creating the first demonstration of gasification of coal in a

fluidized bed. Winkler saw the mass of particles lifted by the drag of the gas to look like a

boiling liquid (Squires, 1983). This experiment initiated a new process called fluidization, the art

of making granular solids behave like a liquid. Though some would argue that many others

observed the phenomenon of fluidized beds in the past, the credit for the invention of the

bubbling fluidized bed (BFB) process, which we use for scores of processes including

combustion and gasification, should go to Winkler. Heavy industrialization & modernization of

society demands in increasing of power cause to research & develop new technology & efficient

utilization of existing power units. Fluidized bed boilers have acquired sufficient operating

experience to be called a matured technology.

When an evenly distributed air or gas is passed upward through a finely divided bed of solid

particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As

air velocity is gradually increased, a stage is reached when the individual particles are suspended

in the air stream – the bed is called “fluidized” The major portion of the coal available in India is

International Journal of Scientific Research in Engineering (IJSRE) Vol. 1 (3), March, 2017

IJSRE Vol. 1 (3), March, 2017 www.ijsre.in Page 70

of low quality, high ash content and low calorific value. The traditional grate fuel firing systems

have got limitations and are techno economically unviable to meet the challenges of future.

Fluidized bed combustion has emerged as a viable alternative and has significant advantages

over conventional firing system and offers multiple benefits – compact boiler design, fuel

flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx

and NOx. The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse &

other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over

100 T/hr. a fluidized state is heated to the ignition temperatures of coal, and coal is injected

continuously into the bed, the coal will burn rapidly and bed attains a uniform temperature. The

fluidized bed combustion (FBC) takes place at about 840oC to 950

oC. Since this temperature is

much below the ash fusion temperature, melting of ash and associated problems are avoided.

Atmospheric classic Fluidized Bed Combustion System (AFBC) The velocity of fluidizing air is

in the range of 1.2 to 3.7 m /sec. The bed depth is usually 0.9 m to 1.5 m deep and the pressure

drop averages about 1 inch of water per inch of bed depth. Very little material leaves the

bubbling bed – only about 2 to 4 kg of solids are recycled per ton of fuel burned.

LITERATURE REVIEW

Fluidized bed boiler has gained popularity, especially in the electric power-generation market,

for its several practical advantages, such as efficient operation and minimum effect on the

environment. Lots of research is going on in this field to addressed different issues related to

boiler operation, boiler performance, increase efficiency, and utilization of most advance tools

like CFD simulation & assistance of CAD/CAE tools to addressed the combustion & flow.

Thenmozhi Ganesan, Dr. Sivakumar Lingappan focused on survey on the growing energy

demands in the power sector. Fluidized bed combustion (FBC) technology is continuously

gaining importance due to its ability to burn different low grade coals and the absence of NOx

production.[1]

The main advantages of the fluidized bed combustion boilers are: reduced NOx, SOx due to

relatively low combustion temperature, better efficiency and reduction in boiler size and design.

It has the ability to burn low grade coal and it is less corrosive as the combustion temperature is

less when compared to that of an utility boiler. In addition to all of these, the startup and shut

down operation of FBC boilers are much easier. [1]

Nan Zhanga, Bona Lua, Wei Wanga, Jinghai Li focoused on 3D CFD Simulation on

Hydrodynamics of 150MW circulating fluidized bed boiler because of owing to the advantages

of low emission and fuel flexibility, circulating fluidized bed (CFB) boilers for utility power

generation have been increasing in the past decades in both capacity and quantity. Proper design

and scale-up of a CFB boiler rely heavily on its hydrodynamic understanding. Berend van

Wachem, Xiao Yu and Tian-Jian Hsu worked to understand the 3D Eulerian-Lagrangian

Numerical Model for Sediment Transport. The motion of the sediment phase is elucidated by a

Lagrangian or Discrete Element Method (DEM), implying that the individual trajectory of each

particle is determined by approximating Newtons second law of motion.

Ning Yang, Wei Wang, Wei Ge, Jinghai Li studied the CFD simulation to understand the two



phase flow. Apart from experimental investigation, recent years have seen a rapid growth of

computer simulation of gas–solid two-phase flow. Most of these simulations are based on the

two-fluid approach in which gas and solid are assumed to be continuous and fully

.interpenetrating in each control volume, so the conservative equations of mass and momentum

originally derived from single-phase flow can be extended to describe the hydrodynamics of

gas–solid two-phase flow.

In 1970 in Houston, texas (U.S.A.) the second international conference on fluidized bed

combustion was held .In the introductory lecture, one of the pioneers of this technology. The

energy crisis in 1972, only the FBC has become commercially available, been able to technically

and economically match conventional energy technologies, and to offer many superior features

especially in terms of emission and fuel flexibility.

METHODS TO CALCULATE THE BOILER EFFICIENCY

There are two methods to find out boiler efficiency.

1. Direct method

2. Indirect method

1. DIRECT METHOD

Boiler efficiency is calculated with this formula

Boiler efficiency η = steam generation x (enthalpy of steam – enthalpy of feed

water) x 100 GCV x Mass of coal consumed

2. INDIRECT METHOD

By this method, efficiency could be measured easily by measuring all the losses occurring in

the boiler. Boiler efficiency η

= 100- (Dry flue gas loss + heat loss due to evaporation of water+ heat loss due to

moisture in air + heat loss due to moisture in fuel + heat loss due to unburnt in fly

ash+heat loss due to unburnt in bottom ash + heat loss due to radiation)

BOILER BED MATERIAL ANALYSIS

Silica (SiO2): 58% Alumina(Al2O): 38.15 %

Iron (Fe2O3): 0.35 % Fusion Temperature: 1300 oC

Bulk density (gms/cc): 1.05 Maximum Particles Size: 2.36mm

Minimum Particles Size: 0.85mm



COAL ANALYSIS REPORT

Coal Indian Lignite Bituminous (%)

Carbon 64.26 59

Sulphur 0.21 1.4

Oxygen 6.98 10.4

Hydrogen 4.49 3.1

Nitrogen 0.22 1.1

Moisture 13.995 12.9

Ash 9.86 12.1

GCV 5504 kcal/kg 5800 kcal/kg

STEAM GENERATION ANALYSIS

Coal Indian Lignite Bituminous

Average steam generation rate 13700 kg/hr 14100 kg/hr

Average fuel consumption rate 2085 kg/hr 2045 kg/hr

Steam generation pressure 8.8 kg/cm2 8.8 kg/cm2

Steam temperature 250 oC 251

oC

Enthalpy of steam 661.4 kcal/kg 661.4 kcal/kg

Feed water temperature 105 oC 105

oC

FLUE GAS ANALYSIS


% of oxygen 7.2% 7.2%

% of carbon dioxide 13.87% 13.87%

% of carbon monoxide 0.42% 0.42%

Flue gas temperature 160 oC` 160 oC

Ambient temperature 33 oC 33 oC

SUPPLY AIR ANALYSIS

Theoretical air requirement : [(11.43*C)+(34.5*(H2- (O2/8)))+(4.32*S)] / 100

Excess air requirement :[%O2 in flue gas*100] / [21- %O2 in flue gas]

Actual mass of air supply : [ 1 +(excess air/100)]* theoretical ai




Humidity of air 0.13 kg/kg of dry air 0.13 kg/kg of dry air

Theoretical air requirement 8.60 kg/kg of fuel 7.43 kg/kg of fuel

Excess air requirement 52% 52%

Actual mass of air supply 13.09 kg/kg of fuel 11.30 kg/kg of fuel

ASH ANALYSIS


Total ash collected per kg of fuel 0.1587 kg 0.1587 kg

GCV of fly ash 2234 kcal/kg 2234 kcal/kg

GCV of bottom ash 1829 kcal/kg 1829 kcal/kg

LOSSES ANALYSIS


Dry flue gas loss 14.30% 13.57%

Mass of flue gas per kg of fuel (m) 17.96 kg/kg of fuel 17.96 kg/kg of fuel

Specific heat (Cp) 0.345 kcal/kg 0.345 kcal/kg

Temp difference (Tf-Ta) 127 oC 127

oC

HEAT LOSSES

Coal Indian Lignite(%) Bituminous(%)

Due to evaporation of water 4.71 3.08

Due to moisture air 1.767 1.447

Due to of moisture in fuel 1.630 1.426

Due to un-burnt in fly ash 1.610 1.528

Due to un-burnt in bottom 3.955 3.753

Due to Radiation & other 2 2

unaccountable losses

Efficiency

Coal Indian Lignite(%) Bituminous(%)

Direct Efficiency 66.4 66.7

Indirect Efficiency 70 73.2



CONCLUSION

Conclusion derived from the data related to the boiler, if higher GCV coal is used, then the

efficiency should be increased. Ash and Moisture content inside the fuel will affect the

efficiency. Here by using semi bituminous coal indirect efficiency is 73.20% because of its high

heating value and less moisture and ash content, while Indian lignite coal gives 70.0% efficiency

on the same boiler because of it has a more ash and moisture contents than the semi bituminous

coal. From this Indirect Method mathematical model, the efficiency should be easily calculated.

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TO STUDY AND INVESTIGATION ON AFBC · PDF fileTO STUDY AND INVESTIGATION ON AFBC BOILER. Poulik Kathiria. 1, Patel Drumil. 2 ... Hydrodynamics of 150MW circulating fluidized bed boiler