Improving the Efficiency of Afbc Boiler by Recycling Carbon Rich Fly-Ash by Group-10

BY

K.ARAVIND

T.JALAL THAJ

R.VEERARAJAN

INTRODUCTION

Energy which is the key in moving the world in faster pace. And this energy is generated in many ways.

Among the various methods Thermal power generation is a important way of generating energy. Day by day , the fuel which runs these Thermal plants goes on decreasing.

At a stage , it will come to stand still, but this may come earlier if we go on running our boilers in the conventional ways.

There are lot of ways have been invented by many engineers and among them recycling the carbon rich fly ash back into the boiler is one way and we are going to do that now.

WHY WE ARE RECYCLING FLY-ASH?

TO IMPROVE THE EFFICIENCY OF THE BOILERTO DECREASE THE LOSS ON IGNITIONTO CONSERVE THE ENERGYTO REDUCE THE COAL CONSUMPTION WITHOUT

COMPROMISING THE LOADTO REDUCE THE POLLUTION

BOILER – DEFINITIONAccording to ASME a steam generating unit or boiler is

defined as

“A combination of apparatus for producing, furnishing or recovering heat together with the apparatus for transferring the heat so made available to the fluid being heated and vapourised.”

INTRODUCTION TO FBC BOILERFluidization –Definition

When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles 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 “fluidised” and the process is called fluidization

The Boiler using this mode of combustion principle is called as Fluidized Bed Combustion Boiler(FBC).

TYPES OF FBC BOILER

DIFFERENCE BETWEEN AFBC AND CFBC

CHARACTERISTICS AFBC CFBC

FLUIDIZATION VELOCITY

1.2 - 3.7 m/s 3.7 – 10 m/s

COAL SIZE 1 – 10 mm 6 – 12 mm

UNBURNT FUEL RECYCLING

NO YES

BOILER SIZE LARGE SMALL

LOSSES DUE TO UNBURNT

HIGH LOW

ASH AND FLUE GAS PATH BEFORE RECYCLING FLY ASH

ASH AND FLUE GAS PATH AFTER RECYCLING FLY ASH

CALORIFIC VALUE OF UNBURNT CARBONThe fuel has been already burnt at a temperature of the

order of 850 to 900 º C, so the volatile matter and the moisture in the un-burnts are expelled out.

The un-burnt are only the fixed carbon.The calorific value of the fixed carbon is 8080 kcal/kg.By means of recycling this un-burnt carbon we can get

reasonable amount of energy, by which the efficiency of the boiler can be improved.

EFFICIENCY OF BOILER BY INDIRECT METHODηboiler = 100 - ( L1+L2+L3+L4+L5+L6+L7)

The losses tabulated in the AFBC column are taken from Thermax Boiler of 152 tonnes/hr @ MCL Tamilnadu.

Losses (L) due to AFBC PF Boiler

L1-Dry flue gas 4.14 % 4 – 5 %

L2-formation of water 6.62 % 3 %

L3-Moisture in fuel 0.76 % 0.5 – 1 %

L4-Moisture in Air 0.1 % ≈ 0

L5-Radiation and Convection

0.4 % 1 %

L6- Un-burnt in Fly Ash (LOI)

2.045 % 1- 2 %

L7- Sensible heat of fly Ash

0.08 % 0.1 – 0.5 %

WEIGHT OF UN-BURNT CARBON PRESENT IN ECO & APH ASHTotal coal consumed per day

Ash produced per day

Ash collected at ECO and APH per day

Weight of un-burnt carbon present in

ECO and APH ash per day.

%15

%15

%20

LOSSES DUE TO UN-BURNTS IN FLY ASH OR LOSS ON IGNITION (LOI) BEFORE RECYCLING

L61 =

=

= ((8080×0.00351) + (8080×0.009945))/5300

= 2.045%

100 fuel of GCV

ashfly in burnts-un of GCV

100 fuel of GCV

ESP from burnts-un of GCV ECO & APH from burnts-un of GCV

LOSSES DUE TO UN-BURNTS IN FLY ASH OR LOSS ON IGNITION (LOI) AFTER RECYCLING

L62 =

= (8080×0.009945)/5300

= 1.5 %

It is found that the LOI gets decraesed by recycling the unburnt carbon in to the boiler

100 fuel of GCV

ESP from burnts-un of GCV

PERCENTAGE OF EFFICIENCY IMPROVED

The percentage of efficiency improved can be calculated by the difference between LOI before and after recycling un-burnt carbons

Efficiency improved = L61 - L62

= 2.045 - 1.5

= 0.54 %

EQUIPMENTS TO BE DESIGNED FOR RECYCLING UNBURNT CARBON

METHOD OF RECYCLING UNBURNT CARBONS IN TO BOILERThere are two methods to recycle UNBURNT CARBON in

to the boiler,

Out of the above two method indirect method is recommended for reliable operation of plant.

DIRECT METHOD INDIRECT METHOD

Injecting directly in to the boiler without mixing with coal.

Injecting in to the boiler by mixing with coal.

FUEL SAVED PER DAY AFTER RECYCLING UNBURNTS

Fuel consumed per day = 300tonnesTotal ash produced per day = 15% of fuel consumed = 45tonnesAsh collected at ECO & APH = 15% of total ash produced

= 6.75tonnesAmount of un-burnt carbon produced in ECO &APH

= 20% ash collected = 0.20 × 6.75 = 1.35tonnes

Gross calorific value of un-burnt carbon = 8080 kcal/kgGross calorific value of coal used = 5166 kcal/kgTotal amount of energy saved from un-burnt carbon

= amount of UBC × GCV of UBC= 1.35 × 1000 × 8080= 10908000kcal/day

Total amount of coal (fuel) saved per day = Energy from UBC/GCV of coal

= 10908000 / 5166= 2111.49 kg/day

TOTAL COST SAVED PER YEAR AFTER RECYCLING UNBURNTSCost of coal (fuel) used per ton = Rs 4100/-Total cost saved per day = 2.11149 × 4100

= Rs 8657.10(approx)Total amount of coal saved per year = 2111.49 × 365

= 770693.85kg

= 770.693tonnesTotal cost saved per year = 8657.109 ×

365

= Rs 31, 59,844.785(approx)

ADVANTAGES

Thermal efficiency of the boiler increased Bulk fly ash LOI decreased Coal use decreased with no load reduction Lower fuel cost Lower ash handling cost Carbon in the fly ash burned at good efficiency over 80% Lower land fill cost Reduced pollution

FUTURE……………

FACTORS TO BE MONITORED IN BOILER TO GET MAXIMUM EFFICIENCYTemperature of gas leaving APH should be less than

150ºC.Increase in the excess air causes decrease in the efficiency

of boiler, O2 at ECO outlet should be 3.5-4%. Excess air should be within 20-25%

Un burnt carbon loss should be kept minimum by regulating excess air, distribution of primary and secondary air.

There should not be any air leakage inside the furnace, it is achieved by closing inspection doors, openings, instrument openings, etc.,

Keeping good feed water quality is very much important for reliable operation of boiler

Sampling of boiler water shall be carried out regularly to monitor its quality as recommended

Removal of dissolved oxygen by deaeration in boiler feed water is important to avoid pressure part corrosion and pitting

feed water temperature at outlet of deaerator at the saturation temperature of the water at the operating pressure and the temperature of water entering economiser at 190 ºC.

RESULTSImproving the efficiency of boiler upto 0.5% to 0.8%Better utilisation of fuel by recycling the ashFuel saved = 2111.49 kg/day (approx)Cost saved per day = Rs 8657.109 /day (approx)Fuel saved = 770.69 tonnes/yr (approx)Cost saved = Rs 31,59,844.78 (approx)

QUESTIONS..?

THANK YOU