1. OIL FIRING SYSTEM
Chapter -3

2. OIL FIRING SYSTEM : INTRODUCTION
Oil is used for initial start up and for furnace stabilization in case of interruptions in lignite supply Each boiler is equipped with four oil burners, two on the left and two on the right side of the furnace, at 20 ML elevation. They are designed to maintain 30% MCR condition of the boiler load. During normal full load operation, fuel oil will not be used in the furnace. However, continuous oil supply upto the burners is maintained so that burners can be cut in immediately in case of necessities. The oil used should be sufficiently pre heated so that its viscosity is reduced to 12 – 15 centi stokes. This preheated oil at the required pressure should be made to flow upto the burner front, and if not used, should be re circulated back.
OIL RECIRCULATION ARRANGEMENT
The oil supplied to the burners is normally heated up to 130 ºc in any one of the two secondary oil heaters. If entire quantity of oil system is kept circulated through heaters the oil temperature at suction pump cannot be controled (which can be 80 c) hence main oil recirculation tapping is taken to secondary heaters to keep oil line warm upto front a small portion of it is taken to burner front and gets recirculated.

3. The quantity of oil re circulated is varied by the pneumatic valve, taking a feed back impulse from the fuel oil pressure.
Thus the fuel oil pressure after the heaters is maintained at a constant value (23 ksc) by varying the recirculation flow corresponding to consumption this recirculation arrangement has a bypass with a single hand operated valve which is used in the case of any problem in the pneumatic valve.
SECONDARY OIL PRE HEATERS :
The fuel oil is primarily heated in the oil tank itself by a floor coil heater and further heated up to ºC in oil suction heater. The oil used should have a viscosity of centi stokes and this is done further preheating in secondary preheater(2 no’s). Each heater is designed for 100% oil flow.
Oil flows through the straight tubes of the heater and is heated to 130ºc by steam, supplied to the shell portion around.
The oil side of the heater is provided with two hand operated valves at the inlet and also at the outlet to isolate the heater as and when it is not in service.
A safety relief valve set at 40 bar is provided at the oil outlet header of the heater
Steam is supplied from auxiliary steam header at a pressure of 16 ksc and temperature of230 ºc

4. The steam is supplied through a Y – type strainer and a diaphragm type control valve
In the steam supply line to each heater, a safety valve is installed for venting out steam in case of pressure increase to 22 bar.
PRESSURE OIL FILTERS :
Two steam-jacketed filters, each designed for 100 % oil flow are arranged in parallel. Each filter has two isolating valves before and two isolating valves after the filter. There is also an air vent and drain for the filter
The steam for heating the filter is supplied from the trace heating steam system
This line has an isolating valve at the inlet and the condensate is drained through a steam trap arrangement. A drain is provided before the filters for draining the oil to drain oil tank.
The cleanliness of the filter element is indicated by a differential pressure switch, which gives an alarm in case of increase in the pressure difference across the filter
FLOW METERING STATION :
Flow elements are provided both in the inlet and return lines of the boiler and the difference in flow rate gives the quantity of oil consumed
The flow elements can be isolated for maintenance by means of the two valves provided on either side.
A drain is also provided for filters and flow metering station connected at zero ML

7. FUEL OIL CONTROL STATION :
In the flow control station, a quick closing type diaphragm valve is located. This valve is actuated by burner management system and cuts off oil supply to all the oil burners when the protection acts.
The following instrument provisions are there in the oil control station
One pressure switch to give a low-pressure alarm.
One pressure switch to give a high-pressure alarm.
A temperature switch to give low temperature indication.
Pressure gauge at local.
Pressure tapping for UCB indication.
Thermo couple to indicate temperature at UCB.
One pressure controller for operating the oil flow control valve.
After the control station, the oil line forms a bus running around the right, rear and left sides of the furnace. Four branches are taken off from this bus for four burners. Pressure gauge and temperature indicator are provided in the left side of the oil bus.

9. The fuel oil supply line terminates at the left side of the furnace where a re circulation line is tapped off. This return line has a diaphragm valve operated by BMS and a non return valve
ATOMIZING STEAM CONTROL S TATION :
The atomizing steam is supplied from the auxiliary steam header located at 19.5 ML. The steam consumption is 960-kg/hr when all the four oil burners are in service. The sources of steam supply to auxiliary steam header are
Main steam lines through pressure reducing de super heating station
Cold reheat lines through pressure reducing de super heating station
From the auxiliary steam headers of other units
There is an isolating valve and a `Y‘ type strainer before the diaphragm valve and an isolating valve only after the diaphragm valve. Bypass arrangement with an isolating valve a steam trap and a drain with two valves is provided for the above diaphragm valve.

11. BURNER VALVE STATION :
The fuel oil supply line has two hand operated isolating valves, one of which is a quick closing valve.
A `Y‘ type strainer provided in the line prevents any possible blocking of intricate oil passages in the burner. Then, there are two solenoid valves of quick closing type operated by BMS.
Purging of burner is done to clean and flush the burner oil passages in order to get rid of any remnant oil particles there, which would other wise cause chocking in the passage.
DRAIN ARRANGEMENTS :
In the three way valve of the purge line, one way is open to atmosphere. Under normal condition it prevents contamination of steam system by any possible leakage of oil through the non- return valve. It also serves as a drain for the locked up steam on the closing of the purge valve. The dirt condensate collected from the bottom of this three-way valve of all the four burners of a boiler join together. The total dirt condensate quantity of all the three boilers will be about 30 kg/hr and is allowed to go as waste.

12. OIL BURNERS:
ARRANGEMENT OF OIL BURNERS:
Each boiler is equipped with four oil burners. The location of oil burners is so chosen to ensure proximity of each oil burner to two p f burners at the lower elevation
OIL BURNER GUN :
The oil burner is of retractable type and is having three concentric tubes. Atomizing steam flows through the inner tube of the burner, while oil flows through the annular space between the inner and middle tube and the cooling air between the middle and the outer tube.
T he burner gun is inserted into the furnace while cutting in a burner and retracted while cutting out.
A flap (a small circular door) is provided at the end of the gun support pipe
This opens when the burner gun is inserted and closes when the gun is retracted. Thus the burner gun and tip are protected from intense radiation from the furnace.
OIL BURNER TIP :
The burner nozzle consists of eight number `Y‘ type holes . The atomizing steam supplied to the burner at a constant pressure of 11 bar flows through the inner tube of the burner gun and comes out through the eight nozzle holes. The velocity of steam increases while passing through the eight divergent nozzle holes arranged at 45º angular intervals.

14. The oil stream gets mixed with the expanding steam stream in the`Y‘ type connection, gets atomized and comes out of the nozzle in a fine spray
COOLING AIR SUPPLY :
A separate air fan supplies cooling air supply. There are two cooling air fans at 15 ML in the furnace rear side, one will be in service and the other is kept as stand by.
Cooling air is feed between middle and outer space coming out of burner tip
The cooling air supplied by the cooling or scanner fans is used for
Cooling of the oil burner gun.
Cooling of the ignitor guns.
Cooling of lignite flame scanner (IR).
Cooling of oil burner flame scanners (UV).
OIL BURNER AIR SUPPLY :
Combustion air supply for the burners is taken from the hot air distribution boxes.
In the burner arrangement surrounding the burner gun, there is a circular ducting of 508 mm diameter. In this duct, 8 stabilizer vanes are there, fixed to the gun support pipe. The primary air supplied is given a vortex motion because of the stabilizer vanes. The secondary air gets supplied through the annular space in between the primary air duct and the outer duct of 910 mm diameter

15. IR FLAME SCANNERS :
Four numbers of Infrared flame scanners are provided in each boiler to detect lignite flame.
In each oil burner assembly, one Infra red scanner is provided to monitor the lignite flame.
IGNITION DEVICE:
One high voltage pulse ignition gun per burner is provided for the ignition of oil
The supply voltage to the igniter 20 to 265 volts d.c or a.c is stepped up to 2000 volts d.c. and a capacitor is charged at this voltage
The energy stored in the capacitor is discharged through the spark plug at the end of the igniter
UV FLAME SCANNERS :
IR scanners and UV flame scanners are placed at 50 mm on either side of the burner gun at an inward angle of 7º each.
The self-monitoring feature guarantees that the `flame out‘ signal will always be initiated should flame failure occur.

16. PUTTING THE SECONDARY OIL PREHEATER INTO OPERATION:

17. CONTROL ROOM OPERATION OF AN OIL BURNER:
The key switch should be selected for control room operation
Ignition release for oil fire existing lamp is ON
STEP-1
The oil gun gets inserted -The UV flame scanner gets switched on
STEP-2
Atomizing steam valves gets opened. Cleaning valves 1 and 2 get opened. Blowing warm operation gets initiated. Blowing warm running lamplights up. The oil and steam passages down stream of valves including the burner gun are now warmed up with steam. This Blowing warm operation duration is two minutes.
STEP-3
On completion of blowing warm operation, both cleaning valves 1 & 2 get closed. -Blowing warm operation running lamp switches off. 65
NOTE: The blowing warm operation gets skipped in case of a HOT START. HOT START‘ Means.
Three or more oil burners are in operation. (or)
Secondary air temperature is more than 200ºc

18. Oil release is existing and
STEP-7
If oil release exists and ignition impulse exists‘ Ignition safety time‘ starts and both oil valves get opened to admit oil into the gun. The ignition safety time is 10 seconds with no oil in the gun and 5 seconds when there is oil in the gun. The flame has to be established and sensed by the UV flame scanner before the completion of ignition safety time. If
Oil release is existing and
Flame detector senses the flame the oil valves will remain open and `Burner ON‘ lamp glows. If flame is not established within ignition safety time, the oil valves will close and red lamp in the control desk will flash. The ignition transformer switches off and ignition gun will retract

19. STEP-4
Ignition gun gets inserted if
Oil gun is in inserted position and
(b) Oil secondary air damper is open. T
The ignition gun insert command exists for a period of 25 second only after which the gun will retract.
STEP-5
On insertion of ignition gun, the ignition transformer gets switched on and sparks are initiated . Now Ignition impulse existing status comes.
STEP-6
OIL RELEASE EXISTING lamp glows now if the following condition are fulfilled.
Ignition release for oil fire exists.
b) Both cleaning valves are closed.
c) Oil gun is in inserted condition.
d) Atomizing steam valves is opened.
e) Oil pressure is more than 3 Kg/cm²
f) Atomizing steam pressure is more than 5 Kg/cm²
g) Combustion air low is more than 14 T/Hr
h) Compressed air pressure is more than 4 Kg/cm² 66

20. Lignite firing System:
In TPS 2 boiler consists 6 BURNERS each comprises
6 - Bunkers
3 - Plate feeders
1- Conveyor belt feeders
1 - Resuction duct
1 – Beater wheel mill
1- Pulverized fuel duct
2 – Pulverized fuel burner
2 – After Burning Grate to collect unburnt ash

22. Boiler Bunker: They are six bunkers for unit with 3 hoppers at bottom.
Start from 30ML to 19.5 ML , it total hight is 11.5mts.
Bunker is steep slope structure for easy flow of lignite by gravity
Three needle gates at top and bottom to isolate the hopper, 186 needle gate are inserted
Mostly choking occurs in bunker to over come choking a polyethylene material of 10mm thickness is lined .

23. LIGNITE REQUIREMENT AND STORAGE:
206.7 tones of lignite has to be burnt per hour (Net calorific value of lignite is 2380 kcal/kg and boiler efficiency is 89.33%)
A fully filled boiler bunker is able to supply lignite at the rate of 42t/hr for a period of 7 ½ hours
PLATE BELT FEEDERS (APRON FEEDERS) :
At the bottom of each bunker, three plate belt feeders having a maximum capacity of 35 t/hr each are provided to transfer the lignite from bunker to a conveyor belt feeder.
PADDLE WHEEL:
This paddle wheel during service breaks the lignite boulders and also ensures uniform feeding of lignite to the belt feeder.

24. SCRAPPER UNDER PLATE BELT:
Scrapper feeder is provided to scrap any spillages from plate belt feeder so that there are no chances of accumulation of lignite and subsequent over tension of plate belt feeder chain.
CONVEYOR BELT FEEDERS:
Three plate belt feeders at the bottom of each bunker feed lignite to a common belt conveyor
Each belt feeder is capable of handling maximum of 65 tones of lignite per hour
The conveyor belt feeder discharges lignite into a rectangular chute which is inclined by 25 degree to the vertical

25. RE SUCTION DUCT:

26. The hot air is supplied at six points, three on either side
The gases for drying lignite is drawn from the furnace through a duct called resuction duct. It is taken off from the furnace at an elevation of 37.8 meters
It is provided with refractory and insulation material for a total thickness of 350 mm consisting of 5 mm thick steel plate ,10 mm thick asbestos sheet, insulation bricks 235 mm thickness and refractory bricks of 100 mm thickness
The gases are drawn at the rate of kg/sec. at a temperature of 950 degrees
The gas is tempered by mill hot air which is supplied from the hot air distribution box at a temperature of 286 at the rate of kg./sec
The hot air is supplied at six points, three on either side
It mixes with the flue gas, tempers it and reduces the temperature of the mixture to 814˚ c.

27. BEATER WHEEL MILLS:
Lignite is discharged through the resuction duct into the beater wheel mill which acts as a centrifugal fan, creates suction for drawl of flue gas and discharges pulverized fuel gas mixture at the rate of m3/sec.
The mill outlet temperature will be in the range of 120 ˚ -180˚C.
PULVERIZED FUEL BURNERS:
Pulverized fuel burners are installed in two elevations i.e., at 20 ML and at 27ML.
The pulverized fuel burners are so arranged that their center lines form tangents to an imaginary circle of 1.5 meter diameter at the center of the furnace.

28. AFTER – BURNING GRATES:

29. IMMERSION DAMPERS:
The discharge of after burning grates will directly fall over the slag bath through an opening at furnace bottom. This opening can be closed by using a device called immersion dampers which normally connects furnace bottom and slag bath.
OPERATION OF LIGNITE FIRING SYSTEM :
In the Lignite Firing system mills and feeders can be taken into service only when adequate ignition energy is available in the furnace .
Ignition temperature of lignite is only 185˚c.
lignite-firing system demands
A drying agent to bring down the moisture level in the lignite
A source of heat enabling ignition of minimum quantity of lignite – air mixture and 87
3. A pulverizing unit to reduce lignite size so that the process of combustion becomes efficient.

30. 3 or more oil burners are in service with an oil flow > 11 t/hr .
3 or more end feeders are in service with lignite flow.
Secondary air temperature is >200 º c.
Boiler inter locking are fulfilled.
The oil firing system must burn a minimum fuel oil at the rate of 11 t/hr with 3 or 4 oil burners. This process will produce adequate heat in furnace so that sufficient hot drying gases (minimum flue gas temperature 500 ºc)
The flue gas temp. is restricted not more than 815ºc.
Incase of using high temp. flue gas, the moisture in the lignite will be reduced to a dangerous limit.
This may be avoided well by admitting mill hot air at a temp. of 286ºc to the hot flue gas and maintaining the mixture of hot flue gas and air temp. not exceeding 815ºc otherwise known as before mill temp
This process of thermal grinding reduces the mixture temp. to 770ºc known as before mill temp.

32. After mill temperature is maintained at 120 to 180 degrees.
Percentage of O2 & % of CO2 in the milling system is kept not less than 7.0 % and not more than 17% respectively.
CONCLUSION :
The co2 in the drying medium should not be less than 8%. Excess air used is normally about 25%. Control range of firing is available down to 50% load conditions without need to shut down any mill. When load through the system gets down to 40% mills need to be shut down.