Boiler

Boiler

A boiler is a closed vessel in which water or other fluid is heated under pressure. The fluid is then circulated out of the boiler for use in various processes or heating applications. Boiler is the most important part of the mill as it is the main station for generating steam and aiding the operation of turbine in the engine room. There are 2 boiler in the mill, the capacity of the 1^st boiler is 45mt/h and the empire boiler is 40mt/h. The both boiler are water tube boiler type. The water are circulates in the tubes and heated externally by the fire. The fuel is burned in the furnace, heat up the water in the steam generating tube. The water from the water drum will flow to the mud drum to be heaated. The water tubes are lines on the wall of the furnace to generate steam. The heated water then rises to the steam drum.

Figure 1: 1^st Boiler layout      

Fans

Force draft fan (FD fan)

-Blow the air from the bottom of the furnace floor. The air is blow through the furnace floor holes for the burning of the fibre.

Induced draught fan (ID fan)

-Induced draft is to flow the air by the effect decreasing the air pressure.

Fuel feeder fan (FF fan)

-to sweep the fibre out from the chute inlet to feed the fibre into the furnace and prevent fibre from clogging at the inlet chute.

Secondary fan

-locate on the wall of the furnace below the fibre feeder chute. It is use to blow the fibre to allow evenly distribution of the fibre throughout the fibre.

Frequently check the ampere reading of all the fans to make sure the fan is working at optimum condition. Incorrect condition of the fans will affect the combustion in the boiler and may lead to boiler trip.

Factor to achieve good combustion

1. Time

Time required for the fuel to totally burn in the boiler furnace. If the time is too short, it can cause the fuel not being burn properly and the chemical energy cannot be change totally. Fuel which does not burn properly will cause clinker in the furnace and came out through chimney.

2. Temperature

For proper combustion, temperature in the boiler furnace must be at optimum level so that the temperature can burn the fuel that being feed to boiler furnace. Low temperature can cause the fuel not properly being burn and came out from the chimney. The suitable temperature should be 260 degree Celsius and above.

3. Turbulence

Turbulence is being produce by the fans such as Fuel Feeder Fan, Secondary Air Fan and Force Draught Fan. Fuel will be feed to the boiler furnace using Fuel Feeder Fan and being distributed by Secondary Air Fan to all part of boiler furnace. During distribution process, most of the fuel is being heated up and burn to produce heat energy.

13 essential fitting

(Safety)

1. Safety valve

-prevent excessive pressure buildup in the boiler which could lead to boiler explosion.

-view release the steam when the pressure reach the limit (460psi)

 Figure 7: safety valve

2. Water gauge

- to indicate the water level in the water drum

 Figure 8: glass gauge  Figure 9: water gauge

3. Steam pressure gauge

-measure steam pressure

 Figure 10: steam pressure gauge

4. Fuse plug (not using in the boiler for this mill)

-low water protection, when the water level is low, the fusible plug will melt, the pressure inside the boiler is released and produce high whistling sound

5. Low water alarm

-give warning on low water level

 Figure 11: The water level display on the board.

6. Low water fuel cut out

-prevent boiler over heating failure, in the event of low water level, every valve, fibre conveyor and fan will be cut off.

(Control)

7. Blow down valve

-For boiler water blow down to control boiler water TDS

-Use in the event of high TDS in the boiler water or high water level in water drum.

 Figure 12: blow down valve

8. Feed pumps

- Feed water from the deaerator into the water drum

-Feed pump need to have enough capacity to overcome the pressure of the steam in the water drum

  Figure 13: double feed pump

9. Mainstream stop valve

- Allow the flow of the steam

   Figure 14: Mainstream stop valve

10. Feed check valve

-control the flow of the water from feed pump into water drum

-ensure single direction flow of the water

 Figure 15: Feed check valve

(Legal)

11. Inspector test pressure gauge attachment (not attaching to the boiler)

-for double check of pressure gauge function, pipe leakage

-hydraulic operated

12. Manufacturer name plate

-Record the specification of the boiler such as working pressure, testing pressure, working tempeature, design code, date of built of the boiler.

 Figure 16: Manufacture name plate

13. Registration plate

-Registration number of the boiler

 Figure 17: registration plate

Vacuum Deaerator

The vacuum deaerator functions to reduce and eliminate gases such as oxygen, which can corrode the boiler tube and steam drums.

The water is feed into the deaerator from the feed tank by gravity. The water is splash up through the nozzels. Steam is supply on the top line and created a vacuum condition that remove the oxygen in the water. The deaerated water will fall to the bottom of the deaerator and flow to the feed pump.

O2 is removed by creating Vacuum using steam jet.

• In vacuum (-20 inHg), water boiling point is lowered (60-70 degree celsius)

• Have to prevent air in-leakage into the system through pump, seals, valve, fittings, flanges of gauge glass. 

Figure 18: deaerator                                                   

 Figure 19: Vacuum deaerator working principle

Softener

Softener is a machine that functions to soften the water by reducing the content of calcium and magnesium in the water with the help of resin with polystyrene beads that carry negative charge. Salt diluted with water will be added into the softener to regenerated the resin after resin exhausted. One boiler require 2 softener to run. The softener will receive the water supply from the overhead tank and supply to the hot water tank after processed. 

Operating procedure

Before:

1. Check the condition of the boiler including the pump, pipe, fan, stone platform, furnace interior and any record of the problems of the boiler that happened the day before. If there are any, the problem should be fixed before starting the boiler

2. Check and ensure that the water level indicated by the gauge glass is one third full.

3. Check the gauge glass and steam pressure on the boiler.

4. Check the condition of the steam stop valve, blow down valve and the drain valve. Ensure they are tightly closed and not clogged.

5. Ensure that the water level in the overhead tank and boiler feed tank are always full.

6. Check softener and vacuum deaerator.

7. Open the air cork, super heater and steam trap.

8. Turn on the the induced draught fan (ID Fan) before filling fibre and shell

9. Check whether the boiler feeding chute is not clogged..

10. Control the amount of fibre and shell goes into the furnace at the initial until the steam pressure reached 400psi. Too much fibre and shell pile up on the floor will stop the combustion.

During:

1. Check and ensure the water level indicated by the gauge glass is below 1/2 level.

2. Control the steam pressure at 420 psi.

3. Ensure the fibre cyclone airlock, fibre conveyor, fibre return feed conveyor and boiler feeding chute is not clogged.

4. Clean and remove the fibre from the furnace every 4 hours to prevent the fibre pile up.

5. Rcord the drum pressure, water level, temperature, deaerator pressure, ID fan, FD fan every hour.

Possible incident

1. Furnace collapsed

Cause: furnace overheat

Prevent: ensure the water level are maintained at 60-70% in the process and no                            tube blockage.

2. Sand blasting effect

Cause: Too high draft that affect sand blasting on the tube

              Soot blower nozzle misaligned

Preventive:Balance the ID fan to the furnace

  Check the soot blower nozzle frequently

3. Tube dislodge and distort due to overheating

Cause: Overheating on the tube due to low water level

Preventive: Check the low water alarm

  Check auto level controller system

  Ensure sufficient pump capacity

Usual incident in the process

1. Low water level

- turn on the bypass valve to allow the water to bypass the regulator.

2. High water level

- use the blowdown valve to drain out the excess water

3. Fibre inlet chute blockage

- need to monitor it all the times to make sure the chute are not clogged.

Boiler trip emergency

1. Power disruption

-close off the main steam stop valve

-ensure there is water in the water drum

-open the ID fan damper and the bottom ash doors

-remove the fibre from the furnace if the disruption is going to be long

-close the MCCB

2. Low water level (water level in glass gauge still visible)

-close the main steam stop valve

-open ID fan damper and bottom ash doors

-extinguish the fire in the furnace and remove the fibre

-turn on the water feed pump to supply water to the boiler

-perform check on the cause of low water

-fill in the water if there is no damage to the tubes

3. Water level is low that cannot be seen through gauge glass

-close main steam stop valve

-open ID fan damper and bottom ash doors

-extinguish the fire in the furnace and remove the fibre

-do not turn on the water feed pump

-let the boiler to cool down naturally

-perform check on the cause of low water

Boiler water treatment

Objective

-prevent corrosion

-prevent scale

Corrosion

-Remove dissolve gas by deaerator before entering boiler

-Maintaining alkaline pH

-Keep dissolve solid within control limit

Scale

-Minimize Hardness in softener water (0-3ppm)

-Maintain Silica level (< 150ppm)

-Maintain Turbidity in feedwater (< 3 NTU)

-Minimize Aluminium carryover (< 0.3 ppm)

-Minimize Iron in feedwater (< 0.3 ppm)

-Maintain good blowdown frequency (< 2500ppm)

-Apply Good Polymer for boiler treatment (Nexguard)

Dosage Chemical used:

Adjunct B                   -5.5 kg

SG sulphite                 -5.5 kg

Adv. Plus 1400           -8 kg

Adjunct HDM            -5 kg                                        Figure 26: water drum locate on top of the boiler

Feedwater:                                                     

M x 20	Cl x 20	pH	H x 10	TDS
25-50	<50	6.5-7.0	<2.0	<110

Softener:

No.1	No.2
< 2.00	< 2.00

Boiler water:

SO3	P x 30	CL x 50	H x 10	TDS	pH	PO4 x 10
20-50	250-450	<350	<3.0	<1500	10-11.5	30-50

Figure 27: Flow of water to the boiler

Figure 24: Clearing the pile up fibre every 4 hours        

Engine room

Engine room is a station that handles the production of electrical energy from Gen set and turbine for machines that use electricity in the mill.

There are 3 gen sets which are rate as 600kw, 400kw and 400kw that use diesel to run and 2 turbines. Turbines is a machine that function to generate electricity via the steam generator. The turbine is operating by high pressure and high speed.The turbine will start to run when boiler start running and able to provide enough steam pressure (>200psi). The steam produced by the boiler would not always be consistent, there are certain time that the steam pressure will drop below the require steam pressure. If the turbine are running at insufficient steam pressure, the rotating turbine will suck up the water from the boiler together with the steam. This can damage the turbine blades. In that situation, diesel generator set will be running to reduce the load on the turbine. This situation can be determined by the frequency of the generated voltage. The ideal frequency is 50.5Hz, when the load of the turbine increased, which also indicated the steam pressure provided to the turbine is insufficient. At this time, gen set need to start up and run to support the turbine. When starting the turbine or the gen set, snychronise process need to be done. The power synchronisation process can be run after the speed and condition of the turbine and gen set reaches equilibrium. The neutral swtich can’t be on the same position for every gen set or turbine, it need to be is set to be either off or on on different gen set and turbines.

Turbine

Main component:

1. Inlet flange

- Steam Supply go through to the inlet flange prior to turbine.

- Steam can go through after the valve is open.

 Figure 30: Inlet flange

2. Combination trip and throttle valve

- Over speed Trip valve is mechanically actuated that interrupts the supply of steam to the turbine during an over speed condition or other emergency.

- Throttle valve is to control the amount of steam entering the turbine and thereby determines the speed and power produced by the turbine.

 Figure 31: Combination trip and throttle valve

3. Governor

- The governor sense the speed of the turbine and open or close the throttle valve, as appropriate, to maintain the set speed

 Figure 32: Governor

4. Inlet casing (steam chest)

- Inlet casing (Steam chest) is the casing section containing the high pressure inlet steam.

- Steam enters the inlet casing from the combo valve and travels through nozzles in the nozzle block and turn the wheel.

5. Exhaust flange

- The flange connects the turbine to the user’s exhaust steam line or back pressure vessel

 

Figure 33: The steam exhaust of the turbine back to back pressure receiver

6. Nozzles & blades

- Turbine stage consists of a stationary blade (or nozzle) and a rotating blade (or bucket). Stationary blades convert the potential energy of the steam (temperature and pressure) into kinetic energy (velocity) and direct the flow onto the rotating blades. The rotating blades convert the kinetic energy into impulse and reaction forces caused by pressure drop, which results in the rotation of the turbine shaft or rotor.

7. Bearings

- Thrust bearings axially locate the turbine rotors.

- Journal bearings are used to support the weight of the turbine rotors.

8. Shaft seals

- The seal does not prevent the steam from leaking, merely reduces the leakage to a minimum. The leaking steam is collected and returned to a low-pressure part of the steam circuit.

 Figure 34: shaft seal

9. Turning gear

Turning gear function to slow the rpm of the turbine speed. This evens out the temperature distribution around the turbines and prevents bowing of the rotors. The turbine speed is running at 4200rpm. Turning gear reduce the speed to 1500rpm to suit the altenator speed as 1500rpm is the maximum speed for all the machinery in the mill.

 There are few meter showing the pressure and temperature reading of the gear box oil, governor oil and oil tank for monitoring of the turbine condition. The temperature should be kept at 50 degree celsius. There is a water coolant for the oil to prevent the temperature of the oil to go up to high. In the process, there are few things need to be monitor which are the steam pressure, pressure and temperature of the oil, the power (kw), voltage (415v), power factor and the frequency of the generated voltage (50.5Hz).

 

Figure 35: meter reading of the pressure and temperature of the lubricating oil

Steam trap

Steam trap function is to remove the water that content in the steam. Some water form from the condensate can be appear in the turbine. The presence of water droplets in the last stages of a turbine causes erosion to the blades. The allowable limit of the wetness in the exhaust steam is imposed at 12%.                                                       

Figure36: Safety blow valve on back pressure receiver