Introduction and Facts about Large Thermal Power Station
Boiler is used for steam generation.
Ball Mill or Bowl mills are used for pulverisation of coal in powder form for efficient firing in boiler.
Raw Coal Feeders are used to supply coal to ball mills in controlled quantity.
Primary Air Fan are used to transport and preheat pulverised coal to burners.
Induced Draught Fan are used to exhaust flue gases to Chimeny and create vaccum in Furnace.
Electrostatic Precipitators are used to separate ash particles from flue gases to control pollution. Here collecting electrode, emmiting electrode and rapping mechanism used to dislodge fly ash particle.
FD Fan used to provide air to boiler for help in firing which is called secondary air.
Steam produced in boiler is further superheated in Superheaters. There are lot superheaters such as platen, pendent, convection and final superheaters.
Boiler drum used for separation of staem from water and storage. Nowadays Drum less once through boiler also used which operates at super critical temerature and Pressure.
Boiler circulation pump used for forced circulation of water in water wall because at high pressure natural circulation is not possible.
Soot Blowers used to remove soot from water wall, Superheater, Reheaters and Air Heaters by injecting steam into heating surfaces.
Ash slurry pumps are used to flush ash with water.
Boiler Feed Pump used to provide water to boiler Drum.
Deaerator used to separate dissolved air from Feed water.
In Turbine heat energy of steam is converted into mechanical energy.
ESV which is called emergency stop valve used to stop supply of steam to turbine when unit trips.
Reheaters used to reheat steam exhausted from HP turbine.After reheating upto 535 degree centrigade same steam is utilised in Intermediate Pressure Turbine.
Barring gear or shaft turning gear is used to ratate turbinr rotor at 3.15 rpm when turbine is not running to check bending of rotor due to its own weight.
LP Heaters and HP Heaters are used to heat condensate and feed water supplied to boiler to increase efficiency by steam bled from turbine extraction.
Economiser are used to heat feed water by flue gages to increase efficiency. Heat of waste flue gas is utilised here.
Air Heaters uses heat of waste flue gases to preheat primary and secondary air.There are two types of air heaters tubular and rotary.
Condenser used to condence steam exhausted from turbine.
Condensate Pump are used to supply water to Deaerator from condenser Hot well.
CW Pump used to cool steam exhausted from turbine into condensers.
Raw Water is Circulated by cw pump into condenser tube hence leakage from condenser tubes must be checked to avoid mixing of raw water into Hot well.
Turbogenerator converts mechanical energy into electrical energy.
H2 Gas used in generators used for cooling of generators.
Seal Oil system used to seal hydrogen gas from escape from generator.
Stator Water Cooling system provides demineralised water into hollow stator conductor of generator for its cooling.
Generating Tansformer steps up volatage for transmission.
Water Treatment Plant is used to produce demineralised water for steam generation. Cation anion and degassifier tower used to separate mineral and gases from water.PAC or alum used to separate mud and silica from water.Here minerals removed from water and ph value is maintained near 7 and silica value must less tham 0.02 ppm
Coal Handling Plant supplies Coal to Boiler.Merry go round system or wagon trippler used to unload coal into hoppers. Coal is crused in crusher to crush it in 25mm size.Magnetic separators used to separate metalic particles from coal.
ABCB,SF6,OCB,MOCB and VCB are circuit breakers used to make or break electricity contact at load.
Isolators are used to make or break contact at no loads.
ABT
ABT is availability based tarrif and frequency based pricing system to maintain Grid discipline.
Purging is done to clean furnace from combustible gases by running ID Fan and FD Fan at atleast 30% load for 5 minutes to avoid furnace explosion.
Furnace explosion may be checked by timely purging and adjusting firing properly using right quantity of primary and secondary air and timely oil support and avoiding leakage of fuel oil in boiler. Furnace must be purged properly again if flame is not established during lightup of boiler.
Flame scanners used to sense flame in boiler to detect flame failure to avoid boiler furnace explosion.
FSSS is furnace safeguards supervisory system to safeguard boiler.
How To avoid Clinker Formation in Boiler?
Clinker Formation in Boiler of Thermal Power Station is due to high Ash Content which have low fusion temperature below 1470 degree centrigrade and Minerals present in it. Due to poor Quality of Coal ash got fused and mineral content stick into Water Wall which is very difficult to remove often requires removal by pneumatic machines. This Clinker deposition may be stopped to some extent if sufficient water is sprayed into hopper and regular poking and using good quality of coal. Ash fusion temperature must be above 1470 degree centrigrade and soot blowing regularly at load by enjecting steam by wall blowers. Overfiring is also responsible hence firing must be properly adjusted by proper balance of primary and secondary air in boiler.
Accumulation of clinker may be checked if poking of hoppers done regularly and any negligence may start process of clinker deposition. If clinker is not removed immediately then same may choke hopper and often workers got burnt due to sudden fall of hot water which accumulated in hopper.
Once clinker formed into hopper than outage of unit is evident otherwise clinker may deposit in huge quantity which will be very difficult to remove because minerals content present in coal fused with ash deposit into water wall. Such hard Lumps of Clinkers requires pneumatic hammering which takes very much time resulting in forced closure of unit for weeks.
Although cause of clinker formation is poor coal quality and high mineral content in coal but accumulation in Water Wall is result of negligence by Workers and Engineers who do not poke hopper regularly and spray insufficient amount of water into hopper which may not flush fused slag to channels. Outage of clinker grinder and soot blower is also matter of concern may be termed as negligence.
Hence it is advised never blame to low coal quality,low GCV,low ash fusion temperature and high mineral content in coal.Instead of blaming to above factors try regular poking and provide sufficient water in hopper.Clinker Grinders must be made operational. Soot blowing must be done regulaly by injecting steam. In India coal supplied to power plants is mostly of low quality which has high ash content so precaution is best solution here to avoid deposition and formation of clinkers in Boiler.
Precaution may stop clinker deposition and formation so remain vigilant.
Boiler Tube Leak Detection by Acoustic Monitoring Instruments
Acoustic Instruments may be used to detect early boiler tube leak to avoid secondary damage to pressure parts.Boiler acoustic tube leak detection system must be used as it prevent damage to costly boiler parts and it is very much cost effective.An increase in boiler availability of just one day will more than cover the cost of a leak detection system.
Traditional leak detection system such hearing hissing sound by ear or monitoring feed water flow or furnace vaccum is not much reliable because it can not detect small leak so damage to vital costly equipment of boiler may not be avoided.Writer noticed many instances where thermal power plants boiler allowed to run for long time due to confusion which caused permanent damage to many boiler tubes,refractory and boiler structures.Hence importance of acoustic monitoring leak detection systems sincerely felt .
Acoustic leak detection sensors detect high frequency emmissions from site of leak and Sensitive piezoelectric sensors mounted to the structure transform these acoustic waves to electronic voltage signals, which are amplified, filtered, and processed to determine energy content.
Early detection by acoustic monitoring instruments results in substantial reduction of repair times and costs with a consequent increase in plant availability and profits. The early detection of a bolier tube leak will give financial savings which will easily exceed the initial capital cost of the detection system even at the very first event.
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How To Run Thermal Power Plant Units Efficiently?
How to run units efficiently and saftly is big question today? Thermal Power Plant Units require great care during operation. Only highly trained Employees and Engineers may handle effectively. Only Quality Training Programmes for Engineers and Operators may ensure efficient Running. Greatest Importance must be given to such Training Programmes. Frequent trippings, damage of auxiliaries and Accidents are seen if Engineers and Employees are not properly Trained. Engineers must know Important facts and Operational Precaution for efficient operation of Units which are descibed below.
Coal is received from mines by Merry Go Round System. Old Power Houses uses the Wagon Tripler which turn Wagon to unload it. Coal is Crushed upto size of 25 mm and Magnetic particles are separated. If Coal is not properly crushed and Iron pieces not seperated then Pulverisers and Raw Coal Feeders will face severe problems. Chain of Raw Coal Feeder may damage due to metallic parts present in Coal. Big Size Coal may affect grinding capacity of our Pulverisers.
Raw Coal Feeders are used to provide controlled quantity of Coal to Pulverisers. Ball Mill or Bowl Mill are being used to grind coal in powder form for efficiently burning Coal.
Primary Air Fan provides air for tranportation of Coal and its drying. Forced Draught Fan provide Secondary Air help burning coal. Important point which must be remember that Ratio of Primary and Secondary must be proper. Quantity of Primary Air, Secondary Air and Pulverised Coal must be properly adjusted and firing must be checked properly by flame scanners so that they may not be unburnt coal.
Air from Feed Water is seperated by Deaerator. Hydrazine is dosed here so that oxygen is removed from feed water. Phosphate dosing is done in Boiler Drum to seperate Silica particles from feed water. Dosing of Phosphate and Hydrazine must be properly monitored. Sample of water must be timely get checked from Lab so that deposition of silica in Boiler Tubes and Turbine Blades may be avoided. Continous Blow Down valve is generally opened upto 10% to 30% as per sample reports from water chemistry lab.
At the start of boiler ignitors or oil rows if the flame is not established then we must relight boiler after purging. Boiler Furnace explosion may be avoided by timely purging and stoppage of leakage of fuel oil in
furnace. Purging is done before every light up of boiler by starting Induced Draft Fan and Forced Draft Fan for five minute and maintain 30% air flow for five minutes so that unburnt fuel and gases present in boiler furnace may escape.
At low load always take fuel oil support to avoid flame failure.
Soot blowing which done to dislodge soot from boiler tubes must be regularly done by injecting steam at sufficient pressure and temperature as per manufacturer's guidlines and intructions.
Poking of ash hoppers must be continiously monitored so that hoppers may not choked and further deposition of clinkers takes place. Clinker grinders must be made operational.
L P Drain which are provided at boiler zero meter for draining water if salt concentration and silica value increases must be operated under strict guidance and monitoring. L P Drain valve must be opened partially, one by one for less than one minutes otherwise water wall may damage due to stoppage of natural cirulation. It is best practice to operate L P Drain at the time of light up of boiler when pressure and temperarure is relatively low.
Isolators must be opened or closed at no Loads and Circuit Breakers may be opened or closed at Load.
Stator water cooling system is provided for cooling of Generator Stator Conductors where Demineralised water is circulated in hollow conductors. Quality of Demineralised water must be monitored.
Power Plant Auxiliaries such as I D Fan, F D Fan, PA Fan must be started at no load because at the time of start of motor it takes nearly 14 times more current. Position of Discharge and Suction Dampers must be properly checked.
For starting Boiler Feed Pump we must ensure that suction valve is opened and discharge valve is closed and recirculation valve must be opened.
Interlock and Protection must be timely checked to know its fuctioning.
At the instant of tripping of unit we must open Main breaker first and after Main breaker is tripped and current in all three phases shows zero then we must open field breaker of generator for its safety. D C Seal oil Pump, D C Lub oil Pump, D C Fire Pump must be started daily to check its functioning.
Barring Gear or Shaft Turning Gear must be immediately engaged when turbine rotor speed reaches to zero to avoid its bending.
At the time of Boiler Tube Leakage we must immediately trip the unit to avoid secondary damage. Feed flow quantity, Deaerator level, Furnace Vaccum must be monitored regularly. Hissing sound may be observed from site in case of tube leakage. Acoustic Monitoring Instruments may also be used to detect small Boiler Tube Leakage upto size of 2.5 mm with its correct location. This system may detect leakage at the moment it starts.
Operation of Modern Thermal Power Plant requires great attention and Precaution for its safe and efficient running although many advanced protection, auto and burner management system which are controlled by latest softawre and computer are provided. Engineers engaged in operation should remain vigilant, understand the procedures to control emergencies and prepare for many more unexpected circustances.
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