GENERAL OVERVIEW OF NSPCL(ROURKELA) THERMAL POWER PLANT AND STUDY OF THE ELECTROSTATIC PRECIPITATOR

Transcription

1 A Project Report on GENERAL OVERVIEW OF NSPCL(ROURKELA) THERMAL POWER PLANT AND STUDY OF THE ELECTROSTATIC PRECIPITATOR By SAYANTAN JANA Under the guidance of J.ARATI(ENGR.,EMD) 1

2 NTPC-SAIL Power Company (Pvt.) Limited, Rourkela CERTIFICATION This is to certify that the project entitled General Overview of NSPCL(ROUKELA) THEMAL POWER PLANT and the study of the Electrostatic Precipitator was undertaken by SAYANTAN JANA under my supervision at NSPCL, Rourkela.He has been working under my guidance from 3 nd to 30 th JUNE During the entire project period it was observed that he was disciplined, punctual, hard working and enthusiastic, fully committed to his task and always interacting with the employees in a way that was positively unique. His approach and conduct at this level was exceptionally nice with everyone with whom he interacted. I wish him a successful future and career. J. Arati Date: Place: 2

3 ACKNOWLEDGEMENT Working on this project has lent me a lot of exposure and has presented an enormous opportunity to learn and understand the actual functioning of the Thermal Power Plant. I would like to take this opportunity to thank my Training Co-ordinator Ms. J. Arati who guided me throughout the procedure and gave me her valuable guidance and relevant information to complete my project work.i would also like to express my gratitude to Mr Deepak Pattanaik,Dy. Supdt (E&M) who played a pivotal role towards my plant exposure by patiently clearing my frequent doubts and assisting me in site visits. I would also take the opportunity to thank all the staff and officials of NSPCL who helped me throughout the training period and gave me immense exposure to enhanced my knowledge regarding the functioning of a Thermal Power Plant. SAYANTAN JANA 3

4 CONTENTS TOPIC 1. Certification 2. Acknowledgement 3. The General Layout and Parts of a Power Plant 4. Electrical System 5. Electrostatic Precipitator An Introduction to Electrostatic Precipitator Principle of Operation Description of the Components of ESP Electric Part of ESP Conclusion 4

5 THE GENERAL LAYOUT AND PARTS OF A POWER PLANT The entire power plant has been divided into various parts and it constitutes of the following parts Coal handling plant 2. Boiler and furnace 3. Air and flue gas path 4. Feed water and steam path 5. Cooling water path 6. Ash handling plant 7. Fuel oil pump house 1. COAL HANDLING PLANT The main function of the coal handling plant is: - 1. Supply coal to the bunkers. 2. Separation of ferrous materials from the coal. 3. Crushing the coal into smaller size. The coal is transported to the site of the plant through rail and unloading is done with the help of the wagon tipplers. The five different paths that are included in the coal handling process are: - 1. Wagon tippler to the coal bunker. 2. Wagon tippler to the stockyard. 5

6 3. MUTH to the coal bunker. 4. MUTH to the stockyard. Each unit has 4 coal bunkers. From coal bunkers the coal is fed to the coal feeders and from coal feeders it is put into the coal mill. 1.1 COAL MILL: - In this part of the plant coal is powdered to the size of 30 mm and this form of coal in the coal mill is pulverized and is dried with the help of P.A FAN (primary air fan). And this P.A fan conveys the coal to the furnace COAL PULVERISER: - The pulverized form of coal has the following advantages: - In pulverized form better combustion is achieved due to use of hot air at temperature ranging from 260 C to370 C. The coal burns completely. Ash removing troubles are removed. The pulverizing coal furnace is outside the furnace therefore it can be repaired without cooling down the unit. The pulverized coal has the following disadvantages: - Coal preparation plant is required which makes the installation expensive. There is risk of explosion as coal is burnt like a gas. The pulverized coal is produced in the medium speed mills connected directly to furnace by coal pipes. The coal mills are ball ring, pressurized type with integral indicator. 2. BOILER AND FURNACE 2.1 PRIMARY AIR FAN (P.A FAN): - 6

7 The primary air fan or mill fan is a single impeller fan with damper on the suction side. The fan is directly coupled with the motor and has a forced lubrication system for its bearing. The P.A fan provides hot air into coal mills which transport the coal into the burners. Another of its functions is to remove the moisture from the coal. And this air used also helps in combustion of the coal. 2.2 SEAL AIR FAN (BLOWER): - Sealing air blower (centrifugal type) provides seal air on the drive shaft of the lower bowl to prevent leakages and works as shaft seal. The sealing air for feeders is taken from the atmosphere. A blower is used to increase the pressure for effective sealing. A plate damper is provided in the path of the seal air to the pulverizer and positive seal air pressure is available. 2.3 COAL FEEDERS: - The coal from the bunkers are located at the front side of the boiler bay is transported to the mills by means of gravimetric belt feeders. Each mill is supplied from its own feeders. Plate type gates are used to isolate the coal bunkers from the feeder and the mill from the feeder. 3. AIR AND FLUE GAS PATH This system consists of two parallel systems (A&B) of two forced draft fans (F.D.FANS), Rotary Air Heaters (RAH),Induced Draft Fans(I.D FANS) and Electrostatic precipitators(e.s.p) working in parallel to each other during normal operation of the system. The F.D. FANS push atmospheric air through the air pre-heater, various air ducts and burners into the furnace. The I.D. FANS pull the combustion gases from the furnace through the heat transfer surfaces in the super heaters, economizers, gas side of air pre-heaters, dust separating equipments into the chimney. 3.1 ROTARY AIR PREHEATERS: - Two rotary regenerative type air heaters are provided for the boilers. The air heater transfers sensible heat in the flue gas leaving the boiler to the combustion air 7

8 through regenerative heat transfer surface in a rotor that turns continuously at low speed through the gas and air streams. The air heaters are located at the rear side of the boiler. The rotor is supported at the bottom through a lower bearing at the cold end of the air heater. Air from the F.D fans pass upwards while flue gases from secondary flow downwards. 3.2 INDUCED DRAUGHT FAN (I.D. FAN): - The I.D fan is a single stage double suction centrifugal fan directly coupled to dual speed motor. The fan is equipped with guide van at suction and flap at discharge. Two fans are provided for boiler with low/high speed selector switch, speed selection can be done for I.D fan motor. The capacity of the fan is controlled by using a movable inlet vane. Variable inlet vanes are more effective in saving than parallel blade inlet box dampers. An inlet vane controlled centrifugal fan is selected to produce full specified flow pressure with no inlet vane present. 3.3 FORCED DRAUGHT FAN (F.D. FAN): - It is a single impeller single suction centrifugal fan with movable control vane at its suction and an on-off damper at the delivery side. The fan takes suction from atmosphere and delivers cold air to the rotary air heater. The capacity of the van is controlled by the suction guide van. The sizes of the vans have been selected so as to supply total air required for proper combustion of the fuel at the boiler Maximum Continuous Rating (MCR). They also provide air to make up for air heater leakage. 4. FEED WATER AND STEAM PATH 4.1 REGENARATIVE FEED HEATING SYSTEM: - To improve the overall efficiency steam is extracted at different stages of the turbine to heat the feed water. This is known as the regenerative feed water heating system. The regenerative feed cycle start from the condenser at low pressure.end to the economizer inlet at high pressure. 8

9 Two types of feed water heater are commonly in service are closed type and the open type. In the closed type heater the fluids do not come in direct contact with each other. In open type heater the fluids come in direct contact with each other. It consists of two low pressure heaters (LPH-1 and LPH-2) a constant pressure deaerator and two high pressure heaters (HPH-1 and HPH-2). There are five extractions from turbine which provide uncontrolled steam flow to two LP heaters, deaerators and two HP heaters. The presence of air in heaters leads to deteriorate the performance of heaters. Hence provision has been made for continuous removal of air in both HP heaters; vents have been connected to deaerators through a restricting globe valve, from LP heaters vents have been connected to condenser through restricting orifice and globe valve LOW PRESSURE HEATERS-1 (LPH-1): - Main condensate passes through the tubes of the heater while steam from the turbine is supplied through extraction-1 to LP heater-1 shell side. Extraction line is provided with on power assisted non-return valve (ES-43) at turbine end for preventing back flow of steam. A motorized isolated valve is also provided in this extraction line at heater end to facilitate heater isolation from steam side LOW PRESSURE HEATERS-2 (LPH-2): - Main condensate passes through the tubes of the heater while steam from turbine is supplied through extraction-2 to LP heater-2 shell side extraction line is provided with one power assisted non-return valve (ES-2) is also provide in their extraction line at heater end to facilitate heater isolation from steam side. In main condensate line hand operated valve (MC-27) is provided for bypassing the heater. An alternate drain line with control valve is provided to divert from LPH-2 to condenser through LP drain flash tank. DEAERATOR: - Main condensate passes to deaerator where dissolved gases get separated from water which is finally collected in the feed water storage tank. Steam from extraction-3 is connected to deaerator. In this extraction line there are two non- 9

10 return quick closing extraction valves (ES-5 and ES-7) at the turbine end. A motor operated valve is provided at deaerator end. 5. COOLING WATER PATH 5.1 COOLING WATER SYSTEM: - The circulating water (CW) system is a closed system in which the cooling water supplied to the condenser is returned to a cooling tower where it is cooled and the recooled water is used again for condenser cooling. The circulating water (CW) system supplied cooling water to the condenser and also a auxiliary cooling water system. 5.2 CIRCULATING WATER PUMP: - The system consists of three no s of vertical turbine of pumps. A motor operated butterfly value is provided on each of the CW pump header. The control is such that when the pump is started the valve opens automatically and when the pump trips the valve automatically closes thus preventing back flow of water. 5.3 AUXILIARY COOLING WATER SYSTEM: - The auxiliary cooling water system (ACW) supplies cooling water for the unit auxiliaries and some of the common services. The ACW system draws its supply from cooling water (CW) header before the inlet of condenser and the hot water is returned to hot CW header after the outlet of condenser AUXILIARY COOLING WATER PUMP (ACWP): - The ACW system consists of three (100% capacity) horizontal centrifugal pumps, one ACW surge tank valves and connected pipelines from the inlet (cold) CW line is a tap-off is taken through a motorized valve to a suction header of ACW pumps. The ACW system supplies cooling water to the following equipments: 10

11 Pulveriser oil coolers Rotary Air heater guide bearing coolers Primary Air fan oil coolers Induced Draft fan bearing oil coolers Seal oil coolers Turbine oil coolers Hydrogen coolers Boiler feed pumps Oil coolers Sealing water coolers Motor water coolers Condensate extraction Pumps Various air conditioning units and chemical analyzer room 5.4 MAKE UP AND CONDENSATE SYSTEM: - Due to leakage and necessary blowing down of boilers some of the water used in the power station heat cycle is lost and must be replaced. The natural water is treated in water treatment plant before introducing into the feed water cycle as make up. Water treatment plant consists of the treatment plant and demineralization plant. While the pre treatment practically removes the suspended impurities and to some extent colloidal impurities, the demineralization plant removes the dissolved impurities to the required level. Circulating water passes through the condenser tubes and picks up the latent heat from the exhaust steam which is passed on the shell side. The condensate is collected in the condenser hot well DM MAKE-UP SYSTEM: - 11

12 The make up water to feed cycle is added at hot well by means of three (100% capacity) make-up pumps. These pumps take their suction from the make up storage tank. The make-up pumps supply make-up to the following points: For initial gland sealing of condensate Extraction pump till the CEP start. Make up line to feed cycle in condenser hot well. Two make up values which are installed in parallel, transfer DM water from the make-up storage tank to condenser hot well for maintaining the water level in hot well. One control valve is provided to return the excess water hot well to make-up storage tank. In addition, an emergency make-up line to hot well with motor operated valve has also been provided to cater to emergency requirements CONDENSATE EXTRACTION PUMP: - There are two condensate extraction pump (100% capacity) provided for the system, with one pump for normal operation and the other for standby. Since the suction pressure of the pump is atmospheric a balancing air line from the pump casing to condenser is provided. This air evacuation line helps to keep the pump primed always. 6. ASH HANDLING PLANT Many countries around the world, including our own, depend on coal and other fossil fuels to produce electricity. A natural result from the burning of fossil fuels, particularly coal, is the emission of fly ash. Ash is mineral matter present in the fuel. For a pulverized coal unit, 60-80% of ash leaves with the flue gas. Historically, fly ash emissions have received the greatest attention since they are easily seen leaving smokestacks. The emission control device for fly ash is the electrostatic precipitator. Electrostatic precipitators have collection efficiency of 99%, but do not work well for fly ash with a high electrical resistivity (as commonly results from combustion of low-sulphur coal). In addition, the designer must avoid allowing unburned gas to enter the electrostatic precipitator since the gas could be ignited. The flue gas laden with fly ash is sent through pipes having negatively charged plates which give the particles a negative charge. The particles are then routed past positively 12

13 charged plates, or grounded plates, which attract the now negatively-charged ash particles. The particles stick to the positive plates until they are collected. The air that leaves the plates is then clean from harmful pollutants. Just as the spoon picked the salt and pepper up from the surface they were on, the electrostatic precipitator extracts the pollutants out of the air. 7. FUEL OIL SYSTEM Top View of ESP Schematic Diagram Fuel oil (FO) is used in the fuel oil burners during startup, until coal firing system gets stabilized. Fuel oil is used during low load operation to support coal firing as also during the shutdown of the boiler, when the coal firing is stopped. The Fuel oil system consists of two independent pumping units which deliver the fuel oil to the burner of two units. 7.1 FUEL OIL STORAGE TANK: - Fuel oil stored in two Main fuel oil storage tanks is transferred to two day oil storage tanks by four transfer pumps whenever the oil level in day oil tanks falls. The transfer system consists of four screw type day oil transfer pumps. Two day oil transfer pumps are connected to one day oil tank. 7.2 FUEL OIL SYSTEM: - Fuel oil is fed to oil burners from both fuel oil day tanks through common suction header. The fuel oil system consists of two fuel oil pumps (multi-screw positive 13

14 displacement, 100% capacity) with coarse duplex strainer at suction (common for both pumps), two fuel oil heaters and a duplex fine strainer on discharge line. In the fuel oil day tank, a steam coil heater is fitted to maintain constant temperature of fuel oil. The discharge of the two fuel oil pumps is connected to one header. From header, fuel oil is supplied to boiler furnace through fuel oil heaters. Steam used in the fuel oil heaters and for steam tracing is taken from the auxiliary steam header. Normally one pump will be in service while the other is kept standby. Similarly one fuel oil heater will be kept in service. ELECTRICAL SYSTEM The power requirement of Rourkela Steel Plant is met partly by import from Orissa State Electricity Board at 132Kv level and balance by its own generation from the captive power plants. The interconnection between the 132Kv lines and captive power plants is done at 132Kv level in the 132Kv switchyard of the captive power plant. The switchyard also provides the starting power requirement of captive power plant. The switchyard also provides the starting power requirement of captive power plant. 132 KV SWITCHYARD The switchyard mainly consists of 132 kv main bus-1, 132 kv main bus-2 and 132 kv transfer bus. The main bus-1 and main bus-2 can be paralleled through a bus coupler breaker. Each feeder breaker has an off-load motor operated isolator on bus end and on the outgoing end. Earthing switches are provided for safety earthing during maintenance of the isolators and breakers. STATION TRANSFORMER The startup power requirement of both auxiliaries and certain common services like coal handling plant, DM plant, etc. which are having HT drives and LT drives for which power supply is derived from a 132 kv/6.6 kv step down transformer connected to the 132 kv grid on its primary side. The 6.6 kv secondary of the transformer is connected to the switchgear. 14

15 6.6 KV STATION BUS AND UNIT BUS The auxiliary system has HT and LT motors for which the power supply is fed from station transformer through station switchgear. The secondary side of the station transformer is connected to the station switchgear which is in two sections namely Station Bus-A and Station Bus-B. The 6.6 kv power supply requirements for unit auxiliaries like HT motors driving pumps, mills, fans and 415V power for motors driving various pumps, valves, etc. are met internally by the unit auxiliary transformer which steps down 11.5kv generator voltage to 6.6 kv level. The LT side of the unit auxiliary transformer is connected to unit switchgear by cables. The unit switchgear is in two sections namely Unit Bus-1 and Unit Bus-2 which are connected in parallel. Each section has a tie to 6.6 kv station bus. 415V UNIT AUXILIARY SYSTEM The boiler, turbine and the other unit auxiliaries which are driven by LT motors are fed from control centers located centrally to the system. The 415 V is derived through 6.6KV/433V step down transformer. There are three 415V switchgear namely Unit Service Switchgear, Station Service Switchgear and Emergency Switchgear. 415V Unit Service Switchgear The Unit Service Switchgear (UST) has two sections, Section-A and Section-B. Each section has one incomer air circuit breaker and a bus coupler air circuit breaker is provided between two sections. The loads on each section are: Section-A Boiler MCC Turbine-Generator MCC Emergency MCC 15

16 Section-B Boiler MCC Turbine-Generator MCC Ash Handling Plant MCC-2 Auxiliary CW MCC 415V Station Service Switchgear The Station Service Switchgear (SSS) has two sections, Section-A and Section-B. Each section has one incomer air circuit breaker and bus coupler air circuit breaker is provided between two sections. The loads on the sections are as follows: Section-A Ash Handling Plant MCC-1 DM Plant MCC Emergency MCC Section-B Ash Handling Plant MCC-1 DM Plant MCC 415 V Emergency Switchgear Certain auxiliaries are essentially to be maintained in running condition under unit trip condition to prevent damage to the equipment. The auxiliary loads which are connected to the emergency switchgear are as follows: Turbine-Generator Emergency MCC Fire Water Pumps 16

17 Lighting 132 KV SWITCHYARD OPERATIONS The outdoor switchyard is of Two Main Transfer Bus arrangement comprising of 132 kv Main Bus-1, Bus-2 and Transfer Bus. There are seven bays in the switch yard for the following equipment: 1. Generator #1 2. MSDS-II Feeder 3. Bus coupler 4. MSDS-III Feeder 5. Generator #2 6. Bus Transfer 7. Station Transformer 17

18 18

19 AN INTRODUCTION TO ELECTROSTATIC PRECIPITATOR:- Many countries around the world, including our own, depend on coal and other fossil fuels to produce electricity. A natural result from the burning of fossil fuels, particularly coal, is the emission of fly ash. Ash is mineral matter present in the fuel. For a pulverized coal unit, 60-80% of ash leaves with the flue gas. And we cannot afford to pollute the atmosphere with such alarming levels of pollutants day after day. This would give way to a plethora of respiratory and other related diseases and make our natural resources irreversibly unusable. So we need to cleanse the exhausted gases from our thermal power plants to the maximum possible extent before they are let out into the atmosphere. This was previously done by traditional fabric filters. The fabric filters are large bag house 19

20 filters having a high maintenance cost (the cloth bags have a life of 18 to 36 months, but can be temporarily cleaned by shaking or back flushing with air). These fabric filters are inherently large structures resulting in a large pressure drop, which reduces the plant efficiency. So they were replaced in the later years by Electrostatic Precipitators (ESP). The first use of corona to remove particles in an electrostatic precipitator from an aerosol was by Hohlfeld in However, it was not commercialized until almost a century later. In 1907Dr. Frederik G. Cottrel applied for a patent on a device for charging particles and then collecting them through electrostatic attraction the first electrostatic precipitator. He was then a professor of chemistry at the University of California, Berkeley. Cottrell first applied the device to the collection of sulfuric acid mist emitted from various acid-making and smelting activities. And now it is being used in thousands of thermal power plants to cut down on the ash content of the atmosphere. An electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream. PRINCIPLE OF OPERATION:- The operation of the ESP is based on the influence of the electric field on the electrically charged particles. A gas polluted with the dust grains or the liquid drops are being directed to the precipitator through a special duct and then it flows through a strong electric field created between the collecting discharge electrodes. The collecting electrodes are earthed, while the discharge electrodes are connected to a D.C. source. The 80 kv DC supply is got from 3 phase 415 V AC supply, by stepping it up and then rectifying it to 80 kv DC. The positive terminal is earthed and the negative terminal is used. The entire procedure has been depicted in the diagram below. 20

21 CIRCUIT DIAGRAM The precipitator is supplied by a voltage of about 80 kv. The principle of dusted gas ionization is illustrated in the figure. The high voltage applied to the discharge electrodes causes a corona discharge. The corona effect provides a source emitting the free electrons. The electrons are ionizing the gas particles within the corona range thus producing positive and negative ions. The gas ions being influenced by the electric field forces are migrating towards the electrodes having opposite polarity. The negative gas ions migrating under the influence of electric field forces in the direction of the collecting electrodes collide with the dust grains being 21

22 carried by the gas flow, adhere to them and impart to them negative electric charge. Being influenced by the electric field forces the negatively charged dust migrates towards the collecting electrodes. These grains after getting in contact with the collecting electrode surfaces or with the dust layers settled on them, pass over their electric load and remain on the electrodes thus forming thicker and thicker layers which next either under the influence of their own weight/ by gravity/ or due to rapping break away from the electrode surfaces and fall down into the collecting hoppers. The positive ions being produced within the corona range have a very short way to get to the surface of the negative discharge electrodes and thus they impart their charge to a relatively small quantity of dust grains, so that a small amount of dust gets deposited on the discharge electrodes. Similarly as in case of collecting electrodes the dust is removed from the discharge electrodes by means of a rapping installation. The above description gives only a general outline of functioning of the ESP, which operate in a far more complicated way due to the numerous side-effects taking place into the ESP /electrostatic precipitators. 22

23 Working Principle of ESP PARTS OF ESP:- 1. ASH COLLECTING HOPPERS:- In the lower part of the ESP chamber the collecting hoppers are suspended being intended for the temporary storage of dust precipitated during the ESP operation. The hopper includes the lower chute and the upper sections. Both the lower chute and the upper sections are made of the steel plate ribbed with rolled steel shapes. The hopper is provided with the inspection manholes for the purpose of internal inspections or repairs. The dust being stored in the hopper shall be regularly and periodically removed to the place of its final destination. 23

24 The maximum level of the dust in the hoppers should never exceed their upper edge. There is a principle, that the ESP should be operated on the empty dust collecting hopper base. That means the dust ought not to collect the over the level which is signaled by means of the signaling devices- attached on the ash collecting hoppers. Functioning of that signaling indicate the intervention necessity. Ash Collecting Hoppers 2. COLLECTING ELECTRODE SUSPENSIONS:- Collecting electrodes are suspended in the precipitator chamber on the special suspension beams. These beams are made up of two evenly spaced channel sections facing each other with their webs and screwed with M16 bolts. The beams on the plate girders of the chamber and are secured against displacement by flatiron spacers, which are attached by welding-after adjustment of the electrode rows in scale/ pitch/ with allowable tolerance of ±2 mm. The whole electrode rows are braced by lacings being welded to the extreme electrode plates. These lacings secure the electrodes against side deflections and are keeping the whole row of electrodes in the vertical plane. In the lower part of the row the electrodes are braced by means of the rapper rods, which are suspended on the extreme electrodes. On one end of the rods 24

25 there are anvils which are being struck by the flip-flop hammers causing the vibration of the whole collecting electrode rows whereby the dust accumulated on them falls down. 3. COLLECTING ELECTRODES: - The collecting electrodes are made of profiled sheets 1.5 mm thick. They are suspended in rows following the direction of the gas flow. The collecting electrodes are intended for accumulation of the dust being precipitated and they form an essential part of the ESP chamber equipment. 4. DISCHARGE ELECTRODE SUSPENSIONS: - Each electric field of the electro filter has supporting insulators installed in the plate girders. The insulators are mounted on the base in the protective tube which in turn is mounted on the channel section structure fixed to the plate girder bottom. On the suspension frames discharge electrodes are suspended. In the plate girder electric heaters are installed in order to protect the supporting insulators against precipitation caused by differences and changes of temperature in the plate girder and the ESP chamber. 5. DISCHARGE ELCTRODE SUSPENSION FRAMES: - Suspension frames for distance electrodes are made up of vertical tubes, ladders, upper cross beams made of channel section, lower cross beams made of angle section and bracings made of tubes. The frames of discharge electrodes are attached to and supported by the cross-beams of the suspension frames. 6. DISCHARGE ELECTRODES: - The discharge electrodes are made up of emitting rods fixed in the frames made of tubes. In the cross tubes of the frames holes are made in which the electrodes are fitted and blocked using special wedge pins so as to provide their good contact with the frame and to prevent them sliding out of the poles. At the top part of the vertical frame tubes carrying supports are fixed on the both sides. In the middle of each frame there is fixed on one side the 25

26 anvil with its holder and on the other side the distance tube with its holder mounted. Discharge Electrodes 7. DISCHARGE ELECTRODE RAPPING SYSTEM: - For shake off dust from the discharge electrodes a flip-flop hammers is used. The rapper system is made up of the shaft, hammers together with their holders, bearings and the drive-set. On the rappers shaft in the axes of discharge electrode frames the holders are attached in which the hammers rise to their upper position from where they begin to drop. The freely dropping hammers strike the anvil of the frame whereby dust accumulated on the electrodes is being shaken down. 8. COLLECTING ELECTRODE RAPPING SYSTEM: - Dust is shaken off the collecting electrodes using hammer type rappers. Each dedusting zone is shaken off by the separate rapping system with a programmed operating cycle. On the shaft part located inside the ESP chamber a holder with hammer is suspended in the axis of each row of the collecting electrodes. The holder is permanently fixed on the shaft, whereas the hammer is freely suspended on a pin fixed into the holder arms. During the shaft rotation the holder raises the hammer to its upper position from the latter falls down and strikes the anvil of the collecting electrode rapper rod shaking off the dust accumulated on the electrodes. 26

27 RAPPERS DRIVE SET OF THE COLLECTING ELECTRODE RAPPERS The driving set includes the following main parts: Electric motor Moto-reducer Coupling Drive-set shield The duty of the diving set is to impart predetermined rotation to the rapping system shaft, which results in the flip-flop hammers mounted on the shaft make movements combined with striking the anvils of the collecting electrode rapper rods. Taking up the impacts the rapper beams impart the energy to the collecting electrodes, which in the effect are set into a vibrating motion causing the shake off the dust accumulated thereon. The rotational speed of the rapper shaft is constant on value of 0-28 rpm. The maximum cycles value should be applied for the inlet zone whereas the minimum cycles value is destined for the outlet zone. For proper operation of the rappers the required rotating direction of the rapper shaft has to be maintained, which is closely connected with the rotating direction of the moto-reducer. The following lubricants are destined for the driving set: 27

28 Gear oil for the reduction gear LT-4 grease for engine bearings DRIVE SET OF THE DISCHARGE ELECTRODE RAPPPERS The driving set includes the following main parts: Electric motor Moto-reducer Driver Drive insulator Drive insulator casing Driving set shield Drive insulator blowing system The duty of the driving set is to impart a predetermined rotation to the rapping system shaft, which the flip flop hammers fixed on the shaft make movements combined with striking the anvils of the discharge electrode frames. Its working is same as that of collector electrode rappers. 9.GAS DUCTS: - Each precipitator is provided with the inlet and outlet gas ducts. The inlet duct begins from the last flange of the gas producing source and it ends at the inlet flange of the precipitator. The outlet duct begins at the outlet flange of the precipitator and it ends at the inlet flange of the fan. The arrangement of ducts as described above refers to the ESP operating at a negative pressure. In the ESP operating at a positive gauge pressure a reversed arrangement of ducts is adopted i.e. fan precipitator and precipitator chimney. ELECTRICAL PART OF ESP 28

29 It contains the description of the electric supply and auxiliary devices of the precipitator which are required for its operation. One complete set of the supply unit includes the control cubicle and the rectifier set. The control cubicle is adapted for a wall-mounted type and it contains control and adjustment apparatus. In the left leaf of the door measuring instruments are located i.e. voltmeter, kilo voltmeter, ammeter and milliammeter. In the lower part are installed the START and STOP pushbuttons, the pushbuttons for starting the measuring instruments, i.e. voltmeter, kilovoltmeter, milliammeter, the keyprotected interlock pushbutton as well as signaling lamps giving information on the performance of the unit. The rectifier set includes the H.T. step-up transformer, the single-phase semiconductor type rectifier in a bridge system and the L.T. rectifier. All the above elements are situated in one common vessel filled with transformer oil. On the cover of the vessel the following elements are installed: safety system thermostat, feeder box, L.T. bushing and other devices. 29

30 PERFORMANCE OF ESP:- Collection efficiency (R):- DETAILED DIAGRAM OF ESP The collection efficiency of an electrostatic precipitator is strongly dependent on the electrical properties of the particles. A widely taught concept to calculate the collection efficiency is the Deutsch model, which assumes infinite remixing of the particles perpendicular to the gas stream. 30

31 FUTURE OF ELECTROSTATIC PRECIPITATOR:- Modern Electrostatic Precipitators:- ESPs continue to be excellent devices for control of many industrial particulate emissions, including smoke from electricity-generating utilities (coal and oil fired), salt cake collection from black liquor boilers in pulp mills, and catalyst collection from fluidized bed catalytic cracker units in oil refineries to name a few. These devices treat gas volumes from several hundred thousand ACFM (actual cubic feet per minute) to 2.5 million ACFM (1,180 m³/s) in the largest coal-fired boiler applications. The original parallel plate weighted wire design has evolved as more efficient (and robust) discharge electrode designs were developed, today focusing on rigid discharge electrodes to which many sharpened spikes are attached, maximizing corona production. Transformer-rectifier systems apply voltages of kilovolts at relatively high current densities. Modern controls minimize sparking and prevent arcing, avoiding damage to the components. Automatic rapping systems and hopper evacuation systems remove the collected particulate matter while on line, theoretically allowing ESPs to stay in operation for years at a time. Wet electrostatic precipitator:- Electrostatic precipitation is typically a dry process, but spraying moisture to the incoming air flow helps collect the exceptionally fine particulates, and helps reduce the electrical resistance of the incoming dry material to make the process more effective. A wet electrostatic precipitator (WESP) merges the operational methods of a wet scrubber with an electrostatic precipitator to make a self-washing, self-cleaning yet still high-voltage device. 31

32 CONCLUSION:- As we can see Electrical Engineers can play an important part in the fight against pollution. Through devices such as the electrostatic precipitator, electrical engineers can protect the environment from harm. Such a design also appeals to the general public as the electricity can be produced cheaply. The electrostatic precipitator is just one example of a device designed by electrical engineers to help the environment. Engineers are responsible for considering environmental impact as part of their original design work.. 32