REPORT ON INPLANT TRAINING IN
NORTH CHENNAI THERMAL POWER STATION
BY
GEETHAPRIYA. T.G NANDHINEE.K
19 DECEMBER , 2011 TH
Visit
Details
Name of the industry : Thermal Power Station
North Chennai
Address : Thermal Power Station,
North Chennai
Athipattu Pudunagar, Chennai. Date of visit 02.12.2011 Duration of the visit
:
:
28.11.2011 –
5 Days
Overview
Introduction Boiler Monitoring Chemical Lab Control & Instrumentation Electrical Maintenance – I Main Relay Testing Coal monitoring Technical Service Electrical Maintenance - II
INTRODUCTION Power generation is the vital infrastructural requirement for the economic growth of our country in recent years. As economy grows the demand for power increases at a very faster rate. The North Chennai Thermal Power Station(NCTPS) comes under the control of TNEB. It was started in the year 1989 and was completed in 1995. The first stage was commissioned in the year 1996. The plant has two stages viz., Stage I(3*210 MW) & Stage II(2*600)MW. On the first day we were given the introduction of the plant. They showed us the model of the plant which was kept there. We were given a power point presentation about the same. On the second day they took us to the Boiler Monitoring and Chemical plant which is used to treat the sea water. On the third day we were taken to Control & Instrumentation unit in the forenoon and to the Electrical Maintenance-I unit in the afternoon. On the fourth day we went to the Main Relay Testing (MRT) where the relays used in the transmission lines are tested for proper functioning. In the afternoon we
went to the Coal Monitoring unit which takes care of the coal handling system of the plant. On the final day they took us to Technical Service unit which ensures the proper functioning of turbines and generators used in the plant. During the afternoon we were taken to the Electrical Maintenance II unit which takes care of the ID(Induced Draft)fan and the FD(Forced Draft)fan.
Boiler Monitoring BOILERS Boilers are used to convert the treated water into steam to run the turbine. In NCTPS there are three boilers.
COMPONENTS IN THE BOILERS The following are the major components of the boiler • • • • • • • •
Air pre-heater Induced draft fan Igniters Seam coil pre-heater Scanner fan Ignition fan Reheaters Super heaters
REACTION OCCURING IN THE BOILER
Water to be heated is made available to the boilers by means of a storage tank.
Firing of fuel takes place in the boiler by means of 4 elevations
Fuel, a mixture of coal and oil will enter into the boiler at different elevations
Firing takes place by formation of the fire ball and the height of the fire ball increases as the fuel strikes the ball at four corners tangentially.
IGNITORS o Ignition oil enters into the boilers through a valve. o At the height of about 18m AB, ignition is at its first stage and it is by light diesel oil. At the height of about 22m CD, it is at second stage and is o due to heavy furnace oil. o After this the fire is developed to some extend and hence coal is used for burning. Inside the boiler a camera is used for monitoring the fire. This camera is provided with special lens and cooling system. In that case of any trip the secondary combustion should be prevented, the heated air is blown of from entering the secondary stage. This process is called purging.
CHEMICAL LAB RAW WATER HANDLING The hardness of the water is removed in this part of the plant. The raw water having the conductivity value of 1200ppm is passed through sand filter to remove impurities. A reverse osmosis plant is provided to reduce the dissolved solids in the raw water. REVERSE OSMOSIS Reverse osmosis (RO) is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective," this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely. In the normal osmosis process the solvent naturally moves from an area of low solute concentration(High Water Potential), through a membrane, to an area of high solute concentration(Low Water Potential). The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates osmotic pressure. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis.
ION EXCHANGE PROCESS It is then passed through the weak acidic cation bed, where cation resins acidic impurities. The water coming out of this bed consists of 50% of Na, Mg and Ca. then the water coming out of strong acidic cation bed, where bicarbonates and sulphates in the water are removed. There are two strong acidic cation beds for one weak acidic cation bed. The cation bed is regenerated using HCl for every 50Hrs. from the strong acidic cation bed the water is sent to anion bed, where silica impurities are removed. There are two weak anion beds for one strong acidic anion bed. The anion bed is regenerated by NaOH. The water then reaches mixed bed where both anionic and cationic impurities left are removed. Now the demineralized water with a conductivity of 0.40.5ppm is sent tot the DME tanks.
CONTROL & INSTRUMENTATION CONTROL AND INSTRUMENTATION(C&I) In order to operate power stations at an optimum level, power technology has, over the years, become more and more dependent on automation and control. Increasing computerization has enabled the use of some very sophisticated techniques for controlling and monitoring power systems. Earlier, control and monitoring systems were usually made up of simple circuits. Operators supervised processes continuously and used their judgment to make necessary changes to set values. Now, monitoring and control in power plants are based almost entirely
on computerized equipment, which has considerably simplified the control of processes involving multiple variables. In fact, control and instrumentation or automation at power plants has become critical to maximizing efficiency and availability. It has allowed faster collection and processing of all data from various parts of the plant and has even provided for remote control of all devices. It has also helped optimize fuel utilization and lower operational costs. 1. High performance Microprocessor based SMART Pressure &
Differential Pressure transmitters 2. High performance Microprocessor based SMART Temperature transmitters 3. Microprocessor based Single & Multi loop Controllers 4. Microprocessor based multi-pen & multi-point Chart and Chartless Recorders. 5. Microprocessor based Gas/Liquid Analyzers and pollution monitoring instruments along with sample handling and conditioning system. 6. CMOS based Integral and Remote type Annunciation systems 7. Flow elements 8. Control Valves 9. Actuators 10. Power Cylinders 11. Control Panels, Desks & racks 12. UPS systems They use various digital instruments and various feedback networks for providing their function in a smooth manner. In this power generation panel controlled unit they use new version which has more advantages than the old escamatic version The advantages are Less number of modules than the old version Less physical difficulty in wiring Effective processors. The only disadvantage is that in case of any failure of processor the whole system gets collapsed, but in older version only the concerned area will be affected.
OPERATION AND EFFICENCY In NCTPS, it is required that 9% of the total power produced be used up by them for their own use. Also, there are two kinds of motor namely High Tension and low tension motors, each requiring different amounts of voltages. The total power generation is 630MV. The process is explained by the following points: ⇒ The generated 15.75KV is stepped up to 230KV by means of a step up transformer. ⇒ This stepped up voltage is then sent to the main grid to be supplied to the other stations. ⇒ Two lines taken from the 15.75KV line and are sent to the step down transformer. ⇒ These transformer steps down the voltage to 6.6 KV. ⇒ This 6.6KV is again sent to another step-down transformer, where it is further stepped down to 440V. ⇒ A separate line is taken out of the 6.6KV line and is given to the High Tension motors. ⇒ The 440V supply is given to the Low Tension Motors. ⇒ Sometimes there is a starting problem for the generator. Then a separate supply called DG Cell is used. ⇒ Also the generator circuits use a number of circuit breakers called Relays.
ELECTRICAL MAINTENANCE – I SWITCH YARD Yard of the thermal station contains current transformer, autotransformer, breaker, isolator, current transformer, earth switch, lightning arrestor, voltage transformer, capacitor voltage transformer and insulator. NCTPS has 3 generating units, each capable of producing 210MW. In the 11KV generator output is stepped-up to 230KV and is fed to the 230KV bus bar. This 210MW unit feeds the KTR, TPT, ETPS substations. SF6-sulphur hexafluoride gas is used inside the insulators due to its special properties. CTs and CVTs are used for protection and measurement.
Here double bus bar scheme is used.
MAIN RELAY TESTING RELAY
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and retransmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly control an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in
modern electric power systems these functions are performed by digital instruments still called "protective relays".
BASIC DESIGN AND OPERATION A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts (there are two in the relay pictured). The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB. When an electric current is passed through the coil it generates a magnetic field that activates the armature and the consequent movement of the movable contact either makes or breaks (depending upon construction) a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage application this reduces noise; in a high voltage or current application it reduces arcing.
COAL MONITORING COAL CONSUMPTION TamilNadu Electricity board has 160 power generating stations comprising thermal, gas based, naphtha based hydel and windmill. There are four thermal power stations located at Tuticorin, Mettur, North Chennai and Ennore; three gas based power mstations at Thirumakottai, Valuthur, Kuthalam and one naphtha based power station at Basin Bridge. The hydel and windmill stations are located in various parts of the state. The installed capacity of the board as on 31st march, 2004 was 5401.035MW. Details of installed capacity and generation achieved by the various power stations, classified on the basis of fuel used. The fuels used in the power generation are coal, furnace oil, high speed diesel oil, gas and naptha. Coal and oil
cost constituted 94.54% of total fuel cost of the Board in 2003-04. The board procures coal from Coal India Limited and its subsidaiaries, oil and naptha from Indian oil Corporation Limited and gas from GAIL(India) Limited.
SCOPE OF AUDIT Purchase and consumption of fuel as a separate activity was not reviewed in the earlier years. This review covers the activities relating to procurement, transportation, storage and consumption of fuel for the five years ending 31st March, 2004. The review conducted during December 2003 to March 2004 covered thermal power stations located at Tuticorin(Tuticorin Thermal Power Station), Mettur(Mettur Thermal power Station)And North Chennai(North Chennai Thermal Power Station). The gas-based Power stations located at Thirumakottai Kovilkalappal Gas Turbine Power Station(TKGTPS), Valuthur(Valuthur Gas Turbine Power Station-VGTPS) and one naptha based ower station at Basin Bridge(Basin Bridge Gas Turbine Power Station) are covered in the present review. The performance of kuthalam gas turbine power station has not been included in the review since it commenced generation in March 2004 only. Ennore (ETPS) was already reviewed and the findings have been included in the Commercial Audit Report for the year ending 31 March 2003.Audit findings, as a result of test check, were reported to the Government/Board in May 2004 with a specific request to attend the meeting of the Audit Review Committee of State Public Sector Enterprises(ARCPSE) so that view points of the Government /Board are taken into account before finalizing the review. The Board received adequate quantity of coal to meet the demand entire requirements of the thermal station. There was no shut down of the power station for want of coal. EXCESS ASH CONTENT IN COAL: Higher ash content in coal is one of the main reasons for excess consumption of coal in thermal power station. The following table indicates the percentage of ash content in coal received at NCTPS is as follows 1 1999-2000 2000-2001 2001-2002 2002-2003
46.60 46.40 45.40 40.20
2003-2004
42.70
BELT CONVEYOR SYSTEM The coal is transferred from the harbor to the plant through belt conveyor system. A conveyor belt (or belt conveyor) consists of two or more pulleys, with a continuous loop of material - the conveyor belt - that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the drive pulley while the unpowered pulley is called the idler .
MILL PLANT The function of the mill plant are to pulverize the coal to 50 - 60 microns. The materials entering the mill plant are coal, hot air and seal air. The mill plant used here are bowl mills. BOWL MILL The bowl mill consists of three rollers mounted on a bull ring inside a bowl. The motion is given to the bowl which also makes the roller to rotate. In this motion the coal gets pulverized. In NCTPS six bowl mills for each boiler are used out of which only four are used and the remaining are standbys. The mill plant consists of the following mechanisms Feeder mechanism Bowl with gear box Rollers
Bull ring system Vane wheel assembly Deflector plates
PROCESS o o
o
o o
o
o
o
o
o
The process taking place in the mill plant is as follows: The raw coal from the bunker goes to the hopper of the feeder mechanism. The feeder mechanism feeds the coal to the inlet of the mill plant. Depending upon the amount of the power required, the speed of feeders are adjusted. The inlet pipe leads the coal to the rotating bowl. In the rotating bowl hot air and seal air is applied to remove he wetness but it should not be heated too much. Due to the rotation of the bowl, the rollers rotate and crush the coal into fine powder. The rollers are placed such that they make 120 degree inclination with the bowl. This pulverized coal is then taken to the boiler by the hot air which comes from below through the vane wheel assembly and the deflector plates. After the process through mill plant, the pulverized coal is further heated by pre-heater and the coal is pushed into the boiler with the help of primary fans. The bowl differential pressure should be maintained within the limit in order to avoid blocks in the path. The lube oil system is used for cooling the gear box and also journal bearings of the mill plan. In NCTPS there are three units of mill plants. Each consists of six mills; each mill plant consumes a power of about 350KW.
ASH HANDLING • •
•
•
The ash is removed from the boiler by special means. This is also collected from the flue gas by means of electrostatic precipitator. This precipitator has 6 rows with 48 hoppers. In the first two row 80% of the ash is collected. The bottom and fly ash slurry is convened to the ash slurry by means of high pressure water jets into the ash trenches. There are three ash slurry sumps, one for each unit.
•
•
•
•
The ash slurry then collected is discharged to the ash disposal area by means of slurry pumps through cast basalt lined pipes. There are two streams of pipelines, each consisting of 950 m3 per hour so as to develop the required total head to pump the slurry to the disposal area. This area is about 3Km away from the project site. The decanted water from the ash water is pumped to the ash water tanks for reuse. Suitable provision is made for dry ash handling considering the commercial utilization of dry ash.
TECHNICAL SERVICE TURBINE
i. ii. iii.
The high pressure, high temperature steam (540 degree Celsius) from the boiler enters into the turbine. Totally there are three turbines operating at different pressure levels. These are as follows: High pressure turbines Intermediate pressure turbine(IPT) Low pressure turbine(LPT) Steam from the boiler enters into the High pressure turbine, where it losses some energy after striking the turbine blades and causing it to rotate at a speed of about 3000 rpm. This steam then passes through the reheater present at the boiler and after gaining some temperature (with loss in pressure), enters into the intermediate pressure turbine, and causes it to rotate. Then the low pressure steam from the intermediate pressure turbine then enters into the low pressure turbine, and causes it to rotate at the same speed (3000 rpm). Thus the heat energy from the steam is converted into mechanical energy by the turbine. Later this mechanical energy is converted into electrical energy by a generator coupled with the shaft of the turbine.
These are the reactions that occur when the steam passes through the turbine.
GENERATOR The mechanical energy in the turbine is converted in to electric energy by generators. Generators installed at the power station have a capacity of generating 15.74 KVA and it has a static stator and dynamic rotor. The mode of cooling is of by using the demineralized water and the mode of cooling the rotor is through hydrogen. Both the rotor cooling and stator cooling system are separate. The generator is coupled with the turbine by means of special box arrangement.
ELECTRICAL MAINTENANCE – II Most boilers now depend on mechanical draught equipment rather than natural draught. This is because natural draught is subject to outside air conditions and temperature of flue gases leaving the furnace, as well as the chimney height. All these factors make proper draught hard to attain and therefore make mechanical draught equipment much more economical. There are three types of mechanical draught: Induced draught : This is obtained one of three ways, the first being the "stack effect" of a heated chimney, in which the flue gas is less dense than the ambient air surrounding the boiler. The denser column of ambient air forces combustion air into and through the boiler. The second method is through use of a steam jet. The steam jet oriented in the direction of flue gas flow induces flue gasses into the stack and allows for a greater flue gas velocity increasing the overall draught in the furnace. This method was common on steam driven locomotives which could not have tall chimneys. The third method is by simply using an induced draught fan (ID fan) which removes flue gases from the furnace and forces the exhaust gas up the stack. Almost all induced draught furnaces operate with a slightly negative pressure. •
Forced draught : Draught is obtained by forcing air into the furnace by means of a fan (FD fan) and ductwork. Air is often passed through an air heater; which, as the name suggests, •
heats the air going into the furnace in order to increase the overall efficiency of the boiler. Dampers are used to control the quantity of air admitted to the furnace. Forced draught furnaces usually have a positive pressure. Balanced draught : Balanced draught is obtained through use of both induced and forced draught. This is more common with larger boilers where the flue gases have to travel a long distance through many boiler passes. The induced draught fan works in conjunction with the forced draught fan allowing the furnace pressure to be maintained slightly below atmospheric. •
CONCLUSION Thus NCTPS play a vital role in the generation and distribution of power to various parts of the state. The inplant training was very knowledgeable. We could compare the theoretical thing with the practical. We would like to thank all the staff who explained us and all the authorities of NCTPS for giving us this great opportunity. We would also like to thank our college for encouraging us in all means.
