INDUSTRIAL TRAINING REPORT (SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIRMENT OF THE COURSE OF B.TECH.)
UNDERTAKEN AT
Haridwar
SUBMITT SUBMITT ED BY: Anurag Chand 10607032 Electr Electr onics onics & Instr umentation
TABLE OF CONTENT
1.
Introduction
BHEL Captive Power plants
2.
Operation
Operation of Power Plant
3.
Control & Instrumentation Instrumentation
Instrumentation Controls
4.
Ind ustrial Automation
PLCs (Programmable Logic Controllers) SCADA
Introduction
BHEL is the largest engineering and manufacturing enterprise in India in the energy-related/infrastructure sector, today. BHEL was established more than 40 years ago, ushering in the indigenous Heavy Electrical Equipment industry in India - a dream that has been more than realized with a well-recognized track record of performance. The company has been earning profits continuously since 1971-72 and paying dividends since 1976-77.
Bhar at Heavy Elec Electr tr icals icals Ltd. (BHEL) (BHEL) H ar idwar idwar has two manufacturing plants and one captive power plant. I was assigned to do my tr aining in in th e captive captive power power plant.
What are captive power plants? Ø
Captive Power Plant is a generating unit(s) with aggregate capacity not exceeding 166 MW which produces power for captive consumption of its owners
Ø
Capacity-23.6 MW.
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It is coal fired.
Operation
ELECT RICI TY FROM COAL Coal from the coal wagons is unloaded with the help of wagon tipplers in the C.H.P. this coal is taken to the raw coal bunkers with the help of conveyor belts. Coal is then transported to bowl mills by coal feeders where it is pulverized and ground in the powered form.
This crushed coal is taken away to the furnace through coal pipes with the help of hot and cold mixture P.A fan. This fan takes atmospheric air, a part of which is sent to pre heaters while a part goes to the mill for temperature control. Atmospheric air from F.D fan in the air heaters and sent to the furnace as combustion air.
Water from boiler feed pump passes through economizer and reaches the boiler drum . Water from from the drum passes through the down comers and goes to the bottom ring header. Water from the bottom ring header is divided to all the four sides of the furnace. Due to heat density difference the water rises up in the water wall tubes. This steam and water mixture is again taken to the boiler drum where the steam is sent to super heaters for super heating. The super heaters are located inside the furnace and the steam is super heated (540 degree Celsius) and finally it goes to the turbine.
Fuel gases from the furnace are extracted from the induced draft fan, which maintains balance draft in the furnace with F.D fan. These fuel gases heat energy to the various super heaters and finally through air pre heaters and goes to electrostatic precipitators where the ash particles are extracted. This ash is mixed with the water to from slurry is pumped to ash period.
The steam from boiler is conveyed to turbine through the steam pipes and through stop valve and control valve that automatically regulate the supply of steam to the turbine. Stop valves and controls valves are located in steam chest and governor driven from main turbine shaft operates the control valves the amount used.
Steam from controlled valves enter high pressure cylinder of turbines, where it passes through the ring of blades fixed to the cylinder wall. These act as nozzles and direct the steam into a second ring of moving blades mounted on the disc secured in the turbine shaft. The second ring turns the shaft as a result of force of steam. The stationary and moving blades together.
THERM AL POWER PLANT PLANT A Thermal Power Station comprises all of the equipment and a subsystem required to produce electricity by using a steam generating boiler fired with fossil fuels or befouls to drive an electrical generator. Some prefer to use the term ENERGY CENTER because such facilities convert forms of energy, like nuclear energy, gravitational potential energy or heat energy (derived from the combustion of fuel) into electrical energy. However, POWER PLANT is the most common term in the united state; While POWER STATION prevails in many Commonwealth countries and especially in the United Kingdom. Such power stations are most usually constructed on a very large scale and designed for continuous
operation.
Typical
diagram
of
a
coal
fired
thermal
power
station
Cooling water pump Three-phase transmission line Step up transformer Electrical Generator Low pressure steam Boiler feed water pump Surface condenser Intermediate pressure steam turbine Steam control valve High pressure steam turbine Deaerator Feed water heater Coal conveyor Coal hopper Coal pulverizer Boiler steam drum Bottom ash hoper Super heater Forced draught fan
Reheater Combustion air intake Economizer Air preheater Precipitator Induced draught(draft) fan Fuel gas stack
The description of some of the components written above is described as follows:
Cooling Cooling tow t ower er s Cooling Towers are evaporative coolers used for cooling water or other working medium to near the ambivalent web-bulb air temperature. Cooling tower use evaporation of water to reject heat from processes such as cooling the circulating water used in oil refineries, Chemical plants, power plants and building cooling, for example. The tower vary in size from small roof-top units to very large hyperboloid structures that can be up to 200 meters tall and 100 meters in diameter, or rectangular structure that can be over 40 meters tall and 80 meters long. Smaller towers are normally factory built, while larger ones are constructed on site. The primary use of large , industrial cooling tower system is to remove the heat absorbed in the circulating cooling water systems used in power plants , petroleum refineries, petrochemical and chemical plants, natura naturall gas processing plants and other industrial facilities . The absorbed heat is rejected to the atmosphere by the evaporation of some of the cooling water in mechanical forced-draft or induced draft towers or in natural draft hyperbolic shaped cooling towers as seen at most nuclear power plants.
Thr ee phase tr ansmi an smiss ssio ion n line line Thr ee phase electric electric p ower ower is a common method of electric power transmission. It is a
type of polyphase system mainly used to power motors and many other devices. A Three phase system uses less conductor material to transmit electric power than equivalent single phase, two phase, or direct current system at the same voltage. In a three phase system, three circuits reach their instantaneous peak values at different times. Taking one conductor as the reference, the other two current are delayed in time by one-third and
two-third of one cycle of the electrical current. This delay between “phases” has the effect of giving constant power transfer over each cycle of the current and also makes it possible to produce a rotating magnetic field in an electric motor. At the power station, an electric generator converts mechanical power into a set of electric currents, one from each electromagnetic coil or winding of the generator. The current are sinusoidal functions of time, all at the same frequency but offset in time to give different phases. In a three phase system the phases are spaced equally, giving a phase separation of one-third one cycle. Generators output at a voltage that ranges from hundreds of volts to 30,000 volts. At the power station, transformers: step-up” this voltage to one more suitable for transmission. After numerous further conversions in the transmission and distribution network the power is finally transformed to the standard mains voltage (i.e. the “household” voltage). The power may already have been split into single phase at this point or it may still be three phase. Where the step-down is 3 phase, the output of this transformer is usually star connected with the standard mains voltage being the phase-neutral voltage. Another system commonly seen in North America is to have a delta connected secondary with a center tap on one of the windings supplying the ground and neutral. This allows for 240 V three phase as well as three different single phase voltages( 120 V between two of the phases and neutral , 208 V between the third phase ( known as a wild leg) and neutral and 240 V between any two phase) to be available from the same supply.
Electrical generator An Electrical generator is a device that converts kinetic energy to electrical energy, generally using electromagnetic induction. The task of converting the electrical energy into mechanical energy is accomplished by using a motor. The source of mechanical energy may be a reciprocating or turbine steam engine, , water falling through the turbine are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment , to 2,000,000 hp(1,500,000 kW) turbines used to generate electricity. There are several classifications for modern steam turbines.
Steam turbines are used in all of our major coal fired power stations to drive the generators or alternators, which produce electricity. The turbines themselves are driven by steam generated in ‘Boilers’ or ‘steam generators’ as they are sometimes called. Electrical power station use large stem turbines driving electric generators to produce most (about 86%) of the world’s electricity. These centralized stations are of two types: fossil fuel power plants and nuclear power plants. The turbines used for electric power generation are most often directly coupled to their-generators .As the generators must rotate at constant synchronous speeds according to the frequency of the electric power system, the most common speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. Most large nuclear sets rotate at half those speeds, and have a 4-pole generator rather than the more common 2-pole one.
Energy in the steam after it leaves the boiler is converted into rotational energy as it passes through the turbine. The turbine normally consists of several stage with each stages consisting of a stationary blade (or nozzle) and a rotating blade. Stationary blades convert the potential energy of the steam into kinetic energy into forces, caused by pressure drop, which results in the rotation of the turbine shaft. The turbine shaft is connected to a generator, which produces the electrical energy.
Boil Boiler er feed wat water er p ump A Boiler feed water pump is a specific type of pump used to pump water into a steam boiler. The water may be freshly supplied or retuning condensation of the steam produced by the boiler. These pumps are normally high pressure units that use suction from a condensate return system and can be of the centrifugal pump type or positive displacement type.
Constr uction uction and operat ion ion Feed water pumps range in size up to many horsepower and the electric motor is usually separated from the pump body by some form of mechanical coupling. Large industrial condensate pumps may also serve as the feed water pump. In either case, to force the water into the boiler; the pump must generate sufficient pressure to overcome the steam pressure developed by the boiler. This is usually accomplished through the use of a centrifugal pump.
Feed water pumps usually run intermittently and are controlled by a float switch or other similar level-sensing device energizing the pump when it detects a lowered liquid level in the boiler is substantially increased. Some pumps contain a two-stage switch. As liquid lowers to the trigger point of the t he first stage, the pump is activated. I f t he liquid continues continues to drop (perhaps because the pump has failed, its supply has been cut off or exhausted, or its discharge is blocked); the second stage will be triggered. This stage may switch off the boiler equipment (preventing the boiler from running dry and overheating), trigger an alarm, or both.
Steam-powe Steam-powerr ed pump s Steam locomotives and the steam engines used on ships and stationary applications such as power plants also required feed water pumps. In this situation, though, the pump was often powered using a small steam engine that ran using the steam produced by the boiler. A means had to be provided, of course, to put the initial charge of water into the boiler(before steam power was available to operate the steam-powered feed water pump).the pump was often a positive displacement pump that had steam valves and cylinders at one end and feed water cylinders at the other end; no crankshaft was required.
In thermal plants, the primary purpose of surface condenser is to condense the exhaust steam from a steam turbine to obtain maximum efficiency and also to convert the turbine exhaust steam into pure water so that it may be reused in the steam generator or boiler as boiler feed water. By condensing the exhaust steam of a turbine at a pressure below atmospheric pressure, the steam pressure drop between the inlet and exhaust of the turbine is increased, which increases the amount heat available for conversion to mechanical power. Most of the heat liberated due to condensation of the exhaust steam is carried away by the cooling medium (water or air) used by the surface condenser.
Control valves Control valves are valves used within industrial plants and elsewhere to control operating conditions such as temperature,pressure,flow,and liquid Level by fully partially opening or closing in response to signals received from controllers that compares a “set point” to a “process variable” whose value is provided by sensors that monitor changes in such
conditions. The opening or closing of control valves is done by means of electrical, hydraulic or pneumatic systems
Deaerator A Dearator is a device for air removal and used to remove dissolved gases (an alternate would be the use of water treatment chemicals) from boiler feed water to make it noncorrosive. A dearator typically includes a vertical domed deaeration section as the deaeration boiler feed water tank. A Steam generating boiler requires that the circulating steam, condensate, and feed water should be devoid of dissolved gases, particularly corrosive ones and dissolved or suspended solids. The gases will give rise to corrosion of the metal. The solids will deposit on the heating surfaces giving rise to localized heating and tube ruptures due to overheating. Under some conditions it may give to stress corrosion cracking. Deaerator level and pressure must be controlled by adjusting control valves- the level by regulating condensate flow and the pressure by regulating steam flow. If operated properly, most deaerator vendors will guarantee that oxygen in the deaerated water will not exceed 7 ppb by weight (0.005 cm3/L)
MAIN GENERATOR
Maximum continuous KVA rating
24700KVA
Maximum continuous KW
210000KW
Rated terminal voltage
15750V
Rated Stator current
9050 A
Rated Power Factor
0.85 lag
Excitation current at MCR Condition
2600 A
Slip-ring Voltage at MCR Condition
310 V
Rated Speed
3000 rpm
Rated Frequency
50 Hz
Short circuit ratio
0.49
Efficiency at MCR Condition
98.4%
Direction of rotation viewed
Anti Clockwise Clockw ise
Phase Connection
Double Star
Number of terminals brought out
9( 6 neutral and 3 phase)
CONTROL AND INSTRUMENTATION
Temperature The hotness or coldness of a piece of plastic, wood, metal, or other material depends upon the molecular activity of the material. Kinetic energy is a measure of the activity of the atoms which make up the molecules of any material. Therefore, temperature is a measure of the kinetic energy of the material in question. 1. RTD The resistance of an RTD varies directly with temperature: - As temperature increases, resistance increases. - As temperature decreases, resistance decreases. RTDs are constructed using a fine, pure, metallic, spring-like wire surrounded by an insulator and enclosed in a metal sheath. A change in temperature will cause an RTD to heat or cool, producing aproportional change in resistance. The change in resistance is measured by a precision prec ision device that is calibrated to give the proper temperature reading.
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•
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2. THERMOCOUPLES Thermocouples will cause an electric e lectric current to flow in the attached circuit when subjected to changes in temperature.The amount of current that will be produced is dependent on the temperature difference between the measurement and reference junction; the characteristics of the two metals used; and the characteristics of o f the attached circuit.
Heating the measuring junction of the thermocouple produces a voltage which is greater than the voltage across the reference junction. The difference between the two voltages is proportional to the difference in temperature and can be measured on the voltmeter (in mill volts). For ease of operator use, some voltmeters are set up to read out directly in temperature through use of electronic circuitry.
Pressure Transducers Bellows-Type Detectors The need for a pressure sensing element that was extremely sensitive to low pressures and provided power for activating recording and indicating mechanisms resulted in the development of the metallic bellows pressure sensing element. The metallic bellows is most accurate when measuring pressures from 0.5 to 75 psig. However, when used in conjunction with a heavy range spring, some bellows can be used to measure pressures of over 1000 psig.
Bourdon tube The bourdon tube consists of a thin-walled tube that is flattened diametrically on opposite sides to produce a cross-sectional area elliptical in shape, having two long flat sides and two short round sides. The tube is bent lengthwise into an arc of a circle of 270 to 300 degrees. Pressure applied to the inside of the tube causes distention of the flat sections and tends to restore its original round cross-section. This change in cross-section causes the tube to straighten slightly. Since the tube is permanently fastened at one end, the tip of the tube traces a curve that is the result of the change in angular position with respect to the center. Within limits, the movement of the tip of the tube can then be used to position a pointer or to develop an equivalent electrical signal to indicate value of the applied internal pressure.
Level Measurement Ball Float The operation of the ball float is simple. The ball floats on top of the liquid in the tank. If the liquid level changes, the float will follow and change the position of the pointer attached to the rotating shaft .
Pressure head method The differential pressure ( ∆P) detector method of liquid level measurement uses a ∆P detector connected to the bottom of o f the tank being monitored. The higher pressure, caused by the fluid in the tank, is compared to a lower reference pressure (usually atmospheric). This comparison takes place in the ∆P detector. Figure illustrates a typical differential pressure detector attached to an open tank .
Flow meters
Differential Flow Transmitter Orifice plates • • •
Flat plates 1/16 to 1/4 in. thick Mounted between a pair of flanges Installed in a straight run of smooth pipe to avoid disturbance of flow patterns due to fittings and valves
Venturi tube • •
Converging conical inlet, a cylindrical throat, and a diverging recovery cone No projections into the fluid, no sharp corners, and no sudden changes in contour
Dall flow tube •
• •
Consists of a short, straight inlet section followed by an abrupt decrease in the inside diameter of the tube Inlet shoulder followed by the converging inlet cone and a diverging exit cone Two cones separated by a slot or gap between the two cones
Electromagnetic flow meter The electromagnetic flow meter is similar in principle to the generator. The rotor of the generator is replaced by a pipe placed between the poles of a magnet so that the flow of the fluid in the pipe is normal to the magnetic field. As the fluid flows through this magnetic field, an electromotive force is induced in it that will be mutually normal (perpendicular) to both the magnetic field and the motion of the fluid. This electromotive force may be measured with the aid of electrodes attached to the pipe and connected to a galvanometer or an equivalent. For a given magnetic field, the induced voltage will be proportional to the average velocity of the fluid. However, the fluid should have some degree of electrical conductivity.
Power plant Controls
Drum Level Control 1. Single element water level control
Only single sensor i.e. level sensor is used to control the level
2. Double Element water level control
This uses two sensors level and flow sensors. It is better and precise than single element control.
Other Temperature, Flow and Pressure control is done by
Feedback loopThis uses a single feedback loop which finds out error from the set point and finds out controller output
Cascaded Feedback loop control This uses two controller: 1. Master 2. Slave The set point of slave controller is decided by the controller output of the master
Feed Forward Control Here the disturbance is eliminated even before it enters the process.The sensor senses the disturbance and feedforward controller nullifies the disturbance
Ratio Control Ratio control is used to ensure that two flows are kept at the same ratio even if the flows are changing. E.g. Air-Fuel Ratio where the proper ratio between air and fuel i.e. pulverized coal has to be maintained.
Controller feed is adjusted according to the ratio of wild feed. The implementation is shown above.
Automation of Processes The main purpose of automation is to minimize human intervention to reduce the errors. Large processes like power plant has large scope for errors. The automation of industrial processes is carried by PLCs and SCADA .
The above figure shows the hierarchy setup of industrial automation. The field devices are connected to the PLC and all the PLCs are connected to the SCADA server based in control room. The SCADA server is connected via LAN to ERP (Enterprise Resource Planning) and the data can be accessed from any where on internet.
PLC (Programmable Logic Controller) Digital electronic device that uses a programmable memory to store instructions and to implement specific functions such as logic , sequencing , timing etc to control machine and processes. Salient features • Cost effective for controlling complex systems. • Flexible and can be reapplied to control other systems quickly and easily. • Computational abilities allow more sophisticated control. • Trouble shooting aids make programming easier and reduce downtime. • Reliable components make these likely to operate for years before failure. PLC HARDWARE Many PLC configurations are available, even from a single vendor. But, in each of these there are common components and concepts. The most essential components are: Power Supply - This can be built into the PLC or be an external unit. Common voltage levels required by the PLC (with and without the power supply) are 24Vdc, 120Vac, 220Vac. CPU (Central Processing Unit) - This is a computer where ladder logic is stored and processed. I/O (Input/Output) - A number of input/output terminals must be provided so that the PLC can monitor the process and initiate actions. Indicator lights - These indicate the status of the PLC including power on, program running, and a fault. These are essential when diagnosing problems. The configuration of the PLC refers to the packaging of the components. Rack - A rack is often large (up to 18” by 30” by 10”) and can hold multiple cards. When necessary, multiple racks can be connected together. These tend to be the highest cost, but also the most flexible and easy eas y to maintain. INPUTS AND OUTPUTS
Inputs to, and outputs from, a PLC are necessary to monitor and control a process. Both inputs inputs and outputs can be categorized into into two basic types: logical or continuous. Consider the example of a light bulb. If it can only be turned on or off, it is logical control. If the light can be dimmed to different levels, it is continuous. Continuous values seem more intuitive, but logical values are preferred because they allow more certainty, and simplify control. As a result most controls applications (and PLCs) use logical inputs and outputs for most applications. Hence, we will discuss logical I/O and leave continuous I/O for later. Outputs to actuators allow a PLC to cause something to happen in a process. A short list of popular actuators is given below in order of relative popularity. · Solenoid Valves - logical outputs that can switch a hydraulic or pneumatic flow. · Lights - logical outputs that can often be powered directly from PLC output boards. · Motor Starters - motors often draw a large amount of current when started, so they require motor starters, which are basically large relays. · Servo Motors - a continuous output from the PLC can command a variable speed or position. Outputs from PLCs are often relays, but they can also be solid state electronics such as transistors for DC outputs or Triacs for AC outputs. Continuous outputs require special output cards with digital to analog converters. Inputs come from sensors that translate physical phenomena into electrical signals. signals. Typical examples of sensors are listed below in relative order of popularity. · Proximity Switches - use inductance, capacitance or light to detect an object logically. · Switches - mechanical mechanisms will w ill open or close electrical contacts for a logical signal. · Potentiometer - measures angular positions continuously, using resistance. · LVDT (linear variable differential transformer) - measures linear displacement
Step 1-CHECK INPUT STATUS-First the PLC takes a look at each input to determine if it is on or off. In other words, is the sensor connected to the first input on? How about the second input? How about the third... It records this data into its memory to be used during the next step. Step 2-EXECUTE PROGRAM-Next the PLC executes your program one instruction at a time. Maybe your program said that if the first input was on then it should turn on the first output. Since it already knows which inputs are on/off from the previous step it will be able to decide whether the first output should be turned on based on the state of the first input. It will store the execution results for use later during the next step. Step 3-UPDATE OUTPUT STATUS-Finally the PLC updates the status of the outputs. It updates the outputs based on which inputs were on during the first step and the results of executing your program during the second step. Based on the example in step 2 it would now turn on the first output because the first input was on and your program said to turn on the first output when this condition is true.
Drawing the ladder logic for flowchart The flowchart is the most encountered problems in industrial processes
Ladder Logic is:
Deadman Switch A motor will be controlled by two switches. The Go switch will start the motor and the Stop switch will stop it. If the Stop switch was used to stop the motor, the Go switch must be thrown twice to start the motor. When the motor is active a light should be turned on. The Stop switch will be wired as normally closed.
SCADA It stands for Supervisory Control and Data Acquisition. It generally refers to an industrial control system: a computer system monitoring and controlling a process. Features of SCADA 1. Supervisory Control-Generally speaking, a SCADA system usually refers to a system that coordinates, coordinates, but does not control processes in real time. The discussion on real-time control is muddied somewhat by newer telecommunications technology, enabling reliable, low latency, high speed communications over wide areas. 2. Redundancy-When any device turns out to faulty the SCADA software will automatically transfer the control to the redundant systems 3. Historical and Real Time Trends 4. Alarm-Alarms can set when a particular hi or low value is breached. 5. LAN Connectivity-It should have good LAN connectivity as it is necessary for connecting to the ERP. 6. Dynamic Process Graphic-This has brought about revolution in automation as previously people would not what was going in the system VISUALLY. But with SCADA software which has large library of symbols the whole process can be modeled accurately. And the process can be monitored by sitting in the control room.
The software used in the SCADA was WONDERWARE INTOUCH.The previous diagram shows the SCADA Screen of Boiler. The important parameters are shown in model itself making it possible to monitor the process from the control room itself
