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CCGT OPERATIONS PRINCIPLES

CCGT OPERATIONS PRINCIPLES. CONTROL & INSTRUMENTATION. Pressure Scales. Gauge Pressure. Differential Pressure. 760mmHg.a 1.013kN/m ².a 1.013bar.a 14.7lbf/in².a. Atmospheric Pressure. Gauge Pressure. Vacuum. Absolute Pressure. Absolute Zero. Manometers. Pressure Measurement.

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CCGT OPERATIONS PRINCIPLES

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  1. CCGT OPERATIONS PRINCIPLES CONTROL & INSTRUMENTATION

  2. Pressure Scales Gauge Pressure Differential Pressure 760mmHg.a 1.013kN/m².a 1.013bar.a 14.7lbf/in².a Atmospheric Pressure Gauge Pressure Vacuum Absolute Pressure Absolute Zero

  3. Manometers

  4. Pressure Measurement ‘C’ Shaped Bourdon Tube with Quadrant & Pinion Movement ‘C’ Shaped Bourdon Tube

  5. Electronic Pressure Transmitters

  6. Capacitance Transducer

  7. Level Measurement • ·Level is defined as the height of the surface of a liquid above a datum point. • ·The datum point is usually the bottom of the vessel containing the liquid. • ( For boiler drum level measurement -The datum is usually taken as the centre line of the drum) • Units used for level measurement are expressed in metres • May be expressed as a volume e.g. cubic metres or litres

  8. Fluid Level Measurement by Sight Glass

  9. RFW Tank Level Measurement Used where tank is open to atmosphere

  10. Pressure Head – Level Measurement • Similar to the - manometer a head of water exerts a force on a device relative to level being measured • Uses a constant head chamber to establish a “reference leg” to compare with the measured leg

  11. Drum Level Measurement Constant Head Chamber Drum centre line 0 mm Reference Leg Output signal – Drum Level +20mm Drum level Transmitter Force on measuring element is equal to height difference

  12. Drum Level Measurement Constant Head Chamber Drum centre line 0 mm Reference Leg Force on measuring element is equal to height difference Output signal – Drum level – 50mm Drum level Transmitter

  13. HYDRASTEP DRUM LEVEL INDICATOR DISPLAY UNIT Electrodes DETECTOR AND LOGIC UNIT

  14. HYDRASTEP DRUM LEVEL INDICATOR

  15. Hydrastep Pressure Vessel

  16. HYDRASTEP DRUM LEVEL INDICATOR Electrode Electrical connection to Detector Ceramic Insulator Electrode Tip Hydrastep Vessel

  17. Hydrastep Block Diagram

  18. Ultra-Sound Transducer

  19. Flow Measurement Rate of flow • is the instantaneous value of the flow of fluid passing through pipework. • Units of measurement are: - • Volumetricm3/sec, litres/sec in S.I. Units • ft3/sec, gallons/sec in imperial units • Masskg/sec in S.I. Units. • lb/hr in imperial units

  20. Quantity Measurement • This measurement is normally made for costing such as town water metering. • It is a "running total" of the quantity of fluid passed through the pipework. • Units of measurement are : • Volumetricm3, litres in S.I. Units ft3, gallons in imperial units

  21. Quantity Measurement • There are two different types of “quantity” meter, inferential and positive displacement meters. • The principle of operation of an inferential quantity meter is that the quantity is inferred by measuring the velocity • The principle of operation of a positive displacement “quantity” meter is that a known volume is passed from the inlet to the outlet of the meter

  22. Helical Vane Type Meter

  23. Sliding Vane Positive Displacement Meter

  24. Venturi Principles • As the fluid passes through the smaller diameter of the orifice, the kinetic energy will increase and therefore the pressure energy (and the pressure) decreases. • Therefore by measuring the difference in pressure across the orifice plate, the rate of flow can be calculated.

  25. Typical Venturi Section

  26. Carrier Ring Orifice

  27. Magnetic Flow Meter A magnetic flow meter is based on the principle that a voltage is produced at two electrodes contained within the wall of the flow meter cell, due to the flow of fluid through the meter cutting the magnetic field set up by an electro magnet.

  28. Temperature Measurement The accepted units for the measurement of temperature on power stations are degrees Celsius • 0o Celsius is the melting point of ice • 100o Celsius is the boiling point of water at an atmospheric pressure of 760 mm Hg

  29. Liquid in Glass Thermometer

  30. Mercury in Steel Thermometer

  31. Thermocouples Temperature measurements based on the use of a thermocouple rely on the basic principle that: If two dissimilar metals are connected at one end to form a measuring (hot) junction and are connected to a temperature indicator at the other end to form a reference (cold) junction, a voltage is produced at the measuring instrument which is determined by the temperature difference between the two junctions. (Thermoelectric effect)

  32. Thermocouple Principles

  33. Typical Base Metal Thermocouples

  34. Mineral Insulated Thermocouple

  35. Practical Thermocouple Measuring Circuit

  36. Resistance Thermometers • The resistance of a metallic conductor will increase with increase in temperature • This principle is utilised in resistance thermometer detectors (RTD's). • Platinum is used for its resistance to corrosion and its stability. • An accurately known value of platinum resistance wire is wound on a suitable former to make the RTD

  37. Characteristics of RTDs • The most common RTD is known as a PT100 38.5 f.I. • The Pt indicates that it is made of platinum and 100 is its resistance in ohms at 0oc. • The 38.5 indicates the resistance change in ohms from 0oc to 100oc(100 ohms to 138.5 ohms) • The temperature range of RTD's is: • -200oc to 600oc.

  38. Construction of RTDs The basic construction of an RTD consists of: Platinum wire wound in a helix and encased in a ceramic insulator Sealed with high temperature glass forming an impervious coating and sealed in a metal sheath similar to a thermocouple.

  39. Control Actuators • Modulating control actuators are the last link in the chain and modify the process being controlled by a control system • The operation of the double acting, single pushrod actuator relies on the application of oil pressure to one side of the piston, oil from the opposite side is returned to drain. • A position feedback device ensures that the actuator accurately drives to a new position as determined by the control signal irrespective of control valve loading

  40. Spring and Diaphragm Actuators

  41. Direct Acting Actuator

  42. Reverse Acting Actuator

  43. Superheater Spray Control Valve

  44. Valve Positioner

  45. Hydraulic Actuator

  46. Hydraulic Actuator

  47. Electrical Actuators

  48. Electric Actuators • Comprise: • A 3 phase squirrel cage motor • A reduction gearbox • Torque and limit switches to suit various valve bodies • Start/stop, forward & reverse control systems • Temperature protection • Designed for continuous operation

  49. Multi-turn Electrical Actuator

  50. Electrical Actuator

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