Basics of I&C
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Transcript of Basics of I&C
Basics of Instrumentation & Control systems
in a TPS
Role of Instrumentation & ControlCase-I
To generate 210 MW we have to introduce steam of 640 TPH at 130 Kg/cm2 and 540 oC
4% of oxygen in the flue gas indicates proper combustion
Furnace pressure shall be maintained at
-10 mmWcl Water level in the drum shall be maintained to
ensure flow of water through boiler tubes
Role of Instrumentation & ControlCase-II
Consider Boiler Feed Pump
To Start the BFP Suction pressure should be adequate Suction valve fully open Recirculation valve fully open Lube oil pressure should be adequate
During Pump Run
Start AOP, if Lube oil pressure falls below 1.5 Kg/cm2
Stop AOP, if Lobe oil pressure reaches 3.5 Kg/cm2
Close the Recirculation valve if the suction flow is >220 TPH
Open the Recirculation valve if suction flow is < 110 TPH
BFP should be Tripped if
Suction pressure < 2.5 Kg/cm2
Discharge pressure < 40 Kg/cm2
Lube oil pressure < 0.8 Kg/cm2
Working oil temperature > 130oC Motor bearing temperature > 80oC Discharge water temperature > 175oC Deaerator level < 1520 mm
Role of Instrumentation & ControlCase-III
Drum Level Super heated steam temperature Main steam pressure Deaerator level control Reheated steam temperature Furnace pressure Mill outlet temperature Oxygen percentage in the flue gas Hotwell level Heater levels
Role of Instrumentation & Controls
Monitoring the parameters Permissives and Interlocks & Protections Controlling the Parameters
MonitoringMost common parameters that are to be
monitored are PressureTemperature LevelFlow
Local Remote
Local Monitoring
Pressure - Gauges
Temperature - Gauges
Level - Gauge glass
Flow - Flow meter
Pressure Gauge
Bourdon Type
Pressure Gauge
Bourdon Type
Temperature Gauge
Mercury Gauge
Gauge Glass
See through glass
Remote
Pressure/Flow/Level
- Transducers Temperature
- Thermocouple, RTD
Transducer
-Converts quantity of physical variable from one form to another
-Pressure transducer converts quantity of process pressure in to Electrical quantity
-Voltage Transducer (0-5, 0-10, 1-5 etc.,)
-Current TransducerTransmitter=Transduce + Transmit
Pressure Transmitter
-4-wire system of measurement
-2-wire system of measurement
-True Zero (0-20 mA) measurement
-Live Zero (4-20 mA) measurement
4-wire Transmitter (0-20/4-20 mA)
+ Tx-
Load Control / Monitoring mA
Wiring schematic of 4-wireTransmitter
+24 V DC
-Ve
2-wire Transmitter (4-20 mA)
+ Tx
-Load
Control / Monitoring
4-20 mA
Wiring schematic of 2-wireTransmitter
+24 V DC
-Ve
- Tx drives constant current up to a Load of 600 Ω
Transmitter Power supply Vs Load
400 600 800 1000 1200
40
30
20
Transmitter
- Capacitance based
Thermocouple- Junction of two dissimilar metals in contact, produce voltage
between the two (unjoined) wire ends
- Any pair of dissimilar metals will produce a measurable voltage when their junction is heated
Voltage is directly proportional to the temperature difference between joined and open ends
Commonly used thermocouples generate
5 µV/oC to 50 µV/oC Relationship between temperature and
voltage is very much Non-linear
Thermocouple
CJC – Cold Junction Compensation
Selection of Thermocouple
Which combination gives more µV/oC Which combination gives better linear
relationship between voltage and temperature
Thermocouple Temp Vs volt
K-Type Thermocouple K type thermocouple has 41 µV/oC
Chromel (Nickel-Chromium alloy) Alumel(Ni-aluminium alloy)
It can measure in the range of -200 to +1200oC
RTD – Resistance Temperature Detector
Electrical resistance of metals changing with temperature
temperature coefficient of metals is of the order - 0.003 to 0.007 ohms/ohm/°C
Most common metals used are
platinum (Pt-100), nickel, copper and molybdenum
2-wire configuration
Wheatstone Bridge
employed to measure
the RTD resistance Lead Resistance causes
error in the
measurement
3-wire configuration
Flow Measurement
Steam Flow
P1 P2
DP across orifice = P1-P2
Level measurement
P1
P2
DP Transmitter
CONTROL SYSTEMS
Control systems
Control systemControl system
Open Loop ControlOpen Loop Control Closed Loop ControlClosed Loop Control
Concentrated controlConcentrated control Distributed controlDistributed control
Distributed Analog
controlDistributed Analog
control
Distributed Digital
Control (DCS)Distributed Digital
Control (DCS)
Open Loop control system
SYSTEMInput Output
Closed Loop Control system
CONTROLLER Final control element
Measurement system
Setpoint
Feedback path
Output
PID controller
Proportional controllerController output α Error
= Kp * e(t)
Where, Kp =Proportional Gain
PID controller
Integral controllerController output α ∫ e(t) dt
= Ki ∫ e(t) dt
Where, Ki = Integral time constant
PID controller
Derivative controllerController output α de(t)/dt
= Kd de(t)/dt
Where, Kd = Derivative time constant
PID controller
DCS Features Single Input can be utilized for monitoring/I&P/Control Modifications in the I&P/control can be done easily in
software Redundancy Isolated Input / Output modules Remove and insert modules while powered Data Highway speed is 10/100 Mbps Centralized Engineering Station for programming,
configuration Point database (Global Data) accessible at any station
across the Network Facility for simulation of control logic schemes with
virtual processor
Points to Remember Monitoring Permissives and Interlocks & Protections Controlling Local and Remote monitoring Current transducers/Live-zero system (4-20 mA)/2-wire Thermocouples require Cold junction
compensation 3-wire configuration of RTDs eliminate error due
to lead wires resistance Distributed control system
Thank You