INDUSTRIAL TRAININGat

RELIANCE INFRASTRUCTUREEPC Division, Noida

onProject: “Design Of Feed Water

Control System” in Thermal Power Plant

Familiarization with Typical Thermal Power Plant

Feed Water & Steam Flow Diagram

Control & Instrumentation System in power plant

1.Furnace Safeguard and Supervisory System(FSSS).

2.Automatic Turbine Run-up System(ATRS).

3.Turbine Digital Electric Hydraulic control system(DEH) .

4.Distributed Control System(DCS).

a) Acquisition & Processing of process data.

b) Open loop and closed control.

c) Calculation and optimization of the plant performance.

d) Monitoring, signaling, operation and visualization of the process.

Feed Water Control

Feed Water Drum Level

Control

Single Element Drum Level

Control

Two Element Drum Level

Control

Three Element Drum Level

Control

Enhance Three Element Drum Level Control

DP Across Feed Regulating Valve

Control

I/P Processing Module &

selection scheme

Comparator

Controller

4-20 mA

I/P Converter

Set Point

Station

F.B. Unit

Transmitters

4-20 mA

O O O

Feed back

Indicator

A/M Station

.

Control Valve

Typical Loop Schematic

O O

TYPICAL AUTO CONTROL LOOP

+ -

Control strategy for feed water flow

Single element control Two element control Three element control

The parameters used in the control system, which are measured, are: -

a) Drum Level

b) Drum Pressure

c) Steam Flow

d) Feed Water Flow

Instruments required for measurement are: -

1. Electronic Transmitter for measuring :-

i. DP across flow nozzle for feed water flow

ii. DP across flow nozzle for steam flow

iii. DP for Drum Level

2. Temperature elements (Thermocouples) for

i. Feed Water Temperature

ii. Steam Temperature

3. Flow Nozzle for

i. FW Flow

ii. Steam Flow

INPUT AND OUTPUT SIGNALSThe inputs for the feed water control system are: -

• Feed water flow signal from DP Transmitter (4-20mA) - 1 no.

• Steam flow signal from DP Transmitter (4-20mA) - 1 no.

• Drum level signal from DP transmitters (4-20mA) - 1 no.

• Drum pressure signal from pressure transmitter (4-20mA) -1 no.

• Feed water temperature signal from thermocouple - 1 no.

• Steam temperature signal (4-20mA) - 1 no.

• Steam pressure signal (4-20mA) - 1 no.

The outputs of the Feed Water Control System are: -

• 4-20 mA output electrical signals for controlling the speed of BFP - 1no.

• 4-20 mA output (Single Element Controller ) for Low Load Feed Control

Valve – 1 no.

HARDWARE REQUIRED FOR FEED WATER CONTROL SYSTEM :-

• Controller for implementing the controls-1 no.• 4-20mA input cards for 6 signals• Thermocouple input cards for 2 signals• 4-20mA output cards for 2 signals.

Typical Architecture Of Control Strategy

Feed Water and Steam Flow Control Elements

CONCLUSION

Feed water level in boiler drum is controlled by singleelement control for low loads (< 30%) and by three elementcontrol for high loads (>30%). The change over of controlregimes from single element control to three elementcontrol is carried out automatically whenever the load(Steam Flow) exceeds 30% of Maximum Continuous Rating(MCR) and vice versa.

For the control process we use process variablesmeasuring instruments (e.g. flow nozzle, thermocouple, DPtransmitters), I/P card(s), process controllers, HumanMachine Interface (HMI), O/P card(s) and requisiteinstruments.