This document discusses safety interlocks in crude heaters using programmable logic controllers (PLCs) at Bharat Petroleum Corporation's Kochi Refinery. It provides an overview of the refinery's process units including the crude distillation unit (CDU) and describes the various components involved in heating crude oil such as the preheater, desalter, crude heater, burners, and distillation columns. It also discusses the use of intrinsic safety barriers and programmable logic controls to monitor parameters and automatically shut down equipment if safety thresholds are exceeded.

1. SAFETY INTERLOCKS IN CRUDE HEATERS USING PLC
BHARAT PETROLEUM CORPORATION LTD.,
KOCHI REFINERY
DEPARTMENT OF INSTRUMENTATION
COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY
KOCHI – 682 022
AZEEM SIDHIQUE KP
90012047
MUHAMMED SALIH P
90012052
SAJNA BEERAN A
90012061
SHAHEEM TM
90012064
SHAMIL AHAMMAD K
90012065
THANSEEM K
90012071

2. OVERVIEW
 Introduction
 Process Involved In Industry
 Different Units
 Crude Distillation Unit
 Programmable Logic Control
 Intrinsic Safety Barriers
 Interlocking
 System Tripping Conditions
 Parameter Description
 CH21 Check Record For Shutdown Systems
 PLC Ladder Diagram
 Conclusion
 References

3. INTRODUCTION
 Interlock system - vital role in the safe shutdown of the plant during hazard situations or
emergencies
 Helps prevent a machine from harming its operator or damaging itself.
 Prevents one element from changing state due to the state of another element.
 For an example, interlocking system avoids over pressurization of the furnace - ID fan failure,
trip the heater.
 Immediate action need to be taken for the safe shutdown of the plant during emergencies.
 Heater operation requires monitoring of many variables.
 If variables exceeds a certain limit - chance for the heater explosion.
 Parameters sensed using various sensors.
 Output of PLC - ON/OFF voltage is given to actuator.
 This output - close or open the valve – controls fuel flow to the heater - operation is tripped.

4. Process Involved in Refinery
₪ Kochi Refinery - crude oil processing capacity 9.5 MMTPA
₪ Processes - 30% of Indigenous and 70% Imported crude oils
₪ Crude oil transported in ships to Kochi - received through Single Point Mooring (SPM) facility
₪ Can handle Very large Crude Carriers (VLCC) - capacities up to 3.0 Lakh Tons
₪ First processed in Crude Distillation Unit - heated up to around 360 to 380oC
₪ Fractionated in a distillation column - lighter fractions : LPG, Naphtha, Kerosene and Diesel
separated.
₪ Products routed to storage locations after cooling to atmospheric temperature.
₪ LPG treated using Di-Ethanol Amine (DEA) - remove impurities.
₪ Part of the Naphtha - processed in the Aromatics Block - produce Benzene, Toluene and SBPS
(Special Boiling Point Spirit).
₪ Part of the Kerosene treated in KHDS - produce Aviation Turbine Fuel (ATF), Mineral
Turpentine Oil (MTO).
₪ Diesel from the CDU processed in DHDS unit.
₪ Remaining heavier portion - distilled in a Vacuum Distillation Unit (VDU) separate Vacuum Gas
Oil (VGO) and Vacuum Residue (VR) as major fractions.

5. ₪ VGO - processed in FCC unit - heavier molecules broken down - produce LPG, Gasoline (also
called Motor Spirit or Petrol) and Diesel.
₪ Vacuum Residue (VR) from VDU - routed to Biturox Unit - produce Bitumen or to Vis-Breaker
Unit (VBU) - produce Furnace Oil (FO).
₪ VR can be directly routed to LSHS (Low Sulphur Heavy Stock – fuel used in Boilers, Power
Plants, etc.) pool if the crude oil - low Sulphur content (less than 0.5 wt.%).
₪ Sulphur Recovery Unit (SRU) recovers Sulphur from the gases produced.
₪ Refinery operates Gas Turbine (GT) - capacity of 22.0 MW , Steam Turbine Generator (STG) -
17.8 MW and Turbo Generator (TG) - 2.5 MW.
₪ Steam requirement of refinery - 8 boilers and 2 Waste Heat Boilers.
₪ A new GT of 34 MW capacity - additional power requirement of CCR and VGO HDS units.
₪ Effluent Treatment Plants (ETP) - liquid effluent from the process units and other off site areas
₪ Treated effluent - meeting the MINAS (Minimum National Standards) discharged to inland
rivers.
₪ Other Utilities and Off-site facilities - tankages flare system , connected pipelines - installed in
refinery – match requirements of processing, storage and products dispatch.

6. Different Units
Crude Distillation Unit (CDU)
Fluidized Catalytic Cracking Unit (FCCU)
Diesel Hydro De-Sulphurization Unit (DHDS)
Continuous Catalyst Regeneration Unit (CCR)
Captive Power Plant (CPP)

7. Crude Distillation Unit (CDU)
₪ Two crude distillation units; CDU-I and CDU-II.
₪ Primary distillation of crude oil occurs in crude distillation unit (CDU).
₪ Products of CDU : LPG, Naphtha, Diesel, Kerosene, Amine, Light Vacuum Gas Oil and Heavy
Vacuum Gas Oil.
₪ First processing of unit in virtually all petroleum refineries.
₪ The CDU distills the incoming oil into various fractions of different boiling ranges, each of
which then processed further in the other refinery process units. The CDU is often referred to as
atmospheric distillation because it is operated slightly above the atmospheric pressure.
₪ Comprises series distillation columns separates crude into several fractions namely refinery gas,
naphtha, kerosene, diesel.
₪ Vacuum residue given to the Feed Preparation Unit (FPU).

8. Overview of CDU-II

9. ₪ Preheater
₪ Desalter
₪ Prefractionator
₪ Naphtha Stabilizer
₪ Crude Heater CH-21
₪ Burner
₪ Stack Damper
₪ Forced Draft Fan And Induced Fan Draft
₪ Fuel Oil, Fuel Gas And Steam Supply
₪ Balancing Atmospheric Heater (CH22)
₪ Atmospheric Distillation Column (CV21)
₪ Vacuum Heater – CH223
₪ Vacuum Column (CV27)
Overview of CDU-II

10. Preheater
₪ Crude from storage pumped to CDU II plant at a pressure of 5.0 to 11.0 kg/cm2 and temperature
of 300C.
₪ Split into two parallel trains through flow ratio control valves on individual preheat trains 1A
and 1B.
₪ Preheat exchangers consists of products.
₪ Heat of products used to heat crude.
₪ Crude heat exchanger train 1A and 1B are then combined.
₪ Crude streams have temperature of 125.60C/127.90C then moves to crude Desalter for removal
of salts and water.
₪ Consists of crude charge pumps which pumps the crude to Desalter.

11. Desalter
₪ Process unit that removes salt from the crude oil.
₪ Salt is dissolved in water in the crude oil, not in the crude oil itself.
₪ First process in crude oil refining.
₪ Salt content after desalter measured in PTB - pounds of salt per thousand barrels of crude oil.
₪ Another specification is Basic sediment and water.
₪ Most frequent salts - calcium, sodium and magnesium chlorides.
₪ If not removed from the oil several problems arise in the refining process.
₪ High temperatures occur downstream in process could cause water hydrolysis which can
corrosive hydrochloric acid.
₪ Sand silts and salt cause deposits and foul the heat exchangers.
₪ Sodium, arsenic and other metals can poison catalysts.
₪ At a preheat temperature 200–250◦F water is injected into crude – dissolve salt.
₪ Mixture Desalter drum contains electrostatic precipitator.
₪ Separated by means of electrostatic precipitation.
₪ Water from the drum sent to sour-water stripper to be cleaned before disposal to the oily water
sewer.

12. ₪ The crude is desalted and leaves at 190 F through set
of exchanges, then into crude charge furnace and
leaves at 600 F and finally into the crude unit
distillation column.
₪ Works by mixing raw crude oil with water in a mix
valve with a high differential pressure.
₪ Causes water and oil to form an emulsion with the
salt dissolved in the water phase.
₪ Emulsion is broken in Desalter by use of gravity,
heat, electrical energy and chemical additives.
₪ After desalter, crude heated to around 198.240C in
another preheater and then pumped to
Prefractionator.

13. Prefractionator
₪ Feed enters the Prefractionator column CV 271, operates at a top pressure of approximately 2.4
– 3.6 Kg/Cm2g.
₪ Column overhead pressure is controlled by split range pressure control.
₪ With higher pressure, gases from overhead column is released to heater CH-21 or flare to
maintain desired pressure and at low pressure, fuel gas is admitted to overhead column to
maintain the desired pressure.
₪ The pre topped crude flow at crude pump discharge is routed to CH-21/CH-22 pass flow
control.
₪ The crude pump CP-225 A/B is provided with independent tube oil system.
₪ Each pump has : reservoir, two tube oil pumps, one water cooler, one flow transmitter from
which low flow switch is generated.
₪ Flow low switch activated – then spare lube oil automatically pump and crude pump CP-225
will trip.
₪ Crude is transferred to Naphtha Stabilizer and Crude Heaters (CH-21/CH-22).

14. Naphtha Stabilizer
₪ Unstabilized naphtha from Prefractionator overhead reflux drum (CV-280) pumped to the
Naphtha stabilizer CV-26 through Prefractionator overhead product pumps.
₪ Stabilizer column has 36 trays with feed entering on the 18th tray
₪ The overhead products condensed in stabilized overhead condenser.
₪ Stabilized Naphtha products from stabilizer column bottom are routed on stabilizer column
bottom level control.
₪ Stream is then combined with Atmospheric overhead.
₪ Unstabilized naphtha from atmospheric distillation column is pumped to naphtha stabilizer
section for separation of stabilized overhead vapors.
₪ Condensed to recover LPG which is treated in caustic and amine treating unit.
₪ Stabilized naphtha is further separated into light, medium and heavy naphtha.

15. Crude Heater (CH-21)
₪ Crude heaters are of twin cell cabin type (CH21 + CH22).
₪ Fed to the heaters through four passes.
₪ Furnace casing crude heater lined with refractory materials and ceramic fibers in inside – forms
combustion chamber.
₪ Radiant section of the heater houses 152 numbers of 6 inch OD bare tubes - arranged
horizontally in four passes.
₪ Convection section - top of radiant section - increase thermal efficiency.
₪ Crude from PHT3 split into two, 70% of total to CH21 and 30% goes to the CH22.
₪ Heaters have four passes arranged in parallel.
₪ Flow through each pass regulated by FC valves (IFV 1401 to 1404).
₪ Each pass has 20 tubes.
₪ Pressure gauge & temperature gauge provided at convection outlet of each pass.
₪ Two rows of (6 each) retraceable soot blowers provided in the convection section.

16. ₪ Heating coils come out from bottom of radiation section in 4 parallel passes and join with
transfer line where crude from CH22 joins.
₪ Partially vaporized crude is then routed to CV 21.

18. Forced Draft Fan and Induced Draft Fan
₪ FD fan suck air from atmosphere and is given to air preheater.
₪ ID fan suck flue gas from stack creating negative pressure inside the stack and flue gas is given
to air preheater.
₪ In air preheater heat recovered from hot flue gas is used to preheat the from the atmosphere -
increase efficiency of heater.
₪ Based on working of ID fan and FD fan, heaters classified into four :
Balanced draft : Both ID and FD fans used
Forced draft : Only FD fan used
Natural draft : Both ID and FD fans not used
Induced draft : Only ID fan used
₪ Suction temperature of FD fan 370C and for ID fan 2500C and motor is HITACHI 980 RPM
motor.

19. Burner
₪ John Zink gas and oil combination burner.
₪ Fire light or heavy fuel oil with steam at a constant
pressure.
₪ Each burner have individual wind box to which air from
the APH is routed through inlet damper got vanes.
₪ Each burner provided with electrically ignited pilot
burner.

20. Stack damper
₪ Stack damper used to direct flue gas to ID fan.
₪ Goes to open condition when ID fan goes out of working.
Fuel oil, Fuel gas and Steam supply
₪ Fuel oil and fuel gas supply are provided to the
burner.
₪ Steam provided to vaporize the fuel oil supply for
increasing the efficiency.

21. Atmospheric Distillation Column (CV21)
₪ vertical cylindrical vessel with an overall height of 51.45 m.
₪ Two sections - bottom stripping section of 6 trays.
₪ Upper section of 41 trays.
₪ Trays and valves from 1 to 36 are made of stainless steel 410 and from
37 to 47 made of Monel.
₪ Has 4 side draws namely heavy naphtha (HN), ATF/MTO, light gas oil
and heavy gas oil all of which are drawn through side strippers.

22. Vacuum Heater – CH223
₪ single cell balanced type draft heater.
₪ Reduced crude oil from bottom of atmosphere distillation column at 345.5/355.5oC enters four
passes of vacuum furnace CH223.
₪ FIC 3401A/ 3402A/ 3403A/ 3404A controls flow of RCO in each pass.
₪ Emergency/ decoking steam connections provided to each pass at downstream flow control
valves for purging/ decoking the coils with MP steam.
₪ Coil steam also provided to each pass in radiation section to maintain flow velocity in coils if
needed.
₪ Pressure indicator PI3522 with PAL alarm is provided.
₪ If pressure falls below required minimum pressure PALL-3519 alarm will be generated on DCS
will be actuated on interlock I3505 to close SDV 2201 and open SDV 2201A to cut off hot well
off gas flow to heater.
₪ Flame arresters (XX – 3501/ 3502) are provided in hot well off gas flow to heater.

23. ₪ Heat carried away by flue gas after convection is utilized for preheating air required for
combustion by APH.
₪ Combustion chamber houses radiant section tubes.
₪ Convection section provided at top of radiation section serves to increase thermal efficiency of
the furnace by removing further heat from flue gas.
₪ RCO enters at top of convection zone in 4 paralleled passes.
₪ Flow through each pass controlled by flow control valves FIC 3401A/ 3402A/ 3403A/ 3404A.
₪ Tubes are made of 9 Cr, 1 Mo alloy steel materials.
₪ Coils come out of bottom of convection zone and return to the radiation zone.
₪ Four coils from radiation section of combustion chamber joins 50 inch header that expands to 56
inch and carries partially vaporized feed to vacuum column. TI’s are provided at outlet of each
coil (TI3407/ 3408/ 3409/ 3410) with TAH and TAL alarm on DCS.

24. Vacuum Column (CV27)
₪ Vacuum column is packed column for facilitating lower pressure drop across the column.
₪ Has 3 different diameters - top section of 600mm diameter, middle 7250mm and bottom section
5000mm diameter.
₪ Bottom keg section has diameter of 1800mm, 44640mm tall.
₪ Tower is made of carbon steel with 3mm thick lining of SS-410 on inner walls up to height of
32210mm from column bottom, rest of height it is provided with 3mm corrosion allowance.
₪ Column is provided with 4 sections.
₪ RCO from vacuum heater is fed to vacuum column at flash zone above tray #5. Flash zone
pressure - 39mmHg and temperature of 391/ 403.3oC.
₪ Vaporized portion enters flash zone of column along with stripped light ends from bottoms,
rises up column and is fractionated into 4 side stream products in 5 packed sections.

25. INTRINSIC SAFETY BARRIERS
₪ Protection technique for safe operation of electrical equipment in hazardous areas by limiting
energy available for ignition.
₪ Done by limiting the energy available for ignition.
₪ This approach simplifies circuits and reduces installation cost over other protection methods.
₪ Measuring instruments in hazardous area may be designed without any large capacitors or
inductors that could discharge in a spark.
₪ Safety barriers ensure that, no matter what accidental contact occurs between instrument circuit
and outside power sources, no more than approved voltage or current enters hazardous area.

26. Hazardous area designation
Any location in which a combustible material is or may be present in the atmosphere in sufficient
condition to produce an ignitable mixture is designated as an hazardous area.
Types of hazardous atmosphere
 Class I – Gas or vapor
 Class II – Dust
 Class III – Fiber or flying (no group designation)

27. Division / Zones
North America IES Std.
Division Method Zone Method
Ignitable mixture present
continuously
Division 1 Zone 0 Zone 0
(Zone 20 – Dust)
Ignitable mixture present
intermittently
Division 1 Zone 1 Zone 1
(Zone 21 – Dust)
Mixture is not normally
present
Division 2 Zone 2 Zone 2
(Zone 22 – Dust)

28. Hazardous areas are grouped according to their ignition property
Typical Gas IES Gas Group North American Group Minimum Ignition Energy
Acetylene IIC A 20 µJ
Hydron IIB + H2 B 20 µJ
Ethylene IIB C 66 µJ
Propane IIA D 100 µJ
Methane *
Metal dust E
Coal dust F
Grain dust F
Fiber G

29. Enclosure protection IP Rating
Protection against solid ingress Protection against water ingress
0 - No protection 0 – No protection
1 – Protection against contact by large surface ( i.e. the
hand)
1 – Protection against drops of condensed water ( i.e.
harmful effect)
2 – Protection against contact by fingers or medium sized
solid bodies.
2 – Liquid drops at 15o from vertical
3 – Contact by tools, wires, objects > 2.5 mm or small solid
bodies.
3 – Rain up to 60o from vertical
4 – Contact by tools, wires, objects > 1mm or small sized
bodies.
4 – Splashing from any direction
5 – Complete protection against contact, ingress of dust not
in harmful quantities.
5 – Water from any direction under stated condition.
6 – Complete protection against contact. Protection against
ingress of dust.
6 – Protection against heavy sea water under stated
conditions.
7 – Protection against water immersion under stated
conditions of pressure and time.
8 – Protection against indefinite immersion in water under
specific pressure.

30. Temperature Classification
T1 4500 C T3A 1800 C
T2 3000 C T3B 1650 C
T2A 2800 C T3C 1600 C
T2B 2600 C T4 1350 C
T2C 2300 C T4A 1200 C
T2D 2150 C T5 1000 C
T3 2000 C T6 850 C

31. Enclosure Ratings
Rating Description
1 Indoor, general purpose. Protection against contact.
2 Indoor, general purpose. Dust proof and protection against dirt and water.
3 Outdoor, protection against wind, dust and rain.
3R Outdoor, protection against rain.
3S Outdoor, protection against wind, dust, rain and ice.
4 Indoor / outdoor, protection against dust, rain, water and ice.
4X Indoor / outdoor, protection against corrosion, dust, rain, water and ice.
6 Indoor / outdoor, protection against water, ice and temporary submersion.
6P Indoor / outdoor, protection against water, ice and prolonged submersion.
7 Indoor use, hazardous class – I, division – I, group A,B,C.
9 Indoor use, hazardous class – II, division – I, group E,F,G.
12/12K Indoor use, protection against dirt dripping water and non-corrosive liquids.
13 Indoor use, protection against dust, dirt, water, oil and non-corrosive liquids.

32. I to P Converter
₪ Converts an analog signal (4-20mA) to a proportional linear pneumatic output (3-15psi).
₪ Delivers a high performance.
₪ Provides a reliable repeatable, accurate means of converting
₪ At lower end of coil is a flapper valve that operates against a precision ground nozzle to
create a back pressure on servo diaphragm on booster delay.
₪ Input current flows in coil and produces a force between coil and flapper valve, which
controls servo pressure and output pressure.
₪ Zero adjustment of unit is made by turning a screw that regulates distance between
flapper valve and air nozzle.
₪ Span adjustment is made by varying a potentiometer, which shunts input current past coil.

34. Solenoid Valve
₪ Electro mechanically operated valve.
₪ Most frequently used control elements in fluidics.
₪ Valve is controlled by an electric current through a solenoid
₪ Tasks are to shut off, release, dose, distribute or mix fluids.
₪ Solenoids offer fast safe switching, high reliability, long service
life, good medium compact ability of the materials used, low
control power and compact design.
FS = P A = Pπd2/4

35. Pressure Switch
₪ Switch that closes an electrical contact when a certain set
pressure has been reached on its input.
₪ Designed to make contact either on pressure rise or on pressure
fall.
₪ Adjustable, by moving the contacts or adjusting tension in
counter balance spring.
₪ Industrial pressure switches may have a calibrated scale and
pointer to show the set point of the switch
₪ Differential range around its set point in which small changes of
pressure do not change the state of the contacts.

36. Flow Switch
₪ Determines flow rate above or below a certain value.
₪ Setpoint can be fixed or adjustable.
₪ When the setpoint reached, response can be the actuation of an electric or pneumatic circuit.
₪ When the flow switch is actuated, it will stay in that condition until the flow rate moves back
from the setpoint by some amount.
₪ Difference between the setpoint and the reactivation point is - switch differential.
₪ Differential can be fixed or adjustable.

37. Temperature Switch
₪ Temperature switches are on-off devices,
₪ Characteristic is that measurement, set point, and control
functions are all combined into a single instrument.
₪ The switch may actuate at its set point on rising (high) or falling
(low) temperature

38. Combustible Gas Monitor
₪ Designed to detect the presence and measure the concentration of combustible gases and vapors
on a continuous basis.
₪ Methods of detecting the presence of combustible gases and vapors can utilize the phenomena of
catalytic combustion, electrical resistance, luminosity, thermal conductivity, infrared (IR)
absorption, or gas ionization.
₪ Widely used is catalytic combustion method
₪ Limits are;
∆ Lower Explosive Limit (LEL)
∆ Upper explosive limit (UEL)
∆ Flash point

39. ₪ Suitable for measurements of ppm to % levels of oxygen in a gas
or mixture of gases.
₪ Determines oxygen concentration using the conductivity of a
zirconia ceramic cell.
₪ Zirconia ceramic cell only allow oxygen ions to pass through at
high temperatures.
₪ Within an instrument the zirconium cell is mounted in
temperature controlled furnace with necessary electronics to
process the signal from the detection cell.
₪ Measurements are displayed directly via a digital display as
oxygen concentration over the range 0.01 ppm to 100%.
₪ O2 analyzer is kept at the top portion of the heater to check the
efficiency of the heater.
Zirconia Oxygen Analyzer

40. Orifice Plate
₪ An orifice plate is a device used for
∆ Measuring flow rate
∆ Reducing pressure
∆ Restricting flow
₪ Either volumetric or mass flow rate may be determined, depending on the
calculation associated with the orifice plate.
₪ Uses the same principle as a venture nozzle, namely Bernoulli’s principle.
₪ States that there is relationship between the pressure of the fluid and the
velocity of the fluid.
₪ When the velocity increases, the pressure decreases ; vice versa.

41. ₪ It consists of two dissimilar conductors that contact each other at one
or more spots, where a temperature differential is experienced by the
different conductors.
₪ It produces a voltage when the temperature of one of the spots differs
from the reference temperature at other parts of the circuit.
₪ The principle behind the operation is Seebeck Effect
Thermocouple

42. Thermocouple Types and Comparison

43. Interlocks are provided for safe guarding in abnormal condition
Plays a vital role in the safe shutdown of the plant during emergencies.
Used to prevent undesired states in a finite state machine.
Safety Interlocks

44. ₪ Today’s industries have more complex process are larger and are operated closer to their
safety limits than in the past.
₪ Plants are more likely to became unsafe, thus having a potential for causing greater damage
₪ This results in costly shutdown.
₪ So design of a plant safety system with their associated alarm is extremely important
Need of Interlocks

45. SYSTEM TRIPPING CONDITIONS
The PLC trip fuel oil and fuel gas when safety shutdown is needed
The fuel oil and fuel gas supply is controlled by solenoid valve for safety shutdown.

46. Conditions for Fuel Oil Trip
 Fuel oil pressure low
 Total feed flow
 Pass flow in any of four is low
 Atmospheric column pressure high
 Stack temperature high
 Atomizing steam pressure low
 FD fan discharge pressure low
 ID fan suction pressure low
 LEL high
 Arch pressure high
 Emergencies stop is pressed.

47. Condition for Fuel Gas Trip
 Fuel gas pressure low
 Total feed flow
 Pass flow in any of four is low
 Atmospheric column pressure high
 Stack temperature high
 FD fan discharge pressure low
 ID fan suction pressure low
 LEL high
 Arch pressure high
 Emergencies stop is pressed.

48. PROGRAMMABLE LOGIC CONTROLLER
₪ Digital computer for automation of electromechanical processes
₪ Designed for multiple inputs and output arrangements
₪ PLCs have,
₪ Extended temperature ranges,
₪ Immunity to electrical noise
₪ Resistance to vibration and impact
₪ Machine control programs are stored in battery backed up or non volatile memory
₪ Hard real time system

49. Ladder Logic
₪ Graphical diagram based on the circuit diagrams of relay logic hardware
₪ Primarily used to develop software for programmable logic controllers
₪ Programs in this language resemble ladders, with two vertical rails and a series of horizontal
rungs in between
₪ Seen as a set of connections between logical checkers (contacts) and actuators (coils).
₪ If path can be traced between the left side of the rung and the output, through asserted (true or
"closed") contacts the rung is true and the output coil storage bit is asserted (1) or true
₪ If no path can be traced, then the output is false (0) and the "coil" by analogy to electro-
mechanical relays is considered "de-energized“.

50. ₪ Ladder logic has contacts that make or break circuits to control coils
₪ Each contact corresponds to the status of a single bit in the PLC's memory
₪ Ladder program refer any number of times to the status of a single bit, equivalent to a relay with
an indefinitely large number of contacts.
₪ Inputs to the programmable controller from physical devices such as pushbuttons and limit
switches via an integrated or external input module represent the status of internal storage bits
which may be generated elsewhere in the program
₪ Typical coil representation
—( )— A regular coil, energized whenever its rung is closed.
—()— A "not" coil, energized whenever its rung is open.
—[ ]— A regular contact, closed whenever its corresponding coil or an input which
controls it is energized.
—[]— A "not" contact, closed whenever its corresponding coil or an input which
controls it is not energized.

51. Basic PLC Components
Processor (CPU)
Rack or mounting
Input assembly
Output assembly
Power supply
Programming Unit

52. RackAssembly
₪ In smaller PLC systems - components may be contained in a single
housing or "brick“.
₪ Smaller systems are sometimes referred to as "bricks" or "shoebox"
PLCs.
₪ Racks are assembled inside the marshalling room.
₪ Most medium to large PLC systems are assembled such that the
individual components
 CPU
 Input/output Assembly
 Power Supply

53. Processor (CPU)
₪ Size and type of CPU will determine
o Programming functions size of the application logic available
o Amount of memory available
o Processing speed
o Flexibility of the PLC
₪ Overall speed is expressed in term of how fast the PLC will scan a given among of memory.
₪ This measure is called as scan rate, typically expressed in milliseconds per thousand words of
memory.

54. Input/outputAssembly
₪ Inputs carry signals from the process into the controller
o Ex: Input switches, Pressure sensors, Operator inputs, etc.
₪ Outputs are the devices that the PLC uses to send changes out to the field.
₪ These are the actuator of the PLC, can adjust motors, lights, relays, pumps, etc.
₪ Many types of inputs and outputs can be connected to a PLC
o Analog and Digital
₪ Digital input/output - Binary change - ON/OFF
₪ Analog input/output change continuously over a variable range
o Ex: Pressure, Temperature and Potentiometer.

55. PowerSupply
₪ Need Internal DC current to operate the processor
logic circuitry and input/output assemblies.
₪ Common power levels used are 24V DC or 120 V AC.
₪ Basic function is to convert field power into more
suitable, for electronic devices that comprise the
PLCs.

56. ₪ PLC is programmed using a specialty programmer or software on a computer that can load and
change the logic inside.
₪ Memory of a PLC can be of two types namely: -
 Volatile
 Non-Volatile
₪ Volatile memory loses its contents when power supply is turned OFF, whereas non-volatile does
not.
₪ PLC use non-volatile memory from a majority of user’s memory because the program must be
retained during the power down cycle.
₪ It is imported that all non-volatile memory in a PLC uses some of the error checking to ensure
that the memory has not changed.
₪ The other memories used in PLCs are:
 Battery Back up CMOS RAM
 EPROM Memory
 EEPROM Memory
Programming Device

57. ₪ Some special processes need to work
permanently with minimum unwanted down
time.
₪ Necessary to design a system which is fault-
tolerant and capable of handling the process
with faulty modules.
₪ In such cases to increase the system availability
in the event of hardware component failure,
redundant CPU or I/O modules with the same
functionality can be added to hardware
configuration for preventing total or partial
process shutdown due to hardware failure.
Redundancy

58. PROGRAMMABLE LOGIC CONTROLLER

59.  Brand-name of a line of Factory Automation Equipment manufactured by Rockwell Automation
 The company was founded in 1903 as the Compression Rheostat Company by Dr. Stanton Allen
and Lynde Bradley with an initial investment of $1,000
 In 1910 the firm was renamed Allen-Bradley Company
 In February 1985, Rockwell Automation purchased Allen-Bradley for $1.651 billion

60. SoftwareforAllen-Bradley PLC Programming

61. BPCL KR PLC Control Room

62. Sl. No Service Parameters Shutdown Set Value Fuel Oil Solenoid Fuel Gas Solenoid Any Other System Remarks
1 PSHH 1611,1612,1613
CV21 O/H PRESSURE HIGH
2.8 Kg/Cm2 + 0.8 Kg/Cm2 (Fill
Head) = 3.6 Kg/Cm2
SOV 1401, 1402
Tripped
SOV 1403
Tripped
CH22, SOV 3301,3102
Tripped
2/3 Logic
2 CF21 SUCTION LEL
GAS MONITOR (CF 21 LEL-1)
60% SOV 1401, 1402
Tripped
SOV 1403
Tripped
CH22, SOV 3301,3102
Tripped
3 EMERGENCY TRIP FIELD/CR
PB.3011 A/B(CH21 & CH22)
- SOV 1401, 1402
Tripped
SOV 1403, 1404
Tripped
CH22, SOV 3301,3102
Tripped
4 FSL-1405,1406,1407,1408
CH21 PASS FLOW LOW LOW
45 T/Hr. SOV 1401, 1402
Tripped
SOV 1403
Tripped
CH22, SOV 3301,3102
Tripped
5 PSLL 1424 FUEL GAS
PRESSURE FLOW
0.3 Kg/Cm2 - SOV 1403
Tripped
-
6 PSLL 1427 FUEL OIL PRESSURE
LOW
3.5 Kg/Cm2 SOV 1401,1402
Tripped
- -
7 PDALL 1477 FO/STM DP FLOW 0.7 Kg/Cm2 SOV 1401,1402
Tripped
- -
8 PSLL 1428 ATOMISING STM
PRESSURE LOW
3.5 Kg/Cm2 SOV 1401,1402
Tripped
- -
9 FSLL 3004, 3005 CF21-A/B
FLOW LOW
28 T/Hr. SOV 1401,1402
Tripped
SOV 1403
Tripped
CH22, SOV 3301,3102
Tripped
10 FSLL 3003 NEW TOTAL FD
FLOW LOW (FT 3001+3002)
28 T/Hr. SOV 1401,1402
Tripped
SOV 1403
Tripped
CH22, SOV 3301,3102
Tripped
11 PSHH 3009
ID SUCTION PRESSURE HIGH
-50mmWC - - STACK DAMPER
OPENED
12 TSHH 3004 ID SUCTION
TEMPERATURE HIGH
2750C - - STACK DAMPER
OPENED
13 TSHH 1436/1436 B CH 21 ARCH
TEMPERATURE HIGH
10000C SOV 1401,1402
Tripped
SOV 1403, 3201
Tripped
CH22, SOV 3301,3102
Tripped
14 PSHH 3004 CH21 ARCH
PRESSURE HIGH
5mH2O - - STACK DAMPER
OPENED
15 COMBUSTION AIR
FLOW/PRESSURE LOW
FSLL 3002/PSLL3012,3006
22 T/Hr.
5mmH2O
SOV 1401,1402
Tripped
SOV 1403, 3201
Tripped
STACK DAMPER
OPENED
2/3 Logic
CH21 CHECK RECORD FOR SHUTDOWN SYSTEM

63.  Fuel oil pressure
 Fuel gas pressure
 Total feed flow low
 Atmospheric column pressure
 Stack temperature high
 Atomizing steam pressure low
 FD fan discharge pressure low
 ID fan discharge pressure low
 Arch pressure high
Parameter Considered

64. PLC Ladder Programming

72. CONCLUSION
₪ Safety interlock is a prerequisite for the safer operation of a heater.
₪ Earlier days safety systems made use of relays to implement safety interlocks.
₪ We designed a PLC based system for the CH21 crude heater.
₪ It is a digital system with redundancy of software.
₪ Using PLC based system we can consider more number of interlocks than that we can
consider while using relay logic.
₪ Considering the conditions of safety we developed ladder logics; which are then implemented
as software.
₪ This system is more reliable and faster than relay based system.

73. References
[1] BPCL Kochi Refinery workers manual CDU-II
[2] https://bharatpetroleum.com/our-business/refinery/kochi-refinery/history.aspx
[3] https://bharatpetroleum.com/our-business/refinery/kochi-refinery/process.aspx
[4] Instrument engineers’handbook: Process measurement and analysis _ Bela G Liptak _ Chilton book
company
[5] Instrument engineers’handbook: Process control _ Bela G Liptak _ Chilton book company
[6] Handbook of Petroleum processing _ David S. J. Jones, Peter R. Pujado _ Springer science and business
media
[7] Refining process handbook_Surinder Parkash_Gulf professional publishing, 2003
[8] Fundamentals of Petroleum Refining _ Mohamed A Fahim ,Taher Al-Sahhaf, Amal Elkilani _ Elsevier