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OISD-STANDARD-152

First Edition March, 1991 FOR RESTRICTED CIRCULATION ONLY

SAFETY INSTRUMENTATION FOR

PROCESS SYSTEM IN

HYDROCARBON INDUSTRY

Prepared by: COMMITTEE ON

PROCESS INSTRUMENTATION, MAINTENANCE & INSPECTION

OIL INDUSTRY SAFETY DIRECTORATE 7TH FLOOR, NEW DELHI HOUSE

27, BARAKHAMBA ROAD NEW DELHI - 110 001.

NOTES

OIL INDUSTRY SAFETY DIRECTORATE publications are prepared for use in the Oil and gas industry under Ministry of Petroleum and Natural Gas. These are the property of Ministry of Petroleum and Natural Gas and shall not be reproduced or copied and loaned or exhibited to others without written consent from OISD.

Though every effort has been made to assure the accuracy and reliability of data contained in these documents, OISD hereby expressly disclaims any liability or responsibility for loss or damage resulting from their use. These documents are intended only to supplement and not replace the existing statutory requirements.

FOREWORD

The Oil Industry in India is nearly 100 years old. Because of various collaboration agreements, a variety of international codes, standards and practices have been in vogue. Standardisation in design philosophies and operating and maintenance practices at a national level was hardly in existence. This, coupled with feed back from some serious accidents that occurred in the recent past in India and abroad, emphasized the need for the industry to review the existing state of art in designing, operating and maintaining oil and gas installations particularly using sophisticated instrumentation. With this in view, the Ministry of Petroleum & Natural Gas, in 1986, constituted a Safety Council assisted by Oil Industry Safety Directorate (OISD), staffed from within the industry, in formulating and implementing a series of self regulatory measures aimed at removing obsolescence, standardising and upgrading the existing standards to ensure safe operations. Accordingly, OISD constituted a number of Functional Committees of experts nominated from the industry to draw up standards and guidelines on various subjects. The present document on “Safety Instrumentation For Process System in Hydrocarbon Industry’ is prepared by the Functional Committee on “Instrumentation”. This document is based on the accumulated knowledge and experience of Industry members and the various national and international codes and practices. It is hoped that provisions of this document when adopted, may go a long way to improve the safety and reduce accidents in oil and gas Industry. Users are cautioned that no standard can be a substitute for a responsible, qualified Instrumentation Engineer. Suggestions are invited from the users after it is put into practice to improve the document further.

This standard in no way supercedes the statutory regulations of CCE, Factory Inspectorate or any other statutory body which must be followed as applicable.

Suggestions for amendments, if any, to this standard should be addressed to:

The Co-ordinator, Committee on

“Process Instrumentation, Maintenance & Inspection” OIL INDUSTRY SAFETY DIRECTORATE

7th Floor, ‘New Delhi House’ 27, Barakhamba Road New Delhi – 110 001

.

COMMITTEE ON

PROCESS INSTRUMENTATION, MAINTENANCE AND INSPECTION

LIST OF MEMBERS

--------------------------------------------------------------------------------------------------------------------------------------- Name Designation / Organisation Status --------------------------------------------------------------------------------------------------------------------------------------- S/Shri S. Raghuraman Sr. Manager (Inst.), EIL Leader K. G. Nair Ch. Inst. Manager, IOCL Member V.K. Agarwal DGM (Tech.) BPCL Member C. S. Osman Chief Manager (Inst.), MRL Member R. D. Shira Sr. Maintenance Manager, BRPL Member A. Majumdar DGM (Inst.), ONGC Member S. Rammohan Sr. Manager (Inst.), GAIL Member R. Murlidharan Manager (M & I), IOCL Member G. R. Rana Joint Director, OISD Member V. M. Ranalkar Dy. Director, OISD Member Co-ordinator. --------------------------------------------------------------------------------------------------------------------------------------- In addition to the above several experts from industry contributed in the preparation, review and finalisation of the document.

SAFETY INSTRUMENTATION FOR PROCESS SYSTEM IN HYDROCARBON INDUSTRY

CONTENTS

------------------------------------------------------------------------------------------------------------------------ SECTION DESCRIPTION PAGE NO. --------------------------------------------------------------------------------------------------------------------------------------- 1. INTRODUCTION 1 2. SCOPE 1 3. DEFINITIONS 1 4. SAFETY INSTRUMENTATION FOR PROCESS SYSTEMS 2 4.1 SEPARATORS 2 4.2 MAIN LINE PUMPS 2 4.3 GAS DEHYDRATOR 3 4.4 CROSS COUNTRY PIPE LINES 3 4.5 ELECTROSTATIC DESALTER 5 4.6 DISTILLATION COLUMN 5 4.7 PROCESS HEATERS 5 4.8 HDS REACTOR 7 4.9 PROCESS GAS COMPRESSOR 7 4.10 FCC REACTOR/REGENERATOR 8 4.11 FLARE GAS SYSTEM 8 4.12 ATMOSPHERIC STORAGE TANKS 9 4.13 AIR COMPRESSORS 9 4.14 TURBINES 9 4.15 LPG PRESSURE STORAGE AND BULK LOADING 9 4.16 COKE CHAMBERS 10 -----------------------------------------------------------------------------------------------------------------------

LIST OF THE FIGURES ATTACHED

-------------------------------------------------------------------------------------------------- Figure No. Description Page No. -------------------------------------------------------------------------------------------------- 4.1 Safety Instrumentation for Separator 12 4.2 Safety Instrumentation for Main Line Pumps 13 4.3 Safety Instrumentation for Gas Dehydrator 14 4.4.1 Safety Instrumentation for Pipeline System 15 4.4.2 Safety Instrumentation for Scrubber 16 4.4.3 Safety Instrumentation for Filter Separator 17 4.6 Safety Instrumentation for Crude Distillation Column 18 4.7.1 Safety Instrumentation for Process Heater 19 4.7.2 Safety Instrumentation for Combustion Air System 20 4.8 Safety Instrumentation for HDS Reactor 21 4.9 Safety Instrumentation for Process Gas Compressor 22 4.10 Safety Instrumentation for Fluidized Catalytic Cracker 23 4.11 Safety Instrumentation for Flare Gas System 24 4.15 Safety Instrumentation for L.P.G Sphere 25 4.16 Safety Instrumentation for Coke Chamber 26 ----------------------------------------------------------------------------------------------

SAFETY INSTRUMENTATION FOR PROCESS SYSTEM IN HYDROCARBON INDUSTRY

1.0 INTRODUCTION The complexity of refinery operations have increased due to increase in the throughput. They are also operated more efficiently and safely to yield better quality products. All this has necessitated additional and more sophisticated process instrumentation. Over the years the operation of these process plants have also been analysed and need has been felt to define the instrumentation which must be provided as a minimum to ensure safe operation and shutdown of the plant in case of emergency. This standard lists the minimum instrumentation required for selected refinery processes for consideration of all concerned associated with design, operation and maintenance of process plants. 2.0 SCOPE This standard covers the onshore production facilities excluding the well head, gas and crude transportation facilities from oil field, gas processing units and refinery process plants. Offshore facilities have been excluded. Only selected process systems have been considered in this standard. Though it is possible that there are more than one method of achieving a process result (For example:-dehydration) only the most widely used method has been considered for each process. This standard broadly follows the guidelines of API-14C and considers only the trips and alarms required for the protection of the equipment. The level of safety considered in the standard is for adequate protection of the equipment depending upon their criticality. For Trip System the standard specifies that all trip switches shall be direct mounted as far as possible accompanied by audio visual

alarms and must be preceded by warning alarms wherever applicable. Details of individual processes in brief have been included in the description of each process. Some mechanical items such as flow safety valves have been included in the scheme for the sake of completeness even though they are not instrument items. Some instrument items such as Restriction Orifices and pressure control valves which do not directly participate in the trip of equipment have also been shown on the sketches for the sake of completeness. 3.0 DEFINITIONS 3.1 EMERGENCY SHUTDOWN SYSTEM(ESD)

A system of manual stations which, when activated, initiate shutdown operation.

3.2 FAILURE:

Improper performance of a device or equipment item that prevents completion of its design functions.

3.3 GAS DETECTION SYSTEM: A system which monitors the

concentration of combustible and toxic gases and initiates and /or shutdown functions at predetermined level of concentrations.

3.4 HIGH LIQUID LEVEL: Liquid level in a process system

above the highest operating level. 3.5 HIGH TEMPERATURE:

Temperature in a process system in excess of the design operation temperature.

3.6 LEAK: The accidental release of liquid

and/or gaseous hydrocarbon to atmosphere from a process system.

3.7 LOW FLOW: Flow in a process system less than

the minimum operation flow rate. 3.8 LOW LIQUID LEVEL: Liquid level in a process system

below the lowest operating level. 3.9 LOW PRESSURE: Pressure in a process system less

than the minimum operating pressure.

3.10 SAFETY DEVICE: An instrument of control use for the

safety of the system. 3.11 SENSOR A device which detects an abnormal

operating condition and transmits a signal to perform a specific shutdown function.

3.12 SHUTDOWN VALVE (SDV): An automatically operated valve

used for the protection of a process equipment in emergencies.

4.0 SAFETY INSTRUMENTATION

FOR PROCESS SYSTEMS 4.1 SEPARATORS 4.1.1 Description: The separator considered here is of

the three phase type to separate gas, oil and water from the emulsion produced from the well.

4.1.2 Safety Instrumentation The following safety instrumentation

shall be provided.(see Fig.4.1) (i) High pressure switch shall be

provided to shut off inflow to the vessel.

(ii) Low pressure switch to shut off

inflow to the vessel. (iii) Safety/Relief valve shall be provided

as per guidelines of OISD Standard 106 on “Pressure Relief and Disposal System”.

(iv) High level switch to shut off inflow to

the vessel in case the down stream component receiving the gas cannot handle liquid.

(v) Low level switch to shut off the liquid

outflow from the separator to prevent gas blow by.

(vi) High temperature switch on

separators like heater-treater to shut off the source of heat in case of high temperature of process fluid.

(vii) Automatic switching-off of the high

voltage transformer used for electrostatic separation in case of abnormal conditions requiring feed cut off and low level of the separator.

4.2 MAINLINE PUMPS 4.2.1 Description Main line pumps are the pumps

used for hydrocarbon oil transportation through pipelines. The pumps considered here are electrical motor driven centrifugal pumps. It is also considered that the pumps are located in the field and all parameters related to the pump are controlled from the central control room located away form the pump provided the downstream equipment are not designed for shut off pressure.

4.2.2 Safety Instrumentation The following instrumentation shall

be provided for main-line pumps:- (see Fig.4.2)

(I) High pressure switch in the pump

discharge for tripping the pump. (ii) Low pressure switch in the pump

discharge for tripping the pump. (iii) Low pressure switch in the pump

suction to trip the pump. (iv) Vibration monitoring and trip shall be

provided as per pump manufacturer’s recommendations.

(v) Temperature sensors ( RTD/

Thermocouple type) for monitoring of bearing temperatures and trip as per recommendations of pump manufacturers.

(vi) Motor operated valves shall be

provided on upstream and down stream of the pump which shall be coupled to the operation of the pump logic. In case of emergency condition local operation shall be considered.

(vii) Check valves shall be provided in

the down stream of each pump in order to minimize back flow.

(viii) Level switch shall be provided in

seal oil system to trip the pump in the event of seal failure.

(ix) Motor bearing and winding

temperature indicators with alarms/trips as per manufacturer’s recommendations.

(x) Provision of Temperature Sensor for

tripping the mainline pump in case of high pump casing temperature as per pump Manufacturer's recommendation.

4.3 GAS DEHYDRATORS 4.3.1 Description

Liquid desiccant method is used in the gas dehydrator considered here. The desiccant considered is tri-ethylene glycol.

The gas saturated with moisture but

free of entrained liquid particles is brought into counter current contact with concentrated triethylene glycol in the contactor tower which has bubble cap trays. The triethylene glycol absorbs the water vapour from the gas and passes out from the bottom of the contactor. First it cools the lean triethylene glycol entering the contactor and then partially condenses the top product of the glycol still in the reflux condenser. The gas then passes through the overhead scrubber where the entrained glycol is knocked off and the dried gas is sent to the pipeline. The bottom stream is sent for glycol recovery and reuse.

4.3.2 Safety Instrumentation: The following instrumentation shall

be provided for gas dehydrators:- (see Fig.4.3)

(I) High pressure switch on the glycol

contactor to shut off inflow of gas. (ii) Low pressure switch on the glycol

contactor to shut off inflow of gas. (iii) Safety/Relief valve shall be provided

as per guidelines of OISD Standard 106 on “Pressure Relief and Disposal System” on the glycol contactor.

(iv) High level switch to trip the glycol

pump and inflow of the gas to the contactor.

(v) Low level switch to shut off the

glycol outlet line. (vi) Blow down valve shall be installed

for depressuring the vessel and discharge to flare in case of emergency.

(vii) Shutdown valves on the Gas inlet and outlet line. 4.4 CROSS COUNTRY PIPELINES Description For this standard the cross country

pipelines considered are pipelines which carry crude petroleum, petroleum products and Natural Gas from producers facilities such as tank farms, Natural Gas Processing Plants, Refineries, Pump Stations etc. to other delivery and processing plants.

The minimum safety instrumentation

required for cross country pipelines are described under the two system:- Oil pipelines system and gas pipelines system.

4.4.1 Oil Pipeline System Major portion of the Oil pipeline

instrumentation is in the main oil pumping station which has been covered under section 4.2. Apart from Electrical drives, Engines using Crude Oil, Diesel or both as fuels are also used to drive Main Line Pumps. In addition to the manufacturer’s recommendations on instrumentation, the following safety instrumentation shall be provided for the Engine:

(I) Low Pressure switch for instrument air. (ii) Low pressure switch on fuel supply. (iii) High temperature switches on gear box pinion bearing and wheel bearing, engine bearing, engine jacket cooling water. (iv) Oil Mist detector. 4.4.2 Gas Pipeline System (I) Description This chapter covers only pipeline

transporting gas and associated

facilities. Since major portion of oil pipeline instrumentation is only at the main oil pumping station, this has been covered under section 4.2.

The pipeline system consists of gas

dispatch terminals, gas receiving terminals and scrapper stations.

The dispatch and receiver terminals

are provided with gas scrubbers, filter separators drums, gas heaters, flow metering and pressure regulating equipment and condensate handling systems (Fig.4.4.1)

(ii) Scrubber The scrubber is used for removal of

foreign particles and condensate droplets.

Safety instrumentation provided

shall be (See Fig.4.4.2) (a) Level indicator with low,

low-low and high alarms. (b) Separate shut off valve on

the condensate line to shut the system in case of low- low level alarm.

(c) Safety/Relief valve shall be

provided as per guidelines of OISD Standard 106 on

“Pressure Relief and Disposal System”

(d) Level control valve. (iii) Filter Separator Filter separator is used to remove

finer droplets using centrifuge filters and wire mesh mist extractors. The safety instrumentation shall be: (see Fig.4.4.3)

(a) Level indicator with low,

low-low and high alarms.

(b) Separate shut off valve to shut the system in case of low-low level.

(c) Safety/Relief valve shall be

provided as per guidelines of OISD Standard 106 on

“Pressure Relief and

Disposal System”. (d) Differential pressure high

alarm across filter drum. (e) Low level tripping of

condensate SDV. (iv) Condensate handling system. The condensate handling system

consists of condensate flash drum, underground sump, overhead storage tank, loading station and burn pits. The condensate flows by gravity to a sump tank. The transfer pump is started and stopped by high and low level switches on the sump tank. The liquid is sent either to the overhead tank or to the burn pit by operating a manual valve.

The following safety instruments

shall be provided: (a) Low level of condensate in

the sump tank shall trip the condensate pump.

(b) High level alarm of the

condensate in the sump tank.

(c) High level alarm in the

overhead tank. (v) Gas heaters The filtered gas is heated before

entering the metering system to keep the gas temperature above its dew point. The safety instruments are:

(a) Safety/Relief valve shall be

provided as per guidelines of OISD Standard 106 on

“Pressure Relief and Disposal System”

(vi) Gas metering /Pressure Reducing

Installation. The clean filtered gas passes

through metering skid and necessary pressure reduction by pressure regulators., the skid consists of filters, flow meters, flow computers and associated temperature and pressure correcting instrument systems.

The safety instrumentation shall be:- (a) Quick shut off valve to isolate

the installation from the main pipe line in case of high pressure. The quick shut valves shall be self actuating type & shall be provided with manual reset only.

(vii) Scrapper stations and

Sectionalising valve stations. Sectionalising valves shall be

provided to isolate the affected sections of a pipeline in case of gas leak or line burst. These valves may be with remote operation facilities.

In all cases the resetting and

opening of the valve shall be possible only locally and should be done after investigation of the cause of the trip.

Scrapper launcher and receiver

barrels shall be provided with pressure relief valves.

4.5 ELECTROSTATIC DESALTER. 4.5.1 Description In a Desalter, the crude is mixed

with water and led into a vessel operating under pressure and having a electrostatic field. The water dissolves the undesirable soluble salts present in the crude and gets separated from the crude

under the influence of electrostatic field.

4.5.2 Safety Instrumentation. The following Safety Instrumentation

shall be provided: (I) High/low level interphase alarms. (ii) Low Oil level trip (iii) Desalter trip annunciation in the control room. (iv) High and low pressure alarm. (v) Safety/Relief valve shall be provided

as per guidelines of OISD Standard 106 on “Pressure Relief and Disposal System”.

4.6 DISTILLATION COLUMN 4.6.1 Description The crude distillation column is used

to fractionate the crude oil into various petroleum products. The crude from the furnace enters the flash zone of the column and flashed vapour rises up and the liquid flows down. Various products are withdrawn as side streams. The vapour from the top is condensed and partially refluxed back. Heat is supplied to the column by reboiler and stripping steam. The top reflux is controlled by a flow recorder and controller (FRC) which is reset by the top temperature recorder and controller (TRC). Pressure of the column overhead is controlled by a PRC. This is split range controller. When the column pressure is above the set point, the controller released gas to flare. When the pressure is below the set point it maintains the same by make up gas from the fuel gas system. Column bottom level is controlled by level controller (LIC).

4.6.2 Instrumentation

The following safety instrumentation shall be provided in a distillation column:-(see Fig.:4.6) (I) Safety/Relief valves shall be

provided as per guidelines of OISD Standard 106 on “Pressure Relief and Disposal System”.

(ii) The column bottom level shall be

monitored by two different instruments with separate tappings.

(iii) High level and low level switches at

column bottom shall be provided independently. Both switches must be direct operated (without air/power)

(iv) There shall be minimum two temperature points for column top temperature, one for indication and one for control with provision for high alarm. (v) A high alarm shall be provided for the column bottom temperature. (vi) High and low level alarm shall be considered for overhead reflux drum. 4.7 PROCESS HEATERS 4.7.1 Description Process heaters are required to

raise the temperature of various process fluids to achieve partial vapourisation of fractionation operation. The fluids enters the heater in convection section in more than one passes and after getting heated passes through the radiant section of tubes normally arranged vertically and finally comes out in one or tow stream. The burners are normally combination type suitable for oil or/and gas firing. In the forced draft design of the furnace, fans are provided to supply air for burning which are associated with drop out doors. The furnaces provided with ID fan and air preheater (APH) will have stack

damper which is kept opened for natural draft operation. The stack damper remains closed in the balanced draft operation.

4.7.2 Safety Instrumentation The following safety instrumentation

shall be considered for safe operation of the heater. Sketch showing safety instrumentation of furnace is shown in fig-4.7.1 & 4.7.2

(I) Feed Section

· Low Feed flow alarms for each pass.

· Low total feed flow switch to

bring the heater to a safe minimum firing position.

· Low low total feed flow

switch to trip the heater.

· High temperature alarm for each pass and at the heater outlet.

· Skin temperature

measurements at 3 locations for each pass.

· Automatic injection of coil

purging steam at the time of furnace trip shall be

considered.

(ii) COMBUSTION AIR SYSTEMS

· Running of FD fan shall be verified in the circuit by Motor contactor closure discharge pressure low low pressure switch. This will ensure positive protection against mal-operation of guide van.

· Low air flow alarm and low air flow combined with motor contactor to warn mal operation of FD fan.

· Air storage tank to ensure

opening of drop out door in

case of air failure provision for mechanically opening shall be provided.

· Provision shall be made to

check up operation of drop out door in running condition. This is referred as crack open test.

· Positive protection for mal

operation of ID fan shall be provided by motor contact closure and pressure switch.

· Tripping/stopping of ID/FD

fan shall have provision to automatically open the stack damper.

· Furnace trip due to high

pressure shall be preceded by high pressure alarm. This very high pressure (PHH) trip shall be sensed preferably by three directly mounted pressure switches and voting logic of two out of three shall be used for furnace tripping.

· Necessary analysers shall

be provided to monitor CO, Nox, SO2 and H2S on flue gases.

· In the event of fuel oil and fuel gas cut off to the furnace, the following sequential action is needed:- (a) Stack Damper Shall

Open. (b) ID Fan to trip (c) FD Fan to trip

(iii) Burner System.

· Low pressure alarm and very low pressure alarm for pilot gas should be incorporated in the safety inter lock system. of the furnace.

· A separate shut off valve

shall be provided on the pilot gas header.

· This shall be linked up with push button trip or full furnace trip.

· Main FO/FG headers shall

be provided with shut off valves operated by low fuel pressure and other reasons of furnace trip.

· Shut down valve operated

by manual push button switches shall be considered for each fuel gas burners, wherever applicable.

· The pressure switches

shall be directly mounted on the FO/FG headers for safety.

· For dual firing the safety

interlock should take care that no interruption in furnace operation takes place during change over of fuel.

· Pilot flame detection

should be provided in the safety interlock wherever remote burner lighting system is existing so that main fuel cannot be admitted without establishment of pilot flame.

· There shall be two sets

push button emergency trip, one located in the central room and one near the furnace.

4.8 HDS REACTOR (HYDRO

DESULPHURISATION) 4.8.1 Description

HDS Reactors are used to remove sulphur from petroleum products like Naphtha, Kerosene, diesel etc. the product to be desulphurised is mixed with Hydrogen and heated in a furnace, the outlet temperature of which is controlled. The outlet of the furnace with controlled temperature enters into a reactor filled with catalyst. In the reactor the sulphur in the petroleum products combine with hydrogen and forms hydrogen sulphide. The reaction product goes to a separator where the gas is separated from the desulphurised product.

4.8.2 Safety Instrumentation The following safety instrumentation shall be provided for HDS unit. (see Fig:4.8) (I) Reactor thermocouple assembly

consisting of number of thermocouples of different lengths to measure and record reactor bed temperature at different heights. High temperature alarms also shall be provided.

(ii) Reactor inlet and outlet temperature

recorder with high alarms. Separate sensors for recorders and alarms shall be provided.

(iii) Reactor inlet temperature control to

be incorporated in the furnace outlet temperature control scheme.

(iv) Safety/Relief valve shall be provided

as per guidelines of OISD Standard 106 on “Pressure Relief and Disposal System”

(v) Safety interlock shall be provided for

low hydrogen flow or low feed or high reactor temperature.

4.9 PROCESS GAS

COMPRESSORS 4.9.1 Description Process gas compressors are used

in the petroleum processing and gas

pipeline processes to increase the pressure of gas for handling and transportation.

4.9.2 Safety Instrumentation The compressors should be

provided with the following instrumentation (see Fig.4.9). Additional instrumentation shall be provided as per manufacturer’s recommendations.

(I) PSH and PSL on suction and

discharge line to trip the compressor.

(ii) Pressure safety valve on the

discharge line and K.O drum of each stage.

(iii) A check valve (FSV) on the

discharge line. (iv) Gas detection and fire detection

devices shall be provided if the compressor is located inside enclosed buildings totally covered on all the sides. The protection shall also include turbine enclosures.

(v) An anti surge controller shall be

provided for centrifugal compressors.

(vi) Devices to monitor and trip in case

of excessive vibration, speed, low lube oil pressure, seal oil low differential pressure, high bearing temperature and high discharge temperature etc. in line with manufacturers recommendations.

(vii) High level switches on the suction

knockout drum shall trip the compressor.

(viii) Automatically operated blow down

valve shall be provided on the discharge line.

Note: Compressor trip shall mean shutting

down the drive unit and closing of suction shut down valve.

4.10 FLUIDISED CATALYTIC CRACKING UNIT REACTOR/ REGENERATOR

4.10.1 Description Lighter products are obtained from

Heavy Vacuum Gas Oil (HVGO) by Catalytic cracking in FCCU, Zeolite catalyst is heated to a temperature of 650 degree C and is then allowed to flow with the feed (HVGO) in the riser pipe of the reactor. Carbon particles are deposited on the catalyst when the feed cracks into lighter ends like Fuel Gas, LPG, Naphtha, diesel and heavy oil. The carbonized catalyst is called spent catalyst and is then taken into the regenerator for regeneration. In the regenerator controlled air is blown through the hot catalyst to convert the carbon into carbon monoxide, thereby releasing equilibrium catalyst for use in the next cycle.

Reactor contains hydrocarbon

vapour and regenerator contains hot air. air should not enter the reactor and hydrocarbon vapour should not find entry into the regenerator. Regenerator is kept at higher pressure (0.5 Kg/CM2) more compared to the reactor. Additional heads due to spent catalyst level in the reactor aids the transfer of spent catalyst from reactor to regenerator. During normal operation spent catalyst slide +valve operation is dependent on the LRC of reactor. The reactor is maintained at a temp around 490 Deg.C by the transfer of hot regenerated catalyst from regenerator. During normal operation regenerator catalyst slide valve opening is controlled by reactor TRC (Fig.4.10)

4.10.2 Safety Instrumentation The following safety instrumentation

shall be provided: (I) Three nos. of low differential

pressure switches in 2/3 voting logic across the spent catalyst slide valve

to shut off the slide valve automatically in the event of low differential pressure.

(ii) Three nos. differential pressure

switches in 2/3 voting logic across the regenerated catalyst slide valve to shut off the valve automatically in the event of low differential pressure.

(iii) Mechanical stopper shall be

provided for the double disc slide valve to prevent closing of the valve against over pressurisation of regenerator.

(iv) Reactor high temperature alarm. (v) Emergency feed by pass switch to

divert feed from the reactor. (vi) Hand jack for all slide valves for

manual operation. In addition local electrical/hydraulic/pneumatic operation shall also be provided.

(vii) Low flow alarm rate and emergency

cut in for steam and bypassing feed to reactor may be considered.

(viii) Low temperature alarm for reactor

cyclone outlet temperature may be considered for prevention of hydrocarbon vapour into regenerator.

4.11.0 FLARE GAS SYSTEM 4.11.1 Description All the gas to be flared come to a

liquid knock out (K.O.) drum. From the K.O. drum the liquid is pumped back to Recovery System and the gas goes to flare through a water seal drum.

4.11.2 Safety Instrumentation The following safety instrumentation shall be provided (see Fig.4.11) (I) Low level alarm set at below the

pump auto stop.

(ii) Knock out drum (K. O. D.) high level

alarms. In case of gas processing units a system trip to restrict the liquid inflow to K.O drum may be considered.

(iii) T.V. monitoring of the flame may be

considered. 4.12 ATMOSPHERIC STORAGE TANKS 4.12.1 Description In petroleum industries, there are usually two types of storage tanks: (I) Cone Roof tanks for heavy products. (ii) Floating Roof tanks for lighter

products. 4.12.2 Safety Instrumentation The following safety instrumentation shall be provided: (I) Indicator with optional high level

alarm. (ii) Temperature indicator with optional

high temperature alarm. (iii) Pressure and vacuum Relief valves

in case of it is not freely vented to atmosphere, with a flame arrest on the downstream side.

4.13 AIR COMPRESSORS 4.13.1 Description Air compressors are used in

hydrocarbon industry for supplying air to pneumatic instruments and as well as for process requirements. The compressors considered here are reciprocating type.

4.13.2 The following safety instrumentation

shall be provided: (I) Pressure safety valve at the

discharge of each stage.

(ii) Cooling water low flow trip. (iii) Discharge temp high trip. (iv) Frame oil low pressure trip. (v) Discharge pressure high trip. (vi) Automatic loading/unloading system

to be considered wherever possible. 4.4 TURBINES 4.14.1 Description: Turbines are steam/gas driven drive

units used in hydrocarbon industry for driving compressors, blowers and alternators in the process units and captive thermal power station.

4.14.2 The following safety Instrumentation

shall be provided: I) Lube Oil pressure low trip. ii) Governor oil to pressure low trip. iii) Turbine exhaust pressure high trip. iv) Over speed trip. v) Axial displacement trip. vi) Vibration high trip. vii) Emergency trip. viii) Condensate level high alarm. ix) Exhaust hood high temperature

alarm. x) Operating temperature high Trip. xi) FG pressure low trip. xii) Exhaust temp.(average of 3

thermocouples in exhaust) high trip. xiii) Lube oil temp. high trip xiv) K.O drum level high trip. xv) Oil tank level alarms.

4.15 LPG PRESSURE STORAGE AND

BULK LOADING 4.15.1 Description LPG is received from the plant

through pipelines. it is stored under pressure at atmospheric temperatures in spheres or bullets. The LPG is pumped to a loading gantry from where it is loaded through loading arms into truck tankers or rail tankers.

When LPG is received through road

or rail tankers, it is pumped into the bullets or spheres by unloading pumps.

4.15.2 Safety Instrumentation. The following safety instrumentation

shall be provided for LPG Sphere (Fig.4.15)

(I) LPG sphere shall be provided with

Pressure Safety Valve as per guidelines of OISD-106 on “Pressure Relief and Disposal System”

(ii) Fire detection and protection system It shall consist of fusible plugs on a

tubing system pressurised by instrument air which shall be provided on LPG spheres, LPG pumps, compressor house etc. The fusible plugs shall be designed to blow at 80 Deg.C. If any of the plug fuses and blows it will depressurise the system. This is sensed by a pressure switch which will activate the security system.

The activation of the pressure switch

shall initiate the following action. - Closure of remote operated valves

in the affected area. - Start up of fire water pump,

activation of deluge valve and activation of the sprinkler system.

- Activation of tone generator in paging or a siren in the particular area.

- Tripping of LPG pumps and

compressors. Emergency push buttons shall be

provided in the control panel and at a safe place in the field to initiate the above actions manually.

ROVS shall be provided with

open/close indications on the control panel.

(iii) Gas Detection Systems Gas detectors shall be provided at

all locations where possibility of build up of LPG vapour exists, which might lead to a fire.

Suggested locations are:

- LPG Pump and compressor house.

- LPG Truck and rail loading

gantries - LPG Sampling Point. - Near ROVS. Gas detectors shall have two levels

of alarms. Suggested values are 20% LEL and 60% LEL.

(iv) Level gauging devices LPG spheres shall be provided with

two independent indicators as a minimum.

(v) Level switches A separate high level switch shall be

provided for alarm in the control room.

A water seal pot shall be provided

on the low pressure side of the DP type level transmitter if use, the seal pot and the connecting pipe shall be of the same rating as that of the

sphere. Alternatively, the low pressure leg of the D. P. transmitter shall be heat traced. The D. P. transmitter shall be provided with level elevation or suppression kit.

4.16 COKE CHAMBERS 4.16.1 Description In a thermal cracking process the

residue from the distillation column is heated to about 500 Deg .C and admitted into the coke chamber. The coke gets deposited on the chamber and cracked vapour goes from the top to fractionation section. After a definite cycle, the reactor is changed over, quenched with oil and cooled. The coke is cut into smaller pieces by high pressure water jet and dumped through the bottom.

4.16.2 Safety Instrumentation The following safety instrumentation

shall be provided in a coke chamber. (See Fig:4.16)

(I) Level alarms at different locations to

avoid foam/coke carry over etc. (ii) High pressure alarm with

independent impulse line. (iii) Temperature indication and high

temperature alarm at vapour outlet (after HGO quench). Skin thermo couple at top/middle/bottom of the chamber.

(iv) Coke cutting water pump trips for

following conditions: (a) Low discharge pressure. (b) If isolation valve on water

line at other chamber is in open position.

(c) If the cutting tool is out of

chamber and discharge does not get routed to storage.

(v) During coke cutting, when the

cutting/drilling tools need to be

brought out for the tool change etc., the coke cutting water pump

discharge shall automatically get routed to storage tank.

Following legends are used in the figures

LS : LEVEL SWITCH LSH : LEVEL SWITCH HIGH LSHH : LEVEL SWITCH HIGH HIGH LSL : LEVEL SWITCH LOW LSLL : LEVEL SWITCH LOW LOW LT : LEVEL TRANSMITTER LI : LEVEL INDICATOR LCV : LEVEL CONTROL VALVE DP : DIFFERENTIAL PRESSURE PSV : PRESSURE SAFETY VALVE PSH : PRESSURE SWITCH HIGH PSL : PRESSURE SWITCH LOW PSLL : PRESSURE SWITCH LOW LOW PCV : PRESSURE CONTROL VALVE FSV : FLOW SAFETY VALVE FSL : FLOW SWITCH LOW FSLL : FLOW SWITCH LOW LOW FCV : FLOW CONTROL VALVE TT : TEMPERATURE TRANSMETER TE : TEMPERATURE ELEMENT TCV : TEMPERATURE CONTROL VALVE TSH : TEMPERATURE SWITCH HIGH TSHH : TEMPERATURE SWITCH HIGH HIGH SDV : SHUT DOWN VALVE BDV : BLOW DOWN VALVE ROV : REMOTE OPERATE VALVE MOV : MOTOR OPERATED VALVE VSHH : VIBRATION SWITCH HIGH HIGH FO : FUEL OIL FG : FUEL GAS

NOTE

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