Safety in CNG Systems

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• Safety in CNG Systems

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TYPES OF CNG STATIONS

• DAUGHTER STATION
• CNG facility not connected to natural gas
  pipeline and dispensing CNG to the vehicles
  through mobile cascades
• DAUGHTER BOOSTER STATION
• CNG facility not connected to natural gas
  pipeline but having a compressor meant to fill
  primarily for vehicles and storage cascade
• CNG ONLINE STATION
• CNG facility connected with natural gas pipeline
  and having a compressor primarily to fill
  stationary cascades for dispensing CNG to
  vehicles.

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SCHEMATIC DIAGRAM
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Schematic Daiagram- MOTHER STATION
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TYPICAL FACILITIES

• Flow meter
• Odorizing Unit
• Compressor
• Storage Cascades
• Dispenser
• ESD
• Fire Extinguishers.

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METERING SKID
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METERING SKID
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METERING SKID
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METERING SKID
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ODORIZING UNIT
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COMPRESSOR
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COMPRESSOR
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COMPRESSOR GAUGE PANEL
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COMPRESSOR CONTROL PANEL
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COMPRESSOR GAUGE PANEL
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COMPRESSOR SAFETY SYSTEMS

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CASCADES
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DISPENSERS

• TYPES
• Car Dispenser
• 10 KG/MIN
• Bus Dispenser
• 70 KG/MIN
• SAFETY FEATURES
• SRV
• Excess Pressure cut off
• Break away coupling
• ESD

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DISPENSER
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DISPENSER
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Emergency Shut Down
Emergency Shut Down
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OISD 179 REQUIREMENTS

• Various components which are to be certified for
  CNG use and marked accordingly by applicable
  statutory authority are
• Cylinders
• (Confirmatory to IS 7285)
• Pressure gauges, regulators,
• (as per clause 18 of SMPV rules ,1981)
• Pressure relief devices including pressure relief
  valves
• (Confirmatory to OISD STD 132)
• Hose and hose connections

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OISD 179 REQUIREMENTS

• Electrical equipment related to CNG systems
• ( Confirmatory to IE rules, Gas Cylinder Rules
  ,IS5572 (Part1),NFPA-52)
• Earthing at the installation, protection against
  ignition
• (Confirmatory to OISD STD 110 and OISD STD
  110)
• Any other device not specified above must be
  constructed to provide safety equivalent to that
  required for other parts of a system and should
  have similar certification/approval as detailed
  above

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OISD 179 REQUIREMENTS

• The principal constituent of CNG is methane
  along with

Co2, partial pressure 7 psi max
Oxygen 0.5 vol. max
Hydrogen sulphide and soluble sulphides, partial pressure 0.05 psi max
Moisture contain 7.0 lb/MMCF .max
Note when the dew point of the gas entering the
cylinder is below the lowest anticipated
container temperature at the maximum anticipated
container pressure, the above shall not apply
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OISD 179 REQUIREMENTS

• ODORIZATION
• Should have a distinctive odour strong enough to
  detect its presence
• Suitable type of filters to limit liquid
  particulate
• The odorization and filtration system shall be
  located in a separate working area from the
  compressor or CNG storage unit but within the
  same fencing. 1.5 M safety distance around
  odorization filtration system
• Should have 100 stand-by capacity

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LAYOUT INTERDISTANCESTABLE-I
OISD 179 REQUIREMENTS
Total capacity of gas storage units (In litres) Min. distance from buildings and boundaries (In meters)
Upto 4500 2.5
4500 to 10000 4.0
10000 to 100000 10
Note The clearance mentioned above can be
reduced to 2 meter if it is not available
provided a 4 H-FRR RCC wall of adequate height
and length covering the cylinder cascades is
constructed at the boundary and adequate clear
space is available on the other side of the wall
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TABLE-II
OISD 179 REQUIREMENTS
Distance from (in mtrs) 1 2 3 4 5 6 7
1 CNG compressor - 3 2 3 6 6 T-I Min 3
2 CNG dispenser 3 - 2 4 6 4 T-I Min 3
3 Storage cascade 2 2 - T-I T-I T-I Min 6 T-I Min 4
4 Outer boundary wall 3 4 T-I - 6 4 T-I Min 4
5 MS/HSD Dispenser 6 6 T-I Min 6 6 - 6 T-I Min 4
6 Vent of MS/HSD u/g st. tanks 6 4 T-I Min 4 4 6 - 6
7 Filling point MS/HSD --------------------T-I (min 3)---------------- --------------------T-I (min 3)---------------- --------------------T-I (min 3)---------------- --------------------T-I (min 3)---------------- --------------------T-I (min 3)---------------- 6 -
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Table II

• Note
• T-I denotes Table I
• Distances shown as - shall be any distance
  necessary for operational convenience
• A suitable curbing platform shall be provided at
  the base of dispenser to prevent vehicles coming
  too near to the unit
• A CNG cascade not exceeding 4500 ltr can be
  mounted on top of the compressor. The assembly
  shall observe 3 M clearance around and also from
  the dispenser. This can be reduced to 2 M as per
  Note-I of Table-1

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OISD 179 REQUIREMENTS

• CNG STORAGE SYSTEM (Static)
• The cylinder fittings of one cascade should not
  face the cylinder fittings of other cascade when
  placed in parallels
• Inter distance between two cylinders in a cascade
  should be minimum 30 mm
• Valves of the cylinders should be on the same
  side of the cascade opposite to the refuelling
  point and arranged to discharge any leakage
  upwards

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OISD 179 REQUIREMENTS

• Cascade shall be installed over a foundation.
  Cascade foundation shall be at 2 m distance from
  fencing.
• Cascade shall have canopy is designed to
  disperse escaped gas
• Adequate means shall be provided to prevent the
  accumulation of flammable liquids

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OISD 179 REQUIREMENTS

• CYLINDERS
• Full conformity to IS7285 Gas cylinder rules,
  1981 with max 250 kg/cm2
• Cylinders should be marked for CNG ONLY.
• Fabricated from steel however cylinders with
  composite materials may be considered after CCOE
  approval
• Cylinders should be re-tested every five years
  according to Gas cylinder rules,1981
• Cylinders should be painted white to reduce solar
  heating and corrosion

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OISD 179 REQUIREMENTS

• VALVES
• A minimum of four shut off valves between the Gas
  storage unit vehicle refueling nozzle as
  explained below
• Quick action isolation valve in the steel supply
  pipe adjacent to storage cascade
• Master shut off valve in steel outlet pipe
  adjacent to gas storage unit
• Quick action emergency and isolation shut off
  valve near dispensing unit
• Refueling shut off valve in the dispenser hose
  with a venting provision
• All these valves shall be suitable for full range
  of pressure temperature and should have marking
  of service rating

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OISD 179 REQUIREMENTS

• CNG HOSES
• Internally braided, electrically continuous,
  non-metallic metallic hoses resistant to
  corrosion in the downstream of emergency and
  isolation shut off valve
• Shall be suitable for most severe pressure
  temperature with a burst pressure of at least
  four times the maximum working pressure
• Shall be tested at least two times the working
  pressure and 400 bar under water prior to use.
• Shall be examined visually and test for leakages
  at an interval of one year
• Shall have permanent markings of manufacturers
  name, working pressure and suitability for CNG

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Preventive measures

• In the CNG Outlets
• Operations by trained staff.
• Efficient Earthing Bonding system
• Periodic testing of pressure parts safety
  tripping devices .
• Functioning of ESD
• Trained driver Operators for LCV operations

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Prevention of vehicular accidents

• In the CNG vehicles
• Check for sound O- rings in auto/ taxis
• Check rectify loose electrical fittings
• Never use Illegal/ Un authorized serviced .
• (Spurious Kits / tanks ).

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Safety SAin CNG refueling

• Supplier Perspective
• Dependency on imported equipments
• Attrition among trained operators
• Low awareness level in operators
• Lack of quality vendors
• Checking up RTO endorsement before refueling

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Safety in CNG refueling

• Customer Perspective
• Low awareness level
• Spurious kits and spares
• Unauthorized retrofitted centre
• Unauthorized tank modification
• Routine servicing/maintenance of CNG kit

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