Safety in CNG Systems

TYPES OF CNG STATIONSDAUGHTER STATION

CNG facility not connected to natural gas pipeline and dispensing CNG to the vehicles through mobile cascades

DAUGHTER BOOSTER STATIONCNG facility not connected to natural gas pipeline but

having a compressor meant to fill primarily for vehicles and storage cascade

CNG ONLINE STATIONCNG facility connected with natural gas pipeline and

having a compressor primarily to fill stationary cascades for dispensing CNG to vehicles.

SCHEMATIC DIAGRAM

Schematic Daiagram- MOTHER STATION

TYPICAL FACILITIES

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

METERING SKID

METERING SKID

METERING SKID

METERING SKID

ODORIZING UNIT

COMPRESSOR

COMPRESSOR

COMPRESSOR GAUGE PANEL

COMPRESSOR CONTROL PANEL

COMPRESSOR GAUGE PANEL

COMPRESSOR SAFETY SYSTEMS

CASCADES

DISPENSERS

TYPES• Car Dispenser

10 KG/MIN

• Bus Dispenser70 KG/MIN

SAFETY FEATURES• SRV

• Excess Pressure cut off

• Break away coupling

• ESD

DISPENSER

DISPENSER

Emergency Shut Down

Emergency Shut Down

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

OISD – 179 REQUIREMENTS

• Electrical equipment related to CNG systems ( Confirmatory to IE rules, Gas Cylinder Rules ,IS:5572

(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

OISD – 179 REQUIREMENTS

The principal constituent of CNG is methane along with

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

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

OISD – 179 REQUIREMENTSODORIZATION

• 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

LAYOUT & INTERDISTANCESTABLE-I

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

OISD – 179 REQUIREMENTS

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

TABLE-IIDistance 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)---------------- 6 -

OISD – 179 REQUIREMENTS

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

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

OISD – 179 REQUIREMENTS

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

CYLINDERS• Full conformity to IS:7285 & 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

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

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 manufacturer’s name, working pressure and suitability for CNG

OISD – 179 REQUIREMENTS

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

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 ).

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

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