Procedure Testing & Commissioning of CNG Station

            Codes for CNG Station Equipment

·         Code for Design, Fabrication and Testing of all Gas Piping - ANSI B31.3.

·         Code of practice for CNG compressor and refueling station - NZS 5425.

·         Standard for Sizing, Selection, and Installation of Pressure-Relieving Devices - API 520.

·         Reciprocating Compressors for Petroleum, Chemical, and Gas Industry Services API 618/ ISO 13631.

·         Standard Specification for Seamless and welded Austenitic Stainless Steel Tubing for General Service - ASTM A 269.

·         Standard for Safety requirements on compress, storage, handling, refueling of natural gas for use in Automotive Section — OISD 179.

·         Standard for Vehicular gaseous fuel system code - NFPA 52.

·         Standard for installation and use of stationary combustion engines and gas turbines -NFPA 37.

 

CNG: Compressed Natural Gas

PLC: Programmable Logic Controller

SCADA: Supervisory Control and Data Acquisition

OISD: Oil Industry safety Directorate

NFPA: National Fire Protection Association

GENERAL DESCRIPTION

CNG Network consists of Compressor, which is connected to the Gas Dispenser and Cascade through proper tubing system. The general description of the CNG station is as follows:

 

·         Steel pipeline is connected to the compressor inlet through a steel reinforced rubber hose conforming to IS 9573 type N to withstand the vibrations of the compressor. Ideally 2 inch NB steel pipeline (tapped from the main steel pipeline) is used for connecting the compressor. An isolation valve shall be provided before the flexible hose.

·         Compressor outlet is connected to the Gas Dispenser and Cascade. The compressor discharge is connected to a cascade to maintain pressure and flow to vehicles, in case of multiple fuelling.

·         The compressor is used to compress the gas from an inlet pressure of 10 bar to 19 bar to a pressure upto 250 bar. In a special case the lower limit & upper limit of inlet pressure range to be 2.5 bar and 65 bar respectively.

·         Compressor discharge/outlet is connected to the Cascade, which consists of set of cylinders connected through tubing (SS 316) to maintain pressure.

·         Complete pipe work and tube work of each compressor package shall be designed so as to cause minimum pressure drop in the system. Supplier will design the whole package in such a way that all equipment and sub-systems are modular in approach for easy maintenance. The scope of supply shall include everything necessary for correct and safe operation of whole package.

·         The Cascade is connected to the Gas Dispenser from where the dispensing staff fills the vehicles (sells the gas). Due to space constraint, the stationary cascade of 3000/4500 ltrs water capacity will be installed suitably on the top of the canopy of compressor.

·         The whole compressor package shall also conform to specific requirement of CNG code/ standard OISD 179/ NFPA 52: 1992 (USA Origin)/ NZS-5425: 1994 (New Zealand Origin)

·         Compressor shall be supplied with following features

1.       For the gas Inlet Pressure measurement, Pressure Transmitter should be installed before and after PRV, the range of the PT should be 0-40 Kg/cm2.

2.       For the discharge pressure measurement, Pressure Transmitter should be installed after each stage; the range of the PT should be 0-400 Kg/ cm2.

3.       For the discharge temperature measurement, temperature transmitter should be installed after each stage & the range of the temperature transmitter should be

0-200 °C.

4.       Pressure transmitter should be installed for lube oil pressure and for water pressure.

5.       In case of water cooled compressor, temperature transmitter should be installed for the Water jacket temperature.

6.       The electrical parameters such as voltage, current data should be provided to the compressor PLC

7.       The Emergency Shut Down (ESD) command should be through PLC.

8.       parameters shall be displayed on PLC.

 

CO2 flooding systems are available at compressor area.

Suitable weighing arrangement shall be provided to facilitate weighing of the cylinders without requiring the cylinders to be detached from the installation.

The package shall be protected by automatically operated CO2 flooding system designed as per NFPA-12.

 

INSTALLATION OF COMPRESSOR & ASSOCIATED EQUIPMENT

·         CNG Installation work includes unloading of compressor onto the foundation, leveling, alignment, grouting etc. The supplier shall arrange for crane, lifting arrangement, manpower required for lifting of compressor, and unloading on the compressor  foundation.

·         Each compressor module shall be housed within a purpose built aluminum / cold rolled carbon steel (CRCS) acoustic enclosure. The unit shall incorporate a rigid framework.

·         A viewing window at operating level to be fitted to allow monitoring of gauges without entering the enclosure.

·         Compressor package (including compressor auxiliary motors installed externally) shall meet the noise level requirement of 70 dBA (max) measured at 1 meter as per the standard.

·         External emergency shut-down (ESD) switches shall be fitted on the wall of enclosure close to main access door. Also similar ESDs to be provided at dispensing area and in the control room (Total 3 ESDs).

·         Suitable gradient shall be provided on the enclosure roof for rain drainage and to avoid water pockets. Enclosures shall be designed with proper rain protection of ventilation ducts or openings (if any), to protect the internal equipment from rain water.

·         All gas piping shall be designed, fabricated and tested in accordance with ANSI B 31.3. The relief valve sizing shall be in accordance to API RP-520. The relief valve and associated piping shall be sized for full block discharge.

·         Separate vent line shall be provided for each SRV pertaining to the dispenser. These vents shall be provided above the dispenser. The material specification for the low pressure return vent line of dispensing nozzle must be SS 304. Height of the vent shall be minimum 3 meters above working level. On opportunistic basis, the low pressure return vent line of GI material should be replaced with SS 304 for the existing CNG Stations.

·         Compressor shall be installed with interlock of CO2 Flooding system. Compressor shall tripon detection of flame at preset level and automatic discharge of CO2 gas shall take place from the main cylinder simultaneously. Compressor shall be provided with all the essential indicators and protection devices (control switches / transmitters).

·         All the electrical equipments and accessories in compressor shall be flameproof. All thebolts shall be in place & properly tightened. The compression glands of proper size & make(Dowell, Brako) shall be in place for cable entries & these glands to be sealed (as applicable).

·         The high pressure piping shall be of suitable size and shall be of stainless steel 316 tubing / piping as per ASTM A 269 with stainless steel compression fittings. Stainless steel compression fittings shall be used for joining the pipes. All fittings and valves on high pressure tube work shall be of SS 316 materials of Swagelok / Parker make only.

               PRE-COMMISSIONING ACTIVITY

               CIVIL:

·         Foundation is as per the OEM drawings & specifications.

·         Compressor mounting is secured on compressor foundation.

·         Dispenser mounting is secured on dispenser island with appropriate high tensile bolts/ fasteners.

·         Foundation height is sufficient to take care of flood water

·         Canopy is available for dispensers

·         Entry and Exit paths are demarcated in forecourt area

·         CNG compressor / storage area is fenced and separated from dispensing facilities

·         Spacing between equipment and fencing/ wall shall be as per OISD-179 guidelines.

·             Compressor surrounding area is cleared off any unwanted material to provide ready access at all time.

·            All chambers and trenches are completely covered.

·         Trench cover should have ventilation slots to avoid accumulation of gas in tren ches.

·         Station layout ensures free vehicular movement.

·        When inside a MS-HSD Service Station, the CNG storage and dispensing facilities is located in an isolated area not interfering in the vehicular movement on the drive way and not coming within the hazardous areas of petroleum facilities as prescribed in the Fourth schedule of the Petroleum Rules, 1976.

              MECHANICAL:

·         Inlet valve of compressor is provided with handle to operate

·         Vent Line of each dispensing point is connected to common vent discharging safely into the atmosphere; 3meter from the working level.

·         Anti vibration pads or any alternate arrangement is done to dampen the vibrations

·         Belt/coupling guard is provided and bolted properly.

·         High pressure tubing is clamped at regular interval of 1meter.

·         Conical strainer is provided in inlet line of compressor.

·         Flexible hose in provided at compressor inlet.

·         Breakaway couplings are provided for dispensers.

·         Ladder equipped with handrails, is provided to make easy and safe access to cascade mounted on compressor canopy.

·         Hand railing is provided around the cascade mounted on top of compressor canopy.

·         Isolation valve is provided for LCV filling point

·         C02 flooding systems are available at compressor area.

·         No damage to any paint or surface coating on any of the components.

·         Hazardous area CCOE signboard is displayed at compressor area.

·         Cylinder fittings of cascades do not face towards cylinder fittings of other cascade, in case there are more than one cascade in the CNG station

·         Cylinder valves of cascades are in opposite side of refueling point.

·         Rain caps are provided for cascade cylinder vent to avoid entry of rain water inside it.

·         There is no sign of leakage /corrosion of cylinders

·         The CNG Cylinders are painted in white colour and "CNG only" is also conspicuously painted

·         All rigid piping, tubing, fittings and other,piping components shall conform to the recommendations of ANSI B 31.3

·         Gaskets, packing and any other materials used, are compatible with natural gas

·         The steel gas pipe lines are laid 30cm above ground level.

·         CNG storage unit provided with quick action isolation valve to enable isolation of individual storage unit

·         Master shut off valve with locking arrangement in close position, is installed in steel outlet pipe outside the fencing but immediately adjacent to the gas storage unit to isolate all downstream equipment from the gas storage unit.

·         Quick action emergency and isolation shut off valve are provided near dispensing unit

·         Vehicle refueling shut off valve with bleed valve provided for each individual flexible refueling hose

·         CNG hoses are internally braided, electrically continuous, and suitable to the natural gas service

·         CNG hoses are pressure tested and test certificates are available

·                  name / identification, working pressure are marked on CNG hoses

·                  Pressure gauges are provided on every CNG storage unit including each cascade

·                  Pressure gauge is provided with isolation valve

·         Calibration certificates are available for all the pressure gauges

·         Pressure gauge dial is graduated to read approximately double the operating pressure but in no case less than 1.2 times the pressure at which pressure relief valve is set to function

 

        The compressor is fitted with the followin alarms, trips and such safety devices

·                  Pressure relief valves on inlet and all stages fitted on compressor

·         High discharge temperature shut down

·         High cooling water temperature switch

·         High, inlet, inter stage and discharge pressures shut down provisions

·         Low lube oil pressure shut down

·         Low cooling water flow switch

·         Remote emergency shutdown switch

·         Safety Relief valves conform to the requirements of OISD-STD-132

·         PRV discharge is directed away from operators/ persons in the close vicinity

·         Safety relief valves have a locking arrangement to prevent any tampering

·         Permanent tag is available on SRV indicating pressure setting, date of re-setting/ setting and capacity

·         Safety relief valves are tested and the test certificates are available Dispensing unit type is approved by the CCOE (PESO)

·         There is no sign of leakage in the dispenser

·         Dispenser equipped with emergency shutdown switch

·         Fire extinguishers are positioned as given below

 

Dispensing Unit 1 x 10 kg. DCP

              Compressor

On-line station  1 x 10 kg. DCP

Mother station 1x 75 kg DCP

CNG Storage      1 x 10 kg. DCP

Cascade refueling 1 x 10 kg. DCP area

MCC/ Electrical 1 x 4.5 kg CO2 for

·         Anti collision bumpers have been provided to protect the dispenser.

·         The valves on the CO2 cylinders connected to the CO2 flooding System are in open condition.

·         Hydro test certificates and NOCs from CCOE (PESO) are available for Portable Fire

·         The CNG cylinder installed horizontally, is separated from another cylinder in cascade by a distance of min 30 mm.

·         Gas storage facility is protected from the effect of weather by roof or canopy designed to facilitate dispersion of free or escaped gas.

·         Gas detectors are interlocked with compressor cut out switch in the electrical system of the compressor, which would automatically switch off the unit in case of major gas leak.

               ELECTRICAL:

·         Sufficient no. of earth pits are provided for compressor (three earth Pits for Compressor, two for Electric Motor and one for canopy)

·      Earth pits are easily visible and accessible

·      Independent earth pit is provided for dispenser

·         Separate earth pit is provided for electronic system (can be clubbed with dispenser earth pit)

·         Size of the earth strip is sufficient as per IS-3043 (40X5mm Cu strip)

·         Earth resistance test values are as per IS-3043 (Below 5ohms for individual earth pit and below 1 ohm for grid)

·      Distance between two earth pits is at least 3meters

·         Double compression glands of proper size are used for cable entries into flameproof panel.

·         All the electrical interlocks are in working condition

·         All the trippings are checked for their desired operation

·         Electrical cables and gas tubes are running through different trenches

·         Electrical cables and earth strips are clamped at regular intervals

·         All the displays of compressor and dispensers are in working condition

·         ESDs are located at appropriate locations and are in working condition (Compressor area, Dispenser area and Sales Room)

·         All the electrical equipment and accessories in compressor area are flameproof and conform to IS 2148 or equivalent international standard.

·         Stationary cascades are equipped with ESD actuator

·         Electrical single Line diagram is displayed in electrical room

·         Electrical insulating mats conforming to IS 15652 are provided with in electrical room and near compressor electrical panel.

·         Proper illumination is provided in electrical room whose switches are at the entry

·         Proper ventilation is provided by installing exhaust fan in electrical room

·         Space is sufficient to provide proper access to the switch gear for maintenance work

·         There are no live conductors/ bus bars in open condition

·         Electric room is labeled with "Electric Room" "Danger 440 Volts" "Restricted Entry"

·         Capacitor bank of required rating is installed in electrical room

·         Inspection certificates from Office Of the Electrical Inspector are available at site(in case of HT supply)

·         Artificial respiration/resuscitation chart available in Electric room

·         Cable trenches inside the substations and switch stations containing cables shall be filled with sand, pebbles or similar non-inflammable materials or completely covered with non-inflammable slabs {as per Indian Electricity Rules, 1956 - clause 64(g)} 28)Bending radius of the cable is according to the standards.

 

Others:

·         All combustible material is removed from the fencing area.

·         Unobstructed approach to compressor and dispenser, cascade

·         Safety Instruction board and Operating instruction board are displayed I the dispensing area

·         No flammable materials are present within 15 M from compressor station/ MCC/ electrical installation

·         Illumination levels in the CNG station are adequate

·         Gascoseeker is available in the CNG station and is calibrated and functional

·         An operational emergency plan is prepared in due consideration of adjoining establishments and local authorities covering all risks and the copy of the same is available in the station

·         Important telephone numbers for emergency use displayed prominently

·         Approvals/ Certificates are available for following components

 

1.       Cylinders

2.       Pressure relieving devices including pressure relief valves

3.       Pressure gauges and regulators

4.    Temperature Gauge

5.   Hose

6.    Vehicle fuelling connections

7.    Electrical equipment related to CNG systems

8.       All parts under pressure carrying CNG/NG valves

                   

 

               COMMISSIONING ACTIVITIES

·      Commissioning of compressor, cascade and dispensers shall be done all the way through charging of suction pipeline. It also involves testing of high pressure gas interconnection tubing between compressor, cascade and dispenser. The tubing shall be checked with the leak detection fluid at all the fittings and valves installed in the line.

·         During the field performance test, the functionality of all equipments shall be checked for sustainability & suitability to put into operation and if found satisfactory CNG station will be handed over by CNG Projects to Operation & Maintenance Department.

 

               POST COMMISSIONING ACTIVITIES         

·         Functioning of all the safety and protection devices, instruments, gauges, measuring                 

·         devices such as ESD, PLC, mass flow meters, priority panel, telecontrol system, etc., will be checked at the site. No isolation valve shall be fitted to the inlet of the pressure relief valves.

·         Performance test of all the compressors using natural gas at specified operating

·         conditions with respect to flow capacity, power consumption and sound level .