A primer to building compressed natural gas (CNG) stations for vehicle refueling. Very good!

1. “Waste-to-Wheels: Building for Success”
Columbus Ohio--Dec. 1, 2010
CNG Station Design
Primer
Presented by:
Marathon Technical Services

2. Presented by:
Rob Adams, P.Eng., CMA, MBA
Marathon Technical Services
MARATHON TECHNICAL SERVICESMARATHON TECHNICAL SERVICES
Slide 2

3. It is critical to accurately project fill time and quantity
of fuel required initially and as the fleet grows:
• Collect number, type and fuel consumption by
vehicle—cardlock data will be useful.
• Review data to determine the highest demand fuel
window—this will govern sizing.
• (Usually) Use average fuel consumption per vehicle
not maximum since maximum will oversize the station
• Gasoline gallons x 120 = standard cubic feet (SCF).
• Diesel gallons x 137 = SCF. (possibly add 10% for
diesel efficiency)
Design Parameters-FleetDesign Parameters-Fleet
Slide 3

4. Type of station required will influence the size and
cost of equipment:
• Time Fill—fill entire fleet directly from the compressor
over a period of hours.
• Cascade Fast Fill—fill each vehicle in 5 to 20 minutes
primarily from stored gas.
• Buffer Fast Fill—fill each (large) vehicle in 5 to 20
minutes primarily from the compressor(s)
Design Parameters-Station TypeDesign Parameters-Station Type
Slide 4

5. Time Fill—useful for fleets that return to base.
• Fill entire fleet directly from the compressor over a
period of hours.
• Simple, reliable technology and very good fills.
Design Parameters-Time FillDesign Parameters-Time Fill
Slide 5

6. Cascade—used where the fleet needs fueling in short (1 to
2 hour) peak periods.
• Fill each vehicle in 5 to 20 minutes primarily from stored
gas.
Design Parameters-CascadeDesign Parameters-Cascade
Slide 6

7. Buffer—used where many large vehicles must be fast
filled back to back for several hours.
• Fill each (large) vehicle in 5 to 20 minutes primarily
from the compressor(s)
• Most common transit station design
• Typically requires very large equipment
Design Parameters-BufferDesign Parameters-Buffer
Slide 7

8. Meet with the Gas Utility to determine available gas:
• Minimum, maximum and typical pressure in service
line with new station load imposed.
• (Medium to large scale) CNG stations can be designed
to accept (higher) floating gas service pressure rather
than (lower) regulated gas pressure.
• Floating service pressure can significantly reduce size,
complexity, initial and operating cost of the station.
• It may be necessary to discuss this need with the Utility
as they may have policies to supply only (low)
regulated pressures.
• Gas composition and moisture content is required.
Design Parameters-Gas SupplyDesign Parameters-Gas Supply
Slide 8

9. Remove moisture
from the gas:
• Inlet drying
recommended
• Regeneration
equipment
recommended.
• Virtually all stations
will require a dryer
to be code
compliant.
Station Equipment-DryerStation Equipment-Dryer
Slide 9

10. Raise gas pressure
from utility service
pressure to 4500
psig:
• Reciprocating
compressor—usually
electric motor
powered.
• Redundancy through
multiple compressors
or portable standby
compressor required
if vehicles are
dedicated CNG.
Station Equipment-CompressorStation Equipment-Compressor
Slide 10

11. Required for Cascade and
Buffer Stations:
• ASME design Code.
• 5500 psig design—4500
psig operating pressure.
• Tubes or spheres.
Station Equipment-StorageStation Equipment-Storage
Slide 11

12. Dispense gas to the
vehicles:
• Time fill or fast fill
• Measurement (usually
only with fast fill-
exception shown)
• Cardlock interface (fast
fill)
Station Equipment-DispenserStation Equipment-Dispenser
Slide 12

13. Most garages will require
some upgrade:
• No open flame or heaters
>750F.
• Continuous exhaust and
makeup air and ventilation
to prevent pocketing.
• Electrical upgrades may
be required—not
necessarily a hazardous
location.
• Gas detection system with
interlocks to alarms,
exhaust fans, doors…
Building ModificationsBuilding Modifications
Slide 13

14. Meet early and often with Authorities Having Jurisdiction
Partial List of Codes:
• NFPA 52-Vehicular Gaseous Fuel Systems Code
• NFPA 70-National Electrical Code
• ASME B31.3-Process Piping
• ASME Section VIII, Division 1-Unfired Pressure Vessels
• NFPA 30A-Code for Motor Fuel Dispensing Facilities….
• International Building Code
• International Fire Code
• International Mechanical Code
• State and Local Codes
Good Engineering / Industry Best Practices
Permitting, Codes and ApprovalsPermitting, Codes and Approvals
Slide 14

15. Several common contracting approaches:
• Conventional Split Contract—Purchase equipment
and construction under separate contracts.
• Design Build—Purchase of Design, Equipment,
Permitting and Installation under a single contract.
• Throughput Contract—Design Build with payment on
a per Therm charge (Lease to own)
• Maintenance can be combined or bid separately from
the station construction.
• Have parts inventory before the station is
commissioned —warranty is not (usually) a
maintenance contract.
Contracting ApproachesContracting Approaches
Slide 15

16. Thank You!
Questions??
MARATHON TECHNICAL SERVICESMARATHON TECHNICAL SERVICES
Slide 16

17. Marathon Technical Services
(519) 699-9250
radams@marathontech.ca
WWW.MARATHONTECH.CA
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