3. CERTIFICATE
Certified that this project report “CNG filling Operations” at
Indraprastha Gas Limited is the work of “Ankur Rawal” who carried out the
project work under the Operations & Maintenance department.
Mr. Amit Kumar Deb
Manager (CNG - O&M)
Mr. Ujwal Bhandari
General Manager (CNG-O&M)
Mr. P.K. Pandey
Chief General Manager (CNG-O&M)
Mr. Manjeet Singh
Vice President (E&P)
2
4. ABSTRACT
Filling operations of Compressed Natural Gas (CNG) in Natural Gas Vehicles
Natural gas is being used as an alternative fuel to gasoline. Natural Gas vehicle
(NGV) refueling stations incorporate a series of processes which make the gas
dispensable. The report focuses on understanding various aspects of these processes
and test and suggest changes in their functioning.
Various tests and observations were made on the compressor and inlet pipes
and pressure drops calculated. Useful characteristics of CNG during the fill process are
temperature, pressure, and flow rate, as well as, total volume dispensed. CNG is
dispensed to an NGV through a process known as the fast fill process, since it is
completed in less than five minutes. The system is being constantly upgraded in order
to result in lower filling time and make it comparable to that of petrol or diesel fillings.
The report also highlights the quality control operations at Indraprastha Gas
Limited (IGL). The Gas Chromatography installation at Mahipalpur Gas Station has
been carefully studied along with viscosity relations with dilution were done for snoop
solution used to test leakage.
3
5. Acknowledgments
I wish to acknowledge all the people who have helped me finish this Report.
Without the generosity of others there is no way that I could have finished it. The report
is an outcome of the advice and tutelage of several people who work at Indraprastha
Gas Limited (IGL).
I would like to thank my advisor and mentor Mr. Ujwal Bhandari (General
Manager CNG-O&M), first of all, for being so patient with me and being an excellent
mentor throughout my time in IGL. Without the advice and knowledge of Mr. Bhandari,
the completion of this document would have been impossible. The other guides of my
endeavor, Mr. Amit Kumar Deb (Manager CNG-O&M Jail Road Control Room) and
Mr. Abhinav Sahay (Additional Manager CNG-O&M Lado Sarai Control Room)
have also been very helpful for advice and knowledge of subjects contained in this
report. The entire team of Engineers and Technicians at Jail Road and Lado Sarai
Control Rooms have in some way or the other helped me understand practical aspects
of whatever I had learnt in texts earlier.
I am highly indebted to Mr. Manjeet Singh (Vice President – E&P) for he
believed in my objectives of undergoing this internship and made an exception in
allowing me to be a part of the organization after completing the second year of my four
year graduation in Chemical Engineering.
My college, USCT has been very supportive as well, to have allowed me to use
their facilities and equipments for a few tests. University Professors such as
Dr. Biswajit Sarkar have helped me with the required textbooks and constantly
answered all my queries regarding fluid dynamics and Heat Exchangers.
Thanks and Regards,
4
6. AN OVERVIEV OF INDRAPRASTHA GAS LIMITED
COMPANY PROFILE
Indraprastha Gas Limited (IGL), a Joint Venture of GAIL (India) limited and BPCL
along with the government of NCT of Delhi was incorporated on December 23, 1998 to
implement the compressed Natural gas (CNG) expansion program and the Piped Natural Gas
(PNG) project for varied application in the domestic and the commercial sector.
In 1999, IGL took over the Delhi City Gas distribution Project started by GAIL (India)
Ltd. which focused on supply and distribution of CNG & PNG in the capital city. Thereafter IGL
worked tirelessly to take the project to new heights.
IGL’S VISION
-‘To be the leading clean energy solution provider, committed to stakeholder
value enhancement, through operational excellence and customer satisfaction’
This vision statement signifies five major attributes of the organization.
Commitment to the environment
Providing complete energy solution and thereby going beyond CNG for transport and
PNG for cooking application
Enhancing value for beneficiaries including customers, stakeholders and employees
Achieving excellence in operations
Providing satisfaction to customer
5
7. CNG-Compressed Natural Gas
Natural Gas is a combination of Methane, Propane and Butane. Conventional Natural
Gas exists above crude oil deposits, and is often wasted or burned in the oil collection process
due to the high costs of capturing and using it. When the gas is burned, it prevents the Methane
from reaching the atmosphere. Carbon Dioxide into the atmosphere is less harmful than
Methane.
Natural Gas produces less air pollution than any other fossil fuel. Use of CNG vehicles
can reduce Carbon Monoxide emissions as much as 93% Nitrogen Oxide reduces about
33% and Hydrocarbons are reduced by about 50%. Natural Gas emits almost no carcinogenic
particulates.
By using CNG to power vehicles a bi-fuel tank can exist; therefore, in locations without
CNG pumps, Petrol may be used by just flipping a switch. Since CNG is a clean-burning fuel,
maintenance costs are lowered. CNG is 130 octanes, which is considerably higher than 93
octanes for Petrol; consequently, the CNG vehicle is more energy efficient. Besides using
Natural Gas to power vehicles, it can also create electricity and heat homes and commercial
buildings.
Compressed Natural Gas (CNG) is natural gas that has been compressed for storage
aboard a natural gas vehicle (NGV), a vehicle whose engine is fueled by Natural Gas. Natural
gas is compressed to high pressure (200 bar/20.7 MPa or higher) to most effectively utilize the
NGV’s limited available space for storage.
ADVANTAGES DISADVANTAGES
Abundant Supplies Nonrenewable Resource
Low Emission Vehicles Decreased Range
Advanced Vehicle Developments New Refueling Sites Required
Reduced engine maintenance Expensive Engine
Modifications Inexpensive
6
8. It is proven manifold that natural gas is a very clean fuel. The world Energy
Conference of Tokyo 1996 announced that natural gas is the No.1 alternative because:
1. Natural gas has excellent combustion properties,
2. Natural gas is a safe fuel (lighter than air, high ignition temperature),
3. Natural gas is a clean fuel (no sulphur, no lead, no particles, little NOx, CO and HC).
4. Natural gas has abundant reserves, wide spread over the globe.
5. Natural gas is a strategic fuel,
6. Natural gas is cheap if we exclude taxes.
Natural Gas Vehicle (NGV) Basics
Natural gas used in vehicles is no different than natural gas used in residential or
commercial markets, except that it is compressed to high pressures for storage purposes.
Compressed natural gas (CNG) is gas compressed to pressure generally ranging from 200 to 259
bar (20.7Mpa to 25Mpa). At the dispenser, Natural Gas is delivered into vehicles either by
weight (in kilograms) or by Gasoline liter equivalents (GLE – an energy equivalent comparison
to gasoline) and carries an octane rating between 122 and 130.
There are many types of natural gas vehicles (NGV’s), including dedicated, Bifuel and
dual fuel models. There are distinguished by whether the engine runs only on natural gas
(dedicated), operates on either natural gas or gasoline (Bifuel), or simultaneously burns a
combination of both liquid fuel (such as Diesel or Petrol) and natural gas (dual fuel).
CNG is stored onboard a vehicle in several types of pressurized vessels that conform to
industry-recognized standards for installation (the NGV 2 standard in Canada & USA or OISD
Standard 226 for City Gas distribution in India)
If NGV’s and equipment are in sound condition, you can expect them to perform reliably
when they are well maintained by a trained technician and drivers are well informed and trained.
7
9. Although conventional wisdom holds that natural gas engines should require fewer oil
changes and perhaps even less frequent scheduled maintenance because of less carbon build-up,
regular maintenance of the vehicle, engine and/or conversion system will ensure the superior
performance of the NGV versus its gasoline and diesel counterparts.
A CNG fueling facility typically consists of a compressor, storage Cascades and a
dispenser system. Dispensers come in two types: fast fill, which delivers fuel at a rate
comparable to gasoline or diesel systems, and time fill, which fuels vehicles over a period of
time. The actual fueling of an NGV is similar to fueling with gasoline or diesel.
CNG Quality Control
An extensive quality control of the incoming Natural Gas for Refueling in the city of
New Delhi is done at the Mahipalpur CNG Station, which comes under the Lado Sarai
Control Room. A Gas Chromatograph monitors and records the quality of the Natural Gas at
all hours of the day all round the year. It measures quantitatively the %composition of various
components of the Natural Gas, which further helps in maintaining exact desirable proportions.
The incoming Gas from GAIL is odorless and therefore, a smelling agent (Ethyl
Mercaptin and Methyl Mercaptin) is mixed into the Gas at IGL’s Patparganj Plant. Where the
smelling agent is introduced at traceable quantities as the concentration magnifies when
compressed. A detailed functioning of the Gas Chromatograph is explained further.
Major contents of the Quality control are: %Composition of C 1 - C6& above, Gross
Calorific Value, Net Calorific Value and specific volume.
As the Gas upon combustion releases water in the form of vapor, this water vapor
releases more heat in the process of condensation. This heat when added to the Gross Calorific
value (GCV) of the fuel is known as the Net Calorific Value (NCV).
Specific Volume is the volume of Gas occupied by 1 Kg of Gas at Standard Temperature
and Pressure (STP).
8
10. Gas Chromatograph (GC)
In a Gas Chromatogram (GC) Analysis, 0.1-10µL (micro liter) of a mixture of
compounds is injected into a heated Injector, where all of the compounds vaporize. A gentle
stream of the Carrier Gas, Helium (He) moves the entire mixture onto the Collumn, the
corresponds of the mixture separate as they pass through the column. The process can be
considered as an exceptionally good Fractional distillation using a superb fractionating column.
Figure 1: Schematic representation of the components of a GC
The Process
The separated compounds pass from the column into a detector that produces an
electrical signal proportional to the amount of compound passing through the detector. A
recorder provides a graph. The Gas Chromatogram is plotted against the detector Signal versus
Retention time. The Gas chromatogram shows a peak for each compound in the mixture. The
retention time can be measured from the Chromatogram. An Integrator measures the areas under
the peaks in the Gas Chromatogram.
9
11. Thermal Conductivity Detector (TCD)
Flame Ionization Detector (FID)
Figure 2 detectors used in Gas Chromatography
The Chromatogram
A chromatogram consists of a base line and a number of peaks. The area of a peak allows
quantitative determinations. Starting point of a chromatogram is the time of injection of a
dissolved sample. The time interval between a peak and the point of injection is called retention
time tR. A component can be identified by its retention time (qualitative determination).
The retention time is the sum of the residence time of a solute in the mobile phase (t 0) and
in the stationary phase (t R' = net retention time); t 0 is also known as dead time. It is the time
required by a component to migrate through the chromatographic system without any interaction
with the stationary phase (also called air or gas peak).
For a given, the area under its peak on the chromatogram is proportional to the amount of
the compound in the sample. Direct comparison of peak areas for different compounds is
unreliable because detectors do not have the same sensitivity to all compounds. For this
reason, a sample of the Natural Gas is maintained in the GC. The Area under the
chromatogram is then compared to that of the sample, and the result is recorded.
10
13. C1: Methane
C2: Ethane
C3: Propane
I-C4: Iso-Butane
N-C4: Normal Butane
N2: DiNitrogen
CO2: Carbon Dioxide
Neo-C5: Neo Pentane
I-C5: Iso Pentane
N-C5: Normal Pentane
C6+: Higher Alkanes
GCV: Gross Calorific Value (J/mol)
SG: Specific Gravity (m3/Kg)
Standard Reaction of HC combustion:
………………….…ΔHr = Gross Calorific Value
Limitations:
Only compounds with vapor pressures exceeding about 10–10 torr can be analyzed by gas
chromatography mass spectrometry (GC-MS). Many compounds with lower pressures can be
analyzed if they are chemically obtained (for example, as trimethylsilyl ethers). Determining
positional substitution on aromatic rings is often difficult. Certain isomeric compounds cannot be
distinguished by mass spectrometry (for example, naphthalene versus azulene), but they can
often be separated chromatographically.
Accuracy:
Qualitative accuracy is restricted by the general limitations cited above. Quantitative
accuracy is controlled by the overall analytical method calibration. Using isotopic internal
standards, accuracy of ±20% relative standard deviation is typical.
12
14. Difference between Gross Calorific Value and Net Calorific Value:
The Water produced in the combustion reaction is in the gaseous state. This water when
condensed to liquid state at ambient temperatures in the cylinder releases the Latent heat of
Condensation which unlike the Gross Calorific Value is released from the exhaust when it
interacts with air at ambient temperature. This additional energy is not used for the expansive
working within the piston cylinder and therefore is not accounted for in the actual Calorific
Value of the gas mixture. The Net Calorific Value is what we read in instruments and we
subtract the known value of Latent heat of condensation of steam at given conditions to obtain
the Gross Calorific Value.
Net Calorific Value (NCV) – Latent heat (condensation) = Gross Calorific Value (GCV)
CNG Refueling Station
A CNG station is a site consisting of interconnected equipment, which is designed to
compress Natural Gas to a high pressure and either store the CNG (if the site is equipped with
storage) or dispense it directly to a natural gas vehicle for refueling.
A CNG station typically consists of one or more compressor packages to compress the
Natural Gas, and several additional systems, which include Cascade storage systems, PLC based
controls system such as a priority controller panel, a temperature/pressure compensation panel, a
buffer panel, gas dryers, fast refueling (CAR dispensers) and time refueling (BUS) dispensing
units.
The Station includes separate areas for Compression, Storage and Dispensing. It includes
Air compressor pipes, Water pipelines etc. It also includes provisions for safety against Fire or
Leakage. The provisions include Carbon dioxide (CO2) Cylinders; Dry Chemical Powder (DCP)
cylinders etc.
13
15. CNG Distribution Network
Main line ~18-20 bar
~18-20 bar
CNG ~250 bar CNG
Compressor Compressor
Mobile Mobile
~18-20 bar ~250 bar
Cascade Cascade
Storage Storage
MOTHER Cascade Cascade ON-LINE
STATION ~200 bar STATION
Dispenser Dispenser
~200 bar ~200 bar
CNG Vehicle Mobile Mobile CNG Vehicle
Cascade Cascade
Booster
~200 bar DAUGHTER
Compressor
DAUGHTER
BOOSTER
STATION
STATION
Dispenser Dispenser
~200 bar
CNG Vehicle CNG Vehicle
Figure 5: Schematic diagram of CNG distribution at IGL
Type of stations at IGL
Mother station: It’s a station where a direct gas line received and SCM capacity of
compressors installed there is more than 1200 SCM and LCV is also filled.
Online station: It’s a station where online gas line is received from GAIL but the
capacity is up to or below 1200 SCM. Cascades filling are also there.
Daughter booster station: It’s a station where compressors are not installed and gas is
being compressed by means of a device named booster.
Daughter station: It’s a station where gas is not compressed at the station itself and is
filled direct from the LCV.
14
16. CNG Station Basics
Key CNG Refueling Station Equipment:
Gas Dryer (inlet or outlet)
Compressor Package System (bare shaft compressor, inter-stage cooler, piping,
separators)
- Driver (electric motor or gas engine)
- Low pressure inlet train
- High pressure outlet system
- Canopy or housing (weather protection/noise attenuation)
Cascade Storage System
Priority Control Panel
Car Dispenser
Dispenser (single or double hose, metering or non-metering, trickle, fast fill)
Compression System
Natural gas is usually transported to the CNG station site from the main Gas Pipeline
provided by GAS AUTHORITY OF INDIA LIMITED (GAIL). This gas can range in pressure
from as low as 12 bar (gauge pressure above atmospheric), to as high as 35 bar/ 3.45 Mpa or
higher. In any case, it is still too low of a pressure for use in vehicle storage systems.
For this reason, the gas must be compressed. However, prior to compressing the gas, the
incoming gas may need to be conditioned further, so as not to damage the compression
equipment or downstream systems. For example, if the gas is “wet”(has an unusually high
concentration of evaporated water), then the gas will first pass through a dryer, if the Sulphur
contents in the gas is higher, it also should be removed. This is a large vessel, surrounded by
related components, which removes water from the gas stream using a “desiccant” material.
15
17. Once the gas is properly conditioned as required, it then enters the compressor. The
compressor is typically the largest and most complex piece of equipment in the entire refueling
station. It raises the pressure of the natural gas to 250 bar (25Mpa), or higher, using a number of
separate stages, which increase the gas pressure in increments.
The Compressors are typically reciprocating compressors. These are driven in a rotational
manner, with the compressor translating this rotational force into a Piston/Cylinder combination.
Much like the reverse of an engine, a compressor uses a series of valves to move the gas
into each cylinder, compress it with a Piston, and then discharge in into the next stage at an
increased pressure. The cylinder configurations can either be a “W” or “V” shape, or horizontally
opposed.
Metering Skid
The first Equipment on the Main Inlet piping is the Metering Skid. It helps monitor
precise Station Inlet GAS characteristics as per requirement up to compressors which helps study
gas loses over compression etc. Flow mater readings help CNG Station Marketing and Sales
Department tally Station reconciliation with respect to sales and also IGL gas reconciliation with
GAIL (India) Pvt. Ltd.
Main Functions:
Pressure regulation.
Gas filtration.
Preventing Pilferage
Precise metering
Cross-Checking of metering
Emergency shut-down of station through Main Isolation Valve
16
18. Major Components
Suction Line Filter
The Suction Line filter includes protection from moisture, inorganic and organic acid
resulting from burnout or chemical changes in the system. It also clears away combustible
dust, which may be introduced through mechanical work done over the Pipeline. It has a 5µm
Filter for such unwanted particles.
Slam shut-off valve
The Slam shut off valve is used in Metering skid for shut off line in case of emergency
when line pressure is above 23 kg/cm2 or below 13kg/cm2. It is a Butterfly Valve which is
also called the Main Isolation Valve which may be used to cut-off the whole station from the
Main Pipeline.
Pressure regulating Valve
It regulates the pressure of gas in flow line according to adjustable limit.
Mass Flow meter
Mass flow meter is used in flow line to continuously monitor the input mass flow of Gas. It
uses a Coriolis Type of mechanism for reading Flow rate.
Pressure and Temperature transmitter
Pressure transmitter and Temperature transmitter is used to sense Pressure and Temperature
in line pressure to Flow Boss. A special Differential Pressure meter is installed across the
Filter, which indicates amount of choking residue on the filter as the pressure drop across it.
A Differential Pressure of 1 bar or above means that the filter requires cleaning.
Flow boss (flow computer)
Each characteristic data such as inlet pressure, temperature, Mass Flow etc. for the Gas at
Inlet is stored in flow boss to log the data in computer.
17
19. F
I
L
T
E
R
Figure 6 Schematic diagram of the metering skid
Compressor drive
The Compressor can be driven either by an Electric Motor, or by a Natural Gas engine.
For an electric motor drive, an electronic device called a starter or soft start applies power to the
motor when the compressor is required to turn on. The motor shaft is coupled to the compressor
shaft either directly, or by means of a belt drive. Typically, larger compressors are direct-driven.
A compressor package also has a great deal of support equipment associated with the
package. Mechanically, the compressor requires a lubricating oil supply to lubricate the
cylinders, pistons, and other moving parts. It also requires a means to remove from the gas
supply oil that is introduced through lubrication.
This typically involves a system of filters and separators. Filters are typically placed at
the inlet and the discharge of the compressor itself, while in-line gas separators are placed
between the stages of compression. Separators spin the gas in a circular motion to use
centrifugal force to condense any liquid out of the gas stream. This results in a collection of
condensates, typically water and oil, which must be periodically removed from the separator
vessels. This is typically done automatically in the packages, with collection in the large
recovery tank(s) and later automatically drained into one of the beams in the skid case.
18
20. Compressor: Dresser Rand
• Maximum Driver HP 250 (186 kW)
• Standard Stroke 7 inch (178 mm)
• Crankshaft Diameter 3.75 inch (95 mm)
• Cylinder Diameter (LP) 4.00 inches
• Cylinder Diameter (HP) 3.25 inches
• Main Bearing Length 3.75 inch (95 mm)
• Piston Rod Diameter (LP) 1.5 inch (38 mm)
• Piston Rod Diameter (HP) 2.25 inch (57.15mm)
• Speed 570 (rpm)
Materials:-
• Frame Cast Iron
• Crankshaft Forged Steel
• Connecting Rod Forged Steel
• Crosshead Aluminum
• Main Bearing Aluminum
• Crankpin Bearing Aluminum
• Pin Bushing Bronze
o Crosshead Pin Steel Alloy
• Design parameters:-
o Suction pressure 14-22 bar
o Inter stage compression ratio Suction Discharge
Ist Stage: 3 14-19 bar 45-60 bar
IInd Stage 2 45-60 bar 120-130 bar
IIIrd Stage 2 120-130 bar 220-250 bar
• Compressor Flow rate:- 1200 SCMH (916 Kg/Hr) at ideal condition
19
21. Cooling System
Compressors generate heat as a natural byproduct of compression. For this reason, they
must be cooled. IGL generally has only air-cooled compressors, which means they employ
forced air-cooling of the compressor and/or gas stream, instead of water cooling like one would
find in a car engine. Some compressor blocks are self-cooling, incorporating a fan onto their
main drive shaft, which forces air over the compressor block and over the compressed gas lines.
Other blocks require separate heat exchangers, which cool the gas after each stage using a
separate fan.
These Heat exchangers (Inter Coolers) are Shell and Tube with Fins, with multiple passes
in order to result in the desired Temperatures at inlet and outlet for each Stage.
Recovery system
Another important system is the blow down recovery system. This system, which
includes the recovery tanks and various automated valves, captures the gas from the compression
system when the machines are shutoff, and maintains a closed loop system by containing and
recycling this gas. It also permits the compressor to start and stop “unloaded”, or without
compressing gas, by re-circulating the gas within the compressor on start-up, and on shut-down.
The majority of this gas is captured in the recovery tanks.
The compression equipment also required a great deal of electronic and electrical control,
as most skids are automated to a high degree. This means that they must have enough
intelligence to turn themselves on, shut themselves off appropriately, and do it all safely, while
watching for possible faults. This is generally accomplished by the electronic controls system
on–board each skid. The vessel is called a Blow Down Vessel (BDV).
A Knock out drum of 900 litres is provided at suction, supply CNG to the compressor
through flexible hose to suction collector and first stage cylinder. BDV also acts as a condensate
collecting bottle. All the condensate and oil are drained into the BDV.
20
22. Gas Flow within Compressor
INTER COOLER INTER COOLER
Inlet AFTER COOLER
PT102 PT103
PT104
3rd
1st 2nd
PCV108 PT101 Stage
Stage Stage
PRV
BDV
(Blow
PRIORITY
Down
Vessel)
PANEL
PT106 Condensate
Figure 7: Schematic layout of Compressor system
Natural Gas
Package Boundary
Condenate (Water + oil)
21
23. Mechanism of Compression
Expulsion of gas
Compression
Expansion of
residual gas
Initial condition
Clearance
volume Suction stroke
Figure 8: PV diagram for Single Stage Reciprocating compressor
Shaded area
represents
net saving in
energy
Figure 9 PV diagram for Multi Stage Reciprocating compressor
22
24. General Physical Parameters
• 1st stage suction pressure (Kg/cm2) = 14.95
• 1st stage discharge pressure (Kg/cm2) = 43
• 2nd stage discharge pressure (Kg/cm2) = 79.49
• 3rd stage discharge pressure (Kg/cm2) = 146
• 1st stage suction temperature (oC) = 37
• 1st stage discharge temperature (oC) = 125
• 2nd stage discharge temperature (oC) = 102
• 3rd stage discharge temperature (oC ) = 96
• Gas temperature after cooler (oC) = 52
• Lube oil pressure (Kg/cm2 ) = 1.02
• Flow meter totalizer reading suction (Kg).
• Flow meter totalizer reading discharge (Kg)
Compressor start preconditions
Tag name Tag description
PT-101 1ST Stage suction pressure.
PT-102 2nd Stage suction pressure.
PT-103 3rd Stage suction pressure
PT-104 3rd Stage discharge pressure.
PT-105 Engine fuel gas pressure.
PT-106 Blow down vessel pressure
PT-401 Engine starting air pressure.
23
25. GD-501 Gas detector
GD-502 Gas detector
FD- 501 Flame detector
FD-502 Flame detector
TE-101 1st Stage gas suction temperature
TE-102 1st Stage gas discharge temperature
TE-104 2nd Stage gas discharge temperature
TE-106 3rd Stage gas discharge temperature
TE202 Engine Jacket Temperature (oC)
TE-301 Engine lubes oil temperature
TE-108 Engine exhausts gas temperature
TE-208 Compressor cooling oil header Temperature
LSL-201 CW surge tank level low
SSHH-101 Engine over speed contact
Emergency stop Emergency stop push button
SOV-101 ON Drain solenoid valve ON
PT-301 Engine lubes oil pressure
PT-302 Compressor lubes system oil Pressure
TE-107 Engine inlet manifold temperature
24
26. Priority panel
The priority panel consists of a priority valves and non return valves, so arranged that
intended use of providing priority to vehicles is achieved. The priority panel is connected to
discharge of compressor at one end and is connected in parallel to cascade (storage) and
dispenser at other end. If there are no vehicles for gas filling, then priority valve directs the gas
flow to cascade.
High Bank
SOV-110 PT-110
Car cascade
Medium Bank
SOV-111 PT-111
Car Cascade
SOV-112 PT-112 Low bank
Car cascade
High bank car
SOV-113 PT-113 dispenser
C
N
SOV-117 Medium bank
G
Car Dispenser
SOV-118 Medium bank
Car Dispenser
SOV-112 PT-112 Bus
Cascade
SOV-112 PT-112 Bus Cascade
Mobile
SOV-112 PT-112
bank NRV: Non Return valve
25
27. LCV Priority Routing
The Mobile Cascade Vehicles, also known as LCV, are Flatbed trucks on which a
Cascade has been securely tied. These contain about 2200-2400 Liters of Natural Gas at 250 bar.
These are filled at Mother Stations and transported to Various Daughter and Daughter Booster
stations under each Control Room. This movement of LCVs around the city has been outsourced
to various Transport Contractors, who charge on per-km basis. The Job of priority routing arises
in order to minimize the Total number of Kilometers that have to be paid for, while still
providing Gas to the Required Daughter and Daughter Booster Stations.
Such a Routing is done every time the Contractor revises the Km-Data chart and/or a new
Station comes up under a Control Room. This form of Assignment is a Linear Programming
Problem (LPP), Transportation Problem. The Following Figures Explain the Priority Routing
under Jail Road control room.
Figure 10: Suggested Priority routing Chart, data in Kms
26
28. Figure 11: Existing Priority chart for Jail Rd Control room
The Priority Routing involves more parameters than assumed, such as licensing issues
and capacity considerations. Jail Road control room consists of 19 LCVs. 13 of which are
contracted to Chowdhary transport and 6 through Orient Transport. There exist two Daughter
and six Daughter stations under this control room and therefore a well planned and executed
priority route results in considerable monetary and energy savings.
27
30. Hazardous Area Classification of a CNG Station
OISD, OIL INDUSTRY SAFETY DIRECTORATE (Government of India, Ministry of
Petroleum and Natural Gas) issues a Safety Standard for the operation and distribution of city
Gas.
A major aspect of understanding Hazardous Areas is to classify them on the basis of the
surroundings and the kind of materials present. Such classification can be found in the National
Electric Code (NEC), which is a standard for classifying Dangerous locations on operational and
breakdown basis. It also includes dangers from all sorts of materials which may be present such
as foam, plastics, combustible dust, etc.
29
31. The Cascade cylinder storage area and the compressor area have been classified as Class
I - Division I as these handle high pressure Natural Gas (Group I), which is present in the
atmosphere at all times of normal functioning and require acute attention in case of a failure or
breakdown.
The dispensing area has been classified as one which is the most prone to Hazards as vent
gas is always present in considerable quantities, under normal functioning. Under an event of
mechanical failures in the tubing etc. this area would be highly dangerous as the General Public
accesses this area for CNG refilling.
The Filtration and Metering skid Area is classified as Class II – Division II –Group E,F,G
as combustible dusts of all composition is present in the incoming Natural Gas and proves to be
harmful in case of maintenance operations.
30
32. Data for Pressure drop in piping at Suction
Buckhardt Compressor date: 25th June2011
Engine gas Flow: 24.8888889 Kg/hr
Engine Inlet Suction Flow meter: 670.555556 Kg/hr
(ρ) Density at 15.07 bar, 29.07oC: 9.483 (kg/m3)
Volumetric flow rate: 70.71133 (m3/hr)
(Q) Volumetric flow rate: 0.01964 (m3/s)
(D) Diameter of pipe (2”): 0.0508 (m)
(v) Velocity: 9.695929 (m/s)
(T) First stage Suction temperature: 29.07 oC
(µ) Viscosity of gas at 15.07 bar, 29.07oC: 1.182*10-5 (kg/m.sec)
(k) Kinematic viscosity of gas: 1.25*10-6 (m2/sec)
(Nre) Reynold’s number: 395194.37
Formulae used
Volumetric flow rate: (Mass flow rate)/Density
Flow (m3/hr)/3600 : Flow(m3/s)
Velocity of Flow: Volumetric flow rate/Cross sectional area of Flow (πD2/4)
Kinematic Viscosity: Dynamic Viscosity/density
Reynolds number: (Diameter*Velocity)/kinematic Viscosity
31
36. Assumptions for Calculations
Natural Gas is assumed to be 100% Methane, and properties of Methane at Low pressure
and High Pressures assumed to be properties of Natural gas at the given Pressures and
Temperatures.
Moody diagram for coefficient of friction has been linearly interpolated between known
values to obtain an approximate coefficient for a given Reynolds number and roughness
factor.
Pressure regulation Valves (PRVs) etc. equipment at the metering Skid have been
assumed to result in zero pressure loss.
35
37. Figure 12: Moody diagram (Ref: College of Nautical Sciences, Glasgow)
36
38. Comparative Data for Pressure Drop in Tubing
Mass Flow rate: 300 Kg/hr
Pressure: 250 bar
Thermodynamic properties of Gas at 250 bar and 21oC
Density (ρ): 192.46225841658 Kg/m3
Viscosity (µ): 2.38456076692404*10-5 N.s/m2
Compressibility (Z): 0.852039803268427
Kinematic Viscosity (ν): 1.23897578*10-7m2/s
Volumetric Flow Rate: 1.558747m3/hr
Volumetric Flow Rate (Q): 4.32985278*10-4m3/s
Tubing data: 3/4" Tubing 1” Tubing 5/4” Tubing
Outer Diameter (O.D.) 1.9cm 2.54cm 3.175cm
Thickness* (from Table 1) 0.095” 0.12” 0.156”
Internal Diameter (D) 0.014174m 0.019304m 0.023825m
Roughness (k) (Table 2) 0.00008m 0.00008m 0.00008m
Roughness Factor(k/D) 0.00564 0.00414 0.00335
Velocity of Gas (v) 2.74409026 m/s 1.47941028 m/s 0.971219582 m/s
Reynold’s Number (Nre) 3.13837927*105 2.30501165*105 1.86761573*105
Coefficient of Friction(λ) 0.032 0.029 0.028
(Fig)
Length of Tubing (L) 10 m 10 m 10 m
Pressure loss (ΔP) using 16364.1139 Pa 3164.05144 Pa 1067.13748 Pa
Formulae
Pressure Loss (ΔP) 0.16364.1139 bar 0.0316405144 bar 0.0106713748 bar
37
39. Table for Tubing Data (Parker Hannifin Corp.)
Table 2: Maximum Allowable Working Pressure for Tubing
*Thickness of tubing required to handle Maximum allowable Working Pressure assumed
to be the next higher available value of pressure above 300bar
38
40. Roughness of Materials
Aluminium, drawn/pressed New 0.0013 - 0.0015 mm
Aluminium, drawn/pressed Used to 0.03 mm
Brass, drawn/pressed New 0.0013 - 0.0014 mm
Brass, drawn/pressed Used to 0.03 mm
Cast iron average city severage 1.2 mm
Cast iron Incrusted to 3.0 mm
Cast iron new, bituminized 0.10 - 0.13 mm
Cast iron new, with skin 0.2 - 0.6 mm
Cast iron operating several years, cleaned 1.5 mm
Cast iron slightly rusty 1.0 - 1.5 mm
Copper, drawn/pressed New 0.0013 - 0.0015 mm
Copper, drawn/pressed Used to 0.03 mm
Glass, drawn/pressed New 0.0013 - 0.0015 mm
Glass, drawn/pressed Used to 0.03 mm
Steel after long operation cleaned 0.15 - 0.20 mm
Steel homogeneous corrosion pits 0.15 mm
Steel intensely incrusted 2.0 - 4.0 mm
Steel slightly rusty and incrusted 0.15 - 0.40 mm
Steel, longitudinal welded new, bituminized 0.01 - 0.05 mm
Steel, longitudinal welded new, galvanized 0.008 mm
Steel, longitudinal welded new, rolling skin 0.04 - 0.1 mm
Steel, weldless new, comm.size galvanized 0.10 - 0.16 mm
Steel, weldless new, neatly galvanized 0.07 - 0.10 mm
Steel, weldless new, pickled 0.03 - 0.04 mm
Steel, weldless new, rolling skin 0.02 - 0.06 mm
Steel, weldless new, unpickled 0.03 - 0.06 mm
Table 3 Roughness of Materials
39
41. Grades of Steel Used:
The Society of Automotive Engineers (SAE) designates SAE steel grades. These are four
digit numbers which represent chemical composition standards for steel specifications.
The American Iron and Steel Institute (AISI) originally started a very similar system. Over time
they used the same numbers to refer to the same alloy, but the AISI system used a letter prefix to
denote the steelmaking process.
Carbon and alloy steel
Carbon steels and alloy steels are designated by a four digit number, where the first digit
indicates the main alloying element(s), the second digit indicates the secondary alloying
element(s), and the last two digits indicate the amount of carbon, in hundredths of a percent by
weight. For example, a 1060steel is a plain-carbon steel containing 0.60 wt% C.
Major classifications of Steel
SAE designation Type
1xxx Carbon steels
2xxx Nickel steels
3xxx Nickel-chromium steels
4xxx Molybdenum steels
5xxx Chromium steels
6xxx Chromium-vanadium steels
7xxx Tungsten steels
8xxx Nickel-chromium-vanadium steels
9xxx Silicon-manganese steels
SAE designation Type
Carbon steels
10xx Plain carbon (Mn 1.00% max)
11xx Resulphurized
12xx Resulphurized and Rephosphorized
15xx Plain carbon (Mn 1.00% to 1.65%)
40
42. Manganese steels
13xx Mn 1.75%
Nickel steels
23xx Ni 3.50%
25xx Ni 5.00%
Nickel-chromium steels
31xx Ni 1.25%, Cr 0.65% or 0.80%
32xx Ni 1.25%, Cr 1.07%
33xx Ni 3.50%, Cr 1.50% or 1.57%
34xx Ni 3.00%, Cr 0.77%
Nickel-chromium-molybdenum steels
43xx Cr 0.50-0.95%, Mo 0.12-0.30%
47xx Ni 1.82%, Cr 0.50-0.80%, Mo 0.25%
Ni 1.82%, Cr 0.50%, Mo 0.12%
81xx
V 0.03% min
81Bxx Ni 1.05%, Cr 0.45%, Mo 0.20%
86xx Ni 0.30%, Cr 0.40%, Mo 0.12%
87xx Ni 0.30%, Cr 0.45%, Mo 0.12%
88xx Ni 0.55%, Cr 0.50%, Mo 0.20%
93xx Ni 0.55%, Cr 0.50%, Mo 0.25%
94xx Ni 0.55%, Cr 0.50%, Mo 0.35%
97xx Ni 3.25%, Cr 1.20%, Mo 0.12%
98xx Ni 0.45%, Cr 0.40%, Mo 0.12%
Nickel
Ni 0.55%, Cr 0.20%, Mo 0.20%
molybdenum
46xx Ni 1.00%, Cr 0.80%, Mo 0.25%
Chromium steels Ni 0.85% or 1.82%, Mo 0.20% or 0.25%
50xx Ni 3.50%, Mo 0.25%
50Bxx Cr 0.27% or 0.40% or 0.50% or 0.65%
51xx Cr 0.50%, C 1.00% min
51xxx Cr 0.28% or 0.50%
51Bxx Cr 0.80%, 0.87%, 0.92%, 1.00%, 1.05%
52xxx Cr 1.02%, C 1.00% min
41
43. Stainless Steel SS316—
The second most common grade (after SS304); for food and surgical stainless steel uses;
alloy addition of molybdenum prevents specific forms of corrosion. It is also known as marine
grade stainless steel due to its increased resistance to chloride corrosion compared to type SS304.
SS316 is often used for building nuclear reprocessing plants. SS316L is an extra low carbon
grade of SS316, generally used in stainless steel watches and marine applications, as well
exclusively in the fabrication of reactor pressure vessels for boiling water reactors, due to its high
resistance to corrosion. Also referred to as "A4" in accordance with ISO 3506, SS316Ti includes
titanium for heat resistance, therefore it is used in flexible chimney liners.
42
44. An example of how the Cascade System Utilizes a Three Stage Storage
Bank to Provide a More Efficient System than the Single Control Volume
Storage Supply
An article published by RP publishing written by Ralph O. Dowling of C.P.
Industries is summarized in this section to better describe the cascade system. The
cascade system as mentioned earlier is a more efficient system than the single
control volume storage supply. A brief description of how the cascade operates will
be described in the following paragraphs. An understanding of the effects of
compression on natural gas is the first step in understanding the cascade system.
43
45. Table 4: Pressure - scm Natural Gas filled per Unit Volume
Table 3 illustrates how Natural Gas is affected when compressed into the same volume as occupied by 1m 3 of water. It
gives the amount of natural Gas in standard cubic metres(scm) that would occupy 1m3 Volume at a given pressure.
44
46. Storage System for Fast Fill: CASCADE
A cascade system is comprised of three banks (low, medium, high), which are
high pressure storage vessels. The whole cascade system holds about 891.96 scm of
Natural Gas at 250bar. These are deployed in two different configurations: 40 cylinder
of 75 Ltr capacity and 50 cylinders of 60 Ltr capacity.
Considering 40 X 75 liter configuration, each of the vessels has a water volume
of 0.075 m3, which would be 3 m3 total water volume. Banking cascade storage vessels
have a design pressure of 275 bar and a storage pressure of 250 bar. At 250 bar
each storage vessel will contain 22.299 scm of natural gas (0.075 m3* 297.32 scm / m3
water = 22.299 scm) at 210C. From Table3, at 250 bar, the volume of Natural Gas is
297.32 scm / m3 water. The Total Natural Gas contained in the system if all three
stages are at 250 bar and 21oC would be 891.96 scm (22.299 * 40).
The following assumptions have been made for the cascade sequence explanation:
Manual cascade system
1. Temperature remains constant
2. Each vehicle cylinder has a water volume of 65liters (0.065 m3)
3. The vehicle cylinder will contain 16.40 scm of natural gas at a pressure of
200bar
4. Each vehicle cylinder(s) is initially empty
5. No replenishment of the cascade bank during the refueling cycle
The liquid volume (empty) of the vehicle cylinders can be calculated by dividing
the specified capacity at 200bar (16.40 scm) by the amount of gas in scm (from Table 3)
contained in 1m3 liquid volume at 200bar. So the total water volume of the vehicle
cylinder would be 16.40 scm / (252.33 scm / m3) = 0.065 m3
45
47. Cascade as a Single Control Volume
The Cascade is first taken to be a single control Volume of 40 cylinders of 75
liter Water Capacity each. Total Capacity is 3000 (75*40) Water Liters at 250 bar.
The Available quantity of Natural Gas to be dispensed at 200 bar would be the
difference of scm of Natural gas held in the Cascade at 250 bar and at 200 bar from
Table3.
Amount of Natural Gas per m3 water at 250 bar: 297.32 scm
Amount of Natural Gas per m3 water at 200 bar: 252.33 scm
Water Capacity of cascade: 3m3
Available Qty of Natural Gas to dispense: (297.32-252.33)*3 = 134.97 scm
Number of Vehicle cylinders filled: (134.97/16.40) = 8.229
Therefore approximately Eight (8) vehicle cylinders can be completely filled at
200 bar from a 3000 water liter cascade at 250 bar without the compressor having to
recharge the cascade.
46
48. Cascade as a Banking System
The Cascade is now divided into separate Banks (Low-med-High) based on the
priority with which they fill the vehicle cylinder. The Ideal configuration is 50% of all
cylinders be deployed for Low Bank, 30% Medium bank, 20% High Bank
Out of 40 cylinders in the Cascade
Low bank cylinders: 25
Medium bank cylinders: 10
High Bank cylinders: 5
Now, assume that the First NGV is ready to be serviced. The first vehicle can be
completely filled from the low storage bank without having to switch to the next storage
bank. The low bank contains 557.475 (=22.299*25) scm of natural gas at 250 bar, after
the first vehicle is serviced, the low bank will contain 541.075 scm (557.475 – 16.40) of
natural gas at (541.075/1.875) = 288.573 scm / m3
From Table 3 interpolate 288.573 scm / m3 to find the pressure in low storage
bank after the first NGV has been filled (239.57 bar).
The Second vehicle is now ready for service. The next vehicle can also be filled
to the 200 bar level from the low bank. The medium bank will not have to be used yet.
The second vehicle will be filled from the low bank until the pressure in the low bank
and the NGV pressures equalize. The same mathematical process for the first NGV
example must be done for the second.
524.675 scm (541.075 -16.40) of Natural gas remains in Low Bank at
(524.675/1.875) 279.82 scm / m3. From Table3 interpolate 279.82 scm / m3 to find the
pressure in the low storage bank (229.24 bar).
47
49. After the Third vehicle is serviced, 508.275 scm (524.675-16.40) of Natural Gas
remains in Low Bank at (508.275/1.875) 271.08 scm / m3, which corresponds to
(218.90 bar) pressure.
After the Fourth vehicle is serviced, 491.875 scm (508.275-16.40) of Natural
Gas remains in Low Bank at (491.875/1.875) 262.33 scm / m3, which corresponds to
(210.28 bar) pressure.
After the Fifth vehicle is serviced,475.475 scm (491.875-16.40) of Natural Gas
remains in Low Bank at (475.475/1.875) 253.58 scm / m3, which corresponds to
(201.67 bar) pressure.
The Sixth vehicle cannot be filled to the 200 bar level from the low bank. The
medium bank will now have to be used to top off the vehicle. The sixth vehicle will
initially be filled from the low bank until the pressure in the low bank and the NGV
pressures equalize. For that, we find the equalization pressure of the Low Bank with the
NGV cylinder, which is the pressure corresponding to
(Available quantity of gas) / (Volume of Low Bank + Volume of NGV cylinder)
= 475.475 / (1.875+0.065) scm gas/m3
= 245.09 scm gas/m3, which from Table3 corresponds to 193.05 bar pressure.
Since the low storage bank and the NGV are equalized, the NGV cylinder(s) now
contain a pressure of 193.05 bar (< 200 bar), the NGV must be topped off by the
medium storage bank to achieve the desired 200 bar fill level. The low bank now
contains 459.543 scm (245.09 scm/m3 * 1.875m3) of natural gas. The vehicle now
contains 15.93 scm of natural gas (0.065m3 * 245.09 scm / m3)
The medium storage bank must provide 0.47 scm (16.40 scm – 15.93 scm) of
natural gas to top off NGV number 6.
The Medium Bank contains 222.99 scm (22.299*10) of Natural Gas. The same
mathematical process as before must be compiled to determine the remaining pressure.
48
50. (222.99-0.47) / 0.75 m3 = 296.693 scm / m3
Using Table3, interpolate 296.693 scm / m3 to determine the total pressure remaining in
the Medium storage Bank (248.21 bar).
This method of calculating total volume and total pressure remaining can be
applied to fill process from a cascade system for Sixteen (16) NGVs. The first Sixteen
vehicles can be filled from the Low and Medium storage banks only with the Low
storing bank containing (326.85 scm at 136.16 bar) and the Medium storage bank
containing (191.150 scm at 201.67 bar) after the Sixteenth NGV has been filled.
NGV number 17 will have to be filled from the low, medium, and high storage
banks. The Seventeenth vehicle will first equalize pressure with Low storage bank
(132.71 bar) 326.85 scm / (1.875 + 0.065) m3 = 168.479 scm / m3
Through interpolation using Table3 the equalization pressure would be
132.71 bar.
After an initial fill from the Low storage bank, 10.95 scm of natural gas would be
contained in the NGV cylinder (0.065 m3 * 168.479 scm / m3).
NGV number 17 will now equalize pressure with the Medium storage bank
(196.50 bar). With 191.150 scm remaining in the Medium storage bank, the pressure in
the Medium storage bank and the NGV cylinder will equalize pressures.
(191.50 + 10.95) scm / (0.75 + 0.065) m3 = 247.97 scm / m3
Through interpolation using Table3 the equalization pressure would be
196.50 bar.
After the Low and Medium storage banks have gone through the equalization process,
the High storage bank must be utilized to top off the vehicle. NGV number 17 now
contains 16.11 scm (0.065 m3 * 247.97 scm / m3) of natural gas. With the NGV
containing 16.11 scm of natural gas, 0.29 scm (16.40 scm – 16.11 scm) must be added
to achieve the full fill level for NGV number 17. The high bank has a capacity of
111.495 scm (22.299*5) of Natural Gas. The remaining natural gas in the high bank
would be 111.205 scm (111.495 scm – 0.29 scm) at a pressure of 248.21 bar.
111.205 scm / 0.375 m3 = 296.54 scm / m3
49
51. Through interpolation, using Table3, the pressure remaining in the third storage
bank would be 248.21 bar.
If this process is continued, 25 NGVs can be filled before this cascade system
will need to be recharged by the compressor. If a single control volume storage
system were used instead of cascading, only 8 vehicles could be recharged before the
system would have to be replenished by the compressor. The Following Table
compares the efficiencies of the two systems.
Number of Natual gas Natural gas Efficiency of
vehicles capacity of capacity (scm) of system = (# of
that can be each NGV system when vehicles * NG
System fueled (scm) fully capacity of each
by the particular charged NGV) / NG
system capacity of the
system
Cascade 25 16.40 891.96 45.96%
Single Control 8 16.40 891.96 14.71%
Volume
50
52. Suggestions for better safety and services
1. PNG
a. It is suggested to have Fuming Strips (perforated strips with smelling
agent) of mercaptin (Ethyl or methyl) to be supplied annually along with
the Gas consumption bill along with an instruction sheet which asks the
consumer to make each family member sniff the Strip and have an idea
about the smell which indicates them the presence of any form of leakage
in the supply system or flow meter. This would enable the consumer to be
able to detect / prevent a major Hazard.
2. CNG
a. I have strongly felt the need for the existence of regular Awareness
Camps at filling stations where consumers get to witness the immediate
remedial steps needed to be taken in case of an emergency within the car.
i. There should be Fuming Strips which replicate the smell of gas
leakage at the concentration at which it exists in the car.
ii. The camp should display protocols to be followed step by step in
case of an emergency’ depicting various complications which may
arise and ways to counteract them.
iii. The camp also shows the dangerously high pressures that exist in
various tubings within the car and how lethal such high pressures
can be. Citing common examples of the muzzle pressure inside an
AK47 making the audience experience a gauge pressure of 1bar on
their hands and explaining how dangerous a 200bar pressure
stream can be. Consumers also need to be repeatedly told about
common characteristic properties of the Natural Gas.
b. Every filling attendant must be given the authority to issue non-compliance
papers to CNG vehicles. Where any vehicle found to have dangerous /
worn out nozzle receivers(female) would be advised to get it changed
within a stipulated time period (suggested:1 Month). Failing which, CNG
51
53. will not be dispensed to the vehicle. This is in direct accordance towards
the safety of the filling attendants as dangerous recoils and snake sliding
in the hose occurs due to ineffective contact between the O-rings and the
female nozzle walls. The current inspection of cylinders at 5 years and
tubing at 1 year does not take into consideration normal daily wear and
faults which need immediate attention. The attendants have been
entrusted with such responsibilities as they witness hands-on the exact
state and seriousness of the issue.
3. CNG Filling Stations
a. UTILISING VENT GAS
i. Vent gas which is released into the atmosphere in order to break
the gas flow path in the dispenser nozzle so that it can be
disconnected from the vehicle should be utilized. A few suggested
uses of the gases (need of further experimentation required):
1. Producing electricity (the gas at approx 200bar can be
effectively used to produce energy by expansion over a
turbine and later combusted to produce a considerable
amount of energy to power the Flood lights on a filling
station.
2. The gas can be collected over an overhead container where
all the dispensers release their vent gas and this gas can be
later combusted to produce energy to power the
infrastructure around a CNG Filling station.
3. Implementation of SCADA, in order to effectively monitor
various units under a control room at once and result in swift
delivery of services and prompt servicing.
4. Quick licensing of compressor packages in order to result in
less effective kilometer usage on transport of LCV’s and
ease in meeting rising gas demands. (eg: licensing of
compressor package at Dwarka sec-20 filling station would
result in a net saving of 10 Km per LCV filling trip)
52
54. References
D. Rood, ”A practical guide to care, maintenance and troubleshooting of capillary
Gas Chromatographic systems“, 2nd edition, Hüthig Verlag, Heidelberg, 1995
Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003). Materials and
Processes in manufacturing (9th edition.). Wiley.
Jeffus, Larry F. (2002). Welding: Principles and Applications. Cengage Learning.
Dowling, Ralph O., .Cascade Basics, RP Publishing, 1993.
Moran, Michael J., Shapiro, Howard N., .Fundamentals of Engineering
Thermodynamics., John Wiley and Sons Inc., New York, pp. 488-449, 1999.
Tubing manual and selection Guide, Product Catalogue: Parker Hannifinn
Corporation, 2007
Ronald A. Hites Mass Spectrometry Gas Chromatography
National electric code (NEC), National Fire protection Association (NFPA),
Batterymarch Park, Quincy, MA
53
