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Project Report on CNG filling         Operations          Ankur Rawal                                1
CERTIFICATE      Certified that this project report “CNG filling Operations” atIndraprastha Gas Limited is the work of “An...
ABSTRACT   Filling operations of Compressed Natural Gas (CNG) in Natural Gas Vehicles       Natural gas is being used as a...
Acknowledgments       I wish to acknowledge all the people who have helped me finish this Report.Without the generosity of...
AN OVERVIEV OF INDRAPRASTHA GAS LIMITEDCOMPANY PROFILE       Indraprastha Gas Limited (IGL), a Joint Venture of GAIL (Indi...
CNG-Compressed Natural Gas        Natural Gas is a combination of Methane, Propane and Butane. Conventional NaturalGas exi...
It is proven manifold that natural gas is a very clean fuel. The world EnergyConference of Tokyo 1996 announced that natur...
Although conventional wisdom holds that natural gas engines should require fewer oilchanges and perhaps even less frequent...
Gas Chromatograph (GC)       In a Gas Chromatogram (GC) Analysis, 0.1-10µL (micro liter) of a mixture ofcompounds is injec...
Thermal Conductivity Detector (TCD)                                                                                Flame I...
Figure 4: Schematic ChromatogramCOMPONENTS   Jan      Feb     Mar     Apr      May      Jun      JulyC1            92.7464...
C1: Methane       C2: Ethane       C3: Propane       I-C4: Iso-Butane       N-C4: Normal Butane       N2: DiNitrogen      ...
Difference between Gross Calorific Value and Net Calorific Value:         The Water produced in the combustion reaction is...
CNG Distribution Network                                        Main line ~18-20 bar                                      ...
CNG Station BasicsKey CNG Refueling Station Equipment:       Gas Dryer (inlet or outlet)       Compressor Package System (...
Once the gas is properly conditioned as required, it then enters the compressor. Thecompressor is typically the largest an...
Major Components     Suction Line Filter     The Suction Line filter includes protection from moisture, inorganic and orga...
F                                    I                                    L                                    T          ...
Compressor: Dresser Rand   •   Maximum Driver HP                    250 (186 kW)   •   Standard Stroke                    ...
Cooling System       Compressors generate heat as a natural byproduct of compression. For this reason, theymust be cooled....
Gas Flow within Compressor                                    INTER COOLER               INTER COOLER        Inlet        ...
Mechanism of Compression                              Expulsion of gas                                                    ...
General Physical Parameters   •   1st stage suction pressure (Kg/cm2) = 14.95   •   1st stage discharge pressure (Kg/cm2) ...
GD-501           Gas detectorGD-502           Gas detectorFD- 501          Flame detectorFD-502           Flame detectorTE...
Priority panel       The priority panel consists of a priority valves and non return valves, so arranged thatintended use ...
LCV Priority Routing       The Mobile Cascade Vehicles, also known as LCV, are Flatbed trucks on which aCascade has been s...
Figure 11: Existing Priority chart for Jail Rd Control room       The Priority Routing involves more parameters than assum...
Hazardous Area Classification of a CNG Station                                                 28
Hazardous Area Classification of a CNG Station        OISD, OIL INDUSTRY SAFETY DIRECTORATE (Government of India, Ministry...
The Cascade cylinder storage area and the compressor area have been classified as ClassI - Division I as these handle high...
Data for Pressure drop in piping at Suction                      Buckhardt Compressor date: 25th June2011                 ...
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Assumptions for Calculations    Natural Gas is assumed to be 100% Methane, and properties of Methane at Low pressure    an...
Figure 12: Moody diagram (Ref: College of Nautical Sciences, Glasgow)                                                     ...
Comparative Data for Pressure Drop in Tubing                                   Mass Flow rate: 300 Kg/hr                  ...
Table for Tubing Data (Parker Hannifin Corp.)                            Table 2: Maximum Allowable Working Pressure for T...
Roughness of Materials   Aluminium, drawn/pressed                      New                  0.0013 - 0.0015 mm   Aluminium...
Grades of Steel Used:   The Society of Automotive Engineers (SAE) designates SAE steel grades. These are fourdigit numbers...
Manganese steels     13xx                         Mn 1.75%                       Nickel steels     23xx                   ...
Stainless Steel SS316—       The second most common grade (after SS304); for food and surgical stainless steel uses;alloy ...
An example of how the Cascade System Utilizes a Three Stage Storage  Bank to Provide a More Efficient System than the Sing...
Table 4: Pressure - scm Natural Gas filled per Unit VolumeTable 3 illustrates how Natural Gas is affected when compressed ...
Storage System for Fast Fill: CASCADE       A cascade system is comprised of three banks (low, medium, high), which arehig...
Cascade as a Single Control Volume      The Cascade is first taken to be a single control Volume of 40 cylinders of 75lite...
Cascade as a Banking System       The Cascade is now divided into separate Banks (Low-med-High) based on thepriority with ...
After the Third vehicle is serviced, 508.275 scm (524.675-16.40) of Natural Gasremains in Low Bank at (508.275/1.875) 271....
(222.99-0.47) / 0.75 m3 = 296.693 scm / m3Using Table3, interpolate 296.693 scm / m3 to determine the total pressure remai...
Through interpolation, using Table3, the pressure remaining in the third storagebank would be 248.21 bar.      If this pro...
Suggestions for better safety and services  1. PNG       a. It is suggested to have Fuming Strips (perforated strips with ...
will not be dispensed to the vehicle. This is in direct accordance towards         the safety of the filling attendants as...
References    D. Rood, ”A practical guide to care, maintenance and troubleshooting of capillary    Gas Chromatographic sys...
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  1. 1. 0
  2. 2. Project Report on CNG filling Operations Ankur Rawal 1
  3. 3. CERTIFICATE Certified that this project report “CNG filling Operations” atIndraprastha Gas Limited is the work of “Ankur Rawal” who carried out theproject work under the Operations & Maintenance department.Mr. Amit Kumar DebManager (CNG - O&M)Mr. Ujwal BhandariGeneral Manager (CNG-O&M)Mr. P.K. PandeyChief General Manager (CNG-O&M)Mr. Manjeet SinghVice President (E&P) 2
  4. 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 gasdispensable. The report focuses on understanding various aspects of these processesand test and suggest changes in their functioning. Various tests and observations were made on the compressor and inlet pipesand pressure drops calculated. Useful characteristics of CNG during the fill process aretemperature, pressure, and flow rate, as well as, total volume dispensed. CNG isdispensed to an NGV through a process known as the fast fill process, since it iscompleted in less than five minutes. The system is being constantly upgraded in orderto 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 GasLimited (IGL). The Gas Chromatography installation at Mahipalpur Gas Station hasbeen carefully studied along with viscosity relations with dilution were done for snoopsolution used to test leakage. 3
  5. 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 reportis an outcome of the advice and tutelage of several people who work at IndraprasthaGas Limited (IGL). I would like to thank my advisor and mentor Mr. Ujwal Bhandari (GeneralManager CNG-O&M), first of all, for being so patient with me and being an excellentmentor 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 myendeavor, Mr. Amit Kumar Deb (Manager CNG-O&M Jail Road Control Room) andMr. Abhinav Sahay (Additional Manager CNG-O&M Lado Sarai Control Room)have also been very helpful for advice and knowledge of subjects contained in thisreport. The entire team of Engineers and Technicians at Jail Road and Lado SaraiControl Rooms have in some way or the other helped me understand practical aspectsof whatever I had learnt in texts earlier. I am highly indebted to Mr. Manjeet Singh (Vice President – E&P) for hebelieved in my objectives of undergoing this internship and made an exception inallowing me to be a part of the organization after completing the second year of my fouryear graduation in Chemical Engineering. My college, USCT has been very supportive as well, to have allowed me to usetheir facilities and equipments for a few tests. University Professors such asDr. Biswajit Sarkar have helped me with the required textbooks and constantlyanswered all my queries regarding fluid dynamics and Heat Exchangers.Thanks and Regards, 4
  6. 6. AN OVERVIEV OF INDRAPRASTHA GAS LIMITEDCOMPANY PROFILE Indraprastha Gas Limited (IGL), a Joint Venture of GAIL (India) limited and BPCLalong with the government of NCT of Delhi was incorporated on December 23, 1998 toimplement 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 IGLworked tirelessly to take the project to new heights.IGL’S VISION -‘To be the leading clean energy solution provider, committed to stakeholdervalue 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. 7. CNG-Compressed Natural Gas Natural Gas is a combination of Methane, Propane and Butane. Conventional NaturalGas exists above crude oil deposits, and is often wasted or burned in the oil collection processdue to the high costs of capturing and using it. When the gas is burned, it prevents the Methanefrom reaching the atmosphere. Carbon Dioxide into the atmosphere is less harmful thanMethane. Natural Gas produces less air pollution than any other fossil fuel. Use of CNG vehiclescan reduce Carbon Monoxide emissions as much as 93% Nitrogen Oxide reduces about33% and Hydrocarbons are reduced by about 50%. Natural Gas emits almost no carcinogenicparticulates. By using CNG to power vehicles a bi-fuel tank can exist; therefore, in locations withoutCNG 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 93octanes for Petrol; consequently, the CNG vehicle is more energy efficient. Besides usingNatural Gas to power vehicles, it can also create electricity and heat homes and commercialbuildings. Compressed Natural Gas (CNG) is natural gas that has been compressed for storageaboard a natural gas vehicle (NGV), a vehicle whose engine is fueled by Natural Gas. Naturalgas is compressed to high pressure (200 bar/20.7 MPa or higher) to most effectively utilize theNGV’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. 8. It is proven manifold that natural gas is a very clean fuel. The world EnergyConference 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 orcommercial 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 259bar (20.7Mpa to 25Mpa). At the dispenser, Natural Gas is delivered into vehicles either byweight (in kilograms) or by Gasoline liter equivalents (GLE – an energy equivalent comparisonto gasoline) and carries an octane rating between 122 and 130. There are many types of natural gas vehicles (NGV’s), including dedicated, Bifuel anddual 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 acombination 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 toindustry-recognized standards for installation (the NGV 2 standard in Canada & USA or OISDStandard 226 for City Gas distribution in India) If NGV’s and equipment are in sound condition, you can expect them to perform reliablywhen they are well maintained by a trained technician and drivers are well informed and trained. 7
  9. 9. Although conventional wisdom holds that natural gas engines should require fewer oilchanges 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 superiorperformance of the NGV versus its gasoline and diesel counterparts. A CNG fueling facility typically consists of a compressor, storage Cascades and adispenser system. Dispensers come in two types: fast fill, which delivers fuel at a ratecomparable to gasoline or diesel systems, and time fill, which fuels vehicles over a period oftime. 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 ofNew Delhi is done at the Mahipalpur CNG Station, which comes under the Lado SaraiControl Room. A Gas Chromatograph monitors and records the quality of the Natural Gas atall hours of the day all round the year. It measures quantitatively the %composition of variouscomponents of the Natural Gas, which further helps in maintaining exact desirable proportions. The incoming Gas from GAIL is odorless and therefore, a smelling agent (EthylMercaptin and Methyl Mercaptin) is mixed into the Gas at IGL’s Patparganj Plant. Where thesmelling agent is introduced at traceable quantities as the concentration magnifies whencompressed. A detailed functioning of the Gas Chromatograph is explained further. Major contents of the Quality control are: %Composition of C 1 - C6& above, GrossCalorific Value, Net Calorific Value and specific volume. As the Gas upon combustion releases water in the form of vapor, this water vaporreleases more heat in the process of condensation. This heat when added to the Gross Calorificvalue (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 Temperatureand Pressure (STP). 8
  10. 10. Gas Chromatograph (GC) In a Gas Chromatogram (GC) Analysis, 0.1-10µL (micro liter) of a mixture ofcompounds is injected into a heated Injector, where all of the compounds vaporize. A gentlestream of the Carrier Gas, Helium (He) moves the entire mixture onto the Collumn, thecorresponds of the mixture separate as they pass through the column. The process can beconsidered as an exceptionally good Fractional distillation using a superb fractionating column. Figure 1: Schematic representation of the components of a GCThe Process The separated compounds pass from the column into a detector that produces anelectrical signal proportional to the amount of compound passing through the detector. Arecorder provides a graph. The Gas Chromatogram is plotted against the detector Signal versusRetention time. The Gas chromatogram shows a peak for each compound in the mixture. Theretention time can be measured from the Chromatogram. An Integrator measures the areas underthe peaks in the Gas Chromatogram. 9
  11. 11. Thermal Conductivity Detector (TCD) Flame Ionization Detector (FID) Figure 2 detectors used in Gas ChromatographyThe Chromatogram A chromatogram consists of a base line and a number of peaks. The area of a peak allowsquantitative determinations. Starting point of a chromatogram is the time of injection of adissolved sample. The time interval between a peak and the point of injection is called retentiontime 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) andin the stationary phase (t R = net retention time); t 0 is also known as dead time. It is the timerequired by a component to migrate through the chromatographic system without any interactionwith 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 ofthe compound in the sample. Direct comparison of peak areas for different compounds isunreliable because detectors do not have the same sensitivity to all compounds. For thisreason, a sample of the Natural Gas is maintained in the GC. The Area under thechromatogram is then compared to that of the sample, and the result is recorded. 10
  12. 12. Figure 4: Schematic ChromatogramCOMPONENTS Jan Feb Mar Apr May Jun JulyC1 92.7464 92.4233 94.102 91.7059 90.8413 88.64 91.4763C2 4.0807 4.2759 4.6296 4.3309 4.4206 5.2094 4.3462C3 0.8629 1.0646 0.7279 0.8726 0.6122 1.3443 0.7145I-C4 0.1161 0.1541 0.1227 0.0991 0.0232 0.1589 0.058N-C4 0.1641 0.2225 0.1657 0.1368 0.0003 0.1705 0.0626N2 0.1745 0.2326 0.1659 0.1904 0.1045 0.0983 0.1364CO2 1.8521 1.627 0.0793 2.6596 4.0063 4.2942 3.2024Neo-C5 0 0 0 0 0 0I-C5 0.0029 0 0.0053 0.0037 0.0008 0.0297 0.0023N-C5 0 0 0.0015 0.001 0.0007 0.0256 0.0013C6+ 0.0003 0.0001 0 0 0 0.0291 0GCV 9294.51 9368.78 9476.66 9230.251 9043.145 9257.759 9142.276SG 0.6059 0.6082 0.5903 0.6145 0.6219 0.6419 0.6164 Table 1: GC data Mahipalpur Plant (Period: Jan-July2011) 11
  13. 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 ValueLimitations: Only compounds with vapor pressures exceeding about 10–10 torr can be analyzed by gaschromatography mass spectrometry (GC-MS). Many compounds with lower pressures can beanalyzed if they are chemically obtained (for example, as trimethylsilyl ethers). Determiningpositional substitution on aromatic rings is often difficult. Certain isomeric compounds cannot bedistinguished by mass spectrometry (for example, naphthalene versus azulene), but they canoften be separated chromatographically.Accuracy: Qualitative accuracy is restricted by the general limitations cited above. Quantitativeaccuracy is controlled by the overall analytical method calibration. Using isotopic internalstandards, accuracy of ±20% relative standard deviation is typical. 12
  14. 14. Difference between Gross Calorific Value and Net Calorific Value: The Water produced in the combustion reaction is in the gaseous state. This water whencondensed to liquid state at ambient temperatures in the cylinder releases the Latent heat ofCondensation which unlike the Gross Calorific Value is released from the exhaust when itinteracts with air at ambient temperature. This additional energy is not used for the expansiveworking within the piston cylinder and therefore is not accounted for in the actual CalorificValue of the gas mixture. The Net Calorific Value is what we read in instruments and wesubtract the known value of Latent heat of condensation of steam at given conditions to obtainthe 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 tocompress Natural Gas to a high pressure and either store the CNG (if the site is equipped withstorage) or dispense it directly to a natural gas vehicle for refueling. A CNG station typically consists of one or more compressor packages to compress theNatural Gas, and several additional systems, which include Cascade storage systems, PLC basedcontrols system such as a priority controller panel, a temperature/pressure compensation panel, abuffer panel, gas dryers, fast refueling (CAR dispensers) and time refueling (BUS) dispensingunits. The Station includes separate areas for Compression, Storage and Dispensing. It includesAir compressor pipes, Water pipelines etc. It also includes provisions for safety against Fire orLeakage. The provisions include Carbon dioxide (CO2) Cylinders; Dry Chemical Powder (DCP)cylinders etc. 13
  15. 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 StorageMOTHER Cascade Cascade ON-LINESTATION ~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. 16. CNG Station BasicsKey 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 Pipelineprovided by GAS AUTHORITY OF INDIA LIMITED (GAIL). This gas can range in pressurefrom as low as 12 bar (gauge pressure above atmospheric), to as high as 35 bar/ 3.45 Mpa orhigher. 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, theincoming gas may need to be conditioned further, so as not to damage the compressionequipment or downstream systems. For example, if the gas is “wet”(has an unusually highconcentration of evaporated water), then the gas will first pass through a dryer, if the Sulphurcontents in the gas is higher, it also should be removed. This is a large vessel, surrounded byrelated components, which removes water from the gas stream using a “desiccant” material. 15
  17. 17. Once the gas is properly conditioned as required, it then enters the compressor. Thecompressor is typically the largest and most complex piece of equipment in the entire refuelingstation. It raises the pressure of the natural gas to 250 bar (25Mpa), or higher, using a number ofseparate stages, which increase the gas pressure in increments. The Compressors are typically reciprocating compressors. These are driven in a rotationalmanner, 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 gasinto each cylinder, compress it with a Piston, and then discharge in into the next stage at anincreased pressure. The cylinder configurations can either be a “W” or “V” shape, or horizontallyopposed.Metering Skid The first Equipment on the Main Inlet piping is the Metering Skid. It helps monitorprecise Station Inlet GAS characteristics as per requirement up to compressors which helps studygas loses over compression etc. Flow mater readings help CNG Station Marketing and SalesDepartment tally Station reconciliation with respect to sales and also IGL gas reconciliation withGAIL (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. 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. 19. F I L T E R Figure 6 Schematic diagram of the metering skidCompressor 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 themotor when the compressor is required to turn on. The motor shaft is coupled to the compressorshaft 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 thepackage. Mechanically, the compressor requires a lubricating oil supply to lubricate thecylinders, pistons, and other moving parts. It also requires a means to remove from the gassupply oil that is introduced through lubrication. This typically involves a system of filters and separators. Filters are typically placed atthe inlet and the discharge of the compressor itself, while in-line gas separators are placedbetween the stages of compression. Separators spin the gas in a circular motion to usecentrifugal force to condense any liquid out of the gas stream. This results in a collection ofcondensates, typically water and oil, which must be periodically removed from the separatorvessels. This is typically done automatically in the packages, with collection in the largerecovery tank(s) and later automatically drained into one of the beams in the skid case. 18
  20. 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. 21. Cooling System Compressors generate heat as a natural byproduct of compression. For this reason, theymust be cooled. IGL generally has only air-cooled compressors, which means they employforced air-cooling of the compressor and/or gas stream, instead of water cooling like one wouldfind in a car engine. Some compressor blocks are self-cooling, incorporating a fan onto theirmain 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 aseparate fan. These Heat exchangers (Inter Coolers) are Shell and Tube with Fins, with multiple passesin 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, whichincludes the recovery tanks and various automated valves, captures the gas from the compressionsystem when the machines are shutoff, and maintains a closed loop system by containing andrecycling this gas. It also permits the compressor to start and stop “unloaded”, or withoutcompressing 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 enoughintelligence to turn themselves on, shut themselves off appropriately, and do it all safely, whilewatching for possible faults. This is generally accomplished by the electronic controls systemon–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 compressorthrough flexible hose to suction collector and first stage cylinder. BDV also acts as a condensatecollecting bottle. All the condensate and oil are drained into the BDV. 20
  22. 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) PANELPT106 Condensate Figure 7: Schematic layout of Compressor system Natural Gas Package Boundary Condenate (Water + oil) 21
  23. 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. 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 preconditionsTag name Tag descriptionPT-101 1ST Stage suction pressure.PT-102 2nd Stage suction pressure.PT-103 3rd Stage suction pressurePT-104 3rd Stage discharge pressure.PT-105 Engine fuel gas pressure.PT-106 Blow down vessel pressurePT-401 Engine starting air pressure. 23
  25. 25. GD-501 Gas detectorGD-502 Gas detectorFD- 501 Flame detectorFD-502 Flame detectorTE-101 1st Stage gas suction temperatureTE-102 1st Stage gas discharge temperatureTE-104 2nd Stage gas discharge temperatureTE-106 3rd Stage gas discharge temperatureTE202 Engine Jacket Temperature (oC)TE-301 Engine lubes oil temperatureTE-108 Engine exhausts gas temperatureTE-208 Compressor cooling oil header TemperatureLSL-201 CW surge tank level lowSSHH-101 Engine over speed contactEmergency stop Emergency stop push buttonSOV-101 ON Drain solenoid valve ONPT-301 Engine lubes oil pressurePT-302 Compressor lubes system oil PressureTE-107 Engine inlet manifold temperature 24
  26. 26. Priority panel The priority panel consists of a priority valves and non return valves, so arranged thatintended use of providing priority to vehicles is achieved. The priority panel is connected todischarge of compressor at one end and is connected in parallel to cascade (storage) anddispenser at other end. If there are no vehicles for gas filling, then priority valve directs the gasflow 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 dispenserCN SOV-117 Medium bankG 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. 27. LCV Priority Routing The Mobile Cascade Vehicles, also known as LCV, are Flatbed trucks on which aCascade 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 Boosterstations under each Control Room. This movement of LCVs around the city has been outsourcedto various Transport Contractors, who charge on per-km basis. The Job of priority routing arisesin order to minimize the Total number of Kilometers that have to be paid for, while stillproviding 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 newStation comes up under a Control Room. This form of Assignment is a Linear ProgrammingProblem (LPP), Transportation Problem. The Following Figures Explain the Priority Routingunder Jail Road control room. Figure 10: Suggested Priority routing Chart, data in Kms 26
  28. 28. Figure 11: Existing Priority chart for Jail Rd Control room The Priority Routing involves more parameters than assumed, such as licensing issuesand capacity considerations. Jail Road control room consists of 19 LCVs. 13 of which arecontracted to Chowdhary transport and 6 through Orient Transport. There exist two Daughterand six Daughter stations under this control room and therefore a well planned and executedpriority route results in considerable monetary and energy savings. 27
  29. 29. Hazardous Area Classification of a CNG Station 28
  30. 30. Hazardous Area Classification of a CNG Station OISD, OIL INDUSTRY SAFETY DIRECTORATE (Government of India, Ministry ofPetroleum and Natural Gas) issues a Safety Standard for the operation and distribution of cityGas. A major aspect of understanding Hazardous Areas is to classify them on the basis of thesurroundings and the kind of materials present. Such classification can be found in the NationalElectric Code (NEC), which is a standard for classifying Dangerous locations on operational andbreakdown basis. It also includes dangers from all sorts of materials which may be present suchas foam, plastics, combustible dust, etc. 29
  31. 31. The Cascade cylinder storage area and the compressor area have been classified as ClassI - Division I as these handle high pressure Natural Gas (Group I), which is present in theatmosphere at all times of normal functioning and require acute attention in case of a failure orbreakdown. The dispensing area has been classified as one which is the most prone to Hazards as ventgas is always present in considerable quantities, under normal functioning. Under an event ofmechanical failures in the tubing etc. this area would be highly dangerous as the General Publicaccesses this area for CNG refilling. The Filtration and Metering skid Area is classified as Class II – Division II –Group E,F,Gas combustible dusts of all composition is present in the incoming Natural Gas and proves to beharmful in case of maintenance operations. 30
  32. 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
  33. 33. 32
  34. 34. 33
  35. 35. 34
  36. 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. 37. Figure 12: Moody diagram (Ref: College of Nautical Sciences, Glasgow) 36
  38. 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 3.175cmThickness* (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*105Coefficient 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. 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 assumedto be the next higher available value of pressure above 300bar 38
  40. 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. 41. Grades of Steel Used: The Society of Automotive Engineers (SAE) designates SAE steel grades. These are fourdigit numbers which represent chemical composition standards for steel specifications.The American Iron and Steel Institute (AISI) originally started a very similar system. Over timethey used the same numbers to refer to the same alloy, but the AISI system used a letter prefix todenote the steelmaking process.Carbon and alloy steel Carbon steels and alloy steels are designated by a four digit number, where the first digitindicates the main alloying element(s), the second digit indicates the secondary alloyingelement(s), and the last two digits indicate the amount of carbon, in hundredths of a percent byweight. 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 steelsSAE 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. 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. 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 marinegrade 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 carbongrade of SS316, generally used in stainless steel watches and marine applications, as wellexclusively in the fabrication of reactor pressure vessels for boiling water reactors, due to its highresistance to corrosion. Also referred to as "A4" in accordance with ISO 3506, SS316Ti includestitanium for heat resistance, therefore it is used in flexible chimney liners. 42
  44. 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. Thecascade system as mentioned earlier is a more efficient system than the singlecontrol volume storage supply. A brief description of how the cascade operates willbe described in the following paragraphs. An understanding of the effects ofcompression on natural gas is the first step in understanding the cascade system. 43
  45. 45. Table 4: Pressure - scm Natural Gas filled per Unit VolumeTable 3 illustrates how Natural Gas is affected when compressed into the same volume as occupied by 1m 3 of water. Itgives the amount of natural Gas in standard cubic metres(scm) that would occupy 1m3 Volume at a given pressure. 44
  46. 46. Storage System for Fast Fill: CASCADE A cascade system is comprised of three banks (low, medium, high), which arehigh pressure storage vessels. The whole cascade system holds about 891.96 scm ofNatural Gas at 250bar. These are deployed in two different configurations: 40 cylinderof 75 Ltr capacity and 50 cylinders of 60 Ltr capacity. Considering 40 X 75 liter configuration, each of the vessels has a water volumeof 0.075 m3, which would be 3 m3 total water volume. Banking cascade storage vesselshave a design pressure of 275 bar and a storage pressure of 250 bar. At 250 bareach storage vessel will contain 22.299 scm of natural gas (0.075 m3* 297.32 scm / m3water = 22.299 scm) at 210C. From Table3, at 250 bar, the volume of Natural Gas is297.32 scm / m3 water. The Total Natural Gas contained in the system if all threestages 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 dividingthe 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 vehiclecylinder would be 16.40 scm / (252.33 scm / m3) = 0.065 m3 45
  47. 47. Cascade as a Single Control Volume The Cascade is first taken to be a single control Volume of 40 cylinders of 75liter 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 thedifference of scm of Natural gas held in the Cascade at 250 bar and at 200 bar fromTable3. 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 at200 bar from a 3000 water liter cascade at 250 bar without the compressor having torecharge the cascade. 46
  48. 48. Cascade as a Banking System The Cascade is now divided into separate Banks (Low-med-High) based on thepriority with which they fill the vehicle cylinder. The Ideal configuration is 50% of allcylinders 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 becompletely filled from the low storage bank without having to switch to the next storagebank. The low bank contains 557.475 (=22.299*25) scm of natural gas at 250 bar, afterthe first vehicle is serviced, the low bank will contain 541.075 scm (557.475 – 16.40) ofnatural gas at (541.075/1.875) = 288.573 scm / m3 From Table 3 interpolate 288.573 scm / m3 to find the pressure in low storagebank after the first NGV has been filled (239.57 bar). The Second vehicle is now ready for service. The next vehicle can also be filledto 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 bankand the NGV pressures equalize. The same mathematical process for the first NGVexample 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 thepressure in the low storage bank (229.24 bar). 47
  49. 49. After the Third vehicle is serviced, 508.275 scm (524.675-16.40) of Natural Gasremains 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 NaturalGas 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 Gasremains 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. Themedium bank will now have to be used to top off the vehicle. The sixth vehicle willinitially be filled from the low bank until the pressure in the low bank and the NGVpressures equalize. For that, we find the equalization pressure of the Low Bank with theNGV 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) nowcontain a pressure of 193.05 bar (< 200 bar), the NGV must be topped off by themedium storage bank to achieve the desired 200 bar fill level. The low bank nowcontains 459.543 scm (245.09 scm/m3 * 1.875m3) of natural gas. The vehicle nowcontains 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) ofnatural gas to top off NGV number 6. The Medium Bank contains 222.99 scm (22.299*10) of Natural Gas. The samemathematical process as before must be compiled to determine the remaining pressure. 48
  50. 50. (222.99-0.47) / 0.75 m3 = 296.693 scm / m3Using Table3, interpolate 296.693 scm / m3 to determine the total pressure remaining inthe Medium storage Bank (248.21 bar). This method of calculating total volume and total pressure remaining can beapplied to fill process from a cascade system for Sixteen (16) NGVs. The first Sixteenvehicles can be filled from the Low and Medium storage banks only with the Lowstoring bank containing (326.85 scm at 136.16 bar) and the Medium storage bankcontaining (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 storagebanks. 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 be132.71 bar.After an initial fill from the Low storage bank, 10.95 scm of natural gas would becontained 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 inthe 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 be196.50 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 nowcontains 16.11 scm (0.065 m3 * 247.97 scm / m3) of natural gas. With the NGVcontaining 16.11 scm of natural gas, 0.29 scm (16.40 scm – 16.11 scm) must be addedto achieve the full fill level for NGV number 17. The high bank has a capacity of111.495 scm (22.299*5) of Natural Gas. The remaining natural gas in the high bankwould 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. 51. Through interpolation, using Table3, the pressure remaining in the third storagebank would be 248.21 bar. If this process is continued, 25 NGVs can be filled before this cascade systemwill need to be recharged by the compressor. If a single control volume storagesystem were used instead of cascading, only 8 vehicles could be recharged before thesystem would have to be replenished by the compressor. The Following Tablecompares 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. 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. 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. 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

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