lecture 12 compressed natural gas revised - iit kanpur 15-17... · · 2016-09-09alternative fuel...

Compressed natural Gas 1

Compressed Natural Gas

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Petroleum Displacement

Energy Diversity Air Quality Improvement

Greenhouse Gas Emission Reductions

Domestic Economic Development

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Why Use Alternative Fuels?


Urban Pollution

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Case Study of Delhi

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Smog Became Pervasive

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FLEET COMPOSITION OF INDIAN VEHICLES (1997) (Source: TERI)

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(Two wheelers (71%) & Three wheelers (5%) occupy significant places in the Indian transportation sector)


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Landmark March 31, 2001, India Supreme

Court ruling


conversion of the entire bus fleet to (CNG). Taxis and auto rickshaws must be replaced with engines

running on clean fuels

A natural gas pipeline from Mumbai supplies natural gas to New Delhi.

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Heavy duty

As of April 1, 2000, non-commercial 4-wheelers must meet Euro II emission standards.

Commercial vehicles, such as taxis, must be also meet Euro II emission standards or use CNG

In order to be registered in the Capital Region of New Delhi.

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Light-duty


Ethanol Natural Gas Propane (LPG)

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Alternative Fuel Vehicles Available Now

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1. Natural gas is one of the cleanest of all fuel sources available

2. Huge potential of unexploited natural gas

reserves exists in India 3. This presentation explores the possibilities

of utilizing unexploited gas reserves by converting them into liquids

Why Natural Gas Chosen?


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1. Gas reserves of NE region ‐ Tripura

2. Gas hydrates in deep sea

3. Gas reserves in deepwater

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Gas Reserves In India


NATURAL GAS

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HISTORY


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Natural Gas Vehicles Dilemma

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Very Low Emissions

Good Performance

Lower Cost Fuel

Limited Range, but adequate for most Applications

Few Refueling Stations

Higher Cost Vehicle

Indian buses generally use 140-160 horsepower engines.

Natural gas can be used in engines in a liquefied compressed gas (LNG).

In order to liquefy it at atmospheric pressure, it is necessary to bring it to a temperature of ‐162 °C.

As a result it is used mainly in the form of Compressed Natural gas (CNG)

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Forms of Natural gas Storage


CNG tanks are regulated to be steel and no composite material is allowed.

A brand new, good quality CNG kit with cylinder costs around 32,000 rupees or $6,400,

while a substandard locally-made welded version is half the amount.

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CNG tanks

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CNG refueling stations using Tulsa Gas technologies equipment.

The India Supreme Court has mandated that at least 90 refueling stations be made available.

Taxi cab drivers and rickshaw drivers fill at 68 “daughter stations.”

Natural gas buses are filled at 3 “mother stations.”

The methane content for compressed natural gas is 88 percent.

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Refueling:

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Uneven distribution of CNG stations

Inadequate pressure in daughter stations

Overrunning of compressors

Non‐availability of continuous power supply

Shortage of trained manpower

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PROBLEMS WITH CNG DISPENSING STATIONS

CNG Induction Techniques

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SI Combustion technology

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Gasoline Car Bi‐Fuel Conversion

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The Cylinder

The Vapor Bag

The High Pressure Pipe

The Refueling Valve

The Pressure Regulator

The Gas‐Air Mixer

The Petrol‐Solenoid Valve

The Selector Switch

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What does the Conversion kit comprise of ?


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Typical Gas Conversion

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Typical Gas regulator

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Typical Gas & Petrol Solenoid


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Various Design of gas mixers

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Fuel Mode Switch


Dedicated CNG Conversion of Diesel Engines

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•Replacing injector by Spark plug

•Machining the piston to decrease CR •Gas Conversion Kit installed

Only two Indian chassis manufacturers exist--TATA and Ashok Leyland.

Natural gas buses are using stoichometric Cummins engines.

private operators are installing conversion kits. Nugas is the certified company for CNG bus conversions.

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Transit buses


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• Stoichiometric engines (=1), in other words, the air fuel ratio is exactly the theoretical required for combustion

• Lean mixture engines (normally = 1.4 )

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Tuning up gas engines:


The best gas powered engines achieve a level of efficiency in the order of 36 ‐ 37%

Which is above petrol engines

Below modern diesel engines

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Efficiency of CNG Engines

Safety with CNG

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Natural Gas

Mainly methane(CH4)

also contains heavier gaseous hydrocarbons such as ethane (C2H6), propane (C3H8) and butane (C4H10), as well as other sulphur containing gases, in varying amounts

exact composition of natural gas varies between gas fields.

What is natural gas?


Composition

component %

Methane(CH4) 80-95

Ethane(C2H6) 5-15

Propane(C3H8) and Butane(C4H10) <5

It is found in oil fields and natural gas fields, and in coal beds

The largest two natural gas fields are probably South Pars Gas Field in Iran and Urengoy gas field in Russia, with reserves on the order of 1013 m³

Gas produced from oil wells is called casinghead gas or associated gas

Sources of natural gas


It can be stored in two forms:

Liquefied natural gas (LNG) and compressed natural gas (CNG)

Storage

Large‐scale use since 1960’s

Some 3,500,000 CNG vehicles now in operation worldwide

Mostly in Italy, Argentina, Brazil, Pakistan, etc. as lower cost fuel

Growing rapidly for transit operations in Europe as lower emission fuel

Some 7,500 fill stations

CNG Fuel


Typically stored at 3,600 psi at 70ºF

If ambient temperature goes up or down, pressure also

correspondingly goes up or down

CNG Fuel – Temperature Effects

During filling, gas heats up as it compresses in the tanks

Typically, stations only fill to service pressure of 3,600 psi

End up with 3,600 psi at some elevated temperature (say 100ºF) in the tanks

As gas cools to ambient (say 70ºF), pressure of gas decreases End result is less gas ‐ instead of having a fill of 3,600 psi at 70ºF, one has say 3,400 psi at 70ºF

CNG Fuel – Filling


Tanks can be slowly filled to allow heat to dissipate

Tanks can be pressured beyond service pressure, i.e. fill so that one gets higher pressure at a higher temperature, thus cooling to 3,600 psi at 70ºF

Tanks actually designed to be filled up to 1.25 times service pressure (all qualification testing done at 1.25 times)

To prevent underfills

4 basic types of tank designs

which design to use depends on need to reduce weight and how much can pay

All designs have equivalent safety, as all meet requirements of same standards

Design type can also determine how a tank may be handled, and how it may be filled

Fuel Tank Technologies


Type 1 ‐ All metal (aluminum or steel)

Cheap but heavy

Type 2 ‐ Metal liner reinforced by composite wrap (glass or carbon fiber) around middle (“hoop wrapped”)

Liner takes 50% and composite takes 50% of the stress caused by internal pressurization

Less heavy, but more cost

Type 1 & Type 2 Tank Designs

Metal liner reinforced by composite wrap

around entire tank (“full wrapped”)

Liner takes small amount of the stress

Light‐weight, but expensive

Type 3 Tank Design


Plastic gas‐tight liner reinforced by composite

wrap around entire tank (“full wrapped”) Entire strength of tank is composite reinforcement

Light‐weight, but expensive

Type 4 Tank Design

The octane rating for CNG is higher than that for gasoline; in a dedicated engine

a CNG vehicle’s power, acceleration, and cruise speed can be

greater than that of a gasoline‐powered vehicle. In addition, due to the cleaner burning characteristics of

natural gas, CNG vehicle engines can run more efficiently than a

gasoline powered vehicle, CNG engines are also generally less noisy than diesel

engines.

CNG performance


CNG has a narrow flammability range, making it an inherently safe fuel.

It is non‐toxic

CNG also disperses rapidly, minimizing ignition risk relative to gasoline

However, leaks indoor may form flammable mixture in the vicinity of ignition source

Safety

Reductions in carbon monoxide emissions of 90 to 97 percent, and reductions in carbon dioxide emissions

of 25 percent.

Reductions in nitrogen oxide emissions of 35 to 60 percent.

Potential reductions in nonmethane hydrocarbon emissions of 50 to 75 percent.

Fewer toxic and carcinogenic pollutants, and little to no particulate matter produced.

Emissions


Proper training is required for all maintenance personnel working on CNG vehicles

The oil in a CNG vehicle does not need to be changed

as frequently because CNG burns more cleanly than gasoline, producing less deposits in the oil.

Maintenance

Liquefied natural gas or LNG is natural gas that has been processed to remove helium, or impurities such as water, and heavy hydrocarbons and then condensed into a liquid at almost atmospheric pressure by cooling it to approximately ‐163 degrees Celsius

LNG is about 1/614th the volume of natural gas at standard temperature and pressure (STP)

Much more cost‐efficient to transport

LNG fuel


Producing LNG by liquefaction

The raw feed gas supply arriving from a producing gas field must be clean and dry before liquefaction can take place

It is scrubbed of entrained hydrocarbon liquids and dirt

Treated to remove hydrogen sulphide and carbon dioxide

Gas is cooled to allowed water to get condensed

Preliminary processes


Then it is further dehydrated to remove even small amounts of water.

If mercury is present then it is also removed at this stage.

Then the gas is filtered to ensure only methane and traces of other hydrocarbons are present.

Liquefaction takes place through cooling of the gas using heat exchangers. In these vessels, gas circulating through aluminum tube coils is exposed to a compressed hydrocarbon‐nitrogen refrigerant.

Heat transfer is accomplished as the refrigerant vaporizes, cooling the gas in the tubes before it returns to the compressor.

The liquefied natural gas is pumped to an insulated storage tank where it remains until it can be loaded onto a tanker.

Liquefaction


LNG offers energy density comparable to gasoline or diesel.

But its high cost of production and need of cryogenic temperatures to store it has prevented its widespread use.

Natural gas fed into LNG plant is treated to remove water, hydrogen sulphide, carbon dioxide and other compounds which freeze at low temperatures.

Basic facts on LNG

LNG above‐ground tanks are mainly of double‐wall, high‐nickel steel construction with extremely efficient insulation between the walls

Large tanks are low aspect ratio (height to width) and cylindrical in design with a domed roof.

Storage pressures are very low, less than 5psig.

Storage


LNG Storage tank

Pipeline system


Smaller quantities, 70,000 gallons and less, are stored in horizontal or vertical, vacuum‐jacketed, pressure vessels.

These tanks may be at pressures any where from less than 5 psig to over 250 psig

LNG must be maintained cold (at least below ‐117°F) to remain a liquid, independent of pressure.

There are no discernible differences in LNG vehicle performance, operation, and utility when compared with

diesel

The high ignition quality of LNG is similar to that of diesel, providing for similar durability and engine life overall.

LNG performance


A LNG vehicle parked indoors and unmoved for a week or more will vent a flammable gas mixture that could catch fire in the vicinity of an ignition source.

refueling vehicles with LNG requires training because of the fuel’s ultra low temperature.

It can cause frostbite if it contacts skin.

Safety

Production of half particulate matter of average diesel vehicles.

Can significantly reduce carbon monoxide emissions.

Reductions of nitrogen oxide and volatile organic hydrocarbon emissions by 50 percent or more.

Potential reductions in carbon dioxide emissions of 25 percent depending on the source of the natural gas.

Drastic reductions in toxic and carcinogenic pollutants.

Emissions


LNG’s cleaner burning characteristics can result in longer engine life and reduced maintenance costs.

Use of LNG eliminates the periodic tank inspections

Because of the fuel’s below freezing temperatures,

only trained personnel should maintain LNG vehicles.

Maintenance

CNG emissions are compared with diesel and B20 ( diesel blend with vegetable oil)

THC, NOx, and PM emissions of CNG engine are significantly lower than diesel, with a reduction of 67%, 98% and 96% respectively.

No significant reduction in CO is observed.

Exhaust emissions


Carbonyl compounds Formaldehyde is most abundant compared to other carbonyl compounds

in the exhaust emissions.

CNG emits 95% lower formaldehyde with respect to diesel fuel.

PAHs and nitro PAHs Use of CNG results in significant decrease in emissions: a reduction of, at least, 98% and 88% was observed for PAHs associated to PM and vapor phase.

Unregulated emissions


Unregulated emissions

PAHs associated with particulate matter

PAHs associated with vapour phase


Carbonyl compounds

There are two types of CNG refueling systems Slow-fill: In slow fill systems, several vehicles are

connected to the output of the compressor at one time. These vehicles are then refilled over several hours of compressor operation. Slow fill is considered practical only for vehicles of single fleet.

Fast-fill:In fast systems, enough CNG is stored so that several vehicles can be refueled one after the other, just like refueling from a single gasoline dispenser

Compressed Natural Gas: Storage and Dispensing


Compressor

Storage

Piping

Dispensers

Basic Elements of a Fast‐Fill CNG Refueling System

• Control system • Leak detection system • Fire suppression system • Lightning protection

Reciprocating compressor

Multistage (usually four stages)

Gas is compressed from 35 kPa to as high as 31 MPa.

Compressors


Cylinders are made according to either U.S. DOT or ASME pressure vessel code.

Cylinders are made only from carbon steel.

Cylinders are placed on a concrete slab without enclosure.

CNG storage cylinders can also be placed in underground vaults but usually not preferred.

Storage

Piping must be compatible with natural gas and capable of four times the rated service pressure without failure.

Stainless steel seamless tubing is commonly used.

Threaded and compression‐type fittings that do not use gaskets or sealants are also allowed.

Piping


Dispensers are used to direct CNG from the storage system into the vehicle (only used for fast‐fill systems).

They typically incorporate a sort of on‐off switch activated by removal of the refueling nozzle and a meter to measure the amount of CNG dispensed.

CNG dispensers are usually made of stainless steel CNG dispenser nozzles are made from aluminum and stainless steel

Dispensers

Control systems are of two types‐mechanically controlled and completely computer controlled.

Computer controlled systems offers flexibility not possible with mechanical systems.

Computer controlled systems provide functions such as accounting of the amount of the fuel dispensed into the vehicle and billing functions.

Control Systems


Leak detection system usually use methane detectors.

Methane detectors are usually placed above the ground level at points where the released gas is likely to pass as methane rises when released.

Most methane detectors are set to alarm when 20% lower flammability limit (LFL) of methane in air is detected (about 1% methane in air).

Some refueling facilities use two‐stage approach to methane detection and alarm.First alarm is sounded when 20% LFL is detected and shutdown of refueling system is initiated when 40% LFL is reached.

Leak Detection Systems

These systems are dry chemical using infrared detectors

A puff test should be normally carried out after installation of fire suppression systems.

Puff tests not only shows the coverage that can be obtained but also tests the components of the fire protection systems.

Fire Suppression Systems


CNG refueling systems located outdoor should take lightning protection into account.

Lightning strikes can damage the refueling system and cause fuel release and/or fires

Lightning Protection

Fuel Quality and Effect on Exhaust Emission

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Diesel

* Cetane number increased from 42 to 45 in 1995 and further increased to 48. Need for further increase in 2005 to be assessed.

* Distillation limits became stringent from year 2000 in view of no clear trends further control of T90/T95 to be examined.

* Sulphur content reduced from 1% to 0.5% in the year 1996 and further reduced to 0.25% in the year 2000. Likely to be 0.05 in 2005 but needs to be linked with engine technology.

* Benefits of multifunctional additives being examined. Likely benefits in terms of fuel economy and emission reduction.

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Fuel Quality Trends in India

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Gasoline Quality And Emissions

Note: (+) Desirable; (-) Undesirable; Blank – NO significant effect


Additives are rapid, economic and easy means for

‐ Improving fuel performance properties.

‐ Control fuel quality during production, distribution and storage.

‐ Control emissions.

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ROLE of Fuel Additives

Gasoline stability problem

‐ inclusion of cracked stocks in gasoline

‐ gasoline deterioration during storage

Results in

‐ formation of gum and sediments in storage.

‐ Gummy deposits in engine intake system.

‐ Engine performance deterioration

‐ Loss of fuel economy.

‐ Increase in emission.

‐ Poor startability.

• Solution of problem

‐ Refinery processing

‐ chemical treatment of gasoline with additives

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MFA In Gasoline


INTERNATIONAL SCENARIO

U.S.A

* As per clean air act gasoline must contain certified additives.

EUROPE

* Growing use of deposit control additives (DCA)

ASIA AND AUSTRALIA

* Japan, Singapore, S. Korea, New Zealand, Australia‐USE guidelines from US EPA

* In Thailand DCA regulation system is in place

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MFA In Gasoline

Unleaded gasoline introduced in four metros from APR.1995 and all over the country from 2000.

Total lead phase out in Delhi from 1.9.98

Volatility limits implemented from 1995 further review for evaporative emission control.

Use of multifunctional additives in gasoline recommended in 1997

Use of oxygenates like MTBE started in some refineries for producing unleaded gasoline

Sulphur limit to be made stringent from year 2000 demand for further control from 2005

Benzene also to be restricted to 5% max. from 2000 demand for reduction upto 1%

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Fuel Quality Trends in India Related to Emissions


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Impact of Diesel Properties on Emissions

Note: (+) Desirable; (-) Undesirable; Blank – NO significant effect

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Fuel Sulphur-PM Emission

Sulphur 0.25%

Sulphur 0.05%

Reduction

Contribution of sulphate & H20 -Absolute Emission g/kwh

0.056 0.011 0.045

% of Euro 1 limit (0.36 g/kwh)

16 3 13

% of Euro 2 limit (0.15 g/kwh)

37 7 30


Main conclusion that flows logically from the overview presented is that India along with most of the world will have to switch to alternative fuels for automobiles, sooner or later, the sooner the better for our own environment.

There is a need for all the players in the industry to look ahead and formulate a strategy to make this switch smooth and timely.

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Conclusion

lecture 12 compressed natural gas revised - iit kanpur 15-17... · · 2016-09-09alternative fuel...

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