232
Alternative Fuels for Transportation
transportation of NG is through pipelines from the processing plant to local
distribution companies. The distribution of NG to refueling stations consists
of high-pressure NG from a transmission pipeline being depressurized and
delivered (MacLeana and Lave 2003).
Natural gas is used in automobiles; hence it is necessary to store the NG
in compact form in order to reduce the weight of the vehicle. There are four
types of vehicles in the market: dedicated fuel systems, dual-fuel modes,
after-market conversions, and hybrid electric systems. Storage systems for
these of vehicles are classified into three types: liquefied gas, compressed
gas, and adsorbed gas.
Liquefied gas systems are generally used for storing NG for long hauling
vehicles like trains, buses, and trucks. For passenger cars, NG is stored in cylinders in compressed form. Natural gas is compressed to about 200 bar and is
stored in cylinders of capacity ranging from 20 to 100 liters. However, regulations require that cylinders to be capable of handling pressures of 600 bar
in case of accidental exposure to fire. Cylindrical and conformable shaped
storage tanks are used for storing the CNG. Conformable shaped tanks are
preferred for on board storage of CNG. However, high-strength pressure
vessels require uniform internal stresses. The low-energy density of CNG
also causes storage problems onboard vehicles, along with the issue of heavy
pressurized storage cylinders necessary to store the gaseous fuel. Cylinders
are made of steel, high-strength aluminum, aluminum wound with fiberglass, or resin composites of glass or carbon fiber.
Adsorbent NG is the latest technology to store natural gas. Activated charcoal
or metallic oxides are used as storage materials. The advantages of adsorbent
technologies include mass storage capacity and use of lower pressures (30–40
bar). This reduces the costs associated with compression and storage. Uniform
stresses are a natural consequence of cylindrical or spherical-shaped tanks, but
achieving uniform stress levels for conformable-shaped tanks requires specialized designs. Among the various options to store natural gas, storing NG
in compressed gas cylinders is preferred by the automotive industry because
of its space optimization in vehicles and to use the existing infrastructure.
8.4 CNG Distribution
There are two types of distribution systems: service stations where distribution is centralized and domestic compressors where consumers can refuel
vehicles in their own garage.
Fuel refueling systems consist of compressor, storage vessel, and dispenser.
Compressors are used to boost the gas pressure in the distribution line to
about 330 bar. Unlike gasoline stations, NG must be stored above ground.
Most of the CNG refueling systems include dryers that remove water vapor,
Alternative Fuels for Transportation
transportation of NG is through pipelines from the processing plant to local
distribution companies. The distribution of NG to refueling stations consists
of high-pressure NG from a transmission pipeline being depressurized and
delivered (MacLeana and Lave 2003).
Natural gas is used in automobiles; hence it is necessary to store the NG
in compact form in order to reduce the weight of the vehicle. There are four
types of vehicles in the market: dedicated fuel systems, dual-fuel modes,
after-market conversions, and hybrid electric systems. Storage systems for
these of vehicles are classified into three types: liquefied gas, compressed
gas, and adsorbed gas.
Liquefied gas systems are generally used for storing NG for long hauling
vehicles like trains, buses, and trucks. For passenger cars, NG is stored in cylinders in compressed form. Natural gas is compressed to about 200 bar and is
stored in cylinders of capacity ranging from 20 to 100 liters. However, regulations require that cylinders to be capable of handling pressures of 600 bar
in case of accidental exposure to fire. Cylindrical and conformable shaped
storage tanks are used for storing the CNG. Conformable shaped tanks are
preferred for on board storage of CNG. However, high-strength pressure
vessels require uniform internal stresses. The low-energy density of CNG
also causes storage problems onboard vehicles, along with the issue of heavy
pressurized storage cylinders necessary to store the gaseous fuel. Cylinders
are made of steel, high-strength aluminum, aluminum wound with fiberglass, or resin composites of glass or carbon fiber.
Adsorbent NG is the latest technology to store natural gas. Activated charcoal
or metallic oxides are used as storage materials. The advantages of adsorbent
technologies include mass storage capacity and use of lower pressures (30–40
bar). This reduces the costs associated with compression and storage. Uniform
stresses are a natural consequence of cylindrical or spherical-shaped tanks, but
achieving uniform stress levels for conformable-shaped tanks requires specialized designs. Among the various options to store natural gas, storing NG
in compressed gas cylinders is preferred by the automotive industry because
of its space optimization in vehicles and to use the existing infrastructure.
8.4 CNG Distribution
There are two types of distribution systems: service stations where distribution is centralized and domestic compressors where consumers can refuel
vehicles in their own garage.
Fuel refueling systems consist of compressor, storage vessel, and dispenser.
Compressors are used to boost the gas pressure in the distribution line to
about 330 bar. Unlike gasoline stations, NG must be stored above ground.
Most of the CNG refueling systems include dryers that remove water vapor,