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126 Cards in this Set
- Front
- Back
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What is the composition of natural gas? |
Mixture of hydrocarbons: methane with lesser amounts of ethane, propane, butane, and other hydrocarbons. |
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Once natural gas has been extracted from the ground, it is processed. What components are removed when it is processed? |
Ethane, propane, and butane are removed, which are valuable in their own right and serve other commercial purposes. |
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What are NGLs? |
NGL = Natural Gas Liquids, which includes ethane, propane, and butane. |
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What does pipeline quality gas refer to? |
Natural gas after it has been processed and meets the quality and standards for long distance transport through pipelines. |
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What is the typical amount of methane in pipeline quality natural gas? |
75 - 98% Methane |
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What is biogas? |
Natural gas produced by the decomposition of organic materials. Large landfills, sewage treatment plants and farms. |
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How is natural gas distributed? |
After processing natural gas is compressed and transported in high-pressure pipeline systems that carry it from production areas to urban areas. From there, low pressure pipeline systems, operated by utilities distribute the gas. |
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Pipeline gas is adequate for boilers, furnaces, and stoves, but not for vehicles. What other elements have to be removed from the gas for vehicle use? |
-Water, which is naturally occuring in the gas. -Oil, which typically comes from compressor lubricating oil while it is being compressed. -Particles, which typically come from the desiccant in the dryer or from the tubing or piping as a result of facility construction activities. |
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Why is water removed from natural gas in the CNG facility? And how is it removed? |
Water is removed to avoid icing and corrosion caused by moisture. It is removed by the gas dryer or dryer. |
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Why is oil in natural gas a problem, and how do you remove oil from natural gas? |
Even small amounts of oil can interfere with CNG vehicle engines. -One way to significantly reduce oil contamination is to use compressors that do not require oil to lubricate pistons. -However, it is important to monitor compressor seals for excessive wear, or lubricating oil from the crankshaft can find its way into the compressor cylinders, and contaminate the CNG. -For compressors that do lubricate the compressor pistons with oil, contamination can be minimized, but not eliminated by using synthetic oil. In this case any small contamination can be elminated by using coalescing filters. These filters must be maintained regularly. |
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What causes particles to be present in the CNG? |
Particles are a result of the degradation of the desiccant in the dryer. Particles may also be in tubing or piping from construction activities. This is remedied using particle filters. |
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Does natural gas smell? |
-No natural gas is odorless. Sulfur compounds called "mercaptans" are added as a safety measure to aid in detecting leaks. -However, natural gas leaks may not always be detectable by smell. In new steel pipe or certain types fresh desiccant can absorb mercaptan compounds. |
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What are mercaptans? |
Natural gas is odorless. Sulfur compounds called "mercaptans" are added as a safety measure to aid in detecting leaks. |
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Why is natural gas compressed for vehicle use? |
-For practical use, natural gas must be compressed to high pressures so that a substantial amount of gas can be stored in a reasonably small space. -In the U.S. CNG is pressurized to 3,600 psi within vehicles. -In older vehicles it may be pressurized to only 3,000 psi. |
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To what psi is CNG pressurized to in vehicles? |
CNG is pressurized to 3,600 psig in vehicles. |
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How does CNG flow from the fueling facility into the vehicle? |
-CNG flows from the fueling facility into the vehicle because of the difference in pressure. -The flow of gas is only possible into the vehicle cylinder. The flow of gas from the vehicle towards the facility or storage vessel is not possible because it is stopped by a "check valve". -To maintain a reasonably rapid flow rate between the fueling facility and the vehicle, CNG fueling facilities typically compress natural gas to between 4,200 and 4,500 psig. |
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What are the dangerous created by CNG? |
-Flammability and high pressure. -Natural gas is flammable. -CNG is pressurized from 3,600 to 4,500 psi, which causes the following hazards: -Any fittings, valves or other high pressure components that are blown off could cause fatal injuries if they strike a person. -Small particles caught up in a high-velocity gas stream could cause injury if they strike a person. -The rupture of a pressure vessel, such as a vehicle fuel cylinder, can produce enormous forces similar to an explosion without any ignition of the gas. -The high intensity noise generated by a leak of high pressure gas could damage hearing. |
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How much natural gas is in gasoline gallon equivalent? |
It takes 5.66 pounds of natural gas to equal one gasoline gallon equivalent. |
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How much natural gas is in diesel gallon equivalent? |
-Diesel has 14% more energy than gasoline. -Therefore, it take more natural gas to equal a diesel gallon equivalent than a gasoline gallon equivalent. -It takes 6.43 pounds of natural gas to equal one diesel gallon equivalent. |
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What are the typical CNG vehicle cylinder capacities? |
-Passenger vehicle = 5-8 GGEs -Pickup trucks = 15-20 GGEs -Medium duty trucks = 30-100 GGEs -Heavy duty trucks = 100-150 GGEs -Larger vehicles will have multiple cylinders |
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How does the CNG fueling system know to stop fueling? |
Sensors monitoring the pressure and flow rate during the dispensing operation will automatically stop the flow of gas when the vehicle fuel cylinder reached a designated pressure or the flow rate from the dispenser to the vehicle has slowed below a minimum flow rate. |
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What are the 3 types of CNG Fueling Systems? |
1. Time-fill 2. Buffer-fill 3. Cascade fill |
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How does a time-fill fueling system work? |
-Time-fill is slow fueling over several hours. -Driver connects the nozzles which causes a change in pressure indicating the vehicle is ready to be fueled. -At which point the compressor may then: -Start immediately. -Start at a specific time when all or most of the vehicles in the fleet have returned to base and are ready to be fueled; or -Start at a programmed time to take advantage of lower nighttime electricity costs. -As soon as the compressor starts, gas begins to flow directly from the compressor into all the vehicle fuel cylinders connected to the time-fill system. -All of the vehicles are fueled simultaneously. -Vehicles with lower pressure in their cylinders will fuel faster than those with higher pressure because of the greater difference in pressure. -As the fueling process continues, the pressure in all of the vehicles will be approximately equal and from that point, all of the vehicles will fuel at a approximately the same rate until all are full. -When all the vehicles are full, then the compressor will automatically turn off. |
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How is the amounted of gas dispensed measured in a time-fill system? |
-The total amount of gas used is measured by the utility meter that supplies the compressor. -The amount of gas dispensed to each vehicle is not measured. -Because there is no cost-effective way to allocate the cost of fuel among individual vehicles, time-fill facilities are usually limited to fleets owned by a single company. |
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What is a "Check Valve"? |
-It is a flow control valve in a piping or tubing system that opens or closes in response to the direction of flow of gas. A check valve only allows flow in one direction. -A check valve allows the flow of gas into a vehicle, but does not allow the gas to flow out of the vehicle. |
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What is a time-fill with storage or buffered time-fill? |
It is a time-fill system, but with storage vessels that will allow the ability to fuel one or two vehicles quickly on an infrequent basis. |
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What is a "Buffered Fast-Fill Fueling System"? |
-In buffered fueling system design, one or more large compressors supply gas to vehicles as needed. -As with time-fill, the gas flows directly from the compressor to the vehicle, but vehicles or fueled one or two vehicles at a time and compressor capacity is much greater than time-fill, so vehicle can be fueled in 5 to 10 minutes. -System gets its name from the buffer vessel which is between the compressor and the vehicle. -Buffer vessel provides a place for the gas to go during short intervals between vehicles. -Without the buffer the compressor would stop when the nozzle is disconnected from the vehicle. Without the buffer, to restart the compressor could take 30 sec. between vehicles. |
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When are Buffer Fueling Systems, the appropriate system to use? |
When there are lengthy periods during each day when numerous vehicles with large capacity fuel cylinders need to be fueled, like with a municipal transit facility. |
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When are Cascade Fueling Systems, the appropriate system to use? |
-Generally used when vehicles are expected to be fueled at irregular intervals throughout the day, with a few peak periods when several vehicles may require fuel at the same time. -Cascade systems are the most versatile type of CNG sytem. -Are appropriate where there are multiple users, including general public. -The fueling strategy is to minimize the number of times the compressor is started and stopped by storing enough CNG to fuel vehicles during low activity periods without starting the compressor. -During peak periods the compressor and the vessels will be used to together to minimize the time to fuel vehicles. |
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How does a Casade Fueling System work? |
-The term "cascade" refers to the use of multiple storage vessels to supply gas in different pressure ranges rather than a single larger capacity storage vessel. -A typical facility will have three storage vessels designated as low-pressure, mid-pressure, and high-pressure vessels. -All of the vessels will be filled to the same pressure about 4,200 to 4,500 psig, whenever the compressor has time to fill them. -The low, mid, and high pressure designation has to do with the order in which the storage vessel are used when the vehicle is fueled. A facility may have more than the three, but all will be assigned to one of the three pressure categories. -When a vehicle begins to fuel it starts with the low-pressure vessel. -As the vehicle continues to fuel, the low pressure vessel starts to empty and the vehicle pressure begins to rise, therefore fueling starts to slow down. -When the flow rate of the gas slows down to a programmed level, the dispenser automatically operates valves to stop the gas flow from the low pressure vessel and start the flow from the mid-pressure vessels. -The same process repeats until the system switches to the high-pressure vessel, which completes the fueling of the vehicle cylinder. -If the high-pressure vessel does not have enough gas to complete filling the vehicle cylinder, then the compressor starts (if it is not already started) bypassing the vessel and directly fills the vehicle until fueling is complete. -The sensors, valves, and control system that manage the flow of fuel into the vehicle fuel cylinder are known as the "sequential fueling system". -By using three storage vessels that operate in different pressure ranges, the difference in pressure between the vessel and the vehicle can be kept as large as possible. This maximizes the rate of gas flow and minimizes the time require to fuel the vehicle. -Cascade fueling systems use dispensers that look and operate like traditional gasoline dispensers. -Each dispenser has one or two nozzles. -The fuel dispensed is measured. -Usually includes fuel tracking/ or fuel payment system. |
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When are combination fueling the most appropriate systems to use? |
-In situations when they have a number of vehicles that can be slow-filled at night, but that they also have vehicles that require immediate fueling during the day. -In combo systems the facility will have major components of both types of facilities. -The two facilities will typically share a gas supply, dryer, and one or more compressors. -However, downstream of the compressor, all of the components of both time and fast fill will be present. |
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Explain the concept of achieving a "Full Fill" with a time-fill system. |
-The issue is that vehicle fuel cylinders are designed to hold a certain amount of pressure, but the pressure of gas inside the cylinder depends on the ambient temperature. -If the temperature of the gas inside the cylinder increases, the pressure will increase. -If the temperature of the gas inside the cylinder decreases, the pressure will decrease. -In normal use, vehicles and their cylinders will be subject to a wide range of temperatures, so the pressure of the gas inside the cylinder will vary along with the temperature. -A vehicle cylinder is considered full when it is at 3,600 psig (3000 some models) when it is at 70 degrees F. -Cylinder are made to within stand 125% of the filling capacity. -If ambient temperatures or lower than 70 degress, you fill the vehicle with less pressure than 3,600 psig. -If ambient temperatures are higher than 70 degrees, you fill the vehicle with more pressure than 3,600 psig. -There is a table which shows the pressures depending on the temperature. -The fueling system makes calculations that take into account the heat of compression this are automatically made to determine the pressure to which the vehicle cylinder must be filled. -If |
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Explain the concept of achieving a "Full Fill" with a buffer or cascade fueling system. |
-The hotter the temperature of the gas, the more pressure in the vehicle cylinder. -As is the case of pressure being created through the ambient temperature, the process of fueling a vehicle quickly also heats up the gas, and creates additional pressure. This is called the "heat of compression". -The fueling system makes calculations that take into account the heat of compression and the ambient temperature are automatically made to determine the pressure to which the vehicle cylinder must be filled. |
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How do frost crystals form on CNG nozzles? |
-The temperature of gas rises as pressure increases and drops as pressure decreases. -The more rapid the drop in pressure, the more dramatic the cooling effect. -In CNG fueling, rapid decompression happens at the connection of the fueling nozzle, especially when the gas begins to flow and the pressure difference between the gas coming from through the nozzle and the gas in the vehicle is the greatest. -The rapid decompression of the gas being transferred to the vehicle may cool the nozzle and vehicle fuel receptacle to well below zero. -If sufficient water vapor is present in the atmosphere, frost may form on the outside of the connection point between the nozzle and the vehicle receptacle, even in summer months. -Frost on the outside of the fueling nozzle may be a nuisance, but it does not pose any serious operational problems or safety hazards. |
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What is the LDC? |
-Local Distribution Company, which is the local natural gas company. |
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What laws regulate the LDC (local distribution company)? |
The Federal Department of Transportation |
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What is the MSA? |
-Meter Set Assembly, which is the utility meter. This equipment pertains to the gas utility. |
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Which laws regulate downstream of the MSA, the CNG facility side of the meter? |
By state and local codes. |
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What is a pressure regulator and its purpose? |
Depending on the inlet pressure from the utility, it may necessary to install a pressure regulator downstream of the MSA. The role of the pressure regulator is to maintain the incoming gas pressure below the design limits of the CNG fueling system. |
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What is a Booster Compressor and what is its function? |
If the inlet pressure from the utility is lower that what is necessary, a Booster Compressor will rapidly increase the pressure of a large of volume of gas, which will improve the primary compressor's efficiency and may lower the number of compression stages necessary to acheive the required discharge pressure. A booster compressor is usually installed before the dryer. |
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What is the function of the gas dryer? |
-Natural gas usually has a certain amount of moisture. The dryer serves to remove the moisture. Liquid water can damage the compressor and cause corrosion in the fueling system. -Dryers are usually placed before the compressor, because it prevents the moisture from condensing inside the compressor cylinders where it can cause corrosion and damage. -Gas entering the dryer should have approximately 7 pounds of water per million cubic feet (MMcf) of gas. -Gas leaving the dryer should have no more than 0.5 pound of water MMcf of gas. |
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What is Desiccant? |
-Desiccant dryers contain a granular material made of alumino-silicate compounds commonly referred to as molecular sieves. -Molecular sieves are the preferred method for reducing moisture in CNG facilities. -As the desiccant adsorbs water vapor, it will eventually reach a point where its ability |
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What is Odorant and what is it purpose? |
-Natural gas is odorless. To aid in leak detection, small amounts of mercaptan compounds are added to natural gas to give its characteristic smell. -However, when the odorized gas passes through new steel pipe or certain types of fresh desiccant , the mercaptan compounds can be unintentionally removed from the gas. This effect wears off and the odor returns after the new pipe has been worn in. |
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What is Pre and Post Dryer Filtration, and what are their purpose? |
-Dryer systems typically include a coalescing filter upstream of the dryer to remove any particles or small slugs of water that may be present in the incoming gas. -The desiccant inside the dryer can introduce particles into the gas stream, so a fine particle filter is usually installed downstream of the dryer to protect the quality of the gas. |
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What is the Dew Point Monitor, and what is its function? |
-To prevent problems in the CNG system and in CNG vehicles should be below -20 degrees F. -The Dew Point Meter measures the moisture content of the natural gas as it leaves the dryer and displays the result as the temperature at which any remaining water vapor in the gas would condense into water droplets. |
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What does the Compressor Package or Compressor Skid contain? |
-compressor -motor to drive the compressor -lubrication system for the compressor -cooling system to reduce the temperature of the gas during and after compression. -blow-down system to relieve pressure in the compressor cylinders between periods of operation. -in colder climates, a heating system to keep the compressor oil and the compressor itself warm. -filters to remove particulates, water, and oil from the gas. -piping and tubing systems to carry the gas -valves to control the flow of gas -instruments to measure various aspects of the operation of the compressor, cooling system and lubrication system -control system to monitor and coordinate the operation of all these different components -skid or framework on which to securely mount all these different components. |
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What are the two types of compressors? |
-Reciprocating Compressors: The vast majority of compressors are reciprocating compressors. Reciprocating compressors operate on the smae basic principle as a standard shop air compressor that have a piston inside a cylinder chamber. A rotating crankshaft, usually driven by an electric motor, moves the piston up and down inside the cylinder chamber. -Hydrallic Compressors: |
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Function of compressor lubrication? |
Compressors have many moving parts that fit together, so reducing friction is important. There are two areas of concern: the crankshaft and rod bearing in the crankcase, and the pistons moving back and forth in the cylinders. |
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How do non-lubricated compressors reduce friction? |
-They incorporate low friction materials, such as Teflon, into the piston rings so that oil-based lubrication between the rings and the cylinder walls is not required. |
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What is the function of Compressor Cooling System? |
-The cooling system is essential component of the compressor to dissipate the large quantity of heat generated. -Cooling systems are usually gas-to-air heat exchangers that operate much like an automobile raditor. -The compressed gas flows through tubing surrounded by cooling fins while a fan blows large amounts of air across the fins of the radiator. |
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What happens when a compressor shuts down? |
-The gas in the compression chambers is automatically exhausted into a low pressure tank, commonly called a blow-down tank. |
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What is the function of a compressor heater? |
-Compressor lubricating oil is a single viscosity il that may thicken significantly at low temperatures. -If even occasional below freezing temperatures are expected, a crankcase oil heater is needed to keep the oil at the proper viscosity. |
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What is the PLC and what is its function? |
-Programmable Logic Controller -The PLC is the industrial computer that monitors and controls the operation of the various components of the CNG fueling system. -Pressure, temperature, liquid levels, ESS. |
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What is the Compressor Skid? |
-Compressor packages are typically mounted on a rugged steel frame or skid. -The compressor packages weighs from 5,000 to 50,000 and requires a substantial concrete base. |
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What is a Priority-Fill Panel and what is its function? |
-Is typically a metal cabinet containing flow control valves, check valves, backpressure regulators and other equipment required to control the flow of CNG from the compressor. |
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What is an Electronic Priority-Fill Panel? |
-They use sensors connected to the PLC to monitor the operation of the fueling system. |
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What are Breakaway Connectors and what are their function? |
-Breakaway connectors protect both dispensers and time-fill posts from damage if a vehicle drives off with the nozzle still connected to the vehicle fuel receptacle. -Breakaway connectors are designed to designed to disconnect and stop the flow gas. |
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What is the function of an Air Compressor in a CNG station? |
-Remotely operated valves used to control the flow of gas at numerous locations in a CNG fueling system is most often operated by compressed air or natural gas. -If air is used than an air compressor is required. |
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What does the Programmable Logic Controller (PLC) monitor and control? |
At the dryer -gas pressure -level of moisture -regeneration cycle of dryer At the compressor -pressure to verify proper operation -pressure in storage vessel to start and stop compressor -pressure in storage vessel to know when to switch between low, mid, and high pressure vessels -startup and shutdown sequence of compressor -temperature to verify if operating within programmed limits -level of compressor vibration -pressure of lubricating oil -level of lubricating oil in compressor -level of liquid in blow-down tank -level of methane detected by any methane sensor -pressure of gas flowing to vehicle fuel cylinders at time-fill and buffer-fill facilities to determine when to stop flow of gas -ambient temperature to provide temperate compensation fueling |
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What are Pressure Sensors? |
-Pressure sensors measure the operating pressures from numerous areas in the fueling system and send this info to the PLC. - When the pressure is outside the programmed limits it may start the compressor or shut down the compressor. Pressure sensors monitor pressure at the following points: -inlet gas pressure to the compressor -pressure between each compression stage -final discharge pressure from the compressor -pressure in the blow-down tank -pressure in the high pressure, mid pressure, and low pressure storage vessels -oil pressure in the compressor crankshaft lubrication system -pressure in the lines supplying gas to a vehicle being fueled |
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What are Temperature Sensors? |
-Temperature sensors measure operating temperature at several points including: -discharge temperature of the gas after each stage of compression -temperature of the gas after the final stage of compression -ambient temperature to determine the temperature compensated fill pressure for vehicle fueling -during the regeneration cycle of dryers, the temperature of the gas going into the desiccant, coming out of the desiccant and after the gas cooler -temperature of the oil in the compressor crankcase -temperature inside a shop-fabricated enclosure to control the ventilation fan or warn of an unusual condition |
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What are Methane Sensors? |
-Methane sensors are typically installed in a shop-fabricated compressor enclosure to detect natural gas. -The methane sensor is connected to the PLC, and will shutdown the compressor and activate the emergency shutdown system if the methane concentration exceeds the programmed limit, usually 20% of the lower explosive level. |
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What is Compressor Vibration Sensor? |
Vibration sensors are mounted in the compressor to warn of an unbalanced condition when the compressor is operating. |
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What is the purpose of a Dispenser Vibration Sensor? |
Dispensers are vulnerable to vehicle impacts. It the sensor is triggered, the emergency shutdown system, shuts down the gas. |
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What are Level Sensors? |
Liquid level sensors measure fluids in the CNG compressor package are at the appropriate levels at the following points: -Level of lubricating oil in the compressor crankcase -Level of liquid in the blow-down tank. |
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What is the purpose of Pressure Gauges? |
-In addition to pressure sensors connected to the PLC, mechanical pressure gauges are typically installed at a number of locations in a CNG fueling facility. -Mechanical guages are convenient to read and can help troubleshoot sensor readings by providing an indepdent measurement of the pressure. |
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What are Remotely Operated Valves? |
The PLC uses remotely operated valves to control the flow of CNG between various components, such as the compressor, storage vessels and vehicles being fueled. |
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How are Valves Operated by Electricity used in CNG systems? |
Valves that control the flow of natural gas are generally not operated directly by electricity. Instead, PLCs energize small low pressure valves operated by a solenoid to convert the electrical signal from the PLC into air or gas pressure that activates flow control valves. |
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What are Valves Operated by Natural Gas? |
If natural gas is used to operate flow control valves, a small pressure regulator is used to reduce the gas pressure from the compressor discharge pressure to approximately 80-125 psig. |
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What are Valves Operated by Instrument-Air Pressure? |
Compressor air valves operate the same way as natural gas valves, but they require a small air compressor. |
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How are Manually Operated Valves used in a CNG system? |
Manually operated valves are used in many places in a CNG fueling system to isolate various components, such as the storage vessels or the dispenser, from the fueling system so they can be serviced. Isolation valves are typically installed at the following locations: At all facilities: -immediately downstream of the MSA -at the gas inlet and outlet of the dryer -at the gas inlet and outlet of the compressor -as needed to isolate regularly serviced items, like filters -to isolate connection points intended for temporary use |
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What are Check Valves? |
-Check valves allow gas to flow through a tube or pipe in one direction only. -When the pressure on the upstream side of the valve is greater than the pressure on the downstream side, the valve opens and the gas is allowed to flow. -If the gas pressure on the downstream side of the valve is greater than on the upstream side, the valve remains closed and does not allow the gas to flow. |
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What is the purpose of Pressure Reducing Regulators? |
-Pressure reducing regulators lower the pressure in the gas tubing or piping downstream from the regulator. |
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What are Backpressure Regulators? |
Backpressure regulators maintain pressure in the tubing or piping upstream from the regulator. The backpressure regulator is a normally closed valve that opens only when the pressure upstream of the valve reaches the pressure setting of the regulator. |
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What is a PRV and what is its funtion? |
Pressure Relief Valve: PRVs are important pressure control devices that protect various components of the fueling system against exposure to pressures in excess of their maximum allowable working pressure. |
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What are Drain Valves? |
Drain valves are installed to remove liquids that may accumulate at the low point in various components of the CNG system. Drain valves are typically installed at the following locations: -coalescing and particle filters -storage vessels -blow-down tanks -compressor crankcase oil drains -dryer regeneration unit liquid collection tanks |
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What is the function of Bleed Valves? |
Manually operated bleed valves are used to safely release the pressure in a component of the fueling facility so maintenance tasks, such as changing filters or hoses, can be done safely. |
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What are ESDs and their function? |
Emergency Shutdown Device: Includes all the different components of the emergency shutdown system, which includes the following: -switches or sensing devices that trigger the operation of the other components -one of more remotely operated valves that stop the flow of natural gas to the compressor and the fueling positions -one or more electrical relays that de-energize electrical circuits in fuel dispensing and compressor areas -the programmable logic controller (PLC) that controls and operation of the compressor -visual and audio alarms to notify personnel -email and text message communication hardware to notify off-site fire service, service technician and facility management personnel who can immediately address the emergency situation |
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What are Emergency Stop Switches? |
Emergency Stop Switches are manually operated switches that trigger the process of shutting down the CNG fueling facility. |
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What are the primary factors to consider when designing a CNG facilility? |
-pressure, volume, and quality of the gas supply available from the utility -available electricity supply -choice of compressor drives -amount of usable space available to develop the facility -number and types of vehicles to be fueled -number of gasoline gallon equivalents (GGEs) or diesel gasoline gallon equivalents (DGEs) of natural gas to be dispensed on a daily basis -time available to fuel vehicles -number of vehicles to be fueled at the same time or within a short period of time -level of reliability needed for the facility -end user's expectations |
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What are the factors regarding pressure, volume and quality of gas supply in designing a CNG station? |
The amount of gas a utility can provide depends on a number of factors including: -size of the utility piping in the area -pressure of the gas at the location In addition to to pressure and volume it is important to obtain the following info from the gas utility: -composition of the gas that will be supplied to the facility -moisture content of the gas -whether propane/air peak shaving is used during high demand periods -rate schedule for the cost of the gas -whether an easement will be required to bring the gas line on site -who will pay the cost of connecting to the gas line, running the supply line to the property, and the meter assembly |
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What are the factors in the available electrical supply when designing a CNG system? |
-A typical electric motor to run a compressor requires a 480-volt, three phase, 60-hertz electrical supply. -Electric motors for CNG fueling facilities typically have current requirements ranging from 200 to 2,000 amps, depending on the number of compressors and the horsepower rating of each motor It is important to obtain the following info from the utility: -whether 480-volt, three phase, 60-hertz electrical power is available -the cost of any upgrades to provide adequate power to the site -whether the onsite power line will be aboveground or belowground -whether an easement is required to bring the power line to the site -the cost of electrical service, including peak demand charges, power factor charges and use charges |
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What is the typical problem with using an internal combustion engine fueled by natural gas or diesel or gasoline to drive a compressor? |
-Because more things can go wrong with an engine vs. a motor, reliability of the facility may suffer. -Maintenance costs for an engine-driven compressor will likely be higher than an electric motor. -Vibrations from the reciprocating engine may also interact with the vibrations from the compressor causing significant problems -Engines will require an air quality permit |
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What are the factors with space requirements when designing a CNG facility? |
-Requirements vary, but a typical CNG compressor compound requires about 3,200 f2. In addition setbacks need to be taken into account. |
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As the number of vehicles to be fueled simultaneously or within a short period of time increases, what else increases? |
-the amount of fuel to be supplied -the size of the compressor(s) -the capacity of storage vessels -the number of fueling positions |
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What are some measures that can be taken to increase the reliability of a CNG fueling facility? |
-Minimizing down time is usually achieved through redundancy in equipment -negociate a supply agreement with another CNG facility in the area to serve as backup -use two smaller compressors instead of one larger compressor, in case one breaks down -design system so a portable compressor system can easily be installed in an emergency -for compressors with electric motors, develop contingency plans for an extended power outage, consider a generator |
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What are the factors in relation to laying out the location of compressor-related equipment in a CNG facility? |
-setbacks, roads, buildings, railroads, and powerlines -components do not interfere with onsite traffic flow -distance from the gas supply to the compressor is minimized -high energy electrical controls, such as the service disconnects, transformers, breaker panel, motor controls and other devices that can generate arcs or sparks, are located outside the classified areas as much as possible -length of high pressure tubing and piping runs, and number of tubing and piping crosscovers are minimized -space between components is sufficient to conveniently conduct maintenance activities -if there will be multiple compressors, the intake and exhaust of the compressor cooling systems are arranged such that the intake for one compressor does not draw in the exhaust from another compressor |
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What is a Classified Area? |
An area where ignitable concentrations of natural gas may be present. |
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What are the 3 different Classes of Classified Areas? |
I. = Flammable gases II. = Combustible dusts III. = Easily ignitable fibers |
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What are the 2 Divisions of Classified Areas? |
1. = ignitable concentrations of gases are frequently present 2. = ignitable concentrations of gases are present under abnormal conditions |
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Where are the Class I, Division 1 Areas of a CNG facility? |
-inside a dispenser cabinet -within a 5-foot radius of the discharge point of vent piping connected to any pressure relief valves or any other vent-like opening that can release gas during normal operation. -within 15 feet of the discharge point of pressure relief valves within 15 degrees on either side of the line of discharge |
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Where are the Class I, Division 2 Areas of a CNG facility? |
-within 5 feet of the dispenser, a time post or a de-fueling panel located outdoors -Between 5 and 15 feet of the discharge point vent piping connected to any pressure relief valves or any other vent-like opening that can release gas during normal operation. -with 15 feet of CNG storage vessels -within 15 of compressors, dryers, priority fill panels, time fill panels, and any other gas containing equipment associated with the compressor. -Canopies over dispensers that can trap released gas. |
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Methods for minimizing electrical ignition hazards? |
-Explosion proof construction -Energy limiting systems -Purging using a small fan or blower -Physical barriers |
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Definition Angstrom |
A unit of measurement used to describe the size of atoms and molecules. One angstrom is one ten-billionth of a meter. |
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Definition Anodeless Riser |
A steel casing with a plastic piping inside used to transition below-grade plastic piping to aboveground. The steel casing protects the plastic piping from physical damage. |
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Definition Blow-Down Tank |
A pressure vessel that receives natural gas from the compressor cylinders when the compressor shuts down. Relieving most of the pressure in the compressor cylinders into the blow-down tank makes it easier for the compressor to restart. In many compressors, the blow down tank also receives water and oil drained from coalescing filters installed after each compression stage. |
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Definition Bollard |
A steel pipe filled with concrete installed vertically in the ground to protect CNG facilities from vehicle impacts. |
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Definition Booster Compressor |
A compressor installed between the gas supply and the main compressor at a CNG facility. The booster compressor increases the pressure of the natural gas supplied to the inlet of the main compressor. |
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Definition Butterfly Valve |
A type of isolation valve that uses a disk mounted on a rotating rod to open and close the valve. The valve is operated by turning the rod so the disk is oriented parrallel to the flow to open the valve and perpendicular to the flow to close the valve. |
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Definition Chase |
A pipe or tube made of noncorrosive material installed underground and used to contain stainless steel tubing. |
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Definition Coalescing Filter |
A device that primarily removes oil and water from a stream of air or natural gas. |
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Definition Dew-Point Temperature |
The temperature at which gas can no longer hold all of the water vapor it contains, and the vapor condenses into a liquid state. |
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Definition Enclosure |
A structure containing a compressor and related equipment that provides security, protection from the weather and noise reduction |
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Definition Ferrule |
A tapered metal ring used to seal and attach high pressure tubing to special fittings. |
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Definition Fuel Receptacle |
The fitting in a vehicle fuel system where the nozzle attaches to deliver CNG to the vehicle fuel cylinder. |
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Definition Fully Ported Valve |
A type of valve that provides minimal restriction to flow when in the open position |
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Definition Hose Assembly |
A length of hose with fittings at each end. In a CNG fueling system, hose assemblies are used to connect the dispenser cabinet or fueling post to the breakaway fitting and the breakaway to the nozzle. |
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Definition Intrinsically Safe Circuit |
A specially designed electrical circuit that cannot generate enough heat or spark energy to ignite a flammable material, even when the wiring within the circuit or the component itself is faulty. |
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Definition Jersey Barrier |
A modular concrete barrier often used to seperate lanes of traffic. |
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Definition K-Rail |
A modular concrete barrier often used to seperate lanes of traffic. This term is used mostly in California. |
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Definition Local Distribution Company (LDC) |
A company that supplies natural gas through a network of buried piping to end users. |
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Lower Explosion Limit (LEL) |
The lowest concentration of gas or vapor in air capable of producing a flash of fire when an ignition source is present. |
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Definition Maximum Allowable Working Pressure (MAWP) |
The highest pressure to which any component of a pressurized system can be exposed. The MAWP of a component must be equal to or greater than the set point of the pressure relief valve connected to that portion of the system. |
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Definition Million Cubic Feet per Hour (MMcf/hr) |
A unit of measurement often used by gas distribution companies to describe the amount of gas that can reliably be provided to the location. |
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Definition Molecular Sieve |
Molecular sieves are alumino-silicate compounds used to remove water from natural gas inside the dryer. Also known as desiccant. |
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Definition Non-Incendive Circuit |
A specially designed electrical circuit that cannot generate enough heat or spark energy to ignite a flammable material when the circuit is operating normally. |
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Definition Pneumatic Testing |
A procedure for establishing the absence of leaks and the structural integrity of components and fittings in a CNG fueling system. |
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Pressure Relief Device (PRD) |
PRDs are required to protect vehicle fuel cylinders from excessive pressure due to high temperatures. PRD apply only to vehicle fuel cylinders. |
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Priority-Fill Panel |
A metal cabinet containing flow control valves, check valves, backpressure regulators and other equipment required to direct the flow of natural gas from the compressor to the storage vessels in a cascade fueling system. |
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Pull Box |
A four-sided frame with a cover usually installed in the ground at grade level. A pull box is often used to pull wires through buried electrical conduit. |
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Purge System |
A method for reducing or eliminating the hazard classification of an enclosed area. Purging prevents the accumulation of flammable gas or vapors in an enclosed area providing a continuous supply of clean air or inert gas to the area. |
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Receiver Tank |
A tank that stores compressed air from an air compressor. The compressed air flows from the receiver tank to its point of use. |
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Regenerative Dryer |
A type of dryer in which the desiccant can be renewed by flowing heated natural gas through the dryer. |
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Set Points |
A measurement of pressure, temperature, fluid level or similar quantity that prompts a response from a component of a fueling system. |
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Type 1 Nozzle |
A class of CNG fueling nozzles in which the mechanism that latches the nozzle to the vehicle fuel receptable and the valve that controls the flow of gas are both controlled by a single lever. |
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Type 2 Nozzle |
One mechanism attaches the nozzle to the vehicle fuel receptacle and a separate mechanism controls the flow of gas. |
