Innovation at the Pump

April 19, 2014

As The Economist put it, “America’s unexpected, and most welcome, bonanza of natural gas from its vast shale deposits seems to be doing as much to reduce pollution as many of the efforts introduced over the years to restrict emissions from vehicles, power stations and other sources. The biggest breakthrough the energy industry has seen in decades, hydraulic fracturing (“fracking”) combined with horizontal drilling, has released unprecedented quantities of gas from this shale. As a consequence, the spot price of domestically produced natural gas has tumbled from a high of over $12 per million British thermal units (BTU) in 2008 to less than $2 in 2012, before settling at around $4 today.”

By comparison, natural gas is 80% cheaper than oil on an energy equivalent basis. As noted by the American Enterprise Institute: “In February [2013] oil was selling for an average of $95.32 per barrel, and natural gas was selling for $3.34 per million BTU. At a multiple of 5.8 times to equal the same amount of energy produced by a barrel of oil, natural gas was selling for the equivalent of only $19.38 per barrel.” And according to Autoblog, “Thanks to the precipitous drop in prices for compressed natural gas (CNG) and liquid propane (LPG), fleets can save a fortune by switching over to these fuels. OEMs such as Freightliner and Thomas Built Bus have jumped into the market. International now offers the Transtar Class 8 semi…that runs on CNG…. A fleet can save well over $150,000 in fuel costs over the six-year life of a truck. For fleets that run their per-mile operating costs to the penny, this is a financial windfall.”

NOTHING FOUND

This represents a huge potential cost savings for landfill operators, one they cannot afford to ignore. But to get there from here, truck fleets have to be converted from diesel to either straight CNG or “flex fuel” CNG/diesel engines. To accomplish this, an extra tank should be added to the truck. Afterwards the driver can switch between fuels with the flip of a switch. In the tank, the gas is kept pressurized at approximately 3,600 psi from the tank, it travels in a high-pressure line to regulators that change the pressure for use in the engine. A solenoid valve controls transmission to the engine’s fuel regulators. Once in the combustion chamber it is ignited to provide power to the engine.

Advantages and Disadvantages of Diesel, Gasoline, and CNG
In addition to cost advantage, CNG offers operational advantages as well. As a general rule of thumb, the rate of fuel consumption for a diesel engine is roughly one gallon of diesel fuel is required per hour to produce 20 horsepower. By comparison, one gallon of gasoline per hour would produce only 15 horsepower. This is because of the higher energy density of diesel with one gallon of diesel fuel containing 147,000 BTU, compared with one gallon of gasoline, which contains 85% of this value, only 125,000 BTU. The higher energy density and the superior efficiency of diesel engines is the main reason why diesel gets better mileage in vehicles and more operating hours in equipment. However, diesel is more expensive per gallon then gasoline. These efficiency, power, and cost factors make diesel more suitable for high-powered engines found in large, long-distance transport trucks and heavy earthmoving equipment, while gasoline dominates the market for personal cars and small utility trucks.

But in the past decade there has emerged a viable third option: CNG. At 20,000 to 22,000 BTU per pound, 5.7 pounds of natural gas has the same energy density as one gallon of gasoline. This amount of energy is referred to as a “gasoline gallon equivalent,” or GGE. A similar rating is diesel gallon equivalent, or DGE. CNG tanks are typically designed for a service pressure of 3,600 psi (250 bar). One GGE of natural gas has a density of 0.0417 to 0.0447 per cubic foot at sea level.

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Using the gas law, the equivalent GGE at 3,600 psi is approximately 0.517 cubic feet or 3.87 gallons. Therefore, a CNG tank with an interior volume of 20 gallons would hold the energy equivalent of 5 to 6 gallons of gasoline. So in practice, CNG vehicles will have shorter driving ranges verses other vehicles with similar size fuel tanks, operating weights, and engines. But CNG costs less than either diesel or gasoline, burns more efficiently, produces less greenhouse gases, and results in longer engine life. CNG vehicles are therefore a good fit for long-service, high-mileage truck fleets that operate within a limited radius but make repeated return trips to central refueling stations. CNG costs up to $1.50 less per DGE, and projections call for this favorable cost trend to extend well into the future. This translates to annual fuel cost savings (natural gas versus diesel) of up to $15,000 per truck (www.cleanenergyfuels.com).

In other words, of all the vehicles and equipment used at a landfill, the waste collection truck fleet would be the prime beneficiary of a transition from diesel to CNG. Both economic and environmental factors are making this transition more attractive. The inexpensive natural gas extracted by hydraulic fracking from previously inaccessible shale formations, the methane produced by anaerobic digesters at nearby wastewater treatment facilities, and the methane component and landfill gas already being produced at the landfill all combine to make this option more economical. This last source of CNG is especially promising for large landfills with high rates of landfill gas generation.

Waste as a Fuel Source
What exactly is landfill gas (LFG)? LFG is generated by the decomposition of the organics portion of the municipal solid waste (MSW) deposited in the landfill. It consists of three components: methane (45%-50%), carbon dioxide (45%-50%), and trace volatile organic compounds (0% to 5%). Methane production rates are difficult to calculate with precision. The amount of LFG produced depends on multiple factors, including temperature, moisture content, percent of disposal space taken up by cover soils, and, most importantly, the percent of the wastestream that is decomposable organics. It is the methane component that is useful as a source of energy.

Though a rough average of organics content can be assumed over the long term for a landfill, this amount can vary widely, with one waste load consisting of organic sludge and another composed of broken concrete construction debris. But using typical quantities, material types, and site characteristics, a standard annual methane production rate of 0.136 cubic feet for every pound of waste (equal to 272 cubic feet per ton of waste) can be assumed. With methane accounting for 50% of the total emissions, the total annual landfill-gas-generation rate would be double this amount.

Methane has a heat value of 1,012 Btus per cubic foot. The approximate 272 cubic feet of methane typically produced each year by a ton of disposed municipal solid waste would have a heat value of over 275,000 Btus. According to USEPA estimates, each American on average throws out 4.5 pounds of MSW each day, or over 0.82 tons each year. With a population of over 300 million citizens, the United States on average generates over 246 million tons of waste each year. With about 72 million tons of waste being recycled each year, the remaining 174 million tons end up in a landfill. At an average heat energy value of 275,000 Btus per ton of waste, the total amount of landfilled waste has a value of 47.85 trillion BTU nationwide. This is equivalent to 382.8 million GGE.

Another waste source of CNG is wastewater treated by anaerobic digesters. These facilities use microorganisms to break down organic materials, as a stage in wastewater treatment, in enclosed containers. After pretreatment in equalizing tanks, wastewater is pumped into the digester. There, in the absence of oxygen at temperatures ranging from about 95ºF to 105ºF, the organic components of the wastewater are digested by bacteria. As part of the digestive process, the bacteria create biogas, which can be easily collected and piped to a pump station for use as vehicle fuel. This, even more than LFG, is a renewable energy source constantly being fed by a never-ending stream of crop residuals, manure, foodwaste, fats, oils, greases, and biological lubricants as well as municipal wastewater. Whether LFG systems or anaerobic digesters, the energy is there; it’s just a question of efficiently extracting the energy-producing methane.

Major Suppliers
Agility Fuel Systems provides cab-mounted fuel systems for truck retrofitting, including the new 120 DGE back-of-cab-mounted fuel system. This system provides a 500-mile operational range while only requiring 31 inches of frame rail space for mounting and less than 88 inches of width. Consisting of three cylinders, each 26 inches in diameter by 80 inches in length, with a total weight of only 2,600 pounds, this system preserves vehicle aerodynamics while providing the industry’s most space-efficient configuration (measured by DGE per inch of frame rail). Further operational efficiency is provided by its integrated fuel management module and enhanced safety from ignition disconnect fuel caps.

Angi Energy Systems designs and manufactures complete systems for CNG vehicle fueling and tube trailer transport and since 1983 has grown to be North America’s leading supplier of CNG refueling equipment. Angi provides a wide range of products with low overall life cycle costs as well as such support services as customer service, project management, maintenance, and training programs. The company’s products and services for NGV refueling systems include dispensing units, fuel management systems, compressors, and distributed control systems. Angi supplies all of the components required for refueling CNG vehicles. This equipment ranges from standard products the company provides around the world to highly specialized custom designs for specific client’s needs, integrated to ensure efficient whole system functionality.

Angi’s standard NGV refueling system components include compressor systems that feature modular design for site integration. Sound attenuated enclosures are available for outdoor weatherproof protection. Integrated systems can include the inlet gas dryer, storage, and priority panel mounted on the compressor skid. Dispensing options are available for single- or dual-hose applications with software that provides independent sequence functions for each hose. Each dispenser offers accurate mass-flow metering, electronic sequencing valves, large LCD display of volume and costing, and an easy-to-use operator interface keypad. The inlet gas dryers remove water vapor prior to storing or using natural gas for a vehicle fuel direct from the compressor. Angi’s dryers typically operate on the low-pressure side of the compression process, using molecular sieve adsorbent desiccant to remove water vapor to extremely low levels. The company’s most common CNG storage system includes ASME vessels having an operating pressure of up to 5,500 psig that are used for filling 3,600-psig vehicles, with varying configurations and vessel sizes available. Application engineers provide research and design support to supply CNG equipment that meets a client’s current and future fueling needs by evaluating and determining the correct equipment design for each specific site. Angi’s engineering services include specification development, custom packaging solutions, project management, site integration and construction design, coordination of commissioning, comprehensive factory and field-testing, fleet fueling demand, and operational cost analysis.

Angi was recently part of a team that received the US Environmental Protection Agency’s 2011 Landfill Methane Outreach Program (LMOP) Project of the Year Award for the Rodefeld Landfill BioCNG Vehicle Fuel Project in Dane County, WI. Together with its partners, the company implemented the BioCNG system, enabling Dane County to fuel converted parks and public works trucks with biomethane, with the potential to expand to supply fuel for waste trucks and other county vehicles. The patent-pending biogas conditioning system economically produces biogas-based fuel that is a fraction of the cost of gasoline or diesel. The system is currently operating at a capacity of 100 gallons of gasoline equivalent (GGE) per day, but the system is now being upgraded to operate at a capacity of 250 GGE. “Angi is happy to be a member of this award-winning team. The BioCNG process scales well. The ROI is known and can be projected into the future. From our perspective, BioCNG is the best use of biogas,” said John Grimmer, chief executive officer of Angi Energy Systems.

Greenfield Compression, a member of the Atlas Copco Group, recently opened a new facility in Houston, TX. This facility specializes in the assembly and testing of Atlas Copco CNG compressors, dryers, and control systems, as well as CNG vehicle station dispensers. This new 96,000-square-foot facility is staffed with specialists experienced in the fabrication and assembly of mechanical equipment, the design and programming of CNG systems, and the installation, maintenance and operation of equipment. The company manufactures a full range of air- or water-cooled high-pressure gas compressors, available in multistage configurations that can be customized to suit various inlet and flow requirements.

Clean Energy is the largest provider of natural gas fuel for transportation in North America, fueling over 30,000 vehicles each day at approximately 400 fueling stations throughout the United States and Canada. The company builds and operates CNG and LNG fueling stations, manufactures CNG and LNG equipment and technologies, and develops renewable natural gas production facilities. For solid waste fleets, Clean Energy’s service includes comprehensive natural gas fueling supply services, long-term fuel contracts and discounted fueling options, fleet fuel station design, construction and ongoing operations, and assistance with securing grant funding, vehicle leasing, and financial incentives.

CNG Cylinders International, a California firm with more than 30 years experience in advanced metal forming, is a producer of CNG fuel storage systems, tanks, and cylinders. Licensed distributers of Type 1 and Type 2 cylinders, the company’s product line includes brackets and valves. It has also developed a forged aluminum liner for Type 3 cylinders, producing cylinders of wide ranging diameters. Aluminum provides superior heat dissipation compared with the composite liners, allowing for a fast fill at 4,175 psi with added DGE, instead of a loss in DGE common with the Type 4 cylinder.

CNG-One LLC is a full-service advanced fuels organization engaged in the business of motor fuel system adaptation conversion to run on CNG as an augment in addition to the factory-designed fuel system. CNG-One also will provide fueling equipment sale and service for personal and fleet applications. CNG small fleet compressors can be placed at your place of business allowing you to fuel for as little as $1.00 per one gas gallon equivalent (GGE).

Crane Carrier is a leading producer of Class 6, 7, and 8 alternate-fueled vehicles equipped with CNG or LNG systems. CNG chassis are factory equipped with factory-installed EnviroMech fuel control modules (FCMs), regulating CNG fuel system pressure, filtration, and delivery to engine manufacturer’s design recommendations, ensuring proper operation and factory support. Crane offers EnviroMech behind-the-cab (BTC) and saddle mount systems in various combinations, configurations and capacities due to their high quality and durable construction, their storage vessels come with a 20 Year Cylinder Service Life. Their Type 3 cylinders are manufactured with aluminum liners, carbon fiber wrap and are neck mounted for increased integrity and serviceability. Safety features include conventional dash-mounted fuel-level gauge with low-level warning light, an emergency shutoff valve located in the FCM, an NGV-1 quick-connect fuel-fill connection also located in the FCM, and ignition cut-out (shutoff) fuel-fill connections.

Partnering with Autocar and other major truck suppliers, Cummins Westport Inc. (CWI) designs, engineers, and markets 6- to 12-liter spark-ignited automotive natural gas engines. These 100% natural gas engines, manufactured in the same Cummins facilities as their diesel counterparts, are designed to meet the most stringent emission regulations. The design of the Cummins Westport natural gas engines is based on the design of Cummins diesel engines and shares many of the same components. The ISL G 8.9-liter heavy-duty natural gas engine is Cummins Westport’s industry-leading product. Introduced in 2007, there are close to 25,000 of these workhorses in service for refuse, transit, and truck customers throughout North America. CWI’s service guidelines indicate the ISL G is for loads up to 66,000 pounds GVW. The larger displacement ISX12 G was introduced in 2013 and offers up to 400 horsepower and 1,450 lb-ft torque. The ISX12 G is designed for use in heavy-duty truck applications with a GVW not to exceed 80,000 pounds. Like the ISL G, the ISX12 G meets current EPA and CARB emissions standards and 2014 EPA greenhouse gas regulations operating on CNG, LNG, or biomethane.

Effenco’s hybrid design is based on an analysis of more than 640 routes from 34 municipalities and boroughs in the US, Canada, and Europe. The results indicated that refuse collection vehicles (even though they vary in design and duty cycle) have the common feature of spending 50% of their operating time at idle with low or zero auxiliary power demand. All in all, more than 25% of their total fuel consumption is at idle. Noting that idle reduction and powering auxiliaries without the engine are excellent opportunities to reduce fuel consumption, the company has developed the Stop-Start Hybrid System to harvest hydraulic energy from braking, toping up if needed with engine power at best efficiency point. In doing so, the engine is turned off when truck is immobile, as the transmission remains engaged for a no-lag start. The now-charged hydraulic motor restarts the engine automatically upon acceleration demand. This modular, stop-start hybrid system is composed of four sub-assemblies mounted on the chassis rails. The design allows for ease of installation or can be retrofitted on an existing vehicle with 30 to 40 man-hours of labor.

With a nationwide CNG fueling infrastructure and maintenance facility program already in progress, ET Environmental Corp. LLC is a leading expert in this field. ET was founded in 1993, creating a unique, integrated model for the delivery of environmental services and construction management. Given the need to navigated the complex codes and regulations of CNG conversion on a local and national scale, this was no easy achievement. Since 1993, it has created a unique, integrated model for the delivery of environmental services and construction management. The company now offers a national network of support, single-point accountability, and function as owner advocates. ET combines clean technologies and traditional engineering practices into innovative design and reliable construction. ET specializes in alternative green initiatives for transportation, businesses, and municipalities. For clients looking to set up a CNG fueling station, ET provides services for site assessment, permitting, sizing, layout, preconstruction planning, and material procurement. To use CNG fuel requires special service and garage facilities that differ from traditional vehicle maintenance. These CNG facilities must be compliant with very unique and stringent life safety, electrical, and fire codes that are often confusing and cumbersome. ET Environmental has the expertise to navigate through the complex process of converting client fleets to CNG. ET will conduct a comprehensive feasibility analysis based on client requirements and budget. Based on that analysis, they make recommendations for client program during the planning and pro forma stages.

Credit: CNG-One LLC
Businesses are discovering the advantages of CNG conversions for vehicles large and small.

Heil Environmental is an in-house producer of customized CNG truck systems designed for various body and chassis combinations. It also provides dedicated CNG fueling stations installed at the landfill. In partnership with Agility Fuel Systems, Heil is able to offer the world’s leading fully integrated CNG systems. Heil will help its customers choose the best configuration for their applications from five key configurations.

Hino Trucks is a CNG leader in foreign markets and will soon be bringing its expertise to the USA. Currently available in Thailand, Hino’s FL1J NGV is a truck that runs on compressed natural gas and has an operational range of more than 500 kilometers. This is the commercial-vehicle manufacturer’s second NGV product, after a tractor head that was launched last year. Hino’s conventional CNG models produced virtually no emissions of particulate matter, and nitrogen oxide emissions of the new models are reduced to less than 0.5g/kWh through improved, built-in, three-way catalyst mufflers, realizing a low-pollution vehicle to follow the existing New Long-Term Emission Regulations. In the meantime, its hybrid technology is available in its 195h model,  a Class 5, 19,500 GVW diesel-electric hybrid offering. Since it is a smaller offering in terms of GVW, it is most suitable for shorter-range routes, and is designed for an urban environment or even landfill operations where maneuverability is essential. It is equipped with the Hino J05 engine rated at 210 horsepower and 440 lb-ft of torque, so it has more than enough power to handle the job. The J05 engine is approved for use of up to B20 biodiesel as well to help further reduce the 195h’s carbon footprint.

With facilities in the United States, Canada, England, France, Germany, and China, Luxfer Gas Cylinders is the world’s largest manufacturer of aluminum and composite high-pressure cylinders, which includes an exclusive line of G-Stor Pro lightweight Type 3 aluminum-lined cylinders for storage and transport of CNG. These lightweight cylinders are integrated into fuel systems that can be roof-mounted in a number of longitudinal and transversal configurations operating at service pressures up to 3,600 psi and can be roof-mounted for ease of retrofitting. Luxfer’s G-Stor Pro cylinders are up to 70% lighter than comparable steel cylinders and up to 17% lighter than other Type 3 cylinders offered in the market. This lesser weight results in lower costs while providing high levels of corrosion resistance. Luxfer Gas Cylinders is an operating company of Luxfer Group.

TerraPro Natural Gas from Mack Trucks provides an alternative fuel engine technology that combines all the advantages of clean-burning natural gas with the power and torque needed for residential and commercial trash collection. TerraPro Natural Gas meets EPA 2010 and CARB emissions levels while achieving lower alternative fuel vehicle life cycle costs. To create the Mack TerraPro Cabover and Low Entry, Mack has partnered with natural gas engine manufacturer Cummins Westport. The TerraPro Natural Gas is capable of operating on compressed or liquid natural gas, landfill gas, or hydrogen compressed natural gas.

McNeilus Next Generation (NGEN) initiatives promote CNG alternative-fuel powered solutions for refuse vehicles and heavy-duty fleets of all types. McNeilus CNG-powered refuse trucks are built for the rugged refuse environment, and are designed with the operator and service team in mind. McNeilus has led the way in offering a route-ready, fully tested, and integrated CNG system. The trucks are configurable to meet customers’ needs, whether time filling or fast filling. All vehicles feature a standard NGV1 fueling receptacle and Deutsch brand electrical connections. At the heart of the plumbing are CNC-formed high-pressure lines, compression fittings, and high-pressure hoses with 5,000-psi working pressure. The frame comes with boss-mounted tanks and integrated three-sixteenth-inch steel guards to protect both ends of tanks. The tanks are lightweight NGV Type 4. Tank covers have no wires or props to abrade tanks. A standard thermal pressure relief device (PRD) provides continuous full-tank-length protection. McNeilus CNG trucks are fueled and tested at the McNeilus campus, and they arrive quickly, ready to work to customer specifications, and all McNeilus CNG vehicles meet NFPA-52 standards. A comprehensive, factory-direct sales and service network supports McNeilus NGEN initiatives. McNeilus is leading the drive toward the next generation of vehicle solutions.

When it comes to CNG-powered alternative fuel vehicle systems, McNeilus has accumulated a great deal of experience and garnered an impressive expertise. McNeilus CNG-powered refuse trucks are built for the rugged environment of waste handling. And they are designed with the operator and service team in mind. The company has fielded more than 8,000 CNG-powered vehicles in cities across the country, including Seattle, New York, Houston, Chicago, Shreveport, Minneapolis, Boston, Los Angeles, and Portland.

For refuse haulers, McNeilus has led the way in offering route-ready, fully tested, and integrated systems. In fact, in 2008, McNeilus manufactured its own fueling station to support large-scale, onsite, seamless manufacturing without requiring an outside third party to install the fuel system. Consequently, McNeilus CNG trucks are fueled and tested at the McNeilus factory, which means they are delivered quickly and ready to work to customer specifications.

McNeilus engineers have refined and improved the company’s CNG systems to make them more efficient, productive, and easier to maintain. For example, at the heart of the McNeilus CNG system’s plumbing are CNC-formed high-pressure lines, compression fittings, and high-pressure hoses with 5,000-psi working pressure. Its frame is equipped with boss-mounted, lightweight, NGV Type 4 tanks and integrated three-sixteenth steel guards for protection. The tank covers have no wires or other impediments that could abrade the tanks. A standard thermal pressure relief device (PRD) provides continuous protection across the full length of the tank. All McNeilus CNG vehicles meet NFPA 52 Standards.

McNeilus is expanding its CNG capabilities and now offers alternative fuel-powered solutions for heavy-duty fleets of all types, including ready-mix concrete trucks, delivery trucks, and Class 8 over-the-road trucks. A comprehensive, factory-direct sales and service network, including 20 installation centers, supports McNeilus CNG initiatives. McNeilus is leading the drive toward the next generation of vehicle solutions.

quasar Energy Group LLC is a leader in the anaerobic digestion industry. Based in Cleveland, OH, the company designs, builds, owns, and operates anaerobic digesters that produce electricity and heat, natural gas, or motor vehicle fuel from organic waste. quasar is collaborating with Ohio State University’s Ohio Agricultural Research and Development Center campus to further the development of Ohio’s growing anaerobic digestion industry. From the company’s statement: “In 2008, quasar relocated its Engineering & Laboratory offices to The Ohio State University’s Ohio Agricultural Research and Development Center (OARDC) campus in Wooster, Ohio, to collaborate with the largest university agro-bioscience research center in the nation. This partnership combines agricultural and biological research to develop an emerging American industry. The location allows quasar’s laboratory to benefit from the knowledge of the distinguished faculty and students performing research in the fields of agriculture and environmental science.”  In doing so, the company has partnered with SWACO on a project in Columbus, OH, providing it with methane vehicle fuel at a facility that is open to the public. In addition to recycling waste and creating cleaner, renewable energy, the company’s anaerobic digestion process produces effluent material that is used to replace chemical fertilizers, improving soil quality in a way that is organic and environmentally safe.

Trillium CNG is a leading provider of CNG fueling services as well as a single-source provider of CNG fueling facility design, construction, operation, and maintenance. Its core services include designing, installing, and operating turnkey CNG fuel. Its CNG station design process includes analyzing customer fueling needs and assessing site layouts and utilities locations to determine the components needed to equip the station. Trillium will manage every step of the CNG fuel station construction process, from permitting to final inspection.

TruStar Energy is a full-service provider of portable stations, time-fill stations, public stations, and combination stations. Time-fill stations represent the most cost-effective way to make the transition to CNG. As a refuse truck fleet returns to a central location each night, a time-fill station allows the fleet to fuel automatically at night, during off-peak energy hours and without the need for a fuel attendant. Drivers simply connect the fuel hoses to their vehicles following their shift, and the compressors do the rest. When drivers return in the morning, their trucks will be waiting fully fueled. If trucks need rapid refueling, the company’s fast-fill station configurations will meet this need. It also allows station owners to provide a public fueling option, turning the fueling station into a revenue-generating asset. TruStar Energy’s portable fueling station (PFS) is the fastest way to fuel CNG vehicles. The PFS allows a refuse fleet to fuel at a central location within four hours of arrival. With the ability to fuel eight vehicles simultaneously, it can fuel a refuse fleet overnight

Westport Fuel Systems Inc. is a leading innovator in CNG fuel technology. Worldwide, Westport and its affiliates have filed over 800 patent applications relating to 200 inventions. This extensive intellectual property portfolio provides a distinct advantage, providing expertise in injectors (combined gaseous fuel/pilot fuel injectors and mono-fuel injectors), combustion chamber geometry and control strategies, engine fuel systems, cryogenic storage and delivery (cryogenic tanks and cryogenic pumps), and compressors. 
About the Author

Daniel P. Duffy

Daniel P. Duffy, P.E., writes frequently on the topics of landfills and the environment.

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