Finally, Fleet Vehicles Find a Profitable, Natural-gas Alternative to Diesel

This LNG filling station contains three main components: the LNG storage tank, the cryogenic pump skid and the dispenser. For CNG delivery, a high pressure pump and vaporizer is added, with electric heaters also required in colder climes.

Siemens partnership with natural-gas leader Cryostar produces a space-saving skid-mounted system that cuts costs up to $2.00/gallon while reducing emissions

At the millennial turn, a Harvard-based study took a hard look at natural gas as a substitute for diesel. Twelve years later, a small town Ohio paper examined the phenomenon of natural gas replacing gasoline in everyday cars such as Honda’s Civic. Both articles cite a shared and lingering concern: the limited current infrastructure for refueling natural gas vehicles. That concern is being addressed as one of the world’s largest industrial gas firms, Cryostar, partners with Siemens to help vehicle operators upgrade to liquefied natural gas (LNG) and liquefied compressed natural gas (LCNG), saving money, cutting emissions, and moving towards more sustainable growth.

Why Natural Gas?

According to the U.S. Department of Energy, natural gas burns cleaner than conventional gasoline or diesel due to its lower carbon content. When used as a vehicle fuel, it can offer life cycle greenhouse gas (GHG) emissions benefits over conventional fuels, depending on vehicle type, drive cycle, and engine calibration. In addition, using natural gas may reduce some types of tailpipe emissions.

The pump skid precisely controls transfer of LNG from the storage tank to the dispenser via a variable speed cryogenic pump and a continuously modulating control valve.

Tailpipe emissions result from fuel combustion in a vehicle’s engine and are emitted from its exhaust system. Of primary concern are the regulated emissions of hydrocarbons, oxides of nitrogen (NOx), carbon monoxide (CO), as well as carbon dioxide (CO2). Due to increasingly stringent emissions regulations, the gap between tailpipe emissions benefits from natural gas vehicles (NGVs) and conventional vehicles with modern emissions controls has narrowed. That’s because the U.S. Environmental Protection Agency (EPA) is holding all fuels and vehicle types accountable to the same levels of air pollutants emitted from vehicle combustion. Still, NGVs continue to provide emissions benefits, especially when replacing older conventional vehicles or considering life cycle emissions. Because of this, conversion of conventional fuels (e.g., gasoline, diesel) to natural gas continues to remain a topic of interest, heightened in the United States because of its vast reserves of natural gas and well-documented dependence on imported petroleum-based fuels.

Partners in Progress

A specialist in cryogenic equipment design and manufacturing for more than four decades, Cryostar, part of the Linde Group, has extensive experience in gas handling equipment. Based in France, Cryostar has business centers worldwide. Cryostar has developed fueling stations to deliver both liquefied natural gas and liquefied compressed natural gas, and aims to cover the entire natural gas supply chain. Its natural gas-based fueling stations already operate in Europe and at three locations in the U.S., including one of the largest in the world at the City of Los Angeles Bureau of Sanitation.

Cryostar’s dispenser can deliver saturated or unsaturated LNG fuel by throwing a switch on the front panel. Sophisticated technology internal to the dispenser enables simple operation by the vehicle operator.

Now, Cryostar plans to roll out a new and improved LNG/LCNG fueling station tailored to U.S. customers, and to power and control these stations with Siemens hardware and software. LCNG offers slightly greater savings over diesel than LNG, but LNG offers superior range. Other advantages of LNG and LCNG over diesel fuel include:

  • Less expensive by about $1.50 to $2.00/gallon
  • Cleaner burning
  • Allows use of abundant natural gas instead of scarce oil reserves
  • Can increase a country’s energy independence

To win over early adopters of this technology, Cryostar needed to find the right partner to automate their LNG/LCNG filling stations. After an exhaustive search, Siemens was selected to provide the required power and control components.

According to Pierre Caudron, design department manager in the Automation Division for Industrial/Medical and LNG/LCNG Filling Stations at Cryostar, Siemens helped Cryostar to meet its goals for this project by covering all the functions needed to power, control, and manage the complete fueling process. “Cryostar is dedicated to stocking all necessary parts worldwide to support its installed base of systems, so Siemens’ global technical support and parts stocking was also a good fit,” he says.

Fueling Success with Automation

In a Cryostar LNG fueling station, the LNG is stored in one or more vacuum insulated storage tanks, usually provided by the customer. LNG is pumped from the storage tank by the pump skid. CNG filling capability can be added by installing a high-pressure pump with vaporizer to convert the LNG to LCNG.

Power and control panel exterior. The graphics panel allows full featured control and monitoring of the entire fueling station through simple touch-screen commands.

Based on Siemens Totally Integrated Automation concept, the new electrical design enabled Cryostar to combine power distribution, controls, and fuel management into a single, more efficient system with easier operation for its customers. The same Siemens power and control panel is provided for both LNG only and LNG/LCNG fueling stations, with panel-mounted components activated as required, greatly simplifying system design.

On the station’s pump skid, a mounted Cryostar cryogenic transfer pump moves LNG from the storage tank to the fleet vehicle via the dispenser. The pump skid has two control loops, both executed within the Siemens PC-based controller, as are most other system control functions. The first loop controls the pump speed via a Siemens variable frequency drive (VFD), maintaining the desired differential pressure between the pump inlet and outlet; the second regulates LNG flow rate with a control ball valve, giving the desired pump outlet pressure.

The dispenser is fitted with two accurate and reliable Siemens’ pressure transmitters, as well as a mass flow meter that measures the LNG liquid as it moves through the dispenser to the vehicle. This meter is connected to the PC-based controller via Modbus RS-485. A custom-designed Cryostar calculator and display module shows the user the exact amount of LNG delivered to the vehicle’s storage tank.

The system meets equipment specifications for Class 1 Div. 1, NEC 500, which means it is safe for use with flammable gases, vapors, or liquids under normal operating conditions. The power and control panel’s compact design helps Cryostar minimize the overall footprint of the filling station, a critical factor in many installations.

The Siemens power and control panel is designed for installation in an unclassified area, so all connections to the pump skid and the dispenser are intrinsically safe. This provides the required degree of protection while allowing the panel to be provided with standard NEMA 4 or 12 ratings, depending on the exact location of installation. The automated system is fully compliant with all relevant national and international standards.

Power and control panel interior. This power and control panel houses a variety of Siemens power and control components. All connections to the pump skid, the dispenser and optional components are intrinsically safe – allowing the panel to be rated NEMA 4 or NEMA 12.

Powerful Advantages

The Siemens power and control system provides a host of benefits for Cryostar, including:

  • One global supplier for all power and control components
  • Worldwide technical support and parts stocking
  • Compliance with all relevant national and international standards
  • Reduction of required footprint from compact design
  • Support for multiple programming languages; speeds and simplifies controller programming
  • PC-based platform provides supports for sophisticated algorithms, and for high-level data handling and storage
  • High-performance Ethernet communications via PROFINET
  • Multi-network capabilities allow interface with wide variety of external components
  • Remote access capabilities, including web server built-in
  • Support for intrinsic safety facilitates operation in classified areas

The PC-based controller provides the necessary support for sophisticated algorithms and for tasks such as high-level data handling and storage that are better suited to a PC than a PLC. At the same time, the controller
provides deterministic real-time control with high reliability, similar to a PLC.

Simply Good at Every Level

Once programmed by Cryostar, the automation system handles all the complex tasks required to operate and monitor the fueling station and presents a simple operator interface to users. The easy-to-use interface is important because, unlike many industrial gas-handling systems, the LNG/LCNG fueling stations will be operated and maintained by personnel not accustomed to process control. The customer simply inserts payment and fills the vehicle with fuel, like at any other filling station.

A recent customer (who is also an investor) commented that the Cryostar solution is more user friendly than other LNG or LCNG options currently available. “Some of the other systems are very complicated—one-off custom systems—so we are very excited that the whole skid system is modular,” he says. “You just add another skid and you’ve expanded the capability of the station without having to start over.” 

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