Choose the best pump for autogas applications

© Blackmer/EbsrayConsumption in 2013 was nearly 26 million metric tons (57 billion pounds), up 57% over the 16.3 million metric tons (36 billion pounds) that were consumed in 2003. This growth expands the need for pumping technology that is capable of adequately handling autogas, with Ebsray® Regenerative Turbine and Blackmer® Sliding Vane Pumps heading the list

For more than a century, gasoline and diesel fuel have dominated the global motor-fuels market. Still, many meaningful attempts have been made to add additional “fuels” to the motor-fuel pool, from biofuels to electricity to compressed natural gas, in an attempt to curb the general reliance of motorists on these two fossil fuels.

Today, the most popular of these so-called “alternative” automotive fuels around the globe is autogas, the name given to liquefied petroleum gas (LPG) when it is used as a motor fuel. autogas has been gaining in popularity because it possesses a number of operational characteristics that are desirable to vehicle manufacturers and operators, namely that it is clean-burning, high octane, abundant and environmentally friendly.

According to the World LP Gas Association’s (WLPGA) Statistical Review of Global LP Gas 2014, global autogas consumption in 2013 rose to 25.8 million metric tons (57 billion pounds), up 5.3% over 2012 and 57% higher than the 16.3 million metric tons (36 billion pounds) that were consumed as recently as 2003. At the conclusion of 2013, there were nearly 25 million autogas-powered vehicles in use with almost 71,000 fueling sites located around the world.

Regionally, according to the WLPGA report, the countries of Europe/Eurasia are the top consumers of autogas, with 12.9 million metric tons (28.4 billion pounds) consumed in 2013, or more than half of reported global consumption. Additionally, 16.7 million vehicles were powered by autogas in European and Eurasian countries in 2013. Within that region, Turkey was the second-largest consumer at 2.7 million metric tons (5.9 billion pounds) and became the first country to have more than 10,000 retail sites that offer autogas (10,089).

The WLPGA also reported that other global hot spots for autogas consumption include South Korea at nearly 4 million metric tons (8.8 billion pounds); Russia, the largest European consumer, at 2.9 million metric tons (6.34 billion pounds); Thailand at 1.8 million metric tons (4.0 billion pounds); and Poland at 1.6 million metric tons (3.5 billion pounds). In North America, autogas consumption has been holding steady in the United States and Canada, with Canadians consuming more in 2013 (518,000 metric tons in Canada as compared to 409,000 metric tons in the U.S.) but with the U.S. offering more retail locations, 2,956 versus 2,228. Mexico was the largest consumer in Central and South America at 654,000 metric tons (1.4 billion pounds) with consumption in the Dominican Republic and Peru also exceeding 400,000 metric tons.

© Blackmer/EbsrayAutogas has been gaining in popularity as a motor fuel because it possesses a number of operational characteristics that are desirable to vehicle manufacturers and operators, namely that it is clean-burning, high octane, abundant and environmentally friendly

So, while the global consumption of autogas—3% of the total motor-fuels market share, according to the WLPGA— pales in comparison to gasoline and diesel, it is becoming a significant part of the motor-fuel landscape in a number of countries. In those areas, retailers of autogas must utilize a pumping technology that will optimize the dispensing of the fuel. This white paper will illustrate how regenerative turbine and sliding vane pumping technologies can be the best choice for those autogas-dispensing operations.

The Challenge
autogas, a utilization of LPG, is a propane-butane mixture. This makes it unique in that it can be transported and stored as a liquid, but when released it will vaporize and burn as a gas. In other words, autogas is easily changed from a liquid state to a gas state. This is a property that no other commercially available motor fuel possesses. Autogas can also be a safer choice than other motor fuels since it has a narrower window of flammability than most motor fuels. However, there are a few main challenges that autogas retailers must confront and overcome when handling the fuel:

• As a liquefied gas, autogas must be stored in an enclosed container under pressure. When stored in a pressurized container, the autogas takes the form of a liquid with any gas vapors on top, which provides the pressure that keeps the liquid from boiling. Any upset in this state of equilibrium will cause the autogas to boil off or vaporize.
• Autogas has a viscosity of about 0.1 centipoise (cP), which makes it approximately 10 times thinner than water. This low viscosity can make autogas difficult to pump since a fluid with low viscosity is harder to seal, while there is a greater risk that “pump slippage” will occur during transfer operations.
• During a pumping operation, if the pump’s inlet pressure falls below the vapor pressure, vapor bubbles will form in the autogas liquid. As the bubbles travel through the pumping chamber and pressure increases, they will implode and cause cavitation. Cavitation produces pressure spikes and results in noise, vibration and damaged pumping-system hardware.

© Blackmer/EbsrayBlackmer LGL150 Series Sliding Vane Pump

Over the years, various types of pumping technologies have been used for the handling and dispensing of autogas. Two that have been utilized but were found to have significant downsides in these applications are centrifugal and side-channel pumps.

The main shortcoming of centrifugal pumps when handling autogas is that they are prone to experiencing vapor lock. Centrifugal pumps used in autogas-handling applications are also not self-priming, unless they are submersible. But there are additional disadvantages with submersible centrifugal pumps, a noteworthy one being that they must be degassed before maintenance can be performed on them, which is an elaborate and time-consuming process.

While side-channel pumps are self-priming, they do introduce a number of negatives that affect their ability to handle autogas. One is that they are very poor for handling any fluids that contain solids, which can be found in lower grades of autogas. Secondly, they have a high purchase price and are expensive to maintain.

© Blackmer/EbsrayEbsray RC Series Model RC25 Regenerative Turbine Pump

The Solution
PSG®, a Dover company, Oakbrook Terrace, IL, USA, offers two product brands that feature standard-setting pump technologies for use in autogas-handling applications: Ebsray® Regenerative Turbine Pumps, Cromer, Australia, and Blackmer® Sliding Vane Pumps, Grand Rapids, MI, USA.

For more than 75 years, Ebsray, acquired by PSG in 2013, has built a reputation as the leading developer and supplier of industry-standard regenerative turbine pumps for use in the LPG markets of Europe, Asia and Australia. Upon its acquisition by PSG, the distribution of portions of the Ebsray regenerative turbine product portfolio in North America was incorporated into Blackmer’s U.S.-based operations. Like Ebsray in Europe, Asia and Australia, Blackmer is the strongest brand in the North American LPG market.

Ebsray Regenerative Turbine Pumps stand out in autogas-dispensing applications because they have been designed and precision-built for high-pressure transfer applications. They feature an innovative impeller design that optimizes hydraulic performance, resulting in high differential pressures even at low flow rates, which is a critical consideration for autogas applications.

© Blackmer/EbsrayThe design of a regenerative turbine pump is unique and works on a different principle than positive displacement pumps. This design, however, allows the pump to operate cavitation-free at speeds up to 3,800 rpm and at high differential pressures with low flow rates, which makes it ideal for use in autogas-handling applications.

The design of Ebsray regenerative turbine pump’s impeller is a rotating, non-contacting disc that has up to 60 small buckets or cells on its periphery. When the liquid enters the suction port of the pump it is picked up by the impeller and accelerated around the narrow hydraulic channel that surrounds the cells. Kinetic energy is imparted to the liquid while circulating radially around the channel. The resultant spiraling of the liquid many times within one revolution builds energy and pressure.

Ebsray regenerative turbine pumps are offered outside of the U.S. in various models and configurations designed for underground, aboveground and submersible LPG installations and applications. In the U.S., Ebsray specifically offers its RC Series Regenerative Turbine Pumps in two models for autogas applications: the RC20 and RC25. The RC20 pumps offer flow rates up to 15 gpm (58 L/min) and flow rates up to 25 gpm (94 L/min) for the RC25 models. Both pumps can operate at differential pressures up to 175 psi (12 bar). Blackmer offers the LGL Series Sliding Vane Pump for use in autogas-handling applications.

The secret to the success of sliding vane pumps in LPG installations can be found in their unique design and method of operation. Sliding vane pumps have a number of vanes that are free to slide into or out of slots in the pump rotor. When the pump driver turns the rotor, a combination of forces (centrifugal, mechanical push rods and liquid), causes the vanes to move outward in their slots and around the inner bore of the pump casing. This forms internal pumping chambers and, as the rotor revolves, the fluid flows through the suction port and into the pumping chambers that are created by the vanes. The fluid is then transported around the pump casing until the discharge port is reached, at which point the fluid is moved into the discharge piping.

© Blackmer/EbsrayThe sliding vane pumping principle is perfect for autogas handling as it delivers smooth, consistent, non-pulsating flow, even at high differential pressures

Blackmer LGL pumps are available in 1" to 4" sizes, with flow rates from 8 to 32 gpm (30.3 to 121 L/min), and all models are UL-listed for LPG service. The LGL pumps feature a cavitation-suppression liner that reduces the noise, vibration and wear that can be caused by entrained vapors. The sliding vane design gives than excellent self-priming and dry-run capabilities. Blackmer LGL150 Series Sliding Vane Pumps were specifically designed for use in autogas-dispensing applications.

Conclusion
Currently, the search for viable alternatives to gasoline and diesel fuel sees autogas gaining ground and becoming an even larger player in many regions of the world. When determining which type of pumping technology to use at autogas-dispensing facilities, there are two standout alternatives: Regenerative Turbine and Sliding Vane pump technologies, especially those offered by Ebsray and Blackmer. These technologies have been proven to offer the operational characteristics and reliability required to successfully optimize autogas-handling operations.

About the Author:
Thomas L. Stone is the PSG® Director of Marketing based in Grand Rapids, MI, USA. He can be reached via e-mail. For more information on Blackmer’s full line of pumps and compressors, please go to www.blackmer.com or call (616) 241-1611. For additional information on Ebsray’s regenerative turbine and positive displacement pump technologies, please visit the website or call +33 1 55 39 07 40. Blackmer and Ebsray are brands of PSG®, Oakbrook Terrace, IL, USA, a Dover company. PSG is comprised of several of the world’s leading pump brands, including Abaque®, Almatec®, Blackmer®, Ebsray®, EnviroGear®, Griswold™, Mouvex®, Neptune™, Quattroflow™, RedScrew™ and Wilden®. You can find more information about PSG at the official website.