DOSSIER

 

Using side channel pumpson LPG tankers


Side channel pumps use a mixture of suction and rotational energy to move a fluid, so are ideal for gas-liquid mixtures, such as LPG. The suction part can move the gas, the rotational energy can move the liquid. The ‘side channel’ refers to a channel the gas-liquid mixture is moved into.

by Klaus Reischl, sales manager, SERO PumpSystems GmbH


Side channel pumps for the delivery of LPG are used on LPG tankers, capable of handling LPG volumes from 0.3 m3/h to 35 m3/h.

They always guarantee an uninterrupted delivery flow, even with gas entrainments in the pumped media.

In extreme cases, the SHP can reach a head of almost 1,200 meters at a flow rate of only 1 m3/h.

SERO’s “SHPmarine” side channel pump can be used in the hybrid ship propulsion system of a LPG gas carrier, in the Secondary Fuel Supply Systems (SFSS), to transport the LPG from the storage tanks on board to the propulsion engine of the seagoing vessel.

Both high-pressure and low-pressure versions have recently been integrated into the Secondary Fuel Supply Systems of various large gas carriers and successfully commissioned. Tugboats fuelled by LPG are also being considered.

The fuel consumption of a typical LPG tanker is between 3,000 and 5,000 litres of propane per hour depending on its size and maximum attainable speed. The SHP is required to consistently feed the SFSS and in turn the main propulsion engine at this rate and with a pressure head of approximately 1100 meters.

 

Background to LPG fuelled tankers


Liquefied petroleum gas (LPG) is a gas mixture liquefied under pressure, consisting of propane and butane. It is produced during the extraction and refining of crude oil.

LPG tankers transport the gas from the point of production to consumers on six continents and in more than 125 countries. They can also use LPG as a fuel. LPG transported on the seaway is usually landed at large LPG terminals where it is temporarily stored for further distribution.

On LPG tankers, the actual transported LPG, previously untouched as cargo, is used as the main fuel source.

After unloading the cargo, the gas consumption used for the voyage is deducted from the initial gross cargo load and payment is settled between the ship owner and the client.

IFO (Intermediate Fuel Oil) now serves only as the back-up fuel or for manoeuvring with minimal engine power. Consequently, smaller loads of diesel fuel are required allowing for faster refuelling of the ship, saving both time and money.

LPG is sulphur free. This means that using it as a fuel allows easier compliance with the stringent emission limits on the high seas and the even stricter regulations near the coast.

Using LPG reduces operating costs as it is significantly cheaper than (low sulphur) IFO.

Bio-LPG can be extracted from waste, residues and sustainably produced vegetable oils, with the same physical and chemical properties as LPG. Both LPG variants can be stored under comparatively low pressure at room temperature, which makes transport easier and more cost-effective.

In comparison, liquefied natural gas (LNG) requires storage temperatures of -170 °C to -120 °C; compressed natural gas (CNG) requires pressurization of 200 bar to 250 bar to remain liquid. Storage technology and distribution logistics with these two energy sources are correspondingly complex.

Even though the LPG supply chain is significantly easier to manage from a technical point of view, for a long time the economic value of LPG was so low that it was simply flared - i.e., disposed.

Attitudes towards LPG have changed, to make efficient use of dwindling resources, to protect the environment by reducing emissions and - at the latest since the beginning of 2022 – also to handle exponentially rising energy costs.

In the chemical industry and in process engineering, LPG is used in a wide variety of applications as an economically interesting raw material and energy source.

As a fuel, LPG is offered by more than 6,000 filling stations in Germany alone. Numerous vehicle manufacturers, such as Renault, are selling vehicles with combined gasoline-LPG drives as an alternative to electric hybrids.

In industry as well as in large residential and building complexes, LPG is being stored in main tanks and made available at a wide variety of consumption points, for example, to feed steam and generate electricity, for heating or to drive engines.

Due to its ease of transportability at low pressure, LPG is suited to be filled into LPG cylinders in automated plants and delivered to private households as well as companies.

The World LPG Association refers to more than 1,000 different applications on its website (www.wlpga.org) - many of them along the logistical LPG supply chain.

 

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