Liquefied petroleum gas (LPG) and Bio- LPG has been gaining significant importance as clean and efficient alternatives to fossil fuels. In the LPG supply chain, side channel pumps efficiently support the transportation,
storage, and distribution processes of these gases because of its special advantages.
By Beate Zientek-Strietz , General Manager of SERO PumpSystems GmbH
Liquified Petroleum Gas- An Ideal Energy Source
Liquified petroleum gas (LPG) is a gas mixture that is liquified under pressure and consists of propane and butane, or a combination. LPG is produced during the extraction and refining process of crude oil. As of recently, Bio-LPG has been gaining momentum in the industry; this resource is extracted from waste, residues, and sustainably produced vegetable oils. It contains the same physiochemical properties as LPG.
Each variant of LPG is kept under low pressure at room temperature, which makes it cost-effective and transportable in comparison toliquified natural gas (LNG) and compressed natural gas (CNG). Liquified natural gas requires storage temperatures of -170 °C to -120 °C; CNG requires pressurization of 200 bar to 250 bar to remain liquid. The storage technology and the distribution logistics involved in transporting these energy sources are increasingly complex.
From a technical point of view, LPG energy is more convenient to manage and for a long time, the economic value of this resource was low. As an effort to make use of diminishing resources, reduce emissions and handle the recent rise in the price of LPG, attitudes towards this source have changed over time. The chemical industry and process engineering use LPG for a wide variety of applications.
In addition to this, large residential and building complexes utilize LPG by storing it in main tanks and making the resource available for various points of consumption, such as feed steam or generating electricity for heating and driving engines. LPG and Bio-LPG are versatile energy sources and are ideally suited for transportation at a low pressure.
Transporting LPG in Hybrid Marine Propulsion Systems
LPG tankers with dual-fuel propulsion systems are used to transport gas from the point of production to consumers on six continents and in over 125 countries. The marine side channel pump is integrated into the secondary fuel supply systems (SFSS) of hybrid ship propulsion units. This pumps LPG to the main shipboard engine. This pump features a low intake head, uninterrupted and constant pressure delivery of low-viscosity media and insensitivity to vibrations. This ensures high functioning reliability and availability of seaworthy side-channel pumps.
Both high and low-pressure versions of these pumps have successfully proven to integrate into SFSS for various large-scale gas carriers.
LPG Terminal- From Tank Farm to LPG Tank Car
When LPG is transported onto the seaway, it goes through a process of being landed on a large LPG terminal where it is stored temporarily for distribution. Once inside the large tanks, LPG is pumped into smaller sized tanks known as tank trucks or LPG tank cars.
Side channel pumps with mechanical seals and ‘seal-less’ pump alternatives that have magnetic couplings are ideal for this process. Both side channel pumps feature low NPSH requirements, operating reliably even at inlet heads of only a few centimetres. Each pump carries a range of speeds to make it possible to adjust the delivery rate and volume output during operation. The gas entrainments that are generated during the pumping process are returned to the suction side tank by a gas displacement line. This is an upstream installment on the pump; any remaining gas is carried along with the pumped media without interrupting the delivery flow. The LPG side channel pumps keep the flow rate constant, even during potential pressure fluctuations.
Transporting LPG to Supply Filling Stations
LPG is transported locally and regionally by trucks with demountable tanks or semi-trailers. From the LPG terminal, the liquified petroleum gas is sent to commercial or industrial LPG filling stations to process engineering operations in chemical companies.
The tank trucks are equipped with side channel pumps that have mechanical seals to transport the LPG from the vehicle tank into the stationary storage tanks. Pumping from the mobile station to the stationary tanks occurs at the boiling point of the liquified gas. The possibility of being able to convey large amounts of gas produced in the process is an advantage of side channel pumps, in addition to its vibration-free and low-noise operation features.
One Pump, Two-Phase Flow
Pumping LPG with low flows at high differential pressures determines the application of the side channel pumps, whether it is using a mechanical seal or a magnetic coupling. The pump is installed directly in the storage tank. If the tank is above-ground, the pumps regulate the low inlet height creating a low NPSH value in the application. A special version of the side channel pump can achieve a geodetic suction head of up to four meters, this allows LPG to be pumped from underground tanks as well.
The pumps can deliver a two-phase flow with up to 50% gas content without tearing and although this may be of no interest to consumers who value ʽbubble-free’ refuelling, gas-free transport cannot always be guaranteed. A gas separator is installed downstream of the side channel pump and removes any gases that occur during the refuelling or withdrawal of LPG, especially during the installation of the pump.
Modular Pump Design- Adaptable Flow Rates
Due to LPG’s versatility, this source is supplied in cylinders which are filled beforehand in individual processes. Side channel pumps with mechanical seals and magnetic couplings are accompanied by hermetically sealed, leak-proof product chambers. These chambers are optimally designed in a modular system to meet the required delivery rates of cylinder filling.
Typically, the process reserves 20% of the delivery rate to compensate for pressure changes to increase system availability and production reliability. During operation, the pumps supply the filling process with liquified gas
which is timed by a filling valve that opens and closes briefly. The various speed range of the pumps enable variable and precision adjustments to delivery rates, simultaneously. Once a cylinder is filled, the cylinder is sealed, and the LPG is pumped back into the tank on the suction side by utilizing a bypass.
Side channel pumps can be found on LPG tankers with dual-fuel propulsion, in tank farms, on tank trucks, at LPG filling stations or for cylinder filling. There are various models of this multi-stage pump which can accommodate pumping capacity requirements, process, and installation conditions. Typically, side channel pumps are designs that include ring-section casing construction, which offers optimum integration options and delivery rates due to its low NPSH values. The side channel pump is capable of handling LPG volumes from 0.3 m3/h to 35 m3/h and always guarantees an uninterrupted delivery flow, despite the possibility of facing gas entrainments in pumped media.