The hydraulic-powered deep-well pump is a firm favourite among tanker owners, but the need to optimise energy efficiency is driving the transition towards an electric-powered alternative
The engineering design of the hydraulic deep-well pump is well established and generations of sea-going engineers have grown familiar with its operation and maintenance. Changes to the fundamental design have been glacial. As a result, the hydraulic-powered deep-well pump is a popular design and the first choice of many owners when drawing up systems for the cargo-handling systems on chemical and product carriers.
MarFlex sales and marketing manager Lisa van Beveren spells out the advantages of the deep-well pump: “In a deep-well pump concept, all the tanks can be discharged individually and the customer is able to transport various cargo types. The concept offers the shipowner flexibility and operational advantages.”
These designs tend to inspire loyalty, as Histria Shipping’s technical director Marius Szabo told Tanker Shipping & Trade during a review of tanker newbuilding Histria Atlas – the first of the EcoMax series at Romanian shipyard Santierul Naval Constanta. “We have ships in the fleet that have run Framo pumps for 14 years without any problems,” he said. These deep-well pumps were hydraulic-powered, and building on this expertise and familiarity, Framo also supplied the hydraulic-based bow thruster control system for Histria Atlas.
A hydraulic-powered deep-well pump system includes a hydraulic power pack, hydraulic cargo pumps, a hydraulic fluid reservoir, filters, hydraulic piping (high and low pressure), a heating and cooling system and a control system. The hydraulic power pack consists of high-pressure pumps driven by electric motors with power supplied by a dedicated generator or from the general-purpose generators. The power pack is situated away from the cargo pumps and connected by high-pressure hydraulic power lines and low-pressure hydraulic return lines and the cargo hydraulic pump is situated in the tank.
The hydraulic power pack provides very high pressure to several deep-well cargo pumps and to stripping pumps and/or ejectors. There will also be hydraulic power take-offs available on the system to allow the use of mobile hydraulic cargo pumps. There will be one or more hydraulic power pack to ensure redundancy cover and in the case of the Histria Atlas, these are also connected to the hydraulic pump in the bow thruster.
A separate control panel exists for the hydraulic system, separate storage for the hydraulic oil and another storage tank for the waste oil. Hydraulic oil works most efficiently within a certain temperature range and provision is required to heat and cool the oil. For instance, Framo states its cargo pump is designed for any cargo temperature prevailing in tankers.
While the vessel is at sea, the hydraulic pressure in the system in maintained by a feed pump, which runs continuously even when cargo operations are not taking place. This prevents moisture contaminating the hydraulic oil if there is a leak. It also maintains a stable temperature in the system by continuously circulating hydraulic drive oil. The hydraulic oil must be tested for impurities and regular maintenance undertaken to check for leaks.
Brands maintain loyalty through incremental changes, detailed training and a full suite of spares. There are decades of goodwill attached to hydraulic-powered deep-well brands.
As Svanehøj’s sales and projects director Johnny Houmann notes: “There has been very little change over the last decade.” The use of hydraulic-powered deep-well pumps in cargo tanks might have continued unchallenged for decades, but for the growing awareness in shipping of the industry’s contribution to greenhouse gas (GHG) emissions. The green shipping movement is at its strongest in Scandinavia, where owners are optimising the specification of tankers to minimise fuel consumption, and at the same time minimise GHG emissions.
Mr Houmann describes the current mood among owners: “There is a new focus on efficiency, more so than in the past. More and more shipping companies want to have a green profile and to truly optimise their vessels for uptime, redundancy, HSE, capex and opex and ultimately to save fuel and CO2 emissions.”
The emphasis has been on saving fuel to reduce emissions, but the big and easy steps have now been taken. Owners and operators must now tackle the harder-to-optimise areas of a tanker. Energy consumption from ancillary processes derived from the cargo-handling process is one such function. This is the area the producers of electric-driven, deep-well pumps are targeting. But it is not all sales talk.
From an engineering point-of-view, using an electric motor to power a pump to pressurise fluid to transfer the energy to another pump does appear to have some redundant steps; there is the potential for energy loss along the way and it is somewhat inelegant. Better surely to power the cargo pump directly with an electric motor? The advent of modern electronics has enabled this step to be taken.
The electric-driven deep-well cargo pump system requires a control panel in the cargo operations space or room, and a separate space to house the frequency converters to control the electric motors. On some ships these are housed in large panels, but there is a move to provide smaller ‘shoebox’ frequency converters.
The space required for the two set-ups is very different. In a widely quoted study from 2007, naval architects Deltamarin of Finland was asked to compare the use of hydraulic-powered deep-well pumps and electric-driven alternatives. The study found that for a 46,000 dwt oil products and chemical tanker, the space required for the hydraulic set up was approximately 80 m2, versus 30 m2 for the converter room. In terms of weight, the difference is approximately: 79.5 tonnes and 75.0 tonnes for the hydraulic and electric system, respectively.
The electric-driven deep-well cargo pump set up is very different. An electric-driven deep-well pump does offer scope to optimise efficiency. The total power consumption compared to a hydraulic-driven deep-well pump system is about 20% lower. Furthermore, an electric-driven deep well pump system has at its core frequency converters.
The converter control system provides insight into the status of the system. The electric-driven system can be operated from multiple locations (bridge, touch screen, cargo computer or local deck control). Noise is also quoted as a beneficial factor among proponents of electric systems, although modern, hydraulic-powered deep-well pumps do not produce the ear-shattering scream of older units.
According to MarFlex’s Ms van Beveren: “The electric-driven system is also relatively simple to install. The hydraulic system has a hydraulic power unit with high pressure pipelines on deck. The installation of a hydraulic system is complex and extensive, since flushing is required which is not necessary with an electric driven system.”
She also notes that: “With only electric motor cables on deck, the risk of hydraulic oil spills is excluded. Altogether, the electric-driven system offers a rapid installation, limited commissioning, easy and efficient maintenance (less wear and tear parts), limited usage of space (and less space in accommodation for the drive system), and limited weight.”
She adds: “The electric-driven system is ideally suited to operate in arctic and tropical environments. Operating the electric-driven system in an arctic environment offers the opportunity to save energy because there is no heating of substantial quantities of hydraulic oil required and naturally, fast recovery and start-up of the pump system after the winterisation period is possible.”
MarFlex says its electric-powered deep-well pump operates down to -60oC and is ATEX compliant according to Annex III of the Directive 2014/34/EU. The EU Declaration of Conformity refers to compliance of MarFlex’s quality management system with Annex IV of the Directive. This means that these type-approved products can be built, tested and delivered without project-based verification by an approved third party. MarFlex also provides specialist services for its deep-well pumps, such as in-house-engineered smart software and strength and tank design calculations to prevent resonance during discharge operations.
Svanehøj’s Mr Houmann explains: “An electrical pumping system is an integrated system. With the installation of frequency converters a great number of other features on board can be utilised. The frequency converters can be used for running and controlling the bow thrusters and for driving the shaft generator as a take-me-home feature for emergency use in case of breakdown of the main engine.”
This is where the latest and most significant gains in optimisation are being derived from among electric-powered deep-well pumps – the interconnectivity and data gathering. The electric nature of the control systems for the deep-well pumps and the integration of the frequency converters with other electric-powered devices opens a pathway to in-depth data gathering on energy use and vessel performance at a micro and macro level.
This represents the next stage of electric-driven deep-well pump development, according to Ms van Beveren: “Based on data analysis and understanding what is happening on board, we developed software in-house that is protecting our pumps during operation. Next to this, the power consumption, in combination with the performance, can be further optimised.”
Mr Houmann also sees a step change in the attitude of shipowners: “We are talking to owners who in the past have only purchased hydraulic-powered deep-well pumps. The potential saving in energy consumption between a hydraulic system and an electrical system is 15-20%. This is very attractive to an efficiency-minded owner.”
Indeed, Furetank of Sweden has specified 12 Svanehøj DL132/150 electric-powered deep-well pumps on eight new intermediate-sized product tankers being delivered between 2019 and 2021. Furetank AB vice managing director Per-Anders Höglund explained: “Electric cargo pumps are more energy efficient, so they help reduce our ships’ fuel consumption and CO2 emissions. We are reducing the risk of oil leaks and, at the same time, avoiding the noise nuisance which is experienced with hydraulic pumps.”