Long in use on land, dry scrubbers are making their appearance at sea, with potentially important consequences under IMO 2020
A three-way partnership between French ferry group La Méridionale, specialist chemicals manufacturer Solvay and scrubber supplier Andritz could revolutionise exhaust gas cleaning in shipping.
Unveiled in November at the Asian Sulphur Cap conference in Singapore, the technology is built around a dry system that fully complies with IMO 2020 while capitalising on low-priced sulphur fuel.
Apart from the favourable economics, the ferry group wanted to please interested parties on terra firma. “[We responded] to the legitimate concerns of the populations, and in particular the residents of the ports in Corsica and Marseille, on the health risks linked to the inhalation of fumes,” said Christophe Séguinor, technical director at La Méridionale. “[The company] needs to be ahead of the curve in the evolution of regulations in the field of air emissions.”
Known as Andritz SeaSOx Dry, the process is based on sodium bicarbonate, a highly reactive absorbent for SO2, and thousands of filter bags to slash the emissions of a range of pollutants down to almost negligible levels. For instance, SO2 escape is reduced to 0.1% and particulate removals come down by a claimed 99%.
Andritz SeaSOx Dry can be installed without recourse to dry-docking; there are no large sea water pumps and electric power consumption is low. Furthermore, the dry scrubbers do not give off discharge water, harmful chemicals or even the white plumes that arouse the ire of climate-change activists.
The filtering process however takes up its fair share of space. Contained in modular chambers, each with 306 bags, the system needs 88kg of bicarbonate per tonne of fuel used.
Although dry scrubbers are new in shipping, the technology has been proved on land, where it has been in operation for decades. However, it had to be made more robust for deep water. For instance, the all-important filter bags were redesigned to withstand pitch and roll.
Convinced of its efficacity, La Méridionale took the plunge in early 2019 and began to retrofit the system to its ferry, Piana. With a total of 38.4 MW of power, the pioneering vessel is an ideal size for a dummy run of SeaSOx Dry. Also, a ferry is a good candidate because it can load up on the chemicals whenever it berths.
The experiment began when the ferry company stipulated a system that would do away with SOx and particulates, but without taking up valuable cargo space or marring the vessel’s stylish aesthetics. Ship management group Orion and Chantiers de l’Atlantique threw their considerable weight into the project.
The main constraints, according to La Méridionale, were the predictable ones of space, weight, effect on stability, susceptibility to vibration and resistance to the salt-water environment. All these had to be tested at sea.
Belgium-headquartered Solvay group provided the sodium-based absorbents on which dry scrubbers rely. Although new in shipping, they are benign mineral powders – non-corrosive, non-irritant and non-toxic – that have long played a role in land-based industry. Onboard, these absorbents neutralise the unwanted residues of combustion. According to the group, the secret of SOLVAir is that the powders are injected directly into the exhaust gas stream where they quickly break down noxious substances.
So far the project has beaten its deadlines; starting in March 2019, the system was installed and all the appropriate certificates issued by October. By early 2020, the first engine in Piana had been retrofitted. The initial tests backed up the claims, with an almost complete eradication of particles. They collapsed to a minimum 99.66% by number and 96.5% by mass.
Fraught in port
The difficulties in disposing of scrubber sludge makes a dry process highly relevant under the new regulations. Although ports are obliged to have sludge-handling facilities under the Marpol regulations, there is considerable doubt about whether they are equipped to do so. “Are ports ready to receive scrubber sludge?” asks one sceptic. “It is not until you actually have a substance you want to discharge to shore that it becomes possible to get a proper answer from the ports.”
Inevitably a lot of paperwork is involved. In Europe, for example, there are a series of EU directives that relate mainly to which particular code is applied to the waste. As IMO 2020 loomed, it was agreed to designate scrubber sludge with a waste code numbered 10 01 18. For the technically minded, this means waste accumulated from a thermal process. Only certified treatment facilities can handle these residues.
Mistaken assumptions about the nature of scrubber sludge are common, in particular that it is scrubbers that create the sludge. In reality scrubbers just end up with it, rather like a dustbin. As Alfa Laval’s specialist in regulatory affairs, Kate Schrøder Jensen, points out in her widely read blog, in a closed-loop operation, scrubbers actually just absorb the by-products of the engines and then clean them up. The result is sludge containing soot and oil compounds – the residue of the combustion process.
“Let me emphasise that there is no material from the scrubber system itself that forms part of the scrubber sludge, as some mistakenly believe,” she says.
Nor is scrubber sludge as dirty as many believe. The residues may be dry (and solid) or wet (and liquid). A liquid sludge usually contains about 5% solids while a dry – or spreadable – sludge contains about 50% dry matter. The watery part of the sludge is composed of mainly water, as you would expect, as well as water-soluble substances such as sulphates and salts that were used in the scrubbing process.
Interestingly, scrubber sludge is not nearly as toxic as some of the headlines have made out. According to experts, it does not contain any more sulphates and salts than, say, the bleed-off water that is discharged (legally) into the sea. And, as the Exhaust Gas Cleaning System Association (EGCSA) points out, while the discharge water is warmer than the ambient temperature by between two and four degrees, it is not nearly as hot as the cooling water off a ship’s engines, which is also discharged into the sea
Scrubbers were widely demonised in the run-up to IMO 2020. As EGCSA points out, they are legal appliances that are in full accordance with all maritime regulations and meet strict turbidity controls.
Moreover, the job of the scrubber is a virtuous one – that is, to neutralise the polluting sulphur oxides into non-polluting compounds of sulphates before the residues are emptied into the sea. All scrubber systems have a compulsory monitoring system that identifies and limits discharges of contaminants.
The numbers support most of the claims for scrubbers. According to EGCSA, although they increase CO2 emissions by between 1% and 2%, this is 10-13% less than the CO2 emissions pumped into the atmosphere from compliant fuel.
The white plume from the funnel of a scrubber-fitted vessel is formed of little more harmful than condensed water. And, it should be said, scrubbers are extremely reliable. According to a range of research, their downtime is put at an infinitesimal 0.01%.
One engine down, three to go
Satisfied with the early results from its dry scrubber, La Méridionale is charging on with a complete retrofit of the system to the ferry’s entire propulsion system – four main engines, three auxiliary engines and two boilers. A smaller ferry, Kalliste, is being studied for its own retrofit to four main engines with a total capacity of 21 MW, three auxiliary engines of 3.0 MW, and two boilers.
Starting in early 2020, the next step, says the group, is to test an integrated filter-bag system that will attack SOx, NOx and fine particles under what is known as ‘multi-pollutant control’. At that point, the economic argument becomes compelling because the ferries would then be as environmentally efficient as LNG-powered vessels.
This would certainly provide food for thought for those shipowners who want to hedge their bets and stay with standard fuel.
Like other manufacturers of scrubbers struggling to cope with a backlog of work, CR Ocean Engineering has a full order book dominated by bulk carriers, container ships, oil and chemical tankers. Of the group’s 159 actual and prospective installations, bulk carriers account for no less than 65, with container ships (33) and tankers (32) a long way behind. Between them, roro, cargo, ropax and cruise ships number 21 installations.
As the global fleet races to comply with IMO 2020, in some cases belatedly, manufacturers like CR Ocean Engineering, which has been in the scrubber business since the 1960s, have found that versatility pays. The global group has different configurations to suit most types of vessel, including open loop, closed loop and hybrid versions.
Overwhelmingly, the global fleet is turning to scrubbers to meet the sulphur cap. According to class society DNV GL, as of September 2019, the figures showed the uptake of exhaust gas cleaning systems ran to an astonishing 3,763 ships. That compares with precisely 890 ships using rival technologies. Of these, battery power and LNG easily dominate with 368 and 354 ships respectively, followed by LNG-ready vessels (141), with hydrogen, methanol and LPG nowhere, at least not yet.
Despite the bad press that scrubbers have received in the last few months, shipowners do not appear to be listening. Figures compiled by DNV GL suggest scrubber assembly lines will be cranked up to full speed for at least the next four years. Existing scrubber orders are heading to 4,000 a year right through to 2023. Bulk carriers and container ships figure most prominently in the queue.
And the clear preference is for open-loop types that account for 80% of expected installations. Japan has come down heavily in favour of open loops on the grounds they remove airborne particulate matter and polycyclic aromatic carbons. Hybrids are running a poor second with 18% and closed-loop scrubbers, the type favoured by environmentalists, with just 2%. Whatever the type, a full three quarters of scrubber projects planned or in hand are for retrofits, with the rest for newbuilds.
Crucial to the scrubber issue will be how fuel prices move in early 2020. If low-sulphur fuel turns out to be too expensive for shipowners, most of the above projects are expected to go ahead, plus a lot more in what amounts to a bonanza for the scrubber industry.