Onboard sulphur filtering: A new 2020 vision
Onboard desulphurisation could offer an alternative to low-sulphur fuel, scrubber installations or LNG for complying with the IMO’s global sulphur cap from 2020, according to maritime technology supplier Green Framework.
Employing a desulphurisation process originating in the oil industry, the New York based company has developed De-Sul, an installation that is claimed to remove almost all of the sulphur from HFO. Sulphur content of 3.5% in HFO 380 would be reduced to 0.1% or less after treatment.
Unlike a scrubber which filters out SOx from exhaust gas, De-Sul removes sulphur from fuel before it enters the engine. The installation is roughly the size of a 20ft container, though slightly taller, and is installed between the main fuel tank and the day tank aboard ocean going vessels above 400gt.
De-Sul gets sulphur out of HFO through a pre-treatment that makes the sulphur molecules stick to the thicker and heavier particles in HFO, which are then filtered out. The sludge has to be collected in a separate tank. Out of every 33 tons of HFO used, one ton of sludge will be separated. At bunker stations, the sludge has to be pumped out. This sulphur waste could then be used for creating purified sulphur for fertilisers and other applications.
The company has built a prototype of De-Sul this year, although the installation has not yet been tested in daily operation aboard a ship. Green Framework's performance expectations are based on earlier runs following the same procedure when desuplhurising crude oil at a Russian test facility. The oil, containing an even higher sulphur level then HFO, was effectively purified down to a sulphur level of 0.1%.
Green Framework CEO Barbara Weingarten said that she hoped that the IMO would consider De-Sul as an authorised device to reduce sulphur emissions below the 0.5% global cap and even the 0.1% fuel sulphur limit in emission control areas. This is likely to happen only after several hundred De-Sul installations have been proven successful aboard ships, she noted. Until then, both day tank fuel samples and continuous exhaust gas monitoring will have to be applied by the ship's crew in order to prove compliance with IMO exhaust regulations.
Weingarten said: “Scrubbers easily cost over a million dollar and will take weeks to install. De-Sul will cost only a fraction, can be installed in two days and takes a lot less space aboard and adds less weight. With De-Sul, the cheaper HFO can be bunkered. First calculations show that the earn-back time for De-Sul can be as short as three to four months, for a vessel that typically sails 300 days a year with a 40–50 tonne fuel consumption every 24 hours.”
The molecular pre-treatment and filtering of sulphur from HFO is different from the method used at oil refineries to get sulphur out of fuel oil. The chemical process of hydro-cracking requires big machines and the addition of large amounts of fresh water. It also causes air contamination in the process. The use of De-Sul would enable ship owners to bunker everywhere along the existing bunkering networks, as no alternative fuels are required. An infrastructure for collecting and re-using the sulphur sludge would be needed.
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