Germany’s Nature and Biodiversity Conservation Union (NABU) announced the results of a study it says shows that “scrubbers are no solution to air pollution from ships.”
The recent tightening of the fuel sulphur limits for fuel used in Sulphur Emission Control Areas (SECAs) requires the use of fuels with a maximum sulphur content of 0.1% in these regions, or a technology that can reduce emissions to an equivalent level, from January, 1st 2015. Most low sulphur fuels are distillates (e.g. marine gasoil MGO, which are more expensive than the residual fuels that are traditionally used by ships (e.g. heavy fuel oil HFO)). Exhaust gas scrubbers, in combination with the use of HFO, have been accepted as an alternative means to lower sulphur emissions.
Four different types of scrubbers are available today:
- Seawater scrubbers (open loop) utilize untreated seawater, using the natural alkalinity of the seawater to neutralize the sulphur from exhaust gases.
- Freshwater scrubbers (closed loop) are not dependent on the type of the water the vessel is operating in, because the exhaust gases are neutralized with caustic soda, which is added to freshwater in a closed system.
- Hybrid scrubbers give the possibility to either use closed loop or open loop technology.
- Dry scrubbers do not use any liquids in process but exhaust gases are cleaned with hydrated lime-treated granulates.
The scrubber market is highly dynamic at the moment, due to the recent tightening of the SECA fuel sulphur limits. The number of scrubbers installed on ships has increased significantly over the last years. About 80 scrubbers are installed at the moment, most of which are hybrid or open loop scrubbers. The number of orders amounts to approximately 300 at the time of writing. Available outlooks forecast a potentially more important role for scrubbers in the next decades as a means to reduce sulphur emissions, but at the moment the majority of ship owners have switched to MGO and investments have been postponed.
The study analyses environmental and economic aspects of the use of exhaust gas scrubbers in comparison to the use of MGO. Seawater scrubbers discharge different kinds of pollutants to the marine environment. Moreover, the study analyses the impacts of the pollutants on aquatic coastal ecosystems. The economic impacts are assessed for a 38,500 DWT product tanker.
Scrubbers reduce the emission of sulphur to the atmosphere by more than 90%. Also PM emissions, in terms of mass not number, are reduced significantly, by 60-90%. The emission of NOx is reduced by 10% or less. Due to the additional power needed to drive pumps and caustic soda consumption, the estimated additional GHG emissions range between 1.5 and 3.5%, including caustic soda consumption for the latter figure. It should be noted, however, that also the use additional MGO in the SECA causes an increase of GHG refinery emissions by roughly 6.5%.
Concentrations of hazardous substances in the discharge of closed loop systems are higher than in open loop systems, but the mass flow rate of these substances determines the environmental impact. This is larger in case of seawater scrubbers, which are not always equipped with discharge water cleaning systems.
The current dominance of seawater and hybrid scrubbers indicate that a large share of the pollutants captured in the wash water may be released to the sea water.
Although the IMO wash water criteria for scrubbers are generally met, scrubbers may have a negative impact on marine environment due to acidification, eutrophication and the accumulation of hazardous hydrocarbons and heavy metals in case dilution is limited. This may lead to a deterioration of the water quality. The long term impacts of the use of open loop scrubbers, especially in vulnerable coastal areas with a reported moderate water quality, therefore needs to be investigated systematically by measuring and modelling of the water quality. On the basis of such results, it should be evaluated if scrubbers can be used in accordance with the European Water Framework Directive and Marine Strategy Framework Directive that set maximum concentrations for certain hazardous pollutants, prohibit deterioration of water quality, and aim to achieve ‘good environmental status’ respectively. Few EU countries decided to ban the use of open loop scrubbers in their waters to protect against potential contamination.
The use of MGO or LNG is inherently cleaner than the use of seawater scrubbers because no contaminated wash water is discharged. Additional impacts of increased MGO production on land, apart from increased energy use, are expected to be limited, due to the stringent environmental legislation and enforcement.
Scrubbers’ business case
The installation of scrubbers requires significant investments. Typical installation costs range between 200 and 400 EUR/kW, which imply an investment of several millions, depending on a ship’s engine power.
It is difficult to draw firm conclusions on the profitability of using scrubbers, as this depends on the operational profile of the ship, the difference between HFO and MGO prices, and the time ships sail in SECAs. The fuel price difference between MGO and HFO ranged between 240 and 300 $/ton between January 2014 and February 2015. When the difference is high, scrubbers are profitable in more cases than when the difference is low.
Under optimistic conditions, ship owners may be able to offer services at relatively low prices, but consequently there is a risk that scrubbers may lead to higher transport costs for operators instead of lower. The annual depreciation costs of scrubber installations are relatively high in comparison to a ship’s annual hire costs, illustrating the significance and potential risk of the investment. Table 1 provides an overview of the impact of uncertain parameters on the annual benefits of scrubber installation.
Due to the additional costs of caustic soda consumption, it is likely that hybrid scrubbers will be used in open loop where possible and that the number of freshwater scrubbers installed will remain limited.
To assess the cost and benefits for the society as a whole, the benefits for ship owners would need to be weighed against the potentially harmful impacts of scrubbers on vulnerable coastal ecosystems. Such an analysis is conditional to the availability of monitoring and modelling of the impact of scrubbers on the water quality and marine ecosystems.
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