Besides OPS, there are several other techniques available for limiting the emissions of ships at berth, the impact of which may differ widely, though, from both an environmental and health perspective. OPS, for example, reduces emissions of air pollutants, CO2, noise and vibration, while most other techniques fail to reduce CO2 or noise. It should be noted, however, that onboard techniques can be applied in any port, whereas the availability of OPS is limited to some ports only. More information on different technical solutions to reduce emissions can be found on the CNSS website. Below, we briefly discuss the most relevant alternative techniques.
There are several other shoreside emission reduction or treatment options available to ships at berth. For implementation of these techniques, except the baghouse system, the receiving vessel requires adaptation. The baghouse system can be used on virtually all visiting ships.
Shoreside electricity production (off-grid shore power)
One option for shoreside power is to use generators installed on the quayside. If these are mobile, it will permit more flexible deployment of the system. Although in some senses similar to OPS, this system will not eliminate the local emissions of power generation.
Generator performance in this respect can be improved by burning relatively clean fuels like Compressed Natural Gas (CNG) or Liquefied Natural Gas (LNG).
Onshore steam production
To limit air pollutant emissions due to the use of fuel boilers while in port, steam can be provided by electrically powered onshore steam boilers.
Onshore gas supply
To limit quayside emissions from auxiliary engines, ships can in principle be fitted with bi-fuel engines so that when docked they can use natural gas provided by an onshore fuel system. Natural gas causes lower emissions of CO2 and air pollutants than standard marine fuels. Quayside supply of gas will mean less extensive redesigning or refitting of vessels, as the need for storage tanks is eliminated. As stated, though, this option means adapting the ship's engines for use of gaseous fuels (dual fuel capability). Such systems are currently being developed and tested, but are not yet commercially operational.
Engine emissions can also be reduced by fitting or retrofitting engines based on enhanced combustion techniques, ranging from water injection into the cylinder to exhaust gas recirculation. The various combustion techniques target specific emissions.
Emissions from auxiliary engines and turbines can be reduced by burning cleaner fuels, ranging from conventional fuels with a lower sulphur content to fuels unconventional to shipping, like LNG. This option is limited to certain ferries and RoRo ships and LNG supply vessels, however. Click here for more information.
Exhaust gas treatment
An alternative to emission prevention is emissions reduction using onboard exhaust gas treatment systems.
Selective catalytic reduction (SCR)
SCR limits NOX emissions by injecting urea/ammonia into the exhaust gases and feeding them through a catalyst. The process converts NOx into nitrogen and water.
Particulate Matter filters
Emissions of particulate matter (PM) can be reduced by means of a particulate filter. In this case the exhaust gases are fed trough a ceramic-coated filter that traps the particles. Once saturated, the filter must be cleaned by burning or mechanically, depending on the type of filter. Particulate filters can only be used in combination with very low fuel sulphur levels (10 ppm).
For more information on this issue, see studies by ENTEC UK on NOX and SOX.