2017-01-03 来源: 51Due教员组 类别: Essay范文
Following the assessment of the amount of emissions to air from shipping in chapter 3 and the effect on climate and ozone described in chapter 4, this chapter focus on alternatives for reduction of emissions to air from ships. In the following both technical and operational measures are presented.
The assessment of various options was performed with both a short term and long term perspective. In the context of this report, short term is closely related to availability of technical measures. As applicability of various measures may be different for new and existing ships, the discussion of the various technical alternatives was divided into one part concerning new ships and one part concerning existing ships.
Short-term considerations – applying state-of-the-art knowledge
Hull and propeller: new shipsThis section focuses on the energy savings that can be obtained by application of current technology within hydrodynamics (hull and propeller) on new ships. Energy savings can then be easily converted into emission reductions.
International merchant shipping is a highly economically optimised business. Fuel cost is a major operating cost of most merchant ships. Ship designs are usually fairly well optimised with respect to maximum profitability. Thus, one should expect that there is not much efficiency to be gained by better design and selection of propulsion systems without changing the external economic conditions. Also in this section, measures that are not currently profitable will be discussed.
Retarded fuel injection timing is the simplest way to reduce NOx from a ship diesel engine. This measure can be implemented without hardware modification or extra cost. Retarded timing alone have a ne
Retarded fuel injection timing is the simplest way to reduce NOx from a ship diesel engine. This measure can be implemented without hardware modification or extra cost. Retarded timing alone have a negative effect on fuel consumption (specific CO2 increases). Reduction of the NOx emission level in the range of 6-8 g/kWh is possible, but at a cost of an increased fuel consumption of 5-7 g/kWh. Most measures imply retrofit and engine modifications aiming for an improved combustion in order to reduce CO2 and NOx emissions. The possible measures descried in the following are all primarily for NOx reduction and imply additional or modified equipment installed.
Low NOx combustion:
Some engine manufacturer can offer retrofit/upgrading packages for ”low NOx combustion” without increase of fuel consumption. A low NOx combustion upgrade on an existing engine implies to some extent engine component retrofit. The reduction of NOx emission is in the range of 4-6 g/kWh [W?rtsil? NSD, 1997].
Water injection to reduce NOx is an effective measure (50-60% NOx reduction) which can be retrofitted on existing engines. The main components are the combined injector, common rail water supply system and electronically control system. Retrofit cost figures are estimated to approximately 25 USD pr. kilowatt. The operating cost inclusive maintenance is about 4-5 % of fuel costs [W?rtsil? NSD, 1998, Diesel & Gas Turbine, 1999].
Fuel emulsion (adding water in fuel) is a NOx reduction measure where the necessary equipment can be installed on existing engines. The reduction potential without penalty on fuel efficiency is in the range of 20-25%.
Humid Air Motor (HAM):Implementation of the HAM technique on existing engines can result in up to 60% reduction of
NOx emission level. The technique is however new and the long-term operational effect is not fully proven. In existing ship it is in most cases difficult to install the HAM equipment, mainly because of the rearrangement of the air supply system to the engine and the additional space required. Most engines have a turbo-charger and aftercooler system that is heavily integrated and matched for the specific engine. Engine manufacturers may be reluctant to modify this original integrated system solution [Bunes et .al, 1998, Munters Europa 1998].
Miller Cycle:The Miller principle and measures as described on new engines are also valid for existing engines.
Exhaust Gas Re-circulation (EGR): Several problems need to be addressed and solved before EGR will be an applicable measure for existing or new ships. The main challenge is the re-entrance of particul
Exhaust Gas Re-circulation (EGR):Several problems need to be addressed and solved before EGR will be an applicable measure for existing or new ships. The main challenge is the re-entrance of particulates damaging for the engine, especially when running on HFO and therefore very limited application is foreseen
[EPA 1998, DNV, 1998].
A properly operating SCR installation can remove up 95 % of NOx components from the exhaust. It can be installed on existing machinery as retrofit packages, which includes the reactor, urea storage/dosing and control system. For installation on an existing ship there are some practical limitations due to the need for space. Although the reactor can replace the exhaust silencer it can be rather costly to install. In addition to the space for the reactor, there is also need for storage space for urea.
CO and HC
Efforts on upgrading an existing engine normally also pay off with minor reductions on CO and HC emissions. In the overall perspective these gains are very small as the CO and HC emissions from the diesel combustion process are very low initially. Due to this reduction measures for CO and HC have not been further assessed in this report.
The SOx emissions are related to the quality of the fuel. Only a dramatic turnover from high sulphur to low sulphur fuel oil can have a major impact on SOx emissions from the existing fleet.