Alarming amounts of ships exhaust gases emitted worldwide forced the International Maritime Organization (IMO) to issue some restricted maritime legislation for reducing the adverse environmental impacts arising from such emissions. Consequently, ships emission reduction became one of the technical and economic challenges that the ship operators are facing. The present paper addresses the different strategies that can be used to reduce these emissions, especially nitrogen oxides and sulfur oxides. Applying one of those strategies is the matter of ship type and working area. The outcomes are very satisfactory from the point of view of environment and economic issues and reflected the importance of implementing these strategies.
Until recently, most people concerned with air pollution impacts did not consider much about oceangoing ships (Trozzi, 2010). Around 90 per cent of world trade is carried by the international shipping industry. Without shipping, the import and export of goods on the scale necessary for the modern world would not have been possible. Seaborne trade continues to expand, bringing benefits for consumers across the world through competitive freight costs.
Thanks to the growing efficiency of shipping as a mode of transport and with increased economic liberalisation, there are bright prospects for the industry’s further growth. There are over 50,000 merchant ships trading internationally, transporting every kind of cargo. The world fleet is registered in over 150 nations and manned by over a million seafarers of virtually every nationality. Shipping is regulated globally by the International Maritime Organisation (IMO). The harsh nature of the sea exposes ships to considerable physical risk, thus a total commitment to safety pervades all deep-sea shipping operations. Shipping is the least environmentally damaging industry compared to land-based industry.
An Overview of Emissions
Exhaust gas emissions is increasingly becoming a topic of public interest in the context of merchant shipping industry, especially from marine diesel engines, comprising nitrogen, oxygen, carbon dioxide (CO2), carbon monoxide (CO), oxides of sulphur (SOx) nitrogen oxides (NOx), hydrocarbons (HC), water vapour and smoke (Corbett et al., 1997). NOx and SOx are of special concern as they are threats to vegetation, the environment and human health (Cooper, 2003). Compared to automobiles, the quality of fuel used in ships is inferior, highly viscous and contains higher sulphur. Seaborne emissions lead to rise in global temperature and melting of glacier and polar ice resulting in damage to ecosystems and contribute to ocean acidification.
Efforts are being made by engineers and scientists to minimise the emission of pollutants viz., CO2, CO, HC, NOx, sulpher dioxide (SO2) and particulate matter (PM) to the environment during incomplete combustion of fuel in an internal combustion engine.
Need for Emission Study along India’s Coastline
It is evident from literature that adequate data is available only for the European shipping routes and minimal data or only satellite data is available for the Indian seas. There is a need for emission study comprising of adequate data collection along the coastline of India. Geographically resolved emissions inventories have shown that ships in global trade operate 70 per cent of the time within 400 km away from shore. With long range transport of air pollution, these emissions near the coastline contribute to poor air quality in the downwind regions. In fact, in many coastal and port regions along heavily travelled international routes, annual emissions from ships equal or exceed those of adjacent land-based sources.
India’s extensive 7,500 km coastline is dotted with a dozen major ports and some 200 minor and intermediate ports. The Port Trust of India, is mandated by the Indian government to run all the major ports. Minor ports are guided by state governments. Coastal region of India comprises major sea ports such as Chennai, Tuticorin, Vizag, Paradip, Haldia, Port Blair, Cochin, Panambur, Marmagao, Mumbai, Nhava Sheva and Kandla. There are numerous private ports on the Indian coast.
Indian ports handled an estimated total of 650 million tonnes (MT) of cargo in March 2007. In 2015-16 the major ports alone handled 606 MT of cargo. The gross Indian shipping tonnage amounted to 10.3 million gross tonnes (GTs).
Inadequate data on seaborne emissions, cost effectiveness for implementation of feasible technologies in the existing ships, compatibility issues and space constraint in existing ships are the major challenges faced in reducing emissions.
Types of Pollutants and Factors causing emissions
During combustion, most of the NOx are generated in the high temperature spots by a reaction between the atmospheric nitrogen and oxygen (Green et al., 2008). These cause eutrophication, acidification and the formation of ozone in the presence of VOC and sunlight. These NOx emissions can be abated by using primary and/or secondary methods.
SOx as a product of fuel oil combustion can be reduced by decreasing the sulphur content in the fuel. The sulphur content in the fuel determines the content of SOx in the exhaust gas. In the combustion chamber the sulphur present in the fuel is being oxidised into SO2. A much smaller portion of about 35 per cent is further oxidised into SO3. Together SO2 and SO3 are called SOx. The cylinder lubrication oil contains substances that serve to neutralise the sulphur and thus prevent damage from sulphuric acid in the engine.
A small fraction of the fuel oil, which consists of hydrocarbons, will pass through the engine unburned and other hydrocarbons are formed during the combustion process. Lubrication oil also contributes to the emission of hydrocarbons (Lamas and Rodriguez, 2012).
PM is a designation for a large variety of extremely small particles of organic and inorganic origin. They can contain carbon, metals, ash, soot (almost purely elemental carbon), acids such as sulphates and nitrates and carbonates. Some PM consists of partly combusted or non-combusted hydrocarbons material (fuel and lubrication oil) and there is an overlap between the designations of PM and hydrocarbons. Ash from fuel and lube oil is only a minor component of the emitted PM and is formed mainly from metals (vanadium and nickel) present in these oils (ibid.).
Chlorofluro carbons (CFCs) are extremely poisonous and the main reason for ozone depletion. Global shipping fleet emits approximately 3,000-6,000 tonnes of CFCs.
Many of the above mentioned emission types also act as greenhouse gasses (GHGs). CO2 is the most important greenhouse gas and one of the main reasons that life can exist on Earth in the form we know (Kamath, 2014). CO2 acts like the glass in a greenhouse trapping heat.
The major emission causing factors relate to use of fuel type; design of ship (hull formation, hull cleaning); types of engines; operational modes of ships; and combustion process of IC engines.
Methods Followed for Emission Reduction
In order to reduce emissions, it is required to first measure the quantity of emission levels along the Indian coastline. For this, data was collected, optimal solutions were identified and the specific solution according to type of vessel was implemented. Emission data has been collected both pre-treatment and post treatment during the implementation of any optimal solution. Thus, the data has been validated. Four types of vessel have been identified for study—research vessel, tanker vessel, defence vessel and fishing trawler.
Some of the methods used to collect emission data from ships by which the average NOx and SOx levels can be identified are mentioned below:
* Using Testo 350, a portable emission and combustion analyser instrument the emission from a particular vessel can be measured periodically. Gas sampling takes place with a special, easy-to-install sampling probe. The certified and durable electrochemical gas sensors (ECS) record the concentrations of the exhaust gas components O2, CO, NOx (NO + NOx separately) and SOx highly accurately and with long-term stability. CO2 is recorded using the certified IR measurement principle. The advantages of using testo 350 are its simplified test and measurement procedures that enable periodic and intermediate examinations, direct measurement and monitoring onboard. In addition, it can be used for official NOx-monitoring measurements to check the NOx limit values prescribed by the MARPOL norms.
* Automatic Identification System (AIS) can be used for improved safety and specifically for collision avoidance as vessels need information regarding the position, details and navigational intentions of other vessels within very high frequency (VHF) range (Perez et al., 2009). As a part of this study AIS instrument was installed onboard a research vessel. The SLR200 is a low cost unit, designed specifically for small commercial, leisure, fishing boat and vessel monitoring markets where vessels are currently not mandated to transmit AIS information. It has been interfaced to an onboard PC running compatible software or plotter by Dolphin Maritime Software Ltd. AIS data transmitted from ships within range can be displayed on the screen giving the shipper or navigator a visual interpretation of the traffic within VHF range.
* Ship emission calculator is a web based tool created by the National Technical University of Athens, Laboratory for Maritime Transport for calculating the exhaust gas emissions (CO2, SOx and NOx) of specific types of ships under a variety of operational scenarios. The most basic results as regards to how emissions were calculated can be summarised as follows:
* CO2 emissions do not depend on type of fuel used or engine type. Generally, to compute CO2 emissions (in tonnes per day) total bunker consumption (in tonnes per day) shall be multiplied by a factor of 3.17.
* SOx emissions depend on type of fuel. Generally, to compute SOx emissions (in tonnes per day) total bunker consumption (in tonnes per day) shall be multiplied by the percentage of sulphur present in the fuel (for instance, 4 per cent, 1.5 per cent, 0.5 per cent, or other) and subsequently by a factor of 0.02.
* NOx emissions depend on engine type. The ratio of NOx emissions to fuel consumed (tonnes
per day to tonnes per day) ranges from 0.087
for slow speed engines to 0.057 for medium speed engines.
The principal gaseous and particle emissions from ships include CO2, H2O, NOx, SOx, CO, unburned hydrocarbons, and particulate matter (Beirle et. al., 2004). The plumes from ship stacks effectively release these species at relatively high local concentrations into the marine boundary layer. Remote sensing measurements of NOx and SOx from space offer the potential for unique insight into this issue.
Optimal and Innovative Reduction Technologies
Reduction techniques: Many mitigation methods and operational techniques are available for the reduction of the pollutants from the exhaust of the ships. Methods such as autopilot upgrade/adjustment, propeller upgrade, water flow optimisation, weather routing, hull cleaning, propeller polishing, hull coating, wind power, waste heat recovery, air lubrication, speed reduction, main engine retrofit, speed controlled pumps and fans, high-efficiency lighting, solar power can be used. Component specific emission reduction techniques for NOx are—Humid Air Method, Exhaust Gas Recirculation (EGR), Water Injection and Water emulsion, High Scavenge Pressure and Compression Ratio, Selective Catalytic Reduction, Two Stage Turbocharger and Engine Component Modification (Brijesh and Sreedhara, 2013); while for SOx are—use of low sulphur fuel oil, Exhaust Gas Scrubber Technology and Cylinder Lubrication.
Innovative technologies: During the course of study new innovative technologies have been identified and developed viz. nano fuel additives, fuzzy logic system, parallel pumping system and non-thermal Plasma technology.
Nano fuel additives: A technology which adds nano additives to marine diesel fuel to reduce emissions from marine diesel engine. To obtain maximum fuel efficiency, to reduce emissions, increase thermal efficiency and overall output of marine diesel engine, nano materials are added to marine diesel fuel as additives. These nano additives boost engine performance and reduce emissions from engine. This reduction technique has been implemented in a research vessel and results have been obtained. Table 2 shows the values of the emission data from pre-treatment and post treatment of the reduction technique. It is evident that after the implementation of the reduction technique the emissions have reduced.
Emissions from ships is considered as one of the important issues in maritime domain, as it has a large negative impact on the marine environment. This paper discusses the various methods which could be carried out to reduce those emissions. Applying one of them depends on some criteria such as the required emission reduction percentage. These methods were studied by implementing it in one of research vessels in the Bay of Bengal. The results showed the possibility to achieve valuable emission reduction percentage, but it is costly and adds to the ships operating cost. However, from the green ship technology perspective it would be a positive step.