We spoke of the “Green Ship” concept before; talking about the types of pollution and emissions from conventional ships and what long-term effects it can leave. Now, it is time to talk about the feasibility of the Green Ship with existing technology; possible to conceive and maintain as well as still have the same efficiency of a conventional ship. [Part 1: bit.ly/1omtf8R]
Firstly, it is worth mentioning that prototypes that are born and currently exist in labs are harder to transfer into the world outside a controlled environment; remaining the main challenge of modern maritime. Transferring the technology from labs to ships requires prioritisation/objectives both of short and long terms; improving the ship’s efficiency by 30% by marine equipment sector; onwards to medium to long term where it is possible to boost it by 60%. Both can be achieved through continuous innovation and increased cooperation among the marine cluster.
Marine equipment sectors, important actors within this operation play the most important role as ships consist of individual parts and runs on interactions between equipment, operators and the environment. Equipment aboard the ship produces certain by-products that were discussed in part 1; requiring discussion of solutions done with existing technology; coming together to from the Green Ship infrastructure.
The first challenge for existing technology is the SOx/Sulphur emissions which are a product of combusting fuel oil. The solution to this is relatively simple as it relates to the type of fuel being used where emissions are influenced by chemical composition of the fuel burnt. Aside from using low-sulphur fuels, the solution will also be usage of dual-fuel engines; allowing the ship to use heavy fuel oil/HFO on high seas while using Liquified Natural Gas/LNG when entering/leaving harbours and sailing coastal areas. Such systems are also used in hybrid cars to switch between electric and petrol operation depending on journeys.
However, replacing the engine is only a part of the entire solution as operations will regardless, release certain amounts of SOx through the exhaust paths; requiring filtration to be placed at the end. SO2 scrubbers will remove SO2 with or without seawater or in a closed loop with additional chemicals; proven to reduce SO2 by 85%.
Finally, usage of waste heat recovery systems can convert energy from exhaust gases coming from propulsion into electrical power; usable onboard and saving power, fuel consumption and reduce SO2.
Another persistent emission at sea is CO2; it is known to contribute to global warming and in progress of receiving a legal obligation for reduction on the basis of Energy Efficient Design Index. CO2 emissions are a result of fuel combustion which also leads to usage of hybrid auxiliary power systems consisting of a fuel cell, diesel-generating set and batteries. This system is also able to consume alternate energy sources such as wind and solar power. Alternative fuel here is LNG while propulsion can be altered with usage of kite technology that can be retro-fitted with modern ships and used alongside conventional propulsion. Kite propulsion involves a kite of 320 square metres (3,400 sq ft)area and flow at an altitude of 100–300 metres (330–980 ft) receiving higher thrust during strong winds. A ship using such propulsion saves up to 10 to 35% fuel.
A practical example of kite propulsion usage is the MS Beluga; a commercial container ship with computer-controlled kite propulsion. The kite is connected to the ship by a rope and controlled by an automatic pod which maximises wind benefits. However, ships produce emissions not only while sailing but also by berthing at port; therefore warranting an alternative from the normal procedure. When a ship is at port it is possible to connect it to a shore-side electrical power generator after engines have been switched off; enabling the ship systems to operate from the incoming electricity and eliminate airborne emissions; this is called Cold Ironing.
Leading more towards an aspect of innovation, ships can not only be powered by Hydrogen fuel cell systems but will become more efficient as hydrogen systems are 50% more effective than existing engines. However this is still being researched by equipment makers and academic institutions. Another part of marine equipment innovation targets rudders which generate 5% of the ship’s overall resistance. Reducing it will save 2-5% of fuel.
Talking about fuel used, it degrades in quality as the industry exists which causes the oil to increase in viscosity which itself wears down the engine and demands more manpower and expensive measures to properly dispose. As oil quality degrades the treatment required before usage increases; leading to production of a useless by-product which causes damage to ecology. Oil treatment is done via separators and breaks it down into heavy fuel and some water molecules; producing the aforementioned damaging product sludge; a mixture of oil and water. This cannot be used for anything and depending on the quality of oil; an average ship produces an average of few litres to several tonnes of sludge. Sludge also cannot be incinerated as well as having a fee for disposal at ports, but still requiring proper control; putting it in a settling tank and pump out the water which settles under the oil layer. Afterwards, pumping it overboard via 15ppm bilge water treatment system; introducing the process where errors such as leaks are most common.
Bilge water components have changed through the years as quality of oils varies which contains:
- Leaked condensed and coolant water.
- Oil from various sources
- Dirt and paint particles
- Corrosion protection agents.
Bilge water, firstly can be addressed by choice of cleaner, higher quality oil which will reduce the waste product during treatment. However, this can be more expensive depending on the supplier therefore presenting another solution; high-speed centrifuge. This separates emulsions and removes residue in bilge water; after the treatment the water portion can be discharged into the sea while oily remains are fed into a tank to be treated later. Technology for this as well as microfiltration for more efficiency is available.
Finally, bilge water can be addressed using cascade tanks where the water is fed into the top of the tanks, followed by gravitational forces passing it through sponges, catching oily substances while collecting cleansed water at the bottom. However this is only possible at some viscocities of oil as smaller oil drops render this method inefficient.
Emissions from ship’s systems are not only the cause of pollution as crew also produce their own waste; commonly disposed away from public eye. This type of waste comes from accommodation, galleys and operations. Counter-measures for this do exist in the form of a ban on disposal of plastics at sea as well as severe restrictions on disposal at coastal waters; to little efficiency as dumping still occurs. 70% of garbage sinks, 15% floats and eventually combines to form “garbage islands;” occurrence of which grows constantly and occasionally have alien species on them which travel to foreign waters and invade other ecosystems.
Firstly, waste takes up space and thus is dumped to make more space aboard a ship during a voyage. Waste can be reduced in volume by squeezing and breaking down and followed by compression. This combination of processes reduces waste in volume for delivery to be properly disposed at shore-based facilities. Plasma technology in conjunction with other systems is another example of effective waste management. Plasma reaches up to 6000C temperature and reduces waste to non toxic sludge; reducing plastics, most hazardous and common waste, into hydrogen and CO2.
The final two emissions which is capable of ecological damage are black, gray waters and ballast water where the formers are results of sewage and domestic disposal while the latter is a result of maintaining of ship stability by liquid means. Discharged waste/black water leads to hygiene problems such as germs released at coastal regions. It also contains a variety of other pollutants; some soluble and some insoluble; along with non-biodegradable elements such as plastic, grain, hair, fibres and fat varieties which have to be removed by periodic de-silting or extraction through filtration systems. Amount of black water aboard depends on the sanitation technology present.
The solutions relating to the above are membrane bio-reactors and vacuum toilets. Membrane bio-reactors cleanse gray and black water where the waste water is fed into its system where organic matter is broken down by biomass; followed by filtration into the second bio-reactor. The final step is feeding the solution through membrane modules leaving a cleaner product that can be discharged into the sea.
Vacuum toilets reduce the amount of black water by 1/3 and compatible with a sludge reactor with membrane filtration which collects gray water which is then used for flushing toilets; reducing waste volume by 75%.
Finally, ballast water which maintains the stability of a ship while carrying cargo which distributes weight unevenly. A ship fills between 10% and 50% of the whole tonnage with ballast water in coastal regions and discharges when the load is changed. For example, an average tanker, when empty fills up to 60,000 tons of ballast water when it has a carrying capacity of 200,000 tons. A container ship fills up 10-20% of their carrying capacity when empty. These figures lead to 10-12 billion tons of salt water being displaced. Such technology is available today as all ships are fitted with ballast water treatments; chemical, heating, filtration and ultraviolet light are some examples.