Internal dryer saves energy and space

The 220,000gt Genesis duo now being built by STX Europe for RCCL will feature a comprehensive Norsk Inova treatment plant to handle wet and dry waste in a healthy and environment friendly way, while using minimum energy

Now nearing completion at STX Europe in Finland, the 360m long Oasis of the Seas will be the largest cruise ship in the world. This vessel’s sheer size will place great demands on many of its systems, including the waste treatment technology, which will have to handle the waste generated by at least 5,400 passengers, and more than 3,000 crew members, at any time.

The plant on Oasis of the Seas, and on its sister, Allure of the Seas, will be provided by the Norwegian company, Norsk Inova, which is today part of the Evac group. This manufacturer has supplied systems for around 95 cruise ships over the past 20 years, and the technology on these Genesis class ships will draw heavily on its lengthy experience in this field.

The waste treatment systems being fitted on Oasis of the Seas are based largely on tried and tested technology, although they do represent the biggest installations of this type yet fitted by Norsk Inova. However, some relatively new technical features have been included, and these are designed to allow the vessel to fulfil its environmental obligations in a more economical way.

Norsk Inova is supplying a comprehensive package for Oasis of the Seas, including equipment for food waste, also bio residue treatment, a waste incinerator, recycling and storage systems, and all controls. Perhaps the most notable feature is that within the incinerator, Norsk Inova will install its patented internal dryer technology, while the equipment also includes a steam dryer for bio residues, a concept developed to reduce odours and reduce burning time.

The internal dryer is said to offer benefits both to shipbuilder and operator. Normally, wet waste, including food and bio residue, is dried in an external dryer and then fed into the incinerator with dry waste. As well as adding to the cost of the treatment installation, this arrangement takes up space and consumes a significant amount of energy.

Norsk Inova’s internal dryer technique uses around 10 per cent of the energy produced, by burning the dry matter to evaporate the water content of the wet waste. Dried food and bio waste produced by the internal dryer burns and creates additional energy, compensating for energy lost in the drying process.

Wet food waste with a dry solids content (DSC) of 20-25 per cent is fed directly from a silo to the internal dryer, where it is transported to the incinerator’s primary chamber. It is then dried and burned, using excess energy from the burning of dry waste or sludge oil. Inside the incinerator, a paddle screw design, variable rotational speed and air injection ensure good waste mixing, sufficient heat transfer and complete burning of the materials.

Since drying of the wet food waste utilises excess energy from the burning of dry waste, the use of an internal dryer eliminates the use of water injection for temperature control. The screw is water cooled to ensure longevity and to prevent high temperature peaks building up.

For a 2,000kW incinerator, the internal dryer is capable of drying and burning up to 420kg/h of wet waste with a DSC content of 20 per cent. The internal dryer will then dry and burn all accumulated food waste and bio residue.

The internal dryer system was first installed on a cruise ship, Crystal Serenity, in 2003. However before the technology was fully embraced by cruise ship operators, Norsk Inova made a number of improvements. Having installed a treatment plant with an internal dryer on Carnival Freedom in 2007 and Carnival Splendour in 2008, the manufacturer now has further contracts for more cruise ships building at Meyer Werft and Fincantieri.

Last year, Celebrity Solstice was also delivered from Meyer Werft with the technology, and the soon-to-be completed Celebrity Equinox will feature the internal dryer and waste treatment technology. The company also has contracts to supply waste treatment packages to two newly confirmed cruise ship orders, for Carnival and Costa Cruises, to be delivered by Fincantieri in 2011.

Interest in the internal dryer technology is mainly for newbuildings, but it can also be retrofitted into existing incinerators, and Norsk Inova has completed a number of projects of this type. PST