NOx reduction system selection and energy efficiency impact evaluation for ships sailing in restricted areas

Abstract

The worldwide shipping provides 90 percent of the goods carriage and in the last 20 years their absolute volume is constantly increasing. However, carriers need to maintain service levels and reduce exploitation costs, and at the same time must ensure higher sustainability in all operations. The growth in number of ships in service inevitably leads to much more harmful emissions released by vessels in to the atmosphere. In the same time, more stringent environmental requirements and laws continue to regulate the maritime transport sector. Progress was made by International Maritime Organization (IMO) towards the ambition on reduction of greenhouse gas (GHG) emissions from ships. That is why IMO based International Convention for the Prevention of Pollution from Ships (MARPOL Convention) and its regulations continuously sets higher thresholds for environment protection expressed by Nitrous Oxides (NO_x), Sulphur Oxides (SO_x) and Carbone Dioxides (CO₂) limitations. The new higher ecological requirements put on the table new technical and economic challenges for the shipowners and ship designers.

In the current paper Selective Catalytic Reduction (SCR) and Exhaust Gas Bypass (EGR) NO_x emissions reduction systems and their affect on the fuel consumption are under consideration. The application of each system depends on the ship’s type, installed propulsion system and its main engines and operational modes.

The numerical study is carried based on 31800 DWT vessel for bulk loads, operating in restricted areas of the Great Lakes of North America. In the course of the research the fulfilment of the following objectives are being leaned: the ship must be capable for operation in Nitrogen Emission Control Areas (NECA’s), as well as its Energy Efficiency Design Index (EEDI) must be in compliance with Required Energy Efficiency Design Index (REEDI) Phase 3 coming in force in 2025.