Safety and CO2 emissions: Implications of using organic fluids in a ship’s waste heat recovery system

Abstract

Current Marine Policies and regulations greatly favour the use of efficiency enhancing technologies such as the Organic Rankine Cycle (ORC) waste heat recovery systems (WHRS), through the entry into force of International Maritime Organisation (IMO) Energy Efficiency Design Index (EEDI). However, safety regulations such as IMO Safety Of Life At Sea (SOLAS), International Gas Code and Classification Societies still consider the use of highly flammable organic fluids on board ships as hazardous and undesirable, requiring special Administration approval. The benefits of organic fluids in emerging technologies will likely increase their usefulness on board in the near future. Furthermore, current ship safety systems and integrated platform management systems greatly reduce the risks associated with their low flash point making them acceptable for marine use given specific design considerations. This paper studies the case of an Aframax tanker navigating the route North Sea-Naantali, Finland using a slow speed diesel engine. A code with a multi-objective optimization approach generated explicitly for this purpose produces different optimal WHRS designs for the vessel's operating profile. The WHRS is installed after the turbo compressors in the exhaust gas system, where it absorbs part of the available waste heat and converts it to electricity using a generator. This results in a reduction in fuel consumption, hence decreasing the emission of greenhouse gases. The different optimal designs are compared with a steam WHRS to show the strengths and weaknesses of using an ORC WHRS on board. The ORC technology is at its early stages of development in the marine field, it is important that safety policies follow the evolution of the technology and its associated safety equipment. This paper will serve to recognize the specific safety considerations associated with the ORC and highlight the advantages of carrying organic fluids on board as a solution to increasing CO 2 emission restrictions and other environmental concerns.

Shipping in changing climates

“…However, it is also useful to consider and anticipate some of the barriers that may be preventing greater levels of uptake of emission reducing technologies now, and that may further hinder, or increase the cost of, deep decarbonisation in the future. Suárez de la Fuente et al [14] describe how waste heat recovery systems can reduce energy demand, but also potentially conflict with existing safety regulations. These regulations are a product of the historic design and operation of ships, yet both have been superseded by the now commonplace use of unmanned machinery spaces, rendering the regulations less justified.…”

“…Whilst this special issue is not focused on the identification and analysis of decarbonisation pathways themselves, a number of papers suggest promising technology and operational options. These include a concerted effort for slow (or even ultraslow) steaming [10], the use of waste heat recovery as mentioned previously [14], and the use of wind-assistance technology [10,12]. In some instances there are synergies that can occur (e.g.…”

Making shipping greener: comparative study between organic fluids and water for Rankine cycle waste heat recovery

“…The IGF recommends the use of double-walled piping, ventilation for the enclosed space to the atmosphere, gas detection and firefighting systems according to the fluid used. Equally important are personnel training, risk management (e.g., enclosed space management system, see Allan 2015) and assessments and safety procedures in case of fire or leakages (Suárez de la Fuente et al 2015). The safety requirements for the marine ORC WHRS selected will increase the initial cost and maintenance costs, but performance may also be affected.…”

“…Quoilin et al (2013) show that the cost of an ORC WHRS module of the size proposed in this paper should be less than £1,640 per kW e 3 , while for an RC WHRS the cost can range between £688 and £862 per kW e (BCS Incorporated 2008). However, the WHRS payback period can be less than three years for any of the cycles tested (Suárez de la Fuente et al 2015). Thus, the installation of a WHRS is an economically-viable green technology.…”

A Comparison of Organic and Steam Rankine Cycle Power Systems for Waste Heat Recovery on Large Ships

“…In terms of power production, the ORC unit outperformed the other two, while the SRC unit ranked high in qualitative assessments concerning working fluid safety, environmental properties and familiarity of the technology. Other authors [21][22][23][24] compared the off-design performance of single pressure SRC and ORC systems, for recovery of exhaust gas heat only [21,22], for recovery of exhaust gas and scavenge air heat [23] and for recovery of exhaust gas, scavenge air and jacket water heat [24]. These studies all found that the ORC systems achieved higher performance than the single pressure SRC systems.…”