Making shipping greener: A vessel’s waste heat recovery system comparative study between organic fluids and water

The largest source of energy loss in a ship is found in the propulsion system. This study focuses on the concept of managing waste heat energy from the exhaust gas. Using waste heat recovery systems to make shipping more efficient represents a good area of opportunity for achieving the shipping industry’s green objectives. Organic Rankine Cycles (ORC) have been applied in land based systems before, showing improvements in performance when compared with the traditional Rankine cycle (RC). ORC plants on board ships face different challenges such as variable operating conditions and limited space. As marine environmental rules require greener vessels and engine thermal efficiency continue to increase, ORC waste heat recovery systems become a more attractive option. The proposed waste heat recovery system (WHRS) was modelled using Matlab with a typical ship installation with a slow speed diesel engine and the WHRS installed after the turbo compressors in the exhaust gas system. The energy recovered from the exhaust gas flow is transformed via the thermodynamic cycle into electricity which will help to cover the ship’s demand. The Matlab code found the highest electric power output varying the WHRS high pressure, maximizing the fuel and CO2 emission reductions. Water and various organic fluids were considered as working fluids and their performance compared over a range of different engine operating scenarios in order to assess the differences between a marine ORC and RC. A representative ship operating profile and a typical marine generator were used to measure CO2 emission reductions and the implications of having flammable organic fluids on-board. This work demonstrates that a simple ORC can be more effective than water based RC for the same engine operating condition

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

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 CO2 emission restrictions and other environmental concerns

Improving Shipping CO₂ emissions: A multi-objective study of marine Waste Heat Recovery Systems

Holding the global temperature rise below 2˚C, when compared to the global pre-industrial levels, is one of the most challenging compromises taken by the international community. Shipping contributes in 3.3% of the total CO2 emissions and it is the transport mode with the highest growth, hence it has an important role in achieving the 2˚C goal

Waste Heat Recovery Systems: Reducing Shipping Carbon Emissions under Real Operative Conditions

Shipping contributes in 3.3% of the total CO2 emissions, it is the transport mode with the highest growth. If nothing is done now, by 2050 the shipping CO2 emissions could grow up to 400% compared with 2007 levels. The International Maritime Organization (IMO) created the Energy Efficiency Design Index (EEDI)- applied only to new ships- to measure and control shipping CO2 emissions. As can be observed in figure 1, as time increases the CO2 emissions reference line (red line) is reduced

Cooling Fluids and Ambient Temperature: Sensitivity Performance of a Container Ship Organic Rankine Cycle Unit

The objective of this paper is to design organic Rankine cycle units that are cooled by air or seawater and show the changes in net power output and power requirement as the ambient air temperatures change both geographically and seasonally. The organic Rankine cycle unit uses the available waste heat from the scavenge air system for a 4,100 TEU container ship. This work uses a two-step single objective optimisation capable of selecting 14 design characteristics of the organic Rankine cycle unit and with the aim of minimising the vessel’s CO2 emissions. The work contributes to the study of off-design operation and different cooling fluids for marine waste heat recovery systems. The results show that the organic Rankine cycle unit is more adaptable to ambient air temperatures when using seawater as a cooling fluid while air is an attractive option for extremely low ambient temperatures

Selection of cooling fluid for an organic Rankine cycle unit recovering heat on a container ship sailing in the Arctic region

As Arctic sea ice coverage declines it is expected that marine traffic could increase in this northern region due to shorter routes. Navigating in the Arctic offers opportunities and challenges for waste heat recovery systems (WHRS). Lower temperatures require larger heating power on board, hence a larger demand for waste heat usage, to cover services and maintaining on board spaces temperatures. However, a lower heat rejection temperature increases the WHRS thermal efficiency. The air temperature for the Arctic route selected is colder than that of the seawater, opening the opportunity of having air as coolant. This paper explores the use of two different coolants, air and seawater, for an organic Rankine cycle (ORC) unit using the available waste heat in the scavenge air system of a container ship navigating in Arctic Circle. Using a two-step single objective optimisation process, detailed models of air and seawater heat exchangers are evaluated as the WHRS condensers. The results suggest that an ORC unit using R1233zd(E) as its working fluid coupled with seawater as its coolant is the preferable option to reduce CO2 emissions. Using the ambient air as the coolant while a less effective option could be cheaper to install

Using the forward movement of a container ship navigating in the Arctic to air-cool a marine organic Rankine cycle unit

Ice coverage in the Arctic is declining, opening up new shipping routes which can drastically reduce voyage lengths between Asia and Europe. There is also a drive to improve ships energy efficiency to meet international emissions design regulations such as the mandated Energy Efficiency Design Index. The organic Rankine cycle is one thermodynamic cycle that is being actively examined to improve the design and operational efficiency of ships. Low heat sink temperatures can significantly increase waste heat recovery systems thermal efficiency. In Arctic regions, the ambient air temperature can be much lower than the sea temperature, presenting interesting opportunities. However, using air as the cooling medium requires larger condensers and power compared to a water-cooled system. This paper investigates the exploitation of the forward movement of a container ship navigating in the Arctic and density-change induced flows as means of moving air through the condenser to reduce the fan power required. The organic Rankine cycle unit uses the waste heat available from the scavenge air to produce electric power. A two-step optimisation method is used with the objective of minimising the annual CO2 emissions of the ship. The results suggest that the supportive cooling could reduce the fan power by up to 60%, depending on ambient air temperature

Cheating on the Edge

We present the results of an individual agent-based model of antibiotic resistance in bacteria. Our model examines antibiotic resistance when two strategies exist: “producers”–who secrete a substance that breaks down antibiotics–and nonproducers (“cheats”) who do not secrete, or carry the machinery associated with secretion. The model allows for populations of up to 10,000, in which bacteria are affected by their nearest neighbors, and we assume cheaters die when there are no producers in their neighborhood. Each of 10,000 slots on our grid (a torus) could be occupied by a producer or a nonproducer, or could (temporarily) be unoccupied. The most surprising and dramatic result we uncovered is that when producers and nonproducers coexist at equilibrium, nonproducers are almost always found on the edges of clusters of producers

High local substrate availability stabilizes a cooperative trait

Cooperative behavior is widely spread in microbial populations. An example is the expression of an extracellular protease by the lactic acid bacterium Lactococcus lactis, which degrades milk proteins into free utilizable peptides that are essential to allow growth to high cell densities in milk. Cheating, protease-negative strains can invade the population and drive the protease-positive strain to extinction. By using multiple experimental approaches, as well as modeling population dynamics, we demonstrate that the persistence of the proteolytic trait is determined by the fraction of the generated peptides that can be captured by the cell before diffusing away from it. The mechanism described is likely to be relevant for the evolutionary stability of many extracellular substrate-degrading enzymes