Due to environmental and legislative incentives and low gas prices, gas-fuelled shipping is expected to increase significantly in the coming years. Concurrently, increasing efforts are devoted to the study and development of waste heat recovery technologies, aiming at reducing the shipping fuel consumption. Among the various waste heat recovery systems, the organic Rankine cycle (ORC) is considered one of the most promising technologies.
This project builds on the experience developed at DTU Mechanical Engineering in the field of design and optimization of ORC units, and aims at deriving guidelines with respect to the optimal utilization of waste heat sources on-board LNG-fuelled ships, identifying the optimal design, implementation and control of ORC units on-board.
Waste heat recovery on board vessels powered by low sulphur fuels
The use of low sulphur fuels results in an increased waste heat recovery potential due to a decreased risk of sulphur acid formation in the heat recovery boiler and a reduced need for service steam on-board. The increased attainable power production, combined with the absence of sulphur oxides in the exhaust gases, enable the use of simpler and cheaper heat exchanger designs. This suggests that it is possible to design ORC units with both a higher power output and a lower specific investment cost, compared to those of units designed for heavy fuel oil-fuelled ships.
Exploiting the liquefied natural gas cold energy
Liquefied Natural Gas (LNG) is stored on board vessels at atmospheric pressure in the liquefied state at about – 160 °C, making it necessary to heat up the gas to about 30 °C before it is injected in the engine. The heat needed for the evaporation and pre-heating of the LNG can be provided by the heat rejected in an ORC condenser. During the first part of the project, novel cycle layouts will be investigated with the aim of integrating the use of the LNG cold energy to boost the performance of ORC-based waste heat recovery units.
Development of a unique experimental facility
A unique experimental facility comprising a diesel engine and an ORC unit will be constructed at DTU Mechanical Engineering, being a fundamental step towards the implementation of the technology on board vessels. Such facility will be used for a range of future maritime activities involving waste heat recovery systems of combustion engines, which will be of great value for the Danish maritime industry. In particular, the experimental facility will enable testing and development of adequate control strategies, ensuring the efficient operation of the ORC unit in connection with different operational conditions of the ship main engine.
Waste heat recovery units of the future
The project allows investigating the requirements of the waste heat recovery units of the future. In particular the variety of emission regimes in different geographical areas make it necessary to develop waste heat recovery units with a greater degree of flexibility, as some of the emission abatement devices will either be used or bypassed depending on the ship location. In addition, the increasing complexity of the ship machinery systems makes it necessary to consider the impact of implementing waste heat recovery units on the performance of both the main engine and of the various emission abatement devices.
Research
The project is defined to provide answers to the identified relevant questions within the field of waste heat recovery on board vessels. The work, framed as a combination of numerical simulations and experimental tests, will be supported by a pool of industrial partners that will ensure that the findings support the future needs of the maritime industry.
In particular, the project aims at identifying the various waste heat sources available on board a vessel and providing guidelines with respect to how to utilize these heat sources in an ORC unit effectively. Second, the interactions between the ORC unit and the ship machinery system will be discussed and investigated – especially concerning the impact of the additional backpressure on the main engine and how this parameter affects the optimal design of waste heat recovery units. Lastly, the project aims at deriving a simplified methodology to assess the waste heat recovery potential on board vessels as a function of the ship main engine characteristics and/or ship dimensions.