Discussing the Implementation of the Clean Hybrid Propulsion Drive
The growing concern for limiting the negative impact of all modes of transport on the natural environment mean that clean technologies are becoming more and more important. The environmental changes and global air pollution from maritime transportation is a growing concern. The trend to design more efficient and versatile ships has increased the variety in hybrid propulsion and power supply architectures.
The objective of work is to provide a clean hybrid propulsion drive in which mechanical power is provided via dual fuel engine and electric power from hydrogen fuel cells. Dual fuel engine is predominantly an engine designed to burn predominantly natural gas but a small amount of diesel is injected to it as a pilot fuel. The dual fuel engine uses natural gas and diesel as fuel adding to the security of energy supply. In addition, these engines are more powerful than the most developed diesel engines. The fuel cells installed uses pure hydrogen produced by electolyzers powered by the renewable energy collected onboard.
In order to achieve the maximum efficiency and minimal emissions, Mechanical and electrical power works together in the propulsion train optimizing the propulsion efficiency for ship with a flexible power demand. The combination delivers propulsion power providing the right amount of power and torque to the propeller in operation modes accordingly. Typically allowing the dual fuel engine to work during load conditions while electrical power to assist the main engine to work under optimal conditions. Electrical propulsion can be utilized for low speed cruising and to provide power onboard.
International initiatives towards reducing CO2 and other emissions are driving the research into alternatives to conventional petroleum-based ship fuels. A wide range of alternative fuels are being discussed, and technologies such as fuel cell systems and Dual fuel engines, which can only be applied efficiently in conjunction with cleaner fuels, have appeared on the agenda. An impressive number of restrictions aiming to improve the environmental footprint of shipping are in force or under preparation.
Practical challenges related to Sulphur reduction are knocking at the door. At the same time, there is an accelerating worldwide trend towards pushing down CO2, NOX and particle emissions. All of these factors are reason enough to intensify the search for fuels and technologies that can help the industry to meet the challenges ahead. So Hybrid propulsion is the proposed solution discussed in this paper.
In most current applications of hybrid propulsion, the ship either operates in direct mechanical mode or in electrical mode. These applications do not yet achieve the full potential of the hybrid propulsion concept. The electric motor can assist the main diesel engine, for example to improve acceleration performance, reduce thermal loading of the main engine or increase top speed. However, to run the main engine and electric drive in parallel, an advanced control strategy is required ships that frequently operate at low speed can benefit from a hybrid propulsion system. In hybrid propulsion, a direct mechanical drive provides propulsion for high speeds with high efficiency.
Additionally, an electric motor which is coupled to the same shaft through a gearbox or directly to the shaft driving the propeller, provides propulsion for low speeds, thus avoiding running the main engine inefficiently in part load. This motor could also be used as a generator for electrical loads on the ships services electrical network. When the mechanical drive engine is running, this system allows generating capacity either from the electric generator or from the generating sets. Typically, rule-based control or the operator determines the generating capacity. Now we will discuss the two components of the Hybrid propulsion driv .Dual fuel engine for mechanical power while Hydrogen fuel cell for Electricity to be supplied to electric motor for assistance to engine.
A dual-fuel engine is designed to burn predominantly natural gas but with a small percentage of diesel as a pilot fuel to start ignition. In operation, a natural gas–air mixture is admitted to the cylinder during the intake stroke, then compressed during the compression stroke. At the top of the compression stroke, the pilot diesel fuel is admitted and ignites spontaneously, igniting the gas– air mixture to create the power expansion. A dual-fuel engine can also burn 100% diesel if necessary, though with the penalty of much higher emissions. The minimum-fuel mode is developed for gas operation. In this mode, the control system will allow any ratio between fuel oil and gas fuel, with a minimum preset amount of fuel oil to be used. The mixed gas mode is offered to give the operator full fuel flexibility and the option to inject a fixed amount of gas fuel. The ME control system will add up with fuel oil until the required load for operation is reached. Gas fuels correspond to low-sulphur fuels, and for this type of fuel.
Fuel cells offer high electrical efficiencies, as well as lower noise and vibration emissions than conventional engines. The main components of a fuel cell power system are the fuel cells, which convert the chemical energy stored in the fuel directly into electrical and thermal energy by electrochemical oxidation. This direct conversion enables electrical efficiencies of up to 60 per cent, depending on the fuel cell type and fuel used.
Fuel reformers convert the original fuel into hydrogen rich fuel for use in the fuel cells. In addition to pure hydrogen, fuel reformers enable the use of fuels such as natural gas, methanol and low-flashpoint diesel. The fuel cell is working in a combustion-free electrochemical process. Consequently, cell technology can reduce emissions to air dramatically Hydrogen production from electrolysis is a known and available technology that can be applied onboard for onsite hydrogen production powered from renewable energy by installing onboard solar panels or vertical wind turbines and locally in port as long as an adequate supply of electrical power is available for the production process, which would eliminate the need for a long-distance distribution infrastructure.
The PEM fuel cell is a mature technology that has been successfully used both in marine and other high energy applications. The technology is available for a number of applications. The maturity of the technology is the main reason why this is one of the most promising fuel cell technologies for marine use, this also leads to a relatively low cost. The operating temperature is low, and operation requires pure hydrogen. The safety aspects are thus delated to the use and storage of hydrogen on a vessel. Using hydrogen as fuel, the only emission is water and low quality heat. The low temperature provides high tolerance for cycling operation.
Research at Delft University of Technology, suggests that hybrid propulsion with hybrid power supply can deliver significant savings in local emissions, partly by using energy from the batteries that are recharged with a shore connection .These savings can be achieved with a heuristic rule based approach. In this approach the control mode of the plant is determined by the operating mode of the vessel (towing, high speed transit, low speed transit or standby) and the battery state of charge. This approach can achieve positive results, because the operating modes of the plant lead to very distinct loading of the system. For example, in low speed transit or standby the main engine loading is very low and, therefore, switching off the engine stops the engine operating inefficiently. However, the amount of fuel and emission savings that can be achieved with a heuristic control strategy strongly depends on the operating profile of the ship and on the sizing of the components.
Because hybrid propulsion is a combination of electrical and mechanical propulsion, it can benefit from the advantages of both providing improve acceleration performance, reduce thermal loading of the main engine or increase top speed. However, in order to achieve these benefits, a proper design (of the hybrid propulsion) is required and often a trade-off between these requirements has to be made. The control strategy allows an optimal trade-off and can use the extra degree of control by transferring electrical power from the mechanical drive to the electrical network and vice versa. The main challenge for the hybrid propulsion design is to balance the tradeoff between all requirements and design a control strategy to achieve this balance.
To summarize, in recent years, the concept of a hybrid drive, especially for inland vessels, has been developed.The hybrid propulsion system can be beneficial from both economic and ecological point of view. It can be a onetime investment. The advantage of hybrid propulsion is particularly visible when the ship is operating at a low speed. Moreover, the major benefit resulting from hybrid propulsion in electric mode was significantly reduced noise pollution. It may be essential factor for urban or environmentally protected areas. The Hybrid propulsion system showed that there is possible to lower operating costs due to lower fuel consumption. However relative benefit resulting from using hybrid propulsion is strongly dependant on the specific aspect of route (i.e., speed limits, current) and vessel speed. If the combustion engine works for most of the time at optimum load (80% of full power), then the fuel savings are minimal. However, if the travel includes different power demands, resulting i.e., from speed limits, then the fuel savings can reach up to 40%. Addition to that use of hydrogen fuel cells for providing the electrical power makes it more environment friendly. This technology can be used as an upgradation in existing technology. Additionally we can harvest electrical energy from renewable sources available onboard like Solar and wind energy which can be supplied to electolyzer to produce hydrogen and use it as fuel in fuel cell. This technology can be implemented small vessels effectively. Currently this technology is under development to be implemented on the large vessels. Moreover, energy storage devices can be used in combination with waste heat recovery systems to optimize the use of energy on board.
