Engines and machinery load and utilisation management

In this chapter are described all operations that are made on board of the ships. Independent of its specialty to carried out the marine adventure of carry goods from a port to another and vice versa, and they need the use of equipment’s and systems of the ship. The use of the before mentioned equipment imply an energy consumption which one must be made in the most efficiency way.

The first equipment that is analysed are the diesel engines and its load during the performance of the same.

Engine Load Management

The index that better define the efficiency of the engines is the specific fuel oil consumption, SFOC, this index give the quantity of fuel is uptake for each power unit in a time unit, kg/kWh, i.e. is the minimum quantity of fuel that engine consumption for each kW per hour is transformed at maximum continuous rating MCR.

However, the specific fuel oil consumption is not fix for the diesel engines; it is variable and depend of the load of the engines. It is due that the engines are design and constructed for a minimum specific fuel oil consumption at the 80% of the nominal power, or what is the same, at the 80% of the Maximum continuous rating, MCR, and when the engines are working with a load lower that the 80% to MCR, the SFOC will rise and the thermal efficiency of the engines will be lower.

For the above, the main engines of the vessel should always work at the 80% of MCR to get the maximum thermal efficiency of the engines. However, whether the ship only has one main engine this will work on demand power, but in the case that the ship has two or more main engines, the engines should work at maximum power to get the maximum thermal efficiency, and never should be working two engines at the 50% per cent of MCR.

Another important averment is that due to the last economic global crisis and the very high prices of the fuel the owners has been forced to reduce the speed of the ship and therefore the output power of the main engines to reduce the consumption of the fuel.

The above measure to reduce the consumption of fuel is contrary to the principle of running of engines to the 80% of MCR to get maximum thermal efficiency, because the specific fuel oil consumption is increased. In the case of the ships, the speed increases the output power of main engines exponentially to the cubic, and in this case if the speed is reducing the output power and the fuel consumption is also reduced in the same quantity.

The reduction of the speed of the ship generally called slow steaming and the main engines is going working with at reduced output power, to reduce the consumption of fuel. Obviously, when the ship is going to slow steaming the fuel consumption is reduced exponentially at the third power. But in the case that the ship sailing to slow steaming for a long period, the running of the engines has a perverse consequences that provoke an abnormally running of the elements of the engines like turbocharges, injections systems, etc. and for this cases it is necessary to do a derating in the engines.

As has been mentioned before, the consumption of fuel of the main engines are penalized for the speed of the ship at the third power. It can also be concluded that if it is consider the fuel consumption of the main engines as function of the navigated distance, the fuel consumption is going penalized for the speed at the third power.

Load Management for Auxiliary Engines

In the case of the Auxiliary Engines for electricity generation of the ship, it is recommended to have running only one auxiliary engine generating all electricity demanded. This planning of the work of the auxiliary engines allow to work close or inside of the 80% of MCR, and therefore with the lower specific fuel oil consumption and high efficiency.

It is not recommended that be working simultaneous two auxiliary engines with sharing the electricity load and working both below the 80% MCR, with a SFOC high and therefore a bigger fuel oil consumption.

Electrical Load Reduction

For reduce the electrical consume of the ship, all equipment and machinery of the ship must be stopped when are not been used. It is necessary to avoid that the machinery and equipment running without load.

The running of Heat, Ventilation, Air Condition equipment has to be optimized, and it must only work when necessary in accordance with the weather conditions. In the case of cruise ships, the HVAC has a very high uptake of electricity energy, and therefore it is very important that it is working in the optimum condition. The environmental temperature of all spaces inhabited of the cruise ships must be not less the 24 ºC degrees.

The departments of deck and engine must be coordinated in the planning of the equipment and machinery that are not necessary during the passage or in port, must be switch off.

Auxiliary Machinery Use Reduction via System Planning

Regarding to the flow machinery like, pumps, fans, compressors, etc. it is necessary check aspects like size of the same, that must be calculated in accordance with the needs of the ship, and this machinery should not be oversized or undersize, in both cases they will rise the consumption of electric energy, therefore of fuel. To avoid oversize or undersize of this equipment, a factor of capacity has been defined that is the ratio between operational capacity and nominal capacity. El optimum factor of capacity ratio is when near the unit.

Generally, the fluid machinery does not work continuously at the same work load, and mainly are driven by an electric motor without regulation control of flow, therefore, the electric motor is working always at the same power output independent of the load, and the electric motor consumption the same electrical power at lower or higher work load. The above, permit that this equipment work with a low efficiency when are working with low flow load.

When the electric motor that are drive the pumps, fans or compressors, has not flow control regulation, the control of the flow load, are make opening or closing the suction or discharge valves.

To avoid that the electric motors that drive the pumps, fans, compressors, etc. be working consumption the same electric output power for the different flows work load, is proposal that the mentioned electric motors be of variable speed, and of this way adjust the electric power consumed to the flow fluid load required, and therefore to have a better efficiency.

The aspects to have account in the fluid machinery, avoid the running idle time, the flow fluid control through the suction and discharge valves, to use electric motors with variable speed, adjust the flow to the needed demand and not more, avoid any kind of loss and to have a very good maintenance.

Electric Motors

The electric motors that drive pumps, fans, compressors, etc. consumption about the 60% of the electricity generated on board, therefore, it is very important, with the target to reduce the consumption of the electricity that the electric motors be working in the optimum conditions and with the maximum efficiency. For that it is necessary to have account its dimensions avoiding oversize it that provoke a high consumption of electricity, they must work, if it is possible, above of the 40% of its nominal power, from this load the electric motors work with the maximum efficiency (MariEMS 2017).