Ship energy requirements and ship energy systems

1. Ship energy requirements

Ship energy demand is the energy consumption of ship operation, which refers to the fuel consumption of the transport ship during operation, including the energy consumption of sailing, moving, loading and unloading, berthing and other work, but does not include the amount of fuel consumed by the ship for shipwrecks, disaster relief, flood control, port operations, etc. during operation and the amount of fuel consumed during non-operational periods.

The basic forms of energy consumed by ship operation can be divided into two categories: heat utilization and power utilization. Various steam (hot water) heaters on ships, cabin heating and steaming rice are typical examples of heat utilization. The propellers that propel the motion of ships and start various sports machinery (such as motors, pumps, fans, machine tools, etc.) and general household appliances (washing machines, TV sets, etc.) are typical examples of utility utilization.

In energy utilization, work is more difficult to obtain than heat, and therefore more valuable; likewise, for heat itself, heat transfer at high temperature is more valuable than heat transfer at low temperature. Therefore, when considering arranging the total energy utilization, the work should be done as much as possible under possible conditions, and the useless transfer of high temperature heat to low temperature heat utilization should be avoided when generating heat, that is, the different utilization forms of energy have different grades. The power utilization is of the highest quality, while the heat utilization is of lower quality. The grade of high temperature heat in thermal utilization is higher than that of low temperature (both refer to the case of higher than ambient temperature). The general principle is to try to make use of high-quality counterparts and avoid high-quality low-utilization.

Large ships develop like a modern “city” moving at sea, and the power plant is the power center and energy center of this “city”. It contains a large number of mechanical devices and systems, and these mechanical devices are closely related and affect each other, forming a complex energy system.

2. Ship energy system

The ship’s energy system is equivalent to the total energy system of the ship’s power plant. Modern ships not only need a heat engine to provide the propulsion mechanical energy to propel the ship’s motion, but also need power plants and steam stations to supply the required electrical energy and steam thermal energy.

The concept of the total energy system of the ship power plant is based on the chemical energy of the fuel consumed by the marine machinery on the ship, and according to the quantity and quality of the energy, the principle of “using energy according to quality” is to do work first and then use heat, to carry out comprehensive and reasonable comprehensive utilization, so that the chemical energy of fuel can be converted into heat energy through combustion; while the heat energy is converted into propulsion mechanical energy or electric energy in the heat engine, and the waste heat of the main engine is used by the waste heat recovery equipment to generate the steam heat energy and electric energy required by the ship; or provide heat sources for heating, cooling and heating onboard to form an energy system organically linked to ship’s power utilization (mechanical power, electricity) and heat utilization, so that the chemical energy consumed by the ship’s fuel consumption can be utilized to the maximum extent. This energy system formed on the ship is called the total energy system of the power plant.

The ship energy system consists of three parts: ship power system, ship power system and ship steam system. Following the law of energy conservation, the ship energy balance model can be established.