Written by: Raul Rogerio Pimentel Ribeiro
Hydrogen Electrolyser
The massive hydrogen production of this facility concept is derived from PEM Electrolyser technology. The available technology provides standards as shown below in table 1:
Table 1: PEM Electrolyser Standard
The PEM Electrolyser installed capacity is dependent on the installed capacity of the floating wind farm. This is crucial to determine the nominal energy consumption of the Electrolysers. There are two scenarios that are evaluated on this project: the optimistic and the pessimistic scenarios. These scenarios are related to the power production of the wind farm and the best scenario is the production of energy equal to the nominal capacity of the electrolysers. The pessimistic scenario takes 50% of the wind farm capacity as the average energy production. The scenario influences the overall hydrogen production and, hence, energy consumption. The efficiency of each system is considered to remain the same to facilitate the estimation of the overall efficiency of the system.
The product between PEM Electrolyser installed capacity and its efficiency will provide the maximum hydrogen production of the system as shown in table 2:
Table 2: PEM Electrolyser energy consumption and Hydrogen nominal production
Desalination System
The chosen desalination system is the Reverse Osmosis Desalination System which is broadly applied in different tasks around the globe due to freshwater supply. The two-stage desalination system performs a unique characteristic regarded to efficiency. The system can achieve up to 72% of efficiency which is a high achievement in order to scale down coupled systems such as water pump and pressure pump systems, and the overall energy consumption and losses. The system also counts with a recovery system that reorients the presented energy in the brine and reinjects into the system. Table 3 shows the desalination nominal power, the energy ratio to achieve the amount of freshwater required by the system, and the total energy consumption.
Table 3: Energy consumption and outputs of the RO desalination system
As seen in the table, although it develops a crucial role in the hydrogen production system, the energy demand for the desalination system represents a small amount of the overall energy available. So, it opens a discussion about the necessity of the energy recovery system in comparison to the increase in the complexity of the system.
Compression System
The compression system is summarised by the energy demand to achieve the pressure up to 700 bar as it is required by the storage system characteristics. The main specifications of the compression system are displayed in table 4.
Table 4: Compression system specifications
The nominal power is dependent on the pressure difference between the input and the output of the system. It is considered the pressure of 30 bars coming from the Electrolyser system into the compressor system and 700 bar as the pressure required by the storage system. Thus, the difference in pressure is 670 bars.
Water Supply System
The water pump system is mostly dependent on the sizing of the water pump and the dimension of the pipelines. The water pump specification is given by the water pump power in horsepower (HP) or kilowatts (kW), the flow rate of liquid, and density of the liquid. The flow rate of liquid must match with the demand of water required by the desalination system and, hence, the PEM Electrolyser freshwater requirement. Bearing it, table 5 shows those values previously described.
Table 5: Water pump specifications
Based on the water flow, it becomes possible to define the dimension of the pipelines. The pipelines dimension and design affect the friction which influences the final water pump power demand. As displayed in table 6, the pipeline dimensions are:
Table 6: Pipeline dimensions
Cooling System
Most of the energy loss in the system comes from heat losses. The heat loss is present in every power system that develops work. Despite the uncontrollable energy loss, overheating can generate damage to the system whether it is not properly controlled. The cooling system is placed to avoid overheating of the main system. The overall demand for energy for the cooling system in hydrogen production and storage is expressed in table 7.
Table 7: Energy consumption of the cooling system
Transformation and Control System
The energy transmitted from the wind farm is sent to the platform for the production of hydrogen. However, it is necessary to adapt this energy to meet the various activities within the platform such as hydrogen production, cooling system, gas compression system, and water supply. The principal facility considered in this project is the transformer facility that will receive the full amount of power from the wind farm and, hence, the highest amount of losses is concentrated in this part of the electrical system. The losses from power devices and connections are negligible. Table 8 displays the transformer specifications and total energy losses.
Table 8: Transformer specification and energy loss
The rectifier system which converts AC to DC and the Programmable Logic Controller (PLC) are unconsidered into calculation due to its negligible contribution to the final amount of losses.