As part of the energy revolution, liquefied natural gas (LNG) can make an important contribution to supply security as a transition solution. This energy source stands out thanks to outstanding availability under competitive conditions. Furthermore, the emissions it produces are lower in comparison with combustion of coal and oil. However, the extracted gas mixture is highly flammable. Natural gas and LNG are classified as explosion group IIA and temperature class T1 according to ATEX and IECEx . This means that explosion protection must be guaranteed across the entire value creation chain, which is achieved with explosion-protected products and systems for all process steps from natural gas extraction to supply.
The conveyed raw natural gas initially flows through a processing plant, which separates out contaminants and pollutants and generates almost pure methane. For further processing, the gas is fed into a gas liquefaction plant, known as an LNG train. This is where it is liquefied using a single- to triple-stage circulation process with high energy consumption due to the deep-cooling and heat dissipation required. To control the pumps and fans needed for the heat exchangers, these systems must be equipped with particularly high-performance, explosion-protected motor controls and power distribution boards. These explosion protection solutions can be designed using a range of types of protection depending on the needs of the system.
Monitoring errors efficiently
The modular enclosure technology enables multiple degrees of protection to be combined efficiently, and control systems and power distribution boards to be configured in a range of sizes; as a result, even high power levels with multiple power outlets are available in hazardous areas. In order to reduce maintenance and servicing costs for the entire LNG train, we recommend connecting the circuit breaker and auxiliary contacts to a remote input/output system, so that the errors on the power distribution board can be read out and monitored via the distributed control system.
Ensuring cooling during transport
Special tanker suppliers mostly take on the transport of LNG. These giant ships have larger and larger dimensions. In spite of its tank insulation, the liquefied gas heats up during transport and could partly evaporate. Compressors used on board ensure that the LNG is cooled down again. To control the compressors, explosion-protected control stations for remote input/output (RIO) are ideal, which transmit the signals from sensors and actuators safely to the decentralised control system. Since the available installation space below deck is limited, the machines and RIO stations must be designed to include input/output modules and digital display and message elements in a very compact size. Systems with 8- or 16-channel modules with type of protection with intrinsic safety type of protection (Ex i modules) mean that the station can be extremely compact, reducing the required space and weight.
Safely converting back into gas
After arriving at the destination, the natural gas is converted back to its gaseous form in regasification units. Alternatively, this process can be performed with smaller quantities flexibly at offshore plants, known as Floating Storage and Regasification Units (FSRUs). The heat for vaporisation is fed in to convert the LNG to its original state. For cost-related reasons, this heat is typically obtained from heat exchangers supplied with seawater. For safety reasons, pump units, which convey the seawater to the heat exchanger, should be equipped with alarm signal emitters, terminal boxes, safety switches and load disconnect switches with AC3 switching capacity. Integrated safety switches safely disconnect the electrical energy supply from machines and system parts for cleaning and repairs.
Since the hazardous zones cover large areas of the plant, explosion protection solutions should not only be used during the actual processing stage, but throughout the entire infrastructure. As well as explosion protection, the use of seawater-resistant enclosure materials, high-quality sealing materials, a vibration-resistant design, and resistance to electromagnetic influences are all deciding factors when choosing which materials and design to use.
Before being supplied to the grid, the natural gas is compressed in a compression plant. The motor control units and power distribution boards, which are required for a number of tasks including controlling compressors and supplying the heat exchangers and evaporation systems, can be made lightweight and compact with explosion-protected enclosure technologies.
LNG is primarily used to generate heat or power, and as an energy source for the process industry. Due to its environmentally friendly nature and positive effect on CO2 emissions, it is also becoming increasingly important as a fuel source for ships and trucks.
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