This document is to introduce the initial design for the Condensate Stabilization Train for the Liquefied Natural Gas (LNG) trains 3 & 4. The system already operates with a Condensate Stabilization Train for LNG trains 1 & 2, this design is an expansion on the system. The main objective is to produce a condensate stabilizer, the purpose of which is to recover condensate from the process. However, during the design, the main objective is to design a process that is viable both economically and environmentally; that is also robust and can withstand changes in the system and has as minimal risks as possible attached to the process.
The process of converting natural gas to LNG undergoes a three-part system: gas treatment, compression of the gas and refrigeration. The system is initially treated to remove gases that are not methane, any impurities and water – which could be a possible threat to the equipment when frozen. Treatment removes the condensates or natural gas liquids. The methane that has been treated has a concentration of 99% is now converted from gas to liquid. There will be two LNG trains running in parallel, their feed flow rates will both be 80300 kg/day. Having two trains operating as opposed to just one tackles the issue of any potential shutdown to one of the LNG trains. This will also increase the life span of the plant as maintenance checks can take place on one of the LNG trains whilst the other one is operating- ensuring both trains function as efficiently as possible. Both of the trains will produce 4 million tonnes of LNG per year.
The condensate from the Slug Catchers and the Plant Pressure Control, is then flashed at 21 bar g in the Condensate Flash Drum where the vapour and liquid are separated using gravitational forces. The vapour is sent to the Stabilizer Column and the liquid is preheated and fed to the Stabilizer. The Heat Transfer liquid or coolant dissipates heat from the heat exchanger to the Reboiler. This ensures heat is recovered and recycled through the system, to provide a more sustainable system as less energy is required. The stabilizer operates at 19 bar g. The feed entering the Stabilizer is … (not sure if there’s a numerical value for this) and is the combined preheated mixture from the Heat Exchanger and the cold vapour from the Flash Drum. The Heat Exchanger is attached to the Condensate Storage Tank and the condensate flows down to the the Storage Tank. The column overheads are partially condensed in the Stabilizer and separated in the Reflux Drum to achieve a more complete separation. The condensed liquids are then cycled back to the top of the tower and flow downwards to allow cooling and condensation of the vapour flowing upwards. The vapours are sent to the Stabilizer Gas Compressor and then to the Feed Gas Header. However, for our design we are only designing up to the Reflux Drum so we don’t need to consider this part of the process. There will not be a recycle from the Condensate Storage Tank the Condensate Flash Drum, only during the start up of the process will condensate be transferred from the Storage Tank to establish equilibrium conditions.
The most well-known environmental impacts from LNG facilities are those associated with the changes to the morphology of the plant site, both onshore and offshore. Onshore, these are associated with the construction and operation of LNG jetty’s and plant site. Considering the construction of the LNG jetty, this will impact the commercial fisheries due to the safety reason which are required to keep clear of the project construction. These reason lead to limited area to access for fishing and fish may have to leave the area according to the construction disturbances. According to a dredging activities for constructing LNG jetty, this might cause an excess amount of sea bed by depositing of fine sediment. This excess of seabed will effect on near shore marine ecology. In the area of constructing plant on land, the topsoil is needed to be exposed in order to better plant construction. According to exposing topsoil will become an unstable surface for rehabilitation and may be rapidly eroded on sloping area. However, this is a temporary environmental impact, as the time goes by and the disturbed areas rehabilitate and stabilize. Another impacts to soil during the operation could as a consideration of natural gases pipeline on land also occur as a result of small leakage of liquid hydrocarbons, fuels, and chemicals, as well as releases cause by accidents. Methane exposure into the atmosphere is a serious negative environmental impact as it has a high global warming potential.
Offshore impacts are mainly associated in natural gases pipeline and drilling area. The drilling of the offshore production will affect to water quality and marine ecology in the offshore area. In the view of offshore pipeline, it likely have large impact on population, community and ecosystem. During the installation of the offshore pipeline, activities such as pipe laying or placement will disturb seafloor habitat and also temporarily increase turbidity. Impacts that are associated with marine fauna can be occurred during construction of the offshore pipeline and project operation. According to the pipe laying will operate 24 hours and emit under water noise. Noises that are generated during pipe lying will possibly interfere with the nearby marine mammal which communicate using sound.
Moreover, LNG trains can be affected in air quality by emission of dust and also have greenhouse gas impact. Greenhouse gas emission can be occurred during both construction and operation but the amount of greenhouse gas emission is relatively small. According to the highly vulnerable and flammable nature of the gas involve, all LNG plants use normally two trains of compressors running in parallel.
It is paramount to consider the safety aspect attached to the process. All safety legislations should be followed, for this design we are following UK safety guidelines. A possible hazard attached to this process is the gas being very flammable which is also a serious risk to workers at the plant and the environment if an explosion occurs. Later in the design task Hazard Identification (HAZID) and Hazard and Operability Study (HAZOP) documents will be produced. These provide simple, clear, structured approaches to identify hazards, their risks and determines the severity. Alongside with these reports, everybody in the plant will need to be fully trained appropriately for their role and be in the appropriate PEP.
Conclusion
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