Study On Scaling Of FLNG Liquefaction System

FLNG is a floating production unit which sets the exploration,liquefaction,storage,load and unload as a whole.However,the construction of floating liquefaction plant in the sea is a huge challenge,and scaling studies needed to be carried out to achieve FLNG large-scale industrial applications.FLNG liquefaction process system is the core of FLNG,which is mainly composed of liquefaction process and key equipment.In this paper,experimental and numerical simulation method were combined to analyze the scaling of FLNG liquefaction process system from two aspects including liquefaction process and key equipment,providing guidance and advice for our FLNG industrial production.For different feed gas treatment capacity,the selection of liquefaction process is also different.Refrigerant and refrigerating methods have a great influence on the liquefaction process capacity.ASPEN HYSYS v7.3 software was used to establish the steady-state simulation model of different liquefaction processes.The effects of refrigerant type,throttle series,expansion series and refrigerant independent cycle on the liquefaction process capacity were studied,which can provide references for the selection of different scale liquefaction processes.Handling capacity of key equipments play a restrictive role in the production capacity of liquefaction processes.Heat transfer performance of the heat exchanger,which is the key equipment in liquefaction process,is directly related to the normal operation of the whole liquefaction system.Based on a cold box dynamic simulation method proposed in this paper,liquefaction processes of different treatment scales were built and then used to analyze the dynamic response characteristics under sereral disturbance conditions.A conclusion was obtained accordingly,the dynamic response speed,the steady speed together with the adaptability of the cold box would increase with the increase of the treatment scale.Therefore,the usage of plate-fin heat exchangers in scaling-up liquefaction systems can make the overall system to better.The selection of compressor and compressor drive can only affect the total power consumption of different treatment scales,and domestic development should learn from foreign experience to develop large-scale units,then to increase the FLNG capacity.Taking the impact of liquefaction process and key equipment on the scaling effect into account,the small and pilot test data of propane pre-cooled double nitrogen expansion liquefaction was used to compare and analyze.It is found that,compared with the small test,the pilot test has a lower specific power consumption,a higher liquefaction rate and a lower sensitivity to the feed gas.In order to evaluate the performance of serial liquefaction process,the concept of net specific power consumption was proposed.The conclusion showed that,with the liquefaction treatment capacity increasing,the net power consumption can be further reduced,and the sensitivity to the feed gas becomes lower.The adaptability of propane pre-cooled double nitrogen expansion liquefaction process was furtherly clarified,and it also showed that the liquefaction process scaling method and the net specific power consumption parameter can be used for the scaling analysis of the liquefaction process.In parallel,they have a great guiding significance in promoting the development of China's FLNG technology.