Design Of Control System For Overwater Liquefied Natural Gas Filling Station

Our country Yangtze River, Pearl River and other natural rivers' water level drop larger in different seasons. Overwater Liquefied Natural Gas(LNG) filling station is a kind of work ship using for supply LNG for LNG power ship sailing in above rivers. LNG control system(control system) is an important part of the LNG filling station, which is the special control equipment for filling LNG to the supplied LNG power ship, and replenishing gas source to the LNG storage tank of LNG filling station. LNG filling barge is the major component of overwater LNG filling station, its resistance ultralow temperature performance is bad, and it is different to save when the barge is in risk, so the filling station should have rich safety margin in risk control. Control system is the important measure and its safety and reliability is important.In this paper, it takes the control system of LNG Filling Station Hua Qiang No.1(this station) for example, designs a series of measures to improve the safety and reliability of control system as follows.Firstly, uses rockwell three layers network structure which is divided into information layer, control layer and device layer, sets double upper computers to realize the information layer hardware redundancy, uses an independent Programmable Logic Controller(PLC) for emergency shut down(ESD) system to achieve control layer hardware redundancy, uses Ethernet-ring to achieve control layer commu nication redundancy.Secondly, sets multiple sensor for important control points to achieve device layer hardware redundancy, sets special Uninterrupted Power Supply(UPS) for control system to achieve power supply redundancy, uses fault closed type emergency cut-off valves to ensure fault safety, selects “Exd” explosion-proof or intrinsic safety instruments and equipments whose explosion-proof class is matched the level of danger area.At the same time, control system adopts semi automatic sequence control to improve the intelligence to reduce the personnel allocation and staffs' workload.