June 2021

Safety reinforcement monitoring system for floating LNG power plant

04 June, 2021

Green Ship Technology Team Han Eun-jung

Floating LNG (Liquidated Natural Gas) based power generating facilities can overcome topographical limitations and minimize engineering works (when compared to other power generating facilities) by generating power through the combustion of LNG. Since LNG is not only a flammable material but is also transported in cryogenic conditions, a BOG (Boil-off Gas) recovery system is an important feature to safely operate floating LNG generation facilities, particularly to minimize the generation of BOG, which is a major cause of fire and explosion incidents.

The BOG recovery system contains information about the hardware and design of the monitoring software for the recovery system that treats BOG generated in LNG plant systems. It was designed to take into consideration the spare safety capacity, piping stress, and the container’s material for the recovery storage for evaporative gas emission generated by LNG. The BOG recovery system was also designed to be divided into ship-mounted and land-plant types for storage vessel types (Fig 1).

Fig 1. Safety Reinforcement Monitoring System for Floating LNG Power Plant

The LNG BOG recovery system contains software (S/W) to detect and monitor the risk of explosions. The software needs to receive measured data from a wide range of measuring instruments. The software includes functions for data filtering processing, data visualization, data visualization based on three-dimensional models, and real-time data visualization.

Figure 2 demonstrates the PFD of designed BOG recovery, and the right side of the figure is a brief representation of the flow of each process.

Facilities are constructed to facilitate a cyclic process by recovering compressing process of gas that is not recovered in cold box and flow of the process connected to recovery tank through the cold box for recovering BOG. KR has tested a range of accident scenarios to prevent possible accidents in advance or scale them down by analyzing and identifying any risks to the BOG recovery systems in floating LNG generation facilities. Key construction and monitoring factors based on hardware design have been identified. Four factors have been identified for monitoring; temperature, flow, level, and pressure which is most important and ascertained by monitoring the cold box outlet. The P&ID of the cold box should also be monitored. The four processes’ data were selected for monitoring at the point of the cold box outlet in the recovery system.

Fig 2. BOG system Plow Diagrams (left), BOG Recovery System P&ID
(Piping & instrument Flow Diagrams) and Monitoring Point (right)

The monitoring system is designed as shown in Figure 2, and it stores data, filtering for various analyses and accuracy measured from four measurement sensors. It can then be visualized using the three-dimensional monitoring system. Explosion-proof monitoring devices are linked to an integrated monitoring system which include surge-resistant circuits capable of detecting waterproof, dirt repellant, and surge tests.

Fig 3. Configuration of Monitoring System

In the monitoring system configuration, a three-dimensional model employs the AB4D component and transforms the FBX file from NavisworksTM 5. The four measured data sources are not consistent in time intervals with the point being measured, so for this purpose, KR uses regularization and interpolation to convert them into sec-wise measurement data and utilize them in the program.

Fig 4. Three-dimensional monitoring system function

The developed monitoring program was developed in the C# language, and the configured modules provide various filters for utilizing data at the expert level by applying data normalization, interpolation, Kalman filter, low-band filter (LPF), high-band filter (HPF), and median filter. It is implemented to demonstrate four seconds of data measured on three-dimensional modeling, and it is illustrated in Fig 5.

Fig 5. Three Dimension Based on BOG Safety Monitoring

The risk of failure of the BOG recovery equipment was represented by using a Risk Matrix. It was set to allow modification by the user depending on the probability of frequency and consequence based on IMO’s FSA (formal safety assessment). In addition, the probability of abnormal activity within the operation of the BOG recovery equipment is calculated by using MTBF (Mean Time Between Failure). Economic evaluation techniques were used in ranking decision plans for a given failure, and the prioritized decision was made through cost reduction (ΔC) resulting from failure rate reduction (ΔF). The costs used for economic assessment were determined using Life Cycle Cost to different propulsion methods depending on the Warning Emergency (Fig 6).

Fig 6. Equipment failure rate calculation and visualization (left), Risk Matrix screen (right)

The incident scenario of the BOG recovery system was designed to minimize BOG which is a major cause of explosion and fire accidents, and to ensure the safe operation of floating LNG generation facilities. Taking into consideration domestic and international laws, the BOG recovery system design and system design were developed to secure price competitiveness according to the operating platform.

Based on the designed system, KR has developed a monitoring program to enhance the safety of the BOG recovery system. Furthermore, the system was designed to enhance user understanding and safety aspects through the use of a three-dimensional plan and process model. Four types of filtering techniques are applied to measure driving data. By comparing this with driving data in real-time, safety was increased. The main equipment analysis of the malfunction and accident development process provided a further basis for preventing or reducing possible accidents.

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