LNG Bunkering Course: Section 3.6 Instrumentation and Monitoring Equipment

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1 LNG Bunkering Course Section 3.6 Instrumentation and Monitoring 1 Overview of Section 3.6: Instrumentation and Monitoring Gauging Systems Probes Ultrasonic Radar Testing Summary and Conclusion 2 References Liquefied Gas Handling Principles on Ships and in Terminals (SIGTTO) Section 4.9 (4.9.1 to 4.9.7) International Code for the Construction and of Ships Carrying Liquefied Gases in Bulk (IGC Code), Chapter 13, Pages Unless otherwise noted, all of the information in this section is based on the above publications, as well as the professional experiences of Capt. John Egan. 3 1

2 IMO Classification for gauging systems: Indirect may be either weighing methods or flow meters. 4 IMO Classification for gauging systems Closed devises most common in LNG trade: Non penetrating: Ultrasonic or radio isotope sources may be used Penetrating: Float gauges Bubble tube indicators 5 IMO Classification for gauging systems Restricted devices most common in LPG trade: Penetrate tank. Release small volumes of liquid/vapor to atmosphere when in use: Fixed or slip-tube gauges. When not in use, kept completely closed. 6 2

3 Bunkering and Fuel Tank Level Monitoring Liquid level gauging: Installed in each fuel tank and operative over the full range of fuel temperature and pressure: Indirect measurement devices such as weight or flow meters. Direct measurement closed gauging devices such as float gauges, capacitance gauges, radar, ultrasonic gauges. 7 Bunkering and Fuel Tank Level Monitoring Liquid level monitoring (Two systems): Includes high level alarm: Fill valve closes. Each tank must have an independent high level alarm: Activates automatic shutoff of manifold valves (ESD). 8 Float Gauge Source: McGuire and White, Liquefied Gas Handling Principles on Ships and In Terminals, 3rd Edition, 2000, page

4 Capacitance Probes: Capacitance: The property of an electric nonconductor that permits the storage. of energy as a result of the separation of charge that occurs when opposite surfaces of the nonconductor are maintained at a difference of potential 10 The measure of this property that is equal to the ratio of the charge on either surface to the potential difference between the surfaces. Measure change in electrical capacitance between two probes as cargo liquid takes up the space between them. Fixed distance between two probes: Tube with a tube. 11 Capacitance Probes: Closed device (measuring system). No cargo liquid or vapor released to atmosphere during level measurement: Source: McGuire and White, Liquefied Gas Handling Principles on Ships and in Terminals, 3rd Edition, 2000, page

5 Radar: Operates on High frequency signal. Approximately 11 GHz. Radar systems are used for liquefied gases. Commonly used on LNG carriers. Closed device (measuring system): No cargo liquid or vapor released to atmosphere during level measurement. 13 Ultrasonic: Echo sounder principle is used> Measure either ullage or liquid depth (innage). Sound waves are reflected from liquid surface. 14 Ultrasonic: Transceiver Can be mounted either in tank dome or at tank bottom, depending on whether ullage or innage is to be measured Can be unreliable on gas carriers Variable readings with temperature and pressure changes 15 5

6 Independent High Level Sensor: Every cargo tank must be fitted with an independent high level sensor: Must give audible and visual alarm. Only Exception is Type C tank having capacity of less than 200 m Independent High Level Sensor: Independent sensor monitors tank levels. Has high level and hi-hi level alarms. Each tank must have an independent sensor which will generate a shutdown of manifold loading valves- required by gas code. 17 Custody Transfer System: LNG carriers fitted with custody transfer equipment. System is a calibrated package of cargo measurement equipment. 18 6

7 Custody Transfer System: Cargo tank volume is calibrated by independent measurer. High accuracy level, temperature and vapor pressure measuring equipment is installed. System includes data logging and cargo calculation capabilities. 19 Custody transfer systems usually approved by local customs officials. Such equipment has been developed from the practice in the LNG trade of relying on shipboard measurement of cargo to determine the quantity of product transferred between seller and buyer. Quantities determined by the system are also used for import duties and fiscal accounting- system accuracy is essential. 20 Such systems normally include the following equipment: Level +/- 7.5 mm at specified temperature over the full tank height. Temperature: In the Range: -150 C to -170 C, +/- 0.2 C In the Range: -10 C to -150 C, +/ C In the Range: +80 C to -200 C, +/- 1.0 C 21 7

8 Custody Transfer System: Pressure: +/ bar Density: Some LNG ships fitted with means to measure cargo density. In most instances the density is derived by the analysis of samples carried out in the terminal. 22 Calibration: Instrumentation only accurate if properly calibrated. Calibration can be done on board by crew using calibration instruments. Can also be done by service engineers using their own equipment. 23 Calibration: Calibration instruments must be calibrated at regular intervals by specialized facilities and carry a calibration certificate. ISM Code, Chapter 9 of SOLAS recommends each ship carries a calibration procedure and that confirmation of compliance with that procedure is available on board. 24 8

9 Pressure and Temperature Monitoring Pressure monitoring throughout system required by gas code: Includes cargo tanks, pumps, and compressor discharge line, liquid and vapor crossovers. Pressure controlled alarms and shutdowns. 25 Pressure and Temperature Monitoring Gas code requires at least two devices for indicating cargo tank temperatures: One at bottom of tank. Second near the tank top, but below the highest allowable liquid level. 26 Pressure and Temperature Monitoring Gas code requires at least two devices for indicating cargo tank temperatures: Tanks requiring a secondary barrier at a temperature below -55 C. 27 9

10 Pressure and Temperature Monitoring Gas code requires a temperature sensing device within the insulation or on the hull structure adjacent to the containment system: Thermo-couples set must provide ample warning alarm prior to the lowest temperature for the hull steel being approached. 28 Pressure and Temperature Monitoring Gas code requires at least two devices for indicating cargo tank temperatures: Gas code recommends more thermometers be fitted to: At least one tank to monitor temperatures during warm-up/cooldown. To avoid thermal stress. 29 Gas Detection Gas code requires gas carriers to have a fixed gas detection system: The system have audible and visual alarms. The system must be fitted in the cargo control room, wheelhouse, and gas detector readout location

11 Gas Detection Detectors are normally fitted in: Cargo compressor room. Electric motor room. Cargo control room (unless classified as gas safe area). Enclosed spaces. 31 Gas Detection Additional locations: Holds: Except holds containing Type C cargo tanks. Inter-barrier spaces. Airlocks. Burner platform vent hoods. Engine room gas supply pipe lines (LNG Carriers only). 32 Gas Detection Locations: Detector heads are fitted in locations dependent upon density of cargo vapors: Heavier then air vapor fixed at low level. Lighter than air vapor fixed at high level

12 Gas Detection Sampling and analysis: Samples are drawn sequentially from each detector head. Gas code requirement- sample intervals must not exceed 30 minutes. Alarm activated when vapor concentration reaches 30% LFL (LEL). 34 Gas Detection In addition, each ship must have: At least two sets of portable gas detection equipment: Adapted to cargos listed in the vessels Fitness Certificate. 35 Gas Detection In addition, each ship must have: to measure oxygen levels in inert atmosphere: Crew must know how to operate the gas detection equipment and know operating principles of the equipment. Manufacturer s instruction to be followed

13 Calibration of Gas Detection Testing of equipment at regular intervals: Usually established by company operation procedures. 37 Calibration of Gas Detection Span Gas: Mixture is certified by lab. To be readily available. Span gas system to be permanently piped, if possible (for fixed system). Small portable span gas cylinders for portable detectors. 38 Summary and Conclusions Instruments and monitoring equipment help the LNG handling process run efficiently and safely. IMO establishes gauge standards which cover a full range of gauging systems. Standards must be strictly followed

14 Summary and Conclusions Electronic sensors, however, must be monitored closely by operation personnel. This requires constant awareness of what is going on and why