Model 6290 LTD

Third generation design guarantees quality and reliability

Probe under operator control allows monitoring of conditions at any level in the tank

Density & temperature profiles allow detection of stratification

Modbus interface allows integration with DCS

Bottom reference provides greatest accuracy

Drive Mechanism Drive Mechanism HousingHousing

Probe EnclosureProbe Enclosure

Pinch Pinch ValveValve

Ball Ball ValveValve

Flameproof Flameproof Control Unit Control Unit EnclosureEnclosure

Model 6290 LTD System

Tank FloorTank Floor

Multi-Sensor Probe AssemblyMulti-Sensor Probe Assembly

Hollow Helical Drive CableHollow Helical Drive Cable

Top of TankTop of Tank

Probe tracks liquid level

Probe drives back to liquid level (stepping motor accurately measures distance)

Level Measurement

Probe drives to bottom

Bottom reference switch activates

Liquid Level Sensors

Probe drives up

Probe drives down

Probe stops

Program logic drives probe until lower sensor touches liquid (hysteresis errors are removed)

Temperature and Density Sensor

Frequency of vibration is converted to density through an

equation in the controller

Connector

PT 100 Temperature SensorPT 100 Temperature Sensor

Pick-Up Pick-Up CoilCoil

Driving Driving CoilCoil

Vibrating SpoolVibrating Spool

To ControllerTo Controller

Tank Profile Scan

Probe tracks liquid level

Probe drives to bottom

Bottom reference switch activates

Probe drives up and stops at programmed intervals to collect profile information

Modes of Operation

Profile – Probe drives to bottom and then back up, stopping at programmed intervals to record data

Cal (Calibrate) – Probe drives to bottom of tank to establish bottom reference, then returns to liquid level and switches to Auto

Auto – Probe tracks liquid level

Top Scan – Probe starts at current position and moves up or down, stopping at programmed intervals to record data

Manual – Probe can be driven up or down according to operator commands. Reports current temperature and density, does not track liquid level.

Two Liquid Level Sensors

Intrinsically Safe “Bottom Reference” Switch

Oscillating-Spool Densitometer for use in various media:

LNG

Propane

Butane

Ethane

Calibrated Platinum Temperature Sensor

Hollow Helical Drive Cable w/

Conductors

Bottom Reference Switch Assembly

Sliding Lower Shroud

Level Sensors

270 mmto bottom of

of lower sensor

Oscillating Spool Densitometer

2 ¼” DIA (57.15 mm)

Probe Assembly Components

Temperature Sensor(Inside Densitometer)

Sliding Shroud (activates reference switch)

Drive Mechanism Housing

Pinch Valve to ball valve transition piece (Optional)

Pinch Valve with Buna liner

Probe enclosure with viewing window

Probe may be driven into Probe enclosure and sealed off from tank using pinch valve for any required maintenance.

Ball valve allows for possible removal of LTD system and assures tank integrity.

Drive Mechanism Housing

Probe Enclosure

Pinch Valve

Ball Valve

FlameproofControl Unit

Enclosure

M6290 Tank Top Items

Flameproof Control Unit Enclosure

Mechanical Unit Components

Take up reel with helical drive cable

Constant tension spring motor

Flexible coupling

Gear box/speed reducer

Drive gear

Back up wheel

Arc plate

Reel feedback switch

Spring MotorFlex coupling

Take up reelGear box

Drive gear

Arc plate

BackupReel FB sw

All electronics to control the system are contained in the control unit, housed in a flame-proof enclosure.

The control unit may not be opened in the presence of gas.

Input power is 110VAC or 230VAC.

Output of all data to control room is via 2-wire RS485.

Field wiring includes power indication and power control

Inside the Control Unit…

Control Unit Contents

Power Supplies

Power Conversion Card

Control Module

Zener Barriers

Motor Driver

Stepping Motor

Drive Coupling

Power Conversion Card

Control Module

Zener Barriers

Stepping Motor

Drive coupling

Tank Gauge Interface Module (TGIM)

Miniature Size, 1/8 DIN Configuration

Termination point for field wiring

Termination point for wiring to DCS

Possible modem connection for remote diagnostics by SI Engineers

Access point for Hand Held PC (HHPC)

Access for HHPC

Field Wiring DCS Connection

Multiple Field Bus System Architecture

LTD Gauge Data

Alarm Gauge Data

Primary Gauge Data

Secondary Gauge Data

Home Page

LTD Gauge Data

Last LTD Profile Data

LTD Alarm Status

LTD Sensor Status

LTD Gauge Detail

List of Profiles Per Day

Temperature Profile

Axes Automatically

Scaled

Density Profile

LTD Profile Display

Hazard of Rollover

Safety Hazard• Uncontrolled pressure rise in storage tank• Uncontrolled release of LNG vapor• Over-pressurization of LNG storage tank• Ignition of vapor cloud

Potential Danger• Receiving Terminals (1)• Peak Shaving Terminals (2)• Production Facilities (3)

LOWER LAYER

UPPER LAYER

VAPOR

FILM

Boiloff

Relief Valve

• Light layer on top of heavy layer

• Influx of heat increases energy

• Energy in lower layer trapped by hydrostatic pressure

• Layers converge with time

• Energy in lower layer suddenly releases

• Layers “roll over,” releasing large amounts of vapor

HEAT

HEATHEAT

HEATHEAT

Cause of Rollover

Hazard of Rollover

Rollover Incidents

• Accurate statistics difficult to obtain

• 7 Major reported incidents (1970-1979)

• 41 Unofficially reported incidents (1970-1982)

• Many (possibly 100’s) of unreported incidents

Prevention of Rollover

• Prevention of layers through proper tank filling

• Destruction of layers through mixing

• Detection of layers through instrumentation

• Continuous monitoring of tank conditions