LPG Operational Practice, 1st Edition, 2022

This publication is designed to give ships’ officers, tanker terminal personnel and terminal management an understanding of the principles involved in the safe loading, transportation and discharging of liquefied petroleum gases and chemical gases. The notes include both theoretical and practical aspects of ship operations, covering in-service, pre-arrival and post-transfer phases.

DETAILED OVERVIEW

It then follows a standard LPG cargo sequence, detailing the operations for drying, inerting, gassing-up, cooldown, loading, while on passage and discharging. Text and graphical information is complemented by 3D models, which allow readers to visualise key LPG operations and system layouts. Other operations such as changing tank atmospheres, stenching, mixing cargoes and conducting ship to ship (STS) operations are also explained.

INTRODUCTION

The publication begins by covering the principal aspects of LPG carrier design, including the cargo containment systems and the equipment on board. It details the basic operation of the cargo handling equipment, including key systems such as the cargo pumps, LPG reliquefaction plant, etc. The publication then follows a standard LPG cargo sequence, looking at the phases for drying, inerting, gassing-up, cooldown, loading, while on passage and discharging. Other operations such as changing tank atmospheres, stenching, mixing cargoes and conducting ship to ship (STS) operations are also explained.

CONTENTS LISTING

Overview of LPG

Section 1 - Equipment and Design

1. Design and Cargo Containment

1.1 Principles of Gas Carrier Design and Construction and The IGC Code

1.2 Liquefied Gas Carriers - Ship Types

1.2.1 Fully pressurised ships

1.2.2 Semi-refrigerated (semi-pressurised)

1.2.3 Fully refrigerated LPG

1.2.4 Ethylene carriers

1.3 General Gas Carrier Layout

1.3.1 General simplified layout of the deck piping on a fully refrigerated LPGC

2. Cargo Handling

2.1 Cargo Piping, Pumping and Valves

2.1.1 Cargo tank piping

2.1.2 Emergency Shutdown (ESD) system

2.1.3 Pressure surge

2.2 Pressure Relief Valves (PRVs)

2.2.1 Pilot operated PRVs

2.2.2 Spring loaded PRVs

2.2.3 Vent arrangements

2.3 Cargo Pumps

2.3.1 Deepwell pumps

2.3.2 Submerged pumps

2.3.3 Booster pumps

2.3.4 Pump performance curves

2.3.5 Running pumps in parallel and in series

2.3.6 Cargo heater

2.3.7 Cargo vaporiser

2.4 LPG Reliquefaction Plant

2.4.1 Reliquefaction plant Single

2.4.2 stage direct cycle Two

2.4.3 stage direct cycle Cascade

2.4.4 direct cycle Cargo

2.4.5 compressors

2.4.6 Compressor suction liquid separator Purge

2.4.7 gas condensor

2.4.8 Typical example of starting a reliquefaction plant (cascade cycle)

2.4.9 Methanol/ethanol injection system

2.5 Inert Gas Systems

2.5.1 Inert gas produced by combustion of gas oil

2.6 Electrical Equipment in Hazardous Areas

2.6.1 Intrinsically safe equipment

2.6.2 Flame-proof (explosion-proof) equipment

2.6.3 Hazardous areas

2.7 Instrumentation

2.7.1 Liquid Level

2.7.2 Float gauges

2.7.3 Capacitance gauge

2.7.4 Ultrasonic gauge

2.7.5 Tank radar gauge

2.7.6 Tank overfill protection

2.7.7 Pressure and temperature monitoring

2.7.8 Vapour detection systems

Section 2 – Initial and In-Service

3. Drying and Inerting

3.1 Drying

3.1.1 Dying methods

3.2 Inerting, Gas Detection and Flammability

3.2.1 Inerting the cargo system

3.2.2 Atmosphere evaluation Fixed

3.2.3 gas detection

3.2.4 Portable gas detection and flammable ranges

3.2.5 Inerting by displacement

3.2.6 Inerting by dilution

4. Gassing-up and Cooldown

4.1 Gassing-up

4.1.1 Gassing up at sea using liquid from deck storage tanks

4.1.2 Gassing-up cargo from the desk storage tanks

4.1.3 Starting the reliquefication plant after gassing-up

4.1.4 Gassing-up alongside

4.2 Cooldown

5. Loading Operations and Loaded Passage

5.1 Prior Loading

5.1.1 Connecting and disconnecting MLAs/hoses

5.2 Loading

5.2.1 Tank filling level

5.2.2 Topping off tanks

5.2.3 Cargo calculations

5.2.4 Operation of the reliquefaction plant

5.2.5 Sampling

5.3 Loaded Passage

6. Discharge Operations and Ballast Passage

6.1 Discharge

6.1.1 Discharge by deepwell or submersible pumps

6.1.2 Discharge using booster pumps and cargo heater

6.1.3 Discharge by vapour pressure

Section 3 Other Operations

7.1 Liquid Freeing (Warming Up/Puddle Heating)

7.2 Inerting

7.3 Aeration

7.4 Purging

7.5 Grade Change

7.5.1 Guidance for when changing from ammonia to LPG

7.5.2 Guidance for when changing from LPG to ammonia

7.5.3 Guidance for changing between butane, butene, butadiene, propane, propene

7.5.4 Guidance for when carrying a previously butadiene cargo

7.5.5 Guidance for changing from butane to propane or vice versa

8. Specialised Cargo

8.1 Odourisation (Stenching)

8.1.1 Method of application

8.1.2 Safety requirements

8.2 Mixing Cargoes (Blending/Co-mingling)

8.2.1 Method of application

8.2.2 Safety requirements and limitations

9. Ship to Ship

9.1 Pre-arrival Stage

9.2 Approach and Mooring Stage

9.3 Cargo Transfer Stage

9.4 Post-transfer Procedure

10. Safety Precautions in LPG

10.1 General Principles

10.2 Terminal and Cargo Operations

10.2.1 Pre-arrival

10.2.2 On arrival

10.2.3 During operations

10.3 Additional Procedures

10.3.1. General operational safety

10.3.2 Other craft and simultaneous operations (SIMOPs)

10.3.3 Protective equipment and protective clothing

10.4 Entry into Enclosed Spaces

ABOUT THE AUTHOR

Witherbys staff have significant expertise in the fields of navigation and hazardous cargoes as well as in the presentation of complex subjects in a graphic and easy to understand manner.