Liquified Petroleum Gas Tanker Practice

LIQUIFIED PETROLEUM GAS TANKER PRACTICE Captain T. W. V. WOOLCOTT GLASGOW BROWN, SON & FERGUSON LTD., NAUTICAL PUBLISHERS 52 DARNLEY STREET, GLASGOW G41 2SG I PREFACE The purpose of this book is to provide a guide to the conduct of the transportation of liquified petroleum gases and ammonia, the coverage of which has not so far been available in a single volume. It is hoped that it will be useful not only to those operating the carriers but also to the staffs of terminals handling these products. Although some treatment is given to the equipment involved, it is not intended that this book shall be a technical guide. I would like to acknowledge the assistance given by Mr. W. R. H. Walters in the preparation of the book and a general acknowledgement of the assistance I have had over a number of years from the officers of the various vessels in which I have served, and also the management of Messrs. Houlder Brothers and Company Limited of London. T. W. V. WOOLCOTT April, 1977 II INTRODUCTION INTRODUCTION The purpose of this book is to examine the technical problems involved in the transportation of L.P.G. and ammonia cargoes, and various other aspects of the running of L.P.G. Tankers. The detailed procedures at all stages will depend upon the conditions under which the cargoes are to be loaded, carried and discharged—whether under fullypressurised, semi-pressurised, or fully-refrigerated at atmospheric pressure conditions. 1. Preparation: At the point of loading, the cargo tanks should have been prepared, so far as is possible, for the reception of the cargo to be carried. The procedure involved, and the degree of readiness would depend upon whether the vessel is loading: (a) a consecutive cargo of the same type; (b) a cargo of a different nature, but compatible with the previous cargo, e.g. butane after propane; (c) a cargo of a different nature, and incompatible with the previous cargo (e.g. to load propane after discharging ammonia would involve gas-freeing); or (d) a first cargo. 2. Loading: This involves differing procedures, depending upon the facilities offered at the loading terminal, e.g. whether or not a vapour return line (see Glossary) is provided. It covers calculations for ascertaining the correct soundings (depths of liquid) to load either a full cargo or a given quantity (part cargo), and to calculate afterwards as accurately as possible the quantity in fact loaded. 3. Transportation: This covers care of the cargo in transit to guard against loss of product; the running of the reliquifaction plant and ensuring that the cargo tanks do not become over-full due to the incorrect operation of the condensate returns from the reliquifaction plant; and the routine checking of tank pressures and adjusting the degree of refrigeration accordingly so that the vessel is ready to discharge on arrival at the terminal. 4. Discharging: The method of discharge will depend upon the facilities for discharge available at the receiving terminal, and the type of discharge required—if direct into fully-refrigerated storage or via the cargo heater into pressure storage. Special Safety Precautions Due to the hazardous nature of the cargoes carried, those responsible f