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Analysis of chosen aspects of a tank gassing-up process on board liquefied petroleum gas carrier. Part II

Wieczorek Agnieszka

Archives of Thermodynamics

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2021

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Vol. 42, no 2

59--69

EN

The paper presents a thermodynamic analysis of the removal of an inert gas from the tank using the vapor of liquefied petroleum gas cargo (called cargo tank gassing-up operation). For this purpose a thermodynamic model was created which considers two extreme cases of this process. The first is ‘piston pushing’ of inert gas using liquefied petroleum gas vapour. The second case is the complete mixing of both gases and removal the mixture from the tank to the atmosphere until desired concentration or amount of liquefied petroleum gas cargo in the tank is reached. On the example of nitrogen as inert gas and ethylene as a cargo, by thermodynamic analysis an attempt was made to determine the technical parameters of the process, i.e., pressure in the tank, temperature, time at which the operation would be carried out in an optimal way, minimizing the loss of cargo used for gassing-up. Calculations made it possible to determine the amount of ethylene used to complete the operation and its loss incurred as a result of total mixing of both gases.

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An experimental gassing-up operation on an ethylene carrier using two cascades with two tanks each

Wieczorek Agnieszka, Nanowski Dariusz

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2020

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nr 61 (133)

136--140

EN

Ethylene is one of the basic raw materials of the petrochemical industry that is used to produce plastics. One of the largest producers of this compound is the USA, and a substantial increase in the demand for ethylene has also been recently observed in the Middle East, the Far East, and China. This requires the transport of this cargo by sea. Ethylene carriers are a type of LPG ships and are equipped with a cascade cycle that uses propylene or refrigerant R404A as a coolant medium. These vessels have been designed to withstand the minimum temperature of ethylene of –104°C for fully-cooled cargo. A mixture of ethylene and air (from concentrations of 2.75–2.6%) becomes explosive during heating under elevated pressures. Hence, it is necessary to form an inert atmosphere in the tanks using mostly nitrogen before the ethylene cargo is loaded. The process of aerating, inerting, gassing-up, and cooling cargo tanks and cargo is constantly repeated during the operation of LPG carriers. Due to the large amounts of ethylene lost during gassing-up, which results in significant financial losses and disruptions in cargo compressors during the cooling of the tanks and cargo, this operation is the most problematic of all. In this article, a solution is proposed for performing the gassing-up procedure which prevents excessive ethylene loss.

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An experimental ethylene carrier gassing-up operation

Wieczorek Agnieszka

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2020

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nr 62 (134)

43--48

EN

Gas carriers are one of the most advanced types of ships and are equipped with the latest technological achievements. Due to the development of this industry, the demand for ethylene transport by sea has increased significantly in recent years. Nonetheless, it is one of the most problematic loads in terms of loading operations. Due to the small density differences between ethylene and nitrogen, ethylene is one of the most problematic hydrocarbons with respect to the efficient gasification of cargo tanks. Additionally, ethylene is one of the most expensive cargoes carried on gas carriers. The above aspects make it necessary to carry out a detailed analysis of the flushing of nitrogen-loaded cargo tanks with ethylene vapors to determine the range of technical parameters to enable more efficient tank gassing-up. This paper provides a detailed analysis of an experimental cargo tank gassing-up operation on an ethylene carrier. The process was carried out in accordance with previously-determined assumptions to optimize the discussed operations, assess how the cargo tank pressure influences this process, reduce cargo loss during gassing-up, and eliminate cargo loss during its cooling. The conclusions from this experiment provide guidelines for subsequent tests.

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Comparative Analysis of Devices Used for Hydrocarbon Concentration Measurements During Cargo Tank Gassing-up Operations on Gas Carriers

Wieczorek Agnieszka

Scientific Journal of Gdynia Maritime University

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2019

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nr 112

35--44

EN

The paper is a detailed analysis of the devices used in measurements of hydrocarbon content on gas carriers during cargo tank gassing-up operations. The characteristics of the Riken Keiki GX-8000 portable gas detector used commonly on ships are described, the types of detection used in the device in relation to the detected gases are discussed, which made it possible to question the validity of using the detector for analysing the concentrations of large quantities of hydrocarbons on gas carriers. Also discussed is a device enabling such analyses to be carried out much more accurately – the Agilent 490 Micro GC chromatograph, which will substantially improve the process of cargo tank gassing-up.

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Operational problems of ethylene transport by LPG gas carriers

Wieczorek Agnieszka, Giernalczyk Mariusz

Journal of KONES

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2019

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Vol. 26, No. 1

191--197

EN

Ethylene is one of the basic raw materials of the petrochemical industry used for the production of plastics, mainly plastic packaging. The USA is the largest producer of this compound. The enormous increase in demand for Ethylene has been observed in recent years in China as well as in the Middle and Far East. This caused an unprecedented increase in the demand for transport of this cargo by sea. Ethylene carriers for its transport are special construction LPG vessels, having a cascade cycle with Propylene medium (less often the refrigerant R 404 A). They have been designed in such a way as to withstand a working pressure of up to 5.4 bar, and the minimum temperature of the transported load is minus 104⁰C for fully cooled Ethylene. This cargo is explosive in the mixture with air (within concentrations of 2.75-2.6%) and during heating under elevation pressure. Therefore, it is required to transport Ethylene in with an inert gas, most often Nitrogen. During the operation of LPG carriers carrying Ethylene, processes of aeration, inerting, gassing-up, cooling tanks and a cargo are repeatedly carried out. The most problematic to carry is gassing-up operation, because it is associated with significant amounts of Ethylene loss, this causes large financial losses. In the article, the authors attempted to diagnose the most serious problems during carrying out the most important for cargo loss the cargo handling operations.

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Optimization of gassing-up operation based on comparative analysis of two twin ethylene carriers

Wieczorek A., Giernalczyk M.

Journal of KONES

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2018

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Vol. 25, No. 1

441--446

EN

The article consists comparative analysis of the gassing-up operation – purging cargo tanks with cargo vapour, on gas carriers carrying primarily Ethylene – one of the most expensive cargo of all hydrocarbons carrying by the sea. The source of the problem constitutes similar densities of both gases under specific conditions – Ethylene and Nitrogen – a gas that tanks are purged before gassing-up. The analysis is made for considerable optimization of the process. The comparison of gassing-up methods is based on tests and measurements on two particular twin gas carriers. In both cases different methods – parallel and cascade were chosen to do the gassing-up (parallel means to purge tanks separately at the same time, cascade means to purge tanks one after the other) what allows specifying beneficial procedure. What was estimated during voyages were technical parameters measured during gassing-up, time of the process and the most important information – loss of the cargo. Analysis of particular stages of the operation also allows estimate the level of gas mixing in the tank. The basic purpose of this profile, based on Ethylene loss, is selecting alternative for carrying this operation in more efficient way, what constitutes determining the most proper method of gassing-up – parallel or cascade and setting temperatures, pressures, mass flows which minimize vapour of Ethylene vented to the atmosphere.

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The Problem of Carrying Insufficiently Optimal Gassing-up Operation after Tanks Inerting with Reference to Ethylene Carriers

Wieczorek A.

Zeszyty Naukowe Akademii Morskiej w Gdyni

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2017

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nr 100

179--186

EN

The paper describes a very crucial problem of carrying insufficiently optimal gassing-up process on ethylene carriers before cooling the cargo during its transport by the sea. At the beginning cascade system of the cargo reliquefaction plant has been described along with its parameters of work. The impact of nitrogen presence on ethylene cascade cycle’s technical work and cooling capacity has been preceded by the detailed depiction of cargo handling operations – tank inspection, inerting and gassing-up. All operations have been circumscribed in terms of oversized amount of ethylene cargo loss, which, in turn, allows to draw a conclusion that gassing-up operation is performed in insufficiently optimal way.

PL

Artykuł opisuje problem nieefektywnego przeprowadzenia operacji gassingup na etylenowcach przed chłodzeniem ładunku podczas transportu. W pierwszej kolejności scharakteryzowano dwustopniowy obieg kaskadowy schładzania etylenu z wyszczególnieniem parametrów pracy kaskady. Opisano wpływ obecności azotu na pracę obiegu. Ze względu na to, że poruszony problem dotyczy początkowych operacji procesu chłodzenia ładunku, omówiono tu pierwsze trzy zabiegi, inspekcję zbiorników, inertowanie oraz gassing-up. Wszystkie operacje scharakteryzowano w odniesieniu do strat znacznych ilości ładunku etylenu, co w konsekwencji pozwala wysunąć wniosek, że gassing-up jest przeprowadzany w niewystarczająco efektywny sposób.