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1

The operation limitation of the two-stage reliquefaction cycle employed on board the ethylene carrier

Nanowski D.

Journal of KONES

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2016

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Vol. 23, No. 4

359--365

EN

Ethylene, propane, commercial propane or HD-5 is cargoes very often carried by sea. In order to reduce the time of loading and later cooling down to required parameters of temperature and pressure in the cargo tanks two-stage reliquefaction cycle is used. For above-mentioned cargoes, two-stage cycle with liquid subcooling and interstage cooler is one of the most often utilized. In this paper operation of this cycle is discussed, based on parameters of the reciprocating cargo compressor and its cycle used on board the one of the biggest – 21 500 m3 – ethylene carrier in the world. It is explained how some vapour mixtures decrease cooling rate during reliquefaction of the cargo and some parameters of pressure and temperature of these mixtures are calculated with help of ProSimPlus – thermodynamic simulator. In this way, changes of the mixtures composition across reliquefaction plant are discussed. Increased pressure of the cargoes condensing as a way of solving of explained problem is analysed. Three stage – cycle of reliquefaction plant used for pure propane or ethylene is shown and some of its disadvantages are explained. Based on this discussion, three-stage cycle with liquid injection is proposed to fulfil operation requirements of the cargoes and improve their loading and cooling processes on board the ethylene carrier. Analysis of refrigeration capacity for both cycles is carried out.

2

The influence of incondensible gases on the refrigeration capacity of the reliquefaction plant during ethylene carriage by sea

Nanowski D.

Journal of KONES

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2016

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Vol. 23, No. 3

359--364

EN

This paper presents a performance of the reliquefaction cascade plant during ethylene carriage by sea. Parameters of this plant are discussed because of dramatic low cooling rate of the cargo. Ability to decrease ethylene temperature from approx. minus 96°C to minus 103°C on board the ship is essential. Modern ethylene carriers are able to keep cooling rate about 2K per day, on the other hand old ones do it with rate approx. 0,2 K per day and require weeks to achieve proper temperature of ethylene for discharging. Of course, economic issue of such journey is not very satisfying but many factors influence on this. In this paper almost new one – nine months – old ship is considered, with capacity 21 000m3. Main reason of problem is analysed, including heat ingress through the cargo tanks insulation. Gassing-up of the ship is explained and influence of presence incondensable gases in the cargo tanks described. Operation of the reliquefaction plant is shown, especially with the vent valve of LPG condenser. Analysis of pressures in the cargo tanks is carried out – on board the ship and with help of ProSimPlus – thermodynamic simulator. Conclusions contain discussion of the reliquefaction plant problems and remarks what should be improved on board the ethylene carrier to avoid such problems.

3

The influence of condensing pressures of the ethylene carrier cascade cycle on its refrigeration capacity

Nanowski D.

Journal of Polish CIMAC

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2014

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Vol. 9, no 3

67--72

EN

Ethylene, Propane and others liquefied gases as a cargo are transported at sea by temperature below 0°C. It requires sufficient efficiency of reliquefaction plant. Short description of that gas plant is shown including cascade system and its cooling processes are described. Based on Mollier diagrams the refrigeration capacity investigation of gas plant is done. This analysis is focused on condensing pressure which takes place in the condenser. Theoretical cycles are taken into account and real condensers of cargo compressor and screw compressor of refrigerant cycle are considered. Thermostatic expansion valves are employed in cascade cycles and their operation parameters are taken into account as well. Conclusions include some guidelines on condensing pressure and related operation parameters to maintain the gas plant with high efficiency of refrigeration capacity.

4

The comparison of theoretical to practical cargo loading rate of butane - analysis of LPG carrier reliquefaction plant

Nanowski D.

Journal of KONES

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2013

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Vol. 20, No. 1

227--231

EN

This paper presents a performance of reliquefaction plant analysis in order to assess possible cargo loading rate for Butane (C4H10). The highest cargo loading rate is essential in use of LPG carriers because of economical point of view. Loading and discharging cargo time at ports substantially influences on a financial effect of the ship owner. Because of different cargo grades, which number is continuously increasing, crucial is to know real efficiency of gas plan, before signing some contract with customer. On board these types of ships the highest efficiency of reliquefaction plant is crucial. After short description of fully refrigerated gas carrier, theoretical data of analysed ship, taken from ship documentation is shown. Taking into account this data, expected cargo compressors parameters and cargo loading rate are discussed, explained and assumed. In next step, real ambient Butane loading process carried out on board LPG carrier is described. All essential values and reliquefaction plant readings, taken in loading port are presented. The comparison of theoretical result based on available documentation to practical effects obtained in the port is performed. Analysis, mainly taking into account gas plan, answers if it operated with the highest possible efficiency and met cargo loading parameters expected according to ship manuals. Conclusions are discussed.

5

Gas plant of ethelyne gas carried and a two stages compression optimization of ethylene as a cargo based on thermodynamic analysis

Nanowski D.

Journal of Polish CIMAC

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2012

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Vol. 7, no 1

183-190

EN

Ethylene as a cargo is more and more popular in maritime transport. Its temperature approx. -104°C during discharging requires sufficient efficiency of reliquefaction plant. Short description of that gas plant is shown including cascade system and processes are described. Based on Mollier diagram and ethylene mass flows, refrigeration capacity of the system is calculated when some changes in the cargo economizer are done. Some of these changes are carried out by crew members of gas carriers in order to reduce second stage discharge temperatures of reciprocating compressors. These losses of refrigeration efficiency are calculated to assess its influence on Ethylene temperature in the cargo tanks. On the other hand some assumptions are used to improve refrigeration capacity by Ethylene compression process.

6

Trendy rozwoju układów napędowych gazowców LNG

Chądzyński W.

Zeszyty Naukowe / Akademia Morska w Szczecinie

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2006

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nr 10 (82)

139-150

PL

Zdolności przewozowe światowej floty gazowców LNG rosną gwałtownie, a ilość zamówień na nowe statki wzrasta bardzo dynamicznie. Niewykluczone, że budowa gazowców LNG zostanie podjęta także w naszym kraju. W niniejszej pracy zostaną przedstawione wymagania, jakie stawiane są przed układem napędowym gazowca LNG, sposoby wykorzystania naturalnych ubytków LNG podczas rejsu, warianty możliwych do zastosowania układów napędowych wraz z ich cechami eksploatacyjnymi, szkic założeń do badań nad optymalnym rozwiązaniem układu napędowego w powiązaniu z wielkością statku.

EN

The global LNG shipping capacity is growing sharply and the number of ordered LNG carriers is very high at the moment. It is possible that Poland will appear among experienced builders of those ships. The author considers the requirements for propulsion systems of modern LNG carriers, the methods of utilising boil-off gas, different alternatives of power sources. Besides, the paper introduces a preliminary idea of research on an optimal solution of propulsion system closely related with the size of the vessel.