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Methane slip during cargo operations on LNG carriers and LNG-fueled vessels

Herdzik Jerzy

New Trends in Production Engineering

2018

Vol. 1, Iss. 1

293--299

In this paper was presented the problems of methane leakages during cargo operations on LNG carriers. Also the leakages are possible on LNG fueled vessels. Due to green-house effect from methane on the atmosphere it should be done some measures to avoid it. Building the cargo tanks with very high capacity, utilization of better thermal insulations limits the quantity of boil-off (BOG). It is used as a fuel in marine power plant, only the overage should be liquefied again. The leakages attend all cargo operations which methane goes directly to the atmosphere through pressure-vacuum valves and gas freeing installation to mast riser or by the ventilation system from cargo pump or compressor room. To minimize the slip on LNG carriers the re-liquefaction systems are installed. They are based on cooling systems which boil-off gas (mainly methane) is liquefied at ambient pressure in temperature about - 161.5°C by pre-cooled nitrogen gas at temperature about -180°C. Compressed nitrogen to a pressure about 25MPa through multistage compressors with intercooling systems is expanded step by step (in intercoolers) to pressure about ambient reaches the temperature about -180°C. The re-liquefaction system needs delivering a lot of electric energy. The total level of methane leakages from mining to the last consumer may be different and sometimes very high. The leakage level starts as minimal 1% and may be raised up to 10%. It was indicated the undertaken actions and next possibilities of methane slip limitations.

Chosen problems of transport and vessel’s fuelling by liquefied natural gas

Herdzik J.

Journal of KONES

2018

Vol. 25, No. 2

157--162

It was presented the possibilities and ways of methane transport by sea. They are still searched new better possibilities of methane transport especially when the gas mining is at the sea. The advantages of using methane as marine fuel are discussed because it seems to be ecological and cheaper one. The lack of LNG bunkering network for vessels is the biggest problem to share methane as a marine fuel. Only a few ports inside the Baltic Sea area give such possibility. Of course, the network is under construction but the development goes too slowly to fulfil the International Maritime Organization (IMO) requirements on 2020 year. A challenge is to prevent failure during cargo operations, loading hose failure, pipe rupture, manifold leak, tank overflowing, or rupture etc. The risk of failure is increased due to very low temperature of liquid methane and the quick temperature change of all elements of cargo system during operations. The aim of the work was to show the indicated problems of vessel’s fuelling by LNG. It was discussed the methane slip during cargo operations and fuelling. The misfires during burning processes into the engines are the biggest problem due to very narrow window of methane self-ignition. It happens the misfiring or knocking cycles. It disturbs the correct work of the engine, resulting in quick engine malfunction or damage.