Natural gas system for ship propulsion

U ovom radu bit će opisani svi sustavi kroz koje ukapljeni prirodni plin prolazi, prije dolaska do potrošača. Najprije su opisani postupci sabiranja i pripreme prirodnog plina. Također, kratki osvrt posvećen je svojstvima metana (udio veći od 70% u smjesi UPP-a) kako bi lakše razumjeli problematiku vezanu uz njegov transport brodom. Na temelju zadanih parametara, izrađen je projekt sustava prirodnog plina za pogon broda. Za skladištenje UPP-a koristi se spremnik tipa C. Dimenzije spremnika proračunate su na temelju maksimalnog volumena tereta. Osim dimenzija, izračunati su i gubici plina u vidu isparavanja zbog ulaska topline kroz spremnik. Cjevovodi ovakvog sustava su poprilično složeni te su posebno proračunati dijelovi cjevovoda ovisno o potrebnom protoku i stanju prirodnog plina. Za cjevovode ukapljenog plina je predviđena dvostruka stjenka. Ispareni plin iz spremnika odlazi do motora gdje se koristi kao glavno pogonsko gorivo. Za isparivanje i zagrijavanje plina, predviđena su dva paralelno povezana izmjenjivača topline (cijev u cijevi s 2 prolaza). Proračunata je potrebna površina izmjene topline te duljina i broj cijevi koji to zadovoljavaju. Također, za iskrcaj tereta i dovod goriva su previđene uronjene centrifugalne pumpe te je izračunata njihova potrebna snaga. U svrhu vraćanja isparenog plina na kopno ili dovoda do motora, koriste se kompresori određene snage.In this thesis, all the systems that liquefied natural gas is passing threw, before they get to the consumer, are going to be described. The procedures for collecting and preparing natural gas are first described. Also, a brief review is devoted to the properties of methane (a share of more than 70% in the mixture of LNG) in order to better understand the problems associated with its transport by ship. Based on the given parameters, a project of natural gas system for ship propulsion was composed. To store the LNG, the tank type C is used. Tank dimensions are calculated for the maximum volume of cargo. In addition to the dimensions, gas losses in the form of evaporation due to heat input through the tank are also calculated. Piping of this system is quite complex and the pipe sections are specifically calculated depending on the required flow and state of the natural gas. Liquefied gas pipeline is provided with a double wall. The evaporated gas from the tank goes to the engine where it is used as the main propulsion fuel. For evaporating and heating the gas, two parallel heat exchangers (shell and tube with 2 passes) are provided. Calculation is required for the heat exchange surface and the length and number of pipes that fulfill the requirements. Also, for the unloading of cargo and fuel supply, an immersed centrifugal pumps are planned and their required power is calculated. For the purpose of returning evaporated gas to the mainland when loading or leading to the engine, compressors of certain power are used