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Rashladni sustavi jako su važan dio brodova za prijevoz ukapljenog prirodnog plina. Parni rashladni uređaji koriste se za klimatizaciju, provijant i ostale stvari, te funkcioniraju uz pomoć tekućina, odnosno radnih tvari koje imaju nisku temperaturu isparavanja i prolaze kroz različite faze kružnog procesa. Sastavni elementi parnih rashladnih uređaja su: kompresor, kondenzator, ekspanzijski ventil i isparivač. Glavni zadatak rashladnih uređaja jest sniziti temperaturu ispod temperature okoline. Na tankerima za prijevoz prirodnog ukapljenog plina koriste se i sustavi za ponovno ukapljivanje isparenog plina. Da bi se prirodni plin ukapljio potrebno ga je ohladiti na -162 ℃, i to se postiže uz pomoć Braytonovog rashladnog procesa. Braytonov proces jest plinski rashladni proces koji sastoji od kruga isparenog plina i kruga radne tvari, odnosno rashladnog dušika. Višestupanjskom kompresijom s međuhlađenjem te pothlađivanjem i ekspandiranjem dušika u rashladnom krugu postiže se dovoljno niska temperatura za ponovno ukapljivanje isparenog plina. Cooling devices are an important part of liquified natural gas tankers. Vapor refrigeration devices are used for air conditioning, proviant and other things, and their principle is based on low evaporation temperatures of liquids that go through different phases of the cooling cycle. The main parts of vapor refrigeration devices are compressor, condenser, expansion valve, evaporator. The main task of these cooling devices is to produce a temperature lower than the surrounding temperature. Reliquification devices are used on liquified gas carriers so that the boil off gas can be condensed again. In order to liquify natural gas it has to be cooled down to -162℃, that is managed by using the reversed Brayton cycle. The reversed Brayton process is an air refrigerant-based process containing the evaporated gas circle and the refrigerant nitrogen circle. The nitrogen is compressed in a multistage compressor with in between cooling, after compression it gets cooled down and then it expands to a temperature that is low enough to liquify natural gas. |
