Describe briefly gas carrier loading routines.
17 Jun '17, 01:58
Before commencement of loading confirm loading order with the owner. In the loading order stated the quantity to be loaded, at which temperature during loading the cargo, and discharge temperature. Further there is information about the loading port and discharging port. There may also stated sizes of the terminal lines and flanges.
The quantity to be loaded is given in metric tons. There are three different ways to state the quantity, either:
- 4000 mt +- 5% MOLOO -- Load from 3800 mt to 4200 mt on owners option
- 4000 mt +- 5% MOLCO -- Load from 3800 mt to 4200 mt on charterer option
- 4000 mt ------------------- Load 4000 mt
MOLOO means that it is the owner, represented by the captain that states the quantity to be loaded. MOLCO means that it is the charter that states the quantity.
The cargo loading temperature is given either fully refrigerated, ambient or on a given temperature. Ambient means the temperature is equal to the air temperature if the shore tank is located on the surface. It also states what temperature the cargo is to be discharged at.
The maximum allowed filling limit when loading is 98% and it is the safety relief valve setting and the cargo temperature that give the filling limit. To find the filling limit either use the operation manual for the vessel or the cargo density table. When using the density table, calculate the temperature of the cargo from the absolute pressure. When obtained the basic information on the cargo, start planning the loading. Calculate the filling limit in each cargo tank and then plan the loading rate. The loading rate is determined by three factors: cargo temperature, the ambient temperature, and whether a vapor return used.
When during loading needed to run the cargo plant, there are various ways to run the plant. It depends on the temperatures and the flexibility of the plant.
If set up to load two different cargoes e.g. ethylene and propane, then the cargoes must be separated from each other. This called segregation of cargo tanks, cargo cooling plants and lines. Taking out small pipes on the cargo lines does segregation, those pipe parts are called "spool pieces". The spool pieces are taken out of the lines and the main line is blanked of flange covers. Additionally segregate the cargo cooling plant e.g. two plants are used for ethylene and one is used for the propane. It is stated in the Certificate of Fitness how the lines and compressors can be segregated. F.e. if there 4 cargo tanks there could be a possible segregation with cargo tank 1+2 and 3+4.
When loading a partial cargo try to use the manifold that is linked directly to the tank that is loaded. F.e. if going to load on tanks 2,3 and 4, then use the manifold for tanks 3+4. All spool pieces are marked according to the diagram. Many of the spool pieces have the same diameter but have a different length, so try to keep your spool pieces orderly. Normally the spool pieces are mounted on the cargo lines, so there should not be any problem keeping them organized.
Before commencing the loading to cool down the tank shell as mush as possible, the optimal is less than 10oC above cargo loading temperature. The resulting temperature of the tank shell depends on how much time is used, the amount of cargo remaining on board, and the arrangement of the lines to the cargo tanks. Thermometers on the outside of the tank shell used in order to achieve the proper temperature. When loading fully refrigerated propane, try to get the temperature on the outside on the cargo tank shell below -35 C before start loading. When the cargo tank shell is chilled down before arrival, the time used for loading will be reduced.
Before arrival to loading port the cargo tank shell must be chilled down, and cargo lines and spool pieces must be readied. Only then will we be able to reduce the time used in port.
When loading, the liquid is either pumped or pressured onboard from the shore tank. If loading by pressure, the vessel's cargo tank pressure must be lower than the shore tanks pressure. This way of loading is mostly used on fully pressurized vessels. When loading by pumps follow the cargo tanks pressure to hold it below the safety valve set point. After completion of the loading, free the loading hose/ arm of liquid by use of hot gas. The hot gas is produced by the vessel's cargo compressor or from the shore tank or terminal's compressor. On some terminals nitrogen used to free the hose/ arm of liquid. When using this method keep a close watch so we do not get so much nitrogen into the cargo tanks. Before commencing of loading a cargo a checklist, load planning, loading log, ship/ shore checklist and a time sheet must be issued. The vessel's plans for loading have to be discussed and agreed to by the terminal loading master and safety officer. Read carefully the checklists and pay special attention to any notes about maximum pressure or minimum temperatures on the loading hose/ arm. All deviations from the planning have to be noted in the deck logbook and discussed with the loading master/ safety officer.
It is very important that to familiarize with both the vessels and the terminals emergency routines, so that everyone aware what to do if there is a cargo leak or uncontrolled venting.
When transferring a cargo from other vessels, follow your company quality manual and the ICS Ship to Ship Transfer Guide.
17 Jun '17, 02:49