When the ship's voyage gets scheduled to cold destination, the ice cold ocean contains the potential for ice or slush to enter sea bays or sea inlet boxes, which blocks the Sea Water flow to the cooling system. This situation is encountered by a majority of ships entering ice covered waters, especially when in ballast at light drafts. If water cannot be obtained for cooling system, the main engines will not perform properly and cause additional overheating problems which will eventually lead to shut down of main engine or to be seriously damaged. The design of ships that operate in ice must prevent the freezing of cooling systems.
Prevention:
- Maintain essential seawater by using inlets situated as low as far aft as possible near the center-line.
- It should be fitted on each side of the ship.
- It should be as deeply as submerged as possible.
- It should be vented to atmosphere by a valved pipe with a cross-sectional area at least equal to that of the cooling sections.
- It should have an area open to the sea of five to six times the total area of pump suctions served by the sea-bay.
- It should be fitted with a low steam pressure connection to clear Strainers.
- It should be fitted with a strainer plate at the ship's side having perforations approx 2 cm diameter to prevent ingestion of ice slush.
Deicing Returns on Sea Box and a Strainer
Freezing:
Water in pipes, valves, and tanks may solidify making it difficult to discharge bilges and ballast tanks, which may likewise bring about basic harm. Fore Peak and After Peak balance tanks are especially powerless against solidifying as they are frequently presented to the surrounding air temperature, being for the most part over the waterline. Wing stabilizer tanks stretching out over the waterline are additionally helpless against solidifying, and any counterweight tank loaded with crisp water will solidify more rapidly than if containing ocean water. In the event that counterweight tanks are squeezed up, with any standing water noticeable all around vent pipes and sounding pipes, these channels may solidify, keeping the stabilizer from being pumped. The boat configuration ought to guarantee that solidifying is minimized or dispensed with by sensible plan of the tanks and funneling, and choice of valves and warming frameworks. At the point when the boat is planned to experience exceptionally frosty air temperatures each exertion ought to be made to strip tanks and lines in which solidifying may happen.
WARNING:
Blockage of the sea boxes can cause the main engine cooling system to overheat, requiring reduced power to be used or the engine to be shut down completely.
Means must be provided to clear the sea bays if they do become blocked by ice. There are several design features that can ease operation or eliminate these problems:
⦁ High and low inlet grilles can be provided as far apart as possible.⦁ DE-icing return(s) can be arranged to feed steam or hot water to the sea inlet box top, where frail ice may have accumulated, or directly to the cooling system suction where a blockage may have occurred.
⦁ Ballast water re-circulation through the cooling water system allows ballast tanks to be used as coolers, alleviating any need to use blocked sea inlet boxes. It should be noted that, while this solution is effective, it is usually a short-term solution unless vast quantities of ballast water are available or if the ship is fitted with shell circulation coolers because the recirculated ballast water will quickly become too warm for effective cooling.
⦁ Means should be provided to clear the systems manually of blockage by ice.
Weir-type Sea Inlet Arrangements:
Weir-type sea inlet boxes will overcome the problem of suction pipe clogging. The principle is commonly used in Baltic icebreakers. The suction is separated from the sea inlet grilles by a vertical plate weir. Any ice entering the box can float to the top and is unlikely to be drawn back down to the suction level.
Subscribe to http://marineengineeringfacts.blogspot.in/
No comments:
Post a Comment