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1、Jimei university,Lesson 16,Marine boilers,Jimei university,There are two distinct types of marine boilers in use on board ship,Jimei university,the fire-tube boiler(烟管锅炉、火管锅炉) in which the hot gases from the furnaces pass through the tubes while the water is on the outside,Jimei university,and the w
2、ater-tube boiler(水管锅炉) in which the water flows through the inside of the tubes while the hot furnace gases pass around the outside.,Jimei university,The water-tube boiler is employed for high pressure, high temperature, high capacity steam applications, e.g. providing steam for main propulsion turb
3、ines or cargo pump(货油泵) turbines.,Jimei university,Fire-tube boilers are used for auxiliary purposes to provide smaller quantities of low pressure steam on diesel engine powered ships.,Jimei university,Firetube boilers were commonly used with steam reciprocating engines on board ship, but because of
4、 their comparative poor efficiency and low power/weight ratio(功率重量比), these systems are no longer installed for propulsion plant.,Jimei university,There are many types of watertube boilers in general use on board ship and each manufacturer has a variety of designs to offer depending upon requirement
5、s.,Jimei university,Water tube boilers have distinct advantages over firetube boilers.,Jimei university,(i) Circulation of the water is natural and immediate on lighting up, thus steam can be raised from cold water in a shorter period of time without,Jimei university,without the danger experienced i
6、n firetube boilers having larger temperature differences between top and bottom parts of the boiler causing unequal expansion resulting in mechanical straining(机械变形).,Jimei university,(ii) The steam and water drums(锅筒) are small in diameter compared with the large shell(锅壳) of the firetube boilers,
7、therefore they are stronger and suitable for much higher steam pressure.,Jimei university,(iii) Less mass of water is carried in the boiler, hence a saving in weight and less space is taken up for the same output.,Jimei university,The watertube boiler does however require greater skill in operating
8、and maintaining，especially with regard to the purity of the feed water, and its upkeep (维修费) is more costly than the firetube boiler.,Jimei university,A later development of water-tube boilers is the bent tube design.,Jimei university,This boiler has two drums, an integral furnace and is often refer
9、red to as the D type because of its shape.,Jimei university,Jimei university,The furnace is at the side of the two drums and is surrounded on all sides by walls of tubes.,Jimei university,These waterwall tubes are connected either to upper and lower headers(联箱) or a lower header and the steam drum.,
10、Jimei university,Between the steam drum and the smaller water drum below, large numbers of smaller diameter generating tubes(蒸发管束) are fitted.,Jimei university,These provide the main heat transfer surfaces for steam generation.,Jimei university,Large bore pipes or downcomers(下降管) are fitted between
11、the steam and water drums to ensure good natural circulation of the water.,Jimei university,A donkey boiler(辅助锅炉) is an auxiliary boiler sometimes included in a steamships installation for supplying steam to the auxiliaries in port,Jimei university,and in motorships with steam auxiliaries for supply
12、ing steam at sea and in port.,Jimei university,In motor ships, an exhaust gas boiler (sometimes called a waste-heat boiler) is often used to recover some of the heat carried in the exhaust gases from the main engines.,Jimei university,Composite boilers(组合式锅炉) are often fitted wherein the generation
13、of steam can be maintained by oil firing when the exhaust gas temperature falls due to slow running of the engines, or cease when the engines are stopped.,Jimei university,Boiler mountings(附件),Certain fittings(附件) are necessary on a boiler to ensure its safe operation.,Jimei university,They are usua
14、lly referred to as boiler mountings. The mountings usually found on a boiler are:,Jimei university,Safety valves,These are mounted in pairs to protect the boiler against(from) overpressure.,Jimei university,Once the valve lifting pressure is set in the presence of a Surveyor(验船师) it is locked and ca
15、nnot be changed.,Jimei university,The valve is arranged to open automatically at the pre-set blow off pressure.,Jimei university,Main steam stop valve,This valve is fitted in the main steam supply line and is usually of the non-return type.,Jimei university,Auxiliary steam stop valve,This is a small
16、er valve fitted in the auxiliary steam supply line, and is usually of the non-return type.,Jimei university,Feed check or control valve(给水止回阀或控制阀),A pair of valves are fitted: one is the main valve, the other the auxiliary or standby. They are non-return valves and must give an indication of their open and closed position.,Jimei university,Water level gauge,Water level gauges or gauge glasses are fitted in pairs, at opposite ends of the boiler, the construction of the level gauge depends on the boiler pressure.,
