1、Lesson 16 Marine Boilers1.Main Contents of the Text2.Useful Vocabulary&Special Terms3.Detailed Analysis of Difficult Sentences4.Review Questions 5.Some Relevant Multiple Choice ExercisesMain Contents of the Texto Types of boilero Firetube boilers and watertube boilerso Boiler mountingso Safety valve
2、so Main steam stop valveo Water level gaugeo Waste heat recovery systemMain Contents of the Texto This unit tells us there are two distinct types of marine boilers,i.e.fire-tube boiler and water-tube boiler.o In this unit,we also can learn different functions of two distinct type of marine boilers a
3、nd their advantages and disadvantages.o We also have to pay attention to the basic structures of marine boilers and functions of mountings of a boiler.Useful Vocabulary&Special Terms1.distinct:completely different from 名词：distinction eg.There are two distinct types of marine boilers in use on board
4、ship.2.mounting:part of a machine (equal to fitting)boiler mountings(fittings)锅炉附件3.analyze:分析 名词：analysis eg.analysis certificate 化验证书 4.refractory 耐火的，耐热的 refractory alloy 高熔点合金 refractory brick 耐火砖 refractory casting tube 耐热铸管 refractory coating 耐火 涂料，耐热层Useful Vocabulary&Special Terms:Definition
5、 of boilerso Fire-tube boiler:the hot gases from the furnace pass through the tubes while the water is on the outside.Water-tube boiler:the water through inside of the tubes while the hot furnace gases pass around the outside.Comparison between two types of boilerso Functions:Fire-tube boiler are co
6、mmonly used with steam reciprocating engines on board ship,but because of their comparatively poor efficiency and low power/weight ratio,these system are no longer installed for propulsion plant.water-tube boiler are used widely on the ship.However,the water-tube boiler require great skill in operat
7、ing and maintaining.esp.with regard to the purity of the feed water,its upkeep is more expensive than the fire-tube boiler.Comparison between two types of boilersWater-tube boiler has distinct advantage over fire-tube boiler:1.The steam can be raised from cold water in short period of time because c
8、irculation of the water is natural and immediate on lighting up.2.The steam and water drums are small in diameter compared with the large shell of the fire tube boilers,therefore they are suitable for much higher steam pressure.3.Less mass of water is carried in boiler,hence a saving in weight and l
9、ess space is taken up for the same output.Cochran spheroid vertical boilerBoiler Mountings:o Safety valves:to protect the boiler against overpressure.o Main stem stop valve:usually fitted in the main steam supply line and is usually of the non-return type.o Auxiliary stem stop valve:a smaller valve
10、fitted in the auxiliary steam supply line,and is usually of the non-return valve.Boiler Mountings:o Blow down valve:This valve enables water to be blown down or emptied from the boiler.o Scum valve:a shallow dish positioned at the normal water level is connected to the scum valve.This enables the bl
11、owing down or removal of scum and impurities from the water surface.44锅炉安全阀Detailed Analysis of Difficult Sentences1 Fire-tube boilers are used for auxiliary purposes to provide smaller quantities of low pressure steam on diesel engine powered ships.火管锅炉应用于辅助的目的，为柴油机动力船提供少量的低压蒸汽。Powered为过去分词作前置定语Det
12、ailed Analysis of Difficult Sentenceso Generation of electric power from a steam turbo-generator and the supply of saturated steam(饱合蒸汽)to heating services by exhaust gas heat recovery systems is effected in many ships.o 在许多船上通过废热回收装置由蒸汽涡轮发动机发电和向加热设备供应饱和蒸汽均有应用。o 该句为主系表结构，is之前皆为主语。Review Questionso 1.What are the two types of marine boilers and what are the differences between them?o 2.What is bent tube design?o 3.What is donkey boiler and its function?o 4.What is waste-heat boiler？
