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1、Lesson 16 Marine boilersJimei universityThere are two distinct types of marine boilers in use on board ship,Jimei universitythe fire-tube boiler(烟烟管管锅锅炉炉、火火管管锅锅炉炉)in which the hot gases from the furnaces pass through the tubes while the water is on the outside,Jimei universityand the water-tube boil
2、er(水水管管锅锅 炉炉)in which the water flows through the inside of the tubes while the hot furnace gases pass around the outside.Jimei universityThe water-tube boiler is employed for high pressure,high temperature,high capacity steam applications,e.g.providing steam for main propulsion turbines or cargo pu
3、mp(货油泵货油泵)turbines.Jimei universityFire-tube boilers are used for auxiliary purposes to provide smaller quantities of low pressure steam on diesel engine powered ships.Jimei universityFiretube boilers were commonly used with steam reciprocating engines on board ship,but because of their comparative
4、poor efficiency and low power/weight ratio(功功率率重重量量比比),these systems are no longer installed for propulsion plant.Jimei universityThere are many types of watertube boilers in general use on board ship and each manufacturer has a variety of designs to offer depending upon requirements.Jimei universit
5、yWater 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 universitywithout the danger experienced in firetube boilers havin
6、g larger temperature differences between top and bottom parts of the boiler causing unequal expansion resulting in mechanical straining(机械变形机械变形).Jimei university(ii)The steam and water drums(锅锅 筒筒)are small in diameter compared with the large shell(锅锅壳壳)of the firetube boilers,therefore they are st
7、ronger 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 universityThe watertube boiler does however require greater skill in operating and maintaining，especially
8、with regard to the purity of the feed water,and its upkeep(维维修修费费)is more costly than the firetube boiler.Jimei universityA later development of water-tube boilers is the bent tube design.Jimei universityThis boiler has two drums,an integral furnace and is often referred to as the D type because of
9、its shape.Jimei universityJimei universityThe furnace is at the side of the two drums and is surrounded on all sides by walls of tubes.Jimei universityThese waterwall tubes are connected either to upper and lower headers(联联 箱箱)or a lower header and the steam drum.Jimei universityBetween the steam dr
10、um and the smaller water drum below,large numbers of smaller diameter generating tubes(蒸蒸发管束发管束)are fitted.Jimei universityThese provide the main heat transfer surfaces for steam generation.Jimei universityLarge bore pipes or downcomers(下下 降降 管管)are fitted between the steam and water drums to ensure
11、 good natural circulation of the water.Jimei universityA donkey boiler(辅辅助助锅锅炉炉)is an auxiliary boiler sometimes included in a steamships installation for supplying steam to the auxiliaries in port,Jimei universityand in motorships with steam auxiliaries for supplying steam at sea and in port.Jimei
12、universityIn 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 universityComposite boilers(组组合合式式锅锅炉炉)are often fitted wherein the generation of steam can be maintained by oil firi
13、ng when the exhaust gas temperature falls due to slow running of the engines,or cease when the engines are stopped.Jimei universityBoiler mountings(附件附件)Certain fittings(附附 件件)are necessary on a boiler to ensure its safe operation.Jimei universityThey are usually referred to as boiler mountings.The
14、mountings usually found on a boiler are:Jimei universitySafety valvesThese are mounted in pairs to protect the boiler against(from)overpressure.Jimei universityOnce the valve lifting pressure is set in the presence of a Surveyor(验验船船师师)it is locked and cannot be changed.Jimei universityThe valve is
15、arranged to open automatically at the pre-set blow off pressure.Jimei universityMain steam stop valveThis valve is fitted in the main steam supply line and is usually of the non-return type.Jimei universityAuxiliary steam stop valveThis is a smaller valve fitted in the auxiliary steam supply line,an
16、d is usually of the non-return type.Jimei universityFeed check or control valve(给给水止回阀水止回阀或控制阀或控制阀)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 universityWater level
17、 gaugeWater 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.Jimei universityAir release cockThese are fitted in the headers,boiler drum,etc.,to release air when filling the boiler or initially raising
18、 steam.Jimei universitySampling connectionA water outlet cock and cooling arrangement is provided for the sampling and analysis of feed water.Jimei universityBlow down valve(排污阀排污阀)This valve enables water to be blow down or emptied from the boiler.It may be used when partially or completely emptyin
19、g the boiler.Jimei universityScum valve(上排污上排污阀阀)A shallow dish positioned at the normal water level is connected to the scum valve.Jimei universityThis enables the blowing down or removal of scum and impurities from the water surface.Jimei universityAutomatic feed water regulatorFitted in the feed
20、line prior to the main check valve,this device is essential to ensure the correct water level in the boiler during all load conditions.Jimei universitySootblowers(吹灰器吹灰器)Operated by steam or compressed air,they are act to blow away soot and the products of combustion from the tube surfaces.Jimei uni
21、versityWaste heat recovery system(W.H.R)Generation of electric power from a steam turbo-generator and the supply of saturated steam(饱饱合合蒸蒸汽汽)to heating services by exhaust gas heat recovery systems is effected in many ships.Jimei universityThe type of W.H.R.unit mainly fitted nowadays for medium to
22、large outputs is made of horizontal extended(水平分布水平分布)surface steel tubes,Jimei universityforce-circulated with water taken from an oil fired boiler and returned as water/vapour emulsion.Jimei universityThe boiler is fired whenever the demand for steam exceeds that available from exhaust gas heating
23、.Jimei universityAdditional heat extraction from(提提取取)the exhaust gases can be effected by adding an economizer(省省煤煤器器，经经济济器器)section to the unit in plants where the arrangement permits the supply of cooled circulating water or feed water at the economizer inlet.Jimei universitySimilar results,but w
24、ith some disadvantages,can be obtained by producing low-pressure steam from a separate heat exchange unit at the tail end of the gas stream.Jimei universityCirculation of the W.H.R.plant(equipment)must be maintained at all times when the main engine is on load.Jimei universityAlso it must be continu
25、ed for at least two hours after the engine has been stopped to ensure that Jimei universitythat any combustion material from the exhaust gas which deposited on the heating surfaces is thoroughly cooled below the ignition point.Jimei university*Circulation should be stopped and the system secured onl
26、y if a long stay in port is expected.Jimei universityWhen leaving an intermediate port(中中途途港港),if the system has been depressurized(减减 压压),circulation of the W.H.R.unit should be commenced before the main engines are started,Jimei universityand any air liberated by the hot circulating water(should b
27、e)released from the header air vents.Jimei universityWhen soot blowers are fitted to the unit,the fires should be lit in the oil-fired boiler to maintain steam pressure,the steam lines drained and the soot blowers operated once daily at sea.Jimei universityIntervals between blowing may be extended w
28、hen observation of the funnel shows that soot discharge is small.Jimei universityA guide to their effectiveness is given by a change in the funnel exhaust temperature immediately after soot blower operation.Jimei universityWater washing of the heating surface must also be carried out at intervals of
29、 three months,or such lesser intervals as may be decided upon from sighting of the surface during intermediate inspections.Jimei universityThe drain provided at the lowest point of the inlet trunk immediately below the W.H.R.unit must be proved clear prior to and during the washing operation.Jimei u
30、niversityAt a constant main engine power level,W.H.R.systems have a rising pressure characteristic on a falling steam demand.Jimei universityThe output can be reduced by bypassing the feed heater on either the feed water or circulating water sides,Jimei universityso increasing the temperature at the
31、 economizer inlet and reducing gas/water temperature differences in this heat exchanger section.Jimei universityOther automatic or manual control arrangements may be controlling flow through an exhaust gas bypass duct by means of dampers(档板档板),Jimei universityand,when sub-divided inlet headers are p
32、rovided,by closing one or more of the isolating valves supplying circulating water to separate sections of the steam generator.Jimei universityValves must be fully open or fully shut and not left in an intermediate position.Jimei universityREADING MATERIAL A.EXTERNAL EXAMINATIONS DURING AUXILIARY BO
33、ILER SURVEYS Jimei universityCochran spheroid vertical boilerJimei universitySpanner vertical boilerJimei universityCommencing the external examination at the boiler crown it is sometimes found that wastage(损损坏坏)exists beneath damp(潮潮湿湿的的)lagging(保保温温层层)around leaking mountings,Jimei universityand i
34、n riveted(铆铆钉钉)boilers any bulges(凸凸出出部部分分)in the lagging should always be investigated(详详 细细 检检 查查),as often they are an indication of a leakage and wasted steam.Jimei universityIn boilers with smoke tubes,the smoke box should be opened and tube ends examined for leakage,particular attention being
35、paid to the stay tubes(牵牵条管条管).Jimei universityThin plain tubes,if leaking at their ends,are best renewed,and in the case of leakage at the threads of stay tubes,provided the tubes are of round section andJimei universityand a fillet weld(填填角角焊焊接接)of t+3.2 mm(1/8 in)(where t is the tube thickness)ca
36、n be applied,then this,where practicable(能能实实行行的的),is the obvious remedy.Jimei universityFurther down the boiler it is sometimes found that leaking mudhole(出出 泥泥 渣渣 孔孔)doors have caused wastage of the door opening and also the internal jointing faces of the shell.Jimei universityBuilding up of the s
37、hell opening by welding as repair is not feasible(可可行行的的)as,after welding,it is practically impossible in most small boilers to face up the inner jointing surface.Jimei universityA satisfactory repair can however be made by positioning inside the boiler a false seating ring for the door,and then fil
38、let welding it in position working from the outside.Jimei universityIn the firebox(烟烟 箱箱)or furnace,of either the cylindrical or hemispherical(半半球球状状的的)type,particular attention must be given to any signs of distortion(变形变形),Jimei universityand to thermal cracking at positions where it is judged hea
39、t concentrations are likely to occur when the boiler is being fired,or through scale encrustations(结结垢垢)being present on the water side.Jimei universityThe flue pipe outlet from Cochran boilers and the flat horizontal tube plate of some Spanner type boilers are two examplesJimei universityin the cas
40、e of the former,when the cracking is extensive,the usual method of repair is to weld in a new flue pipe with a flanged extension which takes in part of the furnace crown.Jimei universityIn the case of riveted vertical boilers,leakage and wastage sometimes occur in way of the three-ply riveting(三层铆焊三
41、层铆焊),Jimei universitywhich is embodied in the construction,at the junction of the double riveted lap seam(缝缝)of the shell and the ogee ring(S形形环环).Jimei universityIn extreme cases a satisfactory repair can be made by cutting out the double riveted seam in the lower course of the boiler shell,Jimei u
42、niversityinserting new piece of plate and raising a butt welded(对对接接焊焊接接)vertical seam on either side of it and,if necessary,part renewing the ogee ring.Jimei universityIf this repair is contemplated(计计划划),it will be appreciated that the two new vertical welded seams must be done under Class I weldi
43、ng conditions as far as practicable,with full X-ray and local stress relief.Jimei universityB.STARTING OF AN AUXILIARY BOILER Prior to starting the boiler,attention should be paid to the following items and through checking should be made on them.Jimei universityBoiler1.All pressure parts are free f
44、rom foreign material.2.All gas side-heating surfaces are clean and all refractors are in good condition.Jimei university3.The furnace bottom and the burner wind box have been cleaned of oil and other foreign material.4.All personnel are clear.Jimei university5.The manhole cover is securely tightened
45、.All access doors on the casing are closed tight.Jimei university6.Inspect the safety valve and see that the gag(压压板板、塞塞盖盖)has been removed and the Easing lever(安安全全阀阀的的开开启启杆杆)is in good condition.Jimei university7.Open the root valves for all instruments and controls connected to the drum.8.Open th
46、e vent valve of the boiler drum.Jimei university9.Open all pressure gauge valves,check and see all valves in the pressure gauge tubing are open.Jimei university10.Check and close all blow-off valves(排排污污阀阀)and drain valves.11.Fill the boiler till water level appears 25 to 50 mm high in the gauge gla
47、ss.Jimei universityThe boiler shall be filled in the following procedure and the feed water line shall be inspected simultaneously.Jimei universitya)When the boiler has been laid up(贮贮存存,搁搁置置)wet(Refer to Boiler protection during outage),drain the boiler till the water level falls down to the bottom
48、 of the gauge glass,Jimei universityand bring the water level up again to about 50 mm high in the gauge glass.Jimei universityb)When the boiler has been laid up dry,fill the boiler to the water level 25 to 50 mm higher than the normal water level through the boiler feed water line.Jimei universityUs
49、e distilled water(蒸蒸馏馏水水)for feed water whenever possible.Boiler compound shall be added as instructed by the expert of boiler water treatment.Jimei universityFuel Burning Equipment 1.Make sure that all fuel oil lines including oil filters,etc.are in good condition.2.Make sure that no oi1 residue is
50、 in the burner wind box.Jimei university3.Make sure that all burner air registers(调调风风器器)are clean and move smoothly.Jimei universityLighting off and Pressure Raising1.Make sure that the boiler water level in the water level gauge is correct.Jimei universityThe water level should fall when the drain