新版轮机英语unit14 boiler mounting,managemnent and maintenance

1、Lesson 14,Boiler mountings, management and maintenance,Boiler mountings(附件),Certain fittings(附件) are necessary on a boiler to ensure its safe operation.,They are usually referred to as boiler mountings(锅炉附件）. The mountings usually found on a boiler are:,Safety valves,These are mounted in pairs （in d

2、uplex) to protect the boiler against (from) overpressure（超压）.,Once the valve lifting pressure(启阀压力） is set in the presence of a Surveyor(验船师) it is locked and cannot be changed.,The valve is arranged to open automatically at the pre-set blow off pressure(启阀压力）.,Main steam stop valve,This valve is fi

3、tted in the main steam supply line and is usually of the non-return type（止回型）.,Auxiliary steam stop valve,This is a smaller valve fitted in the auxiliary steam supply line, and is usually of the non-return type.,Feed check or control valve(给水单向阀或控制阀),A pair of valves are fitted: one is the main valv

4、e, the other the auxiliary or standby.,They are non-return valves and must give an indication（指示） of their open and closed position.,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 pr

5、essure.,Air release cock（放气阀）,These are fitted in the headers（联箱）, boiler drum（锅筒）, etc., to release air when filling the boiler or initially raising steam（升汽）.,Sampling connection,A water outlet cock and cooling arrangement is provided for the sampling and analysis of feed water.,A provision（装置） ma

6、y also be made for injecting water treatment chemicals.,Blow down valve(下排污阀),This valve enables water to be blow down or emptied（放空） from the boiler. It may be used when partially （部分）or completely emptying the boiler.,Scum valve(上排污阀),A shallow dish（浅盘） positioned at the normal water level is conn

7、ected to the scum valve.,This enables the blowing down or removal of scum（浮渣） and impurities（杂质） from the water surface.,Whistle（汽笛） stop valve,This is a small bore non-return valve which supplies the whistle with steam straight from the boiler drum（锅筒）.,Water tube boiler, because of their small wat

8、er content in relation to their steam raising capacity, require certain additional mountings:,Automatic feed water regulator（自动给水调节器）,Fitted in the feed line prior to the main check valve（主给水阀）, this device is essential to ensure the correct water level in the boiler during all load conditions.,Boil

9、ers with a high evaporation rate will use a multiple-element feed water control system.,Low level alarm,It is a device to provide auditory（听觉） of low water level conditions.,Superheater circulating valves,Acting also as air vents, these fittings ensure a flow of steam when initially warming through

10、and raising steam in the boiler.,Sootblowers(吹灰器),Operated by steam or compressed air, they are act to blow away soot（烟灰） and the products of combustion（燃烧产物） from the tube surfaces.,Several are fitted in strategic places（关键位置）. The soot-blower lance（喷头） is inserted, soot is blown and the lance is w

11、ithdrawn（取出）.,General management principles and operating procedures are well known and must always be followed to avoid boiler mishaps(意外事故、损坏). In particular:,With many small package boilers(小型锅炉）, the automatic control sequence（自动控制时序） usually ensures that the boiler fire is initially ignited（点火）

12、 from a diesel oil supply,and changed over to the usual source when ignition is completed.,With good management, to facilitate subsequent starting from cold, the fuel system of large boilers will have been flushed through with diesel oil when the boiler was on light duty immediately prior to being s

13、ecured（停炉）.,When burning such diesel fuel it is essential for safety that only the correct (small) burner tip(油头) should be used.,It should be kept in mind（牢记） that if fire does not light, immediately shut off fuel and vent furnace.,Complete ignition of fuel in the furnace is essential. The burner f

14、lame, the smoke indicator (烟气指示器) and the funnel（烟囱） should be frequently observed.,With satisfactory combustion, the flame should appear incandescent (极亮) with an orange shade(色度) at the flame tip, and a faint brownish（淡褐色） haze(烟雾、薄雾) should show at the funnel.,If on first ignition the flame is un

15、certain, badly shaped and separated from the primary swirler(旋流配风器), momentary（瞬时） opening or closing of air register(调风门)air regulator may correct.,The pH value of the boiler feed water should be kept between 8 and 9 and the boiler density（浓度） less than 300 ppm.,But, if water samples show a heavy c

16、oncentration（浓度） of suspended mater（悬浮物）, short blow-downs（下排污） of 20 seconds duration（持续的时间） should be given until the sludge content is seen reduced.,The boiler should be blown down when the oil burner is operating,the water level lowered and then restored to prove the functioning of the low water

17、 cut-out（低水位切断） and the oil burner start-up（燃烧器起动） equipment.,The boiler scum valve should also be operated at this time to keep the water level clear from floating scum（浮渣）.,Fuel burner components（燃烧器部件） and igniter electrodes（点火电极） should be cleaned weekly and the furnace examined to ensure that t

18、here are no excess carbon deposits（积炭）.,Tubes in the exhaust gas section of the boiler should be brushed through at about six-monthly intervals,and those in the oil burning section periodically examined and cleaned as necessary with a wire bristle brush（钢丝刷）.,With correct feed water treatment, blow

19、down procedures and sludge contents in water samples at a stable level,it should not be necessary to wash out the water side of the boiler more than once every three or four months.,Boiler fires may be out for long periods when a ship is at sea and the boiler steaming maintained by heat input from w

20、aste heat recovery plant（废热回收装置）.,This operation is free from hazard(危险), but feed water and boiler water treatment must be maintained to prevent internal deterioration（腐蚀） or scale formation.,Water level controllers must be kept operable to protect external steam-using plant from water “carry-over”

21、(汽水共腾) danger.,If a boiler is isolated from the steam-using system it must be kept either in closed dry storage with a suitable internal desiccant(干燥剂), or completely full of treated water,or under a low steam pressure preferably maintained by a steam-heated coil（蒸汽盘管）.,Regular testing of boiler pro

22、tective devices must be implemented(执行).,Frequent comparison of drum-mounted and remote-reading water level indicators:,Discrepancies（差异） between these have contributed to failures because of overheating through shortage of water, when a boiler was being oil-fired.,If in doubt as to the true boiler

23、water level, i.e. whether a water level indicator sightglass（水位计观察镜） is completely full or empty,when a unit is being oil-fired the fire should be immediately extinguished until the true level is resolved(恢复).,Procedures should be predetermined（预定） and followed in the event of shortage of water, bul

24、ging(凸出) or fracture(破裂) of plates（管板） or furnace, or bursting（爆裂） of water tubes.,In general, fires should be immediately extinguished by remote tripping of fuel supply valves(燃油遥控速闭阀);,forced draught（拖，拉） air pressure maintained if there is any risk of escaping steam entering the boiler room;,stea

25、m pressure relieved if metallic(金属的) fractures（破裂） seem possible; and boiler water level maintained, where practicable, until the boiler begins to cool down.,Regular operation of soot blowers, if these are fitted, when the boiler is on oil-fired operation.,The steam supply line（供气管路） must be thoroug

26、hly warmed and drained before the blowers（吹灰器） are used, the air/fuel ratio（风油比） increased throughout the action, and blowers greased（涂油脂） after use.,Immediate investigation of any high salinity(盐度) alarms in condensate system（冷凝系统）, andelimination（清除） of any salt water or oil contamination of boile

27、r feed water system.,Safety precautions (should be) taken before entering a boiler connected to another boiler under steam.,If this is to be done for a prolonged period it is advisable to allow a current of air to flow through the boiler by removing manhole（人孔门）, sighthole（观察窗） and mudhole covers（泥渣

28、盖板）.,The main engine may be kept in operation with the boiler dry and the gases passing through the exhaust gas section.,If refilling a hot boiler the main engine speed should be reduced to slow for half an hour and the feed water supplied be as hot as possible;,thereafter the main engine may be bro

29、ught up to power over a similar period.,Boiler start-up,For boilers of the direct-fired（直接燃烧）, smoke tube type the steps（起动步骤） are relevant.,With scotch boilers（烟管锅炉）, circulation should be commenced as soon as the boiler gets warm, using the circulation pump,and working pressure should not be raise

30、d in less than 12 hours (preferably 24 hours) to reduce expansion stresses（膨胀应力）.,Time required for other boiler types will vary with construction and water content（蓄水量）, but it is always desirable to heat through evenly（均匀加热）,and if necessary blow down（下排污） some of the contents to sea to displace c

31、old water from the lowest part of the boiler shell, to minimize temperature differentials and thermal stress（热应力） in the pressure parts.,For procedures for large, water tube boilers starting and testing of protective devices for alarm, logic and control systems are relevant to modern auxiliary boile

32、rs.,The boiler should be filled to normal level (1/2 gaugeglass) when the feed control valve（给水控制阀） is automatically closed and the panel indicating light extinguished(off).,Raising steam,The forced draught（强制通风） fan should be started and air passed through the furnace for several minutes to purge(清

33、扫) it of any exhaust gas or oil vapors（油蒸汽）.,The operating burner can now be lit and adjusted to provide a low firing rate with good combustion.,The fuel oil pressure and forced draught pressure should be matched to ensure good combustion with a full steady（稳定） flame.,When water level nears the top

34、of the gauge glass, due to expansion, the initial level should be restored（恢复） by draining off water through the scum valve(上排污阀）.,When a drum pressure of about 210 KN/m2 has been reached, the drum air vent(放气阀） may be closed.,The boiler must be brought slowly up to working pressure in order to ensu

35、re gradual expansion and,and to avoid overheating the superheater（过热器） elements and damaging any refractory(耐火材料) material due to expansion stresses.,The time required will vary with boiler types and construction.,If necessary blow down some of the contents to sea to displace cold water from the low

36、est part of the boiler shell, to minimize temperature differentials and the thermal stresses.,The main and auxiliary steam lines（汽管路） should now be warmed by crack opening of the boiler main and auxiliary stop valves. When the lines are hot close the drains（放残阀）.,In addition the water level gauges s

37、hould be blown through（冲洗） and checked for correct reading.,When the steam pressure is about 300 KN/m2 below the normal operating value（工作压力）, the safety valves should be lifted and released using the easing gear(释放机构).,Once at operating pressure, the boiler may be put on load and the superheater ci

38、rculating valves（过热循环阀） closed.,All other vents（放气阀）, drains（放水阀) and by-passes(旁通阀） should then be closed. The water level in the boiler should be maintained.,Boiler shut-down,This operation may have to be done normally at the end of a voyage or in emergency.,For normal shut-down the suitable proce

39、dure is: -Carry out soot blowing（吹灰）, if permissible.,-Change combustion control from automatic to manual. -Change fuel supply to diesel oil; shut steam off fuel heaters and trace heating(伴随管加热蒸汽）.,Close burner supply valves and main fuel shut off valve(主燃油截止阀）. -Purge boiler furnaces with air for t

40、hree to five minutes; stop forced draught fan（强制风机）.,-Close steam stop valves（停汽阀） on boiler when pressure is reduced. Drain boiler when it has cooled down or fill with treated water.,Steam system must be warmed through（暖管） as steam is being raised on the boiler by: 1. Opening steam range drains to

41、bilge and to steam traps（蒸汽分离器，除汽器）.,2.Opening steam line valves to the required services; 3.Cracking open boiler stop valve（停汽阀） when drum pressure is 2 bar;,4.Throttling（节流） steam line drains as range warms through; 5.Opening boiler stop valve(停气阀）full before auxiliaries are started;,6.Closing ste

42、am line direct drains and steam trap(除汽器） bypass on trapped lines when lines are hot.,Waste heat recovery system (W. H. R),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 sh

43、ips.,The type of W. H. R. unit mainly fitted nowadays for medium to large outputs is made of horizontal extended(水平分布) surface steel tubes,force-circulated with water taken from an oil fired boiler and returned as water/vapour emulsion.,The boiler is fired whenever the demand for steam exceeds that

44、available from exhaust gas heating.,Additional heat extraction from(提取) the exhaust gases can be effected by adding an economizer(省煤器，经济器) section to the unit in plants where the arrangement permits the supply of cooled circulating water or feed water at the economizer inlet.,Similar results, but wi

45、th some disadvantages, can be obtained by producing low-pressure steam from a separate heat exchange unit at the tail end of the gas stream.,Circulation of the W. H. R. plant(equipment) must be maintained at all times when the main engine is on load.,Also it must be continued for at least two hours

46、after the engine has been stopped to ensure that,that any combustion material from the exhaust gas which deposited on the heating surfaces is thoroughly cooled below the ignition point.,*,Circulation should be stopped and the system secured only if a long stay in port is expected.,When leaving an in

47、termediate port(中途港), if the system has been depressurized(减压), circulation of the W. H. R. unit should be commenced before the main engines are started,and any air liberated by the hot circulating water (should be) released from the header air vents.,When soot blowers are fitted to the unit, the fi

48、res 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.,Intervals between blowing may be extended when observation of the funnel shows that soot discharge is small.,A guide to their effectiveness is given by a cha

49、nge in the funnel exhaust temperature immediately after soot blower operation.,Water washing of the heating surface must also be carried out at intervals of three months, or such lesser intervals as may be decided upon from sighting of the surface during intermediate inspections.,The drain provided

50、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.,At a constant main engine power level, W.H.R. systems have a rising pressure characteristic on a falling steam demand.,The output can be reduced by bypassing the

51、 feed heater on either the feed water or circulating water sides,so increasing the temperature at the economizer inlet and reducing gas/water temperature differences in this heat exchanger section.,Other automatic or manual control arrangements may be controlling flow through an exhaust gas bypass d

52、uct by means of dampers(档板),and, when sub-divided inlet headers are provided, by closing one or more of the isolating valves supplying circulating water to separate sections of the steam generator.,Valves must be fully open or fully shut and not left in an intermediate position.,If the main engine i

53、s suddenly reduced or circumstances dictate an emergency engine stop, the potential for steam generation from the W.H.R. until will obviously reduce or cease.,A considerable amount of residual heat initially remains in the heated metal of the steam generator/economizer and in the water in the boiler

54、 drum and circulating system.,This allows steam generation at a failing pressure to continue for some minutes after an emergency engine stop.,The precise time available can best established by trials, but typical installations tests have shown that a turbo-generator supplied with steam from a W.H.R.

55、 plant will continue to carry the full sea load for periods up to 12 minutes.,This usual gives ample time to bring on-line alternative sources of supply for heat and power to allow for:,(a) automatic starting of a diesel generator and or lighting off a boiler fire in the event of steam pressure fail

56、ing to a pre-set level or bridge control application of a speed reduction.,(b) preferential tripping of power supplies to non-essential circuits in similar events;,(c) automatic load sharing with a diesel driven generator set; (d) initiating of (a) or (c) from an engine control room;,(e) operation o

57、f override controls on boiler-firing circuits to allow manually-controlled lighting-off if automatic ignition is prevented by high or low water level automatic cut-outs.,In the unlikely event of a steam generator/economizer tube leaking while at sea, it may be necessary to defer repairs or tube inst

58、allation until it is convenient to stop the main engine for a period or until arrival in port,But if heavy leakage is observed the main engine should be stopped immediately.,The circulating pump should then be stopped, the steam generator/ economizer is isolated and drained, and, preferably, the tub

59、es water washed or soot blown if blowers are fitted.,The main engine may then be restarted after proving that water is not present in the exhaust system before the W.H.R. unit.,Similar procedures should be followed if it is necessary to stop circulation due to leakages external to the unit, or, if the associated boiler or circulating pump is inopenable.,In such cases the main engine may be stopped when it is safe to do so but, whenever possible, circulation must be continued until this is done.,With s