Lesson 16 Marine boilers boilers(锅炉) 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, furnaces(炉膛) Jimei university

and the water-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 turbines 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 their comparative poor efficiency and low power/weight ratio(功率重量比), these systems are no longer installed for propulsion plant. comparative(相当的) 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 requirements. ‘a variety of’ –’多种的‘. 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 lighting up(点燃), Jimei university

without the danger experienced in 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, therefore they are stronger and suitable for much higher steam pressure. ‘steam drum’—’汽筒‘ ‘water drum’—’水筒’ 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. a saving in weight and less space 指同一设备，因而谓语用单数‘is’。 taken up(占据) Jimei university

The watertube boiler does however require greater skill in operating 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. ‘dose’—表示强调语气。 skill(技能) costly(昂贵的) Jimei university

A later development of water-tube boilers is the bent tube design. ‘bent tube boiler’—’弯管锅炉‘。 bent(弯的) Jimei university

This boiler has two drums, an integral furnace and is often referred to as the ‘D’ type because of its shape. referred to as(称为) Jimei university

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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. 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 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 steamship’s installation for supplying steam to the auxiliaries in port, ‘A donkey boiler’ is a small vertical auxiliary boiler for supplying steam-winches and other deck machinery board ship when the main boilers are not in use. installation(装置) Jimei university

and in motorships with steam auxiliaries for supplying 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. an exhaust gas boiler(废气锅炉) Jimei university

Composite boilers(组合式锅炉) are often fitted wherein the generation 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 usually referred to as boiler mountings They are usually 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. overpressure(超压). Jimei university

Once the valve lifting pressure is set in the presence of a Surveyor(验船师) it is locked and cannot be changed. in the presence(在场，出席) of Surveyor(检查员，验船师) 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 smaller 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. Jimei university

Air release cock These are fitted in the headers, boiler drum, etc., to release air when filling the boiler or initially raising steam. initially(初始的) Jimei university

Sampling connection A water outlet cock and cooling arrangement is provided for the sampling and analysis of feed water. Sampling(取样) analysis(分析) Jimei university

Blow down valve(排污阀) This valve enables water to be blow down or emptied from the boiler. It may be used when partially or completely emptying the boiler. Jimei university

Scum valve(上排污阀) A shallow dish positioned at the normal water level is connected to the scum valve. Scum(泡沫、浮渣) shallow(浅的) Jimei university

This enables the blowing down or removal of scum and impurities from the water surface. Jimei university

Automatic feed water regulator Fitted in the feed 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 university

Sootblowers(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. soot(烟灰) Jimei university

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 ships. Waste heat recovery(废热回收) Jimei university

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, 文中所指的boiler应为：强制循环盘香管式废气锅炉。 Jimei university

force-circulated with water taken from an oil fired boiler and returned as water/vapour emulsion. Jimei university

The boiler is fired whenever the demand for steam exceeds that available from exhaust gas heating. Jimei university

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. Jimei university

Similar results, but with 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 university

Circulation of the W. H. R. plant(equipment) must be maintained at all times when the main engine is on load. Jimei university

Also it must be continued for at least two hours after the engine has been stopped to ensure that Jimei university

that 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 only if a long stay in port is expected. secured(关闭，封闭) Jimei university

When leaving an intermediate 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, Jimei university

and any air liberated by the hot circulating water (should be) released from the header air vents. Jimei university

When 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 university

Intervals between blowing may be extended when observation of the funnel shows that soot discharge is small. funnel(烟囱) Jimei university

A guide to their effectiveness is given by a change in the funnel exhaust temperature immediately after soot blower operation. Jimei university

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. Jimei university

The 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 university

At a constant main engine power level, W. H. R At a constant main engine power level, W.H.R. systems have a rising pressure characteristic on a falling steam demand. Jimei university

The output can be reduced by bypassing the feed heater on either the feed water or circulating water sides, Jimei university

so increasing the temperature at the economizer inlet and reducing gas/water temperature differences in this heat exchanger section. Jimei university

Other automatic or manual control arrangements may be controlling flow through an exhaust gas bypass duct by means of dampers(档板), Jimei university

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. Jimei university

Valves must be fully open or fully shut and not left in an intermediate position. Jimei university

A. EXTERNAL EXAMINATIONS DURING AUXILIARY BOILER SURVEYS READING MATERIAL A. EXTERNAL EXAMINATIONS DURING AUXILIARY BOILER SURVEYS SURVEYS(检验) Jimei university

Cochran spheroid vertical boiler Jimei university gusset plate 结[节]点板, 联接板, 角片 gusset stay 角板撑条, 结节撑 Cochran spheroid vertical boiler Jimei university

Spanner vertical boiler Jimei university

Commencing the external examination at the boiler crown it is sometimes found that wastage(损坏) exists beneath damp(潮湿的) lagging(保温层) around leaking mountings, wastage(漏失、耗蚀) beneath(在...之下) Jimei university

and in riveted(铆钉) boilers any bulges(凸出部分) in the lagging should always be investigated(详细检查), as often they are an indication of a leakage and wasted steam. Jimei university

In boilers with smoke tubes, the smoke box should be opened and tube ends examined for leakage, particular attention being paid to the stay tubes(牵条管). Jimei university

Thin 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 and plain tubes光管 thread螺纹 provided倘若 Jimei university

and a fillet weld(填角焊接) of t+3 and a fillet weld(填角焊接) of t+3.2 mm (1/8 in) (where t is the tube thickness) can be applied, then this, where practicable(能实行的), is the obvious remedy. Jimei university

Further down the boiler it is sometimes found that leaking mudhole(出泥渣孔) doors have caused wastage of the door opening and also the internal jointing faces of the shell. Jimei university

Building up of the shell opening by welding as repair is not feasible(可行的) as, after welding, it is practically impossible in most small boilers to face up the inner jointing surface. Jimei university

A satisfactory repair can however be made by positioning inside the boiler a false seating ring for the door, and then fillet welding it in position working from the outside. ‘false’—临时的、补助的。 Jimei university

In the firebox(烟箱) or furnace, of either the cylindrical or hemispherical(半球状的) type, particular attention must be given to any signs of distortion(变形), Jimei university

and to thermal cracking at positions where it is judged heat concentrations are likely to occur when the boiler is being fired, or through scale encrustations(结垢) being present on the water side. judged判断 Jimei university

The flue pipe outlet from Cochran boilers and the flat horizontal tube plate of some Spanner type boilers are two examples— flue(烟道) Jimei university

—in the case 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 university

In the case of riveted vertical boilers, leakage and wastage sometimes occur in way of the three-ply riveting(三层铆焊), Jimei university

which is embodied in the construction, at the junction of the double riveted lap seam(缝) of the shell and the ogee ring(S形环). Jimei university

In extreme cases a satisfactory repair can be made by cutting out the double riveted seam in the lower course of the boiler shell, Jimei university

inserting new piece of plate and raising a butt welded(对接焊接) vertical seam on either side of it and, if necessary, part renewing the ogee ring. Jimei university

If this repair is contemplated(计划), it will be appreciated that the two new vertical welded seams must be done under Class I welding conditions as far as practicable, with full X-ray and local stress relief. appreciated 重视，赏识认识到…的质量、显著性或重要性 Jimei university

B. 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 university

1. All pressure parts are free from foreign material. Boiler 1. All pressure parts are free from foreign material. 2. All gas side-heating surfaces are clean and all refractors are in good condition. Jimei university

4. All personnel are clear. 3. The furnace bottom and the burner wind box have been cleaned of oil and other foreign material. 4. All personnel are clear. Jimei university

5. The manhole cover is securely tightened 5. The manhole cover is securely tightened. All access doors on the casing are closed tight. Jimei university

6. Inspect the safety valve and see that the gag(压板、塞盖) has been removed and the Easing lever(安全阀的开启杆) is in good condition. Jimei university

8. Open the vent valve of the boiler drum. 7. Open the root valves for all instruments and controls connected to the drum. 8. Open the vent valve of the boiler drum. Jimei university

9. Open all pressure gauge valves, check and see all valves in the pressure gauge tubing are open. Jimei university

10. Check and close all blow-off valves(排污阀) and drain valves. 11. Fill the boiler till water level appears 25 to 50 mm high in the gauge glass. Jimei university

The boiler shall be filled in the following procedure and the feed water line shall be inspected simultaneously. Jimei university

a) When the boiler has been laid up(贮存, 搁置) wet (Refer to 'Boiler protection during outage'), drain the boiler till the water level falls down to the bottom of the gauge glass, Outage: 断供期，停歇, 运转中断; 停用(尤指船或机器等在检修时) Jimei university

and bring the water level up again to about 50 mm high in the gauge glass. Jimei university

b) 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 university

Use distilled water(蒸馏水) for feed water whenever possible Use distilled water(蒸馏水) for feed water whenever possible. Boiler compound shall be added as instructed by the expert of boiler water treatment. Jimei university

Fuel 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 in the burner wind box. Jimei university

3. Make sure that all burner air registers(调风器) are clean and move smoothly. Jimei university

Lighting off and Pressure Raising 1. Make sure that the boiler water level in the water level gauge is correct. Jimei university

The water level should fall when the drain valve of the level gauge is opened, and should return to the previous level when the valve is closed. Jimei university

2. Attention must be paid not to mistake the empty level gauge for full of water or stains on the gauge glass for water level. stain [简明英汉词典] [stein] n.污点, 瑕疵 v.染污, 沾污 Jimei university

3. Prior to lighting off, purge the furnace thoroughly by operating the forced draft(通风装置) fan, as explosive gases may be present in the furnace. Jimei university

4.In the start-up from cold condition, oil flow to the burner should be controlled to a minimum to sustain(维持，支撑) burning for about 30 minutes after lighting off. Jimei university

It is desirable to bring the boiler to the normal pressure in at least 2.5 to 3 hours. Jimei university

When, the furnace is sufficiently hot, however, this period can be shortened to 0.5 to 1 hour. Jimei university

The sudden rise of temperature and pressure that causes severe thermal stresses and expansions of the furnace walls and other boiler parts should be avoided to prevent damages on the boiler. Jimei university

5. Close the air vent valve if it begins to blow steam. 6. When the boiler is brought nearly to normal pressure, crack the main steam valve to warm the steam line gradually. Jimei university

C. VACUUM DISTILLATION SYSTEM (真空蒸馏系统) Distillation is the production of pure water from sea water by evaporation(蒸发) and re-condensing(冷凝): Jimei university

On motor ship, distilled water is usually produced as a result of evaporating sea water by a vacuum boiling(真空沸腾) or a vacuum flash(真空闪发) process. Jimei university

The machine used is called an ‘evaporator(蒸发器、造水机)’, although the word ‘distiller(蒸馏器)’ is also used. Jimei university

The saturation temperature of water or steam is the temperature at which water evaporates or steam condenses and this depends upon the pressure, saturation(饱和 Jimei university

the higher the pressure the higher the saturation temperature, the lower the pressure the lower the saturation temperature. Jimei university

The saturation temperature in the vacuum evaporator is quite low, around 40℃ for example, the energy from diesel engine jacket water is usually used to produce distilled water. Jimei university

Vacuum boiling evaporator (真空沸腾式造水机) A single-effect vacuum boiling evaporator consists of a evaporating section and a condensing section. single-effect单级 Jimei university

Vacuum boiling evaporator 6—Air ejector Sea water Jacket water 5—Brine pump 4—Distillate pump 2—Sea pump Jimei university

The lower part of the evaporating section is the heater which houses the stack(管束) of sea water tubes. Jimei university

Hot diesel engine jacket water passes over the stack and heats the sea water passing through the tubes. Jimei university

Because of the reduced pressure in the machine, some of the sea water boils as it flows through the tubes. Jimei university

The steam produced rises to the upper part of the evaporating section, and passes through a water separator or demister(汽水分离器) which prevents water droplets passing through. Jimei university

In the condensing section the steam becomes pure water, which is drawn off by a distillate pump(凝水泵). Jimei university

The remainder of the sea water fed, the brine, is drawn out by a brine pump(排盐泵). An air ejector(喷射泵式真空泵) draws out the air from the evaporator to maintain the vacuum in it. Jimei university

Flash evaporator(闪发蒸发器) Flush evaporation is the result of liquid containing a reasonable amount of sensible heat(显热) at a particular pressure being admitted to a chamber at lower pressure. Jimei university

The liquid immediately changes into steam, i. e The liquid immediately changes into steam, i.e. it flashes, without boiling taking place. Jimei university

A single stage flash evaporator consists of a flash chamber, a demister and a vapour condenser. Jimei university

An air ejector or a vacuum pump is used to keep a very low pressure in the evaporator. Jimei university

When the sea water from the pre-heater enters the evaporator shell, some of the water flashes off into steam. Jimei university

The demister removes any water droplets from the steam as it rises. Jimei university

The vapour is then condensed, collected and pumped out by the distillates pump. Jimei university

Any unevaporated sea water is pumped out by the brine pump. Jimei university

More than one stage of evaporation can take place by admitting the sea water into chambers with progressively lower pressures, but usually, two stage flash evaporators are used on board ship. Jimei university