galyatova_v_n_lelet_i_a_angliyskiy_yazyk

supported by bearings at either end; one bearing incorporates a thrust collar to resist any axial loading.

The turbine casing completely surrounds the rotor and provides the inlet and exhaust passages for the steam. At the inlet point a nozzle box is provided which admits varying amounts of steam to the nozzles in or­ der to control the power developed by the turbine. The first set of noz­ zles is mounted in a nozzle ring fitted into the casing. Diaphragms are circular plates fastened to the easing which are fitted between the turbine wheels. The diaphragms contain the nozzles for steam expansion and a gland is fitted between the rotor and the diaphragm.

The construction of a reaction turbine differs somewhat in that there are no diaphragms fitted and instead fixed blades are located between the moving blades.

Rotor. The turbine rotor acts as the shaft which transmits the me­ chanical power produced to the propeller shaft via the gearing. It may be a single piece with the wheels integral with the shaft or built up from a shaft and separate wheels where the dimensions are large. The blades are fitted into grooves of various designs cut into the wheels.

Blades. When the turbine rotor is rotating at high speed the blades will be subjected to considerable centrifugal force and variations in steam velocity across the blades will result in blade vibration. Expansion and contraction will also occur during turbine operation; therefore a means of firmly securing the blades to the wheel is essential.

Glands and gland sealing. Steam is prevented from leaking out of the rotor high-pressure end and air is prevented from entering the low-pressure end by the use of glands. A combination of mechanical glands and a gland sealing system is usual. Mechanical glands are usually of the labyrinth type.

Diaphragms. Only impulse turbines have diaphragms. Dia­ phragms are circular plates made up of two semi-circular halves. A cen­ tral semi-circular hole in each is provided for the shaft to pass through.

Nozzles. Nozzles serve to convert the high pressure and high energy of the steam into a high-velocity jet of steam with a reduced pressure and energy content.

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Exercise I.

Make these sentences passive.

1.A rotor carries the blades.

2.Bearings support and keep in position turbine rotors.

3.Flexible couplings join turbine-driven auxiliary units to the tur­

bine.

4.We fill the oil reservoir through an oil filler hole.

5.Oil lubricates the bearings and gear on the oil pump and gover­ nor shaft.

Exercise II.

Speak of the main turbine parts.

Exercise III.

Read and translate text В in written form.

Text B.

Turbine Construction (Part II)

Drains. During warming through operations or when maneuve­ ring, steam will condense and collect in various places within the turbine and its pipelines. A system of drains must be provided to clear this water away to avoid its being carried over into the blades, which may damage. Localized cooling or distortion due to uneven heating could also be caused. Modem installations now have automatic drain valves which open when warming through or maneuve-ring and close when running at normal speed.

Flexible coupling. A flexible coupling is always fitted between the turbine rotor and the gearbox pinion. It permits slight rotor and pinibn misalignment as well as allowing for axial movement of the rotor due to expansion. Various designs of flexible coupling are in use using teeth, flexible discs, membranes, etc.

Turning gear. The turning gear on a turbine installation is a re­ versible electric motor driving a gear wheel which meshes into the highpressure turbine primary pinion. It is used for. gearwheel and turbine rotation during maintenance or when warming through prior to maneu­ vering.

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Bearings. They are used to support and guide sliding or rotating members, and also to compensate for axial or radial thrust. Bearings may be classified, in accordance with their functions, as:

1.Radial. Radial bearings retain the axis of a rotating shaft in ra­ dial alignment and prevent its movement in a radial direction.

2.Thrust. Thrust bearings keep the rotor in its correct axial posi­

tion.

Lubricating oil system. Lubricating oil serves two functions in a steam turbine:

1.It provides an oil film to reduce friction between moving parts.

2.It removes heat generated in the bearings or conducted along the

shaft.

A common lubrication system is used to supply oil to the turbine, gearbox and thrust bearings and the gear sprayers. The turbine, rotating at high speed, requires a considerable time to stop. If the main motor driven lubricating oil pumps were to fail an emergency supply of lubri­ cating oil would be necessary. This is usually provided from a gravity tank, although main engine driven lubricating oil pumps may also be re­ quired. Oil is drawn from the drain tank through strainers and pumped to

the coolers. Leaving the coolers, the oil passes through another set of fil­ ters before being distributed to the gearbox, the turbine bearings and the gearbox sprayers. Some of the oil also passes into the gravity tank from which it continuously overflows (this can be observed through the sight glass).

Exercise IV.

Put 10 questions to the text.

Exercise V.

Translate the sentences paying attention to the translation of - ing forms.

1.Modem turbines use steam packing glands operating upon the labyrinth principle.

2.The steam passing through each annular space is subject to a

throttling action.

3. The labyrinth gland is a series of nozzles, each nozzle progres­ sively reducing the pressure of the steam passing through the gland.

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4. Bearings are used to support and guide sliding or rotating mem­

bers.

5.For large turbines driving the propeller through a reduction gear or turbines driving auxiliaries, where the driving and driven units each have their own two bearings, a flexible coupling is necessary.

6.Gears or toothed wheels are used to transmit rotary motion and torque from one shaft to another which operate at speeds ranging between 3,000 and 10,000 r.p.m. and are connected to large, slowturning propellers.

to ensure the safe operation обеспечить безопасную работу

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Text A.

Boilers

A boiler in one form or another will be found on every type of ship. Two basically different types of boiler exist, namely the water-iube and the fire-tube. In the water-tube the feed water is passed through the tubes and the hot gases pass over them. In the fire-tube boiler the hot gases pass through the tubes and the feed water surrounds them.

Where the main machinery is steam powered, one or more large water-tube boilers will be fitted to produce steam at very high tempera­ tures and pressures. On a diesel main machinery vessel, a smaller boiler will be fitted to provide steam for the various ship services. Even within the two basic design types, water-tube and fire-tube, a variety of designs and variations exist.

A boiler is used to heat feed water in order to produce steam. The energy released by the burning fuel in the boiler furnace is stored (as temperature and pressure) in the steam produced. All boilers have a fur­ nace or combustion chamber where fuel is burnt to release its energy. Air is supplied to the boiler furnace to enable combustion of the fuel to take place. A large surface area between the combustion chamber and the water enables the energy of combustion, in the form of heat, to be transferred to the water.

A drum must be provided where steam and water can separate. There must also be a variety of fittings and controls to ensure that fuel oil, air and feed water supplies are matched to the demand for steam. Fi­ nally there must be a number of fittings or mountings which ensure the safe operation of the boiler.

In the steam generation process the feed water enters the boiler where it is heated and becomes steam. The feed water circulates from the steam drum to the water drum and is heated in the process. Some of the feed water passes through tubes surrounding the furnace, i.e. waterwall and floor tubes, where it is heated and returned to the steam drum.

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Large-bore downcomer tubes are used to circulate feed water between the drums. The downcomer tubes pass outside of the furnace and join the steam and water drums. The steam is produced in a steam drum and may be drawn off for use from here. It is known as 'wet' or saturated steam in this condition because it will contain small quantities of water, alternatively the steam may pass to a superheater which is lo­ cated within the boiler. Here steam is further heated and 'dried', i.e. all traces of water are converted into steam. This superheated steam then leaves the boiler for use in the system. The temperature of superheated steam will be above that of the steam in the drum. An 'attemperator', i.e. a steam cooler, may be fitted in the system to control the superheated steam temperature.

The hot gases produced in the furnace are used to heat the feed wa­ ter to produce steam and also to superheat the steam from the boiler drum. The gases then pass over an economizer through which the feed water passes before it enters the boiler. The exhaust gases may also pass over an air heater which warms the combustion air before it enters the furnace. In this way a large proportion of the heat energy from the hot gases is used before they are exhausted from the funnel.

Exercise I.

Complete the sentences using the words from the list.

(the furnace; the air heaters; the steam drum; the economizer; the superheater; the water drums; a steam drum)

•... provides a reservoir for the water supply and its distribution to the tubes.

•... is used for combustion of fuel and generating hot gases.

•... are installed to heat the air.

•... is a feed water heater in which flue gases are used as a heating medium.

«... provide a space for the accumulation of suspended solids.

•... proves a place for separation of steam and water and collec­

tion of the steam for delivery.

• ... used to heat the steam above the temperature of saturation.

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Exercise II.

Put the statements in the correct sequence.

1.The feed water is In passed through the water-tube the tubes.

2.Water used is to heat used feed A boiler in to produce order

steam.

3.Chamber have boilers a furnace All or combustion.

4.Downcomer water The tubes the steam join and drums.

5.Water The gases used to heat are hot the feed.

Exercise III.

Translate the sentences into English.

1.В водотрубном котле вода проходит через трубки, а горя­ чие газы омывают ее снаружи.

2.В огнетрубном котле через трубки проходят горячие газы, а питательная вода омывает их.

3.На дизельном судне имеется один небольшой котел, обес­ печивающий получение пара для различных судовых нужд.

4.Для работы котлов применяется питательная вода.

5.Все котлы имеют топку или камеру сгорания, в которую подается воздух.

6.Котел должен иметь барабан, в котором пар и вода могли

бы отделяться один от другого.

7.Горячие газы, образующиеся в топке, служат для нагрева воды, получения из нее пара и для перегрева пара.

8.В экономайзере подогревается питательная вода перед поступлением в котел.

Exercise IV.

Read and translate text В in written form.

Text B.

How to Operate a Boiler?

Boiler Starting Procedure - Checks and Techniques

Learn the practical way of starting a boiler on board a ship. Also, know about the precautions that are to be taken before starting the boiler.

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The operating procedure of a boiler depends on the type and the manufacturer's instruction. Yet, there are few common points that should be kept in mind while operating any type of boiler on board a ship. So let’s get down to some basic boiler operation training and the general procedures for operating a boiler are as follows.

Before starting the boiler

The following things should be checked thoroughly before start­ ing the boiler:

. All the up-takes for the exhaust gases should be checked pro­ perly for a clear flow and to prevent any kind of obstacle or diversion. All the dampers should be checked for open posi­ tion. All the vents should also be kept open.

. All feed water connections, combustion air connections and pressure gauges should be opened or checked for proper wor­ king condition.

•Alarms should be checked for sound and proper working con­ dition.

•The connections to the super heater and those in between the super heaters should be opened fully to prevent any kind of disturbance in the steam flow.

•All the boiler water drains and blow-down cocks should be properly closed.

•The boiler should only be filled with De-aerated water till slightly below the working level

•All the header vents should be closed to prevent water leakage

•Water level in the economizer should be checked and the vents should be shut off after blowing out any trapped air.

•Forced draft fans should be checked for speed and sound. In case exhaust gas air heaters are provided, the connections to the forced draft fans should be diverted.

•Fuel oil system should be checked for any closed valves and the fuel oil should be adequately heated before circulation to prevent any kind of pipe blockage.

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Starting procedure

. Firstly, the forced draft fans should be started to purge the sys­ tem to remove any trapped exhaust gases or oil vapours.

•All the air slides at different registers should be checked and closed, except the "lightning up" burner.

. The operating burner should then be lit for low firing rate and efficient combustion

•The fuel oil flow should be matched with the speed of the fan to ensure a complete combustion with steady flame.

•Once the boiler starts and steam starts coming out of the su­ perheater vents, the superheater header vents should be closed.

•As soon as the pressure reaches 210 kpa, the air drum vents

should be closed.

. The working pressure should be brought up gradually to avoid overheating and damage to refractory material.

. After the main and auxiliary lines are warmed through, the drains should be closed.

•All the water level gauges should also be blown through and checked to ensure correct reading.

•The safety valves should be lifted and released when the pres­ sure is 3 bar below the normal operating value.

•Once the operating pressure is reached , the boiler should be put on load and the superheater circulatory valves should be

closed.

. All the vents, drains and by passes should also be closed.

The water level in the boiler should be properly checked and the cascade system should be monitored for correct operation.

Exercise V.

Put 10 questions to the text.

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