Boilers / Exhaust gas Economizers Flashcards
What is the difference between a safety valve and a relief valve?
Safety Valve must be able to reduce the pressure while something is still working at full capacity. For instance, a boiler is still firing, and feed water pumps are working. Relief valves stop operation until system pressure reaches a safe level. Safety valves also start to open a small amount before pressure reaches the set point and then fully open at set point or a specified value after the set point. Relief valves open at the set point.
Explain what is meant by the setpoint in reference to a safety Valve or a relief valve
Predetermined pressure limit set for the valve to open automatically to relieve pressure. The set point is set below overpressurization conditions and above the working pressure range.
How many safety valves are fitted to a boiler?
As per SOLAS chapter 2 every boiler must be provided with not less than 2 safety valves. They can be both in same valve chest, however this valve chest must be separate from any other valve chest. If boiler has a super heater that can be shut off from boiler than it also must be fitted with a safety valve.
Explain the working principle of a safety valve
Force generated by steam pressure and area of valve exposed to that pressure is balanced by spring force holding valve shut. When force generated by steam pressure becomes too much for spring the valve operates as it does steam pressure acts upon a large area. This results in larger force against the spring and therefore quick opening. Pressure in boiler drops below opening pressure before valve closes because valve is kept open by steam acting upon larger area. Safety valve must be the correct size in order to release more steam than boiler has the capacity to produce. Valve must be sized , positioned and set correctly so that boiler cannot exceed maximum allowable accumulated pressure. Valve must be subjected to testing, which is required by classification society and flag state inspectors.
what is the meaning of discharge coefficient and how is it related to boiler safety valve?
Coefficient of Discharge may be defined as ratio of the actual discharge to the theoretical or ideal discharge. If discharge coefficient whose value depends on type of valve is increased diameter must be reduced. If diameter is reduced lift of valve must be increased to avoid any accumulation of pressure. This can be achieved by improving type of valve fitted to boiler.
what are the different types of safety valve?
improved high lift type
full lift safety valve
full bore safety valve
what improvement have been to the improved high lift type safety valve
Improvements to valve are removal of valve wings, which improves waste steam flow and reduces risk of seizure and floating ring added which further reduces risk of seizure. The three different types of safety valves all make use of valve seat and a lip on valve which increases valve lift against downward force of spring.
This valve increases valve lift without increase in boiler pressure in two ways, one is the specially shaped valve seat, the other being to use the lower spring carrier in the fashion of a piston, which acted upon by the pressure of waste steam helps to compress the spring.
describe the full lift safety valve
This valve does not use a waste steam piston instead the valve itself operates inside a guide acting as a piston in a cylinder. Details of spring, compression nut and valve chest are similar to improved high lift type valve. When the valve lifts a small amount the exiting steam pressure acts upon area of valve. This increases the lift until the lower edge of the valve just enters the guide. Reaction pressure generated by the exiting steam with the guide cause valve to lift further until its fully open. When valve is fully open escape area is equal to area of supply through seating.
describe the operation of a full bore safety valve
This is a relay operated valve suitable for water tube boilers whose working pressure exceeds 21bar [2.1MN/m2]. when boiler pressure reaches desired blow off pressure the valve lifts, as it does this the valve skips a series of ports leading to atmosphere. Steam is introduced through the connecting pipe into the cylinder of the main valve and because area of piston is around twice that of the valve, the valve opens against boiler pressure. When boiler pressure decreases valve closes and uncovers the ports above it. This links the cylinder of the main valve with the atmosphere and the boiler pressure then causes main valve to close quickly. This valve is suitable for high pressure boilers because the greater the boiler working pressure the quicker the valve will close and therefore the greater the saving in steam.
with reference to the boiler valve chest what is the function of the drainpipe and where is it located?
Drain pipe must be fitted to lowest part of valve chest on discharge side of valves and should be clear of boiler. Pipe cant have a valve or cock fitted. This drain pipe is very important and should be regularly checked because it drains excessive amounts of water from boiler and if it becomes blocked there is a possibility of overloading of the valves due to hydraulic head or damage resulting from water.
what materials are used for constructing a safety valve?
Materials used for valve, valve seat, spindles, compression screws and bushes must be non corrodible metal, since corrosion for any of the components will result in valve not operating correctly. Often materials used are bronze, stainless steel or monel metal, depending on conditions. Valve chest is made of cast steel. Spring must be relied upon for performance in required parameters. Standard safety valves typically use carbon steel for moderate temperatures. Tungsten steel is used for higher temperatures, non corrosive applications and stainless steel is used for corrosive. For higher temperature applications monel hastelloy can be used.
describe the maintenance carried out for a boiler safety valve?
All safety valves fitted to boiler must have easing gear so that valve can be checked for correct operation while boiler is running and for surveyors. During inspections and surveys the manufacturers figures stating lip clearances, seating widths, wing clearances etc. must be adhered to. All working parts should be checked for alignment and functionality. Digital camera can be used to record the sequence of dismantling. When unassembled individual parts are hung by a cord and sounded by gently tapping with a hammer. If they do not ring true, examine for faults. Check drains and easing gear. All parts should surveyed by surveyor which requires additional testing with non destructive techniques. Its helpful when replacement parts that are needed are placed next to original parts so surveyor can see any defects and inspect the replacement parts. If surveyor has been called due to a failure, parts aren’t to be dismantled cleaned or replaced before work has been approved by surveyor.
Describe the procedure for adjusting and or setting the safety valves set point
Remove compression ring
Screw down compression screws
Raise boiler pressure to required blow off pressure
Screw back compression screw until valve blows
Continue screwing down compression screw and at the same time tap the valve spindle downwards very lightly until valve returns to its seat and remains closed
Once set split compression rings have to be fitted, then hoods, keys, padlocks and easing gear.
finally check and operate easing gear to ensure valve operates correctly
With a system that has many boilers, raise pressure of all boilers to required blow off pressure making sure all boilers are connected up then do the same as above setting each valve one by one
why is it necessary to carry out a accumulation of pressure test for safety valves?
Classification societies require newly fitted safety valves to be subjected to an accumulation of pressure test to ensure that valves are of the correct discharge capacity for boiler.
Describe how to carry out a accumulation of pressure test
To preform this test all feed inlets and steam outlets to and from boiler must be closed and maximum firing to be arranged. Accumulation of pressure must not exceed 10% working pressure. During the test water permitting must not exceed 15mins for cylindrical boilers and 7mins for water tube boilers. For water tube boilers test can be waived if its going to cause damage to super heaters or economizer. To test safety valve you will need a blank flange with a screwed-in fitting. Bolt the flange to the bottom of the safety valve (which has been removed from the boiler) and fit a tee to the flange fitting with a pressure gauge on one branch, the fitting on one and a source of pressure, either water or air, high enough to pop the valve at the correct pressure, on the other. Pressurise and pop, while monitoring the gauge.
With the aid of simple sketches describe the procedure for blowing through a boiler gauge glass. (16)
see EOOW ORAL Sketch Pack for drawing
1.Close steam and water cocks then open drain. Nothing should blow out of gauge if steam and water cocks have no leaks
2.Open and close water cock to check that water cock connection to boiler is clear
3.Open and close steam cock to check that steam cock connection to boiler is clear
4.Close drain cock
5.Open water cock, water should gradually rise up to top of gauge glass
6.Open steam cock and water in glass should fall to level of water in boiler. Ensure level in gauge glass is correct there should be low and high level markings on gauge glass if not consult manual and or C/E
what kind of problems could occur when doing boiler gauge glass blow through?
- When water cock is opened and water does not flow up gauge glass, it means the water level in boiler is below water cock connection to boiler and its unsafe to put feed water into boiler.
- Water could flow to top of gauge glass and the when steam cock is opened water flows down and out of glass, then it means water level is between water cock connection to boiler and bottom of gauge glass and its safe to put feed water into boiler.
- Gauge glass could be full of water and steam cock is opened and water level in glass doesn’t fall, this means the water level is above the steam cock connection to boiler and there is danger of priming the boiler if more feed water is put in.
Why is it required for a boiler to have a remote water level indicator
Boiler water tubes must have the correct level otherwise water tubes will be at risk of being overheated and burning can occur. In the event of an emergency its quicker to have remote level indicating equipment for the boiler that way boiler water level can be checked from a more convenient position like ECR as oppose to having to go to the boiler platform.
Draw a remote water level indicator and explain the working principle
see EOOW ORAL Sketch Pack for drawing
Made of U tube type manometer. The lower portion of u tube consists of red type fluid, whose density is greater than water and it does not mix with the water so it’s a immiscible liquid. If the water level in the boiler falls, ‘h’ will be reduced, ‘x‘ will be increased and ‘H‘ must therefore be increased. The level of the water in the condenser reservoir being maintained by condensing steam. If the water level in the boiler rises, ‘h‘ will be increased, ‘x‘ will be reduced and ‘H‘ must therefore be reduced. Water will therefore flow over the weir in the condenser reservoir in order to maintain the level constant. A strip light is fitted behind the gauge which increases the brightness of the red indicating fluid, which enables the operator to observe at a glance from a considerable distance whether the gauge is full or empty.
Describe with the aid of a sketch a plate type water gauge glass
see EOOW ORAL Sketch Pack for drawing
This is suitable for high pressures of up to 79bar. This toughened soda lime glass plate is capable of withstanding severe mechanical stress and temperature but it need to be protected from solvent action of boiler water. This can be done by using a mica strip between the glass and steam joint so water doesn’t come into contact with glass. Light is deflected up through louvre plate and is reflected downwards by water meniscus, which shows up as a bright spot.
Describe the Klinger reflex gauge glass type
Can be fitted new with its own glands and cocks or can be installed into existing gauge cock fittings. It has steel tubes, which has spanner flats, that enable gauge to be fitted in place of a glass tube without having to dismantle cocks. In operation, light is reflected from steam space and absorbed in water space giving a bright and dark strip whose contrast can be seen clearly at a distance. No protective glass is required but reflex glass is only suitable for pressures up to 20.6bar because as temperature and pressure increases so does solvent action of water.
can boilers be started in auto?
Modern boilers can be started in auto and follow an automatic lighting sequence which is a series of actions done before burning commences include a period of time before ignition when the boiler fan will run to remove any unburnt gases that may have been left in the furnace, an officer watches this to get familiar with process.
What device is used to detect if boiler is alight?
Modern flame monitoring sensor are fitted to detect when boiler is alight. They use ultra violet or infra-red detection or a combination of the two. Some will also include self cleaning lenses and self checking mechanisms. One type uses a shutter that closes off the flame and the electronic circuits monitor the operation of the shutter in relation to the boiler flame. If the boiler flame fails to light the boiler will try to relight. A secondary failure will result in a boiler lock out and an alarm to the ECR.
How does the preformance ratio relate to the boiler
The boiler can also be described as a evaporator and so performance ratio relates to it as well. However you cant only use the performance ratio because the heat source for a boiler is normally exhaust gas from diesel engine meaning there’s no useful work (energy) before entry. performance is affected by scale formation and frequency of blow down
How often is boiler surveying carried out?
All boilers must have a minimum of two internal examinations every 5 years during dry dock. A general external examination is to be carried out at the time of the Annual Survey. An external survey of boilers including tests of safety and protective devices, and tests of safety valves using their relieving gear, is to be carried out annually within the range dates of the Annual Survey of the ship. The safety valves are to be tested by the Chief Engineer at sea within the dates of the Annual Survey. This test is to be recorded in the log book and reviewed by the attending Surveyor prior to completion
what are some boiler surveying requirements?
The survey of auxiliary boilers includes ancillary equipment which, together with the controls, should be examined under working conditions and the correct adjustment of any safety devices to be verified.
A thorough external examination of boilers is to be undertaken. It is to be verified that boiler supports, chocks, rolling stays, uptakes and the funnel base are in satisfactory condition.
Thorough examination of each boiler, together with super heater, superheat control, air heater and economiser, if fitted. If a boiler has not been sufficiently cleaned to allow a proper examination of pressure parts, the survey cannot be regarded as complete until this has been done.
Where the construction of a boiler does not allow direct visual internal examination of the shell, drums or headers, the attending Surveyor(s) are to be satisfied that the boiler is in a safe working condition by using remote viewing instruments, Ultrasonic Testing (UT), or hydraulic testing to determine a safe working pressure.
Longitudinal stays attached to end plates by external and internal welds should be examined at the inner welds for possible cracking. All such stays should be drilled at the ends with holes 5 mm diameter and of sufficient depth to penetrate the centre of the stay beyond the inner weld.
Every effort is to be made to complete the survey prior to departure. If, for any reason, the survey is not completed, the definite intentions of the Owner/Operator regarding completion are to be ascertained.
If a later date, more than two months after the date on which the internal examination was held, is required in cases where a ship remains in port without the appliance being placed under steam, a further internal survey is to be carried out
Rolling stays, expansion/sliding feet arrangements and freedom of pins and holding down bolts are to be specially examined in way of attachments to the shell or casings and freedom of pins is to be verified
The joints of manhole, hand hole doors are to be examined and to ensure that the jointing faces are in good condition and that the clearances do not exceed 1.5 mm
what surveying is preformed when boiler is in operating conditions?
Verify the calibration of the boiler pressure gauges. Where the calibration cannot be readily verified, a written statement is to be obtained from the Master/Chief Engineer confirming that the gauges have been calibrated. Alternatively, consideration may be given to a second gauge for verification of the primary gauge.
Establishing that water level indicators are operating correctly by utilising a methodical blow down sequence.
Comparison of bench tested valves previously set under workshop conditions to respective pressures as set at sea.
Establishing that water level indicators are operating correctly by utilising a methodical blow down sequence.
Testing all safety and alarm equipment.
Observation of boiler starting sequences and firing.
Verification of the calibration of the boiler pressure gauges. Where the calibration cannot be readily verified, a written statement is to be obtained from the Master/Chief Engineer confirming that the gauges have been calibrated. Alternatively, consideration may be given to a second gauge for verification of the primary gauge.
Testing all safety and alarm equipment & observation of boiler starting sequences and firing.
A general examination of the associated oil fuel system including fuel tank valves, pipes, deck control gear are also to be carried out.
why carry out boiler alarm surveying?
Survey of alarms, controls and safeguard lights during periodical surveys is a requirement of the appropriate Rules and Regulations. The purpose is to ensure that the alarms, controls or safeguards remains functional in service.
Records of changes to the hardware and software used for control and monitoring systems for propelling and essential auxiliary machinery since the original issue (and their identification) are to be reviewed.
Satisfactory operation of the alarms, controls and safeguards is to be verified.
what are safety valve surveying requirements?
Safety valves are to be adjusted under steam to not more than 103 per cent of the approved design pressure shown in the Register Book and the Survey Preparation Package (SPP). In all cases, a record of the pressure to which the safety valves have been set should be left on board.
Where more than one safety valve used, the other(s) are to be gagged (prevented from opening) whilst the safety valve is tested. On completion this role is to be reversed so that in turn, all valves have been tested.
Verification of the calibration of the boiler pressure gauges
When surveying Main Boilers, Auxiliary Boilers, Exhaust Gas Boilers, Economisers or any steam plant, examination of the drain lines fitted to the safety valves to ensure they are independent, clear, unblocked and in accordance with the appropriate Rules and Regulations.
What Is A Boiler Hydrostatic Test?
hydrostatic test is a stress procedure used to determine the integrity of all aspects of a given boiler unit. The test involves filling the boiler with water and pressurizing to at least one and half times the maximum specified operating pressures for a short duration.
how to preform a boiler hydrostatic test?
After boiler repairs a hydraulic test is done. In preparation of the test all equipment and foreign matter is removed from the water space of the boiler and everything is examined. Any permanent welding should be done by a professional welder and welds are subjected to non destructive testing techniques. Test is preformed to hold the safety valves and boiler mountings closed while equipment is subjected to a hydrostatic test. With the exception of feed check valve and air cock. To avoid damage to the spindle and/or seat, care is required so the gag screw is not tightened. Boiler is then filled with clean fresh water and purged of air. Using a hydraulic pump unit connected by a small bore pipe to boiler directly or to feed line and then pressure is gradually applied. Testing pressure used is 1.5 times the working pressure applied for at least 30mins. When boiler is under pressure its examined for leakages and faults. Weld repairs should be checked repeatedly with blows by a hammer.
describe the procedure for blowing down and opening up a boiler?
If an examination of boiler has to be done boiler has to be emptied of water.its always better if time is available to allow boiler to cool down for a period of time after shut down and then you pump the water out. Avoid sudden shock of cooling due to complete blow down. Allow as much time for blow down as possible after shut down and before starting if blowing down to the sea. Ship side blow down cock must be opened first and then blow down valve for boiler is gradually opened. This way engineer has better control of operation. For example if external blow down pipe between boiler and ship side is in a corroded condition and engineer opens boiler blow down valve first this leads to rupturing of blow down pipe. As a safety measure when handle is removed valve must be in closed position this way the valve cannot be accidentally left open. When blow down process starts noise level falls and pressure is low. Ensure no cold sea water can enter boiler. When boiler is empty of water it still contains steam, which can condense and cause a vacuum condition. This increases risk of entry of cold sea water but to prevent entry boiler blow down valve is non return type with some water tube boilers having a double shut off. Even with these arrangements its recommended to start closing boiler blow down valve when pressure is low enough and down to the desired value, the blow down valve is then closed tightly as well as ship side cock. After this allow time for boiler to cool down and lose all its pressure. When pressure is atmospheric, open air cock and gauge glass drain to ensure pressure inside boiler is atmospheric. Then boiler door is unbolted and manholes knocked in top or bottom but not both. If top door secure rope to eye bolt then secure other end of rope. Loosen the retaining nuts but don’t take them off yet. Then take a long plank of wood stand back and knock door down. When door open remove retaining nuts. Do not then immediately open bottom manhole because if boiler is hot this will lead cool air passing through as well as thermal shock.
with the aid of a sketch explain a three element boiler water level control system
see EOOW ORAL Sketch Pack for drawing
A three element boiler water level control system is shown above.
The measured variables or elements are ‘steam flow’, ‘drum flow’ and ‘feed water flow’. Since in a balanced situation steam flow must equal feed flow, these two signals are compared in a differential relay. The relay output is fed to a two term controller and comparator into which the measured drum level signal is also fed. Any deviation between the desired and actual drum level and any deviation between feed and steam flow will result in controller action to adjust the feed water control valve. The drum level will then be returned to its correct position. A sudden increase in steam demand would result in a deviation signal from the differential relay and an output signal to open the feed water control valve. The swell effect would therefore not influence the correct operation of the control system. For a reduction in steam demand, an output signal to close the feed water control valve would result, thus avoiding shrinkage effects. Any change in feed water pressure would result in feed water control valve movement to correct the change before the drum level was affected.
Describe with the aid of a sketch an ogee ring for a boiler
see EOOW ORAL Sketch Pack for drawing
the above drawing shows an ogee ring for a boiler
Tell-tale holes are drilled at equal circumferential intervals in the boiler shell this enable leakage between the Ogee ring and the boiler shell. Connecting the bottom of the furnace to the boiler shell plating is a seamless Ogee ring. This ring is pressed out of thicker plating than the furnace; the greater thickness is necessary since circulation in its vicinity is not as good as elsewhere in the boiler and deposits can accumulate between it and the boiler shell plating. Hand hole cleaning doors are provided around the circumference of the boiler in the region of the ‘Ogee’ ring.
why does a boiler require a boiler water level control system?
Thereactionsof steam and water in the drum are complicated and require a control system based on a number of measured elements. When a boiler isoperatingthewater levelin thegaugeglass reads higher than when the boiler is shut down. This is because of the presence of steam bubbles in the water, a situation which is accepted in normal practice. If however there occurs a higher increase in steam demand from the boiler the pressure in the drum will fall. Some of the water present in the drum at the higher pressure will now ‘flash off’ and become steam. These bubbles of steam will cause the drum level to rise. The reduced mass of water in the drum will also results in more steam being produced, which will further raise the water level. This effect is known as ‘swell’. When the boiler load returns to normal the drum pressure will rise and steam bubble formation will reduce, causing a fall in water level. Incoming colder feed water will further reduce steam bubble formation and what is known as ‘shrinkage’ of the drum level will occur. The problems associated with swell and shrinkage are removed by the use of a second measuring element, ‘steam flow’ . A third element ‘feed water flow’ is added to avoid problems that would occur if the feed water pressure were to vary.
Name the different types of boiler fuel oil atomizer
Simple Pressure Jet Atomizer
Spill type of pressure jet atomizer
Constant differential type atomizer
Plunger type of pressure jet atomizer
Rotary or spinning cup jet boiler fuel oil atomizers
describe with the aid of a sketch a simple pressure jet atomizer
see EOOW ORAL Sketch Pack for drawing
Sketch above shows diagrammatically
the principle of the simple pressure jet boiler fuel oil atomizers.
Oil fuel at a pressure of not less than 8 bar is supplied to the tangentially arranged ports, wherein it falls in pressure, resulting in the oil swirling around at high velocity inside the chamber. The greater the pressure drop the greater would be the velocity, but generally supply oil pressure would not be greater than 25 bar, high pressures create pumping and sealing problems. At outlet from the short sharp edged orifice (care must be taken not to damage the orifice during cleaning) a hollow expanding cone of fuel droplets is produced whose initial film thickness reduces as oil supply pressure increases.
what are some features of the simple pressure jet boiler fuel oil atomizer?
1.Simple, inexpensive and robust.
2.No moving parts, hence no possibility of seizure.
3.Large range of droplet size for one pressure.
4.Turn down ratio is low, about 2.5 to 1. Turn-down ratio is the ratio of the burner throughput maximum to minimum. If say the maximum throughput is 2500 kg/hr, then with a turn down ratio of 2.5 to 1 the minimum throughput will be 1000 kg/hr.
Maximum throughput is about 3200 kg/hr
5.No alteration in air register arrangement for all outputs, this is a consequence of the low turndown ratio of this type of burner.
6.To vary throughput the pressure must be altered, this results in variation in droplet size, hence atomization and combustion will be affected.
describe a constant differential type atomizer
With the differential pressure between delivery and spill kept constant the pressure drop across the tangential ports is kept constant and the rotational velocity of the fuel in the swirl chamber will not alter. This will keep fuel cone angle and atomization constant.
The main disadvantage with these types of boiler fuel oil atomizers is the large quantity of hot oil being returned, it may prove difficult to keep control over oil temperature.
Describe with the aid of a sketch plunger type of pressure jet atomizer
see EOOW ORAL Sketch Pack for drawing
drawing above shows the principle of operation of this type of burner, as the oil supply pressure is increased the spring loaded plunger moves to uncover extra tangential oil entry holes. The pressure drop and hence the rotational velocity of the oil remains nearly constant.
Describe with the aid of a sketch a Rotary or spinning cup jet boiler fuel oil atomizer
see EOOW ORAL Sketch Pack for drawing
As seen in the drawing above the atomizer consists of a motor driven fan, metering pump and fuel cup. The fuel cup which rotates at 70 to 100 rev/second is supplied with oil at low pressure (1.7 to 4.5 bar) from the metering pump which is used to control the throughput. Due to centrifugal force and opposite swirl of air to fuel the oil film leaving the cup is rapidly broken down into relatively even sized droplets.
what are some features of a Rotary or spinning cup jet boiler fuel oil atomizer
1.High output possible, up to 3600 kg/h.
2.Low oil supply pressure.
3.At low throughputs atomization due to reduced oil film thickness is improved.
4.Wide turndown ratio, up to 20:1 possible.
5.Oil viscosity need only be reduced to 400 seconds Redwood number 1 for satisfactory operation.
name the different types of desuperheaters
internal desuperheater
spray type external desuperheater
external desuperheater
what is the purpose of desuperheaters
Desuperheaters remove the superheat in the steam that is to be used for auxiliary purposes, the reason is that if high temperature steam was used for auxiliaries then the materials used would have to be capable of withstanding high temperatures, this leads to increased initial cost.
describe with the aid of a sketch a internal desuperheater
see EOOW ORAL Sketch Pack for drawing
Desuperheaters are generally coils situated in the water spaces that are supplied with steam from the superheated section outlet; this type of Desuperheaters is generally called as internal Desuperheaters. If this type of Desuperheaters develops a leakage then water loss from the boiler occurs since boiler pressure is greater than steam pressure in the Desuperheaters coil. This water loss could result in water hammer and subsequent damage in the auxiliary system.
describe with the aid of a sketch a spray type external desuperheater
see EOOW ORAL Sketch Pack for drawing
Spray type external Desuperheaters is shown in the diagram above, in which feed water of low solids content at 3.5 bar above steam pressure is supplied at a controlled rate into a vertically arranged vessel to mix with superheated steam. The excess water is kept to a minimum, collects at the bottom of the vessel and passes out through the drain and then the superheated steam moves up the annular space formed by the mixing compartment and the outer container to the auxiliary steam supply line.
describe with the aid of a sketch a external desuperheater
see EOOW ORAL Sketch Pack for drawing
Another type of external Desuperheaters is shown in the figure below. This is really part of the boiler externally arranged. It has a steam and water connection to the boiler drum so that the circulation through the Desuperheaters takes place, taking heat from the superheated steam in the solid drawn steel ‘U’ shaped tubes. A blow down valve is fitted in order to remove any sludge that may accumulate in the lower portion of the vessel. This type of Desuperheaters is for large steam demands since the 3 pass U tube arrangement would be too large to accommodate in the water space of the steam drum. Good combustion is essential for the efficient running of the boiler. It gives the best possible heat release and minimum amount of deposits on the heating surfaces.
what is a boiler?
Boiler is a pressure vessel (unit) used on ships in which the water is heated to evaporate and generate the steam andthe unit is arranged so that the generated steam is accumulated in it. The two main types are water tubeand fire tube. steam is then used for heating of fuel and water as diesel oil is in limited supply and expensive
Explain how steam is classified?
Steam can be classified into two main types saturated and superheated.
Saturated steam
Saturated steam is steam that is in equilibrium with water at the same temperature and pressure. This means that saturated steam contains both water vapour and liquid water droplets. The temperature and pressure of saturated steam depend on each other and are determined by the boiling point of water at that pressure. For example, at atmospheric pressure (101.3 kPa), the boiling point of water is 100°C, and the saturated steam has the same temperature. However, if the pressure is increased to 10 bar (1000 kPa), the boiling point of water rises to 180°C, and the saturated steam also has a higher temperature.
Superheated steam
Superheated steam is steam that has been heated to a temperature higher than its saturation temperature at the same pressure. This means that superheated steam does not contain any liquid water droplets and is completely dry, high-temperature steam with significantly more energy content. Superheated steam can be produced by passing saturated steam through a separate heating device called a super heater , which transfers additional heat to the steam by contact or by radiation.
What are some advantages of water tube boiler
1.High efficiency (generally greater than 85 %) hence reduced fuel consumption.
2.Flexibility of design – important space consideration.
3.Capable of high output (i.e. high evaporation rate).
4.High pressures and temperatures improve turbine plant efficiency.
5.Flexible in operation to meet fluctuating demands of the plant – superheat control rapidly responsive to changing demands.
6.Generally all surfaces are circular hence no supporting stays are required.
7.Steam can be raised rapidly from cold if the occasion demands (3 to 4 hours compared to 24 hours for smoke tube or fire tube boilers) because of the positive circulation.
8.Consider a fire tube or smoke tube boiler and a water tube boiler with similar evaporation rates the water tube boiler would be compact and relatively light by comparison and its water content would be about 7 tonnes or less compared with the smoke tube or fire tube boiler’s 30 tonnes.
9.With double casing radiation loss can be cut to 1 % or less.
why is it necessary to reduce the boiler load after repair work on a refractory?
when starting-up boiler after any repair work of the refractory, it is very important to reduce boiler load. This is because the new refractory still contains a small amount of water. When heated the water vaporises and expands which might cause fissures and cracks in the refractory. The burner must therefore only be operated at minimum load and in intervals of 1-2 minutes for the first hours. Between each operation interval the burner should remain stopped for approximately 8-10 minutes. Boiler refractory is heat-resistant materials that are used to line the boiler to help it retain heat. This prevents thermal loss during boiler operation. It also helps the boiler retain heat even when it is not firing.
what are some check to be made before starting up a boiler
Before start-up of the boiler plant, following general work and check procedures must be followed
1.Check that the main steam valve, by-pass valve and circulation valves if provided, scum valve, and blow-down valves are closed.
2.Open the feed water valves and the air valve. Fill the boiler with feed water to approximately 50 mm below normal water level. The water level rises due to expansion when the boiler is heated. If the temperature difference between the boiler and feed water exceeds approximately 50ºC, the boiler must be filled very slowly.
3.When filling a pressure less boiler, the shut-off valve after the feed water pump must be throttled. Otherwise the pump motor will be overloaded.
4.Check the water level in the water level gauges. Check frequently during the complete start-up. The water level gauges should be blown down several times to ensure a correct indication.
5.Check that the water level control system is connected and operational.
6.Check the oil system and start the fuel oil supply pump. Pre-heat the fuel oil if the burner should operate on heavy fuel oil.
7.Check the burner and the safety functions according to the manufacturer instruction.
Describe the procedure for starting up a Boiler
The following work procedures must be followed during start-up of the boiler.
1.Check that the gauge board valve and pressure gauge valves are opened.
2.Check that the air valve is open if the boiler pressure is below 1.0 bar.
3.Start the burner on manual control and on low load. Check that the water level does not rise too high during the pressure rising period.
4.Drain via the blow down valves if the water level is too high.
5.If the air valve was opened close it when only steam blows out. A pressure reading should be indicated on the boiler pressure gauge before the air valve is closed.
6.Tighten all covers such as manholes, hand holes, inspection doors, etc. during the pressure rising period. If required, check all flange joints on the plant.
7.Change to automatic control of the burner when the boiler pressure is 0.5 bar lower than the working pressure of the boiler.
8.Open the by-pass valve slowly to heat-up and pressurise the steam system. If the boiler is not provided with a by-pass valve, the main steam valve should be used to heat-up and pressurise the steam system.
9.Open the main steam valve and close the by-pass valve.
10.Open the valves to the steam consumers carefully in order to avoid water chocks.
11.When the boiler is in normal operation, check that the water level control system and the gauge board functions are fully operational.
Describe the procedure for opening up a boiler for inspection
Change over boiler fuel oil to diesel oil.
Make sure all diesel engines are stopped or changed over to diesel oil.
Electric fuel oil heaters can be put in use if fitted on board.
Shut main steam stop valve and put off feed water pump.
Carry out scum blow down to remove floating oil, sludge, etc.
Carry out bottom blow down after scum blow down, otherwise oil carry over may occur.
Boiler blow down to be carried out in steps to avoid thermal stresses. Excessive stresses may lead to cracking.
Sudden cooling down and drop in pressure may cause stresses in boiler. So reduction of pressure must be gradual.
Make sure nobody is standing near ship side blow down valve.
Gradually reduce boiler pressure in steps, 5bar—–>4.5bar——>4bar and so on. This helps in gradual reduction in boiler temperature also.
Safety gear to be used by the personnel operating blow down valves.
When boiler pressure reaches 1bar, open up the vent.
Now if the ship is loaded and having high draft, it may not be possible to drain boiler water completely. In such case arrangements to be made for transferring remaining boiler water to bilges.
Once the boiler is fully de pressurized, slack top manhole door first, make sure no pressure is inside, support the door with chain block, and slowly remove it and secure enter the boiler when it is sufficiently cold.
Check the welding in the boiler. A careful examination should be carried out with respect to any possible corrosion or crack formation.
Special care should be taken to the water line area in the pressure vessel where oxygen pitting may occur. If deposits are found to be forming in the boiler tubes, the boiler should be chemically cleaned.
It is advisable to consult a company of cleaning specialists who will examine the boiler deposits and treat the boiler accordingly. After chemical treatment the boiler should be blown-down at least twice a day for approximately one week. This will ensure that excessive sludge deposits due to chemical treatment do not collect in the bottom of pressure vessel.
what happens if a boiler is contaminated?
If the boiler is contaminated with foreign substances like oil, chemicals, corrosion products etc., it is very important to act immediately to avoid damages to the boiler. Layers of thin oil films, mud, etc. exposed to the heating surfaces causes a bad heat transfer in the boiler, leading to overheating followed by burned out pressure parts. In order to remove such contamination, a boiling out or acid cleaning have to be performed immediately. Corrosion products from the pipe system or insufficient boiler water treatment may result in corrosion in the boiler itself. It is therefore important to observe that such circumstances do not occur in the system.
how often should the boiler furnace be inspected and what kind of checks should be carried out?
The furnace should be inspected at least twice a year.
During this inspection the following issues should be taken into consideration.
Check for cracks at the refractory lining and that the furnace walls are free from excessive soot deposits.
Examine carefully the area opposite the burner. Too much soot deposits indicate that the burner should be adjusted.
Check that the pin-tube elements are intact and that soot deposits are within normal limits.
what kind of daily checks must be done on a boiler?
1.Check the boiler steam pressure and the water level.
2.Check that the feed water control system is operational.
3.Check the boiler water condition and make necessary countermeasures with regard to the feed and boiler water treatment. If necessary blow-down the boiler.
4.Check the function of the oil burner at different capacities through the inspection holes on the boiler.
5.Check the flue gas (a mixture of gases produced by the burning of fuel) temperature after and/or the draft loss across the boiler. If either the temperature or the draft loss is too high, the pin-tube section must be cleaned.
what actions could be taken to reduce the chances of a boiler uptake fire?
Regularly inspect boiler flame to ensure correct air fuel ratio is maintained. This makes complete combustion with clean flue gas.
Carry out boiler burner and swirler routines as per PMS.
Regularly soot blow economisers and water wash periodically to remove soot deposits.
Use proper grade of fuel oil for boiler.
Fuel oil used for boiler to be treated well.
Avoid low load operation of boiler for long period.
Running boiler near full load periodically, helps in expelling out carbon deposits adhered in uptake passages and reduces chances of boiler uptake fire considerably.
what is a boiler uptake fire?
Auxiliary boiler uptake or flue gases normally pass through economisers or air pre-heaters or feed water heaters. All these types of heat exchangers are fin type. Hence large amount of carbon or soot deposits on the fins. Along with the flue gases some un-burnt carbon particles also get deposited on the economisers. Normally dry soot deposits have a very high ignition temperature. But when the soot gets wet with hydrocarbon vapours, their ignition temperature comes down to around 150 degree Celsius. This may result in boiler soot fire or boiler uptake fire. When an uptake fire is suspected, never soot blow the economiser or boiler. Soot blow with steam causes steam to convert as hydrogen gas and result in metal fire.
What is caustic embrittlement and How can it be prevented?
It is inter crystalline fracture. It is cause by high concentration of caustic soda and the materialunder stress. The stress corrosion cracks follow the grain or crystal boundaries of the material andfailure. Sodium sulphate or sodium nitrate is used for the prevention of caustic embrittlement. It can be found in highly stress area in boiler. Such as tube and tube plate connection, rivetedhead, seam and boiler mountings.
what action would you take if gauge glass showing low water level ?
If water level has not yet dropped completely out the sight glass, water may be put into theboiler.
If water drops completely out of sight glass, check another sight glass, if both disappear water;do not add water until the boiler is cool enough to prevent any possible damage due to rapid cooling ofover heated plate.
The fire must be immediately stopped by extinguishing it with appropriate means of fire extinguishing media. The main steam stop valve must be closed.
Blow down and cool down the boiler. Check leakage, drum outside, locate the cause of trouble and make necessary repair.
Enter the boiler after it has cooled and examined any possible damage. After repair, water fill up slowly and restore to normal operation. If no damage occurred, inject the water slowly into the boiler and restore it to operation.
describe a normal boiler shut down
Normal boiler shut down
Boiler can be stopped by turning selector switch at control panel to stop. When the boiler is stopped, sudden temperature and pressure drops should be avoided as they might expose mountings, pipe lines, and the boiler plant to inadmissible temperature gradients. When minimum load is obtained, stop the burner. Keep the water level at normal level until the boiler stops producing steam. Stop the feed water pump and close the feed water valves. Close the main steam valve.
describe when an emergency boiler shut down is carried out?
The boiler must be taken out of service immediately ifparts of the heating surface have been glowing or the boiler shows recognisable deformations.
The supervising authorities must be informed, and the boiler must not be used until approval from these authorities is availablea substantial loss of water is notedthe feed water system is unable to provide the necessary amount of feed water, e.g. due to failure of partsthe safety valve cannot functionsudden cracks or damage are noted in the refractory, and if steam or moisture is coming out of the refractoryoil in the feed water is detectedtoo high salinity level is detected. If an emergency shut down must be carried out, the fuel supply should be stopped. The main steam valve should be closed gradually, and the boiler must be cooled. The safety valves must not be operated. Parallel working boilers should be disconnected at once.
what measures should be taken when the boiler is shut down for repair or inspection.
1.Clean the boiler from soot with water.
2.Operate the burner for at least 15 minutes after the soot removal to dry out the remaining water.
3.Stop the boiler as mentioned previously.
4.Check the furnace and the pin tubes with regard to cleanliness.
5.Empty the boiler from water and clean it. Check if lime stone appears.
6.Check and clean the outer fittings. Change gaskets where required.
7.Clean the feed water tank and feed water pipes.
8.Clean and grease the bearings of motor, pump, and fan.
9.Check and align the burner, if necessary.
10.If the boiler is shut down for a long period of time, the pin tubes must be thoroughly cleaned.
11.Check that the necessary spare parts are available. Order complementary parts in time.
It is of extreme importance that the boiler is NOT operated without water when the oil burner is in operation, e.g. due to disconnection of the water level safety devices. This will immediately cause complete break down of the boiler.
name the types of boiler and include the working pressure ?
1.Low pressure boiler – up to 10Kg / Cm^2
2.Medium pressure boiler – 10-25 Kg /Cm^2
3.High pressure boiler– Over 25 Kg / Cm^2
kg/cm^2 is not the standard unit in the International System of Units (SI). In the SI system, the unit of pressure is the pascal (Pa), which is defined as one newton per square meter (N/m2).
1 kg/cm² = 98066.5 pascals
1 Pa = 1 N / m2
What is water hammering and how will you prevent it ?
It is the impact of moving water in steam line when the steam is allowed to enter a line withcondensed water. The steam condenses and partial vacuum occurs and moves back the wateralong the pipe with very high velocity, and the water will strike at the vent or valves.
To prevent the water hammering;
1.Install steam trap in the line
2.Open the drain first before allowing the steam into the line.
3.Crack open steam valve at first and open slowly in increments as oppose to fully opening it quickly
How do you take boiler water sample ?
Slowly open the salinometer cock until clean hot water is coming out.
Then collect the boiler sample with copper jar if available or tin. Copper is used if possible, rather than steel (an alloy of iron) because copper does not react with either water or steam, whereas iron reacts with steam
How do you know if scum blow down valve is open or not ?
It can be check by opening of ship side blow down valve. Banging noise will appear, scum blowdown valve is in open position. It can also detect, over heating of scum blow down pipe.
Where are manhole doors fitted ?
one is fitted at steam side and other one at water side.
what is the effect of foaming and priming ?
1.Can cause water hummer
2.Can cause contamination and scaling.
3.Can cause fluctuation of working water level.
What is boiler blow back ?
It occurs when lighting up with explosive gas and oil droplet (Oil residue) inside the furnacewithout pre-purging sufficiently.
The ignition results in a large flue gas inside the furnace and these gases blow out withincrease high pressure through the furnace opening.
Procedure for hydraulic pressure test on marine boilers ?
Hydraulic pressure test is 1.25 times working pressure, ( 10 minutes maintain)
1.Close all openings.
2.Open air vent cock.
3.Fill up boiler water fully
4.Close the air vent cock
5.Place hydraulic jack to feed water line.
6.Fit standard pressure gauge.
7.Applied hydraulic pressure 1.25 times of working pressure and maintain 10minutes.
What is liquid coagulant in marine boilers ?
It has more molecular weight, colourless solution, containing sodium aluminate, starch, terming, and resin.
Once being dose into the boiler water floating solid particles and suspended solid are settled tothe bottom of the boiler and easily remove by blowing down.
how do u fit a new boiler gauge glass?
1.Shut steam and water cocks and open drain cock.
2.Check any leakage from the respective cock.
3.Slacken the gland nuts.
4.Open the cap and remove gauge glass.
5.Fit new gauge glass, correct size and length into its space.
6.Give the expansion allowance 1/8 in vertical clearance.
7.Use new packing.
8.Close the cap.
9.After fitting, warm the glass by steam.
10.Tighten the gland nut.
11.Then steam and water pressure should be tested whether they clear.
12.Close the drain and open the water and steam side cocks.
13.Check the leakage; all are satisfactory put back into operation.
What is meant by erosion inboilers?
It is a mechanical attack on the metal surface which may be due to a disturbance in the flow ofthe fluid over the metal surfaces, resulting in a loss of metal. Suspended abrasive matters in the fluidcan increase the rate of metal losses.
What is meant bycorrosionin boilers ?
It is the deterioration of metals due to oxidation. The presence of water in an acidic conditionprovides the electrolyte required for corrosion action.
there are two forms of corrosion
Direct chemical attack
It occurs when metal at high temperature comes into contact with air or other gases, resulting inoxidation of the metal.
Electro-chemical action
Galvanic action, this being set up when two dissimilar metals are placed in an electrolyte. Thenoble of the two metals form a cathode to the base metal which, forming the anode, is wasted away.
What is meant by caustic embrittlement in boilers?
Caustic embattlement is a form of inter crystalline cracking, which results from a solution ofsodium hydroxide or caustic soda, becoming more and more concentrated at the bottom of a crack orfissure (narrow opening) which may be the result of fatigue, in the boiler plate or furnace.
The plate must be stressed, so that wastage take placeat the bottom of crack, the plate weakens, the crack extends to expose new metal to the caustic actionand thus it proceed.
Caustic embattlement will only occur when there is a high caustic alkalinity that is when theratio of NaOH to the alkalinity is high. To keep this ratio at the safe level the sodium sulphate to sodiumhydroxide should be maintained above 2:5.
The sodium sulphate comes out of solution in high sodiumhydroxide concentration and by doing forms a protective layer on the surface of the plate.
Also keep the lowest T.D.S level. (Total dissolved suspended & solid)
what is some routine boiler maintenance carried out on ships ?
1.Clean the rotating cup.
2.Check and adjust the belt tension between motor and rotating shaft.
3.Clear the pilot burner nozzle and fitter.
4.Clean carbon deposit on electrodes ( igniter ) and adjust the gap.
5.Check the fuel valve and air register linkages and joints.
6.Check and clean the flame eye cover glass.
7.Check and clean inspection peep hole glass cover.
8.Clean fuel oil fitter.
9.Check the fuel oil pressure.
When is boiler safety valve set point made ?
Every boiler survey and After safety valve overhaul.
Why ship side blow down valve is open first and close last ?
To prevent pressure build up in blow down line and a pipe burst, which can cause injury to watch keeper.
What would be some effects of no test treatments for boiler ?
Reduction in boiler efficiency due to poor heat transfer
Reduction in tensile strength
Reduction in factor of safety
Overheating of metal resulting
distortion and eventual failure
Increase in fuel consumption
Excess concentration of NaOH (caustic soda) may cause caustic embrittlement on boiler metaland tend to failure of boiler metal
Corrosion
Scale formation
Foaming, Priming, carry over (due to increase T.D.S level, foaming is present and tend tocarried over and priming)
What is meant by soot blowing ?
It’s the process of removing soot, to prevent EGE fire, soot fire and or boiler fire. It maintains steam generating efficiency and increases heat transfer efficiency. Its done on daily basis at sea and or in accordance with manufacturer and C/E guidance.
What is the procedure for soot blowing?
1.Inform to bridge
2.Check wind direction, good if transverse direction
3.Raise boiler pressure
4.Open drain cock until soot blow pipe drain clear
5.Open soot blower valve
6.Increase the air to boiler to more than 50 %
7.Open steam valve & carried out by turning wheel 20 -30 sec
8.Then close steam valve, soot blower valve
9.Open drain valve
What are the causes ofboiler furnace blow back?
1.Insufficient purging time
2.Accumulation of oil in furnace from the leaky burners
3.Boiler tubes and uptake have full of soot deposits.
4.Air registers control not operating for the high flame mode.
5.Too little air
6.Insufficient oil temperature
What are some reasons to do boiler water treatment?
To prevent scale formation ( Trisodium phosphates is used)
To remove trace of oxygen (sodium sulphide or hydrazine is used )
To give alkalinity and minimize corrosion.(sodium hydroxide is used )
To reduce risk of caustic cracking ( sodium sulphate or sodium nitrate is used)
What is the procedure of accumulation pressure test ?
This test is carried out a new boiler or new safety valve.
1.Shut off feed water
2.Closed main steam stop valve.
3.Increase cut off pressure of boiler.
4.Bypass high pressure cut off of the boiler.
5.Arrange the boiler fire rate to a maximum.
6.Safety valve will be lift during the test.
7.The test is carried out as long as the water permits in the boiler.
8.Accumulation pressure should not exceed 10% of working pressure in the specified time.
9.Specified time is 15 minsfor a smoke tube boiler and 7 mins for water tube boiler.
What is the purpose of accumulation pressure test ?
To know if the safety valve is suitable for this boiler or not.
To limit the rise in boiler pressureunder full fire condition.
What is boiler priming and how to prevent it ?
It is condition in which large amount of water are carried along with the steam into the steamline.
It is caused by:
1.Excessive foaming
2.Improper amount of steam space
3.By a suddenrush of steam such as is produced when steam stop valve is suddenly opened.
To prevent priming, never keep the water level too high.Open steam stop valve slowly.
What actions should be taken in case of foaming and priming ?
1.Scum blow down
2.Reduce boiler fire rate
3.Check whether boiler chemical added are in excess
4.Detect the source of contamination
5.In case of bad priming the boiler may have to be taken out of service, shut down.
Note:For contamination due to oil, auxiliary boiler have to be chemically cleaned.
Describe the boiler start up procedure from cold condition ?
The boiler is carried out firing from cold condition to normal working pressure condition very slowly to avoidthermal stress.
1.Check the boiler blow down valve in close position.
2.Shut the main steam stop v/v.
3.Open the air vent cocks.
4.Open the feed check valve and pumping up to ¼ of gauge glass level.
5.Start the force draft fan with dampers, open correctly to purge the furnace and combustionspace of any foul gas.
6.Light the burner after closing the recirculating valve.
7.Normally allow the fire to burn for 5-minutes and stop for 15 mins. This step continues untilsteam come out.
8.When steam coming out from the air vent close the air vent (at 1 to 2 bar pressure).
9.Rise up the working pressure step by step slowly. (Allow the fire to burn for 30 mins and stopthe fire for 10 min.)
10.When the steam pressure reached is working pressure drain the steam line. (to avoid waterhammer)
11.Main steam stop valve open slowly (crack opening)
what is the procedure for opening up and carrying out a boiler inspection?
1.To remove top man hole door, slacken the dog holding nuts but do not remove them until firstbroken the joint
2.Remove nuts and dogs and take out the door.
3.The bottom door can be removed after warning personnel to keep clear of the top door.
4.Make ventilation before entering. Do not allow naked light near the boiler.
5.Preliminary internal inspection carried out before cleaning, to check scale deposits and any specialpoints.
6.Plug orifice to blow down valve to prevent choke, place guards over the manholes landings toprevent damage.
7.Carried out cleaning and internal works.
8.When all works completed, afull internal examinationmust be carried out
9.Cleanliness, all openings are clear, water level gauge connection clears from deposits
10.All internal pipes and fittings have been replaced correctly and securely attached,
11.Remove plug from the blow down valve orifice
12.The face of manhole doors and landings inspect to clean and undamaged.
13.Replace manhole doors by using new joints.
14.Operate all boiler mountings. Open air vent cock and fill the boiler with water to sufficient level.
What is foaming in auxiliary boilers and how to prevent it ?
It is the formation of thick layer of steam bubbles on the top of the water surface inside theboiler due to:
High concentration of impurities.
By the animal or vegetable fats in feed water carry over from the oil heaters.
Increase in level of dissolved & suspended solid TDS level.
Increase in water level.
To prevent foaming, surface or scum blow down should be done frequently to expel any floatingimpurities for the boiler and no lube oil should be allowed to enter the boiler.
How do you to take a boiler out of service ?
For fire tube boiler out of service for short period
The boiler must be completely filled withalkaline water.
The boiler must be topped up periodically and any air in the system must be got rid off.
Regularly test the boiler water and keep the alkalinity in the range ofrecommended value.
If the boiler is to be taken out of service for long period
It should be drained completely and open up.
Dried out by means of heater units.
Then the trays of quick lime (moisture absorbent material) should be place internally in suitable positions.
Blanks should be fitted to the pipe connections in the event of steam being maintained in otherboiler and blow down line.
The quick lime should be renewed at least once every two months.
how do u carry out the the boiler cool down procedure ?
1.Change the fuel oil burning system from HO to DO and then shut down the burning system.
2.Stop feed p/p close feed check valve.
3.Drain down the boiler after allowing it to cool down.
4.If no sufficient time to do this, lower the boiler pressure to 3 to 4 bar.
5.Shut the main steam stop valve.
6.Open the ship side valve then open the blow down valve.
7.Banging noise will appear when boiler is empty.
8.Close the boiler blow down valve and ship side valve.
9.Then release the steam pressure through safety v/v by means of easing gear.
10.When pressure is off, open the air vent and allow boiler to cool down.
What action would you take if gauge glassis chocked ?
Steam and water cocks and passages in the gauge can be cleared while the boiler is stillsteaming.
To do this, shut the steam and water cocks and open the drain cock.
Remove the check plugopposite the obstruction.
Insert the cleaning plug. Screw in the plug with small hole about 5 mmdiameter, drilled through it in place of the cleaning plug.
Insert into this hole a rod of such a size thatheld by a gloved hand, it can be easily moved without being stuck.
Then open the chocked and push the rod through to clear the blockage.
When clear, opendrain to prevent a build up of pressure and only a small amount of steam will blow past the rod, theglove protecting the operator from injury.
Then close the cock and replace the normal cleaning plug. The gauge glass can be tested nowand if satisfactory return to service.
Do not carry out this operation on a plate type glass on a high pressure boiler.
What is meant by accumulation pressure in marine boilers?
Accumulation pressure is the rise in boiler pressure which take place when the spring loadedsafety valve lift due to the increase loading caused by further compression of the spring.
What do you understand bycomposite boiler?
If exhaust gas and oil fired can be used the same time, it is termed the composite boiler.
In this type a separate tube nest of tube for exhaust gas is provided, situated above the return tubesfrom the fire furnace.
Uptake from the tube nest are separated.
define what is meant by pH value for boiler water?
It is the logarithm of reciprocal of hydrogen iron concentration.
if too much chloride is found in boiler water what will you do ?
Blow down frequently
Reduce the boiler load to minimum.
If highly contaminant shut down completely and wash out.
Trace and find out the fault and remedies.
Describe the procedure for setting the safety valve set point under steam pressure ?
1.Take standard pressure gauge (approved by surveyor) for accuracy.
2.Fill up water up to ¼ of gauge glass level, and shut main steam stop valve, feed check valve.
3.Without compression rings, hoods and easing gears, reassembled the safety valves withspring compression less than previous setting.
4.Raise the boiler pressure to desired blow off pressure.
5.Screw-down spring compression nuts of any lifting valves, until all are quite.
6.Arrange to have the desired steam pressure
7.Adjust each valve in turn: Slacken compression nut until the valve lifts.Screw-down compression nut sufficiently enough, so that when the valve spindle islightly tapped, valve return to its seat and remain seated.Measure gap between compression nut and spring casing.Make a compression ring equal to this gap, and insert under compression nut.Gag the spindle of this safety valve, to prevent opening, while remaining valve is beingset.
8.Remaining valve is again set and insert compression ring.
9.Remove gag and retest both valve to lift and close together.
10.Cap, cotter and easing gear to be refitted
11.Caps and cotter pins padlocked to prevent accidentally altering the setting.
12.When the surveyor satisfied the setting pressure, easing gear should be tested.
13.All safety valves set to lift at not greater than 3% above approved working pressure (designpressure).
