zxc ® 26-Июн-2013 23:47

Marine Boilers | 3rd Edition


Language: english
Author: GTH Flanagan
Publisher: GTH Flanagan
Format: PDF
Quality: Scanned pages
Number of pages: 121
Contents:
Preface 1
1 Stresses in boiler shells 1
2 Auxiliary boilers 7
3 Water tube boilers 27
4 Superheaters and uptake heat exchangers 49
5 Boiler mountings 67
6 Combustion of fuel in boilers 91
7 Boiler operation 105
Index 117

Дополнительно

CHAPTER 7
Boiler Operation
A. If the boiler has been opened up for cleaning or repairs check that all work has been completed, and carried out in a satisfactory manner. Ensure that all tools, etc. have been removed. Examine all internal pipes and fittings to see that they are in place, and properly fitted. Check that the blow down valve is clear. Then carry out the following procedure:
Fit lower manhole door. Check external boiler fittings to see they are in order. See that all blanks are removed from safety valves, blow down line, etc.
Fill boiler with water to about one-quarter of the water level gauge glass. If possible hot water heated by means of a feed heater should be used. The initial dose of feed treatment chemicals, mixed with water, can be poured in at the top manhole door at this stage if required. Then fit top manhole door. Make sure air vent isopen.
Set one fire away at lowest possible rate. Use the smallest burner tip available. By-pass air heater if fitted. Change furnaces over every twenty minutes.
After about one hour start to circulate the boiler by means of auxiliary feed pump and blow down valve connection, or by patent circular if fitted. If no means of circulation is provided, continue firing at lowest rate until the boiler is well warmed through especially below the furnaces. Running or blowing out a small amount of water at this stage will assist in promoting natural circulation if no other means is available. Continue circulating for about four hours, raising the temperature of the boiler at a rate of about 6°-7°C per hour. Water drawn off at the salinometer cock can be used to check water temperature below 100°C.
At the end of this time set fires away in all furnaces, still at the lowest rate. Close the air vent.
Nuts on manhole doors, and any new joints should be nipped up. Circulating the boiler can now be stopped, and steam pressure slowly raised during the next 7-8 hours to within about 100 kN/m2 of the working pressure.
Test the water gauge. The boiler is now ready to be put into service. About 12 hours should be allowed for the complete operation provided some means of circulating the boiler is provided. If circulation cannot be carried out, the steam raising procedure must be carried out more slowly, taking about 18-24 hours for the complete operation. This is due to the fact that water is a very poor conductor of heat, and heat from the furnace will be carried up by convection currents leaving the water below the furnace cold. This will lead to severe stresses being set up in the lower sections of the circumferential joints of the boiler shell if steam raising is carried out too rapidly, and can lead to leakage and ‘grooving’ of the end plate flanging.
If steam is being raised simultaneously on more than one boiler, use the feed pump to circulate each boiler in turn, for about ten minutes each.
Q. Describe the procedure for opening up a Scotch boiler. WhaLin&pectians-siiouid be carfrert THTr tre'fofelhe Boiler is again boxed up?
A. Empty the boiler, preferably by allowing the boiler to cool down, and then running or pumping out. If there is not sufficient time for this, allow boiler pressure to fall to 300-400 kN/m2 and blow down. When pressure is off the boiler, open the air vent and allow the boiler to cool down.
When the boiler is cool, make sure there is no vacuum in the boiler ; this should be done by opening the drain cock on the water level gauge glass in case the air vent is choked.
Then commence to open up the boiler by first removing the top manhole door. To do this, slacken back the nuts holding the dogs, but do not remove them until first breaking the joint. This precaution should be taken in the event of pressure or vacuum existing in the boiler. The nuts and dogs can then be removed, and the door removed. Depending upon the weight of the door, it may be necessary to rig a lifting block to the door in order to do this.
The opening should then be roped off, and all personnel warned to keep clear. The bottom door can now be removed, again taking care when breaking the joint in case water is still above the sill of the door. If this should be the case, pump out before removing door.
It is important that this sequence be followed as, when the lower door is removed, it allows a through-draught and hot vapour rising through the top door may scald anyone standing over the hole. Hot vapour can remain in a Scotch boiler even after a considerable period of time allowed for cooling down.
With the doors removed, allow the boiler to ventilate before attempting to enter. Do not allow naked lights near the boiler until it has ventilated due to the danger of explosive gas in the boiler. If in doubt, use a safety lamp to test the atmosphere in the boiler is safe to breathe before entering.
A preliminary internal inspection should be carried out before cleaning is commenced to check the general condition. Note scale deposits and any special points.
Plug the orifice to the blow down valve to ensure it does not get choked during cleaning operations, and place guards over the manhole landings to ensure they are not damaged. The boiler can now be cleaned, and any internal work carried out.
When all work is completed, a full internal examination must be carried out. It is advisable to keep a record of the boiler, consisting of a drawing on which any troubles, repairs, etc. can be shown, and a book in which remarks regarding scale formation, corrosion, deformation, etc, can be kept.
Check to see all cleaning has been carried out efficiently, especially where the tubes enter the tube plates. See that all tools and other articles have been removed from the boiler, paying special attention to combustion chamber top, tube nests, and bottom of boiler. Make sure all openings are clear, takingspecia) care with the water level gauge connections to ensure they are clear and free from deposits. Make sure al I internal pipes and fittings have been replaced correctly, and are securely attached. The guards can be removed, and the faces of the manhole doors and landings inspected to see they are clean and undamaged.
Remove the plug from the blow down valve orifice. Replace the lower manhole doors, using a new joint. Operate all boiler mountings and see they work correctly. Leave in a closed position, except for water level gauge steam and water cocks, and air vents.
The boiler can now be filled to one-quarter level in the gauge glass if steam is to be raised, or filled completely if a hydraulic test is to be carried out.
Q.- State the regulations concerning the hydraulic testing of a Scotch boiler. Describe how you would carry out such a test.
New boilers having a design pressure in excess of 690 kN/m2, together with their components, must be subjected to a hydraulic test at a pressure = (1-5 x design pressure + 350) kN/m2 upon completion. For boilers working at pressures below this value the test value is 2 x design pressure.
The test must be carried out in the presence of an authorized surveyor, who upon satisfactory completion of the test will stamp the boiler with the official DOT stamp if it is for a passenger vessel, or if a classification society surveyor is concerned, their official stamp will be used. The surveyor’s initials are also put on alongside the stamp, which is usually on the bottom front plate, near the furnace.
Boilers which have undergone structural repairs must be subjected to a hydraulic test at a pressure at least equal to the design pressure.
The surveyor may call for a hydraulic test at any survey, the test pressure being to the surveyor’s requirements.
The procedure for such a test is carried out as follows. Close or blank off all openings. Measuring tapes may be placed around the boiler, and deflection gauges in the furnace. Lagging should be removed as required to facilitate inspection of joints,
The boiler is then completely filled with water, the air vent being left open until water shows to ensure no air is trapped inside, ft should be noted that the use of hot water places the boiler closer to working conditions, but may scald in the event of failure if the water is hot enough to flash off into steam with the resultant drop in pressure.
The force pump, and test gauges can now be fitted. The gauge glasses should be shut off if the test pressure is to be above the design pressure. The readings on the measuring tapes, and deflection gauges should be noted. The boiler can now be pressurized by means of the force pump. Care should be taken to ensure that the pressure rises smartly in response to the pumping action; if it appears sluggish, open the air vent to remove any air remaining in the boiler. Listen carefully during application of pressure in case any combustion stays, etc. fracture.
Then examine all joints, especially if these are riveted. Check flanges for cracks. All flat surfaces should be checked with a straight edge for signs of bulging due to stay failure, overheating, or thinning of the plate. Look for signs of leakage at tell-tale holes in the combustion chamber stays and welded compensating rings. Examine all tube ends for signs of leakage. Check, and note readings on measuring tapes, and deflection gauges.
The test pressure must be maintained until the surveyor has completed his examination, and must in any case be kept on for at least ten consecutive minutes. The pressure can then be released. Readings on the measuring tapes and deflection gauges should again be checked to ensure they have returned to their initial values. The boiler can then be emptied, and examined inside and out.
Describe a procedure for closing up, and then raising steam on a water tube boiler.
A. Before closing up the boiler inspect the internal surfaces to ensure they are clean, all openings to the boiler mountings clear, and tubes proved to be free of obstruction by means of search balls, flexible wires, air or water jets.
Replace any internal fittings which have been removed, checking to ensure they are correctly positioned and secured.
The header handhole plugs and lower manhole doors are now replaced.
Operate all boiler mountings to ensure they work freely, leaving all the valves in a closed position.
Check the gas side of the boiler is clean and in good order. Make sure the soot blowers are correctly fitted, and operate over their correct traverse. Operate any gas or air control dampers fitted to ensure they move freely for their full travel. Leave them closed or in mid-position as necessary. The boiler casing doors are now replaced.
Open the direct reading water level gauge isolating cocks, together with all boiler vents, alarm and pressure gauge connections. The superheater drains are also opened. Check that all other drains and blow down valves are closed.
Commence to fill the boiler with hot deaerated water. At this stage the initial dose of chemical treatment can be added through the top manhole doors, which arc then replaced.
Continue to fill until water just shows in the water level gauges. Close any header vents as water issues.
Remove the funnel cover, and ensure that all air checks operate correctly and that the forced draught fans are in working order. If gas air heaters are fitted they should be by-passed.
Check the fuel oil system to ascertain it is in good order. Start up the fuel oil service pumps and check for leaks. The boiler is now ready to commence raising steam.
Heat the fuel oil to the required temperature, using the recirculating line to get the heated oil through the system. If no heat is available for this, use gas oil until sufficient steam is available to heat the residual fuel oil normally used.
Start the forced draught fan, and with all the air checks full open purge the boiler, makingsure any gas control dampers are in mid-position so giving a clear air passage.
Carry out a final check to make sure water level gauge cocks are open, water is showing in the glass, and that steam drum and superheater vents are open.
Now close all the air checks except for the burner to be flashed up, this beingdone by means of ignition equipment or a paraffin torch. Use the lowest possible firing rate. Adjust the air supply so as to obtain the best combustion conditions and check that, as the boiler heats up, the water level in the glass begins to rise.
After about one hour steam should show at the drum and superheater vents and, when issuing strongly, open the superheater circulating valve and close the air vents.
When the steam pressure has reached a value of about 300 kN/m2 blow through the water level gauges to ensure they are working correctly. The isolating valves on the remote reading water level indicator can now be opened, and the indicator placed in service.
With the steam pressure at about 1000 kN/m2 follow up the nuts on all new boiler joints.
At a pressure of about 1400 kN/m2 open the drains on the auxiliary steam lines, crack open the auxiliary stop valve and warm the auxiliary line through. Now close the drains and fully open the auxiliary stop valve.
Various auxiliary equipment such as fuel oil heaters, turbo-feed pumps, etc. can be put into service and, provided this entails a flow of steam through the superheater, the superheater circulating and drain valves are closed.
Bring the boiler up to working pressure, keeping the firing rate as steady as possible, and avoiding intermittent flashing up.
Check the water level alarms.
Open the main steam line drains, and crack open the main stop valve and warm through the main steam line. Then close the drains and fully open the main stop valve.
The procedure from flashing up to coupling up at full working pressure should take about four to six hours. Only in emergency should it be carried out more rapidly. If new refractory material has been installed carry out the procedure more slowly.
At all times during the raising of steam the superheaters must be circulated with steam to prevent them overheating. If the temperature of the superheaters goes above the permitted value for the boiler reduce the rate of firing.
It must be noted that, due to the great variety of water tube boiler designs in use, the foregoing procedure is only to be taken as a guide; for example, header boilers with their greater amount of refractory material will require about eight hours to reach full pressure. Thus the engineer should always follow the procedure laid down for his particular boiler, which may vary in detail from the basic principles previously stated.
Q. Describe the procedure for carrying out a hydraulic test on a water tube boiler. To what pressure would you subject the boiler for purpose of testing.
A. New boilers having a design pressure in excess of 690 kN/m2 together with their components must be subjected to a hydraulic test at 1-5 times the approved design pressure, carried out to the surveyor’s requirements.
Although the surveyor may call for a hydraulic test at survey, it is not normally required for routine survey unless limited access prevents a practicable visual examination. After repairs to pressure parts a hydraulic test to 1-25 times working pressure is usually accepted; for minor repairs such as tube renewal, testing to just below working pressure will suffice.
For purpose of testing the boiler is considered to extend from economiser inlet to main steam stop valve.
Before testing, carry out a thorough inspection of the boiler to ensure that all necessary work has been completed, all internal surfaces are clean, and all tools etc. have been removed. Remove any casing as necessary for a proper inspection of the pressure parts undergoing test. In some instances it may be necessary to remove some of the boiler insulation.
Gag the safety valves and shut off the water level indicators, alarms etc. if going above the working pressure, and isolate or blank off any parts not designed to withstand the test pressure. Pay particular attention to attemperators or de-superheaters, as these are often designed to cope only with the differential pressures between the drum and superheater; it may be necessary to equalise pressures across them during the test, in some cases by slacking back one of the flanged connections.
Check that all valves operate freely and seat properly. Then close all valves, drains etc. on the boiler but leave all vents open. All manhole doors can be closed, and any header plugs replaced.
Fit the force pump and any test gauges required, ensuring that these are properly calibrated.
Start to fill the boiler using water as close to the metal temperature as possible, but not less than 7°C, as any sudden change in temperature such as may be caused by filling a warm boiler or superheater with cold water may cause leakage by way of expanded joints. The boiler must also be protected against mechanical or thermal shock during the test, so never put a hydraulic test on a hot boiler or superheater. During filling, check for leaks, open drains etc. and if any are found stop filling until they are rectified. Close vents as water issues from them, continuing to fill until the boiler is completely pressed up, and all air is released.
The force pump can now be used, building up the pressure slowly so as to avoid shock. If the pressure does not begin to rise with the first few strokes of the pump, check all vents to ensure that all air has been released.
When fully pressurised, check all visible seams, expanded joints etc. for signs of leakage or distortion, maintaining the test pressure for at least 30 minutes.
With inspection completed, slowly release the test pressure. If any leaks have been delected, the water level need only be dropped sufficiently for the leak to be recified. Retest until no leakage occurs.
Before draining the boiler it is a convenient time, after the gags have been removed, to use hydraulic pressure to reset the safety valves if required. They will then only need a final adjustment under steam.
Should raw water have been used for testing, completely drain and then flush out the boiler with distilled water before returning to service.
A. Surveys are carried out to ensure that the boiler is in a safe working condition and likely to remain so until the next survey. Main water tube boilers of passenger ships are surveyed annually, while for cargo ships bi-annual survey is sufficient. The normal procedure for auxiliary boilers is bi-annual for the first eight years, thereafter annual, although a concession may be made for auxiliary water lube to continue on a two year cycle, provided that they are in good condition and with good records, especially those for water treatment.
The survey will cover the boiler from burner front, or exhaust gas inlet, to funnel lop, including all pressure containment parts, valves and fittings.
During the survey the boiler, economiser and air heater are to be examined both internally and externally as far as access permits, and where considered necessary pressure parts subjected lo a hydraulic test. Thickness of plates and lubes is to be determined, usually by ultrasonic test equipment.
The principal boiler mountings are to be examined externally, and opened up for internal inspection where considered neccssary. Boiler casings, supports etc. will be examined to see they are in good order, and allow for free expansion. Automatic control equipment for water level and for fuel oil is to be checked, with special regard to safety cut-outs.
Isolate the boiler from all working systems, and open up both water and gas sides, removing any internals necessary for a proper visual examination. A visual inspection should be made to ascertain general boiler conditions, before it is cleaned both internally and externally.
Previous records, if any, should be examined and note taken of any previous defects or repairs, so these can be given special attention. A convenient survey procedure
Give the basic survey procedure to be carried out on a marine boiler.
taking into account the layout of the boiler should be decided upon. This will vary from one boiler to another, but a typical procedure will be as follows. The steam drum is examined internally and externally together with its mountings, then all top headers and the burner positions, including carriers and associated pipework. Economiser and superheater headers can be inspected before entering the water drum. Under the boiler, any mountings and supports are checked.
Do not carry out any gas side inspections until all internal examinations are complete, in order to avoid carrying grease, dirt etc. into the water spaces.
On the gas side, start with the furnace (staging may be required in large roof-fired units). Then in turn the superheater, economiser, and air heater can be inspected.
A note pad with pencil securely attached, an unbreakable torch and a mirror on a rod should be available, together with other items if desired such as a straight-edge, an introscope to examine tube bores, and a polaroid camera to record any defects found during the examination. In the case of welded boilers with limited access, blanket radiography pictures using portable gamma ray equipment may be obtained, and used to look for suspected internal foreign objects inside tubes etc.
The survey is not complete until the boiler has been examined under steam, and the pressure gauges checked against a test gauge. The water level indicators and protective devices must be tested, and the safety valves adjusted to their correct blow-off pressures. The fuel oil system is to be checked under pressure, and remote operated fuel oil cut-off gear tested.
In the case of exhaust gas boilers where steam cannot be raised in port, the ship’s Chief Engineer will be responsible for the correct setting of the safety valves at sea, with the boiler survey record not being completed until he confirms that this has been done satisfactorily.
jO.J Discuss some of the common problems that can arise in thgi?p.eration^fiiiarine pgijers.
A. Boiler damage can be considered under five main headings: corrosion, erosion, overheating, cracking and mechanical damage.
Corrosion There are two principal forms of corrosion. One is direct chemical attack and mainly occurs in superheaters due to the high metal temperatures involved. It can result in pitting or cracking in tube bores, or in scaling or flaking on the gas side of tubes. This form of corrosion also occurs when loss of water circulation causes the metal to overheat in the presence of steam.
The more comon form of corrosion found in boilers is the result of electro-chemical attack usually involving acidic water conditions in the presence of dissolved oxygen. General wastage of the boiler metal due to this form of attack has been virtually eliminated by the use of chemical feedwater treatment, but isolated pitting can still occur if the treatment is not operated within the correct limits. It may be found along the water level in the drum, generally as the result of poor shut-down and storage procedures where the boiler is left partly filled with cold water. Pitting along the roof of the drum can result from condensation. In the lower parts of the boiler it can be due to poor drainage, pools of water remaining in drums and headers. However, isolated pitting can also result from operating with the boiler water allowed to remain at too low a pH value, and in this case will also tend to occur in the bores of lubes subjected to the highest rates of heat exchange, such as screen and water wall tubes.
Erosion This is a mechanical wearing away of the boiler metal due to water, steam or gas flowing over the metal surface. Thus tubes can wear thin in the region of bends, due to water impingement, or wear externally as they stand in the flow of hot abrasive gases leaving the furnace. Serious local erosion can result from the direct impingement onto the tube surface of a steam jet from a badly aligned soot blower.
Overheating In-service boiler metal subjected to the heat of combustion must be continually cooled by water or steam. If for any reason this cooling affect is lost, or greatly reduced, the boiler metal overheats, loses strength and distorts. This can result in expanded tubes pulling out of tube plates, local bulging of tube surfaces with eventual rupture, the sagging of superheater tubes between their supports, etc.
Loss of water brings about the most immediate and serious damage, but loss of circulation through lubes will also quickly result in damage. A build-up of deposits on the water side acts as an insulating layer, reducing the rate of heat transfer through the metal so causing it to overheat and leading to eventual distortion. Oil entering the boiler only forms a thin, but efficient, insulating layer upon heated surfaces, but also encourages a further build-up of scale deposits.
Superheaters at their operational metal temperatures are very vulnerable to overheating, and a circulation of steam through them must be provided at all times when the boiler is steaming, circulating to atmosphere if not load is available. Priming and carry-over must be avoided, as impurities passing over with the water will result in a build-up of deposits in the superheater tubes, again causing eventual overheating.
Direct flame impingement onto water walls will lead to overheating and distortion. Fire in uptakes or superheaters due to a build up of deposits in the gas passages can also result in serious overheating and damage even to pressure parls of the boiler.
Cracking Welded boilers are especially vulnerable to fatigue cracking resulting from bad design, poor workmanship or both. Cracks of this nature, even if starting in a minor weld, can continue to propagate even into the main shell plate.
Fatigue cracking is also associated with thermal cyclic stressing, which can result from poor steam-raising procedures, lack of expansion, or even from a continual carry-over of water droplets causing cracking inside superheater headers.
Over-expansion of tubes into tubeplates can lead to cracking of the bellmouthing and in some cases to cracks forming in the tubeplate between the holes.
Cracking due to caustic embrittlement can take place in boilers of riveted construction, due to slight leakage allowed to continue over a period of time in a riveted seam.
Mechanical Damage This can result from poor workmanship, such as damage to tube plates by over-expanding during tube attachment, scoring of joint faces, distortion of doors by overtightening.
Another source of damage are explosions in the furnace due to bad flashing-up procedures. These can be especially serious in roof-fired radiant heat boilers with gas tight water wall panels; the force of the explosion acting directly upon these can cause them to suffer severe distortion. It is normal practice to warm this type of furnace with heated air etc. before attempting to flash up from cold.
Q. State the general precautions to be followed by a watchkeeper in charge of a water tube boiler installation.
A. The watchkeeping officer must familiarise himself with the plant of which he is in charge, and.be aware of all individual equipment operating control signals, flow rates, temperatures and general load conditions. He must check these regularly so as to become aware quickly of any deviations from the norm. Rarely do emergency conditions arise without some previous indication, which an alert watchkeeper should recognise, investigate, and then take corrective action before the situation gets out of hand.
Ensure that all boiler and associated safety shut-down devices are maintained in full operational condition, and tested at regular intervals so as to be ready for instant operation. All alarm and automatic control systems must be kept within the manufacturer's recommended operating limits. Do not allow equipment to be taken out of operation for reasons which could reasonably be rectified.
All control room check lists must be kept up to date, with any known deviations from normal operating procedures noted, both for immediate reference and to inform oncoming watchkeepers of the ongoing situation. Remember that any deterioration in watchkeeping standards can give rise to circumstances whereby deviations remain un-noticed and may build up to potentially serious conditions.
Automatic control loops do not think for themselves, and subjected to external irregularities will still try to perform as normal. This can result in their final control action being incorrect, or to some other piece of equipment being overworked in an attempt to compensate. In situations where the automatic control of critical parameters is not dependable, or where it becomes necessary to use manual control, reduce operating conditions so as to increase acceptable margins of error.
High performance water tube boilers demand high quality feed water, so do not tolerate any deterioration of feed water conditions; immediately trace the source of any contamination, and rectify the fault.
Do not neglect leakage of high pressure, high temperature steam, as even minor leaks will rapidly deteriorate. No attempt should be made to approach the site of leakage directly, but the defective system should be shut down as soon as is practicable and the leakage rectified. Do not allow steam and water leaks to go un-corrected as, apart from reduction in plant efficiency, they also lead to increased demand for extra feed with an inevitable increase in boiler water impurities.
Always be alert for conditions which increase the potential fire risk within the engine room: the best method of fire fighting is not to allow one to start. Thus all spaces, tank tops etc. must be kept clean, dry, and well lil. This not only improves the work environment, but also makes for the early detection of any leakage and encourages early repair.
Store any necessary stocks of combustibles remote from sources of ignition. Maintain all oil systems tight and free from leaks and overspills.
Follow correct flashing-up procedures for the boiler at all times, especially in the case of roof-fired radiant heat boilers.
Be familiar with the ship’s fire fighting systems and equipment, and ensure that all
under your direct control are kept at a full state of readiness at all limes.
Assess particular risk areas, especially in engine room spaces, and formulate your approach in case of emergency; decide in some detail how you would deal with fires at various sites in the engine room.
Make sure that your are familiar with the quick closing fuel shut-off valves, the remotely operated steam shut-off valves etc. to enable the boiler to be put in a safe
condition if having to abandon the machinery spaces in the event of a fire.
Q. Stale a basic procedure to be followed for the cleaning of a boiler after a period of service.
A. The frequency of boiler cleaning depends upon various factors such as the nature of the service in which the vessel has been engaged, the quality of feed water and fuel with which the boiler has been supplied. In general, every reasonable opportunity should be taken, whenever the boiler is shut down, to examine internal and external surfaces.
Records of uptake and superheat temperatures taken during the passage will give a guide to the condition of the boiler, as deposits forming upon any heated surfaces of the boiler will reduce the rate of heat transfer; thus uptake gas temperatures tend to show an increase, while superheat temperatures decrease.
Where possible the boiler should be shut down at least 24 hours prior to cleaning, with if practicable the soot blowers being opera ted just before shut-down. When boiler pressure has fallen to about 400 kN/m2, open blow down valves on drums and headers to remove sludge deposits. Finally empty the boiler by running down through suitable drains etc. Do not attempt to cool the boiler forcibly as this can lead to thermal shock. All fuel, feed and steam lines must be isolated, and the appropriate valves locked or lashed shut. Air vents must be left open to prevent a vacuum forming in the boiler as it cools down.
Internal Cleaning With boiler cooled, open the steam drum doors, followed by water drum doors and any bolted header plugs where filled. Take care to avoid any remaining hot vapour or water, and allow the boiler to ventilate before making any attempt to enter. Light covers should be fitted in place of the manhole doors to protect the boiler interior when work is not in progress. With a man standing by outside the door, the boiler interior can be inspected to ascertain if cleaning is required.
Should cleaning prove to be necessary, remove any internal fittings required to provide access to tubes etc., keeping a record of any items removed. Also note that all attachment bolts are present, and that all are accounted for when refitting.
Where the boiler design permits, cleaning can be carried out by mechanical brushes with flexible drives; if these are not suitable, chemical cleaning must be used. After cleaning, flush the boiler through with distilled water.
Upon completion of cleaning, tubes etc. must be proved clear. Where access is available, search balls or flexible search wires can be used. Where neither is practical, high pressure water or air jets can be used, the rate of discharge from the outlet end being used to indicate whether any obstruction is present within the tube. Where necessary, welded nipples are removed to permit sighting through headers. With welded boilers the tubes must be carefully searched before welding takes place, and suitable precautions then taken to avoid the entry of any foreign matter into tubes etc. Where work is to be carried out in the drum, rubber or plastic mats can be used, with flexible wires attached and secured outside the drum so that they are not left inside when the boiler is closed up.
Check all orifices to boiler mountings to prove that they are clear, and ensure that all tools, cleaning materials etc. have been removed from the boiler. All internal fittings removed must be replaced. Fit new gaskets to all doors and headers, and close up the boiler.
All personnel working in the boiler must be impressed with the importance of the avoidance of any objects entering the tubes after the boiler has been searched, but that if a mishap should occur it must be reported before the boiler is finally closed up.
External Cleaning Spaces between tubes can become choked with deposits which are not removed by soot blowing. Where sufficiently loose they may be removed by dry cleaning using brushes or compressed air, but in most cases water washing will be necessary.
Washing will require hot water, preferably fresh, under pressure and delivered by suitable lances. The water serves two purposes, dissolving the soluble deposits and then breaking up and flushing away the loosened insoluble residue.
Once started, washing should be continuous and thorough, as any half-dissolved deposits remaining tend to harden off, baking on hard when the boiler is again fired, then to prove extremely difficult to remove during any subsequent cleaning operations.
Prior to cleaning, a bitumastic paint should be applied around tubes where they enter refractory material, in order to prevent water soaking in to cause external corrosion. Efficient drainage must be provided, with sometimes drains below the furnace floor requiring the removal of some furnace refactory. Where only a particular section is to be washed, hoppers can be rigged beneath the work area, and the water drained off through a convenient access door.
For stubborn deposits a wetting agent may be sprayed on prior to washing.
After washing, check that no damp deposits remain around tube ends, in crevices etc., removing any remaining traces found. In a similar manner remove any deposits in double casings around economiser headers etc., especially if they have become damp due to water entering during the washing process.
Ensure that all cleaning materials, tools, staging etc. have been removed, and any refractory removed has been replaced, after which the access doors can be replaced.
Run the fans at full power with air registers full open for some minutes to clear any loose deposits. Then dry the boiler out by flashing up in the normal manner. If this can not be done immediately, then hot air from steam air heaters or from portable units must be blown through to dry the external surfaces.
Q. Give a routine procedure for a soot blowing operation, suitable for use with high performance water tube boilers.
A. Before soot blowing is commenced, ensure that sufficient reserve feed water is available, that the soot blowing system is in good order with correct oil levels in blower gearboxes, and that where required bearings have been lubricated with a high temperature grease. Make sure that the boiler flame failure devices and low water level alarm and cut-outs are in full working order. Note the uptake temperatures if these are not already recorded. Then inform the bridge that soot blowing is about to start. They may require time to alter course etc. and will ring back when ready.
The soot blower main steam supply valve can now be cracked open and lines allowed to warm through and drain. The drain valves, if non-automatic, are then closed, and the steam supply valve is fully opened. In many cases two supply valves are fitted in series, with a drain between them to ensure that no steam can leak through to the soot blowing system when it is not in use.
Automatic combustion control can be shut off, or set to the blowing mode, whichever is applicable, and boiler operating conditions, such as superheat temperature, reduced if necessary. Shut off gas sampling lines to C02 recorders etc. and inert gas systems if fitted. Any gas or air control dampers should be set to their optimum position for soot blowing. The combusion air fans should be speeded up unless otherwise instructed.
Soot blowing can now begin, starting with the topmost blower and then, when this has completed blowing, proceeding to the lowest blower, operating this and the subsequent units in turn along the line of the gas flow. When the topmost blower is again reached, it is operated for a second time. Ensure that each unit performs correctly in sequence and over its full traverse. Operate any faulty units manually.
Throughout the operation maintain a constant watch on boiler operating conditions, and if necessary stop blowing.
When soot blowing is finished, inform the bridge. Then restore all the boiler functions to their normal operating conditions. Close the soot blower steam supply valves and fully open the drains. Check the reserve feed tank, and adjust the make-up feed supply as required to restore the water level in the tank. The gas sampling lines can be reopened, together with any inert gas system fitted. Note the uptake temperatures and compare them with previous readings; any marked variations can indicate some fault in the soot blowing system.
It is usual to operate soot blowers once every 24 hours, with rotary air heaters, where fitted, being blown every 12 hours.
116

Table of contents

Index
Accumulation of pressure, 83, 87 Acid attack, 63, 111 Air checks, 98, 102, 108 Air register, 36, 38, 92, 93, 94, 97, 99,
Air vents, 63, 69, 105, 106, 107, 114 Allborg boiler, 15 Alloy steel, 42, 51, 55, 57 Atomization, 61, 91, 94 Attemperators: air cooled, 41, 58 water cooled, 41, 59 Automatic control, 17, 19, 38, 42, 94, 95, 96, 98, 103, 113, 115 Auxiliary stop valve, 67
Babcock Willcox boilers, 36, 38 Baffles, 13, 15, 24, 33, 35, 40, 52, 53, 57, 98
Balance connections, 60, 79, 81, 82 Bell mouth, 9, 13,27,45, 57, 112 Bend test, 6
Blow down effect, 83, 88, 89, 90 Blow down valves, 18, 30, 68, 105, 114 Blow off pressure, 21, 83, 85, 87, 89 Boiler cleaning, 114, 115 Boiler drum, 17, 28, 44 Boiler feed regular, 68 Boiler shell, 4
Bonded deposits, 44, 45, 56, 59
Carbon deposits, 92 Carry over, 112 Castable refractory, 102 Chemical cleaning, 114 Chemical dosing valve, 69
Chrome, 57 . ' ' '
Chrome ore, 102 Circumferential joint, 8 Circumferential stress, 1, 2 Clarkson boiler, 12 Cochran boiler, 10 Collision chock, 7 Combustion: air, 91,96, 98
chamber, 4, 7, 11, 12, 18, 24, 73 process, 91 Compensation, 3, 4, 107 Composite boiler, 22, 23 Condensation, 50, 74, 111 Conduction formula, 27 Consolidated safety valve, 89 Control dampers, 19, 38, 41, 53, 56, 60,
115
Controlled superheat boiler, 51 Corrosion, 9, 10, 28, 31, 44, 62, 63, 103, 111
Corten steel, 66 Cracking, 12, 107, 111, I 12 Cyclone steam separators, 38
Dampers, 19, 38, 39, 41, 51, 53, 56, 57, 115
Density, 30, 33, 35 De-superheater, 53, 55, 60 Dew point temperature, 24, 25, 63, 64 Diaphragm water wall, 44, 46 Double casing, 33, 34, 36, 41, 59 Downcomers, 15, 28, 30, 32, 34, 36, 37, 39,41,42,44 Drain valve, 63, 69, 99, 103, 115 D-type boiler, 35, 37, 54
117
INDEX
Dual pressure boiler, 20
Easing gear, 73, 85, 86, 89 Economiser, 40, 52, 64 Enamel coating, 66 Erosion, 104, 112 ESD. I typeboiler, 39 ESD. II typeboiler, 41 ESD. Ill typeboiler, 42 Excess air, 42, 44, 47, 93 Exhaust gas boiler, 11, 15, 16, 21, 22, 25,
111
Fatigue cracking, 12 Feathering, 85, 87, 89 Feed water check valve, 67 Flame failure device, 12, 19, 101, 115 Flash off, 69
Forced circulation boiler, 16, 17, 18,24, 25
Force draught fan, 18
Foster wheeler boiler, 35, 39, 40
Fuel oil system, 100
Full bore safety valve, 85
Full lift safety valve, 86
Furnace, 7, 10, 11, 12, 13, 14,35,43
Gamma ray equipment, 11J Gas/air heater, 8, 43, 64, 65, 108 Generating tube, 15, 24, 31, 33, 34, 35,
37, 38, 43,44 Girder stay, 7, 8 Gusset slay, 11
Handhole door, 11 Header, 15, 27, 30, 33, 36, 39, 56 Header boiler, 33, 64, 109 Hemispherical furnace, 11,18 Hollow column, 72 Hopkinson safety valve, 87 Hydraulic test, 30, 107, 109, 110
Igema gauge, 78 Ignition temperature, 92
Improved high lift, 83 Internal cleaning, 106, 114 Integral furnace boiler, 36, 84 Internal inspection, 106, 108, 110
Joint efficiency, 2
Kaldo steel, 5 Kinetic energy 96, 102
Latent heat, 19, 49, 50 LD steel, 5
Longitudinal joint, I, 2, 8, 29 Louvre plate, 77
Low water level alarm, 19, 68, 80, 81, 83, 115
Main stop valve, 67
Manhole door, 2, 4, 8, I 1, 13, 15, 18, 20, 29, 30, 38,40, 105, 106, 108, 109 Manoeuvring, 51, 55 Membrane water wall, 46 Mica, 76, 77
Multi-loop economiser, 62 Multi-loop superheater, 39, 41, 45, 57 Multi-tubular boiler, 7 Molybdenum, 32, 57 Monolithic refractory, 102 Mono water wall, 41, 43, 46
Natural circulation,
Nozzle reaction, 86
Ogee ring, 10, II, 12, 13 Oil contamination, 19, 20, 112 Orifice plate, 61, 94, 104 Overheating, 10, 11, 12, 31, 53, 54, 55,
58, 73, 11 1, I 12
Package boiler, 18 Parallel flow, 17, 42, 52, 64 pH value, 111 Plate glass gauge, 75, 76 Pop action, 89
Pressure jet burner, 93 Primary combustion air, 92, 97 Primary flame, 92 Primary superheater, 40, 41, 44, 59 Priming, 112
Quad, 11,92, 99 Quick-closing valve, 100, 113
Radiant heat, 11, 15, 31 Radiant heat boiler, 31, 32, 44, 65 Raising steam, 105, 107 Recirculating valve, 100 Reflex water gauge, 75 Refraction, 71, 73, 75 Refractory, 11, 12, 15, 36, 38,40,41,46, 48,99, 101, 102 Relief valve, 63
Remote reading gauge, 78, 108 Riser, 32, 36, 44
Riveted joint, 3, 5, 6, 8, 11, 14, 28, 107,
112
Roof firing, 42, 112, 113 Rotary air heater, 44, 65 Rotary cup burner, 95
Safety valve, 19, 21, 55, 67, 73, 83, 85,
86, 109, 111 Salinometer valve, 69, 105 Scale, 8, 14, 20, 28, 106, 112 Scotch boiler, 7, 8, 18, 27, 64, 70, 105, 106 107
Screen tube, 31, 33, 35, 37, 38, 41, 52,
57, 111 Scum valve, 69 Seal welding, 10
Secondary combustion air, 93, 97 Secondary flame, 92
Secondary superheater, 40, 41, 42, 44, 59 Selectable superheat boiler, 38, 55 Settling tank, 99 Single boiler casing, 41, 44, 47 Smoke box, 8, 11, 14, 18 Smoke tube, 8, 9, 14
Sodium, 52, 63, 64
Soot blower, 41, 43, 63, 64, 65, 66, 102, 108, 115
Soot blower master valve, 70, 103, 115 Spanner boiler, 14 Spheroid boiler, 11 Spheroidal furnace, 11 Spray type attemperator, 45 Spray type de-superheater, 51,61 Steam/air heater, 66 Steam blast jet burner, 96, 99 Steam drum, 15, 16, 22, 28, 30, 33, 35,
38, 39, 41, 43, 59, 60, 67, 68, 78, 81, 108, 111 Steam/steam generator, 19 Steaming economiser, 45, 64 Stay, 5, 7, 11, 13, 15, 18 Stay tube, 8,9, 11, 12, 15, 18 Stub tube, 29 Studded tube, 36, 38, 46 Sulphur, 63, 93
Superheater circulation, 52, 53, 55, 58, 60, 67, 69 Superheater circulating valve, 69 Superheater support tube, 32, 45, 51, 52, 54, 56, 57, 111 Superheater temperature control, 33, 34, 36 38, 40, 41, 42, 44, 45, 51, 53, 55, 58 Superheater tube, 32, 39, 52, 55, 56, 58 Survey procedure, 110 Suspended flame, 91 Swirl plate, 94 Swirlyflo tube, 15
Tangential firing, 43 Tangential water wall, 44, 46 Tank boiler, 7, 10, 14, 23, 25 Tensile test, 6 Test piece, 6, 29 Testing of safety valve, 110, 111 Testing ofWL gauges, 71, 74, 79, 105, 108, 110, 111 Thermal efficiency, 22, 49 Thermodisc valve seat, 89
,ljl|faube, 12, 13 e[| formula, 27, 29 C 92, 99
hment, 9, 10, 11, 12, 13, 19, 2, 36, 44, 45, 54, 56, 57, 62,
er
late
rair heater, 64, 65 TubuJj^VL gauge, 70, 71, 73 Tuni do>*n ratio, 94, 95, 96 Two^S*ujn boiler, 34, 38
Ultra-sonic test, 110 Uptake, 8,13,15,18, 23, 35, 44, 57, 62, 63,64, 116 Uptake fire, 63, 64, 65 Uptake fouling, 63, 64, 65, 66, 99 Uptake heat exchanger, 63, 64, 65 Underfloor tube, 35, 36, 37, 39,41
Valve lift, 83, 85, 87 Vanadium, 52, 102
Venturi, 97
Vertical boiler, 10, 12, 13, 14, 16, 23 Viscosity, 91, 99, 100 Vortices, 91, 92, 99
Waste heat boiler, 17, 22, 23 Waste steam pipe, 83, 85 Water circulation, 8, 13, 15, 16, 18, 20, 24, 25
Water drum 30, 35, 37, 38, 39, 41, 43 Water level gauge, 68, 70, 71, 73, 75, 76, 78
Water wall, 15, 31, 34, 35, 37, 38, 39, 41, 44, 46 Water washing, IJ5 Welded joints, 8, 10, 11, 13, 14, 15, 19, 28, 38, 45, 46 Wrapper plate, 28, 29
X-ray examination, 29
Y-jet burner, 96
120
Оценка: 4.9 / 5 (Голосов: 17)
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