MARINE AUXILIARY BOILERS 1.Smoke tube Tank type Combustion gas pass through inside of tubes, water is outside of tubes. •
2. Water tube Drum type Water is in tubes, smoke pass outside of tubes. •
Smoke tube single pass composite Boiler
24 February 2013
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WATER TUBE BOILER (1) Steam drum One largest cylinder at top. Collect & separate steam & water, come up from generating tubes. Steam leave from top. Distribute water to down comer tubes. Receives feed water. –
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(2) Water drum Cylindrical shape, half size of steam drum at bottom. Distribute water to screen& generating tubes. Provides a space for accumulating suspended solids precipitated from boiler water. Blow down v/v is fitted. 1 manhole is at front end. –
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(3) Headers Cylindrical or rectangular shape, half size of water drum, At bottom opposite side of water drum. Perform as water drum. Only hand hole at front end for cleaning. –
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(4) Generating tubes Large quantity small diameter (32mm) tubes placed in main flow of hot gases between steam drum& water drum, large heat exchange surfaces. Steam generated at mid portion of generating tubes and raise up together with hot water to steam drum. –
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(5) Screen tubes Place in front of generating tubes to protect from direct heat of flame. Large diameter (50mm) to keep ratio of steam to water, to prevent over heating –
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(6) Down comer tubes Water from steam drum down to header(50mm) –
Water tube boiler steam drum
steam water
Down comer tube 1300 C
Furnace front
header
under floor tubes
water drum
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AUXILIARY BOILER MOUNTINGS Mounting mean v/vs & fittings direct attached to pressure sides. (1) SAFETY VALVE Protect overpressure. 2 valves on same chest with single pipe at top of steam space. Drain pipe without v/v fitted at chest, draining condensate. (2) STEAM STOP VALVE SLSD v/v on top of steam space. –
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(3) MAIN & AUXILIARY FEED V/VS
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Fitted to steam space,
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1 feed check v/v (NR) and 1 feed stop v/v between shell and feed check v/v. 2 inlet lines are fitted on same feed line. Extended spindles fitted to operate from convenient position-- Always ensure v/v can be operated easily & quickly
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have open/ close position indicator
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feed p/ps are positive pumps.
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(4) WATER LEVEL INDICATOR (GAUGE GLASS)
At least 2 for each boiler, at water level. Place on each side of boiler at direct visible positions. (5) LOW AND HIGH WATER LEVEL ALARM
Float and Electrically operated. To prevent loss of water in boiler Due to burst tube or fail to feed.
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(6) BOTTOM BLOW DOWN V/VS Fitted to lower water space to blow out water and sediments, internal pipe reach to bottom. Consist 2 v/vs in series, connected by a pipe to ship side discharge v/v. (7)SCUM BLOW DOWN V/V Fitted in upper water space to discharge oil or floating particles on surface of water in way of a pan just below normal water level. Pipe from this v/v connected between 2 bottom blow down v/vs. –
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(8)DRAIN VALVE At lowest water space. To drain water completely. (9)AIR VENT At top of steam drum, To release air at filling water or raising steam. (10)SALINOMETER V/V Fitted at mid of water space to get water sample. (11)PRESSURE GAUGE At top of steam space, Direct and remote reading, Connect to pressure switch for a auto combustion.
Cycle of steam and water
SAFETY DEVICES ON BOILER 1.Low and high water level alarm. 2.Very low water level cut out burner. 3.Low and high pressure alarm. 4.Very high steam pressure cut out burner. 5.Safety valve & easing gear prevent over pressure.
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1. SINGLE SIDED GLASS PLATE TYPE (Used in LP 17 bar and MP17~ 30 bar) Forged steel body in which is reflex glass plate.
2. DOUBLE SIDED GLASS PLATE TYPE (HP above 30bar).
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METHODS OF FITTING ON BOILER 1. Direct on shell 2. On bore pipe 3. On hollow column 4. On solid column
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GAUGE GLASS CROSS BLOWDOWN
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COCK POSITIONS Steam & water cocks are vertical downward at open& horizontal at close. Drain is vertical downward at close & horizontal at open, to prevent change of position due to vibration.
BOILER F.O BURNING SYSTEM•
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F.O about 60C come from F.O tank. Pass coarse filter& pump. Then heated in heater about 100C controlled by viscorator. If temp. high cracking occur, form gas in fuel line. If low, poor combustion and back fire. Then pass through auto-clean fine filter, rotated by motor or hand Then oil pass an control v/v, which regulate oil pressure to burner relative steam pressure in boiler, then enter burner.
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Air controller maintain correct ratio of fuel & air to furnace. 2 emergency v/vs are fitted, one quick shut off v/v or safety cock, shut by hand rapidly in emergency, and another one shut of v/v with a steam actuator, to shut off fuel when boiler water loss. To maintain oil temp. at desired value, a v/v is fitted to circulate oil back to p/p suction and closed when burner is in operation. D.O line also fitted for flash up boiler from cold.
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Burner is ignited by 2 electrodes. Pressure gauges & thermometers are fitted. Quick closing v/v on fuel tank outlet pipe & Emergency stop of fuel p/p operated from out side of E/R is fitted. Whole system should be above floor plate, well lighted to see leakage Can easily change to manual, bypassing automatic control v/v and oil supply pressure by hand wheel on spring loaded relief v/v.
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SAFETY DEVICES ON FUEL BURNING SYSTEM (UMS) Flame failure alarm & cut out burner (by photo cell) Low & high fuel temp. alarm & cut out burner.(by temp. sensor) Low fuel pressure alarm & cut out burner (by pressure switch) Force draught fan failure alarm & cut out burner (by electric relay) Power failure alarm.(relay) High flue gas temperature alarm & cut out (temp. sensor) Smoke density alarm & cut out burner (by photo cell) Air fuel ratio alarm & cut out controlled by air damper.
BOILER RAISING STEAM FROM COLD
1. open air vent , pressure gauge, gauge glass v/vs steam & water. Other v/vs kept shut. 2. Fill up water about ¼ of sight glass. 3. Run force draught fan to purge out furnace. 4. First 3,4 times flash up 5min./ 45 min., then 5min./ 30 min. 5. When boiler get warm more firing times till air come out from vent. 6. When steam come out from vent, close vent v/v, raise steam to working pressure.
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ACTION TO BE TAKEN WHEN WATER LEVEL DISAPPEAR IN GAUGE GLASS
Stop fire. Close non essential steam consumers. Close main steam stop v/v Make sure lower or higher than glass. If higher- blow down, If lower-reduce boiler load and fill water. When water level come into glass. Restart burning and put in service. If water level still disappearing, inform to C/E to stop engine, and inform to duty officer if
Boiler operation
CHECK POINTS ON BOILER AT BIGINING AND KEEPING WATCH
1. Gauge glass water level about ½ glass. 2. Cross blow gauge glass. 3. Boiler pressure always in limit 4 to 7 bar. 4. FO temp.& press. in limit. 5. No leakage in steam and fuel v/vs or pipes. 6. Flame color must be clean, clear and bright yellow, not white or black smoke. 7. Drain oil from feed tank water surface, wipe out with paper, fill water. ( feed tank sketch) 8. Safety v/v easing gear to be made ease.
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BOILER BACK FIRE Unburnt fuel due to improper combustion (by low fuel temp., nozzle defect, improper air/fuel ratio, oil leak fr. burner, collect on floor. Then get firing temp. by radiation of burning flame, suddenly explode during firing (or) Flammable gases in furnace from previous time explode when supply air and ignition for next start. Fire blow back to boiler front through inspection door and air passage. To prevent, well ventilate furnace before ignite fuel, maintain correct fuel temperature, air/fuel ratio and burner in good condition, clean burner tip. Keep good combustion.
BOILER MAINTENANCE •
(1) Boiler water test and treat daily.
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(2)Clean gas side and water side regularly.
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(3) Combustion system
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Maintain correct fuel pressure, temperature. Clean and overhaul burner. Check and clean air regulator system.
BOILER BLOW DOWN •
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Open ship side discharge cock and v/v first, to prevent high pressure in pipe between boiler & ship side. Handle on cock can be removed when only close position. Fully open blow down v/v (scum or bottom), crack and gradually open intermediate v/v to control discharge rate. Never control discharge rate by boiler v/v, to prevent seating of v/v from damage and leakage when closed. noising at high press discharging, when press. low, noise level fall. While blowing down, watch gauge glass water level and pressure gauge all the time. When fall to ¼, close blow down v/v first, then close ship side cock. Ship side v/vs are usually non-return or one more n-r v/v fitted before ship side cock.
BOILER PROBLEMS 1. SCALES 2.CORROSION 3. SLUDGE 4.PRIMING 5. FOAMING 6. CARRY OVER . 1. SCALES
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Dissolved alkaline ( temporary hardness) decompose by heat and become (permanent hardness). Then stick on heating surfaces and become scale. SCALE r educe heat transfer & boiler efficiency. Tubes over heat& damage.
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Oxidation / Reduction Reaction If a metal meet acid or alkaline, become oxidized. Iron is more ready to dissolve in acid. Iron can corrode even in pure water(condensate) High chloride show s.w leak to boiler and get corrosion.
3. SLUDGE --Combination of suspended materials in water (loose corrosion products, insoluble mineral precipitates & oil), baked on heat surfaces and become insulation. To prevent Make sludge down to bottom by (Liquid Coagulant) and blow down. 4. PRIMING Surface suddenly rise by expansion large amount of water. 5. FOAMING Thick bubbles form on water surface, due to oil, organic substances and high amount of total dissolved solids (TDS) in water. 6. CARRY OVER Water carry with steam, by rapid opening steam stop v/v or high water level in boiler. Effecting water hammer, contaminate and scaling in steam lines, loss of water. –
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BOILER WATER TESTS 1.Excess phosphate test or hardness test . 2.Phenolphthalein alkalinity test 3.Total alkalinity test or pH test 4.Chloride test 5.Hydrazine test
WHY BOILER WATER TEST AND TREAT •
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By Test--- Know condition in boiler, dose, blow down. By treat---(1) Remove scale forming particles (2) Maintain alkaline condition to prevent corrosion (3) Improve boiler efficiency.(4) Remove suspended solids & dissolved oxygen. # Taken while boiler is in operation # Before taking blow off salinometer valve to clear scales . SAMPLING
If test Alkalinity, no need pH test. pH is tested with litmus, maintain pH11. If test excess phosphate, no need hardness test. Hardness is tested with soap solution. One shot water treatment (DREW AKG 100) is enough for LP boiler.
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FEED WATER TREATMENT To reduce TDS, use evaporated water To arrest suspended solids (use feed line filter) to prevent feed system corrosion (maintain correct pH of feed water by GC) To reduce dissolved O2 (dose Amerzine and maintain hot well temp. 60~70C to promote de aeration of hot well)
