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BOILER AUXILIRIES

boilers are important part of mechanical engineering

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BOILER AUXILIRIES

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  1. BOILER'S AUXILIARIES

  2. SEQUENCE OF PRESENTATION BOILER AUXILIARIES BOILER MOUNTINGS SAFETY VALVES

  3. BOILER AUXILIARIES: These are the devices incorporated in the boiler circuit to boost up the efficiency and performance of the steam generation plant and assist in the systematic & adequate operation of the boiler unit for prolonged period.

  4. Whats are they: Usually a boiler is fitted with the following auxiliaries (Accessories): i) Super heater. ii) De-super heater. iii) Economizer. iv) Air pre heater. v) Boiler feed pumps. vi) Forced draft & induced draft fans. vii) Mechanical Separator. Continued..

  5. viii) Equipment tanks: a) Feed Water Tank. b) Deaerator c) Continuous blow down expender d) Drainage expender. ix) Chemical Dozing system x) Soot blowers & wall blowers xi) Pressure reducing valve xii) Pulverizes and fuel firing system xiii) Ash handling system.

  6. SUPER HEATER: It is a boiler auxiliary designed to super heat saturated steam produced in the evaporator to a specified temperature.

  7. CLASSIFICATION SUPER HEATER: Depending on the mode of heat transfer from the furnace to super heat surfaces, the super heaters and divided into: • CONVECTIVE SUPER HEATERS • RADIANT SUPER HEATERS • PLATEN SUPER HEATERS

  8. a) CONVECTIVE SUPER HEATER Which absorb heat mainly by convention. They are placed in the convective gas duct. b) RADIANT SUPER HEATER Which absorb radiant heat from the flame in the furnace core. c) PLATEN SUPER HEATER That absorb both radiant & convective heat. These are mounted on the top of the furnace & partially in the flue gas duct between the convective & radios of heating surface.

  9. KINDS OF SUPER HEATERS DEPLOYED • PRIMARY SUPER HEATER • INTERMEDIATE SUPER HEATER

  10. 1. PRIMARY SUPER HEATER To super heat the saturated steam produced in the evaporator. 2. INTERMEDIATE SUPER HEATER It is to re-heat the turbine exhaust steam to a super heat temperature once more. Intermediate super heaters are also called re-heaters.

  11. SUPER HEATING Production of steam at a temperature higher than the saturation temperature is called super heating. DEGREE OF SUPER HEATING It is the temperature imparted to steam above its saturation temperature at a given pressure.

  12. HOW CAN THE CONDITION OF SUPER HEAT BE EXPRESSED This can be done in two ways. 1. In term of Degree of super heater for a given pressure. 2. The actual temperature & pressure of the steam.

  13. WHEN DOES THE SIGNIFICANCE OF THE TERM SUPER HEAT FAILS At steam pressure above the critical point, because beyond this point no saturation steam exists. So that term super heat is no longer applicable.

  14. WHY IS SUPER HEATED STEAM LESS EROSIVE & CORROSIVE THEN WET, SATUARTED STEAM Wet saturated steam carries water droplets, but super heater steam has no entrained moisture and as such the latter is less erosive & corrosive than the former.

  15. DE SUPPER HEATER • De Supper is installed with supper heater mainly due to: • To control the super heated steam temperature by injecting DM water to supper heater steam. • to produce saturated steam to run the boiler auxiliaries

  16. ECONOMOZER This is the heat recovery equipment that pick up heat from the combustion product of a boiler furnace to heat up the boiler feed water

  17. PURPOSE OF INSTALLATION-ECONOMIZER Forming essential parts of a complete system of steam generating unit, this is installed to conserve as much heat of fuel combustion in the boiler furnace as is possible and to increase the capacity of a boiler or decrease the size of prospective boiler for a stipulated output. The fundamental basis of its installations is to reduce the steam out put cost.

  18. BOILER FEED PUMP • A pump that feeds boiler water (polished water) to the steam drum via the economizer. • Important criteria of a boiler feed pump • It must be absolutely positive & reliable under all variable operating conditions • KINDS OF BOILER FEED PUMP • A) a direct acting pump driven by its own cylinders • B) a reciprocal pump driven by a motor or betters to the machinery • C) a centrifugal pump turbo driven or electrically driven by motor.

  19. DIRECT ACTING PUMP CLASSIFICATION • These may be classified as simplex, duplex and triplex pumps. • The simplex pump has one engine cylinder • In duplex and triplex pumps there are two and three pump cylinders respectively.

  20. KIND OF RECIPROCATINGPUMPs • Both plunger driven and piston driven. • NOTE Among the three kind of pumps we will prefer centrifugal pump as boiler feed pump due to following reasons. • Delivery study flow of BFW • Supplying the largest quantity of boiler feed water under a given head. • Accepting load variation most easily. • Trouble free and smooth operation, less floor space is required and maintenance cost is low.

  21. PURPOSE OF INSTALLATION OF BOTH TURBO DRIVEN & MOTOR DRIVEN CENTRIFUGAL PUMPS • During start up, the motor driven pumps are lined up to establish circulation. • When the unit is in full operation and steam is available, one or two turbo driven pumps may be lined up to spare corresponding number (s) of motor driven pumps for reserve, rest, repairing or saving of electricity which is costlier than steam. Motor driven pumps will continue to circulate BFP through the boiler unit when the latter trips. • Turbo driven pump is always prefer due to steam is cheaper than electricity.

  22. AIR PRE-HEATERS Flue gas–to-air heat exchanger installed in the flue gas stream leaving the boiler and the combustion air stream entering the boiler are called air pre heaters. They are used to transfer heat from the boiler flue gas to the combustion air. Boiler efficiency is improved at all loads because the flue gas temperature is reduced. An additional benefit may be the potential for reducing excess air by using pre heated combustion air.

  23. TYPES OF AIR PRE-HEATERS There are three general types of air pre-heater: • Tubular Air Preheater. • Rotary Regenerative Air Preheater. • Heat Pipe Air Preheater.

  24. 1. TUBULAR AIR PREHEATER The arrangements of a tubular air preheater with flue gas flowing through the tubes and air flowing around the tubes. In this design the tubes act as a solid barrier between the flue gas and the combustion air. 2. ROTARY RE GENERATIVE AIR PREHEATER In this exchanger the heating surface are heated in the flue gas stream and rotate into the air stream where the heat is given up. A disadvantage of this type is air leaking through the seals into the flue gas. Due to its compact size and flexible installation arrangement, such an air preheater usually is easier to add to an existing boiler than a tubular air preheater. 3. HEAT PIPE AIR PREHEATER This exchanger uses heat pipes partially filled with a heater transfer vaporizing fluid and is a relatively new development.

  25. BLOW DOWN AND DEAERATOR VENT RECOVERY The blowdown water is admitted to the blowdown flash tank. The heat in the water causes some of the water to flash into low pressure steam. The steam then is used to heat feed water in the deaerating heater, which returns the heat to the boiler. This recovers approximately 50% of the heat in the blowdown water. The water remaining in the blowdown flash tank then is cooled further in a heat exchanger called a blowdown cooler. This heat exchanger generally is used to heat feed water before it enters the deaerating heater , thus returning the heat to the boiler. The cooled blowdown water with a high concentration of water chemicals then is discharged to the sewer. Using this type of heat exchanger recovers approximately another 25 percent of the heat from the boiler blowdown.

  26. BOILER MOUNTINGS • Safety and Relief Valves • Low-water Cut-offs • Water Feeders • Water gages • Try Cocks

  27. 1. SAFETY AND RELIEF VALVES It is necessary to provide a positive protective device on the boiler to prevent the pressure from exeeding that for which the vessel was designed. Such automatic firing devices includes the following: POP SAFETY VALVE When the pressure reaches a predetermined point, the valve pops wide open and tays open untill the pressure drops. SAFETY RELIEF VALVES When the pressure reaches a predetermined point, the valve opens slightly to pass some liquid, on further pressure rise, the valve pops wide open. PRESSURE & TEMPERATURE RELIEF VALVE When the pressure reaches a predetermined point, or if the temp. approaches the boiling point, either the valve opens or a fusible element melts.

  28. 2. LOW-WATER CUT-OFFS All automatically fired steam boilers are required to have a low-water cut-off, which will prevent operation of the fuel burner unless there is adequate water in the boiler. Many hot water boilers are also equipped with low-water. A typical unit consists a float-operated switch. The cut-off, may be incorporated into the water column, or the float may also be included. All units have a blow-off valve for periodic flusing of collected sediment. 2. WATER FEEDERRS The customary practice is to feed water to the boiler automatically whenever, the water level drops to a predetermined point. At pressure blow 250 PSIG, a float operated valve is often used, usually in combination with the low-water cut-off. At higher pressures, it is comes necessary to depend upon the expansion of a pipe (from contact with steam) to operate the device. Some combination low-water cut-off and water feeder units are of the electrode type, passing electricity through the boiler water.

  29. 3. WATER GAGES All steam boilers are fitted with a water gage permitting visual determination of the quantity of water in the boiler. The design of these gages varies with the pressure to which they are subjected. They are fitted with shut-off valves (some types work automatically if the glass breaks) and drain cocks. 4. TRY COCKS Valves are provided at three elevations of the gage glass, allowing the operator to determine if the water level in the boiler agrees with the gage glass indication.

  30. AUXILIARY EQUIPMENT • Blowdown • Instrumentation • Soot-blowers • Boiler Piping • Feed Water Injection • Whistles • Feed Water Treatment • Feed Water Injection

  31. 1. BLOWDOWN In Boiler requiring quantities of makeup water, there will be a gradual increase in the concentration of sediment and soluble salts in the boiler water unless the feed-water is treated sufficiently to remove all traces of hardness. This material is removed by blow-down, which may be periodic or continuous. The hot water will flash into steam as the pressure is relived. It is customary to condense this steam and cool the blowdown water prior to discharge to the sewer. With continuous blow-down, it is feasible to use the process to provide some heat to the feed water. 2. INSTRUMENTATION Steam boilers are required to have a steam pressure gage and a thermometer. Other instrumentation may include a makeup water meter, steam flow meter, flue gas thermometer, and other recording or indicating instruments. Large installation have elaborate automatic controls for the economizer, feed water treatment, feed water heater, de-super heater, and air heater, as well as the steam pressure and temperature control.

  32. 3. SOOT BLOWERS The fireside passage of the boiler have a tendency to collect soot and fly ash. Special steam or air lances, permanently installed, are used to dislodge these combustion products. 4. BOILER PIPING It is necessary, of course, to remove the steam or hot water form the boiler. The connecting piping, as well as the inter connecting piping to the super heater and economizer, must have adequate provisions for expansion without subjecting the boiler components to strain.

  33. DEAERATION AND DEOXYGENATION • DEAERATION Dearation is the process of removing dissolved corrosive gases (Oxygen & Carbon mono dioxide) This process is also called degasification. Dearation is a thermal process, water heated to bring about degasification. DEOXYGENATION It is the process of removal of only oxygen. deoxygenation is carried out mainly by chemical techniques.

  34. TYPES OF DEARATORS Types working pressure • Vacuum dearator 0.116 MN/m2 • Atmosphere dearator 0.12-0.17MN/m2 • High pressure dearator 0.17-0.7MN/m2

  35. VACUUM DEARATOR • Deaeration is carried out in vacuum at a pressure less than atmospheric pressure APPLICATIONS Low capacity, low pressure boiler, requiring water at a temperature less than 373K

  36. ATMOSPHERIC DEAERATOR • Atmospheric deaerator can be divided into direct contact ( mixing) deaerator and over heated water deaerators

  37. FUNCTION OF DIRECT –CONTACT DEAERATORS • They consists of a deaerator column fitted on top of the storage tank • The deaerator column is hollow cylindrical vessel provided with a) Perforated, horizontal trays arranged one above the other. b) Water distribution direct at the top c) Steam distribution at the bottom

  38. FUNCTION OF DIRECT –CONTACT DEAERATORS • Feed water enters the deaerator from the top and is evenly distributed by means of the distributing device into the perforated trays fitted at the bottom. Water fills the perforations ( dia5-7mm) and rain down and comes in contact with heating steam delivered into the lower portion of the deaerator columns through the steam distributor. As a result of heat exchange between the steam going up and the feed water stream flowing down, the water gets heated upto its boiling points and the gases( O2 and CO2) dissolved in it or transfer to the gas face. These gases together with non-condensing vapour are vented into the atmosphere through a vent valve or pass into a vent condenser where the steam is condensed and the O2 and Co2 are vented. • The deaerated water is collected in the storage tank which is fitted with gauge glass, pressure gauge and hydraulic seals to avoid the formation of high pressure or vacuum in the deaerator

  39. TYPE OF DEAERATORS IN ACCORDANCE WITH THE MODE OF STEAM WATER DISTRIBUTION • Automizing deaerator • Tray type deaerator • Film type deaerator

  40. CONDITION FOR SUCCESS OPERATION OF THE DEAERATOR • The temperature of deaerated water must be equal to the saturation temperature of water corresponding to the pressure at which the deaerator operates. • Sufficient heating steam must be delivered to the deaerator to ensure continuous boiling of water undergoing deaeration. • The feed water charged to the deaerator must be disintegrated into fine droplets to ensure better heat transfer between the heating steam and feed water. Hence perforated trays find widest application. • The deaerator must be provided with sufficient venting to purge all the non-condensing gases out of the system and to ensure minimum partial pressures of these gases in the upper part of the deaerator. • If two or more deaerator are operated in parallel, all must be operated at same pressure.

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