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Steam generator part 1

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Try to explain about the steam generator (boiler), it has three parts. Part 1 cover the types, part 2 about its parts & auxiliaries & accessories and part 3 about performance.

Try to explain about the steam generator (boiler), it has three parts. Part 1 cover the types, part 2 about its parts & auxiliaries & accessories and part 3 about performance.

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  • Taking full advantage of the steam utility depends on a thorough understanding of its potential and properties. The more you know, the greater the benefit you'll enjoy. To say it another way, the more you know about steam and how to control and use it, the greater the return on the investment in a steam system.The first few lessons of steam basics are intended to ground you on the basics of steam. So let's start where every well designed lesson should begin: at ground zero.
  • In 200 B.C., a Greek named Hero designed a simple machine that used steam as a power source (Fig. 1).He began with a cauldron of water, placed above an open fire. As the fire heated the cauldron, the cauldron shell transferred the heat to the water. When the water reached the boiling point of 212F (100C), it changed form and turned into steam. The steam passed through two pipes into a hollow sphere, which was pivoted at both sides. As the steam escaped through two tubes attached to the sphere, each bent at an angle, the sphere moved, rotating on its axis.It is a closed vessel in which water is firstly heated, then vaporized & finally converted into steam.The pressure at which steam generated is always higher than the atmospheric pressure.The energy which is used to produced steam is “Heat Energy” & it is measured in calorie.
  • This is a schematic overview of a boiler room:As you can see, the boiler system comprises of a feed water system; a steam system as well as a fuel systemThe feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and repair. The water supplied to the boiler that is converted into steam is called feed water. The two sources of feed water are:(1) Condensate or condensed steam returned from the processes and(2) Makeup water (treated raw water) which must come from outside the boiler room and plant processes. For higher boiler efficiencies, an economizer preheats the feed water using the waste heat in the flue gas. The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system.
  • There are different types of boilers based on different fuels and with various capacities. What type of boilers do you know of? What kind of boilers do you use in the industry where you work? We will look closer at the following types of boilers: Fire Tube Boiler, Water Tube Boiler, Packaged Boiler, Fluidized Bed Boiler, Stoker Fired Boiler, Pulverized Fuel Boiler and Waste Heat Boiler.
  • Cylindrical shell: The shell is vertical and it attached to the bottom of the furnace. Greater portion of the shell is full of water which surrounds the furnace also. Remaining portion is steam space. The shell may be of about 1.25 metres diameter and 2.0 meters height.Cross-tubes: One or more cross tubes are either riveted or flanged to the furnace to increase the heating surface and to improve the water circulation.Furnace (or fire box): Combustion of coal takes place in the furnace (fire box).Grate: It is placed at the bottom of fire box and coal is fed on it for burning.Fire door: Coal is fed to the grate through the fire door.Chimney (or stack): The chimney (stack) passes from the top of the firebox through the top of the shell.Manhole: It is provided on the top of the shell to enable a man to enter into it and inspect and repair the boiler from inside it. It is also, meant for cleaning the interior of the boiler shell and exterior of the combustion chamber and stack (chimney).Hand holes: These are provided in the shell opposite to the ends of each cross tube for cleaning the cross tube.Ashipt: It is provide for collecting the ash deposit, which can be removed away at intervals.Working: The fuel (coal) is fed into the grate through the fire hole and is burnt. The ashpit placed below the grate collect the ashes of the burning fuel.The combustion gas flows from the furnace, passes around the cross tubes and escapes to the atmosphere through the chimney.Water goes by natural circulation due to convection currents, from the lower end of the cross tube and comes out from the higher end.The working pressure of the simple vertical boiler does not exceed 70 N/cm^2.
  • Shell; It is hemispherical on the top, where space is provided for steam.Grate; It is at the bottom of the furnace where coal is burnt.Fire box (furnace );It is also dome-shaped like the shell so that the gases can be deflected back till they are passed out through the flue pipe to the combustion chamber.Flue pipe: It is a short passage connecting the fire box with the combustion chamber.Fire tubes: A number of horizontal fire tubes are provided, thereby the heating surface is increased.Combustion chamber: It is lined with fire bricks on the side of the shell to prevent overheating of the boiler. Hot gases enter the fire tubes from the flue pipe through the combustion chamber.Chimney: It is provided for the exit of the flue gases to the atmosphere from the smoke box.Manhole: It is provided for inspection and repair of the interior of the boiler shell.Normal size of a Cochran boiler:Shell diameter – 2.75 meters:Height of the shell – 6 meters.Working of the Cochran boiler: Coal is fed into the grate through the fire hole and burnt. Ash formed during burning is collected in the ashpit provided just below the grate and then it is removed manually.The host gases from the grate pass through the flue pipe to the combustion chamber. The hot gases from the combustion chamber flow through the horizontal fire tubes and transfer the heat to the water by convection.The flue gases coming out of fire tubes pass through the smoke box and are exhausted to the atmosphere through the chimney.Smoke box is provided with a door for cleaning the fire tubes and smoke box.The following mountings are fitted to the boiler:Pressure gauge: this indicates the pressure of the steam inside the boiler.Water gauge: this indicates the water level in the boiler. The water level in the boiler should not fall below a particular level, otherwise the boiler will be over heated and the tubes may burn out.Safety valve: the function of the safety valve is to prevent an increase of steam pressure in the boiler above its normal working pressure.Steam stop valve: it regulates the flow of steam supply to requirements.Blow-off cock: it is located at the bottom of the boiler. When the blow-off cock is opened during the running of the boiler, the high pressure steam pushes (drains) out the impurities like mud, sand, etc., in the water collected at the bottom.Fusible plug: it protects the fire tubes from burning when the water level in the boiler falls abnormally low.Salient features of Cochran boiler:The dome shape of the furnace causes the hot gases to deflect back and pass through the flue. The un-burnt fuel if any will also be deflected back.Spherical shape of the top of the shell and the fire box gives higher area by volume ratio.It occupies comparatively less floor area and is very compact.It is well suited for small capacity requirements.
  • Construction of Lancashire Boiler:It consists of Cylindrical shellFurnace tubes, bottom flue and side fluesGrateFire bridgeDampersCylindrical shellIt is placed in horizontal position over a brick work. It is partly filled up with water. The water level inside the shell is well above the furnace tubes.Furnace tubes, bottom flue and side flues:Two large internal furnace tubes (flue tubes) extend from one end to the other end of the shell. The flues are built-up of ordinary brick lined with fire bricks. One bottom flue and two side flues are formed by brick setting, as shown in the figure.Grate; The grate is provided at the front end of the main flue tubes. Coal is fed to the grate through the fire hole.Fire bridge: A brickwork fire bridge is provided at the end of the grate to prevent the flow of coal and ash particles into the interior of the furnace (flue) tubes. Otherwise the coal and ash particles carried with gases form deposits on the interior of the tubes and prevent the heat transfer to the water.Dampers: Dampers is in the form of sliding doors are placed at the end of the side flues to control the flow of gases from side flues to the chimney flue.Working of Lancashire boiler; Coal is fed to the grate through the fire hole and is burnt. The hot gases leaving the grate move along the furnace (flue) tubes upto the back end of the shell and then in the downward direction to the bottom flue. The bottom of the shell is thus first heated. The hot gases, passing through the bottom flue, travel upto the front end of the boiler, where they divide into two streams and pass to the side flues. This makes the two sides of the boiler shell to become heated. Passing along the two side flues, the hot gases travel upto the back end of the boiler to the chimney flue. They are then discharged into the atmosphere through the chimney. With the help of this arrangement of flow passages of hot gases, the bottom of the shell is first heated and then its sides. The heat is transferred to water through the surface of the two flue tubes (which remain in water) and bottom and sides of the shell. The arrangement of flues increases the heating surface of the boiler to a large extent. Dampers control the flow of hot gases and regulate the combustion rate as well as steam generation rate.The boiler is fitted with necessary mountings. Pressure gauge and water level indicator provided at the front. Safety valve, steam stop valve, low water and high steam safety valve and man-hole are provided on the top of the shell.High steam low water safety valve: It is a combination of two valves. One is lever safety valve, which blows-off steam when the working pressure of steam exceeds. The second valve operates by blowing-off the steam when the water level falls below the normal level.Blow-off clock: It is situated beneath the front portion of the shell for the removal of mud and sediments. It is also used to empty the water in the boiler during inspection.Fusible plug: It is provided on the top of the main flues just above the grate. It prevents the overheating of the boiler tubes by extinguishing the fire when the water level falls below a particular level. A low water level alarm is mounted in the boiler to give a warning when the water level falls below the preset value.Salient features of Lancashire Boiler; The arrangement of flues in this boiler increases the heating surface of shell to a large extent. It is suitable where a large reserve of steam and hot water is needed. Its maintenance is easy.Superheated can be easily incorporated into the system at the end of the main flue tubes. Thus overall efficiency of the boiler can be increased.Note : The simple vertical Boiler, Cochran and Lancashire Boilers discussed till this post are Fire tube boilers. In the upcoming posts, I will write about water tube boilers namely Babcock and Wilcox Boiler.
  • In a water tube boiler, boiler feed water flows through the tubes and enters the boiler drum. The circulated water is heated by the combustion gases and converted into steam at the vapour space in the drum. These boilers are selected when the steam demand as well as steam pressure requirements are high as in the case of process cum power boiler / power boilers.Most modern water boiler tube designs are within the capacity range 4,500 – 120,000 kg/hour of steam, at very high pressures. Many water tube boilers are of “packaged” construction if oil and /or gas are to be used as fuel. Solid fuel fired water tube designs are available but packaged designs are less common. The features of water tube boilers are: Forced, induced and balanced draft provisions help to improve combustion efficiency.Less tolerance for water quality calls for water treatment plant.Higher thermal efficiency levels are possible
  • Steam separator drum; The la Mont boiler consists of a steam separator drum which is placed wholly outside the boiler setting . The drum receives a mixture of steam and water from the evaporator tubes and feed water from the economizer. The steam is separated from water in the drum.Circulating pump; The water from the drum is then drawn to the circulating (centrifugal) pump through the down-comer. The pump circulates water (“forced circulation”) equal to 8 to 10 times the weight of steam evaporated. This prevents the tubes from being overheated.Distributing header; The circulating pump delivers the feed water to the distributing header with orifices at a pressure above the drum pressure.Evaporator; The header distributes water through orifices into the evaporator tubes acting in parallel. Orifice in the header controls the flow of water to the evaporator tubes. Here part of the water is evaporated and a mixture of steam and water from these tubes enters the drum.Convection superheater; The steam produced in the boiler is nearly saturated. This steam as such should not be used in the steam turbine. The presence of moisture in it will cause corrosion of turbine blades, etc. to raise the temperature of steam and thereby to increase the turbine efficiency, superheater is used.The principle of convection superheater is similar to steam generating tubes of the boiler. The hot flue gases at high temperature sweep over convection superheated tubes and raise the temperature of steam. Convection superheater thus receives heat from the flue gases flowing from the combustion chamber, entirely by convective heat transfer. Such a superheater may be more conveniently located since it is not necessary for it to “see” the furnace.Saturated steam from the top of the drum enters the convection superheater placed in the path of the flue gases and is superheated.Steam outlet; Superheated steam from the superheater passes out to the steam turbine through the steam outlet.Economizer; The quantity of superheated steam thus delivered to turbine is continuously made up in the form of feed water. Feed water supplied by the feed pump is heated in the economizer on its way to the steam separator drum.The economizer is a device used to preheat the feed water using the hot gases leaving the boiler. Before the gases are let off to the atmosphere, they are made to flow in a definite passage in the economizer so that some of the heat in the hot gases, which otherwise gets wasted, can be used to preheat the feed water. The preheated water requires only a small amount of heat to be supplied in the boiler, resulting in some saving of the fuel burnt. This results in an increase in the boiler efficiency.Air preheater; Since the heat of the exit gases cannot be fully extracted through the economizer, the air preheater is employed to recover some of the heat escaping in these gases. These exit gases preheat the air from the blower in the air preheater. The preheated air is supplied to the furnace for combustion.Capacity; The capacity of la-mont boiler is about 50 Tonnes/hr of superheated steam at a pressure of 170 kgf/sq.cm. and at a temperature of 500’C.
  • The major difficulty experienced in La-Mont boiler is deposition of salt and sediment on the inner surfaces of water tubes. The deposition reduces the heat transfer, ultimately, the generating capacity. This difficulty was solved in Loeffler boiler by preventing the flow of water into the boiler tubes. Feed water is evaporated in the drum using part of the superheated steam coming out from the water-heater. Thus only the dry saturated steam passes through the tubes. Poor feed water can, therefore, be used without any difficulty in the boiler, which is great advantage of this boiler.Working principle of Loeffler Boiler; The image shows the outline diagram of Loeffler Boiler.Economiser; The feed water from the feed tank is supplied to the economiser by feed pump. In the economiser the feed water is made to flow through a number of tubes surrounding which the hot gases leaving the furnace pass over. There is a heat exchange from the hot gases to the feed water, which is preheated in the economiser.Evaporated Drum; It is housed away from the furnace. It contains a mixture of steam and water. The feed water from the economiser tubes enters the evaporator drum into which is also passed two-thirds of the superheated steam generated by the boiler. The superheated steam gives its superheat to the water in the drum and evaporates it to saturated steam.Mixing Nozzles; The nozzles distribute and mix the superheated steam throughout the water in the evaporator drum.Steam circulating pump; A steam circulating pump forces this saturated steam from the evaporator drum to the radiant superheater through the tube of the furnace wall.Radiant superheater; The radiant superheater is placed in the furnace. The hot gases in the furnace are used for superheating the saturated steam from the drum. The radiant superheater receives heat from the burning fuel through radiation process.Convection superheater; Steam from the radiant superheater enters the convection superheater where it is finally heated to the desired temperature of 500’C. The convection superheater receives heat from the flue gases entirely by convective heat transfer. Both radiant and convection superheater are arranged in series in the path of the flue gases.Steam outlet; About one-third of the superheated steam from the convection superheater passes to the steam turbine while the remaining two-thirds is passed on to evaporator drum to evaporated the feed water to saturated steam.Capacity; Capacity of the Loeffler boiler is about 100 Tonnes/Hr of superheated steam generated at a pressure of 140 kgf/sq.cm and at a temperature of 500’C.
  • Working of Benson boilerFeed water passes through economizer to water cooled walls of the furnace.Water receives heat by radiation ,the temperature rises to critical temperature.It then enters the evaporator and may get superheated to some degrees.Finally passed through the superheater to obtain desired superheated steam.The Benson boiler usually consists of small diameter tubes (ca. 25 mm bore) spirally wound to form the furnace envelope. Feed water enters the bottom of the furnace at high sub-critical or supercritical pressure and is evaporated to high quality in the spiral section. A balancing header is commonly provided near the top of the furnace to alleviate any differences in steam quality resulting from variations in heat absorption in different parallel spiral circuits before the steam/water mixture is introduced to the open boiler pass. Here, it is superheated in the upper parts of the furnace envelope and subsequently in pendant tube banks. The balancing header also serves as a means of separating excess liquid when, at low loads, the furnace flow rate exceeds the steam demand from the boiler as a whole. As in other forms of Fossil Fuel-Fired Boilers, the flue gasses are used for reheat, economizer and air-heating duties.Along with other types of Once-Through Boiler, the convective heating surfaces may be mounted either in a vertical up-pass above the furnace (a tower boiler) or in a horizontal and vertical down-pass behind the furnace (a two-pass boiler). Illustrations of both types appear in the article on Once-Through Boilers.Advantages of Benson boiler1- Steam is directly obtained without boiling. 2- Initial cost is low, as there is no water and steam drum. 3- Since there is no limit ,thus supercritical pressure may be employed. 4- Quick start ( within 15 min.) and increased heat transfer rate. 5- Light in weight. 6- Thermal efficiency 90%. Modern applications of Benson boilerThe steam produced may be supplied :To an external combustion engine ,i.e., a steam engine and turbine.As a high pressured steam is a good source of energy it can be also used.At low pressure used in many industries like cotton mills, sugar factories, breweries, etc.Used for producing hot water further used for heat installation at low pressure.
  • The Babcock & Wilcox boiler is built in two general classes, the longitudinal drum type and the cross drum type. Either of these designs may be constructed with vertical or inclined headers, and the headers in turn may be of wrought steel or cast iron dependent upon the working pressure for which the boiler is constructed. The headers may be of different lengths, that is, may connect different numbers of tubes, and it is by a change in the number of tubes in height per section and the number of sections in width that the size of the boiler is varied.The longitudinal drum boiler is the generally accepted standard of Babcock & Wilcox construction. The cross drum boiler, though originally designed to meet certain conditions of headroom, has become popular for numerous classes of work where low headroom is not a requirement which must be met.
  • Does anyone recognize what type of boiler this is? This is a packaged boiler. More specifically, it is a typical 3 pass, oil fired packaged boiler.The packaged boiler is so called because it comes as a complete package. Once delivered to a site, it requires only the steam, water pipe work, fuel supply and electrical connections to be made to become operational. Package boilers are generally of a shell type with a fire tube design so as to achieve high heat transfer rates by both radiation and convection. The features of packaged boilers are: Small combustion space and high heat release rate resulting in faster evaporation. Large number of small diameter tubes leading to good convective heat transfer. Forced or induced draft systems resulting in good combustion efficiency. Number of passes resulting in better overall heat transfer. Higher thermal efficiency levels compared with other boilers. These boilers are classified based on the number of passes - the number of times the hot combustion gases pass through the boiler.
  • Boilers are occasionally distinguished by their method of fabrication. Packaged boilers are assembled in a factory, mounted on a skid, and transported to the site as one package, ready for hookup to auxiliary piping. The features of packaged boilers are: * Small combustion space and high heat release rate resulting in faster evaporation. • Large number of small diameter tubes leading to good convective heat transfer. • Forced or induced draft systems resulting in good combustion efficiency. • A number of passes resulting in better overall heat transfer. • Higher thermal efficiency levels compared with other boilers.
  • “D” type boilers have the most flexible design. They have a single steam drum and a single mud drum, vertically aligned. The boiler tubes extend to one side of each drum. “D” type boilers generally have more tube surface exposed to the radiant heat than do other designs. “Package boilers” as opposed to “field-erected” units generally have significantly shorter fireboxes and frequently have very high heat transfer rates (250,000 btu per hour per sq foot). For this reason it is important to ensure high-quality boiler feedwater and to chemically treat the systems properly. Maintenance of burners and diffuser plates to minimize the potential for flame impingement is critical.
  • “O” design boilers have a single steam drum and a single mud drum. The drums are directly aligned vertically with each other, and have a roughly symmetrical arrangement of riser tubes. Circulation is more easily controlled, and the larger mud drum design renders the boilers less prone to starvation due to flow blockage, although burner alignment and other factors can impact circulation
  • Fluidized bed combustion has emerged as a viable alternative and has significant advantages over conventional firing system and offers multiple benefits – compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx and NOx. The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse & other agricultural wastes. The fluidized bed boilers have a wide capacity range.
  • With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface. The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid – “bubbling fluidized bed”. At higher velocities, bubbles disappear, and particles are blown out of the bed. Therefore, some amounts of particles have to be recirculated to maintain a stable system – “circulating fluidised bed”. Fluidization depends largely on the particle size and the air velocity.If sand particles in a fluidized state is heated to the ignition temperatures of coal, and coal is injected continuously into the bed, the coal will burn rapidly and bed attains a uniform temperature. The fluidized bed combustion (FBC) takes place at about 840OC to 950OC. Since limestone is used as particle bed, control of sulfur dioxide and nitrogen oxide emissions in the combustion chamber is achieved without any additional control equipment. This is one of the major advantages over conventional boilers. Since this temperature is much below the ash fusion temperature, melting of ash and associated problems are avoided. The lower combustion temperature is achieved because of high coefficient of heat transfer due to rapid mixing in the fluidized bed and effective extraction of heat from the bed through in-bed heat transfer tubes and walls of the bed. The gas velocity is maintained between minimum fluidisation velocity and particle entrainment velocity. This ensures stable operation of the bed and avoids particle entrainment in the gas stream.
  • In AFBC, coal is crushed to a size of 1 – 10 mm depending on the rank of coal, type of fuel feed and fed into the combustion chamber. The atmospheric air, which acts as both the fluidization air and combustion air, is delivered at a pressure and flows through the bed after being preheated by the exhaust flue gases. The velocity of fluidising air is in the range of 1.2 to 3.7 m /sec. The rate at which air is blown through the bed determines the amount of fuel that can be reacted. Almost all AFBC/ bubbling bed boilers use in-bed evaporator tubes in the bed of limestone, sand and fuel for extracting the heat from the bed to maintain the bed temperature. The bed depth is usually 0.9 m to 1.5 m deep and the pressure drop averages about 1 inch of water per inch of bed depth. Very little material leaves the bubbling bed – only about 2 to 4 kg of solids are recycled per ton of fuel burned.
  • Most operational boiler of this type is of the Atmospheric Fluidized Bed Combustion. (AFBC). In this boiler, atmospheric air, which acts as both the fluidization and combustion air, is delivered at a pressure, after being preheated by the exhaust fuel gases.In Pressurized Fluidized Bed Combustion (PFBC) type, a compressor supplies the Forced Draft (FD) air and the combustor is a pressure vessel. A deep bed is used to extract large amounts of heat. This will improve the combustion efficiency and sulphur dioxide absorption in the bed. The steam is generated in the two tube bundles, one in the bed and one above it. Hot flue gases drive a power generating gas turbine. The PFBC system can be used for cogeneration (steam and electricity) or combined cycle power generationWhen an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream – the bed is called “fluidized”. With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface. The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid – “bubbling fluidized bed”.The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse & other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr.The fluidized bed combustion (FBC) takes place at about 840oC to 950oC. Fluidized bed combustion (FBC) has emerged as a viable alternative and has significant advantages over a conventional firing system and offers multiple benefits – compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx and NOx. Three types of FBC boilers are explained on the next slides.
  • Advanced PFBC; A 1½ generation PFBC system increases the gas turbine firing temperature by using natural gas in addition to the vitiated air from the PFB combustor. This mixture is burned in a topping combustor to provide higher inlet temperatures for greater combined cycle efficiency. However, this uses natural gas, usually a higher priced fuel than coal.APFBC. In more advanced second-generation PFBC systems, a pressurized carbonizer is incorporated to process the feed coal into fuel gas and char. The PFBC burns the char to produce steam and to heat combustion air for the gas turbine. The fuel gas from the carbonizer burns in a topping combustor linked to a gas turbine, heating the gases to the combustion turbine's rated firing temperature. Heat is recovered from the gas turbine exhaust in order to produce steam, which is used to drive a conventional steam turbine, resulting in a higher overall efficiency for the combined cycle power output. These systems are also called APFBC, or advanced circulating pressurized fluidized-bed combustion combined cycle systems. An APFBC system is entirely coal-fueled.GFBCC. Gasification fluidized-bed combustion combined cycle systems, GFBCC, have a pressurized circulating fluidized-bed (PCFB) partial gasifier feeding fuel syngas to the gas turbine topping combustor. The gas turbine exhaust supplies combustion air for the atmospheric circulating fluidized-bed combustor that burns the char from the PCFB partial gasifier.CHIPPS. A CHIPPS system is similar, but uses a furnace instead of an atmospheric fluidized-bed combustor. It also has gas turbine air preheater tubes to increase gas turbine cycle efficiency. CHIPPS stands for combustion-based high performance power system.
  • This figure illustrates another type of fluidized bed combustion, the atmospheric circulating fluidized bed combustion boiler.In a circulating system the bed parameters are maintained to promote solids elutriation from the bed. They are lifted in a relatively dilute phase in a solids riser, and a down-comer with a cyclone provides a return path for the solids. There are no steam generation tubes immersed in the bed. Generation and super heating of steam takes place in the convection section, water walls, at the exit of the riser. Benefits: CFBC boilers are generally more economical than AFBC boilers for industrial application requiring more than 75 – 100 T/hr of steam. For large units, the taller furnace characteristics of CFBC boilers offers better space utilization, greater fuel particle and sorbent residence time for efficient combustion and SO2 capture, and easier application of staged combustion techniques for NOx control than AFBC steam generators.
  • For large units, the taller furnace characteristics of CFBC boiler offers better space utilization, greater fuel particle and sorbent residence time for efficient combustion and SO2 capture, and easier application of staged combustion techniques for NOx control than AFBC generators. CFBC boilers are said to achieve better calcium to sulphur utilization – 1.5 to 1 vs. 3.2 to 1 for the AFBC boilers, although the furnace temperatures are almost the same. CFBC boilers are generally claimed to be more economical than AFBC boilers for industrial application requiring more than 75 – 100 T/hr of steam CFBC requires huge mechanical cyclones to capture and recycle the large amount of bed material, which requires a tall boiler. A CFBC could be good choice if the following conditions are met. 1. Capacity of boiler is large to medium 2.Sulphur emission and NOx control is important 3.The boiler is required to fire low-grade fuel or fuel with highly fluctuating fuel quality.
  • Circulating bed boiler (At a Glance)-At high fluidizing gas velocities in which a fast recycling bed of fine material is superimposed on a bubbling bed of larger particles. The combustion temperature is controlled by rate of recycling of fine material. Hot fine material is separated from the flue gas by a cyclone and is partially cooled in a separate low velocity fluidized bed heat exchanger, where the heat is given up to the steam. The cooler fine material is then recycled to the dense bed.
  • This turbulent mixing of air and fuel results in a residence time of up to five seconds. The combination of turbulent mixing and residence time permits bubbling bed boilers to operate at a furnace temperature below 1650°F. At this temperature, the presence of limestone mixed with fuel in the furnace achieves greater than 90% sulfur removal. Boiler efficiency is the percentage of total energy in the fuel that is used to produce steam. Combustion efficiency is the percentage of complete combustion of carbon in the fuel.Incomplete combustion results in the formation of carbon monoxide (CO) plus unburned carbon in the solid particles leaving the furnace. In a typical bubbling bed fluidized boiler, combustion efficiency can be as high as 92%. This is a good figure, but is lower than that achieved by pulverized coal or cyclone-fired boilers. In addition, some fuels that are very low in volatile matter cannot be completely burned within the available residence time in bubbling bed-type boilers.
  • To begin with we will look at spreader stokers. These stokers utilize a combination of suspension burning and grate burning.Spreader stokers utilize a combination of suspension burning and grate burning. The coal is continually fed into the furnace above a burning bed of coal. The coal fines are burned in suspension; the larger particles fall to the grate, where they are burned in a thin, fast-burning coal bed. This method of firing provides good flexibility to meet load fluctuations, since ignition is almost instantaneous when the firing rate is increased. Due to this, the spreader stoker is favored over other types of stokers in many industrial applications.
  • This picture illustrates a chain grate or traveling grate stoker. Coal is fed onto one end of a moving steel grate. As the grate moves along the length of the furnace, the coal burns before dropping off at the end as ash. The coal-feed hopper runs along the entire coal-feed end of the furnace. A coal gate is used to control the rate at which coal is fed into the furnace by controlling the thickness of the fuel bed. Coal must be uniform in size as large lumps will not burn out completely by the time they reach the end of the grate.
  • The coal is pulverized to a fine powder until less than 2% of the coal is +300 micro meter and 70-75% is below 75 microns for bituminous coal. The pulverized coal is then blown with part of the combustion air into the boiler plant through a series of burner nozzles.The combustion takes place at temperatures ranging between 1300-1700 degrees Celsius depending mainly on the coal grade. The particle residence time in the boiler is typically 2 to 5 seconds an dthe particles has to be small enough to be completely combusted during this time period.This system has many advantages such as ability to fire varying quality of coal, quick responses to changes in load, use of high pre-heat air temperatures etc. One of the most popular systems for firing pulverized coal is the tangential firing using four burners corner to corner to create a fireball at the center of the furnace. This is shown in the figure.
  • A waste heat boiler can be economically installed wherever waste heat can be available at medium or high temperatures.Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbine-generator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines.
  • A waste heat boiler can be economically installed wherever waste heat can be available at medium or high temperatures.Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbine-generator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines.
  • A waste heat boiler can be economically installed wherever waste heat can be available at medium or high temperatures.Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbine-generator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines.
  • A waste heat boiler can be economically installed wherever waste heat can be available at medium or high temperatures.Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbine-generator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines.
  • A waste heat boiler can be economically installed wherever waste heat can be available at medium or high temperatures.Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbine-generator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines.
  • A waste heat boiler can be economically installed wherever waste heat can be available at medium or high temperatures.Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbine-generator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines.
  • A waste heat boiler can be economically installed wherever waste heat can be available at medium or high temperatures.Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbine-generator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines.
  • Transcript

    • 1. BOILER Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor Saba Power Plant
    • 2. Steam Generator (Boiler) Hello, I am trying to explain about Steam Generator (Boiler) in this session, due to length of said presentation, I am deciding to divide it in three parts. Part 1 cover the “Introduction & Types of Steam Generator” Part 2 cover about the “Parts of Steam Generator and Its Accessories & Auxiliaries” and Part 3 cover the “Efficiency & Performance” Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor Saba Power Plant
    • 3. BOILER Part 1 Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor Saba Power Plant
    • 4. Steam Fundamentals  Steam is uniquely adapted, by its availability and advantageous properties, for use in industrial and heating processes and in power cycles. The fundamentals of the steam generating process and the core technologies upon which performance and equipment design are based are described in this section Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 5. What is Steam? Steam is an invisible gas that's generated by heating water to a temperature that brings it to the boiling point. When this happens, water changes its physical state and vaporizes, turning from a liquid into a gas. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 6. How the Energy of Steam Is Used The uses for steam are many and varied. Like : 1. Power Generation 2. Industrial Process 3. Heating From the plastic and vinyl components of our automobiles to the paints and stains we use on our homes to the preparation and presentation of the food we eat, steam is used in a variety of ways to make our lives more comfortable and convenient. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 7. What is a Boiler?  A boiler is an enclosed vessel that provides a means for combustion heat to be transferred to water until it becomes heated water or steam. OR  Steam generators, or boilers, use heat to convert water into steam for a variety of applications. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 8. What is a Boiler Capacity  Boiler loads, or the capacity of steam boilers, are often rated in boiler horse powers (BHP), lbs of steam delivered per hour, or BTU.  Large boiler capacities are often given in lbs of steam evaporated per hour under specified steam conditions. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 9. Boiler Capacity Boiler Horsepower - BHP The Boiler Horsepower (BHP) is the amount of energy required to produce 34.5 pounds of steam per hour at a pressure and temperature of 0 Psig and 212 oF, with feed water at 0 Psig and 212 oF. A BHP is equivalent to 33,475 BTU/hr or 8430 Kcal/hr and it should be noted that a boiler horsepower is 13.1547 times a normal horsepower. 1 horsepower (boiler) = 33445.6 Btu (mean)/hr = 140671.6 calorie/min (thermo) = 140469.4 calorie (mean)/min = 140742.3 calorie (20oC)/min 9.8095x1010 erg/sec = 434107 foot-pound-force/min = 13.1548 horsepower (mech) = 13.1495 horsepower (electric) = 13.3372 horsepower (metric) = 13.1487 horsepower (water) = 9809.5 joule/sec = 9.8095 kilowatt Horsepower (hp) can be converted into lbs of steam by multiplying hp with 34.5. or some time called 1 BHP = 33479 Btu/hr Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 10. INTRODUCTION STEAM TO POWER GENERATION, INDUSTRIAL PROCESS & HEATING EXHAUST GAS STACK VENT DEAERATOR BFW PUMPS ECONOMIZER VENT BOILER BURNER BLOW DOWN SEPARATOR WATER SOURCE FUEL BRINE CHEMICAL FEED SOFTENERS Figure: Schematic overview of a boiler room Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 11. Classification Steam Generator Boiler Fuel Fossil, Waste, Nuclear Tube Contain Fire Tube, Water Tube Furnace Natural, Pressurized, Induced, Balance Pressure Method Water of Firing Circulation of Steam Externally, Internally, HRSG Natural, Forced Low, Medium, High Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 12. Classification Fossil Fuel Fuel Waste Heat Nuclear Fuel Waste Fuel Biomass Oil Natural Gas Coal Gas Turbine Exhaust Diesel or Gas Engine Exhaust Uranium Bagasse Fission Rise Husk Wood Pallets Forestry Residues Mill Residues Agricultural Residues Chemical Recovery Fuels Animal Wastes Dry Animal Manure Wet Animal Manure (Dairy Manure Slurry) Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 13. Types of Boilers 1. Fire Tube Boiler 2. Water Tube Boiler 3. Packaged Boiler 4. Fluidized Bed (FBC) Boiler 5. Stoker Fired Boiler 6. Pulverized Fuel Boiler 7. Waste Heat Boiler (HRSG) 8. Nuclear Steam Generating Systems Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 14. CLASSIFICATION BASED ON PRESSURE  Low pressure boiler under 20 kg/cm2.  Medium pressure boiler 20 – 75 kg/cm2.  High pressure boiler over 75 kg/cm2. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 15. Fire Tubes Vs Water Tubes Boilers  Fire tubes boilers has a large volume of water, therefore      more flexible and can meet the sudden demand of steam without much drop of pressure. Fire tubes boiler is rigid and of simple mechanical construction, so greater reliability and low in first cost. Fire tube boilers can be made in smallest sizes therefore simple to fabricate and transport, occupies less floor space but more height. Due to mostly externally fired water tubes boiler so furnace can be altered considerably to meet the fuel requirements. Water tubes boilers are more readily accessible for cleaning, inspection and repairs, compared to the fire tube boilers. Modern trend is in the favors of water tube boiler due to continuous increase in capacities and steam pressures. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 16. FIRE TUBE BOILER Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 17. FIRE TUBE BOILER  Relatively small steam capacities (12,000 kg/hour), 3,500 to 35,000 lbs/hr (120 Bhp – 1,200 Bhp)  Low to medium steam pressures (18 kg/cm2), 350 psig  Operates with oil, gas or solid fuels  Scotch Marine – most popular  Two, three, and four pass designs  Constant pressure with wide load fluctuations Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 18. FIRE TUBE BOILER  Simple Vertical Boiler  Cochran Boiler  Locomotive Boiler  Lancashire Boiler  Cornish Boiler Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 19. FIRE TUBE BOILER Simple Vertical Boiler: The image shows the simplest form of an internally fired vertical fire-tube boiler. It does not require heavy foundation and requires very small floor area. Parts • Cylinder Shell • Cross Tubes • Furnace or Fire Box • Grate • Fire Door • Chimney or Stack • Manhole • Hand Hole • Ash Pit Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 20. FIRE TUBE BOILER Cochran Boiler It is a multi-tubular vertical fire tube boiler having a number of horizontal fire tubes. T is the modification of a simple vertical boiler where the heating surface has been increased by means of a number of fire tubes. Parts • Shell • Crate • Fire box • Flue pipe • Fire tubes • Combustion chamber • Chimney • Man-hole Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 21. FIRE TUBE BOILER Locomotive Boiler Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 22. FIRE TUBE BOILER Locomotive Boiler Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 23. FIRE TUBE BOILER Lancashire Boiler It is a stationary, fire tube, internally fired boiler. The size is approximately from 7-9 meters in length and 2-3 meters in diameter. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 24. FIRE TUBE BOILER Cornish Boiler  It is a similar type of Lancashire boiler in all respects, except there is only one flue tube in Cornish boiler instead of two in Lancashire boiler.  The diameter of Cornish boiler is generally 1m to 2m and its length various from 5m to 7.5m.  The diameter of flue tube may be 0.6 times that of shell. as compared to Lancashire boiler. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 25. WATER TUBE BOILER • La-Mont boiler • Loeffler boiler • Benson boiler • Babcock and Wilcox boiler Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 26. WATER TUBE BOILER  Fuel burned within combustion         chamber Combustion gas surrounds water tubes within vessel Low water content allows rapid steam production Capable of high pressure and superheated steam Preferred ranges are below 3,500 lbs/hr (120 Bhp) and above 35,000 lbs/hr (1,200 Bhp) Capacity range of 4,500 – 120,000 kg/hour Used for high steam demand and pressure requirements Combustion efficiency enhanced by induced draft provisions Lower tolerance for water quality and needs water treatment plant Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 27. WATER TUBE BOILER Water tube boilers are designed to circulate hot combustion gases around the outside of a large number of water filled tubes. The tubes extend between an upper header, called a steam drum, and one or more lower headers or drums. Almost any solid, liquid or gaseous fuel can be burnt in a water tube boiler. Coal-fired water tube boilers are classified into three major categories: stoker fired units, PC fired units and FBC boilers. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 28. WATER TUBE BOILER  Modular Boilers  Array of smaller boilers meet load more effectively without cycling  Improved combustion efficiency  Reduced jacket losses  Fin tube design less durable  Piping and controls important  Mostly for commercial markets Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 29. WATER TUBE BOILER La-Mont boiler A La-Mont boiler is a type of forced circulation watertube boiler in which the boiler water is circulated through an external pump through long closely spaced tubes of small diameter. The mechanical pump is employed to in order to have an adequate and positive circulation in steam and hot water boilers. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 30. WATER TUBE BOILER Loeffler Boiler This is also a modern high pressure water tube boiler using the forced circulation principle and named after Prof. Loeffler. Salient features of Loeffler Boiler The novel feature of the Loeffler Boiler is to evaporate water solely by means of superheated steam. The furnace heat is supplied only to economizer and super heater. In other words, steam is used as a heat absorbing medium. Capacity of the Loeffler boiler is about 100 tones/hr of superheated steam generated at a pressure of 140 kg/sq.cm and at a temperature of 500’C. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 31. WATER TUBE BOILER Benson boiler A Benson boiler is a type of Once-Through Boiler patented by Marc Benson in Germany in 1923.  A high pressure, drum less, water tube steam boiler works on forced circulation.  Feed water enters at one end and discharge superheated steam at the other end.  Feed pump increase pressure of water to supercritical pressure.  Water directly transforms into steam without boiling. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 32. WATER TUBE BOILER Babcock and Wilcox boiler. It is a water tube boiler used in steam power plants. In this, water is circulated inside the tubes and hot gases flow over the tubes. The Babcock & Wilcox boiler is built in two general classes, the longitudinal drum type and the cross drum type. Either of these designs may be constructed with vertical or inclined headers. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 33. WATER TUBE BOILER Babcock and Wilcox boiler. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 34. Packaged Boiler • Comes in complete package • Features • High heat transfer • Faster evaporation • Good convective heat transfer • Good combustion efficiency • High thermal efficiency To Chimney Oil Burner • Classified based on number of passes Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 35. Packaged Boiler All have steam drums for the separation of the steam from the water, and one or more mud drums for the removal of sludge . “A Type”. This design is more susceptible to tube starvation if bottom blows are not performed properly because “A” type boilers have two mud drums symmetrically below the steam drum. Drums are each smaller than the single mud drums of the “D” or “O” type boilers. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 36. Packaged Boiler “D” type boilers have the most flexible design. They have a single steam drum and a single mud drum, vertically aligned. The boiler tubes extend to one side of each drum. “D” type boilers generally have more tube surface exposed to the radiant heat than do other designs. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 37. Packaged Boiler “O” design boilers have a single steam drum and a single mud drum. The drums are directly aligned vertically with each other, and have a roughly symmetrical arrangement of riser tubes. Circulation is more easily controlled, and the larger mud drum design renders the boilers less prone to starvation due to flow blockage, although burner alignment and other factors can impact circulation. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 38. Fluidized Bed Combustion (FBC) Boiler • Particles (e.g. sand) are suspended in high velocity air stream: bubbling fluidized bed • Combustion at 840 – 950 C • Capacity range 0,5 T/hr to 100 T/hr • Fuels: coal, washery rejects, rice husk, bagasse and agricultural wastes • Benefits: compactness, fuel flexibility, higher combustion efficiency, reduced SOx & NOx Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 39. Fluidized Bed Combustion (FBC) Boiler Fluidized bed combustion (FBC) is a combustion technology used in power plants. Fluidized beds suspend solid fuels in upward-blowing jets of air during the combustion process. The result is a turbulent mixing of gas and solids. The tumbling action, much like a bubbling fluid, provides more effective chemical reactions and heat transfer. Since limestone is used as particle bed, control of sulfur dioxide and nitrogen oxide emissions in the combustion chamber is achieved without any additional control equipment. This is one of the major advantages over conventional boilers. Combustion process requires the three “T”s that is Time, Temperature and Turbulence. In FBC, turbulence is promoted by fluidisation. Improved mixing generates evenly distributed heat at lower temperature. Residence time is many times greater than conventional grate firing. Thus an FBC system releases heat more efficiently at lower temperatures. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 40. Fluidized Bed Combustion (FBC) Boiler principle of fluidisation Fixing, bubbling and fast fluidized beds As the velocity of a gas flowing through a bed of particles increases, a value is reaches when the bed fluidises and bubbles form as in a boiling liquid. At higher velocities the bubbles disappear; and the solids are rapidly blown out of the bed and must be recycled to maintain a stable system. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 41. Fluidized Bed Combustion (FBC) Boiler FBC systems fit into essentially two major groups, atmospheric systems (FBC) and pressurized systems (PFBC), and two minor subgroups, circulating fluidized bed (CFB) & bubbling fluidized bed (BFB). Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 42. Advantages of Fluidised Bed Combustion Boilers 1. High Efficiency FBC boilers can burn fuel with a combustion efficiency of over 95% irrespective of ash content. FBC boilers can operate with overall efficiency of 84% (plus or minus 2%). 2. Reduction in Boiler Size High heat transfer rate over a small heat transfer area immersed in the bed result in overall size reduction of the boiler. 3. Fuel Flexibility FBC boilers can be operated efficiently with a variety of fuels. Even fuels like flotation slimes, washer rejects, agro waste can be burnt efficiently. These can be fed either independently or in combination with coal into the same furnace. 4. Ability to Burn Low Grade Fuel FBC boilers would give the rated output even with inferior quality fuel. The boilers can fire coals with ash content as high as 62% and having calorific value as low as 2,500 kcal/kg. Even carbon content of only 1% by weight can sustain the fluidised bed combustion. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 43. 5. Ability to Burn Fines Coal containing fines below 6 mm can be burnt efficiently in FBC boiler, which is very difficult to achieve in conventional firing system. 6. Pollution Control SO2 formation can be greatly minimised by addition of limestone or dolomite for high sulphur coals. 3% limestone is required for every 1% sulphur in the coal feed. Low combustion temperature eliminates NOx formation. 7. Low Corrosion and Erosion The corrosion and erosion effects are less due to lower combustion temperature, softness of ash and low particle velocity (of the order of 1 m/sec). 8. Easier Ash Removal – No Clinker Formation Since the temperature of the furnace is in the range of 750 – 900o C in FBC boilers, even coal of low ash fusion temperature can be burnt without clinker formation. Ash removal is easier as the ash flows like liquid from the combustion chamber. Hence less manpower is required for ash handling. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 44. 9. Less Excess Air – Higher CO2 in Flue Gas The CO2 in the flue gases will be of the order of 14 – 15% at full load. Hence, the FBC boiler can operate at low excess air - only 20 – 25%. 10. Simple Operation, Quick Start-Up High turbulence of the bed facilitates quick start up and shut down. Full automation of start up and operation using reliable equipment is possible. 11. Fast Response to Load Fluctuations Inherent high thermal storage characteristics can easily absorb fluctuation in fuel feed rates. Response to changing load is comparable to that of oil fired boilers. 12. No Slagging in the Furnace-No Soot Blowing In FBC boilers, volatilisation of alkali components in ash does not take place and the ash is non sticky. This means that there is no slagging or soot blowing. 13 Provisions of Automatic Coal and Ash Handling System Automatic systems for coal and ash handling can be incorporated, making the plant easy to operate comparable to oil or gas fired installation. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 45. 14 Provision of Automatic Ignition System Control systems using micro-processors and automatic ignition equipment give excellent control with minimum manual supervision. 15 High Reliability The absence of moving parts in the combustion zone results in a high degree of reliability and low maintenance costs. 16 Reduced Maintenance Routine overhauls are infrequent and high efficiency is maintained for long periods. 17 Quick Responses to Changing Demand A fluidized bed combustor can respond to changing heat demands more easily than stoker fired systems. This makes it very suitable for applications such as thermal fluid heaters, which require rapid responses. 18 High Efficiency of Power Generation By operating the fluidized bed at elevated pressure, it can be used to generate hot pressurized gases to power a gas turbine. This can be combined with a conventional steam turbine to improve the efficiency of electricity generation and give a potential fuel savings of at least 4%. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 46. Fluidized Bed Combustion (FBC) Boiler a. Atmospheric Fluidized Bed Combustion (AFBC) Boiler Atmospheric fluidized beds use limestone or dolomite to capture sulfur released by the combustion of coal. Jets of air suspend the mixture of sorbent and burning coal during combustion, converting the mixture into a suspension of red-hot particles that flow like a fluid. These boilers operate at atmospheric pressure. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 47. Fluidized Bed Combustion (FBC) Boiler b. Pressurized Fluidized Bed Combustion (PFBC) Boiler • Compressor supplies the forced draft and combustor is a pressure vessel • Used for cogeneration or combined cycle power generation. • The first-generation PFBC system also uses a sorbent and jets of air to suspend the mixture of sorbent and burning coal during combustion. However, these systems operate at elevated pressures and produce a high-pressure gas stream at temperatures that can drive a Gas Turbine. Steam generated from the heat in the fluidized bed is sent to a Steam Turbine, creating a highly efficient Combined Cycle system. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 48. PFBC Boiler for Cogeneration Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 49. Fluidized Bed Combustion (FBC) Boiler Atmospheric Circulating Fluidized Bed Combustion (CFBC) Boiler • Solids lifted from bed, rise, return to bed • Steam generation in convection section • Benefits: more economical, better space utilization and efficient combustion Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 50. Fluidized Bed Combustion (FBC) Boiler This CFBC technology utilizes the fluidized bed principle in which crushed (6 –12 mm size) fuel and limestone are injected into the furnace or combustor. The particles are suspended in a stream of upwardly flowing air (60-70% of the total air), which enters the bottom of the furnace through air distribution nozzles. The fluidising velocity in circulating beds ranges from 3.7 to 9 m/sec. The balance of combustion air is admitted above the bottom of the furnace as secondary air. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 51. Bubbling Bed Boilers In the bubbling bed type boiler, a layer of solid particles (mostly limestone, sand, ash and calcium sulfate) is contained on a grid near the bottom of the boiler. This layer is maintained in a turbulent state as low velocity air is forced into the bed from a plenum chamber beneath the grid. Fuel is added to this bed and combustion takes place. Normally, raw fuel in the bed does not exceed 2% of the total bed inventory. Velocity of the combustion air is kept at a minimum, yet high enough to maintain turbulence in the bed. Velocity is not high enough to carry significant quantities of solid particles out of the furnace. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 52. Bubbling Bed Boilers Features of bubbling bed boiler Fluidised bed boiler can operate at near atmospheric or elevated pressure and have these essential features: • Distribution plate through which air is blown for fluidizing. • Immersed steam-raising or water heating tubes which extract heat directly from the bed. • Tubes above the bed which extract heat from hot combustion gas before it enters the flue duct. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 53. Bubbling Bed Boiler
    • 54. Stoke Fired Boilers Stokers are classified according to the method of feeding fuel to the furnace and by the type of grate. The main classifications are spreader stoker and chain-gate or traveling-gate stoker. a) Spreader stokers • Coal is first burnt in suspension then in coal bed • Flexibility to meet load fluctuations • Favored in many industrial applications Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 55. Stoke Fired Boilers b) Chain-grate or traveling-grate stoker • Coal is burnt on moving steel grate • Coal gate controls coal feeding rate • Uniform coal size for complete combustion Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 56. Pulverized Fuel Boiler • Coal is pulverized to a fine powder, so that less than 2% is +300 microns, and 70-75% is below 75 microns. • Pulverized coal powder blown with combustion air into boiler through burner nozzles • Combustion temperature 1300 -1700 °C • Benefits: varying coal quality coal, quick response to load changes and high pre-heat air temperatures at Tangential firing Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 57. Pulverized Fuel Boiler Advantages  Its ability to burn all ranks of coal from anthracitic to lignitic, and it permits combination firing (i.e., can use coal, oil and gas in same burner). Because of these advantages, there is widespread use of pulverized coal furnaces. Disadvantages  High power demand for pulverizing  Requires more maintenance, fly ash erosion and pollution complicate unit operation Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 58. Waste Heat Boiler • Used when waste heat available at medium/high temp • Auxiliary fuel burners used if steam demand is more than the waste heat can generate • Used in heat recovery from exhaust gases from gas turbines and diesel engines Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 59. Waste Heat Boiler (HRSG) • A waste heat boiler can be economically installed wherever waste heat can be available at medium or high temperatures. • Wherever the steam demand is more than the steam generated during waste heat, auxiliary fuel burners are also used. If there is no direct use of steam, the steam may be let down in a steam turbine-generator set and power produced from it. It is widely used in the heat recovery from exhaust gases from gas turbines and diesel engines. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 60. Waste Heat Boiler (HRSG) Heat recovery steam generator (HRSG), located at the exhaust end of gas turbine or Engine. During plant operation, the gas turbine engine discharges a high volume of exhaust flue gas containing a considerable amount of thermal energy. The HRSG reclaims the exhausted thermal energy for the purpose of generating superheated steam for use in the steam turbine generator. Efficient reclamation of the gas turbine exhaust prevents wasted energy, resulting in a significant increase of overall plant efficiency. The installation of the HRSG gives the plant its ’combined cycle’ status, in that it represents a major component of the Rankine cycle portion of the power plant. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 61. Waste Heat Boiler (HRSG) Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 62. Waste Heat Boiler (HRSG) Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 63. Nuclear Steam Generating Systems Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 64. Nuclear Steam Generating Systems Steam generators are heat exchangers used to convert water into steam from heat produced in a nuclear reactor core. They are used in pressurized water reactors (PWR) between the primary and secondary coolant loops. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 65. Nuclear Steam Generating Systems Nuclear steam generating systems include a series of highly specialized heat exchangers, pressure vessels, pumps and components which use the heat generated by nuclear fission reactions to efficiently and safely generate steam. The system is based upon the energy released when atoms within certain materials, such as uranium, break apart or fission. Fission occurs when a fissionable atom nucleus captures a free subatomic particle – a neutron. This upsets the internal forces which hold the atom nucleus together. The nucleus splits apart producing new atoms as well as an average of two to three neutrons, gamma radiation and energy. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 66. Nuclear Steam Generating Systems In commercial power plants steam generators can measure up to 70 feet (~21m) in height and weigh as much as 800 tons. Each steam generator can contain anywhere from 3,000 to 16,000 tubes, each about three-quarters of an inch (~19mm) in diameter. The coolant (treated water), which is maintained at high pressure to prevent boiling, is pumped through the nuclear reactor core. Heat transfer takes place between the reactor core and the circulating water and the coolant is then pumped through the primary tube side of the steam generator by coolant pumps before returning to the reactor core. This is referred to as the primary loop. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 67. Nuclear Steam Generating Systems Types Westinghouse and Combustion Engineering designs have vertical U-tubes with inverted tubes for the primary water. Canadian, Japanese, French, and German PWR suppliers use the vertical configuration as well. Russian VVER reactor designs use horizontal steam generators, which have the tubes mounted horizontally. Babcock and Wilcox plants have smaller steam generators that force water through the top of the OTSGs (once-through steam generators; counterflow to the feedwater) and out the bottom to be recirculated by the reactor coolant pumps. The horizontal design has proven to be less susceptible to degradation than the vertical U-tube design. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor
    • 68. Prepared by: Mohammad Shoeb Siddiqui Sr. Shift Supervisor Saba Power Plant shoeb.siddiqui@sabapower.com shoeb_siddiqui@hotmail.com www.youtube.com/shoebsiddiqui

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