Boilers introduction 2. High Pressure Boilers 3. Boiler Auxiliaries 4. Boiler Mountings and Accessories 5. Boiler Operation Inspection and Maintenance 6. Boiler Calculations 7. Draught 8. Primary Fuels 9. Principles of Combustion The Chemistry of Combustion Coal Pulverization Pulverized Coal Fired Furnaces Upgrading PC-Fired Boilers Fuel Oil and Gas Fired Furnaces Continue to keep up the superb operate.
In search of forward to studying more from you in a while!? I require an expert in this house to solve my problem. May be that is you! Nice weblog here! Also your website a lot up fast! What host are you using? Can I am getting your affiliate hyperlink on your host? I wish my website loaded up as fast as yours lol. Skip to content 13 January Whai about the expansion problem in steel boiter? Properly designed steef boilers present litte expansion difficulty and is relatively free from stres- sesdne 19 expaasion and contraction.
The connecting pipelines should be adequately provided for expan sion and moverneat. Whar is the effect of expansion ar contraction stresses on tubes? Leakage develops where the tubes are bent into the drum or tubesheet, Q. What about the expansion and contractionprob- lem ina cast-iron boiler?
Ans, Thermal stresses induced due to expansion or contraction wilt wanp sections of the cast-iron boiler. And deformed sections take a permanent shape. Re- placement may be difficult, Q. How does flame impingement affect the potter? Bollers 41 ANS. Q Does a draft affect boiler operation? Ans, The draft problems that are encountered when a chimney alone is used are eliminated if draft fans are installed. Practical experiences show that a draft fan is far more economical than a chimney of adequate height sin all cases excep those of small installations.
Q Soachimney can be eliminated fdraft fans are instatted. Is it? No, Some kind of chimney or stack is neces- sary despite the installation and operation of draft fans. What is the need for a large water capacity? Ans, If sudden load-changes are prevalent, boilers having fess of a small water capacity will be more responsive to quicker load fluctuations. Compare warertube and firetube boilers in the light of water capacity?
Watertube boilers have a smaller water capacity than firetwbe boilers, Therefore wateriube boilers are more responsive to a rapid load change. The targer water capacity of firetube boilers im- parts stability but does not permit rapid load fluctua- ton.
Q How does water circulation affect a boiler? Firetnbe boilers usually have poor circulation compared to watertube boilers. Q What are she steaming characteristics of a firetube boiler? Firetube boilers in general, are not fast steamers. The steaming rate of a firebox type boiler is much faster than that of externally fired boilers, However, the steaming characteristics ofa firetube boiler vary with differing design and with she ratio of fheating surface to water volume.
Q What are the steaming characteristics ofa pack- aged boiler? Packaged boilers have quicker steaming rate than fitetube boilers because of alarge heating surface with smaller water volume. Whar are she steaming characteristics of water. Fast, Q. Whar are the steaming characteristics of cast- iron botlers? Stow steaming cate, except those having smaller water volume.
This is because alarge quamtily of metal is involved in a cast-iron boiler. Althe start-up, the steaming rate is low but there- after such boilers have riatively stable steaming characteristics, QL What are the effecis of low-water in the case of a steel boiler? Ans, Replacement of exposed tubes or crown sheets is required.
This means a considerable downtime lass as the boiler is shutdown and kept out of service tit the repair jobs are completed Q. Waal are the effecis of low-water operation in the case of cast-iron boilers? Warpuge may sometime invite replacernent of the boiler.
How can siudge be removed from the boiler? Periodic blowdown is the method most prac- lised to remove sludge deposited on the mud drum or mud ring. Tei has become solid cake, a high-pressure water hoke is hamessed to dislodge the cake during shut- down perious, If it sull remains, itis chipped out Due to lack of adequate clearance. How can she boiler ibe scaies be removed? The boiler is then carefully heated 3. Cold water is sprayed on the tubes to induce themmat stress in the solidified scale aad romove the ruptured scales, Scales inside a boiler tube are turbined reammed out carefully with special equipment.
Improper combustion is the cause of soot Tor nuttion in the boiler furnace. Combustion-gas-borne soot gets deposited in the boiler flue passes. QL What ts the effect of soot deposinon in the flue gas passage of « boiler? Compare the soot blowing characteristics of a steel firetube boiler and w steel warertube boiter?
Ans, Annual or biannual soot blowing nay be ade- quate for stee! Large installations fave soot blowers. Ans, Initially there is some soot buildup and with that there occurs initial efficiency reduction. After that there is little additional soot development be- cause of the large size of passageways.
And so 00 further efficiency drop takes place. What about the relative ease of servicing of cast- iran boiler, ste! Forcast-iron boilers, the waterside is inacces- sible whereas the fireside is accessible for inspection and maintenance by simply opening the doors.
The flue ducts are large and lend themselves to easy cleaning. The waterside of watertube steel boilers and pack- aged units is accessible for inspection and main- tenance jobs through manholes, handholes or washout plugs, The mere opening of doors makes the fireside aocessible to inspection and maintenance, Accessibility to tubes for firetube boilers is gained through ttinged, front flue doors. Soot cleaning is ac- complished through the doors set in the rear strioke box, It the fitetube boilers are fitted with smaller steel tubes they present more difficulty in cleaning than cast-iron boilers because the latter provide ample cleaning space.
The waterside of a packaged firctube unit is acees- sible for inspection trough manholes. The rear wall is to be unbolted and removed to get access to the fireside, Hence firemube packaged boilers are not generally considered gasily accessible for main- tenance and cleaning.
Why do she present duy boiler designers not recommend maximum flue gas velocities in boilers? Boller 43 Ans, Ttis due to deteriorating fuel quality. This erosiou problem being propor- tional to an exponential function of flue-gas velocity, the latter is a major consideration in boiler design. Why is chromizing of watervall, superheater and reheater tubes done?
This strengthens she tubes in combating flyash erosion problems. Chromium, a powerful corrosion resistant metal, diffuses into the base metal of the tubes of the heat exchangers, viz..
Why are imernally ribbed tubes laid out in the high-heat-absorplion zones of naturai circulation drum-type boilers operating at high supercritical pressures? Itensures high availability of the boilers. When intemally ribbed tubes are arranged in the high-heat-absorption zones of the combustion chamber, they provide a far greater margin of safety against tube failure from departure from nucteate boiling DNB conditions.
They impart a centrifugal action to the working Quid that forces water droplets towards the waterwall tube surface and inhibits the Formation of a steam film,. Is iturwe then thai the DNB is more possible with smooth tubes than with internally ribbed tubes? Ans, Yes. What do you mean by cycling service?
It means boilers must be designed to cycle on and off, For example, a typical requirement may be nightly or weekend shutdowns. This change is required to permit operation at sated steam temperatures at all Toads. How is the start-up system for cycling units designed to allow quicker matching of final steam-ta- turbine temperature?
This allows more rapid final steam-to-turbine temperature matching than is experienced by a. Why do she spray systems of some superheaters and reheaters on some cycling boilers have Pwice as much capacity as those of non-cycling boiler designs? Ans, Thisextra spray capability endows the cycling system with a greater control flexibility for maintain- ing the boilerube metal temperature within recom- mended limits, Q.
Whar is the Exropean by-pass system? Ang, is the full by-pass system [Fig. This system bestows: 1. Q What factors affect the combustion efficiency of boilers? Combustible Losses: itis the heat lost due to incompletely bumt products of combustioa,. What parameters are to be monitored to calcu. If, on the other hand, stack temperature is kept too low, it may result in coldend corrosion, Q. What components will you get in flue gas analysis?
Oxygen, carbon dioxide, water vapour, sul- phur dioxide, sulphur trioxide, oxides of nitrogen, and unburnt combustibles, viz. Ans, The presence of minimum O,, maximum CO, and oil combustibles in the flue gas.
Bollers 45 Q. Whar is she disadvamage of using excess air io reduce the combustibles convent in flue gas to zero? Itwill 1. Ans, tt assists im setting the damper correctly for various loads.
Excessive draft can result in increase of net stack temperature and lower the percentage of CO, in the flue gas. If, on the other hand, the draft is inadequate, it will resultin insufficient combustion air and smoky opera- tion.
Ans, This is obtained by a tial and exror method, as the precise relationsinp between damper position and the amount of draft is not known. So the correct draft for minimum excess air compatible with smokeless conibustion is determined for various loads by a tial method using a flue gas analyzes to monitor the levels of excess air, as dictated by the damper position and.
The combustion efficiency curve shows that the rate of energy toss in case of excess fucl, ie. Ans, It will ensure: betier heat transfer rate increase in combustion efficiency. The apparatus is cumbersome. The monitor- ing of flue gas with itis a time consuming process, It also suffers from inaccuracies. It calls for special skills of the personne! Do you recommend the use of stand-alone analyzers for monitoring flue gases?
Ans, No, Q Why? These stand-alone systems may sometimes prove their worth under specific circumstances, yet theit use for monitoring total combustion efficiesicy suffers from certain specific limitations. What are these specific limitations? Take the case of COp- Analyzer. Ttneeds 1, bigher maintenance 2. These factors in combination make CO, monitoring dif- ficult.
Take the case of On-line CO-Analyzer, It uses infrared techniques that suffer from tnter- ference problems at elevated temperatures. Also, the presence of particulate solids in the flue gases impart inaccuracy. Tey interfere with the reading by block- ing the light source, Besides analyzers measuring CO only do not indicate the magnitude of fuel wastage dug to the presence of other combustibles. Ans, Portable, multivariable combustion analyzer. Any specific example?
It is manufactured and marketed by Energy Bificiency Systems, tne. What are the important and striking features of a good portable combustion analyzer? Ans, A good portable analyzer shonkd have the following features: i should monitor 1. Avoiding low combustion air temperature 6, Avoiding low primary air velocity 7. This means maintaining rated steam parameters at the tur- bine inlet and the back pressure of the turbine exhaust. What may be the cause of a fall in condenser vacuuen in the surface condenser?
High air ingress in the condenser 4, High cooling water inlet temperature. Ifa thermal powerpiant burns inferior coal of a quality different from the designed coal specification of the boiters, what harm will t cause? Use of inferior quality of coal in baifers may lead to 1, operational problems 2, excessive use of coal 3, malfunctioning of coal handling plants 4, chocking of chutes 5.
What factors may lead to excessive fuel oil con- Sunption in coal fired boilers of ihermal power sta- tions? Buming of inferior quality coal. Operating the plant at part ioad. What is the drawback of operating boiler at part load condition? Despite being under part joad of steam genera- tion, the running equipment consume almost the same amount of energy as ima full load condition, QL How can start-up and siutdown tosses be cut down?
Ans, A fast startup is highly desirable, as it cuts down the energy consumption during this period, A few thermal powerplants follow an open valve boiler start-up. This saves half of coal start-up costs. What is the jurn-down ratio of a steam control vatve?
It is the ratio of normal design flow to mini- mum comollable flow. What is the rangeabitity ratio ofa steam control. Why is high pressure steam in growing demand in power plans? Ans, To increase the efficiency of the plant and reduce the cost of production of electricity. QQ What are the unique feaures of high pressure boilers? QL Why ts nanerad cirexlation limited so subcritical boilers? Ans, Natural circulation works on the basis of den- sity differegce benvcen steam and water. Hence natural circutation is operative de the case of subcritical boilers.
Why are she water subes arranged in paratier? Ang, To reduce the pressure loss and to get enter control over the quality of the steam.
Note: There would fave been a large pressure drop duc te friction if the weer Dow were to take place through one continuous tube, GQ What are the advansages of high pressure botiers? Chances of scale formation on tube walls are very low due 16 high velocity of feedwater. Quick start-up from cold is possible if power from an external source is available.
AS a result, more work outpol is available from the expansion turbine. Fig, 2. Fitfor meeting variable load quickly, as steam can be raised quickly. Light-weight tubes with benter heating char- acteristics can be used to reduce the cost, erection time and spave requirement for tube fayout.
Danger of overheating and thermal shock is minimized due to all pants being uniformly heated. Q Who first introduced the forced circulation boiter? Credit gocs to La Mont for introducing the forved circulation boiler for the first time Briefly describe a La Mont Boiler. Itconsists primarily of three circuits: a Air circuit -— Cold air is blown by a blower through the air preheater whore it gots heated up in the process of heat exchange with flue Fig.
Water circuit—Deaerated BFW is pumped through the economizer—acoil type heater— bya BFW pump and fed to the steam separa ing drum from whick itis forced through the tubes of radiant evaporators and convective evaporator by a circulating pump.
Steam circuit—The steam separated in the steam drum is saturated steam. Note: This boiler is adaptable for all pressures from subcritical to supereritical; capacity exceeding 50vh.
What is she ratio of BFW circulation so tonnage of steam produced? Ans, Water circulation is 8 to 10 times the weight of the steam produced. To prevent the evaporator tbes from over- heating. What is the main drawback af La Mont boiter?
Reduced heat transfer coefficient due to for- mation and attachment of steam bubbles on the inner surface of watertubes, Q. How can this be eliminated? By operating the boiler at critical pressure 28 atm. At this pressure the density of water is equal to that af steam. Hence no bubble wiil form,. What is the minimum steam generating pressure ofa Benson boiler? Ans, atm. When did such a boller go into operation first?
High Pressure Rovers 3? Briefly describe a Benson boiler. Ans, Itconsists mainly of two circuits Fig, 2. Water-steam circuit: Forced circulation is introduced to generate superheated steam in this open hydraulic system. What is the major problem associated with a Benson boiler? Salt deposition in the transformation zone where all remaining water is converted into steam, Q. How can this be avoided? By Anshing out the boiler after every working hours.
QQ What are she maximum operating temperature and pressure achieved so far ina commercial Benson boiler? There is no dorter drum, which mneans a reduc- tiga ia the overall weight of the boiler and a cot in capital investment.
There is no expansion joiut as the boiler is of the forced circulation type. Since al pans are welded at their sites, itis easier aud quicker to erect a Beason boiter 3.
Start-up is quicker because of welded joints, Evaporator Separator ms Btw A preheater Paimaty eyvouit 4, Needs comparatively less floor-space than other boilers of the same capacity 5, Better and more efficient protection of fur- nace walls as the high pressure boiler tubes have smaller diameters and are closely spaced 6. Economic operation at partial load or aver toad is possible 7. What is the nanure of circulation in the primary circuit of a Schmidt-Harimann boiler?
Ans, Natural circulation. Will it be sufficient to effect the necessary rate Of heat transfer as 10 overcome the thermo-siphon head of about 2 t0 10 m of water column? What isthe rate ofheat transfer jrom the primary circuit to the secondary cirewit? About kim? What are the advantages of Schmid! Chances of overheating are minimal as the highly heated compovents carry pure water with no risk of salt deposition at alt 2.
What is the speciality of a Velox boiler? Hence com- pressed air 2. Ans, Air is compressed to 2. Jnside each tube is another concentric tube of 2. Ans, With the increase of the capacity of Velox boilers, greater is the power requirement of the air compressor, so as to detiver more camfurstion air at supersonic velocity. That is why the size of the Velox boiler is fimited to th and the power requirement of the ait com- Dressor at this velocity is kW.
What is a supercritical boiler? Ans, Boiler praducing steam above critical pres- sure, L. Furnace Q. Waat fs the basic difference between subcritical and supercritical boilers? What are the advantages of supercritical boilers over subcritical ones? What is a supercharged boiler? A boiler where combustion is carried out under pressure in the combustion chamber by supply- ing compressed air.
Ans, The flue gas is also under pressure about 5 atm which is utilized to drive the gas turbine to run the air compressor coupled with it 10 supply the compressed air for combustion, Due 0 pressurized combustion, the overall heat transfer coefficient is very high. And that means a drastic saving in material cost 3.
Quicker start-up possible. A Vb super- charged boiler can be brought to full toad in Jess than half an hour 4, Better response to control 5, The power available from the gas turbine can be utilized to nim the auxiliaries Q. What is the main drawback of sucha pressurized combustion system?
Ans, See Fig. What are ihe specific advaniages of super. Ans, Three. One radiation zone Zone I and two convec- tion zones Zones I and Whar do you mean by boiter auxitiaries? What are hey? Usually a boiler is fitted with the following auxiliaries accessories : 1, Air preheater 2. Economicer 3. Superheater 4, Desuperheater 5. Boiler feed pumps 6. Forced draft and induced draft fans 7. Mechanical separator 8.
Chemical dosing system Soot blowers and wall blowers 11, Pressure reduction valve Pulverizers and fuel firing system Ash handling system, Q. What is a boiler feed pump?
A pump that feeds boiler water polished water 19 the steam drum via the economizer for preheating. What are the two mosi imporiant criteria of a boiter feed pump? It must be absolutely positive and reliable under all variable operating conditions, Q.
Whai kind of pump should it be? How are direct acting pumps ciassified? Q What is the basic difference between these three? Ans, The sitnplex pamp has one pump cylinder and one engine cylinder, Induplex and triplex pamps there are two and three pump cylinders respectively. What kinds of reciprocating pumps can be used? Both phinger driven and piston driven. Among the three kinds of pumps—direct acting, reciprocating and centrifiagat—which one wiit you prefer as a boiler feedwater pump?
Centrifugal pump. A centrifugal pump is capable of: 1. Why are both nurbo-driven and motor driven cenirifugal BOW prenigs insiatied?
During startup, the motor driven pumps are lined up to establish circulation. Suppose both steam and electricity are avait- able, Which centrifugal pump would you prefer to switch on?
Ans, Turho-driven, Q Why? Steam is cheaper than electricity. Why is the FD fan installed before the air preheater and not after? Ans, This reduces the volume of air wandled by the FD fan. The volume of air increases considerably after, the air preheater. The size of the ID fan is always larger than the ED fan. Greater the specific volume of the gas handled, larger will be the size of the fan.
Air handled by FD fans is clean, i. The efficiency of the backward curved blades is higher than forward curved blades. Why are backward curved blades with radial sips used in 1D fans? ID fans bandle flue gas containing soot and grit. This is ta avoid water hammer due to sudden condensation of pockets of steam, Q. BFW should not enter the economizer below a certain temperature.
Before being delivered to the boiler drum, BFW is preheated itt the economizer, by indirect heat exchange with the flue gas,—either in crossflow or counterflow with the BFW. However, BFW is aot allowed to enter the economizer below a minimum temperature, for, this may cause a sharp drop in the temperature of the flue gas. Problem 6. Efficiency of waste heat boiler 2 Sandip Warbhe. Prakash Kakani. Chandra Kaladhar. Anand Swami. Raju Sk. Parameswararao Billa. Anonymous IN80L4rR.
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