Hi all my APP ( Ask Power Plant) readers I hope everything gonna be all right. I got many requests from my readers about who appeared in the BOE [ Boiler OPeration Engineering ] exam this year for the past couple of months. so as per looking into their request I started working on their request and start writing articles on BOE PAST EXAM PAPERS-2 SOLUTIONS so today I write about A.P (ANDHRA PRADESH BOE -2010 EXAM PAPERS-2 SOLUTIONS this article helps those readers who want to give BOE exam in this year as well as who preparing for BOE examination for upcoming BOE exam which conducting by different-2 states. this article also helps for those who wants to give viva-voce for BOE examination and also for who face the job interview for power plant hire. so let us discuss A.P (ANDHRA PRADESH BOE -2010 EXAM PAPERS-2 SOLUTIONS.
Q.1 a) What are the factors which affect circulation in the Boiler?
Ans: The following factors affect the circulation system:
a) The demand on load from the boiler.
b) The operating pressure at which the boiler is operating.
c) The fluctuations in drum level associated with disturbance in boiler load conditions.
d) Change in rate of fuel firing and the variations in the pattern of heat loading inside the furnace.
Q. 1 b) Write about the boiling mechanism
Ans. BOILING MECHANISM :
Remember that an express a machine facilitates to basic function to make express and steam. The different boiling mechanisms determine how efficiently it can do these two actions express brewing temperature should be around more temperature. Generally, in boiler mechanisms, there are two types of boiling mechanisms.
1. Nucleate boiling :
It is the formation and release of steam bubbles at the tube surfaces with water still wetting the surface is closer to saturation temperature the tube always safe against failure.
2. Film boiling: Film boiling is the formation of steam film at the tube surface in which the metal temperature rise sharply this leads to instantaneous or long-term overheating of tubes and failure film bolling begins due to high heat flow or low velocity or inclined tubes.
Transition Boiling :
Transition boiling is a stage between nucleate and film boiling having features of both of these stages.
Q.1 C) Discuss the role of the boiler operation engineer while the steam turbine is rolling.
Ans. 1. Ensure turbine protection & interlocks are in service.
2. Ensure the quality of steam to be entered into the turbine.
3. Follow entire SOPs recommended by manufacturers.
4. Turbine speed should not behold at the critical speed of the turbine.
5. Line charging, rolling starting, shocking, vacuum pulling, etc. Procedure to be followed as per SOPs.
6. All the safety protections have to be taken while the turbine rolling.
7. Physical observation has equally important during rolling.
8. Noise, vibration, Axial shift, differential expansion & temperature difference between top & bottom casing is much more important during turbine rolling between top & bottom casing is much more important during turbine rolling.
Q.1 d) Why chimneys are made of round sections?
Now, these days different types of chimneys are used in industry to discharge the flue gases into the environment. These are either made of steel, masonry or concrete. Among them, concrete chimneys are mostly used in boilers time steel chimneys si also used in small boilers.
The chimney is normally cylindrical in construction it is exposed to a tough environment on the inside and outside flue gas with its abrasive and corrosive characteristics can damage the structure material. For this normally the chimney is one with suitable material like fire bricks.FRP etc. Mostly bricking is preferred in boiler chimneys.
Castable supported bricking with suitable air space between the concrete shell and bricking is preferred by most power engineers.
Q.2 a) what is a steam attemperator and how does it work?
Spray type attemperator :
In spray type attemperator feed water takes from boiler feed pump and it’s directly sprayed to the steam coming out from the primary superheater through a nozzle. Here the temperature of steam reduces. After that steam passes through the secondary superheater. If the outlet temperature of the secondary superheater is higher than the desired value in this condition control valve allows more spray water through the nozzle to reduce temperature According to the given figure. The temperature control valve is put in auto mode so that the spray water quantity can be adjusted automatically.
In spray type attemperator the spray nozzle is fitted to the steam header with a suitable pipe connection. Feedwater is connected to this pipe. A metallic protective jacket around 4 to 5 m in length is provided at the header. Feedwater is sprayed into the steam with the help of a nozzle. At the end of the jacket, spray water evaporates completely so that the hot main steam header does not come in contact with this water and thermal shock is avoided.
Sometimes purity of steam is important in this condition feedwater cannot be sprayed directly because when it mixes with steam, chances of steam contamination have emerged. In this situation instead of direct feedwater spray, saturated steam from the boiler is condensed and that condensed is used for spray. This method minimizes the chances of steam contamination.
SURFACE TYPE ATTEMPERATOR :
In this type of attemperator, feed water is not Directly mixed with superheated steam. Steam temperature is controlled with the help of varying the feedwater flow in a heat exchanger. In this method, feedwater flows in the shell of the heat exchanger and the superheated steam flows inside the tubes. When it is required to decrease the steam temperature more water is allowed to flow through the heat exchanger by closing the control valve as shown in the figure.
The main advantage of this system is that the feedwater does not mix with steam, so the purity of steam maintained
BOILERS TUBING MATERIALS SPECIFICATIONS MATRIX:-
|ASME Spec.||ASME Grade||Type||Description||Typical Uses||Max allowable Temp. Deg. C|
|SA-178||A||ERW||Low carbon steel C=0.18 max.||Boiler tubes, economizers, Low-temperature superheaters||510|
|SA-178||C||ERW||Medium carbon steel-C=0.35 max,||Boiler tubes, economizers, Low-temperature superheaters||510|
|SA-178||D||ERW||Carbon-manganese steel-C=0.27 max||Not in common uses||510|
|SA-192||Seamless||Low carbon steel-C=0.18 max||water wall, economizers, low temp. superheaters||510|
|SA-210||A1||Seamless||Medium carbon steel-C=0.27 max||water wall, economizers, , superheaters||510|
|SA-210||C||Seamless||Medium carbon steel-C=0.35 max||water wall, economizers, superheaters||510|
|SA-209||T1||Seamless||Low alloy steel-low carbon,1/2% moly||superheaters||510|
|SA-209||T1a||Seamless||Low alloy steel-medium carbon,1/2% moly||superheaters||510|
|SA-209||T1b||Seamless||Low alloy steel-low carbon,1/2% moly||superheaters||510|
|SA-213||T2||Seamless||Intermediate alloy-1/2% Chrom,1/2% moly||water walls, superheaters, not in common use||565|
|SA-213||T11||Seamless||Intermediate alloy-1,1/4% chrom,1/2% moly||water walls , superheaters||565|
|SA-213||T22||Seamless||Intermediate alloy-2 1/4% chrom,1% moly||water walls , superheaters||607|
|SA-213||T5||Seamless||Intermediate alloy-5% chrom,1/2% moly||High temperatures superheaters are not in common use||607|
|SA-213||T9||Seamless||Intermediate alloy-9% chrom,1% moly||High temperatures superheaters, no longer in common use||607|
|SA-213||T91||Seamless||Intermediate alloy-9% chrom,1% moly, 1/4% vanadium||High temperatures superheaters-the latest and greatest||649|
|SA-213||Tp-304||Seamless||Stainless steel-18% chrom,8% nickel||Superheaters||760|
|SA-213||Tp-304H||Seamless||Stainless steel for high temperature||High-Temperature superheaters||760|
|SA-213||Tp -316||Seamless||Stainless steel-16% chrom,11% nickel||Superheaters||760|
|SA-213||Tp-316H||Seamless||Stainless steel for high temperature||High-Temperature superheaters||760|
|SA-213||Tp-321||Seamless||Stainless steel-17% chrom,9%nickel,0.60% titanium||Superheaters||760|
|SA-213||Tp-321H||Seamless||Stainless steel for high temperature||High-Temperature superheaters||760|
|SA-213||Tp-347||Seamless||Stainless steel-17% chrom,9% nickel ,columbium+tantalum=1.00% max||Superheaters||760|
|SA-213||Tp-347H||Seamless||Stainless steel for high temperature||High-Temperature superheaters||760|
Q. What are the causes of boiler tube failure?
CAUSES OF BOILER TUBES FAILURE :
Failure in superheater tubes is rarely caused by corrosion except for the condition of the steam boiler being maintained or standing by in long term. failure in superheater tubes often occurs because of overheating either ” short term overheating ” or ” long term overheating “.
Overheating is caused by an attached deposit in internal tubes which is carried over by bad quality steam which brings suspended solids or dissolved solids ( hardness). The hardness can be carried over with the steam because the separation process of the steam-water mixture can not be executed perfectly in the steam drum. The deposit can be removed by adding chemical injection (phosphate) in a steam drum to make hardness be soluble then the next step is to discharge it through the blowdown process.
Failure in superheater tubes may also occur during a bad start-up process. if combustion temperature increases rapidly without doing water and steam balance flow, the superheater will feel overheating in the short term because there is no steam flow which has function as a cooler. steam flow through superheater tubes acts as a cooler because the temperature of the steam is lower than the temperature of radiant combustion. so startup procedure shall be established to perform good combustion.
Hi all power engineers myself Joginder Chauhan. I am the founder of the website www.askpowerplant.com. I am also a power plant engineer and have more than 10-year experience in the field of power sectors during this time period I learned about different power technology like AFBC, CFBC, TRAVELLING GRATE, PULSATING GREAT, PF BOILER, WHRS, and many more things. my motive for this site sharing my power sector knowledge with each and everyone who belongs to this field, in this website I share information related to boiler operation, boiler maintenance, turbine operation & maintenance, boiler & turbine question answer, D.M plant, and all topic related to power plant sector please join this website for latest updation regarding power plant ………..thanks ( JOGINDER CHAUHAN )