This article is about BOILER QUESTION AND ANSWERS INSTRUMENTATION where you will study lot of important questions related to boiler instrumentation.
FIRING EQUIPMENT BOILER QUESTION AND ANSWERS
Q.1. What type of air register is provided with boiler?
Answer. MITSUBISHI MY-N200 type of package boiler is mainly composed of two sets of Air registersSE-1OO type.
Q.2. How many air registers are there in boiler?
Answer. There are two (02) air register for each boiler. Each burner consists of an air register for introducing combustion air, gas burners for burning fuel gas, a gas ignitor, and burner frontal piping which is attached in front of the boiler.
Q.3. Name the main parts of air register?
Answer. Each air register is equipped with the primary air drum and secondary air vanes, so that the combustion condition can be adjusted by modulating the setting of primary air drum and secondary air vanes.
Q.4. How many sets of flame detectors are there in boiler?
There are three sets of flame detectors. One set for monitoring the ignitor and main gas flame, the other set for monitoring the main gas flame.
Q.5. What type of flame detectors are there in boiler?
The flame detectors are OPTICAL type.
Q.6. What will be the appearance of flame at high load?
Answer. The soft yellowish purple flame can be seen at high load, when fuel gas is burnt.
Q.7. What will be the appearance of flame at middle and low load?
Answer. Luminous flame with transparent blue color around ignition part can be seen at middle and low load, when fuel gas is burnt.
Q.8. Why there is a difference in flame appearance at high load and low load?
Answer. (HOLD) To be provided later.
Q.9. What do you mean by incomplete combustion?
Answer. Incomplete combustion happens as a result of the shortage of the combustion air or in other words poor air to fuel ratio will lead to incomplete combustion.
Q.10. What will be the appearance of flame in case of incomplete combustion?
Answer. A dark red colored flame may be seen due to the excessive incomplete combustion. If air flow is excessively decreased, the flame stabilization around the ignition part is considerably deteriorated and the combustion oscillation may occur in the worst case.
Q.11. What corrective action to be taken in case of incomplete combustion?
Answer. The fuel-air ratio should be adjusted immediately to establish a proper combustion, when the combustion state becomes unstable and heavy smoke is generated.
Q.12. Explain Flame Impingement?
Answer. Flame impingement is a phenomenon when Flame including unburned fuel directly touches on the tubes and makes deposit of unburned carbon.
Please read also: INSTRUMENTATION AND CONTROL ENGINEERS QUESTIONS AND ANSWERS
Q.13. What do you mean by Combustion Gas Brushing?
Answer. Combustion Gas Brushing is a phenomenon when Soft gas flame which is a part of flame tip touches on the boiler tubes and do not make deposit of unburned carbon.
Q.14. Is Combustion Gas Brushing a hazardous condition?
Answer. As per Boiler Vendor it has been recognized that combustion gas brushing is observed as usual phenomenon during the boiler operation.
Q.15. Explain how Combustion Gas Brushing is useful for NOx reduction?
Answer. MHI (Boiler Vendor) done some actual field tests on several industrial boilers and observed that the metal surface temperature of the furnace water tubes being brushed by the hot combustion gas is only about 20-^30^
higher than the saturated water temperature in the furnace water tubes because of the water circulation, even if the combustion gas brushing on the furnace water tubes is continuously observed. And even if the carbon adhered
to the surface of the furnace water tubes because of the flame impingement, the metal surface temperature of the tubes deposited the carbon will become lower than the ordinal temperature, because the thermal conductivity of the
tubes deposited the carbon tends to decrease.
Q.16. Explain how Combustion Gas Brushing is useful for NOx reduction?
Answer. The combustion gas brushing is useful for NOx reduction as it will decrease the temperature of the flame.
Q.17. What is the main cause of burnout trouble of water tubes in boiler?
Answer. The burnout trouble of the water tube is mainly caused by the scale adhesion at the tube inner side in consequence of the bad feed water reatment and boiler internal treatment.
Q.18. In which condition “One burner operation” is allowed?
Answer. The one burner operation is allowed only during the boiler starting operation.
Q.19. Which burner should be used for “One Burner Operation”?
Answer. If one burner operation is performed, such as the boiler starting period, the lower burner shall be used.
Q.20. Why one burner operation should be avoided?
Answer. The one burner operation shall be avoided in order to prevent the thermal unbalance between upper and lower part of the super heater tube.
Q.21. What is the maximum allowable time limit for one burner operation during Star-up?
Answer. The allowable maximum continuous operation period of one burner operation is about 2 hours (as per vendor) and this should be during start up only.
Q.22. What are the consequences of “One Burner Operation” as usual operation?
If the boiler is operated with one burner as usual operation, following consequences will be considered.
1) Water circulation Furnace dimension of this boiler will be designed as based on flame configuration of burners in service. In case of only upper burner should be operated, upper part of furnace tubes will be heated but lower part of the tubes will not be heated so much. Therefore circulation force will be decreased since effective height for natural circulation boiler becomes small. It may be cause the burst problem of the tubes. 2) Flow unbalance for SH The flue gas will go into super-heater tubes with un-uniformed flow that is unbalanced in up and down part of flue gas passing area. Therefore each set of super-heater tubes can not equally heated. This phenomenon cause steam flow unbalance and unfavorable steam temperature rise. 3) Heat damage of idle burner Idle burner can be cooled by leakage air through register. But it may be damaged by flame radiation, if one burner operation should be done continuously for long period.
Q.23. Why stable composition is important for effective combustion?
Answer. Fuel gas composition is one of the important factor to establish a successful combustion, because the fuel gas burning equipment is designed for the specified gas composition. When the fuel gas composition varies from the design value, fuel gas flow of the gas burner., gas pressure at burner, required combustion air flow, and so on are also changed and
these changes affect the combustion condition. Air-fuel ratio and minimum gas flow for the stable combustion should be re-adjusted. Therefore, it is important to supply the fuel gas in stable composition.
Q.24. Define Mothballing boiler and which gas is available at boilerfor this operation?
Answer. (HOLD) To be provided later.
Q.25. List the important safety considerations before Light off and ignition?
Answer.
Do not ignite when the drum water level is below low limit.
Do not ignite before completion of prepurge.
Do not light off the gas burner before unless the ignition of the ignitor.
Q.26. List the important safety considerations for boiler operation?
Answer.
Interlock must not be bypassed.
In case of the boiler is tripped by the interlock, do not light off the gas burner unless its cause is found and resolved.
Does not change the boiler load quickly as the ACCK Auto Combustion Control ___________ not follow
Q.27. Describe the construction of SE type Air Register?
Answer. The ―SE‖ type air register is mainly composed of a primary air djusting drum., secondary air vanes, a primary air nozzle, a swirler, a cover plate with a type MGC gas gun and a front plate with type MGL gas guns.
Q.28. Name the streams in which combustion air entering from the wind box is divided into?
Answer. The combustion air entering from the wind box is divided into a primary air stream and a secondary air stream.
Q.29. Describe the flow path of primary air?
The primary air flows through the (inner) primary air nozzle that surrounds the GC gas gun.
Q.30. What is the pupose of primary air?
Answer. The purpose of the primary air is two-fold:(a) it introduces air for initial ignition at the burner nozzles and (b) it fills the vortex created by combustion in the secondary air zone (burner throat), thereby presenting the fire from being
drawn back into the burner nozzles.
Q.31. Explain the purpose of drum adjusting rods and the swirler?
The primary air adjusting drum is operated by the drum adjusting rods. The swirler imparts rotation and velocity to the primary air at the same time in order to mix the air with the fuel and to stabilize the flame.
Q.32. Describe the flow path of primary air?
Answer. The secondary air flows around the primary air nozzle to the burner throat where it provides the necessary and sufficient air to maintain the combustion.
Q.33. Explain how secondary air rotates?
Adjustable vanes are provided at the entrance between primary and secondary air nozzles to give rotation to the secondary air.
Q.34. What is the benefit of Adjustable vanes provided at the entrance between primary and secondary air nozzles?
Answer. They are adjusted to establish desirable flame shape.
Q.35. How air-fuel ratio will be maintained in case either of two burners is out of service?
Answer. The boiler equips with two burners. When either of these two burners is out of service, the air flow through the secondary air nozzle of the burner, which is out of service, is restricted automatically by shutting the secondary air vanes to operate the air cylinder in accordance with sequence of control system to maintain allowable air-fuel ratio on the firing burner. However, the one burner operation is not suitable as described in section.
Q.36. Describe the construction of front plate in boiler?
Answer. Two observation ports, three flame detectors., a vane control lever, a quadrant for the secondary air vanes, and a gas ignitor are provided on the front plate.
Q.37. At which phase the Final position of the primary air adjusting drum and the secondary air vanes should be selected?
Answer. Final position should be selected after adjusting combustion condition on initial trial operation during initial start up or after the replacement of these parts of unit under operation.
Q.38. What is the purpose of Primary air adjusting drum and secondary air vanes?
Answer. The purpose of primary air adjusting drum and secondary air vanes is to adjust combustion condition only. It should not be used to adjust total combustion air flow.
Q.39. Why close attention should be paid to the air vanes operation mechanism?
Answer. Since the setting position of the air adjusting drum and the air vanes influences delicately to combustion condition, a close attention should be paid to the air vanes operation mechanism and the drum adjusting rods.
Q.40. What is the purpose of swirler?
Answer. The swirler and the connecting drum are made of stainless steel to prevent thermal damage.
Q.41. What is the material of construction of swirler?
The swirler and the connecting drum are made of stainless steel to prevent thermal damage.
Q.42. What will be the impact of long and continuous heat radiation on wirler?
Long and continuous heat radiation to the material may damage these parts.
Q.43. How many Observation ports are there in each boiler?
Answer. There are 02 Observation Ports are in each boiler.
Q.44. How many nozzle pipes are there for MGL type gas gun?
The gas gun assembly of type MGL consists basically of eight, parallel nozzle pipes.
Q.45. Describe the arrangement of MGL Type gas burner?
The eight pipes are arranged radially around the secondary air nozzle as a symmetrical pattern connected to the gas chamber welded on the back of the front plate of the air register.
Q.46. How fuel gas is introduced to the MGL Type gas burner?
Answer. The fuel gas (passed through the burner piping) is introduced to the inlet flange on the front plate, accumulated in the gas chamber, distributed to eight gas guns, and then discharged from the nozzle with the required atomizing angle.
Q.47. What do you mean by Atomizing Angle with respect to gas burner in boiler?
Answer. HOLD
Q.48. What are the advantages of the type of gas assembly used in boiler?
Answer. This type of gas gun assembly, which is multi-guns type separated radially, increases the area of the fuel gas contacting to the combustion air and accelerates a mixing with the combustion air for efficient combustion.
Q.49. List the equipments of electric gas ignition?
Answer. The electric gas ignition equipment is composed of
an ignitor body
an ignition plug
A high tension cable with flexible conduit tube
A transformer
Ignitor gas piping, and
Electrical wiring.
Q.50. Explain the construction of Electric Gas ignitor?
Answer. The gas ignitor is composed of
The spark plug with insulator
A insulator base
A gas pipe with nozzle
A burner tube and
A setting flange.
Q.51. Which part of the spark plug prevents current leakage?
Answer. The insulator prevents the electric current leakage of the spark plug. Moreover, the insulator covered by the insulator base to provide the excellent insulation without fear of leakage. The steatite insulator withstands high temperature.
Q.52. What can go wrong if high tension charge is continued for too long hours for ignitor?
Answer. When the high tension charge is continued for too long hours, thermal damage may be generated.
Q.53. What is the maximum time limit given by the vendor to avoid damage to ignitor?
Ignitor should not continue the discharge more than 15 minutes.
Q.54. How ignition takes place through Ignitor?
Answer. The air introduced from the air inlet holes is mixed with a small amount of gas ejected from a small nozzles at the partition plate. The air-gas mixture forms a pilot flame at these small nozzles by electric sparks and main flame of the ignitor is ignited by this pilot flame.
Q.55. How main flame is stabilized in the burner?
Answer. The produced main flame is stabilized by the air introduced through numerous small holes at the top end of the burner tube.
Q.56. How long life of the burner tube can be assured?
Answer. The gas pipe with nozzles and the top of the burner tube are made by stainless steel to assure the long life.
Q.57. What type of Air register is installed in boiler?
Answer. It is Mitsubishi SE Type.
Q.58. What type Gas Burner Guns are there in Boiler? Name them?
Answer. There are two type of Burner Guns in Boiler.
Lance Gun (Mitsubishi MGL Type)
Center Gun (Mitsubishi MGC Type)
Q.59. How many numbers of guns are there in each Air Register?
Answer. There are eight sets per register of each type of Burner Guns. Total are sixteen.
Q.60. What is the rated capacity of Lance Gun type Burner?
Answer. The rated capacity of Lance Gun Type burner is 5,888 Nm3/h per register.
Q.61. What is the rated capacity of Center Gun type Burner?
Answer. The rated capacity of Lance Gun Type burner is 1,472 Nm3/h per
register.
