Q.1. Under what condition boiler is fired and describes briefly the path of flue gas?
Answer. The boiler is fired under a positive pressure (pressurized) and the Flue Gasses (products of combustion) travel the full length of the furnace before entering the convection bank.
Q.2. How many passes are there in boiler for flue gasses?
Answer. The Boiler unit is a single pass, that is, the gases make one full turn at the rear side of the furnace and are discharged at the front end of the unit.
Q.3. How high ratio of furnace cooling is achieved in the Boiler package?
Answer. The furnace is almost composed of water cooled tube panels thus providing a very high rat io of furnace cool ing to furnace volume. The high rat io of furnace wal l cooling results in rapid & efficient heat absorption. It will also reduce the Flue gas temperature that is entering the convection bank.
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Q.4. What kind of tubes used for furnace walls, floor and roof?
Answer. The furnace walls, floor and roof consist of fin-welded tubes, backed by sufficient insulation to afford a cool casing wall.
Q.5. The abbreviation “PSV” stands for?
Answer. PRESSURE SAFETY VALVE.
Q.6. What is the purpose of PSVs?
Answer. The purpose of PSV is to protect the Pressure parts in the system by relieving the system material to dedicated place (Atmosphere or any other system) in case system pressure exceeds the set value of PSV.
Q.7. How many PSV are there at Boiler steam drum?
Answer: There are two PSV‘s in steam drum.
Q.8. Which design feature helps to get high purity steam?
Answer. The steam drum and the drum internals are designed in such a way that these will give high steam purity.
Q.9. What is the purpose of providing large steam drum?
Answer. The boiler is equipped with a large steam drum to provide an adequate steam storage capacity corresponding to its pressure and evaporation rate and minimize drum water level fluctuations caused from sudden changes of steam demand.
Q.10. What type of Steam/Water mist separator is installed in steam drum?
Answer. The steam drum is equipped with scrubber and centrifugal type of Steam/Water mist separator.
Q.11. What do you mean by term “entrained water” with reference to steam drum and how it is being removed?
Answer. The steam generated in the furnace tubes and boiler tubes is discharged into the steam drum, where entrained water is effectively removed by drum internals.
Q.12. What is the concentration of Na, Fe, SiO2 and Cl- in steam leaving the
steam drum?
Steam drum internals are designed to produce steam containing not more than 0.02 ppm of Na, Fe, SiO2 and 0.01 ppm of Cl with the recommended boiler water concentrations.
Q.15. Describe Primary separation with reference to steam drum?
Answer. Steam/Water mixture entering the drum from the riser tubes is collected in the chamber formed by baffle plates.
The steam/water mixture is led to the centrifugal separator to remove moisture particles from them.
Q.16. Describe Secondary separation with reference to steam drum?
After this primary separation, the steam/water mixture rises upward again. During this process, moisture is removed by the gravity forth as secondary separation.
Q.17. What is the purpose of Scrubber type steam dryers in steam drum?
The Purpose of Scrubber type steam Dryers is to remove the remaining moisture left after Primary and Secondary separation.
Q.18. Explain how “separated water” from “Scrubber type steam dryers”
mixed with Feed Water in steam drum?
Answer. The water separated from steam/water mixture is returned to the ater side of the drum through the drain pipes from this scrubber type steam dryers and is mixed with feed water before it enters into the down-comer tubes.
Q.19. How solid concentration is being maintained in steam drum?
Answer. A part of solids concentrated in the boiler water is discharged through the continuous blow-down pipe from this steam drum.
Q.20. What is the purpose of IBD?
Answer. The intermittent blow-down prevents concentration of impurities in boiier water.
Q.21. What is the size of IBD nozzle and how many nozzles are there in each boiler?
Answer. The Intermittent blow-down nozzle size is 2″ mm and there are 2 sets of each in each boiler. FURNACE
Q.22. Which side of the furnace is not covered with water tubes? Why?
Answer. The front wall of the furnace is not covered with water tubes as it consists of burner register, wind box. The inner steel skin-casing covered with fire brick, cast-able refractory.
Q.23. Why furnace bottom is covered with fire bricks?
Answer. The furnace bottom is covered with fire bricks to protect the wall from higher heat radiation and to make sufficient water circulation. BANK TUBES
Q.24. What do you understand by IN-LINE Arrangement of tubes?
Answer. IN-LINE arrangement means (HOLD)
Q.25. What is the advantage of in line arrangement of convection bank tubes?
Answer. The boiler convection bank tubes are arranged in line. The in line’ arrangement has advantages of easy inspection and easy replacement of tubes. All bank tubes are connected to the drums by expanding. SUPERHEATER
Q.26. What type of super-heater is installed in Boiler?
Answer. Super-heater is of Horizontal drainable type super-heater.
Q.27. How heat is transferred to super-heater?
Answer. Heat from combustion gas is transferred by radiation and Convection.
Q.28. How heat is distributed uniformly to super-heater?
Answer. Baffle wall is constructed with spaced tubes and fire bricks, which separates Super-heating area from boiler bank area and also helps combustion gas going through super-heater uniformly.
Q.29. Which design feature helps in adjusting final steam temperature at the outlet of super-heater?
Answer. Final steam temperature is adjusted by the opening of superheater baffle wall by installing fire bricks between spaced wall tubes. DESUPERHEATER
Q.30. What is the purpose of Desuperheater?
Answer. The purpose of Desuperheater is to control total steam temperature.
Q.31. What type of Desuperheater is installed in our steam system?
Answer. Desuperheater is of Water Spray type. BOILER CASING
Q.32. By what mean the boiler and furnace is enclosed?
Answer. The boiler and furnace is enclosed by means of gas tight pressurized welded wall.
Q.33. What is the material of construction of Boiler outer casing?
Answer. The material of construction of Boiler outer casing is ribbed galvanized steel plate. Its thickness is 0.8 mm.
Q.34. Which material is used to cover the gap between Welded wall and Boiler outer casing?
Answer. Rock Wool (Mineral Glass Wool) Blanket Insulation is used between welded wall and boiler outer casing. These are fixed on welded walls.
Q.35. Which phenomenon helps the expansion of Pressure parts without putting excessive stress?
Answer. Rock Wool (Mineral Glass Wool) Blanket Insulation Boards which are used to insulate the most part of the casing, are very soft and light, due to this the casing freely expand entirely without excessive stresses.
BOILER INSULATION QUESTION AND ANSWERS
Q.36. What is Insulation?
Answer. Insulation is nay material that is a poor conductor of heat, and thus can serve to keep heat confined or excluded by preventing or resisting heat transfer.
Q.37. Explain Thermal Conductivity?
Answer. The amount of heat flowing through a given thickness of material with a given temperature difference between two faces is known as thermal conductivity of that material.
Q.38. Why Boiler & Furnace are insulated?
Answer. The boiler and furnace are insulated entirely with adequate insulating materials to minimize the heat loss from the surface of the casings.
Q.39. Which insulation material in Boiler is Fire-Proof?
Answer. The fire bricks for floor covering and cast-able refractory for pocket fillings are the only Fire-Proof insulating materials.
Q.40. What is Castable Refractory?
Answer. (HOLD) Castable refractory material between furnace roof tubes and furnace roof skin casing, in particular those below roof tube center inside the furnace), may partially fall due to pattern of castable refractory material pouring, however there are no problem for boiler operating continuously. No any repair and/or replacement works are needed.
Castable and plastic refractory materials contain moisture. As drying and dehydration expansion during operation show cracks due to creep in compression.
Usually, the furnace wall has score line or separation cut to absorb this shrinkage so that cracks may be minimized. Cracks may occur for various reasons. They may be observed on areas other than the score line and separation cut.
Q.41. When Castable Refractory needs repair if cracks observed?
Answer. Castable Refractory need repair of these depends on following phenomena.
Bulge
Separated block surrounded by cracks which become loose and move.
ECONOMIZER QUESTIONS AND ANSWERS
Q.42. What is function of Economizer?
Answer. The function of the economizer is to preheat the boiler feed water before it is led to the steam drum, by recovering some of the heat of the flue gas leaving the boiler.
Q.43. Which type of Economizer we have and where it is installed?
Answer. The economizer is located beside the boiler and it is of Counter Flow Type.
Q.44. What type of tubes are used in economizer and why?
Answer. The Economizer is consists of one block and is composed of a number of staggered, fined tubes. Fined tubes are used to increase the amount of effective heating surface.
Q.45. How much heating surface is available in economizer?
Answer. The Heating surface available in economizer is 1,875 m2 . FIRING EQUIPMENT
Q.46. What type of Air register is installed in boiler?
Answer. It is Mitsubishi SE Type.
Q.47. 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.48. 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.49. 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.50. 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.
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