Basics to know for beginners in boiler operation

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1. The equipment in the boiler room consists of two parts: the boiler itself and its auxiliary equipment. 2. The boiler itself is mainly composed of two major parts: the (“boiler”) and the (“furnace”). 3. Boiler auxiliary equipment: ① Coal handling and ash removal systems ② Ventilation system ③ Water and steam systems ④ Instrument control system. 4. Evaporation rate: The rated amount of steam produced by a steam boiler per hour, usually denoted by the symbol D, with the unit being t/h. For hot water boilers, the rated thermal efficiency is used to indicate their capacity; it is commonly denoted by the symbol Q, with the unit being MW. The so-called thermal power refers to the power at which the heat balance temperature rise of a reducer during continuous operation does not exceed the maximum allowable value. For ordinary small and medium-sized reducers, their thermal power is either higher than their mechanical power or quite close to it. 5. Evaporation rate of boiler heating surfaces: The amount of steam generated per hour per square meter of heating surface; it is denoted by the symbol D/H, with the unit being kg/(m²•h). 6. Heat generation rate of the heating surface: The amount of heat produced per hour per square meter of the heating surface in a hot water boiler, denoted by the symbol Q/H, with the unit being kJ/(m2•h). 7. The industrial analysis of coal involves determining the contents of moisture (M), volatile matter (V), fixed carbon (C), and ash (A) in coal, in order to indicate certain combustion properties of the coal. 8. After the moisture and volatile components are removed from coal samples, the remaining solid material is called coke, which consists of fixed carbon and ash. 9. Standard coal refers to coal for which the lower heating value on a received basis is assumed to be 29,308 kJ/kg (7,000 kcal/kg). 10. The heat balance equation for a boiler can be expressed as follows: Heat input to the boiler = Heat effectively utilized by the boiler + Sum of all heat losses. 11. This heat balance equation can also be written as Qr = Q1 + Q2 + Q3 + Q4 + Q5 + Q6, in kJ/kg. 12. Heat loss due to incomplete combustion of solids: In boilers that use solid fuels, some of the solid combustibles do not burn completely inside the furnace or are discharged outside without being fully burned, resulting in heat loss; this is also known as mechanical incomplete combustion loss. 13. Heat loss due to incomplete combustion of solids is one of the major types of heat losses in boilers that use solid fuels. 14. For boilers burning gaseous or liquid fuels, q4 can be considered as 0 during normal combustion; it is larger for solid fuels. 15. The main factors affecting the heat loss due to incomplete combustion of solids include the boiler’s combustion method, fuel properties, and the operating conditions of the boiler. 16. Flue gas heat loss: The temperature of flue gases is higher than that of the air entering the boiler. The heat lost when these gases leave the boiler and are released into the atmosphere constitutes a significant portion of the boiler’s total heat losses. 17. The main factors affecting the heat loss from exhaust smoke are (exhaust smoke temperature) and (exhaust smoke volume). 18. Heat loss due to incomplete combustion of gases: refers to the heat loss that occurs as a result of some of the combustible gases (such as CO, H2, etc.) failing to burn and release heat, and thus being expelled with the flue gases; it is also known as heat loss due to chemical incomplete combustion. 19. A reasonable excess air coefficient should minimize the sum of the three types of heat losses: q2, q3, and q4.
20. There are various types of steam-water separators; those commonly used in industrial boilers include: ① inlet baffles; ② orifice plates submerged in water; ③ uniform steam distribution plates; ④ steam collection pipes; ⑤ shell-type separators.
21. Internal components within the steam drum of hot water boilers include: ① water distribution pipes; ② water separation plates; ③ hot water outlet pipes.
22. Natural water circulation is widely employed in steam boilers.
23. Common water circulation failures include the following: ① stagnation of steam and water; ② stratification of steam and water; ③ presence of steam in downcomer pipes.
24. Water wall tubes are vertically arranged along the inner walls of the furnace; their primary function is to absorb radiant heat from high-temperature flue gases. They represent one of the main heating surfaces of the boiler. Additionally, they help reduce damage to the furnace walls caused by slag and high-temperature flue gases, thereby protecting the walls.
25. The methods for connecting convection tube bundles are expansion jointing and welding.
26. Convection tube bundles can be arranged either in a staggered pattern or in an in-line pattern.
27. The heat transfer efficiency of convection tube bundles primarily depends on the flow velocity of flue gases.
28. Steam superheaters can be classified into radiant type, semi-radiant type, and convective type based on their mode of heat transfer ； Based on the installation method, they are divided into vertical and horizontal types. 29. Economizer and its function: An economizer is a boiler component that uses the heat from the flue gases at the rear of the boiler to heat the feed water, thereby reducing the exhaust gas temperature; it is installed in the flue duct behind the convective tube bank. The boiler feedwater is heated by the economizer, which raises its temperature and lowers the flue gas temperature. This reduces heat loss, thereby saving fuel and improving the boiler’s thermal efficiency. 30. Steel tube economizers belong to (boiling-type economizers).
31. An air preheater is a heat exchanger that utilizes the waste heat from the flue gases at the boiler’s tail end to heat the air required for combustion; it is generally installed after the economizer. 32. The use of air preheaters (advantages): on the one hand, it can reduce the heat loss in the boiler’s exhaust gases and improve the boiler’s thermal efficiency ； On the other hand, it converts the cold air entering the furnace into hot air, improving the combustion conditions inside the furnace, raising the combustion temperature, and enhancing the heat transfer effect. 33. Corrosion in air preheaters usually occurs on the flue gas side. 34. The furnace wall is the outer wall that constitutes the boiler’s combustion chamber and flue ducts; it prevents heat from escaping, serves to insulate and seal, and ensures that the flue gas flows in the desired direction. 35. For solid fuels, *it is conventionally divided into three stages: the preparation stage for combustion, the combustion stage, and the burnout stage. 36. Advantages and disadvantages of coal pulverized fuel boilers (essay question): Since the coal is ground into very fine powder, the surface area in contact with air **increases**, which accelerates the ignition and combustion of the fuel. Therefore, coal-fired boilers can adapt to various fuels, and combustion is relatively complete; the thermal efficiency of such boilers exceeds 90%. Almost all power station boilers in China use this type of combustion method. However, this type of boiler requires a complex pulverizing system, and its operation consumes a great deal of electricity. Furthermore, the furnace temperature fluctuates with changes in the amount of coal burned, affecting the stable combustion of pulverized coal. As a result, the load of pulverized coal furnaces can only be adjusted within the range of 70% to 100%; it is not possible to dampen the fire as can be done in grate-fired furnaces. Furthermore, the dust concentration in the flue gas emitted from pulverized coal furnaces is high, resulting in severe dust pollution; this somewhat limits the application of pulverized coal furnaces in industrial boilers. 37. Fuel oil furnaces typically use (heavy oil) as fuel, while small and medium-sized boilers use light diesel oil. ) 38. Since the boiling point of fuel is always lower than its ignition point, fuel typically burns in a gaseous state. 39. A horizontal water-tube and fire-tube boiler is a horizontal external combustion boiler that combines (water tubes) and (fire tubes). 40. The selection of boiler types and quantities depends mainly on: ① the heat load of the boiler room, ② the requirements regarding the heating medium and its parameters, ③ the type of fuel to be used. 41. Once the thermal load of the boiler room and the type of fuel have been determined, the following requirements should be considered comprehensively when selecting the type of boiler: ① It must meet the requirements regarding the type and parameters of the heating medium ； ②It can effectively burn the fuel used ； ③ The selected boiler offers good economic and environmental benefits in terms of capital investment, operation and management, as well as environmental protection, and can adapt to changes in heat load in an economical and efficient manner. 42. Setting up a reasonable ash and slag removal system is one of the important conditions for ensuring the normal operation of boilers. This system is generally divided into (manual), (mechanical), and (hydraulic) ash removal systems. 43. For gas boiler rooms, there is a gas supply system for the boiler room, which consists of gas supply pipeline inlet devices, piping systems within the boiler room, as well as purge and vent pipelines. 44. Vent pipes shall be installed in the gas system at the following locations: ① In front of the main shut-off valve on the inlet pipe of the boiler room (in the direction of flow) ； ②The end of the gas main; the highest point of pipes and equipment ； ③Pipe section between the two shut-off valves before the burner ； ④Other appropriate locations in the system to consider for venting. 45. The soot in the flue gas from coal-fired boilers consists of two components. Part of it consists of tiny carbon particles (carbon black) resulting from the thermal decomposition of coal; these particles have a diameter of 0.05–1.0 μm. When there is a large amount of carbon black in the flue gas, black smoke is formed. Another portion consists of ash particles and tiny carbon particles that are carried away due to the disturbance caused by the flue gases; these are also known as fly ash, with particle sizes generally ranging from 1 to 100 μm. 46. Soot concentration: The soot concentration in the flue gas emitted by boilers is defined as the mass of soot contained in 1 m³ of flue gas, measured in milligrams; this value is referred to as the soot concentration. 47. The common dust removal methods used in boilers are (dry) and (wet). 48. Working principle of cyclone separators: Dust-laden flue gas enters tangentially at a speed of 15–20 m/s into the annular space between the separator shell and the exhaust pipe, forming a downward-moving outer swirling airflow. At this point, the flue gas begins to move in intense rotational motion; under the effect of this motion, the particles contained within the flue gas are thrown against the wall of the cylinder, and then move downward along the cone together with the flue gas, eventually falling into the ash hopper at the bottom of the dust collector. Due to the rotation of the air flow and the suction effect of the exhaust fan, a negative pressure is created at the center of the cyclone chamber. This causes the flue gas, which has moved to the bottom of the chamber and been purified, to change direction; the axis of the dust collector then moves upward, creating a rotating upward airflow that is discharged through the exhaust pipe at the top of the collector. 49. The flue gas volume often varies greatly during boiler operation; it increases when the boiler is operating at high load ； During low-load operation, the smoke exhaust volume is low. 50. There are three types of mechanical ventilation: negative pressure ventilation, positive pressure ventilation, and balanced ventilation. 51. Air and flue gas ducts: The boiler air supply duct refers to the duct running from the air intake to the inlet of the forced draft fan, and then from the outlet of the forced draft fan to the furnace ； Smoke exhaust ducts refer to the connecting pipes that run from the smoke outlet of the boiler or economizer to the inlet of the exhaust fan, and then from the outlet of the exhaust fan to the inlet of the chimney; these two types of pipes are collectively referred to as air and smoke ducts. 52. The resistance generated by the flow of air and flue gas in the boiler ventilation system includes the frictional and local resistances in the air and flue gas ducts, the resistance of combustion equipment Δhr, the resistance of the boiler proper Δhg, the resistance of the economizer Δhs, the resistance of the air preheater Δhk, the resistance of the dust collector Δhc, and the resistance of the chimney Δhyc. 53. For boilers equipped with mechanical ventilation, the flue resistance is primarily overcome by fans. The main function of the chimney is to discharge soot and dust into the upper atmosphere for dispersion, thereby reducing the environmental pollution caused by fly ash and flue gases, and keeping the surrounding environment within acceptable pollution levels. 54. The exhaust fan should be located behind the dust collector, in accordance with the flue gas flow direction, to reduce wear on the fan blades and casing caused by dust. 55. There are two methods for adding chemicals to the pot: ① intermittent addition ② continuous addition. 56. Factors to be considered when determining the thermal system of a hot water boiler: ① The outlet water pressure during the operation of the hot water boiler should not be less than the saturation pressure corresponding to the maximum feedwater temperature of the boiler plus 20°C, in order to prevent boiling within the boiler (except for hot water systems that maintain pressure using steam generated by the boiler itself). ②In boiler rooms utilizing multiple heating pipes and multiple return pipes, distributors and collectors shall be installed; their diameter is estimated at 1.5–3dmax. ③Measures shall be taken to prevent or mitigate boiler water vaporization and water hammer caused by the sudden shutdown of the system’s circulating pump. ④Attachments for the hot water system: ⑤ Installation of the circulation pump; ⑥ Installation of the make-up water system; ⑦ Pressure stabilization setup. 57. Soft water is injected into the boiler to heat it and raise its pressure to 0.3–0.4 Mpa, after which the flanges, manholes, access holes, and other connection bolts within the boiler are tightened while the boiler is still hot. 58. The seating pressure should be 1.12 times the operating pressure, and must not be less than the operating pressure plus 0.07 MPa ； The safety valve with a higher seat pressure should be 1.14 times the operating pressure, and shall not be less than the operating pressure plus 0.1 Mpa. 59. Regulation for the normal operation of boilers: ① Control the water level; ② Adjust the gas pressure; ③ Control the water quality; ④ Regulate the negative pressure in the furnace. 60. Hot water boilers operate with a full water level; therefore, there is no need for water level regulation. The combustion regulation is the same as that for steam boilers. 61. Shutdown methods: ① Smothering shutdown; ② Normal shutdown; ③ Emergency shutdown. 62. The commonly used methods for boiler shutdown maintenance include (dry maintenance) and (wet maintenance). 63. Causes of boiler accidents: lack of water in the boiler, excess water in the boiler, foaming, tube rupture, and furnace explosion. 64. Common faults of hot water boilers: ① Over-temperature vaporization of hot water boilers; ② Tube rupture in hot water boilers. 65. Periodic inspections for in-service pipelines, including ① external inspection, ② internal inspection, and ③ hydrostatic test.