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Inspections and preparations before boiler operation: Boilers are important devices that generate thermal energy by burning a working medium; they are also special types of equipment that are subject to pressure and heat, pose explosion risks, yet are widely used in various industries. Therefore, it is crucial to use the boiler properly, and to detect and handle any accidents that occur during its operation in a timely manner. Only by ensuring the safe operation of the boiler can its true function be realized. Technicians, managers, and boiler operators responsible for the management and use of boilers must have a thorough understanding of the boiler’s structure and performance. In particular, boiler operators need to possess a high sense of responsibility. They must fully understand the principles behind boiler operation, master the patterns of its functioning, and strictly adhere to all operating procedures, shift-handover protocols, and job-related responsibilities. I. Inspections before boiler ignition For newly installed boilers, boilers that have been repaired, or those that have been out of use for a long time, a thorough inspection must be carried out before starting the boiler. This is an important aspect in ensuring the safe operation of boilers, and preventing failures and accidents caused by operating them with defects. (1) Internal inspection before boiler ignition 1. The internal components of the boiler drum, such as the steam-water separator, continuous blowdown pipe (surface blowdown pipe), periodic blowdown pipe, water inlet pipe, and partitions, should be complete and in good condition. 2. The dirt inside the boiler shell (such as the shell, furnace chamber, and head of a shell-and-tube boiler), the header, and the heat-exchanging tubes must be removed completely; there should be no defects or damage, and no tools or other debris should remain inside the boiler. 3. If there are doubts regarding the degree of removal of scale from water-tube boilers or the quality of bending or installation of the boiler tubes, it is possible to use a ball-passing test to check whether the tubes are unobstructed, if necessary. After passing the internal inspection, tighten all manhole covers and access covers. (II) External inspection before boiler ignition 1. The furnace interior should be free of coking, ash accumulation, and debris, and the furnace walls, furnace arch, and fire partitions should be intact and airtight. 2. The outer surfaces of the water wall tubes and exhaust tubes shall be free of defects. 3. The dust accumulated in the air ducts and flue ducts must be removed completely; no tools or other debris should be left inside. The control valves and shutters in the air ducts and flue ducts must be intact and airtight, the switches must operate smoothly, and the opening degree indication must be accurate. After the inspection, for boilers equipped with economizers, the flue dampers of the economizer should be closed, while the bypass flue dampers should be opened. In the absence of a bypass flue, the valve on the economizer recirculation water pipe should be opened. L 4. The external furnace wall of the boiler should be intact and airtight, with devices such as the furnace door, ash door, viewing door, and manholes being complete and properly closed. 5. The auxiliary heating surface devices such as superheaters, economizers, and air preheaters are in good condition and undamaged. (III) Inspection of safety accessories and various instruments: Safety valves, pressure gauges, level gauges, thermometers, alarm devices, various thermal measurement instruments, and control devices should be complete, in good condition, clean, and well-lit. After passing the inspection, put the water level gauge into operation (open the steam and water valves, close the drain valve), and also put the pressure gauge into operation (connect the pressure measurement points). (IV) Inspection of steam and water pipes: The steam pipes, feedwater pipes, drain pipes, and sewage pipes of the boiler should be unobstructed. The supports for these pipes, as well as the insulation and connections between the pipes and valves, must be in good condition. The valve handles on all pipes should be intact, and the valves themselves should operate smoothly. After the inspection is complete, open the drain valves on the steam pipes and those on the superheater outlet headers. Also open all the valves on the feedwater pipes (the feedwater control valves should remain closed). Close the main steam valve, isolation valves, and all the sewage valves. ( V ) Inspection of combustion and auxiliary equipment 1. The combustion apparatus and grates must be in good condition. The mechanical transmission system, coal conveying system, ash discharge system, etc., are free of defects and are well lubricated. The coal gate valve moves smoothly, and the coal gate scale provides accurate readings. The eagle’s iron is neat and sturdy; the ash-flipping board is intact, and its movements are agile. After inspection, it is necessary to conduct operational tests on each mechanical transmission separately. 2. Auxiliary equipment (exhaust fans, blowers, water pumps, etc.) must be in good condition. The coupling should be firmly connected. The lubricating oil in the tank should be of good quality and in sufficient quantity. The cooling water is flowing smoothly. After inspection, install the safety guards and conduct trial runs separately. 3. The dust removal equipment should be in standby mode. (6) Inspection platforms, stairs, and fences in the boiler room and other areas must be in good condition. All scaffolding used for maintenance must be removed; the work area and pathways around the equipment should be clean and unobstructed, with adequate lighting. The electrical control instruments in the boiler room control room, as well as the instruments and protection/alarm devices installed on the control panels, are in good working condition; all the tools commonly used by boiler operators are available. After the inspection is completed, the inspection process and the steps taken to address any issues should be recorded in a logbook. II. Preparations before boiler ignition (1) Filling the boiler with water: The boiler can be filled with water only after it has been checked to meet the operational requirements. Before adding water, it is necessary to contact the operators of the boiler that is in operation to avoid interfering with its water supply. When filling water, soft water that has passed quality testing should be used. Water enters the boiler through the economizer. The feed water temperature should not be too high, to prevent uneven heating of the boiler, which could lead to thermal stress, or to the formation of gaps at the expansion joints that might cause leakage. For cooled boilers, the inlet water temperature shall not exceed 90 in summer. C, not exceeding 60 in winter. C. During the water filling period, it is necessary to check whether there are any leaks in the manholes and handhole covers of the boiler drum and header, as well as in the valves, flanges, plugs, and other components throughout the system. If a leak is detected, the water supply should be stopped immediately to carry out repairs. Water should be added slowly, and even more slowly as the water level rises; it should reach the level between the low-water mark and the normal water level. For boilers that have just been filled with water, those that are newly installed, have undergone major repairs, or have been out of use for more than a year, pressure testing, drying, and boiling tests must also be carried out; those that have been out of use for a shorter period can be started up and put into operation. (II) Ovens: For newly installed boilers with brick walls, as well as those whose wall and arch structures are fully or partially renewed during maintenance, the mortar joints in these walls and arches contain a large amount of moisture, which needs to be dried and hardened. If it is put into operation without a gradual drying process, as the temperature in the furnace rises rapidly, the parts of the furnace walls and arches that are exposed to high temperatures expand due to heat. The moisture in the mortar evaporates quickly, causing it to dry fast under the effect of steam. However, the outer layers of the furnace walls and arches have lower temperatures; the mortar there has not dried yet and lacks sufficient strength and cohesion. Under the forces exerted by the expanding inner layers of the furnace walls and the generated steam, these outer layers will inevitably deform, develop cracks, or even collapse. Therefore, before operating a furnace with newly built furnace walls and arches, it is necessary to carry out baking and drying of the furnace walls and arches. This process of pre-drying the furnace walls and arch is called furnace drying (or baking). Before heating the furnace, the following tasks must be completed: 1. The boiler equipment, safety accessories, and auxiliary devices have been inspected to ensure they are in proper working condition, and water has been added following the specified procedures and requirements. 2. The expansion indicators on the boiler drum and header shall be in good condition. 3. Open the air valve of the boiler and the drain valve of the superheater outlet header. 4. The boiler water level should be maintained at the minimum level, and the water level gauge should be pressure flushed in one direction. 5. Install temperature measuring instruments on the furnace wall surface at the superheater outlet or between the first and second fire partitions. 6. Set the mortar sampling points and temperature measurement points in the furnace chamber. The mortar sampling point is located 1.5–2 meters above the grate, at a depth of 100 mm in the red bricks of the exterior wall. 7. Prepare enough wood, fuel, and ignition materials (flammable or explosive items are not allowed to be used as ignition materials). Firewood used for mechanical grills must not contain nails, to prevent the grill from getting stuck and causing malfunctions), as well as tools for stoking the fire in the oven. The method, time, and procedure for heating the furnace are as follows: Heating the furnace is an important and delicate task; it is essential to avoid being impatient and increasing the heat level excessively. In the initial stage of furnace drying, the furnace walls and arch should be dried evenly at a lower temperature, after which the drying temperature should be increased gradually to allow the moisture within the furnace walls and arch to evaporate over time, until they are completely dry. The length of the furnace drying time and the rate of temperature rise should be determined based on the type of boiler, the structure of the furnace walls, the degree of wear on those walls, and the duration of natural drying. The drying time for general industrial boilers is 3 to 14 days, and the temperature rise rate can be referred to in Table 8-1. For boilers with locally renewed furnace walls, the rate of temperature rise can be determined based on the times and temperatures listed in the table; however, the drying time must be no less than 3 days. The rate of furnace temperature rise is controlled by the flue gas temperature at the superheater outlet; for boilers without a superheater, it is controlled by the flue gas temperature between the first and second fire partitions. During the first 3 to 6 days of heating the furnace, use wood for heating in order to avoid excessively high local temperatures that could cause defects such as deformation and cracks; wet wood should be dried first or used mixed with dry wood. Around the fourth day of heating the furnace, a small amount of coal can be added to the burning wood, so as to gradually replace the wood with coal for heating the furnace. The precautions are as follows: 1. After heating the furnace with coal, it is acceptable for the water in the pot to be at a slight boil; if the boiling is too intense, it should be reduced, and water can be added or removed as appropriate to lessen the degree of boiling. 2. During heating, the steam generated by the boiler should be discharged through an air valve or a lifted safety valve. The boiler water level must be maintained at the lowest mark indicated by the water level gauge; water should be added promptly if a drop in level is observed. 3. During the heating up of the chain furnace, the grate must be rotated regularly to prevent damage. 4. During the baking process, it is necessary to control the rate of temperature increase in accordance with the specified times and temperatures for heating. Fluctuations in temperature are not allowed, nor is any interruption during the process; at the same time, records of the temperature increase must be kept. Acceptance criteria for furnace drying: (1) The surface temperature of the furnace wall is uniform, with the temperature at the sampling point reaching 50. After C, continue baking for 48 hours to be considered qualified. Boiling the furnace can be carried out simultaneously within these 48 hours. (2) Take mortar samples from the sampling points and analyze their moisture content; if the moisture content of the mortar is below 2.5%, the furnace is considered qualified. When the moisture content is close to 2.5%, furnace heating can begin. (III) Boiling out: Boilers that are newly installed, have their pressure-bearing components overhauled, or have been out of use for a long time must undergo a boiling-out process before being put into operation. Boiler descaling involves adding chemicals to the boiler water and then boiling it, thereby dissolving, loosening, and removing dirt and rust from the metal surfaces inside the boiler. This prevents corrosion and overheating of the heating surfaces, ensuring the quality of the boiler water and steam during operation. The boiling process can be carried out immediately after baking, or it can be done simultaneously during the later stages of baking. Before starting to boil the water, the chemicals and equipment for adding them should be prepared. Dosage and method of adding chemicals: The dosage of chemicals to be used in the boiler can be determined based on the amount of dirt and rust inside the boiler, in accordance with the specifications given in Table 8-2. Note: ① Drugs are calculated based on 100% purity. ②When preparing the medication, the amount of water in the pot should be calculated as 1.25 to 1.5 times the volume of water when the pot is at its maximum level. ③In the absence of trisodium phosphate, anhydrous sodium carbonate (Na2CO3) can be used as a substitute, in an amount equal to 1.5 times that of trisodium phosphate. First, dissolve stannum hydroxide and trisodium phosphate in water, stir well to prepare a 20% concentration solution, and remove impurities. When adding chemicals, the boiler should be kept at its lowest water level; the prepared solution is then added to the boiler from the top. It is also possible to use devices for adding chemicals inside the boiler, or alkali pumps, to introduce the chemicals into the boiler. After adding the chemical, fill the boiler with water up to the maximum level. Method of boiling the furnace: 1. Start a low flame in the furnace chamber and slowly bring the water in the pot to a boil; the steam generated can be released through the air valve or the lifted safety valve. 2. Adjust the opening of the combustion and air valves (or safety valves). Maintain the boiler at 25% operating pressure (for 6–12 hours at a steam generation rate of 5%–10%). If boiling the furnace is carried out simultaneously in the later stages of drying, this boiling time can be appropriately reduced. 3. Reduce combustion, lower the pressure in the boiler to 0.1 MPa, allow the regular blowdown valve to discharge waste sequentially, and add make-up water or the remaining amount of chemical solution. 4. Increase the combustion further to raise the pressure inside the boiler to 50% of the operating pressure, and maintain an evaporation rate of 5%~10% for 6~20 hours. 5. Reduce the combustion to lower the pressure, discharge waste water from the regular blowdown valves one by one again, and add make-up water. 6. Raise the pressure in the pot to 75% of the operating pressure, and maintain a evaporation rate of 5%~10% for 6~20 hours. During boiler operation, the water level in the boiler should be maintained at the maximum level. When the water level drops, water should be replenished promptly. To ensure the effectiveness of boiler operation, water samples from the upper and lower boiler drums as well as from various drain points should be taken every 3–4 hours. The alkalinity and phosphate content of the boiler water are analyzed; if there are significant differences, adjustments can be made by draining water. If the alkalinity of the boiler water is below 1 mmol/L, chemicals should be added to the boiler. Boiling standard: When the content of trisodium phosphate stabilizes, it indicates that the chemical reactions between the chemicals in the boiler water and the rust and scale on the inner surface of the boiler have essentially come to an end, and thus the boiling process can be concluded. After the boiling process is complete, extinguish the remaining fire in the furnace, drain all the water from the boiler once it has cooled down, and clean the interior of the boiler with clean water. It is necessary to prevent foam from forming in the boiler water due to the highly alkaline solution remaining in the boiler after it starts operating normally, as this could affect the quality of the steam. After brushing, it is also necessary to inspect the inner walls of the boiler drum and header tanks, removing all debris thoroughly. In particular, careful attention should be paid to the blowdown valve and water level gauge, to prevent deposits formed during boiling from blocking the passages. After passing the inspection, add water to the boiler again and turn on the heat to bring it back into normal operation. Precautions for boiler operation: 1. Solid chemicals must not be added directly into the boiler; when preparing or adding chemical solutions to the boiler, protective equipment should be worn and safe operating procedures must be followed. 2. In boilers equipped with superheaters, it is necessary to prevent alkaline water from entering the superheater. 3. The processes of increasing heat input and pressure during boiler operation should comply with all the regulations and procedures applicable during normal boiler operation (such as flushing the water level gauge, tightening screws on access holes and manholes, and other precautions).