Maintenance of boilers

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Maintenance of Boilers I. Maintenance when the Boiler is Shut Down Boiler maintenance is a measure to prevent metal corrosion and thinning. The condition for corrosion to occur on the heating surfaces of a boiler is when the metal comes into contact with moisture and oxygen. Therefore, to prevent corrosion, it is necessary to either remove all moisture from the pot, or eliminate oxygen from the water inside the pot, or prevent the oxygen in the water from reacting chemically with the metal. If the shutdown lasts around 10 days, anti-corrosion measures that eliminate oxygen in the water inside the boiler can be employed. After shutting down the boiler, close all doors and baffles to seal it, thereby slowing down cooling significantly; maintain the steam pressure inside the boiler above atmospheric pressure and keep the temperature of the water at 100 degrees. C or above, to prevent corrosion. If the shutdown period is long and the boiler must be completely cooled, additional measures should be taken. There are generally two types of anti-corrosion measures used in small boilers: dry method and wet method. 1. Dry maintenance: The principle of dry maintenance is to keep no moisture inside the pot. The specific procedure is to first clean the scale, dirt, and rust from inside the boiler, then open the manholes and access holes, and dry out the interior of the boiler either by allowing it to air dry or by using wood to create a very small flame on the grate in order to dry it out. If there is a vertical superheater, it must be dried using compressed air or hot air. After that, an uncovered non-metallic container containing desiccant should be placed inside the boiler. Once it is in place, it is necessary to ensure that no debris or other items remain inside the boiler. All valves, water valves, manholes, and access holes must then be tightly closed to prevent air from entering and to keep the internal surfaces of the boiler dry over time. To prevent external corrosion on the outer surface of the pot due to water vapor condensation, it can be baked at a very low heat level from time to time (or desiccants can be used). Desiccants generally include anhydrous calcium chloride, quicklime, or silica gel. For each cubic meter of volume, 1–2 kg of anhydrous calcium chloride, 2–3 kg of quicklime, or 1.5–3.0 kg of silica gel should be added. After placing the desiccant in the pot, it should be checked every three months or so to replace any expired desiccant promptly. Before starting the fire, simply remove the container holding the desiccant and close the manhole, after which water can be added as specified to start the fire. Dry maintenance is suitable for boilers that will be out of use for a long time. 2. Wet method maintenance: The principle of wet method maintenance is to prevent oxygen in the water inside the pot from reacting with the metal surface. When the pot is filled with an alkaline solution of a certain concentration, an alkaline bubble protective layer is formed on the metal surface, preventing the metal from corroding. The specific steps for wet maintenance are the same as those for dry maintenance: it is necessary to clean away scale and rust from inside the pot, and then add an alkaline solution. Before adding liquid, all relevant valves should be checked and tightly closed to prevent the alkaline solution from leaking into the operating system, and at the same time to prevent water from the operating system from leaking into the standby boiler, which could reduce the concentration of the alkaline solution. Reduce the heat to a low level, keeping the outside of the boiler dry while heating the water inside to 80–100 degrees. c. As convection occurs due to the heating of the solution, this helps to make the concentration of the solution uniform throughout the pot. The amount of chemical added to the tank is as follows: soft water is used in the tank, with 10 kg of NaOH or 20 kg of Na3PO4 added per ton of water. Test the pH value of the boiler water every 5 days, with the target range being 10–12. If the alkalinity is low, more alkali solution needs to be added. Wet maintenance is suitable for boilers that will be out of use for a short period of time. It is not advisable to use wet maintenance in areas with low temperatures, to prevent the boiler water from freezing and damaging the boiler. II. Regular maintenance of boilers: The regular maintenance of boilers should be carried out jointly by operators and maintenance staff. During the operation of the boiler, maintenance work should be carried out primarily by the boiler operators, with the maintenance staff playing a supporting role; this type of maintenance is known as level 1 maintenance. In addition to carrying out level 1 maintenance, scheduled shutdowns of the plant to perform equipment repairs or replace components are referred to as level 2 maintenance. Secondary maintenance work should be carried out primarily by maintenance personnel, with operational staff playing a supporting role. 1. Primary maintenance of boiler equipment: Under normal circumstances, primary maintenance should be carried out once every 1 to 3 months while the boiler is in operation. Special issues (such as leaks in water level gauges, damaged lighting, etc.) should be addressed promptly during routine operation and maintenance as well as during routine inspections. The specific timing of the maintenance cycle, as well as the contents and requirements for maintenance, are as follows: (1) Shell-and-tube boilers. For shell-and-tube boilers with an evaporation capacity of 1 t/h or less, maintenance is required once per month during operation; for those with an evaporation capacity of 1 t/h or more (including gt/h), maintenance is needed once every three months. The parts to be maintained, as well as the maintenance tasks and requirements, are shown in Table 8-9. (2) Water-tube boilers. For water-tube boilers with an evaporation capacity of 1 t/h or less, maintenance is required once per month during operation; for those with an evaporation capacity of 1 t/h or more (including 1 t/h), maintenance is required once every 3 months. The parts to be maintained, as well as the details and requirements for maintenance, are shown in Table 8-10. (3) Quick-install boilers. Quick-install boilers require primary maintenance once every 3 months of operation. The parts to be maintained, as well as the details and requirements for maintenance, are shown in Table 8-11. 2. Secondary maintenance of boiler equipment: After the boiler equipment has been in operation for one year, secondary maintenance is required. (1) Shell and tube boilers. The parts, maintenance tasks, and requirements for the maintenance of shell-and-tube boilers are shown in Table 8-12. (2) Water-tube boilers. The areas, tasks, and requirements for the maintenance of water-tube boilers are shown in Table 8-13. (3) Quick-install boilers. The parts, maintenance tasks, and requirements for the maintenance of quick-install boilers are shown in Table 8-14. III. Maintenance of fuel and gas boilers when they are shut down: The maintenance of fuel and gas boilers after they are shut down primarily involves the upkeep of the burners. The maintenance of burners mainly includes the following: (1) Cleaning and maintenance of the burner: Loosen the hinge shaft of the burner and open the combustion head; clean the combustion components with a cleaner or cloth, check and adjust the gap of the ignition rod, clean the flame detector with a soft cleaning cloth, and thoroughly clean the air ducts and fan impellers. (2) Maintenance of the fuel and gas systems: Remove the fuel lines, clean the fuel filter, and open the drain valve of the daily use fuel tank to remove water and dirty oil impurities. (3) Maintenance of the circuit system: Check whether all connection points are secure and whether the contact components are in good condition, etc