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Safety management for boiler operation 1. Key safety points for boiler startup (1) Comprehensive inspection: A thorough inspection must be carried out before starting the boiler; only after meeting the startup requirements can further operations proceed. The inspection includes checking whether all levels of the steam system, the combustion system, the air and flue gas systems, the boiler itself, and the auxiliary equipment are in good condition ； Check whether the manholes, handholes, fire viewing doors, explosion-proof doors, various types of valves, and connection plates are in good condition ； Check that the safety accessories are complete, in good condition, and in the positions required for operation ； Check whether all measuring instruments are in good condition. (2) Supply water: To prevent excessive stress, the maximum temperature of the supply water should not exceed 90~100℃ ； The water filling speed should be slow; the total time required for filling water should be no less than 1 hour in summer and no less than 2 hours in winter. Water filling should be stopped once the furnace reaches the lowest safe water level, to prevent the water level from becoming too high due to thermal expansion. (3) Drying and cooking of the boiler: The drying process should be carried out in accordance with the pre-determined heating curve. The total drying time varies depending on the size and model of the boiler, ranging generally from 3 to 14 days. Boiling the furnace can be carried out simultaneously in the later stages of furnace drying. When boiling the furnace, add an alkaline agent to the water in the pot; the steps are as follows: fill it with water up to the maximum level ； Add an appropriate amount of chemical (2~4kg/t) ； Heat the water in the pot to boiling using combustion, without increasing pressure, and maintain this state for 10–12 hours ； Reduce combustion; add water appropriately after discharging pollutants ； Increase combustion and raise the boiler pressure to 25%~100% of the operating pressure, then operate for 12~24 hours ； Shut down the furnace for cooling, drain the boiler water, and clean the heating surfaces. (4) Ignition and pressure raising: Generally, ignition and pressure raising can be carried out once water is supplied to the boiler ； For boilers that undergo drying and flushing processes, after the flushing is complete, water is drained for cleaning, then water is added again before lighting the fire to increase pressure. Points that need attention include: ① Preventing explosions inside the furnace; ② Preventing damage caused by thermal stress and thermal expansion; ③ Monitoring and adjusting various changes. (5) Pipe warming and gas integration: Pipe warming involves using steam to slowly heat components such as valves and flanges, allowing their temperature to rise gradually. This is done to avoid introducing steam suddenly into pipes that are at a cold or lower temperature, thereby preventing excessive thermal stress that could damage the pipes, valves, and other components. At the same time, it drives out the condensate in the pipeline to prevent water hammer during steam supply. The heating time for cold steam pipes is generally not less than 2 hours, while for hot steam pipes it is usually 0.5 to 1 hour. Parallel operation also referred to as combined operation or parallel firing means that boilers in operation supply steam to a common steam system. During steam merging, the combustion should be stable, the operation should be normal, and the steam quality must be satisfactory; moreover, the steam pressure should be slightly lower than the pressure in the main steam pipeline. 2. Key safety points during boiler operation (1) During boiler operation, protective devices and interlocks must not be disabled. When inspection or repair is required, it must be approved by the relevant senior leadership. (2) During boiler operation, the safety valve shall be manually tested for steam release once a day. The electrical circuit test of the electromagnetic safety valve should be conducted once a month. After the safety valve’s steam discharge test, its setting pressure, returning pressure, and disc opening height shall meet the specified requirements, and these values shall be recorded. (3) During boiler operation, sludge discharge tests should be conducted regularly. 3. Safety considerations when shutting down a boiler (1) Normal shutdown (planned shutdown) The main issue to be addressed during shutdown is to prevent too rapid a drop in pressure and temperature, so as to avoid excessive thermal stress on the boiler components due to uneven contraction as a result of the temperature drop. For a proper shutdown of a boiler, the fuel supply should be stopped first, followed by the cessation of air supply, with the draft air being reduced as well ； At the same time, gradually reduce the boiler load and correspondingly decrease the water supply to the boiler, but the boiler water level should be maintained slightly above the normal level. After the boiler stops supplying steam, its connection to the steam main should be isolated to release steam and reduce pressure. At the same time, continue to monitor the boiler; once there is no steam pressure inside, open the air valve to prevent a vacuum from forming as the temperature drops. (2) Emergency shutdown: During boiler operation, the boiler water level drops below the visible edge at the bottom of the water level gauge ； More efforts are being made to supply water to the boiler and other measures are taken, but the water level continues to drop ； The boiler water level exceeds the highest visible level (full water), and the water level cannot be seen even after draining water ； All feed water pumps have failed or there is a fault in the feed water system, preventing water from being supplied to the boiler ； The water level gauge or safety valve has completely failed ； Damage to boiler components endangers the safety of operators ； Severe threats to the safe operation of forging furnaces include damaged combustion equipment, collapsed furnace walls, or boiler frames that become red-hot ； Other abnormal conditions endanger the safe operation of the boiler. Procedure for emergency shutdown of the furnace: Immediately stop feeding fuel and air supply, reduce the exhaust airflow, and at the same time try to extinguish the fuel inside the furnace. For conventional layer-fired furnaces, sand or wet ash can be used to put out the fire; in the case of chain grate furnaces, the grate can be operated at high speed to push the glowing embers into the ash pit ； After extinguishing the fire, open the furnace door, ash door, and flue dampers to enhance ventilation and cooling, allowing the pressure inside the boiler to drop more quickly and enabling the water to be replaced. The water can be drained once it has cooled to around 70°C. However, when the boiler is shut down urgently due to a water shortage, it is strictly prohibited to supply water to the boiler, nor shall the air valve or safety valve be opened to reduce pressure rapidly. An emergency shutdown is a necessary measure taken to prevent the expansion of an accident from leading to more severe consequences. However, the emergency shutdown process itself inevitably causes the boiler components to cool and lose pressure rapidly, generating significant thermal stress that can damage those components. 4. Maintenance when the boiler is shut down: After the boiler is shut down, maintenance is necessary to prevent corrosion. The common methods are dry, wet, and thermal. (1) Dry maintenance: Dry maintenance is only used for boilers that are not in use for a long time. After normal shutdown, drain all the water, remove scale, rust, and soot from the boiler’s heating surfaces as well as from the inside and outside of the boiler drum. Dry the boiler using a low heat source, and then insert desiccants inside it. Then close all doors and openings to ensure a tight seal. After one month, open the manholes and access holes for inspection; if the desiccant has turned into powder and lost its ability to absorb moisture, replace it with new desiccant. The time for the next examination will be shortened or extended depending on the results of the current check. If the shutdown period exceeds three months, after internal and external cleaning, an anti-rust paint should be applied to the inside of the heat-exchanging surfaces. The boiler accessories should also be repaired and inspected, coated with oil for protection, and then maintained using the aforementioned methods. (2) Wet maintenance: Wet maintenance is also applicable to boilers that have been out of use for a long time. After shutting it down, clean the inner and outer surfaces, then fill the boiler with water (preferably soft water). Dissolve an appropriate amount of sodium hydroxide or sodium phosphate in the water and add it to the boiler. Heat it over low heat until the outer surface of the boiler is dry; due to convection, the concentration of alkali becomes uniform throughout the interior. Once the water temperature inside the boiler reaches 80–100°C, turn off the heat. Test the water in the pot every 5 days to keep its alkalinity within the range of 5–12 mg·L‑1. (3) Thermal maintenance: When the equipment has been out of use for about 10 days, thermal maintenance is advisable. After shutting down the furnace, close all air and flue dampers to allow the furnace temperature to drop slowly; it is sufficient to keep the boiler’s steam pressure above atmospheric pressure (i.e., the water temperature above 100°C). If the steam pressure cannot be maintained, a low fire can be used or the steam from an operating boiler can be employed for heating.