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Preliminary risk analysis of the thermal system of oil-fired and gas-fired boilers 1) The main components of the thermal system of oil-fired and gas-fired boilers The annular square header is a pressure-bearing component, which contains water (lower header) and saturated steam. There are multiple pipe seats on the upper header, and are connected to the main steam valve, safety valve, pressure gauge and water level gauge, steam connecting pipe, pressure controller, etc. The lower header is also equipped with water inlet pipes, sewage pipes, water level meters, water connecting pipes, etc. on corresponding short seats. The sensing elements for controlling pressure and water level are also in the header. 2) Analysis of dangerous and harmful factors Water shortage accidents are caused by misoperation by the boiler, failure of the water level gauge or automatic water supply device, leakage of a large amount of water from the economizer, lax closing of the sewage valve, or failure of the check valve. Severe water shortage accidents can cause the heating surface to overheat and burn, reduce the load-bearing capacity of the heating surface steel, cause metallographic degradation, furnace tube blasting, and even cause a boiler explosion. The boiler's negligence, water level gauge failure, and automatic water filling device failure can also cause flooding accidents. A large amount of water in the steam will reduce the quality of the steam and even cause water hammer, damage the pipelines and destroy the steam equipment. However, if the water quality does not meet the requirements, the salt content of the boiler water reaches a critical amount, or the boiler water is overloaded, the steam consumption suddenly increases, and the pressure decreases too quickly, which can cause steam-water azeotrope, destroy the water cycle, deteriorate steam quality, and cause water shock vibration, affecting the safe operation of steam equipment. Poor boiler steel or welding quality, fillet welding structure, poor water quality, severe corrosion and scaling, and water circulation failure can also cause accidents such as furnace tube blasting or even explosion. If the operating pressure exceeds the maximum allowable pressure of the boiler, the stress of the steel plate (pipe) increases beyond the limit value, and the safety valve and overpressure chain failure will also cause an overpressure explosion. Improper ignition, or the combustibles (oil, gas) in the furnace are not removed after flameout, and the mixture with air reaches the lower explosion limit. Under the action of ignition or detonation energy, a furnace explosion will occur. 3) Preliminary risk analysis In summary, the main risk factors of the thermal system are boiler explosions or pipe blasting accidents caused by water shortage, substandard steel quality, welding defects, overpressure and other factors. According to the aforementioned analysis of the main dangerous and harmful factors, the possible accidents or failures of the system are:: (1) bit accident: Lacking water, full of water, and soda-water azeotrope. (2) Preliminary risk analysis of explosion accidents is shown in the table. Preliminary risk analysis of thermal system No. Main hazard source location Accident, fault type Triggering conditions Hazard level 1 (1) Feed water pump regulator, water level gauge, alarm interlock device water level failure Operation error, water level gauge, water supply regulator failure, drain valve leakage II 2 (2) Boiler ① Heating surface tube burnt and blasted, or even boiler explosion (especially sudden addition of water) The boiler is short of water Ⅲ~Ⅳ②, the steam carries water, causing water hammer to damage the pipes, and the steam boiler is full of water. Blocked pipes are burned out or metal pipe walls are corroded. Improper water treatment, the hardness and dissolved oxygen in the water are not effectively removed. II~III