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I combined the classifications of boilers. Please let me know if there is anything wrong: Boilers can be classified by their purpose into power station boilers, industrial boilers, boilers for vehicles and ships, domestic boilers, etc ； Classified by fuel: coal-fired boilers, oil-fired boilers, gas-fired boilers, etc ； Classified by the outlet steam pressure: low-pressure boilers (P〈2.5MPa), medium-pressure boilers (2.5〈P〈4.0MPa), high-pressure boilers (4.0〈P≤10MPa), ultra-high-pressure boilers (10〈P≤13.7MPa), subcritical boilers (13.7〈P≤16.7MPa), and supercritical boilers (P≥22MPa). Power station boilers are used in power plants, while industrial boilers are commonly used in factories other than power plants. Boilers for vehicles and ships are mainly used on ships. 1. What is a boiler? A device that converts other forms of thermal energy into thermal energy of a working fluid, in order to produce a working fluid with specified parameters and quality, is called a boiler. In boiler equipment, the part that absorbs heat is called the boiler, while the part that generates heat is called the furnace. For example, the heat-absorbing parts such as the water wall, superheater, and economizer can be regarded as the boiler ； The furnace chamber, burner, fuel pump, as well as the supply and exhaust fans can be regarded as part of the furnace. Modern boilers are not as clearly separated from the pots and stoves used in ordinary households. For example, the air preheater is both a part that absorbs heat and a part that generates heat; it can be considered part of the boiler as well as part of the furnace. 2. How are boilers classified? Boilers can be classified in different ways: Based on the combustion method, they can be divided into stratified combustion boilers, chamber combustion boilers, and boiling (fluidized bed) boilers, which fall between the former two. Classified by the boiler water circulation method, they can be divided into natural circulation boilers, forced circulation boilers, and combined cycle boilers. Classified by the presence or absence of a drum, they can be divided into drum boilers and once-through boilers. Based on whether water or flue gas flows through the tubes, they can be classified into fire-tube boilers, water-tube boilers, and combined fire-and-water-tube boilers. 3. What is a fire-tube boiler? A fire-tube boiler is one in which the flue gases generated by fuel combustion flow through the fire tubes or smoke tubes, thereby heating the water, steam, or steam-water mixture outside these tubes. 4. What is a water-tube boiler? A water-tube boiler is a type of boiler in which water, steam, or a mixture of steam and water flows inside the tubes, while the flame or flue gases burn and flow outside the tubes. 5. What is a circulating fluidized bed boiler? A circulating fluidized bed boiler is a new type of boiler that has been developed as an improvement on fluidized bed boilers (also known as bubbling bed or boiling bed boilers). Circulating fluidized bed boilers retain all the advantages of fluidized bed boilers, while avoiding and eliminating their disadvantages such as low thermal efficiency, severe wear on the tube-type heating surfaces, inadequate utilization of limestone as a desulfurization agent, high consumption, and difficulties in scaling up to larger sizes. The bed material in a circulating fluidized bed boiler is in a fluidized state, just like in a conventional fluidized bed boiler. The main difference between the two is that the fluidization speed in the former is higher; the concentration of material in the flue gas at the boiler outlet is very high. A large amount of this material is separated by the material separator at the outlet and sent back into the furnace, meaning that a significant quantity of material circulates between the furnace and the material separator. 6. Steam boilers: Steam boilers are devices that use thermal energy to heat water (the working fluid) in order to generate steam. It consists of two parts: the boiler and the furnace. The boiler is the part where heat is absorbed, and it transfers this heat to the heating surface system of the working fluid ； The furnace refers to the space in a boiler where the chemical energy of fuel is converted into thermal energy, as well as the passage for the flow of flue gases. The capacity of a boiler is usually expressed in “tons per hour” or “t/h”. The rated pressure of the boiler is expressed in “Mpa” or “megapascals” (the old unit is “kilogram-force per square centimeter” or “kgf/cm2”), while the temperature of saturated steam and superheated steam at that rated pressure is indicated in “℃” (degrees Celsius). 7. A hot water boiler refers to a boiler whose heat carrier is hot water. Typically, “MW” (megawatts) is used; the old units were “10,000 kilowatts/hour” or “10,000 kcal/hour”, that is, “104 kcal/h”, to indicate the capacity of the boiler. “Mpa” is used to represent the rated pressure of the boiler, while “℃” is used to indicate the temperature of the hot water. Hot water boilers are mainly used for heating in the northern regions. They are divided into high-temperature hot water boilers (with a hot water temperature of 130°C or higher) and low-temperature hot water boilers (with a hot water temperature below 95°C). In the past, low-temperature hot water boilers were more commonly used; however, there is a trend toward the use of high-temperature hot water boilers in the future. Hot water boilers can operate either through natural circulation or forced circulation. Our horizontal three-pass shell-and-tube hot water boilers operate on natural circulation. 8. An organic heat carrier furnace refers to a new type of thermal energy conversion device in which the heat transfer medium is high-temperature heat transfer oil (also known as a heat carrier). The capacity of the furnace is usually expressed in “MW” (megawatts); older units were also used, such as “10,000 kilowatts/hour” or “10,000 kcal/hour”, that is, “104 kcal/h”. Organic heat carrier boilers (also known as heat transfer oil boilers) are widely used due to their advantages of \"high temperature and low pressure\" as well as stable operation. Organic heat carrier furnaces are divided into liquid-phase and gas-phase types. Our company’s organic heat carrier furnaces operate in the liquid phase. 9. Boiler capacity refers to the ability of steam boilers, hot water boilers, and organic heat carrier boilers to supply thermal energy. Large capacity, high heating capacity, and high output ； Conversely, it is small. For example, a steam boiler with a capacity of 1 t/h means that it is capable of converting 1 ton of water into saturated steam at a certain pressure within 1 hour ； For example, a 0.7 MW hot water boiler or an organic heat carrier boiler means it can generate heat equivalent to 0.7 MW of power within 1 hour (equivalent to the heat produced by 1 ton of steam). 10. The heating surface of a boiler generally refers to the metal surface area on the side that is in contact with the flame or flue gases (the other side being in contact with water or heat transfer oil). The heat exchange in a boiler takes place through such metal surface areas. It is generally measured in square meters (m2); the larger the heating surface area, the greater the boiler capacity, and vice versa. 11. Temperature is a state parameter that indicates the degree of hotness or coldness of an object, and it is generally expressed in “℃” (degrees Celsius). Countries such as the UK and the US previously used “℉” (Fahrenheit); the boiling point of water is 100°C, which equals 212°F in Fahrenheit scale. 12. Boiler pressure: In the boiler industry, boiler pressure (or stress) refers to the force per unit area of the container’s wall, expressed in “Mpa”; the old unit was “kilogram-force per square centimeter” (kgf/cm2). 13. Saturated steam: The water in a boiler boils and turns into steam when heated by the heat released from fuel combustion at a certain pressure; the temperature of the water in this boiling state is that of saturated steam ； The higher the pressure in the pot, the higher the temperature of the saturated steam. For example, the saturation temperature of steam at 1.0 Mpa is 184°C, and at 1.25 Mpa it is 193°C. 14. Superheated steam: Steam whose temperature is higher than the saturation temperature at the corresponding pressure is called superheated steam. Superheated steam has a high heat enthalpy and high entropy, giving it great capacity to do work. When used as a heat source in equal quantities to saturated steam, it enables the temperature of the medium being heated to rise significantly; when fed into a steam turbine generator, it can produce more electricity. 15. The thermal efficiency of a boiler refers to the percentage of the heat absorbed by water, steam, or heat transfer oil during the heat transfer process, compared to the total heat released upon the complete combustion of the fuel fed into the boiler. Heat absorbed by the boiler (useful heat) Heat released from complete combustion of fuel Common units and conversions for boilers 1. Boiler evaporation rate and boiler thermal efficiency 1 ton/hour (t/h) ≈ 60×10^4 kilocalories/hour (kcal/h) ≈ 0.7 megawatts (MW) 2. Boiler evaporation rate and boiler horsepower 1 ton/hour (t/h) ≈ 71.1 boiler horsepower (BHP) 3. Boiler pressure: engineering units and international units 1 megapascal (Mpa) ≈ 10 kilograms-force per square centimeter (kgf/cm2) 4. Megapascal and pascal 1 megapascal (Mpa) = 10^6 pascals (Pa) 1 pascal (Pa) = 0.01 mbar (millibar) ≈ 10^-5 kilograms-force per square centimeter (engineering atmosphere) (kgf/cm2) 1 pascal (Pa) ≈ 0.1 millimeter of water column (mmH2O) 5. Force and gravity 1 kilogram-force (kgf) = 9.81 newtons (N) 6. Heat 1 kilocalorie (kcal) = 4.187 kilojoules (KJ) 7. Volume 1 cubic meter (m3) = 1000 liters (L) 1 liter (L) = 1000 milliliters (ML)