Explanations of technical terms related to gas generators

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1. Fixed bed, Fluidized bed, Gas-flow bed When a fluid flows continuously upward through a layer of solid particles, as the flow velocity increases, the bed layer takes on three different states: fixed bed, fluidized bed, and gas-flow bed. 　　Fixed bed: When the fluid flow rate is low, the solid particles remain stationary, and the fluid passes only through the gaps between the particles; the height of the bed layer remains essentially constant. In this case, the bed layer is referred to as a fixed bed. 　　Fluidized bed: When the velocity of the fluid flowing through the bed layer increases to a certain level, the particles become loose, the gaps between them widen, and the volume of the bed layer expands. If the fluid velocity is increased further, the bed will no longer be able to maintain a fixed-bed state. At this point, all the particles are suspended in the fluid, exhibiting rather irregular motion. As the flow velocity increases, the movement of the particles becomes more intense, and the expansion of the bed layer also increases; however, the particles remain within the bed layer and are not carried away by the fluid. This state of the bed, similar to that of a liquid, is called a fluidized bed. 　　Gas flow bed: When the fluid velocity is increased beyond a certain level, the bed can no longer remain in a fluidized state. The upper surface no longer exists; the solid particles are dispersed and suspended in the fluid, and begin to be carried away by it. This is the dispersed flow of solid particles, similar to the flow of gas particles. A bed in this state is called a fluidized bed. 　　2. Gasified coal gas: Raw coal or coke is burned in industrial furnaces (such as generator furnaces, water gas generators, etc.), with air and steam being introduced; the combustible gas resulting from this process, which consists mainly of carbon monoxide and hydrogen, is known as gasified coal gas. 　　3. Carbonization gas: Coal is heated in industrial furnaces (such as coke ovens and Wood’s furnaces) in an air-free environment; the process by which physical and chemical changes occur in the coal is called carbonization. The combustible gas produced by carbonization, after purification, can also yield chemical products such as tar, ammonia, and crude benzene; what remains in the furnace after carbonization is coke. 　　4. Producer gas 　　Producer gas is a flammable gaseous fuel produced by using a gas generator to convert solid fuels. Depending on the type of gasifying agent, producer gas is classified into air producer gas, water gas, oxygen-enriched gas, and mixed producer gas. 　　5. Air-based gas generator gas In a gas generator, air is used as the gasifying agent for coal, and the gas produced is known as air-based gas generator gas. Air-generation furnace gas has a low calorific value, and the high temperature in such furnaces tends to cause slag to fuse, which is why it is rarely used in industrial furnaces. 　　6. Water gas 　In a gas generator, gas produced using water vapor as a gasifying agent is called water gas. Water gas has a high calorific value, but it cannot be widely used due to the low thermal efficiency of the generator, high costs associated with the gas, and complex equipment; it is only employed in the chemical industry where special requirements exist. 　　7. Oxygen-enriched gas 　Gas produced in a gas generator by using oxygen, either in addition to air or as the sole gasifying agent, is called oxygen-enriched gas. Oxygen-enriched gas has the advantages of high production volume and the ability to gasify low-quality coal, thereby increasing the calorific value of the gas. However, due to the high cost of oxygen, which raises the cost of gas, it cannot be widely used. 　　8. Mixed producer gas – Gas produced by using a mixture of air and water vapor as the gasification agent is called mixed producer gas. This type of mixed producer gas is commonly used in machinery factories. Mixed producer gas is further divided into cleaned producer gas (cold gas) and hot producer gas, depending on whether it has been purified. 　　9. Cleaning producer gas (cold gas) Producer gas contains a significant amount of coal tar and dust. To meet specific usage requirements, gas is cleaned and purified; the purified gas is known as cleaned producer gas. Since the temperature of the hot gas drops to room temperature after cleaning and purification, this purified gas is sometimes also referred to as cold gas. 　　10. Heat generator gas: Mixed generator gas that has only been roughly dedusted but not thoroughly purified is referred to as heat generator gas. Thermally mixed furnace gas is widely used in the machinery industry. 　　11. Carbonization of coal A method of thermally processing coal under conditions free from air. Based on the temperature of carbonization, it is further divided into low-temperature carbonization, medium-temperature carbonization, and high-temperature carbonization. 　　Low-temperature carbonization: The carbonization of coal at temperatures between 500 and 550°C. The gas produced contains large amounts of hydrogen, methane, and unsaturated hydrocarbons. 　　Medium-temperature carbonization: This occurs when coal is carbonized at temperatures between 800 and 850°C. It is usually carried out in a carbonization furnace, hence the resulting gas is called carbonization furnace gas. 　　High-temperature carbonization: This occurs when coal is carbonized at temperatures of 900–1000°C. It is usually carried out in a coke oven, which is why it is also known as coking; the resulting gas is called coke oven gas, and it has a high hydrogen content. 　　12. Gasification intensity: The amount of raw material gasified per unit time and per unit cross-sectional area of the gasifier (Kg/(m2.h)); it is one of the indicators used to evaluate the gasification process in the gasifier. 　　13. Gas yield: The amount of gas produced from 1 kg of raw material after gasification. Gas yield is one of the indicators used to evaluate the gasification process in a producer. 　　14. Calorific value: The total amount of heat released when a unit quantity (1 kmol, 1 Nm3, or 1 Kg) of gas is completely burned. The units are KJ/Kmol, KJ/Nm3, and KJ/Kg respectively. KJ/Nm3 is commonly used in gas engineering, while KJ/Kg is sometimes used for liquefied petroleum gas. It can be divided into high calorific value and low calorific value. 　　15. Low calorific value: The heat released when a unit amount of gas burns completely, such that its combustion products and the surrounding environment return to their temperatures before combustion, excluding the heat released due to the condensation of water vapor. 　　16. High calorific value: The total amount of heat released when a unit quantity of gas burns completely, such that the combustion products and the surrounding environment return to their temperatures before combustion, with the water vapor present being condensed into water at the same temperature. 　　17. Volatiles 　　The yield of volatile organic substances obtained when coal is heated in the absence of air under specified conditions. Heating causes the remaining solid residues to be called ash.