What is furnace gas ?
Coal gas is a gaseous fuel composed of a variety of flammable components. There are many types of coal, and the composition is also very complex, which can generally be divided into two categories: natural gas and artificial gas, and natural gas is obtained after thermal decomposition or gasification of solid or liquid fuels, such as coke oven gas, oil gas, generator gas, etc. From the above, it can be seen that the furnace gas we want to explain is a kind of artificial gas, the generator gas is a kind of gas obtained in the furnace of special equipment using solid fuel as raw material, and the gasifier we use to make the furnace gas is air and water vapor. According to the different gasifiers used, furnace gas with different components and properties can be prepared, which is usually divided into four categories. 1. Air gas - using air (actually oxygen in the air) as a gasifier; 2. Mixed gas - a mixture of air and water vapor as a gasifier (i.e., the current gas generator) 3. Water gas - water vapor is used as gasifier; 4. Oxygen-rich gas-gas, water vapor and oxygen (plus pure oxygen) mixture as gasifier; The principle of gas production in a gas generator In a gas generator, the coal is from top to bottom, and the gasifier (the air and the vapor at a certain temperature sent into the furnace by blast) is counter-current from the top down, and chemical reactions and heat exchange occur between them. In this way, several areas are formed in the gas generator, which we generally call "layers". According to the procedure of gasification in the gas generator, we can divide the inside of the generator into six layers: Ash layer: When the coal is burned, it produces ash and forms a layer of ash, which is in the lowest part of the furnace and covers the grate. Its main functions are: A, Protect the furnace grate and hood from being burned by the high temperature of the oxide layer; B, Preheat the gasifier, after the gasifier enters from the bottom of the furnace, it first passes through the ash layer for heat exchange, so that the temperature of the ash layer decreases and the temperature of the gasifier increases. Generally, the gasifier is distributed as evenly as possible in the furnace. C, The ash layer also acts as an air distribution, so that the incoming gasifier is evenly distributed in the furnace. Oxide layer: Also known as the burning layer (fire layer). The oxygen and carbon in the gasifier that rises from the ash are violently burned to form carbon dioxide and release a large amount of heat. It is one of the main areas in the gasification process. The height of the oxide layer is generally 3-4 times the lump degree of the fuel used, generally 100-200 mm. The temperature of the oxide layer is generally less than the ash melting point of coal, which is controlled at about 1200 °C. Reduction layer: Above the oxide layer is the reducing layer, the red hot one has a strong ability to seize the oxygen in the oxide and combine with it, so in the reducing layer, carbon dioxide and water vapor are reduced by carbon into carbon monoxide and hydrogen, and this layer is also named because of this, called the reducing layer. Because the reducing layer is located above the valve passage layer and obtains a large amount of heat from the rising gas, the reducing layer has a higher temperature of about 800-1100 °C, which provides conditions for the reduction reaction that needs to absorb heat. Strictly speaking, the reduction layer is divided into the first and second layers, the lower temperature is higher and the place is called the first reduction layer, the temperature is 950-1100 °C, the thickness is about 300-400 mm, the second layer is between 700-950 °C, and its thickness is 1.5 times that of the first layer, about 450 mm. Dry Layer: The retort layer is located in the upper part of the reducing layer, and the gas rising in the reducing layer gradually decreases with the consumption of heat, so the temperature of the retort layer is about 150-700 °C. The height of the retort layer varies with the volatile content of the fuel and the operation of the gas furnace, but generally > 100 mm. Drying layer: The drying layer is located on top of the retort layer, which is the surface layer of the fuel. Rising hot gas vs. freshly baked fuel newpearl_user Page 4 Wednesday, December 20, 2023, December 20, 2023At the meeting of the layers, heat exchange takes place, and the water in the fuel is heated and evaporated. The drying temperature is generally considered to be between room temperature and 150°C, and the height of this layer also varies depending on the operation. Empty Layer: The empty layer is the upper part of the fuel, the free space in the furnace body, and its main function is to collect gas. From the above six layers of simple description, we can see that the gasification process in the gas generator is relatively complex, that is, there is a gasification reaction, there is also a dry distillation and drying process. Moreover, in actual production, the stratification is not very strict, and the temperature of the two adjacent layers is often staggered with each other, and the temperature of each layer is also gradually transitioned, which is difficult to divide specifically. The change of gas composition in each layer is more complicated, but through the above brief discussion, it can help us understand the various situations of fuel gasification in the gas generator, and it is useful for us to understand the gas generator and correctly select the gasification index and operation method.