Atmospheric pressure fixed-bed gas generator (single-stage)

Thread Content

This post was last edited by lflsedin on 2015-5-26 21:49. The atmospheric pressure fixed-bed gas generator consists of a mechanical feeding system, a gas generation system, a steam generation system, and a slag breaking and removal system. It features a simple structure, high safety, easy operation, and produces mixed semi-water gas with a high calorific value ； Integrated with various industrial furnaces, it makes full use of the waste heat from gas, thereby saving energy and reducing consumption. No smoke, no dust, and no noise during production ； The rotary tower type has strong capabilities for slag discharge, removal, and crushing; the slag is discharged into a water seal tank, preventing dust from being generated. It is suitable for a wide range of coals – in principle, all coals can be used as long as they form little or no slag or lumps. A gas generator is a device that uses coal as raw material to produce gas for use in gas-powered equipment. Solid raw coal is fed from the top of the furnace and moves downward as the gas furnace operates. There, it comes into counterflow contact with the gasifying agents (air, steam) that enter from the bottom of the furnace; simultaneously, it is heated by the hot gases from the fuel layer at the furnace bottom, resulting in physical and chemical reactions that produce crude gas. This raw gas (i.e., hot gas), after rough dust removal, can be used directly in combustion equipment. In a typical gas generator, coal moves from top to bottom, while the gasifying agent moves from bottom to top in a countercurrent manner; chemical reactions and heat exchange occur between them. In this way, several zones are formed in the gas generator, which we generally refer to as “layers”. 　　Following the sequence of the gasification process within the gas generator, its interior can be divided into six layers: 1) Ash layer ； 2) Oxide layer (also known as fire layer) ； 3) Reduction layer ； 4) Dry distillation layer ； 5) Drying layer ； 6) Empty layer ； Among them, the oxidation layer and the reduction layer are collectively referred to as the reaction layer, while the carbonization layer and the drying layer are collectively referred to as the coal preparation layer. 　　(1) Ash layer: Ash is produced as a result of coal combustion, forming an ash layer that is located at the very bottom of the producer, covering the grate. Its main functions are: a) to protect the grate and air caps from being damaged by the high temperatures of the oxide layer ； 　　b Preheat the gasifying agent; after entering from the bottom of the furnace, it first passes through the ash layer for heat exchange, which lowers the temperature of the ash layer while raising the temperature of the gasifying agent. Typical gasifiers can preheat to around 300-450°C. 　　The c ash layer also serves to distribute the air, ensuring that the gasifying agent entering the furnace is distributed as evenly as possible. 　　(2) Oxidation layer: Also known as the combustion layer (fire layer). The oxygen in the gasifying agent rising from the ash undergoes intense combustion with carbon to produce carbon dioxide, releasing a large amount of heat. It is one of the main areas in the gasification process, and its primary reaction is: C+O2→CO2+97,650 calories. The thickness of the oxidation layer is generally 3-4 times that of all the fuel blocks, usually ranging from 100 to 200 millimeters. The temperature of the gasification zone is generally lower than the ash fusion point of coal, and is kept around 1200°C. 　　(3) Reduction layer: Above the oxidation layer is the reduction layer. Red-hot carbon has a strong ability to snatch oxygen from oxides and combine with it, so in the reduction layer, carbon reduces carbon dioxide and water vapor into carbon monoxide and hydrogen. This layer is thus named the reduction layer. Its main reactions are as follows:
CO + C → 2CO + 38,790 calories
H2O + C → H2 + CO + 28,380 calories
2H2O + C → CO2 + 2H2 + 17,970 calories
Since the reduction layer is located above the oxidation layer, it receives a large amount of heat from the rising gases; as a result, its temperature is relatively high, ranging from 800 to 1,100°C. This high temperature provides the conditions necessary for the reduction reactions that require heat absorption. Strictly speaking, the reduction layer can be further divided into a first and a second layer; the area with a higher temperature at the lower part is referred to as the first reduction layer, where the temperature ranges from 950–1100°C, and its thickness is around 300–400 millimeters ； The second layer is at a temperature of 700–950°C, and its thickness is 1.5 times that of the first reduction layer, approximately 450 millimeters. 　　(4) Carbonization layer: The carbonization layer is located above the reduction layer. As the gases rising from the reduction layer lose heat, their temperature gradually decreases. Therefore, the temperature in the carbonization layer ranges from 150 to 700°C. At these temperatures, the coal undergoes a process of low-temperature carbonization; the volatile components in the coal break down to produce substances such as methane, olefins, and tar. When heated, these substances turn into gas, which constitutes coal gas and escapes through the upper drying layer, thus becoming part of the coal gas. The height of the carbonization layer varies depending on the volatile content in the fuel and the operation conditions of the gas furnace, generally being >100 millimeters. 　　(5) Drying layer: The drying layer is located above the dry distillation layer, that is, on the surface layer of the fuel. The rising hot gas meets the fuel that has just entered the furnace in this layer, where heat exchange takes place; the moisture in the fuel evaporates as a result of the heat. It is generally believed that the drying temperature ranges from room temperature to 150°C, and the height of this layer also varies depending on different operating conditions; there is no relatively constant layer height. 　　(6) Empty layer: The empty layer is the area above the fuel layer, the free space within the furnace, and its main function is to collect gas. Some comrades believe that while the gas stays in the empty space, and when the temperature inside the furnace is high, some side reactions occur, such as the decomposition of CO and the release of some carbon black: 2CO→CO2+C. There is also the reaction 2H2O+CO→CO2+H2. From this brief description of the six processes, it can be seen that the gasification process taking place inside the gas generator is quite complex, involving not only gasification reactions but also processes of carbonization and drying. Moreover, in actual production blast furnaces, the stratification is not very strict; adjacent layers often overlap each other, and the temperature across different layers changes gradually, making it difficult to draw clear boundaries. The variations in the gas composition within each layer are even more complex, and even in specialized research, opinions vary. Structure of gas stoves: There are various structural types for fixed-bed gas stoves, which are described below by different components: 1. Coal feeding device: Intermittent coal feeding cover ； Double bell ； Vibrating coal feeder ； Tooth-turning coal feeder. 2. Furnace structure: pressure-rated full water jacket ； Semi-water jacket ； No water jacket (refractory lining) ； Atmospheric pressure, full water jacket. 3 Grates: Pagoda shape ； Steel section welding type. 4 Gray disc drive structure: tooth-shifting type ； Worm and worm gear type.