What are the technical characteristics of gasification in air flow reactors?

1. The coal type has strong adaptability. The coal fed into the furnace is injected in powder form (or as wet slurry), and each particle is separated by high-speed air currents; thus, it undergoes pyrolysis, gasification, and slag formation independently, without any interaction between particles. This prevents sticking during expansion and softening, meaning that the cohesion properties of the coal do not have an impact. In principle, any type of coal can be used for fluidized-bed gasification, but the gasification temperature in the furnace must be higher than the ash melting point of the coal to facilitate slag formation. Additionally, from an economic perspective, it is advisable to use coals with high volatile content and low fixed carbon content, such as lignite, as this can **improve the gasification conditions**； The raw coal used in the human furnace should be as fine as possible; the smaller the coal particles, the greater their specific surface area, which leads to a faster gasification rate, a shorter reaction time, and a higher carbon conversion rate. 2. The residence time of the reactants in the furnace is short, with the reaction time ranging from 1 second to 3 seconds. The fly ash carried out of the furnace along with the gas contains unreacted carbon, and by recycling this fly ash back into the furnace, the carbon conversion rate can be increased ； Moreover, since the residence time of coal powder in the gasifier is extremely short, a very high reaction temperature must be maintained to carry out the reactions. Therefore, pure oxygen is often used as the gasifying agent, allowing the gasification temperature to reach up to 1500°C; the ash is discharged in a molten state, with a low carbon content. The structure for discharging the liquid slag is simple, enabling smooth slag removal. However, the furnace lining is subject to erosion by the flowing molten slag, which can lead to damage and reduce its lifespan. 3. To achieve a gasification temperature of around 1500°C, a large amount of oxygen is required, which affects economic efficiency. As the steam decomposition rate increases at high temperatures, the steam consumption decreases. 4. The temperature of the gas exiting the furnace is very high, resulting in significant sensible heat losses; this heat can be recovered using a waste heat boiler to improve thermal efficiency. To prevent viscous ash from entering the waste heat boiler, the gas exiting the furnace can first be cooled to 900°C–1100°C using recycled cold gas, so that the ash can be separated before it enters the waste heat boiler. 5. The components of the gas exiting the furnace are mainly CO, H2, CO2, and H2O; the methane content is very low, and thus the calorific value is not high. The product does not contain tar. The gas product has a high concentration of useful components, no phenolic-containing wastewater is generated, and the flue gas purification system is simple

Characteristics of fluidized bed gasification technology: (1) Strong adaptability to coal types. In principle, various types of coal can be used in fluidized bed gasification, but the gasification temperature inside the furnace must be higher than the ash melting point of the coal in order to facilitate slag formation. Furthermore, from an economic perspective, coals with high volatiles and low fixed carbon, such as lignite, should be chosen, as this can **improve gasification conditions** ； The raw coal fed into the furnace should be as fine as possible; the smaller the coal particles, the larger their specific surface area, which leads to a faster gasification rate, a shorter reaction time, and a higher carbon conversion rate. The coal fed into the furnace is injected in a powdered form (or as wet slurry), and the individual particles are separated by high-speed air currents. Each particle undergoes pyrolysis, gasification, and slag formation separately, with no interaction between them; thus, there is no bonding that occurs during expansion and softening, meaning the coal’s cohesive properties have no impact. ⑵The residence time of the reactants in the furnace is short, with a reaction time of approximately 1 s to 3 s. The fly ash carried out of the furnace with the gas contains unreacted carbon, and recycling it back to the furnace can improve the carbon conversion rate ； Furthermore, since the residence time of coal powder in the gasifier is extremely short, a very high reaction temperature must be maintained to complete the reaction. Therefore, pure oxygen is often used as the gasifying agent, with a gasification temperature that can reach up to 1500°C. The ash is discharged in a molten state, and the carbon content in the slag is low. The slag discharge structure for liquid slag is simple, ensuring smooth slag removal. However, the furnace wall lining is eroded by the flow of high-temperature slag, making it prone to damage and reducing its lifespan. ⑶To achieve a vaporization temperature of around 1500°C, a large amount of oxygen is required, which affects economic efficiency. As the steam decomposition rate increases at high temperatures, the steam consumption decreases. ⑷The temperature of the exhaust gas from the furnace is very high, resulting in significant sensible heat losses; waste heat boilers can be used to recover this heat and improve thermal efficiency. To prevent viscous ash from entering the waste heat boiler, the gas exiting the furnace can first be rapidly cooled to 900°C–1100°C using circulating cold gas, allowing the ash to be separated before it enters the waste heat boiler. ⑸The components of the gas released upon heating are mainly CO, H2, CO2, and H2O; the methane content is very low, and its calorific value is not high. The product contains no tar. Gas products have a high content of active ingredients, do not generate phenol-containing wastewater, and require a simple flue gas purification system.

The characteristics of fluidized beds mentioned online are rather one-sided. In fluidized bed reactors, the reaction time is short, which requires powder with a particle size of 90 microns or less. This poses risks to the coal preparation system; high volatile content can lead to dust explosions, so such powder is not acceptable. Powder with too poor grindability is also not suitable ； The high reaction temperature, combined with small particle size, results in a higher carbon conversion rate. Additionally, the high temperature melts the ash; this molten ash adheres to the walls, providing a protective effect by using slag to counteract further slag formation. However, this approach does not work for coals with too high an ash melting point or too low an ash content ； At high temperatures, if there are too many harmful elements such as chlorine and fluorine in the coal, it causes severe corrosion of the furnace walls, which is also not acceptable ； Finally, consider the issue of heat recovery: the slag temperature drops from 1400 degrees to 200 degrees, and the same is true for the syngas. How should heat losses be managed? Yet compared to other processes, its thermal efficiency remains very high.