What is Carbon Burning?
Carbon particle combustion [1] is a chemical reaction between carbon particles and oxygen that exothermic and emit light. Fixed carbon is the main combustible substance of coal, so studying the combustion law of carbon / carbon particles is of great significance to understand the combustion process of coal. The combustion of carbon particles in an oxidizing atmosphere is a complex system that includes multiple surface reactions and gas phase reactions. A continuous film model of modern combustion theory. In many practical industrial applications, such as tender firing in a circulating fluidized bed, there is a relative velocity between the carbon particles and the gas flow. At this time, the rule of natural firing under static conditions is not used for the combustion process of carbon / carbon particles. Effect of forced convection on carbon / char particles. The ignition of carbon particles, the combustion stage of pulverized coal, the combustion mechanism, and the effects of CO and sodium carbonate on the combustion of carbon particles are introduced in detail.
- Ignition: The transient process in which the fuel changes from a slowly oxidized state to a high-speed combustion state is called ignition. [3]
- (1) Preparation stage before fire
- The pulverized coal gas stream is sprayed into the furnace until the ignition stage is the preparation stage before ignition. The preparation phase before the fire is an endothermic phase. During this phase, the pulverized coal gas stream is continuously heated by the flue gas, and the temperature gradually increases. After the pulverized coal is heated, the water is evaporated first, and then the dried pulverized coal is thermally decomposed and volatiles are precipitated. It is generally believed that the volatiles precipitated from the pulverized coal first catch fire. Volatile matter
- Charcoal surface burning process:
- Temperature below 1200
- The combustion of carbon particles in an oxidizing atmosphere is a complex system that includes multiple surface reactions and gas phase reactions. The continuous film model of modern combustion theory has theoretically clarified the spatial reaction pairing of the primary products CO and O 2 on the surface of carbon particles The impact of the carbon particle surface temperature and its overall reaction rate is extremely complicated [']. However, due to the highly non-linear gas phase combustion and the carbon particle surface reaction, the complexity of the theoretical treatment of heat and mass is complicated, and the capture duration is extremely short. The difficulty of experimental measurement of CO flame on the surface of particles. In the field of experimental study of the reaction kinetics of pulverized coal combustion and the mathematical model of pulverized coal flame, it is currently widely used to assume that CO does not burn in the particle boundary layer. Membrane model. Theoretical calculations show that whether CO can be ignited near the particle surface and the particle surface temperature difference caused by it can be as high as hundreds of degrees. The uncertainty of this particle surface temperature calculation, the burning of coal powder, fuel N The impact of the release of NO and the numerical simulation of NO 2 generation and control process is huge. Because of this, this subject is still a coal combustion theorist Hotspot Note [4]
- The strengthening of the combustion process by sodium carbonate is mainly achieved by reducing the activation energy of the carbon-oxygen reaction. The activation energy of carbon atoms has a great relationship with the lattice structure of graphite, and the carbon atoms at the surface and edges of the lattice have the highest activity. Carbonic acid The catalytic effect of sodium on combustion can be known from its chemical properties, which mainly occurs at 700-1300 ° C. Due to the temporary intervention of Na 2 CO 3 [6], the graphite lattice is distorted and the carbon atom activity is increased, making C 3 O 4 easier. De-lattice decomposition into CO and CO 2 accelerates the formation and decomposition of C 3 O 4 at the same time. When the temperature is higher than 950 ° C, part of Na 2 CO 3 is decomposed into Na 2 0 and CO 2. This reaction makes the graphite lattice distortion worse, and the carbon atom activity is further improved. The impact of CO: and C 3 O 4 makes C 3 O 4 decomposition is accelerated. Relatively speaking, the CO generated from the decomposition of Na 2 O 3 : diffuses in the air, for C30. The effect of dissociation equilibrium is not great. At temperatures above 1275 ° C, Na 2 O sublimes, and the catalytic effect is lost. Due to the relatively loose structure of the carbon particles, the combustion continues to intensify until it is burned out.