Source of information: Beijing Weima Wall-Hung Boiler After-Sales Service Phone Number http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3778832. Weima Wall-Hung Boiler Repair Q&A; Factors Affecting the Speed of Chemical Reactions The speed of a chemical reaction depends not only on the properties of the original reactants involved in the reaction, but also on the conditions of the reaction system. Key conditions include: concentration of reactants, temperature, pressure in the reaction space, catalytic reactions, and chain reactions.
(1) Reactant Concentration Chemical reactions occur under specific conditions through effective collisions between different reactant molecules. The more effective collisions there are within a unit of time, the faster the chemical reaction will be. The frequency of molecular collisions is determined by the number of reacting molecules per unit volume, i.e., the substance concentration. In multi-phase combustion chemical reactions, the speed of the chemical reaction is expressed by the decrease in oxidizer concentration per unit of time, which is the rate of oxidizer consumption. The combustion of coal-air mixtures falls under multi-phase combustion. This reaction occurs on solid surfaces, and at this point, the concentration of solid fuel can be considered constant. Therefore, the chemical reaction speed of coal powder combustion is directly proportional to the oxygen concentration near the fuel surface. In multi-phase combustion chemical reactions, increasing the concentration of reactant oxygen can enhance the speed of the chemical reaction.
(2) Temperature Temperature has a significant effect on the speed of chemical reactions. When the concentration of reacting substances does not change over time, the reaction speed mainly depends on the reaction temperature T and the size of the activation energy E. At a certain temperature, the higher the activation energy, the fewer the activated molecules, and the slower the reaction speed; conversely, if the activation energy is smaller, there will be more activated molecules, and the reaction will be faster, meaning the reaction can proceed at lower temperatures. Activation energy E is related to the nature of the fuel. Fuels with high volatile matter have lower activation energy, while those with low volatile matter have higher activation energy. With a fixed activation energy, the higher the temperature, the more activated molecules there are, and the faster the reaction speed; conversely, the lower the temperature, the fewer the activated molecules, and the slower the reaction speed. For fuels with high activation energy like anthracite and lean coal, it is necessary to increase the temperature to enhance their combustion. For combustion reactions, raising the furnace temperature is an important method to accelerate the combustion reaction and shorten the combustion time. However, the furnace temperature should not be too high, as excessively high temperatures can lead to slagging inside the furnace and increased emissions of harmful gases.
(3) Reaction Space Pressure The pressure in the reaction space also affects the reaction speed. When the reaction temperature is constant, the reaction speed primarily depends on the concentration of the reactants, and under unchanging reaction system conditions, increasing the pressure of the reaction system means increasing the concentration of the reactants, thereby enhancing the speed of the chemical reaction. The chemical reaction is proportional to the nth power of the system pressure (greater than 0 and OIMPa), where n is the reaction order. Therefore, the furnace pressure can also be increased (P > 0.0 MPa) to intensify the combustion process. Positive-pressure combustion boilers can be used to enhance combustion and reduce boiler size. However, under current conditions, the sealing problem of the combustion system has not been well resolved, limiting the widespread use of positive-pressure boilers.
(4) Catalytic Reaction If a small amount of catalyst is added to the reaction system, it can alter the speed of the chemical reaction. This action is called catalysis. The common feature of catalysis is that under certain conditions, a catalyst can only change the speed of the chemical reaction and not the extent to which the reaction proceeds under those conditions, meaning it cannot change the equilibrium state but only the time it takes to reach equilibrium. From the perspective of activation energy, a catalyst can alter the activation energy of the reactants.
(5) Chain Reaction Chain reactions allow chemical reactions to automatically and continuously accelerate. The mechanism of chain reactions is as follows: In chemical reactions, due to some form of action (thermal activation, photon interaction, or other excitation), the reactants form initial activated molecules. Under certain favorable conditions, these activated molecules can initiate a series of intermediate reactions within the chemical reaction process. These intermediate reactions are mostly very simple chemical reactions. During the intermediate reaction process, new activated molecules are simultaneously produced, forming chains. These activated molecules require less activation energy, so once an activation chain forms, the reaction can automatically and continuously accelerate until the reactants are exhausted or the chain is interrupted.