Changes in gas composition in fixed-bed gasification

The increase in CO2 and CH4 should be directly related to the furnace temperature of the fixed-bed reactor. The composition of the gas at high furnace temperatures will be better.

This post was last edited by zjing80 on 2016-11-24 at 11:58. Reasons for high carbon dioxide levels: One can look up the reaction equations for gasification, as well as those for the reaction between carbon and oxygen to produce carbon monoxide. It can be seen that the volume of the gas produced as carbon monoxide is 0.66 times that of the original reactant gases, while the volume of carbon dioxide produced is 0.5 times that of the original reactant gases. The other three main endothermic reactions involve either an increase or no change in gas volume; therefore, high pressure is most favorable for the production of carbon dioxide. Thus, it is easy to understand why high pressure leads to high carbon dioxide levels. Similarly, high pressure also results in a higher temperature in the flame zone. Reasons for high methane levels: An increase in pressure leads to more carbon dioxide being produced, which in turn results in more heat release and a higher temperature in the fire zone. Methane is primarily generated during the carbonization process; a high furnace temperature provides sufficient heat for this process, so the amount of methane produced is greater compared to when the temperature is lower. These calculations are based on an analysis under constant other conditions; in production, multiple conditions often change, but regardless of how they change, the principle of reaction remains unchanged.

My view is as follows: In the oxidation zone of a fixed-bed gasifier, the main reaction is the complete combustion of carbon, which generates large amounts of CO2. This CO2 then enters the reduction zone, where carbon reacts with CO2 to produce CO, and carbon reacts with water vapor to produce both CO and H2. Both of these reactions are endothermic reactions. Both of these reactions are reactions that result in an increase in volume; therefore, as pressure increases, the forward progress of the reactions is suppressed. This must be the reason why the CO2 content increases and the decomposition rate of water vapor decreases after pressurization of the fixed-bed. As for the increase in methane content, in addition to the reasons mentioned above, it is also possible that factors such as an increase in side reactions like methanation of C and H2, as well as conversion reactions of CO, due to rising pressure, are contributing to this effect.

The last edit to this post was made by zjing80 on 2016-11-24 at 14:41. Regarding the first question, in fixed-bed gasification reactions, the oxidation layer and reduction layer are artificially defined for the purpose of analyzing the reactions; in reality, these layers coexist within the furnace. If oxidation occurs first, then the temperature of the oxidation layer would not be around 1200 degrees alone. The gasification reaction is the result of three substances reacting simultaneously at a certain temperature; without any one of these substances, it is no longer a gasification reaction. Therefore, it cannot be divided into an oxidation layer and a reduction layer; it is the reaction layer (also referred to as the fire layer in the industry). The second issue: it’s hard to say whether the carbon and hydrogen mentioned by the original poster can undergo a methanation reaction at high temperatures; this is still subject to discussion. Personally, I think the possibility is low, as it depends on how high the temperature is, what the pressure is, and whether the conditions for such a reaction can be met. Under normal circumstances, since the pressure increase isn’t significant, this reaction does not occur. Let’s communicate more if we get the chance.