Factors Affecting NCG Yield and Composition in Pyrolysis

Factors Affecting NCG Yield and Composition in Pyrolysis

During the pyrolysis process, the yield and composition of non-condensable gas (NCG) generated from different raw materials are not fixed or consistent, and the variations are comprehensively determined by five core factors:

Raw material composition is the primary influencing factor. For raw materials with high hydrocarbon content such as waste tires, the NCG yield accounts for approximately 3%–5% of the raw material mass, with C1-C4 low-carbon hydrocarbons as the main component. In contrast, biomass materials like wood and straw have a high proportion of oxygen-containing components, resulting in a significant increase in the proportion of carbon dioxide and water vapor in the produced NCG, and a corresponding decrease in the proportion of combustible hydrocarbons.

Raw material pretreatment degree affects the stability of gas production. Excessively high moisture content in raw materials will generate a large amount of water vapor, diluting the concentration of combustible components in NCG. On the other hand, a uniform particle size of raw materials ensures sufficient and stable pyrolysis reaction, making the NCG yield and composition more controllable; otherwise, it is prone to fluctuations in gas production.

Pyrolysis process parameters directly regulate the gas production status. In the main pyrolysis stage (450–550℃) of the batch-type process, the NCG yield reaches its peak. When the temperature exceeds 600℃, it will promote the further cracking of macromolecular gases, increasing the proportion of low-carbon hydrocarbons, while the overall gas production volume changes little.

Pyrolysis reaction atmosphere alters the pathways of gas consumption and generation. An inert gas atmosphere (e.g., nitrogen) can prevent the oxidation and consumption of combustible gases, increasing the proportion of effective hydrocarbons in NCG. If air is mixed into the reaction system, some combustible gases are prone to incomplete combustion, which not only reduces the effective gas production rate but also increases the content of carbon monoxide and carbon dioxide in the exhaust gas.

Raw material impurity content determines the impurity components in NCG. Sulfides in raw materials will make NCG carry trace amounts of hydrogen sulfide, while chlorine-containing plastics will produce corrosive gases such as hydrogen chloride. Meanwhile, metal impurities in raw materials may catalyze the pyrolysis reaction, indirectly affecting the gas generation rate and component proportion.