The recycled plastic waste is sorted and crushed into plastic particles or flakes of uniform size. The plastic waste is fed into the cracking kettle for cracking through an automatic feeder. The residue after cracking can be discharged by the slag discharge device. The cracking and condensation process is accompanied by the generation of cracking gas. The cracking gas can be recovered by the tail gas treatment device and used as fuel gas. The cracking oil obtained after condensation can be fractionated to obtain gasoline, diesel and heavy oil.
1. Temperature
Within a certain range, the higher the temperature, the faster the bond breaking cracking rate, and the conversion rate of heavy oil and gasoline increases accordingly. After the temperature tends to a certain range, the cracking rate of plastic waste does not change significantly, and the carbon deposition rate decreases. When the temperature continues to rise, the yield of liquid oil decreases, accompanied by a large amount of gas products and residual solids. Excessive temperature not only increases energy consumption, but also increases gasification and side reactions, and even reduces the activity of the catalyst. The optimal cracking temperature varies with the composition and type of plastic waste. Generally speaking, the larger the substituent of the polymer side chain, the easier it is to decompose. The cracking reaction temperature of several common plastics is PS<PP<PVC from low to high.
2. Pressure
Pressure has a great influence on the cracking reaction. When the cracking pressure of PP and other products increases from 0.1MPa to 2.0MPa, the coking rate increases, the oil-liquid conversion rate decreases, and the overall change in the recovery rate of liquid products is not large. When cracking PE under the same conditions, as the pressure increases, the cracking liquid products change from C5~C32 to C5~C16. It can be seen that low-pressure operation is conducive to the production of oil by PE cracking. Judging from the effects of decompression cracking equipment at home and abroad, appropriate decompression can make the cracking gas discharged in time, avoid the side reactions caused by secondary degradation caused by gas reflux, and can also increase the reaction rate and liquid recovery rate, and reduce the amount of coking. However, when the pressure is too low, the cracking gas is not easy to condense, resulting in an increase in cracking gas and a decrease in cracking oil, and even an increase in energy consumption and a higher requirement for the air tightness of the equipment.
3. Time coefficient
In the cracking process, under the condition of constant temperature, within a certain time range, the longer the residence time, the deeper the degree of cracking, the more primary cracking products, the increase in heavy oil conversion rate and gasoline yield, and the decrease in coking rate. But when the residence time exceeds the limit time, the appearance of secondary reaction affects the product quality and makes the recovery rate of the primary product decrease, and the cracking liquid yield decreases. Therefore, the time coefficient is also the key to the conversion rate and quality of the cracking oil.
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