Pyrolysis of the Municipal Mixed Plastic Waste


Direct recycling of waste  plastics not always possible, e.g. waste plastics can be contaminated; moreover, they often mixed with different sorts of materials such as paper, glass, metal, biowaste, etc. Food and beverage packaging is a typical example when plastic attached to other materials (aluminium/polymer laminate). It is impossible to separate this laminate from paper at the recycling facility.
 
At the waste plastics pyrolysis facility the plastics bales are continuously shredded, dried, and pelletized.  Since municipal waste plastics mixture contains PVC and PET, initial waste is pre-treated. Then polymer is fed into the pyrolysis rotary kiln reactor to treat at ~ 400 C. The gas discharged from the reactor is liquefied and stored in the oil drum. The pyrolysis oil stored in the oil drum is fed into the distillation column and separated into three fractions; light oil from the top, medium oil from the middle and heavy oil from the bottom of the column. These three types of oils are stored in separate oil tanks and sent to the furnaces and cogeneration system in the plant as fuel through piping, or loaded onto a tank lorry for shipment to customers. The energy of hot off-gases is used to generate steam. 

Typical average composition of the initial mixed plastic waste: Polyethylene, polypropylene, polystyrene ~ 71 %; PVC's ~ 4.5%: PET ~ 12.5 %, Other plastics ~ 9.5%; Other materials (foil, etc) - 2.5%

Process Characteristics:

• No catalyst
• Easy operation and maintenance due to atmospheric pressure process.  
• Energy recovery use of product oil, gas and residue.
• Chlorine recovery from PVC as hydrochloric acid.
• Product oil usage for furnaces in plant as well as co-generation as fuel.
• Full automatic operation, computer control system.

Long-term large scale commercial experience demonstrates that all of the products and by-products from pyrolysis are utilized for feedstock recycling or energy recovery, except for hydrochloric acid obtained from PVC