Techno-economic evaluation of high temperature pyrolysis processes for mixed plastic waste.

Three pyrolysis processes for Mixed Plastic Waste (MPW) with different reactors (Bubbling Fluidized Bed, Circulating Fluidized Bed and Rotating Cone Reactor, respectively BFB, CFB and RCR) were designed and evaluated. The estimated fixed capital investment for a 50 kton/year MPW pyrolysis plant build in 1996 in the Netherlands varies from 14 million Nlg for the RCR to 20 million Nlg for the CFB pyrolysis plant. The Return On Investment (ROI) of the RCR plant (29.5%) is significantly higher than the ROI of the BFB and CFB pyrolysis plants (respectively 21.7 and 14.2%). The lower temperature levels (less energy required) and the fact that the RCR requires no or little additional utilities are important operational advantages of the RCR. The chlorine from PVC was removed in this process using low temperature pyrolysis converting 98% of the chlorine into HCl gas. The remaining chlorine is subsequently converted to CaCl2 by reaction with CaCO3 , but this is unattractive from an economical and environmental point of view as a large amount of sand has to be disposed of to prevent agglomeration of CaCl2 and sand at high CaCl2 concentrations. Removal of the last 2w% of chlorine using NH3 or NaHCO3 is probably preferable. A dedicated product separation section for a MPW pyrolysis plant of this size is economically not feasible as only 50 to 60% of the polymer is converted to product gas, resulting in an economically unattractive scale for the product separation section. Integration of the pyrolysis plant with an existing chemical complex (naphtha cracker) should be preferred. The use of a dedicated product separation section should only be considered, if this is required for non technical/economic or geographical reasons