# A Critical Review of SCWG in the Context of Available Gasification Technologies for Plastic Waste
## 6 Gasification of Plastic Waste: An Overview
### Co-Gasification  
Co-gasification is a relatively new process where the industrial know-how is far from exhaustive, even if the scientific literature is full of interesting research studies on the co-feeding effect of different fuels mainly into fluidized bed gasifiers. [PERSON] et al. [148] in 2006 studied the high temperature air/steam gasification technique (HTAG) for a particular feedstock named Rofire(r). This name indicates a fuel consisting of paper fibers mixed with other substances such as fabric fiber, wood chips, and plastics. Small amounts of PVC are also present. The feedstock was gasified in a fixed bed updraft reactor using a mixture of air and steam at a temperature of 1400 \({}^{\circ}\)C. The process resulted in syngas with an LHV of 9.5 MJ/Nm\({}^{3}\) and yields as high as 3.4 Nm\({}^{3}\)/kg. The high calorific value of the gas is due to the high content of synthetic polymers in the raw material and favorable conditions for cracking. In the same year, [PERSON] et al. [48] investigated the co-gasification of ternary mixtures: Coal, biomass (pine sawdust), and automotive plastic waste. The studies were conducted using a fluidized bed reactor and air as a gasifying agent. The gasifier bed consisted of silica sand mixed with dolomite. Operating variables studied were the gasifier bed temperature (750-880 \({}^{\circ}\)C), equivalence ratio (0.30-0.46), feedstock composition, and the influence of secondary air insertion in freeboard. The optimal operating conditions identified experimentally were a bed temperature of 850 \({}^{\circ}\)C and an ER of 0.36. In these conditions, a syngas with LHV: 4-8 MJ/Nm\({}^{3}\) dry basis, was obtained. The injection of secondary air into the freeboard reduces the tar content to less than 0.5 g/m\({}^{3}\)n.  
[PERSON] et al. in 2010 [86] studied co-gasification of coals, plastics, and wood into a pre-pilot scale fluidized bed gasifier. During the study, they observed that each component can change the overall behavior of the process, for example, there was the possibility of reducing the level of tar by adding wood. Wood favors the formation of a solid phase of pure carbon, thus reducing the presence of hydrocarbons in the syngas and making it cleaner. Always, [PERSON] et al. [149] in 2011 investigated co-gasification in a fluidized bed of a mixture of coal, plastic (PE and PP), and wood, using oxygen enriched air. Quartz sand was used as a bed material. The main advantage of using O\({}_{2}\) enriched air is the ability to increase the bed temperature. Or, working at low temperatures, to reduce the size of the cross section and the total cost of the preheating. [PERSON] et al. [150] in 2012 studied co-gasification with air of a mixture of PP and sawdust at a fixed feed gas flow rate in a packed-bed reactor. The reactor temperature was varied from 400 to 800 \({}^{\circ}\)C. The increase in temperature led to \"a decrease in the solid fraction and a convex shape curve for the gas yield\". Moreover, it increased the liquid fraction, favoring the cracking of the latter. In particular, the liquid phase is rich in hydrocarbons containing oxygen. In the same year, [PERSON] et al. [151] studied the co-gasification of wood pellets, biomass/plastic, and olive husks using a catalytic fluidized bed gasifier in which inert quartzite sand or nickel-based catalyst supported on \(\gamma\)-alumina, were used as a bed material. Gasification experiments were conducted both in the presence and absence of steam. Pelletization, which consists of reducing the size of the material, is an effective strategy to make the feedstock more homogeneous and facilitate the feeding of the device. Independently of the fuel used, the presence of steam favors the production of H\({}_{2}\). The presence of the catalyst greatly increases H\({}_{2}\) production and reduces the tar content, more effectively than steam.