Design, Manufacturing, and testing of small scale plastic pyrolysis plant (Case study: Jimma town)

Abstract

Plastics are non-biodegradable synthetic organic materials produced by polymerization. Since its very synthesis in 1900s, plastics have substituted many types of materials such as wood, metals, and ceramics in production of goods, as they are light, durable, resistant to corrosion, diversity of applications, ease of processing and low cost. Since many plastic waste can be generated daily, it appears difficult for plastic waste management. Recycling, incineration, and thermal or catalytic cracking are the basic mechanism implemented by the world to manage plastic waste. Since it is most environmental friendly, this research is all about using thermal cracking as a method of plastic waste management in Jimma town. There are two types of plastic waste. The first is industrial plastic waste. This type of plastic waste is easy to recycle due to its homogeneity. The other is municipal plastic waste, which is difficult to recycle because it is heterogeneous. The daily per capital waste generation of Ethiopia is 0.3kg/day, of which 2% is plastic waste (Daniel Hoornweg, 2012). In Jimma town, the daily per capital waste generation is 0.157kg/day (Beneberu, 2011), of which 3.35% is plastic waste (Dereje T., 2017). Up on the use of thermal pyrolysis, these waste plastics can be converted to either solid, liquid, or gaseous fuel. Temperature, types of reactor, residence time, use of catalyst, pressure, particle size, and chemical composition of feedstock are the basic factors which affects the pyrolysis. The reactor is selected to be batch type, and designed to decompose 30liter of feedstock at a time. Counter flow shell and tube heat exchanger is selected as a primary condensation mechanism, which is designed to a length of 1.8m. The shell side pyrolysis gas is supplied at rate of 0.01103kg/s. The heat exchanger is designed to 8 number of tube, and the rate of tube side cooling water is 0.1847kg/s. Based on the designed dimensions, both reactor and condenser are manufactured. Only using distillation cooling, test pyrolysis is conducted for polyethylene theraphthalate. From pyrolysis of polyethylene theraphthalate 350ml of liquid fuel and 3.0105kg solid fuel is obtained. The liquid fuels obtained have a heating value of 37.86MJ/kg and viscosity of 2.7mm2 /s. The solid fuel have 67.096%wt carbon content and calorific value of 25.887MJ/kg.