Pyrolytic conversion of waste plastics to energy products: A review on yields, properties, and production costs.

In recent years, about 370 million tonnes of waste plastic are generated annually with about 9 % recycled, 80 % landfilled and 11 % converted to energy. As recycling of waste plastics are quite expensive and labour-intensive, the focus has now been shifted towards converting waste plastics into energy products. Pyrolysis of waste plastic generates liquid oil (crude), gas, char and wax among which liquid oil is the most valuable product. In this review, emphasis has been given on the pyrolysis products yield from both thermal and catalytic pyrolysis and the factors that affect pyrolysis products yield. The use of homogenous catalysts, for example AlCl3, can significantly improve the quality of waste plastic pyrolytic oil (WPPO), reduce time and energy consumption of the process, and help remove the contaminants of waste plastic. This study also thoroughly reviewed physico-chemical properties of WPPO to understand their thermal stability, elemental composition, and functional groups. Although liquid oil exhibits comparable heating value with commercial fuel (diesel/petrol), for example higher heating value of Polypropylene (PP) and Polyethylene (PE) are 50 and 42 MJ/kg which is between 42 and 46 MJ/kg for commercial diesel the other properties depend on several parameters such as plastic and pyrolysis reactor types, temperature, feed size, reaction time, heating rate and catalysts. A techno-economic analysis indicate that the liquid oil production cost could be about 0.6 USD/l if plant capacity is ≥175,000 million litres/year with a breakeven of 1 year. After-treatment of WPPO through distillation and hydrotreatment is recommended for improving the physio-chemical properties comparable to commercial fuel to use in automobile applications. This paper will be a valuable guide for stakeholders, and decision and policy makers for proper utilization of waste plastics.

Harnessing waste-to-energy potential in developing countries: a case study of rural Ghana.

This study examines factors that define a suitable waste-to-energy (WTE) technology and identifies an appropriate WTE technology that can be deployed to improve waste management in rural areas. Observations, questionnaires and interviews were used to collect data from waste management experts at Atwima Kwanwoma District and the residents in Kwanwoma township in Ghana. This study established that the following major factors define a suitable WTE technology for the Kwanwoma township: the initial capital or set-up costs, feedstock type, required plant size, and required input volume. The study also revealed that sanitary landfill with gas capture is the most suitable WTE technology for the Kwanwoma township based on the least set-up costs and scalability. The study provides the next steps for government action on WTE technology at the township, district, and national levels.

Can support policies promote the innovative diffusion of waste-to-energy technology?

Currently, China is facing severe pressure of environmental emission reduction. As a kind of clean energy, waste-to-energy technology has the advantages of renewability, low pollution, and stable supply. To establish an affordable, effective, and sustainable waste disposable method is critical for the low carbon society transition. Therefore, the innovation diffusion of waste incineration power technology is a problem worth studying. Based on this, in order to answer this question scientifically, this paper constructs a system dynamics model of innovative diffusion, and analyzes the internal mechanism of innovation diffusion. The results show that firstly, the government support policies have a positive influence on the innovation and diffusion of waste incineration power technology; secondly, compared with the R&D policy, feed-in tariffs policy is more efficient to expand the installed capacity of waste incineration power; At last, technological innovation caused by government support policies is the main driving force of waste incineration power industry investment cost reduction.

Life cycle assessment of pyrolysis, gasification and incineration waste-to-energy technologies: Theoretical analysis and case study of commercial plants.

Municipal solid waste (MSW) pyrolysis and gasification are in development, stimulated by a more sustainable waste-to-energy (WtE) option. Since comprehensive comparisons of the existing WtE technologies are fairly rare, this study aims to conduct a life cycle assessment (LCA) using two sets of data: theoretical analysis, and case studies of large-scale commercial plants. Seven systems involving thermal conversion (pyrolysis, gasification, incineration) and energy utilization (steam cycle, gas turbine/combined cycle, internal combustion engine) are modeled. Theoretical analysis results show that pyrolysis and gasification, in particular coupled with a gas turbine/combined cycle, have the potential to lessen the environmental loadings. The benefits derive from an improved energy efficiency leading to less fossil-based energy consumption, and the reduced process emissions by syngas combustion. Comparison among the four operating plants (incineration, pyrolysis, gasification, gasification-melting) confirms a preferable performance of the gasification plant attributed to syngas cleaning. The modern incineration is superior over pyrolysis and gasification-melting at present, due to the effectiveness of modern flue gas cleaning, use of combined heat and power (CHP) cycle, and ash recycling. The sensitivity analysis highlights a crucial role of the plant efficiency and pyrolysis char land utilization. The study indicates that the heterogeneity of MSW and syngas purification technologies are the most relevant impediments for the current pyrolysis/gasification-based WtE. Potential development should incorporate into all process aspects to boost the energy efficiency, improve incoming waste quality, and achieve efficient residues management.