Pyrolysis and combustion of waste plastics

Two million tons of plastic waste per year are generated in Brazil. Only 16.5% by mass of this plastic waste is mechanically recycled, most of the rest is taken to landfills or dumps. All of this material could be incinerated, thus reducing the mass of the landfilled volume by up to 90%, and using its energy content to generate steam or energy.

This investigation was carried out on the incomplete combustion products emitted from the pyrolysis and steady state combustion of polyethylene and polystyrene in an electrically heated two-stage vertical furnace. Separately, the polymers in the sprayed form were pyrolysed at a constant temperature of 1000 ° C and, after mixing with N2 / O2, the pyrolysis products were burned at 900, 1000 and 1100 ° C.

The tests were conducted with 21% O2. Different fuel and air ratios were used in the combustion furnace, by varying the polymer feed rate in the pyrolysis furnace. The motivation for the indirect combustion of PE and PS was to obtain the nominally pre-mixed combustion of the pyrolysis gases with air, thus obtaining lower emissions of the incomplete combustion products compared to the direct combustion of the solid polymer.

This work examined the effects of combustion temperature and the equivalent ratio of air to fuel. The pyrolysis and combustion effluents were analyzed, and the emissions of CO, CO2, O2, light hydrocarbons, polycyclic aromatic hydrocarbons and particulate materials were measured. In addition, the particulate material was characterized in terms of particle size.

It was observed that while the amount of pyrolysis gas decreased with the increase in the feed rate of the polymer, its composition remained practically independent of the feed rate. CO2 emissions were maximum close to the equivalent ratio 1, while CO emissions increased with the increase in the equivalent ratio. The total emissions of light hydrocarbons and PAH in combustion increased both with an increase in the equivalent ratio and an increase in temperature. Most of the particulate material was smaller than one micron.

In general, the emissions of PAH and particulate matter from the indirect combustion of PE and PS were an order of magnitude lower than the corresponding emission from the direct and heterogeneous combustion of the solid polymer, obtained in other works. As the pyrolysis of these polymers requires a nominal minimum heat input in relation to the amount of heat generated in their combustion, the implementation of this technique can be advantageous.

The disposal or disposal of waste entails expenses both with its transport and with the control of the deposit areas, in addition to suffering social pressure associated with this theme. An economical and ecological solution for the disposal of solid waste is energy recycling. Brazil still has low energy recycling values, however, in Europe, USA and Japan this technology is well established. In addition to creating new energy matrixes, this process allows you to reduce the volume of your waste by up to 90%. For this line of research, a partnership has been established with Northeastern University (Boston, USA). The studies cover the combustion and pyrolysis processes of plastic waste, sugarcane bagasse and used tires.

The annual consumption of plastics in Brazil is approximately 20 Kg / inhab, and in the United States this value reaches 100 Kg / inhab and in Europe the average is 80 Kg / inhab. The large consumption of plastic materials generates an increasing production of waste, which can become a problem, especially for cities with space problems for the destination of solid urban waste.

The traditional production of sugar associated with the growing production of alcohol (bioethanol) makes the sugar and alcohol industry one of the main segments of the Brazilian economy. The Brazilian industry is responsible for around 50% of world sugar exports, and has the absolute leadership in the production of alcohol from sugar cane. Approximately 630 million tons of sugarcane were processed in 2009, generating about 142 million tons of sugarcane bagasse. The auto industry broke production records in 2007, according to ANFAVEA (National Association of Motor Vehicle Manufacturers), there was a 13.9% growth in production and 27% in sales during the year.

Tires production follows the growth of the auto industry. In the world tire production ranking, Brazil ranks seventh for automobiles and fifth for trucks, buses and trucks. In 2007 alone, new tire manufacturers in Brazil put 57.3 million units on the market.