Design of a flexible plastics feeding system to a pyrolyzer for power generation

Transcription

1 Design of a flexible plastics feeding system to a pyrolyzer for power generation Design Team Brandon Fisher, Heather Taft, Chris Tompson,Will Zhu, Michael Ziolek Design Advisor Prof. Yiannis Levendis Abstract Pyrolysis of waste plastics into a stream of gaseous hydrocarbon facilitates the recycling and reuse of plastics as a clean and sustainable energy source. Researchers at Northeastern University are developing such a system under the supervision of Professor Levendis. To increase the functionality of the system, a flexible feeding sub-system has been designed. The specifications for this design are dynamic. Some of these specifications include the ability to handle continuous flow of either granulated, shredded, or film plastics; be seamlessly interfaced with the current version of the apparatus; be insulated, airtight, and lightweight; and be able to completely remove oxygen from the feeding chamber before inserting it into the system. The design process was broken into two designs. The first design addresses the immediate concern of providing a working feeding system to allow for the testing of the pyrolyzer. The second design addresses the remaining concerns such as material inputs and nitrogen usage. This design involves two rollers that create a self-sealing system. The self-sealing will reduce the need for constant nitrogen input into the feeding system. For more information, please contact y.levendis@neu.edu. 23

2 The Need for Project As the use of plastics production increases, the need for a viable use for the resulting wastes becomes more imperative. Due to the nature of conventional plastics recycling, the material from plastic bottles can never be used for the same purpose again. With 30 million metric tons of post-consumer plastics produced every year in the US alone, the issue will only get worse. As a solution, converting plastic waste into a natural gas-like substance using a plastics pyrolyzer is a method for achieving environmentally friendly recycling of plastic wastes. These wastes include plastic bottles, films, and pellets. The pyrolyzer gasifies the input plastic waste, mixes it with air, and then produces an energy-rich and clean gas without any residue. This gas can then be burned for energy when mixed with air. By cleanly converting waste into energy and minimizing the emission of pollutants, a full recycling of the plastic can be achieved. There has been an ongoing effort to design this system involving previous capstone groups and graduate students under Professor Levendis s direction. In order to allow for more efficient testing of the pyrolyzer system, a continuous feeding system is required. By doing this, the potential functionality and control of the existing system will be expanded. The Design Project Objectives and Requirements A feeding system is needed to allow for the continuous flow of input materials into the pyrolyzer at a reliable feed rate. Design Objectives The goal of this project is to design a feeding system that is compatible with the existing pyrolyzer system. It must transport a variety of materials including plastic pellets, shredded plastic films, and shredded plastic fragments. In addition to plastic wastes, it is desired for the feeding system to be able to input biomass, such as wood pellets, into the pyrolyzer. This will broaden the usability of the pyrolyzer as a system. The system needs to be self-sustaining in order to be successful. If the system required too much energy, then the overall pyrolysis process would become counter-productive. Design Requirements Input material must be fed into the existing pyrolyzer at a rate of approximately 1 g/min. In order for the design to be efficient and self-sustaining, the energy required to power both the feeding system and the pyrolyzer must be less than the 24

3 energy produced by the system. The system currently produces 45 J per gram of plastic processed. Another aspect of the overall system efficiency is to minimize the amount of nitrogen needed to purge oxygen from the system. Design Concepts Considered We developed three design concepts of which two fully meet the requirements. While several concepts were considered initially, three designs were selected as candidates for further consideration. These three designs included an auger system, a conveyor belt system, and a roller system. Of these three designs, two final designs were chosen to address the various objectives of the project. The auger-based system was selected to address the immediate issues of establishing a working feeding system to feed pellets to the pyrolysis chamber to enable the testing of the pyrolyzer system. The roller system was designed to address the shortcomings of the auger-based system. The auger-based system is not able to handle the feeding of plastic films or shredded pieces and the roller system accommodates this variation in input materials. The conveyor design was rejected as a result of initial scalability analysis and the potential cost of prototyping the design. Recommended Design Concept Two designs, an auger-based design and a self-sealing roller design, were created to address the issues of this Capstone project. Design 1 The first design consisted of a hopper, an auger bit, and a feed tube. Input material is fed into the hopper and then the system is flushed to remove all traces of oxygen. Once purged, the material drops down from the hopper onto the auger bit where it moves at a rate of 1 g/min through the feed tube. The auger bit is rotated using a motor. From there, the material drops into the pyrolysis chamber. 25

4 To qualify this design, extensive feed rate testing was performed. Also, the feeding system is connected to the pyrolyzer so overall functionality can be assessed. Advantages to this design include the ease of assembly, the relatively low cost of prototyping, and the high controllability of the system, which leads to consistent feed rate results. Design 2 The second design includes an external housing and two rollers. The rollers are composed of a pliant material and positioned in such a way that they will constantly be in compression against each other. This constant contact prevents oxygen from entering the system. The left roller rotates clockwise while the right roller rotates counter clock-wise. As the two rollers rotate, material is pulled down between the two rollers. In order to qualify this design, feed rate testing will need to be performed. The self-sealing properties of the system will reduce the need for constant nitrogen and allow for an open-air hopper to feed the system. Having an open-air hopper will allow the system to be continuously batch-fed. 26

5 Financial Issues The prototyping of both designs collectively cost approximately $1000 including the purchase of a new motor. The main sources of cost involved with both designs were the purchases of a new motor and gears for both the gearbox and the roller assembly and the rapid prototyping of the housing for the roller assembly. Manufacturing costs were kept down by performing the majority of the machining in-house and by using commercial-off-the-shelf (COTS) parts. Recommended Improvements Some aspects of the design, such as total system nitrogen usage, were not fully investigated in this Capstone project and are a topic for future research. The use of nitrogen within the feeding system has not been fully researched and explored in connection to the designs. While the roller design is set to allow for continuous feeding from an open-air hopper, the overall use of nitrogen within the system can be further analyzed and optimized. The benefits of reduced nitrogen usage include the decreased cost involved in the constant requirement of nitrogen and potential improvements in the combustion process. Scalability of the overall system may also pose an issue in the future. While the focus of this Capstone project was the design of a bench-top scaled feeding system, all future designs and alterations will need to be scalable to meet the overall project goal, to create a solution to the plastics problem. 27