A System to Convert Waste Plastic into Clean Energy

Transcription

1 A System to Convert Waste Plastic into Clean Energy Design Team Anna Craver, Katherine Dixon, Chris Flanagan, Brittne Lynn, Mason Riley Design Advisor Prof. Yiannis Levendis Abstract The 20 th century will forever be known as the Petroleum Age. However, the increasing need for energy and depleting values of fossil fuels necessitates a jump start to a new era. This design, planted on the firm foundation that is the research of Professor Yiannis Levendis, will function as a stepping stone into the much needed ienergy Age. Why waste plastics? Three reasons: 1) Waste plastics are capable of generating energy comparable to that of gasoline, 2) Plastics pollution is an ever increasing concern for marine environments and landfills at the very least, and 3) Plastics degrade over time in the recycling process (meaning that the grade of plastic decreases each time it is recycled until it is no longer valuable). This design has been procured to extract the maximum amount of thermal energy from waste plastics, while not negatively impacting the environment by releasing toxic chemicals into the air (what commonly happens when solid plastic is ignited). Waste plastic inserted into system Compression Chamber Exhaust gasified plastic to be harnessed as fuel Waste plastic liquefied Liquefied plastic gasifying in pyrolysis chamber Energy added to system (eventually harnessed from exhaust gasified plastic)

2 The Need for the Project Waste plastics are highly sensible to use as an alternative form of power generation because there are limited uses for recycled plastic and they possess approximately 44 MJ/kg of energy, which is comparable to that of gasoline. With traditional energy sources depleting rapidly by the minute, it has become increasingly evident that other, less traditional energy methods must gain momentum to balance the needs of modern society. In tandem with this comes the necessity to take preventive and regenerative actions on the environment itself. Waste plastics is not only a major solid pollutant to the environment, but also has a large amount of energy that can be extracted with the right tools. With that in mind, managing waste plastics can not only help clean up the environment, but also supplement the increasing demand for energy all over the globe. The Design Project Objectives and Requirements The objective of this design is to Design Objectives create a system that will gasify The primary design objective is to create a continuously fed system plastic, mix this gas with air and that will convert waste plastic into energy through a sequential process finally combust the mixture in in a clean and efficient manner. This system must gasify the plastic in order to produce thermal energy. the absence of oxygen so that the plastic will not combust prematurely. Then the gasified plastic must be mixed with air, to finally combust the gasified plastic to produce thermal energy. A flow chart of this process is shown to the left for reference. Design Requirements For the prototype model, the system must efficiently convert at least 1 gram of plastic per minute to thermal energy. Two major challenges were to control the gasification of the plastic without premature combustion, and dealing with temperatures from 273K to in excess of 1273K inside the system. A thermal analysis is shown to the left as reference.

3 Design Concepts considered We considered two options for The project was comprised of two major sub-systems, the feeder, and both of the subsystems. the pyrolysis chamber. For the feeder sub-system, the design came in the form of a chamber with liquefied plastic to maintain a seal. To feed that chamber, there could be either cartridges that would lock in place, and dispense additional plastic. Alternatively, to add plastic to the melting chamber, the concept of using a chamber with sealed doors on the top and bottom will act as an air-lock, allowing the feeder to be purged before releasing the plastic into the melting chamber. For the doors, various mechanisms were considered, specifically, butterfly valves, trap doors, sliding plates, and rotating chambers. For the pyrolyzer system, a proposed design was to use a vertically stacked set up. The chambers were to be placed within and on top of each other. Essentially, the pyrolysis chamber would be seated within the combustion chamber. This set up maximizes the amount of heat transferred between the various levels. On the outer most layer, the combustion chamber was to be wrapped with external insulation. An alternative set up was a side-by-side design, using heat exchangers to transfer the heat between the chambers, again, insulating the external walls of the chamber. Recommended Design Concept Our finalized design concept uses In the recommended design, the most beneficial set-up for the system a compartmentalized design, with is a compartmentalized design with stacked chambers seen in the stacked chambers to facilitate heat figure on the left (refer to page 1 for chamber labels). The chambers and pressure flow through the are stacked so the natural flow of plastic waste is from top to bottom: system. compression chamber to liquefaction chamber to pyrolysis chamber. The final feeding idea chosen for the preliminary design uses liquefied plastic in the liquefaction chamber. Not only will the liquid create a seal between the pyrolysis chamber and the atmosphere air, but it also allows for continuous flow into the pyrolysis chamber. The liquid pool of plastic will be pressurized by nitrogen in a capped chamber that will force the liquid into the pyrolysis chamber, while the pyrolysis chamber is pressurized to a slightly smaller degree, in an

4 attempt to control flow of the system. This pressure gradient will ensure the correct flow of the system as a whole. The compression chamber is one key component in keeping a continuous flow. The top of this compression chamber has an air tight valve that one can open to insert solid plastic that will then enter the system. The valve is resealed, and the initial chamber is pressurized to the same pressure as the liquefaction chamber. The chamber is to be purged then pressurized with nitrogen to rid the chamber of oxygen. The recommended pressure gates at the top of the compression chamber and between the liquefaction chamber and compression chamber are butterfly valves. The floor of the compression chamber flips and drops all material into liquefaction chamber to melt and to help continuously feed the system. The bottom chamber is the pyrolysis chamber, where the plastic is gasified. This is final step is the most critical, where the gasified plastics will leave this chamber ready to combust and generate the energy desired. The chamber is heated by a source beneath it which is currently an external source to better control the heat generation rate. To determine the estimated temperature ranges, a thermal flow analysis and a mathematical model were generated and compared. These two methods made it possible to determine the required dimensions of the product based on the desired power output. To test the system, three different stages were designed to test each chamber separately, building from the liquefaction chamber down. The first stage of testing was used to prove that plastic can be liquefied and to determine a melting temperature range for the different plastics in use. Pyrex glasses and a 290 Watt heater were used to create liquefied plastic. The second stage of the testing used a steel crucible will small holes (a scaled down version of the liquefaction chamber), wrapped with a high power heat wrap, and the compression chamber to determine the mass flow rates of the plastics. It was found that Polyethylene powder flows through one hole.125 in diameter at an average rate of 1 g/min. The third stage of the testing includes testing the pyrolysis chamber (see in the figure above). This stage of the test includes the crucible set inside the pyrolysis chamber with the feeder on top.

5 Financial Issues The total cost for the prototype and testing materials was $ dollars.. The main financial issues in manufacturing the prototype would be due to the machining cost of the liquefaction chamber. The prototype price of dollars does not include machining costs since all parts were made by design group members. If the system were to be scaled up, safety materials pertaining to the high temperatures of the combustion chamber would also be of financial concern. Recommended Improvements Some recommended The next major step is to bring the exhaust gasses from the pyrolysis improvements are to better chamber back to the system by finishing the design of the combustion harness the current exhaust gasses chamber, so that the system is completely self-sustaining. Another as fuel for sustaining the system major improvement would be to create a more robust insulation as well as increasing system system to reduce losses to the outside environment. insulation.