Team Members
Abdulla Amer, Bridget Talbot, Khalfan Almesmari, Renata Swarbrick, and Roxanna Mendoza
Mentor: Michael Armstrong
Abstract
Plastic wastes have posed serious threats to the environment, including the decrease of soil nutrient effectiveness and agricultural production as well as emergence of ecological instability. And increasing population leads to an increase in plastic waste, which is a big issue in every country. The dominant plastics produced worldwide are (29.6%) polyethylene, (18.9%) polypropylene, and others with smaller percentage significance. The plastic waste can be managed by landfill and incineration. But the disadvantage of landfills and incineration is carbon dioxide emission. Although plastic waste can be reused and recycled, in the end it will be garbage or become non-recyclable. In order to add value to plastic waste, the conversion of plastic waste to other products has received much attention.
In this work, the thermal degradation of high-density polyethylene (HDPE) has been carried out using a fluidized bed reactor. A commercial FCC catalyst based on a zeolite active phase has been used for catalytic pyrolysis of HDPE. We investigated the influence of FCC catalyst, reaction temperatures, and catalyst to plastic ratio. This work also addresses the optimization of catalyst steaming and pyrolysis temperature in order to maximize the production of diesel-oil fraction.
Both HDPE primary decomposition and wax cracking reactions take place inside the reactor. Secondary wax and tar reactions are small. The thermal degradation of the material, the product distribution and consequently the economics of the process are strongly influenced by the experimental conditions used. The influence of the operating parameters on the product distribution has been studied using various scientific literature.
The catalytic pyrolysis produced liquid and gas fractions comprised of a wide range of hydrocarbons, mainly distributed within C1 to C17. This catalyst gives way to 8 wt% gas yield, 22 wt% medium hydrocarbon (gasoline) fraction, and a yield of 69 wt% C10+ (diesel) fraction. It was found that severe steaming of the catalyst at 816 °C for 8 hours resulted in a higher diesel product composition.
In summary for our process, the pyrolysis of 2,000 metric tons of HDPE resulted in 9,916 barrels/day of diesel fraction, 2,798 barrels/day of medium fraction and 165.2 metric tons/day of gases. It can be noted that the results are estimates based on specific experimental data from similar processes in literature. Although there are a few experimental studies concentrated on catalytic pyrolysis of HDPE plastic waste, using theoretical calculation based on Aspen Plus simulation is an essential task. The obtained results can be guidelines in the real operation. A simulation of the whole process can provide the possibility of using this process in a real-world or large-scale application.
Problem Definition and Significance
The goal of this project is the production, characterization, and evaluation of alternative diesel fuel from pyrolysis using High-Density Polyethylene (HDPE) waste plastic
The largest amount of plastic wastes is disposed of by land filling (65-70%), incineration (20-25%) and recycling which is only about 10 percent
The problem of waste plastic cannot by solved by land filling and incineration, because suitable and safe depots are expensive, and incineration contributes to the increasing emission of harmful, greenhouse gases
Market Analysis
500 billion pounds of new plastics are produced globally. 33% serves single-use purposes
From 35.7 millions tons of plastics produced in the U.S. 8.7% is being recycled
10 million tons account for HDPE production in the U.S.
Production of HDPE is expected to increase to 66.96 million tons throughout 2022
Most recycled types of plastic: HDPE with a 29.3% recycling rate and PET with a 29.1% recycling rate
The production of “clean diesel” has become more attractive through the years due to the declining reserves of fossil fuels
Pyrolysis accounts for a revenue share of 65.3% in the global market as of 2019
The global plastic to fuel market size (as of 2020) was valued at 231 million US dollars and is expected to grow by 29.5% from now to 2028
Value Chain
The selection of the plant location considered the following factors:
- Feedstock supply (HDPE) - 1262 available Recycling facilities in California
- Availability and cost of labor - hourly employer cost is $40.74 (as of June 2021)
- Market location - price of conventional diesel in California is higher than that of renewable diesel
- Environmental impact - California is the top consumer for biofuels due to the economic benefits in the California’s Low Carbon Fuel Standard which aims to reduce petroleum dependency by providing a greater range of low-carbon and renewable alternatives
Economic benefits in the California’s Low Carbon Fuel Standard which aims to reduce petroleum dependency by providing renewable alternatives
Block Flow Diagram
Personal Protective Equipment (PPE)
Flame Retardant Overalls, Earmuffs, Safety, Shoes, Hard Hat, Heat Resistant Gloves, Goggles, and Particulate Dust Mask are essential safety wears in the pyrolysis plant.
Operational Safety Concerns (Reactor/Regenerator)
Prevention and Mitigation:
Slide/gate valve between Reactor and Regenerator to control the flow of the FCC catalyst
Valve closes in case of an emergency
Emergency Shutdown Instrumentation is required for FCCs.
Gases should not be released into the atmosphere, so relief valves at the top of the main fractionation unit (T-100) will open such that the gases travel into a flare system.
Safety and Environmental Analysis
Air emissions: -
One major point of concern in terms of carbon emissions is the regenerator unit (R-101)
The expected carbon emissions for this plant are 72,000 MT per year, which exceed the allowed annual limit for industrial facilities in the state of California
Plant must abide to the Cap-and-Trade program where permits or allowances can be bought per every exceeding ton of carbon emissions
Solid Waste Disposal: -
The catalytic pyrolysis process (reactor unit, R-100) requires a constant FCC catalyst feed, and the used catalyst needs to be removed
How to deal with this?
- Sell this product to other FCC operators if the catalyst has still enough activity
- One disposal company in California is USA Services Inc., located in Adelanto.
- The services include catalyst removal at the fluidized catalytic cracking unit directly, as well as vacuum services for collecting and transporting wet and dry hazardous materials
Disposing of the FCC catalyst in the landfill is not environmentally friendly and can be costly, ranging from $25.29 to >$300 per ton of industrial waste
Capital Cost Summary
Fixed Cost of Production
Variable Cost of Production
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