Waste Plastics into Fuel Oil?

One way to clear the existing mountains of waste plastics is to turn them into clean fuel oil; a company in New York appears to have done just that at a cost of 11 cents a gallon using unsorted, unwashed plastic wastes in a safe, environmentally friendly, and highly efficient process; but will this perpetuate our dependence on fossil fuel? Dr. Mae-Wan Ho

Plastics are organic polymers, most of them chains of carbon atoms alone or with oxygen, sulphur, or nitrogen. The conversion of waste plastics into fuel oil by thermal depolymerization (also called pyrolysis or cracking) involves using moderate heat in the absence or oxygen to break down the long-chain hydrocarbons into short-chain hydrocarbon gases and oil. Much effort has gone into developing an efficient, safe, and cost-effective process since the late 1990s (see [1] Waste Plastics into Oil, SiS 29).

The most successful and closest to commercial production to-date is a patent-pending process developed by the company Plastic2Oil based in Niagara Falls, New York, in the United States [2]. It turns unsorted, unwashed waste plastics into clean low sulphur fuel without the need for refinement. The latest plant, improved and scaled up in successive versions since 2009, processes 40 tons of waste plastics a day, converting 86 % of the waste into liquid fuel, powered predominantly by low-boiler gas produced in the process. The cost of operating the processor, including utilities, staff and depreciation works out to be $0.11 per gallon. This is highly competitive even as crude oil prices continue to drop below US $50 a barrel and wiping out thousands of jobs [3].

From recovering old data to fixing plastic wastes

John Bordynuik on a pile of mixed unwashed plastic waste, from [5]

It began with John Bordynuik who designed a laboratory desktop processor unit that uses a proprietary catalyst to turn mixtures of unwashed waste plastic into marketable fuel [4]. According to an extended interview he gave to the Niagara Magazine in 2010 [5], Bordynuik started life as a computer whizz kid who learned to programme at the age of 10, lived in Toronto for more than a decade where he served as Director of Research and Development for the Ontario Provincial Legislature, then moved back to Niagara and set up John Bordynuik Inc. (JBI), a company dedicated to technical fixes. One of the first such fixes was to recover lost data for MIT’s Computer Science and Artificial Intelligence Laboratory, and then for NASA.

After his successes with MIT and NASA, Bordynuik began buying up abandoned data storage devices, especially old data tapes, eventually building up an engineering archive of 60 million documents, representing a lot of research data to be mined. Perhaps it was information from that archive that led him to the pyrolytic breakdown of plastic wastes into fuel oil.

Bordynuik focussed on non-recyclable waste plastics [4], which according to the Environment Protection Agency (EPA) constituted over 92 % of waste plastic in 2010, and growing at 8 % a year. He saw a critical need for a viable and environmentally sound general purpose recycling process for hydrocarbon streams that fall outside accepted refinery standards, and would have been landfilled or melted into products of low value.

The 1-gallon desktop processor was soon scaled up to 3 000 gallons, and finally progressed to the current 40 ton/day processor. At every stage, the process and products were assessed and validated and the design improved. It is instructive to follow his progress.

Bordynuik pointed out some of the challenges at the start [4]: “Waste plastics have some of the most undesirable properties of any substance when considered for thermal processing. Plastics have low-surface area, poor heat transfer, exceptional tensile strength and are considered an insulator. During the melting process, plastics absorb heat and will stick to anything cooler, resulting in exigent “glue” that will seize or bind some of the largest high-torque feed technologies.”

At the time, most processes were based on a batch method. The resultant product is typically a low flashpoint, unstable, unsaturated mix of random hydrocarbon chains, ranging from c5 to c80. Unsaturated alkenes are undesirable in fuels and highly reactive. This results in poor energetic value, high residue and high total hydrocarbon emissions (THCs) when burnt. Large refineries generally refuse such products due to their low value, impurities, acids, and possible damaging contaminants. The residue (coke) resulting from the batch method can also be a problem as it forms on the wall of the reactors or tubes, and must be scraped or drilled out. The emissions from batch-based processes are generally not desirable and usually need a thermal oxidizer to incinerate volatiles, organics and low boil gas created in the process.

Bordynuik decided on a list of ‘must haves’ for the process that included viability, accepting waste continuously, with minimum requirements (no extrusion), accepting composite waste materials with metals, operating on the off-gas generated from cracking the hydrocarbon chains, anti-coking, and good seals.

Initial scaling up and testing

The small 1-gallon continuously charged reactor was assembled and operated for several months, gathering data for scaling up the process. It was charged with 100 g of plastic every 5 minutes. Over 44 runs, the reactor processed shredded waste plastics including food waste packaging, agricultural film, and shredded gas tanks as well as high density polyethylene regrind in some runs to establish ideal conditions. The low boilers (methane, ethane, butane, propane, and hydrogen) were analysed with a gas chromatograph (CG) and quantified. The resulting fuels underwent typical petroleum tests including automatic distillation and flash and pour point evaluation. The fuel output consisted of a diesel/naphtha mix. GC testing showed a total absence of wax-like hydrocarbon chains in the C20-C60 range. Additionally hydrocarbon production was predominantly in the C13 diesel range.

A 55-gallon processor was constructed while the 1-gallon reactor was being tested. The 55-gallon processor output was identical to the 1-gallon processor with the added feature that it was now operating on its own low-boiler gas.

At this point, the process

· Proved repeatable and scalable

· Converted 85 -95 % of waste plastic to “near diesel” fuel, 8 % to usable off gas much like natural gas, and 1 % remaining as residue

· Emitted no air toxins

· Had a positive energy balance greater than 2

The test results were sufficiently impressive that the New York State Department of Environmental Conservation (NYSDEC) issued a consent letter for constructing a 3 000 gallon reactor pilot plant to gather data and emission information for future air and waste permits. That meant building a pilot plant in less than 2 months. So a “Silicon Valley-like startup structure was created with 20 talented people in Niagara Falls” consisting of chemists, welders, fabricators, chemical operators, material handlers, administration and security.  The plant was finished in less than two months.

The plastic waste is loaded on a scaled hopper, and fed through a series of slide gate valves to control the volume of plastics. Oxygen is purged by feeding nitrogen into the space. The final slide-gate is opened to drop the waste plastic onto a screw conveyor driven by a 2 HP motor, so there is no power available to overcome any plastic if it starts to melt in transit. This problem was solved by applying a proprietary coating on the screw (to prevent the melt from sticking) and rotating it at high speeds. The reactor is an indirectly fired kiln, heated with a 4 MBTU Maxon burner combining low boiler gases from the process and city natural gas for starting up and instantaneous short periods when low boiler gases are unavailable. The rotating kiln added many desirable features for the process including automatic residue removal and tumbling plastic waste, which allows for effect heat transfer and mixing.

Special seals were developed for the rotating kiln to keep the 400 °C vapour (with hydrogen) from escaping. Effective heat transfer in the kiln is accomplished through a mechanical assembly that transfers heat to the plastic; the assembly also scrubs the coke off the walls ensuring that heat can be transferred to the insides of the kiln. Generally 2 % of the waste plastic fed into the processor will remain in petroleum coke. The mechanical coke cleaning turns the residue into a fine carbon black that is easily removed.

The gas leaving the reactor contains a variety of fuels, some water vapour (if the plastic was wet), hydrogen, methane, thane, butane, and propane, and some nitrogen. The vapour passes from the reactor through a catalyst tower which ensures the resulting fuels contain no halides. The column also facilitates the selection of the types of fuels to be produced. A cyclone was added between the reactor and the catalyst tower to capture fine carbon black entrained in the vapour.

The vapour then passes through a column designed to condense a specific fuel product: Napha, Fuel Oil #2, or Fuel Oil #6. This column also controls how much low-boiler gas is created for the process. The final tower is a water seal used to prevent oxygen from entering the system.

After the fuel condenses, the remaining gas containing hydrogen, methane, ethane, butane, propane and possibly some water vapour is compressed and redirected to the burners.

The 20T a day pilot plant (from [5])

The process is run by a custom-programmed, data acquisition and control system with thermocouples, pressure sensors, a scale, an oxygen sensor, level sensors and proximity sensors installed at appropriate locations. Data are collected by a Honeywell HC900 PLC (programmable logic controller), which also responds to automation actuation requests. Pump, valves, and motors are all controlled by the PLC.

The PLC is connected to an HPDL580 server with a program written to capture and log data from the process every 10 seconds, and in addition, controls all of the devices through the PLC. Human operators interact with the process through custom software written to run on Windows or Ubuntu (Linux).

Process safety is designed through various levels of hardware installed to ensure proper and safe operation. Early triggers for potentially unscheduled events are monitored by operators through the software managing the process. Risk is greatly reduced by operating the process at slightly above atmospheric pressure. There is a 12 inch burst disc at the output of the reactor to vent combustion should it occur. The burst disc successfully vents high pressures, which if they were to occur could cause disassembly of the processor. The reactor was designed to store minimal fuel in-process. Fuel production is limited to a few gallons per minute, thereby keeping the system manageable if pump failure were to occur. The safe design has resulted in zero time loss in accidents during 3 years of process evolution.

An emissions stack test conducted on the pilot plant less than 6 months after its construction verified that process emissions were very low and could operate within NYSDEC regulations. In December 2010, the NYSDEC issued a rare consent order for the plant to continue operating while air and solid waste permits were being acquired.

Separate reactions for ASTM spec fuel production and other improvements

In the succeeding generations of processors, throughput and runtime were improved by separating the reactions that previously all occurred in the main reactor. A standardized fuel tower was developed to handle each type of fuel produced in the system. These greatly improved runtime and fuel production. Additionally, they resulted in the production of ASTM (American Society for Testing and Materials) specification fuels.

In early 2011, the system evolved to include a pre-melt reactor, multiple fuel columns and an internally designed low boiler compression system that could handle the various flows and volumes of low boiler gas generated. Low NOx burners were also installed to further reduce emissions. Two 4.5 MBtu burners were installed on each kiln to provide more heat. High volume, low head, high temperature pumps to move liquid fuel products up to 350 °C were needed; these were designed in house at 1/10 of what it would cost commercially.

As a result, the system can now produce in-spec fuels with higher waste plastic feed rates. In addition, a larger feeder was added to accommodate bigger pieces of plastic. In the new processor, plastic is fed via a 24-inch feeder (upgraded from the 6-inch feeder of the pilot) to a pre-melt rotary kiln. Typical plastics fed include off-spec Crayola markers and crayons, gas tanks, food packaging, wine bags, agricultural waste plastics and various scrap plastics from local industrial sources. The mixture is melted into a liquid form.

By liquefying the plastic first, if contaminants like PVC were to get into the system, HCl could be separated and removed before fuel production in the reactor. However, molten plastic is highly endothermic (absorbs heat) and will freeze up in a pipe if pumped too far. In addition, molten plastic has widely varying viscosities depending on temperature and composition. This problem was solved by locating the pre-melt and reactor kilns as close together as possible.

The final 40 tons/day plant was built, and a stack test successfully conducted in December 2011.

The 40 T/day plant (from [4])

After that, work focused on continually processing waste plastics and producing in-spec fuels consistently. Once that was accomplished a new problem emerged. The 2 % residue accumulated in the reactor until it was full. This necessitated taking the system out of steady-state operation to remove the residue, which meant it could not run continuously without interruption. This is solved by installing a third kiln, half the length of the pre-melt and reactor in the 3^rd generation design, which will condition and remove coke and residue continuously using a screw similar to the feeder but located at the end of the process. The estimated volume of residue is approximately 70 lbs/h.

In March 2013, the company had a significant breakthrough. They were able to develop a catalyst that allows the process to handle up to 20 % PET (polyethylene terephthalate) and PC (polycarbonate) without affecting processor operation or fuel quality. This is significant because the pyrolysis of PET and PC typically yield terephthalic acid and benzoic acid; the former generally sublimes and clogs piping.

In addition, the company is working on feedstock pre-processing technologies that will enable them to dry and compact plastic during feeding using the significant waste heat resulting from the process and excess electricity from co-generation.

The fuels created by the processor are Fuel Oil No. 6, Diesel, and Naphtha. Fuel Oil No. 6 and Naphtha do not need any additives and are shipped directly to the customer. The diesel fuel has very low sulphur so a lubricity additive is injected prior to shipping to the customer. The fuel has been tested by InterTek, Petrolabs, Southwest Research, and Alberta Research Council.

To conclude

The company has succeeded in developing a viable general purpose continuous refinery capable of processing solids and liquids at a cost similar to that of crude refineries.

• Waste is charged continuously through a low-power feeder
• Feedstock can include liquids or solids and does not need pre-sorting
• Approximately 86 % of the waste is converted into a liquid fuel
• The process is primarily powered from low boiler gas produced
• Diesel power generators converted for propane can operate on low boiler gas
• The process emissions are less than those of a natural gas furnace of similar size
• The 2 % residue waste is primarily carbon black and ash
• During the SAIC (Science Applications International Corporation) 3-day review, the processor was fed 121 318 pounds of waste plastics, and produced 10 287 gallons of fuel oil (~7.5 lb/gallon) and 4269 gallons (~7.2 lb/gallon) of naphtha
• The actual cost of operating a processor, including utilities, staff and depreciation is $0.11 per gallon
• As unwashed, unsorted waste plastics from industrial sources can be used, input feedstock costs are primarily preprocessing and transportation
• In 2010 the plant produced 15 350 gallons of fuel
• In 2011 the plant produce 122 244 gallons of fuel
• In 2012 the plant produced 317 255 gallons of fuel
• The plant has recycled millions of pound of plastic waste that would otherwise have gone to landfills

In addition, Bordynuik told a journalist in 2010[5] that they used 2 000 BTUs (British thermal units) of energy to convert one kilogram of plastic to fuel with 44 000 BTUs of energy. In other words, the output energy is an incredible 22 times the input.

The technology is obviously ideal for ridding the planet of the existing mountains of plastic wastes and at the same time recovering useful fossil fuels. But is it a long term solution for dealing with plastic wastes?  Looking into the future, would it result in competition for plastic wastes that will drive up the price so it is no longer economical? More importantly, would it indirectly encourage the production of non-recyclable plastics that ought to be phased out? Would it thereby lock society into exploiting fossil fuels in one way or another? These are important questions to consider.

Article first published 21/01/15

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References

1. Ho MW. Waste plastics into oil. Science in Society 29, 42-43, 2006.
2. Plastic2Oil. http://www.plastic2oil.com/site/home
3. “Crude oil’s collapse will cost 9,000 jobs”, Gary Strauss, USA Today 16 January 2015, http://www.usatoday.com/story/money/2015/01/15/crude-oils-collapse-will-cost-9000-jobs-at-schlumberger/21826189/
4. Bordynuik JW. Viable production of diesel from non-recyclable waste plastics. Proceedings of the 21st Annual North American Waste-to-Energy Conference. Fort Myers, Florida, 22-24 April 2013.
5. “John Bordynuik’s plan to fix the world”, Brock Dickinson, photography David Haskell, Niagara magazine September/October 2010, 36-40.