Thermal depolymerization

The loading station of the pilot plant in Carthage, Missouri Thermal depolymerization ('''TDP''') is a process for the reduction of complex organic materials (usually waste products of various sorts, often known as biomass) into light crude oil. It mimics the natural geological processes thought to be involved in the production of fossil fuels. Under pressure and heat, long chain polymers of hydrogen, oxygen, and carbon decompose into short-chain petroleum hydrocarbons with a maximum length of around 18 carbons. The process has been referred to with various names, including thermal conversion process ('''TCP'''). Thermo chemical conversion ('''TCC''') is a similar technology, but is not identical.

History

Thermal depolymerization is similar to the geological processes that produced the fossil fuels used today, except that the technological process occurs in a timeframe measured in hours. Until recently, the human-designed processes were not efficient enough to serve as a practical source of fuel—more energy was required than was produced. A new approach that exceeded break-even was developed by Illinois microbiologist Paul Baskis in the 1980s and refined over the next fifteen years. The technology was finally developed for commercial use in 1996 by Changing World Technologies. A demonstration plant was completed in 1999 in Philadelphia, and the first full-scale commercial plant was constructed in Carthage, Missouri, about 100 yards (100 m) from ConAgra Foods' massive Butterball Turkey plant, where it is expected to process about 200 tons of turkey waste into 500 barrels (21,000 US gallons or 80,000 liters) of oil per day.

Theory and process

Previous methods to create hydrocarbons from depolymerization expend a lot of energy to remove water from the materials. This hydrous pyrolysis method instead uses water to improve the heating process and contribute hydrogen from water to the reactions. The feedstock material is first ground into small chunks, and mixed with water if it is especially dry. It is then fed into a reaction chamber where it is heated to around 250 °C and subjected to 600 lbf/in² (4 MPa) for approximately 15 minutes, after which the pressure is rapidly released to boil off most of the water. The result is a mix of crude hydrocarbons and solid minerals, which are separated out. The hydrocarbons are sent to a second-stage reactor where they are heated to 500 °C, further breaking down the longer chains, and the resulting petroleum is then distilled in a manner similar to conventional oil refining. Working with turkey offal as the feedstock, the process proved to have yield efficiencies of approximately 85%; in other words, the energy required to process materials could be supplied by using 15% of the petroleum output. Alternatively, one could consider the energy efficiency of the process to be 560% (85 units of energy produced for 15 units of energy consumed). The company claims that 15 to 20% of feedstock energy is used to provide energy for the plant. The remaining energy is available in the converted product. Higher efficiencies may be possible with drier and more carbon-rich feedstocks, such as waste plastic. By comparison, the current processes used to produce ethanol and biodiesel from agricultural sources have energy efficiencies in the 320% range when the energy used to produce the feedstocks is considered (in this case, usually sugar cane, corn, soybeans and the like). The process breaks down almost all materials that are fed into it. TDP even efficiently breaks down many types of hazardous materials, such as poisons and difficult-to-destroy biological agents such as prions.

Feedstocks and outputs

The processing area of the pilot plant in Carthage, Missouri |- |Turkey offal | |- |Sewage sludge | |- |Medical waste |

Limitations

The process only breaks long molecules into shorter ones. Longer molecules are not created, so short molecules such as carbon dioxide or methane can not be converted to oil through this process. Nevertheless, it is interesting that the turkey-processing plant is creating fuel from atmospheric carbon dioxide which was collected by the growing plants which provided food for the turkeys. The process cannot remove radioactivity from radioactive waste, but can still process it into oil. The Environmental Protection Agency estimates that in 2001 there were 229 million tons of municipal solid waste, or 4.4 pounds generated per day per person in the USA. http://www.epa.gov/epaoswer/non-hw/muncpl/facts.htm Industrial facilities in the USA create 7.6 billion tons of industrial wastes each year and, as a whole, the USA creates over 12 billion tons of total waste. http://www.epa.gov/epaoswer/non-hw/industd/questions.htm Many agricultural wastes could be processed, but many of these are already used as animal feed on individual farms.

Current status

According to a recent article by Fortune Magazine, the Carthage plant is currently producing about 400 barrels per day of crude oil. This oil is being refined as No. 2 (a standard grade oil which is used for diesel and gasoline) and No. 4 (a lower grade oil used in industrial heating). As of February, 2005, the Carthage plant received an economic setback. It was thought that concern over mad cow disease would prevent the use of turkey waste as cattle feed, and thus this waste would be free. However, turkey waste is still used as feed, so the feed stock costs from $30 to $40 per ton, adding $15 to $20 per barrel to the cost of the oil. On top of the expenses, the roughly $42 per barrel biofuel tax credit on production costs that had been hoped for didn't materialize because the oil produced did not meet the definition of "biofuel" according to the relevant American tax legislation. Final cost is $80/barrel ($1.90/gal), making it uneconomic compared to the net wholesale price of conventional diesel of about $72/barrel ($1.73/gal) (as of April 2005 - view current price). However, this setback does not apply to other forms of waste such as plastics. In addition, the UK has outlawed using turkey waste as cattle feed. The pilot plant in Carthage, Missouri was temporarily shut down due to smell complaints, but was soon restarted when it was discovered that many of the smells were not actually generated by the plant. (reported by the Kansas City Star, April 12, 2005). Furthermore, the plant agreed to install an enhanced thermal oxidizer and to upgrade its air scrubber system under a court order. http://www.joplinglobe.com/story.php?story_id=188739&c=87 Since the plant is located only four blocks from the tourist-attracting town center, this has strained relations with the mayor and citizens of Carthage. If it cannot be resolved, this could lead to NIMBYism, making it difficult to implement this technology widely.

References

Category:Industrial processes Category:Petroleum production Category:Waste management fa:وابسپارش گرمایی

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